JPH01219821A - Liquid crystal optical shutter - Google Patents

Abstract

PURPOSE:To obtain a sufficient contrast ratio over a wide temperature range by varying the directions of the axes of polarization of two polarizing plates. CONSTITUTION:The directions of the axes of polarization of the two polarizing plates are variable. The tilt angle theta varies with temperature, so the relative position between a smetic layer normal and the vibration direction of the polarizing plates is fixed and then the contrast ratio varies abruptly with the temperature. Here, the directions of the axes of polarization of the polarizing plates are made variable to obtain the sufficient contrast over the wide temperature range. Consequently, the fast camera liquid crystal shutter which has a wide use temperature range is formed.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a liquid crystal optical shutter.

(Prior Art) Conventionally, as a camera shutter, in addition to a mechanical shutter that mechanically moves a light shielding plate at high speed, a liquid crystal optical shutter has been proposed.

[Invention or problem to be solved]

Mechanical shutters have high contrast, a high amount of transmitted light when opened, and are limited in speed, up to about 1/4000 seconds, and are expensive. In addition, in a liquid crystal optical shutter using ferroelectric liquid crystal, its response speed is several 7z se
It is extremely fast, on the order of c.c, and high-speed photography is possible without the use of a special strobe. However, when a ferroelectric liquid crystal is used, as is well known, the angle between the stable molecular orientation direction of the tilt angle θ and the normal to the smectic layer has temperature characteristics as shown in Figure 2. However, there is a problem in that the amount of transmitted light and contrast change depending on the temperature.

Regarding this operating principle, please refer to N and A.

C1ark and S, T, Lagerwall:
Appl, P'hys, Lett.

35 (+980) 899, so it will be omitted here.

Figure 3 shows the positional relationship between the moving direction of the polarizing plate and the axis of the liquid crystal molecules. 11 is the normal direction of the smectic layer, 12.13 is the two stable alignment directions of the liquid crystal molecules, and 14.15 is the polarizing plate, respectively. is the vibration direction of the analyzer plate, θ (To) is the angle between the two molecular orientation directions 12.13 and the layer normal 11 (clockwise is positive), α and β are the vibration direction 14.15 and the layer normal, respectively. It is the angle formed by In order to maximize the contrast at a certain temperature To, α=θ(To), β=α−π
/2 The polarizing plate and the analyzer plate may be installed so that the polarizing plate and the analyzing plate are set so that α=θ(To) at the temperature To in FIG. 3.

I is the amount of transmitted light when the liquid crystal molecules are aligned in the direction 12 where the tilt angle θ is positive. 22. The amount of transmitted light when oriented in the negative direction 13 is I. In Figure 4, I ON, I
The amount of transmitted light is the output voltage of the photodetector. As can be seen from this figure, due to the temperature change in θ (Fig. 2), I. □ varies greatly, so even though the maximum contrast can be obtained at 700, the temperature range in which a sufficient contrast ratio can be obtained is limited to IO.
'c or less.

The object of the present invention is to solve these problems and provide a liquid crystal shutter for a camera that is high-speed and can be used over a wide temperature range.

[Means to solve the problem]

The liquid crystal optical shutter of the present invention includes a liquid crystal layer and a means for applying a voltage to the liquid crystal layer between two polarizing plates, in which the directions of the polarization axes of the two polarizing plates are movable, A ferroelectric liquid crystal is used as the liquid crystal.

[For production]

As already mentioned, θ changes depending on the temperature, so if the relative position between the normal to the smectic layer and the vibration direction of the polarizing plate is fixed, the contrast ratio will change rapidly depending on the temperature. Therefore, as shown in FIG. 1, by adjusting their positional relationship depending on the temperature, sufficient contrast can be obtained over a wide temperature range. Next, the effect will be explained.

