JPS59119225A - Light applied sensor - Google Patents

Abstract

PURPOSE:To improve a measurement range and linearity by generating a series of light emission spectra by such plural light sources for measurements that center wavelengths of light emission are different from one another and light emission spectra overlap one another successively. CONSTITUTION:For example, light from the light sources 12-14 for measurement such as LEDs and semiconductor laser, etc. are received by fibers 15a-15c. The light from the respective light sources including a reference light source 2 is guided to a single input fiber 5. The light sources 12, 13, and 14 have different center wavelengths lambda1, lambda2, and lambda3 of light emission and then their light emission spectrum distribution overlap one another successively. Further, lambda1<lambda2<lambda3. Consequently, when the transition of an absorption terminal occurs from the center wavelength lambda1 of light emission to the lambda3, the quantity of photodetection by a photodetecting element 9 is nearly linear to temperature variation.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an optical sensor using a semiconductor material whose optical absorption edge changes in response to changes in physical quantities such as temperature or pressure, and which is used, for example, in temperature measurement. can do.

[Technical Background of the Invention] FIG. 1 shows a configuration diagram of a conventional temperature sensor based on this kind of principle.

In the figure, 1 is a measuring light source having an emission spectrum with an emission center wavelength of λ, 2 is a reference light source having an emission spectrum with an emission center wavelength of λ0, 3a and 3b are each light source 1,
2 is a fiber that receives and enters light, 4 is each fiber 3a,
3b is an optical coupler that guides the guided light from the input fiber 5 to a single input fiber 5; 6 includes a semiconductor material 7 whose optical absorption edge changes according to temperature changes;
9 is a light-receiving element that receives guided light from the output fiber 8 . The sensor body 6 includes a supporter 10 that holds the input fiber 5 and the output fiber 8 so that they face each other with the semiconductor material 7 in between, and a holder 11 with good thermal conductivity that holds the semiconductor material 7. have

The relationship between the emission spectrum of each of the light sources 1 and 2 and the optical absorption edge (hereinafter referred to as absorption edge) of the semiconductor material 7 is shown in FIG. In Figure 2, (a) is the emission spectrum of the measurement light source 1, (b) is the emission spectrum of the reference light source, (α),
(β) and (γ) indicate the absorption edge characteristics of the semiconductor material 7 as the temperature changes.

The emission spectrum (a) of the measurement light source 1 has a wavelength that overlaps with the transition of the absorption edge as the temperature changes in the semiconductor material 7, while the emission spectrum (b) of the reference light source 2 has a wavelength that overlaps with the transition of the absorption edge as the temperature changes. It has a wavelength that is not affected by changes in the absorption edge. The absorption edge of the semiconductor material 7 shifts toward longer wavelengths from (α) to (β) to (γ) as the temperature increases. This is because the energy gap (Eg) of the semiconductor material decreases as the temperature rises, and the absorption edge wavelength (λ0=2πh/Eo, h Niblank constant), which is closely related to this, increases. The amount of light transmitted through the semiconductor material 7 is proportional to the amount of light corresponding to the portion surrounded by the emission spectrum (a) and the absorption edge, and as the temperature rises, the absorption edge will appear on the longer wavelength side outside the distribution width of the emission spectrum (a). As the temperature shifts, it becomes zero, and as the temperature decreases, the absorption edge shifts to the shorter wavelength side outside the 945 width, and becomes the maximum.

Next, temperature measurement using the temperature sensor having the above configuration will be explained.

First, the reference light source 2 is caused to emit light, and the amount of light received by the light receiving element 9 is subjected to Δ/D conversion and then held. Next, the measuring light source 1 is caused to emit light, and the amount of light received through the semiconductor material 7 is A/D converted, and then divided by the amount of received light of the held reference light, and the quotient is used as temperature information. Output as .

As described above, the amount of measurement light received follows the change in the absorption edge of the semiconductor material 7 due to temperature change, so temperature can be measured based on the change in the amount of received light.

Note that the reason why the amount is divided by the amount of received reference light is to compensate for effects such as changes in fiber loss.

[Problems with background technology] The temperature sensor having the above configuration has the following drawbacks.

Since the emission spectrum of a semiconductor light source such as (+) LED has a narrow emission wavelength range, the overlapping range with the absorption edge of the semiconductor material is narrow, and therefore the measurement range is narrow.

(2) Since the emission spectrum of LEDs, etc., deviates from the emission center wavelength, the amount of light decreases rapidly, so as shown in Figure 3, the amount of light received by the light receiving element 9 with respect to temperature changes is determined by a slight temperature change from a certain temperature. This results in large fluctuations and poor linearity, and as a result, an amplifier with a very large dynamic range is required on the light receiving side.

Such problems occur not only in temperature measurement but also in detecting changes in other physical quantities from the light absorption edge of a semiconductor.

``Object of the Invention'' The present invention is intended to improve the above-mentioned problems of the conventional technology.The purpose of the present invention is to have a wide measurement range, prevent sudden changes in the amount of received light with respect to changes in the physical quantity to be measured, and further reduce the amount of received light. An object of the present invention is to provide an optical sensor capable of making the rate of change substantially uniform, that is, improving linearity.

[Summary of the Invention] A feature of the present invention for achieving the above object is that the present invention includes a light source having an emission spectrum with an almost uniform emission wavelength, and a semiconductor material whose optical absorption edge wavelength changes in accordance with changes in physical quantities. An optical application sensor having a sensor body, an optical fiber that guides the light from the light source through a semiconductor material of the sensor body, and a light receiving element that receives the guided light of the fiber,
A plurality of the light sources are configured so that each light source has a different emission center wavelength and their emission spectra partially overlap one another, and the optical absorption of the semiconductor material is added to the series of emission spectra from each light source. In addition to the above-mentioned characteristics, it is preferable that the emission center wavelength of each light source is such that the sum of each emission spectrum is the maximum of the emission center wavelengths. The above-mentioned optical sensor is selected so as to give a substantially flat spectrum between the maximum and the minimum.

[Embodiment of the Invention] FIG. 4 is a configuration diagram of a temperature sensor showing an embodiment of the present invention. In the figure, reference numerals 12, 13, and 14 indicate measurement light sources such as LEDs or semiconductor lasers, whose emission center wavelengths have substantially the same emission spectrum, and 15a, 15b, and 15c.
16 is a fiber that receives and receives the light from each light source, 16 is an optical coupler that guides the light from each light source including the reference light source 2 to a single input fiber 5, and the other components are the same as those in FIG. It is.

The relationship between the emission spectra of each measurement light source 12, 13, and 14, and the emission spectra of these light sources and the semiconductor material 7
The relationship between the absorption edge and the absorption edge is shown in FIG.

In FIG. 5, (c) is the emission spectrum of the first measurement light source 12 having the emission center wavelength λ1, (d) is the emission spectrum of the second measurement light source 13 having the emission center wavelength λ2, and (d) is the emission spectrum of the second measurement light source 13 having the emission center wavelength λ2. ) is the emission spectrum of the third measuring light source 14 that corresponds to the emission center wavelength λ3. As mentioned in Figure 2, (b) is the emission spectrum of the reference light source, (α
).

(β) and (γ) are absorption edge characteristics of the semiconductor material 7.

As shown in FIG. 5, the measurement light sources 12, 13, and 14 have different emission center wavelengths λ1, λ2, and λ3.
Furthermore, the respective emission spectrum distributions are in a relationship in which they partially overlap in sequence. Emission center wavelength λ1.

The relationship between λ2 and λ3 is λ1<λ2<λ3.

As shown in Fig. 6, these emission center wavelengths λ1, λ2, and λ3 are such that the sum of each emission spectrum is approximately between the maximum (λ3) and minimum (λ1) of the respective emission center wavelengths. It is desirable to select such that it gives a flat-11 spectrum. As a result, from the emission center wavelength λ1 to 23
When the absorption edge changes between 1 and 2, the amount of light received by the light receiving element 9 has a characteristic that is almost linear with respect to temperature changes, as shown by the solid line in FIG. Note that the broken line in FIG. 7 indicates the characteristics in FIG. 3. Returning to FIG. 5, the relationship between each measurement light source 12, 13, 14 having the above relationship and the absorption edge of the semiconductor material 7 is as follows:
A series of emission spectra (c) and (d) from each light source
, (e) are constructed so that the transition ranges of the absorption edge due to temperature changes overlap. As a result, temperature measurement becomes possible in the range from the shortest emission wavelength of the emission spectrum (c) to the longest emission wavelength of the emission spectrum (e).

As the cliff conductor material 7, Cd Te (absorption edge wavelength at 300° 0.85 flm>), Ga As (
300”K absorption edge wavelength o, 911m), T
n P (absorption edge wavelength at 300° 1.00 tim)
, Si (300'K absorption edge wavelength 1.127
1m), Ge (absorption edge wavelength at 300° 1.8
7 μm) etc. are available. As the semiconductor material 7,
For example, instead of using CdTe or GaAS, for example GaAst-
XPX-based and/or AQxGa+-xAS-based IFDs can be used. The QaAsh-XPX system can obtain light with an emission center wavelength of 0.65 to 0.9 μm by selecting the value of 7) Since light having a central emission wavelength can be obtained, a semiconductor material and a measurement light source that satisfy the conditions shown in FIG. 5 can be used.

