JP2024043454A - Optical integrated circuit and optical receiver - Google Patents

Abstract

To provide an optical integrated circuit that comprises wavelength multiplexing/demultiplexing elements having robustness against manufacturing tolerance, and an optical receiver.SOLUTION: An optical integrated circuit comprises wavelength multiplexing/demultiplexing elements each having a directional coupler and a delay line. The wavelength multiplexing/demultiplexing elements are connected on a plurality of stages in a cascade manner.SELECTED DRAWING: Figure 8

Description

The present disclosure relates to optical integrated circuits and optical receivers.

A wavelength separation element in which Mach-Zehnder interferometers are connected in series is known (for example, see Patent Document 1).

Japanese Patent Application Publication No. 2020-194092

Crosstalk or insertion loss between output ports is an important characteristic of silicon photonics devices. It is required to realize sufficient characteristics of crosstalk or insertion loss on silicon photonics chips.

The present disclosure aims to provide an optical integrated circuit and an optical receiver that include a wavelength multiplexing/demultiplexing element that is robust against manufacturing tolerances.

An optical integrated circuit according to an embodiment of the present disclosure includes a wavelength multiplexing/demultiplexing element having a directional coupler and a delay line, and the wavelength multiplexing/demultiplexing element is cascaded in a plurality of stages.

An optical receiver according to an embodiment of the present disclosure includes the optical integrated circuit.

An optical integrated circuit and an optical receiver according to an embodiment of the present disclosure can provide a wavelength multiplexing/demultiplexing element that is robust against manufacturing tolerances.

FIG. 1 is a block diagram illustrating a configuration example of an optical receiver according to an embodiment. FIG. 2 is a block diagram showing a configuration example of an optical receiver having an edge coupler as an input section. 3 is a block diagram showing an example of the configuration of an optical receiver in the case where a delay device is further provided in the configuration example of FIG. 2. FIG. 4 is a block diagram showing a configuration example of an optical receiver when the polarization splitter rotator in the configuration example of FIG. 3 is replaced with a polarization splitter. FIG. 4 is a block diagram showing a configuration example of an optical receiver when the delay device connected before the photodiode in the configuration example of FIG. 3 is replaced with a variable attenuator. FIG. 6 is a block diagram showing a configuration example of an optical receiver in a case where a delay device is further provided between the variable attenuator connected before the photodiode and the photodiode in the configuration example of FIG. 5; FIG. 2 is a cross-sectional view showing an example of a strip waveguide. FIG. 2 is a cross-sectional view showing an example of a rib-type waveguide. 1 is a block diagram showing an example of the configuration of a duplexer according to an embodiment; 9 is a diagram showing an example of arrangement of interferometers and ports of the duplexer shown in FIG. 8; FIG. FIG. 2 is a diagram showing an example of the arrangement of waveguides of an interferometer. It is a graph which shows an example of the characteristic of the 1st and 3rd element of a 1st group when a strip type waveguide is used. It is a graph which shows an example of the characteristic of the 2nd element of a 1st group when a strip type waveguide is used. 13 is a graph showing an example of characteristics of the first, third and fourth elements of the second group when a strip-type waveguide is used. It is a graph which shows an example of the characteristic of the 2nd, 5th, and 6th element of a 2nd group when a strip type waveguide is used. 11 is a graph showing an example of design values of characteristics of a duplexer when a strip-type waveguide is used. 11 is a graph showing an example of actual measured values of characteristics of a duplexer when a strip-type waveguide is used. It is a graph which shows an example of the characteristic of the 1st and 3rd element of a 1st group when a rib type waveguide is used. 13 is a graph showing an example of the characteristics of the second element of the first group when a rib-type waveguide is used. It is a graph which shows an example of the characteristic of the 1st, 3rd, and 4th element of a 2nd group when a rib type waveguide is used. It is a graph which shows an example of the characteristic of the 2nd, 5th, and 6th element of a 2nd group when a rib type waveguide is used. 7 is a graph showing an example of design values of characteristics of a duplexer when a rib-type waveguide is used. It is a graph which shows an example of the actually measured value of the characteristic of a duplexer when a rib type waveguide is used. FIG. 2 is a diagram illustrating a configuration example of a wavelength multiplexing/demultiplexing element including a resistive element. 11 is a diagram showing an example of the positional relationship between a resistive element and a waveguide; FIG. It is a graph showing an example of wavelength characteristics of a wavelength multiplexing/demultiplexing element using a strip type waveguide. It is a graph showing an example of wavelength characteristics of a wavelength multiplexing/demultiplexing element using a rib type waveguide.

