Optical transceiver

Abstract

A first polarization splitter (101) splits, into first light which has a first wavelength and which is first polarized light perpendicular to a fast axis and second light which has a second wavelength that is different from the first wavelength and which is second polarized light perpendicular to a slow axis, optical source light in which the first light and the second light are combined. The optical source light is input via a first optical fiber (121). A first polarization rotator (102) changes, by 90°, the direction of the vibration plane of the first light which has been obtained through split by the first polarization splitter (101) and thus turns the first light into the second polarized light. A first power splitter (103) branches the first light that has been turned into the second polarized light by the first polarization rotator (102).

Description

Optical Transceiver

[0001] The present invention relates to an optical transceiver.

[0002] The explosive growth in network traffic accompanying the spread of the Internet and mobile networks has led to a continuous increase in the speed and capacity of optical fiber transmission. Optical transport networks, which have been expanding their capacity in this context, have achieved 100 Gbit / s transmission systems, using digital coherent technology (Non-Patent Document 1). This technology achieves an expansion in transmission capacity by, for example, multiplexing two polarized lights for transmission.

[0003] In an optical transceiver used in this type of optical transport network, light source light from an external light source is input to an optical front end 300 shown in FIG. 2 via an optical fiber 321, and the light source light is split by a power splitter 301. One of the light source lights split by the power splitter 301 is split by a polarization splitter 302 into a component perpendicular to the fast axis (first polarization) and a component perpendicular to the slow axis (second polarization). The first polarized light source light split by the polarization splitter 302 has its vibration plane changed by 90° by a polarization rotator 303 to become a second polarized light, and is input to a first transmission circuit 304. The second polarized light source light split by the polarization splitter 302 is input directly to a second transmission circuit 305.

[0004] The first transmission circuit 304, which has received the light source light whose vibration plane has been changed by 90° to become the second polarization, converts the first transmission electrical signal input to the first transmission circuit 304 into an optical signal and outputs a first transmission optical signal. The first transmission optical signal of the second polarization output from the first transmission circuit 304 has the vibration plane changed by 90° by the polarization rotator 306 and is input to the polarization coupler 307.

[0005] Furthermore, the second transmission circuit 305, which has received the second polarized light source light, converts the second transmission electrical signal received in the second transmission circuit 305 into an optical signal and outputs a second transmission optical signal. The second transmission optical signal of the second polarized light output from the second transmission circuit 305 is input to the polarization coupler 307. The first transmission optical signal, whose vibration plane has been changed by 90° to become the first polarization, and the second transmission optical signal of the second polarized light are multiplexed by the polarization coupler 307 and output via the optical fiber 322.

[0006] Each transmission circuit can include a quadrature modulator (IQ modulator), a driver for driving the quadrature modulator, and the like.

[0007] Furthermore, the other light source light split by the power splitter 301 is split into first and second polarized light by the polarization splitter 312. The first polarized light source light split by the polarization splitter 312 has the direction of the vibration plane changed by 90° by the polarization rotator 313 to become second polarized light and is input to the first receiving circuit 314. The second polarized light source light split by the polarization splitter 312 is input to the second receiving circuit 315 as is.

[0008] Furthermore, a received optical signal in a state in which the first received optical signal of the first polarization and the second received optical signal of the second polarization are multiplexed is input via the optical fiber 323 and is split into the first received optical signal of the first polarization and the second received optical signal of the second polarization by the polarization splitter 317. The first received optical signal of the first polarization split by the polarization splitter 317 has its vibration plane orientation changed by 90° by the polarization rotator 316 and is received by the first receiving circuit 314. The second received optical signal of the second polarization split by the polarization splitter 317 is received by the second receiving circuit 315 as is.

[0009] The second polarized light source light input to the first receiving circuit 314 is mixed with the second polarized first received optical signal received by the first receiving circuit 314, and is converted into a first received electrical signal and output from the first receiving circuit 314.

[0010] In addition, the second polarized light source light input to the second receiving circuit 315 is mixed with the second polarized second received optical signal received by the second receiving circuit 315, and is converted into a second received electrical signal and output from the second receiving circuit 315.

[0011] Each receiving circuit can be configured from a coherent mixer that mixes the light source light and the received optical signal, a photodiode, and a TIA (Trans Impedance Amplifier) ​​that converts the output signal of the photodiode into a voltage signal.

[0012] Furthermore, in the core network, optical signals from each local network are concentrated, but signals of the same wavelength cannot be transmitted over a single optical link. This problem can be solved by using light of different wavelengths for transmission and reception. However, in this case, as shown in Figure 3, an optical fiber 321a for transmission and an optical fiber 321b for reception are used to capture light from an external light source in the optical front end 300'. Note that in this case, a power splitter is not used.

[0013] Yusuke Nasu and Shogo Yamanaka, "Special Feature: IOWN Initiative - Photonics-Electronics Convergence Technology for Realizing an All-Photonics Network - Development of Photonics-Electronics Converged Optical Transceiver Module Using Silicon Photonics Technology," NTT Journal, August 2020, pp. 10-14.

[0014] However, in the above-mentioned technology, when light of different wavelengths is used for transmission and reception, the number of optical fibers increases, which increases costs.

[0015] The present invention has been made to solve the above problems, and has as its object to suppress an increase in the number of optical fibers and to use light of different wavelengths for transmission and reception.

[0016] The optical transceiver according to the present invention includes a first polarization splitter that splits light from a light source into the first light and the second light, the light being a first light with a first wavelength and a first polarization perpendicular to a fast axis and a second light with a second wavelength different from the first wavelength and a second polarization perpendicular to a slow axis; a first polarization rotator that changes the direction of the vibration plane of the first light split by the first polarization splitter by 90° to make it a second polarization; a first power splitter that splits the first light that has been made the second polarization by the first polarization rotator; a first transmission circuit that receives one of the first lights split by the first power splitter, converts a first transmission electrical signal into an optical signal, and outputs a first transmission optical signal; a second transmission circuit that receives the other of the first lights split by the first power splitter, converts a second transmission electrical signal into an optical signal, and outputs a second transmission optical signal; a second polarization rotator that changes the direction of the vibration plane of the second-polarized first transmission optical signal output from the first transmission circuit by 90° to make it a first polarization; the first transmission optical signal that has been made first polarized by the second polarization rotator; a polarization coupler that multiplexes the first and second transmission optical signals to generate an optical transmission signal of a first wavelength; a second power splitter that splits the second light split by the first polarization splitter; a second polarization splitter that splits an optical reception signal, which is a combination of a first reception optical signal of a first wavelength polarized and a second reception optical signal of a second wavelength polarized, into a first reception optical signal and a second reception optical signal; and a third polarization rotator that changes the direction of the vibration plane of the first reception optical signal split by the second polarization splitter by 90° to generate a second polarization. a first receiving circuit that receives as input one of the second lights split by the second power splitter and the first received optical signal that has been converted to the second polarization by the third polarization rotator, mixes the input second light with the first received optical signal, converts it into a first received electrical signal, and outputs it; and a second receiving circuit that receives as input the other of the second light split by the second power splitter and the second received optical signal that has been demultiplexed by the second polarization splitter, mixes the input second light with the second received optical signal, converts it into a second received electrical signal, and outputs it.

[0017] As described above, according to the present invention, the first polarization splitter multiplexes light from a first light of a first wavelength that is polarized perpendicular to the fast axis and light from a second light of a second wavelength that is polarized perpendicular to the slow axis and is different from the first wavelength, and splits the combined light into the first light and the second light. This allows the light source light to be input through a single optical fiber, suppressing an increase in the number of optical fibers and enabling light of different wavelengths to be used for transmission and reception.

[0018] Fig. 1 is a block diagram showing the configuration of an optical transceiver according to an embodiment of the present invention, Fig. 2 is a block diagram showing the configuration of a conventional optical transceiver, and Fig. 3 is a block diagram showing the configuration of a conventional optical transceiver.

[0019] An optical transceiver according to an embodiment of the present invention will now be described with reference to Fig. 1. This optical transceiver includes an optical front end 100, which includes a first polarization splitter 101, a first polarization rotator 102, a first power splitter 103, a first transmission circuit 104, a second transmission circuit 105, a second polarization rotator 106, a polarization coupler 107, a second power splitter 113, a second polarization splitter 117, a third polarization rotator 116, a first reception circuit 114, and a second reception circuit 115.

[0020] The first polarization splitter 101 splits light source light, which is a combination of a first light having a first wavelength and a first polarization perpendicular to the fast axis and a second light having a second wavelength different from the first wavelength and a second polarization perpendicular to the slow axis, into the first light and the second light. The light source light is input via a first optical fiber 121. The first optical fiber 121 may be a polarization-maintaining optical fiber.

[0021] The first polarization rotator 102 changes the direction of the vibration plane of the first light split by the first polarization splitter 101 by 90° to make it a second polarized light. The first power splitter 103 splits the first light that has been made into the second polarized light by the first polarization rotator 102.

[0022] The first transmission circuit 104 receives the first light, one of the first light beams split by the first power splitter 103, converts the first transmission electrical signal into an optical signal, and outputs a first transmission optical signal. The second transmission circuit 105 receives the other first light beam split by the first power splitter 103, converts the second transmission electrical signal into an optical signal, and outputs a second transmission optical signal. Each transmission circuit may include an IQ modulator, a driver for driving the IQ modulator, and the like.

[0023] The second polarization rotator 106 changes the direction of the vibration plane of the first transmission optical signal of the second polarization output from the first transmission circuit 104 by 90° to convert it to the first polarization. The polarization coupler 107 combines the first transmission optical signal, which has been converted to the first polarization by the second polarization rotator 106, with the second transmission optical signal to generate an optical transmission signal of the first wavelength. The optical transmission signal is output to the second optical fiber 122.

[0024] The second power splitter 113 branches the second light separated by the first polarization splitter 101. The second polarization splitter 117 separates an optical reception signal, which is a combination of a first reception optical signal with a first wavelength and a first polarization and a second reception optical signal with a second wavelength, into a first reception optical signal and a second reception optical signal. The optical reception signal is input via a third optical fiber 123. The third polarization rotator 116 changes the direction of the vibration plane of the first reception optical signal separated by the second polarization splitter 117 by 90° to obtain the second polarization.

[0025] The first receiving circuit 114 first inputs one of the second lights split by the second power splitter 113 and the first received optical signal that has been converted to the second polarization by the third polarization rotator 116, mixes the input second light and the first received optical signal, converts it into a first received electrical signal, and outputs it.

[0026] The second receiving circuit 115 first inputs the other second light split by the second power splitter 113 and the second received optical signal separated by the second polarization splitter 117, mixes the input second light and the second received optical signal, converts it into a second received electrical signal, and outputs it.

[0027] As described above, according to the embodiment, first light and second light, each having a different wavelength, can be input as light source light using only the first optical fiber 121, so that an increase in the number of optical fibers can be suppressed and light of different wavelengths can be used for transmission and reception.

[0028] Next, the operation of the optical transceiver according to the embodiment will be described. A light source light, which is a combination of a first light having a first wavelength and a first polarization perpendicular to the fast axis and a second light having a second wavelength different from the first wavelength and a second polarization perpendicular to the slow axis, is input via a first optical fiber 121. The input light source light wave is split into a first light and a second light by a first polarization splitter 101.

[0029] The first light split by the first polarization splitter 101 is converted into second polarized light by changing the direction of the vibration plane by 90° in the first polarization rotator 102. The first light converted into second polarized light is split by the first power splitter 103.

[0030] One of the first light beams (second polarization state) split by the first power splitter 103 is input to the first transmission circuit 104. The first transmission circuit 104 receives the first light beam of the second polarization as a light source, converts a first transmission electrical signal input from an electrical circuit (not shown) into an optical signal, and outputs the optical signal as a first transmission optical signal. The first transmission optical signal of the second polarization output from the first transmission circuit 104 has the direction of the vibration plane changed by 90° by the second polarization rotator 106 to become the first polarization.

[0031] The other first light (second polarization state) split by the first power splitter 103 is input to the second transmission circuit 105. The second transmission circuit 105, which receives the first light of the second polarization as a light source, converts a second transmission electrical signal input from an electrical circuit (not shown) into an optical signal and outputs it as a second transmission optical signal.

[0032] The first transmitted optical signal having the first polarization and the second transmitted optical signal having the second polarization are combined by the polarization coupler 107 to form an optical transmitted signal having the first wavelength, which is output to the second optical fiber 122.

[0033] On the other hand, the second light separated by the first polarization splitter 101 is branched by the second power splitter 113. An optical reception signal obtained by combining a first reception optical signal of a first wavelength and a first polarization with a second reception optical signal of a second wavelength and a second polarization is input via a third optical fiber 123. The input optical reception signal is branched by the second polarization splitter 117 into the first reception optical signal and the second reception optical signal.

