Optical integrated circuit and optical transceiver

Abstract

The optical integrated circuit includes: a first element having a function of separating each polarized wave from an electromagnetic wave including a plurality of polarized waves or a function of rotating at least a portion of the polarized waves after separating each polarized wave from an electromagnetic wave including a plurality of polarized waves; and a second element having a function of separating components of a plurality of wavelengths included in the electromagnetic wave into components of respective wavelengths. The first element and the second element are in cascade connection.

Description

[0001] Cross-reference to related applications

[0002] This application claims the priority of Japanese Patent Application No. 2022-148601 (filed on September 16, 2022) and Japanese Patent Application No. 2022-197457 (filed on December 9, 2022), and the disclosures of these applications are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure relates to an optical integrated circuit and an optical transceiver. Background Art

[0004] There is known a wavelength multiplexing / demultiplexing element that can expand the effective wavelength band (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 of one embodiment of the present disclosure has a first element and a second element. The first element has a function of separating each polarization wave from an electromagnetic wave including a plurality of polarization waves or a function of rotating at least a part of the polarization waves after separating each polarization wave from an electromagnetic wave including a plurality of polarization waves. The second element has a function of separating the components of a plurality of wavelengths contained in the electromagnetic wave into components of each wavelength. The first element and the second element are connected in cascade.

[0009] An optical transceiver according to an embodiment of the present disclosure may include the optical integrated circuit. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0012] Figure 3 This is a block diagram showing a configuration example of an optical integrated circuit having a two-dimensional grating coupler as an input unit.

[0013] Figure 4 It means in Figure 2 A block diagram of a structural example of an optical integrated circuit in which the structural example also includes a delay device.

[0014] Figure 5 It means in Figure 4A block diagram of a structural example of an optical integrated circuit when the polarization light separator rotor is replaced by a polarization light separator in the structural example.

[0015] Figure 6 It means in Figure 4 A block diagram of a configuration example of an optical integrated circuit in which a delay device connected before a photodiode in a configuration example is replaced with a variable attenuator.

[0016] Figure 7 It means in Figure 6 A block diagram of a configuration example of an optical integrated circuit in which a delay device is further provided between a variable attenuator connected before the photodiode and the photodiode in the configuration example.

[0017] Figure 8 This is a block diagram showing a configuration example of an optical integrated circuit according to an embodiment.

[0018] Fig. 9 It is a plan view showing a configuration example of a polarization splitter rotor according to one embodiment.

[0019] Fig.10 yes Fig. 9 BB cross-sectional view.

[0020] Fig.11 yes Fig. 9 CC cross-sectional view.

[0021] Fig.12 yes Fig. 9 DD cross-sectional view.

[0022] Fig.13 yes Fig. 9 EE cross-sectional view.

[0023] Fig.14 yes Fig. 9 FF cross-sectional view.

[0024] Fig.15 This is a graph showing an example of simulation results of the output characteristics of the polarization splitter rotor according to one embodiment.

[0025] Fig.16 This is a graph showing an example of the measured results of the output characteristics of the polarization splitter rotor according to one embodiment.

[0026] Fig.17 This is a block diagram showing a configuration example of a branching filter according to one embodiment.

[0027] Fig.18 This is a graph showing an example of the measured results of the loss characteristics of the splitter.

[0028] Fig.19A It is a cross-sectional view showing an example of a strip-type waveguide.

[0029] Fig.19B It is a cross-sectional view showing an example of a rib type waveguide.

[0030] Fig. 20 Yes means Fig.17 A diagram showing an example of the configuration of the wavelength combining and decomposing elements and ports of a wavelength splitter.

[0031] Fig.21 It is a diagram showing an example of the arrangement of waveguides of a wavelength multiplexing / demultiplexing element.

[0032] Fig. 22 This is a graph showing an example of the measured results of the magnitude of the loss of each polarization component of the electromagnetic wave propagating through the rib type waveguide.

[0033] Fig.23 This is a graph showing an example of the measurement result of the component with wavelength λ1 further separated by the wavelength splitter from the polarized wave of the TE mode separated by the polarization splitter rotor.

[0034] Fig.24 This is a graph showing an example of the measurement result of the component with a wavelength of λ3 which is further separated by the wavelength splitter from the polarized wave of the TE mode separated by the polarization splitter rotor.

[0035] Fig.25 This is a graph showing an example of the measurement result of the component with a wavelength of λ4 which is further separated by the wavelength splitter from the polarized wave of the TE mode separated by the polarization splitter rotor.

[0036] Fig.26 This is a graph showing an example of the measurement result of the component with a wavelength of λ2 which is further separated by the wavelength splitter from the polarized wave of the TE mode separated by the polarization splitter rotor.

[0037] Fig. 27 This is a graph showing an example of the measurement result of the component with wavelength λ1 further separated by the wavelength splitter from the polarized wave of TM mode separated by the polarization splitter rotor.

[0038] Fig.28 This is a graph showing an example of the measurement result of the component with a wavelength of λ3 which is further separated by the wavelength splitter from the polarized wave of the TM mode separated by the polarization splitter rotor.

[0039] Fig.29 This is a graph showing an example of the measurement result of the component with a wavelength of λ4 which is further separated by the wavelength splitter from the polarized wave of the TM mode separated by the polarization splitter rotor.

[0040] Fig.30This is a graph showing an example of the measurement result of the component with a wavelength of λ2 which is further separated by the wavelength splitter from the polarized wave of the TM mode separated by the polarization splitter rotor.

[0041] Fig.31 It means in Figure 8 A block diagram of a structural example in which a polarization light separator rotor is replaced with a polarization light separator in an optical integrated circuit. DETAILED DESCRIPTION

[0042] For input waves whose polarization is not determined, the performance of wavelength separation may not be maintained. According to the optical integrated circuit and the optical transceiver disclosed in the present invention, wavelength separation can be performed with good performance for input waves whose polarization is not determined.

[0043] 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 volume of optical communications within data centers increases, higher-density data transmission is required, and optical integrated circuits using silicon are being studied, especially optical transceivers with small wavelength-multiplexed optical circuits. Among them, as wavelength-multiplexed optical circuits implemented by silicon, series Mach-Zehnder interferometers or arrayed waveguide gratings can be used. 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 optical fiber networks already installed in 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, it is necessary to design an optical integrated circuit so that the characteristics of the optical integrated circuit can be uniform for any polarization wave. An optical integrated circuit with uniform characteristics for any polarization wave is realized in the following manner: a polarization light separator rotor is set at the front stage of the optical circuit to separate the incident light into TE (Transverse Electric) component and TM (Transverse Magnetic) component, which are respectively incident on their respective wavelength multiplexing optical circuits, and the output of the wavelength multiplexing optical circuit is received by a photodiode, and the sum of the outputs of the photodiodes corresponding to each polarization wave component is detected.

[0044] In addition, when the separation degree (extinction ratio) of polarization wave components is low, the wavelengths may not be separated properly. In addition, interference between the previous signal frame and the next signal frame may occur, which is called jitter. Therefore, it is required to improve the extinction ratio.

[0045] An optical integrated circuit 1 (see Figure 1 The optical signal transmitting structure may include a light source and a modulator.

[0046] 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 varying the intensity of the electromagnetic wave. The modulator may also, for example, pulse modulate the electromagnetic wave.

[0047] The structure for transmitting an optical signal may 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 acquired by the signal input unit.

[0048] (Configuration Example of Optical Integrated Circuit 1)

[0049] The optical integrated circuit 1 is configured to receive an optical signal. Hereinafter, a configuration example of the optical integrated circuit 1 according to one embodiment of the present disclosure will be described.

[0050] like Figure 1 As shown, the optical integrated circuit 1 includes an input unit 81 , a polarizing splitter rotator (PSR: Polarizing Splitter Rotator) 82 , a demultiplexer (demultiplexer or DEMUX) 83 , and a photodiode (PD: Photo Diode) 10 .

[0051] The input unit 81 is configured to receive an input of an optical signal generated by the above-mentioned modulator or the like. The polarization beam separator rotor 82 separates the TE mode optical signal and the TM mode optical signal contained in the input optical signal, and converts the TM mode optical signal into the TE mode optical signal. The demultiplexer 83 separates each of the TE mode optical signals converted from the TE mode optical signals separated by the polarization beam separator rotor 82 and the TM mode optical signals separated by the polarization beam separator rotor 82 for each wavelength. Figure 1 In FIG. 8 , the wavelength splitter 83 is configured to separate the optical signal into light of n wavelengths represented by λ1 to λn.

[0052] The photodiode 10 includes photodiodes 10-1 to 10-n corresponding to light of each wavelength. Each photodiode 10 is connected to a splitter 83 that separates the TE mode optical signal for each wavelength and a splitter 83 that separates the TE mode optical signal after converting the TM mode optical signal for each wavelength. Each polarization wave component of the TE mode or TM mode can be detected by each photodiode 10 or by one photodiode 10.

[0053] (Configuration Example of Optical Integrated Circuit 1)

[0054] like Figure 2 As shown, the optical integrated circuit 1 can be configured to use a photodiode 10 having input ports located in two directions. The optical integrated circuit 1 has an edge coupler 811 as an input portion 81. The edge coupler 811 is configured to input light from the chip end face. The optical integrated circuit 1 also has a polarization separator rotator (PSR) 82 and a demultiplexer (DEMUX) 83. In the optical integrated circuit 1, circuits that process optical signals before inputting them to the photodiode 10 are collectively referred to as optical circuits. The optical circuit separates the optical signal input to the optical integrated circuit 1 into an optical signal propagating in a TE mode and an optical signal propagating in a TM mode. In the optical integrated circuit 1 of the present embodiment, it is assumed that the optical signal propagating in the TE mode corresponds to the first optical signal. The optical signal propagating in the TM mode corresponds to the second optical signal.

[0055] In the optical integrated circuit 1, the TE mode optical signal and the TM mode optical signal are mixed in the edge coupler 811, and the optical signal of the mixed n wavelengths is input. The polarization light separator rotor 82 separates the TE mode optical signal and the TM mode optical signal. In addition, the polarization light separator rotor 82 converts the TM mode optical signal into the TE mode optical signal. The splitter 83 further separates each optical signal separated by the polarization light separator rotor 82 into n wavelengths.

[0056] A signal obtained by separating the TE mode optical signal for each wavelength and a signal obtained by converting the TM mode optical signal into a TE mode optical signal and separating the signal for each wavelength are input to each of the photodiodes 10-1 to n. As a result, each of the photodiodes 10-1 to n outputs an electrical signal corresponding to the intensity of the signal obtained by separating the TE mode and TM mode mixed optical signal input to the edge coupler 811 for each wavelength.

[0057] The optical integrated circuit 1 of the present embodiment may further include a transimpedance amplifier for converting the electrical signal output from the photodiode 10. The optical integrated circuit 1 of the present embodiment can detect the optical signal for each wavelength using one photodiode, compared to the case where two light receiving elements for detecting the optical signal of the TE mode and the optical signal of the TM mode are used for each wavelength. In this way, it is possible to achieve a higher speed or a lower power consumption and a lower circuit size due to a reduction in parasitic capacitance.