In optical communications within data centers, direct modulation and direct detection methods are widely used because digital signal processors are simple and consume low power. On the other hand, with the increase in optical communication traffic within data centers, higher density data transmission is required, and optical integrated circuits using silicon, especially optical transceivers with compact wavelength-multiplexed optical circuits, are being considered. . Among these, a series Mach-Zehnder type interference system or an arrayed waveguide type grating can be used as a wavelength multiplexing optical circuit realized using silicon. All of these wavelength multiplexing optical circuits are characterized in that their characteristics vary greatly depending on the polarization of light. On the other hand, single-mode optical fibers are widely used in existing optical fiber networks within data centers. However, this optical fiber does not have polarization maintaining characteristics. Therefore, the polarization of the light changes randomly every time the light passes through a bent portion or a connected portion of the wiring. Therefore, in order to make the characteristics of the optical receiver uniform for any polarization, a polarization splitter rotator is installed at the front stage of the optical circuit, and the incident light is divided into TE (Transverse Electric) component and TM (Transverse Magnetic) component. It is necessary to separate them into two parts and input each into separate wavelength multiplexing optical circuits. In the direct modulation direct polarization method, after polarizing the light to either TE or TM, it is necessary to receive the output of the wavelength multiplexing optical circuit with a photodiode and detect the sum of the photodiode outputs corresponding to each polarization component. There is.

The optical receiver 1 (see FIG. 1 etc.) according to an embodiment of the present disclosure may be used in an optical communication system in combination with a configuration for transmitting optical signals. An arrangement for transmitting an optical signal may include a light source and a modulator.

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 devices that emit electromagnetic waves of various wavelengths. The modulator modulates the electromagnetic waves by changing their intensity. The modulator may pulse modulate the electromagnetic waves, for example.

The configuration for transmitting an optical signal may further include a signal input section. The signal input section receives signal input from an external device or the like. The signal input section may include, for example, a D/A converter. The signal input section outputs a signal to the modulator. The modulator modulates the electromagnetic wave based on the signal acquired by the signal input section.

As shown in FIG. 3, the optical receiver 1 is arranged between the polarization splitter rotator 82 and each of the two demultiplexers 83, and between the demultiplexer 83 and each of the n photodiodes 10-1 to n. Additionally, a delay device 84 may be further provided. Delay device 84 delays propagation of the optical signal. The optical receiver 1 uses a delay device 84 to compensate for deviations in the delay of the optical signal caused by manufacturing errors in the waveguide. By including the delay device 84, the optical receiver 1 reduces jitter of the signal output from the photodiode 10, which is a combination of the TE mode optical signal and the TE mode optical signal obtained by converting the TM mode optical signal. can.

For example, the delay device 84 may be configured as a waveguide having a predetermined length, and may be configured to be able to adjust the effective refractive index of the waveguide using a heater. The delay device 84 may be configured as a phase modulator having a predetermined length, and may be configured to be able to adjust the amount of phase modulation by applying a voltage.

As shown in FIG. 4, in the optical receiver 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 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 receiver 1 may include a delay device 84 to compensate for a delay difference between the TE mode optical signal and the TM mode optical signal.

