Phase adjuster and semiconductor optical integrated element

Abstract

A phase adjuster (500) according to the present disclosure is provided with: a first optical waveguide section (10a) having a strip-shaped ridge structure including a lower cladding layer (101), an optical waveguide core layer (102), and an upper cladding layer (103) laminated on the surface of a semiconductor substrate (100); a phase adjustment unit (20) that is provided in contact with the first optical waveguide unit (10a) in the strip direction and has a ridge-shaped structure; a second optical waveguide section (10b) provided in contact with the phase adjustment section (20) in the strip direction and having a ridge-shaped structure; an upper phase adjustment electrode (211) that is provided on the top of the ridge structure of the phase adjustment section (20) and that extends in the strip direction; a lower phase adjustment electrode (210) electrically connected to the lower cladding layer (101); a first extraction electrode (220) electrically connected to the upper phase adjustment electrode (211); and a second extraction electrode (221) electrically connected to the upper phase adjustment electrode (211).

Description

Technical Field

[0001] This disclosure relates to phase adjusters and semiconductor optical integrated devices. Background Technology

[0002] As semiconductor optical integrated devices for optical communication, Mach-Zehnder type optical interferometers using optical splitters, phase modulators, phase adjusters, and optical multiplexers have been disclosed (e.g., Patent Documents 1-3).

[0003] In patent documents 1-3, a phase adjuster is disclosed that uses the following methods to change the phase of signal light transmitted in an optical waveguide: a method of applying a reverse bias voltage to a diode disposed in the optical waveguide; a method of applying a forward bias voltage to a diode disposed in the optical waveguide to allow current to flow; and a method of changing the temperature of the optical waveguide by allowing current to flow through a heater electrode disposed around the periphery of the optical waveguide.

[0004] Existing technical documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-163876

[0006] Patent Document 2: Japanese Patent Application Publication No. 2016-133664

[0007] Patent Document 3: Japanese Patent Application Publication No. 2019-191252 Summary of the Invention

[0008] In phase adjusters, when the phase is adjusted by applying a reverse bias, both the phase change and the optical loss increase sharply with respect to the applied voltage. Therefore, in the bias region where a sufficient phase change can be obtained, the optical loss of the optical signal transmitted in the optical waveguide increases dramatically, posing a challenge to control.

[0009] When using a heater to adjust the phase, a phase change that is approximately proportional to the applied power can be obtained, thus offering the advantage of easy control. However, there are challenges such as difficulty in adjusting light loss and the need to apply relatively large power to the heater electrodes.

[0010] Applying a positive bias voltage to allow current to flow is a method that exhibits intermediate characteristics between the two methods mentioned above and is relatively easy to control. However, in small phase adjusters, there are challenges in achieving both the desired amount of phase change and the desired amount of optical loss.

[0011] Furthermore, when multiple phase adjusters using the methods described in Patent Documents 1-3 are combined in series, although the controllability of the amount of phase change and the amount of light loss can be improved, there is a problem of increased component size.

[0012] This disclosure was made to solve the aforementioned problems, with the aim of obtaining a miniaturized phase adjuster capable of adjusting the loss and phase change of an optical signal transmitted in an optical waveguide, and a semiconductor optical integrated device formed by integrating the aforementioned phase adjuster onto a semiconductor substrate.

[0013] The phase adjuster disclosed herein includes:

[0014] The first optical waveguide section has a strip-shaped ridge structure, which includes a lower cladding layer, an optical waveguide core layer, and an upper cladding layer stacked on the surface of the semiconductor substrate.

[0015] The phase adjustment section is grounded to the first optical waveguide section in the strip direction and has the ridge structure;

[0016] The second optical waveguide is grounded to the phase adjustment section in the strip direction and has the ridge structure.

[0017] The upper phase adjustment electrode is disposed on the top of the ridge structure of the phase adjustment part and extends along the strip direction;

[0018] The lower phase adjustment electrode is electrically connected to the lower coating layer;

[0019] The first lead-out electrode is electrically connected to the upper phase adjustment electrode; and

[0020] The second lead-out electrode is electrically connected to the upper phase adjustment electrode.

[0021] The semiconductor optical integrated device disclosed herein includes:

[0022] An optical splitter branches the incident signal light into multiple optical waveguides;

[0023] Multiple optical modulators, one end of which is connected to the multiple optical waveguides respectively;

[0024] The aforementioned phase adjuster has one end connected to the other end of each of the plurality of optical modulators via the optical waveguide; and

[0025] An optical multiplexer / demultiplexer is connected to the other end of the plurality of phase adjusters via the optical waveguide.

[0026] According to the phase adjuster disclosed herein, a phase adjuster is obtained that can adjust the amount of loss and phase change of the optical signal transmitted in the optical waveguide and is miniaturized.

