Optical amplifier and inspection method of optical amplifier

Abstract

An optical amplifier and a method for inspecting an optical amplifier. An optical amplifier includes: an optical amplifier chip including a pair of semiconductor optical amplifiers (SOAs); a U-shaped waveguide connecting the pair of SOAs; and two electrodes corresponding to and separated from the pair of SOAs; and a substrate including a common metal wiring connecting the two electrodes, and the optical amplifier chip is mounted on the substrate.

Description

Technical Field

[0001] The embodiments discussed herein relate to optical amplifiers and methods of inspecting optical amplifiers. Background Art

[0002] Generally, optical communication equipment used in optical communication systems requires high transmission light output and high sensitivity. In order to meet these requirements, there is a method of amplifying transmitted light and received light by using an optical amplifier. When using an optical amplifier, from the viewpoint of reducing the size of the optical communication equipment, a semiconductor optical amplifier (SOA) with a small chip size can be used.

[0003] Figure 7 A structural example of the optical amplifier 10 using the SOA chip is shown. Figure 7 The upper figure in FIG. 1 is a plan view of the optical amplifier 10. Figure 7 The lower figure in FIG. 1 is a side view of the optical amplifier 10. Figure 7 As shown, the base substrate 11 has a concave platform portion 11a formed therein, and an SOA chip 12 is arranged on the platform portion 11a. The SOA chip 12 is positioned so that the end surface of the waveguide 11b formed in the base substrate 11 and the end surface of the core layer 12a of the SOA chip 12 are opposite to each other and optically coupled, and is fixed to the platform portion 11a by the bump 13.

[0004] The terrace portion 11a has a width capable of arranging the SOA chip 12 having the maximum chip length in consideration of the variation in chip length of the SOA chip 12. Therefore, when the SOA chip 12 is arranged on the terrace portion 11a, gaps having widths d1, d2 can be formed between the end surface of the waveguide 11b and the end surface of the core layer 12a, respectively. When the widths d1, d2 become larger, the optical coupling loss in these gaps increases, and the amplification characteristics of the optical amplifier 10 deteriorate.

[0005] To solve this problem, for example, Figure 8 As shown, an optical amplifier 20 in which a U-turn type SOA chip is used has been developed. Figure 8 There is shown a structure of an optical amplifier 20 in which a U-turn type SOA chip is used. Figure 8 The upper figure in FIG. 1 is a plan view of the optical amplifier 20. Figure 8 The lower figure in FIG. 2 is a side view of the optical amplifier 20 .

[0006] like Figure 8As shown, the base substrate 21 has a concave platform portion 21a formed therein, and the SOA chip 22 is arranged on the platform portion 21a. In the SOA chip 22, two SOAs 22a are connected via a U-turn waveguide 22b. Therefore, the end surfaces of the two SOAs 22a are exposed on the same side surface of the SOA chip 22, and the input end and the output end are arranged at one side surface of the SOA chip 22. The SOA chip 22 is positioned so that the end surface of the waveguide 21b formed in the base substrate 21 and the end surface of the SOA 22a of the SOA chip 22 are opposite to each other and optically coupled, and fixed to the platform portion 21a by a bump 23.

[0007] The U-turn waveguide 22b is a waveguide having a high mesa structure in which the core layer is not buried in the semiconductor material, which can enhance the confinement of light and reduce the curvature radius of the waveguide turn. Therefore, the miniaturization of the SOA chip 22 can be achieved. In addition, since the input end and the output end of the SOA chip 22 are arranged on the same side surface, the end surfaces of the two waveguides 21b and the end surfaces of the two SOAs 22a can be made close to each other, thereby making the width d3 of the gap small. As a result, the optical coupling loss can be suppressed, and the amplification characteristics of the optical amplifier 20 can be improved.

[0008] Patent Document 1: U.S. Patent No. 4794346

[0009] Patent Document 2: Japanese Laid-Open Patent Publication No. 2012-4441

[0010] It is common to check whether the SOA chip performs optical amplification correctly before mounting it on a base substrate. Specifically, an optical fiber is brought close to one end surface of the SOA to optically couple with it, and light is input to the SOA from the optical fiber. In addition, an optical fiber is brought close to the other end surface of the SOA to perform optical coupling, and the intensity of light output from the SOA is measured. The characteristics of the SOA are thereby evaluated.

