JP2013198121A - Distortion compensation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distortion compensation system capable of compensating distortion generated in an optical link by feeding an optical signal back with simple constitution.SOLUTION: A distortion compensation system 100 includes a distortion compensation block 110 and a feedback block 120. The distortion compensation block 110 includes a distortion compensation section 111, a delay unit 112, and an adder 113, and the distortion compensation section 111 computes a difference between an RF signal input from the feedback block 120 and an RF signal input from a BPF 101. The difference corresponds to an amount of distortion generated while the RF signal is transmitted through an optical link 10. The distortion compensation section 111 finds a signal of reverse characteristics for canceling the computed difference, and outputs the signal as a distortion compensation component to the adder 113. The adder 113 adds the distortion compensation component to the RF signal input from the BPF 101 and outputs the resulting signal to the optical link 10.

Description

  The present invention relates to a radio over fiber technology in which an optical signal is intensity-modulated with a radio signal (modulated carrier wave) and transmitted by an optical fiber, and is composed of an electric / optical converter, an optical / electrical converter, and an optical fiber. The present invention relates to a distortion compensation system that compensates for distortion of an optical signal generated in an optical link.

  In recent years, the development of portable base station devices has been promoted, and the coverage area has been expanded, and services are being developed in buildings, road tunnels, and railway tunnels. In the maintenance of such a portable base station apparatus, Radio Over Fiber technology is used in which a modulated radio signal is directly transmitted on an optical signal and transmitted through an optical fiber.

  In a high-frequency circuit or the like that processes an RF (high-frequency) signal, conventionally, distortion generated in the signal is compensated using a simple feedback system. In the distortion compensation by the feedback system, since the generated distortion is detected and controlled to compensate for it, the distortion can be compensated with high accuracy. Recently, a circuit (IC) that compensates for distortion in the RF region has also appeared. On the other hand, in a field such as an optical transmission system that converts an electric signal into an optical signal and transmits the optical signal through an optical fiber, a technique for compensating for distortion of the optical signal using a feedback system is an A / D converter and a D A circuit using a circuit that performs distortion compensation in the baseband region using an A converter is known (Non-Patent Document 1).

  In an optical transmission system that transmits an optical signal obtained by electrical / optical conversion, for example, an optical component such as a laser diode (LD) that generates an optical signal or an optical fiber that transmits an optical signal, or an LD drive power Distortion occurs in the optical signal due to the distortion characteristics of each of the power amplifier that amplifies the optical signal. As a technique for compensating for the distortion generated in such an optical signal, a technique using a circuit having a characteristic opposite to the distortion characteristic of an optical component or a power amplifier is known.

  As an example, in order to compensate for the distortion of the LD built in the electrical / optical converter, a circuit that generates a signal having a distortion characteristic opposite to that of the LD is configured, and the circuit has an inverse characteristic in advance to the signal. A technique for reducing distortion generated in an LD by adding distortion (predistortion) and inputting the same into the LD is known (for example, Patent Document 1). Also, the optical signal output from the electrical / optical converter is branched by a coupler and input to the optical / electrical converter, and the regenerated electrical signal is converted to a baseband signal, and this baseband signal is used as a feedback signal for LD. An attempt has been made to predistort the input signal (Non-Patent Document 1).

JP 2003-29221 A

S. Nadarajah et al., "Adaptive digital predistortion of laser diode nonlinearity for wireless applications", Electrical and Computer Engineering, 2003. IEEE CCECE 2003, Vo.1, pp.159-162 (May 2003).

  Since the compensation circuit for improving distortion of the LD disclosed in Patent Document 1 is not configured to feed back an output signal, there is a problem that it is difficult to follow changes in characteristics of optical components due to environmental changes. Further, in the technique described in Non-Patent Document 1, predistortion is performed using a feedback system configuration. However, since the predistortion is performed in the baseband region, a D / A converter and an A / D conversion are performed. And an IQ modulator / demodulator are required, resulting in a complicated and large-scale configuration.

  Furthermore, even in an optical fiber that transmits an optical signal, chromatic dispersion distortion occurs in the optical signal due to the distortion characteristics of the optical fiber, but it is not necessary to compensate for the distortion generated in such an optical fiber. It was not done until.

  The present invention has been made in view of the above problems, and an object thereof is to provide a distortion compensation system capable of compensating for distortion generated in an optical link by feeding back an optical signal with a simple configuration.

  In order to solve the above-described problems, a first aspect of the distortion compensation system of the present invention includes an electric / optical converter that inputs a high-frequency signal for transmission, performs electric / optical conversion, and outputs a converted optical signal, and the converted optical signal. Generated by an optical link comprising: an optical fiber that transmits and transmits a post-transmission optical signal transmitted through the optical fiber; and an optical / electrical converter that performs optical / electrical conversion and outputs an output-side high-frequency signal. A distortion compensation system for compensating for distortion, wherein the conversion optical signal is branched from the optical fiber and inputted, processed to output a feedback high frequency signal, and externally input side high frequency Distortion for inputting a signal and inputting the feedback high-frequency signal from the feedback block to compensate for the amount of distortion occurring in the feedback high-frequency signal A distortion compensation block that calculates a compensation component, calculates the transmission high-frequency signal by adding the distortion compensation component to the input-side high-frequency signal, and outputs the transmission high-frequency signal to the optical link. Features.

  In another aspect of the distortion compensation system of the present invention, the feedback block causes the branched optical signal to generate substantially the same distortion as that generated when the converted optical signal is transmitted through the optical fiber. After that, the high-frequency signal for feedback is output after optical / electrical conversion.

  According to another aspect of the distortion compensation system of the present invention, the feedback block includes a feedback optical fiber having substantially the same length as the optical fiber, and the branched input to the feedback optical fiber. A feedback optical / electrical converter that inputs the optical signal after transmitting the optical signal and converts the optical signal into electrical / electrical power and outputs the feedback high-frequency signal, and the distortion compensation block includes the input A high-frequency signal is branched and input, a difference from the high-frequency signal for feedback is calculated, and the distortion compensation component that outputs the difference and outputs the distortion compensation component; and the input high-frequency signal is branched and input A delay unit that delays and outputs the input-side high-frequency signal for the processing time of the distortion compensation unit; and Calculated to be characterized by having a an adder for outputting the transmission high-frequency signal.

  In another aspect of the distortion compensation system of the present invention, the feedback block causes the branched optical signal to generate substantially the same distortion as that generated when the converted optical signal is transmitted through the optical fiber. A second feedback block for optically / electrically converting and outputting the feedback high-frequency signal; and a second feedback block for directly optically / electrically converting the branched and input optical signal to output the feedback high-frequency signal. A feedback block, and the distortion compensation block inputs the high frequency signal on the input side and inputs the high frequency signal for feedback from the first feedback block, and the amount of distortion generated in the high frequency signal for feedback Is calculated as a first distortion compensation component, and the first distortion compensation component is calculated on the input side. A first distortion compensation block that adds a frequency signal and outputs a distortion addition signal; inputs the distortion addition signal from the first distortion compensation block; and inputs the feedback high-frequency signal from the second feedback block Then, a distortion compensation component for compensating for the amount of distortion occurring in the feedback high-frequency signal is calculated as a second distortion compensation component, and the transmission is performed by adding the second distortion compensation component to the distortion addition signal. A second distortion compensation block that outputs a high-frequency signal for use, wherein the first distortion compensation block receives the high-frequency signal adjusted so that no distortion occurs in the electric / optical converter of the optical link. When the input high-frequency signal is input, the first distortion compensation component is calculated and stored, and when the input high-frequency signal is input from the outside, the stored first distortion compensation is calculated. And calculates the distortion addition signal using a minute.

  According to another aspect of the distortion compensation system of the present invention, the first feedback block includes a feedback optical fiber having substantially the same length as the optical fiber, and the branch to the feedback optical fiber. A feedback optical / electrical converter for inputting the optical signal after transmitting the input optical signal and performing optical / electrical conversion and outputting the high-frequency signal for feedback, and the second feedback The block has another feedback optical / electrical converter that optically / electrically converts the branched optical signal and outputs the feedback high-frequency signal, and the first distortion compensation block includes the input side A high frequency signal is branched and input, and a difference from the high frequency signal for feedback input from the first feedback block is calculated, and this is inverted. A first distortion compensation unit that stores the first distortion compensation component, or reads and outputs the stored first distortion compensation component, and branches and inputs the input-side high-frequency signal; A first delay unit that delays and outputs the input-side high-frequency signal for a processing time of one distortion compensation unit; and the first distortion-compensation component is added to the input-side high-frequency signal that is input from the first delay unit. A first adder that adds and outputs the distortion addition signal, and the second distortion compensation block branches and inputs the distortion addition signal and inputs from the second feedback block A second distortion compensator that calculates a difference from the high-frequency signal for feedback, converts the difference into an inverse characteristic, and outputs the second distortion compensation component; and branches and inputs the distortion addition signal; The distortion addition signal is delayed by the processing time of the distortion compensator. And a first adder that adds the second distortion compensation component to the distortion addition signal input from the second delay element and outputs the high-frequency signal for transmission. It is characterized by having.

