JPH03280015A - Optical modulator - Google Patents

Abstract

PURPOSE:To excellently improve the contrast ratio without any boosting in driving voltage to an optical modulating means which uses a high polymer liquid crystal compound material by providing a polarizing means and an analyzing means on the light incoming side and output side of the optical modulating means. CONSTITUTION:This optical modulator is equipped with the polarizing means 36 which polarizes incoming light and the analyzing means 38 which obtains a polarization- directional component by the polarizing means 36 among the rays of the modulated outgoing light. Namely, the light which is polarized by the polarizing means 36 is made incident on the optical modulating means 30, so the polarization state of the incoming light polarized is eliminated at the time of the scattering of the incoming light to the optical modulating means 30 and when the light whose polarization is eliminated is made incident on the analyzing means, its transparent quantity is reduced. Therefore, the quantity of transparent light of the whole optical modulator is varied greatly through the operation of the polarizer 36 and analyzer 38 according to whether or not the driving voltage is applied, so that the contrast is improved. Consequently, the contrast ratio can be improved excellently without any boosting in the driving voltage.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention performs light modulation by changing the degree of light scattering by liquid crystal droplets that are phase-separated and dispersed and held in a polymer. This invention relates to an optical modulator using a polymer liquid crystal composite, and particularly relates to improvement of its contrast ratio.

[Prior Art] For example, a polymer liquid crystal composite in which liquid crystal droplets are dispersed and held in a polymer, or an optical modulator using the same, is
There is one disclosed in the patent publication No. 502128 published in 1999. Such a light modulating material has a faster response speed than the normally used cell-type TN liquid crystal, and can provide a bright display because it does not use a polarizing plate. It has the advantage of being easy to manufacture because it does not require an alignment film.

FIG. 2 schematically shows the optical modulator disclosed in the publication. As shown in the figure, the light modulating material 10 has a structure in which a large number of liquid crystal droplets 12 are dispersed and held in a polymer matrix 14.

Transparent electrodes 16 and 18 are formed on both sides of the light modulating material IO, and a drive power source 22 is connected through a switch 20 between these transparent electrodes 16 and 18.

In such an optical modulator, the switch 20 is roFF
In the case of J, the liquid crystal molecules of each liquid crystal droplet 12 are oriented in random directions as shown in +A) of the same figure. Therefore, the light incident from the arrow FA is scattered by the liquid crystal droplet 12, and only a small amount of light passes through the light modulating material 10, as shown by the arrow FB. in this case.

The light modulator 10 is observed as cloudy.

On the other hand, when the switch 20 is turned on, the same figure (
As shown in B), the molecular arrangement of the liquid crystal droplet 12 is, for example,
They become aligned in the direction of the electric field formed by the zero voltage. Therefore, the light modulating material 10 becomes transparent, and the arrow F
The light incident as shown by A is transmitted through the light modulating material 10 as shown by arrow FC.

[Problems to be Solved by the Invention] However, such an optical modulator has the following disadvantages. First, the modulating material has a structure in which polymer and liquid crystal are mixed. For this reason, the applied driving voltage is applied to the polymer portion with substantially high resistance, and the voltage applied to the liquid crystal portion becomes low.Therefore, it is necessary to set the driving voltage to a certain degree high.

Furthermore, in the conventional example, light modulation is performed by scattering light. Therefore, the transmitted light intensity T (%) of the optical modulator is
-1og (T/100) for modulator cell thickness d
= to -d (K is a constant). Therefore, in order to obtain a sufficient contrast ratio of the image, it is necessary to increase the cell thickness d.However, since the driving voltage is approximately proportional to the cell thickness d, if you try to obtain a good contrast ratio, Furthermore, the driving voltage becomes higher.

In addition, regarding optical modulators that are thermally driven,
Similarly, in order to increase the contrast ratio, it is necessary to increase the driving temperature difference.

It is also possible to increase the degree of light scattering or transmittance in the modulating material, but this value is largely related to the difference between the refractive index of the polymer matrix and the extraordinary refractive index of the liquid crystal, and is limited by the material. exists.

The present invention has been made in view of this point, and even when using a polymer liquid crystal composite in which liquid crystal droplets are dispersed in a polymer matrix, the contrast ratio can be improved satisfactorily without an increase in driving voltage. It is an object of the present invention to provide an optical modulator that can achieve the following.

[Means for Solving the Problems] The present invention provides an optical modulator that modulates and outputs incident light using a light modulating means in which a large number of liquid crystal droplets are dispersed in a polymer matrix. The present invention is characterized by comprising a polarizing means for performing the above, and an analyzing means for obtaining a polarization direction component of the modulated output light by the polarizing means.

[Operation] According to the present invention, light polarized by the polarizing means is incident on the light modulating means. When the light modulation means scatters the incident light, the polarization state of the polarized incident light is canceled. When the depolarized light enters the analyzer, the amount of transmission thereof is reduced.

[Examples] Examples of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an embodiment of an optical modulator according to the present invention. In the same figure, (AI) shows the state in which a driving voltage is applied as described later, and (B
) shows a state where no driving voltage is applied.

<Configuration of Examples> In these figures, a cell (hereinafter referred to as "liquid crystal cell") 30 in which a polymer liquid crystal composite is used as a light modulating material is as follows.
Similar to the conventional example described above, each of the transparent electrodes 30B and 30C is provided, and the light modulating material 30A is sandwiched between the transparent electrodes 30B and 30C.

A drive power source 34 is connected to the transparent electrodes 30B and 30C via a switch 32.

A polarizer 36 whose polarization direction is vertical in the figure is arranged on the light incident side of the liquid crystal cell 30.
Further, on the light output side of the liquid crystal cell 30, an analyzer 38 whose polarization direction is vertical in the figure, that is, parallel to the polarizer 36, is arranged.

<Operation of the embodiment> Next, the operation of the embodiment configured as described above will be explained.

First, with reference to FIG. 1 (FB), the case where the switch 32 is roFFJ and the drive voltage of the drive power supply 34 is not applied will be described.

In this state, in the light modulating material 30A, the liquid crystal molecules are aligned along the walls of the voids in the polymer matrix.
A strong scattering effect on the light occurs. However, when light passes through the liquid crystal portion, its polarization axis also shifts. The amount of deviation of this polarization axis varies depending on the direction of incidence of light on the liquid crystal portion and the position of the liquid crystal portion.

By the way, in this embodiment, the light that has been polarized by the polarizer 36 enters the liquid crystal cell 30 (+8 in the figure) along the arrow F1.
(see arrow F2), such linearly polarized light enters the liquid crystal cell 3.
When the light is incident at zero, the light will be scattered and the polarization axis will be shifted by the liquid crystal portions dispersed in large numbers in the polymer matrix. Therefore, the light transmitted through the liquid crystal cell 30 has a very weak intensity, and has a random polarization direction with almost no linear polarization, as shown by the arrow F3 in FIG. 3(B).

When such transmitted light enters the analyzer 38, only its linearly polarized light component is output. Therefore, the final optical output becomes very weak, as shown by arrow F4 in FIG. In other words, the amount of transmitted light is reduced by an amount corresponding to the cancellation of linearly polarized light by the liquid crystal cell 30.

When b and are turned on, next, referring to fA) in the same figure, the switch 32 is turned on.
A case where the drive voltage of the drive power supply 34 is applied will be described.

In this case, for example, if the refractive index anisotropy of the liquid crystal is positive, the long axes of the liquid crystal molecules will be aligned in the direction of the electric field.

Therefore, the linearly polarized light shown by the arrow F2 in the figure (Al) almost passes through the liquid crystal cell 30 as shown by the arrow F5.This light also passes through the analyzer 38 almost unchanged. (see arrow F6 in the same figure (A)),
Thus, according to this embodiment, the polarizer 36. Analyzer 3
Due to the effect of 8, the amount of transmitted light of the optical modulator as a whole changes greatly depending on whether or not a driving voltage is applied.
The contrast ratio will be improved.

Here, the contrast ratio is calculated as follows, for example. Polarizer 36. The X-direction light transmittance of the analyzer 38 is respectively AI and A2, and the X-direction light transmittance is B1. B
Set it to 2. Further, the light transmittance of the liquid crystal cell 3o when a drive voltage is applied is set as a reference "l", and the light transmittance when a drive voltage is not applied is set as J.

First, polarizer 36. When the analyzer 38 is not used, that is, the contrast ratio CRI of the liquid crystal cell 30 itself is: =l/J.

