Optical integrated circuit and optical receiver

Abstract

This optical integrated circuit is provided with wavelength multiplexing / demultiplexing elements (831-1 to 832-6), and each of the wavelength multiplexing / demultiplexing elements (831-1 to 832-6) is provided with a directional coupler and a delay line. The wavelength multiplexing / demultiplexing elements are connected in a multi-stage cascade.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Japanese Patent Application No. 2022-148602 (filed on September 16, 2022) and Japanese Patent Application No. 2022-197478 (filed on December 9, 2022), the entire disclosures of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to optical integrated circuits and optical receivers. Background Art

[0004] A wavelength separation element in which Mach-Zehnder interferometers are connected in cascade is known (for example, refer to Patent Document 1).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2020-194092 Summary of the invention

[0008] An optical integrated circuit according to one embodiment of the present disclosure includes a wavelength multiplexing / demultiplexing element including a directional coupler and a delay line, wherein the wavelength multiplexing / demultiplexing element is connected in cascade in multiple stages.

[0009] An optical receiver according to one embodiment of the present disclosure includes the optical integrated circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a block diagram showing a configuration example of an optical receiver according to one embodiment.

[0011] Figure 2 : is a block diagram showing a configuration example of an optical receiver having an edge coupler as an input unit.

[0012] Figure 3 It is shown in Figure 2 A block diagram of a structural example of an optical receiver in which the structural example also includes a delay device.

[0013] Figure 4 It is shown in Figure 3 A block diagram of a configuration example of an optical receiver in which the polarization beam rotator is replaced by a polarization beam splitter in the configuration example.

[0014] Figure 5 It is shown in Figure 3 A block diagram of a structural example of an optical receiver in which a delay device connected before a photodiode in a structural example is replaced with a variable attenuator.

[0015] Figure 6 It is shown in Figure 5 A block diagram of a configuration example of an optical receiver in which a delay device is further provided between a variable attenuator connected before a photodiode and the photodiode in a configuration example.

[0016] Fig. 7A This is a cross-sectional view showing an example of a strip-type waveguide.

[0017] Figure 7B This is a cross-sectional view showing an example of a ridge type waveguide.

[0018] Figure 8 This is a block diagram showing a configuration example of a branching filter according to one embodiment.

[0019] Fig. 9 It is shown Figure 8 Diagram of an example of the configuration of the interferometer and ports of the wave splitter.

[0020] Fig.10 This is a diagram showing an example of the configuration of a waveguide of an interferometer.

[0021] Fig.11 This is a graph showing an example of characteristics of the first element and the third element of the first group in the case of using a strip-type waveguide.

[0022] Fig.12 This is a graph showing an example of the characteristics of the second element of the first group when a strip-type waveguide is used.

[0023] Fig.13 This is a graph showing an example of characteristics of the first element, the third element, and the fourth element of the second group in the case of using a strip-type waveguide.

[0024] Fig.14 This is a graph showing an example of characteristics of the second element, the fifth element, and the sixth element of the second group in the case of using a strip-type waveguide.

[0025] Fig.15 This is a graph showing an example of design values ​​of characteristics of a branching filter when a strip-type waveguide is used.

[0026] Fig.16 This is a graph showing an example of measured values ​​of characteristics of a branching filter when a strip-type waveguide is used.

[0027] Fig.17 This is a graph showing an example of characteristics of the first element and the third element of the first group in the case of using a ridge waveguide.

[0028] Fig.18 This is a graph showing an example of the characteristics of the second element of the first group when a ridge waveguide is used.

[0029] Fig.19 This is a graph showing an example of characteristics of the first element, the third element, and the fourth element of the second group in the case of using a ridge waveguide.

[0030] Fig. 20 This is a graph showing an example of characteristics of the second element, the fifth element, and the sixth element of the second group in the case of using a ridge waveguide.

[0031] Fig.21 This is a graph showing an example of design values ​​of characteristics of a splitter when a ridge waveguide is used.

[0032] Fig. 22 This is a graph showing an example of measured values ​​of characteristics of a splitter when a ridge waveguide is used.

[0033] Fig.23 It is a diagram showing a structural example of a wavelength multiplexing / demultiplexing element having a resistor element.

[0034] Fig.24 This is a diagram showing an example of the positional relationship between the resistor element and the waveguide.