[0027] According to the semiconductor optical integrated device disclosed herein, a semiconductor optical integrated device is formed by integrating a miniaturized phase adjuster that can adjust the loss and phase change of an optical signal transmitted in an optical waveguide onto a semiconductor substrate. Attached Figure Description

[0028] Figure 1 This is a cross-sectional view of the phase adjuster according to Embodiment 1, in a direction parallel to the transmission direction of the signal light.

[0029] Figure 2 This is a top view of the phase adjuster involved in Embodiment 1.

[0030] Figure 3 This is a cross-sectional view of the optical waveguide section of the phase adjuster according to Embodiment 1, in a direction perpendicular to the transmission direction of the signal light.

[0031] Figure 4 This is a cross-sectional view of the phase adjustment section of the phase adjuster according to Embodiment 1, in a direction perpendicular to the transmission direction of the signal light.

[0032] Figure 5 This is a cross-sectional view of the phase adjuster according to Embodiment 2, in a direction parallel to the transmission direction of the signal light.

[0033] Figure 6 This is a cross-sectional view of the phase adjuster according to Embodiment 3, in a direction parallel to the transmission direction of the signal light.

[0034] Figure 7 This is a top view of the phase adjuster involved in Embodiment 3.

[0035] Figure 8 This is a top view of the semiconductor optical integrated device involved in Embodiment 4.

[0036] Figure 9 This is a cross-sectional view of the direction parallel to the transmission direction of the signal light in the optical modulator of the semiconductor optical integrated element according to Embodiment 4.

[0037] Figure 10 This is a cross-sectional view of the optical modulator of the semiconductor optical integrated element according to Embodiment 4, in a direction perpendicular to the transmission direction of the signal light. Detailed Implementation

[0038] Implementation method 1.

[0039] Figure 1 This is a cross-sectional view of a phase adjuster 500, which is an example of a phase adjuster according to Embodiment 1, in a direction parallel to the transmission direction of the signal light. Figure 2 This is a top view of a phase adjuster 500, which is an example of a phase adjuster according to Embodiment 1.

[0040] <Structure of the phase adjuster according to Embodiment 1>

[0041] The phase adjuster 500 according to Embodiment 1 includes on a semiconductor substrate 100: a first optical waveguide 10a, a phase adjustment section 20 disposed in the strip direction and grounded to the first optical waveguide 10a, and a second optical waveguide 10b disposed in the strip direction and grounded to the phase adjustment section 20.

[0042] Figure 3 This is a cross-sectional view of the first optical waveguide section 10a and the second optical waveguide section 10b of the phase adjuster 500 according to Embodiment 1, in a direction perpendicular to the transmission direction of the signal light. The first optical waveguide section 10a and the second optical waveguide section 10b have a strip-shaped ridge structure, which includes a lower cladding layer 101, an optical waveguide core layer 102 and an upper cladding layer 103 sequentially stacked on the surface of the semiconductor substrate 100.

[0043] The refractive index of the material constituting the optical waveguide core layer 102 is greater than the refractive index of the material constituting the lower cladding layer 101 and the upper cladding layer 103. Based on the refractive index difference between the optical waveguide core layer 102 and the lower and upper cladding layers 101, the signal light input to the phase adjuster 500 can be constrained in the vertical direction within the optical waveguide core layer 102 and transmitted towards the light output side.

[0044] Furthermore, regarding the horizontal direction relative to the surface of the semiconductor substrate 100, as described above, the first optical waveguide portion 10a and the second optical waveguide portion 10b have a strip-shaped ridge structure. By forming a protective insulating film 300 with a refractive index smaller than that of the optical waveguide core layer 102 in a manner that covers the aforementioned ridge structure, the input signal light can be constrained within the optical waveguide core layer 102 in the horizontal direction relative to the surface of the semiconductor substrate 100 and transmitted to the light output side based on the aforementioned refractive index difference.

[0045] Figure 4 A cross-sectional view of the phase adjustment section 20 in a direction perpendicular to the transmission direction of the signal light is shown. The phase adjustment section 20 has a strip-shaped ridge structure, which includes a lower cladding layer 201, an optical waveguide core layer 202, and an upper cladding layer 203 sequentially stacked on the surface of the semiconductor substrate 100.

[0046] like Figure 1 as well as Figure 2 As shown, an upper phase adjustment electrode 211, electrically connected to the upper cladding layer 203, is formed on the surface of the upper cladding layer 203 of the phase adjustment section 20. Additionally, a lower phase adjustment electrode 210 is formed on the back side of the semiconductor substrate 100. The lower phase adjustment electrode 210 is electrically connected to the lower cladding layer 201. Furthermore, in Figure 3 In this configuration, the lower phase adjustment electrode 210 is electrically connected to the lower cladding layer 201 via the semiconductor substrate 100. However, the lower phase adjustment electrode 210 can also be formed on the lower cladding layer 201, for example, and configured to be directly electrically connected to the lower cladding layer 201. Furthermore, the connection between the two sides of the lower phase adjustment electrode 210 described above can be represented as the lower phase adjustment electrode 210 being electrically connected to the lower cladding layer 201. Figure 2 In the diagram, the optical waveguide core layer 102 of the first optical waveguide section 10a and the second optical waveguide section 10b is shown as optical waveguide core layer 102a, although it is not visible from the top side. For ease of explanation, the internal position is shown as optical waveguide core layer 102a.

