Semiconductor optical integrated element, method for manufacturing semiconductor optical integrated element, semiconductor optical device, and method for controlling semiconductor optical device

Abstract

A semiconductor optical integrated element (11) according to the present invention comprises a DFB laser (12), an EA modulator (13), a bent waveguide (162), and an SOA (14) in the stated order on a substrate and further comprises an optical monitor (15) which is disposed on substantially the same axis as an optical axis (18) of emitted light of the DFB laser and into which leakage light from the bent waveguide enters. Also, a region (125) not including a diffraction grating may be disposed in a vicinity of one end of the DFB laser.　The present invention can thereby provide a semiconductor optical integrated element capable of suppressing degradation of integrated elements and controlling the integrated elements.

Description

Semiconductor optical integrated element, manufacturing method of semiconductor optical integrated element, semiconductor optical device, and control method of semiconductor optical device

[0001] The present invention relates to a semiconductor optical integrated element having an optical monitor, a method for manufacturing a semiconductor optical integrated element, a semiconductor optical device, and a method for controlling the semiconductor optical device.

[0002] In recent years, the spread of video streaming services and the growing demand for mobile traffic have led to an increase in network traffic. In the optical transmission lines that support these networks, progress has been made in reducing the cost of networks by increasing transmission rates, reducing power consumption, and extending transmission distances. Semiconductor modulated light sources used in optical transmission lines are also required to be low in power consumption, high in speed, and high in output.

[0003] Electroabsorption modulator-integrated DFB (EADFB) lasers have been widely used due to their superior extinction and chirp characteristics compared to directly modulated lasers. A conventional EADFB laser 61, as shown in FIG. 11 , has a structure in which a DFB laser 62 and an EA modulator 63 are integrated on the same chip. The DFB laser 62 has an active layer 622 made of a multiple quantum well (MQW) and oscillates at a single wavelength using a diffraction grating 624 formed in the resonator. The EA modulator 63 has an optical absorption layer 632 made of a multiple quantum well (MQW) with a different composition from the DFB laser 62, and changes the amount of optical absorption by voltage control. By driving the DFB laser 62 under conditions that transmit or absorb the output light, the light is blinked, converting the electrical signal into an optical signal. However, the EADFB laser 61 has difficulty achieving high output power due to the large optical loss of the EA modulator 63.

[0004] Therefore, as shown in Figure 12, an EADFB laser (SOA Assisted Extended Reach EADFB Laser, AXEL) 71 has been proposed, in which a semiconductor optical amplifier (SOA) is further integrated at the light-emitting end of the EADFB laser (Non-Patent Document 1). In the AXEL 71, the signal light modulated by the EA modulator 73 is amplified by the integrated SOA 74, thereby improving the optical output. This allows for output characteristics that are approximately twice as high as those of a typical EADFB laser.

[0005] AXEL71 uses the same MQW structure as DFB lasers for the active layer of the SOA. Therefore, there is no need to add a regrowth process for integrating the SOA region, and the device can be fabricated using the same manufacturing process as conventional EADFB lasers.

[0006] AXEL71 can operate with high efficiency due to the SOA integration effect, so when driven under operating conditions that provide optical output equivalent to that of a typical EADFB laser, power consumption can be reduced by approximately 40%.

[0007] On the other hand, in the AXEL71, compared to a general EADFB laser, there is a concern that the influence of reflected light on the operating characteristics will become more pronounced due to the high optical output characteristics associated with SOA integration.

[0008] In optical transmitters such as general semiconductor lasers, light reflected from the end face of a semiconductor chip and returning to the inside of the chip adversely affects the operating characteristics of the device. Therefore, in semiconductor optical transmitters, an anti-reflection coating (AR-Coating) is applied to the chip end face to suppress light reflected back from the chip end face to the inside.

[0009] Due to its high output power, even a small amount of reflected feedback light has a significant impact on the operating characteristics of the AXEL (SOA-integrated EADFB laser) 71. If the optical amplification effect of the SOA in the SOA-integrated EADFB laser is +3 dB compared to a conventional EADFB laser, the average optical output power will be increased by +3 dB, and the intensity of the reflected feedback light will also increase by 3 dB. Furthermore, since the reflected feedback light at the facet is amplified again within the SOA 74, the intensity of the reflected feedback light reaching the DFB laser 72 will be increased by +6 dB compared to the EADFB laser.

[0010] Therefore, in order to suppress the influence of reflected light in the AXEL, an AXEL 81 using a curved waveguide has been proposed, as shown in FIG.

[0011] Typically, the light-emitting end face of a semiconductor chip is a crystal plane formed by cleavage, and the waveguide within the semiconductor chip is formed at a perpendicular angle to this light-emitting end face. Therefore, light propagating through the waveguide enters the light-emitting end face perpendicularly and is emitted from the semiconductor chip.

[0012] On the other hand, in the AXEL 81, in a configuration in which a DFB laser 82, an EA modulator 83, and an SOA 84 are connected by waveguides 861 to 863, a curved waveguide 862 is provided between the EA modulator 83 and the SOA 84, so that the light propagating through the waveguide is angled θ ｗｇ The light is incident at an incident angle θ with respect to the exit end face of the waveguide, and is emitted from the exit end face. This makes it difficult for the light reflected at the exit end face to be coupled back into the waveguide, thereby suppressing reflected back light. Generally, the incident angle θ with respect to the exit end face of the waveguide to suppress reflection is ｗｇ In the AXEL71 chip, the DFB laser 82 and the EA modulator 83 are usually formed in a linear waveguide region with a waveguide direction in which light propagates perpendicular to the cleaved end face. On the other hand, the SOA 84 has an incident angle θ ｗｇ The waveguide direction is formed in an oblique waveguide region having an angle of .

[0013] In modulated light sources including AXEL, it is necessary to maintain a constant optical intensity of the optical signal during operation. Conventional EAD DFB lasers have used a method (APC, auto power control) in which the optical intensity output from the semiconductor chip of the optical transmitter is monitored externally and the current injected into the DFB laser is controlled so that the monitored optical intensity remains constant. This allows the amount of current to be increased to compensate for changes in optical output and maintain a constant output when the optical output of the DFB laser deteriorates due to long-term operation.

[0014] Conventionally, APC drive has been used in AXEL 81, in which an optical monitor is placed outside the chip to control the current of the DFB laser or SOA. As an example, as shown in Figure 14, a configuration is shown in which the drive current of the DFB laser 82 is controlled so that the optical intensity monitored by the optical monitor 92 is kept constant.

[0015] In the AXEL 81 chip, light emitted from a DFB laser 82 is modulated by an electric input signal 95 in an EA modulator 83, amplified by an SOA 84, and then output to the outside of the chip.

