Optical transmitting and receiving system, optical transmitting device, and optical receiving device

Abstract

To provide an optical transmission and reception system configured to improve transmission characteristics of an optical signal.SOLUTION: An optical transmission and reception system includes: an optical transmitter that converts an electrical data signal into an optical signal and transmits the optical signal; and an optical receiver that receives the optical signal input from the optical transmitter via an optical transmission line and converts the optical signal into the data signal. The optical transmitter includes a first compensator that compensates for a loss generated in the optical transmitter based on a first coefficient in which an upward peak of a power of a band is on a higher frequency side in a frequency band of the electrical data signal, and a second coefficient in which the power of the band increases as a frequency becomes lower in a part of the band on a lower frequency side than the peak in the frequency band of the electrical data signal. The optical receiver includes a second compensator that compensates for a loss generated in the optical transmission line based on a third coefficient in which the power of the band decreases as the frequency becomes lower in a part of the band on the lower frequency side than the peak.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to an optical transmission and reception system, an optical transmission device, and an optical reception device. [Background technology]

[0002] In digital coherent optical communications, a DSP (Digital Signal Processor) is used to improve the transmission characteristics of optical signals by compensating for factors that degrade signal performance that occur in optical transmitters, optical receivers, and optical transmission paths. Factors that degrade signal performance include inter-symbol interference, skew, and chromatic dispersion caused by bandwidth characteristics.

[0003] One method used for compensation is to offset performance degradation factors by applying the inverse characteristics of the performance degradation factors that occur in an optical transmitter, an optical receiver, or an optical transmission path to the signal characteristics of the main signal, for example. For compensation of inter-symbol interference caused by the bandwidth characteristics in an optical transmitter, one method is to apply the inverse characteristics of the performance degradation factors in the optical transmitter to the signal characteristics in a pre-equalization circuit in a DSP. A method of multiplying the signal characteristics by the inverse characteristics of the transmission path frequency characteristics is known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-096513 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, a DAC (Digital-Analog Converter) is located after the DSP in an optical transmitter, and there is an upper limit to the signal strength (hereinafter referred to as power) characteristics of the electrical signal that the DAC can output. Therefore, if the signal contains power that exceeds this upper limit, the waveform of the signal in that power portion will be suppressed to the DAC's upper limit and distorted, causing degradation of signal performance. This degrades the transmission characteristics of the optical signal. To prevent this degradation of signal performance, it is assumed that the signal power will be reduced overall to a level where performance degradation does not occur before inputting it to the DAC.

[0006] However, even when signal power is reduced, signal performance can still deteriorate. For example, DACs generate noise such as quantization noise and thermal noise. As a result, noise is superimposed on signals that pass through the DAC. In other words, the performance of the signal deteriorates due to the noise. The degree of this deterioration varies depending on the SNR (Signal to Noise Ratio), which is the ratio of noise power to signal power. If the SNR is sufficiently high, signal performance deterioration can be ignored, but reducing signal power decreases the SNR, resulting in deterioration of signal performance. This ultimately deteriorates the transmission characteristics of the optical signal.

[0007] Therefore, in one aspect, an object is to provide an optical transmission and reception system, an optical transmission device, and an optical reception device that improve the transmission characteristics of an optical signal. [Means for solving the problem]

[0008] In one embodiment, an optical transmission and reception system includes an optical transmission device that converts an electrical data signal into an optical signal and transmits it, and an optical reception device that receives the optical signal input from the optical transmission device via an optical transmission line and converts it into the data signal, the optical transmission device having a first compensation unit that compensates for loss occurring within the optical transmission device based on a first coefficient that causes an upward peak of power in a band to be on the high frequency side within the frequency band of the data signal, and a second coefficient that causes band power to increase as the frequency becomes lower within a portion of the frequency band of the data signal that is on the low frequency side of the peak, and the optical reception device: It has an amplification characteristic opposite to that of the second coefficient. The optical transmission line includes a second compensation section that compensates for loss occurring in the optical transmission line based on the third coefficient.

[0009] In one embodiment, an optical transmission and reception system includes an optical transmission device that converts an electrical data signal into an optical signal and transmits the optical signal, and an optical reception device that receives the optical signal input from the optical transmission device via an optical transmission line and converts the optical signal into the electrical data signal, the optical transmission device having a first compensation unit that compensates for a loss that occurs in the electrical data signal based on a first compensation coefficient, and a first setting unit that sets the first compensation coefficient for the first compensation unit, the first setting unit setting a first coefficient for amplifying power of a band on the high frequency side of a frequency band of the electrical data signal so that the loss that occurs in the optical transmission device is compensated for, and and a second coefficient for amplifying the power of a lower frequency band of the frequency band of the electrical data signal so that the signal quality of the first compensation coefficient is equal to or higher than a predetermined value. The optical receiving device has a second compensation unit that compensates for a loss occurring in the optical transmission path for the electrical data signal based on the second compensation coefficient, and a second setting unit that sets the second compensation coefficient for the second compensation unit, and the second setting unit generates the second compensation coefficient based on a third coefficient for amplifying the electrical data signal and a fourth coefficient for amplifying the electrical data signal based on an amplification characteristic inverse to that of the second coefficient so that the loss occurring in the optical transmission path is compensated for. [Effects of the Invention]

