Patent Application
20180183542
The present invention relates to an optical transmission device, an optical reception device, an optical transmission system, and an optical transmission method.
To perform long-distance large-capacity transmission with an optical fiber, a problem is to overcome high-density signal multiplexing and a fiber nonlinear optical effect.
In an optical transmission device, it is possible to increase a transmission capacity per one optical fiber by carrying different kinds of information on a plurality of optical carrier waves or optical sub-carrier waves, which are sub-carriers, and performing high-density wavelength multiplexing. The optical carrier waves and the optical sub-carrier waves to be multiplexed are respectively called channels. It is also possible to increase the transmission capacity by multiplexing a modulation scheme.
As the modulation scheme, On Off Keying (OKK) for allocating binary signals to presence and absence of light and transmitting one bit per one symbol has been used. However, as in Quaternary Phase-Shift Keying (QPSK) or 16 Quadrature Amplitude Modulation (QAM), it is possible to increase a transmission capacity by increasing signal points and increasing the number of transmission bits per one symbol. In the QPSK and the 16QAM, in an optical transmission device, signals are allocated to an in-phase axis (I axis) and a quadrature-phase axis (Q axis).
There is a known scheme for increasing the number of transmission bits per one symbol by a factor of two by using polarization multiplexing. In polarization multiplexing, it is possible to independently allocate signals to vertical polarization and horizontal polarization, which are two polarization components that are orthogonal to each other.
For demodulation of an OOK signal, a direct detection scheme for detecting and identifying presence or absence of an optical signal on a reception side has been used. For demodulation of a Differential Binary Phase-Shift Keying (DBPSK) signal, a Differential QPSK (DQPSK) signal, and the like, a delay detection scheme or a direct delay detection scheme for directly detecting an optical signal after causing delayed interference of the optical signal has been used. In the polarization multiplexing, a digital coherent scheme for compensating, with digital signal processing, an electric signal obtained by performing coherent detection for causing mixed interference of a local-oscillation light source and a reception signal at a reception end and detecting the reception signal is used. In the digital coherent scheme, a polarization multiplexing QPSK scheme is widely used (see, for example, Non Patent Literature 1 and 2).
On the other hand, when long-distance optical transmission is performed, to secure signal quality at a reception end, an optical signal power-to-noise power ratio corresponding to a bit rate, a modulation scheme, a detection scheme, and the like is necessary. Therefore, it is necessary to perform signal transmission with high optical power. At this time, waveform distortion due to a nonlinear optical effect occurring in an optical fiber deteriorates signal quality (see, for example, Patent Literature 1). The nonlinear optical effect can be roughly divided into an effect occurring in a channel and an effect occurring between channels.
Examples of the nonlinear optical effect occurring in the channel include Self-Phase Modulation (SPM). As a narrow definition, the SPM is classified into Intra-channel SPM (ISPM), Intra-channel Cross-Phase Modulation (IXPM), Intra-channel Four-Wave Mixing (IFWM), and the like. Examples of the nonlinear optical effect occurring between channels include Cross-Phase Modulation (XPM), Four-Wave Mixing (FWM), and Cross Polarization Modulation (XPolM). All of the XPM, the FWM, the XPolM, and the like conspicuously occur when the optical power density of a signal is high and when a transmission distance is long. In the nonlinear optical effect occurring between channels, polarization states of optical signals of the channels have a correlation for a long time in a transmission line when local wavelength dispersion of the transmission line is small or when a wavelength interval of the channels to be wavelength-multiplexed is narrow. When interaction continues, quality deterioration is conspicuous.
In a polarization multiplexed signal, a polarization state changes according to an optical phase difference between vertical polarization and horizontal polarization. Therefore, a relation between a signal carried on the vertical polarization and a signal carried on the horizontal polarization affects a polarization state of a signal.
To reduce the nonlinear optical effect in the channel, there has also been proposed a scheme for performing Return-to-Zero (RZ) pulsing of a signal based on polarization multiplexing and then halving a pulse width of the signal and allocating signal orthogonal polarization alternately for each half symbol (see, for example, Patent Literature 1).
In an orthogonal polarization multiplexed signal, a scheme for applying the RZ pulsing and shifting the RZ pulse by a half symbol between orthogonal polarizations without changing the pulse width of the signal is known as an interleaved RZ (iRZ) scheme. A Binary Phase-Shift Keying (BPSK) scheme that can improve resistance against waveform distortion due to the nonlinear optical effect is also used because an inter-signal point distance can be further expanded than the QPSK widely used in the digital coherent scheme. With polarization multiplexed iRZ-BPSK obtained by combining the iRZ and the polarization multiplexed BPSK, it is possible to expand a system margin in most cases in long-distance optical transmission (see, for example, Non Patent Literature 3).
However, according to the conventional technologies of Non Patent Literature 3 and Patent Literature 1, there is a problem in that a large number of components are used in the optical transmission device, such as a modulator for RZ pulsing, an optical modulator for polarization multiplexed BPSK, and an optical filter. There is also a problem in that, among the components, there are components that are not versatile and are not easily acquired. There is also a problem in that the conventional optical transmission device does not have compatibility with other modulation and demodulation schemes, for example, schemes such as the polarization multiplexed QPSK, the polarization multiplexed 16QAM, and a modulation scheme not requiring the RZ pulsing. There is a problem in that signal quality deterioration due to a band characteristic and the like of the modulator for RZ pulsing occurs. Further, there is a problem in that, depending on a transmission condition, it is difficult to secure a system margin even if not only the polarization multiplexed QPSK signal but also the polarization multiplexed BPSK signal is used.
The present invention has been devised in view of the above, and an object of the present invention is to obtain an optical transmission device capable of transmitting an optical signal having high nonlinear resistance with a simple configuration of components.
To solve the problems and achieve the object, an optical transmission device of the present invention includes a data duplicating unit that duplicates signals of lanes subjected to symbol mapping and sets a number of the lanes to a number of lanes of a first number. The optical transmission device includes a waveform converting unit that waveform-converts, concerning the signals of the lanes, a signal that can take a value of a type of a second number into a signal that can take a value of a type of a third number larger than the second number. The optical transmission device includes a polarity inverting unit that inverts polarity of signals of one or more lanes among the lanes in which the numbers of the values that the signals can take are converted. The optical transmission device includes a lane replacing unit that performs replacement of lanes in two or more lanes. The optical transmission device includes an optical-signal generating unit that converts electric signals of the signals of the lanes input from the lane replacing unit into optical signals and combines and outputs the optical signals of the lanes.
The optical transmission device according to the present invention achieves an effect that it is possible to transmit an optical signal having high nonlinear resistance with a simple configuration of components.
Optical transmission devices, optical reception devices, optical transmission systems, and optical transmission methods according to embodiments of the present invention are explained in detail below with reference to the drawings. Note that the present invention is not limited by the embodiments.
An operation in which the optical transmission device 100 transmits an optical signal and the optical reception device 300 receives the optical signal via the transmitting unit 200 in the optical transmission system 1 is explained here.
The symbol mapping unit 111 of the transmission-electricity processing unit 110 performs symbol mapping on logical signals, which are binary data signals of two lanes, one for an X polarized wave and another for Y polarized wave input from external destinations (step S1). After the symbol mapping, the symbol mapping unit 111 outputs the binary electric field signals of the two lanes to the data duplicating unit 112. The binary data signals of the two lanes input to the symbol mapping unit 111 are, for example, data signals obtained by adding parity for error correction or the like to a 50 Gbit/s-class data signal in which Optical Transport Unit Level 4 (OTU4) is duplicated. The symbol mapping unit 111 maps one data signal onto one symbol. In the following explanation, a state in which one data signal is present in one symbol is represented as 1 Sample/Symbol. The symbol mapping unit 111 performs processing on 1 Sample/Symbol.
The data duplicating unit 112 performs duplication processing on the binary electric field signals of the two lanes input from the symbol mapping unit 111 (step S2). The data duplicating unit 112 generates binary electric field signals in four lanes by using the duplication processing and outputs the generated binary electric field signals of the four lanes to the waveform converting unit 113. The data duplicating unit 112 performs processing on 1 Sample/Symbol. The data duplicating unit 112 duplicates the binary electric field signal of the lanes subjected to symbol mapping and sets the number of lanes to a number of lanes that is equivalent to a first number. The first number is four.
The waveform converting unit 113 inserts zero between sample points with respect to the binary electric field signals of the four lanes represented by 1 Sample/Symbol input from the data duplicating unit 112 and converts the waveform, or waveform-converts, of the binary electric field signal into 2 Sample/Symbol (step S3). The waveform converting unit 113 performs a compensation that is well known in the industry related to band limitation in the optical-signal generating unit 120 and outputs a four-lane multi-value signal represented by 2 Sample/Symbol to the polarity inverting unit 144. Specifically, the waveform converting unit 113 converts the binary electric field signals into a multi-value signal that can take three values: Hi, Low, and the inserted zero. The waveform converting unit 113 waveform-converts, concerning the duplicated binary electric field signals of the lanes, a signal that can take a value of a type of a second number into a signal that can take a value of a type of a third number larger than the second number. The second number is two and the third number is three.
The polarity inverting unit 114 inverts the polarity of a signal of any lane with respect to the four-lane multi-value signal represented by 2 Sample/Symbol input from the waveform converting unit 113 (step S4). The polarity inverting unit 114 outputs the four-lane multi-value signal represented by 2 Sample/Symbol, in which the polarity of the signal of any lane is inverted, to the delay adding unit 115. The polarity inverting unit 114 inverts the polarity of signals of one or more lanes among the lanes of the four-lane multi-value signal in which the number of values that a signal can take is converted.
The delay adding unit 115 adds a delay among the four lanes with respect to the four-lane multi-value signal represented by 2 Sample/Symbol input from the polarity inverting unit 114 (step S5); however, in this embodiment, the delay adding unit 115 sets the delay amount among the four lanes to zero, i.e., it does not perform the addition of a delay. The addition of a delay is explained in a second embodiment and subsequent embodiments. The delay adding unit 115 does not perform the delay addition in the first embodiment; however, the delay adding unit 115 performs compensation that is well known in the industry related to an unintended delay shift occurring in the optical-signal generating unit 120 and outputs the four-lane multi-value signal represented by 2 Sample/Symbol to the lane replacing unit 116.
The lane replacing unit 116 performs lane replacement on the four-lane multi-value signal represented by 2 Sample/Symbol input from the delay adding unit 115 (step S6). The lane replacing unit 116 outputs the four-lane multi-value signal represented by 2 Sample/Symbol after the lane replacement to the optical-signal generating unit 120. The lane replacing unit 116 performs replacement of lanes on two or more lanes.
The optical-signal generating unit 120 generates an optical signal on the basis of the four-lane multi-value signal represented by 2 Sample/Symbol input from the lane replacing unit 116 of the transmission-electricity processing unit 110 and outputs the optical signal to the transmitting unit 200 (step S7). The optical-signal generating unit 120 converts an electric signal of the four-lane multi-value signal input from the lane replacing unit 116 into an optical signal and combines and outputs optical signals of the lanes.
The operation of the optical-signal generating unit 120 is explained in detail here. The digital/analog converter 51 of the optical-signal generating unit 120 performs digital/analog conversion on a digital signal of the four-lane multi-value signal represented by 2 Sample/Symbol input from the lane replacing unit 116 of the transmission-electricity processing unit 110 and outputs an analog signal after the conversion to the modulator driver 52. For example, when the digital signal input from the lane replacing unit 116 of the transmission-electricity processing unit 110 is configured to have four lanes, which are a vertical polarization I-axis signal, a vertical polarization Q-axis signal, a horizontal polarization I-axis signal, and a horizontal polarization Q-axis signal, then the digital/analog converter 51 performs digital/analog conversion processing on each of the four lanes. The digital/analog converter 51 outputs analog signals of the four lanes to the modulator driver 52.
Note that, in the following explanation, “vertical” of the vertical polarization I-axis signal and the vertical polarization Q-axis signal is sometimes represented as V (Vertical). The vertical polarization I-axis signal and the vertical polarization Q-axis signal are sometimes represented as V polarization I-axis signal and the V polarization Q-axis signal. “Horizontal” of the horizontal polarization I-axis signal and the horizontal polarization Q-axis signal is sometimes represented as H (Horizontal). The horizontal polarization I-axis signal and the horizontal polarization Q-axis signal are sometimes represented as H polarization I-axis signal and the H polarization Q-axis signal.
