JPS62218827A - Infrared detector - Google Patents

Abstract

PURPOSE:To transmit incident infrared rays alone with a certain wavelength to match with an optical shutter with the wavelength thereof, by arranging the optical shutter to be composed of an electrooptical element and a voltage applying means for applying a cycle electric field to the element. CONSTITUTION:A plate 25 comprising an electrooptical element PLZT is sandwitched between polarizing plates 21 and 22 with the directions of polarization thereof orthogonal to each other. Two parallel grooves are formed in the plate 25 and electrodes 23 and 24 are formed in the grooves. Only components of light along the direction of polarization of the polarizing plate 21 among those reaching it are allowed to be transmitted therethrough 21 and reach the plate 25. While no voltage is applied between the grooves of the plate 25, there is no change in the direction of polarization and of the light after passing through the plate 25, none is allowed to pass through the polarizing plate 22. When a voltage is applied to the plate 25, the plate 25 turns the polarizing plane of an incident light. Thus, the light leaving the plate 25 can pass through the polarizing plate 22 by properly setting the voltage to be applied to a shift the angle of rotation of the polarizing plane to 90 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an infrared detection device, and more specifically, to an infrared detection device using an optical shutter that cuts off incident infrared rays.

<Conventional technology> Conventionally, infrared detection devices have been equipped with an optical filter that transmits infrared rays having a wavelength emitted by an object to be detected, and an optical shutter that cuts off the incident infrared rays that have passed through the optical filter, in front of an infrared detection element. There is.

In such an infrared detection device, infrared detection sensitivity can be increased by intermittent incident light by driving an optical shutter and detecting the output signal from the infrared detection element in synchronization with the intermittent operation of the shutter. .

The optical shutters used in this type of infrared detection device are: - one that uses a mechanical structure consisting of a motor and a metal disk with multiple slits to cut off the incident infrared rays, and - that has a slit for transmitting the infrared rays. There is a device that is equipped with a chopper plate and uses a piezoelectric vibrator as a driving source to vibrate the chopper plate back and forth to open and close a slit, thereby intermittent incoming infrared rays.

<Problems to be solved by the invention> In any of the infrared detection devices using an optical shutter, an optical filter that transmits infrared light in accordance with the infrared wavelength is fixed to an aperture that transmits infrared light. It was set up as follows. Therefore, if the wavelength you want to detect is different,
Since it is not possible to replace just the filter, it was necessary to replace the infrared detection device itself or prepare as many as needed.

In addition, the optical chopper with the mechanical configuration (■) uses a motor to rotate a metal disk, so it has a large volume and weight.
Moreover, power consumption also tended to increase.

In addition, the optical chopper in ■ solves the problem in ■, but
Due to long-term use of the piezoelectric vibrator, the electrodes formed on the piezoelectric vibrator may become misaligned, or the electrodes may be cut due to the growth of microcracks that occur in the piezoelectric vibrator. Characteristics may deteriorate.

Purpose of the Invention The present invention has been made in view of the above-mentioned problems, and provides a small, lightweight, and long-life optical shutter that can match the wavelength of incident infrared rays and transmit only infrared rays of that wavelength. An object of the present invention is to provide an infrared detection device having the following features.

Means for Solving the Problems> To achieve the above object, the infrared detection device of the present invention includes an optical shutter that interrupts incident infrared rays, and an infrared detection element that detects the interrupted infrared rays through the optical shutter. In the infrared detection device configured as above, the optical shutter is configured by an electro-optical element and a voltage applying means for applying a periodic electric field to the electro-optical element.

The voltage applying means may be capable of changing the bias value of the applied voltage.

<Function> With the infrared detection device having the above configuration, by applying a periodic electric field to the electro-optic element through the voltage application means, it is possible to interrupt the incident infrared rays by utilizing the electro-optic effect of the electro-optic element. .

Further, by changing the bias value of the applied voltage value, only infrared rays of a certain wavelength can be selectively transmitted.