As shown in FIG. 5, the delay device 84 connected between the demultiplexer 83 and each of the n photodiodes 10-1 to 10-n in the optical receiver 1 illustrated in FIG. It may be replaced by a Variable Optical Attenuator (VOA) 85. The variable optical attenuator 85 may include, for example, a silicon pin diode. The variable optical attenuator 85 absorbs light and attenuates the light intensity by injecting a current. By adjusting the current injected into each variable optical attenuator 85, optical loss occurring in the polarization splitter rotator 82 or the demultiplexer 83 can be compensated for. Therefore, even if the optical loss in the polarization splitter rotator 82 or the demultiplexer 83 is not uniform due to the difference in polarization or wavelength of the optical signal, the variable optical attenuator 85 allows the optical signal with a large optical loss to pass through. By decreasing the current value of the variable optical attenuator 85 and increasing the current value of the variable optical attenuator 85 through which the optical signal under the condition of small optical loss passes, the light receiving sensitivity of the optical signal of any polarization or wavelength can be made close to uniform.

As shown in FIG. 6, the optical receiver 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. good.

As described above, the optical receiver 1 according to this embodiment can detect an optical signal by the photodiode 10 configured to reduce returning light. By reducing the returning light, the optical signal returning to the input unit 81 can be reduced. By reducing the optical signal returning to the input unit 81, stable operation of the light source or modulator that transmits the optical signal to the input unit 81 can be maintained. As a result, the reliability of the optical communication system that uses the optical receiver 1 can be improved.

(Example of configuration of optical integrated circuit)
The optical integrated circuit may include a demultiplexer 83. The demultiplexer 83 not only separates an electromagnetic wave containing components of a plurality of wavelengths into components of each wavelength, but also performs wavelength combining to combine each of the components of a plurality of different wavelengths into an electromagnetic wave containing components of a plurality of wavelengths. It may function as a wave element.

The duplexer 83 may be configured to include a directional coupler and a delay line. A directional coupler or delay line includes a waveguide 140. The waveguide 140 may be configured as a strip waveguide, as shown in FIG. 7A, or as a rib waveguide, as shown in FIG. 7B. The cross-sectional shape of the strip waveguide is rectangular. The cross-sectional shape of the rib-type waveguide has a convex shape at least in part.

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

The demultiplexer 83 may be configured to include wavelength multiplexing/demultiplexing elements (Mux) connected in series in multiple stages, as illustrated in FIG. 8 . The duplexer 83 may include a cascade delay Mach-Zehnder interferometer (CMZI). It is assumed that the electromagnetic wave input to port 0 of the demultiplexer 83 includes four wavelength components. It is assumed that each wavelength is expressed as λ1, λ2, λ3, and λ4. In this configuration example, it is assumed that the values of each wavelength are as follows.
λ1=1.27μm
λ2=1.29μm
λ3=1.31μm
λ4=1.33μm

The demultiplexer 83 separates the electromagnetic waves into two by a configuration in which the first element 831-1, the second element 831-2, and the third element 831-3 of the first group are combined, and one is divided into two by the second element 831-3. It may be configured such that one output element is output from one element 831-3 and the other element is output from a third element 831-3. In the example of FIG. 8, the second element 831-2 outputs electromagnetic waves including λ1 and λ3. The third element 831-3 outputs electromagnetic waves including λ2 and λ4.

The splitter 83 may be configured to split the electromagnetic wave output from the second element 831-2 of the first group into two by combining the first element 832-1, the third element 832-3, and the fourth element 832-4 of the second group, and output one of the two from the third element 832-3 and the other from the fourth element 832-4. In the example of FIG. 8, an electromagnetic wave containing λ1 is output from port 4 connected to the output of the third element 832-3. An electromagnetic wave containing λ3 is output from port 5 connected to the output of the fourth element 832-4.

The splitter 83 may be configured to split the electromagnetic wave output from the third element 831-3 of the first group into two by combining the second element 832-2, the fifth element 832-5, and the sixth element 832-6 of the second group, and output one of the two from the fifth element 832-5 and the other from the sixth element 832-6. In the example of FIG. 16, an electromagnetic wave containing λ2 is output from port 7 connected to the output of the sixth element 832-6. An electromagnetic wave containing λ4 is output from port 6 connected to the output of the fifth element 832-5.

In other words, the demultiplexer 83 includes a wavelength multiplexing/demultiplexing element having a directional coupler and a delay line. In the demultiplexer 83, wavelength multiplexing/demultiplexing elements are connected in series in multiple stages. The wavelength multiplexing/demultiplexing elements may be connected in four stages. The wavelength multiplexing/demultiplexing elements constituting the first group of the demultiplexer 83 are also referred to as first composite elements. The wavelength multiplexing/demultiplexing elements constituting the second group of the demultiplexer 83 are also referred to as second composite elements. In the duplexer 83, a first composite element and a second composite element may be connected in series. In the example of FIG. 8, in the first group of the demultiplexer 83, the wavelength multiplexing/demultiplexing elements are connected in cascade in two stages. That is, in the first composite element, the wavelength multiplexing/demultiplexing elements are connected in two stages in cascade. Further, in the second group of the demultiplexer 83, the wavelength multiplexing/demultiplexing elements are connected in two stages in cascade. That is, in the second composite element, the wavelength multiplexing/demultiplexing elements are connected in two stages in cascade. In the first composite element, wavelength multiplexing/demultiplexing elements may be connected in N stages. In the second composite element, wavelength multiplexing/demultiplexing elements may be connected in M stages. N and M are natural numbers.

The waveguides and ports of the duplexer 83 may be arranged as illustrated in FIG. The terminals of the wire pairs shown as ports represent terminations. Further, each wavelength multiplexing/demultiplexing element may be configured as illustrated in FIG. 10. The wavelength multiplexing/demultiplexing element includes a first portion configured such that two waveguides 140 are located along each other, and a delay line 170 such that the two waveguides 140 have different lengths. and a second portion. The wavelength multiplexing/demultiplexing element illustrated in FIG. 10 includes four first parts and three second parts between each of the first parts. In FIG. 10, the lengths of each of the four first portions are represented as Lc1, Lc2, Lc3, and Lc4. The one-way length differences between the two waveguides 140 in each of the three second portions are expressed as ΔL1, ΔL2, and ΔL3. That is, the difference in the round trip length of the two waveguides 140 in each of the three second portions is expressed as ΔL1×2, ΔL2×2, and ΔL3×2. The unit is μm (micrometer). The structure of the wavelength multiplexing/demultiplexing element can be specified by these seven parameters.

The wavelength multiplexer/demultiplexer has two waveguides 140 that are physically connected. The two waveguides 140 are electromagnetically coupled at the first portion. When an electromagnetic wave input to one of the two waveguides 140 is output from the same waveguide 140 as is, the output port is also called a straight port. In other words, the wavelength multiplexer/demultiplexer has an output port on the straight side of the directional coupler. The straight port is a port that is physically connected from the input port of the electromagnetic wave by the waveguide 140.

When an electromagnetic wave input to one of the two waveguides 140 is transferred to the other waveguide 140 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. The cross port is a port that is electromagnetically coupled to the input port of the electromagnetic wave by the waveguide 140 but is not physically connected.

Among the plurality of wavelength multiplexing/demultiplexing elements included in the demultiplexer 83, the wavelength multiplexing/demultiplexing elements connected after the second stage may have an output port on the straight side of the directional coupler. In addition, when the first group of the demultiplexer 83 includes wavelength multiplexing/demultiplexing elements connected to N stages, and the second group includes wavelength multiplexing/demultiplexing elements connected to M stages, the second to N stages The wavelength multiplexing/demultiplexing elements connected up to the second stage or from the N+2th stage to the N+Mth stage may have an output port on the straight side of the directional coupler. That is, the wavelength multiplexing/demultiplexing element that does not branch the output in the demultiplexer 83 may have an output port on the straight side of the directional coupler. On the other hand, the first stage wavelength multiplexing/demultiplexing element of the first group and the N+1 stage wavelength multiplexing/demultiplexing element of the second group that branch the output in the demultiplexer 83 are on the straight side of the directional coupler. It has an output port on both the and cross side.

The output to the crossport is sensitive to device manufacturing tolerances. In other words, the sensitivity of the output to the crossport to device manufacturing tolerances is high. By having the duplexer 83 have an output port on the straight side of the directional coupler, the influence of manufacturing tolerances of the elements can be reduced. For example, in the second element 831-2 of the first group, the side that is output to the cross port of the first element 831-1 of the first group (the side of the second element 831-2) is connected to the second element 831-2. It may be designed to be output to a straight port.

The characteristics of the wavelength multiplexing/demultiplexing element may differ depending on whether the waveguide 140 is a strip-type waveguide or a rib-type waveguide. The characteristics of the wavelength multiplexing/demultiplexing element when the waveguide 140 is a strip waveguide or a rib waveguide will be described below.

<When the waveguide 140 is a strip waveguide>
The first element 831-1 and the third element 831-3 of the first group in FIG. 8 or 9 have the following parameters.
Lc1=40, Lc2=25, Lc3=20, Lc4=10
ΔL1=9.6/2, ΔL2=9.6, ΔL3=9.5

The characteristics of the first element 831-1 and the third element 831-3 of the first group in this case are shown in the graph of Figure 11. In the graph of Figure 11, the horizontal axis represents wavelength. The unit of wavelength is assumed to be nm (nanometers). The vertical axis represents insertion loss. The unit of insertion loss is assumed to be dB (decibels). The larger the value on the vertical axis (the higher the plot on the graph), the smaller the loss. The solid line represents the output of the straight port. The dashed line represents the output of the cross port. The meanings of the vertical and horizontal axes of the graph, and the solid and dashed lines, are assumed to be the same in the following Figures 12 to 14 and Figures 17 to 20.

The second element 831-2 of the first group in FIG.
Lc1=35, Lc2=25, Lc3=25, Lc4=10
ΔL1=9.9/2, ΔL2=9.9, ΔL3=9.8
The characteristics of the second element 831-2 of the first group in this case are shown in the graph of FIG.

The first element 832-1, third element 832-3, and fourth element 832-4 of the second group in FIG. 8 or 9 have the following parameters.
Lc1=35, Lc2=25, Lc3=15, Lc4=5
ΔL1=5.2/2, ΔL2=5.2, ΔL3=5.1
The characteristics of the first element 832-1, third element 832-3, and fourth element 832-4 of the second group in this case are shown in the graph of FIG.

The second element 832-2, fifth element 832-5, and sixth element 832-6 of the second group in FIG. 8 or 9 have the following parameters.
Lc1=35, Lc2=25, Lc3=15, Lc4=5
ΔL1=5.3/2, ΔL2=5.3, ΔL3=5.2
The characteristics of the second element 832-2, fifth element 832-5, and sixth element 832-6 of the second group in this case are shown in the graph of FIG.

In the case where each wavelength multiplexing/demultiplexing element has the above-mentioned characteristics, design values of the output characteristics of ports 4 to 7 of the demultiplexer 83 are shown in FIG. Furthermore, actual measured values of the output characteristics of ports 4 to 7 of the duplexer 83 are shown in FIG. In the graphs of FIGS. 15 and 16, the horizontal axis represents wavelength. It is assumed that the unit of wavelength is nm (nanometer). The vertical axis represents insertion loss. It is assumed that the unit of insertion loss is dB (decibel). Assume that an electromagnetic wave containing components with wavelengths λ1 to λ4 is input to a port of the demultiplexer 83. In FIGS. 15 and 16, the actual measured values of the components output from port 4 are shown by solid lines. The actual measured value of the component output from port 7 is indicated by a broken line. The actual measured value of the component output from port 5 is indicated by a dashed line. The actual measured value of the component output from port 6 is indicated by a two-dot chain line. As shown in the graphs of FIGS. 15 and 16, the components output from each port include many components of each wavelength in both the designed value and the actual measured value. In other words, the actual measurement results also show that the demultiplexer 83 formed of a strip waveguide is able to separate components of each wavelength from λ1 to λ4. As a result, insertion loss characteristics and crosstalk characteristics can be improved.

<When the waveguide 140 is a rib-type waveguide>
The first element 831-1 and the third element 831-3 of the first group in FIG. 8 or 9 have the following parameters.
Lc1=55, Lc2=35, Lc3=30, Lc4=10
ΔL1=10.4/2, ΔL2=10.4, ΔL3=10.3
The characteristics of the first element 831-1 and the third element 831-3 of the first group in this case are shown in the graph of FIG.

The second element 831-2 of the first group in FIG. 8 or 9 has the following parameters.
Lc1=65, Lc2=40, Lc3=30, Lc4=10
ΔL1=10.7/2, ΔL2=10.7, ΔL3=10.5
The characteristics of the second element 831-2 of the first group in this case are shown in the graph of FIG.

The first element 832-1, third element 832-3, and fourth element 832-4 of the second group in FIG. 8 or 9 have the following parameters.
Lc1=55, Lc2=40, Lc3=25, Lc4=10
ΔL1=5.3/2, ΔL2=5.3, ΔL3=5.2
The characteristics of the first element 832-1, third element 832-3, and fourth element 832-4 of the second group in this case are shown in the graph of FIG.

The second element 832-2, the fifth element 832-5 and the sixth element 832-6 of the second group in FIG.
Lc1=50, Lc2=30, Lc3=25, Lc4=15
ΔL1=5.5/2, ΔL2=5.5, ΔL3=5.4
The characteristics of the second element 832-2, the fifth element 832-5 and the sixth element 832-6 of the second group in this case are shown in the graph of FIG.

When each wavelength multiplexing/demultiplexing element has the above-mentioned characteristics, the design values of the output characteristics of ports 4 to 7 of the demultiplexer 83 are shown in FIG. 21. Also, the actual measured values of the output characteristics of ports 4 to 7 of the demultiplexer 83 are shown in FIG. 22. In the graphs of FIG. 21 and FIG. 22, the horizontal axis represents wavelength. The unit of wavelength is assumed to be nm (nanometers). The vertical axis represents insertion loss. The unit of insertion loss is assumed to be dB (decibels). Assume that an electromagnetic wave containing components with wavelengths of λ1 to λ4 is input to the port of the demultiplexer 83. In FIG. 21 and FIG. 22, the actual measured values of the components output from port 4 are shown by solid lines. The actual measured values of the components output from port 7 are shown by dashed lines. The actual measured values of the components output from port 5 are shown by dashed lines. The actual measured values of the components output from port 6 are shown by dashed lines. As shown in the graphs of FIG. 21 and FIG. 22, in both the design values and the actual measured values, the components output from each port contain a large amount of each wavelength component. In other words, in actual measurements, the splitter 83, which is made up of a rib-type waveguide, is able to separate the components of each wavelength λ1 to λ4. As a result, the insertion loss characteristics and crosstalk characteristics can be improved.

<Summary>
As described above, the optical integrated circuit according to this embodiment has wavelength multiplexing/demultiplexing elements connected in series in multiple stages. Sufficient crosstalk can be ensured by cascading multiple stages of wavelength multiplexing/demultiplexing elements. Furthermore, wavelength separation can be achieved with low insertion loss. As a result, insertion loss characteristics and crosstalk characteristics can be improved.

(compensation circuit)
As shown in FIG. 23, the wavelength multiplexing/demultiplexing element may include a waveguide 140 located on a substrate and a resistive element 180. Resistance element 180 is configured to heat waveguide 140 with heat generated by current flowing through resistance element 180, thereby changing the temperature of waveguide 140. Resistive element 180 may be positioned overlying waveguide 140 . As shown in FIG. 24, the resistive element 180 may be positioned so as to overlap at least a portion of the waveguide 140 when the substrate is viewed from above. The resistive element 180 may be located so as not to overlap the waveguide 140 in a plan view of the substrate, as long as the temperature of the waveguide 140 can be changed.

The resistive element 180 may be made of, for example, titanium nitride (TiN). The resistive element 180 is not limited to TiN and may be made of various other conductive materials that are compatible with the process of forming the waveguide 140 on the substrate.

The wavelength multiplexing/demultiplexing element may change the temperature of at least a portion of the waveguide 140 by passing a current through the resistance element 180. By changing the temperature of at least a portion of waveguide 140, the refractive index of at least a portion of waveguide 140 changes. By changing the refractive index of at least a portion of the waveguide 140, the wavelength characteristics of the wavelength multiplexing/demultiplexing element change. Therefore, the wavelength multiplexer/demultiplexer can change the wavelength characteristics of the wavelength multiplexer/demultiplexer by changing the temperature of at least a portion of the waveguide 140. The wavelength characteristics of a wavelength multiplexing/demultiplexing element may vary due to manufacturing tolerances or the influence of the surrounding environment. By including the resistance element 180, the wavelength multiplexing/demultiplexing element can compensate for variations in wavelength characteristics.

Specifically, as shown in FIGS. 25A and 25B, the wavelength characteristics of the wavelength multiplexing/demultiplexing element change depending on the power consumption of the resistive element 180. FIG. 25A shows the wavelength characteristics of the wavelength multiplexing/demultiplexing element when the waveguide 140 of the wavelength multiplexing/demultiplexing element is of a strip type. FIG. 25B shows the wavelength characteristics of the wavelength multiplexing/demultiplexing element when the waveguide 140 of the wavelength multiplexing/demultiplexing element has a rib type. In FIGS. 25A and 25B, 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 graph is plotted), the smaller the loss.

In FIGS. 25A and 25B, the solid line graph represents the wavelength characteristics when the power consumption of the resistive element 180 is 0 mW (milliwatt). In other words, the solid line graph represents the wavelength characteristics when no current is flowing through the resistance element 180. The broken line graph represents wavelength characteristics when the power consumption of the resistive element 180 is 10 mW (milliwatt). The dashed-dotted line graph represents wavelength characteristics when the power consumption of the resistive element 180 is 20 mW (milliwatt). The graph of the two-dot chain line represents the wavelength characteristic when the power consumption of the resistance element 180 is 30 mW (milliwatt). As shown in FIGS. 25A and 25B, the wavelength characteristics of the wavelength multiplexing/demultiplexing element are adjusted according to the power consumption of the resistive element 180. The wavelength multiplexing/demultiplexing element may determine the current to be passed through the resistive element 180 depending on manufacturing tolerances or the surrounding environment.

Although embodiments according to the present disclosure have been described based on various drawings and examples, it should be noted that those skilled in the art can make various modifications or modifications based on the present disclosure. Therefore, it should be noted that these variations or modifications are included within the scope of this disclosure. For example, functions included in each component can be rearranged so as not to be logically contradictory, and a plurality of components can be combined into one or divided. It is to be understood that these are also encompassed within the scope of the present disclosure.

In this disclosure, descriptions such as "first" and "second" are identifiers for distinguishing the configurations. For configurations that are distinguished by descriptions such as “first” and “second” in the present disclosure, the numbers in the configurations can be exchanged. For example, the first element 831-1 can exchange the identifiers "first" and "second" with the second element 831-2. The exchange of identifiers takes place simultaneously. Even after exchanging identifiers, the configurations are distinguished. Identifiers may be removed. Configurations with removed identifiers are distinguished by codes. The description of identifiers such as "first" and "second" in this disclosure should not be used to interpret the order of the configuration or to determine the existence of lower-numbered identifiers.

In the present disclosure, the X-axis, Y-axis, and Z-axis are provided for convenience of explanation, and may be interchanged with each other. Configurations according to the present disclosure have been described using a Cartesian coordinate system comprised of an X-axis, a Y-axis, and a Z-axis. The positional relationship of each component according to the present disclosure is not limited to being in an orthogonal relationship.

In one embodiment, (1) an optical integrated circuit includes a wavelength multiplexing/demultiplexing element having a directional coupler and a delay line, and the wavelength multiplexing/demultiplexing element is cascaded in a plurality of stages.

(2) In the optical integrated circuit according to (1) above, the wavelength multiplexing/demultiplexing elements may be connected in four stages.

(3) In the optical integrated circuit according to (1) or (2) above, the wavelength multiplexing/demultiplexing element connected after the second stage has an output port on the straight side of the directional coupler. You may do so.

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

(5) In the optical integrated circuit according to (4) above, the wavelength multiplexing/demultiplexing elements connected from the second stage to the Nth stage or from the N+2nd stage to the N+Mth stage have the directionality The coupler may have an output port on the straight side.

(6) The optical integrated circuit according to any one of (1) to (5) above may be formed using silicon photonics technology.

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

(8) In the optical integrated circuit described in (7) above, at least a portion of the resistive element may be positioned so as to overlap at least a portion of the waveguide in a plan view of the substrate.

(9) In the optical integrated circuit according to (7) or (8) above, the resistance element may include titanium nitride.

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

1 Optical receiver (81: input section, 82: polarization splitter rotator (PSR), 822: polarization splitter (PS), 83: demultiplexer (DEMUX), 831-1 to 3: 1st to 3rd of the 1st group elements, 832-1 to 6: first to sixth elements of second group, 84: delay device, 85: variable optical attenuator (VOA))
10 photodiode 140 waveguide 150 substrate (151: insulating layer, 152: cladding layer)
170 Delay line 180 Resistance element

Claims (10)

1. An optical integrated circuit comprising a wavelength multiplexing/demultiplexing element having a directional coupler and a delay line, the wavelength multiplexing/demultiplexing element being cascaded in a plurality of stages. The optical integrated circuit according to claim 1, wherein the wavelength multiplexing/demultiplexing elements are connected in four stages. 2. The optical integrated circuit according to claim 1, wherein the wavelength multiplexing/demultiplexing element connected after the second stage has an output port on the straight side of the directional coupler. The optical integrated circuit according to claim 1, in which a first composite element in which the wavelength multiplexing/demultiplexing elements are connected in N stages and a second composite element in which the wavelength multiplexing/demultiplexing elements are connected in M stages are connected in cascade. According to claim 4, the wavelength multiplexing/demultiplexing element connected from the second stage to the Nth stage or from the N+2nd stage to the N+Mth stage has an output port on the straight side of the directional coupler. The optical integrated circuit described. The optical integrated circuit according to any one of claims 1 to 5, formed by silicon photonics technology. Any one of claims 1 to 5, wherein the wavelength multiplexing/demultiplexing element has a waveguide located on a substrate and a resistance element configured to change the temperature of at least a portion of the waveguide. The optical integrated circuit according to item 1. 8. The optical integrated circuit according to claim 7, wherein at least a portion of the resistive element is located so as to overlap at least a portion of the waveguide in a plan view of the substrate. 9. The optical integrated circuit according to claim 8, wherein the resistor element includes titanium nitride. An optical receiver comprising the optical integrated circuit according to any one of claims 1 to 5.

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