Receiving device, transmitting device, transmission system, receiving method, and transmitting method

Abstract

The present invention includes a reception unit that receives a signal in which an X-polarized wave and a Y-polarized wave are polarization-multiplexed, converts the received signal into reception signals corresponding to the X polarized wave and the Y polarized wave, respectively, and outputs the reception signals; a first signal decoding unit that decodes one series of the transmission signal from the reception signals output by the reception unit; a polarization separation unit that polarization-separates the reception signals output by the reception unit and corresponding to the X polarization and the Y polarization, respectively; a second signal decoding unit that decodes the reception signals polarization-separated by the polarization separation unit; and a first polarization process switching unit that receives the reception signals output by the reception unit and corresponding to the X polarized wave and the Y polarized wave, respectively and changes an output destination of the received reception signals to one of the first signal decoding unit and the polarization separation unit on the basis of information indicating a modulation method.

Description

[Technical field]

[0001] The present invention relates to a receiving device, a transmitting device, a transmission system, a receiving method, and a transmitting method. [Background technology]

[0002] In order to realize high-speed optical transmission, a method of increasing communication capacity by polarization multiplexing is used. By combining polarization multiplexing with digital coherent technology, it becomes possible to further increase communication capacity. When polarization multiplexing and digital coherent technology are combined, the receiving side can obtain information on the optical complex amplitude in each of the polarization directions of the X direction and the Y direction by receiving the polarization multiplexed optical signal using, for example, a polarization diversity receiver. By performing digital signal processing of polarization separation processing on the obtained information on the optical complex amplitude in each of the polarization directions of the X direction and the Y direction, it is possible to demodulate the transmission signal given as a modulated signal to each of the optical modulators for the X direction and the Y direction at the time of modulation on the transmitting side (for example, see Non-Patent Document 1).

[0003] The transmission processing function, which requires processing of the entire main signal as described above and requires a large amount of calculation, has conventionally been realized as a dedicated circuit, such as being implemented in an ASIC (Application Specific Integrated Circuit). In contrast, in recent years, research has been conducted to improve the flexibility of communication devices in response to user and application requests by implementing the transmission processing function in software, and to reduce CAPEX (Capital Expenditure) and OPEX (Operating Expense) in communication devices by using general-purpose hardware (see, for example, Non-Patent Document 2). For example, implementing the transmission processing function in software as described above makes it possible to change the function, but in order to accommodate a variety of transmission services in a single communication device, it is important to adaptively change the transmission processing function while maintaining low latency. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Kazuo Kikuchi, "New coherent optical communication technology using digital signal processing", Laser Research, Vol. 37, No. 3, pp. 164-170 (March 2009) [Non-Patent Document 2] T. Suzuki, S. Kim, J. Kani, et al., “Demonstration of Fully Softwarized 10G-EPON PHY Processing on a General-Purpose Server for Flexible Access Systems,” Journal of Lightwave Technology, vol.38, no.4, pp.777-783, Feb 2020 Summary of the Invention [Problem to be solved by the invention]

[0005] 14 is a block diagram showing the configuration of a transmission system 600 that transmits a general optical signal employing polarization multiplexing and digital coherent technology. In the transmitting device 300, a polarized beam splitter 302 splits the light output from a signal light source 301 into an X-polarized light (hereinafter referred to as "X-polarized light") and a Y-polarized light (hereinafter referred to as "Y-polarized light"). The polarized beam splitter 302 outputs the split X-polarized light to an IQ (In-phase Quadrature) modulation unit 303-1, and outputs the Y-polarized light to an IQ modulation unit 303-2.

[0006] The IQ modulation unit 303-1 modulates the X-polarized light based on the transmission signal provided by the transmission signal generation unit 304-1. The IQ modulation unit 303-2 modulates the Y-polarized light based on the transmission signal provided by the transmission signal generation unit 304-2. The polarization beam combiner 305 polarization-multiplexes the X-direction and Y-direction modulated optical signals modulated by the IQ modulation units 303-1 and 303-2, and transmits them to the optical fiber transmission line 500.

[0007] In the receiving device 400, a coherent receiving unit 402 receives an optical signal transmitted by an optical fiber transmission line 500. The receiving device 400 detects the received optical signal by coherently detecting the optical complex amplitude components in each of the X and Y directions using a local oscillation light (hereinafter referred to as "local light") output by a local oscillation light source 401. The coherent receiving unit 402 converts the detected optical complex amplitude components in each of the X and Y directions into digital receiving signals E in each of the X and Y directions. x ,E y Convert it to and output it.

[0008] The received signal E output by the coherent receiver 402 x ,E y The clock synchronization unit 403 performs clock synchronization to obtain a received signal E x (n),E y (n) is obtained, where n is the sample number. The received signal E x (n),E y For (n), signal detection is performed by the signal detection unit 404, and further, polarization separation is performed by the polarization separation unit 405.

[0009] Received signal E in the X direction after polarization separation X (n) and the received signal E in the Y direction Y After carrier recovery is performed on (n) by carrier recovery units 406-1 and 406-2, decoding processes such as symbol determination are performed by decoding units 407-1 and 407-2. Then, the transmission signal used to modulate the polarized light in the X direction, i.e., the transmission signal generated by the transmission signal generation unit 304-1, and the transmission signal used to modulate the polarized light in the Y direction, i.e., the transmission signal generated by the transmission signal generation unit 304-2, are restored.

[0010] In the transmission system 600 for transmitting a general optical signal employing the above-mentioned polarization multiplexing and digital coherent technology, the receiving device 400 is configured on the premise of receiving an optical signal in which the X-polarized light and the Y-polarized light are modulated by different transmission signals. On the other hand, when the communication capacity required by a user or an application is small, it is assumed that it is sufficient to modulate, for example, either the X-polarized light or the Y-polarized light by the transmission signal. In such a case, if the receiving device 400 always performs a process of decoding both the X-polarized light and the Y-polarized light, it will waste computational resources, resulting in problems such as a decrease in resource utilization efficiency and an increase in power consumption.

[0011] In view of the above circumstances, an object of the present invention is to provide a technique capable of demodulating a signal transmitted by a transmitting device while suppressing the computational resources used by a receiving device. [Means for solving the problem]

[0012] One aspect of the present invention is a receiving device comprising: a receiving unit that receives a polarization-multiplexed signal of X polarization and Y polarization, converts the received signal into a received signal corresponding to each of the X polarization and the Y polarization, and outputs the converted signal; a first signal decoding unit that decodes a series of transmission signals from the received signal output by the receiving unit; a polarization separation unit that polarization-separates the received signal corresponding to each of the X polarization and the Y polarization output by the receiving unit; a second signal decoding unit that decodes the received signal polarization-separated by the polarization separation unit; and a first polarization processing switching unit that takes in the received signal corresponding to each of the X polarization and the Y polarization output by the receiving unit, and switches the output destination of the taken-in received signal to either the first signal decoding unit or the polarization separation unit based on information indicating a modulation method.

[0013] One aspect of the present invention is a transmitting device including: a modulation signal switching unit that selectively outputs both or either of two transmission signals based on information indicating a modulation method; a polarization generation unit that separates a carrier wave into an X direction and a Y direction to generate an X polarization and a Y polarization; a modulation unit that modulates each of the X polarization and the Y polarization generated by the polarization generation unit based on the transmission signal selectively output by the modulation signal switching unit; and a polarization multiplexing unit that polarization-multiplexes and transmits the modulated signals in the X direction and the Y direction modulated by the modulation unit.

[0014] One aspect of the present invention is a transmission system including a transmitting device and a receiving device, the transmitting device including: a modulation signal switching unit that selectively outputs both or either of two transmission signals based on information indicating a modulation method; a polarization generating unit that separates a carrier wave into an X direction and a Y direction to generate an X polarized wave and a Y polarized wave; a modulation unit that modulates each of the X polarized wave and the Y polarized wave generated by the polarization generating unit based on the transmission signal selectively output by the modulation signal switching unit; and a polarization multiplexing unit that transmits the modulated signals in the X direction and the Y direction modulated by the modulation unit through polarization multiplexing. The receiving device receives a signal in which the X polarized wave and the Y polarized wave are polarization multiplexed, and transmits the received signal as follows: The transmission system includes a receiving unit that converts received signals corresponding to X polarization and Y polarization and outputs the converted signals, a first signal decoding unit that decodes a series of transmission signals from the received signals output by the receiving unit, a polarization separation unit that polarization separates the received signals corresponding to X polarization and Y polarization output by the receiving unit, a second signal decoding unit that decodes the received signals polarization separated by the polarization separation unit, and a first polarization processing switching unit that takes in the received signals corresponding to X polarization and Y polarization output by the receiving unit, and switches the output destination of the taken-in received signals to either the first signal decoding unit or the polarization separation unit based on information indicating a modulation method.

[0015] One aspect of the present invention is a receiving method in which a receiving unit receives a signal in which X polarization and Y polarization are polarization-multiplexed, converts the received signal into a received signal corresponding to each of the X polarization and the Y polarization, and outputs the received signal, a first polarization processing switching unit takes in the received signal corresponding to each of the X polarization and the Y polarization output by the receiving unit, and switches an output destination of the taken-in received signal to either a first signal decoding unit or a polarization separation unit based on information indicating a modulation method, the first signal decoding unit decodes a series of transmission signals from the received signal output by the first polarization processing switching unit, the polarization separation unit polarization-separates the received signal corresponding to each of the X polarization and the Y polarization output by the first polarization processing switching unit, and a second signal decoding unit decodes the received signal polarization-separated by the polarization separation unit.

[0016] One aspect of the present invention is a transmission method in which a modulation signal switching unit selectively outputs both or either of two transmission signals based on information indicating a modulation method, a polarization generation unit separates a carrier wave into an X direction and a Y direction to generate an X polarization and a Y polarization, a modulation unit modulates each of the X polarization and the Y polarization generated by the polarization generation unit based on the transmission signal selectively output by the modulation signal switching unit, and a polarization multiplexing unit polarization-multiplexes and transmits the modulated signals in the X direction and the Y direction modulated by the modulation unit. Effect of the Invention

[0017] According to the present invention, it is possible to demodulate a signal transmitted by a transmitting device while suppressing the computational resources used by a receiving device. [Brief description of the drawings]

[0018] [Figure 1] 1 is a block diagram showing a configuration of a transmission system according to a first embodiment. [Diagram 2] 1 is a block diagram showing a configuration of a transmitting device according to a first embodiment. [Diagram 3] 1 is a block diagram showing a configuration of a receiving device according to a first embodiment. [Figure 4] 2 is a block diagram showing a configuration of a polarization splitter unit according to the first embodiment. FIG. [Diagram 5]4 is a block diagram showing the configuration of a signal decoding unit that decodes a signal modulated by a first single polarization modulation scheme in the first embodiment. FIG. [Figure 6] FIG. 4 is a diagram illustrating a flow of processing by a transmitting device of the first embodiment. [Figure 7] FIG. 4 is a diagram showing a flow of processing by a receiving device of the first embodiment. [Figure 8] FIG. 11 is a block diagram showing a configuration of a transmitting device according to a second embodiment. [Figure 9] FIG. 11 is a block diagram showing a configuration of a receiving device according to a second embodiment. [Figure 10] FIG. 11 is a block diagram showing the configuration of a signal decoding unit that decodes a signal modulated by a first single polarization modulation method in the second embodiment. [Figure 11] FIG. 13 is a block diagram showing a configuration of a receiving device according to a third embodiment. [Figure 12] FIG. 11 is a diagram showing a flow of processing by a receiving device of the third embodiment. [Figure 13] FIG. 4 is a block diagram showing another example of the configuration of the receiving device according to the first embodiment. [Figure 14] 1 is a block diagram showing a configuration of a general transmission system that employs polarization multiplexing and digital coherent technology. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (First embodiment) Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram showing a configuration of a transmission system 100 according to a first embodiment. The transmission system 100 includes a transmitting device 1, a receiving device 2, and an optical fiber transmission line 3. The optical fiber transmission line 3 connects the transmitting device 1 and the receiving device 2.

[0020] (Configuration of the transmitting device of the first embodiment) 2 is a block diagram showing the configuration of the transmitting device 1. The transmitting device 1 includes a polarization generating unit 10, a modulation unit 13, transmission signal generating units 14-1 and 14-2, a polarization multiplexing unit 15, a modulation signal switching unit 16, and an operation unit 17. The polarization generating unit 10 includes a signal light source 11 and a polarizing beam splitter 12. The modulation unit 13 includes IQ modulation units 13-1 and 13-2.

[0021] The signal light source 11 generates and outputs continuous light that serves as a carrier wave. The polarizing beam splitter 12 splits the continuous light output by the signal light source 11 into light polarized in the X direction (hereinafter referred to as "X polarized light") and light polarized in the Y direction (hereinafter referred to as "Y polarized light"). The X polarized light split by the polarizing beam splitter 12 is input to an IQ modulation unit 13-1, and the Y polarized light is input to an IQ modulation unit 13-2.

[0022] Each of the transmission signal generators 14-1 and 14-2 generates a sequence of transmission signals, which are digital electrical signals, and outputs the generated transmission signals to the modulation signal switching unit 16. It is assumed that the transmission signal generators 14-1 and 14-2 each generate a different sequence of transmission signals.

[0023] The operation unit 17 receives an operation from a user of the transmission system 100 and acquires information indicating one of three predetermined modulation methods selected by the user. The operation unit 17 outputs the acquired information indicating the modulation method. Hereinafter, the three modulation methods are referred to as a polarization multiplexing modulation method, a first single polarization modulation method, and a second single polarization modulation method.

[0024] The modulation signal switching unit 16 selectively outputs both or either of the two transmission signals generated by each of the transmission signal generating units 14-1 and 14-2 based on information indicating the modulation method output by the operation unit 17. More specifically, when the operation unit 17 outputs information indicating the polarization multiplexing modulation method as information indicating the modulation method, the modulation signal switching unit 16 connects the connection end of the transmission signal generating unit 14-1 to the connection end of the IQ modulation unit 13-1, and connects the connection end of the transmission signal generating unit 14-2 to the connection end of the IQ modulation unit 13-2. When the operation unit 17 outputs information indicating the first single polarization modulation method as information indicating the modulation method, the modulation signal switching unit 16 connects the connection end of the transmission signal generating unit 14-1 to the connection end of the IQ modulation unit 13-1 and the connection end of the IQ modulation unit 13-2. When the operation unit 17 outputs information indicating the second single polarization modulation method as information indicating the modulation method, the modulation signal switching unit 16 connects the connection end of the transmission signal generation unit 14-1 to the connection end of the IQ modulation unit 13-1.

[0025] The IQ modulation unit 13-1 phase-modulates the X-polarized light provided from the polarizing beam splitter 12 based on the transmission signal output from the modulation signal switching unit 16. The IQ modulation unit 13-2 phase-modulates the Y-polarized light provided from the polarizing beam splitter 12 based on the transmission signal output from the modulation signal switching unit 16. Here, each of the IQ modulation units 13-1 and 13-2 includes, for example, two MZ (Mach-Zehnder) modulators, and a phase shifter that shifts the phase by 90 degrees is included in the output of one of the MZ (Mach-Zehnder) modulators. In this case, each of the IQ modulation units 13-1 and 13-2 generates modulated signals of I and Q components from the transmission signal provided to each of them. Inside each of the IQ modulation units 13-1 and 13-2, the modulated signals of I and Q components are combined to generate a QPSK (Quadrature Phase Shift Keying) optical signal.

[0026] The polarization multiplexing unit 15 is, for example, a polarization beam combiner, and polarization multiplexes the X-polarized modulated optical signal output by the IQ modulation unit 13-1 and the Y-polarized modulated optical signal output by the IQ modulation unit 13-2. When the X-polarized modulated optical signal and the Y-polarized modulated optical signal are QPSK optical signals, the modulated optical signal polarization-multiplexed by the polarization multiplexing unit 15 becomes a polarization-multiplexed QPSK optical signal. The polarization multiplexing unit 15 transmits the optical signal generated by polarization multiplexing to the optical fiber transmission line 3.

[0027] In the above-mentioned transmitting device 1, for example, when the operation unit 17 outputs information indicating the polarization multiplexing modulation method to the modulation signal switching unit 16 in response to a user's operation, the IQ modulation units 13-1 and 13-2 modulate the X-polarized light and the Y-polarized light provided thereto based on different transmission signals. Therefore, the state of the optical signal generated by the polarization multiplexing unit 15 through polarization multiplexing is a state in which different transmission signals are superimposed on the X-polarized light and the Y-polarized light by modulation.

[0028] In the transmitting device 1, when the operation unit 17 outputs information indicating the first single polarization modulation method to the modulation signal switching unit 16 in response to the user's operation, each of the IQ modulation units 13-1 and 13-2 modulates the X-polarized light and the Y-polarized light provided to each of them based on the same transmission signal, that is, the transmission signal generated by the transmission signal generating unit 14-1. Therefore, the state of the optical signal generated by the polarization multiplexing unit 15 through polarization multiplexing is a state in which the same transmission signal is superimposed on the X-polarized light and the Y-polarized light by modulation. In this case, the transmission signal can be obtained by demodulating either the X-polarized light or the Y-polarized light, and it can be said that the transmission signal is substantially superimposed on a single polarization.

[0029] In the transmitting device 1, when the operating unit 17 outputs information indicating the second single polarization modulation method to the modulation signal switching unit 16 in response to a user's operation, the IQ modulation unit 13-1 modulates the X-polarized light based on the transmission signal generated by the transmission signal generating unit 14-1. Therefore, the state of the optical signal generated by the polarization multiplexing unit 15 through polarization multiplexing is a state in which the transmission signal is superimposed on the X-polarized light and the transmission signal is not superimposed on the Y-polarized light, i.e., a state in which the transmission signal is superimposed on a single polarization.

[0030] (Configuration of the Receiving Device of the First Embodiment) 3 is a block diagram showing the configuration of the receiving device 2. The receiving device 2 includes a receiving unit 21, a polarization processing switching unit 22-1, a polarization splitting unit 23, a signal decoding unit 24-1, a signal decoding unit 24-2, and an operation unit 25. The operation unit 25 receives an operation by a user of the transmission system 100 and acquires information indicating one of three modulation methods selected by the user from among three predetermined modulation methods. Here, the information indicating the modulation method acquired by the operation unit 25 is information indicating one of the polarization multiplexing modulation method, the first single polarization modulation method, and the second single polarization modulation method, similar to the operation unit 17 of the transmitting device 1. The operation unit 25 outputs the information indicating the acquired modulation method to the polarization processing switching units 22-1 and 22-2.

[0031] The receiving section 21 includes a local oscillation light source 31, a coherent receiving section 32, a clock synchronizer 33, and a signal detector 34. The local oscillation light source 31 generates local light and outputs it to the coherent receiving section 32.

[0032] The coherent receiver 32 receives an optical signal transmitted by the optical fiber transmission line 3. The coherent receiver 32 coherently detects the received optical signal using the local light output by the local oscillation light source 31, and derives a received signal E, which is a digital electrical signal in the X direction, from the received optical signal. x and the received signal E, which is a digital electrical signal in the Y direction. yMore specifically, the coherent receiving unit 32 separates the local light output by the local oscillation light source 31 into X-polarized light and Y-polarized light. Based on the received optical signal and the separated X-polarized light of the local light, the coherent receiving unit 32 detects an optical complex amplitude component corresponding to the X-polarized light from the received optical signal as an analog electrical signal. Based on the received optical signal and the separated Y-polarized light of the local light, the coherent receiving unit 32 detects an optical complex amplitude component corresponding to the Y-polarized light from the received optical signal as an analog electrical signal. The coherent receiving unit 32 converts the optical complex amplitude component corresponding to the X-polarized light from analog to digital, thereby converting the optical complex amplitude component corresponding to the X-polarized light into a received signal E, which is a digital electrical signal in the X direction. x The coherent receiver 32 converts the optical complex amplitude component corresponding to the Y-polarized light from analog to digital, converting the optical complex amplitude component corresponding to the Y-polarized light into a received signal E, which is a digital electrical signal in the Y direction. y Convert to.

[0033] The clock synchronizing unit 33 synthesizes the received signal E x ,E y The clock synchronization unit 33 performs clock synchronization processing on each of the reference clocks provided in the transmitting device 1 and the receiving device 2 to correct the error in the reference clocks provided in each of the transmitting device 1 and the receiving device 2. x (n) and the received signal E in the Y direction y (n), where n is the sample number.

[0034] The signal detector 34 detects the received signal E x (n),E y The signal detector 34 detects a signal having an intensity value exceeding a predetermined intensity value from among (n). The signal detector 34 outputs the detected signal. Here, the predetermined intensity value is, for example, a maximum intensity value in a state where the transmitting device 1 is not transmitting an optical signal.

[0035] The polarization processing switching unit 22-1 judges whether the information indicating the modulation method output by the operation unit 25 is information indicating the first single polarization modulation method. The polarization processing switching unit 22-1 determines whether the received signal E output by the signal detection unit 34 is the first single polarization modulation method according to the result of the judgment. x (n),E y (n) to either the signal decoder 24-1 or the polarization splitter 23. More specifically, when the polarization processing switcher 22-1 determines that the information indicating the modulation method output by the operation unit 25 is information indicating the first single polarization modulation method, the polarization processing switcher 22-1 switches the output destination of the received signal E x (n),E y When the polarization processing switching unit 22-1 determines that the information indicating the modulation method output by the operation unit 25 is information other than the information indicating the first single polarization modulation method, the polarization processing switching unit 22-1 switches the output destination of the received signal E x (n),E y The output destination of (n) is switched to the polarization separator 23.

[0036] The signal decoder 24-1 decodes the received signal E x (n),E y Assuming that the received signal E (n) is modulated by the first single polarization modulation method, x (n),E y The process of decoding a sequence of transmitted signals is performed from (n).

[0037] When the optical signal transmitted by the transmitting device 1 is an optical signal in which X-polarized light and Y-polarized light are polarization-multiplexed, polarization dispersion occurs during transmission of the optical signal through the optical fiber transmission line 3 due to the influence of birefringence of the optical fiber, and the two polarization-multiplexed signals are mixed. x (n),E y Polarization separation is performed by filtering the mixed components contained in (n).

[0038] 4 is a block diagram showing the configuration of the polarization splitter 23. The polarization splitter 23 is a so-called butterfly type FIR (Finite Impulse Response) filter, xx Filter section 71, p xy Filter section 72, p yx Filter section 73, p yy The digital filter 70 includes a filter unit 74, complex addition units 75-1 and 75-2, and coefficient calculation units 76-1 and 76-2.

[0039] p xx Filter section 71, p xy Filter section 72, p yx Filter section 73 and p yy The filter unit 74 is, for example, an FIR filter. xx The filter unit 71 receives the X-direction reception signal E x (n) is taken in. xx The filter unit 71 receives the received signal E x (n) with filter coefficient p xx Perform filtering by multiplying (n).

[0040] p xy The filter unit 72 receives the Y-direction reception signal E y (n) is taken in. xy The filter unit 72 receives the received signal E y (n) with filter coefficient p xy Perform filtering by multiplying (n).

[0041] The complex adder 75-1 is p xx The filtered received signal E output by the filter unit 71 x (n) and p xy The filtered received signal E output by the filter unit 72 y (n) is added. The complex addition unit 75-1 adds p xx The filter coefficient p of the filter unit 71 xx (n) and p xy The filter coefficient p of the filter unit 72 xyWhen (n) and (n) are in an optimal state, the received signal E after filtering is x The Y-direction component mixed in (n) is the received signal E after filtering. y (n) and contains only the X-direction component. X (n) is obtained.

[0042] p yx The filter unit 73 receives the X-direction reception signal E x (n) is taken in. yx The filter unit 73 receives the received signal E x (n) with filter coefficient p yx Perform filtering by multiplying (n).

[0043] p yy The filter unit 74 receives the Y-direction reception signal E y (n) is taken in. yy The filter unit 74 receives the received signal E y (n) with filter coefficient p yy Perform filtering by multiplying (n).

[0044] The complex adder 75-2 is p yx The filtered received signal E output by the filter unit 73 x (n) and p yy The filtered received signal E output by the filter unit 74 y (n) is added. By the addition by the complex adder 75-2, p yx The filter coefficient p of the filter unit 73 yx (n) and p yy The filter coefficient p of the filter unit 74 yy When (n) and (n) are in an optimal state, the received signal E after filtering is y The X-direction component mixed in (n) is the received signal E after filtering. x (n) and contains only the Y-direction component. Y (n) is obtained.

[0045] Since the polarization state of the optical signal changes over time while being transmitted through the optical fiber transmission line 3, it is necessary to perform polarization splitting by adaptive control. xx Filter section 71, p xy Filter section 72, p yx Filter section 73, p yy The filter coefficient p applied to the filter section 74 xx (n),p xy (n),p yx (n),p yy (n) is the received signal E x (n),E y Calculate the coefficient for updating every (n) sampling interval.

[0046] The coefficient calculation unit 76-1 calculates the received signal E X The coefficient calculation unit 76-1 takes in the received signal E X Based on (n), the coefficient calculation unit 76-1 calculates the coefficient value shown in the following equation (1). xx A filter unit 71 and a xy The signal is output to the filter unit 72.

[0047]

number

[0048] The coefficient calculation unit 76-2 calculates the Y-direction received signal E Y The coefficient calculation unit 76-2 takes in the received signal E Y Based on (n), the coefficient calculation unit 76-2 calculates a coefficient value shown in the following equation (2). yx A filter unit 73 and a yy The result is output to the filter unit 74. Note that μ in the formulas (1) and (2) is a step size parameter.

[0049]

number

[0050] p xx The filter unit 71 receives the coefficient value output by the coefficient calculation unit 76-1. xx The filter unit 71 calculates the coefficient value and the filter coefficient p xx (n) and the received signal E in the X direction at sample number n x Based on the complex conjugate of (n), the filter coefficient p corresponding to sample number n+1 is calculated by the following equation (3). xx Calculate (n+1).

[0051]

number

[0052] p xy The filter unit 72 receives the coefficient value output by the coefficient calculation unit 76-1. xy The filter unit 72 calculates the coefficient value and the filter coefficient p xy (n) and the received signal E in the Y direction at sample number n y Based on the complex conjugate of (n), the filter coefficient p corresponding to sample number n+1 is calculated by the following equation (4). xy Calculate (n+1).

[0053]

number

[0054] p yx The filter unit 73 receives the coefficient value output by the coefficient calculation unit 76-2. yx The filter unit 73 calculates the coefficient value and the filter coefficient p yx (n) and the received signal E in the X direction at sample number n x Based on the complex conjugate of (n), the filter coefficient p corresponding to sample number n+1 is calculated by the following equation (5). yx Calculate (n+1).

[0055]

number

[0056] p yy The filter unit 74 receives the coefficient value output by the coefficient calculation unit 76-2. yy The filter unit 74 calculates the coefficient value and the filter coefficient p yy (n) and the received signal E in the Y direction at sample number n y Based on the complex conjugate of (n), the filter coefficient p corresponding to sample number n+1 is calculated by the following equation (6). yy Calculate (n+1).

[0057]

number

[0058] As a result, the polarization splitter 23 splits the received signal E x (n),E y For (n), adaptive polarization splitting is performed in response to changes in the polarization state over time.

[0059] When the transmitting device 1 transmits using the second single polarization modulation method, the optical signal transmitted by the transmitting device 1 has the transmission signal superimposed on the X-polarized light and the transmission signal not superimposed on the Y-polarized light. When the receiving device 2 receives the optical signal transmitted using the second single polarization modulation method, the polarization separation is performed by the polarization separation unit 23, and due to the filter characteristics of the polarization separation unit 23, the received signal E in the X direction is X (n) and the received signal E in the Y direction Y (n) has almost the same amplitude value.

[0060] The signal decoder 24-2 decodes the received signal E X (n),E YThe signal decoding unit 24-2 includes a polarization processing switching unit 22-2, a signal decoding unit 24-3, and a signal decoding unit 24-4.

[0061] The polarization processing switching unit 22-2 determines whether the information indicating the modulation method output by the operation unit 25 is information indicating the polarization multiplexing modulation method or information indicating the second single polarization modulation method. According to the result of the determination, the polarization processing switching unit 22-2 changes the received signal E X (n),E Y In more detail, when the polarization processing switching unit 22-2 determines that the information indicating the modulation method output by the operation unit 25 is information indicating the polarization multiplexing modulation method, the polarization processing switching unit 22-2 switches the output destination of the received signal E X (n),E Y When the polarization processing switching unit 22-2 determines that the information indicating the modulation method output by the operation unit 25 is information indicating the second single polarization modulation method, the polarization processing switching unit 22-2 switches the output destination of the received signal E X (n),E Y The output destination of (n) is switched to the signal decoding unit 24-4.

[0062] The signal decoder 24-3 decodes the received signal E X (n),E Y Assuming that (n) is modulated by the polarization multiplexing modulation method, the received signal E x (n),E y The signal decoder 24-4 decodes the two-series transmission signals E(n) from the polarization processing switch 22-2. X (n),E Y Assuming that the received signal E (n) is modulated by the second single polarization modulation method, x (n),E y The process of decoding a sequence of transmitted signals is performed from (n).

[0063] Next, the internal configuration of the signal decoding units 24-1, 24-3, and 24-4 will be described. Fig. 5 is a block diagram showing the configuration of the signal decoding unit 24-1. The signal decoding unit 24-1 includes an adder unit 40, an FIR filter unit 41, a carrier recovery unit 42, and a decoding unit 43. As shown in Fig. 3, the signal decoding unit 24-3 includes carrier recovery units 52-1 and 52-2, and decoding units 53-1 and 53-2. As shown in Fig. 3, the signal decoding unit 24-4 includes an adder unit 60, a carrier recovery unit 62, and a decoding unit 63.

[0064] In the signal decoding unit 24-1, the adder 40 receives the received signal E x (n),E y Add each of (n) to get the sum E x (n)+E y The FIR filter unit 41 calculates a received signal E(n) output from the adder unit 40. x (n)+E y A filtering process is performed to remove noise contained in (n).

[0065] In the signal decoding unit 24-4, the adder 60 receives the received signal E X (n),E Y Add each of (n) to get the sum E X (n)+E Y The received signal (n) is calculated.

[0066] The carrier recovery units 42, 52-1, 52-2, and 62 perform carrier recovery processing including frequency offset compensation processing and phase compensation processing on the received signal. Here, the frequency offset compensation processing is processing to compensate for the deviation of the center frequency when there is a deviation between the center frequency of the signal light generated by the signal light source 11 included in the transmitting device 1 and the center frequency of the local light generated by the local oscillation light source 31 included in the receiving device 2. The phase compensation processing is processing to compensate for the phase difference between the signal light generated by the signal light source 11 included in the transmitting device 1 and the local light generated by the local oscillation light source 31 included in the receiving device 2.

[0067] The decoding units 43, 53-1, 53-2, and 63 restore the transmission signal by performing decoding processing such as symbol determination on the received signal after the carrier recovery processing has been performed by the carrier recovery units 42, 52-1, 52-2, and 62 connected thereto. Note that, unlike the signal decoding unit 24-1, the signal decoding units 24-3 and 24-4 do not include a functional unit corresponding to the FIR filter unit 41 because the filtering processing by the polarization separation unit 23 performs processing equivalent to the filtering processing performed by the FIR filter unit 41 to remove noise and the like.

[0068] (Processing by the transmitting device of the first embodiment) 6 is a flowchart showing a flow of processing by the transmitting device 1. A user of the transmission system 100 operates the operation unit 17 to select one of the polarization multiplexing modulation method, the first single polarization modulation method, and the second single polarization modulation method (step Sta1). When the polarization multiplexing modulation method is selected, the operation unit 17 outputs information indicating the polarization multiplexing modulation method as information indicating the modulation method to the modulation signal switching unit 16. When the first single polarization modulation method is selected, the operation unit 17 outputs information indicating the first single polarization modulation method as information indicating the modulation method to the modulation signal switching unit 16. When the second single polarization modulation method is selected, the operation unit 17 outputs information indicating the second single polarization modulation method as information indicating the modulation method to the modulation signal switching unit 16.

