JPH01147437A - Optical heterodyne and homodyne detecting and receiving device - Google Patents

Abstract

PURPOSE:To constitute the title device in such a manner that locally oscillated light can cover a wide-band frequency range by building an optical switch which selectively switches the exit light of a local oscillation light source and multiplexes the same with signal light into the device. CONSTITUTION:While the signal light 2 is multiplexed with the local oscillated light by an optical coupler 3, the locally oscillated light is obtd. by selecting one of the exit light rays from the 1st-4th local oscillation light sources (LO) 12-15 by the optical switch 16. The synthesized light is heterodyne-detected at a front end 4, is amplified by an IF amplifier 5 and is inputted to a frequency discriminator 7. The frequency fluctuation of the IF signal is detected in the frequency discriminator 7 and the control signal for stabilizing the same is taken out. The pulses of the beats for the respective channels observed at the time of frequency sweeping of the locally oscillated light are also taken out and are inputted to a controller 8. The controller 8 receives the channel selection instruction from a channel selector 9 and sends the signal to allow passage of the exit light of the prescribed Lo to a driving circuit 17 of the optical switch 16. The signal receiving device of the wide frequency range is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to optical communications, particularly coherent optical communication devices.

(Prior Art) A coherent optical communication system that uses the wave properties of light for communication has the characteristics of being able to significantly improve receiving sensitivity compared to a direct detection system and being suitable for high-density frequency multiplexing. The optical heterodyne detection receiver conventionally used in this method includes one local oscillation light source, a multiplexer for combining signal light and local oscillation light, and a photodetector for receiving this combined light. It consists of a demodulation circuit for extracting a data signal from the intermediate frequency signal appearing at the output of this photodetector, a frequency control circuit for local oscillation light, and a polarization control circuit for matching the polarization of signal light and local oscillation light. was. (Emura et al. “FSK Optical Heterodyne Single Filter Detection Transmission Experiment Using DFB-LD” National Conference of the Institute of Electronics and Communication Engineers in 1982) (Problems to be Solved by the Invention) By the way, coherent optical communication It has the characteristic that it is suitable for dense frequency multiplexing (FDM).Therefore, it is possible to apply the multi-channel FDM coherent optical communication system to broadband optical subscriber systems, broadcasting systems, etc.In this case, the receiver On the side, the desired channel is extracted from the transmitted multi-channel signals and light by adjusting the frequency of the local oscillation light. (The oscillation frequency can be adjusted by changing the bias current of the light source or the resonator length. Therefore, a wide frequency variable range is required for the local oscillation light source.However, for example, in an image broadcast type system with about 100 channels (the bit rate per channel is 100 Mb/
Since the frequency band occupied by all the signal lights, including the channel spacing, is approximately 50 to 100 GHz, one local oscillation light source can cover this entire band with small power fluctuations and a constant svector width. It was very difficult to cover.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a receiving device with a wide frequency variable range.

(Means for Solving the Problems) The present invention includes a plurality of local oscillation light sources, a multiplexer for multiplexing signal light and local oscillation light oscillated from the local oscillation light sources, Optical heterodyne/homodyne detection including a photodetector for receiving a light beam, a demodulation circuit for extracting a data signal from an intermediate frequency signal appearing at the output of the photodetector, and a circuit for controlling the frequency of the locally oscillated light. The optical heterodyne/homodyne detection receiving apparatus is characterized in that the receiving apparatus includes an optical switch for selectively switching the light emitted from the plurality of local oscillation light sources and combining it with the signal light.

(Function) The optical heterodyne/homodyne detection receiver according to the present invention incorporates a plurality of local oscillation light sources with different oscillation wavelength bands and an optical switch for selectively switching the emitted light and combining it with signal light. The feature is that the locally oscillated light can cover a wide frequency range.

For example, assume that the occupied frequency band of all signal lights is f'a-fb (a<a). If the allowable variable frequency range per local oscillation light source is fc, the number n of local oscillation light sources required is an integer that satisfies fc. Therefore, the number of input terminals of the optical switch is also n
pcs are required. In actual operation, the optical switch is switched so that the light emitted from the local oscillation light source covering the frequency band of the desired signal channel is combined with the signal. Information can then be extracted by changing the oscillation frequency of the relevant local oscillation light source and tuning to a desired signal channel.

(Embodiment) FIG. 1 shows the configuration of a first embodiment of the present invention. FIG. 2 shows the occupied frequency band of the signal light and the variable frequency band of the locally oscillated light in the first embodiment. In the first embodiment, the present invention is applied to a television broadcast subscriber system with a bit rate of 100 Mb/s per channel and 100 channels. All signal lights have a modulation index of 3
The frequency of each channel is 700 MHz. (See FIG. 2) Therefore, the occupied frequency band of all channels is 200.0 OTHz to 200.07 THz. 1st
In the figure, 100 channels of signal light 2 are transmitted through an optical fiber 1 and then multiplexed with local oscillation light by an optical coupler 3. This local oscillation light is transmitted from the first local oscillation light source to the fourth local oscillation light source 12.13.14.15 (hereinafter referred to as Lo).
, 1. Lo, 2. (abbreviated as Lo, 3° Lo, 4)
This is obtained by selecting one of the four laser beams emitted by the optical switch 16. Furthermore, the polarization control element 11 controls the polarization state of the local oscillation light so that it matches the polarization state of the signal light.
automatically controlled by. The combined light of the signal light 2 and the local oscillation light is subjected to heterodyne detection at the front end 4.

The output of the front end 4 is amplified by an IF amplifier 5, branched, and input to a demodulation circuit 6, a frequency discriminator 7, and an automatic polarization control circuit 10. The demodulation circuit 6 performs differential wave number discrimination detection of the IF multiplied signal and obtains an image signal. Served. The automatic polarization control circuit 10 monitors the IF signal level and controls the polarization control element 11 so that the IF signal level becomes maximum. The frequency discriminator 7 detects the IF multiplied signal frequency fluctuation and extracts a control signal for stabilizing it, and also extracts the beat pulses for each channel observed during the frequency sweep of the locally oscillated light. This control signal and pulses are input to the controller 8. At the same time as the power of the controller 8 itself is turned on, the controller 8 sequentially sweeps the frequency from Lo, 1 (12) to Lo, 4 (15) from the low frequency side, and stores the number of pulses from the frequency discriminator 7 in memory. to be memorized. At this time, the frequency sweep range of each laser is Lo, 1 (12
) is 200.00~200.02THz, L
o,2(13) from 200.02THz to 200.
04THz, Lo, 3(14) is 200.04THz
From 200.06THz, Lo, 4(15)
is 200.06 THz to 200.07 THz. Note that the frequency sweep ranges of these light sources are set by storing the bias current sweep ranges in the memory in advance. The beat pulse for each channel picked up by the frequency discriminator is determined based on which local oscillation light source among Lo, 1 to 4 (12 to 15) each signal channel can beat with, and the frequency sweep range. It is used to recognize the position from the low frequency side in . For example, when receiving channel 70 where a beat can be obtained 20th from the low frequency side of Lo, 3 (14), controller 8 first receives a selection command for channel 70 from channel selector 9, and then switches optical switch 16. A signal is sent from the controller 8 to the drive circuit 17 to allow the output light of Lo, 3 (14) to pass through. Lo, 3(
When the output light of 14) and the signal light 3 are in a state where the beat can be obtained, the controller 8 outputs a signal for sweeping the frequency of Lo, 3 (14) from the low frequency side.

During the sweep, the controller 8 counts the pulses from the frequency discriminator 7, and when the count reaches 20, the sweep is stopped. Next, the controller 8 connects the frequency discriminator 7
Lo, 3 (14
) is switched to add to the bias current. This completes the frequency pull-in stabilization of the channel 70. FIG. 3 shows the configuration of a twenty-ninth embodiment of the present invention. The second embodiment has a frequency band of 200.00 THz to 20
The present invention is applied to an optical heterodyne detection system that can instantaneously receive burst signals of unspecified frequencies in the range of 0.10 THz. When the signal light 2 is not received, the controller 8 switches between Lo, 1 (12) and Lo, 2 (13).
) are sequentially swept in frequency.

The sweep range of Lo, 1 (12) is from 200.00 THz to 200.05 THz, and the sweep range of Lo, 2 (13) is from 200.05 THz to 200.10 THz. When Lo,1 (12) is swept from the low frequency side to the high frequency side, Lo,2 (13) is set to 200.05 THz. And the optical switch 16 is Lo, 1(1
It receives a signal from the controller 8 that transmits the emitted light of 2). When Lo, 1 (12) reaches 200.05 THz, the output of the photodetector 20 has Lo, 1 (12) and L.
Since the beat signal of o, 2 (13) appears, when the controller 8 receives this signal, a signal is sent from the controller 8 to stop the frequency sweep of Lo, 1 (12) and to start the frequency sweep of Lo, 2 (13). Output. Also,
At this time, the optical switch 16 is switched and Lo, 2 (13
) is in a state where the emitted light is transmitted. Lo, 2 (13)
When the frequency reaches 200.10 THz, it is then swept back towards the lower frequency side. Lo, 2 (13)
When the frequency of reaches 200.05 THz, the beat signal is output again to the output of the photodetector 20, so contrary to the above, the frequency sweep changes from Lo, 2 (13) to Lo, 1 (12
). In this way, the local oscillation light is 200.
It is swept in the range from 00 THz to 200.10 THz. During sweeping of the local oscillation light, a signal is sent from the automatic polarization control circuit 10 to randomly modulate the polarization state so that the front end 4 can detect a beat even if the polarization of the signal light 2 is in any state. is output. When the transmission of the signal light 2 is started, a pulse appears in the output of the frequency discriminator 7 as in the first embodiment, so the controller 8 receives this and stops the local oscillation optical frequency sweep and polarization scrambling. let Subsequently, as in the first embodiment, IF multiplied signal frequency control and automatic polarization control are started, and at the same time, a data signal is output from the demodulation circuit 6. The second embodiment can be applied not only to optical fiber communication but also to the case where a burst signal of an unspecified frequency is received in space propagation type optical communication such as inter-satellite optical communication.

(Effects of the Invention) As described in detail above, by using the present invention, wideband signals that were previously unreceivable can be quickly received with one receiver. FIG. 2 is a diagram showing the frequency arrangement of signal light in the first embodiment, and FIG. 3 is a diagram showing a second embodiment of the non-emission period. In each figure, l: optical fiber 2
: Signal light 3: Optical coupler 4: Front end 5: IF amplifier 6: Demodulation circuit 7: Frequency discriminator 8: Controller 9:
Channel selector 10 Polarization control circuit 11: Polarization control element 12: First local oscillation light source 13: Second local oscillation light source 14: Third local oscillation light source 15: Fourth local oscillation light source 16: Optical switch 17 :Drive circuit 20: A photodetector.

Claims (1)

[Claims] A plurality of local oscillation light sources, a multiplexer for combining signal light and local oscillation light oscillated from the local oscillation light sources, a photodetector for receiving the combined light beam, and this photodetector. In an optical heterodyne/homodyne detection receiving apparatus including a demodulation circuit for extracting a data signal from an intermediate frequency signal appearing at the output of a plurality of local oscillation light sources, and a circuit for controlling the frequency of the local oscillation light, An optical heterodyne/homodyne detection receiver comprising an optical switch for selectively switching emitted light and combining it with signal light.