The modulator driver 52 amplifies the analog signal input from the digital/analog converter 51 and outputs the analog signal after the amplification to the polarization multiplexed I/Q optical modulator 54. For example, when the analog signal input from the digital/analog converter 51 is configured to have four lanes, which are the H polarization I-axis signal, the H polarization Q-axis signal, the V-polarization I-axis signal, and the V-polarization Q-axis signal, then the modulator driver 52 performs amplification processing on each of the four lanes. The modulator driver 52 outputs the analog signal after the amplification of the four lanes to the polarization multiplexed I/Q optical modulator 54.
The light source 53 generates unmodulated light having a wavelength that follows the grid of a C band of the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T), i.e., in a C band of 1530 nanometers to 1565 nanometers conforming to ITU-T G694.1, and outputs the unmodulated light to the polarization multiplexed I/Q optical modulator 54.
The polarization multiplexed I/Q optical modulator 54 modulates the unmodulated light input from the light source 53 with the amplified analog electric signal input from the modulator driver 52 and outputs the unmodulated light to the transmitting unit 200.
The transmitting unit 200 transmits the optical signal input from the polarization multiplexed I/Q converter 54 of the optical-signal generating unit 120 of the optical transmission device 100 and outputs the optical signal to the optical reception device 300. It is assumed that the configuration of the transmitting unit 200 includes, besides a transmission line fiber, for example, an optical multiplexing and demultiplexing device in a configuration that includes a wavelength selective switch (WSS), an arrayed waveguide grating (AWG), an interleaver, an optical coupler; an optical amplifier for loss compensation; and an optical fiber for wavelength dispersion compensation.
The local-oscillation light source 61 of the optical-signal detecting unit 320 generates, for example, unmodulated light at a wavelength that follows the ITU-T grid of the C band and outputs the unmodulated light to the coherent receiver 62, which is a polarization diversity-type integrated coherent receiver. The wavelength of the unmodulated light emitted by the local-oscillation light source 61 needs to substantially coincide with the wavelength of a carrier wave or a sub-carrier wave of an optical signal input to the coherent receiver 62 from the transmitting unit 200.
The coherent receiver 62 causes mixed interference of the optical signal input from the transmitting unit 200 and the unmodulated light input from the local-oscillation light source 61; converts the optical signal into an electric signal; and outputs the electric signal to the analog/digital converter 63. When detecting a reception signal separately in four lanes, which are an H′ polarization I′-axis component, an H′ polarization Q′-axis component, a V′ polarization I′-axis component, and a V′ polarization Q′ axis component, on the basis of local oscillation light, the coherent receiver 62 converts the optical signals of the four lanes respectively into electric signals; amplifiers the respective electric signals of the four lanes after the conversion to an amplitude necessary for processing at a post stage; and outputs the electric signals. Note that “′” is given to H′, V′, I′, and Q′. This is to indicate that, in the optical reception device 300, a horizontal polarization component, a vertical polarization component, an in-phase axis component, and a quadrature phase axis component obtained from a received optical signal are not always the same as a horizontal polarization component, a vertical polarization component, an in-phase axis component, and a quadrature phase axis component of the lanes generated by the optical transmission device 100.
The analog/digital converter 63 analog/digital-converts the electric signal input from the coherent receiver 62 and outputs an electric digital signal after the conversion to the received electricity processing unit 310. The analog/digital converter 63 performs analog/digital conversion processing related to each of the four lanes of the H′ polarization I′-axis component, the H′ polarization Q′-axis component, the V′ polarization I′-axis component, and the V′ polarization Q′ axis component.
The waveform equalizing unit 313 of the received electricity processing unit 310 performs, on the electric digital signal input from the analog/digital converter 63 of the optical-signal detecting unit 320, waveform equalization processing that is well known in the industry to compensate for waveform distortion such as a physical delay difference, wavelength dispersion, and band constriction caused in the optical-signal generating unit 120, the transmitting unit 200, and the optical-signal detecting unit 320 (step S12). The waveform equalizing unit 313 outputs the electric digital signal after the waveform equalization processing to the adaptive equalizing unit 312.
The adaptive equalizing unit 312 performs, on the electric digital signal input from the waveform equalizing unit 313, adaptive equalization processing to compensate for polarization mode dispersion, a polarization state change, symbol timing extraction, an optical frequency difference and an optical phase difference between a carrier wave or a sub-carrier wave and local oscillation light, and the like (step S13). When restoring a transmission signal by using the adaptive equalization processing, the adaptive equalizing unit 312 outputs the transmission signal after the restoration to the symbol demapping unit 311. The adaptive equalizing unit 312 of the received electricity processing unit 310 specifically compensates, by using the adaptive equalization processing, for phase rotation and polarization rotation added to the electric digital signal by the optical transmission device 100, and also collectively restores the electric digital signal related to the processing performed by the waveform converting unit 113, the polarity inverting unit 114, the delay adding unit 115, and the lane replacing unit 116 of the optical transmission device 100. As the adaptive equalization processing performed by the adaptive equalizing unit 312, a digital signal processing well known in the industry can be used. The restored transmission signal changes to, for example, signals of the four lanes XI, XQ, YI, and YQ generated by the data duplicating unit 112 of the transmission-electricity processing unit 110 of the optical transmission device 100. The signals of the four lanes XI, XQ, YI, and YQ are respectively represented as AX[t], AX[t], AY[t], and AY[t].
The symbol demapping unit 311 performs symbol demapping on the basis of the signals of the four lanes, i.e., the transmission signal, after the restoration input from the adaptive equalizing unit 312 (step S14). The symbol demapping unit 311 converts, by using the symbol demapping, the transmission signal after the restoration into binary data signals of two lanes and additional data signals and outputs the binary data signals and the additional data signals to external destinations. The symbol demapping unit 311 is not limited to a 0/1 hard decision and can perform soft decisions for giving reliability information as the additional data signals.
Note that, in the example explained above, the adaptive equalizing unit 312 collectively restores the electric digital signal related to the processing performed by the waveform converting unit 113, the polarity inverting unit 114, the delay adding unit 115, and the lane replacing unit 116 of the optical transmission device 100. The symbol demapping unit 311 performs the symbol demapping on the basis of the signals of the four lanes. However, not only this, but, for example, the adaptive equalizing unit 312 can collectively restore the electric digital signal related to the processing performed by the data duplicating unit 112, the waveform converting unit 113, the polarity inverting unit 114, the delay adding unit 115, and the lane replacing unit 116 of the optical transmission device 100. The symbol demapping unit 311 can perform the symbol demapping on the basis of signals of two lanes.
In the first embodiment, the configuration for performing alternation of the polarization multiplexed BPSK signal is explained. However, this is an example. The optical-signal generating unit 120 of the optical transmission device 100 is compatible with general modulation schemes such as polarization multiplexed QPSK and polarization multiplexed m-value QAM. In the optical-signal generating unit 120 of the optical transmission device 100, it is also possible to realize any spectral shaping.
An example of changes made to signals by processing performed by the components of the optical transmission device 100 according to the first embodiment is explained here.
As a comparative example, an example of signal point arrangement of a polarization multiplexed BPSK signal is explained here.
Note that the phase rotation and the polarization rotation are compensated for by the adaptive equalization processing performed by the adaptive equalizing unit 312 of the received electricity processing unit 310 of the optical reception device 300. For example, the adaptive equalizing unit 312 can restore AX[t] in accordance with the arithmetic operation “(EH[t]+EV[t])/2” and can restore AY[t] in accordance with the arithmetic operation “(EH[t]−EV[t]/(2j)”.
As explained above, according to this embodiment, the optical transmission device 100 configured from the transmission-electricity processing unit 110 and the optical-signal generating unit 120, which can be configured from versatile components and is compatible with the other modulation schemes, duplicates each of the binary data signals of two lanes and thus configures binary data signals of four lanes; generates optical signals on the basis of a four-lane multi-value signal generated by performing, on the binary data signals of the four lanes, conversion into a waveform of a ternary value or greater, polarity inversion, delay addition, and lane replacement; and transmits a signal obtained by combining the optical signals of the four lanes. In this way, the optical transmission device 100 can generate and transmit, with a simple configuration of components having high versatility, an optical signal that, like the polarization multiplexed RZ-BPSK signal, can reduce a fiber nonlinear optical effect caused during long-distance fiber transmission and suppress quality deterioration of a reception signal. It is possible to achieve a reduction in the cost and to extend the transmission distance of the optical transmission system 1.
In the second embodiment, the delay adding unit 115 of the transmission-electricity processing unit 110 of the optical transmission device 100 adds a delay to an input four-lane multi-value signal. Note that the configurations of the optical transmission system 1 and the devices are the same as the configurations in the first embodiment. The differences from the first embodiment are explained here.
A difference from the first embodiment is in setting of the delay adding unit 115. The delay adding unit 115 adds a delay among four lanes with respect to a four-lane multi-value signal represented by 2 Sample/Symbol input from the polarity inverting unit 114. In the second embodiment, the delay adding unit 115 performs delay addition of a half symbol, i.e., TS/2, to the YI lane and the YQ lane. The delay adding unit 115 outputs the four-lane multi-value signal represented by 2 Sample/Symbol to the lane replacing unit 116.
An example of changes of signals made by the processing performed by the components of the optical transmission device 100 according to the second embodiment is explained.
Note that the phase rotation and the polarization rotation are compensated for by the adaptive equalization performed by the adaptive equalizing unit 312 of the received electricity processing unit 310 of the optical reception device 300. The adaptive equalizing unit 312 of the received electricity processing unit 310 performs adaptive equalization processing to compensate for the phase rotation and the polarization rotation added to the electric digital signal by the optical transmission device 100. For example, the adaptive equalizing unit 312 can restore AX[t] in accordance with the arithmetic operation of “(EH[t]+EV[t])/2” and can restore AY[t] in accordance with the arithmetic operation of “(EH[t−TS/2]−EV[t−TS/2]/(2j)”.
The delay adding unit 115 desirably corrects delay amounts given to the lanes XI, XQ, YI, and YQ to minimize the absolute value of a delay adjustment value from an initial condition. In the second embodiment, the delay adding unit 115 sets relative delay amounts of the lanes as XI: 0, XQ: 0, YI: TS/2, and YQ: TS/2. However, this is an example. The delay adding unit 115 can set the relative delay amounts as XI: −TS/4, XQ: −TS/4, YI: TS/4, and YQ: TS/4.
In the second embodiment, switching speed of a four-lane optical signal is a double of switching speed for each one lane. Therefore, changing speed of a polarization state that changes depending on a data pattern is also a double. Consequently, it is possible to randomize and reduce the influence of a fiber nonlinear optical effect that occurs in the transmitting unit 200 when the polarization state is fixed. In this way, when the four-lane multi-value signal is delayed by the delay adding unit 115, signal switching speed of the optical signal output from the optical-signal generating unit 120 is m times, here, twice as large compared with the signal switching speed of the optical signal output from the optical-signal generating unit 120 when the four-lane multi-value signal is not delayed by the delay adding unit 115 as in the first embodiment. Note that a value of m is a positive number larger than 1.
As explained above, according to this embodiment, the optical transmission device 100 configured by the transmission-electricity processing unit 110 and the optical-signal generating unit 120, which can be configured by versatile components and is compatible with the other modulation schemes, duplicates each of the binary data signals of two lanes into two and configures binary data signals of four lanes; generates optical signals on the basis of a four-lane multi-value signal generated by performing, on the binary data signals of the four lanes, conversion into a waveform of a ternary value or greater, polarity inversion, delay addition, and lane replacement; and transmits a signal obtained by combining optical signals of the four lanes. In this way, the optical transmission device 100 can generate and transmit, with a simple configuration of components having high versatility, an optical signal that, equal to or more than the polarization multiplexed iRZ-BPSK signal, can reduce a nonlinear optical effect caused during long-distance fiber transmission and suppress quality deterioration of a reception signal. It is possible to achieve a reduction in the cost and to extend the transmission distance of the optical transmission system 1. Compared with the first embodiment, it is possible to increase switching speed of the four-lane optical signal.
The optical transmission device 100 can generate and output an optical signal without using non-versatile optical components for inter-polarization delay difference addition. It is possible to avoid signal quality deterioration due to a shift of an inter-polarization delay difference addition amount.
In a third embodiment, an example different from the second embodiment is explained related to the case in which the delay adding unit 115 of the transmission-electricity processing unit 110 of the optical transmission device 100 adds a delay to an input four-lane multi-value signal. Note that the configuration of the optical transmission system 1 and the devices are the same as the configurations in the first embodiment. The difference from the first embodiment is explained.
A difference from the first embodiment is setting of the delay adding unit 115. The delay adding unit 115 adds a delay among four lanes with respect to a four-lane multi-value signal represented by 2 Sample/Symbol input from the polarity inverting unit 114. In the third embodiment, the delay adding unit 115 performs delay addition of a half symbol, that is, TS/2 to the YI lane and the YQ lane. The delay adding unit 115 performs delay addition of a quarter symbol, that is, TS/4 to the XQ lane and the YQ lane. A delay amount in the YQ lane is ¾ symbol, that is, 3 TS/4 in total. The delay adding unit 115 outputs the four-lane multi-value signal represented by 2 Sample/Symbol to the lane replacing unit 116.
An example of changes of signals made by the processing by the components of the optical transmission device 100 according to the third embodiment is explained.
Note that the phase rotation, the polarization rotation, the inter-polarization delay difference are compensated by the adaptive equalization performed by the adaptive equalizing unit 312 of the received electricity processing unit 310 of the optical reception device 300. The adaptive equalizing unit 312 of the received electricity processing unit 310 performs adaptive equalization processing to compensate for the phase rotation, the polarization rotation, and the inter-polarization delay difference on the polarization surfaces added to the electric digital signal by the optical transmission device 100. For example, the adaptive equalizing unit 312 can restore AX[t] in accordance with the arithmetic operation of “(EH[t]+EV[t−TS/4])/2” and can restore AY[t] in accordance with the arithmetic operation of “(EH[t−TS/2]−EV[t−3 TS/4]/(2j)”.
The delay adding unit 115 desirably corrects delay amounts given to the lanes XI, XQ, YI, and YQ so as to minimize the absolute value of a delay adjustment value from an initial condition. In the third embodiment, the delay adding unit 115 sets relative delay amounts of the lanes as XI: 0, XQ: TS/4, YI: TS/2, and YQ: 3TS/4. However, this is an example. The delay adding unit 115 can set the relative delay amounts as XI: −3 TS/8, XQ: −TS/8, YI: TS/8, and YQ: 3 TS/8.
In the third embodiment, switching speed of a four-lane optical signal is a quadruple of switching speed for each one lane. Therefore, changing speed of a polarization state that changes depending on a data pattern is also a quadruple. Consequently, it is possible to randomize and reduce the influence of a fiber nonlinear optical effect that occurs when the polarization state is fixed. In this way, when the four-lane multi-value signal is delayed by the delay adding unit 115, signal switching speed of the optical signal output from the optical-signal generating unit 120 is m times, here, four times as large compared with the signal switching speed of the optical signal output from the optical-signal generating unit 120 when the four-lane multi-value signal is not delayed by the delay adding unit 115 as in the first embodiment.
A hardware configuration of the optical transmission device 100 is explained.
When the processing circuit 82 is the dedicated hardware, the processing circuit 82 corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel-programmed processor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or a combination of the foregoing. The respective functions of the symbol mapping unit 111, the data duplicating unit 112, the waveform converting unit 113, the polarity inverting unit 114, the delay adding unit 115, and the lane replacing unit 116 of the transmission-electricity processing unit 110 can be realized by the processing circuit 82 or the functions of the units can be collectively realized by the processing circuit 82.
When the processing circuit 82 is a CPU or the like, the functions of the symbol mapping unit ill, the data duplicating unit 112, the waveform converting unit 113, the polarity inverting unit 114, the delay adding unit 115, and the lane replacing unit 116 of the transmission-electricity processing unit 110 are realized by software, firmware, or a combination of the software and the firmware. The software and the firmware are described as programs and stored in the memory 84. The processor 83 reads out and executes the programs stored in the memory 84, whereby the processing circuit 82 realizes the functions of the units. That is, the optical transmission device 100 includes a memory for storing programs that, when being executed by the processing circuit 82, resultantly execute a step of performing symbol mapping on a signal input from the outside, a step of performing duplication processing for increasing the number of lanes, a step of performing waveform conversion by zero insertion, a step of inverting the polarity of a signal of any lane, a step of adding a delay between lanes, and a step of performing lane replacement. The programs are considered to be programs for causing a computer to execute procedures and methods of the symbol mapping unit 111, the data duplicating unit 112, the waveform converting unit 113, the polarity inverting unit 114, the delay adding unit 115, and the lane replacing unit 116 of the transmission-electricity processing unit 110. The memory 84 corresponds to, for example, a nonvolatile or volatile semiconductor memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable programmable ROM (EPROM), or an electrically erasable programmable ROM (EEPROM), a magnetic disk, a flexible disk, an optical disk, a compact disc, a minidisc, or a Digital Versatile Disc (DVD).
Note that, concerning the functions of the symbol mapping unit 111, the data duplicating unit 112, the waveform converting unit 113, the polarity inverting unit 114, the delay adding unit 115, and the lane replacing unit 116 of the transmission-electricity processing unit 110, a part of the functions can be realized by dedicated hardware and a part of the functions can be realized by software or firmware. For example, the functions of the symbol mapping unit 111, the data duplicating unit 112, and the waveform converting unit 113 can be realized by the processing circuit 82 functioning as dedicated hardware. The functions of the polarity inverting unit 114, the delay adding unit 115, and the lane replacing unit 116 can be realized by the processing circuit 82 reading out and executing the programs stored in the memory 84.
In this way, the processing circuit 82 can realize the functions explained above with the hardware, the software, the firmware, or a combination of the hardware, the software, and the firmware.
A hardware configuration of the optical reception device 300 is explained.
As explained above, according to this embodiment, the optical transmission device 100 can be configured by the transmission-electricity processing unit 110 and the optical-signal generating unit 120, which can be configured by versatile components and is compatible with the other modulation schemes. The optical transmission device 100 duplicates each of the binary data signals of two lanes into two and configures binary data signals of four lanes; generates optical signals on the basis of a four-lane multi-value signal generated by performing, on the binary data signals of the four lanes, conversion into a waveform of a ternary value or greater, polarity inversion, delay addition, and lane replacement; and transmits a signal obtained by combining optical signals of the four lanes. In this way, the optical transmission device 100 can generate and transmit, with a simple configuration of components having high versatility, an optical signal, equal to or more than the polarization multiplexed iRZ-BPSK signal, that can reduce a nonlinear optical effect caused during long-distance fiber transmission and suppress quality deterioration of a reception signal. It is possible to achieve a reduction in the cost and to extend the transmission distance of the optical transmission system 1. Compared with the second embodiment, it is possible to increase switching speed of the four-lane optical signal.
The optical transmission device 100 can generate and output an optical signal without using non-versatile optical components for inter-polarization delay difference addition. It is possible to avoid signal quality deterioration due to a shift of an inter-polarization delay difference addition amount.
Note that, it goes without saying that, in the symbol mapping unit ill, the data duplicating unit 112, the waveform converting unit 113, the polarity inverting unit 114, the delay adding unit 115, and the lane replacing unit 116, the processing other than the processing examples described in the first embodiment to the third embodiment is possible. In particular, any optimization of the delay addition amount in the delay adding unit 115 is possible according to a transmission condition.
In the first embodiment to the third embodiment, the alternation method of the polarization multiplexed RZ-BPSK signal and the polarization multiplexed iRZ-BPSK signal is explained. However, besides the contents described in the first embodiment to the third embodiment, the present invention can be partially used by, for example, changing the symbol mapping unit 111 to a symbol mapping unit adapted to the polarization multiplexed QPSK, the polarization multiplexed m-value QAM, or any modulation scheme. That is, it is possible to contribute to reception signal quality improvement by the RZ, the polarization rotation, the inter-polarization delay difference addition, and the like.
In the present invention, to execute, with electric processing, the RZ, the delay difference addition, and the like, it is possible to suppress deterioration that occurs because of a yield and the like of conventional optical components.
In the present invention, it is assumed that a symbol rate per one channel is mainly set in a range of 1 Gsymbol/s to 100 Gsymbol/s and is used. However, the present invention does not limit the symbol rate to the range mentioned above. It is also possible to mix signals of different symbol rates among a plurality of channels.
The optical transmission device, the optical reception device, the optical transmission system, and the optical transmission method are useful for long-distance large-capacity optical transmission.
The configurations explained in the embodiments indicate examples of the contents of the present invention. The configurations can be combined with other well-known technologies. It is possible to omit or change a part of the configurations in a range not departing from the spirit of the present invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/068708 | 6/29/2015 | WO | 00 |
