JPS61260227A - Infrared light controlling method using ferroelectric liquid crystal - Google Patents

Abstract

PURPOSE:To control effectively the transmission and the reflection of the infrared light by sandwiching a ferroelectric liquid crystal between electrodes and impressing a voltage between electrodes. CONSTITUTION:In a call having a very simple construction which sandwiches a ferroelectric liquid crystal 2 between two electrode plates 1 and is provided with a driving electric power source 4, the voltage may be impressed between both electrodes. Thus, the transmission, reflecting, etc., of the infrared ray can be controlled. When the double refraction, or the optical activity of the infrared light is used, the element constructed to arrange a polarizer 3 at the front side or the front/rear side of the cell may be used. Actually, besides these electrode plates and the polarizer, the construction material or protective material is included in a case as a cell supporting body. In case of the transmitting type element, both electrode plates and in case of the reflecting type element, at least one side electrode plate is necessary to have permeability for the infrared light to control. In the transmission factor of the infrared light, the higher factor is desirable, and especially, it is not limited.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is used in the fields of optical communications, various sensors, energy applications, etc., and is used to control transmission, reflection, etc. switches, modulation, etc. of infrared light. Concerning how to do.

[Prior art]

In recent years, high-speed, high-precision transmission, processing, recording, etc. of large amounts of information have become extremely important, and therefore optoelectronics that use light in this information-related technology has begun to develop significantly. As light used for such purposes, it is considered appropriate to use light in the infrared region due to the transmission characteristics of optical fibers used for light transmission, efficiency of light emitting elements, manufacturing issues, etc. ing. On the other hand, so-called infrared sensing technology, which uses infrared rays to detect and analyze people, objects, etc., is becoming highly developed, as is the case with infrared photography from door opening/closing monitors and artificial hygiene. In other words, high-speed,
Highly accurate control of switches, modulation, etc. is required.

Conventionally, various methods have been used to control infrared light, such as a mechanical shutter method and a combination of a polarizer and a Bockel element, but these methods are not very fast, are large-scale, and require extremely high driving voltage. It has disadvantages such as being expensive. Therefore, there has been a demand for an infrared light control element that is fast, has a simple structure, has a low driving voltage, and is inexpensive.

On the other hand, it is well known that there has been significant progress in nematic liquid crystal technology in recent years, resulting in revolutionary changes in optical elements, devices, and the like. Liquid crystals that utilize light in the visible range in such devices include TN type, DSM type, and the like. However, since the driving principle of these nematic liquid crystals is based on the anisotropy of the dielectric constant of liquid crystal molecules, it has been difficult to increase the speed. However, recently, smectic liquid crystals that exhibit ferroelectricity,
So-called ferroelectric liquid crystals have been developed and are attracting much attention as they can be used to realize high-speed display devices. However, all of these have been researched targeting light in the visible range, and there has been no idea of using them to control light in the infrared range.

[Purpose of the invention]

Therefore, it is an object of the present invention to provide an effective method for controlling the transmission or reflection of infrared light.

[Structure of the invention]

As a result of intensive research, the present inventors discovered for the first time that ferroelectric liquid crystals exhibit excellent operating characteristics even with respect to light in the infrared region. The present invention attempts to control the transmission or reflection of infrared light by utilizing the excellent operating characteristics of this ferroelectric liquid crystal.

That is, the present invention is a method for controlling transmission or reflection of infrared light by sandwiching a ferroelectric liquid crystal between electrodes and applying a voltage between the electrodes.

The present invention will be described in detail below with reference to the accompanying drawings.

In order to carry out the method of the present invention, for example, as shown in FIG. In the cell, a voltage may be applied between both electrodes. Thereby, transmission, reflection, etc. of infrared light can be controlled. Further, as shown in FIG. 1, etc., when utilizing the birefringence or optical rotation of infrared light, an element having a structure in which a polarizer 3 is disposed in front of or behind the cell may be used. Of course, in reality, in addition to these electrode plates and polarizers, a structural material protecting material as a cell support may also be included.

In the case of a transmissive element, both electrode plates must be transparent to the infrared light to be controlled, and in the case of a reflective element, at least one electrode plate must be transparent to the infrared light to be controlled.

The transmittance of infrared light is preferably higher, but is not particularly limited. When relatively near-infrared light is controlled, these electrode materials may be NESA (i.e., coated or vapor-deposited with metal oxides such as InzO!l, Sn02, etc.) glass, quartz plate, or plastic plate. However, it is also possible to use a substrate coated with a conductive material such as metal by some means such as vapor deposition or painting. Furthermore, when controlling infrared light in a long wavelength range, various semiconductors such as Si and Ge can be used directly. As described above, in the present invention, any material can be used for the electrode plate as long as it is transparent to the infrared light to be controlled and is conductive, and is not limited to any particular material. .