  According to the present invention, it is possible to provide a distortion compensation system capable of compensating for distortion generated in an optical link by feeding back an optical signal with a simple configuration.

1 is a block diagram illustrating a configuration of a distortion compensation system according to a first embodiment of the present invention. It is a block diagram which shows the structure of the distortion compensation system which concerns on the 2nd Embodiment of this invention in a training period. It is a block diagram which shows the structure of the distortion compensation system which concerns on the 2nd Embodiment of this invention in the real time distortion compensation period.

  A distortion compensation system according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. Each component having the same function is denoted by the same reference numeral for simplification of illustration and description.

  The distortion compensation system of the present invention has a simple configuration that performs distortion compensation for an electric signal in an RF (high frequency) region, instead of performing distortion compensation in the baseband region using an A / D converter and a D / A converter. A feedback system circuit is used to compensate for signal distortion generated by an optical component such as an LD or an optical fiber provided in an optical link or an LD driving amplifier. ADVANTAGE OF THE INVENTION According to this invention, the distortion compensation system which can perform stable distortion compensation at low cost can be provided by applying the feedback type circuit used conventionally to distortion compensation of an optical link.

(First embodiment)
A distortion compensation system according to a first embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a block diagram showing a configuration of a distortion compensation system 100 of this embodiment connected to an optical link 10. The optical link 10 has a configuration in which an optical / electrical converter 12 provided on the input end 11 side and an optical / electrical converter 14 provided on the output end 15 side are connected by an optical fiber 13. ing. The optical link 10 converts the RF signal input to the input end 11 into an optical signal by the electric / optical converter 12 and transmits this optical signal to the far side by the optical fiber 13. The optical signal transmitted through the optical fiber 13 is converted again into an RF signal by the optical / electrical converter 14 and output to the outside from the output end 15.

  The RF signal (input-side high-frequency signal) input to the input terminal 11 is an RF signal obtained by receiving a radio signal (modulated carrier wave) such as a mobile phone, a wireless LAN, or a terrestrial digital television broadcast. The optical link 10 converts a received RF signal into an optical signal with a high frequency and transmits the optical signal to a remote location through an optical fiber 13.

  The electrical / optical converter 12 includes an LD that converts an electrical signal into an optical signal, and is configured to be driven by an RF signal input to the input terminal 11. In the configuration of the optical link 10 shown in FIG. 1, an LD driving amplifier 16 that amplifies an RF signal input to the input terminal 11 is provided. After the RF signal is amplified by the LD driving amplifier 16, electrical / optical conversion is performed. In this configuration, the LD built in the device 12 is driven.

  When an RF signal is input to the input terminal 11, the RF signal is amplified by the LD driving amplifier 16 to drive the LD built in the electric / optical converter 12. As a result, the electrical / optical converter 12 outputs an optical signal that is intensity-modulated with an RF signal (conversion optical signal). The optical signal output from the electrical / optical converter 12 is input to the optical fiber 13 and transmitted to the optical / electrical converter 14. The optical / electrical converter 14 returns the optical signal (post-transmission optical signal) input from the optical fiber 13 to the RF signal (output-side high-frequency signal) again, and outputs this from the output end 15 to the outside. The RF signal output from the output terminal 15 is radiated again into the air, for example, as a radio signal for a mobile phone, a wireless LAN, digital terrestrial television broadcasting, or the like.

  The distortion compensation system 100 of the present embodiment is provided on the input end 11 side of the optical link 10 and includes a band pass filter (BPF) 101, a distortion compensation block 110, and a feedback block 120. The BPF 101 limits the RF signal input to the input terminal 11 to a necessary band and outputs it to the distortion compensation block 110. Hereinafter, an RF signal output from the BPF 101 to the distortion compensation block 110 is denoted by S1.

  The distortion compensation block 110 includes a distortion compensation unit 111, a delay unit 112, and an adder 113. The distortion compensation block 110 adds a predetermined distortion compensation component to the RF signal S1 input from the BPF 101 and outputs the result to the optical link 10. ing. An RF circuit (IC) that performs distortion compensation in the RF region instead of the BB region can be applied to the distortion compensation unit 111.

  The feedback block 120 is provided to feed back the distortion characteristics of the optical link 10, and includes a coupler 121 provided on the connection side of the optical fiber 13 to the electrical / optical converter 12, and an optical fiber (feedback optical fiber). 122, an optical / electrical converter (feedback optical / electrical converter) 123, and a BPF 124. The distortion characteristics of the optical link 10 obtained by the feedback block 120 are fed back to the distortion compensation block 110, and the distortion compensation block 110 is controlled to compensate for it.

  Since the LD driving amplifier 16 and the electric / optical converter 12 (built-in LD) constituting the optical link 10 have nonlinearity, distortion occurs in the input RF signal. Further, due to the optical wavelength dispersion of the optical fiber 13, waveform distortion occurs in the optical signal during transmission through the optical fiber 13. Furthermore, since the optical / electrical converter 14 also has non-linearity, distortion occurs when the optical signal is returned to the RF signal again. The optical link 10 has all these distortions, and this is the distortion characteristic of the optical link 10.

  The distortion compensation system 100 of this embodiment is configured to compensate for the distortion characteristics of the optical link 10 described above. The RF signal S1 input from the BPF 101 to the distortion compensation block 110 is branched into two and input to the delay unit 112 and the distortion compensation unit 111, respectively. The RF signal (referred to as S2) that has passed through the delay unit 112 is input to the adder 113. On the other hand, the RF signal S1 input to the distortion compensator 111 is used by the distortion compensator 111 to generate a distortion compensation component (referred to as S3). The distortion compensation component S3 generated by the distortion compensation unit 111 is output to the adder 113, where it is added to the RF signal S2 output from the delay unit 112. The RF signal (referred to as S4) obtained by adding the distortion compensation component S3 to the RF signal S2 by the adder 113 is an RF signal predistorted by the distortion compensation component S3, and this is input to the optical link 10.

  The RF signal (high-frequency signal for transmission) S4 input to the optical link 10 is amplified by the LD driving amplifier 16 and then drives the electrical / optical converter 12 to output an optical signal (referred to as S5). The optical signal S5 is an optical signal whose intensity is modulated by the RF signal S4. The optical signal S5 output from the electrical / optical converter 12 is branched into two by the coupler 121, and one of the optical signals S5 is transmitted to the optical / electrical converter 14 via the optical fiber 13. The other of the optical signals S5 is input to the feedback block 120.

  The optical signal S5 input to the feedback block 120 is input to the optical fiber 122 and transmitted to the optical / electrical converter 123. Here, the optical signal S5 input to the optical / electrical converter 123 is converted into an RF signal and output. The RF signal output from the optical / electrical converter 123 is limited to a necessary band by the BPF 124 and input to the distortion compensation block 110. An RF signal (high frequency signal for feedback) input from the BPF 124 to the distortion compensation block 110 is set to S6.

  The optical fiber 122 of the feedback block 120 has substantially the same characteristics as the optical fiber 13 of the optical link 10 and is formed to have substantially the same length. In addition, the optical / electrical converter 123 also has substantially the same non-linearity as the optical / electrical converter 14. Thus, the optical fiber 122 and the optical / electrical converter 123 of the feedback block 120 are formed so as to have substantially the same characteristics as the optical fiber 13 and the optical / electrical converter 14 of the optical link 10, respectively. The RF signal output from the optical / electrical converter 123 has substantially the same distortion as the RF signal output from the optical / electrical converter 14.

  Note that the optical / electrical converters 14 and 123 may change the amount of distortion when the intensity of the input optical signal is different. In this case, the amount of distortion of the RF signal output from the optical / electrical converter 14 and the amount of distortion of the RF signal output from the optical / electrical converter 123 are different. A change in the amount of distortion due to the difference in signal intensity is small, and the amount of distortion due to the LD of the electrical / optical converter 12 becomes more dominant, so there is no significant performance deterioration.

  The RF signal S6 input to the compensation block 110 from the optical / electrical converter 123 via the BPF 124 is input to the distortion compensation unit 111 and used to generate the distortion compensation component S3. The distortion compensation unit 111 calculates the difference between the RF signal S6 input from the feedback block 120 and the RF signal S1 input from the BPF 101. This difference corresponds to the amount of distortion that occurs while the RF signal S1 is transmitted through the optical link 10. The distortion compensation unit 111 obtains a signal having an inverse characteristic for canceling the calculated difference (distortion amount), and outputs the signal to the adder 113 as a distortion compensation component S3.

  The adder 113 receives one RF signal S1 branched into two from the BPF 101 and a distortion compensation component S3 output by processing the other branched RF signal S1 with the distortion compensation unit 111. It is adding. Here, when one RF signal S1 is directly input to the adder 113 without passing through the delay unit 112, it is necessary for the distortion compensator 111 to input the other RF signal S1 and calculate the distortion compensation component S3. One RF signal S <b> 1 is input to the adder 113 earlier by the processing time. Therefore, in order to eliminate the delay time of the distortion compensation component S3 with respect to one RF signal S1, the delay device 112 is passed through the one RF signal S1. One RF signal S <b> 1 is input to the adder 113 with a delay time equivalent to the above delay time while passing through the delay device 112. From the adder 113, the RF signal S4 predistorted so as to compensate for the amount of distortion generated in the optical link 10 is input to the optical link 10.

  As described above, the RF signal S4 output from the distortion compensation block 110 is added with a distortion amount (distortion compensation component S3) opposite to the distortion characteristic of the optical link 10, so that the RF signal S4 is converted into the optical link. The amount of distortion predistorted during transmission of 10 is eliminated. At the output end 15, the distortion amount predistorted by the distortion compensation block 110 and the distortion amount generated while passing through the optical link 10 are canceled out, and an RF signal without distortion is obtained. Similarly to the RF signal output from the output terminal 15, the RF signal S6 output to the distortion compensation block 110 via the feedback block 120 is also an RF signal without distortion.

  The distortion compensation system 100 of the present embodiment is configured to output an RF signal S6 that is substantially equivalent to the RF signal output from the optical link 10 to the output end 15 from the feedback block 120 to the distortion compensation block 110. Thereby, the distortion compensation unit 111 of the distortion compensation block 110 can determine the distortion compensation component S3 so as to compensate the distortion generated in the optical link 10 by feeding back the RF signal S6. Further, even when the distortion characteristics of the optical link 10 change, the distortion compensation component S3 can be determined so as to compensate for the fluctuation of the distortion characteristics by feeding back the RF signal S6.

  In the distortion compensation block 110 according to the present embodiment, an A / D converter and a circuit that performs distortion compensation in the baseband region using the D / A converter are not used, and an RF circuit that performs distortion compensation processing in the RF region. Is used. As such an RF circuit, for example, a distortion compensation circuit (IC) used for an RF amplifier can be applied. Thereby, the structure of the distortion compensation block 110 can be simplified. In addition, by arranging an optical fiber 122 having the same length as the optical fiber 13 used in the optical link 10 in the feedback block 120, third-order intermodulation distortion due to wavelength dispersion generated particularly in a long-distance optical fiber is simultaneously compensated. can do.

  Since the distortion compensation system 100 according to the present embodiment includes the feedback block 120 as a feedback system, distortion compensation can be performed following changes in the environment. In addition, since a circuit that compensates for distortion in the RF region is used, the configuration can be made simpler than a circuit that compensates for distortion in the baseband region. Further, since the feedback block 120 is configured to input the optical fiber 122 having the same fiber length as the optical fiber 13 disposed in the optical link 10 and input to the optical / electrical converter 123, the feedback block 120 is generated in the optical fiber 13. Distortion due to chromatic dispersion can also be compensated.

(Second Embodiment)
In the first embodiment, a feedback block 120 including an optical fiber 122 is provided in order to feed back waveform distortion due to optical chromatic dispersion of the optical fiber 13 disposed in the optical link 10 in real time, and this is always connected. It was configured to compensate for distortion.

  On the other hand, in the distortion compensation system 200 of the second embodiment, the distortion amount of the RF signal due to the optical wavelength dispersion of the optical fiber in the optical link is acquired in advance, and the distortion compensation component for compensating this is determined in advance. Yes. When performing distortion compensation in real time, a distortion compensation component determined in advance is used as a fixed value, and the distortion amount due to the optical fiber is compensated with the distortion compensation component having a fixed value. In this embodiment, a training period is provided in order to obtain in advance the amount of distortion of the RF signal due to the optical wavelength dispersion of the optical fiber in the optical link.

  The distortion compensation system 200 of the present embodiment is different in configuration between the training period and the real-time distortion compensation period. FIG. 2 shows the configuration of the distortion compensation system 200 of the present embodiment during the training period, and FIG. 3 shows the configuration of the distortion compensation system 200 of the present embodiment during the real-time distortion compensation period. Hereinafter, it is assumed that the distortion compensation system 200 shown in FIG. 2 is 200a, and the distortion compensation system 200 shown in FIG. 3 is 200b.

  The optical link to which the distortion compensation system 200 of the present embodiment is applied has a different configuration from the optical link 10 to which the distortion compensation system 100 of the first embodiment is applied, as shown in FIGS. 2 and 3, the LD driving amplifier 16 provided on the input side of the optical link 10 is not provided. The optical link 20 is configured to directly drive the LD built in the electrical / optical converter 22 with the RF signal input from the input terminal 21. However, the optical link to which the distortion compensation system 200 of this embodiment is applied is not limited to this, and can also be applied to the optical link 10.

  The distortion compensation system 200a of the present embodiment during the training period includes two distortion compensation blocks and two feedback blocks. That is, the first distortion compensation block 210 and the second distortion compensation block 230 are provided as the distortion compensation block, and the first feedback block 220 and the second feedback block 240 are provided as the feedback block. The first feedback block 220 is connected to the first distortion compensation block 210, and the second feedback block 240 is connected to the second distortion compensation block 230.

  The distortion compensation system 200 a of this embodiment includes a band pass filter (BPF) 201, a first distortion compensation block 210, and a second distortion compensation block 230 sequentially from the input end 21. Further, a first feedback block 220 and a second feedback block 240 are provided between the optical fiber 23 disposed in the optical link 20 and the first distortion compensation block 210 and the second distortion compensation block 230, respectively. ing. The first feedback block 220 is connected to the optical fiber 23 by a predetermined optical signal line 225, and the second feedback block 240 is connected to the optical fiber 23 via a coupler 221.

  Similar to the distortion compensation block 110 of the first embodiment, the first distortion compensation block 210 includes a distortion compensation unit 211, a delay unit 212, and an adder 213. In addition, the distortion compensation unit 211 is configured to input a signal from the first feedback block 220. Similarly, the second distortion compensation block 230 also includes a distortion compensation unit 231, a delay unit 232, and an adder 233, and the distortion compensation unit 231 receives a signal from the second feedback block 240. It has become.

  Similar to the feedback block 120 of the first embodiment, the first feedback block 220 includes an optical fiber 222, an optical / electrical converter 223, and a BPF 224. On the other hand, the second feedback block 240 includes an optical / electrical converter 243 and a BPF 244, but does not include an optical fiber. The optical fiber 222 has substantially the same characteristics as the optical fiber 23 of the optical link 20 and is formed to have substantially the same length. Further, both the optical / electrical converters 223 and 243 have non-linearity substantially equal to that of the optical / electrical converter 24 provided in the optical link 20.

  In the training period, the distortion amount due to the optical fiber 23 of the optical link 20 is detected using the first distortion compensation block 210 and the first feedback block 220, and a distortion compensation component (hereinafter referred to as a first distortion compensation component) for compensating this is detected. Of distortion compensation component). Here, in order to detect only the amount of distortion due to the optical fiber 23, as an RF signal input to the input terminal 21, the electrical / optical converter 22, the coupler 221, and the optical / electrical converters 223 and 224 of the optical link 20 are used. A signal that does not cause distortion is used. For example, the LD built in the electric / optical converter 22 has a current range having a linear characteristic in which the intensity of the output light linearly changes with respect to the input current, and an RF having an intensity within that range is determined. A signal is input to the input terminal 21.

  When the RF signal is input to the input terminal 21, the RF signal is limited to a desired band by the BPF 201 and then input to the first distortion compensation block 210. In the first distortion compensation block 210, similarly to the distortion compensation block 110 of the first embodiment, a distortion compensation component (first distortion compensation component) is added to the input RF signal and output. The RF signal output from the first distortion compensation block 210 is then input to the second distortion compensation block 230. However, the second distortion compensation block 230 in the training period outputs the input RF signal as it is without being processed. The RF signal output from the second distortion compensation block 230 is input to the optical link 20. The RF signal input to the optical link 20 drives the electrical / optical converter 22 to output an optical signal, and the output optical signal is transmitted through the optical fiber 23.

  The first feedback block 220 inputs an optical signal transmitted to the optical fiber 23 via the optical signal line 225. The optical signal input via the optical signal line 225 passes through the optical fiber 222 and the optical / electrical converter 223 of the first feedback block 220, and thus has the same distortion as the RF signal output from the optical link 20. The amount of generated RF signal is output to the BPF 224. The RF signal input to the optical link 20 is a signal that does not cause distortion in the electrical / optical converter 22, the coupler 221, and the optical / electrical converters 223 and 224. The amount of distortion is only the amount of distortion generated in the optical signal when transmitted through the optical fiber 222. The RF signal output to the BPF 224 is limited to a desired band here and is output to the first distortion compensation block 210.

  In the first distortion compensation block 210, the RF signal input from the first feedback block 220 is input to the distortion compensation unit 211, where a distortion compensation component is calculated. The distortion compensation component calculated here is the first distortion compensation component, and becomes a distortion compensation component for compensating for the amount of distortion generated in the optical fiber 23 of the optical link 20. The first distortion compensation component is used in the distortion compensation system 200b as a fixed value regardless of the RF signal input to the input terminal 21 in the real-time distortion compensation period.

  The distortion compensation system 200b of the present embodiment used in the real-time distortion compensation period has a configuration in which the first feedback block 220 is separated. In the first distortion compensation block 210, the distortion compensation unit 211 outputs the first distortion compensation component calculated during the training period to the adder 213 without using the feedback signal from the optical link 20. Since the distortion compensation unit 211 does not perform the process of calculating the distortion compensation component as in the training period, the delay unit 212 may output the input RF signal to the adder 213 without delaying the input RF signal.

  When an RF signal (distortion addition signal) obtained by adding the first distortion compensation component is input from the first distortion compensation block 210 to the second distortion compensation block 230, it is input to the second distortion compensation block 230. The received RF signal is input to the delay unit 232 and the distortion compensation unit 231. In addition, the RF signal output from the second feedback block 240 is also input to the distortion compensation unit 231. The distortion compensation unit 231 calculates a second distortion compensation component from the RF signal input from the first distortion compensation block 210 and the RF signal input from the second feedback block 240. This second distortion compensation component compensates for the distortion amount excluding distortion due to chromatic dispersion generated in the optical fiber 23, that is, the distortion amount due to the electrical / optical converter 22 and the optical / electrical converter 24. This distortion amount is compensated in real time.

  As with the optical / electrical converters 14 and 123 of the first embodiment, the optical / electrical converters 24 and 243 may change the amount of distortion when the intensity of the input optical signal is different. As in the first embodiment, the change in the amount of distortion is small, and the amount of distortion due to the LD of the electrical / optical converter 22 becomes dominant, so there is no significant performance degradation. In addition, when detecting the amount of strain due to the optical fiber 222 during the training period, the optical / electrical converter 223 may also be distorted. In that case, the first distortion compensation component includes a component for compensating for distortion caused by the optical / electrical converter 223. As a result, in the distortion compensation control in the real-time distortion compensation period, the distortion compensation component for the optical / electrical converter 223 is excessively compensated. Even in that case, since feedback control is performed, there is no problem even if an extra distortion compensation component is included.

  As described above, in the distortion compensation system 200 of this embodiment, when performing distortion compensation in real time, it is not necessary to arrange the optical fiber 222 similar to the optical fiber 23 of the optical link 20 in the feedback block 240. Thereby, the configuration of the distortion compensation system 200 can be further simplified in real-time distortion compensation.

  In addition, the first distortion compensation component acquired during the training period is not limited to one, but is acquired in advance with optical fibers of various lengths, and in real-time distortion compensation, the light actually used The first distortion compensation component corresponding to the fiber 23 can be selected and used. That is, the first distortion compensation component corresponding to the optical fiber 23 actually used is selected from the plurality of first distortion compensation components acquired during the training period, and this is selected as the first distortion compensation block 210. It can be downloaded to the distortion compensation unit 211 and used.

  Note that the description in the present embodiment shows an example of the distortion compensation system according to the present invention, and the present invention is not limited to this. The detailed configuration and detailed operation of the distortion compensation system in the present embodiment can be appropriately changed without departing from the spirit of the present invention.

10, 20 Optical link 11, 21 Input end 12, 22 Electric / optical converter 13, 23, 122, 222 Optical fiber 14, 24, 123, 223, 243 Optical / electric converter 15, 25 Output end 16 For LD drive Amplifier 100, 200 Distortion compensation system 101, 201 BPF
110, 210, 230 Distortion compensation block 111, 211, 231 Distortion compensation unit 112, 212, 232 Delay device 113, 213, 233 Adder 120, 220, 240 Feedback block 121, 221 Coupler 124, 224, 244 BPF
225 Optical signal line

Claims (5)

