WO2025013161A1 - Semiconductor optical integrated element, method for manufacturing semiconductor optical integrated element, semiconductor optical device, and method for controlling semiconductor optical device - Google Patents

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 for semiconductor optical integrated element, semiconductor optical device, and control method for semiconductor optical device

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 a semiconductor optical device.

　Network traffic is increasing in recent years due to the spread of video distribution services and the growing demand for mobile traffic. In the optical transmission lines that support the network, progress has been made in reducing the cost of networks by increasing transmission rates, lowering power consumption, and extending transmission distances. There is also a demand for lower power consumption, higher speeds, and higher output for the semiconductor modulated light sources used in optical transmission lines.

Electroabsorption modulator integrated DFB (EADFB) lasers have high extinction characteristics and excellent chirp characteristics compared to direct modulation lasers, and have been widely used. As shown in FIG. 11, a conventional EADFB laser 61 has a structure in which a DFB laser 62 and an EA modulator 63 are integrated in 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 by a diffraction grating 624 formed in the resonator. The EA modulator 63 has a light absorption layer 632 made of a multiple quantum well (MQW) with a different composition from the DFB laser 62, and changes the amount of light absorption by voltage control. By driving under conditions that transmit or absorb the output light from the DFB laser 62, the light is blinked and the electrical signal is converted into an optical signal. However, with the EADFB laser 61, it is difficult to achieve high output due to the large optical loss of the EA modulator 63.

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 output 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, improving the optical output. This provides output characteristics that are approximately twice as high as those of a typical EADFB laser.

In AXEL71, the active layer of the SOA uses the same MQW structure as a DFB laser. Therefore, there is no need to add a regrowth process to integrate the SOA region, and the device can be manufactured using the same manufacturing process as a conventional EADFB laser.

The AXEL71 can operate with high efficiency due to the SOA integration effect, so when operated under operating conditions that provide the same optical output as a typical EADFB laser, power consumption can be reduced by approximately 40%.

On the other hand, there are concerns that the high optical output characteristics of the AXEL71, which accompanies SOA integration, may have a significant effect on the operating characteristics due to reflected back light, compared to typical EADFB lasers.

In optical transmitters such as general semiconductor lasers, the light reflected by the end face of the semiconductor chip and returning to the inside of the chip has a negative effect on 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 the light reflected back from the chip end face to the inside.

In the AXEL (SOA integrated EADFB laser) 71, due to its high output characteristics, even a small amount of reflected light has a large effect on the operating characteristics. If the optical amplification effect of the SOA of the SOA integrated EADFB laser is +3 dB compared to a conventional EADFB laser, the average optical output will be increased by +3 dB and the reflected light intensity will also increase by 3 dB. Furthermore, since the reflected light at the end face is amplified again within the SOA 74, the reflected light intensity reaching the DFB laser 72 will increase by +6 dB compared to the EADFB laser.

In order to suppress the effect of reflected light in AXEL, AXEL81 has been proposed, which uses a curved waveguide, as shown in Figure 13.

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, the light propagating through the waveguide enters the light emitting face perpendicularly and is emitted from the semiconductor chip.

On the other hand, in the AXEL81, in a configuration in which the DFB laser 82, the EA modulator 83, and the SOA 84 are connected by the 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 incident at an incident angle of θ _wg with respect to the output end face and is output from the output end face. This makes it difficult for the light reflected at the output end face to be coupled back to the waveguide, so that reflected back light can be suppressed. In general, the incident angle θ _wg with respect to the output end face of the waveguide to suppress reflection is set to 4 to 8 degrees. Usually, in the AXEL71 chip, the DFB laser 82 and the EA modulator 83 are formed in a straight waveguide region having a waveguide direction in which light propagates perpendicular to the cleaved end face. On the other hand, the SOA 84 is formed in an oblique waveguide region in a waveguide direction having an incident angle θ _wg with respect to the output end face.

