Optical integrated circuit and photoelectric integrated circuit

Abstract

This optical integrated circuit comprises a demultiplexer, a plurality of isolators, and a multiplexer. The demultiplexer divides input light into a plurality of different wavelength bands. The plurality of isolators have isolation functions respectively corresponding to the plurality of wavelength bands. The multiplexer is connected to the outputs of the plurality of isolators.

Description

Optical and optoelectronic integrated circuits

[0001] The present disclosure relates to optical and optoelectronic integrated circuits.

[0002] There is known technology relating to an isolator that uses a reciprocal phase shifter that generates a phase difference in light propagating through two waveguides that is independent of the propagation direction, and a non-reciprocal phase shifter that imparts a phase change whose magnitude varies depending on the propagation direction (see, for example, Patent Document 1).

[0003] International Publication No. 2007 / 083419

[0004] An optical integrated circuit according to an embodiment of the present disclosure includes a demultiplexer, a plurality of isolators, and a multiplexer. The demultiplexer splits input light into a plurality of different wavelength bands. The plurality of isolators have isolation functions corresponding to the plurality of wavelength bands, respectively. The multiplexer is connected to outputs of the plurality of isolators.

[0005] An optoelectronic integrated circuit according to an embodiment of the present disclosure includes the optical integrated circuit described above and a plurality of heaters provided in each of the isolators. Each of the isolators has a waveguide or a waveguide that guides light split by the splitter. Each of the heaters is configured to heat at least a portion of the waveguide or a waveguide to change the effective refractive index of the at least a portion of the waveguide or a waveguide. The electrode pads of the plurality of heaters are common.

[0006] Fig. 1 is a diagram showing a schematic configuration of an optical integrated circuit according to one embodiment. Fig. 2 is a diagram showing a schematic configuration of each isolator in Fig. 1. Fig. 3 is a cross-sectional view of the nonreciprocal line taken along line A-A in Fig. 2. Fig. 4 is a diagram showing a schematic configuration of an optical integrated circuit according to another embodiment. Fig. 5 is a diagram showing a schematic configuration of each isolator in Fig. 4.

[0007] In general, the operating bandwidth of an isolator is narrower than the specified bandwidth of a wavelength-tunable laser such as a wavelength-tunable semiconductor laser (tunable laser diode). Therefore, it is difficult for a single isolator to cover the entire specified bandwidth of a wavelength-tunable laser. Therefore, the optical integrated circuit according to the embodiment of the present disclosure described below employs a configuration in which output light from a wavelength-tunable semiconductor laser is split into multiple wavelength bands and multiplexed via isolators that provide isolation functions for each wavelength band. This makes it possible to provide isolation functions for electromagnetic waves in a bandwidth wider than the operating bandwidth of each isolator.

[0008] In this disclosure, "light" such as "input light" is used in a broad sense to include electromagnetic waves in the ultraviolet, visible, and infrared regions. "Light" includes electromagnetic waves with wavelengths from 1 nm to 1 mm. In the following description, "light" will be referred to as electromagnetic waves where appropriate.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The drawings used in the following description are schematic. The dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones.

[0010] <Overall Configuration of Optical Integrated Circuit> As shown in FIG. 1 , an optical integrated circuit 10 according to an embodiment of the present disclosure includes a demultiplexer 11, a plurality of isolators 12a to 12d, and a multiplexer 13. Hereinafter, the isolators 12a to 12d may be referred to as isolators 12. The demultiplexer 11, the isolator 12, and the multiplexer 13 may be formed on the same substrate 14. Furthermore, a light source unit 15 may be provided on the substrate 14. The light source unit 15 and the demultiplexer 11 are connected by a waveguide 16. The demultiplexer 11 and each of the isolators 12 are connected by waveguides 17a to 17d. Hereinafter, the waveguides 17a to 17b may be referred to as waveguides 17. The isolators 12 and the multiplexer 13 are connected by waveguides 18a to 18d. Hereinafter, the waveguides 18a to 18d may be referred to as waveguides 18.

[0011] For the following explanation, the X-axis, Y-axis, and Z-axis directions are defined. The Y-axis direction is perpendicular to the substrate surface 14a of the substrate 14 and is the direction from the substrate surface 14a toward the side where the optical integrated circuit 10 is formed. The Z-axis direction is along the substrate surface 14a and is the direction from the demultiplexer 11 side toward the multiplexer 13 side. The X-axis direction is perpendicular to the Y-axis and Z-axis directions.

