JP2512520B2 - Optical repeater - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical repeater that performs an optical pulse regeneration / identification function by an optical control pulse.

2. Description of the Related Art Conventionally, as shown in FIG. 2, an optical repeater has conventionally used an optical-electrical (O / E) converter 1 to convert an attenuated optical pulse after propagation through an optical transmission line.
After being converted into an electric signal by the equalizing amplifier 2, the equalizing amplifier 2 performs equalizing amplification, the timing circuit 3 extracts timing from the equalized waveform after the amplification, and the discrimination circuit 4 uses the timing signal to perform equalization. After identifying the waveform, regenerate the optical pulse by the electro-optical (E / O) converter 5,
This regenerated pulse is sent to the optical transmission line in the next stage. However, using the above configuration, for example, number + Gb
It is difficult to realize an it / s ultra-high-speed transmission system because the processing speed or response speed of electric signals is limited.

Therefore, recently, the optical pulse is controlled by directly applying an ultrahigh-speed electrical clock signal equivalent to the transmission rate to the gate element, and the 3R function required for the repeater [Reshaping (waveform shaping), Retiming (timing extraction), Regenerating (Identifying and Regenerating)] optical repeater (IEEE Journal of Quan
tam Electronics Vol.QE19, P1718 to P1723), an optical repeater in which a saturable absorber and an optical amplification element are combined and the electric system is completely eliminated from the optical repeater (Optics Letters Vol.11, 19).
86. See P392-P394) and the like have been proposed.

(Problems to be solved by the invention) However, according to the optical repeater realizing the above 3R function, the electrical response speed limit of the gate element itself or the generation limit of the high-speed electric clock signal is high speed performance of the optical repeater itself. It has become a limiting factor and has been a major problem in constructing an ultra-high speed transmission system. In addition, since the optical repeater without the electrical system is essentially a 2R function optical repeater lacking the timing extraction function, it is impossible to remove the jitter component contained in the optical pulse. there were.

In view of the above problems, the object of the present invention is to overcome the processing speed limit caused by the electric signal processing part of the optical repeater and the response speed limit by using the optical signal processing, and to have a 3R function,
Another object 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 provides a first optical directional coupler for demultiplexing an optical pulse input from an optical transmission line, and the first optical directional coupler. 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, and the phase A second optical directional coupler that multiplexes the modulated optical pulse and the optical clock pulse, and an optical signal when the multiplexed optical pulse is input and the phase-modulated optical pulse and the optical clock pulse overlap each other. A first optical AND gate that outputs a pulse, a photodetector that converts the optical pulse output from the optical AND gate into an electrical signal, an oscillator that oscillates a signal of 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 detection signal, and the other demultiplexed optical pulse of the first optical directional coupler And the optical clock pulse and the third
Optical directional coupler, a second optical AND gate for extracting only overlapping portions of the combined optical pulse, and optical amplification for obtaining an optical intensity output that is non-linear with respect to the intensity of the output optical pulse of the optical AND gate An optical pulse waveform shaper, which is composed of an element and an optical element having a nonlinear effect, and shapes the waveform of the amplified optical pulse is provided.

(Operation) According to the present invention, the optical pulse propagated through the optical transmission line and attenuated and deteriorated is first demultiplexed by the first optical directional coupler. One of the demultiplexed optical pulses is subjected to phase modulation by the optical pulse phase modulator, and then is multiplexed with the optical clock pulse output from the optical clock pulse generator by the second optical directional coupler to produce the first optical pulse.
It is input to the optical AND gate of. Next, if the optical pulse subjected to the phase modulation 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 the photodetector and converted into an electric signal. Then, in the detection circuit, the same frequency component as the oscillation frequency of the oscillator is detected from this electric signal, and the detection signal based on this is output to the optical clock pulse generator, which causes 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 of the first optical directional coupler and the optical clock pulse are combined by the third optical directional coupler,
This combined optical pulse is input to the second optical AND gate.
In the second optical AND gate, the input optical pulse and the optical clock pulse are extracted only at the overlapping portions, whereby the random jitter of the input optical pulse is removed and further amplified by the optical amplification element to make the peak value uniform. To be done. The optical pulse subjected to this amplification is subjected to waveform shaping by the optical pulse waveform shaper due to the non-linear effect, and is output to the optical transmission line of the next stage.

(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 an attenuated and deteriorated optical pulse after propagation through an optical transmission line (not shown) with a constant linear polarization. Reference numeral 11 is an optical directional coupler composed of an optical fiber or an optical waveguide, and splits the output optical pulse of the polarization state controller 10 into two directions. Reference numeral 12 denotes an optical pulse phase modulator including an optical fiber and a driving device (not shown), which is driven based on a signal B from a low frequency oscillator described later, and which is an optical directional coupler 11
The pulse phase of one demultiplexed light pulse is modulated. An optical clock pulse generator 13 is, for example, a voltage controlled oscillator (VC
O), which consists of a semiconductor laser whose gain has been switched, an optical fiber, an optical pulse compression device composed of a dispersive delay path, etc., and generates an optical clock pulse which is an ultrashort optical pulse train such as a transmission speed phase. An optical directional coupler 14 demultiplexes the optical clock pulse into two directions. An optical directional coupler 15 combines the output optical pulse of the optical pulse phase modulator and one of the demultiplexed optical pulses of the optical directional coupler 14, that is, an optical clock pulse. Reference numeral 16 is a first optical AND gate composed of a polarization rotation element by the Kerr effect, and if the optical pulse subjected to the phase modulation and the optical clock pulse in the optical pulse combined by the optical directional coupler 15 overlap, The pulse is output to the optical fiber 17.

FIG. 3 is a diagram for explaining the operation of the first optical AND gate 16. According to FIG. 3, the optical pulse P undergoes phase modulation in the left-right direction toward the drawing as shown in the drawing,
When the optical clock pulse CP overlaps the optical pulse area, the optical pulse a is output.

Reference numeral 18 is a photodetector composed of a PIN diode or the like, which converts the output optical pulse of the optical AND gate 16 received through the optical fiber 17 into an electric signal A. A low frequency oscillator 19 outputs a signal B having a predetermined frequency to the optical pulse phase modulator 12 and a multiplier described later. 20 is a multiplier, which is the output electric signal A of the photodetector 18.
And the output signal B of the low frequency oscillator 19 are multiplied, and the result is output as a signal C. A low-pass filter 21 outputs a DC voltage having a value corresponding to the signal C to the optical clock pulse generator 13. The multiplier 20 and the low-pass filter 21 constitute a detection circuit.

Reference numeral 22 denotes an optical directional coupler, which combines the other split optical pulse of the optical directional coupler 11, that is, the input optical pulse with the other split optical pulse of the optical directional coupler 14, that is, an optical clock pulse. To do. 23 is a second optical AND gate, which is an optical directional coupler 2
Among the combined optical pulses of 2, the optical pulse extracted from only the portion where the input optical pulse and the optical clock pulse overlap each other is output to the optical fiber 24. Figure 4 shows optical AND gate 2
FIG. 4A is a diagram for explaining the operation of FIG. 3, FIG. 4A is a diagram showing a combined optical pulse waveform, and FIG. 4 is a diagram showing an output pulse waveform of the optical AND gate 23. As can be seen from FIG. 4, since the input optical pulse contains random jitter and the input optical pulse P and the optical clock pulse CP do not completely coincide with each other, only the overlapping portions as shown in FIG. Light and
Random jitter contained in the input optical pulse is removed by taking out with the 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 it appears as fluctuation of the peak value of the optical pulse.

Reference numeral 25 is an optical amplification element composed of a semiconductor laser amplifier and a saturable absorber, which obtains a non-linear light intensity with respect to the optical pulse input through the optical fiber 24, and as shown in FIG. 4 (b) above. Eliminate the fluctuation of the peak value. 26 is an optical pulse waveform shaper made of an optical fiber
Performs waveform shaping of the optical pulse amplified by.

Next, the operation of the above configuration will be described. When the optical pulse propagated through the optical transmission line and attenuated and deteriorated is input to the optical repeater according to the present invention, first, the polarization state controller 10 aligns the polarization plane to a constant linear polarization, and then the optical direction The coupler 11 demultiplexes into two directions. One of the demultiplexed optical pulses is phase-modulated by the optical pulse phase modulator 12, and is combined at the optical directional coupler 15 with the optical clock pulse by the optical clock pulse generator 13 demultiplexed by the optical directional coupler 14. It is waved and input to the first optical AND gate 16. The optical AND gate 16 outputs an optical pulse to the optical fiber 17 when the optical pulse subjected to the phase modulation and the optical clock pulse overlap each other. This light pulse is a photodetector
The light is received by 18 and converted into an electric signal A. Then multiplier 20
Then, the low-pass filter 21 synchronously detects the same frequency component as the frequency of the signal B from the electric signal A, and the DC voltage is output to the optical clock pulse generator 13 to be input to the optical repeater according to the present invention. The phase shift between the generated optical pulse 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 input to the second optical AND gate 23. It In the optical AND gate 23, random jitter of the input optical pulse is removed, and optical pulses with different wave light values are sent to the optical fiber.
Output to 24. This output optical pulse continues to the optical amplification element.
25, the unevenness of the crest values is made uniform and is amplified, and further inputted to the optical pulse waveform shaper 26, which undergoes self-phase modulation by the Kerr effect, and the optical solute and its waveform gradually change. As a result, the waveform of the optical pulse is shaped and output to the optical transmission line of the next stage.

In this embodiment, an optical fiber is used for the optical pulse phase modulator 12, but it is not limited to this, and an optical waveguide or a discrete optical component may be used. Similarly,
A traveling wave type semiconductor laser amplifier or the like may be used as the optical AND gates 16 and 23, and two CW laser light sources having slightly different wavelengths may be used instead of the semiconductor laser of the optical clock pulse generator 13. An inductive Raman amplifier, a fiber laser amplifier, or the like may be used instead of the semiconductor laser amplifier of the optical amplification element 25.

(Effects of the Invention) As described above, according to the present invention, except for the optical clock pulse generator, the oscillator, and the detection circuit, the optical circuit does not include an electrical system. High-speed signal processing can be realized as compared with the conventional optical repeater, which is limited in response speed, and it has an advantage that it can be applied as an optical repeater for ultrahigh-speed optical communication, especially optical soliton transmission.

[Brief description of drawings]

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 first optical AND.
FIG. 4 is a diagram for explaining the operation of the gate, and FIG. 4 is a second optical AN.
It is a figure for explaining operation of a D gate. In the figure, 11,14,15,22 ... Optical directional coupler, 12 ... Optical pulse phase modulator, 13 ... Clock pulse generator, 16 ... First optical AND gate, 18 ... Optical detection Device, 19 ... Low-frequency oscillator, 20 ... Multiplier, 21 ... Low-pass filter, 23 ... Second optical AND gate, 25 ... Optical amplification element, 26 ... Optical pulse waveform shaper.

Continuation of front page (56) Reference JP-A-51-130102 (JP, A) JP-A-60-17409 (JP, A) JP-A-62-189830 (JP, A)

Claims (1)

(57) [Claims] 1. A first optical directional coupler for demultiplexing an optical pulse input from an optical transmission line, and an optical pulse phase for phase-modulating one of the demultiplexed optical pulses of the first optical directional coupler. A modulator, an optical clock pulse generator that generates an optical clock pulse that adjusts the phase shift of the input optical pulse based on a detection signal, and the phase-modulated optical pulse and the optical clock pulse are combined. A second optical directional coupler, a first optical AND gate that inputs the combined optical pulse, and outputs an optical pulse when the phase-modulated optical pulse and the optical clock pulse overlap each other; A photodetector that converts the optical pulse output from the AND gate into an electrical signal, an oscillator that oscillates a signal of a prescribed frequency, and a frequency component that is the same as the oscillation frequency of the oscillator is synchronously detected from the electrical signal output from the photodetector. Then, the inspection A detection circuit that outputs a wave signal, a third optical directional coupler that combines the other demultiplexed optical pulse of the first optical directional coupler and the optical clock pulse, and the combined optical pulses A second optical AND gate that extracts only the overlapping portion, an optical amplification element that obtains a non-linear optical intensity output with respect to the intensity of the output optical pulse of the optical AND gate, and an optical element that has a non-linear effect. And an optical pulse waveform shaper for shaping the waveform of the generated optical pulse.