[0016] A portion of the output light is branched by a half mirror 91 and enters an optical monitor 92. The optical intensity detected by the optical monitor 92 is input to a current control unit 93, which performs feedback control to adjust an input current 94 of the DFB laser 82. The current control unit 93 controls the value of the input current 94 of the DFB laser 82 so that the optical intensity detected by the optical monitor 92 is always constant. Similarly, when controlling the current 96 of the SOA 84, a portion of the output light from the chip is branched and detected by the optical monitor 92, and then the current control unit 93 adjusts the input current 96 of the SOA 84, thereby controlling the optical intensity detected by the optical monitor 92 to be constant.

[0017] W Kobayashi et al., “Novel approach for chirp and output power compensation applied to a 40-Gbit / s EADFB laser integrated with a short SOA,” Opt. Express, Vol. 23, No. 7, pp. 9533-9542, Apr. 2015.

[0018] However, in the above-described conventional configuration, the light transmitted through the DFB laser 82 and the SOA 84 is observed from outside the chip, so when the optical output fluctuates, it is not possible to determine whether the fluctuation is due to deterioration of the DFB laser 82 or the SOA 84.

[0019] Generally, the deterioration of an optical semiconductor device is accelerated by the amount of current injected. Therefore, if the optical output of AXEL 81 is reduced due to deterioration of DFB laser 82, and the current 94 of DFB laser 82 is increased to maintain a constant optical output intensity, the deterioration of DFB laser 82 may be accelerated, resulting in a shortened device life.

[0020] Furthermore, if the optical output of AXEL 81 decreases due to deterioration of SOA 84, and the current 96 of SOA 84 is increased to maintain a constant optical output intensity, the deterioration of SOA 84 may be accelerated, resulting in a shortened element lifespan.

[0021] In order to solve the above-mentioned problems, the semiconductor optical integrated device according to the present invention comprises, on a substrate, a DFB laser, an EA modulator, a curved waveguide, and an SOA, in that order, and further comprises an optical monitor that is arranged approximately coaxially with the optical axis of the light emitted from the DFB laser and into which leaked light from the curved waveguide is incident.

[0022] According to the present invention, it is possible to provide a semiconductor optical integrated element, a method for manufacturing a semiconductor optical integrated element, a semiconductor optical device, and a method for controlling a semiconductor optical device, which are capable of suppressing and controlling deterioration of integrated elements.

[0023] FIG. 1 is a schematic top view showing the configuration of a semiconductor optical integrated device according to a first embodiment of the present invention. FIG. 2 is a flowchart illustrating a method for manufacturing a semiconductor optical integrated device according to the first embodiment of the present invention. FIG. 3 is a diagram illustrating a method for manufacturing a semiconductor optical integrated device according to the first embodiment of the present invention. FIG. 4 is a diagram illustrating a method for manufacturing a semiconductor optical integrated device according to the first embodiment of the present invention. FIG. 5 is a diagram illustrating a method for manufacturing a semiconductor optical integrated device according to the first embodiment of the present invention. FIG. 6 is a block diagram showing the configuration of a semiconductor optical device according to a second embodiment of the present invention. FIG. 7 is a flowchart illustrating a method for controlling a semiconductor optical device according to the second embodiment of the present invention. FIG. 8 is a schematic top view showing the configuration of a semiconductor optical integrated device according to a first example of the present invention. FIG. 9 is a schematic top view showing the configuration of a semiconductor optical integrated device according to a second example of the present invention. FIG. 10 is a diagram illustrating the operation of a semiconductor optical integrated device according to the second example of the present invention. FIG. 11 is a schematic cross-sectional view showing the configuration of a conventional semiconductor optical integrated device. FIG. 12 is a schematic cross-sectional view showing the configuration of a conventional semiconductor optical integrated device. FIG. 13 is a schematic top view showing the configuration of a conventional semiconductor optical integrated device. FIG. 14 is a block diagram showing a configuration for controlling a conventional semiconductor optical integrated device.

[0024] First Embodiment A semiconductor optical integrated device and a method for manufacturing the semiconductor optical integrated device according to a first embodiment of the present invention will be described with reference to FIGS.

[0025] 1 shows a schematic top view of a semiconductor optical integrated device 11 according to this embodiment. In the figure, cladding layers, contact layers, and the like are omitted. Dotted lines indicate an example of the electrodes of each device.

[0026] As shown in FIG. 1, a semiconductor optical integrated device 11 according to this embodiment includes a DFB laser 12, an EA modulator 13, an SOA 14, and an optical monitor 15 on a substrate (not shown).

[0027] The DFB laser 12 and the EA modulator 13 are connected via an optical waveguide 161. Alternatively, the DFB laser 12 and the EA modulator 13 may be directly connected.

[0028] The EA modulator 13 and the SOA 14 are connected via an optical waveguide 162 .

[0029] The SOA 14 is disposed at an oblique position (at a predetermined angle θ ) with respect to the optical axis 18 (the optical axis of the emitted light from the DFB laser 12 ) (the dashed line in the drawing) of the DFB laser 12 and the EA modulator 13 . ｗｇ (with)

[0030] The optical waveguide 162 is disposed so that the emitted light propagates obliquely with respect to the optical axis 18 of the emitted light from the DFB laser 12. The optical waveguide 162 is a curved waveguide, and is curved at a predetermined angle θ ｗｇ To bend or curve at.

[0031] An optical waveguide 163 is connected to the output end face of the SOA 14, and the output light of the semiconductor optical integrated device 11 is emitted from the optical waveguide 163. An optical waveguide does not have to be connected to the output end face of the SOA 14, and the output light of the semiconductor optical integrated device 11 may be emitted directly from the output end face of the SOA 14.

[0032] The output light of the semiconductor optical integrated device 11 is emitted from the output end face at a position ΔY (waveguide offset) away from the optical axis 18 of the emitted light of the DFB laser 12 .

[0033] The optical monitor 15 is disposed on the output side of the EA modulator 13, without an optical waveguide, at a position away from the DFB laser 12 and the EA modulator 13, and is disposed substantially coaxial with the optical axis 18 of the DFB laser 12 and the EA modulator 13 (the optical axis of the light emitted from the DFB laser 12). In other words, the optical monitor 15 is disposed so that a portion of the light emitted from the EA modulator 13 enters the optical monitor 15 as leaked light from the bent waveguide 162. Therefore, a portion of the light emitted from the EA modulator 13 (leakage light) enters the optical monitor 15 without passing through the SOA 14. "Substantially coaxial" includes the coaxial axis and refers to the range of the optical axis in which the leaked light from the bent waveguide 162 enters the optical monitor 15.

[0034] The DFB laser 12 has a diffraction grating like a normal DFB laser, but does not have a diffraction grating near the end face opposite to the end face connected to the EA modulator 13 (described later).

[0035] A buried semiconductor layer 17 is disposed as a current blocking layer in the region other than the waveguide portion from the DFB laser 12 through the EA modulator 13 and SOA 14 to the output end of the semiconductor optical integrated device 11 and the optical monitor 15 .

[0036] The output light from the DFB laser 12 of the semiconductor optical integrated device 11 propagates through the straight waveguide portion, is modulated by the EA modulator 13, and then propagates through the curved waveguide 162. As a result, the guiding direction of the output light is angled at a predetermined angle θ from the optical axis direction of the output light from the DFB laser 12. ｗｇ will be changed.

[0037] At this time, part of the light guided through the curved waveguide 162 propagates in the optical axis direction of the emitted light from the DFB laser 12 and is radiated from the curved waveguide 162 as leaked light.

[0038] By integrating an optical monitor 15 that monitors this leaked light in the semiconductor optical integrated device 11, it is possible to directly monitor the optical output of the DFB laser 12 without going through the SOA 14. Since this leaked light is guided in the optical guiding direction of the DFB laser 12, i.e., on an extension of the optical guiding direction of the linear waveguide region, the optical monitor 15 has a waveguide structure that is arranged on an optical axis 18 that is approximately the same as the waveguide of the DFB laser 12.

[0039] The optical monitor 15 uses the same layer structure as the DFB laser 12. This eliminates the need for an additional regrowth process for integrating the optical monitor 15, and allows it to be manufactured using the same process as conventional processes.

[0040] <Method of Manufacturing Semiconductor Optical Integrated Device> An example of a method of manufacturing the semiconductor optical integrated device 11 according to this embodiment will be described with reference to FIGS. 2 to 5. FIG. 2 shows a flowchart for explaining an example of a method of manufacturing the semiconductor optical integrated device 11. FIG. 3 shows two unit element patterns 110 and 110_2 adjacent in the X direction in an element pattern consisting of a plurality of unit element patterns formed in the X and Y directions on a substrate (wafer) in the manufacturing process of the semiconductor optical integrated device 11. In the figure, the unit element patterns 110 and 110_2 are areas surrounded by dotted lines. For example, on a (100) semiconductor substrate, the X direction is the crystal orientation

[011] (or [0-1-1]), and the Y direction is the crystal orientation [01-1] (or [0-11]).

[0041] First, as shown in FIG. 3, a plurality of unit element patterns 110 each including, in order, a DFB laser structure 120, an EA modulator 13, the curved waveguide 162, and an SOA 14 are formed on a substrate (wafer) (step S11).

[0042] The unit element patterns 110 are arranged so that the optical axes 18 of the DFB laser structures 120 of the respective unit element patterns 110 coincide with each other in the X direction on the wafer. Since the positions of the optical axes are determined by the lithography process, they can be accurately positioned by the lithography mask design.

[0043] A region 23 having no diffraction grating is disposed at one end of the DFB laser structure 120. This region 23 having no diffraction grating extends toward another adjacent unit element pattern 110_2. In detail, the one end of the DFB laser structure 120 is located on the side that contacts the other unit element pattern 110_2 with respect to a straight line that passes through the output end of the optical waveguide portion that passes through the DFB laser structure 120, the EA modulator 13, the bent waveguide 162, and the SOA 14 in the other unit element pattern 110_2 and is perpendicular to the optical axis of the DFB laser structure 120.

[0044] Next, the element pattern consisting of the unit element patterns 110 and 110_2 is divided (cleaved) into the semiconductor optical integrated element 11 and another adjacent semiconductor optical integrated element 11_2 (step S12).

[0045] The element pattern is divided by cleavage into semiconductor optical integrated elements 11 and 11_2 at cleavage positions 21. The light-emitting end faces of the semiconductor optical integrated elements 11 and 11_2 are formed by cleavage.

[0046] At this time, the DFB laser structure 120 is divided (cleaved) at the region 23 having no diffraction grating. As a result, one of the divided DFB laser structures 120 is disposed in the adjacent semiconductor optical integrated device 11_2, and the other semiconductor optical integrated device 11_2 constitutes the optical monitor 15.

[0047] The other of the divided DFB laser structures constitutes the DFB laser 12 of the semiconductor optical integrated device 11 .

[0048] In this way, a part (one part) of the DFB laser structure 120 functions as the optical monitor 15 as it is, so the optical monitor 15 has the same layer structure (waveguide structure) as the DFB laser 12. Therefore, no additional regrowth process or waveguide fabrication process is required to integrate the optical monitor 15, and the semiconductor optical integrated device 11 can be fabricated using the same process as conventional processes.

[0049] Furthermore, since the optical monitor 15 and the DFB laser 12 are formed on the wafer with their optical axes 18 substantially aligned, the optical monitor 15 can reliably monitor the light emitted from the DFB laser 12 .

[0050] The process of dividing the DFB laser structure 120 will be described in detail below.

[0051] In a normal cleavage process, there is a manufacturing error (hereinafter referred to as "cleavage error") ±ΔL with respect to the designed cleavage position. ｅ It is necessary to design the configurations of the DFB laser 12 and the optical monitor 15 taking this cleavage error into consideration so that the functions of the DFB laser 12 and the optical monitor 15 can be ensured.

[0052] A DFB laser can emit highly monochromatic light in a single mode using a diffraction grating. However, if an optical monitor has a diffraction grating, the diffraction grating prevents external light from entering the optical monitor, making the optical monitor less sensitive. Furthermore, light reflected from the diffraction grating propagates again within the semiconductor optical integrated device and couples with the DFB laser or SOA 14, destabilizing the device's operation.

[0053] 4 shows a cross-sectional view of the DFB laser structure 120 in the optical waveguide direction during the division (cleavage) process. In FIG. 4, the planned cleavage position 22 is indicated by a dashed-dotted line, and the cleavage error range is indicated by a dotted line. The DFB laser structure 120 has a lower SCH (Separated Confinement Heterostructure) layer 121, an active layer 122, an upper SCH layer 123, and a diffraction grating 124.

[0054] A region 23 having no diffraction grating is provided at one end of the DFB laser structure 120 in the unit element pattern 110. This region 23 having no diffraction grating extends toward another adjacent unit element pattern 110_2.

[0055] The cleavage separates the semiconductor optical integrated device 11 from another adjacent semiconductor optical integrated device 11_2. At this time, the DFB laser structure 120 is divided by a region 23 that does not have a diffraction grating. As a result, as shown in Fig. 4, the DFB laser 12 is disposed in the semiconductor optical integrated device 11, and the optical monitor 15 is disposed in the adjacent semiconductor optical integrated device 11_2, with the cleavage position 21 in between. As a result, no diffraction grating is formed in the optical monitor 15.

[0056] On the other hand, the DFB laser 12 has a diffraction grating 124 formed thereon, and has a region 125 where no diffraction grating is formed (hereinafter referred to as a "diffraction grating non-formed region") near the end on the optical monitor 15 side.

[0057] Since a normal cleaving process involves manufacturing errors (cleavage errors), a cleavage margin region is provided near the cleavage position where the semiconductor optical integrated device (chip) is separated in case the cleavage position deviates from the intended cleavage position.

[0058] In the semiconductor optical integrated device 11 according to this embodiment, a region 23 having no diffraction grating (hereinafter also referred to as a "DFB margin region") is designed as a cleavage margin region in the DFB laser structure 120 to be sufficiently large relative to the cleavage error so that no diffraction grating remains in the optical monitor 15 after cleavage when the cleavage position 21 deviates from the planned position 22.

[0059] As a result, a part of the DFB margin region 23 remains as a diffraction grating-free region 125 in a part (near one end) of the DFB laser 12 .

[0060] In a DFB laser, if the diffraction grating-free region 125 is too long, it will affect the performance of the DFB laser, so the length of the diffraction grating-free region 125 is preferably 50 μm or less.

[0061] For example, if the cleavage error is ±ΔL ｅ When the length of the DFB margin region 23 is 2ΔL ｅ The planned cleavage position 22 is set at a distance ΔL from the end of the diffraction grating of the DFB laser 12. ｅ The actual cleavage position 21 is set to be closer to the DFB laser 12 than the planned cleavage position 22 by ΔL ｅ If it deviates (+ΔL ｅ ), the length of the diffraction grating-free region 125 of the DFB laser 12 is 0 μm, and the optical monitor 15 does not include a diffraction grating. ｅ If it deviates (-ΔL ｅ ), the length of the diffraction grating-free region 125 of the DFB laser 12 is 2ΔL ｅ and the optical monitor 15 does not include a diffraction grating.

[0062] Thus, the length of the DFB margin region is 2ΔL ｅ At this time, the length of the diffraction grating non-forming region 125 of the DFB laser 12 is preferably 0 μm to 2ΔL. ｅ It is desirable that the following:

[0063] When a normal cleavage error is about ±10 μm, it is desirable that the length of the diffraction grating non-forming region 125 of the DFB laser 12 be 0 μm to 20 μm or less.

[0064] As described above, according to the manufacturing method of the semiconductor optical integrated device of this embodiment, it is possible to easily arrange the optical monitor 15 and the DFB laser 12 so that their optical axes are substantially aligned. This simplifies the manufacturing process and enables the optical monitor 15 to reliably monitor the emitted light from the DFB laser 12.

[0065] The steps on the wafer in the method for manufacturing a semiconductor optical integrated device according to this embodiment will be described with reference to FIG.

[0066] First, an element pattern consisting of a plurality of unit element patterns is formed on a substrate (wafer) in the X and Y directions. Figure 5 shows an element pattern consisting of two unit element patterns in the X direction and three in the Y direction on a portion of a wafer.

[0067] Next, the semiconductor optical integrated devices (e.g., semiconductor optical integrated devices 11, 11_2) are divided (cleaved) in the Y direction shown in Fig. 5. As a result, the semiconductor optical integrated devices are divided into a state in which they are arranged in a line in the Y direction. Hereinafter, this state will be referred to as a "semiconductor device bar." By cleaving, an emission end face of the semiconductor optical integrated devices (chips) of the semiconductor device bar is formed, and all of the semiconductor optical integrated devices (chips) in the semiconductor device bar have the same emission end face.

[0068] As described above, the DFB laser structure is cleaved in an area that does not have a diffraction grating, and an optical monitor is placed in the semiconductor optical integrated element of one of the semiconductor element bars formed by the cleavage, and a DFB laser is placed in the semiconductor optical integrated element of the other semiconductor element bar.

[0069] Finally, the semiconductor element bar is divided (cleaved) in the X direction between the individual semiconductor optical integrated elements to produce the semiconductor optical integrated elements.

[0070] According to the semiconductor optical integrated device of this embodiment, of the integrated DFB laser and SOA, only the optical output of the DFB laser can be detected (monitored). Furthermore, according to the manufacturing method of the semiconductor optical integrated device of this embodiment, this semiconductor optical integrated device can be easily manufactured.

[0071] Second Embodiment A semiconductor optical device and a method for controlling the semiconductor optical device according to a second embodiment of the present invention will be described with reference to FIGS.

[0072] <Configuration of Semiconductor Optical Device> As shown in FIG. 6 , a semiconductor optical device 30 according to this embodiment includes the above-described semiconductor optical integrated element 11, an optical branching unit 31, another optical monitor (external monitor) 32, and a current control unit 33.

[0073] A half mirror is used for the optical branching unit 31. Output light from the SOA 14 of the semiconductor optical integrated device 11 is incident on the optical branching unit 31, and a portion of the incident light is transmitted and emitted as output light from the semiconductor optical integrated device 11. The other portion of the light is reflected and output to another optical monitor (external monitor) 32.

[0074] Another optical monitor (external monitor) 32 receives light from the half mirror, converts it into electricity, and generates a current I ｅｘｔ is output to the current control unit 33.

[0075] The optical monitor 15 of the semiconductor optical integrated device 11 receives a part of the light emitted from the DFB laser 12 as leakage light, converts it into electricity, and generates a current I ｉｎｔ is output to the current control unit 33.

[0076] The current control unit 33 controls the current I ｉｎｔ and the current I from another optical monitor (external monitor) 32. ｅｘｔ Based on this, the current I ＤＦＢ , I ＳＯＡ is output and feedback control is performed.

[0077] <Method of Controlling Semiconductor Optical Device> An example of a method of controlling the semiconductor optical device according to this embodiment will be described with reference to Fig. 7. Fig. 7 shows a flow chart for explaining the method of controlling the semiconductor optical device.

[0078] First, in the semiconductor optical device, the current control unit 33 controls the output current I ｉｎｔ and the output current I of the other optical monitor 32. ｅｘｔ and are measured (step S21).

[0079] Next, the current control unit 33 controls the output current I ｅｘｔ The change over time is determined (step S22).

[0080] The output current I of the other optical monitor 32 ｅｘｔ decreases over time, the output current I of the optical monitor 15 ｉｎｔ The change over time of the output current I of the other optical monitor 32 is determined (step S23). ｅｘｔ If does not decrease over time, the output current I of the optical monitor 15 is again ｉｎｔ and the output current I of the other optical monitor 32. ｅｘｔ and are measured (step S21).

