JP4768289B2 - Surface light modulation element, surface light modulation element unit, and surface light modulation element unit array - Google Patents

Description

  The present invention relates to a surface light modulation element, a surface light modulation element unit, and a surface light modulation element unit array.

  The surface light modulation element can be used as a light modulation or light switch, particularly as a light modulation / light switch for high output light, and can be used as a bandpass filter with variable wavelength selectivity.

  Therefore, the surface light modulator of the present invention can be used for a light source for optical writing of a printer, a light source for an optical communication device, a display device, and the like.

The electro-optic effect is known as “a phenomenon in which the refractive index changes due to the action of an electric field”. In order to generate the electro-optic effect, a ferroelectric crystal represented by LiNbO ₃ is used. As the electro-optic effect, the Pockels effect and the Kerr effect are known. The Pockels effect is an electro-optical effect in which the refractive index changes in proportion to the applied electric field, and the Kerr effect is an electro-optical effect in which the refractive index changes in proportion to the square of the applied electric field. For example, LiNbO ₃ is a material that exhibits the Pockels effect, and PLZT is a material that exhibits the Kerr effect.

  Various optical elements utilizing the electro-optic effect are conventionally known (for example, Patent Documents 1 to 3).

  The optical element described in Patent Document 2 includes a transparent substrate, first and second dielectric multilayer films having different refractive indexes and alternately stacked on the transparent substrate, and the first and second dielectric layers. The dielectric thin film includes a “refractive index variable layer in which an electro-optic thin film whose refractive index changes due to an electro-optic effect is sandwiched between transparent conductive thin films serving as electrodes”, and the electro-optic thin film is interposed through the transparent conductive thin film. By applying a voltage to the light, the refractive index is changed by the electro-optic effect, and the wavelength range to be transmitted is changed by changing the optical path length.

  In this type of `` light modulation element using an etalon (resonator) containing a material having an electro-optic effect '', the refractive index is changed by `` applying a voltage to the material having an electro-optic effect '', and the optical path accompanying the change in the refractive index. Modulation is performed by changing the length, but the “transmission / reflection characteristics” are sensitive to the incident angle of incident light. When the number of multilayer films constituting the etalon increases, transmission / reflection occurs with a slight deviation in incident angle. The characteristics may change, and for example, the reflectance or transmittance may deteriorate and the light utilization efficiency may deteriorate, or the ON / OFF intensity ratio of the switch function may deteriorate.

JP2002-062515 JP 2003-207753 A JP 2003-195238 A

  The present invention has been made in view of the above circumstances, and in a surface light modulation element using a multilayer reflective layer as an etalon, the incident angle of incident light is different from or changes to a “predetermined incident angle”. It is an object of the present invention to effectively prevent or reduce deterioration or decrease in optical characteristics of the element due to the failure.

The surface light modulator of the present invention is “a light modulator having an ON / OFF layer made of a material whose refractive index changes depending on a signal voltage in a resonator formed of a multilayer reflective layer”, (Claim 1).
That is, in addition to the ON / OFF layer, the resonator has a “control layer made of a material that can be applied with a voltage independently of the ON / OFF layer and whose refractive index changes according to the applied voltage”.
The “ON / OFF layer” has a function of switching the “intensity of light emitted from the resonator” by changing the refractive index according to the applied signal voltage, and the “control layer” is ON / OFF When the layer is in the OFF state, the refractive index is increased by the applied voltage, and the “correction of the incident angle of the incident light to the resonator from the normal incidence” is corrected.

In both the ON / OFF layer and the control layer in the surface light modulation element according to claim 1, “material having an electro-optic effect” can be used as a material whose refractive index is changed by an applied voltage (claim 2). Examples of the material having an electro-optic effect include LiTaO ₃ and PLZT, but LiNbO ₃ can be preferably used as in Examples described later (Claim 3).

4. The planar light modulation element according to claim 2, wherein the ON / OFF layer and the control layer are both formed by sandwiching “a layer of a material having an electro-optic effect” between the transparent electrode films. Further, a structure in which a transparent electrical insulating layer is interposed therebetween can be employed. In this case, a ZnO thin film can be suitably used as the transparent electrode film, and a SiO ₂ thin film can be suitably used as the insulating layer.