In modulated light sources including AXEL, it is necessary to keep the optical intensity of the optical signal constant during operation. Conventional EADFB 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 outside the chip, and the current injected into the DFB laser is controlled so that the monitored optical intensity remains constant. This makes it possible to increase the amount of current in the DFB laser, correct the change in optical output, and maintain a constant output when the optical output of the DFB laser deteriorates due to long-term operation.

Conventionally, AXEL81 has been driven by APC, 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 FIG. 14, a configuration is shown in which the drive current of the DFB laser 82 is controlled so that the light intensity monitored by the optical monitor 92 is constant.

Inside the AXEL81 chip, the light emitted from the DFB laser 82 is modulated by the electrical input signal 95 in the EA modulator 83, amplified by the SOA 84, and then output outside the chip.

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 the 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 light 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.

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.

However, in the conventional configuration described above, the light that passes 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.

In general, the deterioration of optical semiconductor devices is accelerated by the amount of current injected. Therefore, if the optical output of AXEL 81 decreases due to deterioration of the DFB laser 82, and the current 94 of the DFB laser 82 is increased to maintain a constant optical output intensity, the deterioration of the DFB laser 82 will be accelerated, which may result in a shortened element lifespan.

In addition, if the optical output of AXEL81 decreases due to degradation of SOA84, and the current 96 of SOA84 is increased in order to maintain a constant optical output intensity, the degradation of SOA84 may be accelerated, resulting in a shortened element lifespan.

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

The present invention provides a semiconductor optical integrated element that can suppress and control the degradation of integrated elements, a method for manufacturing a semiconductor optical integrated element, a semiconductor optical device, and a method for controlling a semiconductor optical device.

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 flow chart for explaining a method for manufacturing a semiconductor optical integrated device according to the first embodiment of the present invention. 3A to 3C are diagrams for explaining a method for manufacturing a semiconductor optical integrated device according to the first embodiment of the present invention. FIG. 4 is a diagram for explaining a method for manufacturing a semiconductor optical integrated device according to the first embodiment of the present invention. FIG. 5 is a diagram for explaining 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 a configuration of a semiconductor optical device according to a second embodiment of the present invention. FIG. 7 is a flow chart for explaining 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 embodiment of the present invention. FIG. 9 is a schematic top view showing the configuration of a semiconductor optical integrated device according to a second embodiment of the present invention. FIG. 10 is a diagram for explaining the operation of the semiconductor optical integrated device according to the second embodiment 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.

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.

<Configuration of semiconductor optical integrated device>
1 is a schematic top view showing the configuration of a semiconductor optical integrated device 11 according to the present embodiment. In the figure, cladding layers, contact layers, etc. are omitted. Dotted lines indicate an example of electrodes of each device.

As shown in FIG. 1, the 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).

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.

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

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

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 bent waveguide, and is bent or curved at a predetermined angle θ _wg .

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.

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

The optical monitor 15 is disposed on the output side of the EA modulator 13, away from the DFB laser 12 and EA modulator 13, without passing through an optical waveguide, and is disposed approximately on the same axis as the optical axis 18 of the DFB laser 12 and EA modulator 13 (the optical axis of the emitted light of the DFB laser 12). In other words, the optical monitor 15 is disposed so that a portion of the emitted light from the EA modulator 13 enters as leaked light from the curved waveguide 162. Therefore, a portion of the emitted light from the EA modulator 13 (leakage light) enters the optical monitor 15 without passing through the SOA 14. "Approximately the same axis" includes the same axis and refers to the range of the optical axis in which the leaked light from the curved waveguide 162 enters the optical monitor 15.

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

A buried semiconductor layer 17 is disposed as a current blocking layer in the area 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.

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 waveguiding direction of the output light is changed by a predetermined angle θ _wg from the optical axis direction of the output light from the DFB laser 12.

At this time, a portion 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 emitted from the curved waveguide 162 as leakage light.

Integrating an optical monitor 15 that monitors this leaked light in the semiconductor optical integrated device 11 makes it 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 positioned on approximately the same optical axis 18 as the waveguide of the DFB laser 12.

In addition, the optical monitor 15 uses the same layer structure as the DFB laser 12. This eliminates the need for additional regrowth processes for integrating the optical monitor 15, and allows it to be manufactured using the same process as conventional methods.