[0012] The substrate 14 may be configured to include a conductor such as a metal, a semiconductor such as silicon, glass, or a resin, etc. In this embodiment, the substrate 14 is made of silicon (Si), but is not limited to this and may be made of various other materials.

[0013] The light source unit 15 is a light source capable of emitting electromagnetic waves in a band wider than the operating bands of the isolators 12a, 12b, 12c, and 12d. In this embodiment, the light source unit 15 may be a wavelength-tunable semiconductor laser. The wavelength-tunable semiconductor laser may be integrated on the substrate 14 together with other optical elements of the optical integrated circuit 10 using a semiconductor process. The wavelength of the electromagnetic waves emitted by the wavelength-tunable semiconductor laser may be controlled by a control circuit external to the optical integrated circuit 10.

[0014] The demultiplexer 11 splits the input light (electromagnetic wave) emitted from the light source unit 15 and guided by the waveguide 16 into electromagnetic waves of different wavelength bands. The demultiplexer 11 is also called a demultiplexer or DeMUX. For example, the demultiplexer 11 splits the input light into four bands b １ ~b ４ The splitter 11 is configured to split the electromagnetic waves into four bands b １ ~b ４ The divided electromagnetic waves are output to the waveguides 17a to 17d, respectively.

[0015] The isolators 12a to 12d are respectively １ ~b ４The isolators 12a to 12d provide an isolation function according to the above. "Isolation function" means a function that transmits electromagnetic waves traveling in the forward direction and reduces or blocks electromagnetic waves traveling in the reverse direction. The isolators 12a to 12d transmit electromagnetic waves incident from the waveguides 17a to 17d to the waveguides 18a to 18d. The isolators 12a to 12d reduce the intensity of the electromagnetic waves incident from the waveguides 18a to 18d and output them to the waveguides 17a to 17d. Alternatively, the isolators 12a to 12d block the electromagnetic waves incident from the waveguides 18a to 18d, preventing them from transmitting to the waveguides 17a to 17d.

[0016] The operating bands of the isolators 12a to 12d are wavelength bands b １ ~b ４ The operating bands of the isolators 12a to 12d may partially overlap with the operating bands of the adjacent isolators 12a to 12d. That is, the operating wavelength bands of the isolators 12a and 12b may partially overlap. The same applies to the isolators 12b and 12c, and the isolators 12c and 12d. This allows the optical integrated circuit 10 as a whole to exhibit isolation function over a continuous wide wavelength band.

[0017] The multiplexer 13 multiplexes the different wavelength bands b １ ~b ４ The electromagnetic waves transmitted through the isolator 12 are combined and output to a single waveguide 19. The combiner 13 is also called a multiplexer or MUX.

[0018] The waveguides 16 to 19 are lines formed on the substrate 14 that can propagate electromagnetic waves. The waveguides 16 to 19 are configured as cores that extend in the direction of propagation of the electromagnetic waves. The cores are covered with cladding. In this embodiment, the cores are made of, for example, silicon (Si), and the cladding is made of, for example, quartz glass or silicon oxide film (SiO ２ )

[0019] In one embodiment, the optical integrated circuit 10 is configured to propagate electromagnetic waves in TM mode (TM waves). TM mode electromagnetic waves are electromagnetic waves whose electric field amplitude direction coincides with the normal direction of the substrate surface 14 a, i.e., the Y-axis direction, when propagating in the Z-axis direction through the waveguide.

[0020] In one embodiment, the light source unit 15 emits electromagnetic waves in the C-band (Conventional-band) used in devices for long-distance optical communication. The C-band is a wavelength band with a wavelength λ of 1530 nm to 1565 nm. This wavelength band is suitable for long-distance transmission because of its low transmission loss in optical fibers. As an example, the demultiplexer 11 demultiplexes input light in the C-band into a band b １ ~b ４ The signal is split into four bands: Band b １ is the wavelength band λ=1525 nm to 1535 nm. ２ is a band of wavelength λ=1535 nm to 1545 nm. ３ is the wavelength band λ=1545 nm to 1555 nm. ４ is the band of wavelength λ=1555 nm to 1565 nm.

[0021] As a result, the input light (electromagnetic wave) input from the light source unit 15 via the waveguide 16 is split into wavelength band b １ ~b ４ The wavelength bands b and b are separated by the demultiplexer 11. １ ~b ４ The electromagnetic waves in the wavelength bands b1 and b2 propagate through the waveguides 17a to 17d and are transmitted through the isolators 12a to 12d. １ ~b ４ The electromagnetic waves propagate through the waveguides 18 a to 18 d and are combined by the combiner 13 to be emitted into one waveguide 19 .