[0069] The modulation signal switching unit 16 receives information indicating the modulation method output from the operation unit 17. The modulation signal switching unit 16 determines the type of information indicating the received modulation method (step Sta2). When the modulation signal switching unit 16 determines that the information indicating the received modulation method is information indicating the polarization multiplexing modulation method (step Sta2, polarization multiplexing modulation method), it connects the connection end of the transmission signal generating unit 14-1 to the connection end of the IQ modulation unit 13-1, and connects the connection end of the transmission signal generating unit 14-2 to the connection end of the IQ modulation unit 13-2 (step Sta3-1). The IQ modulation unit 13-1 modulates the X-polarized light output from the polarizing beam splitter 12 with the transmission signal generated by the transmission signal generating unit 14-1 and provided via the modulation signal switching unit 16, and outputs the modulated light to the polarization multiplexing unit 15. The IQ modulation unit 13-2 modulates the Y-polarized light output from the polarizing beam splitter 12 with a transmission signal generated by the transmission signal generation unit 14-2 provided via the modulation signal switching unit 16, and outputs the modulated light to the polarization multiplexing unit 15 (step Sta4-1).

[0070] When the modulation signal switching unit 16 determines that the information indicating the captured modulation method is information indicating the first single polarization modulation method (step Sta2, first single polarization modulation method), it connects the connection end of the transmission signal generating unit 14-1 to the connection end of the IQ modulation unit 13-1 and the connection end of the IQ modulation unit 13-2 (step Sta3-2). The IQ modulation unit 13-1 modulates the X-polarized light output from the polarized beam splitter 12 with the transmission signal generated by the transmission signal generating unit 14-1 given via the modulation signal switching unit 16, and outputs the modulated modulated light to the polarization multiplexing unit 15. The IQ modulation unit 13-2 modulates the Y-polarized light output from the polarized beam splitter 12 with the transmission signal generated by the transmission signal generating unit 14-1 given via the modulation signal switching unit 16, and outputs the modulated modulated light to the polarization multiplexing unit 15 (step Sta4-2).

[0071] When the modulation signal switching unit 16 determines that the information indicating the captured modulation method is information indicating the second single polarization modulation method (step Sta2, second single polarization modulation method), it connects the connection end of the transmission signal generating unit 14-1 to the connection end of the IQ modulation unit 13-1 (step Sta3-3). The IQ modulation unit 13-1 modulates the X-polarized light output from the polarized beam splitter 12 with a transmission signal generated by the transmission signal generating unit 14-1 and provided via the modulation signal switching unit 16, and outputs the modulated light to the polarization multiplexing unit 15. The IQ modulation unit 13-2 does not perform modulation because no transmission signal is provided from the modulation signal switching unit 16, and outputs the Y-polarized light output from the polarized beam splitter 12 to the polarization multiplexing unit 15 as it is (step Sta4-3).

[0072] The polarization multiplexing unit 15 polarization multiplexes the light output from each of the IQ modulation units 13-1 and 13-2 to generate an optical signal, and transmits the generated optical signal to the optical fiber transmission line 3 (step Sta5).

[0073] As a result, when a user of the transmission system 100 selects the polarization multiplexing modulation method, the transmitting device 1 transmits an optical signal in which the X-polarized light and the Y-polarized light are polarization multiplexed, with the X-polarized light being modulated by the transmission signal generated by the transmission signal generating unit 14-1 and the Y-polarized light being modulated by the transmission signal generated by the transmission signal generating unit 14-2. When a user of the transmission system 100 selects the first single polarization modulation method, the transmitting device 1 transmits an optical signal in which the X-polarized light and the Y-polarized light are polarization multiplexed, with each of the X-polarized light and the Y-polarized light being modulated by the transmission signal generated by the transmission signal generating unit 14-1. When a user of the transmission system 100 selects the second single polarization modulation method, the transmitting device 1 transmits an optical signal in which the X-polarized light and the Y-polarized light are polarization multiplexed, with the X-polarized light being modulated by the transmission signal generated by the transmission signal generating unit 14-1 and the Y-polarized light not being modulated.

[0074] In the process by the transmitting device 1 of the first embodiment described above, it is assumed that the transmission signal generating units 14-1 and 14-2 continuously generate different transmission signals. In contrast, when the operation unit 17 outputs information indicating the polarization multiplexing modulation method to the modulation signal switching unit 16, it may output a transmission signal generation instruction signal to each of the transmission signal generating units 14-1 and 14-2 to instruct them to start generating a transmission signal, and each of the transmission signal generating units 14-1 and 14-2 may start generating a different transmission signal upon receiving the transmission signal generation instruction signal. When the operation unit 17 outputs information indicating the first or second single polarization modulation method to the modulation signal switching unit 16, the transmission signal generated by the transmission signal generating unit 14-2 is not a transmission target, so it may output a transmission signal generation instruction signal only to the transmission signal generating unit 14-1, and the transmission signal generating unit 14-1 may start generating a transmission signal upon receiving the transmission signal generation instruction signal.

[0075] In the transmitting device 1 of the first embodiment described above, when the information indicating the captured modulation method is information indicating the second single polarization modulation method, the modulation signal switching unit 16 connects the connection end of the transmission signal generating unit 14-1 to the connection end of the IQ modulation unit 13-1 in step Sta3-3. On the other hand, the modulation signal switching unit 16 may connect the connection end of the transmission signal generating unit 14-1 to the connection end of the IQ modulation unit 13-2 in step Sta3-3. In this case, the polarization multiplexing unit 15 generates and transmits an optical signal in which the X-polarized light and the Y-polarized light are polarization-multiplexed, in a state in which the Y-polarized light is modulated by the transmission signal generated by the transmission signal generating unit 14-1 and the X-polarized light is not modulated.

[0076] (Processing by the receiving device of the first embodiment) FIG. 7 is a flowchart showing the flow of processing by the receiving device 2. Before the processing of FIG. 7 is started, the following processing is performed. The user of the transmission system 100 operates the operation unit 25 to select one of the polarization multiplexing modulation method, the first single polarization modulation method, and the second single polarization modulation method. When the polarization multiplexing modulation method is selected, the operation unit 25 outputs information indicating the polarization multiplexing modulation method as information indicating the modulation method to the polarization processing switching units 22-1 and 22-2. When the first single polarization modulation method is selected, the operation unit 25 outputs information indicating the first single polarization modulation method as information indicating the modulation method to the polarization processing switching units 22-1 and 22-2. When the second single polarization modulation method is selected, the operation unit 25 outputs information indicating the second single polarization modulation method as information indicating the modulation method to the polarization processing switching units 22-1 and 22-2.

[0077] 7 starts when the coherent receiver 32 of the receiver 21 of the receiver 2 receives the optical signal transmitted by the transmitter 1 through the optical fiber transmission line 3. The coherent receiver 32 coherently detects the received optical signal using the local light output by the local oscillation light source 31, and derives a received signal E in the X direction from the received optical signal. x and the received signal E in the Y direction y The coherent receiver 32 generates the generated received signal E x ,E y to the clock synchronization unit 33.

[0078] The clock synchronizing unit 33 synthesizes the received signal E x ,E y The clock synchronization unit 33 receives the received signal E x ,E y The clock is synchronized with the received signal E at each sampling interval according to the clock signal. x (n),E y The clock synchronizing unit 33 generates the generated reception signal E x (n),E y (n) is output to the signal detection unit 34.

[0079] The signal detector 34 detects the received signal E x (n),E y The signal detector 34 receives the received signal E(n). x (n),E y The signal detector 34 detects a signal having an intensity value exceeding a predetermined intensity value from among (n) and outputs the detected signal to the polarization processing switcher 22-1 (step Sra1).

[0080] The polarization processing switching unit 22-1 detects the received signal E x (n),E y The polarization processing switching unit 22-1 takes in information indicating the modulation method output by the operation unit 25. The polarization processing switching unit 22-1 determines the type of the information indicating the taken-in modulation method (step Sra2). When the polarization processing switching unit 22-1 determines that the information indicating the taken-in modulation method is information indicating the first single polarization modulation method (step Sra2, first single polarization modulation method), the polarization processing switching unit 22-1 selects the first single polarization modulation method from the taken-in received signal E x (n),E y (n) is switched to the signal decoding unit 24-1, and the received signal E x (n),E y (n) is output to the adder 40 of the signal decoding unit 24-1 (step Sra3).

[0081] The adder 40 receives two series of received signals E x (n),E y The adder 40 takes in the received signal E x (n),E y (n) is added to obtain a series of received signals E x (n)+E y The adder 40 calculates the calculated received signal E x (n)+E y The FIR filter unit 41 outputs the received signal E x (n)+E yThe FIR filter unit 41 receives the received signal E x (n)+E y The FIR filter unit 41 performs filtering on the received signal E(n). x (n)+E y (n) is output to the carrier recovery unit 42 (step Sra5).

[0082] The carrier recovery unit 42 recovers the filtered received signal E x (n)+E y The carrier recovery unit 42 receives the received signal E x (n)+E y The carrier recovery unit 42 performs carrier recovery processing on the received signal E(n) after the carrier recovery processing. x (n)+E y (n) is output to the decoding unit 43 (step Sra6).

[0083] The decoder 43 receives the carrier recovery processed received signal E x (n)+E y The decoder 43 receives the received signal E(n). x (n)+E y The decoder 43 performs a decoding process on (n). The decoder 43 restores the transmission signal generated by the transmission signal generator 14-1 through the decoding process, and outputs the restored transmission signal to the outside (step Sra7).

[0084] As described above, the polarization multiplexed optical signal undergoes polarization dispersion due to the influence of birefringence in the optical fiber while being transmitted through the optical fiber transmission line 3, and the two polarization multiplexed signals are mixed together. However, the same transmission signal, which is generated by the transmission signal generator 14-1, is superimposed by modulation on each of the X-polarized light and the Y-polarized light of the optical signal modulated by the first single polarization modulation method. Therefore, when the influence of polarization dispersion is small, the received signal E x (n) and the received signal E yTherefore, in the case of the first single polarization modulation method, the received signal E x (n) and the received signal E y (n) is added by the adder 40 to the received signal E x (n)+E y In (n), the received signal E x (n) and the received signal E y Therefore, the information of the transmission signal superimposed on the FIR filter unit 41 and the carrier recovery unit 42 is not lost. x (n)+E y By decoding (n), it is possible to restore the transmission signal generated by the transmission signal generating unit 14-1.

[0085] On the other hand, in step Sra2, if the polarization processing switching unit 22-1 determines that the information indicating the acquired modulation method is information other than the information indicating the first single polarization modulation method, that is, information indicating the polarization multiplexing modulation method or the second single polarization modulation method (step Sra2, polarization multiplexing modulation method or second single polarization modulation method), x (n),E y (n) is switched to the polarization separator 23, and the received signal E x (n),E y (n) is output to the polarization separator 23 (step Sra8).

[0086] The polarization splitter 23 splits the received signal E x (n),E y The polarization splitter 23 takes in the received signal E(n). x (n),E y (n) is subjected to polarization separation, and the polarization-separated received signal E X (n),E Y The polarization splitter 23 generates the polarization-split received signal E(n). X (n),E Y (n) is output to the polarization processing switching unit 22-2 of the signal decoding unit 24-2 (step Sra9).

[0087] The polarization processing switching unit 22-2 receives the received signal E X (n),E Y The polarization processing switching unit 22-2 takes in information indicating the modulation method output by the operation unit 25. The polarization processing switching unit 22-2 determines the type of the information indicating the modulation method taken in (step Sra10). When the polarization processing switching unit 22-2 determines that the information indicating the modulation method taken in is information indicating the polarization multiplexing modulation method (step Sra10, polarization multiplexing modulation method), it selects the polarization multiplexing modulation method from the received signal E X (n),E Y (n) is switched to the signal decoder 24-3, and the received signal E X (n) is output to the carrier recovery unit 52-1, and the received signal E Y (n) is output to the carrier recovery unit 52-2 (step Sra11).

[0088] The carrier recovery unit 52-1 converts the received signal E X The carrier recovery unit 52-1 receives the received signal E X The carrier recovery unit 52-1 performs carrier recovery processing on the received signal E(n) after the carrier recovery processing. X The carrier recovery unit 52-2 outputs the received signal E (n) output by the polarization processing switching unit 22-2 to the decoding unit 53-1. Y The carrier recovery unit 52-2 receives the received signal E Y The carrier recovery unit 52-2 performs carrier recovery processing on the received signal E(n) after the carrier recovery processing. Y (n) is output to the decoding unit 53-2 (step Sra12).

[0089] The decoder 53-1 decodes the received signal E after carrier recovery processing output from the carrier recovery unit 52-1. X The decoder 53-1 receives the received signal E XThe decoder 53-2 performs a decoding process on the received signal E(n) after carrier recovery processing output by the carrier recovery unit 52-2 to restore the transmission signal generated by the transmission signal generator 14-1. Y The decoder 53-2 receives the received signal E Y The decoders 53-1 and 53-2 each perform a decoding process on (n) to restore the transmission signal generated by the transmission signal generator 14-2. Each of the decoders 53-1 and 53-2 outputs the restored transmission signal to the outside (step Sra13).

[0090] On the other hand, in step Sra10, when the polarization processing switching unit 22-2 determines that the information indicating the acquired modulation method is information indicating the second single polarization modulation method (step Sra10, second single polarization modulation method), X (n),E Y (n) is switched to the signal decoder 24-4, and the received signal E X (n),E Y (n) is output to the adding unit 60 (step Sra14).

[0091] The adder 60 receives two series of received signals E X (n),E Y The adder 60 receives the received signal E X (n),E Y (n) is added to obtain a series of received signals E X (n)+E Y The adder 60 calculates the calculated received signal E X (n)+E Y (n) is output to the carrier recovery unit 62 (step Sra15).

[0092] The carrier recovery unit 62 recovers the received signal E X (n)+E Y The carrier recovery unit 62 receives the received signal E X (n)+E YThe carrier recovery unit 62 performs carrier recovery processing on the received signal E(n) after the carrier recovery processing. X (n)+E Y (n) is output to the decoding unit 63 (step Sra16).

[0093] The decoder 63 receives the carrier recovery processed received signal E X (n)+E Y The decoder 63 receives the received signal E X (n)+E Y The decoder 63 performs a decoding process on (n). The decoder 63 restores the transmission signal generated by the transmission signal generator 14-1 through the decoding process, and outputs the restored transmission signal to the outside (step Sra17).

[0094] In the receiver 2 of the first embodiment, the signal decoder 24-1, which is the first signal decoder, decodes the received signal E x (n),E y The second signal decoder 24-2 decodes a sequence of the transmission signal E(n) from the polarization separator 23. X (n),E Y The first polarization processing switching unit 22-1 decodes the received signal E corresponding to the X-polarized wave and the Y-polarized wave output by the receiving unit 21. x (n),E y The polarization processing switching unit 22-1 receives the received signal E(n) based on the information indicating the modulation method output by the operation unit 25. x (n),E yThe output destination of (n) is switched to either the signal decoder 24-1 or the polarization separator 23. As a result, when the receiver 2 receives an optical signal modulated by the first single polarization modulation method, the receiver 2 performs the decoding process using the signal decoder 24-1 without using the polarization separator 23. On the other hand, when the receiver 2 receives an optical signal modulated by the polarization multiplexing modulation method or the second single polarization modulation method, the receiver 2 performs the decoding process using the polarization separator 23 and the signal decoder 24-2. Therefore, the receiver 2 has a configuration that switches the usage state of the polarization separator 23 depending on the modulation method of the received optical signal.

[0095] Furthermore, in the receiving device 2, the signal decoding unit 24-2, which is the second signal decoding unit, includes a signal decoding unit 24-3, which is the third signal decoding unit, a signal decoding unit 24-4, which is the fourth signal decoding unit, and a polarization processing switching unit 22-2, which is the second polarization processing switching unit. X (n),E Y The signal decoder 24-3 decodes the two-series transmission signal from the polarization separator 23. X (n),E Y The polarization processing switching unit 22-2 decodes one series of transmission signals from the polarization splitter 23. The polarization processing switching unit 22-2 outputs the reception signals E X (n),E Y The polarization processing switching unit 22-2 receives the received signal E(n) based on the information indicating the modulation method. X (n),E YThe output destination of (n) is switched to either one of the signal decoder 24-3 and the signal decoder 24-4. As a result, when the receiver 2 receives an optical signal modulated by the polarization multiplexing modulation method, the receiver 2 performs the decoding process using the signal decoder 24-3 including two carrier recovery units 52-1 and 52-2 and two decoders 53-1 and 53-2. On the other hand, when the receiver 2 receives an optical signal modulated by the first single polarization modulation method, the receiver 2 performs the decoding process using the signal decoder 24-1 including the adder 40, the FIR filter unit 41, one carrier recovery unit 42, and one decoder 43. Furthermore, when the receiver 2 receives an optical signal modulated by the second single polarization modulation method, the receiver 2 performs the decoding process using the signal decoder 24-4 including the adder 60, one carrier recovery unit 62, and one decoder 63. That is, the receiver 2 is configured to switch between the signal decoders 24-1, 24-3, and 24-4 having appropriate computation resources according to the modulation method of the received optical signal. Therefore, by selecting the computation resources to be used by the receiver 2 according to information indicating the modulation method using the polarized waves applied by the transmitter 1, it becomes possible to demodulate the signal transmitted by the transmitter 1 while suppressing the computation resources to be used.

[0096] Second Embodiment Fig. 8 is a block diagram showing the configuration of a transmitting device 1a according to the second embodiment. Fig. 9 is a block diagram showing the configuration of a receiving device 2a according to the second embodiment. The transmission system of the second embodiment includes a transmitting device 1a, a receiving device 2a, and an optical fiber transmission line 3, and hereinafter, when referring to the transmission system of the second embodiment, the reference symbol "100a" is added and the system is referred to as a transmission system 100a. Note that in the second embodiment, the same reference symbols are used for the same configurations as in the first embodiment, and hereinafter, configurations different from the first embodiment will be described.

[0097] (Regarding the transmitting device of the second embodiment) As shown in Fig. 8, the transmitting device 1a includes a polarization generating unit 10, a modulating unit 13a, transmission signal generating units 14-1 and 14-2, a polarization multiplexing unit 15, a modulated signal switching unit 16, and an operating unit 17. The modulating unit 13a includes optical intensity modulating units 13a-1 and 13a-2. That is, the transmitting device 1a includes optical intensity modulating units 13a-1 and 13a-2 that perform optical intensity modulation instead of the IQ modulating units 13-1 and 13-2 in the transmitting device 1 of the first embodiment. Each of the optical intensity modulating units 13a-1 and 13a-2 performs OOK (On Off Keying) modulation on the X-polarized light and the Y-polarized light provided thereto based on a transmission signal provided thereto. Therefore, in the transmitting device 1a, when a transmission signal generated by the transmission signal generating unit 14-1 is provided to the optical intensity modulation unit 13a-1 and a transmission signal generated by the transmission signal generating unit 14-2 is provided to the optical intensity modulation unit 13a-2, the transmitting device 1a performs polarization multiplexed OOK modulation on the light output by the signal light source 11.

[0098] The processing in the transmitting device 1a of the second embodiment is the same as that in the transmitting device 1 of the first embodiment shown in FIG. 6, except that in the processing of steps Sta4-1, Sta4-2, and Sta4-3, intensity modulation is performed by optical intensity modulation units 13a-1 and 13a-2 instead of phase modulation.

[0099] (Regarding the receiving device of the second embodiment) 9, the receiving device 2a includes a receiving unit 21a, a polarization processing switching unit 22-1, a signal decoding unit 24a-1, a polarization separation unit 23, a signal decoding unit 24a-2, and an operation unit 25. The receiving unit 21a includes a polarizing beam splitter 35, photodetection units 36-1 and 36-2, a clock synchronizer 33, and a signal detector 34. The polarizing beam splitter 35 receives an optical signal transmitted by the optical fiber transmission line 3, and separates the received optical signal into X-polarized light and Y-polarized light.

[0100] The photodetector 36-1 receives the X-polarized light output from the polarizing beam splitter 35. The photodetector 36-1 detects the intensity of the received X-polarized light and detects the light intensity amplitude component as an analog electrical signal. The photodetector 36-1 converts the detected light intensity amplitude component from analog to digital, converting the light intensity amplitude component corresponding to the X-polarized light into a digital electrical signal, which is a received signal E x The optical detection unit 36-2 receives the Y polarized light output from the polarizing beam splitter 35. The optical detection unit 36-2 detects the optical intensity of the received Y polarized light and detects the optical intensity amplitude component as an analog electrical signal. The optical detection unit 36-2 converts the detected optical intensity amplitude component from analog to digital, converting the optical intensity amplitude component corresponding to the Y polarized light into a received signal E, which is a digital electrical signal. y The photodetectors 36-1 and 36-2 convert the converted received signal E x ,E y to the clock synchronization unit 33.

[0101] As shown in FIG. 10, the signal decoder 24a-1 includes an adder 40, an FIR filter 41, and a decoder 43. The signal decoder 24a-2 includes a polarization processing switch 22-2, and signal decoders 24a-3 and 24a-4. The signal decoder 24a-3 includes decoders 53-1 and 53-2. The signal decoder 24a-4 includes an adder 60 and a decoder 63. Unlike the first embodiment, the signal decoders 24a-1, 24a-2, and 24a-3 do not include carrier recovery units 42, 52-1, 52-2, and 62 because, in the second embodiment, the optical signal received by the receiver 2a is intensity modulated, not phase modulated, and therefore frequency offset compensation and phase compensation are not required.

[0102] The processing in the receiving device 2a of the second embodiment is similar to the processing in the receiving device 2 of the first embodiment, except that in the processing of step Sra1 shown in FIG. 7, processing is performed by the polarized beam splitter 35 and the photodetection units 36-1 and 36-2 instead of the processing performed by the coherent receiving unit 32, and the processing of steps Sra6, Sra12, and Sra16 performed by the carrier recovery units 42, 52-1, 52-2, and 62 is excluded.

[0103] The receiving device 2a of the second embodiment has a configuration in which it switches between signal decoders 24a-1, 24a-3, and 24a-4 having appropriate computation resources according to the modulation method of the received optical signal, as in the first embodiment. Therefore, the receiving device 2a selects computation resources according to information indicating the modulation method using the polarized waves applied in the transmitting device 1a, and thus it becomes possible to demodulate the signal transmitted by the transmitting device 1a while suppressing the computation resources used.

[0104] (Third embodiment) 11 is a block diagram showing the configuration of a receiving device 2b according to the third embodiment. The transmission system of the third embodiment includes a transmitting device 1a, a receiving device 2b, and an optical fiber transmission line 3, and hereinafter, when referring to the transmission system of the third embodiment, the reference numeral "100b" is added and the transmission system is called a transmission system 100b. Note that in the third embodiment, the same reference numerals are added to the same configurations as those of the first and second embodiments, and hereinafter, configurations different from those of the first and second embodiments are described.

[0105] In the first and second embodiments, on the premise that the influence of polarization dispersion is small, in the case of the first single polarization modulation method, the polarization splitter 23 does not perform polarization splitting, and the signal decoders 24-1 and 24a-1 decode the received signal E x (n) and the received signal E y(n) and performing a decoding process to restore the transmission signal generated by the transmission signal generator 14-1. In contrast, the third embodiment has a configuration different from the first and second embodiments in that it determines whether the effect of polarization dispersion is small enough to be negligible, and if the effect of polarization dispersion cannot be negligible, it performs polarization separation by the polarization separator 23 even in the case of the first single polarization modulation method.

[0106] 11, the receiving device 2b includes a receiving unit 21a, a polarization processing switching unit 22b-1, a signal decoding unit 24a-1, a polarization separation unit 23, a signal decoding unit 24b-2, an operation unit 25, and a polarization processing determination unit 26. The signal decoding unit 24b-2 includes a polarization processing switching unit 22b-2, and signal decoding units 24a-3 and 24a-4.

[0107] The polarization process determination unit 26 includes a filter having the same configuration as the polarization separation unit 23 shown in FIG. x (n),E y The polarization processing determination unit 26 receives the received signal E x (n),E y (n) is a polarization-separated received signal E X (n),E Y (n) and the captured received signal E x (n),E y Based on (n), it is determined whether or not polarization splitting is required.

[0108] However, the polarization processing determination unit 26 receives the received signal E x (n),E y (n), the polarization separation is not performed on all of the received signals E x (n),E y (n) of a received signal E for a predetermined period of time x (n),E y Here, the polarization separation is performed on the received signal E x (n),E y(n) is, for example, a predetermined number of samples, which is a number of consecutive samples in a time series, of the received signal E x (n),E y The polarization processing determination unit 26 receives the received signal E x (n),E y (n) to the polarization processing switching unit 22b-1, and also outputs the determination result as to whether or not polarization splitting is necessary to the polarization processing switching unit 22b-1.

[0109] The polarization processing switching unit 22b-1 judges whether or not the information indicating the modulation method output by the operation unit 25 is information indicating the first single polarization modulation method. When the polarization processing switching unit 22b-1 judges that the information indicating the modulation method output by the operation unit 25 is information indicating the first single polarization modulation method, it further judges whether or not the judgment result output by the polarization processing determination unit 26 is a judgment result indicating that polarization splitting is necessary. When the judgment result output by the polarization processing determination unit 26 is a judgment result indicating that polarization splitting is not necessary, the polarization processing switching unit 22b-1 judges whether or not the received signal E output by the signal detection unit 34 is a judgment result indicating that polarization splitting is necessary. x (n),E y The output destination of (n) is switched to the signal decoding unit 24a-1.

[0110] When the determination result output by the polarization processing determination unit 26 indicates that polarization separation is necessary and when the information indicating the modulation method output by the operation unit 25 is information other than information indicating the first single polarization modulation method, the polarization processing switching unit 22b-1 outputs the received signal E x (n),E y The output destination of (n) is switched to the polarization separator 23.

[0111] The polarization processing switching unit 22b-2 judges whether the information indicating the modulation method output by the operation unit 25 is information indicating the polarization multiplexing modulation method, information indicating the first single polarization modulation method, or information indicating the second single polarization modulation method. When the polarization processing switching unit 22b-2 judges that the information indicating the modulation method output by the operation unit 25 is information indicating the polarization multiplexing modulation method, the polarization processing switching unit 22b-2 selects the received signal E X(n),E Y When the polarization processing switching unit 22b-2 determines that the information indicating the modulation method output by the operation unit 25 is information indicating the first single polarization modulation method or the second single polarization modulation method, the polarization processing switching unit 22b-2 switches the output destination of the received signal E X (n),E Y The output destination of (n) is switched to the signal decoding unit 24a-4.

[0112] (Processing by the receiving device of the third embodiment) FIG. 12 is a flowchart showing the flow of processing by the receiving device 2b. Before the processing of FIG. 12 is started, the following processing is performed as in the first embodiment. A user of the transmission system 100b operates the operation unit 25 to select one of the polarization multiplexing modulation method, the first single polarization modulation method, and the second single polarization modulation method. When the polarization multiplexing modulation method is selected, the operation unit 25 outputs information indicating the polarization multiplexing modulation method as information indicating the modulation method to the polarization processing switching units 22b-1 and 22b-2. When the first single polarization modulation method is selected, the operation unit 25 outputs information indicating the first single polarization modulation method as information indicating the modulation method to the polarization processing switching units 22b-1 and 22b-2. When the second single polarization modulation method is selected, the operation unit 25 outputs information indicating the second single polarization modulation method as information indicating the modulation method to the polarization processing switching units 22b-1 and 22b-2.

[0113] 12 is started when the polarizing beam splitter 35 of the receiving section 21 of the receiving device 2b receives the optical signal transmitted by the transmitting device 1a through the optical fiber transmission line 3. The polarizing beam splitter 35 separates the received optical signal into X-polarized light and Y-polarized light, outputs the separated X-polarized light to the photodetection section 36-1, and outputs the separated Y-polarized light to the photodetection section 36-2. The photodetection section 36-1 detects the optical intensity of the X-polarized light output by the polarizing beam splitter 35, and outputs a received signal E, which is a digital electrical signal corresponding to the X direction. x and the generated received signal E xto the clock synchronization unit 33. The optical detection unit 36-2 detects the optical intensity of the Y-polarized light output by the polarizing beam splitter 35 and outputs a digital electrical reception signal E y and the generated received signal E y to the clock synchronization unit 33.

[0114] The clock synchronizing unit 33 synthesizes the received signals E x ,E y The clock synchronization unit 33 receives the received signal E x ,E y The clock is synchronized with the received signal E at each sampling interval according to the clock signal. x (n),E y The clock synchronizing unit 33 generates the generated reception signal E x (n),E y (n) is output to the signal detection unit 34.

[0115] The signal detector 34 detects the received signal E x (n),E y The signal detector 34 receives the received signal E(n). x (n),E y The signal detector 34 detects a signal having an intensity value exceeding a predetermined intensity value from among (n) and outputs the detected signal to the polarization processing determiner 26 (step Srb1).

[0116] The polarization processing determination unit 26 detects the received signal E x (n),E y The polarization processing determination unit 26 first receives the received signal E x (n),E y A received signal E for a predetermined period starting from (n) x (n),E y The polarization processing determination unit 26 selects the received signal E(n) of the selected multiple samples. x (n),E y (n) is polarized and separated into multiple sample received signals E X(n),E Y The polarization processing determination unit 26 generates a received signal E(n) included in the selected samples. x (n) and the received signal E y For the combination of (n), an addition operation is performed on the same sample numbers to obtain E corresponding to each of the multiple samples. x (n)+E y The polarization processing determination unit 26 calculates a received signal E(n) contained in the multiple samples generated by polarization separation. X (n) and the received signal E Y For the combinations of (n), an addition operation is performed on the same sample numbers to obtain E X (n)+E Y The received signal (n) is calculated.

[0117] The polarization processing determination unit 26 calculates the received signal E x (n)+E y The change pattern of (n) and the calculated received signal E for each of the multiple samples X (n)+E Y Whether or not polarization separation is necessary is determined based on whether the change pattern of (n) is similar to that of (n).

[0118] The polarization processing determination unit 26, for example, receives a plurality of samples of a received signal E x (n)+E y (n) and the received signal E X (n)+E Y Based on (n), a calculation is performed to calculate the sum of the absolute values ​​of the differences for each sample number, that is, the calculation of the following equation (7).

[0119]

number

[0120] In equation (7), the first received signal E x (i),E yThe sample number i in (i) is “n”, and N is the number of samples selected by the polarization processing determination unit 26. N is an integer equal to or greater than 2, and is preferably a predetermined value large enough to identify the degree of similarity between change patterns.

[0121] When the sum of the absolute values ​​of the differences calculated by the formula (7) is less than a predetermined threshold, the polarization processing determination unit 26 determines E x (n)+E y The pattern of change in (n) and the corresponding E for multiple samples calculated X (n)+E Y In this case, the effect of polarization dispersion can be regarded as being negligibly small, and the polarization processing determining unit 26 determines that there is no need to perform polarization splitting.

[0122] On the other hand, when the sum of the absolute values ​​of the differences calculated by the formula (7) is equal to or greater than a predetermined threshold, the polarization processing determination unit 26 determines E x (n)+E y The pattern of change in (n) and the corresponding E for multiple samples calculated X (n)+E Y In this case, the effect of polarization dispersion cannot be regarded as being negligibly small, and the polarization processing determination unit 26 determines that polarization separation is required.

[0123] The polarization processing determination unit 26 receives all the received signals E x (n),E y (n) to the polarization processing switching unit 22b-1, and also outputs the determination result to the polarization processing switching unit 22b-1 (step Srb2).

[0124] The polarization processing switching unit 22b-1 receives the received signal E x (n),E yThe polarization processing switching unit 22b-1 takes in information indicating the modulation method output by the operation unit 25. The polarization processing switching unit 22b-1 determines the type of the taken-in information indicating the modulation method (step Srb3). When the polarization processing switching unit 22b-1 determines that the taken-in information indicating the modulation method is information indicating the first single polarization modulation method (step Srb3, first single polarization modulation method), the polarization processing switching unit 22b-1 further determines whether or not the taken-in determination result is a determination result indicating the need to perform polarization splitting (step Srb4).

[0125] When the determination result output by the polarization processing determination unit 26 indicates that polarization splitting is not necessary, and therefore the determination result indicates that polarization splitting is not necessary (step Srb4, No), the polarization processing switching unit 22b-1 switches the received signal E x (n),E y The polarization processing switching unit 22b-1 switches the output destination of the received signal E x (n),E y 7. In the process of step Srb7, the FIR filter unit 41 outputs the filtered received signal E x (n)+E y (n) is output to the decoding unit 43, not to the carrier recovery unit .

[0126] If the polarization processing switching unit 22b-1 determines in step Srb3 that the information indicating the acquired modulation method is information other than the information indicating the first single polarization modulation method, i.e., information indicating the polarization multiplexing modulation method or the second single polarization modulation method (step Srb3, polarization multiplexing modulation method or second single polarization modulation method), or if the polarization processing switching unit 22b-1 determines in step Srb4 that the determination result output by the polarization processing determination unit 26 indicates that polarization separation is necessary (step Srb4, Yes), the polarization processing switching unit 22b-1 x (n),E y (n) is switched to the polarization separator 23, and the received signal E x (n),E y (n) is output to the polarization separator 23 (step Srb9).

[0127] The polarization splitter 23 splits the received signal E x (n),E y The polarization splitter 23 takes in the received signal E(n). x (n),E y (n) is subjected to polarization separation, and the polarization-separated received signal E X (n),E Y The polarization splitter 23 generates the polarization-split received signal E(n). X (n),E Y (n) is output to the polarization processing switching unit 22b-2 of the signal decoding unit 24b-2 (step Srb10).

[0128] The polarization processing switching unit 22b-2 receives the received signal E X (n),E Y The polarization processing switching unit 22b-2 takes in information indicating the modulation method output by the operation unit 25. The polarization processing switching unit 22b-2 determines the type of the taken-in information indicating the modulation method (step Srb11). When the polarization processing switching unit 22b-2 determines that the taken-in information indicating the modulation method is information indicating the polarization multiplexing modulation method (step Srb11, polarization multiplexing modulation method), it selects the taken-in reception signal E X (n),E Y(n) is switched to the signal decoding unit 24a-3, and the received signal E X (n) to the decoding unit 53-1, and the received signal E Y (n) is output to the decoding unit 53-2 (step Sra12). After that, in step Srb13, the same process as in step Sra13 in FIG.

[0129] On the other hand, in step Srb11, when the polarization processing switching unit 22b-2 determines that the information indicating the acquired modulation method is information indicating the first single polarization modulation method or information indicating the second single polarization modulation method (step Srb11, first or second single polarization modulation method), X (n),E Y (n) is switched to the signal decoding unit 24a-4, and the received signal E X (n),E Y (n) to the adder 60 (step Srb14). After that, in steps Srb15 and Srb16, the same processes as those in steps Sra15 and Sra17 in FIG. 7 are performed by the adder 60 and the decoding unit 63 of the signal decoding unit 24a-1. Note that in the process of step Srb15, the adder 60 outputs the calculated received signal E X (n)+E Y (n) is output to the decoding unit 63 rather than to the carrier recovery unit 62.

[0130] In the receiver 2b of the third embodiment, the polarization process determination unit 26 is configured to determine whether or not polarization separation is necessary, that is, whether or not the polarization dispersion in the optical fiber transmission line 3 is negligibly small, based on the reception signals corresponding to the X-polarized wave and the Y-polarized wave output by the receiver 21 and the reception signals obtained by polarization separation of the reception signals corresponding to the X-polarized wave and the Y-polarized wave output by the receiver 21. Therefore, when the polarization dispersion in the optical fiber transmission line 3 is not negligibly small, the receiver 2b can perform polarization separation by the polarization separation unit 23 on the optical signal modulated by the first single polarization modulation method. Therefore, in addition to the effects achieved by the receivers 2 and 2a of the first and second embodiments, the receiver 2b of the third embodiment can perform more accurate decoding processing when receiving an optical signal modulated by the first single polarization modulation method.

[0131] In the third embodiment described above, after the polarization processing determination unit 26 outputs the determination result to the polarization processing switching unit 22b-1 in the process of step Srb2 in FIG. 12, the received signal E x (n),E y When (n) is captured, the captured received signal E x (n),E y In response to this, the polarization processing determination unit 26 continues to output the received signal E(n) to the polarization processing switching unit 22b-1 for a predetermined period of time. x (n),E y (n) is not output, and the received signal E output by the signal detection unit 34 thereafter x (n),E y When (n) is captured again, the process of step Srb2 may be performed again and the new determination result may be output to the polarization processing switching unit 22b-1. In this case, the polarization processing switching unit 22b-1 performs the process of step Srb4 in FIG. 12 based on the new determination result output by the polarization processing determination unit 26 to obtain the received signal E x (n),E y The output destination of (n) is selected to be either the signal decoding unit 24a-1 or the polarization separation unit 23.

[0132] In the third embodiment, the polarization processing determination unit 26 detects the received signal E x (n),E y The polarization processing determination unit 26 first receives the received signal E x (n),E y N consecutive received signals E in time series starting with (n) x (n),E y In response to this, the polarization processing determination unit 26 selects the received signal E x (n),E y The polarization processing determination unit 26 receives the received signal E x (n),E y (n) of any N consecutive received signals E x (n),E y Alternatively, option (n) may be selected.

[0133] In the third embodiment described above, the polarization processing determination unit 26 determines whether or not the sum of the absolute values ​​of the differences calculated by equation (7) is less than a predetermined threshold value in the process of step Srb2 in Fig. 12. In contrast, the polarization processing determination unit 26 may determine whether or not the sum of the absolute values ​​of the differences is equal to or less than the threshold value, depending on how the threshold value is defined.

[0134] (Other configuration examples of each embodiment) As another configuration example of the first embodiment, similarly to the third embodiment, when an optical signal modulated by the first single polarization modulation method is received in a state in which the influence of polarization dispersion cannot be ignored, the receiving device 2 may perform polarization separation by the polarization separation unit 23. That is, in the receiving device 2 of the first embodiment, the polarization processing switching unit 22b-1 of the third embodiment may be applied instead of the polarization processing switching unit 22-1, the polarization processing switching unit 22b-2 of the third embodiment may be applied instead of the polarization processing switching unit 22-2, and a polarization processing determination unit 26 connected to the signal detection unit 34 and the polarization processing switching unit 22b-1 may be provided.

[0135] As another configuration example of the first embodiment, the polarization processing switching unit 22c-1 shown in FIG. 13 may be applied instead of the polarization processing switching unit 22-1 included in the receiving device 2 of the first embodiment, and the signal decoding unit 24b-1 shown in FIG. 13 may be applied instead of the signal decoding unit 24-1. The signal decoding unit 24b-1 includes an FIR filter unit 41, a carrier recovery unit 42, and a decoding unit 43, and differs from the signal decoding unit 24-1 of the first embodiment in that it does not include the adder unit 40. When the information indicating the modulation method output by the operation unit 25 is information indicating the first single polarization modulation method, the polarization processing switching unit 22c-1 performs the steps of: x (n) and the received signal E y 13, the polarization processing switching unit 22c-1 has the same configuration as the polarization processing switching unit 22-1 of the first embodiment, except that the polarization processing switching unit 22c-1 outputs one of the received signals E x 4. In the case of the first single polarization modulation method, the received signal E x (n) and the received signal E y Therefore, the decoding unit 43 included in the signal decoding unit 24b-1 decodes the received signal E x (n) and the received signal E y Even if the decoding process is performed based on either one of (a) and (b), the transmission signal generated by the transmission signal generator 14-1 can be restored. That is, when the signal decoder 24-1 of the first embodiment decodes the two-series received signal E x (n),E y (n) to E, a series of received signals x (n)+E y (n) to decode a single sequence of transmitted signals, whereas the signal decoder 24b-1 decodes two sequences of received signals E x (n),E y In other words, one sequence of transmitted signals is decoded from one sequence of received signals of either one of (n).

[0136] 13, the signal decoding unit 24-4 and the polarization processing switching unit 22-2 included in the receiving device 2 of the first embodiment may be configured as follows. That is, the signal decoding unit 24-4 is configured without the adder 60. The polarization processing switching unit 22-2 is configured so that when it is determined that the information indicating the modulation method output by the operation unit 25 is information indicating the second single polarization modulation method, the received signal E output by the polarization separation unit 23 is X (n),E Y After switching the output destination of (n) to the signal decoding unit 24-4, the received signal E X (n) and the received signal E Y (n) is output to the carrier recovery unit 62 of the signal decoding unit 24-1, which is configured without the adding unit 60. As described above, in the case of the second single polarization modulation method, the polarization splitting process by the polarization splitter 23 outputs the received signal E X (n) and the received signal E Y Therefore, the decoding unit 63 decodes the received signal E X (n) and the received signal E Y Even if the decoding process is performed based on either one of (n), the transmission signal generated by the transmission signal generating unit 14-1 can be restored.

[0137] In the second and third embodiments, the signal decoder 24a-1 is configured to exclude the adder 40, and the signal decoder 24a-4 is configured to exclude the adder 60. In this case, when the polarization processing switchers 22-1 and 22b-1 output the signal decoder 24a-1, the received signal E x (n) and the received signal E y (n) and the polarization processing switching units 22-2 and 22b-2 output the received signal E X (n) and the received signal E Y It is also possible to configure the device to output either one of (n).

[0138] In the above-mentioned first embodiment, as an example, the IQ modulation units 13-1 and 13-2 of the transmitting device 1 perform modulation by the QPSK modulation method. In contrast, the IQ modulation units 13-1 and 13-2 may perform modulation by a higher multi-level modulation method than QPSK, such as 16QAM (Quadrature Amplitude Modulation). In this case, the receiving device 2 needs to have a polarization separation unit as shown in the following reference document that performs polarization separation in the high multi-level modulation method, instead of the polarization separation unit 23. The coherent receiving unit 32 of the receiving device 2 needs to have a configuration that coherently detects the optical signal modulated by the high multi-level modulation method.

