JPS59226999A - Optical detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical detection device using an optical fiber, and can be used, for example, to measure temperature or mechanical displacement.

[Technical background of the invention] FIG. 1 shows a conventional configuration of this type of optical detection device.

In FIG. 1, 1 is a first light source that emits light with a wavelength λ1, 2 is a second light source that emits light with a wavelength λ2 different from λ1,
3a and 3b are input fibers that receive the light from the light sources 1 and 2; 4 is an optical coupler that guides the guided light from the input fiber 3a or 3b to the input fiber 5 and the monitoring fiber 6; 7 is an input fiber 5 is a physical change detection section that receives the guided light; 8 is an output fiber that guides the output light of the physical change detection section 7; 9 is a light receiving element that receives the guided light of the output fiber 8; 10 is the monitoring fiber. This is a monitor light-receiving element that receives the guided light of No. 6. The physical change detection unit 7 outputs the light having a wavelength λ1 from the first light source 1 after modulating the intensity according to physical changes such as temperature or mechanical reception, and outputs the light having a wavelength λ2 from the second light source 2, which is different from this. The light is output almost as is without being subjected to the intensity modulation described above. Reference numeral 11 indicates control for driving the first light source 1 and the second light source 2 to emit light in a time-alternative manner, and for controlling the divider 12 and the storage calculation section 13, which will be described below, to operate in synchronization with the driving of each light source. Part, 12
is a divider that inputs the photoelectric outputs of the light receiving element 9 iJ3 and the monitor light receiving element 10 and calculates and outputs a division value between both outputs;
Reference numeral 13 denotes a memory calculation unit having a temporary memory function and calculating the ratio between the division value based on the light emission of the first light source 1 and the division value based on the light emission of the second light source 2 and outputting this as a physical change detection signal. It is.

With the above configuration, when first the first light source 1 is driven to emit light, the light of wavelength λ1 from this light source 1 is transmitted through the input fiber 3a, the optical coupler 4 and the input fiber 5.
After entering the detection unit 7 through the optical fiber 8 and receiving intensity modulation according to physical changes such as temperature or displacement, the output fiber 8 leads to the light receiving element 9, and the optical coupler 4 and the monitoring fiber 6 lead to the monitor light receiving element. leading to. Each photoelectric output based on the light emission of the first light source 1 of the light receiving element 9 and the monitor light receiving element 10 is given to the divider 12, and after division between both outputs is performed here, the divided value is stored in the storage calculation section. 13 and is temporarily stored until a division value based on the second light source, which will be described next, is given.

Next, when the second light source 2 is driven to emit light instead of the first light source 1, the light of wavelength λ2 from the light source 2 passes through the input fiber 31) and passes through the light receiving element in the same way as the light from the first light source 1. 9 and a monitor light receiving element 10.

After these photoelectric outputs are divided by a divider 12, they are given to an arithmetic unit 13. The storage calculation unit 13 divides the division value based on the second light source 2 and the division value based on the first light source 1, and outputs the quotient as a physical change detection signal.

[Problems with Background Art] According to the above configuration, light of each wavelength is transmitted to the light receiving element 9,
Since the light is received by the monitor light receiving element 10 and the quotient is taken by the divider 12, fluctuations in the light output from each light source can be compensated for.

However, due to fluctuations in the driving current of each light source, fluctuations in the light conversion efficiency of the light emitting element, and differences in the length of the fiber between the light emitting element and the light receiving element and between the light emitting element and the monitor light receiving element, the connection of the fiber joint may be further affected. Due to variations in the optical transmission efficiency of the fiber section due to the method, it is necessary to use a divider with a large dynamic range, and in order to obtain sufficient calculation accuracy for the entire output level of the photodetector, a high-precision analog divider or It has drawbacks such as requiring a Δ/[) converter with high resolution, resulting in high cost.

[Object of the Invention] The present invention is intended to improve the above-mentioned drawbacks of the conventional technology, and its purpose is to enable the light receiving element to maintain a constant output level in response to fluctuations in transmission loss such as fluctuations in the light source and transmission distance of the optical fiber. The object of the present invention is to provide an optical detection device that can be maintained.

[Summary of the Invention] A feature of the present invention for achieving the above object is to intensity-modulate light with a wavelength λ1 according to physical changes, and generate light with a different wavelength λ2.
a first light source that emits light with the wavelength λ1, a second light source that emits the light with the wavelength λ2, and a physical change detector that outputs the light almost as it is; an optical fiber that guides the wave, a light receiver that receives the guided output light of the optical fiber, a monitor light receiver that motors the emission intensity of each light source, and a light receiver that controls the output of the second light source to be constant. a first control means for controlling a drive current of the second light source; and a first control means for driving the first light source so that an output of the first light source at the monitor light receiving section is equal to that of the second light source. and a second control means for controlling the current, and the light receiving section output of the first light source is used as an output signal.

[Embodiment of the Invention] FIG. 2 is a block diagram showing an embodiment of an optical detection device according to the present invention, and the same reference numerals as in FIG. 1 indicate the same components.

In FIG. 2, light with a wavelength λ1 from a first light source 1 and light with a wavelength /jl2 from a second light source 2 are transmitted through an input fiber 3a,
3b, a configuration in which the light from each light source is supplied to the light receiving element 9 via the optical coupler 4, the input fiber 55, the physical change detection unit 7 and the output fiber 8, and the light from each light source is transmitted via the optical coupler 4 and the monitoring fiber 6. The configuration provided to the monitor light receiving element is the same as that shown in FIG.

In the present invention, in order to eliminate the influence on the output level of the light receiving element due to fluctuations in the drive current of the light source and fluctuations in the transmission loss of the optical fiber, the photoelectric output of the seven light receiving elements due to light emission from the second light source 2 is kept constant. The first control means controls the drive current of the second light source 2 so that the photoelectric output of the photodetector 10 is monitored by the light emission of the second light source 2. A second control means is provided for controlling the drive current of the first light source 1 so that it becomes equal to the photoelectric output of the light receiving element 10.

The first control means includes a filter 2l and a filter 21 which input the photoelectric output of the light receiving element 9 due to light emission from the second light source 2 via the amplifier circuit 20 and the switch SW-1, and take out and output the DC component. A deviation detection circuit 22 that extracts the deviation between the output and the reference power source ES, an adjustment circuit 23 that outputs an adjustment voltage that makes the deviation zero according to the deviation output of the circuit 22, and a current conversion circuit for the output of the adjustment circuit 23. The second light source 2 has a V/I conversion circuit 24 which supplies the current to the light source 2 as a drive current for the second light source 2. The second control means controls the second light source 2
A filter 26 inputs the photoelectric output of the monitor light receiving element 10 due to 0 emission through the amplifier circuit 25 and switch SW-2, extracts the DC component and outputs it, and a monitor light receiving element 10 due to the light emission of the first light source 1. Amplifying circuit 2
5 and switch SW-3, a filter 27 which takes out the DC component and outputs it, and a filter 26.
a deviation detection circuit 28 that extracts the deviation between the output from the second light source 2 of the filter 27 and the output from the first light source of the filter 27; and an adjustment circuit 28 that outputs an adjustment voltage that makes the deviation zero according to the deviation output of the circuit 28. It has two circuits and a V/I conversion circuit 30 that converts the output of the adjustment circuit 29 into a current and supplies it to the light source 2 as a drive current for the first light source 1.

The physical change detection signal increases the photoelectric output of the light receiving element 9 caused by the light emission of the first light source 1 through the multiplication circuit 20 and the switch SW4-.
It is input as the output of the filter 31 which takes out the DC component.

32 is a clock, and the aforementioned switch SW-1. SW-2
, SW-3, SW-4, and the first light source 1
Switch SWl/-5 and second light source 2 inserted in parallel to
Switch SW-6 inserted in parallel is opened and closed. clock 3
2 are switches SW-1, SW-2 and SW
-5 are provided through inverters 34, 35, and 36, respectively. Therefore, when clock 32 is turned on, SW-3
, SW-4, and SW-6 are opened, and the light source 1 of A11 is driven to emit light (the resulting light with wavelength λ1 passes through the light receiving element 9, the amplifier circuit 20, the switch SW-4, and the filter 3) 1. The signal is output through the monitor light receiving element 10, the amplifier circuit 25, the switch SW-3, and the filter 27, and is then applied to the deviation detection circuit 28.

On the other hand, when the clock 32 is off, SW-1.8W-"2
and SW-5 are in the open state, the second) light source 2 is driven to emit light, and the resulting light of wavelength λ2 is transmitted to the light receiving element 9.
, the amplifier circuit 20, the switch SW-1d and the filter 21 to the deviation detection circuit 22, and the monitor light receiving element 10, the multiplying circuit 25, the switch SW-2 and the filter 2G to the deviation detection circuit 28. It's going to happen.

The operation of the above configuration will be explained below.

When the second light source 2 is driven to emit light when the clock 32 is turned off, the fiber 3b is irradiated with light having a wavelength λ2. The photoelectric output of the light-receiving element 9 based on this light is given to the deviation detection circuit 22 of the first control means via the amplifier circuit 20, switch SW-1 and filter 21, and the monitor light-receiving element based on the light of wavelength λ2 The photoelectric output of 10 is given to the deviation detection circuit 28 of the second control means via the amplifier circuit 25, switch SW-2 and filter 26. The deviation detection circuit 22 of the first control means detects the deviation of the photoelectric output of the light receiving element 9 based on the light emission from the second light source 2 with respect to the reference power source ES. If a deviation exists, the drive current of the second light source 2 is controlled by the adjustment circuit 23 and the V/■-conversion circuit 24 so that the deviation becomes zero. As a result, fluctuations in the intensity of the light from the second light source 2 are compensated for. The deviation detection circuit 28 of the second control means detects the photoelectric output of the monitor light receiving element 10 based on the light emission of the second light source 2, and detects the photoelectric output of the monitor light receiving element 10 due to the light emission of the first light source 1 when the clock 32 is turned on. It is held until the output is given to the detection circuit 28.

Next, when the clock 32 is turned on and the first light source 1 is driven to emit light, the photoelectric output of the light receiving element 9 based on the light with the wavelength λ1 is transmitted via the amplifier 20, the switch SW-4, and the filter 31. In addition to being output as a detection signal corresponding to a physical change such as temperature or displacement, the photoelectric output of the monitor light receiving element 10 based on the light of wavelength λl is transmitted to the second filter via the amplifier circuit 25, switch SW-3, and filter 27. It is applied to the deviation detection circuit 28 of the control means.

The deviation detection circuit 28 of the second control means detects the deviation between the photoelectric output of the monitor light receiving element 10 caused by the light emission of the first light source 1 and the photoelectric output of the monitor light receiving element 10 caused by the light emission of the second light source 20. . If a deviation exists, the adjustment circuit 2
9 and the V/I conversion circuit 30 control the drive current of the first light source 1 so that the deviation becomes zero. As a result, fluctuations in the first light source 1 are compensated for.

As a result of the above-described control regarding the first light source 1 and the second light source 2, the influence on the detection signal due to transmission loss of the optical fibers 5, 8, etc. is also compensated for. That is, if a change occurs in the transmission loss of the input fiber 5 and/or the output fiber 8, the photoelectric output of the light receiving element 9 based on the light emission of the second light source 2 will naturally change in accordance with the above change. A deviation from the reference power source ES is detected by the deviation detection circuit 22 of the first control means. As a result, the drive current of the second light source 2 is controlled so that the deviation becomes zero, so the photoelectric output of the monitor light receiving element 10 based on the light emission of the second light source 2 also changes. Therefore, in the second control means, the drive current of the first light source 1 is controlled based on the photoelectric output of the monitor light receiving element 10 due to the light emission of the second light source 2, which has changed in accordance with the fluctuation of the transmission loss of the fiber. As a result, fluctuations in the light source output of the light receiving element 9 based on the first light source 1 due to fiber transmission loss are compensated for.

[Effects of the Invention] As explained above, according to the present invention, the drive current of the second light source is controlled so that the light emission power of the second light source is constant, and the light emission power of the second light source is controlled. Since the driving current of the first light source is controlled as a reference, it is possible to eliminate fluctuations in the output level of the light receiving element due to fluctuations in the light source and fluctuations in transmission loss such as the transmission distance of the optical fiber. It is possible to provide an optical detection device that does not require bullet splitting processing for compensation for such fluctuations.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a conventional optical detection device, and FIG. 2 is a configuration diagram showing an embodiment of the optical detection device according to the present invention. 1... First light source 2... Second light source 5... Input fiber 7... Physical change detection section 8... Output fiber 9... Light receiving element 10... Monitor light reception Element 21.26.27.31...Filter 22.28...
- Deviation detection circuit 23.29... Adjustment circuit 24.30... V/I conversion circuit

Claims (1)

[Claims] a physical change detection unit that modulates the intensity of light with a wavelength λ1 according to a physical change and outputs light with a different wavelength λ2 almost unchanged; a first light source that emits the light with the wavelength λ1; and a first light source that emits the light with the wavelength λ2. A second light source that emits light, an optical fiber that guides the light from these light sources via a physical change detection section, a light receiving section that receives the guided output light of this optical fiber, and a monitor that monitors the emission intensity of each light source. a light receiving section; a first control means for controlling a drive current of the second light source so that the output of the light receiving section of the second light source is constant; and an output of the first light source at the monitor light receiving section; a second control means for controlling a driving current of the first light source so that the current is equal to that of the second light source, and the output signal of the light receiving section of the first light source is used as an output signal. An optical detection device characterized by: