Photoelectric integrated circuit

Abstract

This photoelectric integrated circuit comprises an isolator and a control unit. The isolator includes a waveguide, and a heating unit that changes the effective refractive index of the waveguide. The effective refractive index affects a change in an operating wavelength band. The control unit controls the heating unit on the basis of information on the wavelength band of input light, which is inputted to the isolator.

Description

Optoelectronic Integrated Circuits

[0001] The present disclosure relates to 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 optical 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] According to an embodiment of the present disclosure, there is provided an optoelectronic integrated circuit including an isolator and a controller. The isolator includes a waveguide and a heater that changes the effective refractive index of the waveguide, and the operating wavelength band changes according to the effective refractive index. The controller controls the heater based on information about the wavelength band of input light to the isolator.

[0005] Fig. 4 is a diagram showing a schematic configuration of an optoelectronic integrated circuit according to one embodiment; Fig. 5 is a diagram showing a schematic configuration of the isolator of Fig. 1; Fig. 6 is a cross-sectional view of the nonreciprocal line of Fig. 2 taken along line A-A; Fig. 7 is a diagram showing a schematic configuration of an optoelectronic integrated circuit according to another embodiment having a groove in the substrate; Fig. 8 is a cross-sectional view of line B-B including the groove of Fig. 4;

[0006] Generally, 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 optoelectronic integrated circuit according to the embodiment of the present disclosure described below employs a configuration in which an isolator is provided with a heating unit that changes the effective refractive index of the waveguide and the heating unit is controlled based on the wavelength band of the input light. This makes it possible to provide isolation functionality for different wavelength bands of the wavelength-tunable semiconductor laser.

[0007] 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.

[0008] 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.

[0009] <Configuration of Optoelectronic Integrated Circuit> As shown in FIG. 1 , an optoelectronic integrated circuit 10 according to an embodiment of the present disclosure includes an isolator 11 and a control unit 12. The optoelectronic integrated circuit 10 may further include a light source unit 13. The input side of the isolator 11 is connected to the light source unit 13 via a waveguide 16. The output side of the isolator 11 is connected to a waveguide 17. The control unit 12 and the light source unit 13 are electrically connected by a signal line 18. The isolator 11 includes a heating unit 14. The control unit 12 and the heating unit 14 are electrically connected by a signal line 19. The isolator 11 is disposed on a substrate 15. Either or both of the control unit 12 and the light source unit 13 may be disposed on the same substrate 15. An "optoelectronic integrated circuit" refers to a circuit in which an optical circuit and an electrical circuit are integrated on the same substrate or the like.

[0010] 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 15a of the substrate 15 and is the direction from the substrate surface 15a toward the side on which the optoelectronic integrated circuit 10 is formed. The Z-axis direction is along the substrate surface 15a and is the direction from the incident side of the isolator 11 to the exit side of the electromagnetic wave 13 emitted from the light source unit. The X-axis direction is perpendicular to the Y-axis and Z-axis directions.

[0011] The isolator 11 provides an isolation function for electromagnetic waves in the operating band. "Isolation function" means the function of transmitting electromagnetic waves traveling in the forward direction and reducing or blocking electromagnetic waves traveling in the reverse direction. The isolator 11 transmits the electromagnetic waves incident from the waveguide 16 to the waveguide 17. The isolator 11 reduces the intensity of the electromagnetic waves incident from the waveguide 17 and outputs them to the waveguide 16. Alternatively, the isolator 11 blocks the electromagnetic waves incident from the waveguide 17 and does not allow them to be transmitted to the waveguide 16.

[0012] The isolator 11 includes a heating unit 14. The heating unit 14 heats at least a portion of a waveguide inside the isolator 11 to change the effective refractive index of the waveguide, thereby changing the operating wavelength band of the isolator 11. In other words, the heating unit 14 is an operating wavelength band adjusting unit that adjusts the operating wavelength band of the isolator 11.

[0013] The control unit 12 includes one or more processors or one or more circuits. Processors include general-purpose processors that load specific programs to execute specific functions, and dedicated processors specialized for specific processing. The control unit 12 includes a microcontroller equipped with a processor. The control unit 12 may be configured with a simple circuit that does not include a processor. The control unit 12 receives input from a signal line 18 and outputs to a signal line 19. The control unit 12 may be disposed on the substrate 15 or may be disposed separately from the substrate 15. In this embodiment, the control unit 12 and the signal lines 18 and 19 are disposed on the substrate 15.

[0014] The control unit 12 controls the heating unit 14 based on information about the wavelength band of the input light to the isolator 11. The control unit 12 matches the operating wavelength band of the isolator 11 to the wavelength band of the input light. For example, the control unit 12 adjusts the wavelength band of the input light so that it is included in the operating wavelength band of the isolator 11. Furthermore, for example, the control unit 12 adjusts the center wavelength of the operating wavelength band of the isolator so that it approaches or matches the center wavelength of the wavelength band of the input light. The control unit 12 may send a signal to operate the heating unit 14 via a signal line 19. The control unit 12 may also supply power to operate the heating unit 14.

[0015] The light source unit 13 is a light source capable of emitting electromagnetic waves in a band wider than the operating band of the isolator 11. In this embodiment, the light source unit 13 may be a wavelength-tunable semiconductor laser. The wavelength-tunable semiconductor laser may be formed on the substrate 15 using semiconductor manufacturing technology. The wavelength band of the electromagnetic waves emitted by the wavelength-tunable semiconductor laser can be controlled by a signal transmitted from the control unit 12 of the optoelectronic integrated circuit 10 via a signal line 18. The light source unit 13 emits electromagnetic waves to the waveguide 16. The light source unit 13 may be disposed outside the optoelectronic integrated circuit 10 and may input electromagnetic waves to the waveguide 16 via a waveguide such as an optical fiber. In this case, the light source unit 13 does not need to be included in the optoelectronic integrated circuit 10.

[0016] The substrate 15 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 15 is made of silicon (Si), but is not limited to this and may be made of various other materials.

[0017] 2, in one embodiment, the isolator 11 has a Mach-Zehnder interferometer (MZI) circuit. The isolator 11 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.

[0018] The isolator 11 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.

[0019] The isolator 11 further includes a heating unit 14 that heats parts of the first waveguide 23 and the second waveguide 24. For compactness, the first waveguide 23 and the second waveguide 24 may have a bent shape in the heating unit 14. The heating unit 14 includes first heaters 31 a and 31 b arranged adjacent to the first waveguide 23 and second heaters 32 a and 32 b arranged adjacent to the second waveguide 24.

[0020] The splitter 21 splits the electromagnetic wave incident from the waveguide 16 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 the multimode interference optical coupler, and a Y-branch circuit, a directional coupler, or the like can also be used.

[0021] 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 17. 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.

[0022] 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.

[0023] 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 .

[0024] 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 toward the heating unit 14. In the first waveguide 23, the nonreciprocal line 27 is provided at a position where the electromagnetic wave incident from the splitter 21 and propagating in the first direction 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 and propagating in the first direction 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.

[0025] Each isolator 11 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 are the same as the phase of the electromagnetic wave that propagates through the second waveguide 24 in the first direction and enters the coupler 22. Also, each isolator 11 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 are opposite to each other.

[0026] 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 propagating in the first direction through the first waveguide 23 from the splitter 21 and the electromagnetic wave propagating in 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 17.

[0027] 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), which is the sum of the reciprocal phase difference of +90° and the non-reciprocal phase difference of +90°, 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. 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 returning light incident from the waveguide 17 is reduced or blocked by the isolator 11.

[0028] The condition under which the isolator 11 exhibits its isolation function depends on the wavelength of the electromagnetic wave incident on the isolator 11. The control unit 12 of the optoelectronic integrated circuit 10 controls the heating unit 14 in response to changes in the wavelength of the input light, thereby adjusting the optical path lengths of the first waveguide 23 and the second waveguide 24. This allows the isolator 11 to exhibit its isolation function.

[0029] The first heaters 31a, 31b include, for example, a heating element disposed on the first waveguide 23 along the waveguide 23. The heating element is formed, for example, by depositing a thin film of titanium nitride (TiN) by sputtering. The first heaters 31a, 31b have electrodes on both ends along the waveguide 23. The first heaters 31a, 31b are connected in series or parallel to the ground electrode 33 and the first electrode 34 by electric wires 35. The first heaters 31a, 31b are heated to a desired temperature by controlling a voltage applied between the ground electrode 33 and the first electrode 34. The second heaters 32a, 32b are configured identically to the first heaters 31a, 31b except that one of the electrodes is connected to the second electrode 36 instead of the first electrode 34 via an electric wire 37. The second heaters 32a, 32b are heated to a desired temperature by controlling a voltage applied between the ground electrode 33 and the second electrode 36. The number and arrangement of heaters described above are merely examples. In the heating section 14, any number of heaters may be arranged in various ways.

[0030] The voltages applied to the first electrode 34 and the second electrode 36 are controlled by the control unit 12. The effective refractive index of the first waveguide 23 is partially changed by heating it with the first heaters 31 a and 31 b. When the effective refractive index changes, the optical path length of the first waveguide 23 changes. Therefore, the optical path length of the first waveguide 23 can be adjusted by heating the first heaters 31 a and 31 b. Similarly, the optical path length of the second waveguide 24 can be adjusted by heating the second heaters 32 a and 32 b. The optical path lengths of the first waveguide 23 and the second waveguide 24 may be adjusted individually.

[0031] The control unit 12 can adjust the phase difference between the electromagnetic wave passing through the first waveguide 23 and the electromagnetic wave passing through the second waveguide 24 by adjusting the optical path length between the first waveguide 23 and the second waveguide 24. For example, the control unit 12 adjusts the phase difference of the return light (electromagnetic wave) that enters the coupler 22 from the waveguide 17, passes through the first waveguide 23 and the second waveguide 24, and reaches the splitter so that the phase is opposite to the center wavelength of the return light (electromagnetic wave). In this way, the control unit 12 can adjust the operating wavelength band of the isolator 11 so as to obtain an optimal isolation function according to the wavelength band of the input light (electromagnetic wave).

[0032] It is not necessary to provide heaters in both the first waveguide 23 and the second waveguide 24. The optoelectronic integrated circuit 10 may have only one of the first heaters 31 a, 31 b in the first waveguide 23 or the second heaters 32 a, 32 b in the second waveguide 24.

[0033] <Configuration Example of Nonreciprocal Line> Next, the configuration of nonreciprocal line 27 will be described. Fig. 3 is a cross-sectional view of nonreciprocal line 27 taken along line A-A in Fig. 2. As shown in the cross-sectional view of Fig. 3, nonreciprocal line 27 includes substrate 15, first waveguide 23, box layer 41, insulating layer 42, nonreciprocal member 25, and insulating layer 43. Box layer 41 is located on substrate surface 15a of substrate 15.

[0034] The first waveguide 23 is located on the box layer 41. The first waveguide 23 extends in the depth direction of the page, that is, along the Z-axis direction.

[0035] The insulating layer 42 is located on the box layer 41 in a portion other than the first waveguide 23. The insulating layer 42 may be formed so that the upper surface of the insulating layer 42 is located closer to the substrate surface 15a than the upper surface of the first waveguide 23. The insulating layer 42 may be formed so that the upper surface of the insulating layer 42 is flush with the upper surface of the first waveguide 23. The insulating layer 42 may be formed so that the upper surface of the insulating layer 42 is located farther from the substrate surface 15a than the upper surface of the first waveguide 23. The insulating layer 42 may cover the upper surface of the core of the first waveguide 23.

[0036] When viewed in a plan view toward the substrate surface 15 a, 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 42. When the top surface of the first waveguide 23 is covered with the insulating layer 42, the nonreciprocal member 25 may be located on the insulating layer 42 overlapping at least a portion of the first waveguide 23.

[0037] The first waveguide 23 is surrounded by a box layer 41 and insulating layers 42 and 43. The first waveguide 23 forms a core. The box layer 41 and the insulating layers 42 and 43 form a cladding. The core and cladding 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 15a and propagates electromagnetic waves along the substrate surface 15a. In other words, the electromagnetic waves propagate through the first waveguide 23 as a core in the direction in which the first waveguide 23 extends.

[0038] 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.

[0039] 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 41 and the insulating layers 42 and 43 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.

[0040] The nonreciprocal member 25 is formed by depositing a film on the substrate 15 in a state in which the box layer 41, the first waveguide 23, and the insulating layer 42 are formed on the substrate 15.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] <Relationship between Characteristics of Nonreciprocal Member and Nonreciprocity> When a magnetic field is applied in the X-axis direction, the first waveguide 23 extending along the nonreciprocal member 25 can exhibit nonreciprocity for the electromagnetic waves propagating through the first waveguide 23. The strength of the nonreciprocity corresponds to the magnitude of the difference in phase shift of the electromagnetic waves in each propagation direction when the electromagnetic waves propagate in opposite directions for a unit length.

[0045] The nonreciprocity member 25 causes nonreciprocity in the electromagnetic wave propagating through the first waveguide 23 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.