[0035] Fig.25A This is a graph showing an example of wavelength characteristics of a wavelength multiplexing / demultiplexing element using a strip waveguide.

[0036] Fig.25B This is a graph showing an example of wavelength characteristics of a wavelength multiplexing / demultiplexing element using a ridge waveguide. DETAILED DESCRIPTION

[0037] As a characteristic of silicon photonics elements, crosstalk or insertion loss between output ports is important. It is required to achieve sufficient crosstalk or insertion loss characteristics on the silicon photonics chip. According to the optical integrated circuit and optical receiver disclosed in the present invention, wavelength multiplexing / demultiplexing elements that are robust to manufacturing tolerances can be provided.

[0038] In optical communications within data centers, direct modulation and direct detection methods are widely used because digital signal processors are simple and low in power consumption. On the other hand, as the traffic volume of optical communications within data centers increases, higher-density data transmission is required, and optical integrated circuits using silicon, especially optical transceivers with small wavelength-multiplexed optical circuits, are being studied. Among them, a series Mach-Zehnder interference system or an arrayed waveguide grating can be used as a wavelength-multiplexed optical circuit implemented by silicon. These wavelength-multiplexed optical circuits all have the characteristic that their characteristics change greatly due to the polarization of light. On the other hand, single-mode optical fibers are widely used in existing optical fiber networks within data centers. However, this optical fiber does not have a polarization-maintaining characteristic. Therefore, whenever light passes through a curved portion or a connecting portion of the wiring, the polarization of the light changes randomly. Therefore, in order to make the characteristics of the optical receiver uniform for any polarization wave, it is necessary to set a polarization beam splitter rotator at the front stage of the optical circuit to separate the incident light into TE (Transverse Electric) component and TM (Transverse Magnetic) component, and make the TE (Transverse Electric) component and TM (Transverse Magnetic) component incident on different wavelength multiplexing optical circuits. In the direct modulation direct polarization wave method, after making the polarization light either TE or TM, it is necessary to receive the output of the wavelength multiplexing optical circuit with a photodiode and detect the sum of the outputs of the photodiodes corresponding to the components of each polarization wave.

[0039] An optical receiver 1 (see Figure 1 The optical signal transmitting structure may include a light source and a modulator.

[0040] The light source may include, for example, a semiconductor laser such as an LD (Laser Diode) or a VCSEL (Vertical Cavity Surface Emitting LASER). The light source is not limited to visible light and may include a device that emits electromagnetic waves of various wavelengths. The modulator modulates by changing the intensity of the electromagnetic wave. The modulator may, for example, pulse modulate the electromagnetic wave.

[0041] The structure for transmitting an optical signal can further include a signal input unit. The signal input unit receives an input of a signal from an external device or the like. The signal input unit may include, for example, a D / A converter. The signal input unit outputs a signal to a modulator. The modulator modulates an electromagnetic wave based on the signal obtained by the signal input unit.

[0042] like Figure 2As shown, the optical receiver 1 may have an edge coupler 811 as the input portion 81. Figure 3 As shown, the optical receiver 1 may further include a delay device 84 between the polarization beam splitter rotator 82 and each of the two splitters 83 and between the splitter 83 and each of the n photodiodes (PD: photodiode) 10-1 to n. The delay device 84 delays the transmission of the optical signal. The optical receiver 1 compensates for the deviation of the optical signal delay caused by the manufacturing error of the waveguide through the delay device 84. By including the delay device 84, the optical receiver 1 can reduce the jitter of the signal obtained by combining the TE mode optical signal output from the photodiode 10 and the TE mode optical signal converted from the TM mode optical signal.

[0043] The retarder 84 may be configured as a waveguide having a predetermined length, and the effective refractive index of the waveguide may be adjusted by a heater. The retarder 84 may be configured as a phase modulator having a predetermined length, and the phase modulation amount may be adjusted by applying a voltage.

[0044] like Figure 4 As shown, in the optical receiver 1, the polarization beam splitter 82 can be replaced by a polarization beam splitter (PS: Polarizing Splitter) 822. The polarization beam splitter 822 separates the input optical signal into an optical signal in TE mode and an optical signal in TM mode. The transmission speed of the optical signal in TE mode is different from the transmission speed of the optical signal in TM mode. The optical receiver 1 can have a delay device 84 to compensate for the deviation of the delay between the optical signal in TE mode and the optical signal in TM mode.

