Optical semiconductor device

Abstract

The optical semiconductor device according to the present disclosure includes: a semiconductor substrate; at least one semiconductor laser disposed on the semiconductor substrate; an optical multiplexer / demultiplexer circuit disposed on the semiconductor substrate that multiplexes or demultiplexes first output light of the semiconductor laser and outputs second output light and third output light; a first waveguide section disposed on the semiconductor substrate that outputs the second output light from an end face of the semiconductor substrate; and a second waveguide section having an optical amplifier that amplifies the third output light and a reflection section, disposed on the semiconductor substrate, the reflection section having a diffraction grating that reflects the third output light amplified by the optical amplifier and feeds it back to the semiconductor laser via the optical amplifier and the optical multiplexer / demultiplexer circuit, and a resonator is formed by the semiconductor laser and the reflection section.

Description

Technical Field

[0001] The present disclosure relates to an optical semiconductor device. Background Art

[0002] A semiconductor laser element is disclosed in Patent Document 1. In this semiconductor laser element, an optical output waveguide portion and an optical feedback waveguide portion are formed on the same semiconductor substrate. The optical output waveguide portion includes: a semiconductor laser portion that oscillates in a single mode; an optical branching circuit portion that branches the oscillating light of the semiconductor laser portion into two; and a first semiconductor amplifier that amplifies and outputs one of the lights branched by the optical branching circuit portion. The optical feedback waveguide portion includes: a second semiconductor amplifier that amplifies the other light branched by the optical branching circuit portion; and a reflector that reflects the light amplified by the second semiconductor amplifier. The light amplified by the second semiconductor amplifier and reflected by the reflector is fed back to the semiconductor laser portion via the optical branching circuit portion. By feeding back a part of the oscillating light of the semiconductor laser, narrowing of the spectral line width can be achieved. The reflector is a cleavage plane exposed on the side surface of the semiconductor chip.

[0003] Patent Document 1: Japanese Patent No. 6245656

[0004] The phase of the oscillation mode of the resonator formed between the semiconductor laser and the cleavage plane needs to be consistent with the phase of the oscillation mode of the semiconductor laser itself. In Patent Document 1, the phase of the oscillation mode of the resonator depends on the position of the cleavage plane. The position accuracy of the cleavage plane is generally about ±20 μm. Therefore, it may be difficult to make the phases of the oscillation modes consistent by adjusting the position of the cleavage plane. Therefore, from the viewpoint of improving the yield, a phase adjustment region for adjusting the phase of the oscillation mode is required. As a result, the semiconductor laser element may be enlarged.

[0005] In addition, in Patent Document 1, a bent waveguide is formed in order to guide light to the cleavage plane exposed on the side surface of the semiconductor chip. For example, when a buried hetero structure is used in the bent waveguide, generally at least about several hundred μm is required as the curvature radius of the bent waveguide. Therefore, the width of the semiconductor chip may increase. Summary of the Invention

[0006] An object of the present disclosure is to obtain an optical semiconductor device capable of achieving miniaturization.

[0007] The optical semiconductor device according to the present disclosure includes: a semiconductor substrate; at least one semiconductor laser disposed on the semiconductor substrate; an optical multiplexer / demultiplexer disposed on the semiconductor substrate that multiplexes or demultiplexes the first output light of the semiconductor laser and outputs second output light and third output light; a first waveguide portion disposed on the semiconductor substrate that outputs the second output light from an end face of the semiconductor substrate; and a second waveguide portion having an optical amplifier that amplifies the third output light and a reflection portion, and disposed on the semiconductor substrate, the reflection portion having a diffraction grating that reflects the third output light amplified by the optical amplifier and feeds it back to the semiconductor laser via the optical amplifier and the optical multiplexer / demultiplexer, and a resonator is formed by the semiconductor laser and the reflection portion.

[0008] In the optical semiconductor device according to the present disclosure, a resonator is formed by the semiconductor laser and the reflection portion. Therefore, a phase adjustment region is not required, and the optical semiconductor device can be miniaturized. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a top view of the optical semiconductor device according to Embodiment 1.

[0010] Figure 2 is a cross-sectional view obtained by cutting along the straight line A-A Figure 1 and obtained.

[0011] Figure 3 is a cross-sectional view of the semiconductor laser according to Embodiment 1 along the optical axis direction.

[0012] Figure 4 is a cross-sectional view obtained by cutting along the straight line B-B Figure 1 and obtained.

[0013] Figure 5 is a cross-sectional view obtained by cutting along the straight line C-C Figure 1 and obtained.