[0081] Output current I of the optical monitor 15 ｉｎｔ The change over time of the output current I of the optical monitor 15 is determined. ｉｎｔ If the current I decreases over time, it is determined that the DFB laser 12 is deteriorating. In this case, the injection current I of the DFB laser 12 is reduced to avoid a burden on the deteriorating DFB laser 12. ＤＦＢ Without increasing the injection current I ＳＯＡ By this feedback control, the light emitted from the DFB laser 12 is amplified by the SOA 14, so that the output light of the semiconductor optical integrated device 11 is maintained.

[0082] On the other hand, the output current I of the optical monitor 15 ｉｎｔ The change over time of the output current I of the optical monitor 15 is determined. ｉｎｔ If the current I does not decrease over time, it is determined that the deterioration of the SOA 14 laser is progressing. In this case, the injection current I of the SOA 14 is increased to avoid a burden on the SOA 14, which is being deteriorated. ＳＯＡ Without increasing the injection current I ＤＦＢ By this feedback control, the output of the DFB laser 12 is increased, so that the output light of the semiconductor optical integrated device 11 is maintained.

[0083] <Effects> In the semiconductor optical integrated device according to this embodiment, the output optical intensity of the DFB laser can be monitored without using an SOA. As a result, when the optical output of the semiconductor optical integrated device decreases due to long-term operation, it can be determined whether the decrease in optical output is due to deterioration of the DFB laser or the SOA.

[0084] Therefore, by performing feedback control to increase the drive current of the DFB laser or the SOA, whichever is not degraded, the progression of element degradation can be suppressed and the life of the semiconductor optical integrated element 11 (AXEL chip) can be improved.

[0085] Furthermore, the semiconductor optical integrated device integrating the optical monitor can be manufactured using the same manufacturing process as conventional semiconductor optical integrated devices. Furthermore, even when the optical monitor is integrated, the characteristics of the DFB laser, EA modulator, and SOA are not degraded.

[0086] According to the semiconductor optical device and the control method for the semiconductor optical device of the present embodiment, it is possible to determine whether the deterioration of a semiconductor element, for example, a semiconductor optical integrated element in which a DFB laser and an SOA are integrated, is caused by the DFB laser or the SOA. Based on the determination result, the DFB laser and the SOA are feedback-controlled, thereby suppressing the deterioration of the DFB laser and the SOA and controlling the semiconductor optical integrated element.

[0087] First Embodiment A semiconductor optical integrated element, a method for manufacturing a semiconductor optical integrated element, a semiconductor optical device, and a method for controlling a semiconductor optical device according to a first embodiment of the present invention will be described with reference to FIG.

[0088] <Configuration of Semiconductor Optical Integrated Device> As shown in FIG. 8, the semiconductor optical integrated device 41 according to this example is a monolithic integrated device, and similarly to the first embodiment, includes a DFB laser 12, an EA modulator 13, an SOA 14, and an optical monitor 15 on the InP substrate (100) surface.

[0089] An AR coating 19 is formed on the output end face of the semiconductor optical integrated device 51 .

[0090] The waveguide structure including the DFB laser 12, EA modulator 13, and SOA 14, and the optical monitor 15, use a buried heterostructure using semi-insulating InP 17, which can provide high heat dissipation and current confinement effects.

[0091] The DFB laser 12 is 300 μm long and is arranged to output light in the

[011] (or [0-1-1]) crystal orientation direction. The DFB laser 12 includes a lower SCH layer, an active layer made of a multiple quantum well layer (MQW1), and an upper SCH layer. The multiple quantum well layer (MQW1) is made of, for example, InGaAsP, and has optical gain in the 1.3 μm oscillation wavelength band. The DFB laser 12 also includes a diffraction grating corresponding to the 1.3 μm oscillation wavelength band.

[0092] The DFB laser 12 has a diffraction grating-free region 125 near the end face.

[0093] The EA modulator 13 includes a lower SCH (Separated Confinement Heterostructure) layer, an active layer made of a multiple quantum well (MQW2) layer, and an upper SCH layer. The multiple quantum well (MQW2) layer is made of, for example, InGaAsP, and has a peak wavelength of 1.25 μm in photoluminescence (PL) measurement, which is shorter than the oscillation wavelength of the DFB laser.

[0094] The output light of the DFB laser 12 propagates through the EA modulator 13 on the same optical axis, and then rotates at an angle θ ｗｇ The propagation direction of the light is changed by the bent waveguide 162 and the light is incident on the SOA 14. Subsequently, the light is optically amplified by the SOA 14 and then output from the semiconductor optical integrated device 41.

[0095] In the curved waveguide 162, the bending angle at which a sufficient reflection suppression effect can be obtained is θ ｗｇ is set to 5°.

[0096] As described above, when the element pattern is divided (cleaved) in the manufacturing process of the semiconductor optical integrated device 41, the optical monitor 15 is formed by dividing the area of ​​the DFB laser structure 120 that does not have a diffraction grating. ｅ(Normally, about ±10 μm) occurs. Therefore, the final length of the optical monitor 15 is determined when cleavage is completed.

[0097] In designing the optical monitor 15, the length of the optical monitor 15 is set to 60 μm, taking into consideration the need for an optical monitor length of 50 μm or more to obtain sufficient sensitivity and the cleavage error (usually about ±10 μm). The length of the optical monitor 15 is preferably set to 100 μm or less, taking into consideration the position and area in which it is placed within the semiconductor optical integrated device 11.

[0098] Therefore, the total length of the DFB laser 12 and the optical monitor 15 at the time of design (before cleavage) is 360 μm.

[0099] In the DFB laser 12, too, a diffraction grating non-forming region is provided with a length of 20 μm in order to ensure a sufficient margin in consideration of cleavage errors.

[0100] As shown in FIG. 8, the optical monitor 15 is placed at a location sufficiently far away from the waveguide in which the EA modulator 13 and the SOA 14 are placed, and therefore does not affect the operating characteristics of the EA modulator 13 and the SOA 14.

[0101] <Method for Manufacturing Semiconductor Optical Integrated Device> A method for manufacturing the semiconductor optical integrated device 41 according to this embodiment will be described.

[0102] The initial substrate used was a semiconductor crystal in which a lower SCH (Separated Confinement Heterostructure) layer, a multiple quantum well (MQW1) active layer, and an upper SCH layer were grown in sequence on an n-InP substrate (100) surface.

[0103] The initial substrate including the multiple quantum wells has a structure optimized for high-efficiency operation of the DFB laser 12. For example, the multiple quantum well layer (MQW1) is an InGaAlAs multiple quantum well (number of well layers: 6) having an optical gain in the 1.3 μm oscillation wavelength band and a layer thickness of 10 nm. The SCH layer is InGaAlAs with a 1.1 μm wavelength composition.

