JP4706970B2 - Photonic crystal semiconductor optical amplifier and integrated optical semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor optical amplifier having a photonic crystal and an integrated optical semiconductor element having the same.

  Photonic crystals are attracting attention as a key technology for realizing next-generation ultra-compact optical integrated circuits, and many research institutions are actively researching both theoretical and experimental aspects. A photonic crystal has a refractive index periodic structure formed by arranging a substance having a refractive index different from that of a semiconductor on a semiconductor or the like with a period of about the wavelength of light. In the photonic crystal, a photonic band gap (PBG) with respect to light is formed according to the solution of the Maxwell equation in the periodic field. Light having a wavelength corresponding to PBG cannot propagate in the photonic crystal in any direction. When a properly designed defect is introduced into such a periodic structure, light is localized at the defect portion. Therefore, for example, an optical resonator can be realized by introducing a point defect into a periodic structure, and an optical waveguide can be realized by introducing a line defect (Non-Patent Documents 1 and 2).

  For example, as a photonic crystal semiconductor optical amplifier having a photonic crystal and having a waveguide formed by introducing a line defect into a periodic structure, as shown in FIG. On the substrate 101 ′, a lower clad layer 102 ′, an active layer 103 ′, an upper clad layer 104 ′, and a contact layer 105 ′ having an upper electrode 107 ′ formed on the upper surface are sequentially laminated. It is formed from 105 ′ to a position deeper than the lower surface of the active layer 103 ′ in the direction in which the active layer 103 ′ is stacked, and a periodic structure having a two-dimensional refractive index is formed in a plane perpendicular to the stacking direction. A photonic crystal semiconductor optical amplifier in which a hole forming region having a plurality of holes 110 'arranged in a lattice pattern and a line defect waveguide region located between the hole forming regions are formed There are 100 '.

  Such a photonic crystal line-defect waveguide has a great feature that it has a unique dispersion relationship that cannot be found in ordinary media. In particular, using the low group velocity effect at the band edge of the photonic band formed by the photonic crystal, that is, the high group refractive index effect, it is possible to propagate light very slowly in the line defect waveguide, Applications to various optical devices are being studied. This low group velocity effect means that light is Bragged near the boundary of the Brillouin zone in the wave number space of the photonic crystal, that is, near the value where the wave number k is k = π / a, where a is the lattice constant of the photonic crystal. This is a phenomenon in which the group velocity decreases due to reflection. Accordingly, the group velocity of light becomes zero at a certain frequency, and light below that frequency cannot propagate through the line defect waveguide. This frequency is called the band edge, and will be called as such in the present application. Non-Patent Document 3 discloses that an extremely large group refractive index of about 90 was observed as an experimental value near the band edge of a line defect waveguide.

If this low group velocity effect is used, the net optical path length becomes long even with a short element length, that is, the optical gain per unit length and the nonlinear optical constant increase. Can be expected. For example, when a photonic crystal optical amplifier is considered, its gain G (λ) is expressed by equation (1).
G (λ) = G ₀ (λ) · _ng (λ) / n ₀ (λ) (1)
Where G ₀ (λ) and n ₀ (λ) represent the gain and group refractive index of the amplifying element without the photonic crystal structure, respectively, and n _g (λ) represents the line defect conductivity in the photonic crystal. Represents the group index of the waveguide. That is, since the gain increases in proportion to the size of the group refractive index of the line defect waveguide, the length of the amplifier required to obtain a predetermined gain decreases in inverse proportion thereto. For this reason, a very small device is realized by using the high group refractive index effect of the photonic crystal.

A. Talneau, et al., “High external efficiency in a monomode full-photonic-crystal laser under continuous wave electric injection”, Applied Physics Letters, v.85, no.11, pp.1913-1915 (2004) H. Takano, et al., “In-plane-type channel drop filter in a two-dimensional photonic crystal slab”, Applied Physics Letters, v.84, no.13, pp.2226-2228 (2004) M. Notomi, et al., "Extremely Large Group-Velocity Dispersion of Line Defect Waveguides in Photonic Crystal Slabs", Physical Review Letters, Volume 87, Page 253902 (2001)

However, in the conventional photonic crystal optical amplifier, as can be seen from the equation (1), the gain is theoretically infinite at the band edge where the group refractive index n _g (λ) is infinite. There was a problem that laser oscillation was likely to occur at a wavelength corresponding to the edge.

  The present invention has been made in view of the above, and provides a photonic crystal semiconductor optical amplifier capable of suppressing the occurrence of laser oscillation at a wavelength corresponding to the band edge, and an integrated optical semiconductor device including the same. The purpose is to do.

  In order to solve the above-described problems and achieve the object, a photonic crystal semiconductor optical amplifier according to the present invention includes an active layer stacked between a lower cladding layer and an upper cladding layer stacked on a semiconductor substrate. A surface perpendicular to the stacking direction from the upper cladding layer to a position deeper than the lower surface of the active layer in the direction in which the active layer is stacked except for a line defect waveguide region that guides desired light. A light that is guided in the active layer of the line defect waveguide region by forming a hole forming region in which a plurality of holes are arranged in a lattice pattern so as to form a periodic structure having a two-dimensional refractive index inside A photonic crystal semiconductor optical amplifier for amplifying the light, comprising an optical attenuator capable of attenuating light at a band edge of the photonic band structure formed by the periodic structure outside the line defect waveguide region This The features.

  In the photonic crystal semiconductor optical amplifier according to the present invention as set forth in the invention described above, the light attenuating part is a light absorbing semiconductor layer having absorptivity with respect to light at the band edge.

  Further, the photonic crystal semiconductor optical amplifier according to the present invention is the above-described invention, wherein the current formed so as to bury the line defect waveguide region from both sides so that an injection current does not flow outside the line defect waveguide region. It has a blocking layer, and the light absorption semiconductor layer is provided in the current blocking layer.

  In the photonic crystal semiconductor optical amplifier according to the present invention, the current blocking layer is formed by stacking a p-type semiconductor layer and an n-type semiconductor layer, and the light absorption semiconductor layer is the p-type semiconductor layer. And an n-type semiconductor layer.

  Further, in the photonic crystal semiconductor optical amplifier according to the present invention, in the above invention, the light attenuating portion is formed with respect to the light at the band edge formed at a position where the electric field of the light at the band edge reaches in the stacking direction. It is a light-absorbing electrode having absorptivity.

  The photonic crystal semiconductor optical amplifier according to the present invention is characterized in that, in the above invention, the active layer is composed of a multiple quantum well.

  An integrated optical semiconductor device according to the present invention includes any one of the above-described photonic crystal semiconductor optical amplifiers according to the present invention and an optical semiconductor device connected to the photonic crystal semiconductor optical amplifier. It is characterized by being accumulated on top.

  According to the photonic crystal semiconductor optical amplifier according to the present invention, the light attenuating portion provided outside the line defect waveguide region corresponds to a band edge having a high gain distributed and distributed outside the line defect waveguide region. It has the property of attenuating the light of the wavelength. This increases the loss at the wavelength corresponding to the band edge and makes it difficult for laser oscillation to occur. For this reason, it is possible to realize a photonic crystal semiconductor optical amplifier capable of suppressing the occurrence of laser oscillation at a wavelength corresponding to the band edge and an integrated optical semiconductor element including the photonic crystal semiconductor optical amplifier.

  Embodiments of a photonic crystal semiconductor optical amplifier and an integrated optical semiconductor device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a plan view schematically showing a photonic crystal semiconductor optical amplifier according to Embodiment 1 of the present invention. FIG. 2 is a perspective view schematically showing the photonic crystal semiconductor optical amplifier of FIG. In FIG. 2, the ridge waveguide formed at both ends is omitted. 3 is a cross-sectional view of the photonic crystal semiconductor optical amplifier of FIG. 1 taken along line XX. 4 is a cross-sectional view of the photonic crystal semiconductor optical amplifier of FIG. 1 taken along line YY.

  As shown in FIGS. 1 to 4, the photonic crystal semiconductor optical amplifier 100 according to the first embodiment includes an n-InP substrate 101 that is a semiconductor substrate and a lower cladding layer that is stacked on the n-InP substrate 101. These are an n-InP buffer layer 102, an InGaAsP active layer 103 having a band gap wavelength of 1550 nm and a mesa stripe shape, which is stacked on the n-InP buffer layer 102, and an upper cladding layer which is stacked on the InGaAsP active layer 103. The p-InP clad layer 104 and the p-InP clad part 104a, the p-InGaAs contact layer 105 which is a contact layer laminated on the p-InP clad layer 104, and the AuGeNi formed on the lower surface of the n-InP substrate 101 N-side electrode 106 made of / Au and p-InGaAsP contact layer 105 And a p-side electrode 107 consisting of formed on the upper surface Ti / Pt / Au.

  Further, on both sides of the mesa stripe-shaped InGaAsP active layer 103, a current blocking layer 108 composed of an n-InP layer 108a and a p-InP layer 108b formed so as to embed the InGaAsP active layer 103, and optical attenuation And an InGaAs light absorption layer 109 that is a light absorption semiconductor layer stacked between the n-InP layer 108a and the p-InP layer 108b.

  A period of a two-dimensional refractive index is formed from the p-InGaAs contact layer 105 to a position deeper than the lower surface of the InGaAsP active layer 103 in the direction in which the InGaAsP active layer 103 is laminated and in a plane perpendicular to the lamination direction. A hole forming region 111 having a plurality of cylindrical holes 110 arranged in a triangular lattice so as to form a structure, and a center plane in the width direction coincide with a center plane in the width direction of the InGaAsP active layer 103. A line defect waveguide region 112 is formed.

  Ridge waveguides 120 and 130 are formed at both ends of the photonic crystal semiconductor optical amplifier 100. The ridge waveguide 120 includes an n-InP buffer layer 121 which is a lower cladding layer stacked on the n-InP substrate 101, and an InGaAsP waveguide layer 122 having a band gap wavelength of 1300 nm stacked on the n-InP buffer layer 121. And p-InP cladding layers 123 and 124, which are upper cladding layers stacked on the InGaAsP waveguide layer 122. The InGaAsP waveguide layer 122 is connected to the InGaAsP active layer 103 in the line defect waveguide region 112. The ridge waveguide 130 has a similar structure.

  The diameter 110a of the hole 110 and the value of the lattice constant 110b of the triangular lattice of the photonic crystal are different depending on the wavelength band to emit light. For example, the lattice constant 110b is 300 to 500 nm. In the photonic crystal semiconductor optical amplifier 100 operating near the wavelength of 1550 nm, the diameter 110a is 240 nm, and the lattice constant 110b is 380 nm. Further, the distance t between adjacent hole centers across the line defect waveguide region 112 is 658 nm, and one line is excluded from the patterns arranged in a triangular lattice pattern. The distance between the holes means the distance between the center axes of the holes when the holes are cylindrical.

  Next, the operation of the photonic crystal semiconductor optical amplifier 100 will be described. When a voltage is applied between the n-side electrode 106 and the p-side electrode 107 and current is injected, no current flows through the current blocking layer 105 in which the p-InP layer 105a and the n-InP layer 105b are stacked, A current flows only in the InGaAsP active layer 103. As a result, the current injection efficiency into the InGaAsP active layer 103 becomes high.

  The light introduced from the InGaAsP waveguide layer 122 of the ridge waveguide 120 into the InGaAsP active layer 103 that has been excited by the current injection is propagated in the waveguide mode of the line defect waveguide region 112, and is in the InGaAsP active layer 103. It is amplified by. On the other hand, spontaneous emission light is generated in the InGaAsP active layer 103, amplified while propagating in the waveguide mode, and becomes amplified spontaneous emission (ASE). At this time, the light propagating through the line defect waveguide region 112 has a different electric field intensity distribution depending on the waveguide mode.

  The manner in which the electric field intensity distribution of light varies depending on the waveguide mode will be described more specifically with reference to the drawings. FIG. 5 is a graph showing the waveguide mode of the line defect waveguide region 112 of the photonic crystal semiconductor optical amplifier 100. The horizontal axis represents the wave number, and the vertical axis represents the normalized frequency. Here, a is the value of the lattice constant 110b of the photonic crystal. A line M0 indicates the dispersion relation of the fundamental mode of light propagating through the photonic crystal line defect waveguide region 112. Line A indicates the lower end of the PBG, and line B indicates the upper end of the PBG. On the other hand, FIG. 6 shows the wave number of the waveguide in the mode corresponding to the wave number k = 0.5π / a, which is far from the band edge k = π / a, that is, the value corresponding to the horizontal axis value 0.25 in FIG. It is a figure which shows the electric field strength distribution of the light of waveguide mode in the length for the crystal lattice 1 period in a longitudinal direction. FIG. 7 shows the wave length of k = π / a at the band edge, that is, the length corresponding to one period of the crystal lattice in the longitudinal direction of the waveguide in the mode corresponding to the value 0.5 on the horizontal axis in FIG. It is a figure which shows the electric field strength distribution of the light of waveguide mode. The bright part in FIGS. 6 and 7 is a part where the electric field strength is large.

  In the mode corresponding to the wave number far from the band end shown in FIG. 6, the electric field E1 is concentrated inside the line defect waveguide region 112, whereas in the mode corresponding to the wave number at the band end shown in FIG. It can be seen that E2 has a distributed shape that extends not only to the inside of the line defect waveguide 112 but also to the outside hole forming region 111.

  At a wavelength corresponding to the band edge, the gain of the InGaAsP active layer 103 in the line defect waveguide region 112 becomes very high, so that laser oscillation is likely to occur. However, as in the photonic crystal semiconductor optical amplifier 100 according to the first embodiment, with respect to the light at the band edge of the photonic band structure by the refractive index periodic structure of the hole forming region outside the line defect waveguide region 112. If the InGaAs light absorption layer 109 having absorptivity is provided, the loss is selectively given to the light in the mode corresponding to the wave number near the band edge, which has a property of being spread and distributed outside the line defect waveguide region 112. Therefore, laser oscillation at a wavelength corresponding to the band edge can be prevented. Since the InGaAs light absorption layer 109 is laminated between the p-InP layer 108a and the n-InP layer 108b, which are current blocking layers, the injected current does not flow and the excited state is not obtained. 109 functions as a light absorber.

  Next, a method for manufacturing the photonic crystal semiconductor optical amplifier 100 according to the first embodiment will be described. First, using an MOCVD (Metal Organic Chemical Vapor Deposition) crystal growth apparatus, an n-InP buffer layer 102 on an n-InP substrate 101, an InGaAsP active layer having a thickness of 500 nm and a band gap wavelength of 1550 nm, and a p-type having a thickness of 300 nm. -InP cladding layers are grown sequentially. The InGaAsP active layer may have a multiple quantum well structure.

  Thereafter, a SiN film is formed on the entire surface of the p-InP cladding layer by a plasma CVD apparatus. Next, the SiN film is processed into a stripe shape having a width of 2 μm by photolithography and RIE (Reactive Ion Etching). Next, the InGaAsP active layer and the p-InP clad layer are formed into a stripe shape having a width of 1 μm by dry etching and wet etching, and the InGaAsP active layer is further formed into a mesa shape having a height of about 1 μm. The InP clad portion 104a and the mesa stripe-shaped InGaAsP active layer 103 are formed.

  Next, using the SiN film as a selective growth mask, a p-InP layer 108b having a thickness of 300 nm, a non-doped InGaAs light absorbing layer 109 having a thickness of 300 nm, and an n-InP layer 108a having a thickness of 400 nm are sequentially buried and grown. Here, by adjusting the thickness of the mesa-shaped portion and the portion of the outer portion that has been buried and grown so that the equivalent refractive index in the stacking direction is substantially equal, the film is guided to the InGaAsP active layer 103. The effect of the photonic crystal structure can be exerted on the light.

  Thereafter, after removing the SiN film, the p-InP cladding portion 104a and the InGaAsP active layer 103 at both ends of the photonic crystal semiconductor optical amplifier 100 are removed by etching in order to form the ridge waveguides 120 and 130. Then, an InGaAsP waveguide layer 122 having a thickness of 500 nm and a band gap wavelength of 1300 nm and a p-InP cladding layer 123 having a thickness of 300 nm are regrown on the removed portion. Thereafter, the p-InP cladding layers 104 and 124 and the p-InGaAs contact layer 105 are sequentially grown. In this embodiment, the thickness of the p-InP cladding layer 104 is set to 1 μm or more so that the electric field of light guided to the InGaAsP active layer 103 does not reach the p-side electrode 107 formed later. . The p-InGaAs contact layer 105 grown on both ends forming the ridge waveguides 120 and 130 is then removed.

  Next, an electron beam drawing apparatus except for a predetermined row of a plurality of circular resist patterns arranged in a triangular lattice pattern so that a two-dimensional refractive index periodic structure is formed; The resist pattern of the ridge waveguide is transferred to the p-InGaAs contact layer 105. Thereafter, using the transferred pattern as an etching mask, an ICP (Inductively Coupled Plasma) dry etching apparatus using chlorine gas is used to etch the bottom surface of the InGaAsP active layer 103 in the direction in which the InGaAsP active layer 103 is laminated from the p-InGaAs contact layer 105. Etching is performed to a depth of about 3 μm to a deeper position, that is, to the n-InP buffer layer 102, and a plurality of cylindrical holes 110 are periodically formed to form a hole forming region 111. . At the same time, at both ends where the ridge waveguides 120 and 130 are formed, the ridge waveguides 120 and 130 having a width of 700 nm are formed by etching in a ridge shape until reaching the n-InP buffer layer 121.

  By this etching, holes are not formed in one row where the circular pattern was not transferred. Therefore, a line defect waveguide region 112 that is a line defect introduced into the periodic structure is formed between the hole forming regions 111. The line defect waveguide region 112 is formed so that the center plane in the width direction coincides with the center plane in the width direction of the mesa stripe-shaped InGaAsP active layer 103.

  Next, after polishing the n-InP substrate 101 side so that the entire laminated substrate manufactured as described above has a thickness of about 120 μm, the n-side electrode 106 made of AuGeNi / Au is attached to the lower surface of the n-InP substrate 101. The p-side electrode 107 made of Ti / Pt / Au is formed on the upper surface of the p-InGaAs contact layer 105, respectively. Finally, the photonic crystal semiconductor optical amplifier 100 can be manufactured by cleaving the laminated substrate for each element.

  In order to confirm the effect of the present invention, the photonic crystal semiconductor optical amplifier according to the first embodiment manufactured by the above method and the photonic manufactured by the same method as described above except that the InGaAs light absorption layer is not formed. The amplification characteristics of the crystal semiconductor optical amplifier were evaluated. Then, it was confirmed that the photonic crystal semiconductor optical amplifier in which the InGaAs light absorption layer is not formed has laser oscillation when the injection current is about 20 mA. However, in the photonic crystal semiconductor optical amplifier according to the first embodiment, It was confirmed that laser oscillation did not occur even when the injection current was 20 mA, and laser oscillation was prevented. It was also confirmed that a gain as high as 30 dB could be realized even if the length of the light propagation direction in the amplifier was as short as 10 μm.

(Embodiment 2)
Next, a photonic crystal semiconductor optical amplifier according to the second embodiment of the present invention will be described. Unlike the photonic crystal semiconductor optical amplifier according to the first embodiment, the photonic crystal semiconductor optical amplifier according to the second embodiment forms light that spreads and distributes from the line defect waveguide region above the upper cladding layer. Is absorbed by the formed electrode.

  FIG. 8 is a perspective view schematically showing the photonic crystal semiconductor optical amplifier according to the second embodiment, and an electric field intensity distribution of light spreading from both sides of the line defect waveguide region to the position in the stacking direction. It is a figure which shows a graph. In FIG. 8, ridge waveguides formed at both ends are omitted. Similar to the photonic crystal semiconductor optical amplifier 100 according to the first embodiment, the photonic crystal semiconductor optical amplifier 200 according to the second embodiment includes an n-InP substrate 201, an n-InP buffer layer 202, and a band gap. An InGaAsP active layer 203 having a wavelength of 1300 nm, a p-InP cladding layer 204, a p-InGaAsP contact layer 205, and an n-side electrode 206 made of AuGeNi / Au formed on the lower surface of the n-InP substrate 201. A ridge waveguide having an InGaAsP waveguide layer with a band gap wavelength of 1100 nm is formed at both ends. A hole forming region 211 having a plurality of cylindrical holes 210 and a line defect waveguide region 212 are formed. However, the InGaAsP active layer 203 is not formed in a mesa stripe, no current blocking layer is formed, and p-side light absorption electrodes 207a and 207b made of Ti / Pt / Au are formed on the upper surface of the p-InGaAsP contact layer 205. Is different.

  In the photonic crystal semiconductor optical amplifier 200 operating near a wavelength of 1300 nm, the diameter of the holes 210 is 200 nm and the lattice constant is 320 nm. Further, the distance between adjacent hole centers with the line defect waveguide region 212 interposed therebetween is 554 nm, and one line is excluded from the patterns arranged in a triangular lattice pattern.

