JPH0514427A - Optical heterodyne fsk dual filter detector - Google Patents

Abstract

PURPOSE:To provide an AFC circuit with simple configuration and the optical heterodyne FSK dual filter detector having the AFC circuit. CONSTITUTION:An AFC circuit receiving a high frequency signal and a low frequency signal and sending a frequency control signal 16 to a local oscillation light source 8 is provided with peak detectors 6,6 detecting respectively the peak level of the high frequency signal and the low frequency signal and a subtractor 7 calculating a difference of the detected peak levels and sending the result of calculation as a frequency control signal 16. Moreover, the optical heterodyne FSK dual filter detector is provided with an optical heterodyne reception section 2 multiplying an FSK optical input signal including the high frequency side signal and the low frequency side signal with an optical signal 17 from the local oscillation light source 8 and converting the result into an intermediate frequency signal, a 1st band pass filter 12 extracting only the high frequency signal of the intermediate frequency signal, a 2nd band pass filter 13 extracting only the low frequency signal of the intermediate frequency signal and an AFC circuit 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical heterodyne FSK (frequency shift keying) dual filter detector used for coherent optical communication, and more particularly to an AFC (automatic frequency control) circuit and this AFC (automatic frequency control) circuit. And an optical heterodyne FSK dual filter detection device.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 4, an AFC circuit of an FSK dual filter detector based on optical heterodyne multiplies an optical input signal 1 and an optical signal of a local light source 8 and outputs a signal () at a center frequency f _0. The optical heterodyne receiving unit 2 that outputs the IF signal 10, 11), the delay unit 21 that delays the output IF signal 11 by τ (time constant), and the IF signal 31 that is a branch signal of the IF signal 11 and the τ delayed. IF signal 3
A multiplier 22 that multiplies by 2, a low-pass filter 23 that removes high-frequency components from the output of the multiplier 22, and a local light source 8 whose oscillation frequency is controlled by using the output of the low-pass filter 23 as a frequency control signal 33. Composed of. In such a conventional FSK dual filter detector using optical heterodyne, the operation of the AFC circuit 30 is as follows. First, the optical input signal 1 is the optical signal 17 of the local light source 8.
And the optical heterodyne receiving unit 2 multiplies the IF signal 10,
It will be 11. These IF signals are branched and one IF signal 10 is input to the dual filter detection unit 20 and demodulated into a baseband signal 9. Also, the other 11 of the IF signal
Is a delay unit 21, a multiplier 22, and a low-pass filter 23.
Is input to the delay detector 30 composed of. Since the delay detector 30 has a frequency discrimination characteristic of a sine waveform as shown in FIG. 5, the IF signal 10 is controlled by controlling the oscillation frequency of the local light source so as to correspond to the output voltage of the low pass filter 23. Can be locked at frequency f ₀ .

[0003]

In the conventional AFC circuit of the heterodyne FSK dual filter detector, adjustment of the delay amount τ is complicated, and the scale of the AFC circuit needs to be exactly the same as that of the detection unit. There was a drawback that it became a simple structure.

Therefore, a technical object of the present invention is to provide an AFC circuit having a simple structure and an optical heterodyne FSK dual filter detector having the AFC circuit.

[0005]

According to the present invention, in an AFC circuit that receives a high frequency side signal and a low frequency side signal and sends a frequency control signal to a local oscillator, the high frequency side signal and It has a peak detector that detects the peak value of the signal on the low frequency side, and a subtractor that calculates the difference between the detected peak values and sends the calculation result as the frequency control signal. An AFC circuit is obtained.

According to the present invention, an optical heterodyne receiving unit for multiplying an FSK optical input signal including a high-frequency side signal and a low-frequency side signal by an optical signal from a local light source to convert it into an intermediate frequency signal, A first band pass filter for extracting only the high frequency side signal of the intermediate frequency signal, a second band pass filter for extracting only the low frequency side signal of the intermediate frequency signal, and the extracted high frequency side signal And a peak detector that detects the peak value of the extracted low-frequency side signal, and a difference between the peak value of the high-frequency side signal and the low-frequency side signal peak value is calculated. Based on this, an optical heterodyne FSK dual filter detector is provided, which comprises a subtracter for controlling the local oscillation light source based on the above.

[0007]

In the AFC circuit of the present invention, the peak detector detects the peak values of the high frequency side signal and the low frequency side signal of the intermediate frequency, respectively. The subtractor calculates the difference between the detected peak values and sends the calculation result as the frequency control signal.

In the optical heterodyne FSK dual filter detector according to the present invention, the FSK optical input signal including the high frequency side signal and the low frequency side signal is mixed with the optical signal from the local light source, and the optical heterodyne receiving section is used. It is multiplied and converted into an IF signal. As for one of the IF signals from the optical heterodyne receiver, only the signal on the high frequency side of the IF signal is extracted by the first bandpass filter. In the other of the IF signals from the optical heterodyne receiving unit, only the signal on the low frequency side of the IF signal is extracted by the second bandpass filter and combined by the adder to become the baseband signal.

On the other hand, the extracted high frequency side signal and the extracted low frequency side signal are input to the AFC circuit. AF
In the C circuit, the peak values of the extracted high frequency side signal and the extracted low frequency side signal are
Each of them is detected, and the subtracter calculates the difference between the peak value of the high-frequency side signal and the peak value of the low-frequency side signal, and the oscillation frequency of the local light source is controlled based on this calculated value.

[0010]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing an optical heterodyne FSK dual filter detector according to an embodiment of the present invention. In FIG. 1, an optical heterodyne FSK dual filter detector is provided with an optical signal 1 having a reference frequency.
7, a local oscillation light source 8 that oscillates 7, an FSK optical input signal 1 including a signal on the high frequency side and a signal on the low frequency side, and the oscillation light 17 from the local oscillation light source 8 for optical heterodyne detection,
IF signal from the heterodyne receiver 2 that outputs an IF signal, the first bandpass filter (for high frequency) 3 that extracts only the IF signal 12 on the high frequency side from the IF signal 10 from the heterodyne receiver 2, and the IF signal from the heterodyne receiver 2 The second band pass filter (for low frequency) 4 which extracts only the low frequency side IF signal 13 from 11, and the high frequency side IF signal and the low frequency side from these first and second band pass filters 3 and 4. Envelope detectors 5 and 5 for performing envelope detection of the IF signals respectively, and an adder 18 for combining the signals from the envelope detectors 5 and 5 and outputting a baseband signal,
An AFC circuit 19 for controlling the oscillation frequency of the local light source 8 based on the IF signal of the high frequency side IF signal and the low frequency side IF signal branched from the first and second band pass filters 3 and 4. It has and.

FIG. 2 shows a first band pass filter (for high frequency) for extracting only the high frequency side IF signal from the IF signal from the heterodyne receiving section and the low frequency side IF from the IF signal.
It is a figure with which the 2nd bandpass filter (for low frequencies) 4 which extracts only signal 13 is explained. The first bandpass filter (for high frequency) and the second bandpass filter (for low frequency) 4 have a bandwidth as shown in FIG.

Returning to FIG. 1, the AFC circuit 19 detects peak frequencies of the high frequency signal 14 from the first band pass filter and the low frequency signal 15 from the second band pass filter 4, and peak detectors 6 and 6 for detecting the peak frequencies. And a subtractor 7 that calculates the difference between the peak detection values from these peak detectors and outputs the calculation result to the local light source 8.

Next, the operation of the optical heterodyne FSK dual filter detector according to the embodiment of the present invention will be described. The optical input signal 1 is multiplied by the oscillation light of the local light source 8,
In the optical heterodyne receiving unit 2, an optical heterodyne detection wave is generated and IF signals 10 and 11 are obtained. One of the branched IF signals 10 is input to the bandpass filter 3 and only the high frequency side signal is extracted. The other IF signal 11 is input to the bandpass filter 4, and only the low frequency side IF signal is extracted. Extracted high frequency side IF signal 12
The IF signal 13 on the low frequency side and the IF signal 13 on the low frequency side are envelope-detected by the envelope detector 5, and then the baseband signal 9 synthesized by the adder 18 and demodulated is demodulated.

On the other hand, in the AFC circuit 19, the peak values f ₁ and f ₂ of the signal 14 on the high frequency side and the signal 15 on the low frequency side are respectively peaked from the band pass filters 3 and 4 of the dual filter detection section 21. The peaks are detected by the detectors 6 and 6, and the subtracter 7 calculates the difference between the detected peak values. The frequency characteristic of the output of the obtained subtractor 7 is shown in FIG.
As shown in FIG. 5, the linear waveform changes linearly from f ₁ to f ₂ with f ₀ as the center and has peaks at f ₁ and f ₂ . By outputting the output from the subtractor 7 as the frequency control signal 16 to the local oscillation light source 8 and controlling the oscillation frequency f ₀ of the local oscillation light source 8, the IF signals 10 and 11 are locked to f ₀ . be able to.

[0016]

As described above, according to the present invention,
It is possible to provide an AFC circuit with a simple configuration that is composed only of a peak detector and a subtractor.

Further, according to the present invention, since this AFC circuit is provided, it is possible to provide an optical heterodyne FSK dual filter detector which simplifies the circuit structure and allows no adjustment.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a bandwidth of the bandpass filter shown in FIG.

FIG. 3 is a graph of frequency discrimination characteristics of FIG.

FIG. 4 is a block diagram showing a conventional example.

5 is a graph of the frequency discrimination characteristic of FIG.

[Explanation of symbols]

1 Optical input signal 2 Optical heterodyne receiver 3 band pass filter (for high frequency) 4 band pass filter (for low frequency) 5 Envelope detector 6 peak detector 7 Subtractor 8 local light sources 9 Baseband signal 10 IF signal 11 IF signal 12 High frequency signal 13 Low frequency signal 14 High frequency signal 15 Low frequency signal 16 Frequency control signal 19 AFC circuit 20 Dual filter detector 21 Delay device 22 Multiplier 23 Low-pass filter 30 AFC circuit

Claims (2)

[Claims] 1. An AFC circuit for receiving a high-frequency side signal and a low-frequency side signal and sending a frequency control signal to a local oscillator, wherein peak values of the high-frequency side signal and the low-frequency side signal are An AFC circuit comprising: a peak detector that detects each of the detected peak values; and a subtracter that calculates the difference between the detected peak values and sends the calculation result as the frequency control signal. 2. An optical heterodyne receiver that multiplies an FSK optical input signal including a high-frequency side signal and a low-frequency side signal by an optical signal from a local light source to convert into an intermediate frequency signal, and the intermediate frequency. A first bandpass filter for extracting only the signal on the high frequency side of the signal, a second bandpass filter for extracting only the signal on the low frequency side of the intermediate frequency signal, the extracted high frequency side signal and the extracted And a peak detector for detecting the peak value of each of the low-frequency signals, and the difference between the peak value of the high-frequency signal and the peak value of the low-frequency signal, and the station based on the calculated value. An optical heterodyne FSK dual filter detector, comprising: a subtractor for controlling a light emitting source.