[0104] First, the DFB laser structure 120, including the DFB laser 12 and optical monitor 15, and the SOA 14 are left, while the other active layers are selectively etched. Then, the lower SCH layer, multiple quantum well layer (MQW2), and upper SCH layer for the EA modulator 13 are grown by butt-joint regrowth. The multiple quantum well layer (MQW2) is an InGaAlAs multiple quantum well (six well layers) with a thickness of 10 nm and optical gain in the 1.2 μm wavelength band. The SCH layer is InGaAlAs with a 1.1 μm wavelength composition.

[0105] Next, the active layers are selectively etched, leaving the DFB laser structure 120, EA modulator 13, and SOA 14. Then, the optical waveguide layer connecting each element is grown by butt-joint regrowth. The optical waveguide layer has a core layer of InGaAsP with a wavelength composition of 1.1 μm to 1.2 μm.

[0106] Here, the DFB laser 12 (DFB laser structure 120), EA modulator 13, and SOA 14 are arranged so that light propagates in this order. Furthermore, in the DFB laser structure 120 including the DFB laser 12 and the optical monitor 15 and the SOA 14, the active layer (core layer) structure formed on the initial substrate remains intact, and they have the same layer structure. The only difference between the layer structure of the DFB laser 12 and other regions is the presence or absence of a diffraction grating. This allows a structure integrating multiple regions to be manufactured at low cost by reducing the number of regrowths.

[0107] Next, a diffraction grating corresponding to an oscillation wavelength band of 1.3 μm is formed in the region of the DFB laser 12 in the DFB laser structure 120. Here, the diffraction grating is formed so that the resonator of the DFB laser 12 outputs light in the substrate orientation

[011] (or [0-1-1]).

[0108] In addition, in the region of the DFB laser 12 in the DFB laser structure 120, for example, the diffraction grating non-formed region 125 is designed to be 20 μm in width. Therefore, a diffraction grating having a length of 280 μm is formed from one end of the DFB laser 12 on the EA modulator 13 side to the other end, and no diffraction grating is formed in other regions.

[0109] The diffraction grating is formed by pattern drawing using an electron beam exposure device and an etching process. Therefore, the diffraction grating non-forming region 125 can be formed in the DFB laser 12 simply by changing the drawing pattern, so the formation of the diffraction grating non-forming region 125 does not increase the load on the manufacturing process.

[0110] Next, a p-InP cladding layer and a p-contact layer are grown over the entire surface of the device by regrowth. For example, the cladding layer is set to a thickness of 2.0 μm so that the optical field propagating through the waveguide does not reach the interface between the upper cladding layer and the electrode. This cladding layer thickness is comparable to that of optical semiconductor devices in the usual communication wavelength band.

[0111] Next, an insulating film mask is formed on the waveguide portion from the DFB laser structure 120 through the EA modulator 13 and the SOA 14 to the output end of the semiconductor optical integrated device 41, and a mesa structure is formed by dry etching. ｗｇ is about 1.5 μm to 2.0 μm. For example, the waveguide width W ｗｇ Let it be 1.75 μm.

[0112] Next, while leaving the insulating film mask, the mesa structure is buried with InP 17 by burying and regrowth. The buried InP 17 is a semi-insulating InP layer doped with Fe, which functions as a current blocking layer. The amount of InP grown during burying and regrowth is adjusted so that the mesa structure of the waveguide is completely buried.

[0113] Next, after removing the insulating film mask, the contact layer between each region is removed by wet etching in order to electrically separate the regions of the DFB laser structure 120, the EA modulator 13, and the SOA 14. Here, the contact layer remains between the region in the DFB laser structure 120 where the DFB laser 12 is formed and the region where the optical monitor 15 is formed, but these regions are divided and electrically separated in a cleavage process described later.

[0114] Next, p-side electrodes for injecting current through the p-contact layers of the DFB laser structure 120, the EA modulator 13, and the SOA 14 were formed.

[0115] Next, the InP substrate is polished to a thickness of approximately 150 μm, and an n-side electrode is formed on the back surface of the InP substrate. The n-side electrode on the back surface of the substrate is a full-surface electrode common to all regions, and is grounded during operation. In this way, an element pattern consisting of multiple unit element patterns is formed on the InP substrate (wafer), including the DFB laser structure 120, EA modulator 13, curved waveguide 162, and SOA 14, and the process on the semiconductor wafer is completed.

[0116] Next, a semiconductor device bar containing multiple semiconductor optical integrated devices 41 (chips) is fabricated by cleaving along the (011) crystal plane. In this process, the DFB laser structure 120 is divided into the optical monitor 15 and the DFB laser 12 by cleavage. A typical semiconductor chip cleavage process is used here, with a cleavage position accuracy of ±10 μm or less.

[0117] Next, in the semiconductor element bar, an AR coating 19_1 is applied to one end face (the end face on the output end face side of the SOA 14) and a high reflection (HR) coating 19_2 is applied to the other end face (the end face on the DFB laser 12 side).

[0118] Finally, the semiconductor element bar is divided into individual semiconductor optical integrated elements 41 .

[0119] In this manner, the semiconductor optical integrated device 41 according to this embodiment is manufactured.

[0120] <Effects> The effects of the semiconductor optical integrated element 41 according to this embodiment, the semiconductor optical device using the same, and the control method thereof will be described.

[0121] The semiconductor optical device has the same configuration as that of the second embodiment.

[0122] In the semiconductor optical integrated device 41 , the DFB laser 12 is driven with an injection current of 80 mA, which is a normal driving condition, and the optical output is measured by the optical monitor 15 .

[0123] A reverse bias of approximately 1 V is applied to the optical monitor 15, and the optical output of the DFB laser 12 is measured and output as a photocurrent. A component of the leaked light from the DFB laser 12 that is coupled to the waveguide of the optical monitor 15 is absorbed in the active layer (MQW1) of the multiple quantum well layer of the optical monitor 15 and detected as a photocurrent. The photocurrent detected by the optical monitor 15 is approximately 0.1 mA.

[0124] Although the optical monitor length varies by 50 μm to 60 μm due to the influence of cleavage errors, it can be measured with sufficient sensitivity by the optical monitors 15 of the multiple semiconductor optical integrated devices 41 fabricated on the same wafer.

[0125] When the semiconductor optical integrated device 41 is driven for a long period of time, the deterioration of the DFB laser 12 progresses and the optical output of the semiconductor optical integrated device 41 decreases, so does the photocurrent of the optical monitor 15. This makes it possible to detect only the deterioration of the DFB laser 12.

[0126] Next, the 25 Gbit / s modulation characteristics of the semiconductor optical integrated device 41 will be described. NRZ, PRBS231-1 is used as the modulation signal. Here, the current value of the DFB laser 12 is set to 80 mA, and the voltage applied to the EA modulator 13 is set to -1.5 V. The drive current of the SOA 14 is set to 70 mA. The 25 Gbit / s modulation characteristics achieve high output characteristics exceeding 10 dBm.