[0046] In the nonreciprocal line 27 illustrated in FIG. 3 , the nonreciprocal member 25 is located in the normal direction of the substrate surface 15 a as viewed from the first waveguide 23. Assume that a TM-mode electromagnetic wave propagates through the first waveguide 23. The TM-mode electromagnetic wave is an electromagnetic wave whose electric field amplitude direction coincides with the normal direction of the substrate surface 15 a, i.e., the Y-axis direction, when propagating through the first waveguide 23 in the Z-axis direction. The electric field energy of the TM-mode electromagnetic wave spreads and distributes in the electric field amplitude direction 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, 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.

[0047] 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. 3. 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). Because the propagation directions of the electromagnetic waves are different in this way, when a uniform magnetic field is applied to the isolator 11 in the X-axis direction, a nonreciprocal phase shift effect is generated between the nonreciprocal line 27 and the nonreciprocal line 28 in opposite directions. As a result, a phase difference is generated between the first waveguide 23 and the second waveguide 24, which is the sum of the magnitudes of the nonreciprocal phase shifts of the nonreciprocal lines 27 and 28. By providing the nonreciprocal lines 27 and 28 in both the first waveguide 23 and the second waveguide 24 in this way, the isolator 11 can be configured more compactly than when a nonreciprocal line is provided in one waveguide. Furthermore, because 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.

[0048] <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 42, and the insulating layer 43. That is, the tops of the first waveguide 23 and the insulating layer 42 are directly covered with the insulating layer 43. The insulating layer 42 and the insulating layer 43 may be integrally formed from the same material. The portion of the second waveguide 24 other than the nonreciprocal line 28 and the waveguides 16 and 17 may also be configured in the same manner.

[0049] As described above, according to the optoelectronic integrated circuit 10 of this embodiment, the control unit 12 controls the heating unit 14 based on information about the wavelength band of the input light input to the isolator 11. This changes the effective refractive index of at least a portion of the first waveguide 23 and the second waveguide 24 included in the isolator 11, thereby making it possible to match the operating wavelength band of the isolator 11 with the wavelength band of the light source unit 13. Therefore, the optoelectronic integrated circuit 10 can provide isolation function even when the wavelength of the light source unit 13 is changed.

[0050] In one embodiment, the wavelength band of the input light from the light source unit 13 is selected as part of the C-band (λ=1530 nm to 1565 nm). The operating wavelength band of the isolator 11 is adjustable within the C-band range. This allows the optoelectronic integrated circuit 10 to be applied to light in the C-band used in optical communications. In particular, the optoelectronic integrated circuit 10 can be used as a light source device for optical communications by including a light source unit 13 that can output light in a wavelength band included in the C-band.

[0051] Furthermore, in one embodiment, the isolator 11 includes a Mach-Zehnder interferometer. The isolator 11 including a Mach-Zehnder interferometer has a wider operating wavelength band than other types of isolators. Examples of other types of isolators include ring resonator-type isolators. Because the isolator 11 has a wide operating wavelength band, it can cover the wavelength band of the input light even with relatively rough adjustment accuracy. This makes it easy for the optoelectronic integrated circuit 10 to adjust the temperature of the heating unit 14 according to the wavelength band of the input light.

[0052] In the above embodiment, the isolator 11, the control unit 12, and the light source unit 13 are all provided on the same substrate 15. However, various configurations are possible for the optoelectronic integrated circuit 10, including a configuration in which the light source unit 13 is disposed outside the substrate 15 and / or a configuration in which the control unit 12 is disposed outside the substrate 15. Furthermore, the light source unit 13 outside the substrate 15 and the isolator 11 may be connected by an optical waveguide such as an optical fiber instead of the waveguide 16.

[0053] In the above embodiment, a tunable semiconductor laser is used as the light source unit 13. However, other tunable lasers may also be used as the light source unit 13. For example, tunable lasers include free electron lasers and dye lasers.

[0054] 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 constituting the isolator can have various shapes, sizes, materials, and arrangements.

[0055] Furthermore, in the above embodiment, the optoelectronic integrated circuit 10 transmits light in TM mode. However, the optoelectronic integrated circuit 10 may be configured to transmit 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.

[0056] In the above embodiment, the control unit 12 controls the wavelength band of the light source unit 13 and also controls the heating unit 14. However, the control unit 12 may be configured to acquire information about the wavelength band of the input light from the light source unit 13. The control unit 12 may also acquire information about the wavelength band of the input light from a sensor disposed in the optical path of the input light. The control unit 12 may control the heating unit 14 based on the acquired information about the wavelength band.

[0057] <Optoelectronic Integrated Circuit Including Groove Portion> When the light source unit 13 is disposed on the same substrate 15 as the isolator 11, heat generated by the light source unit 13 may be transmitted through the substrate 15 and affect the temperature of the waveguide in the isolator 11. If the heat generated by the light source unit 13 affects the temperature of the waveguide in the isolator 11, there is a concern that it may become difficult for the control unit 12 to accurately control the operating wavelength band of the isolator 11. Therefore, in an optoelectronic integrated circuit 10A according to one embodiment, a deep groove portion 50 is formed in the substrate 15 between the isolator 11 and the light source unit 13, as shown in FIG.

[0058] The groove 50 can have various shapes. For example, the groove 50 can be rectangular when viewed from a direction perpendicular to the substrate surface 15a. The shape of the groove 50 is not limited to a rectangle. As shown in the cross-sectional view of FIG. 5 , the groove 50 is formed by scraping away from the box layer 41 and the insulating layer 42 side to the inside of the substrate 15. The insulating layer 43 is integrated with the insulating layer 42. The portion where the groove 50 is formed has a reduced thickness, which makes it difficult for heat to be conducted. Therefore, heat generated by the light source unit 13 is less likely to be transmitted to the isolator 11.

[0059] 4, the waveguide 16 connecting the light source unit 13 and the isolator 11 is arranged so as to bypass the groove 50 when viewed in plan facing the substrate surface 15a. The other configurations and functions of the optoelectronic integrated circuit 10A are the same as those of the optoelectronic integrated circuit 10 shown in FIG. 1, and therefore the same components are designated by the same reference numerals and their description will be omitted.

[0060] With the above-described configuration, the optoelectronic integrated circuit 10A reduces or prevents the risk of heat from the light source unit 13 affecting the operating wavelength band of the isolator 11. Therefore, the control unit 12 can more accurately control the operating wavelength band of the isolator 11 based on information about the wavelength band of the input light from the light source unit 13.

[0061] 4, a groove 50 is provided between the light source unit 13 and the isolator 11 to make it difficult for heat from the light source unit 13 to be transmitted to the isolator 11. However, instead of the groove 50, a cutout portion penetrating the substrate 15 may be provided between the light source unit 13 and the isolator 11. This makes it even more difficult for heat from the light source unit 13 to be transmitted to the isolator 11.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] In one embodiment, (1) an optoelectronic integrated circuit includes: an isolator including a waveguide and a heating unit that changes the effective refractive index of the waveguide, and whose operating wavelength band changes depending on the effective refractive index; and a control unit that controls the heating unit based on information about the wavelength band of input light input to the isolator.

[0066] (2) In the optoelectronic integrated circuit of (1) above, the isolator may include a Mach-Zehnder interferometer.

[0067] (3) In the optoelectronic integrated circuit of (1) or (2) above, the wavelength band of the input light may be selected as a part of the C-band (λ=1530 nm to 1565 nm), and the operating wavelength band of the isolator may be adjustable within the C-band.

[0068] (4) In any of the optoelectronic integrated circuits (1) to (3) above, a light source unit that emits the input light may be further provided, the isolator and the light source unit may be formed on a substrate, and the substrate may have a groove or a cutout formed between the light source unit and the isolator.

[0069] REFERENCE SIGNS LIST 10 Light source unit 11 Isolator 12 Control unit 13 Light source unit 14 Heating unit (operating wavelength band adjusting unit) 15 Substrate 16, 17 Waveguide 18, 19 Signal line 21 Splitter 22 Coupler 23 First waveguide 24 Second waveguide 25, 26 Nonreciprocal member 27, 28 Nonreciprocal line 31a, 31b First heater 32b, 32b Second heater 33 Ground electrode 34 First electrode 35 Second electrode 36 Electric wire 37 Electric wire 41 Box layer 42, 43 Insulating layer

Claims

1. An optoelectronic integrated circuit comprising: an isolator including a waveguide and a heating unit that changes the effective refractive index of the waveguide, and whose operating wavelength band changes depending on the effective refractive index; and a control unit that controls the heating unit based on information about the wavelength band of input light input to the isolator.

2. The optoelectronic integrated circuit of claim 1, wherein said isolator comprises a Mach-Zehnder interferometer.

3. The optoelectronic integrated circuit of claim 1 or 2, wherein the wavelength band of the input light is selected as part of the C-band (λ=1530 nm to 1565 nm), and the operating wavelength band of the isolator is adjustable within the C-band.

4. An optoelectronic integrated circuit according to any one of claims 1 to 3, further comprising a light source section that emits the input light, the isolator and the light source section being formed on a substrate, and the substrate having a groove or cutout section formed between the light source section and the isolator.

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