[0139] [Reference: Irshaad Fatadin, et al., “Blind Equalization and Carrier Phase Recovery in a 16-QAM Optical Coherent System”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 27, NO. 15, AUGUST 1, 2009]

[0140] In the above first to third embodiments and other configuration examples of each embodiment, common functional units, for example, each of the addition units 40, 60, each of the carrier recovery units 42, 52-1, 52-2, 62, and each of the decoding units 43, 53-1, 53-2, 63 in the receiving device 2 of the first embodiment, may share circuits when configured in hardware, or may share functions when configured in software.

[0141] In the above first to third embodiments and other configuration examples of each embodiment, the operation units 17, 25 are configured to output information indicating one of the polarization modulation method, the first single polarization modulation method, and the second single polarization modulation method in response to a user's operation. Alternatively, an external device may be connected to the operation units 17, 25 so that the user can operate the operation units 17, 25 via the external device, or the operation units 17, 25 may output information indicating the modulation method in response to a request from an application running in the external device.

[0142] In the above first to third embodiments and other configuration examples of each embodiment, the transmitting device 1, 1a may be configured to generate and emit a radio signal into the air instead of an optical signal, and the receiving devices 2, 2a, 2b may be configured to receive the radio signal.

[0143] The operation unit 17, the transmission signal generating units 14-1 and 14-2, the modulation signal switching unit 16, the polarization processing switching units 22-1, 22-2, 22b-1 and 22b-2, the polarization splitting unit 23, and the signal decoding units 24-1, 24-3, 24-4, 24a-1, 24a-3 and 24a-4 in the above-mentioned embodiment may be realized by a computer. In this case, a program for realizing the functions may be recorded in a computer-readable recording medium, and the program recorded in the recording medium may be read into a computer system and executed to realize the functions. Note that the "computer system" here includes hardware such as an OS and peripheral devices. Also, the "computer-readable recording medium" refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, and a storage device such as a hard disk built into a computer system. Furthermore, the term "computer-readable recording medium" may include a medium that dynamically holds a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, and a medium that holds a program for a certain period of time, such as a volatile memory inside a computer system that serves as a server or client in such a case. The above program may be one for implementing part of the above-mentioned functions, or may be one that can realize the above-mentioned functions in combination with a program already recorded in the computer system, or may be one that is realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0144] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and designs that do not deviate from the gist of the present invention are also included. [Industrial Applicability]

[0145] The present invention can be applied to a receiving device that receives a signal modulated by a polarization multiplexing modulation method or a single polarization modulation method. [Explanation of symbols]

[0146] 1...transmitting device, 2...receiving device, 3...optical fiber transmission line, 10...polarized wave generating unit, 11...signal light source, 12...polarized beam splitter, 13...modulating unit, 13-1, 13-2...IQ modulating unit, 14-1, 14-2...transmitting signal generating unit, 15...polarized wave multiplexing unit, 16...modulated signal switching unit, 17...operating unit, 21...receiving unit, 22-1, 22-2...polarized wave processing switching unit, 23... Polarization separation unit, 24-1, 24-2, 24-3, 24-4...signal decoding unit, 31...local oscillator light source, 32...coherent receiving unit, 33...clock synchronization unit, 34...signal detection unit, 40, 60...adding unit, 41...FIR filter unit, 42, 52-1, 52-2, 62...carrier recovery unit, 43, 53-1, 53-2, 63...decoding unit, 100...transmission system

Claims

1. a receiving unit that receives a signal in which X polarization and Y polarization are polarization-multiplexed, converts the received signal into a received signal corresponding to each of the X polarization and the Y polarization, and outputs the received signal; a first signal decoding unit that decodes a sequence of a transmission signal from the reception signal output by the reception unit; a polarization splitter that splits the received signals corresponding to the X-polarized wave and the Y-polarized wave output from the receiver; a second signal decoding unit that decodes the received signal that has been polarization-separated by the polarization separation unit; a first polarization processing switching unit that receives a received signal corresponding to each of the X-polarized wave and the Y-polarized wave output from the receiving unit, and switches an output destination of the received signal to either the first signal decoding unit or the polarization splitter based on information indicating a modulation method; A receiving device comprising:

2. the information indicating the modulation method is information indicating that the X-polarized wave and the Y-polarized wave are signals modulated by the same transmission signal, or information indicating that the X-polarized wave and the Y-polarized wave are signals other than signals modulated by the same transmission signal, The first polarization processing switching unit includes: when the information indicating the modulation method indicates that the X-polarized wave and the Y-polarized wave are signals modulated by the same transmission signal, the output destination of the captured received signal is switched to the first signal decoding unit, and when the information indicating the modulation method indicates that the X-polarized wave and the Y-polarized wave are signals other than signals modulated by the same transmission signal, the output destination of the captured received signal is switched to the polarization separation unit.

2. The receiving device according to claim 1.

3. The second signal decoding unit a third signal decoding unit that decodes the received signal that has been polarization-separated by the polarization separation unit into two series of transmission signals; a fourth signal decoding unit that decodes the received signal that has been polarization-separated by the polarization separation unit into a single series of transmission signals; a second polarization processing switching unit that receives a received signal corresponding to each of the X-polarized wave and the Y-polarized wave separated by the polarization separation unit, and switches an output destination of the received signal to either the third signal decoding unit or the fourth signal decoding unit based on information indicating the modulation method; Equipped with The information indicating the modulation method is any one of information indicating that the X-polarized wave and the Y-polarized wave are signals modulated by the same transmission signal, information indicating that the X-polarized wave and the Y-polarized wave are signals modulated by different transmission signals, and information indicating that either the X-polarized wave or the Y-polarized wave is a signal modulated by a transmission signal; The second polarization processing switching unit includes: when the information indicating the modulation method indicates that the X-polarized wave and the Y-polarized wave are signals modulated by different transmission signals, the output destination of the captured received signal is switched to the third signal decoding unit, and when the information indicating the modulation method indicates that either the X-polarized wave or the Y-polarized wave is a signal modulated by a transmission signal, the output destination of the captured received signal is switched to the fourth signal decoding unit.

3. The receiving device according to claim 2.

4. a polarization processing determination unit that determines whether or not polarization separation is required based on received signals obtained by polarization separation of the received signals corresponding to the X-polarized wave and the Y-polarized wave output by the receiving unit and the received signals corresponding to the X-polarized wave and the Y-polarized wave output by the receiving unit, The first polarization processing switching unit includes: when the information indicating the modulation method is information indicating that the X-polarized wave and the Y-polarized wave are signals modulated by the same transmission signal and the determination result of the polarization processing determination unit is not a determination result that polarization separation is necessary, the output destination of the captured received signal is switched to the first signal decoding unit; when the information indicating the modulation method is information indicating that the X-polarized wave and the Y-polarized wave are signals modulated by the same transmission signal and the determination result of the polarization processing determination unit is a determination result that polarization separation is necessary, the output destination of the captured received signal is switched to the polarization separation unit; The second polarization processing switching unit includes: when the information indicating the modulation method is information indicating that the X-polarized wave and the Y-polarized wave are signals modulated by different transmission signals, the output destination of the captured received signal is switched to the third signal decoding unit, and when the information indicating the modulation method is either information indicating that the X-polarized wave and the Y-polarized wave are signals modulated by the same transmission signal or information indicating that either the X-polarized wave or the Y-polarized wave is a signal modulated by a transmission signal, the output destination of the captured received signal is switched to the fourth signal decoding unit.

4. The receiving device according to claim 3.

5. Two transmission signal generators for generating different transmission signal sequences; a modulation signal switching unit that selectively outputs both or one of the two transmission signals of the different transmission signal sequences generated by the two transmission signal generating units, based on information indicating a modulation method; a polarization generating unit that separates a carrier wave into an X direction and a Y direction to generate an X polarized wave and a Y polarized wave; a modulation unit that modulates each of the X-polarized wave and the Y-polarized wave generated by the polarization generation unit based on the transmission signal selectively output by the modulation signal switching unit; a polarization multiplexing unit that transmits the X-direction and Y-direction modulated signals modulated by the modulation unit through polarization multiplexing; A transmitting device comprising:

6. A transmission system including a transmitting device and a receiving device, The transmitting device a modulation signal switching unit that selectively outputs both or one of the two transmission signals based on information indicating a modulation method; a polarization generating unit that separates a carrier wave into an X direction and a Y direction to generate an X polarized wave and a Y polarized wave; a modulation unit that modulates each of the X-polarized wave and the Y-polarized wave generated by the polarization generation unit based on the transmission signal selectively output by the modulation signal switching unit; a polarization multiplexing unit that transmits the X-direction and Y-direction modulated signals modulated by the modulation unit through polarization multiplexing; Equipped with The receiving device includes: a receiving unit that receives a signal in which X polarization and Y polarization are polarization-multiplexed, converts the received signal into a received signal corresponding to each of the X polarization and the Y polarization, and outputs the received signal; a first signal decoding unit that decodes a sequence of a transmission signal from the reception signal output by the reception unit; a polarization splitter that splits the received signals corresponding to the X-polarized wave and the Y-polarized wave output from the receiver; a second signal decoding unit that decodes the received signal that has been polarization-separated by the polarization separation unit; a first polarization processing switching unit that receives a received signal corresponding to each of the X-polarized wave and the Y-polarized wave output from the receiving unit, and switches an output destination of the received signal to either the first signal decoding unit or the polarization splitter based on information indicating a modulation method; A transmission system comprising:

7. a receiving unit receiving a signal in which the X-polarized wave and the Y-polarized wave are polarization-multiplexed, converting the received signal into a received signal corresponding to each of the X-polarized wave and the Y-polarized wave, and outputting the received signal; a first polarization processing switching unit that receives reception signals corresponding to the X-polarized wave and the Y-polarized wave output from the receiving unit, and switches an output destination of the received reception signals to either a first signal decoding unit or a polarization separation unit based on information indicating a modulation method; the first signal decoding unit decodes a series of transmission signals from the reception signals output by the first polarization processing switching unit; the polarization splitter performs polarization splitting of the reception signal corresponding to each of the X-polarized wave and the Y-polarized wave output from the first polarization processing switching unit, a second signal decoding unit that decodes the received signal that has been polarization-separated by the polarization separation unit; Receiving method.

8. Two transmission signal generators generate different transmission signal sequences; a modulation signal switching unit selectively outputs both or either one of the two transmission signals of the different transmission signal series generated by the two transmission signal generating units, based on information indicating a modulation method; A polarization generation unit separates the carrier wave into an X direction and a Y direction to generate an X polarized wave and a Y polarized wave, a modulation unit modulating each of the X-polarized wave and the Y-polarized wave generated by the polarization generation unit based on the transmission signal selectively output by the modulation signal switching unit; a polarization multiplexing unit that polarization-multiplexes the modulated signals in the X direction and the Y direction modulated by the modulation unit and transmits the signals; Transmission method.

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