[0045] like Figure 5 As shown, in Figure 2 In the illustrated optical receiver 1, the delay device 84 connected between the splitter 83 and each of the n photodiodes 10-1 to 10-n can be replaced with a variable optical attenuator (VOA) 85. The variable optical attenuator 85 can be configured as, for example, a pin diode including silicon. The variable optical attenuator 85 absorbs light by injecting current to attenuate the light intensity. By adjusting the current injected into each variable optical attenuator 85, it is possible to compensate for the optical loss generated in the polarization beam rotator 82 or the splitter 83. Therefore, even if the optical loss in the polarization beam rotator 82 or the splitter 83 is not uniform due to the difference in polarization or wavelength of the optical signal, the optical reception sensitivity of the optical signal of any polarization or wavelength can be made close to uniform by reducing the current value of the variable optical attenuator 85 through which the optical signal under the condition of large optical loss passes and increasing the current value of the variable optical attenuator 85 through which the optical signal under the condition of small optical loss passes.

[0046] like Figure 6 As shown, the optical receiver 1 may include a variable optical attenuator 85 and a delay device 84 between the splitter 83 and each of the n photodiodes 10 - 1 ˜n.

[0047] As described above, the optical receiver 1 of the present embodiment can detect an optical signal by using the photodiode 10 configured to reduce the return light. By reducing the return light, the optical signal returned to the input unit 81 can be reduced. By reducing the optical signal returned to the input unit 81, the stable operation of the light source or modulator that sends the optical signal to the input unit 81 can be maintained. As a result, the reliability of the optical communication system using the optical receiver 1 can be improved.

[0048] (Structural Example of Optical Integrated Circuit)

[0049] The optical integrated circuit may have a demultiplexer 83. The demultiplexer 83 can not only separate an electromagnetic wave containing components of multiple wavelengths into components of each wavelength, but also function as a wavelength combining and demultiplexing element that combines each of components of multiple different wavelengths into an electromagnetic wave containing components of multiple wavelengths.

[0050] The wave splitter 83 may be configured to include a directional coupler and a delay line. The directional coupler or the delay line may be configured to include a waveguide 140. Fig. 7A As shown, the waveguide 140 can be configured as a strip-type waveguide, such as Figure 7B As shown, the waveguide 140 may also be configured as a ridge waveguide. The cross-sectional shape of a strip waveguide is rectangular. The cross-sectional shape of a ridge waveguide has a convex shape at least in part.

[0051] The waveguide 140 may be formed to include silicon. The waveguide 140 may be formed on a substrate 150 of silicon. The substrate 150 may have an insulating layer 151 and a cladding layer 152. The waveguide 140 may be surrounded by the insulating layer 151 and the cladding layer 152. By forming the waveguide 140 from silicon, the wavelength multiplexing and demultiplexing element can be easily manufactured by silicon photonics technology. The waveguide 140 is not limited to silicon, and may also include various other dielectric materials.

[0052] like Figure 8 For example, the splitter 83 can be configured to include a wavelength multiplexing and splitting element (Mux) connected in a multi-stage cascade. The splitter 83 can be configured to include a cascade delay Mach-Zehnder interferometer (CMZI). Assume that the electromagnetic wave input to the port 0 of the splitter 83 contains 4 wavelength components. Each wavelength is represented by λ1, λ2, λ3 and λ4. In this structural example, the value of each wavelength is as follows.

[0053] λ1=1.27μm

[0054] λ2=1.29μm

[0055] λ3=1.31μm

[0056] λ4=1.33μm

[0057] The splitter 83 can be configured to separate the electromagnetic wave into two parts by combining the first element 831-1, the second element 831-2 and the third element 831-3 of the first group, and output one part from the second element 831-2 and the other part from the third element 831-3. Figure 8 In the example of , an electromagnetic wave including λ1 and λ3 is output from the second element 831 - 2 , and an electromagnetic wave including λ2 and λ4 is output from the third element 831 - 3 .

[0058] The splitter 83 can be configured to separate the electromagnetic wave output from the second element 831-2 of the first group into two parts by combining the first element 832-1, the third element 832-3 and the fourth element 832-4 of the second group, one part is output from the third element 832-3, and the other part is output from the fourth element 832-4. Figure 8 In the example of , an electromagnetic wave including λ1 is output from port 4 connected to the output of the third element 832-3. An electromagnetic wave including λ3 is output from port 5 connected to the output of the fourth element 832-4.