<Example> Hereinafter, embodiments will be described in detail with reference to the accompanying drawings showing examples.

FIG. 1 is a diagram showing the structure of an infrared detection device. The infrared detection device (1) has a stem (12) made of gold a, gold ff
A cap (13) that covers and seals the stem (12) made of
), an aperture (15) formed on the top surface of the cap (13) through which light enters, an optical shutter (2) that seals the aperture (15) and cuts off infrared rays incident from the aperture (15), an infrared detection element (3), etc. It is placed inside.

Optical shell, PLZT board (25), J5J:tFPL
It is composed of polarizing plates (21) and (22) having polarization directions perpendicular to each other, sandwiching both sides of a ZT plate (25).

The infrared detection element (3) is made of a single crystal pyroelectric material such as lithium tantalate, and is mounted on a metal stem (12). Electrodes Fl (41, (4')) each having a thickness of 500 to 1000 Å made of Ni-Cr or the like are formed on the front and back surfaces of the infrared detection element (3).

The back electrode (4') is supported on the upper surface of the stem (12) by a support base (5) made of gold wA made of copper, phosphor bronze, etc.
The conductive adhesive (6), such as silver paste, is used to fix the conductive adhesive. The electrode (4') is electrically connected to the external terminal via the adhesive (6) and the support base (2).The surface electrode (4) of the infrared detection element (3) has a metal lead wire ( 9) is connected, and the other end of the lead wire (9) is connected to a conversion circuit (71) for extracting a signal to an external circuit provided on the substrate (8) made of alumina. The conversion circuit (the sword is a pyroelectric element ('2J) has a high resistance, so it is provided for impedance conversion with the outside.The conversion circuit (the force output signal is transmitted through the electrode terminal (14) The stem (12) is taken out.

The infrared rays incident through the aperture (15) are interrupted by the optical shutter (2) and are irradiated onto the surface of the infrared detection element (3).The infrared detection element (3) is made of a single crystal pyroelectric material such as lithium tantalate. Therefore, when the temperature of the pyroelectric material changes due to incident infrared rays, spontaneous polarization appears inside,
Electric charge is generated on the surface. Since the movement of this surface charge is slow, it stays on the surface for a certain period of time, and the infrared detection element (3)
It appears as a voltage between the electrodes (4) and (4') provided on both sides. That is, the electrode (4) is electrically connected to an external terminal via the lead wire (9), the substrate (8), and the conversion circuit ('7), and the electrode (4') is connected to the adhesive (6) and the support base. (5)
The voltage can be detected by connecting a load to both terminals.

However, since the electric charge generated on the surface of the pyroelectric body is transient, the output voltage cannot be detected when the temperature of the pyroelectric body changes and reaches a steady state. Therefore, in order to obtain continuous output, it is necessary to intermittent the incident infrared rays at regular intervals to change the temperature of the pyroelectric material. For this purpose, an optical shutter is used to cut off the incident infrared rays.

The operation of the optical shutter of the present invention will be explained in detail below.

FIG. 2 is a diagram showing the principle of an optical shutter. An electro-optical element P L Z T ((Pb, La) (Zr, Ti
)03) is sandwiched between the plates (25). PLZ
As shown in FIG. 3(A), two grooves parallel to each other are formed in the T-plate (25). The depth J of both grooves is 800 μm, and the distance d between both grooves is 400 steps. 2
Electrodes (23) and (24) are formed in the grooves of the book, and when light passes between the grooves, the light undergoes a change in refractive index due to the electro-optic effect. . In addition, the electrodes (23) and (24) are P as shown in FIG. 3(B).
It may also be two planar electrodes formed on the top surface of the LZT plate (25).

The light that has passed through the aperture (15) contains light in all polarization directions before passing through the polarizing plate (21), but only the component of light along the polarizing direction of the polarizing plate (21) passes through the polarizing plate (21). (21) and reaches the PLZT plate (25).

