JP3876646B2 - Optical receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical clock signal synchronized with an input optical signal data sequence and an optical receiver that reproduces and outputs the optical data sequence using an optical saturable absorber.
[0002]
[Prior art]
The apparatus shown in FIG. 4 is an optical digital reproducing apparatus disclosed in Japanese Patent Laid-Open No. 2000-236302, which is an example of a conventional all-optical optical receiver, and is referred to as an electroabsorption optical modulator (hereinafter referred to as EA modulator. What is EA? This is based on the saturable absorption characteristic of Electro-Absorption. In general, when an optical input signal and an optical clock pulse generated by an optical pulse generator are input to an optical saturable absorber, absorption saturation occurs when the input signal has sufficient strength according to the characteristics of the optical saturable absorber. Therefore, when the input optical signal is “1”, the optical pulse generated by the optical pulse generator passes, and when the input optical signal is “0”, it is absorbed and encoded. At this time, the optical clock pulse serving as the reproduction output light source and the input signal pulse must be synchronized in the optimum phase state in the saturable absorber to be encoded.
For this reason, in the example of FIG. 4, a clock electrical signal synchronized with the repetition frequency of the input optical signal data string is obtained from the light absorption current taken out from the electrode of the EA modulator 36 which is a saturable absorber. Extraction is performed using the amplifier 42 and the phase shifter 44, and the EA modulator 56 is driven by the extracted electrical clock signal to generate an optical clock pulse synchronized with the optical input signal.
[0003]
[Problems to be solved by the invention]
As described above, the optical signal encoding by the optical signal using the optical saturable absorber maintains the optimum phase relationship while the synchronization of the optical signals in the optical saturable absorber is established. It is necessary to be However, in the conventional optical digital reproducing apparatus as shown in FIG. 4, the process of extracting the synchronous clock electric signal from the optical signal and performing the electric / optical conversion of the clock electric signal is performed. There was a problem that it was difficult to compensate for the variation inherently. Furthermore, since an electric circuit that requires a high-speed operation equivalent to the optical signal speed is required, there is a problem that the cost increases.
[0004]
The present invention has been made to solve the above problems, and an object thereof is to provide an optical receiver with high accuracy and low cost.
[0005]
[Means for Solving the Problems]
An optical receiver according to the present invention includes: an optical clock pulse generation light source that generates an optical clock pulse; and a first optical current that is output based on the optical clock pulse generated from the optical clock pulse generation light source and an optical input signal. An optical saturable absorber, a control circuit for controlling the optical clock pulse generation light source based on the photocurrent output from the first optical saturable absorber, and an optical clock generated from the optical clock pulse generation light source And a second optical saturable absorber that outputs an optical output signal based on the pulse and the optical input signal.
[0006]
The optical clock pulse generation light source has a repetition frequency of 1 / n (n is a natural number) of the optical input signal bit rate.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
FIG. 1 is a functional configuration diagram of an optical receiver according to a first embodiment of the present invention.
In FIG. 1, 1 is an optical pulse generator as an optical clock pulse generating light source whose repetition frequency can be varied by input current / voltage, 2 is an optical data input terminal, 3 is a first optical saturable absorber, and 4 is a second. 5 is an optical bandpass filter (OBPF), 6a, 6b, 6c, 6d and 6e are optical multiplexers / demultiplexers, 7 is a loop circuit as a control circuit for controlling the optical pulse generator 1, 8 Is an optical clock output terminal, 9 is an optical data output terminal, and 10 is an optical delay line.
[0008]
As the optical multiplexer / demultiplexers 6a, 6b, 6c, 6d, and 6e, optical couplers, planar optical waveguides, wavelength multiple polymerization demultiplexers, and the like can be used. The three or four optical saturable absorbers are, for example, EA modulators and semiconductor optical amplifiers. The optical pulse generator 1 includes, for example, a mode-locked laser that can vary the pulse repetition frequency by an injection current or an applied voltage, or a combination of a VCO 102, an optical modulator 101, and a DC oscillation laser 100 as shown in FIG. Can be used. In the latter configuration, although it is necessary to handle a high-speed electric clock signal, it is not necessary to compensate for the phase fluctuation.
[0009]
Hereinafter, the operation of the optical receiver will be described with reference to FIG. The optical receiver of FIG. 1 signals an optical clock signal using the second optical saturable absorber 4 and a circuit for synchronizing the optical clock output using the first optical saturable absorber 3 with the signal light input. The circuit is roughly divided into two circuits that encode with light.
[0010]
First, a circuit for synchronizing an optical clock output using the first optical saturable absorber 3 with a signal light input will be described. The first optical saturable absorber 3 is inputted with two kinds of optical signals of signal light and clock light (optical clock pulse) simultaneously. The signal light is input from the optical data input terminal 2 and input to the first optical saturable absorber 3 via the optical multiplexer / demultiplexers 6c and 6d. The clock light is output from the optical pulse generator 1 and input to the first optical saturable absorber 3 via the optical multiplexer / demultiplexers 6a and 6d. Then, in the first optical saturable absorber 3 to which these two types of optical signals are input, the optical absorption current (photocurrent) including the phase difference signal of the two optical signals is generated by the intermodulation effect due to the absorption saturation characteristic. 1 is taken out from the electrode of the photo-saturable absorber 3. The optical absorption current including the phase difference signal of the two optical signals is input to the loop circuit 7, and the loop circuit 7 sends the optical pulse generator 1 to the optical pulse generator 1 so that the two optical signals of the signal light and the clock light are synchronized. Perform feedback control. That is, the first optical saturable absorber 3 is operated as a phase comparator for optical signal input and electrical signal output. Accordingly, when the optical pulse generator 1 capable of electrically varying the repetition frequency and the loop circuit 7 are combined, the optical clock output can be easily synchronized with the signal light input in the same manner as a PLL of a general electric circuit. be able to.
[0011]
Further, here, among the frequency components of the light absorption current taken out from the electrode of the first optical saturable absorber 3, what is necessary for the operation is equal to or less than the difference frequency between the envelopes of the two optical signals, and the speed of the optical signal. Can be kept low. For this reason, the electric circuit of the loop circuit 7 does not need to be an expensive electric circuit that is required to operate at high speed, and an inexpensive electric circuit that can process a light absorption current at a low frequency may be used, thereby reducing the cost. Can do.
[0012]
Next, a circuit for encoding an optical clock signal using the second optical saturable absorber 4 with signal light will be described. The second optical saturable absorber 4 includes an optical clock signal synchronized with the signal light using the absorption current of the first optical saturable absorber 3 and an appropriate delay, and signal light. Input simultaneously. The signal light is input from the optical data input terminal 2 and input to the second optical saturable absorber 4 via the optical multiplexer / demultiplexers 6c and 6e. As for the clock light, an optical clock signal synchronized with the signal light using the absorption current of the first optical saturable absorber 3 as described above is output from the optical pulse generator 1, and the optical multiplexer / demultiplexer 6a. , 6b, an appropriate delay is given by the optical delay line 10, and further, via the optical multiplexer / demultiplexer 6e, is synchronized with the signal light at an optimum phase and input to the second optical saturable absorber 4. The In the second optical saturable absorber 4 to which these two types of optical signals are input, for example, if the signal light is set sufficiently strong with respect to the clock light, the absorption saturation effect by the signal light becomes dominant, and the light The clock signal is encoded by the signal light. The encoded optical clock signal is output from the optical data output terminal 9 as an optical data output signal via the optical bandpass filter 5. In other words, since the second optical saturable absorber 4 encodes the optical clock signal synchronized with the signal light with the optimum phase using the signal saturation, using the absorption saturation characteristic, the data signal is processed with high accuracy. be able to.
[0013]
As described above, an optical clock signal that is accurately synchronized with the signal light can be generated by the circuit that synchronizes the optical clock output using the first optical saturable absorber 3 with the signal light input. However, since a certain amount of phase difference may occur due to a circuit that synchronizes the optical clock output using the first optical saturable absorber 3 with the signal light input, the optical delay line 10 is used to correct the phase difference. Is arranged. By providing an appropriate delay by the optical delay line 10, an optical clock signal synchronized with the signal light at an optimum phase is input to the second optical saturable absorber 4.
[0014]
As described above, the first optical saturable absorber 3 is used to synchronize the optical clock output with the signal light input, and the second optical saturable absorber 4 is used to synchronize the optical clock signal with the signal light. Since encoding is performed using signal light, an accurate and low-cost all-optical optical receiver (optical 3R receiver) that does not require a high-speed electric circuit can be realized.
[0015]
Embodiment 2. FIG.
In the first embodiment, the case where the repetition frequency is the same as the signal light bit rate in the optical pulse generator 1 has been described. However, in the second embodiment, the repetition frequency is not changed without changing the pulse width of the optical clock pulse generation light source. Is described as 1 / n (n is a natural number) of the signal light bit rate.
[0016]
FIG. 3 is a functional configuration diagram of the optical receiver according to the second embodiment of the present invention.
In FIG. 3, the configuration is the same as in FIG. 3 and FIG. 1 are different in the pulse generated by the optical pulse generator 1, and in FIG. 3, the repetition frequency is set to 1 / n of the signal light bit rate without changing the pulse width of the optical clock pulse generation light source (n is a natural number). It is said. The same operation as that of the first embodiment is performed using an optical clock in which the repetition frequency is 1 / n of the signal light bit rate. Thereby, a separation (DEMUX) function can be realized. In other words, by using an optical clock whose repetition frequency is 1 / n of the signal light bit rate, a frequency-divided optical clock pulse synchronized with the input signal light is reproduced without using a high-speed electric circuit, and an optical separation data reproduction operation is performed. And an all-optical type optical receiver (optical 3R receiver) that performs separation of multiplexed optical signals, frequency-divided optical clock pulse regeneration, and separated optical pulse regeneration is realized.
[0017]
As described above, by using an optical clock whose repetition frequency is 1 / n of the signal light bit rate, all-optical light that does not require a high-speed electric circuit, is highly accurate, low-cost, and has a separation function A receiver can be realized.
[0018]
【The invention's effect】
As described above, in the optical receiver according to the present invention, the optical current is generated based on the optical clock pulse generation light source that generates the optical clock pulse, the optical clock pulse generated from the optical clock pulse generation light source, and the optical input signal. A first optical saturable absorber to be output; a control circuit for controlling the optical clock pulse generating light source based on a photocurrent output from the first optical saturable absorber; and the optical clock pulse generating light source. By providing a second optical saturable absorber that outputs an optical output signal based on the generated optical clock pulse and the optical input signal, high-accuracy and low-cost optical reception that does not require a high-speed electrical circuit Can be realized.
[0019]
Further, the optical clock pulse generating light source has a repetition frequency of 1 / n (n is a natural number) of the optical input signal bit rate, so that no high-speed electric circuit is required, high accuracy, low cost, and separation. An optical receiver having a function can be realized.
[Brief description of the drawings]
FIG. 1 is a functional configuration diagram of an optical receiver according to a first embodiment of the present invention. FIG. 2 is an explanatory diagram showing a specific example of an optical pulse generator. FIG. 3 is an embodiment of an optical receiver according to the present invention. Functional configuration diagram of Embodiment 2 [FIG. 4] Functional configuration diagram of a conventional all-optical optical receiver [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical pulse generator 2 Optical data input terminal 3 1st optical saturable absorber 4 2nd optical saturable absorber 5 Optical bandpass filter 6a-6e Optical multiplexer / demultiplexer 7 Loop circuit 8 Optical clock output terminal 9 Light Data output terminal 10 Optical delay line 100 DC oscillation laser 101 Optical modulator 102 VCO
103 Optical clock pulse output terminal 104 Repetition frequency control terminal 105 Amplifier

Claims (2)

An optical clock pulse generation light source for generating an optical clock pulse;
A first optical saturable absorber that outputs a photocurrent based on an optical clock pulse generated from the optical clock pulse generation light source and an optical input signal;
A control circuit for controlling the optical clock pulse generation light source based on the photocurrent output by the first optical saturable absorber;
An optical receiver comprising: a second optical saturable absorber that outputs an optical output signal based on an optical clock pulse generated from the optical clock pulse generation light source and an optical input signal. 2. The optical receiver according to claim 1, wherein the optical clock pulse generation light source has a repetition frequency of 1 / n (n is a natural number) of the optical input signal bit rate.

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