[0011] However, in the above-mentioned U-turn type SOA chip, the end surface of the SOA is exposed on the same side surface, so there is a problem that it is difficult to inspect and evaluate the SOA. Figure 8 In the SOA chip 22 shown, the curvature radius of the U-turn waveguide 22b is small to reduce the chip size as small as possible, and the two SOAs 22a are arranged close to each other. Therefore, it is difficult to bring the optical fiber close to the end surfaces of the two SOAs 22a.

[0012] Specifically, the two SOAs 22a are arranged to be separated from each other by, for example, 200 μm, and therefore, the distance between the end surfaces of the two SOAs 22a exposed on the side surface of the SOA chip 22 is also about 200 μm. On the other hand, since the diameter of a general optical fiber is 250 μm, it is difficult to bring the two optical fibers close to the end surfaces of the two SOAs 22a exposed on the same side surface of the SOA chip 22 to be optically coupled. In addition, even when a thin optical fiber having a diameter of, for example, 125 μm is used, it is not easy to keep the two optical fibers at the end surfaces of the two SOAs 22a located closely adjacent to each other, and the efficiency of characteristic evaluation of the SOA chip 22 is reduced.

[0013] The disclosed technology has been achieved in view of the above-mentioned problems, and an object thereof is to provide an optical amplifier and an inspection method of the optical amplifier which efficiently evaluate an optical chip and can guarantee good optical amplification characteristics. Summary of the invention

[0014] According to one aspect of an embodiment, an optical amplifier includes: an optical amplifier chip, the optical amplifier chip including a pair of semiconductor optical amplifiers (SOAs); a U-shaped waveguide connecting the pair of SOAs; and two electrodes, the two electrodes respectively corresponding to the pair of SOAs and separated from each other; and a base substrate, the base substrate including a common metal wiring connecting the two electrodes, and the optical amplifier chip is mounted on the base substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 shows the structure of an optical amplifier according to one embodiment;

[0016] Figure 2 shows the structure of the base substrate;

[0017] Figure 3 shows the structure of an optical amplifier chip;

[0018] Figure 4 is shown along Figure 1 A schematic diagram of a cross section taken along line II in FIG.

[0019] Figure 5 is shown along Figure 1 A schematic diagram of a cross section taken along line II-II in FIG.

[0020] Figure 6 is a diagram for explaining a method of inspecting an optical amplifier chip according to one embodiment;

[0021] Figure 7 shows a structural example of an optical amplifier; and

[0022] Figure 8 Another structural example of the optical amplifier is shown. DETAILED DESCRIPTION

[0023] Preferred embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments are not intended to limit the present invention.

[0024] Figure 1 The structure of an optical amplifier 100 according to one embodiment is shown. Figure 1 The upper figure in FIG. 1 is a plan view of the optical amplifier 100. Figure 1 The lower figure in FIG. 1 is a side view of the optical amplifier 100 .

[0025] The optical amplifier 100 has a structure in which an optical amplifier chip 120 is mounted on a base substrate 110. That is, on the base substrate 110, a concave terrace portion 110a is formed, and the optical amplifier chip 120 is arranged on the terrace portion 110a.

[0026] The base substrate 110 is made of silicon or silicon dioxide (SiO 2 ) and has waveguides 111a, 111b for inputting and outputting light with respect to the optical amplifier chip 120. On the bottom surface of the terrace portion 110a of the base substrate 110, a metal wiring 112 is formed, and the optical amplifier chip 120 is connected and fixed to the metal wiring 112 via a bump 150 formed on the metal wiring 112. Figure 1 Although not shown, the other ends of the waveguides 111a, 111b that are not connected to the optical amplifier chip 120 (ends in the right direction in the figure) may be connected to other optical components such as an optical modulator and an optical fiber.

[0027] The optical amplifier chip 120 is formed using a compound semiconductor material and has two SOAs 121a and 121b and a U-turn waveguide 122 connecting them. Figure 1, the SOA active layer is shown as SOA 121, 121a, 121b, and the U-turn waveguide core layer is shown as U-turn waveguide 122. For this reason, hereinafter, they may be represented as "SOA active layer 121a, 121b" and "U-turn waveguide core layer 122". The end surfaces of the two SOAs 121a, 121b are exposed from the same side surface of the optical amplifier chip 120, and are opposite to the end surfaces of the waveguides 111a, 111b formed in the base substrate 110 to be optically coupled thereto. On the surface of the optical amplifier chip 120 opposite to the base substrate 110 (hereinafter referred to as the "upper surface"), a common cathode 123 is arranged, which covers the SOAs 121a, 121b and the U-turn waveguide 122. In addition, as described below, two independent anodes 124 corresponding to the SOAs 121a and 121b are arranged on the surface of the optical amplifier chip 120 on one side of the base substrate 110 (hereinafter referred to as the "lower surface"), respectively. The two anodes 124 are electrically connected to the monolithic metal wiring 112 through bumps 150, respectively.