In PLZT, when no voltage is applied between the grooves of the PLZT plate (25), there is no change in the polarization direction even after the light passes through the PLZT plate (25) because PLZT is an isotropic medium. Therefore, the light that has passed through the PLZT plate (25) does not pass through the polarizing plate (22) because its polarization direction is perpendicular to the polarizing direction of the polarizing plate (22).

Next, when voltage V is applied to the PLZT plate (25), PL
ZT acts like a uniaxial optically anisotropic medium and rotates the plane of polarization of incident light. Therefore, PLZT board (25)
If the rotation angle Δφ of the polarization plane is set to π/2 by appropriately setting the voltage V applied to the PLZT plate (25
), the polarization direction of the light is perpendicular to the polarization direction of the polarizing plate (22), and the light can pass through the polarizing plate (22).

Here, the light 111 passing through the polarizing plate (22) is expressed by the following equation.

1=Ksin 2(Δ$/2) = (1/2)K (1-cos(θ1πV/vλ/
2) ■) Vλ/2=λod/n, 3rcJ
(I) However, ■ is the applied voltage, Δφ is the phase shift that light undergoes in the crystal, λ0 is the wavelength of light, no is the normal refractive index of PLZT, n is the extraordinary refractive index, r and r are e
33 13 Each component of the electro-optic tensor of PLZT. θ, r
is determined by the following equation.

θ= 2πJ(n□−n,)/λ0 r=r−(no/no) '13■AI
□ is determined by the wavelength of light, the electro-optical constant, and the dimensions of the PLZT plate, and is the applied voltage that can obtain the maximum transmission wavelength (hereinafter referred to as "half-wave voltage").

From equation (1), by setting Vλ/2 according to the wavelength of light, etc., and changing the applied voltage V around the half-wave voltage ■A/2, it is possible to change the light ff1I according to equation (I). . K is the light transmittance of PLZT when no voltage is applied at the wavelength.

FIG. 4 is a graph showing the wavelength dependence of light transmittance. From the figure, it can be seen that PLZT transmits infrared rays in the wavelength range of 0.5 to 7/a, so it can be effectively used in this wavelength range. Note that even in the wavelength range of 0.5 to 1p, there is a loss of 20 to 30% due to reflection on the PLZT plate surface, which corresponds to K in the above formula.

FIG. 5 is a graph showing the relationship between the light transmittance and the applied voltage (2) when the incident infrared ray has a wavelength of the absorption infrared ray (wavelength 3.3μ peak) of 0114 gas. In this case, each religion on the PLZT board is n.

-2,5, n = 2.505, ro = 6.12
x1G (m/V), J = 800/ffi, d
= 400/7m. From the same figure, the half-wave voltage is 17
It turns out that the voltage is 2V.

Curve (a) in Figure 6 shows that a half-wave voltage is set for infrared light with a wavelength of 3.3-, and the half-wave voltage is fixed as it is.
It is a graph showing changes in light transmittance when changing the wavelength of light. Curve (b) in Figure 6 shows that a half-wavelength voltage is set for infrared light with a wavelength of 6° and 2μ, the half-wavelength voltage is fixed, and the wavelength of the light is changed! It is a graph showing changes in light transmittance in different cases. As described above, since the optical shutter is used as an optical filter and the half-wave voltage can be set according to the center wavelength of the incident infrared rays, it is possible to always obtain a highly sensitive infrared detection device regardless of the center wavelength of the incident infrared rays.

FIG. 7 is a graph plotting the change in half-wave voltage with respect to the wavelength of incident infrared rays.

Next, an example in which the infrared detection device of the present invention is applied to a gas sensor will be explained using FIG. 8.

This gas sensor has a radiation source (for example, a nichrome heater) that has a radiation wavelength corresponding to the absorption wavelength of the gas to be measured.
31). A reflection 1 (32) is arranged with the position of the radiation source (31) as a focal point. Both sides of the gas box (33) filled with the gas to be measured are sealed with plates (36) and (31) made of, for example, 3i, which transmit infrared rays. The gas to be measured is introduced into the gas box (33) through the gas introduction hole (38), and is introduced into the gas box (33) through the gas exhaust hole (38).
39). A concave reflecting mirror (34) is arranged on the other side of the gas box (33), and an infrared detection device (35) of the present invention is arranged at its focal plane. The light of the infrared detector (35)! The center wavelength of the ivy is matched to the infrared absorption wavelength of the gas sealed inside the gas box (33).