[0047] The lower cladding layer 101 of the first optical waveguide section 10a and the second optical waveguide section 10b, and the lower cladding layer 201 of the phase adjustment section 20, can be either a continuous semiconductor layer or different semiconductor layers as crystal growth layers. Similarly, the optical waveguide core layer 102 and upper cladding layer 103 of the first optical waveguide section 10a and the second optical waveguide section 10b, and the optical waveguide core layer 202 and upper cladding layer 203 of the phase adjustment section 20, can also be either a continuous semiconductor layer or different semiconductor layers as crystal growth layers. Furthermore, as a ridge structure, the first optical waveguide section 10a, the phase adjustment section 20, and the second optical waveguide section 10b can either share a continuous ridge structure or have different optical waveguide core layer structures.

[0048] The refractive index of the waveguide core layer 202 is greater than that of the lower cladding layer 201 and the upper cladding layer 203. Based on the refractive index difference between the waveguide core layer 202 and the lower and upper cladding layers 201, the input signal light can be constrained in the vertical direction within the waveguide core layer 202 and transmitted to the light output side.

[0049] Furthermore, regarding the direction horizontal to the surface of the semiconductor substrate 100, as described above, the phase adjustment section 20 has a strip-shaped ridge structure. By forming a protective insulating film 300 with a refractive index smaller than that of the optical waveguide core layer 202 in a manner that covers the aforementioned ridge structure, the input signal light can be constrained within the optical waveguide core layer 202 in a horizontal direction relative to the surface of the semiconductor substrate 100 and transmitted to the light output side based on the aforementioned refractive index difference.

[0050] In the phase adjustment section 20, the upper phase adjustment electrode 211, which is disposed on the surface of the upper covering layer 203 exposed at the top of the ridge structure, extends along the direction of signal light transmission, i.e., the strip direction. In the phase adjustment section 20, the first lead electrode 220 is electrically connected to one end of the upper phase adjustment electrode 211, i.e., the side where the signal light is input, and the second lead electrode 221 is connected to the other end of the upper phase adjustment electrode 211, i.e., the side where the signal light is output. Furthermore, the first lead electrode 220 and the second lead electrode 221, except for the portion connected to the upper phase adjustment electrode 211, are formed on the protective insulating film 300.

[0051] A potential difference is provided between the first lead electrode 220 and the second lead electrode 221 by a power supply located outside the phase adjuster 500. Based on this potential difference, current flows inside the upper phase adjuster electrode 211 along the strip direction extending from the upper phase adjuster electrode 211.

[0052] The upper phase adjustment electrode 211 has electrical resistance relative to the direction of the extended strip, so Joule heating occurs when current flows through it. That is, the upper phase adjustment electrode 211 functions as a heater. When the Joule heat generated from the upper phase adjustment electrode 211 is conducted to the optical waveguide core layer 202 via the upper cladding layer 203, the refractive index of the optical waveguide core layer 202 changes due to the thermo-optic effect. That is, the phase of the signal light transmitted within the optical waveguide core layer 202 of the phase adjustment section 20 can be changed using the thermo-optic effect.

[0053] Furthermore, when a potential difference is provided between the first lead electrode 220 and the second lead electrode 221, a potential difference is also provided between the first lead electrode 220 and the second lead electrode 221 and the lower phase adjustment electrode 210 by a power supply located outside the phase adjuster 500. Current flows through the lower cladding layer 201, the waveguide core layer 202, and the upper cladding layer 203 based on this potential difference.

[0054] When the amount of charge carriers in the optical waveguide core layer 202 changes due to the flow of the aforementioned current, the refractive index and optical loss of the optical waveguide core layer 202 change due to the carrier plasma effect. That is, by adjusting the amount of current passing through the lower cladding layer 201, the optical waveguide core layer 202, and the upper cladding layer 203, the phase and optical loss of the signal light transmitted in the optical waveguide core layer 202 of the phase adjustment section 20 can be changed.

[0055] Therefore, according to the phase adjuster 500 of Embodiment 1, the phase adjustment function realized by the heater using electrical resistance and the phase and light loss adjustment function realized by the current passing through the optical waveguide core layer 202 can be obtained simultaneously in the phase adjustment section 20. Thus, the miniaturization of the phase adjuster can be realized, and even the miniaturization of the semiconductor optical integrated element that integrates the above-mentioned phase adjuster can be realized.