<Method of Manufacturing Semiconductor Optical Integrated Device>
An example of a manufacturing method of the semiconductor optical integrated device 11 according to the present embodiment will be described with reference to Figs. 2 to 5. Fig. 2 shows a flow chart for explaining an example of a manufacturing method of 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 direction and the Y direction 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]).

First, as shown in FIG. 3, multiple 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).

In the X direction on the wafer, the unit element patterns 110 are arranged so that the optical axes 18 of the DFB laser structures 120 coincide with each other. Since the position of the optical axis is determined by the lithography process, it can be accurately positioned by the lithography mask design.

A region 23 that does not have a diffraction grating is disposed at one end of the DFB laser structure 120. This region 23 that does not have a diffraction grating extends toward another adjacent unit element pattern 110_2. In detail, 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 perpendicular to the optical axis of the DFB laser structure 120 that passes through the output end of the optical waveguide portion that passes through the DFB laser structure 120, the EA modulator 13, the curved waveguide 162, and the SOA 14 in the other unit element pattern 110_2.

Next, the element pattern consisting of 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).

The element pattern is divided into semiconductor optical integrated elements 11 and 11_2 at cleavage position 21 by cleavage. The emission end faces of semiconductor optical integrated elements 11 and 11_2 are formed by cleavage.

At this time, the DFB laser structure 120 is split (cleaved) at the region 23 that does not have a diffraction grating. As a result, one of the split DFB laser structures 120 is placed in the adjacent semiconductor optical integrated device 11_2, and the other semiconductor optical integrated device 11_2 constitutes the optical monitor 15.

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

In this way, a part (one part) of the DFB laser structure 120 functions as the optical monitor 15 as 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.

In addition, the optical monitor 15 and the DFB laser 12 are formed on the wafer with approximately the same optical axis 18, so the optical monitor 15 can reliably monitor the light emitted from the DFB laser 12.

The process for dividing the DFB laser structure 120 is described in detail below.

In a normal cleavage process, a manufacturing error (hereinafter referred to as a "cleavage error") of ±ΔL _e occurs with respect to the designed cleavage position. It is necessary to design the configurations of the DFB laser 12 and the optical monitor 15 in consideration of this cleavage error so as to ensure the functionality of each of them.

The DFB laser can emit highly monochromatic light in a single mode using a diffraction grating. On the other hand, if the optical monitor has a diffraction grating, the diffraction grating prevents light from entering the optical monitor from the outside, so the optical monitor does not obtain sufficient sensitivity. In addition, 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 operation of the device.

Figure 4 shows a cross-sectional view of the DFB laser structure 120 in the optical waveguide direction during the division (cleavage) process. In Figure 4, the planned cleavage position 22 is shown by a dashed line, and the range of cleavage error is shown 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.

A region 23 that does not have a diffraction grating is provided at one end of the DFB laser structure 120 in the unit element pattern 110. This region 23 that does not have a diffraction grating extends toward another adjacent unit element pattern 110_2.

By cleaving, the semiconductor optical integrated element 11 is separated from the adjacent semiconductor optical integrated element 11_2. At this time, the DFB laser structure 120 is divided at the region 23 that does not have a diffraction grating. As a result, as shown in FIG. 4, the DFB laser 12 is arranged in the semiconductor optical integrated element 11, and the optical monitor 15 is arranged in the adjacent semiconductor optical integrated element 11_2, with the cleavage position 21 in between. As a result, no diffraction grating is formed in the optical monitor 15.

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

Since normal cleavage processes have manufacturing errors (cleavage errors), a cleavage margin area is provided near the cleavage position that separates the semiconductor optical integrated devices (chips) in anticipation of cases where the cleavage position deviates from the intended cleavage position.

In the semiconductor optical integrated device 11 according to this embodiment, a region without a diffraction grating (hereinafter also referred to as the "DFB margin region") 23 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 if the cleavage position 21 deviates from the planned position 22.