[0014] Figure 6 is a cross-sectional view obtained by cutting along the straight line D-D Figure 1 and obtained.

[0015] Figure 7 is a cross-sectional view of the reflection portion according to Embodiment 1 along the optical axis direction.

[0016] Figure 8 is a top view of the optical semiconductor device according to Embodiment 2.

[0017] Figure 9 is a top view of the optical semiconductor device according to Embodiment 3.

[0018] Figure 10It is a top view of the optical semiconductor device according to Embodiment 4.

[0019] Figure 11 It is a cross-sectional view along the optical axis of the reflection part according to Embodiment 4.

[0020] Figure 12 It is a top view of the optical semiconductor device according to Embodiment 5.

[0021] Figure 13 It is a cross-sectional view along the optical axis of the semiconductor laser according to Embodiment 5.

[0022] Figure 14 It is a cross-sectional view along the optical axis of the reflection part according to Embodiment 5. Specific Embodiments

[0023] The optical semiconductor device according to each embodiment will be described with reference to the accompanying drawings. The same or corresponding components are denoted by the same reference numerals, and redundant descriptions may be omitted sometimes.

[0024] Embodiment 1

[0025] Figure 1 It is a top view of the optical semiconductor device 100 according to Embodiment 1. In the optical semiconductor device 100, a plurality of semiconductor lasers 60, a plurality of waveguides 61, an optical multiplexer / demultiplexer 62, a waveguide 63, an optical amplifier 64, a waveguide 71, an optical amplifier 72, a waveguide 73, and a reflection part 74 are provided on the same semiconductor substrate 10. The semiconductor substrate 10 has a front end face 52 and a rear end face 51.

[0026] The plurality of semiconductor lasers 60 form a semiconductor laser array. Although in Figure 1 an example in which the optical semiconductor device 100 includes 4 semiconductor lasers 60 is shown, the number of semiconductor lasers 60 only needs to be plural. For example, the number of semiconductor lasers 60 may be 16. The semiconductor laser 60 is, for example, a DFB-LD (Distributed Feedback-Laser Diode). The semiconductor laser 60 outputs first output light from the front end side. In addition, the semiconductor laser 60 outputs rear end face side output light from the rear end side. Each semiconductor laser 60 can oscillate light in a single mode. In addition, the plurality of semiconductor lasers 60 oscillate at different wavelengths. Further, a spare semiconductor laser 60 may be mounted on the optical semiconductor device 100. In this case, the plurality of semiconductor lasers 60 may also include semiconductor lasers that oscillate light having the same wavelength.

[0027] The plurality of waveguides 61 connect the plurality of semiconductor lasers 60 and the optical multiplexing / demultiplexing circuit 62. The plurality of waveguides 61 guide the first output light of the plurality of semiconductor lasers 60 to the optical multiplexing / demultiplexing circuit 62. The plurality of waveguides 61 constitute a waveguide array. The same number of waveguides 61 as the number of semiconductor lasers 60 is provided.

[0028] The optical combining and demultiplexing circuit 62 combines or demultiplexes the first output light of the semiconductor laser 60, and outputs the second output light and the third output light. The optical combining and demultiplexing circuit 62 of this embodiment is connected to a plurality of waveguides 61 on the input side, and is connected to waveguides 63 and 71 on the output side. The optical combining and demultiplexing circuit 62 combines the first output light of the semiconductor laser 60, and outputs the combined first output light as the second output light and the third output light to the waveguides 63 and 71, respectively. The optical combining and demultiplexing circuit 62 is a multi-input dual-output. When 16 semiconductor lasers 60 are provided, the optical combining and demultiplexing circuit 62 is, for example, 16×2-MMI (Multi-Mode Interference). The optical combining and demultiplexing circuit 62 may not be MMI.

[0029] The waveguide 63 connects the optical multiplexing / demultiplexing circuit 62 and the optical amplifier 64. The optical amplifier 64 amplifies the second output light and outputs it as the output light 80 to the outside of the optical semiconductor device 100. The waveguide 63 and the optical amplifier 64 of the present embodiment constitute a first waveguide section that outputs the second output light from the front end face 52 of the semiconductor substrate 10. In addition, the first waveguide section only needs to be able to output the second output light to the outside, and the optical amplifier 64 may not be provided.

[0030] The optical amplifier 72 is connected to the waveguide 71. The optical amplifier 72 amplifies the third output light and outputs it to the waveguide 73. The reflector 74 is connected to the waveguide 73. The optical amplifier 72, the waveguide 73, and the reflector 74 constitute the second waveguide 70. The second waveguide 70 is linear.

[0031] The reflector 74 is a SG-DBR (Sampled Grating-Distributed Feedback Reflector) having multiple reflection peaks. The oscillation wavelengths of the multiple semiconductor lasers 60 are consistent with the multiple reflection peaks of the SG-DBR. The reflector 74 has multiple diffraction gratings as described later. The reflector 74 reflects the third output light amplified by the optical amplifier 72 through the multiple diffraction gratings, and feeds it back to the multiple semiconductor lasers 60 via the optical amplifier 72 and the optical multiplexing and demultiplexing circuit 62. In addition, each semiconductor laser 60 and the reflector 74 form a resonator.

[0032] In the optical semiconductor device 100 of the present embodiment, the output light 80 output from the optical amplifier 64 is used for optical communication. Figure 1In the example shown, the portion of the optical amplifier 64 on the upstream side in the traveling direction of light extends in the longitudinal direction of the optical semiconductor device 100. In addition, the portion of the optical amplifier 64 on the downstream side in the traveling direction of light is inclined with respect to the longitudinal direction of the optical semiconductor device 100. Therefore, the output light 80 is output obliquely with respect to the perpendicular line of the front end face 52. The rear end face 51 and the front end face 52 of the optical semiconductor device 100 are formed by cleavage. For example, an AR (Antireflection) coating is applied to the rear end face 51 and the front end face 52.

[0033] Next, the longitudinal structure of the optical semiconductor device 100 will be described. The longitudinal structures of the optical amplifiers 64 and 72 are the same. In addition, the longitudinal structures of the waveguides 61, 63, 71, and 73 are the same.

[0034] Figure 2 is a cross-sectional view obtained by cutting along the straight line A-A Figure 1 The semiconductor laser 60 includes a semiconductor substrate 10 made of InP. A first cladding layer 12 made of InP is provided on the upper surface of the semiconductor substrate 10. An active layer 18 and a current blocking layer 14 made of InP are provided on the upper surface of the first cladding layer 12. The current blocking layer 14 is provided on both sides of the active layer 18. The active layer 18 is formed by a mixture of InGaAsP, InGaAlAs, or InGaAsP and InGaAlAs. A second cladding layer 16 made of InP is provided on the upper surfaces of the active layer 18 and the current blocking layer 14. The first cladding layer 12, the active layer 18, the current blocking layer 14, and the second cladding layer 16 constitute an epitaxial structure portion. An anode electrode 32 is provided on the upper surface of the epitaxial structure portion. A cathode electrode 30 is provided on the back surface of the semiconductor substrate 10.

[0035] Figure 3 is a cross-sectional view of the semiconductor laser 60 according to Embodiment 1 along the direction of the optical axis 81. The direction along the optical axis 81 is the direction from the rear end face 51 to the front end face 52, and is the direction along the second waveguide portion 70. A diffraction grating 20 is provided on the upper surface or the back surface of the active layer 18. Although in Figure 3 the diffraction grating 20 is provided on the first cladding layer 12, the diffraction grating 20 may also be provided on the second cladding layer 16. In addition, although a contact layer is provided on the upper surface of the second cladding layer 16, that is, the surface of the epitaxial structure portion, it is omitted in Figure 2 、 3

[0036] ​When a forward bias is applied, the semiconductor laser 60 is injected with current from the anode electrode 32, and gain is generated in the active layer 18. As a result, spontaneous emission light is generated. Through the diffraction grating 20, the spontaneous emission light of a specific wavelength becomes the seed light for stimulated emission. If the injected current exceeds a predetermined threshold current, the semiconductor laser 60 oscillates in a laser mode.

[0037] The cathode electrode 30 is an electrode shared by the semiconductor laser 60, the optical amplifiers 64 and 72. The cathode electrode 30 is formed, for example, on the entire back surface of the semiconductor substrate 10.

[0038] Figure 4 is a cross-sectional view obtained by cutting along the line B-B Figure 1 The optical amplifier 64 includes the semiconductor substrate 10 and an epitaxial structure portion provided on the upper surface of the semiconductor substrate 10. The difference between the epitaxial structure portion of the optical amplifier 64 and that of the semiconductor laser 60 is that the active layer 18 is replaced with the active layer 22. An anode electrode 32 is provided on the upper surface of the epitaxial structure portion. In addition, the contact layer is omitted. The active layer 22 is formed of InGaAsP, InGaAlAs, or a mixture of InGaAsP and InGaAlAs that has gain for the light guided in the waveguide 63. In the optical amplifier 72 having the same longitudinal structure as the optical amplifier 64, the active layer 22 is also formed to have gain for the light guided in the waveguide 71.