[0127] Next, a description will be given of the control of the semiconductor optical device when the semiconductor optical integrated element 41 is driven for a long period of time. In the semiconductor optical device, the optical output of the semiconductor optical integrated element 41 is controlled to be constant.

[0128] The optical monitor (integrated monitor) 15 in the semiconductor optical integrated device 41 is used to detect deterioration of the DFB laser 12. Furthermore, another optical monitor (external monitor) 32 is disposed outside the semiconductor optical integrated device 41 to measure the output of the semiconductor optical integrated device 41.

[0129] At the beginning of driving, the semiconductor optical integrated device 41 is driven under the above-mentioned driving conditions (DFB laser current I ＤＦＢ =80mA, SOA14 current I ＳＯＡ = 70 mA).

[0130] Also, the photocurrent I detected by the integrated monitorｉｎｔ and the photocurrent I detected by the external monitor. ｅｘｔ is constantly monitored (measured).

[0131] Current value I of external monitor ｅｘｔ detects the optical output of the semiconductor optical integrated device 41. When either the DFB laser 12 or the SOA 14 deteriorates, ｅｘｔ In order to drive the semiconductor optical integrated device 41 with a constant optical output, I ｅｘｔ The driving conditions are controlled (feedback controlled) so that the current value is constant.

[0132] Current value I of the integrated monitor ｉｎｔ Since only the output of the DFB laser 12 is monitored, the output voltage decreases only when the DFB laser 12 deteriorates.

[0133] The current control unit 33 monitors these current values ​​I ｅｘｔ , I ｉｎｔ Based on this, the DFB laser current I ＤＦＢ and the SOA current I ＳＯＡ Control.

[0134] I ｅｘｔ Only the decrease in I ｉｎｔ If there is no change, it is determined that the SOA 14 has deteriorated. In this case, feedback control is performed to increase the current of the DFB laser 12, which is not deteriorating. ｅｘｔ The DFB laser current I ＤＦＢ Increase the

[0135] On the other hand, I ｅｘｔ and I ｉｎｔ If both of I and I decrease, it is determined that the DFB laser 12 has deteriorated. In this case, feedback control is performed to increase the current value of the SOA 14, which is not deteriorating, and I ｅｘｔ is set to the initial value I ＳＯＡ Adjust.

[0136] In this way, by constantly identifying elements (DFB laser 12, SOA 14) that are deteriorating and controlling them by increasing the current load on elements that are not deteriorating, it is possible to suppress excessive deterioration of the elements (DFB laser 12, SOA 14). This control method can improve the element life by an average of 10% compared to a normal control method for semiconductor optical devices (which controls only the current value of the DFB laser 12).

[0137] According to the semiconductor optical device using the semiconductor optical integrated element 41 of this embodiment and the control method thereof, it is possible to determine whether the deterioration of the semiconductor element, for example, a semiconductor optical integrated element in which a DFB laser and an SOA are integrated, is caused by the DFB laser or the SOA. Based on the determination result, the DFB laser and the SOA are feedback-controlled, thereby suppressing the deterioration of the DFB laser and the SOA and controlling the semiconductor optical integrated element.

[0138] Second Embodiment A semiconductor optical integrated device according to a second embodiment of the present invention will be described with reference to FIGS.

[0139] <Configuration of Semiconductor Optical Integrated Device> As shown in FIG. 9, a semiconductor optical integrated device 51 according to this embodiment includes a DFB laser 12, an EA modulator 13, an SOA 14, and an optical monitor 55 on a substrate.

[0140] The configurations of the DFB laser 12, the EA modulator 13, and the SOA 14 are the same as those in the first embodiment and the first example.

[0141] The optical monitor 55 has a tapered waveguide structure 552 near the incident end face.

[0142] 10 shows an enlarged view of the bent waveguide 162 and the vicinity of the optical monitor 55 in this embodiment. In the optical monitor 55, a length L １ In the region of ｗｇ１ A waveguide 551 having a length L ２ In the region of the tapered waveguide 552, the width of the waveguide is increased. ２ In the region, the waveguide width is W ｗｇ１ From Wｗｇ２ Increases to W ｗｇ１ is 1.75 μm as in Example 1, and W ｗｇ２ is 4.5 μm.

[0143] Also, L １ Taking into account the cleavage error, the length of the cleavage error 2ΔL ｅ It is necessary to design it as follows. Considering that the general cleavage error is ±10 μm, １ was set to 20 μm. ２ The length of the entire optical monitor 55 was set to 60 μm, similarly to the first embodiment.

[0144] Length L １ Since there is a restriction on the area in which the optical monitor can be arranged within the chip, it is desirable that the width be 15 μm or more and 60 μm or less.

[0145] In the manufacturing process of the semiconductor optical integrated device 51, the optical monitor 55 and the DFB laser 12 are formed by dividing the DFB laser structure 120, so that the waveguide in contact with the output end face of the optical monitor 55 has the same waveguide width as the DFB laser 12. In this embodiment, the waveguide in contact with the output end face of the optical monitor 55 has the same waveguide width W as the DFB laser 12 in the first embodiment. ｗｇ１ As a result, the DFB laser 12 has a waveguide width W ｗｇ１ , and has the same operating characteristics as those of the first embodiment. In this way, the optical monitor 55 does not affect the operating characteristics of the DFB laser 12.

[0146] In the first embodiment and the first example, in the semiconductor optical integrated device, the leaked light from the curved waveguide propagates through the InP region that does not have a waveguide, and the beam diameter of the leaked light expands during propagation due to the diffraction effect. As a result, the amount of leaked light that does not couple with the waveguide of the optical monitor increases, and the sensitivity of the optical monitor to receive the leaked light decreases.

[0147] In this embodiment, a tapered waveguide structure is disposed near the incident end face of the optical monitor 55, so that leakage light (indicated by the dotted line in the figure), whose beam diameter expands during propagation, can be easily coupled to the waveguide of the optical monitor 55, improving the light receiving sensitivity of the optical monitor 55.

[0148] The sensitivity of the optical monitor 55 can be improved by about 15% compared to an optical monitor without a tapered structure (for example, Example 1).

[0149] According to the semiconductor optical integrated device of this embodiment, only the optical output of the integrated DFB laser can be detected (monitored) with high sensitivity.

[0150] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configuration, manufacturing method, control method, etc. of the semiconductor optical integrated element and semiconductor optical device are shown, but the present invention is not limited to these examples. Anything that can demonstrate the functions and effects of the semiconductor optical integrated element and semiconductor optical device may be used.