  In addition, the “multilayer film reflective layer” constituting the resonator in the surface light modulation device according to any one of claims 1 to 5 is configured as a “dielectric multilayer film” as in the embodiments described later. It can also be configured as a “multilayer film made of a semiconductor material film” as disclosed in Patent Document 3.

The surface light modulation element unit according to the present invention is a surface light modulation element unit using the surface light modulation element according to any one of claims 1 to 5, and includes output light monitoring means and control means ( Claim 6).
“Output light monitoring means” is means for monitoring the output light of the surface light modulator.
The “control unit” is a unit that controls the voltage applied to the control layer by a signal from the output light monitoring unit.

  A plurality of surface light modulation element units according to claim 6 may be arranged in an array to form a surface light modulation element unit array (claim 7). As in Example 3 to be described later, each of the planar light modulation element units arranged in an array may be configured to modulate light of different colors.

  As described above, the surface light modulation element of the present invention has an ON / OFF layer in which a “control layer made of a material whose refractive index changes according to an electric signal” is provided in the resonator. By applying an electrical signal independent of the electrical signal applied to the control layer to the control layer, the refractive index of the control layer can be changed independently of the ON / OFF layer, so the refractive index of the control layer is changed. As a result, the incident angle error and incident angle fluctuation of incident light can be reduced, and the deterioration and reduction of the “optical characteristics as a surface light modulator” can be effectively achieved regardless of the incident angle error and incident angle fluctuation. Can be reduced or prevented.

  Hereinafter, embodiments of the invention will be described as examples.

FIG. 1A illustrates the configuration of the surface light modulation element in an explanatory manner.
The “planar light modulation element” has a structure in which the ON / OFF layer 13 and the control layer 14 are sandwiched between the dielectric multilayer films 11 and 12 in the vertical direction in the figure.
The dielectric multilayer films 11 and 12 are obtained by alternately laminating two kinds of dielectric thin films having different refractive indexes. In the first embodiment, TiO ₂ (refractive index: n = 2.58) and SiO ₂ (refractive index: n = 1.46) films are alternately stacked.
In FIG. 1A, a film denoted by reference numeral 11a is a TiO ₂ film (hereinafter referred to as “TiO ₂ film”), and a film 11b laminated on the TiO ₂ film 11a is an SiO ₂ film (hereinafter referred to as “hereinafter referred to as“ TiO ₂ film ”). It is referred to as “SiO ₂ film”.
The TiO ₂ film 11a and the SiO ₂ film 11b are “film pairs”, and there are 14 “film pairs”, and among these 14 pairs, the “lower 7 pairs” shown in FIG. Constitutes the dielectric multilayer film 11, and “upper seven pairs” constitute the dielectric multilayer film 12. These dielectric multilayer films 11 and 12 are “multilayer reflection layers” and constitute a resonator.

  FIG. 1B illustrates the configuration of the ON / OFF layer 13 and the control layer 14 sandwiched between the dielectric multilayer films 11 and 12.

  Both the ON / OFF layer 13 and the control layer 14 have a configuration in which a thin layer (hereinafter referred to as “electro-optic effect layer”) made of a material having an electro-optic effect is sandwiched between transparent and conductive “transparent electrode films”. It has become. That is, the ON / OFF layer 13 has the electro-optic effect layer 130 sandwiched between the transparent electrode films 131 and 132, and the control layer 14 has the electro-optic effect layer 140 sandwiched between the transparent electrode films 141 and 142. . A transparent electrical insulating layer 150 is interposed between the transparent electrode films 132 and 141 adjacent to each other.

The dielectric multilayer film 11 is formed on a transparent substrate (not shown in FIG. 1A), and light enters from the transparent substrate side. The ideal incidence of light is “perpendicular incidence” that is incident perpendicular to the film surface of the dielectric multilayer film (specifically, the film surface of the TiO ₂ film 11a).
More specifically, the surface light modulation element of the first embodiment is described as follows: “Use wavelength is set to 660 nm, light having the use wavelength is incident on the dielectric multilayer film 11, and the intensity of the incident light is modulated on / off. What is taken out from the dielectric multilayer film 12 ”.
The film thicknesses of the TiO ₂ film and the SiO ₂ film constituting the dielectric multilayer films 11 and 12 are 63.95 nm and 113.01 nm, respectively, and these films are formed by a film forming technique such as vapor deposition.

The material of the electro-optic effect layers 130 and 140 in the ON / OFF layer 13 and the control layer 14 is LiNbO ₃ (refractive index: n ₀ = 2.2). The film thickness of LiNbO ₃ is 75.0 nm for both layers and is formed by vapor deposition or the like.

The transparent electrode films 131, 132, 141, 142 are all ZnO thin films (refractive index: n = 2.0), and the film thicknesses are all 82.5 nm. The transparent electrode films 131, 132, 141, 142 made of these ZnO thin films are formed by sputtering or the like. The transparent electrical insulating layer 150 is a SiO ₂ film having a thickness of 113.01 nm and is formed by sputtering or the like.
LiNbO ₃ which is a material of the electro-optic effect layers 130 and 140 is a “trigonal negative uniaxial crystal”, and its electro-optic constant tensor is as shown in FIG.

As is well known, when an electric field is applied to a material having an electro-optic effect, its refractive index changes. If material having an electro-optical effect of LiNBO _3, the electro-optical effect having the LiNBO ₃ is a Pockels effect described above, the electric field along the optical axis (Z-axis): The application of Ez, normal propagating in the Z-axis direction For light rays, refractive index change: Δn ₀ is
Δn ₀ = r ₁₃ n ₀ ³ Ez / 2 (1)
It becomes.

In the formula (1), “r ₁₃ ” is an electro-optic constant of LiNbO ₃ , which is a component of the electro-optic constant tensor shown in FIG. 1 (c), and for wavelength: λ = 660 nm,
8.6 × 10 ⁻¹² (m / V)
It is.

In Example 1, the Z axis which is the optical axis of the electro-optic effect layers 130 and 140 of LiNbO ₃ used for the ON / OFF layer 13 and the control layer 14 is the vertical direction in FIG. This is the thickness direction of the optical effect layers 130 and 140.

  The spectrum of transmitted light when light having a working wavelength of 660 nm is perpendicularly incident (incident angle: 0 degree) on the film surface of the dielectric multilayer film in the surface light modulator of Example 1 is shown in FIG. As shown in curve 2-1, there is a sharp transmittance peak at a wavelength of 660 nm. This state is a state where no electric field is applied to the electro-optic effect layer 130 of the ON / OFF layer 13 and is an “OFF state”.

When an electric field: Ez is applied to the electro-optic effect layer 130 of the ON / OFF layer 13 by the transparent electrode films 131 and 132 in the Z-axis direction (thickness direction of the electro-optic effect layer 130), light propagates in the Z-axis direction. Refractive index change: Δn ₀ is given by (1) above.

In the formula (1), “r ₁₃ ” is r ₁₃ = 8.6 × 10 ⁻¹² (m / V)
Therefore, when a voltage of 10 V is applied to the electro-optic effect layer 130 of LiNbO ₃ of the ON / OFF layer 13 (ON state), the refractive index change is
Δn ₀ = r ₁₃ n ₀ ³ Ez / 2
= 8.6 × 10 ⁻¹² × 2.2 ³ × {10 / (75 × 10 ⁻⁹ )} / 2
= 0.006
It becomes.

  The spectrum of the transmitted light at this time is as shown by the curve 2-2 in FIG. 2, and the peak transmittance of the spectrum at the OFF time decreases.

  Accordingly, when a semiconductor laser having an emission wavelength of 660 nm is used as the light source, and the light from this light source is converted into a parallel light flux and vertically incident on the surface light modulation element of the first embodiment as described above, the electrical characteristics of the ON / OFF layer 13 are as follows. By turning ON / OFF the application of an electric field to the optical effect layer 130, the intensity of light ("transmitted light") emitted from the dielectric multilayer film 12 of the surface light modulation element is determined according to ON / OFF of the applied electric field. Can be switched.