[0039] When a forward bias is applied, the optical amplifier 64 amplifies the output light output from the semiconductor laser 60. The optical amplifier 64 is designed not to oscillate in a laser mode alone. In addition, when no forward bias is applied to the optical amplifier 64, the active layer 22 operates as a light absorption layer. Therefore, the optical amplifier 64 can be used as a shutter when switching wavelengths.

[0040] Figure 5 is a cross-sectional view obtained by cutting along the line C-C Figure 1 The waveguide 61 includes the semiconductor substrate 10 and an epitaxial structure portion provided on the upper surface of the semiconductor substrate 10. The difference between the epitaxial structure portion of the waveguide 61 and that of the semiconductor laser 60 is that the active layer 18 is replaced with the optical confinement layer 24. The optical confinement layer 24 is formed of InGaAsP. In addition, a cathode electrode 30 is formed on the back surface of the semiconductor substrate 10. The cathode electrode 30 is not essential for the function of the waveguide 61.

[0041] Figure 6 is a cross-sectional view obtained by cutting along the line D-D Figure 1The cross-sectional view thus obtained. In the reflecting portion 74, a first cladding layer 12 is provided on the upper surface of the semiconductor substrate 10. A light confinement layer 26 and a current blocking layer 14 are provided on the upper surface of the first cladding layer 12. The light confinement layer 26 is formed of InGaAsP. The current blocking layer 14 is provided on both sides of the light confinement layer 26. A second cladding layer 16 is provided on the upper surface of the light confinement layer 26 and the upper surface of the current blocking layer 14. The first cladding layer 12, the light confinement layer 26, the current blocking layer 14, and the second cladding layer 16 constitute an epitaxial structure portion. In addition, although the cathode electrode 30 is not essential for the function of the reflecting portion 74, a cathode electrode 30 is formed on the back surface of the semiconductor substrate 10 below the light confinement layer 26.

[0042] Figure 7 is a cross-sectional view of the reflecting portion 74 according to Embodiment 1 along the direction of the optical axis 81. The reflecting portion 74 includes a plurality of diffraction gratings 28 that are discretely arranged along the optical axis 81 in the first cladding layer 12. Each diffraction grating 28 has a periodic structure of refractive index. That is, the diffraction grating 28 is formed by periodically arranging layers having a refractive index different from that of the first cladding layer 12 in the first cladding layer 12. A plurality of reflection peaks are achieved by the plurality of diffraction gratings 28. The plurality of diffraction gratings 28 may also be provided in the second cladding layer 16.

[0043] The active layers 18, 22, and the light confinement layers 24, 26 are epitaxial layers formed using, for example, an MOCVD (Metal Organic Chemical Vapor Deposition) apparatus, an MBE (Molecular Beam Epitaxy) apparatus, etc. The active layers 18, 22, and the light confinement layers 24, 26 are separately formed on the upper surface of the first cladding layer 12 using photolithography technology and etching technology. When the active layers 18, 22, and the light confinement layers 24, 26 are formed of the same material, after forming the epitaxial layer on the upper surface of the first cladding layer 12, the active layers 18, 22, and the light confinement layers 24, 26 can be formed simultaneously by etching.

[0044] As a core technology for high-speed and large-capacity optical transmission methods, there is a digital coherent method that utilizes the phase information of light in modulation. In the digital coherent method, since the phase information of light is used, the phase noise of the light source becomes a problem. As an index of the phase noise of the light source, the spectral line width is used. Therefore, narrowing of the spectral line width is particularly important.

[0045] Generally, by externally feeding back a part of the oscillating light of a semiconductor laser, narrowing of the line width can be achieved. In the present embodiment, by using the reflection unit 74 to return a part of the output light of the semiconductor laser 60 to the semiconductor laser 60, the spectral line width can be reduced. By feeding back a part of the light, the spectral line width can be reduced by about two orders of magnitude.

[0046] The SG-DBR as the reflection unit 74 of the present embodiment is a waveguide-type reflection structure that essentially exhibits a reflection spectrum with multiple periodic reflection peaks. In the present embodiment, by making the interval between the oscillation wavelengths of multiple semiconductor lasers 60 coincide with the period of the reflection peaks of the SG-DBR, a reflection structure that can operate in the entire C-band domain, for example, can be obtained.

