JPS63224425A - Method and device for optical reception - Google Patents

Abstract

PURPOSE:To easily extract a desired optical signal from a light frequency multiplexing signal, to simplify constitution, and to lower cost, by providing a semiconductor laser with oscillation light frequency control function and a light delay apparatus in a method and a device for light reception which injects and synchronizes the semiconductor laser with the optical signal. CONSTITUTION:The optical signal 1 is demultiplexed to signals 1a and 1b by an optical demultiplexer 3. The semiconductor laser 4 is provided with the oscillation light frequency control function and by adjusting a control signal, it can fit injecting and synchronizing width to the light frequency of the optical signal of desired channel in the optical signal 1b. As a result, the semiconductor 4 outputs the optical signal 1c including only the optical signal of desired channel by injecting and synchronizing only with the light frequency of desired channel. Meanwhile, the optical signal 1a, after receiving delay equivalent to one pulse of a transmission signal, is multiplexed with the optical signal 1c. Multiplexed light 1d is square-detected at a square detector 7, and can output only an electrical signal 2 of desired channel.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical reception method and device for injection-locking a semiconductor laser with an optical signal, and particularly relates to extraction of a desired optical signal from an optical frequency multiplexed signal. is easy.

The present invention relates to a method and apparatus having a simple structure and low cost.

[Conventional technology]

Conventional devices are disclosed in Japanese Patent Publication Nos. 61-43693 and 61-4.
No. 3694 and No. 61-43691.

Japanese Patent Publication No. 61-43693 and No. 61-43694 disclose a device for heterodyne detection of an optical signal (modulated by amplitude shift keying (ASK), frequency shift keying (FSX), or phase shift keying (PSK)). This is an example. In heterodyne detection, the frequency difference between the optical signal and the reference light must always be constant.

In the case of Japanese Patent Publication No. 61-43693, in order to obtain a reference light whose frequency difference from the optical signal is always constant, the frequency of the optical output of an injection-locked semiconductor laser is converted by an optical frequency modulator. 0 where the optical output of the modulator becomes the reference light
The amount of frequency conversion depends on the frequency of the signal driving the frequency modulator. In the case of Special Publication No. 61-43694.

Directly modulate an injection-locked semiconductor laser at a constant frequency.

The sideband generated by modulation is synchronized with one branched optical signal. As a result, the difference between the frequency of the optical output of the semiconductor laser and the frequency of the optical signal is always constant, and the optical output of the semiconductor laser can be used as reference light.

Above, Special Publication No. 61-43693 and No. 61-436
In No. 94, in order to obtain a reference light whose frequency difference from the optical signal is always constant, frequency modulation of the optical output of the semiconductor laser or direct modulation of the semiconductor laser is performed at the same time as injection locking of the semiconductor laser by the optical signal. ing.

Japanese Patent Publication No. 61-43691 is an example of a device for homodyne detection of an optical signal (ASK or PSK modulated). In homodyne detection, although the frequencies of the optical signal and the reference light are the same, it is necessary to control the phase difference between the optical signal and the reference light. In the case of Japanese Patent Publication No. 61-43691, the phase difference between the optical signal and the reference light is controlled by controlling the optical output of the semiconductor laser with a phase shifter. Since the phase of the optical output of a semiconductor laser, which is also used as a light source for transmission, is extremely unstable, the phase of the optical signal is also unstable, making the above-mentioned phase shifter indispensable.

[Problem that the invention seeks to solve]

The above conventional technology has the following problems.

1. In the case of heterodyne detection, an optical frequency modulator, a modulation circuit, and a frequency stable oscillator are required, which increases the complexity and cost of the device.

The operating speed of the two modulator circuits and the oscillator must be set to at least twice the signal transmission speed.For example, if the transmission speed is I Gb/s, the operating speed of the two modulator circuits and the oscillator must be set at 2 GHz or higher. It needs to work. Therefore, when the transmission speed is high, the cost of the device increases particularly significantly.

2. In the case of homodyne detection, a single phase shifter is required.

Although the phase of the optical output of a normal semiconductor laser is unstable,
Since the semiconductor laser is also used as a transmission light source, the phase of the optical signal is also unstable.

Therefore, in order to control the phase difference between the optical signal and the reference light,
It is necessary to detect the phase difference by some method and drive the phase shifter based on the result. As a result,
Equipment becomes more complex and costly.