[0059] The splitter 83 can be configured to separate the electromagnetic wave output from the third element 831-3 of the first group into two parts by combining the second element 832-2, the fifth element 832-5 and the sixth element 832-6 of the second group, one part is output from the fifth element 832-5, and the other part is output from the sixth element 832-6. Fig.16 In the example of , an electromagnetic wave including λ2 is output from port 7 connected to the output of the sixth element 832-6. An electromagnetic wave including λ4 is output from port 6 connected to the output of the fifth element 832-5.

[0060] In other words, the splitter 83 has a wavelength multiplexing and demultiplexing element, which has a directional coupler and a delay line. In the splitter 83, the wavelength multiplexing and demultiplexing elements are connected in cascade in multiple stages. The wavelength multiplexing and demultiplexing elements can be connected in 4 stages. The first group of wavelength multiplexing and demultiplexing elements constituting the splitter 83 is also called the first composite element. The second group of wavelength multiplexing and demultiplexing elements constituting the splitter 83 is also called the second composite element. In the splitter 83, the first composite element and the second composite element can be connected in cascade. Figure 8In the example of , in the first group of splitters 83, the wavelength multiplexing and demultiplexing elements are connected in two stages of cascade connection. That is, in the first composite element, the wavelength multiplexing and demultiplexing elements are connected in two stages of cascade connection. In addition, in the second group of splitters 83, the wavelength multiplexing and demultiplexing elements are connected in two stages of cascade connection. That is, in the second composite element, the wavelength multiplexing and demultiplexing elements are connected in two stages of cascade connection. In the first composite element, the wavelength multiplexing and demultiplexing elements may be connected in N stages. In the second composite element, the wavelength multiplexing and demultiplexing elements may be connected in M ​​stages. N and M are natural numbers.

[0061] The waveguides and ports of the wave splitter 83 may be as follows Fig. 9 The terminals of the lines that form a pair with the lines represented as ports are referred to as terminals. Fig.10 The wavelength multiplexing / demultiplexing element includes a first portion and a second portion. The first portion is configured such that two waveguides 140 are arranged along each other. The second portion includes a delay line 170 so that the two waveguides 140 have different lengths. Fig.10 The wavelength multiplexing and demultiplexing element shown in the example has four first parts and three second parts between the first parts. Fig.10 , the lengths of the four first parts are represented by Lc1, Lc2, Lc3 and Lc4. The difference between the one-way lengths of the two waveguides 140 in each of the three second parts is represented by ΔL1, ΔL2 and ΔL3. That is, the difference between the round-trip lengths of the two waveguides 140 in each of the three second parts is represented by ΔL1×2, ΔL2×2 and ΔL3×2. The unit is μm (micrometer). The structure of the wavelength multiplexing and demultiplexing element can be determined by these 7 parameters.

[0062] The wavelength multiplexing and demultiplexing element has two waveguides 140 that are physically connected. The two waveguides 140 are electromagnetically coupled in the first portion. In the case where an electromagnetic wave input to one of the two waveguides 140 is directly output from the same waveguide 140, the output port is also referred to as a through port. In other words, the wavelength multiplexing and demultiplexing element has an output port on the through side of the directional coupler. The through port is a port that is physically connected from the input port of the electromagnetic wave through the waveguide 140.

[0063] In the case where the electromagnetic wave input to one of the two waveguides 140 is transferred and output to the other waveguide 140, the output port is also called a cross port. In other words, the wavelength multiplexing / demultiplexing element has an output port on the cross side of the directional coupler. The cross port is a port that is electromagnetically coupled from the input port of the electromagnetic wave through the waveguide 140 but is not physically connected.

[0064] Among the multiple wavelength multiplexing and demultiplexing elements included in the splitter 83, the wavelength multiplexing and demultiplexing elements connected after the second stage can have an output port on the straight-through side of the directional coupler. In addition, in the case where the first group of the splitter 83 has wavelength multiplexing and demultiplexing elements connected with N stages, and the second group has wavelength multiplexing and demultiplexing elements connected with M stages, the wavelength multiplexing and demultiplexing elements connected from the second stage to the Nth stage or from the N+2th stage to the N+Mth stage can have an output port on the straight-through side of the directional coupler. That is, the wavelength multiplexing and demultiplexing elements that do not perform output branching in the splitter 83 can have an output port on the straight-through side of the directional coupler. On the other hand, the wavelength multiplexing and demultiplexing elements of the first stage of the first group that perform output branching in the splitter 83 and the wavelength multiplexing and demultiplexing elements of the N+1th stage of the second group have output ports on both the straight-through side and the cross-side of the directional coupler.