[0022] On the other hand, if there is unintended return light (electromagnetic wave) incident on the multiplexer 13 from the waveguide 19, the return light is transmitted to the multiplexer 13 through the wavelength band b １ ~b ４ The separated wavelength band b １ ~b ４These electromagnetic waves pass through the waveguides 18a to 18d and are reduced or blocked by the isolators 12a to 12d, respectively. This allows the optical integrated circuit 10 to reduce the possibility that the returning light will reach the light source unit 15 and cause adverse effects. Adverse effects of the returning light include noise generation in the light source unit 15, destabilization of the operation of the light source unit 15, and damage to the light source unit 15.

[0023] Therefore, by adopting the circuit configuration described above, the optical integrated circuit 10 can provide isolation function for a wide band of input light (electromagnetic waves) using multiple isolators 12 that operate in a relatively narrow wavelength band.

[0024] 2, in one embodiment, the isolator 12 has a Mach-Zehnder interferometer (MZI) circuit. The isolator 12 functions as an optical isolator due to the interaction between a phase difference (nonreciprocal phase difference) generated by the nonreciprocal phase shift effect of electromagnetic waves propagating through two waveguides and a phase difference (reciprocal phase difference) that is independent of the propagation direction.

[0025] The isolator 12 includes a splitter 21, a coupler 22, and a first waveguide 23 and a second waveguide 24 that respectively connect the splitter 21 and the coupler 22. Nonreciprocal members 25 and 26 are disposed adjacent to parts of the first waveguide 23 and the second waveguide 24, respectively. The part where the nonreciprocal member 25 is adjacent to the first waveguide 23 and the part where the nonreciprocal member 26 is adjacent to the second waveguide 24 are nonreciprocal lines 27 and 28, respectively. The nonreciprocal lines 27 and 28 extend in the Z-axis direction.

[0026] The splitter 21 splits the electromagnetic wave incident from the waveguide 17 into a first waveguide 23 and a second waveguide 24. A 1x2 multimode interference (MMI) optical coupler can be used as the splitter 21. The 1x2 multimode interference optical coupler can distribute the incident light equally to the two waveguides. The splitter 21 is not limited to a multimode interference optical coupler, and a Y-branch circuit, a directional coupler, or the like can also be used.

[0027] The coupler 22 couples the electromagnetic waves propagating through the first waveguide 23 and the second waveguide 24, and outputs the combined waves to the waveguide 18. A 2x1 type multimode interference optical coupler can be used as the coupler 22. As with the splitter 21, the coupler 22 is not limited to a multimode interference optical coupler, and a Y-branch circuit or a directional coupler can also be used.

[0028] The first waveguide 23 and the second waveguide 24 propagate electromagnetic waves in TM mode. The first waveguide 23 and the second waveguide 24 generate a phase difference between the propagating electromagnetic waves by adjusting the difference in optical path length. This phase difference is a phase difference (reciprocal phase difference) that does not depend on the propagation direction of the electromagnetic waves.

[0029] On the other hand, the nonreciprocal line 27 included in the first waveguide 23 and the nonreciprocal line 28 included in the second waveguide 24 have nonreciprocity. Nonreciprocity refers to the property that the effect on an electromagnetic wave propagating through a waveguide differs depending on the propagation direction of the electromagnetic wave. The propagation direction of the electromagnetic wave in the first waveguide 23 and the second waveguide 24, from the splitter 21 to the coupler 22, is defined as a first direction. The propagation direction of the electromagnetic wave from the coupler 22 to the splitter 21 is defined as a second direction. In the nonreciprocal lines 27 and 28, a nonreciprocal phase shift effect occurs due to the magneto-optical effect, in which the amount of phase change differs between the electromagnetic wave propagating in the first direction and the electromagnetic wave propagating in the second direction. In this embodiment, the phase shift amounts due to the nonreciprocal lines 27 and 28 are added together to form a phase difference (nonreciprocal phase difference) due to the nonreciprocal phase shift effect between the first waveguide 23 and the second waveguide 24 .

[0030] 2, in this embodiment, the first waveguide 23 and the second waveguide 24 extend from the splitter 21 in the +Z-axis direction, bend in a U-shape to extend in the −Z-axis direction, and then bend again in a U-shape to extend in the +Z-axis direction. In the first waveguide 23, the nonreciprocal line 27 is provided at a position where the electromagnetic wave incident from the splitter 21 is directed in the −Z-axis direction. In the second waveguide 24, the nonreciprocal line 28 is provided at a position where the electromagnetic wave incident from the splitter 21 is directed in the +Z-axis direction. As will be described later, this arrangement makes it possible to apply a uniform magnetic field in the X-axis direction to produce a nonreciprocal phase shift effect.

[0031] Each isolator 12 is adjusted so that the phases of the electromagnetic wave that is branched by the splitter 21, propagates through the first waveguide 23 in a first direction, and enters the coupler 22, and the electromagnetic wave that propagates through the second waveguide 24 in the first direction and enters the coupler 22, are in phase. Also, each isolator 12 is adjusted so that the phases of the electromagnetic wave that is branched by the coupler 22, propagates through the first waveguide 23 in a second direction, and enters the splitter 21, and the electromagnetic wave that propagates through the second waveguide 24 in the second direction and enters the splitter 21, are opposite to each other.

[0032] As an example, when an electromagnetic wave propagates in the first direction through the first waveguide 23, a phase difference (reciprocal phase difference) that is independent of the propagation direction of +90° (+π / 2) occurs with respect to the second waveguide 24. Also, when the electromagnetic wave propagates in the first direction through the first waveguide 23, a phase difference (non-reciprocal phase difference) of −90° (−π / 2) occurs with respect to the second waveguide 24 due to a non-reciprocal phase shift effect. In this case, the electromagnetic wave that propagates through the first waveguide 23 in the first direction from the splitter 21 and the electromagnetic wave that propagates through the second waveguide 24 become in phase with each other at the coupler 22, pass through the coupler 22, and are output to the waveguide 18.

[0033] On the other hand, when the electromagnetic wave propagates through the first waveguide 23 in the second direction, a phase difference (non-reciprocal phase difference) of +90° (+π / 2) occurs with respect to the second waveguide 24 due to the non-reciprocal phase shift effect. Therefore, a phase difference of +180° (+π) occurs between the electromagnetic wave propagating through the first waveguide 23 in the second direction from the coupler 22 and the electromagnetic wave propagating through the second waveguide 24, which is the sum of the phase difference of +90° independent of the propagation direction and the phase difference of +90° due to the non-reciprocal phase shift effect. Therefore, the electromagnetic wave propagating through the first waveguide 23 and the electromagnetic wave propagating through the second waveguide 24 enter the splitter 21 as electromagnetic waves of opposite phases and cancel each other out. In this way, the return light incident from the waveguide 18 is reduced or blocked by the splitter 21.

[0034] <Configuration Example of Nonreciprocal Line> Next, the configuration of the nonreciprocal line 27 will be described. Fig. 3 is a cross-sectional view of the nonreciprocal line 27 of Fig. 2 taken along line A-A. As shown in the cross-sectional view of Fig. 3, the nonreciprocal line 27 of the first waveguide 23 includes the substrate 14, the first waveguide 23, a box layer 31, an insulating layer 32, a nonreciprocal member 25, and an insulating layer 33. The box layer 31 is located on the substrate surface 14a of the substrate 14.

[0035] The first waveguide 23 is located on the box layer 31. The first waveguide 23 extends in the depth direction of the page, that is, along the Z-axis direction.

[0036] The insulating layer 32 is located on the box layer 31 in a portion other than the first waveguide 23. The insulating layer 32 may be formed so that the upper surface of the insulating layer 32 is located closer to the substrate surface 14a than the upper surface of the first waveguide 23. The insulating layer 32 may be formed so that the upper surface of the insulating layer 32 is flush with the upper surface of the first waveguide 23. The insulating layer 32 may be formed so that the upper surface of the insulating layer 32 is located farther from the substrate surface 14a than the upper surface of the first waveguide 23. The insulating layer 32 may cover the upper surface of the first waveguide 23.

[0037] When viewed in a plan view toward the substrate surface 14a, the nonreciprocal member 25 is located so as to overlap at least a portion of the first waveguide 23. The nonreciprocal member 25 may be located on the insulating layer 32. When the top surface of the first waveguide 23 is covered with the insulating layer 32, the nonreciprocal member 25 may be located on the insulating layer 32 overlapping at least a portion of the first waveguide 23.

[0038] The first waveguide 23 is surrounded by a box layer 31 and insulating layers 32 and 33. The first waveguide 23 forms a core. The box layer 31 and insulating layers 32 and 33 form a clad. The core and clad may be configured to include a dielectric. The first waveguide 23 is also referred to as a dielectric line. The first waveguide 23 as a core is located along the substrate surface 14a and propagates electromagnetic waves along the substrate surface 14a. In other words, the electromagnetic waves propagate through the first waveguide 23 as a core in the direction in which the waveguide 23 extends.

[0039] The materials of the core and the cladding are determined so that the relative dielectric constant of the core is greater than that of the cladding. In other words, the materials of the core and the cladding are determined so that the refractive index of the cladding is smaller than that of the core. In this way, the electromagnetic wave propagating through the core can be totally reflected at the boundary with the cladding. As a result, the loss of the electromagnetic wave propagating through the core can be reduced.

[0040] In this embodiment, the material of the first waveguide 23 as a core is silicon (Si), but is not limited to this and may be various other materials. The material of the box layer 31 and the insulating layers 32 and 33 as cladding may be silica glass or silicon oxide film (SiO ｘ ), but is not limited to this and may be various other materials. The relative dielectric constants of silicon and quartz glass are approximately 12 and approximately 2, respectively. Silicon can propagate electromagnetic waves having near-infrared wavelengths of approximately 1.2 μm to approximately 6 μm with low loss. When the first waveguide 23 is made of silicon, it can propagate electromagnetic waves having wavelengths in the 1.3 μm band or 1.55 μm band used in optical communications with low loss.

[0041] The nonreciprocal member 25 is formed by being deposited on the substrate 14 in a state in which the box layer 31, the first waveguide 23, and the insulating layer 32 are formed on the substrate 14.

[0042] The nonreciprocity member 25 may be composed of a nonreciprocal material, such as magnetic garnet, ferrite, iron, or cobalt. In one embodiment, YIG (yttrium-iron-garnet) is used as the material of the nonreciprocity member 25. In this embodiment, Ce:YIG is used as the material of the nonreciprocity member 25. Ce:YIG is a material in which part of the yttrium is substituted with Ce. A transparent magnetic material such as Bi:YIG may also be used as the material of the nonreciprocity member 25. Bi:YIG is a material in which part of the yttrium is substituted with Bi. The element that substitutes part of the yttrium is also referred to as a substitution element. The substitution element is not limited to Ce or Bi. In addition to Ce or Bi, a rare earth element may also be used as the substitution element. By substituting part of the yttrium with a substitution element, the strength of the nonreciprocity exhibited by the nonreciprocity member 25 is adjusted. Also, non-reciprocity can become strong.

[0043] YIG in which yttrium is not substituted may be used as the material of the nonreciprocal member 25. Hereinafter, YIG in which part of the yttrium is substituted with Ce, Bi, or the like, and YIG in which yttrium is not substituted will be collectively referred to simply as YIG.

[0044] YIG is a film in which yttrium, iron, and oxygen form crystals with a garnet structure, and can be formed by, for example, sputtering a target containing yttrium, iron, and oxygen in an atmosphere of a mixed gas of argon and oxygen.

[0045] <Relationship between characteristics of nonreciprocal member and nonreciprocity> The first waveguide 23 extending along the nonreciprocal member 25 can exhibit nonreciprocity for electromagnetic waves propagating through the first waveguide 23. The strength of the nonreciprocity corresponds to the magnitude of the difference in phase shift between the electromagnetic waves in each propagation direction when the electromagnetic waves propagate in opposite directions for a unit length.

[0046] When a magnetic field is applied in the X-axis direction, the nonreciprocity member 25 causes the electromagnetic wave propagating through the first waveguide 23 to exhibit nonreciprocity when the energy of the electric field of the electromagnetic wave propagating through the first waveguide 23 is effectively distributed within the nonreciprocity member 25. The range in which the energy of the TM mode electromagnetic wave is effectively distributed is, for example, when the energy of the electric field component is 1 / e of the maximum energy. ２ It may be defined as a range that is equal to or greater than the range.

[0047] In the nonreciprocal line 27 illustrated in FIG. 3 , the nonreciprocal member 25 is located in the normal direction of the substrate surface 14 a as viewed from the first waveguide 23. Assume that a TM mode electromagnetic wave propagates through the first waveguide 23. The electric field energy of the TM mode electromagnetic wave is distributed in the Y-axis direction, which is the amplitude direction of the electric field, and decreases outside the first waveguide 23 as it moves away from the top surface of the first waveguide 23 in the Y-axis direction. As a result, the electric field energy of the TM mode electromagnetic wave is effectively distributed within the nonreciprocal member 25, which is located in the Y-axis direction as viewed from the first waveguide 23. Therefore, the nonreciprocal member 25 imparts nonreciprocity to the TM mode electromagnetic wave propagating through the first waveguide 23.

[0048] The nonreciprocal line 28 of the second waveguide 24 may also be configured in the same manner as the cross-sectional view of the nonreciprocal line 27 of the first waveguide 23 shown in FIG. 2 . However, as shown in FIG. 2 , in the first waveguide 23, the electromagnetic wave branched by the splitter 21 propagates through the nonreciprocal line 27 in the negative direction of the Z axis (−Z direction). In contrast, in the second waveguide 24, the electromagnetic wave branched by the splitter 21 propagates through the nonreciprocal line 28 in the positive direction of the Z axis (+Z direction). Due to the different propagation directions, when a uniform magnetic field is applied to the isolator 12 in the X-axis direction, a nonreciprocal phase shift effect occurs between the nonreciprocal line 27 and the nonreciprocal line 28 in opposite directions. As a result, a nonreciprocal phase difference, which is the sum of the magnitudes of the nonreciprocal phase differences of the nonreciprocal line 27 and the nonreciprocal line 28, occurs between the first waveguide 23 and the second waveguide 24. In this way, by providing the nonreciprocal lines 27 and 28 in both the first waveguide 23 and the second waveguide 24, the isolator 12 can be configured more compactly than when a nonreciprocal line is provided in one waveguide. Furthermore, since it is only necessary to apply a magnetic field in one direction, the magnetic field required to exhibit a nonreciprocal phase shift effect can be generated with a simple configuration.

[0049] <Configuration of Portions Other Than the Nonreciprocal Line of the Waveguide> In the portion of the first waveguide 23 other than the nonreciprocal line 27, there is no nonreciprocal member 25 between the first waveguide 23 and the insulating layer 32, and the insulating layer 33. That is, the tops of the first waveguide 23 and the insulating layer 32 are directly covered with the insulating layer 33. The insulating layer 32 and the insulating layer 33 may be integrally formed of the same material. The portion of the second waveguide 24 other than the nonreciprocal line 28 may also be configured in the same way. Furthermore, the waveguides 16 to 19 outside the isolator 12 of the optical integrated circuit 10 may also be configured in the same way.

[0050] As described above, according to this embodiment, a plurality of isolators 12 corresponding to the respective wavelength bands of electromagnetic waves demultiplexed by the demultiplexer 11 are provided. This allows the optical integrated circuit 10 as a whole to provide an isolation function for input light in a wavelength band wider than the operating band of each isolator 12. Furthermore, when a wavelength-tunable laser whose wavelength is tunable over a range wider than the operating band of a single isolator 12 is used as the light source unit 15, the optical integrated circuit 10 can provide a continuous isolation function as the wavelength of the light source unit 15 changes.

[0051] Furthermore, in one embodiment, the demultiplexer 11 is configured to split input light including the C-band (λ=1530 nm to 1565 nm). This allows the optical integrated circuit 10 to be applied to light in the C-band used in optical communications. In particular, by including the light source unit 15, the optical integrated circuit 10 can be used as a light source device for optical communications.

[0052] In one embodiment, the isolator 12 includes a Mach-Zehnder interferometer. The isolator 12 includes a Mach-Zehnder interferometer, which has a wider operating wavelength band than other types of isolators. Examples of other types of isolators include ring resonator isolators. Therefore, the optical integrated circuit 10 can isolate electromagnetic waves in a desired wavelength band by dividing them into fewer bands. This allows the optical integrated circuit 10 to be configured more compactly.

[0053] Furthermore, the Mach-Zehnder interferometer (MZI) circuit used in a typical waveguide isolator includes a heater circuit to adjust for manufacturing errors (see, for example, FIG. 4 ). When the circuit linewidth deviates from the design value due to manufacturing errors, the effective refractive index changes, causing a change in the optical path length difference between the waveguides in the MZI circuit. In conventional isolators, heater circuits are provided to adjust the peak shift of the isolator's operating wavelength caused by changes in the optical path length difference. On the other hand, in the optical integrated circuit 10 of this embodiment, manufacturing errors in the waveguide linewidth occur roughly uniformly across the entire wafer during the semiconductor process, so the errors in each MZI circuit in the circuit configuration are also roughly uniform. Therefore, in the optical integrated circuit 10 of this embodiment, each isolator 12 can be configured without a heater circuit. This allows the optical integrated circuit 10 to be configured more compactly.

[0054] Furthermore, in the above embodiment, the optical integrated circuit 10 can be made compact because the demultiplexer 11, the isolator 12, the multiplexer 13, and the light source section 15 are integrated on the same substrate 14.