[0047] The spectral line width Δν0 of the DFB-LD is represented by Equation (1).

[0048] [Equation 1]

[0049]

[0050] Here, R sp is the spontaneous emission rate, K z is the longitudinal Petermann coefficient, S av is the average photon density, V act is the volume of the active layer, and α is the line width increase coefficient. In a semiconductor laser with strong optical feedback conditions, the line width reduction rate is represented by Equation (2).

[0051] [Equation 2]

[0052]

[0053] Here, Δν represents the spectral line width of the external resonator, and Δν0 represents the spectral line width of the LD. In addition, n a is the refractive index of the LD for transmission, L a is the LD length, f ext is the ratio of the feedback light to the output light of the LD, n p is the refractive index of the passive region in the external resonator for transmission, L p is the external resonator length.

[0054] For example, when L a = 1200 μm, L p = 4000 μm, Δν0 = 100 kHz, and f ext = 0.3, according to Equation (2), Δν is reduced to about 25 kHz.

[0055] However, there is an optimal value for the amount of optical feedback. If the amount of feedback is too large, the oscillation of the semiconductor laser becomes unstable and the spectral line width may increase. The optical amplifier 72 can adjust the amount of feedback of the light reflected in the reflection section 74 and fed back to the semiconductor laser 60 in such a way that the spectral line width of the output light 80 becomes minimum. The optical amplifier 72 amplifies the third output light in such a way that the line width of the output light 80 becomes at least smaller than that in the case where the third output light is not amplified.

[0056] In a configuration using a cleavage plane as the reflection section as in Patent Document 1, for example, by injecting a current of 35 mA into the amplifier that adjusts the amount of feedback light, the spectral line width is reduced from about 1 MHz to about 10 kHz. Here, the reflectivity in the cleavage plane is generally about 30%. In contrast, in the case of using the DBR configuration as the reflection section 74 as in the present embodiment, a reflectivity of 90% or more can generally be achieved. Therefore, compared with the configuration using a cleavage plane as the reflection section, the current injected into the optical amplifier 72 can be suppressed while achieving the same spectral line width.

[0057] In addition, when light is fed back to the semiconductor laser 60, phase control is important. In the optical semiconductor device 100, there are two oscillation modes, that is, the oscillation mode of the semiconductor laser 60 itself and the oscillation mode of the resonator formed by the semiconductor laser 60 and the reflection section 74. In order to reduce the spectral line width using optical feedback, in the present embodiment, the phase of the oscillation mode of the semiconductor laser 60 is made to coincide with the phase of the oscillation mode of the resonator formed by the semiconductor laser 60 and the reflection section 74. In the present embodiment, in order to make the phases of the two oscillation modes coincide, it is only necessary to adjust the positions of the plurality of semiconductor lasers 60.

[0058] In addition, in the case of using a DFB-LD as the semiconductor laser 60, an EB (Electron beam) exposure device is used, for example, to form the diffraction grating 20. The drawing accuracy of the EB exposure device is about 1 nm, for example. According to this accuracy, the phases of the two oscillation modes can be made to coincide.

[0059] In the present embodiment, it is not necessary to use a cleavage plane as the reflection section for optical feedback. Therefore, a phase adjustment region is not required, and the optical semiconductor device 100 can be miniaturized. In addition, it is not necessary to form a bent waveguide to guide light to the cleavage plane. In the present embodiment, it is only necessary to form the second waveguide section 70 in a linear shape extending along the length direction of the optical semiconductor device 100. Therefore, an increase in the width of the optical semiconductor device 100 compared to the configuration without optical feedback can be suppressed. Therefore, the optical semiconductor device 100 can be miniaturized.

[0060] In addition, in the field of optical communication, the high-speed and large-capacity development of optical transmission methods continues. As its core technology, the wavelength-division multiplexing (WDM) method of multiplexing and transmitting multiple optical signals with different wavelengths through a single optical fiber has been popularized. In order to perform stable optical communication using the WDM method, a standby light source is sometimes ensured to guard against the stoppage of an unexpected signal light source. However, if a standby light source is ensured for each wavelength of the multiplexed optical signals, the number of standby light sources increases. In particular, in a structure in which one semiconductor laser is mounted on one optical semiconductor device, the cost for maintaining the light source may increase.

[0061] To suppress the cost, as in the present embodiment, a wavelength-variable light source capable of outputting lasers of multiple wavelengths from one optical semiconductor device is effective. In the optical semiconductor device 100, the plurality of semiconductor lasers 60 include standby semiconductor lasers, whereby the cost can be suppressed and stable optical communication can be performed. When 16 semiconductor lasers 60 are mounted on the optical semiconductor device 100, two sets of semiconductor laser groups capable of outputting lasers of 8 wavelengths can be mounted. In addition, when 16 semiconductor lasers 60 are mounted on the optical semiconductor device 100, four sets of semiconductor laser groups capable of outputting lasers of 4 wavelengths can be mounted.

[0062] The materials of the respective layers of the optical semiconductor device 100 are not limited to the above materials. In addition, the second waveguide portion 70 and the waveguide 71 may be curved. In this case, a phase adjustment region is not required either, whereby the optical semiconductor device 100 can be miniaturized.

[0063] The above modifications can be appropriately applied to the optical semiconductor devices according to the following embodiments. In addition, for the optical semiconductor devices according to the following embodiments, since there are many common points with Embodiment 1, the description will focus on the differences from Embodiment 1.

[0064] Embodiment 2

[0065] Figure 8 FIG. is a top view of an optical semiconductor device 200 according to Embodiment 2. The optical multiplexer / demultiplexer circuit 262 of the present embodiment is multi-input and multi-output. The optical multiplexer / demultiplexer circuit 262 is connected to a plurality of waveguides 63 and 267 on the output side. When using an MMI as the optical multiplexer / demultiplexer circuit 262, in principle, the optical loss of the second output light and the third output light is not increased, and the number of output ports of the optical multiplexer / demultiplexer circuit 262 can be increased. The number of output ports can be increased to the same number as the number of input ports.

[0066] An optical amplifier 265 is connected to the waveguide 267, for example. The fourth output light output from the optical multiplexer / demultiplexer circuit 262 is amplified by the optical amplifier 265 and emitted from the front end face 52 as output light 82. The output light 82 can be used for wavelength monitoring, for example. The output light 82 can also be used as local oscillation light in an optical receiving system in digital coherent communication.

[0067] The longitudinal structure of the waveguide 267 is the same as that of the waveguide 61. Additionally, the longitudinal structure of the optical amplifier 265 is the same as that of the optical amplifier 64.

[0068] In Figure 8 the upstream portion of the optical amplifier 265 in the light traveling direction extends in the length direction of the optical semiconductor device 200. Additionally, the downstream portion of the optical amplifier 265 in the light traveling direction is inclined with respect to the length direction of the optical semiconductor device 200. Therefore, the output light 82 is output obliquely with respect to the perpendicular line of the front end face 52. In Figure 8 the optical amplifier 265 is inclined in the opposite direction to the optical amplifier 64. The optical amplifier 265 may not be inclined. Additionally, the optical amplifier 265 may not be provided.

[0069] Embodiment 3

[0070] Figure 9 is a top view of the optical semiconductor device 300 according to Embodiment 3. In the present embodiment, the structure of the second waveguide portion 370 is different from the structure of the second waveguide portion 70. In the second waveguide portion 370, a waveguide 375 is connected to the reflection portion 74. An optical absorption portion 376 is connected to the waveguide 375. In this way, the second waveguide portion 370 has the optical absorption portion 376, which is provided on the side opposite to the optical amplifier 72 with respect to the reflection portion 74 and absorbs the light that has passed through the reflection portion 74.

[0071] The longitudinal structure of the waveguide 275 is the same as that of the waveguide 61. Additionally, the longitudinal structure of the optical absorption portion 376 is the same as that of the semiconductor laser 60. As Figure 2 shown, the optical absorption portion 376 includes a first cladding layer 12 provided on the upper surface of the semiconductor substrate 10 and an active layer 18 provided on the upper surface of the first cladding layer 12. Additionally, current blocking layers 14 are provided on both sides of the active layer 18 on the upper surface of the first cladding layer 12. A second cladding layer 16 is provided on the upper surface of the active layer 18 and the upper surface of the current blocking layer 14. Additionally, the optical absorption portion 376 does not have an anode electrode 32.

[0072] Sometimes, a part of the light incident on the reflection portion 74 is not reflected but passes through the reflection portion 74 to become stray light. Generally, the spectral line width is affected by stray light. The more the stray light increases, the wider or more unstable the spectral line width becomes. Therefore, in order to narrow the line width, it is important to remove stray light. In the present embodiment, the light transmitted through the reflection portion 74 can be absorbed by the light absorption portion 376. Therefore, stray light can be suppressed, and the spectral line width can be further reduced.

[0073] Embodiment 4

[0074] Figure 10 FIG. 7 is a plan view of the optical semiconductor device 400 according to Embodiment 4. The difference between the present embodiment and Embodiment 1 is that the optical multiplexer / demultiplexer 462 has one input and two outputs. The optical semiconductor device 400 includes only one semiconductor laser 60. In addition, the second waveguide portion 470 includes a reflection portion 474. The reflection portion 474 is a DBR (Distributed Feedback Reflector) having one reflection peak. The oscillation wavelength of the semiconductor laser 60 coincides with the reflection peak of the DBR. The optical semiconductor device 400 is used as a single wavelength light source.

[0075] Figure 11 FIG. 11 is a cross-sectional view of the reflection portion 474 according to Embodiment 4 along the optical axis 81. The difference between the longitudinal structure of the reflection portion 474 and the longitudinal structure of the reflection portion 74 is that a diffraction grating 434 is provided instead of the plurality of diffraction gratings 28 arranged discretely. The diffraction grating 434 may also be provided in the second cladding layer 16.

[0076] In the present embodiment, optical feedback to the semiconductor laser 60 can be achieved by the DBR. Therefore, the same effect as in Embodiment 1 can be obtained.

[0077] Embodiment 5

[0078] Figure 12 FIG. 12 is a plan view of the optical semiconductor device 500 according to Embodiment 5. In the optical semiconductor device 500, a single semiconductor laser 560 is provided. The semiconductor laser 560 is an SG (Sampled Grating)-DFB having a plurality of gain peaks. In addition, the second waveguide portion 570 includes a reflection portion 574. The reflection portion 574 is a CSG (Chirped Sampled Grating)-DBR having a plurality of reflection peaks. Different from the SG-DBR, the CSG-DBR has a reflection spectrum with slightly different periods for the plurality of reflection peaks.

[0079] Figure 13This is a cross-sectional view of the semiconductor laser 560 according to Embodiment 5 in the direction along the optical axis 81. A plurality of diffraction gratings 536 are discretely formed along the optical axis 81 in the first cladding layer 512 of the semiconductor laser 560. The plurality of diffraction gratings 536 may also be provided in the second cladding layer 16. The semiconductor laser 560 has a gain structure with a plurality of gain peaks having periodicity. An anode electrode 532 is provided directly above each of the diffraction gratings 536, or a heater 540 is provided with an insulating film 538 interposed therebetween. The region directly below the anode electrode 532 in the semiconductor laser 560 is a gain region 10a, and the region directly below the heater 540 is a phase shift region 10b.

[0080] In the gain region 10a, carriers are injected from the anode electrode 532, and photons are generated. The temperature of the phase shift region 10b can be changed by the heater 540. Thereby, the refractive indices of the first cladding layer 512 and the second cladding layer 16 and the optical path length of the phase shift region 10b can be changed. Therefore, the resonator formed by the semiconductor laser 560 and the reflection portion 574 can be changed, and the emission wavelength of the optical semiconductor device 500 can be adjusted.

[0081] Figure 14 This is a cross-sectional view of the reflection portion 574 according to Embodiment 5 in the direction along the optical axis 81. A plurality of diffraction gratings 542 are discretely formed along the optical axis 81 in the first cladding layer 512 of the reflection portion 574. The plurality of diffraction gratings 542 may also be provided in the second cladding layer 16. In addition, a heater 540 is provided on the upper surface of the second cladding layer 16 with an insulating film 538 interposed therebetween.

[0082] The period of the reflection peak of the reflection portion 574 is different from the period of the gain peak of the semiconductor laser 560. In the reflection portion 574, a plurality of reflection peaks can be adjusted by the heater 540. Specifically, the heater 540 can change the optical characteristics such as the refractive index by changing the temperature of the waveguide directly below. Therefore, the reflection spectrum can be shifted. Thereby, the semiconductor laser 560 outputs light having a wavelength that coincides with the plurality of reflection peaks of the reflection portion 574 among the plurality of gain peaks.

[0083] In this way, in the present embodiment, a wavelength variable mechanism can be realized by the combination of the semiconductor laser 560 and the reflection portion 574. In the present embodiment, for example, a wavelength variable light source that can oscillate in the entire C band can be realized.

[0084] The technical features described in each embodiment can also be used in appropriate combination.

[0085] Description of Reference Numerals

[0086] 10... Semiconductor substrate; 10a... Gain region; 10b... Phase shift region; 12... First cladding layer; 14... Current blocking layer; 16... Second cladding layer; 18... Active layer; 20... Diffraction grating; 22... Active layer; 24, 26... Optical confinement layer; 28... Diffraction grating; 30... Cathode electrode; 32... Anode electrode; 51... Rear end face; 52... Front end face; 60... Semiconductor laser; 61... Waveguide; 62... Optical multiplexer / demultiplexer circuit; 63... Waveguide; 64... Optical amplifier; 70... Second waveguide section; 71... Waveguide; 72... Optical amplifier; 73... Waveguide; 74... Reflective section; 80... Output light; 81... Optical axis; 82... Output light; 100, 200... Optoelectronic device; 262... Optical multiplexer / demultiplexer circuit; 265... Optical amplifier; 267... Waveguide; 275... Waveguide; 300... Optoelectronic device; 370... Second waveguide section; 375... Waveguide; 376... Optical absorption section; 400... Optoelectronic device; 434... Diffraction grating; 462... Optical multiplexer / demultiplexer circuit; 470... Second waveguide section; 474... Reflective section; 500... Optoelectronic device; 512... First cladding layer; 532... Anode electrode; 536... Diffraction grating; 538... Insulating film; 540... Heater; 542... Diffraction grating; 560... Semiconductor laser; 570... Second waveguide section; 574... Reflective section.

Claims

1. A photonic semiconductor device, characterized in that, the photonic semiconductor device includes: a semiconductor substrate; at least one semiconductor laser, disposed on the semiconductor substrate; a wavelength multiplexer / demultiplexer circuit, disposed on the semiconductor substrate, multiplexing or demultiplexing first output light of the semiconductor laser, and outputting second output light and third output light; a first waveguide section, disposed on the semiconductor substrate, outputting the second output light from an end face of the semiconductor substrate; and a second waveguide section, having an optical amplifier for amplifying the third output light and a reflection section, and disposed on the semiconductor substrate, the reflection section having a diffraction grating that reflects the third output light amplified by the optical amplifier and feeds it back to the semiconductor laser via the optical amplifier and the wavelength multiplexer / demultiplexer circuit, the semiconductor laser and the reflection section forming a resonator, the second waveguide section having an optical absorption section that is disposed on a side opposite to the optical amplifier with respect to the reflection section and absorbs light that has passed through the reflection section, the second waveguide section being linear.

2. The photonic semiconductor device according to claim 1, characterized in that, a phase of an oscillation mode of the semiconductor laser is identical to a phase of an oscillation mode of the resonator.

3. The photonic semiconductor device according to claim 1 or 2, characterized in that, the optical amplifier amplifies the third output light in such a manner that a line width of the second output light becomes smaller than a case where the third output light is not amplified.

4. The photonic semiconductor device according to claim 1 or 2, characterized in that, a plurality of the semiconductor lasers are provided, the reflection section is an SG-DBR having a plurality of reflection peaks, oscillation wavelengths of the plurality of semiconductor lasers are identical to the plurality of reflection peaks of the SG-DBR.

5. The photonic semiconductor device according to claim 1 or 2, characterized in that, one semiconductor laser is provided, the reflection section is a DBR having one reflection peak, an oscillation wavelength of the semiconductor laser is identical to the reflection peak of the DBR.

6. The photonic semiconductor device according to claim 1 or 2, characterized in that, one semiconductor laser is provided, the semiconductor laser is an SG-DFB having a plurality of gain peaks, the reflection section is a CSG-DBR having a plurality of reflection peaks, the semiconductor laser outputs light having a wavelength identical to the plurality of reflection peaks among the plurality of gain peaks.

7. The photonic semiconductor device according to claim 6, characterized in that, the CSG-DBR has a heater, and the plurality of reflection peaks can be adjusted by the heater.

8. The photonic semiconductor device according to claim 1 or 2, characterized in that, the reflection section includes: a first cladding layer, disposed on an upper surface of the semiconductor substrate; an optical confinement layer, disposed on an upper surface of the first cladding layer; a current blocking layer, disposed on both sides of the optical confinement layer on the upper surface of the first cladding layer; and a second cladding layer, disposed on the upper surface of the optical confinement layer and the upper surface of the current blocking layer.

9. The optical semiconductor device according to claim 1 or 2, characterized in that the light absorption part includes: a first cladding layer provided on the upper surface of the semiconductor substrate; an active layer provided on the upper surface of the first cladding layer; a current blocking layer provided on both sides of the active layer on the upper surface of the first cladding layer; and a second cladding layer provided on the upper surface of the active layer and the upper surface of the current blocking layer.

Images