As a result, a portion of the DFB margin region 23 remains as a diffraction grating non-formation region 125 in a portion of the DFB laser 12 (near one end).

If the diffraction grating non-forming region 125 in a DFB laser is too long, it will affect the performance of the DFB laser. It is desirable for the length of the diffraction grating non-forming region 125 to be 50 μm or less.

For example, when the cleavage error is ±ΔL _e , the length of the DFB margin region 23 is set to 2ΔL _e , and the planned cleavage position 22 is set to ΔL _e from the end of the diffraction grating of the DFB laser 12. If the actual cleavage position 21 is shifted from the planned cleavage position 22 toward the DFB laser 12 by ΔL _e (+ΔL _e ), the length of the diffraction grating non-formed region 125 of the DFB laser 12 is 0 μm, and the optical monitor 15 does not include a diffraction grating. If the actual cleavage position 21 is shifted from the planned cleavage position 22 toward the optical monitor 15 by ΔL _e (−ΔL _e ), the length of the diffraction grating non-formed region 125 of the DFB laser 12 is 2ΔL _e , and the optical monitor 15 does not include a diffraction grating.

In this way, it is desirable that the length of the DFB margin region is 2ΔL _e or more. In this case, it is desirable that the length of the diffraction grating non-forming region 125 of the DFB laser 12 is 0 μm to 2ΔL _e or less.

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

In this way, according to the manufacturing method of the semiconductor optical integrated device of this embodiment, the optical monitor 15 and the DFB laser 12 can be easily arranged so that their optical axes are substantially aligned. This simplifies the manufacturing process, and the emitted light of the DFB laser 12 can be reliably monitored by the optical monitor 15.

The steps performed on a wafer in the manufacturing method of a semiconductor optical integrated device according to this embodiment will be described with reference to FIG. 5.

First, an element pattern consisting of multiple unit element patterns is formed in the X and Y directions on a substrate (wafer). 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.

Next, the semiconductor optical integrated elements (e.g., semiconductor optical integrated elements 11, 11_2) are divided (cleaved) in the Y direction shown in FIG. 5. As a result, the semiconductor optical integrated elements are divided into a state in which they are arranged in a row in the Y direction. Hereinafter, this state is referred to as a "semiconductor element bar." The cleavage forms the emission end faces of the semiconductor optical integrated elements (chips) in the semiconductor element bar, and all of the semiconductor optical integrated elements (chips) in the semiconductor element bar have the same emission end face.

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 on the semiconductor optical integrated element of one of the semiconductor element bars formed by the cleavage, and a DFB laser is placed on the semiconductor optical integrated element of the other semiconductor element bar.

Finally, the semiconductor element bar is split (cleaved) in the X direction between each semiconductor optical integrated element to produce the semiconductor optical integrated elements.

The semiconductor optical integrated device according to this embodiment can detect (monitor) only the optical output of the DFB laser among the integrated DFB laser and SOA. In addition, the manufacturing method of the semiconductor optical integrated device according to this embodiment can easily manufacture this semiconductor optical integrated device.

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.

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

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

Another optical monitor (external monitor) 32 receives light from the half mirror, converts it into electricity, and outputs a current I _ext to a current control unit 33 .

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 outputs a current I _int to the current control unit 33 .

The current control unit 33 outputs currents I _DFB and I _SOA to the DFB laser 12 and the SOA 14, respectively, based on the current I _int from the optical monitor 15 and the current I _ext from another optical monitor (external monitor) 32, and performs feedback control.

<Method of controlling semiconductor optical device>
An example of a method for controlling the semiconductor optical device according to the present embodiment will be described with reference to Fig. 7. Fig. 7 shows a flow chart for explaining the method for controlling the semiconductor optical device.

First, in the semiconductor optical device, the current control unit 33 measures the output current I _int of the optical monitor 15 and the output current I _ext of the other optical monitor 32 (step S21).

Next, the current control unit 33 determines the change over time in the output current I _ext of the other optical monitor 32 (step S22).

