JPH08250795A - Light transmitting-receiving system - Google Patents

Abstract

PURPOSE: To effectively compensate distortion which occurs when signals are transmitted and received through an optical transmission line. CONSTITUTION: By feeding back transmitting signals transmitted to an optical transmission line 13 from an optical receiver 8, the amplitude of the transmitting signals is controlled in accordance with the amplitude of the fed-back signals within a specific frequency range. At the time of controlling the amplitude of the transmitting signals, the amplitude of the fed-back signals within the specific frequency range is detected by means of a band-pass filter 6 and detector 15 and the amplitude of the transmitting signals is controlled by means of a pre-distortion generating circuit 2 in accordance with the compared results of a comparator which compares the detected amplitude with a prescribed reference signal Vref.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission / reception system, and more particularly to an optical transmission / reception system for optically transmitting a plurality of frequency-multiplexed signals.

[0002]

2. Description of the Related Art Generally, in a system of this type, distortion occurs in a signal to be transmitted / received due to the characteristics of an element for converting an electric signal into an optical signal and an element for converting the signal into the optical signal. This distortion adversely affects the main signal as noise. Therefore, various methods for compensating for this distortion have been conventionally proposed.

FIG. 2 shows a distortion compensation system disclosed in Japanese Patent Laid-Open No. 2-148929.

In this system, as shown in the figure, intermodulation occurs between optical transmission lines by inserting a suppression signal larger than the main signal by 7 to 10 [dB] outside the main signal band. It suppresses distortion. Therefore, in order to minimize the signal deterioration due to the intermodulation distortion that occurs in the optical transmission path section on the receiving circuit side after passing through the optical transmission path section, feedback is applied to the suppression signal generation circuit on the transmission side to suppress the suppression signal. Is automatically adjusted in amplitude and phase.

On the other hand, FIG. 3 shows a distortion compensation system disclosed in Japanese Patent Laid-Open No. 4-132430.

In this system, as shown in the figure, the distortion generated by the non-linearity of the laser diode (LD) 17 itself is fed back in the transmitter to generate the distortion generating circuit 2.
It is a configuration that corrects by controlling.

Specifically, first, the output of the laser diode 17 is converted into an electric signal by a photodiode (PIN-PD) 18, and this electric signal is converted into a bandpass filter (B
PF) 6 takes out only the distortion component. Then, the peak value of the extracted distortion component is detected, and the predistortion generating circuit 2 is controlled according to the detected value. Incidentally, 19 is an automatic power control circuit, and 16 is an LD drive circuit.

[0008]

The above-mentioned prior art has the following drawbacks.

First, in the technique disclosed in Japanese Patent Laid-Open No. 2-148929, it is possible to compensate the intermodulation distortion generated in the optical transmission line section, but it occurs in the transmitter or the receiver. There is a drawback in that intermodulation distortion cannot be compensated in principle. In addition, it is assumed that a huge signal other than the main signal is input, the laser diode becomes overmodulated, and as a result, overmodulation distortion, which is a level far greater than the distortion caused by nonlinearity, can occur. However, there is also a drawback that the setting condition of the suppression signal is restricted.

On the other hand, in the technique disclosed in Japanese Patent Application Laid-Open No. 4-132430, since it is a system for compensating only the non-linear distortion of the laser diode, a non-linear element other than the laser diode, for example, a photo diode in the receiving device is used. There is a drawback that the distortion generated in a diode, an electric amplifier or the like cannot be compensated.

The present invention has been made to solve the above-mentioned drawbacks of the prior art, and an object thereof is optical transmission / reception capable of effectively compensating for distortion when signals are transmitted / received using an optical transmission line. It is to provide a system.

[0012]

An optical transmission / reception system according to the present invention is an optical transmission device for transmitting a transmission signal to be transmitted to an optical transmission line, and an optical reception device for receiving the transmission signal transmitted to the optical transmission line. An optical transmission / reception system comprising: an information feedback unit provided in the optical receiving device for returning the transmission signal; and a specific frequency range of a feedback signal returned by the information feedback unit provided in the optical transmitting device. Amplitude control means for controlling the amplitude of the transmission signal according to the amplitude is included.

[0013]

The transmission signal transmitted to the optical transmission line is returned from the optical receiving device. The amplitude of the transmission signal is controlled according to the amplitude of the returned feedback signal in the specific frequency range. In that case, the amplitude of the feedback signal in the specific frequency range is detected, and the amplitude of the transmission signal is controlled by the attenuator according to the result of comparison between the detected amplitude and the predetermined reference signal.

[0014]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of an optical transmission / reception system according to the present invention, and the same portions as those in FIG. 3 are designated by the same reference numerals. In the figure, an optical transmission / reception system according to an embodiment of the present invention includes a transmitter 1 and a receiver 8.

The transmitter 1 receives a plurality of carriers as input, and a variable distortion predistortion generating circuit 2 which intentionally generates distortion.
And an optical transmission circuit 3 that converts the main signal and the distortion signal output from the distortion generation circuit 2 into an optical signal.

