Phase adjuster, and semiconductor optical integrated element

Abstract

To achieve a phase adjuster that enables an adjustment of an optical signal, and is made compact.SOLUTION: A phase adjuster 500 comprises: a first optical waveguide part 10a that has a ridge structure; a phase adjustment part 20 that contacts with the first optical waveguide part 10a, and has the ridge structure; a second optical waveguide part 10b that contacts with the phase adjustment part 20, and has the ridge structure; a protection insulation film 300 that covers surfaces of the first optical waveguide part 10a, phase adjustment part 20 and second optical waveguide part 10b; a top part phase adjustment electrode 211 that is provided at an apex of the ridge structure of the phase adjustment part 20, and extends in a stripe direction; a lower part phase adjustment electrode 210 that is connected to a lower part clad layer 101; a first lead-out electrode 220 that is formed on the protection insulation film 300, and connected to the top part phase adjustment electrode 211; and a second lead-out electrode 221 that is formed on the protection insulation film 300, and connected to the top part phase adjustment electrode 211.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a phase adjuster and a semiconductor optical integrated device. [Background technology]

[0002] As a semiconductor optical integrated device for optical communication, a Mach-Zehnder type optical interferometer using an optical splitter, a phase modulator, a phase adjuster, and an optical multiplexer has been disclosed (for example, Patent Documents 1 to 3).

[0003] Patent documents 1 to 3 disclose phase adjusters that use a method of applying a reverse bias voltage to a diode provided in the optical waveguide to change the phase of signal light propagating through an optical waveguide, a method of applying a forward bias voltage to a diode provided in the optical waveguide to pass a current through it, and a method of passing a current through a heater electrode provided around the optical waveguide to change the temperature of the optical waveguide, etc. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-163876 A [Patent Document 2] JP 2016-133664 A [Patent Document 3] JP 2019-191252 A Summary of the Invention [Problem to be solved by the invention]

[0005] When adjusting the phase in a phase shifter by applying a reverse bias, the phase shift and optical loss increase sharply with respect to the applied voltage. Therefore, in the bias region where a sufficient phase shift is obtained, the optical loss of the optical signal propagating through the optical waveguide increases sharply, making it difficult to control.

[0006] The method of adjusting the phase using a heater has the advantage of being easy to control, since the amount of phase change obtained is roughly proportional to the applied power. However, it has issues such as the difficulty of adjusting the optical loss and the need to apply a relatively large amount of power to the heater electrode.

[0007] The technique of applying a forward bias voltage to pass a current has intermediate characteristics between the two techniques mentioned above and is relatively easy to control. However, it is difficult to obtain both the desired phase shift amount and the desired optical loss amount in a compact phase shifter.

[0008] Furthermore, when a plurality of phase adjusters using the techniques described in Patent Documents 1 to 3 are combined in series, the controllability of the amount of phase change and the amount of optical loss can be improved, but there is a problem that the element size becomes large.

[0009] The present disclosure has been made to solve the problems described above, and has an object to provide a miniaturized phase adjuster that is capable of adjusting the amount of loss and the amount of phase change of an optical signal propagating through an optical waveguide, and a semiconductor optical integrated device in which such a phase adjuster is integrated on a semiconductor substrate. [Means for solving the problem]

[0010] The phase adjuster according to the present disclosure includes: a first optical waveguide portion having a striped ridge structure including a lower cladding layer, an optical waveguide core layer, and an upper cladding layer laminated on a surface of a semiconductor substrate; a phase adjustment section having the ridge structure, the phase adjustment section being provided in contact with the first optical waveguide section in the stripe direction; a second optical waveguide portion having the ridge structure and provided in contact with the phase adjustment portion in the stripe direction; a protective insulating film covering at least surfaces of the first optical waveguide portion, the phase adjustment portion, and the second optical waveguide portion; an upper phase adjustment electrode provided on the top of the ridge structure of the phase adjustment portion and extending along the stripe direction; a lower phase adjustment electrode electrically connected to the lower cladding layer; a first extraction electrode formed on the protective insulating film and electrically connected to the upper phase adjustment electrode; a second extraction electrode formed on the protective insulating film and electrically connected to the upper phase adjustment electrode; Equipped with.

[0011] The semiconductor optical integrated device according to the present disclosure comprises: an optical demultiplexer that branches an incident signal light into a plurality of optical waveguides; a plurality of optical modulators, one end of each of which is connected to the plurality of optical waveguides; the phase adjuster, one end of which is connected to the other end of each of the optical modulators via the optical waveguide; an optical multiplexer / demultiplexer connected to the other ends of the plurality of phase adjusters via the optical waveguide; Equipped with. Effect of the Invention

[0012] Advantageous Effects of Invention The phase adjuster according to the present disclosure has the advantage that it is possible to adjust the amount of loss and the amount of phase change of an optical signal propagating through an optical waveguide, and a compact phase adjuster can be obtained.

[0013] The semiconductor optical integrated device according to the present disclosure has an advantage in that it is possible to adjust the amount of loss and the amount of phase change of an optical signal propagating through an optical waveguide, and to obtain a semiconductor optical integrated device in which a miniaturized phase adjuster is integrated on a semiconductor substrate. [Brief description of the drawings]

[0014] [Figure 1] 2 is a cross-sectional view of the phase adjuster according to the first embodiment in a direction parallel to the propagation direction of a signal light. [Diagram 2] 2 is a top view of the phase adjuster according to the first embodiment. FIG. [Diagram 3] 2 is a cross-sectional view of the phase adjuster according to the first embodiment in a direction perpendicular to the propagation direction of a signal light in the optical waveguide portion. [Figure 4]3 is a cross-sectional view of a phase adjustment unit of the phase adjuster according to the first embodiment in a direction perpendicular to the propagation direction of signal light. [Diagram 5] 11 is a cross-sectional view of a phase adjuster according to a second embodiment in a direction parallel to the propagation direction of a signal light. FIG. [Figure 6] 11 is a cross-sectional view of a phase adjuster according to a third embodiment in a direction parallel to the propagation direction of a signal light. FIG. [Figure 7] FIG. 11 is a top view of a phase adjuster according to a third embodiment. [Figure 8] FIG. 11 is a top view of a semiconductor optical integrated device according to a fourth embodiment. [Figure 9] 11 is a cross-sectional view in a direction parallel to the propagation direction of signal light in an optical modulator of a semiconductor optical integrated device according to a fourth embodiment. FIG. [Figure 10] 11 is a cross-sectional view taken along a direction perpendicular to the propagation direction of signal light in an optical modulator of a semiconductor optical integrated device according to a fourth embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Embodiment 1 Fig. 1 is a cross-sectional view of phase adjuster 500, which is an example of the phase adjuster according to the first embodiment, in a direction parallel to the propagation direction of signal light. Fig. 2 is a top view of phase adjuster 500, which is an example of the phase adjuster according to the first embodiment.

[0016] <Configuration of Phase Adjuster According to First Embodiment> The phase adjuster 500 according to the first embodiment includes, on a semiconductor substrate 100, a first optical waveguide portion 10a, a phase adjuster portion 20 provided in contact with the first optical waveguide portion 10a in the stripe direction, and a second optical waveguide portion 10b provided in contact with the phase adjuster portion 20 in the stripe direction.

[0017] 3 is a cross-sectional view of the first optical waveguide portion 10a and the second optical waveguide portion 10b of the phase adjuster 500 according to the embodiment 1 in a direction perpendicular to the propagation direction of the signal light. The first optical waveguide portion 10a and the second optical waveguide portion 10b have a striped ridge structure including a lower cladding layer 101, an optical waveguide core layer 102, and an upper cladding layer 103, which are sequentially stacked on the surface of the semiconductor substrate 100.

[0018] 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 refractive index of the material constituting the upper cladding layer 103. Due to the difference in refractive index between the optical waveguide core layer 102 and the refractive indexes of the lower cladding layer 101 and upper cladding layer 103, the signal light input to the phase adjuster 500 can be confined in the vertical direction within the optical waveguide core layer 102 and propagated to the optical output side.

[0019] As described above, the first optical waveguide portion 10a and the second optical waveguide portion 10b have a striped ridge structure in the horizontal direction relative to the surface of the semiconductor substrate 100. By forming the protective insulating film 300 having a smaller refractive index than the optical waveguide core layer 102 so as to cover this ridge structure, the input signal light can be confined in the optical waveguide core layer 102 in the horizontal direction relative to the surface of the semiconductor substrate 100 due to the refractive index difference described above, and can propagate to the optical output side.

[0020] 4 shows a cross-sectional view of the phase adjustment unit 20 in a direction perpendicular to the propagation direction of the signal light. The phase adjustment unit 20 has a striped ridge structure including a lower cladding layer 201, an optical waveguide core layer 202, and an upper cladding layer 203, which are sequentially laminated on the surface of the semiconductor substrate 100.

[0021] As shown in Fig. 1 and Fig. 2, an upper phase adjustment electrode 211 electrically connected to the upper clad layer 203 is formed on the surface of the upper clad layer 203 of the phase adjustment section 20. A lower phase adjustment electrode 210 is formed on the back surface of the semiconductor substrate 100. The lower phase adjustment electrode 210 is electrically connected to the lower clad layer 201. Note that in Fig. 3, the lower phase adjustment electrode 210 is electrically connected to the lower clad layer 201 via the semiconductor substrate 100, but the lower phase adjustment electrode 210 may be formed on the lower clad layer 201, for example, and may be arranged so that the lower phase adjustment electrode 210 is directly and electrically connected to the lower clad layer 201. Note that both of the above-mentioned connection modes of the lower phase adjustment electrode 210 are expressed as the lower phase adjustment electrode 210 being electrically connected to the lower clad layer 201. In FIG. 2, the optical waveguide core layers 102 of the first optical waveguide portion 10a and the second optical waveguide portion 10b are not actually visible from the top surface side, but for convenience of explanation, the internal position is shown as the optical waveguide core layer 102a.

[0022] 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 may be a single continuous semiconductor layer as a crystal growth layer, or may be different semiconductor layers. The optical waveguide core layer 102 and the 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 the upper cladding layer 203 of the phase adjustment section 20 may also be a single continuous semiconductor layer as a crystal growth layer, or may be different semiconductor layers. Furthermore, the ridge structure may be a common continuous ridge structure in the first optical waveguide section 10a, the phase adjustment section 20, and the second optical waveguide section 10b, or may be different optical waveguide core layer structures.

[0023] The refractive index of the optical waveguide core layer 202 is greater than the refractive index of the lower cladding layer 201 and the refractive index of the upper cladding layer 203. Due to the difference in refractive index between the optical waveguide core layer 202 and the refractive index of the lower cladding layer 201 and the upper cladding layer 203, the input signal light can be confined in the vertical direction within the optical waveguide core layer 202 and propagated to the optical output side.

[0024] As described above, the phase adjustment unit 20 has a striped ridge structure in the direction horizontal to the surface of the semiconductor substrate 100. By forming the protective insulating film 300 having a smaller refractive index than the optical waveguide core layer 202 so as to cover the ridge structure, the input signal light can be confined in the optical waveguide core layer 202 in the horizontal direction to the surface of the semiconductor substrate 100 due to the refractive index difference described above, and propagates to the optical output side.

[0025] In the phase adjustment section 20, the upper phase adjustment electrode 211 provided on the surface of the upper cladding layer 203 exposed at the top of the ridge structure extends along the direction in which the signal light propagates, i.e., the stripe direction. In the phase adjustment section 20, a first extraction 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 a second extraction 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. Note that the first extraction electrode 220 and the second extraction electrode 221 are formed on the protective insulating film 300 except for the portion connected to the upper phase adjustment electrode 211.

[0026] A potential difference is applied between the first extraction electrode 220 and the second extraction electrode 221 by a power supply provided outside the phase adjuster 500. In response to this potential difference, a current flows inside the upper phase adjustment electrode 211 along the stripe direction in which the upper phase adjustment electrode 211 extends.

[0027] Since the upper phase adjustment electrode 211 has electrical resistance in the extending stripe direction, when a current flows in the upper phase adjustment electrode 211, Joule heat is generated. 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 thermally 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 propagating in the optical waveguide core layer 202 of the phase adjustment unit 20 can be changed by using the thermo-optic effect.

[0028] Furthermore, when a potential difference is applied between the first and second extraction electrodes 220 and 221, a potential difference is also applied between the first and second extraction electrodes 220 and 221 and the lower phase adjustment electrode 210 by a power source provided outside the phase adjuster 500. In response to this potential difference, a current flows through the lower cladding layer 201, the optical waveguide core layer 202, and the upper cladding layer 203.

[0029] When the amount of carriers present in the optical waveguide core layer 202 changes due to the flow of such a current, the carrier plasma effect changes the refractive index and the amount of optical loss of the optical waveguide core layer 202. In other words, 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, it is possible to change the phase and the amount of optical loss of the signal light propagating through the optical waveguide core layer 202 of the phase adjustment unit 20.

[0030] Therefore, according to phase adjuster 500 of the first embodiment, it is possible to simultaneously obtain a phase adjustment function by a heater utilizing electric resistance in phase adjustment section 20 and a phase and optical loss adjustment function by a current passing through optical waveguide core layer 202. This makes it possible to realize a miniaturized phase adjuster, and ultimately to miniaturize a semiconductor optical integrated device that integrates such a phase adjuster.