[0065] The output to the cross port is sensitive to the manufacturing tolerance of the element. In other words, the sensitivity to the manufacturing tolerance of the element to the output to the cross port is large. Wave splitter 83 has an output port on the straight-through side of the directional coupler, which can reduce the influence of the manufacturing tolerance of the element. For example, the second element 831-2 of the first group can be designed as a side (second element 831-2 side) of the first element 831-1 of the first group output to the cross port in the second element 831-2 to the straight-through port output.

[0066] The characteristics of the wavelength multiplexing / demultiplexing element may differ when the waveguide 140 is a strip waveguide and when the waveguide 140 is a ridge waveguide. The characteristics of the wavelength multiplexing / demultiplexing element when the waveguide 140 is a strip waveguide and when the waveguide 140 is a ridge waveguide are described below.

[0067] <When the waveguide 140 is a strip-type waveguide>

[0068] Figure 8 or Fig. 9 The first element 831 - 1 and the third element 831 - 3 of the first group have the following parameters.

[0069] Lc1=40, Lc2=25, Lc3=20, Lc4=10

[0070] ΔL1=9.6 / 2, ΔL2=9.6, ΔL3=9.5

[0071] The characteristics of the first element 831-1 and the third element 831-3 of the first group in this case are as follows Fig.11 As shown in the diagram. Fig.11In the graph, the horizontal axis represents wavelength. Assume that the unit of wavelength is nm (nanometer). The vertical axis represents insertion loss. Assume that the unit of insertion loss is dB (decibel). The larger the value of the vertical axis (the higher the plot point of the graph), the smaller the loss. The solid line represents the output of the straight-through port. The dotted line represents the output of the crossover port. The meaning of the vertical and horizontal axes of the graph and the solid and dotted lines will be explained later. Figure 12 to Figure 14 as well as Figures 17 to 20 The same is true in .

[0072] Figure 8 or Fig. 9 The second element 831 - 2 of the first group has the following parameters.

[0073] Lc1=35, Lc2=25, Lc3=25, Lc4=10

[0074] ΔL1=9.9 / 2, ΔL2=9.9, ΔL3=9.8

[0075] In this case, the characteristics of the second element 831-2 of the first group are Fig.12 is shown in the diagram.

[0076] Figure 8 or Fig. 9 The first element 832 - 1 , the third element 832 - 3 and the fourth element 832 - 4 of the second group have the following parameters.

[0077] Lc1=35, Lc2=25, Lc3=15, Lc4=5

[0078] ΔL1=5.2 / 2, ΔL2=5.2, ΔL3=5.1

[0079] The characteristics of the first element 832-1, the third element 832-3 and the fourth element 832-4 of the second group in this case are as follows Fig.13 as shown in the chart.

[0080] Figure 8 or Fig. 9 The second element 832-2, the fifth element 832-5 and the sixth element 832-6 of the second group have the following parameters.

[0081] Lc1=35, Lc2=25, Lc3=15, Lc4=5

[0082] ΔL1=5.3 / 2, ΔL2=5.3, ΔL3=5.2

[0083] The characteristics of the second element 832-2, the fifth element 832-5, and the sixth element 832-6 of the second group in this case are as follows: Fig.14 as shown in the chart.

[0084] When each wavelength multiplexing / demultiplexing element has the above characteristics, the design values ​​of the output characteristics of ports 4 to 7 of the demultiplexer 83 are as follows: Fig.15 In addition, the measured values ​​of the output characteristics of ports 4 to 7 of the splitter 83 are as follows: Fig.16 As shown. Fig.15 and Fig.16 In the graph, the horizontal axis represents wavelength. Assume that the unit of wavelength is nm (nanometer). The vertical axis represents insertion loss. Assume that the unit of insertion loss is dB (decibel). Assume that an electromagnetic wave containing components with wavelengths of λ1 to λ4 is input to the port of the splitter 83. Fig.15 and Fig.16 In FIG. 1 , the measured value of the component output from port 4 is indicated by a solid line. The measured value of the component output from port 7 is indicated by a dashed line. The measured value of the component output from port 5 is indicated by a dashed dotted line. The measured value of the component output from port 6 is indicated by a dashed double dotted line. Fig.15 and Fig.16 As shown in the graph, in both the design value and the measured value, the components output from each port contain a large number of components of each wavelength. That is, in the measured results, the splitter 83 composed of the strip waveguide can also separate the components of each wavelength of λ1 to λ4. As a result, the characteristics of insertion loss and crosstalk can be improved.

[0085] <When the waveguide 140 is a ridge waveguide>

[0086] Figure 8 or Fig. 9 The first element 831 - 1 and the third element 831 - 3 of the first group have the following parameters.

[0087] Lc1=55, Lc2=35, Lc3=30, Lc4=10

[0088] ΔL1=10.4 / 2, ΔL2=10.4, ΔL3=10.3

[0089] The characteristics of the first element 831-1 and the third element 831-3 of the first group in this case are as follows Fig.17 as shown in the chart.

[0090] Figure 8 or Fig. 9 The second element 831 - 2 of the first group has the following parameters.

[0091] Lc1=65, Lc2=40, Lc3=30, Lc4=10

[0092] ΔL1=10.7 / 2, ΔL2=10.7, ΔL3=10.5

[0093] The characteristics of the second element 831-2 of the first group in this case are Fig.18 is shown in the diagram.

[0094] Figure 8 or Fig. 9 The first element 832 - 1 , the third element 832 - 3 and the fourth element 832 - 4 of the second group have the following parameters.

[0095] Lc1=55, Lc2=40, Lc3=25, Lc4=10

[0096] ΔL1=5.3 / 2, ΔL2=5.3, ΔL3=5.2

[0097] The characteristics of the first element 832-1, the third element 832-3 and the fourth element 832-4 of the second group in this case are as follows Fig.19 as shown in the chart.

[0098] Figure 8 or Fig. 9 The second element 832-2, the fifth element 832-5 and the sixth element 832-6 of the second group have the following parameters.

[0099] Lc1=50, Lc2=30, Lc3=25, Lc4=15

[0100] ΔL1=5.5 / 2, ΔL2=5.5, ΔL3=5.4

[0101] The characteristics of the second element 832-2, the fifth element 832-5, and the sixth element 832-6 of the second group in this case are Fig. 20 is shown in the diagram.

[0102] When each wavelength multiplexing / demultiplexing element has the above characteristics, the design values ​​of the output characteristics of ports 4 to 7 of the demultiplexer 83 are as follows: Fig.21 In addition, the measured values ​​of the output characteristics of ports 4 to 7 of the splitter 83 are as follows: Fig. 22 As shown. Fig.21 and Fig. 22 In the graph, the horizontal axis represents wavelength. Assume that the unit of wavelength is nm (nanometer). The vertical axis represents insertion loss. Assume that the unit of insertion loss is dB (decibel). Assume that an electromagnetic wave containing components with wavelengths of λ1 to λ4 is input to the port of the splitter 83. Fig.21 and Fig. 22 In FIG. 1 , the measured value of the component output from port 4 is indicated by a solid line. The measured value of the component output from port 7 is indicated by a dashed line. The measured value of the component output from port 5 is indicated by a dashed dotted line. The measured value of the component output from port 6 is indicated by a dashed double dotted line. Fig.21 and Fig. 22As shown in the graph, in both the design value and the measured value, the components output from each port contain more components of each wavelength. That is, in the measured results, the splitter 83 composed of the ridge waveguide can also separate the components of each wavelength of λ1 to λ4. As a result, the characteristics of insertion loss and crosstalk can be improved.

[0103] Summary

[0104] As described above, the optical integrated circuit of the present embodiment has a wavelength multiplexing and demultiplexing element, and the wavelength multiplexing and demultiplexing element is connected in a multi-stage cascade. By connecting the wavelength multiplexing and demultiplexing elements in a multi-stage cascade, sufficient crosstalk can be ensured. In addition, wavelength separation can be achieved with less insertion loss. As a result, the characteristics of insertion loss and crosstalk can be improved.

[0105] (Compensation Circuit)

[0106] like Fig.23 As shown in FIG. 1 , the wavelength multiplexing / demultiplexing element may include a waveguide 140 and a resistor 180 located on a substrate. The resistor 180 is configured to heat the waveguide 140 by heat generated by current flowing through the resistor 180, thereby changing the temperature of the waveguide 140. The resistor 180 may also overlap the waveguide 140. Fig.24 As shown, when the substrate is viewed from above, the resistor element 180 may overlap at least a portion of the waveguide 140. The resistor element 180 may not overlap the waveguide 140 when the substrate is viewed from above within a range that allows the temperature of the waveguide 140 to change.

[0107] The resistor element 180 may be made of, for example, titanium nitride (TiN). The resistor element 180 is not limited to TiN, but may be made of other various conductive materials suitable for the process of forming the waveguide 140 on the substrate.

[0108] The wavelength multiplexing and demultiplexing element can change the temperature of at least a portion of the waveguide 140 by passing a current through the resistor 180. The refractive index of at least a portion of the waveguide 140 changes by changing the temperature of at least a portion of the waveguide 140. The wavelength characteristics of the wavelength multiplexing and demultiplexing element change by changing the refractive index of at least a portion of the waveguide 140. Therefore, the wavelength multiplexing and demultiplexing element can change the wavelength characteristics of the wavelength multiplexing and demultiplexing element by changing the temperature of at least a portion of the waveguide 140. The wavelength characteristics of the wavelength multiplexing and demultiplexing element may deviate due to manufacturing tolerances or the influence of the surrounding environment. The wavelength multiplexing and demultiplexing element can compensate for the deviation of the wavelength characteristics by having the resistor 180.

[0109] Specifically, if Fig.25A and Fig.25BAs shown, the wavelength characteristics of the wavelength multiplexing / demultiplexing element change according to the power consumption of the resistor element 180 . Fig.25A The wavelength characteristics of the wavelength multiplexing / demultiplexing element are shown in the case where the waveguide 140 of the wavelength multiplexing / demultiplexing element is a stripline type. Fig.25B The wavelength characteristics of the wavelength multiplexing / demultiplexing element are shown in the case where the waveguide 140 of the wavelength multiplexing / demultiplexing element is a ridge type. Fig.25A and Fig.25B In the graph, the horizontal axis represents wavelength. The unit of wavelength is nm (nanometer). The vertical axis represents power. The unit of power is dBm (decibel milliwatt). The larger the value of the vertical axis (the higher the plot point on the graph), the smaller the loss.

[0110] exist Fig.25A and Fig.25B In the graph, the solid line represents the wavelength characteristics when the power consumption of the resistor element 180 is 0 mW (milliwatt). That is, the solid line represents the wavelength characteristics when no current flows through the resistor element 180. The dashed line represents the wavelength characteristics when the power consumption of the resistor element 180 is 10 mW (milliwatt). The dashed line represents the wavelength characteristics when the power consumption of the resistor element 180 is 20 mW (milliwatt). The double dashed line represents the wavelength characteristics when the power consumption of the resistor element 180 is 30 mW (milliwatt). Fig.25A and Fig.25B As shown, the wavelength characteristics of the wavelength multiplexing / demultiplexing element are adjusted according to the power consumption of the resistor element 180. The wavelength multiplexing / demultiplexing element can determine the current flowing through the resistor element 180 according to the manufacturing tolerance or the surrounding environment.

[0111] Although the embodiments of the present disclosure have been described according to the drawings and embodiments, it should be noted that those skilled in the art can make various deformations or changes according to the present disclosure. Therefore, it should be noted that these deformations or changes are all included in the scope of the present disclosure. For example, the functions included in each structural part, etc. can be reconfigured in a logically non-contradictory manner, and multiple structural parts, etc. can be combined into one or divided. It should be understood that the scope of the present disclosure also includes these situations.

[0112] In the present disclosure, records such as "first" and "second" are identifiers used to distinguish the structure. The structure distinguished by the records such as "first" and "second" in the present disclosure can replace the number in the structure. For example, the first element 831-1 can replace the "first" and "second" as identifiers with the second element 831-2. The replacement of the identifier is carried out simultaneously. After the identifier is replaced, the structure can still be distinguished. The identifier can also be deleted. The structure with the identifier deleted is distinguished by the figure mark. The interpretation of the order of the structure and the basis for the existence of the identifier with a smaller number should not be based solely on the records of the identifiers such as "first" and "second" in the present disclosure.

[0113] In the present disclosure, the X-axis, Y-axis, and Z-axis are provided for convenience of description and can be interchanged. The structure of the present disclosure is described using an orthogonal coordinate system consisting of the X-axis, Y-axis, and Z-axis. The positional relationship of each structure of the present disclosure is not limited to an orthogonal relationship.

[0114] In one embodiment, (1) an optical integrated circuit includes a wavelength multiplexing / demultiplexing element having a directional coupler and a delay line, wherein the wavelength multiplexing / demultiplexing element is connected in cascade in multiple stages.

[0115] (2) In the optical integrated circuit described in (1) above, the wavelength multiplexing and demultiplexing elements may be connected in four stages.

[0116] (3) In the optical integrated circuit described in (1) or (2) above, the wavelength multiplexing / demultiplexing element connected after the second stage may have an output port on the through side of the directional coupler.

[0117] (4) In the optical integrated circuit described in any one of (1) to (3) above, the first composite element in which the wavelength multiplexing / demultiplexing elements are connected in N stages and the second composite element in which the wavelength multiplexing / demultiplexing elements are connected in M ​​stages may be connected in cascade.

[0118] (5) In the optical integrated circuit described in (4) above, the wavelength multiplexing / demultiplexing elements connected from the second stage to the Nth stage or from the N+2th stage to the N+Mth stage may have an output port on the through side of the directional coupler.

[0119] (6) The optical integrated circuit described in any one of (1) to (5) above can be formed using silicon photonics technology.

[0120] (7) In the optical integrated circuit described in any one of (1) to (6) above, the wavelength multiplexing / demultiplexing element may include a waveguide located on a substrate and a resistor element configured to change the temperature of at least a portion of the waveguide.

[0121] (8) In the optical integrated circuit described in (7) above, when the substrate is viewed in plan, at least a portion of the resistor element overlaps at least a portion of the waveguide.

[0122] (9) In the optical integrated circuit described in (7) or (8) above, the resistor element may be configured to include titanium nitride.

[0123] In one embodiment, (10) an optical receiver includes the optical integrated circuit according to any one of (1) to (9) above.

[0124] Description of reference numerals:

[0125] 1: Optical receiver (81: input unit, 82: polarization beam rotator (PSR), 822: polarization beam splitter (PS), 83: demultiplexer (DEMUX), 831-1 to 3: first to third elements of the first group, 832-1 to 6: first to sixth elements of the second group, 84: delay device, 85: variable optical attenuator (VOA))

[0126] 10: Photodiode

[0127] 140: Waveguide

[0128] 150: substrate (151: insulating layer, 152: coating layer)

[0129] 170: Delay Line

[0130] 180: Resistor

Claims

1. An optical integrated circuit, wherein: A wavelength multiplexing / demultiplexing element is provided, wherein the wavelength multiplexing / demultiplexing element has a directional coupler and a delay line, and the wavelength multiplexing / demultiplexing element is connected in cascade in multiple stages.

2. The optical integrated circuit according to claim 1, wherein: The wavelength combining and demultiplexing elements are connected in four stages.

3. The optical integrated circuit according to claim 1, wherein: The wavelength multiplexing / demultiplexing element connected after the second stage has an output port on the through side of the directional coupler.

4. The optical integrated circuit according to claim 1, wherein: The first composite component in which the wavelength multiplexing / demultiplexing elements are connected in N stages and the second composite component in which the wavelength multiplexing / demultiplexing elements are connected in M ​​stages are connected in cascade connection.

5. The optical integrated circuit according to claim 4, wherein: The wavelength multiplexing / demultiplexing element connected from the second stage to the Nth stage or from the N+2th stage to the N+Mth stage has an output port on the through side of the directional coupler.

6. The optical integrated circuit according to any one of claims 1 to 5, wherein: The integrated circuit is formed by silicon photonics technology.

7. The optical integrated circuit according to any one of claims 1 to 5, wherein: The wavelength multiplexing / demultiplexing element includes a waveguide located on a substrate and a resistor element configured to change the temperature of at least a portion of the waveguide.

8. The optical integrated circuit according to claim 7, wherein: When the substrate is viewed in plan, at least a portion of the resistor element overlaps at least a portion of the waveguide.

9. The optical integrated circuit according to claim 8, wherein: The resistor element is configured to include titanium nitride. 10 . An optical receiver comprising the optical integrated circuit according to claim 1 .

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