JPH0429969B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber application measuring device that can measure at multiple points simultaneously by connecting multiple sensors in series.

Conventionally, as this type of device, one shown in FIG. 1 has been proposed. In the figure, 1 is a light source that emits light including wavelengths λ ₀ and λ ₁ , 2 and 4 are optical fibers, and 3
5 is a sensor, 5 is an optical demultiplexer, 6a and 6b are optical fibers, 7a and 7b are photoelectric conversion devices, 8a and 8b are sample and hold amplifiers, and 9 is a divider.

The sensor 3 has a characteristic that the optical fundamental absorption edge wavelength λ _q changes depending on the physical quantity to be measured. Taking an optical temperature sensor as an example, λ _q shifts to the longer wavelength side as the temperature rises. Therefore, a combination is selected such that λ _q of the sensor 3 is between the wavelengths λ ₀ and λ ₁ of the output light of the light source 1, and the light with the wavelength λ ₀ is used as the reference light and the light with the wavelength λ ₁ is used as the signal light. By using this, it is possible to compensate for changes in light intensity in areas other than the first part of the sensor. For example, when GaAs (λ _q 0.87 mμ at room temperature) is used as the material for the sensor 3, an InGaAsP LED (λ ₀ 1.3 mμ) is used as a light source with wavelength λ ₀ where the transmitted light intensity is almost constant, and An AlGaAs LED (λ ₁ 0.87 mμ) is used as a light source for light with a temperature-dependent wavelength λ ₁ .

The light from the light source 1 passes through the optical fiber 2 and the sensor 3, and then passes through the optical fiber 4 to the optical demultiplexer 5.
By the demultiplexer 5, the light with the wavelength λ ₀ passes through the optical fiber 6a to the photoelectric conversion device 7a, and the light with the wavelength λ ₁ passes through the optical fiber 6b to the photoelectric conversion device 7b.
and each is converted into an electrical signal. Changes in the amount of light due to bending of the optical fibers 2 and 4, fluctuations in the output power of the light source 1, etc. act in almost the same way on the light of wavelengths λ ₀ and λ ₁ , so each of the photoelectric conversion devices 7a and 7b Almost the same will appear in the electrical output signal. Therefore, the output signals of the photoelectric conversion devices 7a and 7b are transmitted to the amplifier 8, respectively.
If we amplify with a and 8b and then divide with divider 9, we get
The measured quantity at the point where the sensor 3 is placed can be accurately known.

Conventional optical fiber applied measurement devices are configured as described above, so the number of sensors that can be used is limited to one per optical fiber measurement device, and when it is necessary to measure at multiple points simultaneously, ,
The required number of optical fiber measuring devices must be installed in parallel, which is disadvantageous in terms of cost.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it is an optical fiber that makes it possible to perform measurements at multiple points simultaneously by using a multispectral light source and a dichroic mirror. The purpose is to provide applied measurement equipment.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, 10 represents three wavelengths λ ₀ , λ ₁ ,
A light source that emits light of λ ₂ in time series, 2 and 4 are optical fibers, 11a, 11b and 11c are dichroic mirrors, 3a and 3b are sensors, 12a
and 12b is an optical multiplexer, 7 is a photoelectric converter, 8
a and 8b are sample and hold amplifiers, and 9 is a divider. Dichroic mirrors 11a, 11b,
11c has reflectance characteristics as shown in FIG. 4, respectively.

The light source 10 is supplied with sample timing signals S1 and S2 shown in FIGS. It is also supplied to a sample and hold amplifier 8b and a divider 9. Then, the light source 10, as shown in FIG. 3c, according to the sample timing signals S1 and S2,
Light of each wavelength λ ₀ , λ ₁ , λ ₂ is emitted sequentially in time series,
This light passes through the optical fiber 2 and enters dichroic mirrors 11a, 11b, and 11c in sequence.

Here, a "dichroic mirror" is a glass plate on which non-absorbing materials with high and low refractive indexes are alternately vacuum-deposited, and through optical interference, only reflects light in a specific wavelength range, while others Refers to a mirror that has the property of transmitting light in the wavelength range. By appropriately selecting the thickness and number of layers of the material with a high refractive index and the material with a low refractive index, the wavelength of the reflected light can be arbitrarily changed.