  Next, the operation principle of the photonic crystal semiconductor optical amplifier 200 will be described. As in the case of the photonic crystal semiconductor optical amplifier 100, light in a mode corresponding to the wave number near the band edge is spread and distributed outside the line defect waveguide region 212. The electric field intensity of light in the vicinity of the band edge spread from the line defect waveguide region has a distribution indicated by a shape like a curve E3 with respect to the stacking direction as shown in the graph of FIG. The side light absorbing electrodes 207a and 207b are formed at a position corresponding to the position P1 in the above graph, that is, a position where the electric field of light near the band edge indicated by the curve E3 reaches. The p-side light absorption electrodes 207a and 207b are made of Ti / Pt / Au and absorb light in the 1300 nm band. Therefore, a loss can be selectively given to light in a mode corresponding to the wave number in the vicinity of the band edge where light is distributed outside the line defect waveguide region 212, so that laser oscillation at a wavelength corresponding to the band edge is achieved. Can be prevented.

  Regarding the method of manufacturing the photonic crystal semiconductor optical amplifier 200 according to the second embodiment, the photonic crystal semiconductor optical amplifier according to the first embodiment is the same except that the InGaAsP active layer is not formed in a mesa stripe shape and a buried layer is not formed. It can carry out similarly to the manufacturing method of 100. However, although the thickness of the upper clad layer 104 is about 1 μm or more in the first embodiment, in the second embodiment, the upper clad layer 204 is grown with a thin thickness of about 400 nm to obtain a line defect waveguide region. The electric field of the light in the vicinity of the band edge that spreads outward from 212 reaches the positions of the p-side light absorption electrodes 207a and 207b with sufficient intensity. Further, the p-side light absorption electrodes 207a and 207b are formed only outside the line defect waveguide region 212 so that only light having a wavelength corresponding to the vicinity of the band edge can be absorbed.

  In order to confirm the effect of the present invention, the amplification characteristics of the photonic crystal semiconductor optical amplifier according to the second embodiment manufactured by the above method were evaluated. Then, it was confirmed that the photonic crystal semiconductor optical amplifier according to the second embodiment did not cause laser oscillation even when the injection current was 30 mA and prevented laser oscillation. It was also confirmed that a gain as high as 30 dB could be realized even if the length of the light propagation direction in the amplifier was as short as 10 μm.

(Embodiment 3)
Next, an integrated optical semiconductor device according to the third embodiment of the present invention will be described. The integrated optical semiconductor device according to the third embodiment includes a photonic crystal semiconductor optical amplifier similar to the photonic crystal semiconductor optical amplifier according to the first embodiment and a plurality of semiconductor lasers connected thereto. Integrated on one substrate.

  FIG. 9 is a plan view schematically showing an integrated optical semiconductor element 1000 according to the third embodiment of the present invention. This integrated optical semiconductor element 1000 has a configuration similar to that of the photonic crystal semiconductor optical amplifier 100 according to the first embodiment, a photonic crystal semiconductor optical amplifier 300 having a ridge waveguide formed only on one side, a wavelength Semiconductor lasers 401 to 404 that emit laser beams having different wavelengths, curved waveguides 501 to 504, and an MMI (Multi-Mode Interference) coupler 600 that is a multiplexer that multiplexes light having different wavelengths It is collected on top.

  Laser beams having different wavelengths emitted from the semiconductor lasers 401 to 404 are guided by the curved waveguides 501 to 504 and multiplexed by the MMI coupler 600. The light intensity of the combined light is reduced by the waveguide loss of the bent waveguides 501 to 504 and the coupling loss of the MMI coupler 600, but is amplified by the photonic crystal semiconductor optical amplifier 300 to compensate for the loss. And emitted from the ridge waveguide.

  In the photonic crystal semiconductor optical amplifier according to the first or second embodiment, a spot size converter may be appropriately provided outside the ridge waveguide for connection to an external light source such as a semiconductor laser.

  In the integrated optical semiconductor device according to the third embodiment, the semiconductor laser may be a line defect type photonic crystal optical semiconductor laser as described in Non-Patent Document 1. The wavelength multiplexer may be a wavelength multiplexer using a point defect type photonic crystal optical resonator as described in Non-Patent Document 2.