  Note that, as described above, when light is incident vertically, no electric field is applied to the electro-optic effect layer 140 of the control layer 14.

  When the incident angle of the incident light on the dielectric multilayer film 11 is deviated from the normal incident, for example, incident at an incident angle of 2 degrees, the spectrum of the transmitted light at the OFF time is as shown by a curve 3-1 in FIG. Originally, a “large peak in the spectrum of transmitted light” should be obtained at a wavelength of 660 nm as shown by the curve 2-1 in FIG. 2, which is almost the same as the ON state despite being in the OFF state. It will deteriorate to the level. In this state, good light modulation cannot be performed.

In the surface light modulation element of the first embodiment, the control layer 14 corrects such “deterioration of the modulation function due to the shift of the incident angle” caused by the setting error of the incident angle and the change of the incident angle with time.
That is, in the OFF state when the incident angle is 2 degrees, an electric field is applied to the electro-optic effect layer 140 of the control layer 14 by the transparent electrode films 141 and 142 to change the refractive index of the electro-optic effect layer 140. Thus, a state where an electric field is applied to the electro-optic effect layer 140 is referred to as a “control layer ON state”, and a state where no electric field is applied to the electro-optic effect layer 140 is referred to as a “control layer OFF state”.

  For example, when the ON / OFF layer 13 is in the OFF state and the incident angle is 2 degrees, the spectrum of the transmitted light is as shown by the curve 3-1 in FIG. 3. In this state, the electro-optic effect layer 140 of the control layer 14 is applied. When a voltage of 5 V is applied to make the “control layer ON state”, the refractive index for light propagating in the Z-axis direction can be calculated in the same manner as described above according to the equation (1). In the above case, the refractive index change of the electro-optic effect layer 130 was 0.006 with respect to the applied voltage of 10 V, but the “voltage applied to turn on the control layer” is 5 V. The refractive index change for light having a wavelength of 660 nm is 0.003.

  That is, since the refractive index of the electro-optic effect element 140 of the control layer 14 is increased by 0.003, the light from the ON / OFF layer 13 side (inclined by 2 degrees with respect to the Z-axis direction) is refracted. The angle increases and the light propagation direction approaches the Z axis. In this way, the tilt angle of the light transmitted through the control layer 14 with respect to the Z axis approaches 0 degrees from the incident angle of 2 degrees, so that the modulation function of the planar light modulator is restored.

  Specifically, when the ON / OFF layer 13 is in the OFF state and the control layer is in the ON state, the spectrum of the transmitted light is as shown by the curve 4-1 in FIG. 4 and an extremely large peak value is obtained with respect to the wavelength: 660 nm. be able to.

  Further, when the control layer 14 is turned on when the ON / OFF layer 13 is in the ON state, the spectrum of the transmitted light is as shown by the curve 4-2 in FIG. 4 and the peak value is close to zero.

  In this way, even when the incident state of the incident light on the surface light modulation element deviates from the normal incidence and becomes a finite incident angle (2 degrees in the above example), the electric field is applied to the control layer 14. By controlling this, good light modulation characteristics can be obtained as in the case of normal incidence.

  That is, the surface light modulator of Example 1 has a surface type in which an ON / OFF layer 13 made of a material whose refractive index changes according to a signal voltage is provided in a resonator composed of the multilayer reflective layers 11 and 12. In the optical modulation element, in addition to the ON / OFF layer 13, a voltage can be applied independently of the ON / OFF layer 13, and a control layer 14 made of a material whose refractive index changes according to the applied voltage is included in the resonator. (Claim 1).

Further, both the ON / OFF layer 13 and the control layer 14 use “materials having an electro-optic effect” as materials whose refractive index changes depending on an applied voltage (Claim 2), and materials having an electro-optic effect are LiNbO. ₃ (Claim 3). Both the ON / OFF layer 13 and the control layer 14 are formed by sandwiching layers 130 and 140 of a material having an electro-optic effect between transparent electrode films 131, 132, 141, and 142, and adjacent transparent electrode films 132 and 141. They are laminated with a transparent electrical insulating layer 150 interposed therebetween. The transparent electrode films 131, 132, 141, 142 are ZnO thin films, and the insulating layer 150 is a SiO ₂ film.

