JPS6285832A - Optical type thermometer - Google Patents

Abstract

PURPOSE:To make always stable temp. measurement with good accuracy at a low cost by constituting a photodetector of an InGaAs semiconductor. CONSTITUTION:The signal light Ls and reference light Lr radiated from respective light emitting devices 6, 10 are joined in a joining device 14 and are thereafter irradiated to a semiconductor temp. sensitive element 4 of a temp. sensor 2. The wavelength of the reference light Lr is larger than the fluctuation range at the optical absorption end of the temp. sensitive element 4 and therefore, said light transmits the temp. sensitive element 4 as it without being absorbed by said element. On the other hand, the signal light Ls receives the absorption corresponding to the temp. change of the temp. sensitive element 4 and the quantity of the light transmitted through the element is changed. The signal light Ls and reference light Lr transmitted through the temp. sensitive element 4 of the temp. sensor 2 are both detected by the photodetector 18 of the PIN photodiode constituted of the InGaAs semiconductor of the photodetector 16. The photodetection signal outputted from the photodetector 18 is transmitted to a signal processing circuit 20 of the next stage by which the external temp. is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a two-wavelength optical thermometer that utilizes temperature changes in the energy gap of a semiconductor.

(b) Prior art and its problems In general, the energy gap of semiconductors such as GaAs changes with temperature changes, and the optical absorption edge changes accordingly. For example, as shown in FIG.
5, T2, T1, and so on, the optical absorption edge shifts from the short wavelength side to the long wavelength side, such as λg1, λg2, λg3, and so on.

Therefore, for a temperature sensing element made of such a semiconductor, signal light Ls (peak wavelength λ
S), the signal light Ls changes depending on the external temperature.
Since the amount of transmitted light changes, an optical thermometer can be constructed by utilizing this phenomenon.

In an optical thermometer using such a semiconductor temperature sensing element, when the signal light Ls is used alone, the transmission may be reduced due to external factors such as loss due to bending of the optical fiber or variation in connection loss of the optical connector. Since the amount of light changes, measurement errors occur, making it impossible to accurately detect the external temperature. For this reason, conventionally, the reference light Lr (peak wavelength λr) whose wavelength is larger than the temperature fluctuation range of the optical absorption edge
A so-called two-wavelength system is adopted in which the transmitting signal light Ls is used at the same time to compensate for changes in the amount of transmitted light of the signal light Ls.

By the way, in a conventional two-wavelength optical thermometer, for example, an AlGaAs light emitting diode is used as the light emitting element for the signal light Ls, and an InG light emitting diode is used as the light emitting element for the reference light Lr.
aAs-based light emitting diodes are used, and
As a light-receiving element, a Ge-based photodiode (
PD or APD) is used. Note that Si-based photodiodes are not suitable for practical use because of poor wavelength sensitivity characteristics.

However, in the above-mentioned Ge-based light-receiving element, the dark current increases exponentially with temperature, so unless this influence is removed, accurate temperature measurement becomes impossible. For this reason, in the past, attempts were made to remove the effects of dark current by placing the light receiving element in a thermostatic chamber, or using a chopper to pulse the incident light and converting the output signal from the light receiving element to AC. However, taking such measures would not only make the device larger and more expensive, but also complicate the signal processing circuit on the light receiving side.Furthermore, with Ge-based light receiving elements, 41
There are problems such as the second row resistance is small, the noise equivalent power is large, and the SZN ratio for weak light is poor.

SUMMARY OF THE INVENTION An object of the present invention is to solve these conventional problems and to provide an optical thermometer that is inexpensive and suitable for practical use, in addition to being able to constantly measure temperature with high precision.

(c) Means for Solving the Problems In order to achieve the objects described in 2., the present invention is provided with a temperature sensor having a semiconductor temperature sensing element whose energy gap changes in response to temperature changes. ifI of
Signal light and reference light having different peak wavelengths are transmitted through the temperature sensing element, and the transmitted signal light and reference light are received by the light receiving element and the external temperature is determined based on the light intensity ratio between the two. In the two-wavelength detection optical thermometer, the light receiving element is made of an InGaAs semiconductor.

(d) Examples Hereinafter, the present invention will be explained in detail based on examples shown in the drawings.

FIG. 1 is a configuration diagram of an optical thermometer according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a two-wavelength optical thermometer, and 2 denotes a temperature sensor including a semiconductor temperature sensing element 11 whose energy gap changes in response to temperature changes. Further, 6 is a first light emitter in which an AlGaAs light emitting diode 8 for generating the signal light Ls is built in, and 10 is a second light emitter in which an InGaAs light emitting diode is built in for generating the reference light Lr. Therefore, in the case of this example, the peak wavelength of signal light Ls is 0.87 μm1 reference light Lr
The peak wavelength of each is set to 1.3 μm.