If the output current _Iext of the other optical monitor 32 decreases over time, the change over time of the output current _Iint of the optical monitor 15 is determined (step S23). If the output current _Iext of the other optical monitor 32 does not decrease over time, the output current _Iint of the optical monitor 15 and the output current _Iext of the other optical monitor 32 are measured again (step S21).

The change over time of the output current I _int of the optical monitor 15 is judged, and if the output current I _int of the optical monitor 15 decreases over time, it is judged that the degradation of the DFB laser 12 is progressing. In this case, in order to avoid burdening the degraded DFB laser 12, the injection current I _DFB of the DFB laser 12 is not increased, but the injection current I _SOA of the SOA 14, which is not degraded, is increased. By this feedback control, the emitted light of the DFB laser 12 is amplified by the SOA 14, so that the output light of the semiconductor optical integrated device 11 is maintained.

On the other hand, by determining the change over time of the output current I _int of the optical monitor 15, if the output current I _int of the optical monitor 15 does not decrease over time, it is determined that the degradation of the SOA 14 laser is progressing. In this case, in order to avoid burdening the degraded SOA 14, the injection current I _SOA of the SOA 14 is not increased, but the injection current I _DFB of the DFB laser 12, which is not degraded, is increased. This feedback control increases the output of the DFB laser 12, so that the output light of the semiconductor optical integrated device 11 is maintained.

＜Effects＞
In the semiconductor optical integrated device according to the present embodiment, the output light intensity of the DFB laser can be monitored without using the SOA, so that when the optical output of the semiconductor optical integrated device is reduced due to long-term operation, it can be determined whether the reduction in optical output is due to deterioration of the DFB laser or the SOA.

Therefore, by performing feedback control to increase the drive current of the DFB laser or the SOA, whichever is not degraded, it is possible to suppress the progression of element degradation and improve the lifespan of the semiconductor optical integrated element 11 (AXEL chip).

In addition, a semiconductor optical integrated device with an integrated optical monitor can be manufactured using the same manufacturing process as conventional semiconductor optical integrated devices. Furthermore, even when an optical monitor is integrated, the characteristics of the DFB laser, EA modulator, and SOA are not degraded.

The semiconductor optical device and the method for controlling the semiconductor optical device according to this embodiment make it 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. By feedback-controlling the DFB laser and the SOA based on the result of this determination, it is possible to suppress the deterioration of the DFB laser and the SOA and control the semiconductor optical integrated element.

First Example
A semiconductor optical integrated device, a manufacturing method for the semiconductor optical integrated device, a semiconductor optical device, and a control method for the semiconductor optical device according to a first embodiment of the present invention will be described with reference to FIG.

<Configuration of semiconductor optical integrated device>
As shown in FIG. 8, the semiconductor optical integrated device 41 according to this embodiment 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.

An AR coating 19 is formed on the output end surface of the semiconductor optical integrated element 51.

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 provides high heat dissipation and current confinement effects.

The DFB laser 12 has a length of 300 μm and is arranged to output light in the crystal orientation [011] (or [0-1-1]). The DFB laser 12 comprises 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, for example, InGaAsP, and has optical gain in the 1.3 μm oscillation wavelength band. It also has a diffraction grating that corresponds to the 1.3 μm oscillation wavelength band.

The DFB laser 12 has a diffraction grating non-forming region 125 near the end face.

The EA modulator 13 comprises a lower SCH (Separated Confinement Heterostructure) layer, an active layer made of a multiple quantum well layer (MQW2), and an upper SCH layer. The multiple quantum well layer (MQW2) is, 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.

The output light of the DFB laser 12 propagates through the EA modulator 13 on the same optical axis, then changes its propagation direction by the bent waveguide 162 at an angle θ _wg with respect to the crystal orientation [011] (or [0-1-1]), and enters the SOA 14. Subsequently, the output light is optically amplified by the SOA 14, and then output from the semiconductor optical integrated device 41.

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

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. At this time, a cleavage error ΔL _e (usually about ±10 μm) occurs in the cleavage process. Therefore, the final length of the optical monitor 15 is determined when cleavage is completed.