[0055] In the above embodiment, the demultiplexer 11, the isolator 12, the multiplexer 13, and the light source unit 15 are all provided on the same substrate 14. However, various configurations are possible for the optical integrated circuit 10, including a configuration in which the light source unit 15 is disposed outside the substrate 14, and a configuration in which the light source unit 15, the demultiplexer 11, and the multiplexer 13 are disposed outside the substrate 14 and only the isolator 12 is disposed on the substrate 14. Furthermore, components outside the substrate 14 may be connected to each other, and components outside the substrate 14 and components on the substrate 14 may be connected at least partially by optical waveguides such as optical fibers instead of the waveguides 16-19.

[0056] In the above embodiment, a tunable semiconductor laser is used as the light source unit 15. However, other tunable lasers may also be used as the light source unit 15. For example, tunable lasers include free electron lasers and dye lasers.

[0057] In the above embodiment, the number of bands into which the demultiplexer 11 divides the input light is four, but the demultiplexer 11 can divide the input light into any number of bands. The optical integrated circuit 10 may include a number of isolators 12 corresponding to the number of bands divided by the demultiplexer 11.

[0058] 2 and 3 in the above embodiment are merely examples. For example, in a waveguide-type isolator, the substrate, waveguide, insulating layer, non-reciprocal member, and other components that make up the isolator can have various shapes, sizes, materials, and arrangements.

[0059] Furthermore, in the above embodiment, the optical integrated circuit 10 is configured to propagate light in TM mode. However, the optical integrated circuit 10 may be configured to propagate light in TE mode. In this case, the nonreciprocal members 25 and 26 are not disposed on the top surface side of the cores of the first waveguide 23 and the second waveguide 24, but on the side surface side, i.e., on the surface side parallel to the YZ plane. In this case, a magnetic field is applied in the Y-axis direction to exhibit a nonreciprocal phase shift effect.

[0060] <Optoelectronic Integrated Circuit> Next, an optoelectronic integrated circuit 10A in which heaters for fine adjustment are provided in the isolators 40a to 40d will be described using Figures 4 and 5. The optoelectronic integrated circuit 10A differs from the optical integrated circuit 10 of Figure 1 in that the configuration of the isolators 40a to 40d is different from that of the isolators 12a to 12d, and in that the optoelectronic integrated circuit 10A has electrode pads 41a to 41c. Since the other configuration is the same as that of the optical integrated circuit 10 of Figure 1, the same components as those of the optical integrated circuit 10 are assigned the same reference numerals as those of the optical integrated circuit 10, and their description will be omitted. Hereinafter, the isolators 40a to 40d may be referred to as isolators 40.

[0061] 5 , in each isolator 40, the first waveguide 23 and the second waveguide 24 are extended, and an optical path difference adjuster 42 is provided in a part of the first and second waveguides 23 and 24. The optical path difference adjuster 42 includes first heaters 43a and 43b arranged adjacent to the first waveguide 23, and second heaters 44a and 44b arranged adjacent to the second waveguide 24.

[0062] The first heaters 43a, 43b include, for example, a heating element disposed on the insulating layer 33 on the first waveguide 23 along the first waveguide 23. The heating element is formed, for example, by depositing a thin film of titanium nitride (TiN) by sputtering. The first heaters 43a, 43b have electrodes at both ends along the waveguide 23. The first heaters 43a, 43b are connected in series or parallel to the ground electrode 45 and the first electrode 46. The first heaters 43a, 43b are heated to a desired temperature by controlling the voltage applied between the ground electrode 45 and the first electrode 46. The second heaters 44a, 44b are configured in the same manner as the first heaters 43a, 43b, except that one of the electrodes is connected to the second electrode 47 instead of the first electrode 46. The number and arrangement of the heaters described above are merely examples. Any number of heaters can be arranged in various ways.

[0063] The effective refractive index of the first waveguide 23 is partially changed by heating it with the first heaters 43a and 43b. The change in the effective refractive index changes the optical path length of the first waveguide 23. Therefore, the optical path length of the first waveguide 23 can be adjusted by the first heaters 43a and 43b. Similarly, the optical path length of the second waveguide 24 can be adjusted by the second heaters 44a and 44b. The optical path lengths of the first waveguide 23 and the second waveguide 24 may be adjusted individually. This allows the isolator 40 to fine-tune the optical path length in accordance with manufacturing errors. Therefore, the optoelectronic integrated circuit 10A can have a more precise isolation function.

[0064] Furthermore, in this embodiment, since the errors of the MZI circuits included in each isolator 40 are approximately uniform, it is possible to share electrode pads to control the first heaters 43a, 43b and second heaters 44a, 44b of each isolator 40. For example, the ground electrode 45, first electrode 46, and second electrode 47 of each isolator 40 may be connected to common electrode pads 41a, 41b, and 41c, respectively. Therefore, the optoelectronic integrated circuit 10A of this embodiment can be configured more compactly than when individual electrode pads are provided for the heaters of each isolator 40. The voltages applied to the electrode pads 41a, 41b, and 41c may be controlled by an external control circuit.

[0065] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art could make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications or alterations are included in the scope of the present disclosure. For example, the functions included in each component can be rearranged so as not to be logically inconsistent, and multiple components can be combined or divided into one.

[0066] In the present disclosure, descriptions such as "first" and "second" are identifiers for distinguishing the configuration. In the present disclosure, the configurations distinguished by descriptions such as "first" and "second" can have their numbers interchanged. For example, the first waveguide 23 can have its identifiers "first" and "second" interchanged with the second waveguide 24. The identifiers are interchanged simultaneously. The configurations remain distinguished even after the identifiers are interchanged. Identifiers may be deleted. A configuration from which an identifier has been deleted is distinguished by a symbol. The identifiers "first" and "second" in the present disclosure should not be used solely to interpret the order of the configurations or to justify the existence of an identifier with a smaller number.

[0067] In this disclosure, the X-axis, Y-axis, and Z-axis are provided for convenience of explanation and may be interchanged. The configurations according to this disclosure have been described using an orthogonal coordinate system formed by the X-axis, Y-axis, and Z-axis. The positional relationship between the components according to this disclosure is not limited to an orthogonal relationship.

[0068] In one embodiment of the present disclosure, (1) an optical integrated circuit includes a demultiplexer that divides input light into a plurality of different wavelength bands, a plurality of isolators having isolation functions corresponding to the plurality of wavelength bands, respectively, and a multiplexer connected to the outputs of the plurality of isolators.

[0069] (2) In the optical integrated circuit of (1) above, the operating band in which the demultiplexer can demultiplex may be wider than the operating band of each of the isolators included in the plurality of isolators.

[0070] (3) In the optical integrated circuit of (1) or (2) above, the demultiplexer can be configured to split the input light including the C-band (λ=1530 nm to 1565 nm).

[0071] (4) In any one of the optical integrated circuits (1) to (3) above, the isolator may include a Mach-Zehnder interferometer.

[0072] In one embodiment of the present disclosure, (5) an optoelectronic integrated circuit includes any one of the optical integrated circuits (1) to (4) and a plurality of heaters provided in each of the isolators, each of the isolators having a waveguide or a waveguide that guides light split by the splitter, each of the heaters is configured to heat at least a portion of the waveguide or the waveguide to change the effective refractive index of the at least a portion of the waveguide or the waveguide, and the electrode pads of the plurality of heaters are common.

[0073] 10 Optical integrated circuit 11 Demultiplexer 12, 12a-12d Isolator 13 Multiplexer 14 Substrate 15 Light source section 16, 17a-17d, 18a-18d, 19 Waveguide 21 Splitter 22 Coupler 23 First waveguide 24 Second waveguide 25, 26 Nonreciprocal member 27, 28 Nonreciprocal line 31 Box layer 32, 33 Insulating layer 40a to 40d Isolator 41a to 41c Electrode pad 42 Optical path difference adjustment section 43a, 43b First heater 44b, 44b Second heater 45 Ground electrode 46 First electrode 47 Second electrode

Claims

1. An optical integrated circuit comprising: a demultiplexer that divides input light into multiple different wavelength bands; multiple isolators that have isolation functions corresponding to the multiple wavelength bands; and a multiplexer that is connected to the outputs of the multiple isolators.

2. The optical integrated circuit according to claim 1, wherein the operating band that can be demultiplexed by said demultiplexer is wider than the operating band of each of the isolators included in said plurality of isolators.

3. The optical integrated circuit according to claim 1 or 2, wherein the demultiplexer is configured to split the input light including the C-band (λ=1530 nm to 1565 nm).

4. An optical integrated circuit according to any one of claims 1 to 3, wherein the isolator comprises a Mach-Zehnder interferometer.

5. An optoelectronic integrated circuit according to any one of claims 1 to 4, comprising an optical integrated circuit according to any one of claims 1 to 4 and a plurality of heaters provided in each of the isolators, each of the isolators having a waveguide or a waveguide for guiding light split by the splitter, each of the heaters being configured to heat at least a portion of the waveguide or a waveguide to change the effective refractive index of said at least a portion of said waveguide or a waveguide, and the electrode pads of the plurality of heaters being common.

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