JPH01241232A - Optical repeater - Google Patents

Abstract

PURPOSE:To attain high speed signal processing by constituting the title optical repeater of optical circuits not including any electric system except an optical clock generator, an oscillator and a detecting circuit. CONSTITUTION:An optical pulse deteriorated by attenuation is arranged into a linearly polarized light whose polarized wave front is constant and branched into two directions. One branched light is subject to phase modulation by an optical pulse modulator 12, multiplexed with an optical clock pulse, inputted to an optical AND gate 16, where the optical pule and the optical clock are phase-modulated. The other branched light pulse is coupled with the remaining branched optical clock from an optical directional coupler 14 and the result is fed to the 2nd optical AND gate 23, where random jitter is eliminated, and outputted to an optical fiber 24, supplied to an optical amplifier element 25, the unarranged component is uniformized, the waveform of the optical pulse is shaped by an optical pulse waveform shaping device 26, and outputted to the optical transmission line.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical repeater that performs the reproduction identification function of optical pulses using optical control pulses.

(Prior Art) Conventionally, an optical repeater has 1. After the optical pulse, which has been attenuated and deteriorated after propagating through the optical transmission line, is once converted into an electrical signal by the opto-electrical (0/E) converter 1, it is equalized and amplified by the equalization amplifier 2, and from the equalized waveform after the amplification, The timing circuit 3 extracts the timing, and the identification circuit 4 uses the timing signal to identify the equalized waveform. Then, the electro-optical (Elo) converter 5 regenerates the optical pulse, and the regenerated optical pulse The structure was such that the signal was sent to the next stage optical transmission line. However, it is difficult to realize an ultra-high-speed transmission system of, for example, several tens of bits/s using the above configuration because there are limits to the processing speed or response speed of electrical signals.

For this reason, recently, optical pulses have been controlled by directly applying an ultra-high-speed electrical clock signal equivalent to the transmission speed to the gate element, and the 3R function required for repeaters [Reshapln
Optical repeater (IEEE Journal
of' Quantum Electronlcs
Vol, QE19. (See PL718-P1723),
An optical repeater that combines a saturable absorber and an optical amplification element and completely eliminates the electrical system from an optical repeater (Optlcs Let
tersVol, 11.198B, P392-P39
4) etc. have been proposed.

(Problem to be Solved by the Invention) However, according to the optical repeater that realizes the above 3R function, the electrical response speed limit of the gate element itself or the generation limit of the high-speed electrical clock signal is the high-speed performance of the optical repeater itself. This was a limiting factor and a major problem in building an ultra-high-speed transmission system. In addition, since an optical repeater without an electrical system is essentially a 2R functional optical repeater lacking a timing extraction function, it has the problem that it is impossible to remove jitter components contained in optical pulses. there were.

In view of the above-mentioned problems, an object of the present invention is to overcome the processing speed limit and response speed limit caused by the electrical signal processing part of an optical repeater by using optical signal processing, and to provide a 3R function.
Another object of the present invention is to provide an optical repeater that realizes high-speed signal processing.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a first optical directional coupler that demultiplexes optical pulses input from an optical transmission line, and a first optical directional coupler that demultiplexes optical pulses input from an optical transmission line. an optical pulse phase modulator that performs phase modulation of one of the demultiplexed optical pulses; an optical clock pulse generator that generates an optical clock pulse that adjusts the phase shift with the input optical pulse based on a detection signal; a second optical directional coupler that combines the modulated optical pulse and the optical clock pulse; and a second optical directional coupler that inputs the combined optical pulse and generates an optical signal when the phase-modulated optical pulse and the optical clock pulse overlap. a first optical AND gate that outputs a pulse; a photodetector that converts the output optical pulse of the optical AND gate into an electrical signal; and an oscillator that oscillates a signal at a predetermined frequency;
a detection circuit that synchronously detects the same frequency component as the oscillation frequency of the oscillator from the output electric signal of the photodetector and outputs the detected signal; and a demultiplexed optical pulse of the other of the first optical directional coupler. and the optical clock pulse.
a second optical AND gate that extracts only the mutually overlapping portions of the multiplexed optical pulses;
an optical amplification element that obtains a nonlinear optical intensity output with respect to the intensity of the output optical pulse of the ND gate; and an optical pulse waveform shaper that is composed of an optical element that has a nonlinear effect and that shapes the waveform of the amplified optical pulse. Prepared.

(Function) According to the present invention, an optical pulse that has propagated through an optical transmission line and has been attenuated and degraded is first demultiplexed by the first optical directional coupler. One of the demultiplexed optical pulses undergoes phase modulation in an optical pulse phase modulator, and then is combined with an optical clock pulse output from an optical clock pulse generator in a second optical directional coupler to form the first optical pulse. It is input to the AND gate. Next, when the optical pulse phase-modulated by the first optical AND gate and the optical clock pulse overlap, an optical pulse is output, and this output optical pulse is received by a photodetector and converted into an electrical signal. Next, a detection circuit detects the same frequency component as the oscillation frequency of the oscillator from this electrical signal, and a detection signal based on this is output to the optical clock pulse generator, which changes the phase of the optical clock pulse and the input optical pulse. The deviation is adjusted.

On the other hand, the other demultiplexed optical pulse and optical clock pulse of the first optical directional coupler are combined by the third optical directional coupler, and this combined optical pulse is input to the second optical AND gate.

The second optical AND gate extracts only the overlapping portion of the input optical pulse and optical tallock pulse, thereby removing the random jitter of the input optical pulse, and further amplifying it with an optical amplification element to equalize the peak value. Ru. The optical pulses subjected to this amplification are subjected to nonlinear effects and waveform-shaped by an optical pulse waveform shaper, and are output to the next stage optical transmission line.

(Embodiment) FIG. 1 is a diagram showing an embodiment of an optical repeater according to the present invention. In the figure, reference numeral 10 denotes a polarization state controller, which aligns the polarization plane of the attenuated optical pulse after propagating through an optical transmission path (not shown) to a constant linear polarization. Reference numeral 11 denotes an optical directional coupler consisting of a leading fiber or a leading wave path, which splits the output optical pulse of the polarization state controller 10 into two directions. Reference numeral 12 denotes an optical pulse phase modulator consisting of an optical fiber and a driving device (not shown), which is driven based on a signal B from a low frequency oscillator (to be described later), and is used to adjust the pulse phase of one of the demultiplexed optical pulses of the forward coupler]-1. Modulate. Reference numeral 13 denotes an optical clock pulse generator, which is composed of an optical pulse compression device composed of a semiconductor laser gain-switched by a 1A voltage controlled oscillator (VCO), an optical fiber, a dispersive delay path, etc. Generates an optical clock pulse, which is a pulse train. 14 is an optical directional coupler which separates the optical clock pulse into two directions. 15
is an optical directional coupler, which combines the output optical pulse of the optical pulse phase modulator with one of the demultiplexed optical pulses of the optical directional coupler 14, that is, the optical clock pulse. 16 is a first optical AND gate consisting of a polarization rotation element using the Kerr effect; if the phase-modulated optical pulse and the optical clock pulse out of the optical pulses combined by the optical directional coupler 15 overlap, the optical The pulse is output to optical fiber 17.

FIG. 3 is a diagram for explaining the operation of the first optical AND gate 16. According to Figure 3, the previous pulse P is ■ in the figure.
As shown in the figure, if the optical clock pulse CP is phase modulated in the horizontal direction in the drawing and overlaps with the optical pulse region, the optical pulse a will be output.

Reference numeral 18 denotes a photodetector made of a PIN diode or the like, which converts the output light pulse of the optical AND gate 16 received via the optical fiber 17 into an electrical signal A. A low frequency oscillator 19 outputs a signal B of a predetermined frequency to the optical pulse phase modulator 12 and a multiplier to be described later.

A multiplier 20 multiplies the output electrical signal A of the photodetector 18 and the output signal B of one low frequency oscillator, and outputs the result as a signal C. 21 is a low-pass filter for signal C
A DC voltage having a value corresponding to the value is output to the optical clock pulse generator 13. These multiplier 20 and low-pass filter 21 constitute a detection circuit.

Reference numeral 22 denotes an optical directional coupler, which combines the other branched optical pulse of the optical directional coupler 11, that is, the human-powered optical pulse, and the other branched optical pulse of the optical directional coupler 14, that is, the optical clock pulse. do. A second optical AND gate 23 extracts only the portion where the input optical pulse and the optical clock pulse overlap each other out of the multiplexed optical pulses produced by the optical directional coupler 22 and outputs the extracted optical pulse to the optical fiber 24. FIG. 4 is a diagram for explaining the operation of the optical AND gate 23.
Figure (a) shows the white wave optical pulse waveform, and Figure 4 shows the optical AN.
3 is a diagram showing an output pulse waveform of a D gate 23. FIG. As can be seen from Figure 4, the input optical pulse contains random jitter, and the input optical pulse P and optical clock pulse CP do not match completely, so the parts where they overlap each other as shown in Figure 4(b) Random jitter contained in the input optical pulse is removed by extracting only the input optical pulse using the optical AND gate 23.

Although this random jitter is removed by the optical AND gate 23, the jitter component in the time axis direction is not removed and appears as a fluctuation in the peak value of the optical pulse.

Reference numeral 25 denotes an optical amplification element consisting of a semiconductor laser amplifier and a saturable absorber, which obtains a nonlinear optical intensity with respect to the optical pulse inputted through the optical fiber 24.
As shown in b): Remove fluctuations in the support high. 26
An optical pulse waveform shaper made of an optical fiber shapes the waveform of the optical pulse amplified by the optical amplification element 25.

Next, the operation of the above configuration will be explained. When an optical pulse that has been attenuated and deteriorated by propagating through an optical transmission line is input into the optical repeater according to the present invention, the polarization state controller 10 first aligns the plane of polarization to a constant linear polarization, and then adjusts the optical direction. A coupler 11 separates the signal into 1-mi waves in two directions. One of the demultiplexed optical pulses is subjected to phase modulation by the optical pulse phase modulator 12, and then the optical directional coupler 1
The optical clock pulse generated by the optical clock pulse generator 13 demultiplexed by the optical clock pulse generator 13 is multiplexed by the optical directional coupler 15 and input to the first optical AND gate 16 . The optical AND gate 16 outputs the optical pulse to the optical fiber 17 if the phase modulated optical pulse and the optical clock pulse overlap.

This light pulse is received by a photodetector 18 and converted into an electrical signal A. Next, the multiplier 20 and the low-pass filter 21 synchronously detect the frequency component of the electrical signal A that is the same as the frequency of the signal B, and a DC voltage is output to the optical clock pulse generator 13. The phase shift between the optical pulse manually input to the optical repeater and the optical clock pulse is adjusted.

On the other hand, the other demultiplexed optical pulse of the optical directional coupler 11 and the remaining demultiplexed optical clock pulse of the optical directional coupler 14 are combined by the optical directional coupler 22 and the second optical AND gate 23
is input. The optical AND gate 23 removes random jitter from the input optical pulse, and outputs optical pulses with different wave light values to the optical fiber 24. This output optical pulse is then inputted to the optical amplification element 25 to equalize the unevenness of the peak values and subjected to an amplification action, and further inputted to the optical pulse waveform shaper 26 and subjected to self-phase modulation due to the Kerr effect. , the optical solint and its waveform gradually change, and as a result, the waveform of the optical pulse is shaped.
It is output to the next stage optical transmission line.

In this embodiment, an optical fiber is used for the optical pulse phase modulator 12, but the present invention is not limited to this, and an optical waveguide or a discrete optical component may also be used. Similarly, a traveling wave semiconductor laser amplifier or the like may be used as the optical AND gate 16.23, and the optical clock pulse generator 13
Two CW laser light sources with slightly different wavelengths may be used instead of the semiconductor laser, and a stimulated Raman amplifier, a fiber laser amplifier, etc. may be used instead of the semiconductor laser amplifier of the optical amplification element 25.

(Effects of the Invention) As explained above, according to the present invention, the parts other than the optical clock pulse generator, oscillator, and detection circuit are composed of optical circuits that do not include an electrical system. Compared to conventional optical repeaters, which are limited by response speed, this optical repeater can realize high-speed signal processing, and has the advantage of being applicable as an optical repeater for ultra-high-speed optical communications, especially for optical soliton transmission.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of an optical repeater according to the present invention, FIG. 2 is a configuration diagram of a conventional optical repeater, and FIG. 3 is a diagram showing a first optical repeater.
FIG. 4 is a diagram for explaining the operation of the D gate, and FIG. 4 is a diagram for explaining the operation of the second optical AND gate. In the figure, 11, 14, 15, 22... optical directional coupler,
12... Optical pulse phase modulator, 13... Black pulse generator, 16... First optical AND gate, 18
...Photodetector, 1 ...Low frequency oscillator, 20...
Multiplier, 21...Low pass filter, 23...Second optical AND gate, 25...Optical amplification element, 26...Optical pulse waveform shaper. Patent applicant Nippon Telegraph and Telephone Corporation Representative Patent attorney Yoshi 1) Takashi Sei

Claims (1)

[Claims] A first optical directional coupler that demultiplexes an optical pulse input from an optical transmission line; and an optical pulse that performs phase modulation of one of the demultiplexed optical pulses of the first optical directional coupler. a phase modulator; an optical clock pulse generator that generates an optical clock pulse that adjusts a phase shift with the input optical pulse based on a detection signal; and a combination of the phase modulated optical pulse and the optical clock pulse. a second optical directional coupler that receives the multiplexed optical pulse and outputs an optical pulse when the phase-modulated optical pulse and the optical clock pulse overlap;
A D gate, a photodetector that converts the output optical pulse of the optical AND gate into an electrical signal, an oscillator that oscillates a signal at a predetermined frequency, and a frequency component that is the same as the oscillation frequency of the oscillator that is output from the photodetector. a detection circuit that performs synchronous detection from an electrical signal and outputs the detected signal; and a third optical directional coupler that multiplexes the other demultiplexed optical pulse of the first optical directional coupler and the optical clock pulse. a second optical AND gate that extracts only mutually overlapping portions of the multiplexed optical pulses; an optical amplification element that obtains a nonlinear optical intensity output with respect to the intensity of the output optical pulse of the optical AND gate; and a nonlinear effect. What is claimed is: 1. An optical repeater comprising an optical element having: an optical pulse waveform shaper that shapes the waveform of the amplified optical pulse.