JPH08201225A - Optical frequency variable light source - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize an optical frequency variable light source capable of linear sweep control of optical frequency. [Structure] E / O converter, temperature control circuit for temperature control of E / O converter, current control circuit for controlling drive current of E / O converter, for modulating optical frequency of E / O converter In the variable optical frequency light source including the control means for outputting the modulated signal, a distributor for branching the output light from the E / O converter,
Delay means for delaying the output light of the distributor, a multiplexer for combining the output light of the delay means and the output light of the distributor, and a photodetector for detecting the output light of the multiplexer, And a phase comparator for detecting a frequency difference or a phase difference between the output signal of the photodetector and the output signal of the oscillator, and the control means includes a modulation signal generator and a phase comparator. And a control circuit that outputs a signal for linearly sweeping the optical frequency of the E / O converter according to the output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source whose optical frequency can be modulated, and more particularly to a light source which is provided with delay means for delaying light to detect deviation of the optical frequency and to perform linear sweep control of the optical frequency. The present invention relates to a variable frequency light source.

[0002]

2. Description of the Related Art Conventionally, there are roughly two methods for linearly sweeping an optical frequency as follows. One is electricity
The optical frequency of the optical converter (hereinafter referred to as E / O converter) is shown in Fig. 1.
This is a method that utilizes proportionality to the drive current as shown in (a) of 0. As shown in FIG. 8, the E / O converter 1 is driven by the output current of the current control circuit 3 and the temperature control circuit 2 is used. In this method, the temperature is controlled by the method, but the drive current of the current control circuit 3 is ramp-wave modulated by the ramp signal output from the ramp wave generator 13, and the E / O converter 1 is driven by this modulation signal. Another method utilizes the fact that the optical frequency of the E / O converter is proportional to the temperature as shown in FIG. 10 (b), and the temperature is ramp-wave modulated by the configuration as shown in FIG. This is a method of controlling the temperature of the / O converter 1.

[0003]

However, there is a drawback that it is difficult to linearly sweep the optical frequency when the modulation is performed only by the driving current or the temperature.

An object of the present invention is to realize an optical frequency variable light source capable of detecting an optical frequency change amount per unit time by providing a delay means for delaying light and performing linear sweep control of the optical frequency. .

[0005]

In order to achieve such an object, in the first aspect of the present invention, an E / O converter and the E / O converter are provided.
A temperature control circuit for controlling the temperature of the O converter;
A current control circuit for controlling the drive current of the converter;
An optical frequency variable light source having a control means for outputting a modulation signal for modulating the optical frequency of an O-converter, wherein E
Splitter for splitting output light from the / O converter, delay means for delaying output light of the splitter, and multiplexer for multiplexing output light of the delay means and output light of the splitter When,
A photodetector that detects the output light of the multiplexer, an oscillator that outputs a known frequency signal, and a phase comparison that detects the frequency difference or phase difference between the output signal of the photodetector and the output signal of the oscillator. And a control means for outputting a signal for linearly controlling the optical frequency of the E / O converter according to the outputs of the modulation signal generator for generating a modulation signal and the phase comparator. It is characterized by including a circuit. In addition, in the second invention, in addition to the configuration of the first invention,
It is characterized in that the output of the phase comparator is once stored in a storage device and is given to a control circuit.

[0006]

A part of the output light of the E / O converter is taken out, it is divided into two, one is delayed and then multiplexed, and this is detected by the photodetector. When the E / O converter is driven by a ramp-wave-modulated current, the optical frequency of its output light is ramp-wave modulated, and the frequency of the signal detected by the photodetector at this time is the product of the slope of the change in optical frequency and the delay time. Is equal to. If the optical frequency of the output light of the E / O converter is swept linearly, the output frequency of the photodetector will be constant. Therefore, the output of the photodetector is compared with a known frequency signal, and the modulation signal is controlled so that the frequencies or the phases coincide with each other to realize the linear sweep.

[0007]

The present invention will be described in detail below with reference to the drawings.
FIG. 1 is a configuration diagram showing an embodiment of an optical frequency variable light source according to the present invention. In the figure, 1 is an E / O converter, 2 is E
A temperature control circuit for controlling the temperature of the / O converter 1 and E /
A current control circuit for controlling the drive current of the O converter 1, 4 is an optical isolator, 5 and 6 are beam splitters for splitting light, and 7 is a delay means for delaying the output light of the beam splitter 6, which is known here. The length of the optical fiber is used. An optical multiplexer 8 combines the output light of the beam splitter 6 and the output light of the optical fiber 7.

Reference numeral 9 is a photodetector for detecting the output light of the optical multiplexer 8, 10 is a bandpass filter for transmitting only a desired frequency component from the output signal of the photodetector 9, and 11 is an oscillator for outputting a known frequency signal. , 12 are bandpass filters 1
A phase comparator that detects a frequency difference and a phase difference between the output signal of 0 and the output signal of the oscillator 11, and 13 is a modulation signal generator that outputs a modulation signal (ramp wave) and a synchronization signal synchronized with the repetition of the modulation signal. is there.

Reference numeral 14 is a control circuit for outputting a signal (referred to as a linear sweep control signal) for controlling the linear sweep of the optical frequency by the output signal of the phase comparator 12 and the output signal of the modulation signal generator 13, and 15 is a modulation signal. An adder for adding the output signal of the generator 13 and the linear sweep control signal of the control circuit 14, 10
0 is an output light, 110 is a modulation signal, and 120 is a synchronization signal.

The operation in such a configuration will be described below. The temperature control circuit 2 controls the temperature of the E / O converter 1 to be constant. The light emitted from the E / O converter 1 passes through the isolator 4 and the beam splitter 5 and is output to the outside. When the ramp wave output from the modulation signal generator 13 is input to the current control circuit 3 to modulate the drive current of the E / O converter 1, the optical frequency of the output light of the E / O converter 1 is as shown in FIG. Ramp wave modulation [a (Δf / Δ
t)].

The light split by the beam splitter 5 passes through the beam splitter 6 and is input to the optical fiber 7 having a known length L. The light emitted from the optical fiber 7 enters the optical multiplexer 8 and is combined with the light split by the beam splitter 6. The light multiplexed by the optical multiplexer 8 is converted into an electric signal by the photodetector 9. At this time, there is a fixed time difference between the light delayed by the optical fiber 7 and the light split by the beam splitter 6 t = n · L / c ₀ , where n is the refractive index of the optical fiber 7 c _{0 is in} vacuum Therefore, the product of the difference in the optical frequency changed within the delay time, that is, the product of the slope of the change in the optical frequency (the amount of change in the optical frequency per unit time) and the delay time due to the optical fiber f = a · t = A signal having a frequency equal to a · n · L / c ₀ is output from the photodetector 9.

Therefore, if the inclination a of the change in the optical frequency is constant (the line is swept), the frequency of the signal output from the photodetector 9 is constant. An unnecessary frequency component is removed from the signal output from the photodetector 9 by the bandpass filter 10, and the frequency and the phase are compared by the phase comparator 12 with the signal of the known frequency output from the oscillator 11. The bandpass filter 10 does not necessarily have to be used. The control circuit 14 outputs a linear sweep control signal so that the frequency of the signal output from the photodetector 9 becomes constant according to the output signal of the phase comparator 12.

The linear sweep control signal output from the control circuit 14 is added to the modulation signal 110 by the adder 15 and enters the current control circuit 3. When the ramp wave modulation is repeatedly performed, the control circuit 14 controls the synchronization signal 12 synchronized with the repetition of the modulation signal output from the modulation signal generator 13.
Based on 0, start and stop are performed as shown in FIG.

By such control, the frequency of the signal output from the photodetector 9 is controlled to be constant, and the linear sweep control of the optical frequency becomes possible.

The present invention is not limited to the above embodiment, but various modifications are possible as follows. For example, as shown in FIG. 3, the polarization-maintaining optical fiber 16 may be used in the optical waveguide for the purpose of delay. In FIG.
2 is that the polarization maintaining fiber 16 is used and the control circuit 14 outputs a control signal only in accordance with the output signal of the phase comparator 12. The operation is the same as the operation in the configuration of FIG. 1 except the operation by the synchronization signal.

Generally, when two lights are combined and converted into an electric signal by a photodetector, the signal intensity of a frequency equal to the difference between the output optical frequencies depends on the deflection state of the combined light. . In the above embodiment, the light transmitted through the optical fiber is disturbed in deflection due to the disturbance applied to the optical fiber,
The signal output from the photodetector 9 contains much noise. However, by using the polarization-maintaining optical fiber 16, since the polarization state of the light when the beam splitter 6 is output is maintained, the noise of the signal output from the photodetector 9 is reduced.

The portion consisting of the modulation signal generator 13 and the control circuit 14 is called control means for linearly sweeping the optical frequency. In the present invention, this control means also supplies the output signal and controls it. It is not limited to the embodiment. In FIG. 4, the output of the control means, that is, the output signals of the control circuit 14 and the modulation signal generator 13 are input to the temperature control circuit 2, and E / O
It is a structural example in the case of controlling the optical frequency of the output light of the converter 1.

In FIG. 5, the output signal of the modulation signal generator 13 is input to the temperature control circuit 2 to modulate the temperature of the E / O converter, and the output signal of the control circuit 14 is input to the current control circuit 3. 2 is a configuration example in which the optical frequency of the output light of the E / O converter 1 is controlled by.

In FIG. 6, the output signal of the modulation signal generator 11 is input to the current control circuit 3 to modulate the drive current of the E / O converter 1, and the output signal of the control circuit 14 is input to the temperature control circuit 2. This is a configuration example in the case of controlling the optical frequency of the output light of the E / O converter by performing.

In FIG. 7, a storage circuit 17 for storing the output of the phase comparator 12 is provided to store the result of frequency sweep without control, and the modulation frequency is linearly swept based on the output result. This is a configuration example in which the output of the signal generator is corrected by the control circuit 14 as described above.

[0021]

As described above, according to the present invention, by providing the delay means for delaying the light, the variation amount of the optical frequency per unit time is detected and the variation amount is controlled to be constant by the control means. Therefore, linear sweep of the optical frequency becomes possible. Further, when the control signal is started and stopped by the synchronization signal synchronized with the repetition of the modulation signal, the optical frequency can be repeatedly swept. Also,
If a polarization maintaining optical fiber is used as the delay means for delaying the light, the deflection of the light incident on the multiplexer can be controlled, so that the S / N ratio of the output signal of the photodetector can be easily improved. it can.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical frequency variable light source according to the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the present invention.

FIG. 3 is a configuration diagram showing another embodiment of the present invention.

FIG. 4 is a configuration diagram showing still another embodiment of the present invention.

FIG. 5 is a configuration diagram showing still another embodiment of the present invention.

FIG. 6 is a configuration diagram showing still another embodiment of the present invention.

FIG. 7 is a configuration diagram showing still another embodiment of the present invention.

FIG. 8 is a main part configuration diagram showing a configuration according to a conventional linear sweep method.

FIG. 9 is a main part configuration diagram showing a configuration according to another conventional linear sweep method.

FIG. 10 is a diagram showing characteristics of an E / O converter.

[Explanation of symbols]

 1 E / O converter 2 Temperature control circuit 3 Current control circuit 4 Isolator 5, 6 Beam splitter 7 Delay means 8 Optical multiplexer 9 Photodetector 10 Bandpass filter 11 Oscillator 12 Phase comparator 13 Modulation signal generator 14 Control circuit 15 adder 16 polarization maintaining optical fiber 17 memory circuit

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Mamoru Arihara 2-3-9 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Co., Ltd.

Claims (8)

[Claims] 1. An E / O converter, a temperature control circuit for controlling the temperature of the E / O converter, a current control circuit for controlling a drive current of the E / O converter, and the E / O conversion. In a variable optical frequency light source having a control means for outputting a modulation signal for modulating the optical frequency of an optical device, a distributor for branching the output light from the E / O converter and a delay for the output light of the distributor. For delaying the output light of the delay means and the output light of the distributor, a photodetector for detecting the output light of the multiplexer, and a known frequency signal is output. With an oscillator, and a phase comparator for detecting a frequency difference or a phase difference between the output signal of the photodetector and the output signal of the oscillator, the control means, a modulation signal generator for generating a modulation signal and the Depending on the output of the phase comparator, the E / O converter A variable optical frequency light source, comprising: a control circuit that outputs a signal for linearly controlling the optical frequency. 2. The control means inputs the output signal of the modulation signal generator and the output signal of the control circuit to the current control circuit to control the optical frequency of the output light of the E / O converter. 2. The variable optical frequency light source according to claim 1, wherein 3. The control means inputs the output signal of the modulation signal generator and the output signal of the control circuit to the temperature control circuit to control the optical frequency of the output light of the E / O converter. 2. The variable optical frequency light source according to claim 1, wherein 4. The control means inputs the output signal of the modulation signal generator to the temperature control circuit to modulate the temperature of the E / O converter, and outputs the output signal of the control circuit to the current control circuit. 2. The variable optical frequency light source according to claim 1, wherein the optical frequency variable light source is configured to control the optical frequency of the output light of the E / O converter by inputting to the optical frequency converter. 5. The control means inputs the output signal of the modulation signal generator to the current control circuit to modulate the drive current of the E / O converter, and controls the output signal of the control circuit to the temperature control. 2. The variable optical frequency light source according to claim 1, wherein the optical frequency variable light source is configured to control the optical frequency of the output light of the E / O converter by inputting it to a circuit. 6. The control means is configured to output a synchronization signal synchronized with the repetition of the modulation signal from the modulation signal generator and input the synchronization signal to the control circuit to perform the repetition control. The variable optical frequency light source according to claim 1. 7. A polarization maintaining optical fiber is used as the delay means, and the deflection of the light incident on the multiplexer is controlled to improve the S / N ratio of the output signal of the photodetector. 2. The variable optical frequency light source according to claim 1. 8. An E / O converter, a temperature control circuit for controlling the temperature of the E / O converter, a current control circuit for controlling a drive current of the E / O converter, and the E / O conversion. A variable optical frequency light source including a control means for outputting a modulation signal for modulating an optical frequency of a light emitting device, wherein the light dividing device divides the light output from the E / O converter, and delays the light output from the light distributing device. For delaying the output light of the delay means and the output light of the distributor, a photodetector for detecting the output light of the multiplexer, and a known frequency signal is output. An oscillator, a phase comparator that detects a frequency difference or a phase difference between the output signal of the photodetector and the output signal of the oscillator, and a storage device that stores the output of the phase detector, and the control means Is a modulation signal generator that generates a modulation signal Optical frequency variable light source, characterized in that it comprises a control circuit for outputting a signal for controlling the linear sweeping the optical frequency of said E / O converter in accordance with the output of the storage device.