The first dichroic mirror 11a has a wavelength λ ₀
It has the property of reflecting only the light of wavelengths λ ₁ and λ ₂ and transmitting it as is. The light of wavelength λ ₀ reflected by this dichroic mirror 11a passes through optical multiplexers 12a and 12b in sequence, and then is guided to a photoelectric converter 7 via an optical fiber 4. Further, in the second dichroic mirror 11b, the first
The wavelength λ ₁ transmitted through the dichroic mirror 11a of
Of the light with wavelength λ 2 and λ ₂ , only the light with wavelength λ ₁ is reflected,
This light is guided to the optical multiplexer 12a after passing through the first sensor 3a. Similarly, the third dichroic mirror 11c reflects light of wavelength λ ₂ , and after passing through the second sensor 3b, this light is guided to the second optical multiplexer 12b. Sensors 3a and 3b
has _the property that the transmittance of light of a _specific wavelength changes _depending on the measured physical quantity as described above _. and λ ₂ light intensity for each sensor 3a and 3
This indicates the measured physical quantity at b,
The output signal of the photoelectric converter 7 has a waveform as shown in FIG. 3d, for example.

The output signal of the photoelectric converter 7 is converted into a sample timing signal S in a sample and hold amplifier 8a.
Therefore, as the output of the sample-and-hold amplifier 8a, a signal as shown in FIG. 3e, which is proportional to the intensity of the light having the reference wavelength λ ₀ , is obtained. In addition, in the other sample and hold circuit 8b, the output signal of the photoelectric converter 7 is sampled and held according to the sample timing signal S2, so that the output signal of the photoelectric converter ₇ is sampled and held in accordance with the sample timing signal _S2 . A changing signal as shown in FIG. 3f is output. These two signals e and f are divided by a divider 9 to obtain a signal as shown in FIG. 3g. This signal g is highly reliable as it is free from the influence of fluctuations due to factors such as a decrease in the output of the light source 11.

FIG. 5 shows another embodiment of this invention,
The light source 13 emits three wavelengths λ ₀ , λ ₁ , λ ₂ according to a timing signal S having a waveform as shown in FIG. 6a.
emit light at the same time. As in the case of FIG. 2, this light is transmitted to the dichroic mirror 11a,
The light is guided to sensors 3a and 3b via 11b and 11c, and then to an optical demultiplexer 14 via optical multiplexers 12a and 12b, where it is demultiplexed into three lights having respective wavelengths. The three separated lights are
The next photoelectric converter 15 converts each signal into an electric signal, resulting in waveform outputs as shown, for example, in FIG. The signals corresponding to the wavelengths λ ₁ and λ ₂ are sent to a multiplexer 1 operating in synchronization with the timing signal S.
7 are alternately selected and supplied to the divider 9. This divider 9 is supplied with a signal corresponding to the light of wavelength λ ₀ from the sample-and-hold amplifier 16, and therefore, by the division operation synchronized with the timing signal S, the sensor 3a and 3
A signal alternately indicating the measured physical quantity b is obtained.

In each of the above embodiments, two sensors are used, but three or more sensors may be provided.

As described above, according to the present invention, light from a multispectral light source is split into light of individual wavelengths by a dichroic mirror, and the light of each wavelength is attenuated by a sensor according to the physical quantity of the object to be measured. Since the measurement results are corrected using the light that does not pass through as the reference light, it becomes possible to perform measurements with multiple sensors simultaneously. Furthermore, the obtained measurement results are not affected by losses due to bending of the optical fiber or fluctuations in the output power of the light source, so that extremely accurate measurement values can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a conventional optical fiber applied measuring device, FIG. 2 is a block diagram showing the configuration of an optical fiber applied measuring device according to an embodiment of the present invention, and FIG. 3 shows each part of FIG. 2. 4 is a transmittance characteristic diagram of each dichroic mirror, FIG. 5 is a block diagram showing another embodiment of the present invention, and FIG. 6 is a timing chart of signals at each part of FIG. 5. It is. 2, 4... Optical fiber, 3a, 3b... Sensor, 7... Photoelectric converter, 8a, 8b... Sample and hold amplifier, 9... Divider, 10... Light source,
11a, 11b, 11c...dichroic mirror, 12a, 12b...optical multiplexer, 13...light source, 14...optical demultiplexer, 15...photoelectric converter, 1
6... Sample and hold amplifier, 17... Multiplexer. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A plurality of dichroic mirrors that reflect different wavelengths of light, a light source that emits light of a plurality of wavelengths including each wavelength of the reflected light of each dichroic mirror, and a light source that emits light from the light source to the dichroic mirror. an optical fiber that is guided sequentially, a plurality of sensors that receive reflected light from each dichroic mirror other than the first dichroic mirror, and attenuate this light in accordance with a measured physical quantity; A photoelectric converter that converts the intensity of the reflected light from the dichroic mirror 1 and the transmitted light from each of the sensors into electrical signals for each wavelength, and a sample hold that samples and holds the output signal level of each wavelength of this photoelectric converter. an amplifier;
Among the outputs of this sample-and-hold amplifier, the outputs corresponding to each of the lights transmitted through each of the above sensors are
an optical fiber application measuring device comprising a divider that divides the light reflected by the first dichroic mirror by an output corresponding to the light reflected by the first dichroic mirror.