WO2024175876A1

WO2024175876A1 - Electrically-pumped organic semiconductor laser arrangement

Info

Publication number: WO2024175876A1
Application number: PCT/GB2024/050258
Authority: WO
Inventors: Junyi GONG; Ifor Samuel; Graham TURNBULL; Kou YOSHIDA
Original assignee: University Court Of The University Of St Andrews
Priority date: 2023-02-23
Filing date: 2024-01-30
Publication date: 2024-08-29
Also published as: GB202302633D0

Abstract

M&C PG450501WO 42 55209372-1 ABSTRACT ELECTRICALLY-PUMPED ORGANIC SEMICONDUCTOR LASER ARRANGEMENT An electrically-pumped organic semiconductor laser arrangement comprises an 5 OLED pump arrangement and an optically-pumped organic semiconductor laser. The OLED pump arrangement is configured to emit pump light from one or more emission regions of the OLED pump arrangement. The optically-pumped organic semiconductor laser includes a laser active layer and a grating structure for feedback of laser light in a grating region of the laser active layer along a feedback direction which is parallel to 10 the laser active layer. The one or more emission regions of the OLED pump arrangement are aligned with the grating region of the laser active layer for illumination of a region of the laser active layer with the pump light, which illuminated region comprises at least a portion of the grating region of the laser active layer, wherein the optically-pumped organic semiconductor laser is configured to emit laser light from at 15 least a portion of the illuminated region, and wherein the illuminated region of the laser active layer is elongated in a direction parallel to the laser active layer. [FIG. 1A]

Description

ELECTRICALLY-PUMPED ORGANIC SEMICONDUCTOR LASER ARRANGEMENT

FIELD

The present disclosure relates to an electrically-pumped organic semiconductor laser arrangement, comprising an organic light emitting diode (OLED) pump arrangement and an optically-pumped organic semiconductor laser which is optically pumped by the OLED pump arrangement.

BACKGROUND

Organic semiconductors are interesting optoelectronic materials for use in LEDs or semiconductor lasers because they can be deposited simply from solution or by evaporation onto a range of substrates (including flexible ones), and the properties of the materials can be tuned by changing their chemical structure. Use of organic semiconductor materials in LEDs or semiconductor lasers may also be of interest for avoiding the use of toxic materials such as arsenic which are used in known inorganic LEDs and semiconductor lasers. However, making an electrically-pumped organic semiconductor laser is challenging. One known approach is to inject charges directly into the organic semiconductor laser gain medium. However, the performance of such directly- injected organic semiconductor lasers is generally not sufficient for many practical applications. For example, the lifetime of such directly-injected organic semiconductor lasers may be limited to only around 20 light pulses, each spaced by 1 ms. Furthermore, such directly-injected organic semiconductor lasers may generate optical output beams which are only observable at distances up to 2 mm.

SUMMARY

According to a first aspect of the present disclosure there is provided an electrically-pumped organic semiconductor laser arrangement, comprising: an OLED pump arrangement; and an optically-pumped organic semiconductor laser, wherein the OLED pump arrangement is configured to emit pump light from one or more emission regions of the OLED pump arrangement, wherein the optically-pumped organic semiconductor laser includes a laser active layer and a grating structure for feedback of laser light in a grating region of the laser active layer along a feedback direction which is parallel to the laser active layer, wherein the one or more emission regions of the OLED pump arrangement are aligned with the grating region of the laser active layer for illumination of a region of the laser active layer with the pump light, which illuminated region comprises at least a portion of the grating region of the laser active layer, wherein the optically-pumped organic semiconductor laser is configured to emit laser light from at least a portion of the illuminated region, and wherein the illuminated region of the laser active layer is elongated in a direction parallel to the laser active layer.

Such an electrically-pumped organic semiconductor laser arrangement provides a better defined laser output beam and clearer lasing characteristics than known directly- injected organic semiconductor lasers. Separation of the OLED active layer and the laser active layer separates the electronic charges which are injected into the OLED active layer from the laser active layer and reduces non-radiative combination in the laser active layer resulting in a reduced current threshold and an improved operational lifetime of the electrically-pumped organic semiconductor laser arrangement compared with known directly- injected organic semiconductor lasers. Moreover, the illumination of a region of the laser active layer which is elongated in a direction parallel to the laser active layer may enable the use of an OLED pump arrangement which is configured to generate exceptionally high intensity pump light.

Optionally, the illuminated region has a length and a width in a plane parallel to the laser active layer, wherein the length is greater than the width.

Optionally, the length of the illuminated region is greater than two times the width of the illuminated region, greater than five times the width of the illuminated region, or greater than ten times the width of the illuminated region.

Optionally, the length of the illuminated region is 100 |_im or more, 500 |_im or more, 1 ,000 m or more, 2,000 m or more, 5,000 pm or more, or 10,000 pm or more.

Optionally, the width of the illuminated region is less than or equal to 1 ,000 pm, less than or equal to 500 pm, less than or equal to 200 pm, less than or equal to 100 pm, less than or equal to 50 pm, or less than or equal to 10 pm.

Optionally, the illuminated region has a rectangular cross-section in a plane parallel to the laser active layer.

Optionally, the OLED pump arrangement comprises a single OLED having an OLED active layer and first and second electrodes, wherein a single emission region is defined in the OLED active layer between the first and second electrodes. Optionally, the first and second electrodes are separated by the OLED active layer in an overlap area where the first and second electrodes overlap one another so as to define the emission region in the OLED active layer between the first and second electrodes in the overlap area.

Optionally, a length of the first electrode defines a length of the overlap area and therefore the length of the emission region.

Optionally, a width of the second electrode defines a width of the overlap area and therefore the width of the emission region.

Optionally, the emission region is elongated in a direction parallel to the laser active layer.

Optionally, the emission region has a length and a width in a plane parallel to the laser active layer , wherein the length is greater than the width.

Optionally, the length of the emission region is greater than two times the width of the emission region, greater than five times the width of the emission region, or greater than ten times the width of the emission region.

Optionally, the length of the emission region is 100 |_im or more, 500 pm or more, 1 ,000 pm or more, 2,000 pm or more, 5,000 pm or more, or 10,000 pm or more.

Optionally, the width of the emission region is less than or equal to 1 ,000 pm, less than or equal to 500 pm, less than or equal to 200 pm, less than or equal to 100 pm, less than or equal to 50 pm, or less than or equal to 10 pm.

Optionally, the emission region has a rectangular cross-section in a plane parallel to the laser active layer.

Optionally, the OLED comprises a flexible support member such as a flexible glass support member and the second electrode is attached to the flexible support member.

Optionally, the second electrode is attached to the flexible support member using a layer of adhesive or epoxy and, optionally also, a buffer layer of 100 nm of M0O3.

Optionally, the OLED pump arrangement is configured to emit pump light from a plurality of emission regions of the OLED pump arrangement.

Optionally, the OLED pump arrangement comprises a plurality of OLEDs, wherein each OLED comprises a corresponding OLED active layer and corresponding first and second electrodes, wherein each emission region is defined in the corresponding OLED active layer between the corresponding first and second electrodes. Optionally, the OLEDs are arranged along a straight line.

Optionally, the corresponding first and second electrodes are separated by the corresponding OLED active layer in a corresponding overlap area where the corresponding first and second electrodes overlap one another so as to define the corresponding emission region of the OLED in the corresponding OLED active layer between the corresponding first and second electrodes in the corresponding overlap area.

Optionally, a length of the corresponding first electrode defines a length of the corresponding overlap area and therefore the length of the corresponding emission region of the OLED.

Optionally, a width of the corresponding second electrode defines a width of the corresponding overlap area and therefore the width of the corresponding emission region of the OLED.

Optionally, each OLED comprises a corresponding flexible support member, such as a flexible glass support member, and wherein the corresponding second electrode is attached to the corresponding flexible support member.

Optionally, the corresponding second electrode is attached to the flexible support member using a layer of adhesive or epoxy and, optionally also, a buffer layer of 100 nm of M0O3.

Optionally, the OLED pump arrangement comprises a common OLED active layer and a plurality of first and second electrodes, wherein each emission region is defined in the common OLED active layer between corresponding first and second electrodes.

Optionally, wherein the plurality of emission regions are arranged in the common OLED active layer along a straight line.

Optionally, the corresponding first and second electrodes are separated by the common OLED active layer in a corresponding overlap area where the corresponding first and second electrodes overlap one another so as to define the corresponding emission region in the common OLED active layer between the corresponding first and second electrodes in the corresponding overlap area.

Optionally, a length of the corresponding first electrode defines a length of the corresponding overlap area and therefore the length of the corresponding emission region. Optionally, a width of the corresponding second electrode defines a width of the corresponding overlap area and therefore the width of the corresponding emission region.

Optionally, the OLED pump arrangement comprises a common flexible support member, such as a common flexible glass support member, and wherein each of the second electrodes is attached to the common flexible support member.

Optionally, each of the second electrodes is attached to the flexible support member using a layer of adhesive or epoxy and, optionally also, a buffer layer of 100 nm of M0O3.

Optionally, the OLED pump arrangement is configured so that each of one or more of the emission regions emits pump light through the corresponding first electrode.

Optionally, each of one or more of the first electrodes is semi-transparent.

Optionally, each of one or more of the first electrodes comprises a metal such as silver.

Optionally, each of one or more of first electrodes has a thickness of 30 nm or less, 20 nm or less, or 10 nm or less. Use of such a thin first electrode comprising a metal such as silver represents a compromise between high optical transmission and low resistance per unit distance in a direction of current flow.

Optionally, each of one or more of the second electrodes comprises a metal such as aluminium.

Optionally, each of one or more of the second electrodes has a thickness of 1 |_im or more, 2 .m or more or 5 |_im or more. Use of such a thick second electrode may reduce the resistance of the second electrode per unit distance in the direction of current flow and may therefore reduce the resistance of the OLED pump arrangement. This may reduce resistive heating in the OLED pump arrangement. This may reduce the rise time of a pulse of pump light emitted by the OLED pump arrangement to more closely match an emission lifetime of the laser active layer for improved coupling efficiency.

Optionally, the OLED pump arrangement comprises first wiring corresponding to each emission region, wherein the first wiring is electrically connected to the corresponding first electrode.

Optionally, the first wiring is thicker than the corresponding first electrode. Use of thicker first wiring may reduce the resistance per unit distance of the first wiring in a direction of current flow. Optionally, the first wiring is opaque to the pump light.

Optionally, the first wiring comprises a corresponding aperture or a gap which is aligned with the corresponding emission region and which is configured to allow transmission of pump light from the corresponding emission region through the corresponding aperture or gap in the first wiring and through a portion of the corresponding first electrode that extends in and/or across the corresponding aperture or gap.

Optionally, a width of the corresponding aperture or gap of the corresponding first wiring is greater than or equal to a width of the corresponding emission region. Such a corresponding aperture or gap may allow the transmission of pump light from the corresponding emission region through the corresponding aperture or gap in the corresponding first wiring and through the portion of the corresponding first electrode that extends in and/or across the corresponding aperture or gap.

Optionally, the width of the corresponding aperture or gap in the first wiring is as close to the width of the corresponding emission region as the manufacturing process will allow to not only allow for transmission of pump light from the corresponding emission region through the corresponding aperture or gap but to also minimise the resistance in a direction of current flow of the portion of the corresponding first electrode that extends in and/or across the corresponding aperture or gap and thereby minimise the resistance. This may reduce resistive heating in the OLED pump arrangement. This may reduce the rise time of a pulse of pump light emitted by the OLED pump arrangement to more closely match an emission lifetime of the laser active layer for improved coupling efficiency. For example, the width of the corresponding aperture or gap in the corresponding first wiring may be less than or equal to ten times the width of the corresponding emission region, less than or equal to five times the width of the corresponding emission region, less than or equal to twice the width of the corresponding emission region, or may be equal, or substantially equal, to the width of the corresponding emission region.

Optionally, a length of the corresponding aperture or gap in the corresponding first wiring is greater than or equal to a length of the corresponding emission region.

Optionally, the corresponding first electrode comprises an anode.

Optionally, the corresponding second electrode comprises a cathode.

Optionally, the corresponding first wiring comprises anode wiring.

Optionally, each of one or more of the OLED active layers comprises 2,7- bis(9,9-spirobifluoren-2-yl)-9,9-spirobifluorene (TSBF). Optionally, the laser active layer comprises a conjugated polymer such as BBEHP-PPV, or a molecular organic semiconductor such as 4,4’-bis[N- carbazole)styryl]biphenyl .

Optionally, the grating structure is configured to couple laser light out of the laser active layer through a light emitting surface of the optically-pumped organic semiconductor laser which is located on an opposite side of the laser active layer to the light receiving surface.

Optionally, the grating structure is configured to couple laser light out of the laser active layer in a vertical direction.

Optionally, the grating structure is configured to couple laser light out of the laser active layer from the whole of the illuminated region.

Optionally, the grating structure comprises a DFB grating structure.

Optionally, the grating structure comprises a sub-structured grating.

Optionally, the grating structure is configured to couple laser light out of the laser active layer from part of the illuminated region.

Optionally, the grating structure comprises two DBR grating sections located either end of a central grating section, wherein the DBR grating sections are configured for feedback of laser light therebetween and the central grating section is configured to couple light out of the laser active layer.

Optionally, the DBR grating sections comprise 1^st-order DBR grating sections and the central grating section comprises a 2^nd-order grating section.

Optionally, the OLED and the optically-pumped organic semiconductor laser are configured so that the laser active layer receives the pump light from the OLED in a vertical direction.

Optionally, the OLED and the optically-pumped organic semiconductor laser are configured so that the shape and size of the illuminated region of the laser active layer corresponds closely to the shape and size of the emission region of the OLED.

Optionally, the OLED pump arrangement has a light emitting surface and the optically-pumped organic semiconductor laser has a light receiving surface, wherein the light emitting surface of and the light receiving surface are in direct contact with one another.

Optionally, the light emitting surface and the light receiving surface are held in conformal contact with one another.

Optionally, the OLED pump arrangement and the optically-pumped organic semiconductor laser are formed separately, and then aligned with one another before the light emitting surface of the OLED pump arrangement and the light receiving surface of the optically-pumped organic semiconductor laser are brought into conformal contact with one another.

Optionally, the OLED pump arrangement and the optically-pumped organic semiconductor laser are integrated monolithically.

Optionally, the or each OLED active layer and the laser active layer are separated by one or more intervening solid layers.

Optionally, the one or more intervening solid layers have a total thickness which is less than or equal to half the width of the one or more emission regions of the OLED pump arrangement. The pump light emitted from the one or more emission regions is highly divergent, especially in a direction parallel to the width of the one or more emission regions. Consequently, use of one or more intervening solid layers having such a total thickness may ensure that the pump light does not diverge unduly before it reaches the laser active layer. Put another way, use of one or more intervening solid layers having such a total thickness may reduce the size of the illuminated region of the laser active layer for a given size of the one or more emission regions thereby increasing the intensity of the pump light incident on the laser active layer and increasing the coupling efficiency for a given size of the one or more emission regions.

Optionally, the one or more intervening solid layers have a total thickness which is less than or equal to one tenth the width of the one or more emission regions, less than or equal to one twentieth the width of the one or more emission regions, or less than or equal to one fiftieth the width of the one or more emission regions.

Optionally, each intervening solid layer has a refractive index which is greater than or equal to the refractive index of the OLED active layer. This may help to improve the coupling efficiency of the pump light from the OLED active layer to the laser active layer.

Optionally, each intervening solid layer has a refractive index greater than or equal to 1 .3 and less than or equal to 2.6, or greater than or equal to 1 .4 and less than or equal to 2.2. Such refractive index values may serve to couple pump light out of the OLED active layer towards the laser active layer.

Optionally, the one or more intervening solid layers comprise one or more intervening solid OLED layers and one or more intervening solid laser layers.

Optionally, each of the one or more intervening solid OLED layers has a refractive index which is greater than or equal to a refractive index of the OLED active layer. Optionally, each of the one or more intervening solid OLED layers has a refractive index which is matched or substantially matched to a refractive index of the OLED active layer. Selecting each of the one or more intervening solid OLED layers to have a refractive index which is matched or substantially matched to a refractive index of the OLED active layer may serve to minimise reflections at an interface between the OLED active layer and the one or more intervening solid OLED layers and maximise the pump light coupled out of the OLED active layer.

Optionally, the one or more intervening solid OLED layers comprise a semitransparent electrode such as a semi-transparent anode of the OLED pump arrangement.

The semi-transparent electrode may comprise a metal such as silver.

The semi-transparent electrode may have a thickness of 30 nm or less, 20 nm or less, or 10 nm or less.

Optionally, the one or more intervening solid OLED layers comprise a wetting layer such as a layer of Mo0₃ and a layer of gold such as a 15 nm thick layer of Mo0₃ and a 1 nm thick layer of gold.

Optionally, the one or more intervening solid OLED layers comprise parylene.

Optionally, the one or more intervening solid OLED layers comprise one or more nanolaminates such as one or more nanolaminates of AI₂O₃/ZrO₂.

Optionally, each nanolaminate is 50 nm thick.

Optionally, the one or more intervening solid OLED layers comprise a first layer of parylene, a first layer of AI₂O₃/ZrO₂, a second layer of parylene, and a second layer of AI₂O₃/ZrO₂.

Optionally, the first and second layers of parylene are each 1 .5 |_im thick.

Optionally, the first and second layers of AI₂O₃/ZrO₂ are each 50 nm thick.

Optionally, the one or more intervening solid laser layers comprise a laser coupling layer.

Optionally, the refractive index of the laser coupling layer is matched or substantially matched to the refractive index of the one or more intervening solid OLED layers. Selecting a laser coupling layer which has a refractive index which is matched or substantially matched to the refractive index of the one or more intervening solid OLED layers may serve to minimise reflections at the interface between the one or more intervening solid OLED layers and the laser coupling layer.

Optionally, the laser coupling layer comprises a layer of parylene.

Optionally, the layer of parylene is 1 .5 |_im thick. Optionally, the one or more intervening solid laser layers comprise a laser cladding layer.

Optionally, the refractive index of the laser cladding layer is less than the refractive index of the laser active layer.

Optionally, the refractive index difference between the refractive index of the laser cladding layer and the refractive index of the laser active layer is less than or equal to 1.0, less than or equal to 0.5, or less than or equal to 0.2. Such a refractive index difference between the refractive index of the laser cladding layer and the refractive index of the laser active layer may provide vertical confinement for the laser light in the laser active layer.

Optionally, the laser cladding layer comprises a layer of PVPy such as a 2.2 .m thick layer of PVPy.

Optionally, the OLED pump arrangement and the optically-pumped organic semiconductor laser are aligned so that the longer dimension of the elongated illuminated region is aligned parallel to the feedback direction. This results in more efficient feedback of the laser light over a greater number of grating periods and a lower lasing threshold than the case where the longer dimension of the illuminated region is misaligned relative to the feedback direction.

Optionally, the OLED pump arrangement and the optically-pumped organic semiconductor laser are aligned so that the longer dimension of the elongated illuminated region is aligned along a direction which is arranged at angle of less than or equal to 10 degrees to the feedback direction, less than or equal to 5 degrees to the feedback direction, or less than or equal to 2 degrees to the feedback direction.

According to a second aspect of the present disclosure there is provided an electrically-pumped organic semiconductor laser arrangement, comprising: an OLED pump arrangement; and an optically-pumped organic semiconductor laser, wherein the OLED pump arrangement comprises an OLED active layer and is configured to emit pump light from one or more emission regions of the OLED active layer, wherein the optically-pumped organic semiconductor laser includes a laser active layer and a grating structure for feedback of laser light in a grating region of the laser active layer along a feedback direction which is parallel to the laser active layer, wherein the one or more emission regions of the OLED pump arrangement are aligned with the grating region of the laser active layer for illumination of a region of the laser active layer with the pump light, which illuminated region comprises at least a portion of the grating region of the laser active layer, wherein the optically-pumped organic semiconductor laser is configured to emit laser light from at least a portion of the illuminated region, wherein the OLED active layer and the laser active layer are separated by one or more intervening solid layers, and wherein the one or more intervening solid layers have a total thickness which is less than or equal to half a minimum dimension of the one or more emission regions of the OLED pump arrangement in a direction parallel to the OLED active layer.

Such an electrically-pumped organic semiconductor laser arrangement provides a better defined laser output beam and clearer lasing characteristics than known directly- injected organic semiconductor lasers. Separation of the OLED active layer and the laser active layer serves to separate the electronic charges which are injected into the OLED active layer from the laser active layer and reduces non-radiative combination in the laser active layer resulting in a reduced current threshold and an improved operational lifetime of the electrically-pumped organic semiconductor laser arrangement compared with known directly- injected organic semiconductor lasers. Moreover, the use of one or more intervening solid layers having a total thickness which is less than or equal to half a minimum dimension of the one or more emission regions of the OLED pump arrangement in a direction parallel to the OLED active layer may enable very efficient coupling between the OLED pump arrangement and the optically-pumped organic semiconductor laser, further improving the operational lifetime of the electrically-pumped organic semiconductor laser arrangement. The pump light emitted from the one or more emission regions of the OLED pump arrangement is highly divergent, especially in a direction parallel to the minimum dimension of the one or more emission regions. Consequently, use of one or more intervening solid layers having a total thickness which is less than or equal to half the minimum dimension of the one or more emission regions of the OLED pump arrangement in the direction parallel to the OLED active layer may ensure that the pump light does not diverge unduly before it reaches the laser active layer. Put another way, the use of the one or more intervening solid layers having a total thickness which is less than or equal to half the minimum dimension of the one or more emission regions of the OLED pump arrangement in the direction parallel to the OLED active layer may reduce the size of the illuminated region of the laser active layer for a given size of the one or more emission regions of the OLED pump arrangement thereby increasing the intensity of the pump light incident on the laser active layer and increasing the coupling efficiency for a given size of the one or more emission regions of the OLED pump arrangement.

Optionally, the one or more intervening solid layers have a total thickness which is less than or equal to one tenth the minimum dimension of the one or more emission regions in the direction parallel to the OLED active layer, less than or equal to one twentieth the minimum dimension of the one or more emission regions in the direction parallel to the OLED active layer, or less than or equal to one fiftieth the minimum dimension of the one or more emission regions in the direction parallel to the OLED active layer.

Optionally, each of the one or more intervening solid OLED layers has a refractive index which is greater than or equal to a refractive index of the OLED active layer.

Optionally, each of the one or more intervening solid OLED layers has a refractive index which is matched or substantially matched to a refractive index of the OLED active layer. Selecting each of the one or more intervening solid OLED layers to have a refractive index which is matched or substantially matched to a refractive index of the OLED active layer may serve to minimise reflections at an interface between the OLED active layer and the one or more intervening solid OLED layers and maximise the pump light coupled out of the OLED active layer.

The semi-transparent electrode may comprise a metal such as silver. The semi-transparent electrode may have a thickness of 30 nm or less, 20 nm or less, or 10 nm or less.

Optionally, the one or more intervening solid OLED layers comprise parylene.

Optionally, each nanolaminate is 50 nm thick.

Optionally, the first and second layers of parylene are each 1 .5 pm thick.

Optionally, the laser coupling layer comprises a layer of parylene.

Optionally, the layer of parylene is 1 .5 pm thick.

Optionally, the one or more intervening solid laser layers comprise a laser cladding layer.

Optionally, the refractive index difference between the refractive index of the laser cladding layer and the refractive index of the laser active layer is less than or equal to 1.0, less than or equal to 0.5, or less than or equal to 0.2. Such a refractive index difference between the refractive index of the laser cladding layer and the refractive index of the laser active layer may provide vertical confinement for the laser light in the laser active layer. Optionally, the laser cladding layer comprises a layer of PVPy such as a 2.2 pm thick layer of PVPy.

Optionally, the illuminated region of the laser active layer is elongated in a direction parallel to the laser active layer.

Optionally, the length of the illuminated region is 100 pm or more, 500 pm or more, 1 ,000 pm or more, 2,000 pm or more, 5,000 pm or more, or 10,000 pm or more.

Optionally, the OLED pump arrangement comprises a single OLED having an OLED active layer and first and second electrodes, wherein a single emission region is defined in the OLED active layer between the first and second electrodes.

Optionally, the first and second electrodes are separated by the OLED active layer in an overlap area where the first and second electrodes overlap one another so as to define the emission region in the OLED active layer between the first and second electrodes in the overlap area.

Optionally, the length of the emission region is greater than two times the width of the emission region, greater than five times the width of the emission region, or greater than ten times the width of the emission region. Optionally, the length of the emission region is 100 |_im or more, 500 pm or more, 1 ,000 pm or more, 2,000 pm or more, 5,000 pm or more, or 10,000 pm or more.

Optionally, the OLED pump arrangement comprises a plurality of OLEDs, wherein each OLED comprises a corresponding OLED active layer and corresponding first and second electrodes, wherein each emission region is defined in the corresponding OLED active layer between the corresponding first and second electrodes.

Optionally, the OLEDs are arranged along a straight line.

Optionally, a width of the corresponding second electrode defines a width of the corresponding overlap area and therefore the width of the corresponding emission region of the OLED. Optionally, each OLED comprises a corresponding flexible support member, such as a flexible glass support member, and wherein the corresponding second electrode is attached to the corresponding flexible support member.

Optionally, a length of the corresponding first electrode defines a length of the corresponding overlap area and therefore the length of the corresponding emission region.

Optionally, a width of the corresponding second electrode defines a width of the corresponding overlap area and therefore the width of the corresponding emission region.

Optionally, each of one or more of the first electrodes is semi-transparent.

Optionally, each of one or more of the first electrodes comprises a metal such as silver. Optionally, each of one or more of first electrodes has a thickness of 30 nm or less, 20 nm or less, or 10 nm or less. Use of such a thin first electrode comprising a metal such as silver represents a compromise between high optical transmission and low resistance per unit distance in a direction of current flow.

Optionally, the first wiring is thicker than the corresponding first electrode. Use of thicker first wiring may reduce the resistance per unit distance of the first wiring in a direction of current flow.

Optionally, the first wiring is opaque to the pump light.

Optionally, the corresponding first electrode comprises an anode.

Optionally, the corresponding second electrode comprises a cathode.

Optionally, the corresponding first wiring comprises anode wiring.

Optionally, each of one or more of the OLED active layers comprises 2,7- bis(9,9-spirobifluoren-2-yl)-9,9-spirobifluorene (TSBF).