In designing the optical monitor 15, the length of the optical monitor 15 is designed to be 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). Taking into consideration the position and area in which the optical monitor 15 is placed within the semiconductor optical integrated device 11, it is desirable for the length of the optical monitor 15 to be 100 μm or less.

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

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

As shown in FIG. 8, the optical monitor 15 is placed far enough away from the waveguide in which the EA modulator 13 and SOA 14 are placed, so that it does not affect the operating characteristics of the EA modulator 13 and SOA 14.

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

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

The initial substrate including the multiple quantum wells has a structure optimized for highly efficient 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) with 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.

First, the DFB laser structure 120 including the DFB laser 12 and the optical monitor 15, and the SOA 14 region are left, and 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 (number of well layers: 6) with optical gain in the 1.2 μm wavelength band and a layer thickness of 10 nm. The SCH layer is InGaAlAs with a 1.1 μm wavelength composition.

Next, the DFB laser structure 120, EA modulator 13, and SOA 14 regions are left, and the other active layers are selectively etched. After that, the optical waveguide layer that connects to 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.

Here, the DFB laser 12 (DFB laser structure 120), EA modulator 13, and SOA 14 are arranged so that light propagates in that order. Furthermore, in the portion of 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 as is, and has the same layer structure. The only difference between the layer structure of the DFB laser 12 and the other regions is the presence or absence of a diffraction grating. This makes it possible to manufacture a structure integrating multiple regions at low cost by reducing the number of regrowths.

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]).

Furthermore, 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. Therefore, a diffraction grating with 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.

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.

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

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 emission end of the semiconductor optical integrated device 41, and a mesa structure is formed by dry etching. In a typical InP-based device in the 1.3 μm wavelength band, the waveguide width W _wg is about 1.5 μm to 2.0 μm. For example, the waveguide width W _wg is 1.75 μm.

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

Next, after removing the insulating film mask, the contact layers between the DFB laser structure 120, EA modulator 13, and SOA 14 regions are removed by wet etching to electrically isolate the regions. Here, the contact layers remain between the region in the DFB laser structure 120 where the DFB laser 12 is formed and the region in which the optical monitor 15 is formed, but these regions are divided and electrically isolated in a cleavage process described below.

Next, p-side electrodes were formed to inject current through the p-contact layers of the DFB laser structure 120, the EA modulator 13, and the SOA 14.

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 common full-surface electrode for each region, and is connected to ground when in operation. In this way, an element pattern consisting of multiple unit element patterns having a DFB laser structure 120, EA modulator 13, curved waveguide 162, and SOA 14 is formed on the InP substrate (wafer), and the process on the semiconductor wafer is completed.

Next, a semiconductor element bar containing multiple semiconductor optical integrated elements 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, and the cleavage position accuracy is within ±10 μm.

Next, an AR coating 19_1 is applied to one end face of the semiconductor element bar (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).

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

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

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

The semiconductor optical device has a configuration similar to that of the second embodiment.

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

In the optical monitor 15, a reverse bias of approximately 1 V is applied, the optical output of the DFB laser 12 is measured, and output as a photocurrent. The 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.

Due to the influence of cleavage errors, the optical monitor length varies by 50 μm to 60 μm, but the optical monitors 15 of multiple semiconductor optical integrated devices 41 fabricated on the same wafer can measure with sufficient sensitivity.

When the semiconductor optical integrated device 41 is operated for a long period of time, the deterioration of the DFB laser 12 progresses, and when the optical output of the semiconductor optical integrated device 41 decreases, the photocurrent of the optical monitor 15 also decreases. This makes it possible to detect only the deterioration of the DFB laser 12.

Next, the 25 Gbit/s modulation characteristics of the semiconductor optical integrated device 41 will be explained. 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 provide high output characteristics exceeding 10 dBm.

Next, we will explain how to control the semiconductor optical device when the semiconductor optical integrated element 41 is operated 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.

The optical monitor (integrated monitor) 15 in the semiconductor optical integrated device 41 is used to detect deterioration of the DFB laser 12. In addition, another optical monitor (external monitor) 32 is placed outside the semiconductor optical integrated device 41 to measure the output of the semiconductor optical integrated device 41.