[0028] Figure 2 The structure of the base substrate 110 is shown. Figure 2 The upper figure in FIG. 1 is a plan view of the base substrate 110, and Figure 2 The lower figure in FIG. 1 is a side view of the base substrate 110 .

[0029] The base substrate 110 is configured, for example, so that a silicon thin waveguide is formed on a silicon-on-insulator (SOI) substrate. Figure 2 As shown, the base substrate 110 has a silicon layer 110b, an insulating SiO 2 Layer 110c, silicon waveguide 111 and insulating SiO 2 The platform portion 110a is formed by cutting away a portion above the silicon layer 110b. On the bottom surface of the platform portion 110a, a U-shaped metal wiring 112 is formed, which is formed with, for example, a Ti / Pt / Au film. Depending on the size of the SOA 121a, 121b mounted on the base substrate 110, the silicon layer 110b may be further cut away in the platform portion 110a to match the height of the waveguide of the SOA 121a, 121b and the height of the waveguide 111a, 111b.

[0030] Two parallel portions 112a, 112b forming the U-shaped metal wiring 112 and being parallel to each other have bumps 150 made using, for example, AuSn (gold tin) as a material formed thereon, and are connected to the anode 124 on the lower surface of the optical amplifier chip 120 through the respective bumps 150. The parallel portions 112a, 112b are connected through the connection portion 112c, and the metal wiring 112 as a whole forms a single piece of the U-shaped metal wiring. When the optical amplifier chip 120 is mounted on the base substrate 110, a portion of the connection portion 112c is exposed without being covered by the optical amplifier chip 120, and external wiring can be connected to the exposed portion. Therefore, a common voltage can be applied to the parallel portions 112a, 112b connected to the respective different anodes 124 via the connection portion 112c, thereby simplifying the control of the optical amplifier chip 120.

[0031] Figure 3 1 shows the structure of the lower surface of the optical amplifier chip 120. Specifically, Figure 3 The lower surface shown is opposite to the bottom surface of the platform portion 110a of the base substrate 110. Figure 3 As shown, anodes 124a and 124b are arranged at positions corresponding to SOAs 121a and 121b, respectively. Anodes 124a and 124b are electrically isolated and independent of each other. In addition, anodes 124a and 124b are arranged at positions covering corresponding SOAs 121a and 121b, but not covering U-turn waveguide 122.

[0032] As described above, since the anodes 124a and 124b are independent of each other, voltages can be applied to the SOAs 121a and 121b, respectively, before the optical amplifier chip 120 is mounted on the base substrate 110. Therefore, it is possible to efficiently perform an inspection for evaluating the SOAs 121a and 121b before the optical amplifier chip 120 is mounted on the base substrate 110. By inspecting the optical amplifier chip 120 before mounting it on the base substrate 110, it is possible to ensure the light amplification characteristics of the optical amplifier 100 having a structure in which the optical amplifier chip 120 is mounted on the base substrate 110. The inspection method of the SOAs 121a and 121b will be described in detail below.

[0033] When the optical amplifier chip 120 is mounted on the base substrate 110, the anodes 124a, 124b are connected to the metal wiring 112 of the platform portion 110a through the bumps 150, respectively. That is, the anode 124a is connected to the parallel portion 112a through the bumps 150, and the anode 124b is connected to the parallel portion 112b through the bumps 150. Therefore, after the optical amplifier chip 120 is mounted on the base substrate 110, the anodes 124a, 124b are electrically short-circuited by the metal wiring 112 to form one continuous electrode. Therefore, after the optical amplifier chip 120 is mounted on the base substrate 110, the SOAs 121a, 121b can be driven by using a common power supply, and the control of the optical amplifier chip 120 can be simplified.

[0034] Next, we will refer to Figure 4 and Figure 5 The structure of the optical amplifier 100 will be described. Figure 4 is shown along Figure 1 Schematic diagram of a cross section taken along line II in FIG. Figure 5 is shown along Figure 1 Schematic diagram of a cross section taken along line II-II in FIG. Figure 4 shows a cross section of a portion of the U-turn waveguide 122, Figure 5 A cross section of a portion of the SOAs 121a, 121b is shown.

[0035] like Figure 4 As shown, on the upper surface of the optical amplifier chip 120, a cathode 123 made of a metal such as Au (gold) as a material is formed in a stacked manner on a substrate 125. The substrate 125 is a substrate made of, for example, n-type conductive indium phosphide (n-InP). On the side of the cathode 125 opposite to the substrate 123, an n-type cladding layer 126, a U-turn waveguide core layer 122, and a p-type cladding layer 127 are formed. The n-type cladding layer 126 and the p-type cladding layer 127 use, for example, n-InP and p-InP as their materials, respectively.

[0036] The U-turn waveguide core layer 122 has an InGaAsP layer in which the band gap wavelength is adjusted to about 1.3 μm so that the absorption coefficient becomes small, for example, in the 1.55 μm band. When the upper and lower surfaces of the U-turn waveguide core layer 122 are in contact with the n-type cladding layer 126 and the p-type cladding layer 127, the side surfaces are not buried in the semiconductor layer. That is, the U-turn waveguide 122 is a waveguide of a high-table structure.

[0037] Since the U-turn waveguide 122 has a high-top structure, even if the waveguide is sharply bent, it is possible to enhance the confinement of light to the core layer and suppress light loss. As a result, the curvature radius of the U-turn waveguide 122 can be made small to arrange the SOAs 121a and 121b nearby, thereby reducing the size of the optical amplifier chip 120.

[0038] Below the U-turn waveguide 122, parallel portions 112a, 112b of the metal wiring 112 are formed, which are formed on the silicon layer 110b of the base substrate 110. The height from the upper surface of the silicon layer 110b to the U-turn waveguide 122 is, for example, about 3 μm to 4 μm. In addition, the height from the U-turn waveguide 122 to the upper surface of the substrate 125 is, for example, about 150 μm. Therefore, since the substrate 125 is relatively thick, by mounting the optical amplifier chip 120 on the base substrate 110 and positioning the substrate 125 upward, the height from the upper surface of the silicon layer 110b to the SOA 121a, 121b, the U-turn waveguide 122, and the waveguides 111a, 111b can be made small. As a result, the depth from the upper surface of the base substrate 110 to the bottom surface of the terrace portion 110a can be made small.

[0039] like Figure 5 As shown, also in a part of SOAs 121a, 121b, on the upper surface of the optical amplifier chip 120, a cathode 123 is formed in a stacked manner on a substrate 125. On the surface of the cathode 125 opposite to the substrate 123, an n-type cladding layer 126, SOA active layers 121a, 121b, a p-type cladding layer 127, an n-type current blocking layer 128, and a contact layer 129 are formed. The n-type cladding layer 126, the p-type cladding layer 127, the n-type current blocking layer 128, and the contact layer 129 are made of, for example, n-InP and p-InP as materials, respectively.

[0040] The SOA active layers 121a and 121b are active layers of an InGaAsP multi-quantum well structure in which the composition is adjusted so as to obtain gain in, for example, a 1.55 μm band. The side surfaces of the SOA active layers 121a and 121b are buried in a p-type current blocking layer whose material is, for example, p-InP. That is, the SOAs 121a and 121b are buried waveguide SOAs.

[0041] On the lower surface of the contact layer 129, anodes 124a and 124b electrically independent of each other are formed at positions corresponding to the SOAs 121a and 121b, respectively. The anodes 124a and 124b are connected to the parallel portions 112a and 112b of the metal wiring 112 formed in the silicon layer 110b of the base substrate 110, respectively, through the bumps 150. Since the parallel portions 112a and 112b are connected by the connection portion 112c in a state where the optical amplifier chip 120 is mounted on the base substrate 110, the anodes 124a and 124b are electrically short-circuited and become a single electrode shared by the SOAs 121a and 121b. As a result, the SOAs 121a and 121b can be driven by a single power supply, and the control of the optical amplifier chip 20 can be simplified.

[0042] Next, an inspection method for evaluating the characteristics of the optical amplifier chip 120 will be described. Before the optical amplifier chip 120 is mounted on the base substrate 110, the anodes 124a and 124b corresponding to the SOAs 121a and 121b are electrically independent of each other. Therefore, by applying different voltages to the anodes 124a and 124b, respectively, the characteristics of the SOAs 121a and 121b can be evaluated.