Pulse voltages of, for example, 172V and 0V are alternately applied to the optical shutter by an optical shutter drive circuit (40). The output from the infrared detection element is detected by an output signal processing circuit (41).

The infrared rays emitted from the radiation source (31) are reflected &1l (32)
It is reflected by the gas box (3
Pass through 3). At this time, infrared rays having a wavelength equal to the absorption wavelength of the gas filling the gas box (33) are mostly absorbed. For example, when the gas is CH4, infrared rays with a wavelength of 3.3In are absorbed. As a result, the light reaching 114 m (34) no longer contains the above wavelength component, so the infrared light D that enters the infrared detection device t (35) located at the focal point of the reflecting mirror (34) decreases. do. For this purpose, an output signal processing circuit (4
1) The amount of signal detected changes, and as a result, the gas to be detected can be detected.

In this gas sensor, the center wavelength of the transmitted infrared rays of the optical shutter can be changed by adjusting the voltage applied to the optical shutter depending on the type of gas to be detected. For example, -a carbon (center wavelength of absorption spectrum is 4.7
μ layer), the half-wavelength voltage may be set to 245V, and in the case of zisso dioxide (center wavelength of absorption spectrum is 6.2ua), the half-wavelength voltage may be set to 323V.

In addition, as shown in FIG. 9, for example, in the above explanation, the example voltages 172V, 245V, 323V (7)
3. (7) By combining and alternating half-wave voltages, one gas detection device can simultaneously detect CH4 gas, CO gas, and NO gas using the same infrared detection device.
Two gases can be detected.

It should be noted that the present invention is not limited to the above-mentioned embodiments; for example, by changing the arrangement of the crystal axes of the electro-optical element (25),
Transparent planar electrodes may be formed on both sides of the element, and infrared light may be modulated by passing through the planar electrodes perpendicularly. Various other design changes may be made within the scope of the invention. It is possible to apply

<Effects of the Invention> As described above, the present invention provides a compact and
By using a lightweight and long-life optical shutter, the transmitted infrared rays can be interrupted by changing the applied voltage.
By applying an applied voltage according to the wavelength of the transmitted infrared rays to the above-mentioned applied voltage, a unique effect is achieved in that sensitivity characteristics can be realized according to the wavelength of the incident infrared rays.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the structure of the infrared detection device of the present invention, Fig. 2 is a diagram of the principle of the optical shutter, and Fig. 3 (^) and Fig. 3 (B) are diagrams of the electrodes formed on the PLZT board. , Fig. 4 is a graph showing the wavelength dependence of the light transmittance of the PLZT board, Fig. 5 is a graph showing the change in light transmittance with respect to the applied voltage of the optical shutter, and Fig. 6 is a graph showing the wavelength characteristics of the light transmittance. Figure 7 is a graph showing the wavelength dependence of half-wave voltage; Figure 8 is a diagram showing the structure of a gas detection device using the infrared detection device of the present invention; Figure 9 is a graph showing the wavelength dependence of the half-wave voltage; Applied voltage waveform to detect. (1)...Infrared detection device, (2)...Optical shutter, (3)...Infrared detection element, (25)...Electro-optical element.

Claims (1)

[Claims] 1. Optical shutter that intermittents incident infrared rays, Detects infrared rays that pass through the light and optical shutters. Infrared rays composed of infrared detection elements In the detection device, the optical shutter Electro-optical elements and surrounding electro-optical elements. by means of voltage application that applies a periodic electric field. Infrared detection characterized by consisting of Device. 2. The voltage applying means is configured to bias the applied voltage. The above features that can change the Infrared detection device according to claim 1 Place.