[0031] The basic semiconductor layer structure of phase adjuster 500 according to embodiment 1 has been described above. Furthermore, in order to reduce the contact resistance between upper phase adjustment electrode 211 and the semiconductor layer, a contact layer made of a low-resistance semiconductor may be formed between upper phase adjustment electrode 211 and upper cladding layer 203. Also, a commonly known structure may be added, such as covering the sidewalls of the ridge shape with a semiconductor layer having a lower refractive index than optical waveguide core layer 202 and then forming protective insulating film 300.

[0032] <Method of Manufacturing Phase Shifter According to First Embodiment> Next, a method for manufacturing phase adjuster 500 according to the first embodiment will be described in detail below. On the surface of an n-type InP (indium phosphide) substrate, which is an example of the semiconductor substrate 100, an n-type InP layer having a thickness of 2.0 μm is crystal-grown to become the lower cladding layer 101 and the lower cladding layer 201, using an epitaxial crystal growth method such as Metal Organic Chemical Vapor Deposition (MOCVD). Then, an alloy semiconductor layer having an appropriate composition selected from Al, In, Ga, As, and P according to the wavelength of the signal light, such as AlInGaAs or InGaAsP to become the optical waveguide core layer 102 and the optical waveguide core layer 202, is crystal-grown. Furthermore, a p-type InP layer having a thickness of 3.0 μm to become the upper cladding layer 103 and the upper cladding layer 203 is crystal-grown in sequence.

[0033] The composition and thickness of the optical waveguide core layer 102 and the optical waveguide core layer 202 may 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 communications, an InGaAsP mixed crystal semiconductor having a layer thickness of 400 nm and having an emission peak wavelength of 1.2 μm by photoluminescence method is given as an example of the mixed crystal semiconductor constituting the optical waveguide core layer 102 and the optical waveguide core layer 202.

[0034] The optical waveguide core layer 102 and the optical waveguide core layer 202 may have a structure called a multiple quantum well structure, in which layers made of alloy semiconductors with different compositions and a layer thickness of about 10 nm are alternately laminated multiple times. In this case, a steep change in refractive index and change in optical loss can be obtained in the optical waveguide core layer 202 when a bias is applied due to the so-called quantum confined Stark effect.

[0035] In addition, in order to efficiently confine light in the optical waveguide core layer, a stacked structure called an SCH (Separate Confinement Heterostructure) layer may be added above and below the optical waveguide core layer 102 and the optical waveguide core layer 202. The stacked structure is made of a mixed crystal semiconductor having a higher refractive index than the lower clad layer 101, the lower clad layer 201, and the upper clad layer 103, the upper clad layer 203, and a lower refractive index than the optical waveguide core layer 102 and the optical waveguide core layer 202.

[0036] Also, different optical waveguide core layer structures may be adopted between the first optical waveguide portion 10a and the second optical waveguide portion 10b and the phase adjustment portion 20. For example, after forming the optical waveguide core layer 202 of the phase adjustment portion 20, the optical waveguide core layer may be selectively removed from the regions that will become the first optical waveguide portion 10a and the second optical waveguide portion 10b by wet etching using a chemical solution or dry etching using plasma of a reactive gas, and an optical waveguide core layer having a different layer structure may be crystal-grown again by MOCVD in the removed regions.

[0037] Next, in order to process the first optical waveguide portion 10a, the second optical waveguide portion 10b and the phase adjustment portion 20 into a ridge shape, a SiO2 film patterned into stripes having a width of 1.0 μm to 3.0 μm is formed as a protective mask by photolithography and etching techniques so as to form a desired optical waveguide shape on the surfaces of the upper clad layer 103 and the upper clad layer 203. The areas not covered with the SiO2 film are etched by dry etching or wet etching until the lower clad layer 101 and the lower clad layer 201 are exposed.

[0038] Next, in order to protect both side surfaces of the ridge-shaped first optical waveguide portion 10a and second optical waveguide portion 10b and the phase adjustment portion 20 and the surface of the semiconductor region other than the ridge structure from contamination, moisture, etc., a protective insulating film 300 such as a SiO2 film having a thickness of, for example, 500 nm is deposited by using a plasma CVD method or the like.

[0039] Next, for the phase adjustment section 20, the upper part of the ridge structure, i.e., the SiO2 film at the top, is selectively removed to expose the upper cladding layer 203 on the surface, and a conductive film that will become the upper phase adjustment electrode 211 is formed. As described above, the upper phase adjustment electrode 211 needs to have a certain resistance value and function as a heater. Therefore, examples of materials that make up the upper phase adjustment electrode 211 include metals such as platinum and titanium, alloys such as nichrome, metal nitrides such as tantalum nitride, and metal oxides such as indium tin oxide. The upper phase adjustment electrode 211 is made up of a thin film with a thickness of about 200 nm.