Next, measurements by the temperature sensor having the above configuration will be explained using FIGS. 8 and 9.

FIG. 8 shows a configuration diagram of a measurement system using the above-mentioned sensor, where 20 is the temperature sensor explained in FIG. 22 is an optical power meter that measures the amount of light received by the light receiving element 9; 23 is an A/D' converter that converts the amount of light measured by the optical power meter 22 into a digital amount; 24 is a processing system; is the reference light source 2 and each measurement light source 1
2゜1'3.14 has a function to increase the drive timing by 5, a function to hold the received light amount according to the drive timing, and a function to add the received light amount of each measurement light and use the added value as the received light amount of M single light. It has a function to convert the divided quotient into temperature information and output it.

Figure 9 shows the reference light source 2 and each measurement light source 12°13.1
/I shows one sheet of drive timing groove, <a>
is the drive time of the reference light source 2, (b) is the drive time of the first measurement light source 12, (C) is the drive time of the second measurement light source 13, and (d) is the drive time of the third measurement light source 14. driving time, (e
) indicates the amount of light received by the light receiving element corresponding to the driving of each light source.

Temperature measurement is started by driving the reference light source 2. As described above, the reference light source 2 has an emission spectrum of a wavelength that is not affected by light absorption by the semiconductor material 7. The reference light source 2 is activated to emit light from time t1 to t2! 11.

On the light receiving side, the received light amount Pλ0 of the reference light is received by the light receiving element 9, measured by the optical power meter 22, converted into AID, and held. Following the emission of the reference light source 2 and the end of the time, the first measurement light source 12 is emitted during the time period 12 to 1°3.
The second measurement light source 13 emits light between times t3 and t4, and the third measurement light source 14 emits light between times t4 and t5. Reception of each measurement light @Pλ1.

Pλ2 and Pλ3 are held as in the case of the reference light. At the end of holding each measurement light, the processing system 24
Addition of the received light amount of each measurement light, Pλ1+Pλ2+Pλ3. and divide the added value by the amount of received reference light, (Pλ+
+Pλ2+Pλ3)/PλO, L/After compensating for the influence of fiber loss changes, etc., the temperature information is converted and output.

Note that in the measurement system shown in Figure 8, the amount of received light of the reference light and each measurement light is A/D converted and the sum of the amounts of each measurement light is calculated. It is also possible to integrate the quantity.

FIGS. 10, 11, and 12 are configuration diagrams of a temperature sensor without showing other embodiments of the present invention, and the same reference numerals as in FIG. 4 do not indicate the same constituent parts.

In the embodiment shown in FIG. 10, 25 indicates a directional coupler, which connects the optical coupler 16 to the fiber 2.
6, the reference light and each measurement light are inputted, most of the light is guided to the measurement fiber 27, and a part of the light is sent to the monitoring fiber 28. The reflected light guided through the fiber 27 is guided to the output fiber 29. The measuring fiber 27 is coupled to the sensor body 30. The sensor body 3o has an output fiber 2
a semiconductor material 7 facing the end face of the fiber 27 , a reflective mirror 31 facing the end face of the fiber 27 across the semiconductor material 7 , a supporter 32 that holds the fiber 27 , and a heat source that holds the semiconductor material 7 and the reflective mirror 31 . It has a holder 33 with good conduction, and the guided light from the light source of the measuring fiber 27 passes through the semiconductor material 7, is reflected by the mirror 31, passes through the semiconductor material 7 again, and is sent out to the measuring fiber 27. The reflected waveguide light from the measurement fiber 27 is guided to the output fiber 29 via the directional coupler 25 and reaches the light receiving element 9 . The monitor fiber 28 has a monitor light receiving element 3.
4, and it is possible to stabilize the light emitting state by using output No. 5 of the element that monitors the light emitting state of the light source. Temperature measurement using the sensor having such a configuration is carried out in accordance with FIGS. 8 and 9, as in the previous embodiment.

In the embodiment shown in FIG. 11, 35 is a dedicated input fiber provided in the reference light source 2, 35a, 35b.
and 35c are dedicated input fibers provided for each measurement light source 12, 13, and 14, respectively; 37 is the sensor body; 3
8 is a single, large diameter output fiber. Each of the input fibers 35.degree. 36a, 36b, and 36c is formed into a fiber bundle 39 and arranged so as to face the output fiber 38 with the semiconductor material 7 sandwiched therebetween within the sensor body 37.

