JPH07280647A - Superposed pilot signal type optical sensor - Google Patents

Abstract

PURPOSE:To provide a superposed pilot signal type optical sensor which is not susceptible to the dark current at an opto-electric converting section or the DC fluctuation of a light receiving/amplifying circuit and ensures a high accuracy in the measurement and in which a sensor output can be delivered along with a pilot signal (reference level). CONSTITUTION:In the optical sensor for detecting variation in the level of an optical signal, a pilot signal (frequency fp) is employed in the optical output control at an electro-optical converting section E/O. Furthermore, a pilot signal (frequency fp) corresponding to the DC component of optical output signal is superposed thereon using an analog drive circuit MIXD with an adder circuit. The pilot signal (frequency fp) is taken out by inserting a filter fpFTL into the output part of a light receiving/amplifying circuit RA and then it is converted through a rectifying circuit REC into a DC signal which is compared with a reference voltage Vr in order to control the optical output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sensor used for voltage or current monitoring, and more particularly to an optical sensor of a pilot signal superposition type.

[0002]

2. Description of the Related Art Conventionally, as this type of device, for example,
Optronics Co., Ltd. published "Optical Sensor Technology Collection" (Published February 19, 1990), "Voltage Sensors, Magnetic Field Sensors" on pages 31-32. The intensity of an electric field or a magnetic field is measured by changing the polarization state of the light passing through the current sensor into a change in the intensity of the light through an analyzer.

FIG. 7 shows a circuit example of a conventional voltage sensor or current sensor, which measures the strength of an electric field or magnetic field of an AC signal having a frequency f1. E / O is an electro-optical converter such as a semiconductor light emitting element, OF is an optical fiber, S is an optical sensor element, and O / E is an opto-electric converter. As the optical sensor element S, a Pockels element having an electro-optical effect is used when measuring a voltage, and a Faraday element having a magneto-optical effect is used when measuring a current. The measurement output is the light receiving amplifier circuit R
It is obtained from the bandpass filter flBPF on the output side of A. In this example, in order to secure the level stability of the optical output OPT1 of the electro-optical conversion unit, a low-pass filter flLPF that blocks the frequency fl of the direct current component of the output of the photoreceiver / amplifier RA.
To extract the reference voltage Vr and the comparison and amplification circuit CMP.
Then, the electro-optical conversion unit E / O is driven by the comparison output through the electro-optical conversion unit analog drive circuit.

FIG. 8 shows the waveforms of the optical signal OPT1 and the optical signal OPT3 shown in FIG. 7, where A is proportional to the intensity of the light source and a is proportional to the intensity of the measured electric field or the measured magnetic field.

[0005]

The conventional device having the above-mentioned structure has the following problems. (1) Since the optical output level is adjusted based on the direct current component of the received light output, the dark current of the photoelectric conversion unit affects the measurement accuracy of the sensor. (2) Similarly, since the optical output level is adjusted based on the DC component of the received light output, the DC fluctuation of the received light amplification circuit affects the measurement accuracy of the sensor. (3) Since there is no reference signal for level control, sensor output level control is required.

In order to solve such problems, it is an object of the present invention to provide a pilot signal superposition type optical sensor having the following features. (1) The measurement accuracy is not affected by the dark current of the photoelectric conversion unit. (2) The measurement accuracy is not affected by the DC fluctuation of the photoreceiver / amplifier circuit. (3) The sensor output can be transferred together with the pilot signal (reference level).

[0007]

To achieve the above object, in the present invention, in an optical sensor for detecting a level change of an optical signal, means for superimposing a pilot signal (AC signal) on an optical signal source, It is characterized in that a means for adjusting the level using the signal is provided.

As means for superimposing the pilot signal, it is possible to superimpose an AC signal in an analog manner or to superimpose an AC signal in a digital manner. As means for adjusting the level, a circuit for comparing the levels of the received pilot signal and the reference signal and controlling the optical output level of the optical signal source by the comparison output signal is provided, or the received pilot signal is received on the receiving side of the optical signal. It is possible to provide a circuit for comparing the levels of the reference signal and the reference signal and performing gain control by the comparison output signal. Further, the received pilot signal can be used as a means for passing the output of the optical sensor.

[0009]

[Operation] The pilot signal superposition type optical sensor of the present invention is
With the above configuration, it has a function of superimposing a pilot signal on the optical sensor light source, a function of adjusting the level based on the pilot signal, and a function of passing the sensor output together with the pilot signal. It produces a working effect. (1) Measurement accuracy is not affected by transmission loss fluctuations in optical transmission systems and gain fluctuations in electrical systems. The output level can be calibrated based on the pilot signal level. (2) Dark current and DC fluctuation of the light receiving system do not affect the measurement accuracy. Since the AC pilot signal is used, it can be separated from the DC fluctuation component. (3) The measurement output can be delivered with high accuracy, and in particular, it can be delivered together with the pilot signal that serves as the reference of the signal level.

[0010]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is an embodiment of the present invention, and is different from the conventional embodiment shown in FIG. 7 in that a pilot signal (frequency fp) is used for the optical output control of the electro-optical conversion unit E / O. . That is, in FIG. 1, E / O is an electro-optical converter such as a semiconductor light emitting device, OF is an optical fiber, S is an optical sensor device, O / E is an opto-electric converter, and the optical sensor device S measures a voltage. In that case, a Pockels element having an electro-optical effect and a Faraday element having a magneto-optical effect when measuring a current are used as in the conventional case.

As a feature of the present invention, an analog drive circuit MIXD with an adder circuit is used to superimpose a pilot signal (frequency fp) corresponding to the direct current component of the optical output level,
A filter fpFIL is inserted into the output part of the light receiving and amplifying circuit RA to take out a pilot signal (frequency fp), a rectifying circuit REC converts it into a direct current signal, and a light output control is performed by comparing with a reference voltage Vr.

FIG. 2 shows the electric signal MIXD of the embodiment of FIG.
out, the waveform of the optical signal OPT1 and the optical signal OPT3,
MIXDout in which both the direct current component (D) and the alternating current component (P) are controlled by the output of the comparison and amplification circuit CMP, the optical signal OPT1 on which the pilot signal (frequency fp) is superimposed, and the light modulated by the measured signal frequency f1 The signal OPT3 is shown.

FIG. 3 shows another embodiment of the present invention, which is different from that of FIG. 1 in that the level adjustment is performed on the output side of the photoreceiver / amplifier circuit RA without controlling the optical output of the electro-optical converter E / O. Other configurations are similar to those of the embodiment of FIG.
That is, the filter fpFI is output from the automatic gain control circuit AGC output.
The pilot signal (frequency fp) is taken out by L, converted into a DC signal by the rectifier circuit REC, compared with the reference voltage Vr, and the output thereof controls the automatic gain control circuit AGC.

In the examples shown in FIGS. 1 and 3, since the relationship between the pilot signal level and the light level needs to correspond at a constant ratio, the linearity of the electric / optical conversion characteristic of the electro-optical conversion unit E / O is obtained. is necessary.

FIG. 4 shows still another embodiment of the present invention. The difference from FIGS. 1 and 3 is that the pilot signals are digitally superimposed instead of analog superimposed.
The other structure is the same as that of the embodiment shown in FIGS. That is, the optical signal OP switched by the pilot signal (frequency fp) in the electro-optical converter digital drive circuit DDR
We are making T1 (see Figure 5).

FIG. 5 shows the waveforms of the optical signal OPT1 and the optical signal OPT3 of the embodiment of FIG.
p) shows the optical signal OPT1 switched and the optical signal OPT3 modulated by the frequency fl of the signal under measurement.

FIG. 6 shows still another embodiment of the present invention, which is shown in FIG.
1 is that the output level adjustment is performed on the output side of the photoreceiver / amplifier circuit RA without controlling the optical output of the electro-optical converter E / O as in FIG. In the example shown in FIGS. 4 and 6, the linearity of the electric / optical conversion characteristic of the electro-optical conversion unit E / O is not required unlike the examples shown in FIGS. 1 and 3.

[0018]

As described in detail above, according to the present invention, since the optical signal on which the pilot signal is superimposed is used, the following effects can be expected. (1) The measurement accuracy is not affected by the transmission loss fluctuation of the optical transmission system and the gain fluctuation of the electric system, and the output level can be calibrated based on the pilot signal level. (2) Dark current and DC fluctuation of the light receiving system do not affect the measurement accuracy,
Since the AC pilot signal is used, it can be separated from the DC fluctuation component. (3) It is possible to deliver the measurement output with high accuracy, and it is possible to deliver it together with the pilot signal that serves as the reference of the signal level.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a pilot signal superposition type optical sensor of the present invention.

FIG. 2 is a waveform diagram of an electric signal and an optical signal of FIG.

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

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

5 is a waveform diagram of the optical signal of FIG.

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

FIG. 7 is a circuit diagram of a conventional optical sensor.

FIG. 8 is an optical signal waveform diagram of FIG.

[Explanation of symbols]

 S optical sensor element E / O electro-optical conversion unit O / E opto-electric conversion unit MIXD analog drive circuit with adder circuit CMP comparison amplification circuit RA photodetection amplification circuit FIL filter REC rectifier circuit OPT1 electro-optic conversion unit optical output signal OPT2 inside optical sensor Optical signal OPT3 Optical-electrical converter Optical input signal Vr Reference voltage fp Pilot signal frequency fl AC signal frequency under test OF Optical fiber MIX Adder circuit AGC Automatic gain control circuit DDR Electrical-optical converter Digital drive circuit

Claims (6)

[Claims] 1. An optical sensor for detecting a level change of an optical signal, comprising means for superimposing a pilot signal on an optical signal source, and means for adjusting the level using the pilot signal. Signal superposition type optical sensor. 2. The pilot signal superposition type optical sensor according to claim 1, wherein an AC signal is superposed in an analog manner as means for superposing the pilot signal. 3. The pilot signal superposition type optical sensor according to claim 1, wherein an AC signal is digitally superposed as means for superposing the pilot signal. 4. A circuit for comparing the levels of a received pilot signal and a reference signal and controlling the optical output level of an optical signal source by the comparison output signal as means for performing the level adjustment. 1. A pilot signal superposition type optical sensor according to 1. 5. A circuit for comparing the levels of a received pilot signal and a reference signal on the receiving side of the optical signal and performing gain control by the comparison output signal is provided as means for adjusting the level. 1. A pilot signal superposition type optical sensor according to 1. 6. The pilot signal superposition type optical sensor according to claim 1, wherein a received pilot signal is used as a means for delivering and receiving the output of the optical sensor.