On the other hand, the polarizer 36. The contrast ratio CR2 when each analyzer 38 is used is AlXA2+BIXB2 CR2= 0.5 (AI+Bll X J (A2+82)
Here, suppose that the polarization is completely canceled when passing through the liquid crystal cell 30, and the polarizer 36. Analyzer 38 has ideal characteristics (
A1. A2 is l, B1. Assuming that B2 is 0), CR2=2/J, that is, polarizer 36. The ideal contrast ratio CR2 when each analyzer 38 is used is as follows compared to the contrast ratio CRI when not used. As described above, according to this embodiment, the improvement magnification of the contrast ratio is ideally doubled, and this value is the same as that of the polarizer 36. Analyzer 38
In principle, it is not related to the contrast ratio value itself (that is, the value of J) when J is not used. Therefore, for example, if this example is applied to a liquid crystal cell with a contrast ratio of 50 = 1, the contrast ratio will be 100. :1, and if this example is applied to a liquid crystal cell with a contrast ratio of 100:l,
A contrast ratio of 200:1 can be obtained.

<Specific example of this embodiment> Next, a specific example according to this embodiment will be explained.

-ILll 1 crystal was BDH's brand name E-9 (cyanobiphenyl liquid crystal), the monomer was 2-ethylhexyl acrylate (E HA), and the oligomer was Nippon Kayaku's brand name KAYARAD's HX620. 7:18:1.
2 (7) weight ratio, and further added 3% by weight of MERK's darocurl 173 as an ultraviolet polymerization initiator.
In addition, a mixed solution was created. This was poured into a cell container made of two glass substrates with transparent electrodes such as ITO having a gap of 10 μm, and irradiated with ultraviolet rays to create a liquid crystal cell 30.

Then, the light transmittance of the liquid crystal cell was measured using light with a wavelength of 633% m. If the light transmittance when the liquid crystal cell is not in the optical axis of the measurement light is 100%, the transmittance when the driving voltage is applied and saturated (applied voltage 35 VR-) is 78.9%, and when no voltage is applied. The transmittance was 1.70%, and the contrast ratio was 46.4:]. In addition, ■□
, indicates the effective value.

EXAMPLE 1 Using the liquid crystal cell of Experimental Example 1, exactly the same measurements were carried out by arranging a polarizer and an analyzer with a degree of polarization of 98% as in this example. The transmittance when the drive voltage was applied and saturated (applied voltage 35■R1, ll1) was 789%,
The transmittance when no voltage was applied was 1.11%, and the contrast ratio was improved to 71·l.

Sample A with different transmittance by variously changing the production conditions of the polymer liquid crystal composite that constitutes the liquid crystal cell.

Samples B, C, and D were prepared and measured in the same manner as in Experimental Example 2 above. The results are shown in Table 1 below.

Table 1 As shown in this table, in all samples, the contrast ratio is improved when a polarizer and an analyzer are provided.

d. Experimental Example 4 Next, using the liquid crystal cell of Experimental Example 2, similar measurements were performed in a case where a polarizer was used but an analyzer was not used. The transmittance is 788% when the drive voltage is applied and saturated (applied voltage 35 V□), and the transmittance when no voltage is applied is 1.74%, and the contrast ratio is 45.3:1.
It became. This is a low value that is almost the same as in Experimental Example 1 in which neither a polarizer nor an analyzer was used.

Other Examples> It should be noted that the present invention is not limited to the above-mentioned embodiments. For example, it is clear that the polarization direction of the polarizer and analyzer may be different from those of the above-mentioned embodiments. be.

Further, as the polarizer and analyzer used, as mentioned above, one having a degree of polarization of about 80 to 99% is sufficiently effective, and it is not necessarily necessary to use one having a particularly high degree of polarization.

Further, this embodiment may be used in combination with other contrast improvement methods such as increasing cell thickness and improving material roughness.

Further, in addition to electrically driven liquid crystal cells, the present invention is similarly applicable to, for example, thermally driven liquid crystal cells.

Further, in the above embodiments, the present invention is applied to a transmissive optical modulator, but this does not preclude application to a reflective type.

[Effects of the Invention] As explained above, according to the optical modulator according to the present invention, the polarizing means and the analyzing means are provided on the light incidence side and the output side of the light modulating means using a polymer liquid crystal composite, respectively. As a result, the contrast ratio can be favorably improved without increasing the driving voltage for the light modulating means.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an optical modulator according to the present invention, and FIG. 2 is an explanatory diagram showing a conventional example. 30... Liquid crystal cell (light modulation means), 30A... Light modulating material, 30B, 30C... Transparent electrode, 32... Switch, 34... Drive power supply, 36... Polarizer [polarized light means), 38...analyzer (analysis means).

Claims (1)

[Scope of Claims] An optical modulator that modulates and outputs incident light using a light modulating means in which a large number of liquid crystal droplets are dispersed in a polymer matrix, comprising: a polarizing means that polarizes the incident light; An optical modulator comprising: an analyzing means for obtaining a polarization direction component of the modulated output light by the polarizing means.