[0010] The transmission characteristics of optical signals can be improved. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 shows an example of an optical transmission and reception system. [Figure 2] 2(a) is a block diagram showing an example of a transmitting DSP, and FIG. 2(b) is a block diagram showing an example of a receiving DSP. [Figure 3] FIG. 3 is a block diagram showing an example of a transmission-side control unit according to the first embodiment. [Figure 4] FIG. 4 is an example of the first table according to the first embodiment. [Figure 5] FIG. 5 is a flowchart showing an example of the operation of the optical transmitting device according to the first embodiment. [Figure 6] FIG. 6 is a diagram illustrating an example of normalization of the first coefficient. [Figure 7] FIG. 7 is a diagram illustrating an example of normalization of the amplification target value. [Figure 8] FIG. 8 is a diagram illustrating an example of generating the second coefficient. [Figure 9] FIG. 9 is a diagram illustrating an example of superimposing the first coefficient and the second coefficient. [Figure 10] FIG. 10 is a diagram illustrating an example of an output signal from an optical transmitter. [Figure 11] Fig. 11(a) is a diagram illustrating an example of an upper limit value of a DAC, Fig. 11(b) is a diagram illustrating an example of clipping, and Fig. 11(c) is a diagram illustrating an example of scaling. [Figure 12] FIG. 12 is a block diagram showing an example of a receiving-side control unit according to the first embodiment. [Figure 13] FIG. 13 is an example of a second table according to the first embodiment. [Figure 14] FIG. 14 is a flowchart showing an example of the operation of the optical receiving device according to the first embodiment. [Figure 15] FIG. 15 is a diagram illustrating an example of superimposing the third and fourth coefficients. [Figure 16]FIG. 16 is a diagram illustrating an example of an output signal from an optical receiving device. [Figure 17] FIG. 17 is a block diagram showing an example of a transmission side control unit according to the second embodiment. [Figure 18] FIG. 18 is a block diagram showing an example of the information generating unit. [Figure 19] FIG. 19 is a flowchart showing an example of the operation of the optical transmitting device according to the second embodiment. [Figure 20] FIG. 20 is a block diagram showing an example of a receiving-side control unit according to the second embodiment. [Figure 21] FIG. 21 is a flowchart showing an example of the operation of the optical receiving device according to the second embodiment. [Figure 22] FIG. 22 is a block diagram showing an example of a transmission side control unit according to the third embodiment. [Figure 23] FIG. 23 is an example of the first table according to the third embodiment. [Figure 24] FIG. 24 is a flowchart showing an example of the operation of the optical transmitting device according to the third embodiment. [Figure 25] FIG. 25 is a block diagram showing an example of a receiving-side control unit according to the third embodiment. [Figure 26] FIG. 26 is an example of the second table according to the third embodiment. [Figure 27] FIG. 27 is a flowchart showing an example of the operation of the optical receiving device according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] (First embodiment) 1, the optical transmitting and receiving system ST includes an optical transmitting device 100 and an optical receiving device 200. The optical transmitting device 100 and the optical receiving device 200 are connected to each other via an optical transmission path 300.

[0014] First, the optical transmitting device 100 will be described in detail. The optical transmitting device 100 includes a transmitting-side DSP (hereinafter referred to as TxDSP) 110, a DAC 120, a CDM (Coherent Driver Modulator) 130, an ITLA (Integrable Tunable Laser Assembly) 140, and a transmitting-side control unit 150. The DAC 120 is an example of a conversion unit. The ITLA 140 is an example of a light source. The transmitting-side control unit 150 is an example of a first setting unit. As shown in FIG. 2(a), the TxDSP 110 includes a framer 111, an FEC (Forward Error Correction) encoding circuit 112, and a pre-equalization circuit 113. The pre-equalization circuit 113 is an example of a first compensation unit.

[0015] The framer 111 receives an electrical client signal in a digital format from a client network. The client signal is, for example, an Ethernet (registered trademark) signal. The client signal may be a main signal, or may be a control signal including only parameters for adjusting transmission characteristics, etc. The framer 111 receives the client signal from the client network, converts it into an OTU (Optical channel Transport Unit) frame, and outputs it to the FEC encoding circuit 112. Therefore, the OTU frame is input to the FEC encoding circuit 112 from the framer 111.

[0016] The FEC encoding circuit 112 generates an FEC as an example of an error correction code for the OTU frame and inserts it into the OTU frame. The FEC encoding circuit 112 outputs the OTU frame as an electrical data signal to the pre-equalization circuit 113. A mapping circuit may be provided between the FEC encoding circuit 112 and the pre-equalization circuit 113. The mapping circuit maps the bit data of the OTU frame to symbols by performing digital modulation processing in accordance with the baud rate and modulation method (specifically, multi-level modulation method) set by the transmitting-side control unit 150. The mapping circuit outputs the electrical data signal obtained by the digital modulation processing to the pre-equalization circuit 113.

[0017] The pre-equalization circuit 113 compensates in advance for various losses that occur in the data signal within the optical transmitting device 100 based on a first compensation coefficient, which will be described later. For example, the pre-equalization circuit 113 performs skew compensation, bandwidth characteristic compensation, etc. The pre-equalization circuit 113 outputs the compensated data signal to the DAC 120.

[0018] As will be described in detail later, the pre-equalization circuit 113 performs scaling on the data signal. Scaling is a process of suppressing the power (e.g., amplitude level) of the data signal to below the upper limit of the DAC 120. Specifically, scaling is a process of reducing the overall power of the data signal to below the upper limit of the DAC 120. This makes it possible to avoid clipping, in which the power of the data signal partially sticks to the upper limit of the DAC 120 when the power of the data signal exceeds the upper limit of the DAC 120.

[0019] Returning to FIG. 1 , the DAC 120 converts the data signal from digital to analog format and outputs it to the CDM 130. The CDM 130 includes an optical modulator, a polarization beam splitter, a polarization beam combiner, and the like. The CDM 130 separates the transmission light input from the ITLA 140 into H polarization and V polarization and optically modulates the H polarization and V polarization with the data signal. The CDM 130 combines the modulated light of the H polarization and V polarization to generate an optical signal and outputs it to the optical transmission path 300. In this way, the optical transmitting device 100 converts the data signal into an optical signal and transmits it to the optical receiving device 200.

[0020] The transmitting-side control unit 150 includes a processor and a memory, and controls the operations of the TxDSP 110, the CDM 130, and the ITLA 140, as shown in FIG. 1. The processor includes, for example, a CPU (Central Processing Unit). When controlling the operation of the TxDSP 110, the transmitting-side control unit 150 controls the operations of the framer 111, the FEC encoding circuit 112, and the pre-equalization circuit 113, as shown in FIG. 2(a). The transmitting-side control unit 150 performs various settings on the framer 111, the FEC encoding circuit 112, and the pre-equalization circuit 113 under control of the operation terminal 10 (see FIG. 1). The operation terminal 10 may be a PC (Personal Computer) or a smart terminal (e.g., a tablet terminal). The transmitting-side control unit 150 sets a line rate for the framer 111 and sets FEC redundancy for the FEC encoding circuit 112.

[0021] The transmitting-side control unit 150 also generates the above-mentioned first compensation coefficient and sets the first compensation coefficient for the pre-equalization circuit 113. The transmitting-side control unit 150 generates this first compensation coefficient based on the first coefficient and the second coefficient. Specifically, the transmitting-side control unit 150 generates this first compensation coefficient by superimposing the first coefficient and the second coefficient on each other. The first coefficient is a coefficient for amplifying the power of the higher-frequency band of the frequency band of the data signal. The first coefficient can compensate for losses (e.g., inter-symbol interference due to band characteristics) that occur within the optical transmitting device 100. On the other hand, the second coefficient is a coefficient for amplifying the power of the lower-frequency band of the frequency band of the data signal. The second coefficient can raise the signal quality (specifically, the SNR) of the data signal to a predetermined value or higher to avoid degradation of the transmission performance of the optical signal.

[0022] Next, the optical receiving device 200 will be described in detail. As shown in Fig. 1, the optical receiving device 200 includes a receiving-side DSP (hereinafter referred to as RxDSP) 210, an ADC (Analogue Digital Converter) 220, an ICR (Integrated Coherent Receiver) 230, an ITLA 240, and a receiving-side control unit 250. The ITLA 240 is an example of a light source. The receiving-side control unit 250 is an example of a second setting unit.

[0023] The ICR 230 receives an optical signal transmitted from the optical transmitting device 100 via the optical transmission path 300. The ICR 230 includes a polarization beam splitter, an optical-electrical converter, and the like. The ICR 230 separates the optical signal into H-polarized and V-polarized components, receives the optical signal using local oscillator light input from the ITLA 240, converts it into an electrical data signal, and outputs it to the ADC 220. That is, the optical receiving device 200 receives the optical signal input from the optical transmitting device 100 via the optical transmission path 300 and converts it into a data signal. The ADC 220 converts the data signal from analog format to digital format and outputs it to the RxDSP 210.

[0024] 2(b), the RxDSP 210 includes a fixed equalization circuit 211, an adaptive equalization circuit 212, an FEC decoding circuit 213, and a deframer 214. The fixed equalization circuit 211 is an example of a second compensation unit.

[0025] The fixed equalization circuit 211 compensates for losses in the data signal that occur in the optical transmitting device 100, the optical receiving device 200, and the optical transmission line 300 in a fixed manner based on a second compensation coefficient, which will be described later. For example, the fixed equalization circuit 211 performs chromatic dispersion compensation, skew compensation, and bandwidth characteristic compensation. The fixed equalization circuit 211 outputs the compensated data signal to the adaptive equalization circuit 212.

[0026] The adaptive equalization circuit 212 adaptively compensates for waveform distortion of the data signal caused by polarization mode dispersion and polarization dependent loss occurring on the optical transmission path 300, based on dynamic parameters. The adaptive equalization circuit 212 outputs the compensated data signal as an OTU frame to the FEC decoding circuit 213. A demapping circuit may be provided between the adaptive equalization circuit 212 and the FEC decoding circuit 213. The demapping circuit is a circuit that performs demapping processing to detect symbols and convert them into bit data, and demodulates the OTU frame from the data signal.

[0027] The FEC decoding circuit 213 extracts the FEC from the OTU frame and performs data error correction. The FEC decoding circuit 213 outputs the OTU frame to the deframer 214. The deframer 214 receives the OTU frame from the FEC decoding circuit 213, converts it into a client signal, and transmits it to a client network.

[0028] The receiving-side control unit 250 includes a processor and a memory, and controls the operations of the RxDSP 210, the ICR 230, and the ITLA 240, as shown in Fig. 1. When controlling the operation of the RxDSP 210, the receiving-side control unit 250 controls the operations of the fixed equalization circuit 211, the adaptive equalization circuit 212, the FEC decoding circuit 213, and the deframer 214, as shown in Fig. 2(b). The receiving-side control unit 250 performs various settings on the fixed equalization circuit 211, the adaptive equalization circuit 212, the FEC decoding circuit 213, and the deframer 214 under control from the operation terminal 10 (see Fig. 1).

[0029] Furthermore, the receiving-side control unit 250 generates the second compensation coefficient described above and sets the second compensation coefficient for the fixed equalization circuit 211. The receiving-side control unit 250 generates this second compensation coefficient based on the third coefficient and the fourth coefficient. Specifically, the receiving-side control unit 250 generates this second compensation coefficient by superimposing the third coefficient and the fourth coefficient on each other. The third coefficient is a coefficient for amplifying the data signal. The third coefficient can compensate for losses that occur within the optical receiving device 200 or the optical transmission line 300. The fourth coefficient is a coefficient for amplifying (i.e., attenuating) the data signal based on amplification characteristics that are inverse to those of the second coefficient. The fourth coefficient can offset the second coefficient, which is adopted to temporarily improve signal quality.

[0030] In this way, the optical transmitting device 100 amplifies the power of the low frequency band based on the second coefficient to make the signal quality of the data signal above a predetermined value, and the optical receiving device 200 restores the signal quality of the data signal to its original state based on the fourth characteristic having an amplification characteristic opposite to that of the second coefficient, thereby improving the overall signal characteristics.

[0031] Next, the transmission side control unit 150 according to the first embodiment will be described in detail with reference to FIGS.

[0032] First, as shown in FIG. 3, the transmitting-side control unit 150 includes a first table 151, a mode setting unit 152, and a target setting unit 153. The transmitting-side control unit 150 also includes a first selection unit 154, a first generation unit 155, and a first superposition unit 156. As shown in FIG. 4, the first table 151 includes an operation mode number, a baud rate, a modulation method, and a first coefficient, which are associated with one another. The operation mode number in the first table 151 is an identifier that identifies the operation mode of the optical transmitting device 100. When an operation mode number is specified, the baud rate, modulation method, and first coefficient associated with the specified operation mode number can be determined. This allows the optical transmitting device 100 to operate at the baud rate, modulation method, and first coefficient corresponding to the specified operation mode number. Note that, without providing an operation mode number, at least one of the baud rate and modulation method may be specified, and the first coefficient may be determined according to the specified baud rate and modulation method.

[0033] 5, the mode setting unit 152 sets an operation mode number to itself in accordance with control from the operation terminal 10 (step S1). Once the operation mode number is set, the target setting unit 153 sets an amplification target value to itself in accordance with control from the operation terminal 10 (step S2). The amplification target value is a target value for the power of the low-frequency band to be amplified. The processing of steps S1 and S2 may be performed at the same timing or at different timings.

[0034] When the amplification target value is set, first selection unit 154 selects a first coefficient corresponding to the operation mode number set in mode setting unit 152 from first table 151 along with a baud rate and a modulation method (step S3). First selection unit 154 outputs the selected baud rate, modulation method, and first coefficient to first superposition unit 156. First selection unit 154 also outputs the first coefficient to first generation unit 155. When the first coefficient is output from first selection unit 154, first generation unit 155 generates a second coefficient based on the amplification target value set in target setting unit 153 and the first coefficient (step S4).

[0035] Specifically, as shown in FIG. 6, first, the first generation unit 155 normalizes the characteristics of the first coefficients. Normalization is a process of lowering the characteristics of the first coefficients overall so that the maximum power in the first coefficients becomes "0 (zero)." Normalization may be performed so that the maximum power becomes the upper limit value of the DAC 120. After normalizing the characteristics of the first coefficients, the first generation unit 155 calculates the relative attenuation amount for each frequency component, with the power "0" as the reference.

[0036] Next, as shown in FIG. 7 , the first generation unit 155 normalizes the characteristics of the amplification target value in the same manner as the normalization of the first coefficient. Specifically, the first generation unit 155 attenuates the characteristics of the amplification target value overall for each frequency component by the same attenuation amount as the attenuation amount of the characteristics of the first coefficient. This results in a characteristic of the normalized amplification target value that is lower than power "0." After obtaining the characteristics of the normalized amplification target value, the first generation unit 155 calculates the difference between the normalized amplification target value and the normalized first coefficient (normalized amplification target value - normalized first coefficient) for each frequency component. Here, if the normalized amplification target value is equal to or smaller than the normalized first coefficient (i.e., difference≦0), the first generation unit 155 adopts the normalized first coefficient as the normalized amplification target value. This results in a characteristic of the normalized amplification target value that partially includes the normalized first coefficient on the high-frequency side. In this specification, a frequency band in which the normalized amplification target value exceeds the normalized first coefficient (that is, difference>0) is referred to as a low frequency band.

[0037] 8, first generation unit 155 subtracts the first coefficient from the difference (i.e., the difference - the first coefficient before normalization) to generate the second coefficient. In other words, first generation unit 155 generates the characteristic obtained by subtracting the first coefficient from the difference as the characteristic of the second coefficient.

[0038] If the characteristic of the second coefficient falls below power "0", the first generation unit 155 fixes the characteristic of the second coefficient to power "0". If the characteristic of the second coefficient falls below power "0", there is a possibility that the signal quality of the data signal due to the second coefficient will fall below a predetermined value. By fixing the characteristic of the second coefficient to power "0", this possibility can be avoided. The first generation unit 155 outputs the generated second coefficient to the first superimposition unit 156. The operation terminal 10 can access the first generation unit 155 to refer to the second coefficient or obtain the second coefficient from the first generation unit 155.

[0039] 5, the first superimposing unit 156 superimposes the first coefficient output from the first selecting unit 154 and the second coefficient output from the first generating unit 155 (step S5). The first superimposing unit 156 generates the above-mentioned first compensation coefficient by superimposing the first coefficient and the second coefficient together. After generating the first compensation coefficient, the first superimposing unit 156 sets the first compensation coefficient in the pre-equalization circuit 113 of the TxDSP 110 (step S6), and ends the process.

[0040] As a result, as shown in FIG. 9, for example, when a data signal is the main signal and the bandwidth of the optical transmitting device 100 is insufficient for the main signal, a first compensation coefficient generated by superimposing the first coefficient and the second coefficient on the main signal can be applied. Here, the first coefficient has an upward peak of band power on the high-frequency side, compensating for losses such as inter-symbol interference caused by band characteristics occurring within the optical transmitting device 100. On the other hand, the second coefficient increases band power as the frequency decreases in a portion of the band lower than the peak of the first coefficient, compensating for degradation of signal quality in the low-frequency band due to scaling. Therefore, the characteristics of the second coefficient remain without being offset by the bandwidth of the optical transmitting device 100. As shown in FIG. 10, an output signal in which the remaining second coefficient is applied to the main signal is output from the optical transmitting device 100 as an optical signal. The first superimposing unit 156 sets the baud rate and modulation method output from the first selecting unit 154 in a mapping circuit (not shown) of the TxDSP 110. The set baud rate and modulation method are used to transmit the main signal.

[0041] The above-mentioned clipping and scaling will now be described with reference to FIGS. 11(a) to 11(c).

[0042] First, as shown in Fig. 11(a), the DAC 120 has an upper limit on the power of the electrical data signal that it can output. For example, if the characteristics of the main signal after first coefficient compensation exceed this upper limit, clipping occurs, where the main signal portion above the upper limit sticks to the upper limit regardless of its original characteristics, as shown in Fig. 11(b). Clipping changes the characteristics of the main signal from their original characteristics, degrading the signal quality of the main signal.

[0043] To avoid clipping, as shown in FIG. 11( c), it is also conceivable to perform scaling in the pre-equalization circuit 113 to reduce the power of the main signal characteristics to a level at which clipping does not occur, and then input the main signal to the DAC 120. However, the scaled main signal may have degraded transmission performance due to its relationship with noise in the DAC 120. Specifically, in the low-frequency band, the SNR between the main signal and the noise in the DAC 120 can be ensured in the main signal before scaling, ensuring a sufficiently high value that degradation in transmission performance of the main signal can be ignored. However, in the main signal after scaling, the SNR between the main signal and the noise in the DAC 120 decreases, resulting in degradation in transmission performance of the main signal. For this reason, in this embodiment, the low-frequency band characteristics of a data signal, such as a main signal, are improved by using a second coefficient.

[0044] Next, the details of the reception-side control unit 250 according to the first embodiment will be described with reference to FIGS.

[0045] First, as shown in FIG. 12, the receiving-side control unit 250 includes a second table 251, a mode setting unit 252, and a coefficient setting unit 253. The receiving-side control unit 250 also includes a second selection unit 254, a second generation unit 255, and a second superposition unit 256. As shown in FIG. 13, the second table 251 includes an operation mode number, a baud rate, a modulation method, and a third coefficient, which are associated with each other. The operation mode number in the second table 251 is an identifier that identifies the operation mode of the optical receiving device 200. When an operation mode number is specified, the baud rate, modulation method, and third coefficient associated with the specified operation mode number can be determined. This allows the optical receiving device 200 to operate at the baud rate, modulation method, and third coefficient corresponding to the specified operation mode number. Note that, without providing an operation mode number, at least one of the baud rate and modulation method may be specified, and the third coefficient may be determined according to the specified baud rate and modulation method.

[0046] 14, the mode setting unit 252 sets an operation mode number to itself under control from the operation terminal 10 (step S11). Once the operation mode number is set, the coefficient setting unit 253 sets a second coefficient to itself under control from the operation terminal 10 (step S12). Regarding the setting of the second coefficient, the operation terminal 10 may acquire the second coefficient from the transmission side control unit 150 (specifically, the first generation unit 155) after the operation terminal 10 has completed setting the transmission side control unit 150. By reconnecting the operation terminal 10 from the optical transmitting device 100 to the optical receiving device 200, the operation terminal 10 can set the second coefficient to the coefficient setting unit 253. The processes of steps S11 and S12 may be performed at the same timing or at different timings.

[0047] When the operation mode number is set in the mode setting unit 252, the second selection unit 254 selects a third coefficient corresponding to the set operation mode number from the second table 251 along with the baud rate and modulation method (step S13). As shown in Fig. 15, the third coefficient has a band power that decreases as the frequency decreases in a portion of the band on the lower frequency side than the peak of the first coefficient. The second selection unit 254 outputs the selected baud rate, modulation method, and third coefficient to the second superimposition unit 256.

[0048] Once the second coefficient is set in the coefficient setting unit 253, the second generation unit 255 generates a fourth coefficient based on the second coefficient (step S14). Specifically, as shown in FIG. 15, the second generation unit 255 generates the fourth coefficient based on an amplification characteristic that is the inverse of the characteristic of the second coefficient. In other words, the second generation unit 255 generates an amplification characteristic that is the inverse of the characteristic of the second coefficient as the characteristic of the fourth coefficient. The second generation unit 255 outputs the generated fourth coefficient to the second superimposition unit 256. Note that the processes of steps S13 and S14 may be performed at the same timing or at different timings.