Optionally, the laser active layer comprises a conjugated polymer such as BBEHP-PPV, or a molecular organic semiconductor such as 4,4’-bis[N- carbazole)styryl]biphenyl .

Optionally, the grating structure comprises a DFB grating structure. Optionally, the grating structure comprises a sub-structured grating.

Optionally, the grating structure is configured to couple laser light out of the laser active layer from part of the illuminated region. Optionally, the grating structure comprises two DBR grating sections located either end of a central grating section, wherein the DBR grating sections are configured for feedback of laser light therebetween and the central grating section is configured to couple light out of the laser active layer.

It should be understood that any one or more of the optional features of any one of the foregoing aspects of the present disclosure may be combined with any one or more of the optional features of any of the other foregoing aspects of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

An electrically-pumped organic semiconductor laser arrangement will now be described by way of non-limiting example only with reference to the accompanying drawings of which: FIG. 1A is a schematic side view of an electrically-pumped organic semiconductor laser arrangement;

FIG. 1 B shows the chemical structure of TSBF;

FIG. 1C shows the chemical structure of BBEHP-PPV;

FIG. 1 D is a schematic plan view of the electrically-pumped organic semiconductor laser arrangement of FIG. 1 A;

FIG. 1 E is a cross-section on KK of FIG. 1 D;

FIG. 1 F is a cross-section on AA of FIG. 1 D;

FIG. 2 shows the evolution of the emission spectrum of the electrically-pumped organic semiconductor laser arrangement of FIG. 1A under different peak current densities below and above threshold;

FIG. 3 shows the integrated lasing intensity as a function of peak current density for the electrically-pumped organic semiconductor laser arrangement of FIG. 1A;

FIG. 4 shows the far-field emission image and averaged line beam profile for laser light emitted from the electrically-pumped organic semiconductor laser arrangement of FIG. 1A;

FIG. 5A shows the normalized laser peak intensity as a function of the number of pump pulses for the electrically-pumped organic semiconductor laser arrangement of FIG. 1A;

FIG. 5B shows the laser spectrum recorded at the start and at the end of the lifetime measurement of FIG. 5A;

FIG. 6A shows the absorption spectrum of a 234 nm thick BBEHP-PPV film, a PL emission spectrum of a TSBF film, and the EL spectrum of a pump OLED of the electrically-pumped organic semiconductor laser arrangement of FIG. 1A; FIG. 6B shows a time profile of a driving current and the resulting time profile of the EL for an OLED of the electrically-pumped organic semiconductor laser arrangement of FIG. 1 A at different peak current densities;

FIG. 6C shows the peak radiant exitance of an OLED of the electrically-pumped organic semiconductor laser arrangement of FIG. 1A as a function of peak current density;

FIG. 7A shows the refractive index spectra of different materials for a laser cladding layer of an optically-pumped organic semiconductor laser of the electrically-pumped organic semiconductor laser arrangement of FIG. 1A;

FIG. 7B shows the calculated out-coupling efficiency of an OLED of the electrically- pumped organic semiconductor laser arrangement of FIG. 1A as a function of the refractive index of the out-coupling media for the OLED and enhancement in the out- coupling efficiency from the OLED compared with the out-coupling efficiency from the OLED to air at 430 nm.

FIG. 8A is a schematic of a measurement set-up for assisted pumping measurements of the electrically-pumped organic semiconductor laser arrangement of FIG. 1 A;

FIG. 8B shows the integrated laser output intensity as a function of peak current density;

FIG. 8C shows the normalized laser intensity as a function of optically pumped power density; and

FIG. 8D shows the assisted OPO power required for lasing as a function of normalized OLED intensity (main figure) and the corresponding time profiles of the OPO and OLED pump pulses and their relative timing during the measurement (inset).

DETAILED DESCRIPTION OF THE DRAWINGS

Referring initially to FIGS. 1A - 1 D there is shown an electrically-pumped organic semiconductor laser arrangement generally designated 2 comprising an OLED pump arrangement in the form of a surface-emitting pump OLED generally designated 4 and an optically-pumped organic semiconductor laser generally designated 6.

As shown in FIGS. 1A, 1 E and 1 F, the OLED 4 includes a substrate 8 comprising a first 1.5 pm thick layer of parylene, a first 50 nm thick nanolaminate layer of AI₂O₃/ZrO₂, a second 1.5 pm thick layer of parylene, and a second 50 nm thick nanolaminate layer of AI₂O₃/ZrO₂. This substrate construction is referred to hereinafter as a “PNPN substrate construction”.

The OLED 4 further includes a wetting layer 9 comprising 15 nm of Mo0₃ and 1 nm of gold (Au), a first electrode in the form of a semi-transparent anode 10 comprising 10 nm of silver (Ag), an OLED active layer 12, a second electrode in the form of a cathode 14 comprising 5 pm of aluminium (Al), a buffer 16 comprising 100 nm of Mo03, a layer of glue 17, and a flexible glass support member 18. It should be understood that by virtue of its thickness, the cathode 14 may be opaque.

As shown in FIG. 1A, the OLED active layer 12 comprises an F₆-TCNNQ:TAPC hole transport layer (HTL) 30, an electron barrier layer (EBL) 32 (2.5 nm PCzAc/7.5 nm TCTA), a 20 nm thick emission layer (EML) 34 of 2,7-bis(9,9-spirobifluoren-2-yl)-9,9- spirobifluorene (TSBF), a 10 nm TPBi hole barrier layer (HBL) layer 36, and a 30nm Cs:BPhen electron transport layer (ETL) 38. For reasons explained in more detail below, it should be understood that the transport layers 30, 38 of the OLED active layer 12 are doped so as to reduce the resistance of the OLED 4.

As shown most clearly in FIGS. 1 D, 1 E and 1 F, the anode 10 and the cathode 14 are separated by the OLED active layer 12 in an overlap area where the anode 10 and the cathode 14 overlap one another so as to define an emission region 12a of the OLED 4 in the OLED active layer 12 between the anode 10 and the cathode 14 in the overlap area.. As shown most clearly in FIG. 1 E, a length of the anode 10 defines a length of the emission region 12a of the OLED 4. As shown most clearly in FIG. 1 F, a width of the cathode 14 defines a width of the emission region 12a of the OLED 4.

As shown in FIGS. 1 D and 1 F, the OLED 4 also includes first and second anode wiring layers 20 and 22 respectively which are electrically connected to the semi-transparent anode 10 and a cathode wiring layer 24 electrically connected to the cathode 14. It should be understood that the first and second anode wiring layers 20 and 22 are generally much thicker than the anode 10 so as to reduce the resistance per unit distance of the first and second anode wiring layers 20 and 22 in a direction of current flow and that the first and second anode wiring layers 20 and 22 may therefore be generally opaque. Similarly, it should be understood that the cathode wiring layer 24 may be relatively thick in order to reduce the resistance per unit distance of the cathode wiring layer 24 in a direction of current flow and that the cathode wiring layer 24 may therefore be generally opaque. It should be understood that the cathode wiring layer 24 is electrically isolated from the first and second anode wiring layers 20 and 22. Moreover, as shown most clearly in FIG. 1 F, the first anode wiring layer 20 comprises an aperture or a gap which is aligned with the emission region 12a of the OLED 4 and which is configured to allow transmission of pump light from the emission region 12a of the OLED 4 through the aperture or gap and the portion of the semi-transparent anode 10 that extends in and/or across the aperture or gap. Specifically, a width of the aperture or gap in the first anode wiring layer 20 is greater than a width of the emission region 12a of the OLED 4 to allow transmission of pump light from the emission region 12a of the OLED 4 through the aperture or gap and the portion of the semi-transparent anode 10 that extends in and/or across the aperture or gap.

For reasons that will be described in more detail below, it is generally desirable to minimise the resistance of the OLED 4. The semi-transparent anode 10 is relatively thin and has a relatively high resistance in the direction of current flow, whereas the relatively thick first and second anode wiring layers 20 and 22 have relatively low resistance in the direction of current flow. Consequently, the width of the aperture or gap in the first anode wiring layer 20 is ideally selected to be only marginally greater than the width of the emission region 12a of the OLED 4 so to minimise the width of the portion of the semi-transparent anode layer 10 in the aperture or gap in the first anode wiring layer 20 and reduce the anode contact resistance associated with the first and second anode wiring layers 20 and 22 in series with the portion of the anode layer 10 in the aperture or gap in the first anode wiring layer 20. In addition, a length of the aperture or gap in the first anode wiring layer 20 is greater than or equal to a length of the emission region 12a of the OLED 4 for reduced anode contact resistance. For the specific example described with reference to FIGS. 1A-1 F, the length of the overlap area between the anode 10 and the cathode 14 (and therefore also the length of the emission region 12a of the OLED 4) is 1 mm and the width of the overlap area between the anode 10 and the cathode 14 (and therefore also the width of the emission region 12a of the OLED 4) is 130 .m. However, it should be understood that the width of the overlap area may be chosen to be less than 130 |_im and the width of the aperture or gap in the first opaque anode wiring layer 20 may be reduced accordingly so as to further reduce the anode contact resistance. It should be understood that, in practice, the minimum practical cathode width may depend on the minimum repeatable feature size than can reproduced by the fabrication equipment used to manufacture the OLED 4. Use of a relatively thick 5 |_im aluminium cathode layer and a relatively thick cathode wiring layer 24 reduces the cathode contact resistance and therefore further reduces the resistance of the OLED 4.

As will be described in more detail below, the OLED 4 comprises a light emitting surface 40, wherein the OLED 4 is configured to emit pump light from the emission region 12a of the OLED active layer 12, which emission region 12a is elongated in a direction parallel to the light emitting surface 40.

Referring to FIG. 1A, the optically-pumped organic semiconductor laser 6 comprises a glass substrate 50, a sub-structured grating layer 52 comprising 350 nm of HSQ, a 230 nm thick laser active layer 54 of BBEHP-PPV, a 2.2 pm thick cladding layer 56 of poly vinyl pyrrolidone (PVPy), and a 1.5 pm thick coupling layer 58 of parylene. The optically-pumped organic semiconductor laser 6 further includes a light receiving surface 60 for receiving pump light from the OLED 4 and a light emitting surface 70 for emitting laser light.

As shown in FIGS. 1A and 1 D, the optically-pumped organic semiconductor laser 6 also includes a sub-structured DFB grating structure 62 for feedback of laser light in a grating region 64 of the laser active layer 54 in a horizontal feedback direction which is parallel to the light receiving surface 60. As will be described in more detail below, the sub-structured DFB grating structure 62 is also configured to couple light out of the laser active layer 54 towards the light emitting surface 70.

As shown in FIG. 1 D, the emission region 12a of the OLED 4 is aligned with the grating region 64 of the optically-pumped organic semiconductor laser 6 with the longer dimension of the emission region 12a of the OLED 4 aligned parallel to the feedback direction. As shown in FIG. 1A, the OLED 4 and the optically-pumped organic semiconductor laser 6 are then brought into direct physical contact with one another without any gap between the light emitting surface 40 of the OLED 4. The light emitting surface 40 of the OLED 4 and the light receiving surface 60 of the optically-pumped organic semiconductor laser 6 are then held in conformal contact by compressing the OLED 4, the optically-pumped organic semiconductor laser 6, and a layer of elastomer material 72 together in a sample holder 74.

Although not shown in FIGS. 1 A-1 F, it should be understood that the OLED 4 is initially formed on a glass carrier substrate coated with a self-assembled monolayer (SAM) of Trichloro(1 H,1 H,2H,2H-perfluorooctyl) silane to enable easy peel-off of the OLED 4 from the glass carrier substrate and transfer printing of the light emitting surface 40 of the OLED 4 onto the light receiving surface 60 of the optically-pumped organic semiconductor laser 6. The glass support member 18 provides support to the OLED 4 during transfer printing to prevent any shrinking or distortion of the OLED 4 that may otherwise occur during transfer printing.

In use, the OLED 4 is driven with current pulses of duration <10 ns at a low reputation rate of 10 Hz to reduce the accumulation of the heat in the OLED 4. This results in the emission of pulses of pump light in a generally vertical direction through the light emitting surface 40. The pulses of pump light illuminate a region of the laser active layer 54, wherein the illuminated region comprises at least a portion of the grating region 64 of the laser active layer 54. The pump light generates optical gain in the illuminated region of the laser active layer 54 and the sub-structured DFB grating structure 62 generates feedback resulting in stimulated emission in the laser active layer 54. As shown in FIG. 1A, the sub-structured DFB grating structure 62 also couples laser light out of the laser active layer 54 in a vertical direction from the whole of the illuminated region through the light emitting surface 70 of the optically-pumped organic semiconductor laser 6.

FIG. 2 shows spectra of the light emitted by the optically-pumped organic semiconductor laser 6 as a function of current density applied to the OLED 4. A spectral peak is observed for higher current densities indicative of lasing in the optically-pumped organic semiconductor laser 6.

FIG. 3 shows the intensity of light emitted by the optically-pumped organic semiconductor laser 6 as a function of peak current density applied to the OLED 4 illustrating a threshold in the light intensity for a peak current density of 2.83 kA/cm² indicative of lasing in the optically-pumped organic semiconductor laser 6.

FIG. 4 shows the far-field emission image and the averaged line beam profile of the optically-pumped organic semiconductor laser 6 below and above the threshold measured at a distance of 6 cm from the light emitting surface 70 of the optically- pumped organic semiconductor laser 6. When the optically-pumped organic semiconductor laser 6 is operated below threshold (2 kA/cm2), the image and the line profile only show fluorescence generated in the BBEHP-PPV active layer 12. When the peak current density is increased above threshold to 4.87 kA/cm², a clear beam with a Gaussian line profile is observed indicative of stimulated emission. The double lobe beam shape is consistent with emission from a typical surface emitting DFB laser with one-dimensional distributed feedback. FIG. 5A shows the laser peak intensity emitted by the electrically-pumped organic semiconductor laser arrangement 2 as a function of the number of pump pulses. FIG. 5B shows the laser spectrum recorded at the start and at the end of the lifetime measurement. The lifetime of the electrically-pumped organic semiconductor laser arrangement 2 was characterised by driving the device at 4.87 kA/cm² (1.7 times threshold current density) with a repetition rate of 10Hz and 100Hz. The narrow laser emission was visible for 9.57x10⁴ pulses, which corresponds to more than two and half hours operating at 10 Hz. This is much longer than known electrically-pumped organic semiconductor laser devices. The operational lifetime of the OLED 4 was also tested under pulsed operation at an initial peak current density of 5.4 kA/cm2 at 10 Hz. An 10% intensity drop was observed after 7.3 x 10⁴ pulses, corresponding to an operation lifetime of 2 hours. Thus, the lifetime of the electrically-pumped organic semiconductor laser arrangement 2 is attributed to degradation of both the OLED 4 and the optically- pumped organic semiconductor laser 6 under pulsed current operation.

It should be understood that the TSBF material of the OLED active layer 12 and the BBEHP-PPV material of the laser active layer 54 are carefully selected so the pump light emitted from the TSBF OLED active layer 12 can efficiently excite BBEHP- PPV. Specifically, as shown in FIG. 6A, BBEHP-PPV has an absorption peak around 430 nm and TSBF has two emission peaks near there, at 407 nm and 427 nm, so the pump light emitted from the TSBF OLED active layer 12 can efficiently excite BBEHP- PPV.

Moreover, it should be understood that the electrically-pumped organic semiconductor laser arrangement 2 is configured so that the pump light generated in the OLED active layer 12 can be transferred efficiently to the laser active layer 54 without its irradiance becoming unduly reduced. In order to generate the high irradiance pump light levels required for lasing, the current density in the emission region 12a of the OLED 4 needs to be relatively high. For a fixed current this requires that the cross-sectional area of the emission region 12a of the OLED 4 in a plane parallel to the light emitting surface 40 needs to be relatively small. As a consequence of the small cross-sectional area of the emission region 12a of the OLED 4, the pump light emitted from the OLED 4 is highly divergent, especially in the direction of the width of the emission region 12a. Consequently, it is important that the OLED active layer 12 and the laser active layer 54 are located within a very short distance from one another and that the materials between the OLED active layer 12 and the laser active layer 54 are chosen carefully for efficient optical coupling between the OLED active layer 12 and the laser active layer 54. In particular, the one or more intervening solid layers between the OLED active layer 12 and the laser active layer 54 should have a total thickness which is less than or equal to half the width of the emission region 12a of the OLED 4. Use of one or more intervening solid layers having such a total thickness may ensure that the pump light does not diverge unduly before it reaches the laser active layer 54. Put another way, use of one or more intervening solid layers having such a total thickness may reduce the size of the illuminated region of the laser active layer 54 for a given size of emission region 12a of the OLED 4 thereby increasing the intensity of the pump light incident on the laser active layer 54 and increasing the coupling efficiency for a given size of emission region 12a of the OLED 4. For example, the one or more intervening solid layers may have a total thickness which is less than or equal to one tenth the width of emission region 12a of the OLED 4, less than or equal to one twentieth the width of emission region 12a of the OLED 4, or less than or equal to one fiftieth the width of emission region 12a of the OLED 4. For the particular example described with reference to FIGS. 1A-1 F, the total thickness of the one or more intervening solid layers between the OLED active layer 12 and the laser active layer 54 is <10 pm. To further improve the coupling efficiency of the pump light from the OLED active layer 12 to the laser active layer 54, each intervening solid layer has a refractive index which is greater than or equal to the refractive index of the OLED active layer 12.

The use of the OLED substrate 8 having the PNPN substrate construction described above, together with the use of the 1 .5 pm thick parylene coupling layer 58 and the 2.2pm thick PVPy cladding layer 56 of the optically-pumped organic semiconductor laser 6 which were also described above results in an optical coupling efficiency from the OLED active layer 12 to the laser active layer 54 which is much higher than the optical coupling efficiency from conventional OLEDs emitting into air. This is because the refractive indices of the polymer layers of the PNPN substrate 8, the parylene coupling layer 58 and the PVPy cladding layer 56 between the OLED active layer 12 and the laser active layer 54 are much higher than the refractive index of air. This is illustrated with reference to FIGS. 7A and 7B. FIG. 7A shows the refractive of PVPy (and other materials CYTOP and NOA68) as a function of wavelength. FIG. 6B shows the simulated optical coupling efficiency from a TSBF- OLED on a PNPN substrate to media with different refractive indices. The optical coupling efficiency of the OLED 4 to the parylene coupling layer 58 and the PVPy cladding layer 56 with a refractive index of 1.53 at 430 nm is around 0.62. This is 2.3 times higher than the coupling efficiency to the air. This demonstrates that the pump light generated in the OLED active layer 12 is transferred efficiently to the laser active layer 54.

It should be understood that the use of an emission region 12a of the OLED 4 which is elongated in a plane parallel to the light emitting surface 40 of the OLED 4 is beneficial for several reasons. Firstly, as already described above with reference to FIG. 1 D, the emission region 12a of the OLED 4 is aligned with the grating region 64 of the optically-pumped organic semiconductor laser 6 with the length (i.e. the longer dimension) of the emission region 12a of the OLED 4 aligned parallel to the horizontal feedback direction so that pump light from the OLED 4 can illuminate an elongated region of the laser active layer 54 which is aligned in the horizontal feedback direction. This results in more efficient feedback of the laser light over a greater number of grating periods and a lower lasing threshold than the case where the length of the emission region 12a of the OLED 4 is misaligned relative to the horizontal feedback direction.

Use of a narrower emission region 12a also permits the use of a narrower aperture or gap in the first anode wiring layer 20 and reduces the distance current has to flow from the edge of the first anode wiring layer 20 through the relatively thin portion of the semi-transparent anode layer 10 that extends in and/or across the aperture or gap in the first anode wiring layer 20 to the emission region 12a thereby reducing resistive heating in the portion of the semi-transparent anode layer 10 in the aperture or gap in the first opaque anode wiring layer 20. Use of a longer emission region 12a further reduces resistive heating in the portion of the semi-transparent anode layer 10 in the aperture or gap in the first anode wiring layer 20. Use of an elongated emission region 12a also allows heat generated in the portion of the semi-transparent anode layer 10 that extends in and/or across the aperture or gap in the first anode wiring layer 20 and in the emission region 12a to be dissipated more readily thereby reducing the operating temperature of the emission region 12a and improving the reliability of operation of the OLED 4.

Use of an elongated emission region 12a to reduce the anode contact resistance and therefore the overall resistance of the OLED 4 also serves to reduce the response time of the current flow in the OLED 4 to changes in the driving voltage and to reduce the rise and falls times of the pump pulse used to pump the optically-pumped organic semiconductor laser 6. Controlling the temporal profile of pump pulse is important because it affects the dynamics of the optical gain in the laser active layer 54 and thus the lasing threshold of the optically-pumped organic semiconductor laser 6. More specifically, in order to minimise non-radiative recombination in the BBEHP-PPV material of the laser active layer 54, the rise time of the pump pulse should be less than or equal to the emission lifetime of the BBEHP-PPV material of the laser active layer 54. FIG. 6B shows the time profile of a driving current pulse for the OLED 4 and the electroluminescence emitted by the OLED 4 at different peak current densities. The shape of the current pulse is triangular but becomes generally rectangular at higher peak current density with a full-wave half-maximum of 5.9 ns at a peak current density of 5.5 kA/cm². The OLED 4 can be operated at a peak current density of 5.5 kA/cm2 without break-down even when the OLED 4 is formed on a poor thermally conductive parylene based substrate 8. This is, at least in part, because the OLED 4 is operated with very short current pulses. As shown in FIG. 6B, the rise time of the pump pulse does not depend on peak current density, but the fall time of the pump pulse increases with increasing peak current density. More specifically, if the rise and fall times are defined as the times for an optical intensity change between 10% and 90% of maximum amplitude, the rise time of the pump pulse is around 1.5 ns, and the fall time is around 6.4 ns at a peak current density of 5.5 kA/cm². The rise time of the OLED 4 is less than twice the emission lifetime of 0.72 ns for the BBEHP-PPV material of the laser active layer 54 and the fall time is slightly shorter than 10 times the emission lifetime of 0.72 ns for the BBEHP-PPV material. Such a short rise time improves the pumping efficiency of the BBEHP-PPV material of the laser active layer 54 with the pump light from the OLED 4 resulting in a lower lasing threshold of the optically- pumped organic semiconductor laser 6 for a fixed peak intensity.

Referring back to FIG. 6A, there is shown an electroluminescence (EL) spectrum of the OLED 4 under pulsed operation at a peak current density of 5.5 kA/cm² at 100 Hz. The spectrum has a maximum around 430 nm and its shape is roughly similar to the emission spectra of a film of TBSF material except for a small oscillation with a period of around 7 nm. This oscillation is due to thin film interference in the PNPN substrate 8. There is a higher degree of overlap between the EL spectrum of the OLED 4 and the absorption spectrum of BBEHP-PPV. More specifically, the overlap integral of the EL spectra and the absorptivity spectrum of a 230 nm thick BBEHP-PPV film is 75%.

FIG. 6C shows peak radiant exitance of the OLED 4 as a function of peak current density. Peak radiant exitance increases with peak current density sub-linearly and reaches around 55 W/cm² at 5.5 kA/cm², which corresponds to nominal EQE of 0.35%. In a second electrically-pumped organic semiconductor laser arrangement which is nominally identical to the electrically-pumped organic semiconductor laser arrangement 2 described with reference to FIGS. 1A - 1 F, it was found that under ns pulsed optical pumping, the lasing threshold measured with an OPO pump was 92 W/cm², much higher than the measured output power density into air from the OLED of the second electrically-pumped organic semiconductor laser arrangement of <60 W/cm². As mentioned above, this can be explained by the enhancement in optical coupling efficiency achieved through optimized integration of the OLED with the optically-pumped organic semiconductor laser. To verify this experimentally, an ‘assisted’ pumping measurement was performed with the OPO as depicted in FIG. 8A. In the measurement, the electrically-pumped organic semiconductor laser arrangement was electrically pumped at a fixed current density and simultaneously excited with a time-synchronized OPO pulse to assist the optically-pumped organic semiconductor laser above threshold even at lower current densities. From the measured OPO power required for laser action, the light output transferred from the OLED to the optically- pumped organic semiconductor laser could be inferred. It is noted that as shown in FIG. 8B, the electrically-pumped organic semiconductor laser arrangement used in this experiment had a higher electrically pumped threshold of 5 kA/cm² than the electrically- pumped organic semiconductor laser arrangement 2 characterised in FIG. 3.

FIG. 8C shows the spectrally integrated laser output as a function of the OPO pump intensity measured for a range of fixed peak current densities of the laser device. When the OLED is off, and the laser is pumped only by the OPO, the optical pumping threshold is 94 W/cm². This OPO threshold starts to decrease when current is simultaneously injected into the pump OLED. With increased current density, the optical pump threshold decreased to about 22 W/cm² when the OLED 4 was operated at 2.76 kA/cm². The 72 W/cm² reduction in the optically pumped laser threshold indicates that the electrical pumping process contributes by an equivalent amount to the onset of lasing. Eventually, at the threshold current density, no assisted OPO power is required to exceed threshold. FIG. 8D shows the assisted OPO power required to reach threshold as a function of OLED intensity normalized to the OLED emission intensity required to reach threshold without any assisted OPO power. The intermediate measured OPO power density sit slightly above this dashed line, probably due to an imperfect synchronization of the OLED and OPO excitation pulses. The assisted pumping measurement indicates that the maximum output from the OLED 4 is around 100 W/cm² (OPO power density equivalent) at 5 kA/cm², which is an enhancement in out-coupling efficiency of twice the output from the OLED into air. This is consistent with the calculated enhancement in power transferred within the electrically-pumped organic semiconductor laser arrangement 2. This shows the clear advantage of the electrically-pumped organic semiconductor laser arrangement 2 to achieve laser action using electrical driving.

In summary, the threshold behaviour, the linewidth narrowing, the observation of an emission beam, the emission characteristic of the specific gain medium and resonator demonstrate that electrically pumped lasing is achieved in the electrically- pumped organic semiconductor laser arrangement 2.

One of ordinary skill in the art will also understand that various modifications are possible to the electrically-pumped organic semiconductor laser arrangement 2 described above. For example, although the OLED 4 and the optically-pumped organic semiconductor laser 6 are described above as being manufactured on separate substrates and then being brought into engagement so that the light emitting surface 40 of the OLED 4 and the light receiving surface 60 of the optically-pumped organic semiconductor laser 6 are held in conformal contact, in other embodiments, the OLED 4 and the optically-pumped organic semiconductor laser 6 may be integrated monolithically.

The OLED 4 and the optically-pumped organic semiconductor laser 6 are described above as being aligned so that the length of the elongated emission region 12a of the OLED 4 is aligned with the feedback direction defined by the grating structure 62 to minimise the lasing threshold of optically-pumped organic semiconductor laser 6. However, in practice it may only be possible to align the length of the elongated emission region 12a of the OLED 4 and the feedback direction with limited accuracy and it is possible that the length of the elongated emission region 12a of the OLED 4 and the feedback direction may be misaligned by an angle of less than or equal to 5 degrees, less than or equal to 2 degrees, or less than or equal to 1 degree.

The sub-structured DFB grating structure 62 is configured to couple laser light out of the laser active layer 54 from the whole of the illuminated region. In an alternative embodiment, a different grating structure may be used for coupling laser light out of the laser active layer 54 from only part of the illuminated region. For example, in an alternative embodiment, the illuminated region may extend along a grating structure comprising two DBR grating sections located either end of a central grating section, wherein the DBR grating sections are configured for feedback of laser light therebetween and the central grating section is configured to couple light out of the laser active layer 54. The DBR grating sections may comprise 1^st-order DBR grating sections and the central grating section may comprise a 2^nd-order grating section.

Although the aspect ratio of the emission region 12a of the OLED 4 in the plane parallel to the light emitting surface 40 described above is approximately 7.7, in other embodiments, a length of the emission region of the OLED may be greater than two times a width of the emission region, greater than five times a width of the emission region, or greater than ten times a width of the emission region.

Although the emission region 12a of the OLED 4 is described above as having a length of 1 ,000 pm, the emission region may have a length of 100 pm or more, 500 pm or more, 1000 pm or more, 2,000 pm or more, 5,000 pm or more, or 10,000 pm or more.

Although the emission region 12a of the OLED 4 is described above as having a width of 130 pm, the width of the emission region may be less than or equal to 1 ,000 pm, less than or equal to 500 pm, less than or equal to 200 pm, less than or equal to 100 pm, less than or equal to 50 pm, or less than or equal to 10 pm.

Although the optically-pumped organic semiconductor laser 6 is described above as being pumped by an OLED pump arrangement comprising a single OLED 4 having an elongated emission region 12a aligned with the grating region 64 of the laser active layer 54 for illumination of an elongated region of the laser active layer 54 with the pump light, which illuminated region comprises at least a portion of the grating region 64 of the laser active layer 54, other OLED pump arrangements are possible. For example, the OLED pump arrangement may comprise a plurality of pump OLEDs arranged along a straight line. Each pump OLED may be configured to emit pump light from a corresponding emission region which may or may not be elongated. The plurality of pump OLEDs may together illuminate an elongated region of the laser active layer 54 with the pump light, which illuminated region comprises at least a portion of the grating region 64 of the laser active layer 54.

Alternatively, the OLED pump arrangement may be configured to emit pump light from a plurality of emission regions of the OLED pump arrangement, wherein the OLED pump arrangement comprises a common OLED active layer and a plurality of first and second electrodes, wherein each emission region is defined in the common OLED active layer between corresponding first and second electrodes, and wherein the plurality of emission regions are arranged in the common OLED active layer along a straight line.

Although the laser active layer 54 is described above as comprising BBEHP- PPV, the laser active layer may comprise any conjugated polymer or molecular organic semiconductor having an absorption spectrum which matches or which has a significant degree of overlap with the emission spectrum of the pump light emitted by the one or more pump OLEDs. For example, the laser active layer may comprise a molecular organic semiconductor such as 4,4’-bis[N-carbazole)styryl]biphenyL

It should be understood that the embodiments of the present disclosure are illustrative only and that the claims are not limited to the embodiments. Those skilled in the art will be able to make modifications to the embodiments of the present disclosure and to contemplate alternatives to the embodiments which fall within the scope of the appended claims. Each feature described above and/or shown in any of the accompanying drawings may be incorporated in any embodiment, whether alone or in any appropriate combination with any other feature described and/or shown in the drawings. In particular, one of ordinary skill in the art will understand that one or more of the features of an embodiment described above and/or shown in any of the accompanying drawings may produce effects or provide advantages when used in isolation from one or more of the other features of the same embodiment and that different combinations of the features are possible other than the specific combinations of the features of the embodiments described above and/or shown in any of the accompanying drawings.

The skilled person will understand that in the preceding description and the appended claims, positional terms such as ‘above’, ‘along’, ‘side’, etc. are made with reference to the accompanying drawings. These terms are used for ease of reference but are not intended to be limiting in nature. These terms are to be understood as referring to an object when in an orientation as shown in the accompanying drawings.

Use of the term "comprising" when used in relation to a feature of an embodiment does not exclude other features or steps. Use of the term "a" or "an" when used in relation to a feature of an embodiment of the present disclosure does not exclude the possibility that the embodiment may include a plurality of such features.

The use of reference signs in the claims should not be construed as limiting the scope of the claims.

Claims

1 . An electrically-pumped organic semiconductor laser arrangement, comprising: an OLED pump arrangement; and an optically-pumped organic semiconductor laser, wherein the OLED pump arrangement is configured to emit pump light from one or more emission regions of the OLED pump arrangement, wherein the optically-pumped organic semiconductor laser includes a laser active layer and a grating structure for feedback of laser light in a grating region of the laser active layer along a feedback direction which is parallel to the laser active layer, wherein the one or more emission regions of the OLED pump arrangement are aligned with the grating region of the laser active layer for illumination of a region of the laser active layer with the pump light, which illuminated region comprises at least a portion of the grating region of the laser active layer, wherein the optically-pumped organic semiconductor laser is configured to emit laser light from at least a portion of the illuminated region, and wherein the illuminated region of the laser active layer is elongated in a direction parallel to the laser active layer.

2. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 1 , wherein the illuminated region has a length and a width in a plane parallel to the laser active layer, wherein the length is greater than the width, and wherein at least one of: the length of the illuminated region is greater than two times the width of the illuminated region, greater than five times the width of the illuminated region, or greater than ten times the width of the illuminated region; the length of the illuminated region is 100 pm or more, 500 pm or more, 1 ,000 pm or more, 2,000 pm or more, 5,000 pm or more, or 10,000 pm or more; the width of the illuminated region is less than or equal to 1 ,000 pm, less than or equal to 500 pm, less than or equal to 200 pm, less than or equal to 100 pm, less than or equal to 50 pm, or less than or equal to 10 pm; or the illuminated region has a rectangular cross-section in the plane parallel to the laser active layer.

3. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 1 or 2, wherein the OLED pump arrangement comprises a single OLED having an OLED active layer and first and second electrodes, wherein a single emission region is defined in the OLED active layer between the first and second electrodes.

4. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 3, wherein the first and second electrodes are separated by the OLED active layer in an overlap area where the first and second electrodes overlap one another so as to define the emission region in the OLED active layer between the first and second electrodes in the overlap area, wherein a length of the first electrode defines a length of the overlap area and therefore the length of the emission region, and a width of the second electrode defines a width of the overlap area and therefore the width of the emission region.

5. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 3 or 4, wherein the OLED comprises a flexible support member such as a flexible glass support member and the second electrode is attached to the flexible support member.

6. The electrically-pumped organic semiconductor laser arrangement as claimed in any one of claims 3 to 5, wherein the emission region is elongated in a direction parallel to the laser active layer and wherein at least one of: the emission region has a length and a width in a plane parallel to the laser active layer, wherein the length is greater than the width; the length of the emission region is greater than two times the width of the emission region, greater than five times the width of the emission region, or greater than ten times the width of the emission region; the length of the emission region is 100 pm or more, 500 pm or more, 1 ,000 pm or more, 2,000 pm or more, 5,000 pm or more, or 10,000 pm or more; the width of the emission region is less than or equal to 1 ,000 pm, less than or equal to 500 pm, less than or equal to 200 pm, less than or equal to 100 pm, less than or equal to 50 pm, or less than or equal to 10 pm; or the emission region has a rectangular cross-section in a plane parallel to the laser active layer.

7. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 1 or 2, wherein the OLED pump arrangement is configured to emit pump light from a plurality of emission regions of the OLED pump arrangement and wherein the OLED pump arrangement comprises a plurality of OLEDs, wherein each OLED comprises a corresponding OLED active layer and corresponding first and second electrodes, wherein each emission region is defined in the corresponding OLED active layer between the corresponding first and second electrodes and, optionally, wherein the OLEDs are arranged along a straight line.

8. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 7, wherein the corresponding first and second electrodes are separated by the corresponding OLED active layer in a corresponding overlap area where the corresponding first and second electrodes overlap one another so as to define the corresponding emission region of the OLED in the corresponding OLED active layer between the corresponding first and second electrodes in the corresponding overlap area, wherein a length of the corresponding first electrode defines a length of the corresponding overlap area and therefore the length of the corresponding emission region of the OLED and wherein a width of the corresponding second electrode defines a width of the corresponding overlap area and therefore the width of the corresponding emission region of the OLED.

9. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 7 or 8, wherein each OLED comprises a corresponding flexible support member, such as a flexible glass support member, and wherein the corresponding second electrode is attached to the corresponding flexible support member.

10. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 1 or 2, wherein the OLED pump arrangement is configured to emit pump light from a plurality of emission regions of the OLED pump arrangement and wherein the OLED pump arrangement comprises a common OLED active layer and a plurality of first and second electrodes, wherein each emission region is defined in the common OLED active layer between corresponding first and second electrodes and, optionally, wherein the plurality of emission regions are arranged in the common OLED active layer along a straight line.

11 . The electrically-pumped organic semiconductor laser arrangement as claimed in claim 10, wherein the corresponding first and second electrodes are separated by the common OLED active layer in a corresponding overlap area where the corresponding first and second electrodes overlap one another so as to define the corresponding emission region in the common OLED active layer between the corresponding first and second electrodes in the corresponding overlap area, wherein a length of the corresponding first electrode defines a length of the corresponding overlap area and therefore the length of the corresponding emission region and wherein a width of the corresponding second electrode defines a width of the corresponding overlap area and therefore the width of the corresponding emission region.

12. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 10 or 11 , wherein the OLED pump arrangement comprises a common flexible support member, such as a common flexible glass support member, and wherein each of the second electrodes is attached to the common flexible support member.

13. The electrically-pumped organic semiconductor laser arrangement as claimed in any one of claims 3 to 12, wherein each of one or more of the first electrodes is semi-transparent, for example wherein each of one or more of the first electrodes comprises a metal such as silver and/or wherein each of one or more of the first electrodes has a thickness of 30 nm or less, 20 nm or less, or 10 nm or less.

14. The electrically-pumped organic semiconductor laser arrangement as claimed in in any one of claims 3 to 13, wherein each of one or more of the second electrodes comprises a metal such as aluminium and/or wherein each of one or more of the second electrodes has a thickness of 1 pm or more, 2 pm or more or 5 pm or more.

15. The electrically-pumped organic semiconductor laser arrangement as claimed in any one of claims 3 to 14, wherein the OLED pump arrangement comprises first wiring corresponding to each emission region, wherein the first wiring is electrically connected to the corresponding first electrode, and wherein the corresponding first wiring comprises a corresponding aperture or gap which is aligned with the corresponding emission region and which is configured to allow transmission of pump light from the corresponding emission region through the corresponding aperture or gap in the corresponding first wiring and through a portion of the corresponding first electrode that extends in and/or across the corresponding aperture or gap.

16. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 15, wherein a width of the corresponding aperture or gap in the corresponding first wiring is less than or equal to ten times the width of the corresponding emission region, less than or equal to five times the width of the corresponding emission region, less than or equal to twice the width of the corresponding emission region, or equal, or substantially equal, to the width of the corresponding emission region.

17. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 15 or 16, wherein a length of the corresponding aperture or gap in the corresponding first wiring is greater than or equal to a length of the corresponding emission region of the OLED.

18. The electrically-pumped organic semiconductor laser arrangement as claimed in any one of claims 3 to 17, wherein the corresponding first electrode comprises an anode and the corresponding second electrode comprises a cathode.

19. The electrically-pumped organic semiconductor laser arrangement as claimed in any one of claims 3 to 18, wherein each of one or more of the OLED active layers comprises 2,7-bis(9,9-spirobifluoren-2-yl)-9,9-spirobifluorene (TSBF) and/or wherein the laser active layer comprises a conjugated polymer such as BBEHP-PPV, or a molecular organic semiconductor such as 4,4’-bis[N-carbazole)styryl]biphenyL

20. The electrically-pumped organic semiconductor laser arrangement as claimed in any one of claims 3 to 19, wherein the or each OLED active layer and the laser active layer are separated by one or more intervening solid layers and, optionally, wherein the one or more intervening solid layers have a total thickness which is less than or equal to half a width of the one or more emission regions, which is less than or equal to one tenth the width of the one or more emission regions, which is less than or equal to one twentieth the width of the one or more emission regions, or which is less than or equal to one fiftieth the width of the one or more emission regions.

21. The electrically-pumped organic semiconductor laser arrangement as claimed in any preceding claim, wherein the OLED pump arrangement and the optically-pumped organic semiconductor laser are aligned so that the longer dimension of the elongated illuminated region is aligned along a direction which is arranged at angle of less than or equal to 5 degrees to the feedback direction, less than or equal to 2 degrees to the feedback direction, less than or equal to 1 degree to the feedback direction, or so that the longer dimension of the elongated illuminated region is aligned parallel to the feedback direction.

22. The electrically-pumped organic semiconductor laser arrangement as claimed in any preceding claim, wherein the OLED pump arrangement comprises a light emitting surface and the optically-pumped organic semiconductor laser comprises a light receiving surface, and wherein the light emitting surface and the light receiving surface are in direct contact with one another, for example wherein the light emitting surface and the light receiving surface are held in conformal contact with one another, or wherein the OLED pump arrangement and the optically-pumped organic semiconductor laser are integrated monolithically.

23. An electrically-pumped organic semiconductor laser arrangement, comprising: an OLED pump arrangement; and an optically-pumped organic semiconductor laser, wherein the OLED pump arrangement comprises an OLED active layer and is configured to emit pump light from one or more emission regions of the OLED active layer, wherein the optically-pumped organic semiconductor laser includes a laser active layer and a grating structure for feedback of laser light in a grating region of the laser active layer along a feedback direction which is parallel to the laser active layer, wherein the one or more emission regions of the OLED pump arrangement are aligned with the grating region of the laser active layer for illumination of a region of the laser active layer with the pump light, which illuminated region comprises at least a portion of the grating region of the laser active layer, wherein the optically-pumped organic semiconductor laser is configured to emit laser light from at least a portion of the illuminated region, wherein the OLED active layer and the laser active layer are separated by one or more intervening solid layers, and wherein the one or more intervening solid layers have a total thickness which is less than or equal to half a minimum dimension of the one or more emission regions of the OLED pump arrangement in a direction parallel to the OLED active layer.

24. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 23, wherein the one or more intervening solid layers have a total thickness which is less than or equal to one tenth the minimum dimension of the one or more emission regions in the direction parallel to the OLED active layer, less than or equal to one twentieth the minimum dimension of the one or more emission regions in the direction parallel to the OLED active layer, or less than or equal to one fiftieth the minimum dimension of the one or more emission regions in the direction parallel to the OLED active layer.

25. The electrically-pumped organic semiconductor laser arrangement as claimed in claim 23 or 24, wherein the OLED pump arrangement comprises a light emitting surface and the optically-pumped organic semiconductor laser comprises a light receiving surface, and wherein light emitting surface of the OLED pump arrangement and the light receiving surface of the optically-pumped organic semiconductor laser are in direct contact with one another, for example wherein the light emitting surface of the OLED pump arrangement and the light receiving surface of the optically-pumped organic semiconductor laser are held in conformal contact with one another, or wherein the OLED pump arrangement and the optically-pumped organic semiconductor laser are integrated monolithically.

26. The electrically-pumped organic semiconductor laser arrangement as claimed in any one of claims 23 to 25, wherein the OLED active layer comprises 2,7-bis(9,9- spirobifluoren-2-yl)-9,9-spirobifluorene (TSBF) and/or wherein the laser active layer comprises a conjugated polymer such as BBEHP-PPV, or a molecular organic semiconductor such as 4,4’-bis[N-carbazole)styryl]biphenyL

27. The electrically-pumped organic semiconductor laser arrangement as claimed in any one of claims 23 to 26, wherein at least one of: each intervening solid layer has a refractive index which is greater than or equal to the refractive index of the OLED active layer; each intervening solid layer has a refractive index greater than or equal to 1 .3 and less than or equal to 2.6, or greater than or equal to 1.4 and less than or equal to 2.2; the one or more intervening solid layers comprise one or more intervening solid OLED layers and one or more intervening solid laser layers; each of the one or more intervening solid OLED layers has a refractive index which is greater than or equal to a refractive index of the OLED active layer; each of the one or more intervening solid OLED layers has a refractive index which is matched or substantially matched to a refractive index of the OLED active layer; the one or more intervening solid laser layers comprise a laser coupling layer; the refractive index of the laser coupling layer is matched or substantially matched to the refractive index of the one or more intervening solid OLED layers; the one or more intervening solid laser layers comprise a laser cladding layer; the refractive index of the laser cladding layer is less than the refractive index of the laser active layer; or the refractive index difference between the refractive index of the laser cladding layer and the refractive index of the laser active layer is less than or equal to 1 .0, less than or equal to 0.5, or less than or equal to 0.2.