The output fiber 38 has an aperture capable of receiving the emitted light from each input fiber through the semiconductor material 7. In the sensor body 37, 40 is a supporter that holds the input fiber bundle 39, 41 is a supporter that holds the output fiber 38, and 42 is a holder with good heat conduction that holds the semiconductor material 7. Humidity measurement using a sensor having such a configuration is also carried out in accordance with FIGS. 8 and 9, as in the previous embodiment. Note that the configuration of this embodiment allows the sensor to be configured without using an optical coupler, resulting in low manufacturing costs and high mass productivity.

In the embodiment shown in FIG. 12, the output fiber in the configuration of FIG. 11 is replaced by the input fiber 35, 36a,
36b, 36C, each light source 2°12; 13.1
4 respectively dedicated fibers 45, 46a, 46 corresponding to
b, 46C, with 4 light receiving elements for each output fiber.
7.48.49.5o. Each output fiber 45° 46a, 46b, 46c is made into a fiber bundle 44 in the same way as the input fiber, and the semiconductor material 7 is sandwiched between the input and output fibers in the sensor body 43. They are provided in a 1:1 ratio.

, the supports for the fiber east 39, 44 and the holder for the semiconductor material 7 are the same as in the case of FIG. The configuration of this embodiment does not use a large-diameter fiber compared to the configuration shown in FIG. 11, so there is less light transmission loss, which is advantageous when light must be transmitted over a long distance.

FIG. 13 shows a driving timing chart of the reference light source and each measurement light source, which is different from FIG. 12 drive time, <C> is the drive time of the second measurement light source 13,
(d> is the driving time of the third measurement light source 14, (e) l
;l; When measuring the amount of light received by the light receiving element -0 -C
1. First, the reference light source 2 is driven with the development light from time t1 to t2, as in the case of FIG. 9. However, each subsequent measurement light source 12. Regarding -13.14, unlike the case in Figure 9, each measurement light source is driven to emit light at the same time between times 12 and 3. As a result, the amount of light obtained by the light receiving element is equal to the amount of light received by each measurement light. sum, Pλ+ +
Pλ20 Pλ3. Therefore, there is no need for addition, and the temperature can be measured using the time t1 to t3 as one cycle, so the measurement time can be shortened compared to the case of FIG. 9.

In each of the above embodiments, the case where there are three light sources for measurement has been described, but it is also possible to combine more light sources so as to satisfy the above-mentioned conditions required for each light source, and this allows for even more light sources to be used. A sensor with a wide measurement range can be realized.

[Effects of the Invention] As explained above, according to the present invention, a plurality of measurement light sources are provided, each having a different emission center wavelength and whose emission spectra partially overlap in sequence, and each light source forms a series of emission spectra. As a result, it is possible to provide a sensor with a wider measurement range compared to conventional sensors, and it is also possible to improve linearity compared to conventional sensors, resulting in a wider dynamic range on the light receiving side. It is not necessary to make the signal large, and it is possible to measure changes in physical quantities with a high S/N ratio.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a conventional optical sensor, Fig. 2 is an explanatory diagram of the operation of the sensor in Fig. 1, Fig. 3 is an explanatory diagram of the relationship between humidity and the amount of light received by the sensor in Fig. 1, and Fig. 4 5 and 6 are diagrams illustrating the operation of the sensor in FIG. 4, and FIG. 7 is a diagram showing the relationship between the temperature and the amount of light received by the sensor in FIG. 8 is a configuration diagram of a measurement system, FIG. 9 is a drive timing chart of each light source, and FIGS. 10, 11, and 12 are diagrams showing other embodiments of the present invention. FIG. 13 is a configuration diagram of a temperature sensor showing an example, and is another drive timing chart of each light source. 12.13, 14: Measurement light source 6.30.37.43: Sensor body 7: Semiconductor material 5, 8.15a, 15b, 15c, 3b, 26
゜27.29, 35.36a, 36b, 36C, 3
8, 45, 46a, 46b, 46c: Fiber 9
．． 47, 48. 49, 50: Light receiving element Figure 1 Figure 2 Figure 3vA Figure 4 Figure 5

Claims (2)

[Claims] (1) A sensor body including a light source having an emission spectrum with a substantially single emission wavelength, a semiconductor material whose optical absorption edge wavelength changes according to changes in physical quantities, and a semiconductor material of the sensor body that uses the light from the light source to an optical fiber that guides the wave through the
In the optical sensor having a light-receiving element that receives the guided light of the optical fiber, a plurality of the light sources are arranged so that each light source has a different emission center wavelength and the emission spectra sequentially partially overlap each other. Additionally, an optical sensor is configured such that an optical absorption edge of the semiconductor material overlaps a series of emission spectra from each of the light sources. (2) Set the emission center wavelength of each of the light sources so that the sum of each emission spectrum gives a substantially flat spectrum between the maximum and minimum emission center wavelengths,
An optical application sensor according to claim 1.