3. No consideration is given to the case where the optical signal is an optical frequency division multiplexed signal and only a desired optical signal is extracted and detected from the optical frequency division multiplexed signal. If a conventional device were to extract and detect a desired optical signal, a device for highly stable control of the temperature of the injection-locking semiconductor laser would be necessary, making the detection device complicated and expensive. In coherent optical communication that uses heterodyne detection, homodyne detection, etc., the number of optical frequency division multiplexes can be increased compared to conventional intensity modulation/direct detection methods, so the desired signal from the optical frequency division multiplexed signal can be extraction and detection are important issues.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to realize an optical reception method and apparatus that can easily extract a desired optical signal from an optical frequency multiplexed signal, have a simple configuration, and are inexpensive.

[Means for solving problems]

The above purpose is to branch optical signals into first and second optical signals containing at least one optical frequency, input this second optical signal to a semiconductor laser with an oscillation optical frequency control function, and The oscillation optical frequency of the semiconductor laser is controlled so as to be injection-locked to the optical frequency of the semiconductor laser, and the first optical signal and the optical output signal of the semiconductor laser are combined after giving a delay difference, and the combined light is This is achieved by square law detection.

[Effect]

A semiconductor laser with an oscillation light frequency control function is one that controls the optical laser resonator length and oscillation light frequency by controlling the optical path length of at least a portion of the laser resonator using current, etc. . Regarding the above semiconductor laser, please refer to "Electronics Letters", Volume 19. Number 17. (1983), pp. 656-657 (Electronics Letters
, Vol. 19. Na17, 1983. pp.

656-657) and others.

On the other hand, the injection locking characteristics of semiconductor lasers have been confirmed during experiments, with a maximum locking width of 30 Hz and a maximum locking gain of 40 d.
B has been obtained (Japanese Patent Publication No. 43693/1983).

The present invention sets the oscillation optical frequency of the semiconductor laser with an oscillation optical frequency control function within the injection locking width with respect to the desired optical frequency in the second optical signal. Injection locking is performed only on the desired optical frequency of the two optical signals.

If the bandwidth of the optical signal of one channel is set to be less than or equal to the injection locking width, and the frequency interval between channels is set to be larger than the injection locking width, the optical output of the semiconductor laser will contain only the optical signal of the desired channel. will be included. Therefore,
By applying a delay equivalent to, for example, one pulse of the transmission signal between the first optical signal and the optical output signal of the semiconductor laser, combining the two and performing square law detection of the two combined lights, the input optical signal is Only the optical signal of the desired channel can be extracted and detected.

According to the present invention, by controlling the oscillation optical frequency of a semiconductor laser with a single oscillation optical frequency control function using current or the like,
Optical frequency modulator and modulation circuit that can easily extract and detect the optical signal of the desired channel.

An optical receiving device can be realized by using an optical delay device, which is a passive element, without using a frequency stable oscillator, 9 phase shifters, 2 phase difference detectors, phase shifter control circuits, etc., so the configuration of the device can be simplified and the cost is low. This has the effect of being able to reduce costs.

〔Example〕

A first embodiment of the present invention will be described below with reference to FIG.

In the figure, 1 is an optical signal input to the device of the present invention. 1 may be a signal obtained by optical frequency division multiplexing of optical signals of a plurality of channels.

2 is an output terminal from which an electrical signal is output.

3 is an optical splitter that branches the optical signal 1 into 18 and 1b. 4 is a semiconductor laser having an oscillation light frequency control function, which is described in detail in the above document. An optical delay device 5 provides a predetermined delay difference between the optical signals 1a and 10, and can be realized using an optical fiber, an electro-optic crystal, or the like. Reference numeral 6 denotes an optical multiplexer, which can be realized using a half mirror 9 optical coupler, a directional coupler, or the like. 7
is a square law detector, and can be realized using an APD, PIN-PD, or the like. Reference numeral 8 denotes a signal input terminal for controlling the oscillation optical frequency of the semiconductor laser 4.

9 is a current input terminal for driving the semiconductor laser 4;

The operation of this embodiment is as follows. Optical signal 1 is.

The optical splitter 3 branches the light into 1a and 1b.

The semiconductor laser 4 can adjust the injection locking width to the optical frequency of the optical signal of a desired channel in the optical signal 1b by adjusting the control signal. As a result, the semiconductor laser 4 is injection-locked only to the optical frequency of the desired channel.
An optical signal 1c containing only the optical signal of the desired channel is output. On the other hand, the optical signal 1a is transmitted to one of the transmission signals by the optical delay device 5.
After receiving a delay equivalent to the pulse, it is combined with the optical signal IC.

The combined light 1d is square-law detected by a square-law detector 7, and only the electrical signal 2 of a desired channel can be output.

According to the present invention, by using a semiconductor laser with an oscillation light frequency control function and an optical delay device that is a passive element, it is possible to obtain a desired signal from an optical frequency multiplexed signal with a simpler structure and at a lower cost than in the past. The present invention has the advantage that it is possible to realize an optical reception method and apparatus for extracting and detecting an optical signal of a channel.

The above effect is obtained when a delay equivalent to one pulse is given between the optical signal 1a and the IC, so when the optical delay device 5 is located between the semiconductor laser 4 and the optical splitter 3, Similar effects can also be obtained when the optical fiber is located between the semiconductor laser 4 and the optical multiplexer 6.

Next, the operation of a second embodiment of the present invention, that is, an embodiment in which the optical signal is an optical FSX signal, will be explained using FIGS. 2 and 3.

FIG. 2 shows the frequency spectrum of the signal, and FIG. 3 shows the time waveform of the signal.

FIG. 2(a) shows a frequency spectrum when a binary FSK modulated optical signal of multiple channels (the number of channels is n2, channels are abbreviated as ah in the figure) is optical frequency division multiplexed. Optical signal 1 in FIG. la, lb is second
It has the frequency spectrum shown in Figure (a). Channel 2 (a
The case of extracting h, 2) will be explained as an example. For example f
Let x be a space, let fz correspond to a mark, and if (fz - fs) is set large compared to the transmission speed, the frequency spectrum Cft, consisting of fz and its sideband, as shown in the same figure, will be obtained, where If the injection locking range of a semiconductor laser with an oscillation optical frequency control function, which has an injection locking width wider than the bandwidth of one channel and narrower than the spacing between channels, is set to channel 2, the semiconductor laser described above becomes By injection locking only to the optical frequency of channel 2, an optical signal having a frequency spectrum as shown in FIG. 2(b) is obtained as an output. That is, the optical signal 1c in FIG.
has the frequency spectrum shown in FIG. 2(b).

FIG. 3 shows time waveforms at various parts of channel 2 (ch, 2) in FIG. 2. Figure 3(a) is.

This is the time waveform of the transmitted signal. FIG. 3(b) is a differentially encoded signal of FIG. 3(a). In FIG. 3(b), optical frequencies ftt and fz correspond to spaces and marks, respectively. Therefore, the waveforms in FIG. 1(b) are la, lb, and 1c input to optical signals 1 and 5 in FIG.
corresponds to the waveform of FIG. 3(c) shows the waveform of FIG. 3(b) delayed by one pulse, and corresponds to the waveform 1a output from 5 in FIG. FIG. 3(d) shows the time waveform of the output electrical signal obtained as a result of square law detection of the combined optical signals of FIG. 3(b) and (c). This waveform corresponds to the waveform of the output signal in FIG. frequency 0
to the signal level 0, and the frequency Δf (=fz−jt
) correspond to the signal level 1, the transmitted signal can be reproduced as shown in the figure. In the figure, frequency O is obtained when the frequencies in Fig. 3(c) and (d) are the same (frequency difference is 0), and frequency Δf is obtained when the frequencies are different (frequency The difference is Δf)
It is. On the other hand, signals of channels other than channel 2 are not reproduced. This is because the optical output IC of the semiconductor laser 4 no longer includes optical signals of channels other than channel 2.

In the case of this embodiment, that is, when the optical signal is an optical FSX signal, the same effect as in the first embodiment is obtained, and at the same time, the stability of the frequency and phase of the semiconductor laser 4 is compared with that in the case of an optical PSK signal. (for example, the frequency stability is about 1/10), the configuration of the device can be simplified;
This has the effect of further reducing costs. This is because in order to stabilize the frequency and phase, stabilization measures such as optical feedback and injection current negative feedback are required for the semiconductor laser, and the higher the stability, the more stabilization measures are required. This is because the equipment used becomes more complex and expensive. Regarding the above stability, for example, "Journal of Optical Communications J 7 (1986)
2. Pages 66 to 78 (Journal of 0
ptical Communications.

7 (1986) 2. It is described in detail in pp. 6-row 67).

FIG. 4 shows a third embodiment of the invention. This embodiment uses a balanced receiver as a square law detector. In the same figure, 10 shifts the phase of a part of the optical signal 1c by 90 degrees and multiplexes it with a part of 1a, and outputs it as 1d. This is a multiplexer that multiplexes a portion of the signal and outputs it as 1e, and can be realized by a directional coupler.

11a and llb are PDs (APD or PIN-PD) that perform square law detection of 1d and 1e, respectively; 12
is an amplifier and outputs an output electrical signal from terminal 2.

In the figure, the electrical signals output by PDlla and llb are added so that the noise components caused by the intensity noise of the semiconductor laser 4 cancel each other out among the noise included in each signal, and the noise is reduced. For more information, see Electronics Letters, Volume 22.
．． Number 8゜ (1986) pages 413 to 415
Page (Electronics Ratters, Vol.
, 22, Nn 8, l 986.

pρ, 413-415), etc.

According to this embodiment, the same effects as the first and second embodiments can be obtained, and at the same time, the noise component caused by the intensity noise of the semiconductor laser 4 can be suppressed, and the signal-to-noise ratio of the output electric signal can be improved. Get the effect.

FIG. 5 shows a fourth embodiment of the invention. In this embodiment, a polarization diversity receiver is used as a square law detector. In the figure, 13 is a polarization separator that separates the optical signal 1d into two orthogonal polarization components 1f and 1g, which can be realized using a polarization beam splitter or the like. 1
Reference numeral 4 denotes a polarization diversity receiving circuit, and the signal combining method may be equal gain combining, 9 selection combining, or maximum ratio combining. Polarization diversity receivers are described in detail in the Technical Research Report JOQE84-25 published by the Institute of Electronics and Communication Engineers.

According to this embodiment, the same effects as the first and second embodiments can be obtained, and at the same time, no matter what polarization state the optical signal 1 is in,
The effect is that deterioration in the signal-to-noise ratio of the output electrical signal 2 can be reduced to zero.

〔Effect of the invention〕

According to the present invention, in an optical reception method and device for injection-locking a semiconductor laser with an optical signal, the device can be realized by including a semiconductor laser with an oscillation light frequency control function and an optical delay device, and Since the optical signal of the desired channel can be extracted and detected by control, it is easy to extract the desired optical signal from the optical frequency multiplexed signal, and it is possible to realize a low-cost optical reception method and device with a simple configuration. There is an effect.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a frequency spectrum diagram of a signal, FIG. 3 is a time waveform diagram of a signal, and FIGS. 4 and 5 are diagrams showing other embodiments of the present invention. FIG. 1... Optical signal, 2... Electric signal output terminal, 3...
Optical splitter, 4... semiconductor laser, 5... optical delay device,
6... Optical multiplexer, 7... Square law detector, 8... Oscillation optical frequency control signal input terminal, 9... Semiconductor laser drive current input terminal, 10... Directional coupler, 11.・・P
D, 12... amplifier, 13... polarization separator,
14...Polarization diversity receiving circuit.

Claims (1)

[Claims] 1. Branching an optical signal containing at least one optical frequency into first and second optical signals, inputting this second optical signal to a semiconductor laser with an oscillation optical frequency control function, and The oscillation optical frequency of the semiconductor laser is controlled so as to be injection-locked to a desired optical frequency in the two optical signals, and a delay difference is provided between the first optical signal and the optical output signal of the semiconductor laser, and then a combination is performed. waves,
An optical reception method characterized by performing square law detection of the combined light. 2. The optical receiving method according to claim 1, wherein the optical signal is a signal subjected to frequency shift keying modulation. 3. The optical receiving method according to claim 1 or 2, wherein the square law detection uses a balanced receiver having at least two light receiving elements. 4. The optical receiving method according to claim 1 or 2, wherein the square law detection uses a polarization diversity receiver having at least a polarization separator and two light receiving elements. 5. An optical splitter that branches an optical signal containing at least one optical frequency into first and second optical signals, and a semiconductor with an oscillation optical frequency control function that injection-locks to a desired optical frequency in the second optical signal. a laser; an optical delay device that provides a delay difference between the first optical signal and the optical output signal of the semiconductor laser before combining the two; and a first optical signal and the optical output signal of the semiconductor laser; An optical receiver comprising an optical multiplexer that multiplexes the multiplexer, and a square law detector that performs square law detection of the output of the multiplexer.