JPS6050838B2 - electro-optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electro-optical devices such as optical modulators and optical deflectors using materials that exhibit large birefringence due to second-order electro-optic effects.

These electro-optical devices all have a cell filled with a liquid material having a secondary electro-optic effect between two electrodes as a common component.

Such an electro-optical device is known as a Kersel in the case of an optical modulator, and is also known as a UWEKR-UG in the case of an optical deflector.
Report of ERs [Proc] IEEE, Vol. 61,
No. 7, PP, 992-1007 (1973)]. Usually, nitrobenzene is used as the liquid material used in these electro-optical devices, but in optical modulators (ker cells) using nitrobenzene, for example, He-Ne laser light (wavelength 633 nm) is used.
m), the voltage (half-wave voltage) required for 100% modulation is approximately 4 KV when the electrode spacing is 1- and the electrode length (optical path length) is m-. The same is true for digital deflectors that utilize the Kerr effect of liquids. Such high voltages have many disadvantages in designing and manufacturing drive circuits for these electro-optical devices, and are especially inappropriate for practical devices that require miniaturization. 5- As a liquid that is generally expected to have a large secondary electro-optic effect (Kerr effect), it has a high dipole efficiency, a large optical anisotropy, and the directions of the dipole efficiency and optical anisotropy match. etc. are required.

As such a liquid material, for example, the above-mentioned KR-UGER
reported a mixture of 7% by volume of methylacetamide and 3% by volume of ethylacetamide, but the Kerr coefficient of this liquid is about three times that of nitrobenzene, and the half-wave voltage is only about 60% lower than that of nitrobenzene. However, it is still insufficient for practical use. It is also known that P-type nematic liquid crystals near the nematic phase isotropic phase transition temperature exhibit a large coefficient of 1. However, most of the currently known P-type nematic liquid crystals have a nematic phase isotropic phase transition temperature of 3.
The temperature is above 0°C and cannot be used below room temperature. The present invention is based on the discovery that by adding an appropriate amount of a suitable additive to a P-type nematic liquid crystal, it can be used even below room temperature without significantly reducing the Kerr coefficient inherent to the liquid crystal.

An object of the present invention is to provide electro-optical devices such as optical modulators and optical deflectors using a new combination of P-type nematic liquid crystal and additives as a secondary electro-optic effect (Kerr effect) material. There is something to do. Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a perspective view showing an example of a cell included in the electro-optical device of the present invention.

In the figure, 11 is the main body of the cell 21, and inside thereof a pair of electrodes 12a and 12b having a length of 11 and a height of h are arranged facing each other with a distance of d, and these are the main parts of the present invention. It is filled with a dielectric liquid 13 having a secondary electro-optic effect. The front surface 14 and rear surface 15 of this cell 21 are made of a material (for example, transparent glass) that has a high transmittance for the light beam to be modulated or deflected, since it is necessary to pass the light beam to be modulated or deflected.
Consists of etc. Although the side surfaces 16 and 17 are made of insulating material 3 in this embodiment, it is also possible to use the electrodes themselves as the side surfaces. Further, in the illustrated example, the top surface is an opening for convenience of explanation, but in actual use, it is sealed by an appropriate method. FIG. 2 is a diagram showing a -4 example of an optical modulator including the cell 21 of FIG. 1.

In the figure, a cell 21 receives power from a modulated power supply 22. 23 and 24 are polarizing plates (hereinafter, 24 will be referred to as an analyzer), and their polarization axes are perpendicular to each other, and are arranged at an angle of 45 degrees with respect to the electric field application direction of the cell 21. There is.

When no electric field is applied to the cell 21, the dielectric liquid 13 is isotropic, so the light beam 26 passes through the cell 2 without changing its polarization direction.
1, so considering the arrangement of the polarizing plate, the detector 2
5 is not reached by the ray 26. When an electric field is applied to the cell 21, the dielectric liquid 13 exhibits birefringence, and there is a difference in the refractive index in the direction of application of the electric field and in the direction perpendicular to it, so the phase velocity of the electric field components in each direction is different. A phase difference occurs. Therefore, the light that has passed through the cell 21 is generally elliptical polarized light. Therefore, some components can be detected by Analyzer 2.
4, and the light beam reaches the detector 25. When the phase difference becomes π radian (corresponding to half a wavelength), the light passing through the cell 21 is detected by the analyzer 2.
The light ray 26 changes into linearly polarized light with the same polarization direction as 4.
reaches the detector 25 almost 100% of the time.

The voltage applied to the cell 21 at this time is half wavelength voltage/voltage (■π)
That's what it means. FIG. 3 is an example of a digital deflector including the cell 21 of FIG.

In the figure, 32 is a prism made of a material exhibiting natural birefringence, such as calcite, and its optical axis is perpendicular to the plane of the paper. The direction of electric field application in the cell 21 makes an angle of 45 degrees with the direction of the polarization plane of the incident deflected light beam. Now, a linearly polarized light beam 33 with an electric field direction parallel to the plane of the paper is sent to the cell 2.
1, if no electric field is applied to the cell 21, the polarization direction will not change and the light will pass through the cell 21 as it is.

When a voltage corresponding to a half-wavelength voltage is applied to the cell 21,
As described above, the polarization direction of the incident light beam 33 is rotated by 90 degrees and becomes perpendicular to the plane of the paper. Therefore, when no voltage is applied, it is refracted in the direction 34 shown in Figure 3 according to the ordinary ray refractive index, and when a voltage is applied, it is refracted in the direction 35 shown in Figure 3 according to the extraordinary ray refractive index. Since the light is refracted in the direction, light can be deflected. The dielectric liquid 13 contained in the cell 21 in the electro-optical device of the present invention is an isotropic liquid and is specific to the liquid crystal in order to lower the temperature at which the P-type nematic liquid crystal transitions from the nematic phase to the isotropic phase. Additives are added.

It was found through measurements that the phase transition temperature could be lowered to below room temperature by adding additives. Specifically, the dielectric liquid has the general formula: is one CH=N-
shows.

] The following general formula: [Here, R'' represents a lower saturated or lower unsaturated alkyl group, or a phenyl group, and Y is a phenyl group. -H1-CNl-NO2,
Or indicates -0H.

] Suitably, it is an isotropic liquid consisting of a mixture to which a compound represented by: is added. It has been found that cyanobiphenyl liquid crystals are particularly good among P-type nematic liquid crystals. Examples are shown below. Example 1 In the cell shown in FIG. 1, the electrode spacing d is 1Tr0n, and the electrode length 1 in the light beam passing direction is 1077177! shall be.

In this cell, a mixture of 4-n-propoxy-4''-cyanobiphenyl, 4-n-pentyloxy-4''-cyanobiphenyl, and 4-n-heptyloxy-45-cyanobiphenyl in a molar ratio of 1°1:1 was mixed with probionitrile. The container was filled with a liquid containing 7.1% by weight of 7.1% by weight and arranged as shown in FIG. The liquid entered an isotropic state at 25.0°C. A He-Ne laser beam (633
As the voltage was applied to the cell using the voltage (nm), the output of the detector 25 reached its maximum at 330 cm. This value indicates that the optical phase difference has reached τ radians, and corresponds to the half-wavelength voltage (Vπ). Kerr coefficient B is LJP'4'
! - calculated as 460 x 10-10 cm/
It is V2.

This value corresponds to about 150 times more than nitrobenzene, and like nitrobenzene, it was measured near room temperature. Example 2 Using the same method as in Example 1, 4-n-propoxy 4
″-cyanobiphenyl, 4-n-pentyloxy-4″
The Kerr effect of a liquid obtained by adding 16.5% by weight of propionitrile to a mixture of -cyanobiphenyl and 4-n-heptyloxy-4''-cyanobiphenyl in a molar ratio of 1:1:1 was measured.

This liquid is in an isotropic phase state at -11.5℃, and the half-wave voltage at this temperature is 340V1 Kerr coefficient 440X10-1
It was 0 crft/V2. From this, it was found that a liquid that exhibits a large effect can be obtained even at temperatures below 0° C., which is impossible with nitrobenzene. Example 3 Using a method similar to Example 1, 4-n-pentyl-4
The Kerr effect of a liquid obtained by adding 3.0% by weight of nitromethane to ``-cyanobiphenyl was measured.

This liquid is in an isotropic state at 20℃, and the half-wave voltage at this temperature is 790V1.The Kerr coefficient is 80×10-10cm.
/V2. Example 4 Using a method similar to Example 1, 4-n-pentyl-4
'-cyanobiphenyl with ethyl alcohol 2. Capacity%
The Kerr effect of the added liquid was measured.

This liquid becomes isotropic at 20℃, and the half-wave voltage at this temperature is 675V1.The Kerr coefficient is 110×10-10C.
It was Tn/V2. Example 5 Using the same method as in Example 1, the Kerr effect of a liquid prepared by adding 2.5% by weight of allyl alcohol to 4-n-pen)thiru-4''-cyanobiphenyl was measured.