1 is a plan view schematically showing a photonic crystal semiconductor optical amplifier according to a first embodiment of the present invention. FIG. 2 is a perspective view schematically showing the photonic crystal semiconductor optical amplifier of FIG. 1. FIG. 2 is a cross-sectional view of the photonic crystal semiconductor optical amplifier shown in FIG. 1 taken along line XX. FIG. 2 is a cross-sectional view of the photonic crystal semiconductor optical amplifier shown in FIG. 1 taken along line YY. 2 is a graph showing a dispersion relationship of waveguide modes in a line defect waveguide region of the photonic crystal semiconductor optical amplifier of FIG. 1. It is a figure which shows the electric field strength distribution of the light of the waveguide mode with respect to one period of the longitudinal direction of a waveguide in the mode corresponded to the wave number of k = 0.5 (pi) / a in FIG. It is a figure which shows the electric field strength distribution of the light of the waveguide mode with respect to one period of the longitudinal direction of a waveguide in the mode corresponded to the wave number of k = (pi) / a in FIG. The perspective view which represented typically the photonic crystal semiconductor optical amplifier which concerns on Embodiment 2 of this invention, and the figure which shows the graph of the electric field strength distribution of the light distributed on both sides from the line defect waveguide area | region with respect to the position of a lamination direction It is. FIG. 6 is a plan view schematically showing an integrated optical semiconductor device according to a third embodiment of the present invention. It is the perspective view which represented the conventional photonic crystal semiconductor optical amplifier typically.

Explanation of symbols

100 to 300 Photonic crystal semiconductor optical amplifier 101, 201 n-InP substrate 102, 202 n-InP buffer layer 103, 203 InGaAsP active layer 104, 204 p-InP clad layer 104a p-InP clad part 105, 205 p-InGaAs Contact layer 106, 206 n-side electrode 107 p-side electrode 108 current blocking layer 108a n-InP layer 108b p-InP layer 109 InGaAs light absorbing layer 110, 210 hole 110a hole diameter 110b lattice constant 111, 211 hole formation Region 112, 212 Line defect waveguide region 120, 130 Ridge waveguide 121 n-InP buffer layer 122 InGaAsP waveguide layer 123, 124 p-InP clad layer 207a, 207b p-side light absorption electrodes 401-404 Semiconductor Laser 501 to 504 bend waveguide 600 MMI coupler 700 substrate 1000 integrated optical semiconductor device

Claims (7)

An active layer is formed by laminating between a lower clad layer and an upper clad layer laminated on a semiconductor substrate, and the active layer is activated from the upper clad layer except for a line defect waveguide region that guides desired light. A plurality of vacancies are arranged in a lattice pattern so as to form a periodic structure having a two-dimensional refractive index in a plane perpendicular to the laminating direction to a position deeper than the lower surface of the active layer in the laminating direction. A photonic crystal semiconductor optical amplifier for amplifying light guided in an active layer of the line defect waveguide region,
2. A photonic crystal semiconductor optical amplifier comprising an optical attenuator capable of attenuating light at a band edge of a photonic band structure formed by a periodical structure outside the line defect waveguide region.   The photonic crystal semiconductor optical amplifier according to claim 1, wherein the light attenuating portion is a light absorbing semiconductor layer having absorptivity with respect to light at the band edge.   A current blocking layer formed so as to bury the line defect waveguide region from both sides so that an injection current does not flow outside the line defect waveguide region; and the light absorption semiconductor layer is formed on the current blocking layer. The photonic crystal semiconductor optical amplifier according to claim 2, wherein the photonic crystal semiconductor optical amplifier is provided.   The current blocking layer is formed by stacking a p-type semiconductor layer and an n-type semiconductor layer, and the light absorption semiconductor layer is stacked between the p-type semiconductor layer and the n-type semiconductor layer. The photonic crystal semiconductor optical amplifier according to claim 3.   The light attenuating portion is a light absorption electrode formed at a position where the electric field of the light at the band edge reaches in the stacking direction and having an absorptivity with respect to the light at the band edge. A photonic crystal semiconductor optical amplifier described in 1.   6. The photonic crystal semiconductor optical amplifier according to claim 1, wherein the active layer is composed of a multiple quantum well.   7. The photonic crystal semiconductor optical amplifier according to claim 1 and an optical semiconductor element connected to the photonic crystal semiconductor optical amplifier are integrated on the semiconductor substrate. An integrated optical semiconductor device.