[0151] It should be noted that the present invention is not limited to the above-described embodiment and examples, and it is clear that many modifications and combinations can be made by a person skilled in the art within the technical spirit of the present invention. For example, the second example may be combined with the second embodiment.

[0152] A part or all of the above-described embodiment or an example thereof can be described as, but is not limited to, the following supplementary notes.

[0153] (Appendix 1) A semiconductor optical integrated device comprising, on a substrate, in this order, a DFB laser, an EA modulator, a curved waveguide, and an SOA, and further comprising an optical monitor arranged approximately coaxially with the optical axis of the emitted light from the DFB laser, and into which leaked light from the curved waveguide is incident.

[0154] (Supplementary Note 2) The semiconductor optical integrated device according to Supplementary Note 1, wherein a region having no diffraction grating is disposed near one end of the DFB laser.

[0155] (Supplementary Note 3) The semiconductor optical integrated element according to Supplementary Note 2, wherein the length of the region not having the diffraction grating is greater than 0 and equal to or less than the cleavage error length.

[0156] (Supplementary Note 4) The semiconductor optical integrated device according to any one of Supplementary Note 1 to Supplementary Note 3, wherein the optical monitor has a tapered waveguide near an end portion on the light input side.

[0157] (Appendix 5) The semiconductor optical integrated device according to any one of appendices 1 to 4, wherein the length of the optical monitor is 50 μm or more and 100 μm or less.

[0158] (Supplementary Note 6) A semiconductor optical device comprising: a semiconductor optical integrated element according to any one of Supplementary Notes 1 to 5; an optical branching unit to which output light from the SOA of the semiconductor optical integrated element is incident; another optical monitor to which light branched by the optical branching unit is input; and a current control unit to which an output current of the other optical monitor and an output current of the optical monitor of the semiconductor optical integrated element are input, wherein the current control unit outputs a current to each of the DFB laser and the SOA, and performs feedback control.

[0159] (Supplementary Note 7) A method for manufacturing a semiconductor optical integrated device according to any one of Supplementary Note 1 to Supplementary Note 5, which is a method for manufacturing a semiconductor optical integrated device according to claim 1, comprising the steps of: forming an element pattern consisting of a plurality of unit element patterns; and dividing the element pattern into the semiconductor optical integrated device and another semiconductor optical integrated device adjacent to the semiconductor optical integrated device, wherein the unit element pattern includes, on a substrate, a DFB laser structure, the EA modulator, the bent waveguide, and the SOA in this order, and does not have a diffraction grating near one end of the DFB laser structure. a region where a large area is arranged, and the one end is located on the side that contacts the other of the unit element patterns with respect to a straight line perpendicular to the optical axis that passes through an output end of an optical waveguide portion that passes through the DFB laser structure, the EA modulator, the curved waveguide, and the SOA in the other of the adjacent unit element patterns, and the dividing step divides the region of the DFB laser structure, and one of the divided DFB laser structures constitutes the optical monitor of the other of the semiconductor integrated optical elements, and the other constitutes the DFB laser of the semiconductor integrated optical element.

[0160] (Supplementary Note 8) A method for controlling a semiconductor optical device according to Supplementary Note 6, comprising the steps of: the current control unit measuring an output current of the optical monitor and an output current of the other optical monitor; and the current control unit increasing a control current to the DFB laser when the output current of the other optical monitor decreases but the output current of the optical monitor does not decrease, and increasing the control current to the SOA when the output current of the other optical monitor decreases and the output current of the optical monitor decreases.

[0161] (Appendix 9) A semiconductor optical integrated element, wherein the cleavage error length is 20 μm.

[0162] (Appendix 10) A semiconductor optical integrated device, wherein the optical monitor comprises a waveguide of a constant width, and the length of the waveguide of the constant width is 15 μm or more and 60 μm or less.

[0163] The present invention can be applied to optical communication devices and optical communication systems.

[0164] 11 semiconductor optical integrated element 12 DFB laser 13 EA modulator 14 SOA 15 optical monitor 162 optical waveguide (bent waveguide) 18 optical axis of emitted light from DFB laser

Claims

1. A semiconductor optical integrated device comprising, on a substrate, in that order, a DFB laser, an EA modulator, a curved waveguide, and an SOA, and further comprising an optical monitor arranged approximately coaxially with the optical axis of the light emitted from the DFB laser, into which leakage light from the curved waveguide is incident.

2. The semiconductor optical integrated device according to claim 1, wherein a region having no diffraction grating is disposed near one end of said DFB laser.

3. The semiconductor optical integrated element according to claim 2, wherein the length of the region not having the diffraction grating is greater than 0 and is equal to or less than the cleavage error length.

4. The semiconductor optical integrated device according to claim 1, wherein said optical monitor has a tapered waveguide in the vicinity of the end portion on the light input side.

5. The semiconductor optical integrated device according to claim 1, wherein the length of said optical monitor is not less than 50 μm and not more than 100 μm.

6. A semiconductor optical device comprising: a semiconductor optical integrated element according to claim 1; an optical branching section into which output light from the SOA of said semiconductor optical integrated element is incident; another optical monitor into which light branched by said optical branching section is input; and a current control section into which an output current of said other optical monitor and an output current of said optical monitor of said semiconductor optical integrated element are input, said current control section outputting currents to said DFB laser and said SOA, respectively, and performing feedback control.

7. A method for manufacturing a semiconductor optical integrated element according to claim 1, comprising the steps of: forming an element pattern consisting of a plurality of unit element patterns; and dividing the element pattern into the semiconductor optical integrated element and another semiconductor optical integrated element adjacent to the semiconductor optical integrated element, wherein the unit element pattern comprises, in this order on a substrate, a DFB laser structure, the EA modulator, the curved waveguide, and the SOA, and an area having no diffraction grating is disposed in the vicinity of one end of the DFB laser structure, and the one end is located on the side that contacts the other unit element pattern with respect to a straight line perpendicular to the optical axis that passes through an output end of an optical waveguide portion that passes through the DFB laser structure, the EA modulator, the curved waveguide, and the SOA in the other adjacent unit element pattern, A method for manufacturing a semiconductor optical integrated element, wherein the dividing step divides the region of the DFB laser structure, and one of the divided DFB laser structures constitutes the optical monitor of the other semiconductor optical integrated element, and the other constitutes the DFB laser of the semiconductor optical integrated element.

8. A method for controlling a semiconductor optical device according to claim 6, comprising the steps of: said current control unit measuring an output current of said optical monitor and an output current of said other optical monitor; and said current control unit increasing a control current to said DFB laser when the output current of said other optical monitor decreases and the output current of said optical monitor does not decrease, and increasing a control current to said SOA when the output current of said other optical monitor decreases and the output current of said optical monitor decreases.

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