[0056] The basic semiconductor layer structure of the phase adjuster 500 according to Embodiment 1 has been described above. Furthermore, to reduce the contact resistance between the upper phase adjustment electrode 211 and the semiconductor layer, a contact layer made of a low-resistance semiconductor can be formed between the upper phase adjustment electrode 211 and the upper cladding layer 203. Additionally, a generally known structure can be added, such as a protective insulating film 300, after covering the ridge-shaped sidewalls with a semiconductor layer having a lower refractive index than the waveguide core layer 202.

[0057] <Manufacturing method of phase adjuster according to embodiment 1>

[0058] Next, details of the manufacturing method of the phase adjuster 500 according to Embodiment 1 will be described below.

[0059] On the surface of an n-type InP (indium phosphide) substrate, which is an example of a semiconductor substrate 100, an n-type InP layer with a thickness of 2.0 μm, serving as the lower cladding layer 101 and the lower cladding layer 201, is crystal grown using an epitaxial crystal growth method such as Metal-Organic Chemical Vapor Deposition (MOCVD). Next, an alloy semiconductor layer, such as AlInGaAs or InGaAsP, which serves as the optical waveguide core layer 102 and the optical waveguide core layer 202, with an appropriate composition selected from Al, In, Ga, As, and P to match the wavelength of the signal light, is crystal grown. Furthermore, a p-type InP layer with a thickness of 3.0 μm, serving as the upper cladding layer 103 and the upper cladding layer 203, is sequentially crystal grown.

[0060] Regarding the optical waveguide core layer 102 and optical waveguide core layer 202, the composition and film thickness can be appropriately selected according to the wavelength of the input optical signal. For example, when the wavelength of the optical signal is 1.55 μm, which is commonly used in optical communication, an example can be an InGaAsP alloy semiconductor with a layer thickness of 400 nm and an emission peak wavelength of 1.2 μm based on photoluminescence method.

[0061] Alternatively, the optical waveguide core layer 102 and the optical waveguide core layer 202 can also be constructed using a multi-quantum-well structure, which involves alternatingly stacking layers of approximately 10 nm thick alloy semiconductors with different compositions multiple times. In this case, a sharp change in refractive index and a change in light loss can be obtained in the optical waveguide core layer 202 when a bias is applied, through the so-called quantum confinement Stark effect.

[0062] In addition, in order to efficiently confine light in the optical waveguide core layer, a stacked structure called SCH (Separate Confinement Heterostructure) layer can be added in the vertical direction of the optical waveguide core layer 102 and the optical waveguide core layer 202. This layer is made of an alloy semiconductor with a refractive index higher than that of the lower cladding layer 101 and the lower cladding layer 201 and the upper cladding layer 103 and the upper cladding layer 203, and a refractive index lower than that of the optical waveguide core layer 102 and the optical waveguide core layer 202.

[0063] Alternatively, different waveguide core layer structures can be used between the first waveguide section 10a and the second waveguide section 10b and the phase adjustment section 20. For example, after forming the waveguide core layer 202 of the phase adjustment section 20, the waveguide core layer can be selectively removed from the regions that become the first waveguide section 10a and the second waveguide section 10b by using a wet etching method with a chemical solution or a dry etching method using plasma with reactive gases, and then a waveguide core layer with a different layer structure can be grown again in the removed regions by MOCVD.

[0064] Next, in order to process the first optical waveguide 10a, the second optical waveguide 10b, and the phase adjustment section 20 into a ridge shape, a SiO2 film with a width of 1.0 μm to 3.0 μm is formed on the surface of the upper cladding layer 103 and the upper cladding layer 203 in a manner that forms the desired optical waveguide shape, using photolithography and etching techniques as a protective mask. The areas not covered by the SiO2 film are etched using dry etching or wet etching until the lower cladding layer 101 and the lower cladding layer 201 are exposed.

[0065] Next, in order to protect the two sides of the first optical waveguide 10a and the second optical waveguide 10b, which have a ridge shape, and the surface of the semiconductor region outside the ridge structure from contamination, moisture, etc., a SiO2 film with a thickness of, for example, 500 nm is formed as a protective insulating film 300 using plasma CVD or the like.

[0066] Next, regarding the phase adjustment section 20, the SiO2 film at the top of the ridge structure is selectively removed, leaving the upper cladding layer 203 exposed on the surface, forming a conductive film that becomes the upper phase adjustment electrode 211. As described above, the upper phase adjustment electrode 211 needs to have a constant resistance value to function as a heater. Therefore, materials constituting the upper phase adjustment electrode 211 can include metals such as platinum and titanium, alloys such as nickel-chromium alloys, metal nitrides such as tantalum nitride, and metal oxides such as indium tin oxide. The upper phase adjustment electrode 211 is composed of a thin film with a thickness of approximately 200 nm.