[0034] The first received optical signal split by the second polarization splitter 117 has the direction of the vibration plane changed by 90° by the third polarization rotator 116 to become a second polarized light. This second polarized first received optical signal and one of the second lights split by the second power splitter 113 are input to the first receiving circuit 114. The first receiving circuit 114 mixes the input second light and the first received optical signal, converts them into a first received electrical signal, and outputs it to an electrical circuit (not shown).

[0035] The other second light split by the second power splitter 113 and the second received optical signal split by the second polarization splitter 117 are input to the second receiving circuit 115. The second receiving circuit 115 mixes the input second light and the second received optical signal, converts them into a second received electrical signal, and outputs it to an electrical circuit (not shown).

[0036] As described above, according to the present invention, a first polarization splitter multiplexes light from a first light having a first wavelength and a first polarization perpendicular to the fast axis and a second light having a second wavelength different from the first wavelength and a second polarization perpendicular to the slow axis, and then demultiplexes the light into the first light and the second light. This allows the light source light to be input into a single optical fiber, thereby suppressing an increase in the number of optical fibers and enabling the use of light of different wavelengths for transmission and reception. Furthermore, compared to a case in which a wavelength filter is used to separate two wavelengths from an external light source, the present invention does not require a control mechanism for controlling the wavelengths to be output to each of the two output ports, and does not require power to operate the control mechanism, resulting in low power consumption.

[0037] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0038] 101...first polarization splitter, 102...first polarization rotator, 103...first power splitter, 104...first transmission circuit, 105...second transmission circuit, 106...second polarization rotator, 107...polarization coupler, 113...second power splitter, 114...first receiving circuit, 115...second receiving circuit, 116...third polarization rotator, 117...second polarization splitter, 121...first optical fiber, 122...second optical fiber, 123...third optical fiber.

Claims

1. a first polarization splitter that splits light from a light source into the first light and the second light, the first light being a first polarization perpendicular to a fast axis and a second light being a second polarization perpendicular to a slow axis and a second wavelength different from the first wavelength; a first polarization rotator that changes the direction of the vibration plane of the first light split by the first polarization splitter by 90° to make it the second polarization; a first power splitter that splits the first light that has been made the second polarization by the first polarization rotator; a first transmission circuit that receives one of the first lights split by the first power splitter, converts a first transmission electrical signal into an optical signal, and outputs a first transmission optical signal; and a second transmission circuit that receives the other of the first light split by the first power splitter, converts a second transmission electrical signal into an optical signal, and outputs a second transmission optical signal. a second polarization rotator that changes the direction of the vibration plane of the first transmission optical signal of the second polarization output from the first transmission circuit by 90° to obtain the first polarization; a polarization coupler that combines the first transmission optical signal and the second transmission optical signal that have been converted to the first polarization by the second polarization rotator to obtain an optical transmission signal of the first wavelength; a second power splitter that splits the second light that has been split by the first polarization splitter; a second polarization splitter that splits an optical reception signal that is a combination of the first reception optical signal of the first wavelength that has been converted to the first polarization and the second reception optical signal of the second wavelength that has been converted to the second polarization, into the first reception optical signal and the second reception optical signal; a third polarization rotator that changes the direction of the vibration plane of the first reception optical signal that has been split by the second polarization splitter by 90° to obtain the second polarization; an optical transceiver comprising: a first receiving circuit that receives as input one of the second light split by the second power splitter and the first received optical signal that has been converted to the second polarization by the third polarization rotator, mixes the input second light and the first received optical signal, converts it into a first received electrical signal, and outputs it; and a second receiving circuit that receives as input the other of the second light split by the second power splitter and the second received optical signal that has been demultiplexed by the second polarization splitter, mixes the input second light and the second received optical signal, converts it into a second received electrical signal, and outputs it.

2. An optical transceiver according to claim 1, wherein the light source light is input via a first optical fiber, the optical transmission signal is output to a second optical fiber, and the optical reception signal is input via a third optical fiber.

3. An optical transceiver according to claim 2, wherein said first optical fiber is a polarization maintaining optical fiber.

4. An optical transceiver as claimed in any one of claims 1 to 3, wherein the first polarization splitter, the first polarization rotator, the first power splitter, the first transmitting circuit, the second transmitting circuit, the second polarization rotator, the polarization coupler, the second power splitter, the second polarization splitter, the third polarization rotator, the first receiving circuit, and the second receiving circuit constitute an optical front end.

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