[0049] 14, the second superimposing unit 256 superimposes the third coefficient output from the second selecting unit 254 and the fourth coefficient output from the second generating unit 255 (step S15). The second superimposing unit 256 generates the second compensation coefficient described above by superimposing the third coefficient and the fourth coefficient on each other. After generating the second compensation coefficient, the second superimposing unit 256 sets the second compensation coefficient in the fixed equalization circuit 211 of the RxDSP 210 (step S16), and ends the process.

[0050] As a result, as shown in FIG. 15 , for example, when a data signal is the main signal and the bandwidth of the optical receiving device 200 is insufficient for the main signal, a second compensation coefficient generated by superimposing the third and fourth coefficients on the main signal can be applied. The third coefficient can compensate for losses such as inter-symbol interference caused by bandwidth characteristics occurring within the optical receiving device 200 or the optical transmission path 300. The fourth coefficient can offset the second coefficient adopted for the purpose of temporarily improving signal quality. Therefore, as shown in FIG. 16 , an output signal in which the second compensation coefficient has been applied to the main signal is output from the optical receiving device 200 as a client signal. The second superimposing unit 256 sets the baud rate and modulation method output from the second selecting unit 254 to a demapping circuit (not shown) of the RxDSP 210.

[0051] As described above, according to the first embodiment, when there is an upper limit to the characteristics of the power of the electrical signal that can be output by the DAC 120, even if normalization such as scaling is performed, the signal quality does not deteriorate in the low frequency band, and the transmission characteristics of the optical signal can be improved.

[0052] (Second embodiment) Next, a second embodiment of the present invention will be described with reference to Fig. 17 to Fig. 21. In the first embodiment described above, the second coefficient is generated by the transmitting-side control unit 150, and the second coefficient is used by the receiving-side control unit 250 to generate the fourth coefficient via the operation terminal 10. In the second embodiment, the second coefficient generated by the transmitting-side control unit 150 is transmitted from the optical transmitting device 100 to the optical receiving device 200, and the received second coefficient is used by the receiving-side control unit 250 to generate the fourth coefficient.

[0053] First, the configuration and operation of the transmission-side control unit 150 according to the second embodiment will be described with reference to Fig. 17 to Fig. 19. In Fig. 17, the same components as those in the transmission-side control unit 150 according to the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0054] 17, the transmission side control unit 150 according to the second embodiment differs from the first embodiment in that it further includes an information generation unit 157. As shown in FIG. 18, the information generation unit 157 includes a frequency modulation setting unit 161, a multi-level setting unit 162, a baud rate setting unit 163, and an integration unit 164.

[0055] The first generating unit 155 outputs the generated second coefficient to the integrating unit 164. The frequency modulation setting unit 161 sets, under control from the operating terminal 10, whether or not to use frequency modulation of the transmission frequency. The multi-level setting unit 162 sets, under control from the operating terminal 10, a multi-level lower than the multi-level used for the main signal. The baud rate setting unit 163 sets, under control from the operating terminal 10, a baud rate lower than the baud rate used for the main signal. Note that these various settings may be made at the same timing as the setting of the operation mode number and the setting of the amplification target value, or at different timings.

[0056] When frequency modulation setting unit 161 is set to use frequency modulation, integration unit 164 generates transmission information that integrates information on the second coefficient with information on either or both of the use of frequency modulation and the baud rate set in baud rate setting unit 163. When frequency modulation setting unit 161 is set to not use frequency modulation, integration unit 164 generates transmission information that integrates information on either or both of the multi-level set in multi-level setting unit 162 and the baud rate set in baud rate setting unit 163 with information on the second coefficient.

[0057] The integrating unit 164 outputs the generated transmission information to the pre-equalization circuit 113 of the TxDSP 150. The pre-equalization circuit 113 generates an electrical control signal including the transmission information based on the transmission information and outputs it to the DAC 120. As a result, a control signal with settings different from the main signal is transmitted from the optical transmitting device 100. This allows the optical receiving device 200 to distinguish between the control signal and the main signal. Note that when frequency modulation is used, the use of multi-level modulation is avoided because frequency modulation is incompatible with phase modulation such as QPSK (Quadrature Phase Shift Keying).

[0058] 19, when the first superimposing unit 156 executes the process of step S6, the information generating unit 157 generates transmission information as described above (step S21) and outputs it to the pre-equalization circuit 113. The pre-equalization circuit 113 generates a control signal including the transmission information (step S22) and outputs it to the DAC 120. Based on the control signal output to the DAC 120, the CDM 130 converts the control signal into an optical signal corresponding to the control signal and transmits it to the optical receiving device 200 (step S23). In this way, the optical transmitting device 100 transmits the control signal to the optical receiving device 200.

[0059] Next, the configuration and operation of the receiving-side control unit 250 according to the second embodiment will be described with reference to Fig. 20 and Fig. 21. In Fig. 20, the same components as those in the receiving-side control unit 250 according to the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0060] The receiving-side control unit 250 according to the second embodiment differs from the first embodiment in that it further includes an information extraction unit 257. The information extraction unit 257 extracts transmission information after digital demodulation by the fixed equalization circuit 211, based on a control signal corresponding to an optical signal received by the optical receiving device 200 (specifically, the ICR 230). The information extraction unit 257 outputs a second coefficient from the extracted transmission information to the second generation unit 255. As a result, similar to the first embodiment, the second generation unit 255 can generate a fourth coefficient based on the second coefficient.

[0061] 21, when the second selection unit 254 executes the process of step S13, the ICR 230 receives an optical signal corresponding to the control signal (step S31). When the ICR 230 receives the optical signal, the information extraction unit 257 extracts transmission information from the control signal corresponding to the optical signal (step S32) and outputs the second coefficient to the second generation unit 255 (step S33). This enables the second generation unit 255 to execute the process of step S14.

[0062] As described above, according to the second embodiment, the optical receiving device 200 can generate the fourth coefficient based on the second coefficient transmitted from the optical transmitting device 100, without having to reset the second coefficient generated by the optical transmitting device 100 to the optical receiving device 200. This reduces the setting burden on the setting person who operates the operation terminal 10. Furthermore, omitting the setting process of the second coefficient by the optical receiving device 200 reduces the processing load.

[0063] (Third embodiment) Next, a third embodiment of the present invention will be described with reference to Fig. 22 to Fig. 27. In the first embodiment described above, the transmitting-side control unit 150 generates a second coefficient, and the receiving-side control unit 250 uses the second coefficient via the operation terminal 10 to generate a fourth coefficient. In the third embodiment, the transmitting-side control unit 150 does not generate a second coefficient, but uses a second coefficient that is associated with the first coefficient in advance by initial setting (for example, at the time of device manufacture, etc.). Furthermore, the receiving-side control unit 250 does not generate a fourth coefficient based on the second coefficient, but uses a fourth coefficient that is associated with the third coefficient in advance by initial setting.

[0064] First, the configuration and operation of the transmission-side control unit 150 according to the third embodiment will be described with reference to Fig. 22 to Fig. 24. In Fig. 22, the same components as those in the transmission-side control unit 150 according to the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0065] As shown in FIG. 22 , a transmission-side control unit 150 according to the third embodiment differs from the first embodiment in that it does not include a target setting unit 153 and a first generation unit 155, but further includes a third selection unit 158. Also, as shown in FIG. 23 , a first table 151 according to the third embodiment differs from the first embodiment in that it associates a first coefficient with a second coefficient. The third selection unit 158 ​​selects a second coefficient from the first table 151 according to the operation mode number set in the mode setting unit 152. The third selection unit 158 ​​outputs the selected second coefficient to the first superposition unit 156. This allows the first superposition unit 156 to superpose the first coefficient output from the first selection unit 154 and the second coefficient output from the third selection unit 158. That is, the first superposition unit 156 can generate a first compensation coefficient.

[0066] 24, when the first selection unit 154 executes the process of step S3, the third selection unit 158 ​​selects the second coefficient as described above (step S41) and outputs it to the first superimposition unit 156. This enables the first superimposition unit 156 to execute the process of step S5.

[0067] Next, the configuration and operation of the receiving-side control unit 250 according to the third embodiment will be described with reference to Fig. 25 to Fig. 27. In Fig. 25, the same components as those in the receiving-side control unit 250 according to the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0068] As shown in FIG. 25 , the receiving-side control unit 250 according to the third embodiment differs from the first embodiment in that it does not include a coefficient setting unit 253 and a second generation unit 255, but further includes a fourth selection unit 258. Also, as shown in FIG. 26 , the second table 251 according to the third embodiment differs from the first embodiment in that it associates a fourth coefficient with a third coefficient. The fourth selection unit 258 selects a fourth coefficient from the second table 251 according to the operation mode number set in the mode setting unit 252. The fourth selection unit 258 outputs the selected fourth coefficient to the second superimposition unit 256. This allows the second superimposition unit 256 to superimpose the third coefficient output from the second selection unit 254 and the fourth coefficient output from the fourth selection unit 258. That is, the second superimposition unit 256 can generate a second compensation coefficient.

[0069] 27, when the second selection unit 254 executes the process of step S13, the fourth selection unit 258 selects the fourth coefficient as described above (step S51) and outputs it to the second superimposition unit 256. This enables the second superimposition unit 256 to execute the process of step S15.

[0070] As described above, according to the third embodiment, the second coefficient can be identified according to the operation mode number and used in combination with the first coefficient, even without setting the amplification target value for the optical transmitting device 100. Furthermore, the fourth coefficient can be identified according to the operation mode number and used in combination with the third coefficient, even without setting the second coefficient for the optical receiving device 200. This reduces the setting burden on the person in charge of setting the operation terminal 10. Furthermore, by omitting the process of setting the amplification target value by the optical transmitting device 100 and the process of setting the second coefficient by the optical receiving device 200, the processing load can be reduced.

[0071] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0072] ST Optical Transceiver System 100 Optical transmitter 113 Pre-equalization circuit (first compensation section) 150 transmitting side control unit (first setting unit) 200 Optical receiving device 211 Fixed equalization circuit (second compensation section) 250 Receiving side control unit (second setting unit)

Claims

1. an optical transmitter that converts an electrical data signal into an optical signal and transmits the optical signal; an optical receiving device that receives the optical signal input from the optical transmitting device via an optical transmission line and converts it into the data signal; The optical transmitter comprises: a first compensating unit that compensates for losses occurring within the optical transmitting device based on a first coefficient that causes an upward peak of power in a band to be on the high frequency side within the frequency band of the data signal, and a second coefficient that causes band power to increase as the frequency becomes lower within a portion of the frequency band of the data signal that is on the low frequency side of the peak; The optical receiving device a second compensation unit that compensates for loss occurring in the optical transmission line based on a third coefficient having an amplification characteristic inverse to that of the second coefficient; An optical transmission and reception system characterized by:

2. an optical transmitter that converts an electrical data signal into an optical signal and transmits the optical signal; an optical receiving device that receives the optical signal input from the optical transmitting device via an optical transmission line and converts the optical signal into the electrical data signal; The optical transmitter comprises: a first compensation unit that compensates for a loss occurring in the optical transmission device with respect to the electrical data signal based on a first compensation coefficient; a first setting unit that sets the first compensation coefficient for the first compensation unit, the first setting unit generates the first compensation coefficient based on a first coefficient for amplifying power of a band on a higher frequency side of the frequency band of the electrical data signal so that loss occurring in the optical transmitting device is compensated for, and a second coefficient for amplifying power of a band on a lower frequency side of the frequency band of the electrical data signal so that signal quality of the electrical data signal becomes equal to or higher than a predetermined value; The optical receiving device a second compensation unit that compensates for a loss occurring in the optical transmission line with respect to the electrical data signal based on a second compensation coefficient; a second setting unit that sets the second compensation coefficient for the second compensation unit, the second setting unit generates the second compensation coefficient based on a third coefficient for amplifying the electrical data signal and a fourth coefficient for amplifying the electrical data signal based on an amplification characteristic inverse to that of the second coefficient so as to compensate for loss occurring in the optical transmission path. An optical transmission and reception system characterized by:

3. the first compensation unit suppresses the power of the electrical data signal to be equal to or less than an upper limit value of a conversion unit that converts the electrical data signal in digital format into the electrical data signal in analog format.

3. The optical transmission and reception system according to claim 2.

4. the optical transmitter transmits the second coefficient to the optical receiver; the second setting unit generates the fourth coefficient based on the second coefficient received by the optical receiving device.

4. The optical transmission and reception system according to claim 2 or 3.

5. the optical transmitter transmits the second coefficients to the optical receiver using a first signal having a baud rate lower than that of the electrical data signal; 5. The optical transmission and reception system according to claim 2, wherein the optical transmission and reception system is a transmission and reception system for transmitting and receiving signals.

6. the optical transmitting device transmits the second coefficients to the optical receiving device using a second signal having a lower multilevel than the electrical data signal; 6. The optical transmission and reception system according to claim 2, wherein the optical transmission and reception system is a transmission and reception system.

7. the optical transmitting device transmits the second coefficient to the optical receiving device using a third signal whose transmission frequency is modulated; 6. The optical transmission and reception system according to claim 2, wherein the optical transmission and reception system is a transmission and reception system.

8. the first setting unit determines the first coefficient in accordance with at least one of a baud rate and a modulation method of the electrical data signal; the second setting unit determines the third coefficient in accordance with at least one of a baud rate and a modulation method of the electrical data signal.

8. The optical transmission and reception system according to claim 2, wherein the optical transmission and reception system is a transmission and reception system.

9. the first setting unit determines both the first coefficient and the second coefficient according to at least one of a baud rate and a modulation method of the electrical data signal; the second setting unit determines both the third coefficient and the fourth coefficient according to at least one of a baud rate and a modulation method of the electrical data signal.

9. The optical transmission and reception system according to claim 8.

10. An optical transmitting device that converts an electrical data signal into an optical signal and transmits the optical signal to an optical receiving device that receives an optical signal input via an optical transmission line and converts the electrical data signal, a first compensation unit that compensates for a loss occurring in the optical transmission device with respect to the electrical data signal based on a first compensation coefficient; a first setting unit that sets the first compensation coefficient for the first compensation unit, the first setting unit generates the first compensation coefficient based on a first coefficient for amplifying power of a band on a higher frequency side of the frequency band of the electrical data signal so that loss occurring in the optical transmitting device is compensated for, and a second coefficient for amplifying power of a band on a lower frequency side of the frequency band of the electrical data signal so that signal quality of the electrical data signal becomes equal to or higher than a predetermined value; The optical receiving device a second compensation unit that compensates for a loss occurring in the optical transmission line with respect to the electrical data signal based on a second compensation coefficient; a second setting unit that sets the second compensation coefficient for the second compensation unit, the second setting unit generates the second compensation coefficient based on a third coefficient for amplifying the electrical data signal and a fourth coefficient for amplifying the electrical data signal based on an amplification characteristic inverse to that of the second coefficient so as to compensate for loss occurring in the optical transmission path. An optical transmitting device characterized by:

11. An optical receiving device that receives an optical signal input via an optical transmission line from an optical transmitting device that converts an electrical data signal into an optical signal and transmits the optical signal, and converts the optical signal into the electrical data signal, The optical transmitter comprises: a first compensation unit that compensates for a loss occurring in the optical transmission device with respect to the electrical data signal based on a first compensation coefficient; a first setting unit that sets the first compensation coefficient for the first compensation unit, the first setting unit generates the first compensation coefficient based on a first coefficient for amplifying power of a band on a higher frequency side of the frequency band of the electrical data signal so that loss occurring in the optical transmitting device is compensated for, and a second coefficient for amplifying power of a band on a lower frequency side of the frequency band of the electrical data signal so that signal quality of the electrical data signal becomes equal to or higher than a predetermined value; The optical receiving device a second compensation unit that compensates for a loss occurring in the optical transmission line with respect to the electrical data signal based on a second compensation coefficient; a second setting unit that sets the second compensation coefficient for the second compensation unit, the second setting unit generates the second compensation coefficient based on a third coefficient for amplifying the electrical data signal and a fourth coefficient for amplifying the electrical data signal based on an amplification characteristic inverse to that of the second coefficient so as to compensate for loss occurring in the optical transmission path. An optical receiving device characterized by:

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