Optical integrated circuit, and optical transceiver

Abstract

This optical integrated circuit comprises: a demultiplexer having a plurality of output terminals for dividing an input optical signal into a plurality of optical signals and outputting the optical signals; a plurality of first optical attenuators connected to the plurality of output terminals,respectively; and a second optical attenuator connected in series to at least one of the plurality of first optical attenuators. The plurality of first optical attenuators are configured to be able to dynamically control the attenuation rate in accordance with the intensity of the optical signal inputted from the plurality of output terminals. The second optical attenuator is configured to attenuate the optical signal at a prescribed attenuation rate.

Description

Optical integrated circuit and optical transceiver Cross-reference to related applications

[0001] This application claims priority from Japanese Patent Application No. 2024-64170 (filed April 11, 2024), the entire disclosure of which is incorporated herein by reference.

[0002] The present disclosure relates to optical integrated circuits and optical transceivers.

[0003] As described in Patent Document 1, a transceiver module is known that separates wavelengths of a wavelength-multiplexed signal using a demultiplexer, adjusts the optical intensity using a variable optical attenuator, and separates polarized waves using a polarization separation rotator.

[0004] US Patent Application Publication No. 2018 / 0351684

[0005] An optical integrated circuit according to an embodiment of the present disclosure includes a demultiplexer having a plurality of output terminals for splitting an input optical signal into a plurality of optical signals and outputting the split optical signals, a plurality of first optical attenuators connected to the plurality of output terminals, respectively, and a second optical attenuator connected in series to at least one of the plurality of first optical attenuators. The plurality of first optical attenuators are configured to dynamically control the attenuation rate in accordance with the intensity of the optical signals input from the plurality of output terminals. The second optical attenuator is configured to attenuate the optical signal by a predetermined attenuation rate.

[0006] An optical transceiver according to an embodiment of the present disclosure includes the optical integrated circuit.

[0007] Fig. 1 is a block diagram showing an example of the configuration of an optical integrated circuit having a two-input detection element; Fig. 2 is a block diagram showing an example of the configuration of an optical integrated circuit having a one-input detection element; Fig. 3 is a circuit diagram showing an example of the configuration in which a voltage is applied in parallel to a plurality of variable optical attenuators; Fig. 4 is a circuit diagram showing an example of the configuration in which a current is passed in series to a plurality of variable optical attenuators; Fig. 5 is a cross-sectional view showing an example of the configuration of a variable optical attenuator using a PIN junction;

[0008] Silicon photonics is attracting attention as a way to realize compact optical transceivers. Silicon photonics is a technology that integrates optical signal-related elements, such as optical waveguides, on a silicon substrate. It is known that signal quality in optical transceivers deteriorates when the optical intensity at the receiver is either too strong or too weak. Variable optical attenuators (VOAs) are often used to adjust the signal intensity to an appropriate range.

[0009] Furthermore, in silicon photonics, the waveguiding characteristics of an optical signal may depend on the polarization, wavelength, or mode of light. In an optical transceiver using silicon photonics, for example, if the waveguiding characteristics of an optical signal differ for each component of TE (Transverse Electric) polarization and TM (Transverse Magnetic) polarization, signal quality may deteriorate. As an extreme example, if there is no insertion loss for TE polarization and there is an insertion loss that reduces the intensity of the optical signal to one-tenth of that for TM polarization, the intensity of the optical signal is represented by 1 and 0 for TE polarization and 0.1 and 0 for TM polarization. In other words, the optical signal of TM polarization is inferior to the optical signal of TE polarization. As a result, detection errors of the optical signal in TM polarization increase. Furthermore, the intensity of the optical signal represented by 0.8 and 0.2 for TE polarization is represented by 0.08 and 0.02 for TM polarization. As a result, detection errors of the optical signal in TM polarization further increase.

[0010] Therefore, in order to adjust the signal intensity within an appropriate range regardless of the polarization, wavelength, mode, etc. of the input light, the polarization, wavelength, mode, etc. of the input light may be separated, and the intensity of each separated optical signal may be adjusted by attenuating it. When the optical signal is degraded due to polarization-dependent loss as described above, one possible approach to reducing the degradation of the optical signal is to connect an optical attenuator only to the waveguide that propagates the optical signal with the least loss among the separated optical signals to compensate for the loss. The characteristics of each element implemented in a photonic integrated circuit (PIC) are determined during manufacturing. In other words, the characteristics of each element implemented in the PIC do not change dynamically. Therefore, feedback control of the compensating optical attenuator is not required. In other words, the attenuation rate of the compensating optical attenuator may be determined according to the characteristics of each element after the PIC is manufactured.

[0011] The optical transceiver may be configured to, for example, separate a wavelength-multiplexed optical signal using a wavelength separation element, appropriately adjust the intensity of the optical signal of each wavelength using a VOA, separate the signals by polarization using a polarization splitter rotator (PSR), and detect phase information of the optical signal of each polarization using optical homodyne detection. In such an optical transceiver, the wavelength separation element and the VOA may be realized using bulk optical elements. The PSR and the detector may be realized using a planar lightwave circuit (PLC) and a PIC.

[0012] One possible solution is to miniaturize the entire optical transceiver by using a PIC. However, since the wavelength separation element becomes polarization-dependent when using a PIC, it is possible to separate the wavelengths by adjusting the optical signal intensity using a VOA after polarization separation. However, this approach cannot handle cases where the intensity of each wavelength after wavelength separation differs.

[0013] Hereinafter, an example of the configuration of an optical integrated circuit will be described, which can appropriately adjust the intensity of optical signals after separation by polarization, wavelength, mode, or the like, and reduce the difference in signal level after separation.

[0014] (Configuration Example of Optical Integrated Circuit) The optical integrated circuit is configured to separate an input optical signal and detect the intensity of each separated optical signal. Hereinafter, a configuration example of the optical integrated circuit according to the present disclosure will be described.

[0015] 1 , the optical integrated circuit 1 includes a demultiplexer 10, VOAs 151 and 152, an optical attenuator 161, and a PD (Photo Diode) 17. The demultiplexer 10 includes an edge coupler 11, a PSR 12, DeMUXs (demultiplexers) 131 and 132, and output terminals 141 and 142.

[0016] The edge coupler 11 is configured to receive an input of an optical signal generated by a modulator or the like. The edge coupler 11 is configured to input the optical signal from a chip end face of the optical integrated circuit 1. The edge coupler 11 may be replaced with an input terminal of another type.

[0017] In the optical integrated circuit 1, the optical signal input to the edge coupler 11 is assumed to be an optical signal containing a mixture of TE polarization and TM polarization and a mixture of multiple wavelengths. The optical signal input to the edge coupler 11 is also referred to as an input optical signal. The PSR 12 separates the TE polarization optical signal and the TM polarization optical signal contained in the input optical signal. The PSR 12 may convert the separated TM polarization optical signal into a TE polarization optical signal.

[0018] The DeMUXs 131 and 132 further separate each of the optical signals separated in the PSR 12 into signals of different wavelengths.

[0019] The output terminals 141 and 142 output the optical signals separated by wavelength in the DeMUXs 131 and 132, respectively. Although the number of output terminals 141 is one in Fig. 1 , the output terminal 141 may include multiple terminals corresponding to the multiple optical signals separated by wavelength in the DeMUX 131. Furthermore, although the number of output terminals 142 is one in Fig. 1 , the output terminal 142 may include multiple terminals corresponding to the multiple optical signals separated by wavelength in the DeMUX 132.

[0020] The optical attenuator 161 is connected to the output terminal 141 of the demultiplexer 10, and adjusts the intensity of the optical signal by attenuating the optical signal output from the output terminal 141. The attenuation rate of the optical signal intensity in the optical attenuator 161 is set according to the measurement results of the characteristics of the demultiplexer 10. Although the number of optical attenuators 161 is one in FIG. 1 , if the output terminal 141 includes multiple terminals for each wavelength, the optical attenuator 161 may include multiple optical attenuators connected to each of the multiple terminals.

[0021] 1, optical attenuator 161 is connected only to output terminal 141. An optical attenuator may also be connected to output terminal 142. The attenuation rate of the optical signal by optical attenuator 161 connected to output terminal 141 and the attenuation rate of the optical signal by the optical attenuator connected to output terminal 142 may be the same as or different from each other.

[0022] The VOAs 151 and 152 are variable optical attenuators configured to perform feedback control of the attenuation rate in response to the dynamically changing optical signal strength in order to adjust the optical signal strength to an strength that can be properly detected by the PD 17.

[0023] The VOA 151 is connected to the output terminal 141 of the demultiplexer 10 via the optical attenuator 161, and adjusts the intensity of the optical signal by further attenuating the optical signal that has been output from the output terminal 141 and attenuated by the optical attenuator 161. Although there is only one VOA 151 in Fig. 1, if the output terminal 141 includes multiple terminals for each wavelength, the VOA 151 may include multiple VOAs connected to each of the multiple terminals.

[0024] The VOA 152 is connected to the output terminal 142 of the demultiplexer 10, and adjusts the intensity of the optical signal by attenuating the optical signal output from the output terminal 142. If an optical attenuator is connected to the output terminal 142, the VOA 152 further attenuates the optical signal output from the output terminal 142 and attenuated by the optical attenuator, thereby adjusting the intensity of the optical signal. Although there is only one VOA 152 in FIG. 1 , if the output terminal 142 includes multiple terminals for each wavelength, the VOA 152 may include multiple VOAs connected to each of the multiple terminals.

[0025] The PD 17 is connected to the output terminal 141 of the demultiplexer 10 via the optical attenuator 161 and the VOA 151, and is also connected to the output terminal 142 of the demultiplexer 10 via the VOA 152. The PD 17 has two input terminals, one connected to each of the output terminals 141 and 142. The PD 17 outputs an electrical signal such as a voltage or current corresponding to the combined intensity of the two input optical signals. In other words, the PD 17 is a two-input detecting element that has two input terminals to which two optical signals are input and detects the combined intensity of the two optical signals. Although the number of PD 17 is one in FIG. 1 , if the output terminals 141 and 142 include multiple terminals for each wavelength, the PD 17 may include multiple two-input detecting elements connected to combinations of the terminals for each wavelength of the output terminals 141 and 142.

[0026] When an optical signal in which only the TE polarization has been separated is output from output terminal 141 and an optical signal in which only the TM polarization has been separated is output from output terminal 142, PD 17 outputs an electrical signal corresponding to the combined intensity of the TE polarization optical signal and the TM polarization optical signal. In other words, the optical integrated circuit 1 shown in Figure 1 can essentially detect the intensity of an optical signal in which an optical signal in which TE polarization and TM polarization are mixed, input to edge coupler 11, has been wavelength-separated without polarization separation.

[0027] The optical integrated circuit 1 may further include a transimpedance amplifier (TIA) that converts the electrical signal output from the PD 17 into the intensity of the optical signal detected by the PD 17 .

[0028] As described above, the optical integrated circuit 1 may include a two-input detector element, i.e., the PD 17. The optical integrated circuit 1 including the two-input detector element is configured to output the sum of the intensities of the TE-polarized and TM-polarized components of the optical signal using a single photodiode. As a result, the optical integrated circuit 1 can detect the intensity of the optical signal for each wavelength using a single photodiode. In other words, since only one photodiode is required to detect the optical signal for each wavelength, the parasitic capacitance of the photodiode is reduced compared to when multiple detector elements for detecting each polarization are used. Furthermore, since a single photodiode can output the sum of the intensities of the TE-polarized and TM-polarized components of the optical signal, the optical integrated circuit 1 does not need to include an electrical circuit that detects and adds the intensities of the TE-polarized and TM-polarized components.

[0029] 2, the optical integrated circuit 2 includes a demultiplexer 10, VOAs 151 and 152, an optical attenuator 161, and PDs 171 and 172. The demultiplexer 10 includes an edge coupler 11, a PSR 12, DeMUXes 131 and 132, and output terminals 141 and 142. The demultiplexer 10, the VOAs 151 and 152, and the optical attenuator 161 are the same as those in the optical integrated circuit 1 of FIG. 1. The optical integrated circuit 2 differs from the optical integrated circuit 1 of FIG. 1 in that the PD 17 is replaced with PDs 171 and 172.

[0030] The PD 171 is connected to the output terminal 141 of the demultiplexer 10 via the optical attenuator 161 and the VOA 151. The PD 172 is connected to the output terminal 142 of the demultiplexer 10 via the VOA 152. The PDs 171 and 172 are configured to receive one optical signal and output an electrical signal such as a voltage or current corresponding to the intensity of the input optical signal. In other words, the PDs 171 and 172 are single-input detection elements configured to receive one optical signal and detect the intensity of the single optical signal. Although the number of PDs 171 and 172 is one each in FIG. 2 , if the output terminals 141 and 142 include multiple terminals for each wavelength, the PDs 171 and 172 may each include multiple single-input detection elements connected to terminals for each wavelength of the output terminals 141 and 142.

[0031] The optical integrated circuit 1 may further include a TIA that converts the electrical signal output from PD 171 into the intensity of the optical signal detected by PD 171, and a TIA that converts the electrical signal output from PD 172 into the intensity of the optical signal detected by PD 172. The optical integrated circuit 1 may further include an arithmetic circuit that adds the intensity of the optical signal detected by PD 171 and the intensity of the optical signal detected by PD 172.

[0032] When a TE polarized optical signal is output from output terminal 141, PD 171 outputs an electrical signal corresponding to the intensity of the TE polarized optical signal. When a TM polarized optical signal is output from output terminal 142, PD 172 outputs an electrical signal corresponding to the intensity of the TM polarized optical signal. The TIA converts the electrical signals output from PDs 171 and 172 into the intensities of the TE polarized and TM polarized optical signals, respectively. The arithmetic circuit adds the intensities of the TE polarized optical signal and the TM polarized optical signal. In other words, the optical integrated circuit 2 in FIG. 2 can essentially detect the intensity of an optical signal that has been input to edge coupler 11 and that has undergone wavelength separation only, without performing polarization separation of an optical signal containing a mixture of TE polarized and TM polarized waves.

[0033] As described above, the optical integrated circuit 2 may include one-input detector elements, namely, the PDs 171 and 172 .

[0034] In the optical integrated circuit 1 or 2 described above, the demultiplexer 10 includes a PSR 12 and DeMUXes 131 and 132. That is, the optical integrated circuit 1 or 2 is configured to perform polarization separation and wavelength separation and adjust the intensity of each separated optical signal. The optical integrated circuit 1 or 2 may be configured to perform only polarization separation and adjust the intensity of each separated optical signal. The optical integrated circuit 1 or 2 may be configured to perform only wavelength separation and adjust the intensity of each separated optical signal. The optical integrated circuit 1 or 2 is not limited to polarization separation or wavelength separation, and may also be configured to perform separation according to the propagation mode of the optical signal and adjust the intensity of each separated optical signal.

[0035] The optical integrated circuit 1 or 2 may be formed by silicon photonics technology. By forming the optical integrated circuit 1 or 2 by silicon photonics technology, the optical integrated circuit 1 or 2 can be made smaller.

[0036] <Example of Adjusting Optical Intensity by Combining First Optical Attenuator and Second Optical Attenuator> In either of the optical integrated circuits 1 or 2 described above, the intensity of the optical signal input to PD 17 or PD 171 or 172 needs to be adjusted according to the detection range of PD 17 or PD 171 or 172. The intensity of the optical signal output from output terminal 141 is determined according to the attenuation rate of VOA 151 and the attenuation rate of optical attenuator 161. The intensity of the optical signal output from output terminal 142 is determined according to the attenuation rate of VOA 152. If optical integrated circuit 1 or 2 further includes an optical attenuator connected to output terminal 142, the intensity of the optical signal output from output terminal 142 is determined according to the attenuation rate of VOA 152 and the attenuation rate of the optical attenuator connected to output terminal 142. VOA 151 or 152 is also referred to as a first optical attenuator. The optical attenuator 161 or the optical attenuator connected to the output terminal 142 is also referred to as a second optical attenuator.

[0037] The VOAs 151 and 152, i.e., the first optical attenuators, are configured as variable optical attenuators. The first optical attenuators appropriately adjust the intensities of the optical signals output from the output terminals 141 and 142 by performing dynamic control, i.e., feedback control, in accordance with the intensities of the optical signals output from the output terminals 141 and 142. In other words, the first optical attenuators may be configured to dynamically control the attenuation rate in accordance with the intensities of the optical signals input from the output terminals 141 and 142.

[0038] When an optical signal is split, the insertion losses of the split components may differ. For example, when an optical signal is split into TE polarization and TM polarization, a difference may occur in the insertion losses of the TE polarization and the TM polarization. That is, a difference may occur between the insertion loss of the split optical signal output from output terminal 141 and the insertion loss of the optical signal output from output terminal 142. The difference in insertion losses of the optical signals output from output terminals 141 and 142 may be compensated for by attenuating the optical signal output from output terminal 141. Furthermore, if optical integrated circuit 1 or 2 further includes an optical attenuator connected to output terminal 142, the difference in insertion losses of the optical signals output from output terminals 141 and 142 may be compensated for by attenuating the optical signal output from output terminals 141 and 142. That is, the attenuation factor of the second optical attenuator may be determined according to the difference in insertion losses of the optical signals output from output terminals 141 and 142.

[0039] The second optical attenuator may be configured as a variable optical attenuator. When configured as a variable optical attenuator, the second optical attenuator is controlled to attenuate the optical signal at an attenuation rate corresponding to the difference in insertion loss between the optical signals output from the output terminals 141 and 142.

[0040] The second optical attenuator may be configured to attenuate the optical signal at a predetermined attenuation factor. That is, the second optical attenuator may be configured so that the attenuation factor cannot be dynamically controlled. For example, when the demultiplexer 10 demultiplexes the input optical signal into TE polarization and TM polarization, the second optical attenuator may be designed to attenuate the optical signal at an attenuation factor corresponding to the difference between the design values ​​of the insertion losses of the TE polarization and the TM polarization.

[0041] The actual value of the insertion loss may vary from the design value due to manufacturing errors of the optical integrated circuit 1 or 2. In other words, the actual value of the insertion loss may be determined by measurement after manufacturing the optical integrated circuit 1 or 2. When configured as a variable optical attenuator, the second optical attenuator may be controlled to attenuate the optical signal by an attenuation factor corresponding to the actual value of the insertion loss.

[0042] In the optical integrated circuit 1 including a two-input detecting element, i.e., PD 17, the second optical attenuator may be connected in series to at least one of the two input terminals of the two-input detecting element. By connecting the second optical attenuator to at least one input terminal of PD 17 and determining the attenuation rate of the second optical attenuator according to the insertion loss, the difference in insertion loss between the two optical signals input to PD 17 is compensated for.

[0043] When the second optical attenuator is designed to attenuate an optical signal at a predetermined attenuation factor, the attenuation factor may be adjustable after the manufacture of the optical integrated circuit 1 or 2 so as to attenuate the optical signal at an attenuation factor corresponding to an actual value of the insertion loss measured after the manufacture of the optical integrated circuit 1 or 2. For example, the second optical attenuator may be configured so that the attenuation factor can be changed by trimming a dummy element, such as a dummy waveguide or a dummy resistor, mounted on the optical integrated circuit 1 or 2 after the manufacture of the optical integrated circuit 1 or 2. In this way, errors in the insertion loss caused by manufacturing errors in the optical integrated circuit 1 or 2 can be easily compensated for.

[0044] When the second optical attenuator is designed to attenuate an optical signal by a predetermined attenuation factor, the optical integrated circuit 1 or 2 does not need to include a power supply that controls the attenuation factor of the second optical attenuator, which simplifies the configuration of the optical integrated circuit 1 or 2 compared to when the second optical attenuator is configured as a variable optical attenuator.

[0045] As described above, the optical integrated circuit 1 or 2 can reduce the difference in signal level after demultiplexing by attenuating the optical signals in accordance with the insertion loss of each demultiplexed optical signal.

[0046] <Control of VOAs by a Common Power Supply> In the optical integrated circuit 1 of FIG. 1 or the optical integrated circuit 2 of FIG. 2, the intensity of each wavelength of an input optical signal is detected as the combined intensity of the TE-polarized optical signal and the TM-polarized optical signal at each wavelength. The ratio of TE polarization to TM polarization in the input optical signal is unknown. Therefore, in either the optical integrated circuit 1 of FIG. 1 or the optical integrated circuit 2 of FIG. 2, the attenuation rate of the TE-polarized optical signal and the attenuation rate of the TM-polarized optical signal at a certain wavelength must be made the same so that the combined intensity of the TE-polarized optical signal and the TM-polarized optical signal can ultimately be detected. In other words, the VOAs 151 and 152 are controlled to attenuate optical signals at the same wavelength by the same attenuation rate. When the VOAs 151 and 152 are controlled to attenuate optical signals at the same attenuation rate, the VOAs 151 and 152 do not need to be controlled independently and may be controlled by a common power supply.

[0047] When the attenuation rates of the VOAs 151 and 152 are controlled by voltage, the VOAs 151 and 152 may be electrically connected in parallel between the power supply 20 and the ground point 30 so that a common voltage is applied to them, as illustrated in Fig. 3. The electrical connection illustrated in Fig. 3 may be employed in either the optical integrated circuit 1 of Fig. 1 or the optical integrated circuit 2 of Fig. 2.

[0048] When the attenuation rates of the VOAs 151 and 152 are controlled by current, the VOAs 151 and 152 may be electrically connected in series between the power supply 20 and the ground point 30 so that a common current flows therethrough, as illustrated in Fig. 4. The electrical connection illustrated in Fig. 4 may be employed in either the optical integrated circuit 1 of Fig. 1 or the optical integrated circuit 2 of Fig. 2.

[0049] Here, for example, if an optical signal is separated into TE polarization and TM polarization by polarization separation, and then the optical signals of each polarization are further separated into multiple wavelengths by wavelength separation, the number of types of optical signals after separation increases. If the intensities of all separated optical signals are individually adjusted using VOAs, the number of VOAs that are subject to feedback control increases. In other words, the number of power supplies required to control the VOAs increases. As illustrated in Figure 3 or Figure 4, the VOAs 151 and 152 can be controlled by a common power supply, thereby reducing the number of power supplies. As a result, the optical integrated circuit 1 or 2 can be easily configured.

[0050] The common power supply that controls the VOAs 151 and 152 may be configured to change the voltage or current it outputs in response to the detection result of the optical signal by the PD 17, or the PDs 171 and 172. In other words, the common power supply may be controlled so as to feed back the detection result of the optical signal.

[0051] <VOA Configuration Example> As illustrated in Fig. 5, the VOAs 151 and 152 may be implemented in the optical integrated circuit 1 or 2 as elements using PIN junctions. In Fig. 5, the VOAs 151 and 152 are collectively referred to as VOA 15. The VOA 15 includes a PIN junction in which a P-type region 15P, an I-type region 15I, and an N-type region 15N are joined in the X-axis direction. Each region of the PIN junction extends in the Y-axis direction. The I-type region 15I functions as a waveguide for an optical signal, propagating the optical signal in the Y-axis direction.

[0052] In the VOA 15 having a PIN junction, the carrier concentration in the I-type region 15I correlates with the current flowing through the I-type region 15I. By passing a current through the PIN junction of the VOA 15 from the P-type region 15P to the N-type region 15N, the carrier concentration in the I-type region 15I is controlled based on the correlation between the carrier concentration and the current.

[0053] Furthermore, the loss of an optical signal propagating through the I-type region 15I correlates with the carrier concentration of the I-type region 15I. By controlling the carrier concentration of the I-type region 15I, the loss of an optical signal propagating through the I-type region 15I can be controlled based on the correlation between the loss of the optical signal and the carrier concentration. The loss of an optical signal propagating through the I-type region 15I corresponds to the attenuation rate of the optical signal in the VOA 15.

[0054] From the above, the attenuation factor of the VOA 15 having a PIN junction is controlled by the magnitude of the current flowing through the PIN junction.

[0055] A Mach-Zehnder element can be considered as a VOA according to a comparative example. A Mach-Zehnder element is an element that branches an input optical signal into two, combines the resulting signal into one, and outputs the resulting signal. The optical signal is attenuated by utilizing the phase difference between the optical signals propagating through each of the branched waveguides. The attenuation rate of an optical signal in a Mach-Zehnder element correlates with the square of the cosine value of the difference between the product of the lengths of the branched waveguides and the effective refractive index, divided by the wavelength of the optical signal. The difference between the product of the lengths of the waveguides and the effective refractive index correlates with the power input to a heater installed in one of the branched waveguides. Therefore, the attenuation rate of an optical signal in a Mach-Zehnder element correlates with the square of the cosine value of the power input to the heater divided by the wavelength of the optical signal.

[0056] The attenuation rate of the VOA according to the comparative example described above varies depending on the wavelength of the optical signal. In other words, the attenuation rate of the VOA according to the comparative example is wavelength dependent. On the other hand, the attenuation rate of the VOA 15 having a PIN junction is not wavelength dependent.

[0057] Furthermore, the attenuation factor of the VOA according to the comparative example correlates with the square of the cosine value of the power input to the VOA divided by the wavelength. On the other hand, the attenuation factor of the VOA 15 having a PIN junction correlates with the current flowing through the PIN junction. In other words, the attenuation factor of the VOA 15 having a PIN junction is calculated more easily than that of the VOA according to the comparative example. As a result, the attenuation factor of the VOA 15 is controlled more easily than that of the VOA according to the comparative example.

[0058] (Summary) As described above, the optical integrated circuit 1 or 2 according to the present disclosure can adjust the intensity of each optical signal separated by the demultiplexer 10 and reduce the difference in signal level after separation. Specifically, when an optical signal containing a mixture of TE polarization and TM polarization and a mixture of multiple wavelengths is input, the optical integrated circuit 1 or 2 can separate the polarization-separated optical signal into individual wavelengths and adjust the intensity of the optical signal by attenuating the optical signal while taking into account the polarization dependency of the wavelength separation. Furthermore, the optical integrated circuit 1 or 2 can detect the intensity obtained by adding up the intensities of the polarization-separated optical signals for each wavelength, and function as a polarization-independent optical transceiver.

[0059] As a comparative example, it is possible to detect an optical signal by performing only wavelength separation without performing polarization separation. In this case, optical signal loss occurs at each wavelength depending on the polarization dependency of wavelength separation. As a result, the detection accuracy of the intensity of the optical signal at each wavelength decreases. On the other hand, the optical integrated circuit 1 or 2 according to the present disclosure detects the intensity of the polarization-separated optical signal and adds the intensities of the components of each polarization, so that the intensity of the optical signal at each wavelength can be detected with higher accuracy than the comparative example without being affected by the polarization dependency of wavelength separation.

[0060] The PD 17 in FIG. 1 or the PD 171 or 172 in FIG. 2 may be replaced with another light receiving element such as a phototransistor capable of detecting an optical signal.

[0061] The optical integrated circuit 1 or 2 according to the present disclosure may be used in an optical transceiver, that is, an optical transceiver including the optical integrated circuit 1 or 2 according to the present disclosure may be realized.

[0062] The optical integrated circuit 1 or 2 according to the present disclosure may be used in combination with a configuration for transmitting an optical signal in an optical communication system. The configuration for transmitting an optical signal may include a light source and a modulator.

[0063] The light source may include, for example, a semiconductor laser such as a laser diode (LD) or a vertical cavity surface emitting laser (VCSEL). The light source may include a device that emits electromagnetic waves of various wavelengths, not limited to visible light. The modulator modulates the electromagnetic waves by changing their intensity. The modulator may, for example, pulse-modulate the electromagnetic waves.

[0064] The optical signal transmitting configuration may further include a signal input unit. The signal input unit receives a signal input from an external device or the like. The signal input unit may include, for example, a D / A converter. The signal input unit outputs a signal to a modulator. The modulator modulates an electromagnetic wave based on the signal acquired by the signal input unit.

[0065] Although the embodiments according to the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art could make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications or alterations are included in the scope of the present disclosure. For example, the functions included in each component can be rearranged so as not to be logically inconsistent, and multiple components can be combined into one or divided. It should be understood that these modifications are also included in the scope of the present disclosure.

[0066] In this disclosure, descriptions such as "first" and "second" are identifiers for distinguishing the configuration. In this disclosure, configurations distinguished by descriptions such as "first" and "second" can have their numbers exchanged. For example, the identifiers "first" and "second" of a first optical attenuator and a second optical attenuator can be exchanged. The exchange of identifiers is performed simultaneously. The configurations remain distinguished even after the exchange of identifiers. Identifiers may be deleted. A configuration from which an identifier has been deleted may be distinguished by a symbol. The descriptions of identifiers such as "first" and "second" in this disclosure should not be used solely to interpret the order of the configurations or to justify the existence of an identifier with a smaller number.

[0067] In this disclosure, the X-axis, Y-axis, and Z-axis are provided for convenience of explanation and may be interchanged. The configurations according to this disclosure have been described using an orthogonal coordinate system formed by the X-axis, Y-axis, and Z-axis. The positional relationship between the components according to this disclosure is not limited to an orthogonal relationship.

[0068] In one embodiment, (1) an optical integrated circuit includes a demultiplexer having a plurality of output terminals for splitting an input optical signal into a plurality of optical signals and outputting the split optical signals, a plurality of first optical attenuators connected to the plurality of output terminals, respectively, and a second optical attenuator connected in series to at least one of the plurality of first optical attenuators. The plurality of first optical attenuators are configured to dynamically control the attenuation factor in accordance with the intensity of the optical signals input from the plurality of output terminals. The second optical attenuator is configured to attenuate the optical signal by a predetermined attenuation factor.

[0069] (2) In the optical integrated circuit described in (1) above, the demultiplexer may be a polarization separation rotator.

[0070] (3) The optical integrated circuit according to (1) or (2) above may further include a two-input detection element having two input terminals connected to two output terminals of the plurality of output terminals, respectively, and the second optical attenuator may be connected in series to at least one of the two input terminals.

[0071] (4) In the optical integrated circuit described in any one of (1) to (3) above, the plurality of first optical attenuators may be electrically connected in parallel to the common power supply so as to be applied with a common voltage.

[0072] (5) In the optical integrated circuit described in any one of (1) to (3) above, the plurality of first optical attenuators may be electrically connected in series to the common power source so as to be supplied with a common current.

[0073] (6) The optical integrated circuit according to any one of (1) to (5) above may be formed by silicon photonics technology.

[0074] In one embodiment, (7) an optical transceiver includes an optical integrated circuit according to any one of (1) to (6) above.

[0075] 1, 2 Optical integrated circuit 10 Demultiplexer (11: edge coupler, 12: polarization separation rotator (PSR), 131, 132: wavelength separation element (DeMUX), 141, 142: output terminal) 15, 151, 152 VOA (15P: P region, 15N: N region, 15I: I region) 161, 162 Optical attenuator 17, 171, 172 Photodiode (PD) 20 Power supply 30 Ground point

Claims

1. An optical integrated circuit comprising: a demultiplexer having a plurality of output terminals that splits an input optical signal into a plurality of optical signals and outputs the split signals; a plurality of first optical attenuators connected to the plurality of output terminals, respectively; and a second optical attenuator connected in series to at least one of the plurality of first optical attenuators, wherein the plurality of first optical attenuators are configured to dynamically control the attenuation rate according to the intensity of the optical signals input from the plurality of output terminals, and the second optical attenuator is configured to attenuate the optical signal at a predetermined attenuation rate.

2. The optical integrated circuit according to claim 1, wherein the demultiplexer is a polarization separation rotator.

3. The optical integrated circuit according to claim 1 or 2, further comprising a two-input detection element having two input terminals connected to two output terminals of the plurality of output terminals, respectively, and the second optical attenuator is connected in series to at least one of the two input terminals.

4. An optical integrated circuit according to any one of claims 1 to 3, wherein the plurality of first optical attenuators are electrically connected in parallel to the common power supply so as to be supplied with a common voltage.

5. An optical integrated circuit according to any one of claims 1 to 3, wherein the plurality of first optical attenuators are electrically connected in series to the common power source so as to be supplied with a common current.

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

7. An optical transceiver comprising an optical integrated circuit according to any one of claims 1 to 6.

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