The transmitting device 1 is designated by an optical receiving circuit 4 which receives an optical signal from the receiving device through an optical cable 14 which is an optical transmission line and restores it into an electric signal, and an output of the optical receiving circuit 4. A demodulator 5 that demodulates a signal modulated by the above modulation method, and a desired frequency range from the signal output from this demodulator 5 (a frequency range corresponding to a distortion component, but a range included in the frequency range of the main signal). And a bandpass filter 6 for extracting (excluding).

Furthermore, the transmitter 1 compares the detector 15 for detecting the intensity of the output signal of the bandpass filter 6 with the output voltage of the detector 15 and an arbitrary reference voltage Vref, and outputs the predistortion. It is configured to include a comparator 7 that controls the intensity of distortion generated by the generation circuit 2.

On the other hand, the receiving device 8 includes an optical receiving circuit 9 for receiving the optical signal output from the transmitting device through the optical cable 14 and restoring it into an electric signal, and a branching device for dividing the output of the optical receiving circuit 9 into two. 10 and 10.

Further, the receiving device 8 converts one of the outputs of the branching device 10 into an input signal and performs a modulation by a specified modulation method, and the modulation signal output from the modulator 11 into an optical signal. Optical transmission circuit 1 for outputting to optical cable 14
2 is included.

In such a configuration, the transmitter 1 receives a main signal composed of a plurality of carrier waves. This main signal is input to the predistortion generating circuit 2 and generates distortion for canceling the distortion generated in the subsequent circuits.

The main signal containing the distortion component of the predistortion generating circuit 2 is input to the optical transmitting circuit 3 and converted into an optical signal, and is transmitted to the optical receiving circuit 9 of the receiving device 8 via the optical cable 13 which is a transmission path. Is entered. The main signal restored to the electric signal by the optical receiving circuit 9 is distributed by the branching device 10, and one of them is output as an output signal. The other output signal from the branching device 10 is modulated by a modulator 11 that adopts a specified modulation method, converted again into an optical signal by an optical transmission circuit 12, and transmitted through an optical cable 14 to an optical reception circuit 4 of the transmission device 1. Entered in. The signal restored to the electric signal by the optical receiving circuit 4 is the modulator 1
It is demodulated by a demodulator that restores the modulation method of No. 1.

The modulation method of the modulator 11 and the parameters for optical transmission are set so that the waveform at this point becomes equal to the output of the branching device 10. Although the frequency range of the main signal and the frequency range of the distorted signal may partially overlap, the bandpass filter 6 extracts the part of the distortion component other than the main signal component from the signal of the demodulator 5, and this bandpass filter The peak value of the signal of the distortion component obtained through 6 is detected by the detector 15. The detected peak voltage value is the comparator 7
Is compared with the value of a predetermined reference voltage Vref. Then, the comparison output controls the amplitude of the signal in the predistortion generating circuit 2 that functions as an attenuator, and controls the amount of distortion generation.

That is, the distortion component originally contained in the input signal, the distortion component generated by the nonlinear element in the optical transmission circuit 3 and the optical reception circuit 9, and the optical multiple reflection in the optical transmission line are generated. The total distortion component together with the distortion component is fed back to the transmitting device to optimally control the distortion canceling effect of the predistortion generating circuit 2. As a result, a signal having a desired distortion value can be obtained as an output.

The reference voltage Vref may be determined according to the characteristics of each part forming the feedback circuit. If necessary, the characteristic of each part may be actually measured, and the value may be set so that the distortion can be minimized according to the measurement result.

As described above, information on the amount of distortion at the output stage is
Since the amount of distortion generated by the predistortion generator is controlled by feeding it back to the input stage, it is possible to compensate for the distortion generated in all the components.

[0027]

As described above, according to the present invention, the received transmission signal is fed back, and the amplitude of the transmission signal is controlled according to the amplitude of the fed back feedback signal in the specific frequency range. There is an effect that distortion can be effectively compensated when a signal is transmitted and received by using.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical transmission / reception system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a distortion compensation principle of a conventional optical transmission / reception system.

FIG. 3 is a block diagram showing a configuration of another conventional optical transmission / reception system.

[Explanation of symbols]

 1 transmitter 2 predistortion generating circuit 3, 12 optical transmitter circuit 4, 9 optical receiver circuit 5 demodulator 6 band pass filter 7 comparator 8 receiver 10 brancher 11 modulator 13, 14 optical fiber

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Claims (3)

[Claims] 1. An optical transmission / reception system including an optical transmission device for transmitting a transmission signal to be transmitted to an optical transmission line, and an optical reception device for receiving the transmission signal transmitted to the optical transmission line, Information feedback means provided in the receiving device for returning the transmission signal, and the amplitude of the transmission signal is controlled according to the amplitude in the specific frequency range of the feedback signal provided in the optical transmission device and returned by the information feedback means. An optical transmission / reception system comprising an amplitude control means. 2. The amplitude control means includes a detection means for detecting the amplitude of the feedback signal in a specific frequency range, a comparison means for comparing the detected amplitude with a predetermined reference signal, and a comparison means for responding to the comparison result. The optical transmission / reception system according to claim 1, further comprising an attenuator that controls the amplitude of the transmission signal. 3. The optical transmission / reception system according to claim 2, wherein the specific frequency range is a frequency range other than the frequency band of the transmission signal.