At the beginning of driving, the semiconductor optical integrated device 41 is driven under the above-mentioned driving conditions (DFB laser current I _DFB =80 mA, SOA 14 current I _SOA =70 mA).

In addition, the photocurrent I _int detected by the integrated monitor and the photocurrent I _ext detected by the external monitor are constantly monitored (measured).

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

The current value I _int of the integrated monitor only monitors the output of the DFB laser 12, and therefore decreases only when the DFB laser 12 deteriorates.

The current control unit 33 controls the DFB laser current I _DFB and the SOA current I _SOA based on these monitor current values I _ext and I _int .

If only _Iext decreases and _Iint does not 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. In other words, the DFB laser current _IDFB is increased so that _Iext becomes the initial value.

On the other hand, if both _Iext and _Iint have decreased, 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 _{the ISOA} is adjusted so that _Iext returns to its initial value.

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 lifespan by an average of 10% compared to the normal control method for semiconductor optical devices (which controls only the current value of the DFB laser 12).

The semiconductor optical device using the semiconductor optical integrated element 41 according to this embodiment and the control method thereof can 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. By feedback-controlling the DFB laser and the SOA based on the result of this determination, the deterioration of the DFB laser and the SOA can be suppressed and the semiconductor optical integrated element can be controlled.

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

<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.

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

The optical monitor 55 has a tapered waveguide structure 552 near the input end face.

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 waveguide 551 having a waveguide width W _wg1 in a region of length L ₁ from the emission end face toward the inside of the optical monitor 55 (chip) is provided. A tapered waveguide 552 is provided, which is connected to the waveguide 551 and has an expanding waveguide width in a region of length L ₂ to the incidence end face. In the tapered waveguide 552, the waveguide width increases from W _wg1 to W _wg2 in the region of length L _2. W _wg1 is 1.75 μm as in the first embodiment, and W _wg2 is 4.5 μm.

Also, taking into account the cleavage error, _L1 needs to be designed to be equal to or greater than the cleavage error length 2ΔL _e . Considering that the general cleavage error is ±10 μm, _L1 was set to 20 μm. Furthermore, _L2 was set to 40 μm, and the overall length of the optical monitor 55 was set to 60 μm, the same as in the first embodiment.

The length _L1 is desirably 15 μm or more and 60 μm or less because there is a restriction on the area in the chip in which the optical monitor can be disposed.

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 is set to be equal to the waveguide width W _wg1 of the DFB laser 12 in the first embodiment. As a result, the DFB laser 12 has a waveguide width W _wg1 and has operating characteristics equivalent to those of the first embodiment. In this way, the optical monitor 55 does not affect the operating characteristics of the DFB laser 12.

In the first embodiment and the first example, in the semiconductor optical integrated device, the leaked light from the curved waveguide propagates through an 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 is not coupled to the waveguide of the optical monitor increases, and the sensitivity of the optical monitor to receive the leaked light decreases.

In this embodiment, a tapered waveguide structure is placed near the incident end face of the optical monitor 55, so that leakage light (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.

The sensitivity of the optical monitor 55 can be improved by about 15% compared to an optical monitor that does not have a tapered structure (e.g., Example 1).

The semiconductor optical integrated device according to this embodiment can detect (monitor) only the optical output of the integrated DFB laser with high sensitivity.

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. Anything that can exert the functions and effects of the semiconductor optical integrated element and semiconductor optical device will do.

The present invention is not limited to the above-mentioned embodiment and examples, and it is clear that many modifications and combinations can be implemented by a person with ordinary knowledge in this field within the technical concept of the present invention. For example, the second example may be combined with the second embodiment.

The above-described embodiment or an example thereof, in whole or in part, may be described as, but is not limited to, the following notes.

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

(Appendix 2) A semiconductor optical integrated device as described in appendix 1, in which a region without a diffraction grating is disposed near one end of the DFB laser.

(Appendix 3) The semiconductor optical integrated element described in appendix 2, in which 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.

(Appendix 4) A semiconductor optical integrated device according to any one of appendices 1 to 3, in which the optical monitor has a tapered waveguide near the end where the light is input.

(Appendix 5) A semiconductor optical integrated device according to any one of appendices 1 to 4, in which the length of the optical monitor is 50 μm or more and 100 μm or less.

(Appendix 6) A semiconductor optical device comprising a semiconductor optical integrated element according to any one of appendices 1 to 5, an optical branching section to which the output light of the SOA of the semiconductor optical integrated element is incident, another optical monitor to which the light branched by the optical branching section is input, and a current control section to which the output current of the other optical monitor and the output current of the optical monitor of the semiconductor optical integrated element are input, the current control section outputting a current to each of the DFB laser and the SOA and performing feedback control.

(Appendix 7) A method for manufacturing a semiconductor optical integrated element according to any one of appendices 1 to 5, 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, the unit element pattern including, on a substrate, a DFB laser structure, the EA modulator, the curved waveguide, and the SOA, in that order, and having a diffraction grating near one end of the DFB laser structure. A method for manufacturing a semiconductor optical integrated element, in which an area where the end is not present is arranged, and the one end is located on the side of the other unit element pattern that is in contact with the other unit element pattern from a straight line perpendicular to the optical axis that passes through the DFB laser structure, the EA modulator, the curved waveguide, and the SOA in the other adjacent unit element pattern, and the dividing step divides the area 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.

(Appendix 8) A method for controlling a semiconductor optical device according to appendix 6, comprising the steps of: the current control unit measuring the output current of the optical monitor and the output current of the other optical monitor; and the current control unit increasing the control current to the DFB laser when the output current of the other optical monitor decreases and 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.

(Appendix 9) A semiconductor optical integrated device in which the cleavage error length is 20 μm.

(Appendix 10) A semiconductor optical integrated device, in which 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.

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

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 (8)

On the substrate, in this order, a DFB laser,
An EA modulator;
A bent waveguide;
The SOA and
The semiconductor optical integrated device further comprises an optical monitor arranged substantially coaxially with an optical axis of the emitted light from the DFB laser, and into which leaked light from the curved waveguide is incident. The semiconductor optical integrated device according to claim 1, in which a region without a diffraction grating is disposed near one end of the DFB laser. The semiconductor optical integrated device according to claim 2, wherein the length of the region not having the diffraction grating is greater than 0 and less than or equal to the cleavage error length. The semiconductor optical integrated device according to claim 1, wherein the optical monitor has a tapered waveguide near the end where the light is input. The semiconductor optical integrated device according to claim 1, wherein the length of the optical monitor is 50 μm or more and 100 μm or less. A semiconductor optical integrated device according to claim 1 ;
an optical branching unit to which output light of the SOA of the semiconductor optical integrated device is incident;
another optical monitor to which the light branched by the optical branching unit is input;
a current control unit to which an output current of the another optical monitor and an output current of the optical monitor of the semiconductor optical integrated device are input,
The current control section outputs a current to each of the DFB laser and the SOA, and performs feedback control. A method for manufacturing the semiconductor optical integrated device according to claim 1, comprising the steps of:
forming an element pattern consisting of a plurality of unit element patterns;
dividing the element pattern into the semiconductor optical integrated element and another semiconductor optical integrated element adjacent to the semiconductor optical integrated element;
the unit element pattern includes, on a substrate, a DFB laser structure, the EA modulator, the bent waveguide, and the SOA, in this order;
a region having no diffraction grating is disposed near one end of the DFB laser structure;
the one end is located on a side that contacts the other one of the unit element patterns with respect to a straight line 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 an adjacent one of the unit element patterns and is perpendicular to the optical axis,
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. 7. A method for controlling a semiconductor optical device according to claim 6, comprising:
a step of the current control unit measuring an output current of the optical monitor and an output current of the other optical monitor;
the current control unit increases a control current to the DFB laser when the output current of the other optical monitor decreases and the output current of the optical monitor does not decrease, and increases 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.

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