[0067] Next, in the phase adjustment unit 20, a first lead-out electrode 220 is formed by grounding a portion near one end of the upper phase adjustment electrode 211, which serves as the input side of the optical signal, and a second lead-out electrode 221 is formed by grounding a portion near the other end of the upper phase adjustment electrode 211, which serves as the output side of the optical signal. Methods for forming the first lead-out electrode 220 and the second lead-out electrode 221 include vapor deposition, sputtering, and plating.

[0068] As materials constituting the first lead electrode 220 and the second lead electrode 221, low-resistivity metals such as gold are used. As an example of materials constituting the first lead electrode 220 and the second lead electrode 221, gold with a film thickness of 3 μm can be cited.

[0069] Here, the resistance value R1 (first resistance value) between the two ends of the upper phase adjustment electrode 211, that is, the resistance value R1 between the first lead electrode 220 and the second lead electrode 221, is preferably set to the same level as the resistance value R2 (second resistance value) of the semiconductor layer when a positive voltage is applied between the upper phase adjustment electrode 211 and the lower phase adjustment electrode 210. The reason for this is that if the resistance value of one side is too low, sufficient current will not flow between the electrodes of the other side, and it will be impossible to simultaneously obtain both the refractive index change achieved by the thermo-optic effect and the refractive index change achieved by the charge carrier plasma effect, as well as the change in light loss.

[0070] Generally, in phase adjusters using InP-based semiconductor materials, to shift the phase of the optical signal by half a wavelength, a power of about 20 mW is required in the current-injected carrier plasma effect, and a power of about 50 mW is required in the thermo-optical effect using a heater. Therefore, in order to allow the current required to manifest each effect to flow, the ratio of the resistance value R1 between the two ends of the upper phase adjustment electrode 211 and the resistance value R2 of the semiconductor layer between the upper phase adjustment electrode 211 and the lower phase adjustment electrode 210, i.e., R1 / R2, should be 100 or less, preferably 10 or less, and more preferably about 1.

[0071] <Effects of Implementation Method 1>

[0072] According to the phase adjuster of Embodiment 1, an upper phase adjustment electrode is provided in the phase adjustment section of the phase adjuster, which is connected to a first lead electrode at one end and a second lead electrode at the other end. Therefore, it achieves the effect of obtaining a phase adjuster that can adjust the amount of loss and phase change of the optical signal transmitted in the optical waveguide and is miniaturized.

[0073] Implementation method 2.

[0074] Figure 5 This is a cross-sectional view of the phase adjuster according to Embodiment 2, in a direction parallel to the transmission direction of the signal light. In the phase adjuster 600 according to Embodiment 2, to prevent the amount of current flowing through the upper phase adjustment electrode 211 from becoming extremely small relative to the amount of current flowing between the upper phase adjustment electrode 211 and the lower phase adjustment electrode 210, the following is done: Figure 5 The structure shown here, in which an insulating film 310 is formed in a portion of the area between the upper phase adjustment electrode 211 and the upper covering layer 203, differs from the phase adjuster 500 described in Embodiment 1.

[0075] In general semiconductor devices, in order to reduce the contact resistance at the interface between the electrode and the semiconductor layer, a semiconductor layer with high impurity concentration or high carrier mobility is used as the contact surface, resulting in a low-resistance semiconductor layer. On the other hand, regarding the upper phase adjustment electrode 211, in order to generate sufficient Joule heating for changing the refractive index of the optical waveguide core layer according to the thermo-optic effect, a thin film metal with a high resistivity is used as the constituent material.

[0076] Here, when the resistance of the semiconductor layer near the interface between the upper phase adjustment electrode 211 and the semiconductor layer is sufficiently smaller than the resistance R1 between the two ends of the upper phase adjustment electrode 211, the current flowing between the first lead electrode 220 and the second lead electrode 221 does not flow through the upper phase adjustment electrode 211, which has a constant resistance value R1, but flows through the semiconductor layer, which has a low resistance. Therefore, sufficient Joule heating for heating the optical waveguide core layer 202 may not occur.

[0077] Therefore, in the phase adjuster 600 according to Embodiment 2, an insulating film 310 is formed in a region between the upper phase adjustment electrode 211 and the upper cladding layer 203. Regarding the region on the insulating film 310 where the upper phase adjustment electrode 211 is formed, current flows only within the upper phase adjustment electrode 211 and not to the semiconductor layer side, thus reliably generating Joule heating based on the resistance value R1 between the two ends of the upper phase adjustment electrode 211. Therefore, in the phase adjuster 600 according to Embodiment 2, both the refractive index change achieved through the thermo-optic effect and the refractive index change achieved through the carrier plasma effect, as well as the change in light loss, can be obtained simultaneously.

[0078] <Effects of Implementation Method 2>

[0079] According to the phase adjuster of Embodiment 2, an insulating film is formed in a portion of the region between the upper phase adjustment electrode and the upper cladding layer. Therefore, it is possible to simultaneously obtain both the refractive index change achieved by the thermo-optic effect and the refractive index change and the light loss change achieved by the carrier plasma effect. Thus, it achieves the effect of obtaining a phase adjuster that can easily adjust the loss and phase change of the optical signal transmitted in the optical waveguide and is miniaturized.