[0040] Next, a first extraction electrode 220 is formed in contact with a portion near one end of upper phase adjustment electrode 211 which is the input side of the optical signal in phase adjustment section 20, and a second extraction electrode 221 is formed in contact with a portion near the other end of upper phase adjustment electrode 211 which is the output side of the optical signal. Methods for forming first extraction electrode 220 and second extraction electrode 221 include vapor deposition, sputtering, plating, and the like.

[0041] A low-resistance metal such as gold is used as a material for forming the first extension electrode 220 and the second extension electrode 221. An example of a material for forming the first extension electrode 220 and the second extension electrode 221 is gold with a film thickness of 3 μm.

[0042] Here, it is preferable to set the resistance value R1 (first resistance value) between both ends of the upper phase adjustment electrode 211, i.e., the resistance value R1 between the first extraction electrode 220 and the second extraction electrode 221, to be approximately the same as the resistance value R2 (second resistance value) of the semiconductor layer when a forward 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 on one side is too low, a sufficient current does not flow between the other electrode, and it is not possible to simultaneously obtain both a refractive index change due to the thermo-optic effect and a refractive index change and a change in the amount of optical loss due to the carrier plasma effect.

[0043] Generally, in order to shift the phase of an optical signal by half a wavelength in a phase adjuster using an InP-based semiconductor material, an applied power of about 20 mW is required for the carrier plasma effect by current injection, and about 50 mW is required for the thermo-optic effect using a heater. Therefore, in order to allow the currents required for each effect to flow, the ratio of the resistance value R1 between both ends of upper phase adjustment electrode 211 to the resistance value R2 of the semiconductor layer between upper phase adjustment electrode 211 and lower phase adjustment electrode 210, that is, R1 / R2, should be 100 or less, preferably 10 or less, and more preferably about 1.

[0044] <Advantages of the First Embodiment> As described above, according to the phase adjuster of embodiment 1, an upper phase adjustment electrode having one end connected to the first extraction electrode and the other end connected to the second extraction electrode is provided in the phase adjustment section of the phase adjuster, thereby making it possible to adjust the amount of loss and the amount of phase change of an optical signal propagating through an optical waveguide and to obtain a compact phase adjuster.

[0045] Embodiment 2 Fig. 5 is a cross-sectional view of a phase adjuster according to the second embodiment in a direction parallel to the propagation direction of the signal light. Phase adjuster 600 according to the second embodiment differs from phase adjuster 500 according to the first embodiment in that, as shown in Fig. 5, insulating film 310 is formed in a part of the region between upper phase adjustment electrode 211 and upper cladding layer 203 so that the amount of current flowing in upper phase adjustment electrode 211 is not extremely small compared to the amount of current flowing between upper phase adjustment electrode 211 and lower phase adjustment electrode 210.

[0046] 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 low resistance is used, for example, by doping impurities at a high concentration or using a semiconductor layer with high carrier mobility as the semiconductor layer that forms the contact surface. On the other hand, the upper phase adjustment electrode 211 uses a thin film metal with a high resistance value as a constituent material in order to generate Joule heat sufficient to change the refractive index of the optical waveguide core layer by the thermo-optic effect.

[0047] Here, if the resistance value of the semiconductor layer near the interface between the upper phase adjustment electrode 211 and the semiconductor layer becomes sufficiently smaller than the resistance value R1 between both ends of the upper phase adjustment electrode 211, the current flowing between the first extraction electrode 220 and the second extraction electrode 221 will not flow through the upper phase adjustment electrode 211, which has a constant resistance value R1, but will flow through the semiconductor layer, which has a low resistance, and there is a risk that sufficient Joule heat will not be generated to heat the optical waveguide core layer 202.

[0048] Therefore, in phase adjuster 600 according to the second embodiment, insulating film 310 is formed in a partial region between upper phase adjustment electrode 211 and upper cladding layer 203. In the region where upper phase adjustment electrode 211 is formed on insulating film 310, current flows only in upper phase adjustment electrode 211 and does not flow to the semiconductor layer side, so that Joule heat can be reliably generated according to resistance value R1 between both ends of upper phase adjustment electrode 211. Therefore, in phase adjuster 600 according to the second embodiment, both a refractive index change due to the thermo-optic effect, and a refractive index change and a change in the amount of optical loss due to the carrier plasma effect can be obtained simultaneously.

[0049] <Advantages of the second embodiment> As described above, according to the phase adjuster of the second embodiment, an insulating film is formed in a partial region between the upper phase adjustment electrode and the upper cladding layer, so that it is possible to simultaneously obtain both a refractive index change due to the thermo-optic effect and a refractive index change and an optical loss change due to the carrier plasma effect. This makes it possible to easily adjust the loss amount and phase change amount of an optical signal propagating through the optical waveguide, and also provides an advantageous effect of providing a compact phase adjuster.

[0050] Embodiment 3 Fig. 6 is a cross-sectional view of the phase adjuster according to the third embodiment in a direction parallel to the propagation direction of the signal light, and Fig. 7 is a top view of the phase adjuster according to the third embodiment.

[0051] 6 and 7, in phase adjuster 700 according to the third embodiment, upper phase adjustment electrode 211 is divided into at least two or more electrodes along the stripe direction, and two extraction electrodes are formed in each of the divided upper phase adjustment electrodes, one of which is connected to an equal potential. In the following, a case where upper phase adjustment electrode 211 is divided into two will be described as an example.

[0052] The upper phase adjustment electrode 211 of the phase adjuster 700 is composed of a first upper phase adjustment electrode 211a and a second upper phase adjustment electrode 211b, which are divided into two along the stripe direction. One end of the first upper phase adjustment electrode 211a is connected to one end of the first extraction electrode 220, and one end of the second extraction electrode 221 is connected to the other end of the first upper phase adjustment electrode 211a. Furthermore, the other end of the first extraction electrode 220 is connected to one end of the second upper phase adjustment electrode 211b, and the other end of the second extraction electrode 221 is connected to the other end of the second upper phase adjustment electrode 211b. In the above description, one end refers to the input side of the optical signal, and the other end refers to the output side of the optical signal.

[0053] In the phase adjuster of the present disclosure, both the current flowing in the upper phase adjustment electrode 211 and the current flowing between the upper phase adjustment electrode and the lower phase adjustment electrode 210 must flow sufficiently. Therefore, in the third embodiment, the phase adjustment section 20 is divided into a plurality of parts, and each divided phase adjustment section 20 is electrically connected in parallel to an external power supply. With this configuration, the current flowing in the upper phase adjustment electrode 211 and the current flowing between the upper phase adjustment electrode 211 and the lower phase adjustment electrode 210 can obtain the current amount required to change the phase in the optical waveguide core layer 202. Therefore, the phase of the optical signal and the amount of optical loss can be easily adjusted without enlarging and complicating the power supply configuration required for the phase adjuster.

[0054] <Advantages of the Third Embodiment> As described above, according to the phase adjuster of the third embodiment, the upper phase adjustment electrode is divided into at least two or more electrodes along the stripe direction, so that the amount of current required to change the phase in the optical waveguide core layer can be obtained, thereby making it possible to easily adjust the amount of loss and the amount of phase change of the optical signal propagating through the optical waveguide, and it is possible to obtain an advantageous effect of obtaining a compact phase adjuster.

[0055] Embodiment 4 Fig. 8 is a top view of the semiconductor optical integrated device 1000 according to the fourth embodiment, Fig. 9 is a cross-sectional view in a direction parallel to the propagation direction of the signal light in the optical modulator of the semiconductor optical integrated device 1000 according to the fourth embodiment, and Fig. 10 is a cross-sectional view in a direction perpendicular to the propagation direction of the signal light in the optical modulator of the semiconductor optical integrated device 1000 according to the fourth embodiment. Note that a Mach-Zehnder type modulator is given as an example of the semiconductor optical integrated device 1000.

[0056] <Configuration of semiconductor optical integrated device according to fourth embodiment> 8, the Mach-Zehnder modulator, which is an example of the semiconductor optical integrated device 1000 according to the fourth embodiment, includes an optical splitter 30 that splits an input signal light into two optical waveguides 10, which are provided on a substrate 100a, an optical modulator 40 that is provided on each of the optical waveguides 10 split into two by the optical splitter 30 and generates a modulated optical signal by applying a high-speed modulated electric signal, and an optical multiplexer / demultiplexer 50 to which a phase adjuster according to any one of the first to third embodiments connected to each of the optical modulators 40 via the optical waveguides 10 is connected, which receives the optical signals of the two optical waveguides 10 as input, further splits the optical signals into two optical waveguides, and outputs optical signals. The substrate 100a may include a semiconductor substrate 100 and each semiconductor layer formed on the semiconductor substrate 10.

[0057] One end of an output from an optical multiplexer / demultiplexer 50 of a Mach-Zehnder modulator, which is an example of a semiconductor optical integrated device 1000 according to the fourth embodiment, is connected to an optical output unit 60 that outputs an optical signal to the outside via an optical waveguide, and the other end is connected to an optical monitor 70. That is, of the two outputs, that is, a first output and a second output, from the optical multiplexer / demultiplexer 50, the first output is connected to the optical output unit 60 via an optical waveguide, and the second output is connected to the optical monitor 70 via an optical waveguide.

[0058] The optical demultiplexer 30 may be, for example, a one-input two-output type or two-input two-output type multi-mode interference optical waveguide (MMI).

[0059] 9 shows a cross-sectional view of the optical modulator 40 in a direction parallel to the propagation direction of the signal light, and FIG. 10 shows a cross-sectional view of the optical modulator 40 in a direction perpendicular to the propagation direction of the signal light. The optical modulator 40 is composed of a lower cladding layer 401 made of n-type InP, an optical waveguide core layer 402 made of an alloy semiconductor layer such as i-type AlInGaAs or InGaAsP, or a quantum well structure in which these are stacked, and an upper cladding layer 403 made of p-type InP, which are successively formed semiconductor layers, 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 can modulate the phase of the signal light propagating through the optical waveguide core layer 402 by applying a high-speed modulated voltage signal to the upper phase modulation electrode 411.

[0060] A commonly used method is to provide a differential signal by pairing the upper phase modulation electrodes 411 formed on the two branched optical waveguides 10. By using this method, an efficiently modulated optical signal can be generated. The optical multiplexer / demultiplexer 50 can be, for example, a two-input, two-output type MMI.

[0061] In the Mach-Zehnder modulator, the optical modulator 40 imparts a phase difference between the signal lights branched and output to the two optical waveguides 10 in the optical demultiplexer 30, and an optical signal is output to the optical output unit 60 or the optical monitor 70 in accordance with this phase difference at the output side of the optical multiplexer / demultiplexer 50. Therefore, an optical signal whose optical intensity and phase have been modulated in accordance with the phase difference imparted by the optical modulator 40 can be output from the optical output unit 60 to the outside of the Mach-Zehnder modulator.

[0062] 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 necessary to match the optical signal intensities. Therefore, by adjusting the phase and the amount of optical loss using the phase adjustment unit of the phase adjuster mounted on the semiconductor optical integrated device 1000 according to the fourth embodiment, it is possible to accurately match the phase and optical signal intensity of the optical signal to desired values. Therefore, the semiconductor optical integrated device 1000 according to the fourth embodiment can realize a Mach-Zehnder type modulator that can be miniaturized and has a high signal-to-noise ratio of the optical signal.

[0063] A photodiode for detecting the intensity of the signal light propagating through the optical waveguide is an example of the optical monitor 70. The photodiode constituting the optical monitor 70 may be a photodiode integrated in the optical waveguide on a semiconductor substrate, or may be a photodiode installed at a position to receive the signal light output from the end of the optical waveguide to the outside of the Mach-Zehnder type modulator.

[0064] The procedure for improving the signal-to-noise ratio of the Mach-Zehnder modulator using the optical monitor 70 will be described below. Signal light input to the Mach-Zehnder modulator is split by the optical splitter 30 and propagates through two optical waveguides 10. By applying a current flowing along the upper phase adjustment electrode 211 of the phase adjustment unit 20 of the phase adjuster connected to each of the two optical waveguides 10 and a current flowing between the upper phase adjustment electrode 211 and the lower phase adjustment electrode 210, the phase and optical intensity of the light propagating through each optical waveguide 10 can be changed.

[0065] In the Mach-Zehnder optical waveguide, the signal light output from the optical multiplexer / demultiplexer 50 changes according to the phase difference between the signal lights propagating through the two optical waveguides 10, respectively. Therefore, by measuring the intensity of the optical signal using the optical monitor 70, the phase difference between the two optical waveguides can be monitored.

[0066] In the semiconductor optical integrated device 1000 according to the fourth embodiment, when the current value to the phase adjustment unit 20 is adjusted so that the optical signal intensity detected by the optical monitor 70 is maximized, the optical output to the other optical output end of the optical multiplexer / demultiplexer 50, i.e., the optical output at the optical output unit 60, becomes minimum due to the optical characteristics of the two-input / two-output type MMI. In the ideal case, that is, when the optical intensities of the two optical waveguides 10 are perfectly matched and the phase difference is a half wavelength, the optical output of the optical output unit 60 becomes zero.