An electric / optical converter that inputs a high-frequency signal for transmission and performs electrical / optical conversion and outputs a converted optical signal, an optical fiber that receives and transmits the converted optical signal, and post-transmitted light transmitted through the optical fiber A distortion compensation system for compensating for distortion generated in an optical link, comprising: an optical / electrical converter that inputs a signal and performs optical / electrical conversion and outputs an output-side high-frequency signal;
A feedback block for branching and inputting the optical signal at the time of conversion from the optical fiber, processing this and outputting a high-frequency signal for feedback;
An input side high frequency signal is inputted from the outside and the feedback high frequency signal is inputted from the feedback block to calculate a distortion compensation component for compensating for a distortion amount generated in the feedback high frequency signal, and the input side high frequency signal A distortion compensation system comprising: a distortion compensation block that adds the distortion compensation component to a signal to calculate the transmission high-frequency signal and outputs the transmission high-frequency signal to the optical link. The feedback block generates a distortion that is substantially the same as that generated when the optical signal at the time of conversion is transmitted through the optical fiber, and then optical / electrically converts the generated optical signal after branching, thereby converting the feedback high frequency signal. The distortion compensation system according to claim 1, wherein a signal is output. The feedback block is
An optical fiber for feedback having substantially the same length as the optical fiber;
A feedback optical / electrical converter that inputs the optical signal after transmitting the optical signal branched and input to the optical fiber for feedback, performs optical / electrical conversion, and outputs the high-frequency signal for feedback; Have
The distortion compensation block is:
The input-side high-frequency signal is branched and input, a difference with the feedback high-frequency signal is calculated, and the distortion compensation component that outputs the distortion compensation component with this being reversed,
A branching device for branching and inputting the input-side high-frequency signal, and delaying and outputting the input-side high-frequency signal for the processing time of the distortion compensation unit;
3. The distortion compensation system according to claim 1, further comprising: an adder that adds the distortion compensation component to the input-side high-frequency signal input from the delay device and outputs the transmission high-frequency signal. 4. . The feedback block is
First, a distortion equivalent to that generated when the optical signal at the time of conversion is transmitted through the optical fiber is generated in the branched optical signal and then optical / electrically converted to output the feedback high-frequency signal. 1 feedback block;
A second feedback block that directly optically / electrically converts the branched optical signal and outputs the feedback high-frequency signal;
The distortion compensation block is:
The input high-frequency signal is input and the feedback high-frequency signal is input from the first feedback block, and a distortion compensation component for compensating a distortion amount generated in the feedback high-frequency signal is a first distortion compensation. A first distortion compensation block that calculates as a component, adds the first distortion compensation component to the input-side high-frequency signal, and outputs a distortion addition signal;
Distortion compensation for inputting the distortion addition signal from the first distortion compensation block and inputting the feedback high-frequency signal from the second feedback block to compensate for the amount of distortion generated in the feedback high-frequency signal. A second distortion compensation block that calculates a component as a second distortion compensation component, adds the second distortion compensation component to the distortion addition signal, and outputs the transmission high-frequency signal;
The first distortion compensation block includes:
When a high-frequency signal adjusted so as not to generate distortion in the electrical / optical converter of the optical link is input as the input-side high-frequency signal, the first distortion compensation component is calculated and stored,
2. The distortion compensation system according to claim 1, wherein when the input-side high-frequency signal is input from the outside, the distortion addition signal is calculated using the stored first distortion compensation component. The first feedback block includes
An optical fiber for feedback having substantially the same length as the optical fiber;
A feedback optical / electrical converter that inputs the optical signal after transmitting the optical signal branched and input to the optical fiber for feedback, performs optical / electrical conversion, and outputs the high-frequency signal for feedback; Have
The second feedback block is
Another optical / electrical converter for feedback that optically / electrically converts the optical signal branched and input and outputs the high-frequency signal for feedback;
The first distortion compensation block includes:
Branching and inputting the high frequency signal on the input side, calculating a difference from the high frequency signal for feedback input from the first feedback block and storing the first distortion compensation component having the inverse characteristic, or A first distortion compensation unit that reads out and outputs the stored first distortion compensation component;
A first delay device for branching and inputting the input-side high-frequency signal, and delaying and outputting the input-side high-frequency signal by a processing time of the first distortion compensation unit;
A first adder that adds the first distortion compensation component to the input high-frequency signal input from the first delay unit and outputs the distortion addition signal;
The second distortion compensation block is:
The distortion addition signal is branched and input, a difference from the feedback high-frequency signal input from the second feedback block is calculated, and the second distortion compensation component is output using the difference as an inverse characteristic. A distortion compensation unit;
A second delay device for branching and inputting the distortion addition signal, and delaying and outputting the distortion addition signal by a processing time of the second distortion compensation section;
5. A first adder that adds the second distortion compensation component to the distortion addition signal input from the second delay unit and outputs the high-frequency signal for transmission. The distortion compensation system described in 1.

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