Optical integrated circuits and optical transceivers

Abstract

To provide an optical integrated circuit and an optical transceiver that can execute wavelength separation with good performance on input in which polarized wave is not specified.SOLUTION: An optical integrated circuit 200 comprises: a first element 82 that has a function to separate a plurality of polarized waves from an electromagnetic wave including the polarized waves, or a function to rotate at least part of the plurality of polarized waves after separating the polarized waves from the electromagnetic wave including the polarized waves; and a second element 83 that has a function to separate a plurality of wavelength components included in the electromagnetic wave into respective wavelength components. The first element 82 and the second element 83 are connected in a cascade manner.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present disclosure relates to an optical integrated circuit and an optical transceiver.

Background Art

[0002] A wavelength multiplexing / demultiplexing element capable of expanding the effective wavelength band is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the configuration described in Patent Document 1, the wavelength separation performance is not maintained for an input in which the polarization is not specified. <000确定波长的输入。

[0005] An object of the present disclosure is to provide an optical integrated circuit and an optical transceiver that can perform wavelength separation with good performance for an input in which the polarization is not specified.

Means for Solving the Problems

[0006] An optical integrated circuit according to an embodiment of the present disclosure includes a first element and a second element. The first element has a function of separating each polarization from an electromagnetic wave including a plurality of polarizations, or a function of rotating at least a part of the polarizations after separating each polarization from an electromagnetic wave including a plurality of polarizations. The second element has a function of separating components of a plurality of wavelengths included in an electromagnetic wave into components of each wavelength. The first element and the second element are connected in series.

[0007] An optical transceiver according to an embodiment of the present disclosure may include the optical integrated circuit.

Effects of the Invention

[0008] According to an optical integrated circuit and optical transceiver according to one embodiment of the present disclosure, wavelength separation can be performed with good performance for inputs where polarization is not specified. [Brief explanation of the drawing]

[0009] [Figure 1] Block diagram showing an example configuration of an optical integrated circuit according to one embodiment. [Figure 2] This is a block diagram showing an example configuration of an optical integrated circuit that has an edge coupler as an input. [Figure 3] This block diagram shows an example configuration of an optical integrated circuit that has a two-dimensional grating coupler as its input. [Figure 4] This is a block diagram showing an example configuration of an optical integrated circuit when a delay device is further included in the configuration example shown in Figure 2. [Figure 5] This block diagram shows an example of the configuration of an optical integrated circuit when the polarization splitter rotator is replaced with a polarization splitter in the example configuration shown in Figure 4. [Figure 6] This block diagram shows an example of the configuration of an optical integrated circuit when the delay circuit connected before the photodiode in the example configuration of Figure 4 is replaced with a variable attenuator. [Figure 7] This block diagram shows an example of the configuration of an optical integrated circuit in which a delay element is further provided between the variable attenuator connected before the photodiode and the photodiode, as shown in the example configuration in Figure 6. [Figure 8] Block diagram showing an example configuration of an optical integrated circuit according to one embodiment. [Figure 9] This is a plan view showing an example configuration of a polarization splitter rotator according to one embodiment. [Figure 10] Figure 9 is a cross-sectional view of BB. [Figure 11] Figure 9 is a cross-sectional view of CC. [Figure 12] Figure 9 is a cross-sectional view of the DD. [Figure 13] This is a cross-sectional view of EE in Figure 9. [Figure 14]It is a cross-sectional view taken along the line F-F of FIG. 9. [Figure 15] It is a graph showing an example of a simulation result of the output characteristics of a polarization splitter rotator according to an embodiment. [Figure 16] It is a graph showing an example of a measured result of the output characteristics of a polarization splitter rotator according to an embodiment. [Figure 17] It is a block diagram showing a configuration example of a wavelength demultiplexer according to an embodiment. [Figure 18] It is a graph showing an example of a measured result of the loss characteristics of a wavelength demultiplexer. [Figure 19A] It is a cross-sectional view showing an example of a strip type waveguide. [Figure 19B] It is a cross-sectional view showing an example of a rib type waveguide. [Figure 20] It is a diagram showing an arrangement example of the wavelength multiplexing / demultiplexing element and ports of the wavelength demultiplexer of FIG. 17. [Figure 21] It is a diagram showing an arrangement example of the waveguides of the wavelength multiplexing / demultiplexing element. [Figure 22] It is a graph showing an example of a measured result of the magnitude of the loss of each polarization component of an electromagnetic wave propagating through a rib type waveguide. [Figure 23] It is a graph showing an example of a measured result of the component having a wavelength of λ1 separated by a wavelength demultiplexer for the TE mode polarization separated by a polarization splitter rotator. [Figure 24] It is a graph showing an example of a measured result of the component having a wavelength of λ3 separated by a wavelength demultiplexer for the TE mode polarization separated by a polarization splitter rotator. [Figure 25] It is a graph showing an example of a measured result of the component having a wavelength of λ4 separated by a wavelength demultiplexer for the TE mode polarization separated by a polarization splitter rotator. [Figure 26] It is a graph showing an example of a measured result of the component having a wavelength of λ2 separated by a wavelength demultiplexer for the TE mode polarization separated by a polarization splitter rotator. [Figure 27]This graph shows an example of the measured results of the λ1 wavelength component, which is separated by a demultiplexer after the polarization of the TM mode has been separated by a polarization splitter rotator. [Figure 28] This graph shows an example of the measured results of the λ3 wavelength component, which is separated by a demultiplexer after the polarization of the TM mode has been separated by a polarization splitter rotator. [Figure 29] This graph shows an example of the measured results of the λ4 wavelength component, which is separated by a demultiplexer after the polarization of the TM mode has been separated by a polarization splitter rotator. [Figure 30] This graph shows an example of the measured results of the λ2 wavelength component, which is separated by a demultiplexer after the polarization of the TM mode has been separated by a polarization splitter rotator. [Figure 31] This block diagram shows an example configuration in the optical integrated circuit of Figure 8 where the polarization splitter rotator is replaced with a polarization splitter. [Modes for carrying out the invention]

[0010] In optical communications within data centers, direct modulation and direct detection methods are widely used due to the simplicity and low power consumption of digital signal processors. However, with the increasing traffic in data center optical communications, higher density data transmission is required, leading to the consideration of silicon-based optical integrated circuits, particularly optical transceivers with compact wavelength division multiplexing (WDM) circuits. Among these, series Mach-Zehnder interferometers or array waveguide gratings can be used as WDM circuits realized by silicon. Both of these WDM circuits exhibit characteristics that change significantly depending on the polarization of the light. Meanwhile, existing optical fiber networks in data centers widely utilize single-mode optical fibers. However, these fibers do not possess polarization-maintaining properties. Therefore, the polarization of the light changes randomly each time it passes through a bend or connection in the wiring. Consequently, optical integrated circuits need to be designed so that their characteristics are uniform regardless of the polarization. An optical integrated circuit that exhibits uniform characteristics for any polarization is realized by placing a polarization splitter rotator in front of the optical circuit to separate the incident light into a TE (Transverse Electric) component and a TM (Transverse Magnetic) component, injecting each into separate wavelength division multiplexing (WDM) optical circuits, receiving the output of the WDM optical circuits with a photodiode, and detecting the sum of the outputs of the photodiodes corresponding to each polarization component.

[0011] Furthermore, if the polarization component separation (extinction ratio) is low, wavelengths may not be properly separated. Also, a phenomenon called jitter may occur, where the preceding signal frame and the following signal frame interfere with each other. Therefore, increasing the extinction ratio is required.

[0012] An optical integrated circuit 1 (see Figure 1, etc.) according to one embodiment of this disclosure may be used in combination with a configuration for transmitting optical signals in an optical communication system. The configuration for transmitting optical signals may include a light source and a modulator.

[0013] 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 may include a device that emits electromagnetic waves of various wavelengths, not limited to visible light. The modulator modulates by changing the intensity of the electromagnetic wave. The modulator may, for example, pulse-modulate the electromagnetic wave.

[0014] The configuration for transmitting optical signals may further include a signal input section. The signal input section receives signals from external devices, etc. The signal input section may include, for example, a D / A converter. The signal input section outputs a signal to a modulator. The modulator modulates an electromagnetic wave based on the signal acquired by the signal input section.

[0015] (Example configuration of optical integrated circuit 1) The optical integrated circuit 1 is configured to receive optical signals. Below, an example of the configuration of the optical integrated circuit 1 according to one embodiment of this disclosure will be described.

[0016] As shown in Figure 1, the optical integrated circuit 1 comprises an input section 81, a polarizing splitter rotator (PSR) 82, a demultiplexer (demultiplexer or demux) 83, and a photodiode (PD) 10.

[0017] The input unit 81 is configured to accept the input of an optical signal generated by the modulator, etc., as described above. The polarization splitter rotator 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 a TE mode optical signal. The demultiplexer 83 separates the TE mode optical signal separated by the polarization splitter rotator 82, and the TE mode optical signal converted from the TM mode optical signal separated by the polarization splitter rotator 82, for each wavelength. In Figure 1, the demultiplexer 83 is configured to separate the optical signal into n types of wavelengths represented by λ1 to λn.

[0018] The photodiode 10 includes photodiodes 10-1 to 10-n corresponding to light of each wavelength. Each photodiode 10 is connected to a demultiplexer 83 that separates the TE mode optical signal by wavelength and another demultiplexer 83 that separates the TE mode optical signal obtained by converting the TM mode optical signal by wavelength. The polarization components of the TE mode or TM mode may be detected by separate photodiodes 10 or by a single photodiode 10.

[0019] (Example configuration of optical integrated circuit 1) As shown in Figure 2, the optical integrated circuit 1 may be configured using a photodiode 10 having input ports located in two directions. The optical integrated circuit 1 includes an edge coupler 811 as an input section 81. The edge coupler 811 is configured to receive light from the chip end face. The optical integrated circuit 1 further includes a polarization splitter rotator (PSR) 82 and a demultiplexer (DEMUX) 83. In the optical integrated circuit 1, the circuit that processes the optical signal before inputting it to the photodiode 10 is collectively referred to as the optical circuit. The optical circuit separates the optical signal input to the optical integrated circuit 1 into an optical signal propagating in TE mode and an optical signal propagating in TM mode. In the optical integrated circuit 1 according to this embodiment, the optical signal propagating in TE mode is associated with the first optical signal. The optical signal propagating in TM mode is associated with the second optical signal.

[0020] In the optical integrated circuit 1, the edge coupler 811 receives an optical signal in which TE mode and TM mode optical signals are mixed, and which has n wavelengths mixed. The polarization splitter rotator 82 separates the TE mode optical signal from the TM mode optical signal. The polarization splitter rotator 82 also converts the TM mode optical signal into a TE mode optical signal. The demultiplexer 83 further separates each of the optical signals separated by the polarization splitter rotator 82 into n wavelengths.

[0021] Each of the photodiodes 10-1 to n receives input from a signal obtained by separating the TE mode optical signal by wavelength, and from a signal obtained by converting the TM mode optical signal to a TE mode optical signal and then separating it by wavelength. 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 wavelength of the optical signal containing both TE mode and TM mode input to the edge coupler 811.

[0022] The optical integrated circuit 1 according to this embodiment may further include a transimpedance amplifier that converts the electrical signal output from the photodiode 10. Compared to the case in which two photodetectors are used to detect the TE mode optical signal and the TM mode optical signal for each wavelength, the optical integrated circuit 1 according to this embodiment can detect the optical signal with one photodiode for each wavelength. This can be done to achieve higher speed by reducing parasitic capacitance, or to reduce power consumption and circuit size.

[0023] As shown in Figure 3, the optical integrated circuit 1 may include a two-dimensional grating coupler (2DGC) 812 as the input section 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 with TE mode polarization. The demultiplexer 83 separates the optical signals of each polarization component by wavelength. Each of the photodiodes 10-1 to 10-n is input with the signal obtained by separating the optical signal of polarization component Px by wavelength, and the signal obtained by separating the optical signal of polarization component Py by wavelength. As a result, the photodiodes 10-1 to 10-n output an electrical signal corresponding to the intensity of the signal obtained by separating the optical signal, which is a mixture of TE mode and TM mode input to the two-dimensional grating coupler 812, by wavelength. When the optical integrated circuit 1 includes a two-dimensional grating coupler 812, it does not need to include a polarization splitter rotator 82.

[0024] As shown in Figure 4, the optical integrated circuit 1 may further include delays 84 between the polarization splitter rotator 82 and each of the two demultiplexers 83, and between the demultiplexers 83 and each of the n photodiodes 10-1 to n. The delays 84 delay the propagation of the optical signal. The optical integrated circuit 1 compensates for the delay in the optical signal caused by manufacturing errors in the waveguide using the delays 84. By including the delays 84, the optical integrated circuit 1 can reduce the jitter of the combined signal, which consists of the TE mode optical signal output from the photodiode 10 and the TE mode optical signal converted from the TM mode optical signal.

[0025] The delay element 84 may be configured, for example, as a waveguide having a predetermined length, and the effective refractive index of the waveguide may be adjustable by a heater. The delay element 84 may be configured as a phase modulator having a predetermined length, and the amount of phase modulation may be adjustable by applying a voltage.

[0026] As shown in Figure 5, in the optical integrated circuit 1, the polarization splitter rotator 82 may be replaced with a polarization splitter (PS) 822. The polarization splitter 822 separates the input optical signal into an optical signal in TE mode and an optical signal in TM mode. The propagation speeds of the optical signal in TE mode and the optical signal in TM mode are different from each other. The optical integrated circuit 1 may be equipped with a delay device 84 to compensate for the delay difference between the optical signal in TE mode and the optical signal in TM mode.

[0027] As shown in Figure 6, the delay units 84 connected between the demultiplexer 83 and each of the n photodiodes 10-1 to n in the optical integrated circuit 1 illustrated in Figure 2 may be replaced with variable optical attenuators (VOAs) 85. The variable optical attenuators 85 may be configured to include, for example, silicon pin diodes. The variable optical attenuators 85 absorb light and reduce the light intensity by injecting current. By adjusting the current injected into each variable optical attenuator 85, optical loss occurring in the polarization splitter rotator 82 or demultiplexer 83 can be compensated. Therefore, even if the optical loss in the polarization splitter rotator 82 or demultiplexer 83 is not uniform due to differences in the polarization or wavelength of the optical signal, the photoreception sensitivity of an optical signal of any polarization or wavelength can be made more uniform by reducing the current value of the variable optical attenuator 85 through which an optical signal with high optical loss passes, and increasing the current value of the variable optical attenuator 85 through which an optical signal with low optical loss passes.

[0028] As shown in Figure 7, the optical integrated circuit 1 may also include both a variable optical attenuator 85 and a delayer 84 between the demultiplexer 83 and each of the n photodiodes 10-1 to n.

[0029] (Example configuration of optical integrated circuit 200) An optical integrated circuit 200 according to one embodiment includes a polarization splitter rotator (PSR) 82 and a demultiplexer (DEMUX) 83, as illustrated in Figure 8. The polarization splitter rotator 82 may be replaced with a polarization splitter 822, as will be described later. The optical integrated circuit 200 is connected between the input section 81 and the detection element 210. The detection element 210 is assumed to include a VOA 85 and a PD 10. The detection element 210 may be configured to include a PD 10 but not a VOA 85. The optical integrated circuit 200 may further include a PD 10 (photodetector). The polarization splitter rotator 82 or polarization splitter 822 is also referred to as the first element. The demultiplexer 83 is also referred to as the second element. In other words, the optical integrated circuit 200 includes a first element having the function of separating each polarization from an electromagnetic wave containing multiple polarizations, or the function of rotating at least some of the polarizations after separating each polarization from an electromagnetic wave containing multiple polarizations. The optical integrated circuit 200 also includes a second element having the function of separating the multiple wavelength components contained in the electromagnetic wave into components of each wavelength. In the optical integrated circuit 200, the first element and the second element are connected in cascading order. The optical integrated circuit 200 may further include a polarizer inserted between the first element and the second element. The polarizer is an element that transmits linearly polarized light in a specific direction.

[0030] The input unit 81 receives electromagnetic waves containing TE mode polarization and TM mode polarization. The polarization splitter rotator 82 separates the electromagnetic waves input to the input unit 81 into TE mode polarization and TM mode polarization, rotates the TM mode polarization to TE mode polarization, and outputs it to the demultiplexer 83. If the optical integrated circuit 200 includes a polarization splitter 822, the polarization splitter 822 separates the electromagnetic waves input to the input unit 81 into TE mode polarization and TM mode polarization and outputs them to the demultiplexer 83. The demultiplexer 83 separates each polarization containing components of multiple wavelengths into components of each wavelength and outputs them to the detection element 210. The detection element 210 detects each wavelength component of the TE mode polarization and each wavelength component of the TM mode polarization (or the TM mode polarization obtained by rotating the separated TM mode polarization).

[0031] <Example configuration of Polarizing Splitter Rotator 82> As illustrated in Figure 9, and Figures 10, 11, 12, 13, and 14, a polarization splitter rotator 82 according to one embodiment comprises 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. The first waveguide 140 and the second waveguide 142 extend in a first direction (Z-axis direction) in at least a portion of each. At least a portion of the first waveguide 140 and at least a portion of the second waveguide 142 may be positioned parallel to each other.

[0032] The first waveguide 140 has an asymmetric portion 141, which is asymmetric in a cross-section normalized to the first direction (Z-axis direction), as illustrated in Figures 11, 12, and 13. Furthermore, the first waveguide 140 is not symmetric with respect to the normal of the surface of the substrate 50 in a cross-section normalized to the first direction. In this 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. At least one of the cross-sectional shapes of the first waveguide 140 or the second waveguide 142 may be asymmetric.

[0033] The first waveguide 140 has a first port 143 at the end on the negative side of the Z-axis and a second port 144 at the end on the positive side of the Z-axis, that is, the end opposite to the first port 143.

[0034] The second waveguide 142 has a first portion 146 located along the first waveguide 140 and a second portion 147 that moves away from the first waveguide 140 as it progresses in the positive Z-axis direction. The second portion 147 may be configured as a curved section or as a straight section inclined with respect to the direction in which the first waveguide 140 extends. The second portion 147 is located on the positive Z-axis side of the first portion 146. The second portion 147 has a third port 145 at the end opposite to the side connected to the first portion 146.

[0035] The first port 143 of the first waveguide 140 may be configured to accept electromagnetic waves as input. The second port 144 may be configured to output electromagnetic waves. The third port 145 of the second waveguide 142 may be configured to output electromagnetic waves. Electromagnetic waves input to the first port 143 propagate through the first waveguide 140 in the positive Z-axis direction. At least a portion of the electromagnetic waves propagating through the first waveguide 140 transfers to the second waveguide 142. Electromagnetic waves remaining in the first waveguide 140 propagate to the second port 144 and are output from the second port 144. Electromagnetic waves that have transferred to the second waveguide 142 propagate to the third port 145 and are output from the third port 145.

[0036] The second port 144 of the first waveguide 140 may be configured to accept electromagnetic waves as input. The third port 145 of the second waveguide 142 may be configured to accept electromagnetic waves as input. The first port 143 of the first waveguide 140 may be configured to output electromagnetic waves. Electromagnetic waves input to the second port 144 propagate through the first waveguide 140 in the negative Z-axis direction. Meanwhile, electromagnetic waves input to the third port 145 propagate through the first part 146 of the second waveguide 142 in the negative Z-axis direction and then transfer to the first waveguide 140. As a result, in the first waveguide 140, a composite electromagnetic wave, a combination of the electromagnetic waves input to the second port 144 and the electromagnetic waves input to the third port 145, propagates in the negative Z-axis direction. The composite electromagnetic wave propagates to the first port 143 and is output from the first port 143.

[0037] Here, the first waveguide 140 and the second waveguide 142 may be configured such that, when an electromagnetic wave containing a first polarization and a second polarization is input to the first port 143, they separate the polarizations and output the first polarization from the second port 144 and the second polarization from the third port 145. Conversely, the first waveguide 140 and the second waveguide 142 may be configured such that, when an electromagnetic wave with the first polarization is input to the second port 144 and an electromagnetic wave with the second polarization is input to the third port 145, they output an electromagnetic wave with the polarizations combined from the first port 143. The above configuration can be realized, for example, by appropriately designing the shape of the asymmetric portion 141 of the first waveguide 140, or the length or spacing of the portion where the first waveguide 140 and the second waveguide 142 are aligned along each other. In this embodiment, the first polarization is assumed to be the polarization of the TE mode. The second polarization is assumed to be the polarization of the TM mode.

[0038] Figure 15 shows the results of a simulation of the characteristics of the polarization splitter rotator 82 according to this embodiment. In the graph of Figure 15, the horizontal axis represents wavelength. The unit of wavelength is nm (nanometer). The vertical axis represents insertion loss (IL). The unit of insertion loss is dB (decibels). In the simulation, an electromagnetic wave containing TE mode polarization and TM mode polarization is input to the first port 143. The TE mode polarization component output from the second port 144 is shown by a dashed line. The TM mode polarization component output from the second port 144 is shown by a double dashed line. The TE mode polarization component output from the third port 145 is shown by a solid line. The TM mode polarization component output from the third port 145 is shown by a dashed line. As shown in the graph of Figure 15, the electromagnetic wave output from the second port 144 contains a large amount of TE mode polarization. The electromagnetic waves output from the third port 145 contain a large amount of TM mode polarization. In other words, according to the simulation, the polarization splitter rotator 82 according to this embodiment is able to separate TE mode polarization from TM mode polarization.

[0039] Figure 16 shows the results of actual measurements of the characteristics of the polarization splitter rotator 82 according to this embodiment. In the graph of Figure 16, the horizontal axis represents wavelength. The unit of wavelength is nm (nanometer). The vertical axis represents insertion loss (IL). The unit of insertion loss is dB (decibels). For the actual measurement, an electromagnetic wave containing TE mode polarization and TM mode polarization was input to the first port 143. The measured value of the TE mode polarization component output from the second port 144 is shown by a dashed line. The measured value of the TM mode polarization component output from the second port 144 is shown by a double dashed line. The measured value of the TE mode polarization component output from the third port 145 is shown by a solid line. The measured value of the TM mode polarization component output from the third port 145 is shown by a dashed line. As shown in the graph of Figure 16, the electromagnetic wave output from the second port 144 contains a large amount of TE mode polarization. The electromagnetic waves output from the third port 145 contain a large amount of TM mode polarization. In other words, the measured results also show that the polarization splitter rotator 82 according to this embodiment is able to separate TE mode polarization from TM mode polarization.

[0040] The polarization splitter rotator 82 according to this 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 located side by side along a first direction (the Z-axis direction in Figure 8). The first waveguide 140 may have a first port 143 configured to allow input or output of electromagnetic waves including a first polarization (e.g., TE mode polarization) and a second polarization (e.g., TM mode polarization), and a second port 144 configured to allow output of a separated first polarization or input of a first polarization. The second waveguide 142 may have a third port 145 configured to allow output of a separated second polarization or a separated and rotated second polarization, or input of a second polarization. The cross-sectional shape of at least one of the first waveguide 140 or the second waveguide 142, with respect to the first direction (the Z-axis direction in Figure 8), does not have to be symmetrical. Furthermore, the cross-sectional shape of the first waveguide 140, with respect to the first direction (the Z-axis direction in Figure 8), may be asymmetrical.

[0041] The first portion 146 of the second waveguide 142 may be configured such that the line width is not constant. The first portion 146 may be configured in a tapered shape, for example, becoming narrower on the side of the first port 143 and wider on the side connecting to the second portion 147. The first portion 146 may be configured as an adiabatic tapered waveguide. The second waveguide 142 may be configured to rotate the polarization of the TM mode separated from the first waveguide 140 and output it as TE mode polarization from the third port 145.

[0042] The first waveguide 140 and the second waveguide 142 may be formed containing silicon. Furthermore, the first waveguide 140 and the second waveguide 142 may be formed on a silicon substrate 150. By forming the waveguides with silicon, the device including the polarization splitter rotator 82 can be easily manufactured using silicon photonics techniques. The first waveguide 140 and the second waveguide 142 may be formed containing various other dielectric materials, not limited to silicon.

[0043] A polarization splitter rotator 82 according to one embodiment may have an asymmetric directional coupler structure. The polarization splitter rotator 82 may be configured such that the shape of the first waveguide 140, which has input / output ports on both sides, is asymmetric, and the shape of the second waveguide, which has input / output ports on one side and branches off from or merges with the first waveguide 140, is symmetric. In other words, the polarization splitter rotator 82 may have a symmetric waveguide for the cross-output port. By configuring the polarization splitter rotator 82 in this way, the width of the asymmetric waveguide can be increased. For example, the width of the asymmetric waveguide can be 300 nanometers (300 nm) or more. As a result, the polarization splitter rotator 82 may have a structure that can be manufactured in a commercial foundry. A commercial foundry may mean a foundry capable of mass production regardless of scale.

[0044] The dimensions and shapes of components mass-produced in commercial foundries are subject to manufacturing tolerances. To mitigate these tolerances, the waveguide width of a symmetrical component may be designed to be non-constant. This makes the component more robust to manufacturing tolerances.

[0045] As described above, a simple polarization splitter rotator 82 can be realized by using an asymmetric directional coupler structure. Furthermore, by designing the polarization splitter rotator 82 so that the waveguide width of the symmetric shape is not constant, it can be manufactured in a commercial foundry.

[0046] <Example configuration of the splitter 83> The demultiplexer 83 may be configured to include a cascade-delayed Mach-Zehnder interferometer (CMZI), as illustrated in Figure 17. Assume that the electromagnetic wave input to the demultiplexer 83 contains four wavelength components. These wavelengths are denoted as λ1, λ2, λ3, and λ4. In this configuration example, the values ​​of each wavelength are as follows: λ1 = 1.27 μm λ² = 1.29 μm λ3 = 1.31 μm λ4 = 1.33 μm

[0047] The demultiplexer 83 may be configured to separate the electromagnetic wave into two by combining CMZI831-1, CMZI831-2, and CMZI831-3, outputting one from CMZI831-2 and the other from CMZI831-3. In the example in Figure 17, an electromagnetic wave containing λ1 and λ3 is output from CMZI831-2. An electromagnetic wave containing λ2 and λ4 is output from CMZI831-3.

[0048] The demultiplexer 83 may be configured to separate the electromagnetic wave output from CMZI831-2 into two by a combination of CMZI832-1, CMZI831-3, and CMZI831-4, outputting one from CMZI832-3 and the other from CMZI832-4. In the example in Figure 17, an electromagnetic wave containing λ1 is output from CMZI832-3, and an electromagnetic wave containing λ3 is output from CMZI832-4.

[0049] The demultiplexer 83 may be configured to separate the electromagnetic wave output from CMZI831-3 into two by a combination of CMZI832-2, CMZI831-5, and CMZI831-6, outputting one from CMZI832-5 and the other from CMZI832-6. In the example in Figure 17, an electromagnetic wave containing λ2 is output from CMZI832-6, and an electromagnetic wave containing λ4 is output from CMZI832-5.

[0050] Figure 18 shows the measured loss characteristics of the demultiplexer 83 according to this embodiment. In the graph of Figure 18, 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 on the vertical axis (the higher the plot on the graph), the smaller the loss. For the measurement, electromagnetic waves containing components with wavelengths of λ1 to λ4 were input to CMZI831-1. The input electromagnetic waves are represented by a thick solid line (Ref). The measured values ​​of the components output from CMZI832-3 are shown by a solid line. The measured values ​​of the components output from CMZI832-4 are shown by a dashed line. The measured values ​​of the components output from CMZI832-5 are shown by a double-dashed line. The measured values ​​of the components output from CMZI832-6 are shown by a dashed line. As shown in the graph in Figure 18, the components output from each CMZI contain a large amount of components at each wavelength. In other words, the measured results also show that the demultiplexer 83 according to this embodiment is able to separate the components at each wavelength from λ1 to λ4.

[0051] <Characteristics of ribbed waveguides> The waveguide of the decoupler 83 may be configured as a strip-type waveguide as shown in Figure 19A, or as a rib-type waveguide as shown in Figure 19B. The cross-sectional shape of the strip-type waveguide is rectangular. The cross-sectional shape of the rib-type waveguide has a convex shape in at least part of it. 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 way that smoothly deforms them.

[0052] The waveguide may have a convex shape in the portion connecting the first element, which includes a polarization splitter rotator 82 or polarization splitter 822, and the second element, which includes a demultiplexer 83, or in the portion within the second element where wavelength multiplexing and demultiplexing elements are connected. The waveguide may have a convex shape, a rectangular shape, and a portion connecting the convex shape and the rectangular shape in the portion connecting the first element and the second element, or in the portion within the second element where wavelength multiplexing and demultiplexing elements are connected. The waveguide may have a curved portion in the portion connecting the first element and the second element, or in the portion within the second element where wavelength multiplexing and demultiplexing elements are connected.

[0053] The waveguides and ports of the decoupler 83 may be arranged as illustrated in Figure 20. Each wavelength multiplexing / decoupler may be configured as illustrated in Figure 21. The wavelength multiplexing / decoupler comprises a first waveguide configured such that two waveguides are aligned parallel to each other, and a second waveguide configured with a delay line 170 such that the two waveguides have different lengths. The wavelength multiplexing / decoupler illustrated in Figure 21 comprises four first waveguides and three second waveguides between each first waveguide. In Figure 21, the lengths of the four first waveguides are represented as Lc1, Lc2, Lc3, and Lc4. The difference in the one-way lengths of the two waveguides in each of the three second waveguides is represented as ΔL1, ΔL2, and ΔL3. That is, the difference in the round-trip lengths of the two waveguides in each of the three second waveguides is represented as ΔL1×2, ΔL2×2, and ΔL3×2. The unit is assumed to be μm (micrometer). The structure of a wavelength multiplexing / demultiplexing device can be determined by these seven parameters.

[0054] A wavelength multiplexing / demultiplexing element has two physically connected waveguides. The two waveguides are electromagnetically coupled in the first waveguide. When an electromagnetic wave input to one of the two waveguides is output from the same waveguide, that output port is also called a straight port. In other words, a wavelength multiplexing / demultiplexing element has its output port on the straight side of a directional coupler. A straight port is a port that is physically connected to the electromagnetic wave input port by a waveguide.

[0055] When an electromagnetic wave input to one of two waveguides is transferred to the other waveguide and output, that output port is also called a cross port. In other words, a wavelength multiplexing / demultiplexing device has an output port on the cross side of a directional coupler. A cross port is a port that is electromagnetically coupled to the input port of an electromagnetic wave by the waveguide, but is not physically connected.

[0056] Among the multiple wavelength multiplexing / demultiplexing elements included in the demultiplexer 83, the wavelength multiplexing / demultiplexing elements connected from the second stage onward may have an output port on the straight side of the directional coupler. Furthermore, if the first group of the demultiplexer 83 includes wavelength multiplexing / demultiplexing elements connected to the N stage, and the second group includes wavelength multiplexing / demultiplexing elements connected to the M stage, the wavelength multiplexing / demultiplexing elements connected from the M+1 stage to the M+N stage may have an output port on the straight side of the directional coupler.

[0057] The output to the cross port is sensitive to the manufacturing tolerances of the elements. In other words, the output to the cross port is highly sensitive to the manufacturing tolerances of the elements. The effect of the manufacturing tolerances of the elements can be reduced by having the demultiplexer 83 have its output port on the straight side of the directional coupler. For example, the CMZI831-2 may be designed so that the side of the CMZI831-1 that outputs to the cross port (the side of the CMZI831-2) outputs to the straight port in the CMZI831-2.

[0058] Figure 22 shows the measured magnitude of the loss when TE mode polarization and TM mode polarization propagate through a rib-type waveguide. In the graph in Figure 22, the horizontal axis represents wavelength. The unit of wavelength is nm (nanometers). The vertical axis represents power. The unit of power is dBm (decibel-milliwatts). The larger the value on the vertical axis (the higher the plot on the graph), the smaller the loss. According to Figure 22, the loss of TE mode polarization propagating through the first waveguide 140 is smaller than the loss of TM mode polarization over a wide wavelength range. In other words, the rib-type waveguide can radiate and attenuate TM mode polarization over a wide wavelength range.

[0059] In a rib-type waveguide, polarization loss of the TM mode can be significant. By connecting a demultiplexer 83 using a rib-type waveguide downstream of a polarization splitter rotator 82, the polarization of the TM mode that could not be separated by the polarization splitter rotator 82 can be radiated. By radiating the polarization of the TM mode through the demultiplexer 83, a high extinction ratio can be achieved over a wide bandwidth. As a result, a polarization-independent wavelength division multiplexing optical integrated circuit can be realized.

[0060] <Characteristics of Optical Integrated Circuit 200> 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. Figures 23, 24, 25, and 26 show the measured characteristics when the TE mode polarization is separated into components of each wavelength by the demultiplexer 83 connected to the port of the polarization splitter rotator 82 that outputs the TE mode polarization. Figures 27, 28, 29, and 30 show the measured characteristics when the TM mode polarization is separated into components of each wavelength by the demultiplexer 83 connected to the port of the polarization splitter rotator 82 that outputs the TM mode polarization. In Figures 23 to 30, the horizontal axis represents wavelength. The unit of wavelength is nm (nanometer). The vertical axis represents insertion loss (IL). The unit of insertion loss is dB (decibels). For the actual measurement, it is assumed that the polarization splitter rotator 82 is input to an electromagnetic wave that includes polarization in TE mode and polarization in TM mode, and that includes components of at least each wavelength from λ1 to λ4.

[0061] In Figure 23, the TE mode polarization component output from CMZI832-3 of the decoupler 83, which is connected to the port of the polarization splitter rotator 82 that outputs the TE mode polarization, is shown by a solid line. The TM mode polarization component is shown by a dashed line. In Figure 24, the TE mode polarization component output from CMZI832-4 of the decoupler 83 is shown by a solid line. The TM mode polarization component is shown by a dashed line. In Figure 25, the TE mode polarization component output from CMZI832-5 of the decoupler 83 is shown by a solid line. The TM mode polarization component is shown by a dashed line. In Figure 26, the TE mode polarization component output from CMZI832-6 of the decoupler 83 is shown by a solid line. The TM mode polarization component is shown by a dashed line. As shown in Figures 23 to 26, the optical integrated circuit 200 is able to separate the polarization component of the TE mode by attenuating the polarization component of the TM mode with the polarization splitter rotator 82.

[0062] In Figure 27, the TE mode polarization component output from CMZI832-3 of the decoupler 83, which is connected to the port of the polarization splitter rotator 82 that outputs the TM mode polarization, is shown by a solid line. The TM mode polarization component is shown by a dashed line. In Figure 28, the TE mode polarization component output from CMZI832-4 of the decoupler 83 is shown by a solid line. The TM mode polarization component is shown by a dashed line. In Figure 29, the TE mode polarization component output from CMZI832-5 of the decoupler 83 is shown by a solid line. The TM mode polarization component is shown by a dashed line. In Figure 30, the TE mode polarization component output from CMZI832-6 of the decoupler 83 is shown by a solid line. The TM mode polarization component is shown by a dashed line. As shown in Figures 27 to 30, the optical integrated circuit 200 is able to separate the polarization component of the TM mode by attenuating the polarization component of the TE mode with the polarization splitter rotator 82.

[0063] <Optical Transceiver> The optical integrated circuit 200 according to this embodiment may be used in an optical transceiver. In other words, the optical transceiver according to this embodiment may include the optical integrated circuit 200 according to this embodiment.

[0064] (Other configuration examples of the optical integrated circuit 200) An optical integrated circuit 200 according to one embodiment includes a polarization splitter (PS) 822 and a demultiplexer (DEMUX) 83, as illustrated in Figure 31. The optical integrated circuit 200 illustrated in Figure 31 corresponds to the optical integrated circuit 200 illustrated in Figure 8 in which the polarization splitter rotator 82 is replaced by a polarization splitter 822. The polarization splitter 822 corresponds to a first element that has the function of separating each polarization from an electromagnetic wave containing multiple polarizations. In other words, the optical integrated circuit 200 may include a polarization splitter 822 as the first element, which has the function of separating each polarization from an electromagnetic wave containing multiple polarizations. The optical integrated circuit 200 illustrated in Figure 8 and the optical integrated circuit 200 illustrated in Figure 31 differ only in that the polarization splitter rotator 82 in Figure 8 is replaced by the polarization splitter 822 in Figure 31; otherwise, they are the same in their configuration.

[0065] <Summary> As described above, the optical integrated circuit 200 according to this embodiment can radiate and attenuate TM mode polarization over a wide wavelength range using a rib-type waveguide. As a result, the extinction ratio can be improved over a wide bandwidth. Furthermore, in the optical integrated circuit 200 according to this embodiment, the polarization splitter rotator 82 or polarization splitter 822 and the demultiplexer 83 are connected in cascading order. In this way, an optical transceiver equipped with the optical integrated circuit 200 according to this embodiment can simultaneously achieve polarization diversity and wavelength division multiplexing, which can be fabricated using standard processes at silicon photonics foundries.

[0066] While embodiments relating to this disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can make various modifications or alterations based on this disclosure. Therefore, it should be noted that these modifications or alterations are included within the scope of this disclosure. For example, the functions included in each component can be rearranged in a logically consistent manner, and multiple components can be combined into one or separated. These are also to be understood as being included within the scope of this disclosure.

[0067] In this disclosure, the terms "First," "Second," etc., are identifiers used to distinguish the configurations. Configurations distinguished by the terms "First," "Second," etc., in this disclosure may have their numbers swapped. For example, the first waveguide 140 and the second waveguide 142 may swap the identifiers "First" and "Second." The identifier swapping occurs simultaneously. The configurations remain distinguishable even after the identifier swapping. Identifiers may be deleted. Configurations from which identifiers have been deleted are distinguished by codes. The terms "First," "Second," etc., in this disclosure should not be used alone to interpret the order of the configurations or to justify the existence of smaller numbered identifiers.

[0068] In this disclosure, the X, Y, and Z axes are provided for explanatory purposes and may be interchanged. The configurations relating to this disclosure have been described using a Cartesian coordinate system composed of the X, Y, and Z axes. The positional relationships of the configurations relating to this disclosure are not limited to being orthogonal.

[0069] In one embodiment, (1) the optical integrated circuit includes a first element having the function of separating each polarization from an electromagnetic wave containing multiple polarizations, or the function of rotating at least some of the polarizations after separating each polarization from an electromagnetic wave containing multiple polarizations, and a second element having the function of separating the multiple wavelength components contained in the electromagnetic wave into individual wavelength components, wherein the first element and the second element are connected in series.

[0070] (2) In the optical integrated circuit described in (1) above, the first element may have a first waveguide and a second waveguide.

[0071] (3) In the optical integrated circuit described in (2) above, the first waveguide and the second waveguide may be located parallel to each other.

[0072] (4) In the optical integrated circuit described in (2) or (3) above, the cross-section of at least one of the first waveguide and the second waveguide does not have to be symmetrical.

[0073] (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 the waveguide included in the second element, may include a curved portion.

[0074] (6) In the optical integrated circuit described in any one of (2) to (5) above, the waveguide between the first element and the second element, or the waveguide included in the second element, may have a convex shape in at least a part of it.

[0075] (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 a convex shape, a portion having a rectangular shape, and a portion connecting the convex shape and the rectangular shape in such a way that they are smoothly deformed.

[0076] (8) The optical integrated circuit described in any one of (1) to (7) above may include a polarizer inserted between the first element and the second element.

[0077] (9) The optical integrated circuit described in any one of (1) to (8) above may be formed by silicon photonics technology.

[0078] (10) The optical integrated circuit described in any one of (1) to (9) above may be equipped with a photodetector.

[0079] In one embodiment, the (11) optical transceiver may include the optical integrated circuit described in any one of (1) to (10) above. [Explanation of Symbols]

[0080] 1. 200 Optical integrated circuits (81: Input section, 811: Edge coupler, 812: Two-dimensional grating coupler (2DGC), 82: Polarization splitter rotator (PSR), 822: Polarization splitter (PS), 83: Demultiplexer (DEMUX), 831-1~3: CMZI, 832-1~6: CMZI, 84: Delay unit, 85: Variable optical attenuator (VOA)) 10 Photodiodes 50 circuit boards 140 First waveguide (141: asymmetrical portion, 143: first port, 144: second port) 142 Second waveguide (145: Third port, 146: First section, 147: Second section) 150 substrate (151: insulating layer) 170 Delay Line 210 detection elements

Claims

1. The device comprises a first element having the function of separating each polarization from an electromagnetic wave containing multiple polarizations, or the function of rotating at least some of the polarizations after separating each polarization from an electromagnetic wave containing multiple polarizations, and a second element having the function of separating components of multiple wavelengths contained in an electromagnetic wave into components of each wavelength. The first element has a first waveguide and a second waveguide, The second waveguide is tapered in at least a portion of the circuit, such that the track width is not constant. An optical integrated circuit in which the first element and the second element are connected in cascading order.

2. The optical integrated circuit according to claim 1, wherein the second waveguide is configured as an adiabatic tapered waveguide in at least a portion of it.

3. The optical integrated circuit according to claim 1, wherein the first waveguide and the second waveguide are located parallel to each other.

4. The optical integrated circuit according to claim 1, wherein the cross-section of at least one of the first waveguide and the second waveguide is not symmetrical.

5. The optical integrated circuit according to claim 1, wherein the waveguide between the first element and the second element, or the waveguide included in the second element, includes a curved portion.

6. The optical integrated circuit according to claim 1, wherein the waveguide between the first element and the second element, or the waveguide included in the second element, has a convex shape in at least a portion of it.

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 a convex shape, a portion having a rectangular shape, and a portion connecting the convex shape and the rectangular shape in such a way that they are smoothly deformed.

8. The optical integrated circuit according to any one of claims 1 to 7, comprising a polarizer inserted between the first element and the second element.

9. An optical integrated circuit according to any one of claims 1 to 7, formed by silicon photonics technology.

10. An optical integrated circuit according to any one of claims 1 to 7, comprising a photodetector.

11. An optical transceiver comprising an optical integrated circuit according to any one of claims 1 to 7.

Images