  Example 2 described below is an example of the “surface light modulation element unit”.

In FIG. 5, a portion denoted by reference numeral 100 is a surface light modulation element, and a specific configuration is the same as that of the surface light modulation element of the first embodiment illustrated in FIG. 1. The same reference numerals are attached.
A prism 17 is provided on the dielectric multilayer film 12 of the surface light modulator 100. The prism 17 branches light emitted from the dielectric multilayer film 12 of the surface light modulator 100 into two by the light separation film 17A, one is emitted as signal light, and the other is incident on the detector 18 as monitor light. Let The light separation by the prism 17 is not signal light: 50% and monitor light: 50%. Most of the light emitted from the dielectric multilayer film 12 (for example, 95%) is “signal light”, and about 5% is monitor light. Thus, the characteristics of the light separation film 17A are set. The prism 17 and the detector 18 constitute “output light monitoring means”.

  The detector 18 is constituted by a photodiode or the like, converts the intensity of incident monitor light into an electric signal, and inputs it to the control circuit 19. The control circuit 19 includes a “control unit configured by an electronic device capable of arithmetic processing such as a microcomputer” and a voltage applying unit, and the voltage applying unit applies the applied voltage controlled by the control unit to the control layer 14. It is like that. The control circuit 19 constitutes “control means”.

  When the control layer 13 is set to the “control layer OFF state”, the ON / OFF layer is set to the OFF state, and incident light is incident on the dielectric multilayer film 11, the light emitted from the dielectric multilayer film 12 is separated by the prism 17, One monitor light enters the detector 18.

  The control circuit 19 changes the voltage applied to the control layer 14 in accordance with the signal input from the detector 18 and applies feedback by program control, for example, to the control layer 14 so that the monitor light becomes maximum. Set and apply the applied voltage.

  In this way, the spectrum of the transmitted light of the surface light modulator 100 becomes as shown by the curves 4-1 and 4-2 in FIG. 4 according to the OFF state and the ON state of the ON / OFF layer 13. The OFF intensity ratio can be kept in a good state. Thus, according to the surface light modulation element unit of the second embodiment, the incident light incident on the surface light modulation element 100 is in a state of being deviated from vertical incidence (when having a finite incident angle). However, by optimizing the voltage applied to the control layer 14, it is possible to realize good light modulation of the signal light.

  That is, the surface light modulation element unit according to the second embodiment is a surface light modulation element unit using the surface light modulation element 100, and the surface light modulation element 100 is the same as that shown in the first embodiment. Output light monitoring means 17 and 18 for monitoring the output light of the optical modulation element, and control means 19 for controlling the voltage applied to the control layer 14 by a signal from the output light monitoring means. ).

  In the case where the light modulation is performed at high speed and the detector 18 is small, a condensing optical element such as a lens is disposed in front of the detector 18 so that the monitor light is detected by the detector 18 You may make it condense effectively to a light-receiving part).

Example 3 is an example of a surface light modulation element unit array.
FIG. 6 conceptually shows the surface light modulation element unit array of the third embodiment.
In the third embodiment, three surface light modulation element units of the type shown in FIG. 5 are arranged close to each other and linearly arranged as an array (one-dimensional array).

  6A is a top view, FIG. 6B is a front view of the main part, and FIG. 8D is a side view. The three surface light modulation element units 100R, 100G, and 100B have different wavelengths of light to be modulated, the surface light modulation element unit 100R is red light (660 nm), and the surface light modulation element unit 100G is green. The light (532 nm) and the surface light modulation element unit 100B perform light modulation of blue light (457 nm).

  Correspondingly, the thickness of the multilayer reflective layer constituting the resonator in these surface light modulation element units, the thickness of the ON / OFF layer, the electro-optic effect layer of the control layer, and the thickness of the transparent insulating layer Is different. Basically, every layer has an optical thickness of ¼ of the wavelength used by the optical length.