Letting θ at a certain temperature To be θ(To), the conditions for the maximum contrast at that temperature are α=θ(To) and always β=α−π/2. Further, the optimum condition when the temperature changes by T is α=θ(TO+ΔT). FIG. 5 shows the results of measuring 1ON, I orr and contrast while setting α and β to optimal values using a liquid crystal having the temperature characteristic of θ shown in FIG. ■ Since the molecular orientation 12 always matches the vibration direction 14 of the polarizing plate. 2F is
It shows an approximately constant value over the entire temperature range. As can be seen from equation (1), ION is 1=1. sin” (2φ) sin”(πd△n/λ
) ......(υ molecular orientation 13 and vibration direction 14
It is determined by the angle φ (=20) formed between the
Since it changes in the range of ~50°, 1ON does not change monotonically but shows the change shown in Figure 5. If a liquid crystal material is used in which the center of the distribution of φ is 45", it becomes even more l.

The distribution range of H can be made smaller. Therefore, it is possible to obtain a high contrast of 600 or more and a sufficiently low OFF level over a very wide temperature range.

Next, the second effect will be explained. Generally, the higher the temperature, the smaller the θ and the smaller the contrast ratio, or as can be seen from FIG. 5, a contrast of 600 or more is obtained at temperatures below 35°C. A contrast of 500 or more is sufficient for a camera shutter, so 35℃
It is possible to make the contrast constant over the entire temperature range based on the contrast at . To achieve this, α and β may be shifted from their optimum values so as to lower the contrast at each temperature to 600. Table 1 shows the results obtained in this manner.

Table 1 (Example) (Example 1) A liquid crystal optical shutter was produced using C3-T913 manufactured by Chisso Corporation as a liquid crystal material. The liquid crystal layer thickness was 2.0 pm, and the zero temperature change of C3-T913 was as shown in FIG. At each temperature, the vibration direction of the polarizing plate must be adjusted so that it matches the direction of molecular orientation. ) The contrast was determined by measuring ltlOFF. The results are shown in FIG. In this way, a stable OFF level and sufficient contrast were obtained over a very wide range.

(Example 2) Here, I tried to keep the contrast almost constant.

x and Ioyp were measured to determine the contrast. The results are shown in Table 1. I when compared with Example 1. 1
Does F fluctuate a little? There was no difference in the distribution range of 8, and a more or less constant contrast could be obtained.

(Effects of the Invention) By making the direction of the polarization axis of the polarizing plate movable as described above, large changes in contrast ratio caused by temperature changes in θ can be corrected, and a sufficient contrast ratio can be achieved over a very wide temperature range. I was able to get things done. It can be applied not only to cameras but also to optical switches.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the positional relationship between the molecular orientation and the vibration direction of a polarizing plate at various temperatures according to the present invention, and FIG. 2 is a diagram showing temperature changes in the tilt angle of a ferroelectric liquid crystal. FIG. 3 is a diagram showing the positional relationship between the molecular orientation and the vibration direction of the polarizing plate at each temperature according to a conventional example. Figure 4 shows ■ in the conventional example. FIG. 5 is a diagram showing the temperature change of the 11vlOFF contrast ratio. 8. A diagram showing temperature changes in I OFF contrast ratio. 11. Smectic layer normal direction 12. Stable alignment direction of liquid crystal molecules (θ is positive) 13.
Stable alignment direction of liquid crystal molecules (θ is negative) 14. Vibration direction of polarizing plate 15. Vibration direction of analyzer plate or more Applicant: Seiko Epson Co., Ltd. Agent Patent attorney Tsutomu Mogami (1 other person) long)
(g) Fig. 1 Wound 71 ('e) Fig. 2 (αn (mu)
Figure 3 Qing (°Lee to D 10 20 3o
4D filtration (°0) Figure 5

Claims (2)

[Claims] (1) A liquid crystal optical shutter in which a liquid crystal layer and a means for applying a voltage to the liquid crystal layer are provided between two polarizing plates, characterized in that the directions of the polarization axes of the two polarizing plates are movable. LCD light shutter. (2) The liquid crystal optical shutter according to item (1), wherein a ferroelectric liquid crystal is used as the liquid crystal.