The operating modes of ferroelectric liquid crystals include those that utilize relatively thick cells, solve the helical structure unique to ferroelectric liquid crystals, and utilize changes in the amount of infrared light transmitted when uniformly aligned.
Or TSM type (for example, Yoshino et al., [Laser Research J 1
2 (1984) 30), the polarity of the electric field in a device that is uniformly oriented and in a highly transparent state is reversed by applying an electric field, and intense molecular movement occurs until the device settles into a new uniformly oriented state in the opposite direction due to the reversal of spontaneous polarization. In addition, in a thin cell of several μm or less, the amount of transmission can be increased by using the change in birefringence that occurs when the orientation forced on the wall surface is reversed by applying an electric field, and by combining it with a polarizer. However, the present invention is characterized by the combination of a ferroelectric liquid crystal cell and infrared light, and is not limited to any particular operation mode.

The ferroelectric liquid crystal used in the present invention is not limited to any particular molecular structure as long as it is transparent in the infrared region. In other words, various ferroelectric liquid crystals including Schiff-based, bifer-based, and ester-based liquid crystals that have been developed so far (for example, Yoshino: Functional Materials 5 (1985)
)16) can be used. In the present invention, any ferroelectric liquid crystal that transmits infrared light can be made stronger by itself, or as a mixture of two or more types, by adding impurities, or by mixing non-ferroelectric materials. All materials exhibiting dielectric properties can also be used.

For example, in Figure 2, P-decyloxybenzylidene-P'-
Amino-2-methylbutylcinnamate (DOBAMB)
C) Figure 3 shows an example of the infrared transmission spectrum of a biphenyl-based mixed ferroelectric liquid crystal, and it can be seen that it can be used in a fairly wide infrared wavelength range. Specific examples of ferroelectric liquid crystals that can be used in the present invention are shown below.

However, the liquid crystal used in the present invention is not limited to these specific examples.

==- This j ==The method of applying the driving voltage to the ferroelectric liquid crystal is not limited to any particular method.

〔Effect of the invention〕

According to the infrared light control method using ferroelectric liquid crystal according to the present invention, control operations such as switching and modulation of light in the infrared region can be performed at extremely high speed. It can be used in various infrared light application fields, such as infrared energy application fields.

Furthermore, the elements used to carry out the present invention can be faster, smaller, more compact, more reliable, and driven at lower voltages than conventional elements, and have a simpler structure and lower cost. Furthermore, it can be applied to new fields that could not be applied to conventional low-speed devices, and can be used in new ways, such as in the dark as well as in bright places, or at night.

As described above, it is inevitable that the present invention will have a great impact on these infrared light application fields.

〔Example〕

Examples of the present invention will be shown below, but the present invention is not limited to these Examples.

Example 1 Two transparent conductive quartz plates coated with lTl2O3 on the surface of the quartz plates were placed facing each other, a Teflon sheet with a thickness of 100 μm was used as a spacer around the quartz plates, and a ferroelectric liquid crystal DOBAMBC was placed in this cell. Insert, thickness 100μ
m elements were created.

The surface of the conductive quartz plate was subjected to a rubbing treatment in advance. In this state, the ferroelectric liquid crystal within the element has a helical structure, so light scatters and the amount of transmitted light is extremely small.

When a DC voltage was applied to this, the amount of transmitted light increased significantly when a voltage of 50 V or higher was applied. This is because scattering is reduced due to the change to uniform orientation. FIG. 4 shows the relationship between the applied voltage and the contrast of transmitted infrared light of various wavelengths. Contrast is the amount of transmitted infrared light when voltage is applied■
and the amount of transmitted infrared light when no voltage is applied! 0 ratio I/I
It is defined as o.

That is, it can be seen that it is possible to control the amount of transmitted light with a large contrast in the infrared region.

The rise time of the change in the amount of transmitted infrared light when a step-like pulse voltage is applied, that is, the response time is 2m5e when 100V is applied.
It was c.

Example 2 A biphenyl-based mixed ferroelectric liquid crystal (mixed liquid crystal whose infrared absorption spectrum is given in FIG. 3) was placed in the same cell as in Example 1.
was inserted to form an element. Further, the same driving method as in Example 1 was adopted, and sufficient contrast could be obtained with infrared light of 1 to 3 μm.

At a wavelength of 1.5 μm, the contrast was 7.

Example 3 The same cell as in Example 1 was used, except that the cell thickness was changed to 30 μm, and the same driving as in Example 1 was performed using DOBAMBC. It was possible to control transmitted light up to 2.5 μm in the infrared region. Although the threshold voltage decreased, the contrast also decreased at the same time. Contrast when applying 30V is 1.5μm
It was 4 at the wavelength of .

Example 4 DOBAMBC was inserted into the same cell as Example 1 and the thickness was 1
A device with a diameter of 0.00 μm was fabricated. By applying a direct current voltage (1) to this element in advance, a state transparent to infrared light was obtained. When the polarity of this applied voltage was reversed and switched to 1, a high transmission state was obtained, but at the moment of polarity switching, strong scattering occurred and the intensity of transmitted infrared rays decreased.

FIG. 5 is a graph showing the results of measuring the relationship between the applied voltage (1) (12 after polarity reversal) and the contrast during light scattering for various infrared wavelengths. Here, the contrast is defined as the amount of infrared transmission in the transparent state when a DC voltage is applied divided by the amount of transmission in the scattering state when the polarity is reversed. As can be seen, this element can sufficiently control infrared rays.

The response time of transmitted infrared rays, that is, the time for the amount of transmission to change, decreases rapidly as the polarity reversal voltage (→-■) increases.
= 100V, the rise time was approximately 150 μsec.

Example 5 Using the same cell as in Example 4, a biphenyl-based mixed ferroelectric liquid crystal was inserted to construct an element, and it was confirmed that the amount of infrared transmission could be controlled using the same driving method as in Example 4. ■(
→-■) is 60V, the rise time is approximately 600μsec
Met. At this time, the contrast is 8 at a wavelength of 1.5 μm.
Met.

Example 6 The surface of a surface conductive quartz plate similar to Example 1 was coated with polyimide and subjected to rubbing treatment, and then the thickness was 1.8
A μm cell was created. Insert DOBAMBC between these cells, and then place polarizers in front and behind the cells as shown in Figure 1 (6).
An element of the type was created. The polarization planes of the two polarizers were set to be orthogonal.

The plane of polarization of the light that passed through the polarizer on the incident light side was set to be approximately 25° with respect to the rubbing direction of the glass. Initially, when a DC voltage was applied, the amount of transmitted light was extremely small, but when a voltage of opposite polarity was applied, the amount of transmitted light increased. 8000A~2.0
Control of this transmittance was possible with infrared radiation having wavelengths in the μm range.

The contrast was 7 for 1 μm infrared light. Although the threshold voltage of this device was extremely low, about 5 .mu.sec, the switching speed increased as the voltage increased, and at a voltage of 30 V, the switching speed became 80 .mu.sec. That is, it has become clear that this device functions as a high-speed, infrared light transmission control device.

[Brief explanation of drawings]

FIG. 1 is a drawing showing the basic structure of a specific example of an infrared control element using ferroelectric liquid crystal that can be used to implement the method of the present invention. (a) When a polarizer is not used; (a) When a polarizer is used 1: An electrode that is transparent to infrared rays (if a reflective type is used, only one side needs to be transparent). 2: Ferroelectric liquid crystal 3: Polarizer 4: Drive power supply Figure 2 shows the infrared absorption spectrum of DOBAMBC, Figure 3 shows the infrared absorption spectrum of biphenyl mixed ferroelectric liquid crystal, and Figure 4 shows the voltage. A type of DOBA that solves the helical structure by
Figure 5 is a graph showing the relationship between applied voltage and contrast at various infrared wavelengths for an element using MBC, and Figure 5 shows the relationship between applied voltage and contrast at various infrared wavelengths for an element using TSM type (transient scattering type). It is a graph showing a relationship. 1m1 (a) Figure 2 Ω previous meeting (am-〇 Figure 3 section table cμm); 1&thing (cm-Re Figure 4 UIIo pressure (V) Figure 5 0 50 too
150 immediate addition @ヱ(V)

Claims (5)

[Claims] (1) A method of controlling the transmission or reflection of infrared light by sandwiching a ferroelectric liquid crystal between electrodes and applying a voltage between the electrodes. (2) The method according to claim (1), wherein the transmission or reflection of infrared light is controlled by transient light scattering due to intense molecular motion accompanying polarity reversal of applied voltage. (3) The method according to claim (1), wherein the transmission or reflection of infrared light is controlled by a change in birefringence accompanying a change in molecular orientation due to a reversal of applied voltage. (4) The method according to claim (1), wherein the transmission or reflection of infrared light is controlled by a change in light scattering due to the disappearance of the helical structure of the ferroelectric liquid crystal due to the application of a voltage. . (5) Claims 1 to 4, wherein the ferroelectric liquid crystal is a single ferroelectric liquid crystal, a mixed ferroelectric liquid crystal, or a liquid crystal containing impurities. the method of.