  Each surface light modulation element unit has prisms PR, PG, and PB that separate the emitted light into signal light and monitor light, and these prisms are disposed on the corresponding surface light modulation elements 15R, 15G, and 15B. ing. Detectors 18R, 18G, and 18B that receive monitor light emitted from the respective prisms PR, PG, and PB are also arranged and arranged as a photodiode array, for example, as shown in FIG. 6B. Is configured.

  The control circuit 19A is shared by the surface light modulation element units 100R, 100G, and 100B, but may of course be provided individually for each unit. As shown in FIG. 6 (d), the control circuit 19A controls the surface light modulation elements 15R, 15G, and 15B of each unit (the surface light modulation element 15R is shown in FIG. 6 (d)). Apply an optimized “control voltage” to the layer.

  Since the configuration and operation of each of the surface light modulation element units 100R, 100G, and 100B are the same as those in the second embodiment, detailed description thereof is omitted. However, it goes without saying that each surface light modulation element unit can operate independently.

As in the case of the second embodiment, when the detector array is small, such as when optical modulation is performed at high speed, a lens array is arranged in front of the arrayed detectors 18R, 18G, and 18B, and individual detection is performed. The monitor light can be condensed on the instrument .
That is, the surface light modulation element unit array of the third embodiment is formed by arranging the surface light modulation element units of the second embodiment in a plurality of units 100R, 100G, and 100B in an array (Claim 7).

  In the above description, “on / off switching” is described as the optical modulation. However, it is of course possible to perform modulation such that the transmittance between the ON state and the OFF state can be taken continuously or discretely. .

It is a figure for demonstrating one Example of a surface-type light modulation element. FIG. 3 is a diagram for explaining light modulation characteristics with respect to perpendicular incident light of the surface light modulation element of Example 1. It is a figure for demonstrating the influence when incidence | injection of the incident light to the surface-type light modulation element of Example 1 deviates from perpendicular incidence. It is a figure for demonstrating the correction effect by the control layer in Example 1. FIG. It is a figure for demonstrating one Example of a surface-type light modulation element unit. It is a figure for demonstrating one Example of a surface-type light modulation element unit array.

Explanation of symbols

11, 12 Dielectric multilayer film (multilayer film reflective layer)
13 ON / OFF layer 14 Control layer 130, 140 Electro-optic effect layer

Claims (7)

In a surface light modulation element having an ON / OFF layer made of a material whose refractive index changes depending on a signal voltage in a resonator formed of a multilayer reflection layer,
In addition to the ON / OFF layer, the ON / and OFF layers can independently applied voltage, the control layer made of a material whose refractive index changes possess within the cavity by an applied voltage,
The ON / OFF layer has a function of switching the intensity of light emitted from the resonator by changing the refractive index according to the applied signal voltage,
The control layer has a function of increasing a refractive index by the applied voltage when the ON / OFF layer is in an OFF state, and correcting a deviation of the incident angle of incident light to the resonator from normal incidence. A surface-type light modulation element. The surface light modulator according to claim 1, wherein
A surface light modulation element characterized in that a material having an electro-optic effect is used as a material whose refractive index changes depending on an applied voltage in both the ON / OFF layer and the control layer. The surface light modulator according to claim 2,
A surface light modulation element, wherein the material having an electro-optic effect is LiNbO ₃ . The planar light modulation element according to claim 2 or 3,
Both the ON / OFF layer and the control layer are formed by sandwiching a layer of a material having an electro-optic effect with a transparent electrode film, and are laminated via a transparent electric insulating layer between adjacent transparent electrode films. A surface light modulator. The surface light modulator according to claim 4,
A surface light modulation element, wherein the transparent electrode film is a ZnO thin film and the insulating layer is a SiO ₂ film. A surface light modulation element unit using a surface light modulation element,
The surface light modulation element is any one of claims 1 to 5,
Having output light monitoring means for monitoring the output light of the surface light modulator;
A surface light modulation element unit comprising control means for controlling a voltage applied to the control layer based on a signal from the output light monitoring means.   A surface light modulation element unit array comprising a plurality of the surface light modulation element units according to claim 6 arranged in an array.

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