This liquid is in an isotropic state at 20°C, and the half-wave voltage at this temperature is 530V1.The Kerr coefficient is 180X10-10.
The CTr was 1/2. Example 6 Using a method similar to Example 1, 4-n-pentyl-4
The Kerr effect of a liquid obtained by adding 3.8% by weight of benzene to '-cyanobiphenyl was measured.

This liquid is in an isotropic phase state at 20'C, and the half-wave 5-length voltage at this temperature is 700V1.The Kerr coefficient is 102X10-1
0C77! /■It was 2. Example 7 Using a method similar to Example 1, 4-n-pentyl-4
The Kerr effect of a liquid obtained by adding 1.1% by weight of probionitrile θ to '-cyanobiphenyl was measured.

This liquid is in an isotropic state at 20°C, and the half-wave voltage at this temperature is 485V1.The Kerr coefficient is 212X10-10.
cm/V2. Example 8 Using a method similar to Example 1, 20.5 wt. % of the added liquid was measured.

This liquid is in an isotropic state at 20°C, and the half-wave voltage at this temperature is 660V1.The Kerr coefficient is 115×10-10
cm/V2. Example 9 Using a method similar to Example 1, a 1:1 mixture of 4-n-pentyloxy-4''-cyanobiphenyl and 4-n-heptyloxy-4''-cyanobiphenyl was treated with 19. The Kerr effect of the liquid added by volume % was measured.

This liquid enters an isotropic state at 20°C, the half-wave voltage at this temperature is 620V, and the Kerr coefficient is 130 x 10-10.
It was cTn/V2. Example 10 Using a method similar to Example 1, 4-n-pentyloxy-4''-cyanobiphenyl, 4-n-heptyloxy-4''-cyanobiphenyl, and 4-n-pentyl-4'-cyanobiphenyl were prepared. Add 12% benzonitrile to the 11:2 mixture. The Kerr effect of the liquid to which the amount of slag was added was measured.

This liquid is in an isotropic phase state at 20℃, and the half-wave voltage at this temperature is 470V1.The Kerr coefficient is 226×10-10c.
It was m/V2. Example 11 Using a method similar to Example 1, p-[(p-butoxybenzylidene)amino]-benzonitrile, p-[(p
-hexyloxybenzylidene)amino]-benzonitrile and p-[(p-octyloxybenzylidene)amino]-benzonitrile in a 1:1:1 mixture with 17.0% by weight of benzene added to the Kerr effect. It was measured.

This liquid is in an isotropic state at 20℃, and the half-wave voltage at this temperature is 660V1.The Kerr coefficient is 115×10-10c.
It was 7n/V2. In all of the above embodiments, it is clear from the measurement results that they respond to frequencies up to at least 1 MHz.

Further, as mentioned above, with ordinary liquid crystals, the Kerr effect can only be observed at temperatures above 30° C., but according to the present invention, the effect can be observed even below room temperature, and the practical value is extremely high. For example, when using the same configuration as shown in Example 1 and using nitrobenzene as the dielectric liquid, the half-wave voltage is 4100V when the Kerr effect is measured at 25°C. In contrast, in the embodiments according to the present invention, all
000V or less, and especially in Example 1, the half-wave voltage at 25°C is 330V, so the 1112 of nitrobenzene
．． 4, and it is clear that the practical effect is great.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a cell for applying an electric field to an isotropic liquid, which is included as a common element in the electro-optical device of the present invention, and FIG. 2 shows an example of a modulator including the cell shown in FIG. The figure shown in FIG. 3 is a diagram showing an example of a digital optical deflector including the cell of FIG. 1. 12a, 12b...electrode, 13...dielectric liquid, 21...cell.

Claims (1)

[Claims] 1. A dielectric liquid that produces birefringence due to a second-order electro-optic effect when an electric field is applied, and the dielectric liquid has a general formula: ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ or ▲ Mathematical formulas, chemical formulas ,
There are tables, etc.▼ [Here, R represents a saturated chain alkyl group or alkoxy group having up to about 10 carbon atoms. ]: The following general formula: R'-Y [Here, R' represents a lower saturated or lower unsaturated alkyl group, or a phenyl group, and Y represents -H , -CN, -NO_2, or -OH. ]: An electro-optical device comprising a mixture to which a compound represented by: is added, and the liquid is an isotropic liquid. 2 In claim 1, the mixture is defined as 4-
n-propooxy-4'-cyanobiphenyl, 4-n-
pentyloxy-4'-cyanobiphenyl, and 4-
An electro-optical device comprising an isotropic liquid that is a mixture of n-heptyloxy-4'-cyanobiphenyl in a molar ratio of 1:1:1 and propionitrile added.