[0043] Specifically, for example, Figure 6 As shown in the above figure, by applying a positive voltage to the anode 124b, a forward current flows into the pn junction of the SOA 121b, so that the SOA 121b outputs amplified spontaneous emission light (ASE light). In addition, by applying a negative voltage to the anode 124a, a reverse bias is applied to the pn junction of the SOA 121a, so that it absorbs the light reaching the SOA 121a from the SOA 121b via the U-turn waveguide 122. Therefore, in the SOA 121a, a photocurrent proportional to the intensity of the ASE light output from the SOA 121b is generated. The photocurrent generated in the SOA 121a is measured by a measuring instrument connected to the anode 124a to measure the intensity of the ASE light output from the SOA 121b, so that the characteristics of the SOA 121b can be evaluated.

[0044] On the other hand, when evaluating the characteristics of the SOA 121a, for example, Figure 6As shown in the figure below, by applying a positive voltage to the anode 124a, a forward current flows to the pn junction of the SOA 121a, so that the SOA 121a outputs ASE light. In addition, by applying a negative voltage to the anode 124b, a reverse bias is applied to the pn junction of the SOA 121b, so that it absorbs the light reaching the SOA 121b from the SOA 121a via the U-turn waveguide 122. Therefore, in the SOA 121b, a photocurrent proportional to the intensity of the ASE light output from the SOA 121a is generated. The photocurrent generated in the SOA 121b is measured by a measuring instrument connected to the anode 124a to measure the intensity of the ASE light output from the SOA 121a, so that the characteristics of the SOA 121a can be evaluated.

[0045] By applying this inspection method, since the end surfaces of the SOAs 121 a , 121 b do not need to be close to each other, evaluation of the characteristics of the optical amplifier chip 120 can be easily performed.

[0046] In addition, as another inspection method, there is a method in which an optical fiber is brought close to only one of the end surfaces of the SOAs 121a, 121b to be optically coupled thereto. Specifically, similarly to the above-mentioned inspection method, a forward current flows to the pn junction of either of the SOAs 121a, 121b, and a reverse bias is applied to the pn junction of the other. Then, light is input to the end surface of one SOA through which the forward current flows through an optical fiber or the like, and a photocurrent generated in the other SOA as a photodiode (PD) under the application of a reverse bias is measured.

[0047] When this method is used, the light intensity input to another SOA as a PD is the light intensity input to one of these SOAs through an optical fiber, etc. and amplified by the SOA. Therefore, the photocurrent generated in the other SOA of these SOAs is proportional to the amplification factor of one of these SOA, and the gain of the one of these SOA can be evaluated.

[0048] By applying this inspection method, it is only necessary to bring the optical fiber close to one of the SOAs on the input side. Therefore, the difficulty of bringing the optical fiber to the end surfaces of both the input and output ends of the SOA to optically couple them is eliminated, and the gain of the SOAs 121a, 121b can be easily evaluated.

[0049] By the inspection method as described above, the characteristics of the optical amplifier chip 120 before being mounted on the base substrate 110 can be efficiently evaluated. In addition, favorable light amplification characteristics of the optical amplifier 100 having a structure in which the optical amplifier chip 120 is mounted on the base substrate 110 can be ensured.

[0050] Since the optical amplifier chip 120 according to the present embodiment has a structure in which two SOAs 121a, 121b are connected via a U-turn waveguide 122, the amount of stray light input to the SOA whose photocurrent is measured is small compared to a structure in which a plurality of SOAs are arranged linearly. Therefore, the original characteristics of the SOA on the input side can be evaluated. In addition, generally, when a plurality of SOAs are monolithically integrated, minute crosstalk is generated between the SOAs. However, in the present embodiment, since a U-turn waveguide having a sufficient length is arranged between the SOA 121a and the SOA 121b, electrical crosstalk can be reduced. As a result, the photocurrent generated in the SOAs 121a, 121b can be accurately measured, and the characteristics of the optical amplifier chip 120 can be accurately evaluated.

[0051] As described above, according to the present embodiment, two electrically independent anodes are formed at positions corresponding to the respective SOAs of the optical amplifier chip having a structure in which two SOAs are connected via a U-turn waveguide. In addition, an optical amplifier is constructed by mounting the optical amplifier chip on a base substrate having one common metal wiring connecting the two anodes. Therefore, before mounting the optical amplifier chip on the base substrate, it is possible to evaluate the characteristics of the SOA by independently applying voltages to the respective node electrodes of the optical amplifier chip and by detecting light output from one of the SOAs at the other of the SOAs. In other words, it is not necessary to bring an optical fiber or the like close to the end surfaces of the two SOAs at the same time, and the optical amplifier chip can be efficiently evaluated to ensure good light amplification characteristics.

[0052] Furthermore, after the optical amplifier chip is mounted on the base substrate, since a common voltage can be applied to two anodes through metal wiring on the base substrate, control of the optical amplifier chip can be simplified during operation of the optical amplifier.

[0053] In the above embodiment, the metal wiring 112 of the base substrate 110 has a U-shape, but the shape of the metal wiring is not limited to the U-shape. That is, as long as it is a monolithic common metal wiring connecting the anodes 124a, 124b of the optical amplifier chip 120, it can be a metal wiring of, for example, a rectangular shape, an elliptical shape, etc.

[0054] Furthermore, in the above-described embodiment, it has been described that the side surface of the core layer of the U-turn waveguide 122 of the optical amplifier chip 120 is not buried in the semiconductor layer, and a gap is generated. However, on the side surface of the core layer and around the cladding layer of the U-turn waveguide 122, for example, an insulating resin or the like may be filled. When the resin is filled in the gap around the U-turn waveguide 122, the rigidity of the optical amplifier chip 120 can be improved.

[0055] The semiconductor material and the conductive material forming the base substrate 110 and the optical amplifier chip 120 are not limited to the materials described as examples in the above embodiments.

[0056] According to one mode of the optical amplifier and the inspection method of the optical amplifier disclosed in the present application, there is produced an effect that the optical amplifier chip can be evaluated efficiently and good light amplification characteristics can be guaranteed.

Claims

1. An optical amplifier, comprising: An optical amplifier chip formed on the first substrate, the optical amplifier chip comprising a pair of semiconductor optical amplifiers, a U-shaped waveguide connecting the pair of semiconductor optical amplifiers, and two anodes respectively corresponding to the pair of semiconductor optical amplifiers and separated from each other and a common cathode; as well as a second substrate including a common metal wiring connecting the two anodes, and the optical amplifier chip is mounted on the second substrate to position the first substrate upward, wherein the U-shaped waveguide connects the pair of semiconductor optical amplifiers so that the other ends of the pair of semiconductor optical amplifiers are exposed on the same side surface.

2. The optical amplifier according to claim 1, wherein: The second substrate comprises: Silicon layer; a first insulating layer, the first insulating layer being laminated on the silicon layer; a waveguide layer formed on the first insulating layer and made of silicon; and A second insulating layer covers the waveguide layer.

3. The optical amplifier according to claim 2, wherein: The second substrate includes a terrace portion formed by cutting away at least the first insulating layer, the waveguide layer, and the second insulating layer, and The optical amplifier chip is mounted on the platform portion.

4. The optical amplifier according to claim 2, wherein: The pair of semiconductor optical amplifiers have side surfaces optically coupled with side surfaces of the waveguide layer.

5. The optical amplifier according to claim 1, wherein: The pair of semiconductor optical amplifiers are driven by a single power supply via the two anodes and the metal wiring.

6. A method for inspecting an optical amplifier, the optical amplifier comprising: An optical amplifier chip formed on the first substrate, the optical amplifier chip comprising a pair of semiconductor optical amplifiers, a U-shaped waveguide connecting the pair of semiconductor optical amplifiers, and two anodes respectively corresponding to the pair of semiconductor optical amplifiers and separated from each other and a common cathode; and a second substrate including a common metal wiring connecting the two anodes, and the optical amplifier chip is mounted on the second substrate to position the first substrate upward, wherein the U-shaped waveguide connects the pair of semiconductor optical amplifiers so that the other ends of the pair of semiconductor optical amplifiers are exposed on the same side surface, the inspection method comprising the following steps: inputting a forward current to one of the semiconductor optical amplifiers of the pair of semiconductor optical amplifiers via one of the two anodes; applying a reverse bias to the other semiconductor optical amplifier of the pair of semiconductor optical amplifiers via the other anode of the two anodes; and A photocurrent generated in the other semiconductor optical amplifier of the pair of semiconductor optical amplifiers is measured.

7. The inspection method of the optical amplifier according to claim 6, further comprising the following steps: Predetermined light is input to an end surface of the one semiconductor optical amplifier of the pair of semiconductor optical amplifiers.

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