[0058] like Figure 3As shown, the optical integrated circuit 1 may also have a two-dimensional grating coupler (2DGC: 2-dimensional grating couplers) 812 as an input unit 81. The two-dimensional grating coupler 812 separates the input optical signal into two polarization components Px and Py, and outputs each polarization component as an optical signal of a polarized wave in a TE mode. The demultiplexer 83 separates the optical signal of each polarization component for each wavelength. A signal after the optical signal of the polarization component Px is separated for each wavelength and a signal after the optical signal of the polarization component Py is separated for each wavelength are input to each of the photodiodes 10-1~n. As a result, the photodiodes 10-1~n output an electrical signal corresponding to the intensity of the signal separated for each wavelength by the optical signal in which the TE mode and TM mode mixed input to the two-dimensional grating coupler 812. In the case of having the two-dimensional grating coupler 812, the optical integrated circuit 1 may not have the polarization light separator rotor 82.

[0059] like Figure 4 As shown, the optical integrated circuit 1 may further include a delay device 84 between the polarization beam splitter rotor 82 and the two splitters 83 and between the splitter 83 and the n photodiodes 10-1 to 10-n. The delay device 84 delays the propagation of the optical signal. The optical integrated circuit 1 compensates for the delay deviation of the optical signal caused by the manufacturing error of the waveguide by the delay device 84. By including the delay device 84, the optical integrated circuit 1 can reduce the jitter of the signal which is a combination of the TE mode optical signal output from the photodiode 10 and the TE mode optical signal after the TM mode optical signal is converted.

[0060] 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.

[0061] like Figure 5 As shown, in the optical integrated circuit 1, the polarization light separator rotor 82 can be replaced by a polarization light separator (PS: Polarizing Splitter) 822. The polarization light separator 822 separates the input optical signal into a TE mode optical signal and a TM mode optical signal. The propagation speed of the TE mode optical signal and the propagation speed of the TM mode optical signal are different from each other. The optical integrated circuit 1 can have a delay device 84 to compensate for the deviation of the delay between the TE mode optical signal and the TM mode optical signal.

[0062] like Figure 6 As shown, in Figure 2In the optical integrated circuit 1 illustrated in FIG. 1 , the delay device 84 connected between the demultiplexer 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 to include, for example, a silicon pin diode. 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 light loss generated in the polarization beam separator rotor 82 or the demultiplexer 83. Therefore, even if the light loss in the polarization beam separator rotor 82 or the demultiplexer 83 is uneven due to the difference in polarization wave or wavelength of the optical signal, by reducing the current value of the variable optical attenuator 85 through which the optical signal under the condition of large light loss passes and increasing the current value of the variable optical attenuator 85 through which the optical signal under the condition of small light loss passes, the light receiving sensitivity of the optical signal of any polarization wave or wavelength can be made close to uniform.

[0063] like Figure 7 As shown, the optical integrated circuit 1 may include both a variable optical attenuator 85 and a delay device 84 between the demultiplexer 83 and each of the n photodiodes 10 - 1 to n.

[0064] (Configuration Example of Optical Integrated Circuit 200)

[0065] like Figure 8 As shown in the example, an optical integrated circuit 200 of one embodiment has a polarization separator rotor (PSR) 82 and a demultiplexer (DEMUX) 83. As described later, the polarization separator rotor 82 can also be replaced by a polarization separator 822. The optical integrated circuit 200 is connected between the input section 81 of the previous stage and the detection element 210 of the subsequent stage. The detection element 210 is configured to include VOA85 and PD10. The detection element 210 can also be configured to include PD10 but not VOA85. The optical integrated circuit 200 can also include PD10 (photodetector). The polarization separator rotor 82 or the polarization separator 822 is also called a first element. The demultiplexer 83 is also called a second element. In other words, the optical integrated circuit 200 has a first element, which has a function of separating each polarization wave from an electromagnetic wave including a plurality of polarization waves or a function of rotating at least a part of the polarization wave after separating each polarization wave from an electromagnetic wave including a plurality of polarization waves. In addition, the optical integrated circuit 200 has a second element having a function of separating components of multiple wavelengths contained in the electromagnetic wave into components of each wavelength. In the optical integrated circuit 200, the first element and the second element are cascade-connected. The optical integrated circuit 200 may further have a polarizer inserted between the first element and the second element. The polarizer is an element for passing linear polarized light in a specific direction.

[0066] The input unit 81 receives an electromagnetic wave including a polarized wave of a TE mode and a polarized wave of a TM mode. The polarized light separator rotor 82 separates the electromagnetic wave input to the input unit 81 into a polarized wave of a TE mode and a polarized wave of a TM mode, rotates the polarized wave of the TM mode into a polarized wave of a TE mode, and outputs it to the splitter 83. In the case where the optical integrated circuit 200 has a polarized light separator 822, the polarized light separator 822 separates the electromagnetic wave input to the input unit 81 into a polarized wave of a TE mode and a polarized wave of a TM mode, and outputs it to the splitter 83. The splitter 83 separates each polarized wave including components of a plurality of wavelengths into components of each wavelength, and outputs it to the detection element 210. The detection element 210 detects the components of each wavelength of the polarized wave of the TE mode and the components of each wavelength of the polarized wave of the TM mode (or the polarized wave of the TM mode after the separated polarized wave of the TM mode is rotated).

[0067] <Configuration Example of the Polarization Splitter Rotor 82>

[0068] like Fig. 9 , Fig.10 , Fig.11 , Fig.12 , Fig.13 and Fig.14 As shown, the polarization light separator rotor 82 of one embodiment includes a first waveguide 140 and a second waveguide 142. The first waveguide 140 and the second waveguide 142 are formed on an insulating layer 151 of a substrate 150. The substrate 150 may be made of various materials such as silicon. The insulating layer 151 may be made of various materials such as silicon dioxide. At least a portion of the first waveguide 140 and the second waveguide 142 extend in a first direction (Z-axis direction). At least a portion of the first waveguide 140 and at least a portion of the second waveguide 142 are arranged parallel to each other.

[0069] like Fig.11 , Fig.12 and Fig.13 As shown in the example, the first waveguide 140 has an asymmetric portion 141 that is asymmetric in a cross section with the first direction (Z-axis direction) as a normal line. In addition, the first waveguide 140 is non-line symmetric with respect to the normal line of the surface of the substrate 50 in a cross section with the first direction as a normal line. In the present embodiment, the cross-sectional shape of the first waveguide 140 is asymmetric, but the cross-sectional shape of the second waveguide 142 may also be asymmetric. The cross-sectional shape of at least one of the first waveguide 140 and the second waveguide 142 may also be asymmetric.

[0070] The first waveguide 140 has a first port 143 at an end on the negative side of the Z axis, and has a second port 144 at an end on the positive side of the Z axis, that is, at an end opposite to the first port 143 .

[0071] The second waveguide 142 includes a first portion 146 that exists along the first waveguide 140 and a second portion 147 that moves away from the first waveguide 140 as it advances in the positive direction of the Z axis. The second portion 147 may be configured as a curved portion or may be configured as a straight line that is inclined with respect to the direction in which the first waveguide 140 extends. The second portion 147 is located closer to the positive direction side of the Z axis than the first portion 146. The second portion 147 has a third port 145 at the end on the opposite side to the side connected to the first portion 146.

[0072] The first port 143 of the first waveguide 140 may be configured to be able to input electromagnetic waves. The second port 144 may be configured to be able to output electromagnetic waves. The third port 145 of the second waveguide 142 may be configured to be able to output electromagnetic waves. The electromagnetic wave input to the first port 143 travels in the positive direction of the Z axis in the first waveguide 140. At least a portion of the electromagnetic wave traveling in the first waveguide 140 is transferred to the second waveguide 142. The electromagnetic wave remaining in the first waveguide 140 travels to the second port 144 and is output from the second port 144. The electromagnetic wave transferred to the second waveguide 142 travels to the third port 145 and is output from the third port 145.

[0073] The second port 144 of the first waveguide 140 may be configured to be able to input electromagnetic waves. The third port 145 of the second waveguide 142 may be configured to be able to input electromagnetic waves. The first port 143 of the first waveguide 140 may be configured to be able to output electromagnetic waves. The electromagnetic wave input to the second port 144 travels in the negative direction of the Z axis in the first waveguide 140. On the other hand, the electromagnetic wave input to the third port 145 travels in the negative direction of the Z axis in the first portion 146 of the second waveguide 142 and is transferred to the first waveguide 140. As a result, in the first waveguide 140, a composite electromagnetic wave combining the electromagnetic wave input to the second port 144 and the electromagnetic wave input to the third port 145 travels in the negative direction of the Z axis. The composite electromagnetic wave travels to the first port 143 and is output from the first port 143.

[0074] Here, when an electromagnetic wave including a first polarization wave and a second polarization wave is input to the first port 143, the first waveguide 140 and the second waveguide 142 may be configured to separate the respective polarization waves, output the first polarization wave from the second port 144, and output the second polarization wave from the third port 145. Conversely, when an electromagnetic wave of a first polarization wave is input to the second port 144 and an electromagnetic wave of a second polarization wave is input to the third port 145, the first waveguide 140 and the second waveguide 142 may be configured to output electromagnetic waves synthesizing the respective polarization waves from the first port 143. The above structure can be achieved by appropriately designing, for example, the shape of the asymmetric portion 141 of the first waveguide 140, or the length or interval of the portions arranged to each other along the first waveguide 140 and the second waveguide 142. In the present embodiment, the first polarization wave is a polarization wave of the TE mode. The second polarization wave is a polarization wave of the TM mode.

[0075] exist Fig.15 The results of simulating the characteristics of the polarization splitter rotor 82 of this embodiment are shown in FIG. Fig.15 In the graph, the horizontal axis represents the wavelength. The unit of wavelength is nm (nanometer). The vertical axis represents the connection loss (Insertion Loss: IL). The unit of connection loss is dB (decibel). In the simulation, an electromagnetic wave including a TE mode polarization wave and a TM mode polarization wave is input to the first port 143. The component of the TE mode polarization wave output from the second port 144 is represented by a dotted line. The component of the TM mode polarization wave output from the second port 144 is represented by a double dotted line. The component of the TE mode polarization wave output from the third port 145 is represented by a solid line. The component of the TM mode polarization wave output from the third port 145 is represented by a dotted line. As shown Fig.15 As shown in the graph, the electromagnetic wave output from the second port 144 includes many TE mode polarization waves. The electromagnetic wave output from the third port 145 includes many TM mode polarization waves. That is, according to the simulation, the polarization light separator rotor 82 of this embodiment can separate the TE mode polarization wave and the TM mode polarization wave.

[0076] exist Fig.16 The results of measuring the characteristics of the polarization splitter rotor 82 of this embodiment are shown in FIG. Fig.16In the graph, the horizontal axis represents the wavelength. The unit of wavelength is nm (nanometer). The vertical axis represents the insertion loss (Insertion Loss: IL). The unit of insertion loss is dB (decibel). During actual measurement, an electromagnetic wave including a TE mode polarization wave and a TM mode polarization wave is input to the first port 143. The measured value of the polarization wave component of the TE mode output from the second port 144 is represented by a dotted line. The measured value of the polarization wave component of the TM mode output from the second port 144 is represented by a double dotted line. The measured value of the polarization wave component of the TE mode output from the third port 145 is represented by a solid line. The measured value of the polarization wave component of the TM mode output from the third port 145 is represented by a dotted line. As shown Fig.16 As shown in the graph, the electromagnetic wave output from the second port 144 includes many TE mode polarization waves. The electromagnetic wave output from the third port 145 includes many TM mode polarization waves. That is, in the actual measurement results, the polarization light separator rotor 82 of this embodiment can separate the TE mode polarization wave and the TM mode polarization wave.

[0077] The polarization beam splitter rotor 82 of the present embodiment may include a first waveguide 140 and a second waveguide 142. At least a portion of the first waveguide 140 and at least a portion of the second waveguide 142 may be aligned along a first direction ( Figure 8 The first waveguide 140 may have: a first port 143 configured to input or output an electromagnetic wave including a first polarization wave (e.g., a polarization wave of a TE mode) and a second polarization wave (e.g., a polarization wave of a TM mode); and a second port 144 configured to output a separated first polarization wave or input a first polarization wave. The second waveguide 142 may have a third port 145, and the third port 145 is configured to output a separated second polarization wave or a separated and rotated second polarization wave or input a second polarization wave. At least one of the first waveguide 140 and the second waveguide 142 is arranged in the first direction ( Figure 8 The shape of the cross section with the first direction (Z-axis direction) as the normal line may not be line symmetric. Figure 8 The shape of the cross section with the Z-axis direction (in the normal direction) as the normal line can be asymmetric.

[0078] The first portion 146 of the second waveguide 142 may be configured so that the line width is not constant. The first portion 146 may be configured, for example, in a tapered shape that is thinner on the first port 143 side and thicker on the side connected to the second portion 147. The first portion 146 may be configured as an adiabatic tapered waveguide. The second waveguide 142 may be configured so that the polarized wave of the TM mode separated from the first waveguide 140 is rotated and output from the third port 145 as a polarized wave of the TE mode.

[0079] The first waveguide 140 and the second waveguide 142 may be formed to include silicon. In addition, the first waveguide 140 and the second waveguide 142 may be formed on a silicon substrate 150. Since the waveguides are formed of silicon, the elements including the polarization splitter rotator 82 can be easily manufactured by silicon photonics technology. The first waveguide 140 and the second waveguide 142 are not limited to silicon, and may also be formed to include various other dielectric materials.

[0080] The polarization light separator rotor 82 of one embodiment may have an asymmetric directional coupler structure. The polarization light separator rotor 82 may be configured such that the shape of the first waveguide 140 having input and output ports on both sides is asymmetric, and the shape of the second waveguide having input and output ports on one side and branching from the first waveguide 140 or merging with the first waveguide 140 is symmetrical. In other words, the polarization light separator rotor 82 may set the cross output port to a waveguide of a symmetrical shape. By configuring the polarization light separator rotor 82 in this way, the width of the asymmetric waveguide can be made thicker. For example, the width of the asymmetric waveguide can be 300 nanometers (300nm) or more. As a result, the polarization light separator rotor 82 may have a structure that can be manufactured in a commercial manufacturer. A commercial manufacturer refers to a manufacturer that can mass-produce regardless of the scale.

[0081] The size or shape of the components mass-produced in commercial manufacturing plants has manufacturing tolerances. As a structure for alleviating the manufacturing tolerances, the width of the waveguide can be designed to be symmetrical and not constant. In this way, the component becomes a structure that is robust to the manufacturing tolerances.

[0082] As described above, by using an asymmetric directional coupler structure, it is possible to realize a simple structure of the polarization splitter rotor 82. In addition, the polarization splitter rotor 82 can be manufactured in a commercial manufacturing plant by designing the waveguide width of the symmetrical shape to be non-constant.

[0083] <Configuration example of the splitter 83>

[0084] like Fig.17 As shown in the example, the splitter 83 can be configured to include a cascade delay Mach-Zehnder interferometer (CMZI). The electromagnetic wave input to the splitter 83 includes four wavelength components. Each wavelength is represented by λ1, λ2, λ3 and λ4. In this structural example, the value of each wavelength is as follows.

[0085] λ1=1.27μm

[0086] λ2=1.29μm

[0087] λ3=1.31μm

[0088] λ4=1.33μm

[0089] The splitter 83 can be constructed by using a structure composed of CMZI831-1, CMZI831-2 and CMZI831-3 to separate the electromagnetic wave into two, one of which is output from CMZI831-2 and the other is output from CMZI831-3. Fig.17 In the example of , electromagnetic waves including λ1 and λ3 are output from CMZI 831 - 2 , and electromagnetic waves including λ2 and λ4 are output from CMZI 831 - 3 .

[0090] The splitter 83 can be constructed by using a structure composed of CMZI832-1, CMZI831-3 and CMZI831-4 to separate the electromagnetic wave output from CMZI831-2 into two, one of which is output from CMZI832-3 and the other is output from CMZI832-4. Fig.17 In the example of FIG. 8 , an electromagnetic wave including λ1 is output from CMZI 832 - 3 , and an electromagnetic wave including λ3 is output from CMZI 832 - 4 .

[0091] The splitter 83 can be constructed by combining CMZI832-2, CMZI831-5 and CMZI831-6 to separate the electromagnetic wave output from CMZI831-3 into two, one of which is output from CMZI832-5 and the other from CMZI832-6. Fig.17 In the example of FIG. 8 , an electromagnetic wave including λ2 is output from CMZI 832-6, and an electromagnetic wave including λ4 is output from CMZI 832-5.

[0092] exist Fig.18 The results of actually measuring the loss characteristics of the splitter 83 of this embodiment are shown in FIG. Fig.18 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 graph of the graph), the smaller the loss. In actual measurement, an electromagnetic wave including components with wavelengths of λ1 to λ4 was input to CMZI831-1. The input electromagnetic wave is represented by a thick solid line (Ref). The measured value of the component output from CMZI832-3 is represented by a solid line. The measured value of the component output from CMZI832-4 is represented by a dotted line. The measured value of the component output from CMZI832-5 is represented by a double-dotted line. The measured value of the component output from CMZI832-6 is represented by a dotted line. As shown Fig.18 As shown in the graph of , the components output from each CMZI include many components of each wavelength. That is, in the actual measurement results, the demultiplexer 83 of this embodiment can separate the components of each wavelength of λ1 to λ4.

[0093] <Characteristics of rib waveguide>

[0094] The waveguide of the splitter 83 can be constructed as follows Fig.19A The strip waveguide shown can also be constructed as Fig.19B The rib waveguide shown. The cross-sectional shape of the strip waveguide is rectangular. The cross-sectional shape of the rib waveguide has a convex shape in at least a portion. The waveguide may have: a portion having a convex shape; a portion having a rectangular shape; and a portion connecting the convex shape and the rectangular shape in a smoothly deformed manner.

[0095] The waveguide may have a convex shape in a portion connecting the first element including the polarization light separator rotor 82 or the polarization light separator 822 and the second element including the wavelength combiner / demultiplexer 83 or in a portion connecting the wavelength combiner / demultiplexer in the second element. The waveguide may have: a portion having a convex shape in a portion connecting the first element and the second element or in a portion connecting the wavelength combiner / demultiplexer in the second element; a portion having a rectangular shape; and a portion connecting the convex shape and the rectangular shape in a smoothly deformed manner. The waveguide may have a curved portion in a portion connecting the first element and the second element or in a portion connecting the wavelength combiner / demultiplexer in the second element.

[0096] The waveguides and ports of the wave splitter 83 may be as follows Fig. 20 In addition, each wavelength combining and decomposing element can be configured as shown in the example. Fig.21 The wavelength multiplexing / demultiplexing element comprises: a first waveguide section configured such that two waveguides exist along each other; and a second waveguide section configured such that the two waveguides have different lengths and include a delay line 170. Fig.21 The wavelength multiplexing / demultiplexing element shown in the example has four first waveguide sections and three second waveguide sections between the first waveguide sections. Fig.21 In the figure, the lengths of the four first waveguides are represented by Lc1, Lc2, Lc3 and Lc4. The difference in the length of the one-way waveguides of the two waveguides in each of the three second waveguides is represented by ΔL1, ΔL2 and ΔL3. That is, the difference in the reciprocating lengths of the two waveguides in each of the three second waveguides 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 seven parameters.

[0097] The wavelength multiplexing / demultiplexing element has two waveguides that are physically connected. The two waveguides are electromagnetically coupled in the first waveguide portion. In the case where an electromagnetic wave input to one of the two waveguides is directly output from the same waveguide, the output port is also called a straight-line port. In other words, the wavelength multiplexing / demultiplexing element has an output port on the straight-line side of the directional coupler. The straight-line port is a port that is physically connected from the input port of the electromagnetic wave using a waveguide.

[0098] In the case where the electromagnetic wave input to one of the two waveguides is transferred to the other waveguide and output, 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. A cross port is a port that uses a waveguide to electromagnetically couple from the input port of the electromagnetic wave instead of physically connecting.

[0099] The wavelength combining / decombining / decombining elements connected after the second stage among the plurality of wavelength combining / decombining / decombining elements included in the splitter 83 may have an output port on the straight line side of the directional coupler. In addition, in the case where the first group of the splitter 83 has wavelength combining / decombining / decombining elements connected to the Nth stage and the second group has wavelength combining / decombining / decombining elements connected to the Mth stage, the wavelength combining / decombining / decombining elements connected to the M+1th stage to the M+Nth stage may have an output port on the straight line side of the directional coupler.

[0100] The output to the cross port is sensitive to the manufacturing tolerance of the element. In other words, the output to the cross port is highly sensitive to the manufacturing tolerance of the element. By having the output port on the straight side of the directional coupler by the splitter 83, the influence of the manufacturing tolerance of the element can be reduced. For example, CMZI831-2 can be designed so that one side (one side of CMZI831-2) outputted to the cross port of CMZI831-1 is outputted to the straight port in CMZI831-2.

[0101] exist Fig. 22 The measured results of the losses of TE mode polarized waves and TM mode polarized waves when propagating in the rib waveguide are shown in FIG. Fig. 22 In the curve 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 graph is on the curve), the smaller the loss. Fig. 22 , the loss of the polarized wave of the TE mode traveling in the first waveguide 140 is smaller than the loss of the polarized wave of the TM mode in a wide wavelength range. In other words, the rib type waveguide can transmit the polarized wave of the TM mode in a wide wavelength range while attenuating.

[0102] In the rib waveguide, the loss of polarized waves in the TM mode can be increased. By connecting the splitter 83 using the rib waveguide to the subsequent stage of the polarized light separator rotator 82, it is possible to emit polarized waves in the TM mode that cannot be separated by the polarized light separator rotator 82. By emitting polarized waves in the TM mode by the splitter 83, the extinction ratio can be improved in a wide band. As a result, a wavelength multiplexing optical integrated circuit that does not depend on polarization waves can be realized.

[0103] <Characteristics of the optical integrated circuit 200>

[0104] The characteristics of the optical integrated circuit 200 can be expressed as the connection loss of each component separated by the polarization splitter rotator 82 and the demultiplexer 83. Fig.23 , Fig.24 , Fig.25 and Fig.26 1 shows the characteristics when the polarization wave of the TE mode is separated into components of each wavelength by the demultiplexer 83 connected to the port of the polarization wave outputting the TE mode of the polarization splitter rotor 82 as the actual measurement result. Fig. 27 , Fig.28 , Fig.29 and Fig.30 2 shows the characteristics when the polarization wave of the TM mode is separated into components of each wavelength by the demultiplexer 83 connected to the port of the polarization wave outputting the TM mode of the polarization splitter rotor 82 as the actual measurement result. Figure 23 to Figure 30 In FIG. 8 , the horizontal axis represents wavelength. The unit of wavelength is nm (nanometer). The vertical axis represents insertion loss (Insertion Loss: IL). The unit of insertion loss is dB (decibel). In actual measurement, an electromagnetic wave including a polarized wave of a TE mode and a polarized wave of a TM mode and at least components of each wavelength of λ1 to λ4 is input to the polarization light separator rotor 82.

[0105] exist Fig.23 The TE mode polarization wave component output from the CMZI832-3 of the splitter 83 connected to the port for outputting the TE mode polarization wave of the polarization splitter rotor 82 is shown by a solid line. The TM mode polarization wave component is shown by a dotted line. Fig.24 In FIG. 8 , the polarization wave component of the TE mode output from the CMZI 832-4 of the splitter 83 is represented by a solid line. The polarization wave component of the TM mode is represented by a dotted line. Fig.25 In FIG. 8 , the polarization wave component of the TE mode output from the CMZI 832-5 of the splitter 83 is represented by a solid line. The polarization wave component of the TM mode is represented by a dotted line. Fig.26 In FIG. 8 , the polarization wave component of the TE mode output from the CMZI 832-6 of the splitter 83 is represented by a solid line. The polarization wave component of the TM mode is represented by a dotted line. Figure 23 to Figure 26 The optical integrated circuit 200 can attenuate the polarization wave component of the TM mode and separate the polarization wave component of the TE mode by using the polarization separator rotator 82 .

[0106] exist Fig. 27 In FIG. 8 , the TE mode polarization wave component output from the CMZI832-3 of the splitter 83 connected to the port for outputting the TM mode polarization wave of the polarization splitter rotor 82 is indicated by a solid line. The TM mode polarization wave component is indicated by a dotted line. Fig.28In FIG. 8 , the polarization wave component of the TE mode output from the CMZI 832-4 of the splitter 83 is represented by a solid line. The polarization wave component of the TM mode is represented by a dotted line. Fig.29 In FIG. 8 , the polarization wave component of the TE mode output from the CMZI 832-5 of the splitter 83 is represented by a solid line. The polarization wave component of the TM mode is represented by a dotted line. Fig.30 In FIG. 8 , the TE mode polarization wave component output from the CMZI 832-6 of the splitter 83 is represented by a solid line. The TM mode polarization wave component is represented by a dotted line. Figure 27 to Figure 30 The optical integrated circuit 200 can attenuate the polarization component of the TE mode by using the polarization separator rotator 82 to separate the polarization component of the TM mode.

[0107] <Optical transceiver>

[0108] The optical integrated circuit 200 of this embodiment can be used in an optical transceiver. In other words, the optical transceiver of this embodiment can include the optical integrated circuit 200 of this embodiment.

[0109] (Other Configuration Examples of Optical Integrated Circuit 200)

[0110] like Fig.31 As shown in the example, the optical integrated circuit 200 of one embodiment includes a polarization separator (PS) 822 and a demultiplexer (DEMUX) 83. Fig.31 The optical integrated circuit 200 shown in the example is equivalent to Figure 8 In the illustrated optical integrated circuit 200, the polarization light separator rotor 82 is replaced with a polarization light separator 822. The polarization light separator 822 corresponds to a first element having a function of separating each polarization wave from an electromagnetic wave including a plurality of polarization waves. That is, the optical integrated circuit 200 may include the polarization light separator 822 as a first element, and the polarization light separator 822 has a function of separating each polarization wave from an electromagnetic wave including a plurality of polarization waves. Figure 8 The optical integrated circuit 200 and Fig.31 The optical integrated circuit 200 shown in the example is different in that Figure 8 The polarization separator rotor 82 is replaced by Fig.31 The polarized light separator 822 has the same other structures.

[0111] <Brief Summary>

[0112] As described above, the optical integrated circuit 200 of the present embodiment can emit a polarized wave of the TM mode in a wide wavelength range and attenuate it by means of a rib-type waveguide. As a result, the extinction ratio can be improved in a wide frequency band. In addition, in the optical integrated circuit 200 of the present embodiment, the polarization beam splitter rotor 82 or the polarization beam splitter 822 is cascade-connected with the splitter 83. In this way, the optical transceiver having the optical integrated circuit 200 of the present embodiment can simultaneously realize polarization diversity and wavelength multiplexing that can be manufactured in a standard process of a silicon photonics manufacturing plant.

[0113] In the embodiments of the present disclosure, descriptions are made based on the drawings and embodiments, but it should be noted that those skilled in the art can make various deformations or changes based on the present disclosure. Therefore, it should be noted that these deformations or changes are included in the scope of the present disclosure. For example, the functions included in each structural part, etc. can be reconfigured as long as they are not logically contradictory, and multiple structural parts, etc. can be combined into one, or divided. It should be understood that these are also included in the scope of the present disclosure.

[0114] In the present disclosure, the records of "first" and "second" etc. are identifiers for distinguishing the structure. In the present disclosure, the structures distinguished by the records of "first" and "second" etc. can exchange the numbers in the structure. For example, the first waveguide 140 can exchange the identifiers "first" and "second" with the second waveguide 142. The exchange of identifiers is carried out simultaneously. After the exchange of identifiers, the structure is also distinguished. The identifier can also be deleted. The structure from which the identifier is deleted is distinguished by the figure mark. The order of the structure should not be interpreted solely based on the records of the identifiers of "first" and "second" etc. in the present disclosure, nor can it be used as a basis for the existence of identifiers with small numbers.

[0115] In the present disclosure, the X-axis, Y-axis, and Z-axis are provided for convenience of description and may 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 the various structures of the present disclosure is not limited to an orthogonal relationship.

[0116] In one embodiment, (1) an optical integrated circuit comprises: a first element having a function of separating each polarization wave from an electromagnetic wave including a plurality of polarization waves or a function of rotating at least a portion of the polarization waves after separating each polarization wave from an electromagnetic wave including a plurality of polarization waves; and a second element having a function of separating a plurality of wavelength components contained in the electromagnetic wave into components of each wavelength; the first element and the second element are cascaded.

[0117] (2) In the optical integrated circuit described in (1) above, the first element may include a first waveguide and a second waveguide.

[0118] (3) In the optical integrated circuit described in (2) above, the first waveguide and the second waveguide may be arranged in parallel.

[0119] (4) In the optical integrated circuit described in (2) or (3) above, a cross section of at least one of the first waveguide and the second waveguide may not be line-symmetric.

[0120] (5) In the optical integrated circuit described in any one of (2) to (4) above, the waveguide between the first element and the second element or included in the second element may include a curved portion.

[0121] (6) In the optical integrated circuit described in any one of (2) to (5) above, at least a portion of a waveguide between the first element and the second element or included in the second element may have a convex shape.

[0122] (7) In the optical integrated circuit described in (6) above, the waveguide between the first element and the second element or included in the second element may have: a portion having the convex shape; a portion having a rectangular shape; and a portion connecting the convex shape and the rectangular shape in a manner that is smoothly deformed.

[0123] (8) The optical integrated circuit in any one of (1) to (7) above may include a polarizer inserted between the first element and the second element.

[0124] (9) The optical integrated circuit described in any one of (1) to (8) above can be formed by silicon photonics technology.

[0125] (10) The optical integrated circuit according to any one of (1) to (9) above may include a photodetector.

[0126] In one embodiment, (11) an optical transceiver may include the optical integrated circuit described in any one of (1) to (10) above.

[0127] Description of Reference Numerals

[0128] 1. 200 optical integrated circuit (81: input unit, 811: edge coupler, 812: two-dimensional grating coupler (2DGC), 82: polarization separator rotor (PSR), 822: polarization separator (PS), 83: demultiplexer (DEMUX), 831-1 to 3: CMZI, 832-1 to 6: CMZI, 84: delay, 85: variable optical attenuator (VOA))

[0129] 10 Photodiode

[0130] 50 substrates

[0131] 140 first waveguide (141: asymmetric portion, 143: first port, 144: second port)

[0132] 142 second waveguide (145: third port, 146: first part, 147: second part)

[0133] 150 substrate (151: insulating layer)

[0134] 170 Delay Line

[0135] 210 detection element

Claims

1. An optical integrated circuit, wherein: have: The first element has a function of separating each polarization wave from an electromagnetic wave including a plurality of polarization waves or a function of rotating at least a part of the polarization waves after separating each polarization wave from an electromagnetic wave including a plurality of polarization waves; as well as The second element has a function of separating components of a plurality of wavelengths contained in the electromagnetic wave into components of each wavelength; The first element and the second element are connected in cascade.

2. The optical integrated circuit according to claim 1, wherein: The first element has a first waveguide and a second waveguide.

3. The optical integrated circuit according to claim 2, wherein: The first waveguide and the second waveguide are arranged in parallel.

4. The optical integrated circuit according to claim 2, wherein: A cross section of at least one of the first waveguide and the second waveguide is not line-symmetrical.

5. The optical integrated circuit according to claim 2, wherein: A waveguide between the first element and the second element or included in the second element includes a curved portion.

6. The optical integrated circuit according to claim 2, wherein: The waveguide between the first element and the second element or included in the second element has a convex shape at least in a portion.

7. The optical integrated circuit according to claim 6, wherein: The waveguide between the first element and the second element or included in the second element has: a portion having the convex shape; a portion having a rectangular shape; and a portion connecting the convex shape and the rectangular shape in a smoothly deformed manner.

8. The optical integrated circuit according to any one of claims 1 to 7, wherein: A polarizer is also provided, and the polarizer is inserted between the first element and the second element.

9. The optical integrated circuit according to any one of claims 1 to 7, wherein: The optical integrated circuit is formed by silicon photonics technology.

10. The optical integrated circuit according to any one of claims 1 to 7, wherein: A light detector is provided.

11. An optical transceiver, wherein: A method comprising providing an optical integrated circuit according to any one of claims 1 to 7.

Images