[0080] Implementation method 3.

[0081] Figure 6 This is a cross-sectional view of the phase adjuster according to Embodiment 3, in a direction parallel to the transmission direction of the signal light. Additionally, Figure 7 This is a top view of the phase adjuster involved in Embodiment 3.

[0082] like Figure 6 as well as Figure 7 As shown, in the phase adjuster 700 according to Embodiment 3, the upper phase adjustment electrode 211 is divided into at least two or more electrodes along the strip direction, and two lead-out electrodes are formed in each of the divided upper phase adjustment electrodes. Each of these lead-out electrodes is connected to the same potential. Hereinafter, the case where the upper phase adjustment electrode 211 is divided into two will be described as an example.

[0083] The upper phase adjustment electrode 211 of the phase adjuster 700 includes a first upper phase adjustment electrode 211a and a second upper phase adjustment electrode 211b, which are divided into two parts along the strip direction. One end of the first upper phase adjustment electrode 211a is connected to one end of the first lead electrode 220, and the other end of the first upper phase adjustment electrode 211a is connected to one end of the second lead electrode 221. Similarly, one end of the second upper phase adjustment electrode 211b is connected to the other end of the first lead electrode 220, and the other end of the second upper phase adjustment electrode 211b is connected to the other end of the second lead electrode 221. Furthermore, in the above description, one end represents the input side of the optical signal, and the other end represents the output side of the optical signal.

[0084] In the phase adjuster disclosed herein, it is necessary to ensure sufficient flow of both the current flowing within the upper phase adjustment electrode 211 and the current flowing between the upper and lower phase adjustment electrodes 210. Therefore, in Embodiment 3, the structure is such that the phase adjustment section 20 is divided into multiple units, and each of the divided phase adjustment sections 20 is electrically connected in parallel to an externally located power supply. According to this structure, both the current flowing within the upper phase adjustment electrode 211 and the current flowing between the upper and lower phase adjustment electrodes 210 can obtain the amount of current required for phase change in the optical waveguide core layer 202. Therefore, without making the power supply structure required for the phase adjuster large and complex, the phase of the optical signal and the amount of optical loss can be easily adjusted.

[0085] <Effects of Implementation Method 3>

[0086] According to the phase adjuster of Embodiment 3, the upper phase adjustment electrode is divided into at least two or more electrodes along the strip direction, so the amount of current required to change the phase in the optical waveguide core layer can be obtained. Therefore, it achieves the effect of obtaining a phase adjuster that can easily adjust the amount of loss and phase change of the optical signal transmitted in the optical waveguide and is miniaturized.

[0087] Implementation method 4.

[0088] Figure 8 This is a top view of the semiconductor optical integrated device 1000 according to Embodiment 4. Figure 9 This is a cross-sectional view of the optical modulator of the semiconductor optical integrated element 1000 according to Embodiment 4, in a direction parallel to the transmission direction of the signal light. Figure 10 This is a cross-sectional view of the optical modulator of the semiconductor optical integrated element 1000 according to Embodiment 4, in a direction perpendicular to the transmission direction of the signal light. Furthermore, as an example of the semiconductor optical integrated element 1000, a Mach-Zehnder type modulator can be cited.

[0089] <Structure of the semiconductor optical integrated device involved in Embodiment 4>

[0090] As an example of the semiconductor optical integrated element 1000 involved in Embodiment 4, a Mach-Zehnder type modulator is as follows: Figure 8 As shown in the top view, the substrate 100a includes: an optical splitter 30 that branches the input signal light into two optical waveguides 10; an optical modulator 40 disposed on each of the two optical waveguides 10 branched by the optical splitter 30, which generates a modulated optical signal by applying a high-speed modulated electrical signal; a phase adjuster according to any of the embodiments 1 to 3, which is connected to the optical modulator 40 via the optical waveguides 10; and an optical multiplexer / demultiplexer 50 that takes the optical signals from the two optical waveguides 10 as input, and then branches them into the two optical waveguides to output optical signals. Furthermore, the substrate 100a may include a semiconductor substrate 100 and semiconductor layers formed on the semiconductor substrate 100.

[0091] As an example of the semiconductor optical integrated element 1000 according to Embodiment 4, one end of the output of the Mach-Zehnder modulator from the optical multiplexer / demultiplexer 50 is connected to the optical output section 60 that outputs signal light to the outside via an optical waveguide, and the other end is connected to the optical monitor 70. That is, among the first output and the second output, which are two outputs from the optical multiplexer / demultiplexer 50, the first output is connected to the optical output section 60 via an optical waveguide, and the second output is connected to the optical monitor 70 via an optical waveguide.

[0092] Optical splitter 30 can, for example, use a 1-input 2-output or 2-input 2-output multimode interference waveguide (MMI).

[0093] Figure 9 A cross-sectional view of the optical modulator 40 in a direction parallel to the transmission direction of the signal light is shown. Figure 10The diagram shows a cross-sectional view of the optical modulator 40 in a direction perpendicular to the transmission direction of the signal light. The optical modulator 40 includes, for example, semiconductor layers sequentially formed as follows: a lower cladding layer 401 composed of n-type InP; an optical waveguide core layer 402 composed of an alloy semiconductor layer such as i-type AlInGaAs or InGaAsP, or a quantum well structure formed by stacking these layers; and an upper cladding layer 403 composed of p-type InP; a lower phase modulation electrode 410 electrically connected to the lower cladding layer 401; and an upper phase modulation electrode 411 electrically connected to the upper cladding layer 403. The optical modulator 40 modulates the phase of the signal light transmitted in the optical waveguide core layer 402 by applying a high-speed modulated voltage signal to the upper phase modulation electrode 411.

[0094] A method is often used to provide a differential signal by forming the upper phase modulation electrodes 411 of the two branched optical waveguides 10 as a pair. This method enables the generation of efficiently modulated optical signals. The optical multiplexer / demultiplexer 50 can, for example, be a 2-input 2-output type MMI.

[0095] In a Mach-Zehnder modulator, a phase difference is provided between the signal lights output from the optical splitter 30 to the two optical waveguide branches 10 by an optical modulator 40. Based on this phase difference, an optical signal is output to the optical output unit 60 or the optical monitor 70 at the output side of the optical multiplexer / demultiplexer 50. Therefore, an optical signal can be obtained by modulating the light intensity and phase corresponding to the phase difference provided by the optical modulator 40 at the external output of the optical output unit 60 to the Mach-Zehnder modulator.

[0096] Here, in order to improve the signal-to-noise ratio of the output optical signal, in addition to accurately controlling the phase difference between the optical signals from the two optical waveguides 10 input to the optical multiplexer / demultiplexer 50, it is also necessary to ensure that the optical signal intensity is consistent. Therefore, by using the phase adjustment section of the phase adjuster mounted on the semiconductor optical integrated device 1000 according to Embodiment 4 to adjust the phase and the amount of optical loss, it is possible to make the phase and intensity of the optical signal accurately match the desired values. Therefore, in the semiconductor optical integrated device 1000 according to Embodiment 4, a miniaturized Mach-Zehnder modulator with a high signal-to-noise ratio of optical signal can be realized.

[0097] As an example of the optical monitor 70, a photodiode for detecting the intensity of signal light transmitted in the optical waveguide can be cited. The photodiode constituting the optical monitor 70 can be a photodiode integrated into the optical waveguide on a semiconductor substrate, or a photodiode disposed at a location that receives signal light output from the end of the optical waveguide to the outside of a Mach-Zehnder modulator.

[0098] The following describes the process of improving the signal-to-noise ratio of a Mach-Zehnder modulator using an optical monitor 70. The signal light input to the Mach-Zehnder modulator is split by an optical splitter 30 and transmitted in two optical waveguides 10. By providing current flowing along the upper phase adjustment electrode 211 of the phase adjustment section 20, which is connected to the two optical waveguides 10 respectively, and by providing current flowing between the upper phase adjustment electrode 211 and the lower phase adjustment electrode 210, the phase and intensity of the light transmitted in each optical waveguide 10 can be varied.

[0099] In a Mach-Zehnder type optical waveguide, the signal light output from the optical multiplexer / demultiplexer 50 changes according to the phase difference of the signal light transmitted in the two optical waveguides 10 respectively. Therefore, by using the optical monitor 70 to measure the intensity of the optical signal, the phase difference between the two optical waveguides can be monitored.

[0100] In the semiconductor optical integrated device 1000 according to Embodiment 4, when the current value to the phase adjustment unit 20 is adjusted in a manner that maximizes the intensity of the optical signal detected by the optical monitor 70, due to the optical characteristics of the 2-input 2-output type MMI, the optical output to the other optical output end of the optical multiplexer / demultiplexer 50, i.e., the optical output unit 60, becomes minimal. In an ideal case, i.e., when the light intensities of the two optical waveguides 10 are completely consistent and the phase difference is half a wavelength, the optical output of the optical output unit 60 becomes zero.

[0101] As explained above, the state after adjusting the current value of the phase adjustment unit 20 is set as the initial state. A high-speed modulated voltage signal is applied to the upper phase modulation electrode 411 of the optical modulator 40, thereby obtaining a high-speed modulated optical output from the optical output unit 60 based on the phase difference between the two optical waveguides. If the optical output in the initial state is made infinitely close to zero, the ratio to the optical output in the on state becomes extremely large, thus enabling the realization of a small-sized Mach-Zehnder modulator with a high signal-to-noise ratio.

[0102] <Effects of Implementation Method 4>

[0103] According to the semiconductor optical integrated device of Embodiment 4, by applying a high-speed modulated voltage signal to the upper phase modulation electrode of the optical modulator, a high-speed modulated light output based on the phase difference between the two optical waveguides can be obtained from the light output section. Therefore, it achieves the effect of obtaining a semiconductor optical integrated device that can adjust the phase of the optical signal and the amount of light loss without making the power supply structure required by the phase adjuster large and complex.

[0104] This disclosure describes various exemplary embodiments and examples, but the various features, forms and functions described in one or more embodiments are not limited to the application of a specific embodiment, but can be applied to the embodiment alone or in various combinations.

[0105] Therefore, numerous variations not illustrated are conceivable within the scope of this disclosure. For example, these include variations of at least one constituent element, addition of at least one constituent element, omission of at least one constituent element, and extraction of at least one constituent element combined with constituent elements of other embodiments.

[0106] Explanation of symbols

[0107] 10: Optical waveguide; 10a: First optical waveguide section; 10b: Second optical waveguide section; 20: Phase adjustment section; 30: Optical splitter; 40: Optical modulator; 50: Optical multiplexer / demultiplexer; 60: Optical output section; 70: Optical monitor; 100: Semiconductor substrate; 100a: Substrate; 101, 201, 401: Lower cladding layer; 102, 102a, 202, 402: Optical waveguide core layer; 103, 203, 403: Upper cladding layer; 210: Lower phase adjustment electrode; 211: Upper phase adjustment electrode; 211a: First upper phase adjustment electrode; 211b: Second upper phase adjustment electrode; 220: First lead-out electrode; 221: Second lead-out electrode; 300: Protective insulating film; 410: Lower phase modulation electrode; 411: Upper phase modulation electrode; 500, 600, 700: Phase adjuster; 1000: Semiconductor optical integrated element.

Claims

1. A phase adjuster, comprising: The first optical waveguide section has a strip-shaped ridge structure, which includes a lower cladding layer, an optical waveguide core layer, and an upper cladding layer stacked on the surface of the semiconductor substrate. The phase adjustment section is grounded to the first optical waveguide section in the strip direction and has the ridge structure; The second optical waveguide is grounded to the phase adjustment section in the strip direction and has the ridge structure. The upper phase adjustment electrode is disposed on the top of the ridge structure of the phase adjustment part and extends along the strip direction; The lower phase adjustment electrode is electrically connected to the lower coating layer; The first lead-out electrode is electrically connected to the upper phase adjustment electrode; and The second lead-out electrode is electrically connected to the upper phase adjustment electrode.

2. The phase adjuster according to claim 1, characterized in that, The first lead-out electrode and the second lead-out electrode are disposed on a protective insulating film.

3. The phase adjuster according to claim 2, characterized in that, The first lead-out electrode is connected to one end of the upper phase adjustment electrode, and the second lead-out electrode is connected to the other end of the upper phase adjustment electrode.

4. The phase adjuster according to claim 3, characterized in that, A portion of the upper phase adjustment electrode is disposed on top of the ridge structure, separated by the protective insulating film.

5. The phase adjuster according to claim 1 or 2, characterized in that, The upper phase adjustment electrode includes a first upper phase adjustment electrode and a second upper phase adjustment electrode, which are divided into two parts along the strip direction. One end of the first upper phase adjustment electrode is connected to one end of the first lead-out electrode, and the other end of the first upper phase adjustment electrode is connected to one end of the second lead-out electrode. One end of the second upper phase adjustment electrode is connected to the other end of the second lead-out electrode, and the other end of the second upper phase adjustment electrode is connected to the other end of the second lead-out electrode.

6. The phase adjuster according to any one of claims 1 to 4, characterized in that, The ratio of the first resistance value between the first lead electrode and the second lead electrode to the second resistance value between the upper phase adjustment electrode and the lower phase adjustment electrode is less than 100.

7. The phase adjuster according to any one of claims 1 to 6, characterized in that, The lower cladding layer and the upper cladding layer are composed of semiconductor layers formed of InP, and the optical waveguide core layer is composed of a semiconductor layer containing an alloy semiconductor formed of either AlInGaAs or InGaAsP.

8. A semiconductor optical integrated device, comprising: An optical splitter branches the incident signal light into multiple optical waveguides; Multiple optical modulators, one end of which is connected to the multiple optical waveguides respectively; The phase adjuster according to any one of claims 1 to 7, wherein one end is connected to the other end of the plurality of optical modulators via the optical waveguide; as well as An optical multiplexer / demultiplexer is connected to the other end of the plurality of phase adjusters via the optical waveguide.

9. The semiconductor optical integrated device according to claim 8, characterized in that, Of the two outputs branching from the optical multiplexer / demultiplexer, the first output is connected to the optical output unit via the optical waveguide, and the second output is connected to the optical monitor via the optical waveguide.

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