[0067] As described above, by applying a high-speed modulated voltage signal to the upper phase modulation electrode 411 of the optical modulator 40 with the current value of the phase adjustment unit 20 adjusted as the initial state, an optical output modulated at high speed according to the phase difference between the two optical waveguides can be obtained from the optical output unit 60. If the optical output in the initial state can be brought as close to zero as possible, the ratio with the optical output in the on state becomes extremely large, so that a small Mach-Zehnder type modulator with a high signal-to-noise ratio can be realized.

[0068] <Advantages of the Fourth Embodiment> As described above, according to the semiconductor optical integrated element of the fourth embodiment, by applying a high-speed modulated voltage signal to the upper phase modulation electrode of the optical modulator, an optical output modulated at high speed in accordance with the phase difference between the two optical waveguides can be obtained from the optical output section, thereby providing an effect of obtaining a semiconductor optical integrated element capable of adjusting the phase and the amount of optical loss of an optical signal without enlarging and complicating the power supply configuration required for the phase adjuster.

[0069] Although the present disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations.

[0070] Therefore, countless modifications not illustrated are assumed within the scope of the technology of the present disclosure, including, for example, modifying, adding, or omitting at least one component, and further, extracting at least one component and combining it with a component of another embodiment. [Explanation of symbols]

[0071] 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 extraction electrode, 221 Second extraction electrode, 300 Protective insulating film, 410 Lower phase modulation electrode, 411 Upper phase modulation electrode, 500, 600, 700 Phase adjuster, 1000 Semiconductor optical integrated device

Claims

1. a first optical waveguide portion having a striped ridge structure including a lower cladding layer, an optical waveguide core layer, and an upper cladding layer laminated on a surface of a semiconductor substrate; a phase adjustment portion having the ridge structure and provided in contact with the first optical waveguide portion in a stripe direction; a second optical waveguide portion having the ridge structure and provided in contact with the phase adjustment portion in the stripe direction; a protective insulating film covering at least surfaces of the first optical waveguide portion, the phase adjustment portion, and the second optical waveguide portion; an upper phase adjustment electrode provided on the top of the ridge structure of the phase adjustment portion and extending along the stripe direction; a lower phase adjustment electrode electrically connected to the lower cladding layer; a first extraction electrode formed on the protective insulating film and electrically connected to the upper phase adjustment electrode; a second extraction electrode formed on the protective insulating film and electrically connected to the upper phase adjustment electrode; A phase adjuster comprising:

2. 2. The phase adjuster according to claim 1, wherein the first lead electrode is connected to one end of the upper phase adjustment electrode, and the second lead electrode is connected to the other end of the upper phase adjustment electrode.

3. 3. The phase adjuster according to claim 2, wherein a part of the upper phase adjustment electrode is provided on the top of the ridge structure via a protective insulating film.

4. the upper phase adjustment electrode is divided into two parts along the stripe direction, a first upper phase adjustment electrode and a second upper phase adjustment electrode, one end of the first lead electrode is connected to one end of the first upper phase adjustment electrode, and one end of the second lead electrode is connected to the other end of the first upper phase adjustment electrode; 3. The phase adjuster according to claim 1, wherein the other end of the first extraction electrode is connected to one end of the second upper phase adjustment electrode, and the other end of the second extraction electrode is connected to the other end of the second upper phase adjustment electrode.

5. 4. The phase adjuster according to claim 1, wherein a ratio of a first resistance value between the first extraction electrode and the second extraction electrode to a second resistance value between the upper phase adjustment electrode and the lower phase adjustment electrode is 100 or less.

6. 4. The phase shifter according to claim 1, wherein the lower cladding layer and the upper cladding layer are made of semiconductor layers made of InP, and the optical waveguide core layer is made of a semiconductor layer containing a mixed crystal semiconductor made of any one of AlInGaAs and InGaAsP.

7. an optical demultiplexer that branches an incident signal light into a plurality of optical waveguides; a plurality of optical modulators, one end of each of which is connected to the plurality of optical waveguides; a phase adjuster according to claim 1 , wherein one end of each of the phase adjusters is connected to the other ends of the plurality of optical modulators via the optical waveguide; an optical multiplexer / demultiplexer connected to the other ends of the plurality of phase adjusters via the optical waveguide; A semiconductor optical integrated device comprising:

8. 8. The semiconductor optical integrated device according to claim 7, wherein of the two outputs branched from the optical multiplexer / demultiplexer, a first output is connected to an optical output section via the optical waveguide, and a second output is connected to an optical monitor via the optical waveguide.

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