14 is the signal light Ls from the first light emitter 6 and the second light emitter 1
This is a merging device that merges the reference light Lr from 0. Also,
Reference numeral 16 denotes a light receiver that receives both the signal light Ls and the reference light Lr that have passed through the temperature sensing element 4 of the temperature sensor 2, and this light receiver 16 includes a PIN photodiode made of an InGaAs semiconductor. A light receiving element 18 is built-in. This InGaAs s semiconductor light receiving element 1
8 has a dark current of about 1nA at 25°C and 10n at 40°C.
It has the characteristics that it is extremely small at about A, has a large parallel resistance, and has a large noise equivalent power.

20 is the signal light Ls received by the light receiver 16 and the reference light Lr.
Signal light L s from each photodetection signal output based on
A signal processing circuit 22 is an optical fiber that calculates the external temperature based on the intensity ratio of the reference light Lr and the reference light Lr.

In the optical thermometer having the above configuration, the signal light Ls is output from the light emitting diode 8 of the first light emitter 6, and the reference light Lr is output from the light emitting diode 12 of the second light emitter 10 in a time division multiplexing manner. The signal light Ls and the reference light Lr emitted from each light emitter 6.10 are combined at the combiner 14, and then both are irradiated onto the conductor temperature sensing element 4 of the temperature sensor 2. At this time, since the wavelength of the reference light L'' is larger than the variation range of the optical absorption edge of the semiconductor temperature sensing element 4, it is not absorbed by the temperature sensing element 4 and is transmitted as it is.

On the other hand, the signal light Ls is absorbed in accordance with the temperature change of the semiconductor temperature sensing element 4, and the amount of transmitted light changes.

The signal light Ls and the reference light Lr that have passed through the semiconductor temperature sensing element 4 of the temperature sensor 2 are both in the InG state of the light receiver 16.
The light is received by the light receiving element 18, which is a PIN photodiode made of an aAs semiconductor. The light-receiving element 18 outputs photodetection signals corresponding to the amounts of the received signal light Ls and reference light Lr, respectively, and these photodetection signals are sent to the signal processing circuit 20 at the next stage. Therefore, the signal processing circuit 20 calculates the external temperature based on the intensity ratio between the signal light Ls and the reference light Lr. That is, now, the detection voltage based on the signal light L-s output from the light receiver 16 is Vs, and the detection voltage based on the reference light Lr is Vs.
If r, Vs=A, αC8α5(t)
(1) V r = A 2 αc t
(2) Here, A1, A are constants determined by the characteristics of the light emitting and light receiving elements and the circuit system, C5(t) is the light transmittance that changes depending on the temperature of the semiconductor temperature sensing element 4,
αC and αC3 are transmittances of light generated during transmission due to bending of the optical fiber 22, respectively. Here, the ratio of the above Vs and Vr is V. Then, Vo=Vs
/ V r−(A I/ A 2) C5(tXαc+/
αC2). In equation (3), A and SA are known values, and the signal light L during transmission through the optical fiber 22
When S and reference light Lr suffer the same loss, αc+
The ratio of /αC7 is l, so V oCca 5(t)
(4) That is, the external temperature is calculated by measuring Vo.

(f) Effect As described above, according to the present invention, the light receiving element is [r+GaA
Since it is constructed from an s-based semiconductor, characteristics such as low dark current, high parallel resistance, and high noise equivalent power can be obtained. Therefore, stable and accurate temperature measurement can be performed at all times, and an optical thermometer that is inexpensive and suitable for practical use can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an optical thermometer showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing the relationships among the optical absorption edge of the temperature sensing element, signal light, and reference destination. DESCRIPTION OF SYMBOLS 1... Optical thermometer, 2... Temperature sensor, 4... Semiconductor temperature sensing element, 18... Light receiving element.

Claims (1)

[Claims] (1) A temperature sensor having a semiconductor temperature sensing element whose energy gap changes in response to temperature changes is provided, and a signal light and a reference light having different peak wavelengths are transmitted through the temperature sensing element of the temperature sensor. , a two-wavelength optical thermometer that receives the transmitted signal light and reference light with a light receiving element and detects an external temperature based on the light intensity ratio of the two, wherein the light receiving element is made of an InGaAs-based semiconductor. An optical thermometer characterized by: