JP3296120B2 - Liquid crystal thick film cell type light modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal thick film cell type light modulator using a ferroelectric liquid crystal, and more particularly, to a visible light and / or an infrared light for blocking or transmitting visible light and / or infrared light. // Can be used as an infrared chopper,
For example, it can be used for a light receiving unit such as an optical measuring device, a gas component analyzing device, an infrared detecting device, a non-contact thermometer, and a temperature sensor of a cooking device. In particular, pyroelectric type infrared detectors,
There are photoconductive types and the like, and information cannot be obtained as electrical signals by simply receiving infrared rays as they are. Therefore, it is necessary to convert infrared rays into AC signals,
Therefore, an infrared chopper is required.

[0002]

2. Description of the Related Art Conventionally, as a liquid crystal thick film cell type optical modulator,
Examples include a refraction type using a polarizer represented by a TN method using a nematic liquid crystal, a dynamic scattering type using a nematic liquid crystal, and a light scattering type using a phase transition between a cholesteric phase and a nematic phase.

In the refraction type, since the wavelength of transmitted light is long, it is necessary to increase the cell thickness in order to obtain a sufficient optical rotation, and the response is very poor. Further, the dynamic scattering type has a problem that it is necessary to lower the driving voltage in order to increase the scattering intensity, so that the response speed is reduced. Further, in the light scattering type, since the speed required to dissolve the helical structure of the cholesteric phase is low, high-speed response is difficult.

On the other hand, ferroelectric liquid crystals are expected to be applied to display panels, light modulation, etc. in recent years because of their extremely high electric field response. Optical modulators using ferroelectric liquid crystal are roughly classified into a thin film type and a thick film type depending on the cell gap in which the liquid crystal is sealed. The thin film type has a cell gap of several μm and uses the birefringence of liquid crystal by using polarizers at both ends, and its application to display panels and the like has been devised. Since the transmittance is reduced to 50% or less and the birefringence mode is used similarly to the TN method, the modulation degree (transparent and scattering states) increases with decreasing refractive index on the long wavelength side such as the infrared region. (Difference in transmittance).

On the other hand, the thick film type has a cell gap of 50 to several tens.
With a thickness of 0 μm, light modulation is possible mainly due to good scattering characteristics utilizing transient scattering. This transient scattering utilizes the backscattering of primary light due to the disorder of the alignment of the liquid crystal that occurs when the polarity of the driving electric field in the smectic C phase is inverted (Japanese Patent Laid-Open Nos. 60-195521 and 60-195).
254120 and 61-260227), and can be manufactured at low cost without using a polarizer, and has a merit that a large degree of modulation (transmission loss) can be expected. Since similar scattering can be expected for infrared rays (light), application to gas analyzers and the like has been considered by utilizing this infrared modulation. In short, it has been known that when a voltage having a symmetrical pulse waveform is applied to both electrodes of the thick-film cell type, a certain degree of modulation with respect to visible light and infrared light can be obtained.

[0006]

In a conventional thick film type optical modulator using a ferroelectric liquid crystal, a driving electric field (voltage) is required when the ferroelectric liquid crystal shifts from a transparent state to a light scattering state.
, The response speed is very high (several tens of sec) due to the response of the ferroelectric liquid crystal itself.

However, it takes a very long time to recover from the scattering state to the transparent state (several tens to several hundreds of meters).
sec). It is considered that the reason for this is that the scattering state occurs in the process of shifting a certain arrangement of liquid crystal molecules from one regular arrangement (transparent state) to another regular arrangement (transparent state). Even in the same transparent state, transition to a state of different arrangement generally requires a long time. Further, a method of maintaining a scattering state (see the above-mentioned JP-A-6
Nos. 0-195521, 60-254120, 61
However, none of these methods could improve the response speed from the scattering state to the transparent state.

Further, in the conventional driving method in which a voltage having a symmetrical pulse waveform is applied, the degree of modulation is less than several tens Hz including refraction type and scattering type. In other words, there was no infrared sensor that received high-frequency modulation corresponding to the modulation, and it was not practical.

[0009]

Thus, according to the present invention, a thick film cell in which a ferroelectric liquid crystal is sealed between a pair of opposing electrode plates, and both electrode plates of the thick film cell. Comprising voltage applying means ,
Ferroelectric liquid crystal aligned to one of two polarities for positive and negative electrodes
Asymmetric duty ratio that can be returned to the original polarity before
And a liquid crystal thick-film optical modulator comprising driving a ferroelectric liquid crystal by applying a pulse voltage having a voltage waveform having the following .

Further, according to the present invention, there is provided a thick film cell in which a ferroelectric liquid crystal is sealed between a pair of opposed electrode plates,
It comprises voltage applying means to both electrode plates of this thick film cell,
A rectangular wave voltage is superimposed on the bias DC voltage by the voltage applying means, and the ferroelectric liquid crystal is adjusted to one of two polarities.
Asymmetric duty that can return to the original polarity before queuing
There is provided a liquid crystal thick-film cell type optical modulator comprising driving a ferroelectric liquid crystal by applying a voltage having a waveform having a ratio . Further, according to the present invention, a thick film cell in which a ferroelectric liquid crystal is sealed between a pair of opposing electrode plates, and voltage applying means for applying voltage to both electrode plates of the thick film cell are provided. When the cell gap of the cell is 50 μm or more, the ferroelectric liquid crystal to be enclosed exhibits a helical pitch in the smectic C layer having a length of 0.7 to 0.95 times the cell gap.
Before the ferroelectric liquid crystal aligns with one of the two polarities
Has an asymmetric duty ratio that can be pulled back to the original polarity
Driving a ferroelectric liquid crystal by applying a voltage with a different waveform
Tona Ru crystal thick cell light modulator is provided.

That is, the present invention provides a method of applying a pulse voltage having a positive / negative voltage waveform with an asymmetrical duty ratio or a voltage in which a rectangular wave voltage is superimposed on a bias DC voltage to both electrode plates of a thick film cell. It has been found that, compared to the case where a conventional symmetric pulse voltage is applied, a high degree of modulation is applied to infrared light as well as visible light, and the response speed is improved to enable high-frequency modulation. Was.
The reason why the response speed is improved by the liquid crystal thick film cell type optical modulator of the present invention is that when the ferroelectric liquid crystal is driven from the scattering state to the transparent state, the reversal of the spontaneous polarization of the ferroelectric liquid crystal is interrupted. It can be considered that this makes it possible to quickly shift to the scattering state. Further, it is considered that the reason why a high degree of modulation is obtained by the liquid crystal thick-film cell type optical modulator of the present invention is that domains formed at the time of scattering are formed to have a size suitable for scattering.

Further, although a sufficiently high degree of modulation and response speed can be obtained with the above modulator, the thick film cell used is the same as a thick film cell in which a ferroelectric liquid crystal is sealed between a pair of opposed electrode plates. Means for applying voltage to both electrode plates of the thick film cell, wherein the thick film cell has a cell gap of 50 μm or more and the ferroelectric liquid crystal to be enclosed is 0.7 to 0.95 of the cell gap. It has been found that with a configuration comprising a helical pitch in a double length of the smectic C phase, a better modulation degree and response speed can be obtained.

In the present invention, a pulse voltage having a voltage waveform that is not symmetrical with respect to the positive and negative electrodes but is asymmetrical is applied to both electrode plates of the thick film cell. The degree of asymmetry is set, for example, such that the ratio of the positive electrode wave time to one cycle time: 100, that is, the duty ratio is preferably 55 to 75%, and more preferably 65 to 75%. Usually, the duty ratio is preferably adjusted to an optimum value according to the design conditions and usage conditions of the thick film cell. Specifically, it is preferable to adjust the duty ratio by incorporating a duty ratio adjustment circuit into the voltage applying means (power supply circuit).

Further, in the present invention, a voltage in which a rectangular wave voltage is superimposed on a bias DC voltage is applied to both electrode plates of the thick film cell. Specifically, when the amplitude (drive voltage) is 40 V, the bias DC voltage is preferably changed as 0 V, 10 V, 20 V, and more preferably about 10 to 15 V, since a large degree of modulation is obtained. This preferable bias DC voltage application condition corresponds to about 20 to 50% of the equivalent value of the applied rectangular wave voltage. The bias DC voltage is preferably adjusted to an optimum value according to the design conditions and use conditions of the thick film cell. Specifically, it is preferable to adjust the bias DC voltage by incorporating a bias DC voltage adjustment circuit into the voltage applying means (power supply circuit). .

It is also possible to apply a voltage in which a rectangular wave voltage is superimposed on a pulse voltage having an asymmetrical voltage waveform and a bias DC voltage. In this case, it is preferable to adjust the voltage by applying a duty ratio adjustment circuit and a bias DC voltage adjustment circuit to the voltage application means (power supply circuit). The specific resistance is preferably 0.5 Ωcm or more, and more preferably 2 Ωcm or more. If it is smaller than 0.5 Ωcm, the infrared transmittance decreases. This decrease becomes large near a long wavelength (10 μm).

In the present invention, the thick film cell is formed by encapsulating a ferroelectric liquid crystal between a pair of electrode plates. Each electrode plate is generally formed by depositing, for example, an ITO film (indium tin oxide film), which can function as an electrode on a glass substrate, or a substrate itself made of silicon or germanium doped with impurities. These one
The pair of electrode plates are opposed to each other with a thick film cell gap of 50 μm or more, preferably 100 to 300 μm, and are maintained and sealed with a spacer [for example, Lumirror (registered trademark) polyester sheet manufactured by Toray Industries, Inc.] to form a thick film cell. Is done.
Here, if the cell gap is 50 μm or less, it is not preferable because a sufficient degree of modulation cannot be obtained.

A ferroelectric liquid crystal is sealed in this thick film cell. The ferroelectric liquid crystal is not particularly limited, and usable ones are Schiff base, azo, azoxy, benzoate, biphenyl, terphenyl, cyclohexylcarboxylate, phenylcyclohexane, and the like. Examples include pyrimidine-based and oxane-based liquid crystals and multi-component liquid crystals that are mixtures thereof. As a specific liquid crystal compound, one having a structure represented by the following formula (Formula 1) can be exemplified.

[0018]

Embedded image

These typical materials are listed in "Structure and Properties of Ferroelectric Liquid Crystal", pp. 229 to 234, "Ferroelectric Liquid Crystal Material and Alignment Control Method", published by Corona. Commercially available ferroelectric liquid crystals usable in the present invention include CS-
1014, CS-1017, CS-1017 (manufactured by Chisso Sekiyu KK), ZLI-1013, ZLI-1011 (manufactured by Merck) and the like.

Further, in the ferroelectric liquid crystal, the helical pitch in the smectic C phase is 0.7 to less than the cell gap.
It preferably has a length of 0.95 times, preferably 0.8 to 0.9 times. Further, when the helical pitch is 0.7 times or less of the cell gap, the orientation of the liquid crystal is deteriorated and the domain becomes too small, so that the transmittance in the bright state deteriorates. Since the spiral structure of the ferroelectric liquid crystal is elongated or unraveled, it is difficult to form a domain that forms a light scattering state, and a sufficient scattering intensity cannot be obtained. From this, it can be seen that the degree of modulation strongly depends on the cell gap and the helical pitch, and when the cell gap is increased, a good degree of modulation cannot be obtained unless the helical pitch is also increased.

Next, when the helical pitch cannot satisfy the condition of 0.7 to 0.95 times the cell gap with only the ferroelectric liquid crystal, an adjusting agent is added to adjust the helical pitch. Is also good. As the regulator, any known regulator used for controlling the helical pitch of the ferroelectric liquid crystal can be used. For example, a known achiral liquid crystal material can be used for the regulator. The addition ratio of the regulator is
For example, when a ferroelectric liquid crystal having a helical pitch of about 5 μm is used and a helical pitch of about 100 μm is to be obtained, a ferroelectric liquid crystal having a desired helical pitch can be obtained by diluting the ferroelectric liquid crystal by 20 times with a regulator. Liquid crystal is obtained.

The liquid crystal thick film cell type light modulator of the present invention can be used in any of the visible and infrared regions, but is particularly preferably used as an infrared light modulator. When near-infrared (wavelength 0.8 to 3 μm) or mid-infrared (wavelength 3 to 8 μm) is used as the infrared ray, the cell gap is preferably 100 μm or more. When far-infrared light (wavelength: 8 to 25 μm) is used, if the cell thickness is large, the inherent infrared absorption of the liquid crystal due to the molecular vibration of the ferroelectric liquid crystal to be used cannot be avoided. Preferably, it is a cell gap.

In particular, in the mid-to-far infrared region, an antireflection film is further formed on both sides of the electrode plate constituting the liquid crystal thick film cell type light modulator, and the antireflection film on the opposite surface side is made of a conductive material. This is preferable because it is possible to obtain an optical modulator with little change over time and high reliability and stability that does not cause malfunction. This is because when using a dielectric film that has been used as an anti-reflection film for infrared rays in a thick liquid crystal cell,
The liquid crystal molecules do not operate at all and do not exhibit the light modulation function, or the change with time is large, so that a practically usable one cannot be obtained. This is because the problem can be solved.

Here, the thickness of the antireflection film depends on the wave used.
Defined according to the length, for example, when the wavelength is in the 5μ band, the film thickness
In the case of about 1 μm and 10 μ band, the film thickness is about 10 μm (hereinafter, 5 μm).
about 1 μm is added for each μ). Anti-reflective coating
Are, for example, metal sulfides such as ZnS, and TiO._Two, C
eO_Two, Ta_TwoO_Five, ZrO_Two, Y_TwoO_Three, MgO, A
l_TwoO_ThreeMetal oxides such as PbF_Two, CeF_Three, LaF
_Three, BaF_Two, CaF _Two, MgF_Two, LiF, Na_ThreeA
IF₆Fluoride, NaF, etc., SiO_Two, SiO, G
e, Si and the like. To make the anti-reflection film conductive
Add an appropriate amount of trace metal or semiconductor (such as Si)
It can be done by doing. In addition, reflection made conductive
The sheet resistance of the protective film is defined according to the wavelength used,
For example, in the case of the wavelength 5μ band, 86000 to 3300000
About MΩ, about 200 ~ 21000MΩ for 10μ band
Degrees. Also, an appropriate amount means a few weight%.
Above, although it is possible to lower the resistance of the antireflection film,
This is not preferable because the transmittance of infrared rays is significantly attenuated.

According to the present invention, a liquid crystal thick-film cell type optical modulator is most preferable when both the driving voltage by the voltage applying means and the relationship between the helical pitch and the cell gap are satisfied.

Furthermore, the present inventors have found that in the above liquid crystal thick film cell type optical modulator, the tilt angle (tilt angle) of liquid crystal molecules with respect to the phase normal of the smectic C phase is 15 ° or more, preferably 20 ° or more. By doing so, it has been found that the degree of light modulation can be further increased. Here, the tilt angle refers to the angle of inclination of the liquid crystal molecules with respect to the phase normal of the smectic C phase. The modulator of the present invention blocks incident light using the light scattering effect. Modulation performance (modulation depth)
Is determined by the transmittance and the scattering intensity of the liquid crystal cell, which greatly depend on the physical properties of the liquid crystal used. In the above, the modulation degree was improved by optimally adjusting the helical pitch, which is a static parameter affecting the scattering intensity, but in addition to this, light scattering is a motion parameter because it is induced by the motion of molecules. By adjusting the telt angle to be equal to or more than the above value, the scattering intensity is further increased, and a modulator with high modulation can be obtained. This is presumably because the larger the tilt angle, the more the disorder of the alignment of the liquid crystal in the liquid crystal layer increases, thereby increasing the scattering intensity.

The following method can be used to obtain a desired tilt angle. First, in general, the tilt angle of a ferroelectric liquid crystal is closely related to the phase transition temperature from the smectic C phase to the A phase, and the higher the phase transition temperature, the larger the tilt angle. Therefore, when a liquid crystal having a large tilt angle is desired, a liquid crystal having a high phase transition temperature can be selected to obtain a desired tilt angle. Also, if liquid crystals with different tilt angles are mixed, most liquid crystals
Since the additivity is satisfied, a desired value of the tilt angle can be obtained by adjusting the mixing ratio. The method for obtaining the desired tilt angle is not limited to the above two methods, and any known adjustment method can be used.

The liquid crystal thick film cell type optical modulator of the present invention having the above-described structure has a high degree of modulation for both visible light and infrared (light) light, has a fast response speed, and enables high-frequency modulation. Therefore, it can be suitably used as an optical measurement device, a gas component analysis device, an infrared detection device, a non-contact thermometer, and a temperature sensor of a cooking device as a chopper of a light receiver.

[0029]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; First, in FIG. 1, a liquid crystal thick-film cell type optical modulator 1 comprises a thick-film cell 8 in which a ferroelectric liquid crystal 4 is sealed between a pair of opposed electrode plates 2 and 3, and both of the thick-film cell. A voltage application circuit 7 for applying a pulse voltage to the electrode plates 2 and 3. Reference numerals 5 and 6 denote spacers for determining a thick film cell gap.

The voltage application circuit 7 includes two electrode plates 2 and 3
Then, an asymmetrical pulse voltage whose voltage waveform is not symmetric with respect to the positive and negative electrodes is applied. The degree of asymmetry, that is, the duty ratio (positive wave time with one cycle time being 100) is 5
5 to 75%. In addition, a direct current is applied to the ferroelectric liquid crystal cell (either positive or negative polarity. In this case, a positive state is used).
When a positive electric field is applied, the liquid crystals are aligned in a single direction (positive side) and are optically transparent. Then, the polarity is changed instantaneously (the general response speed μsec of ferroelectric liquid crystal).
When the liquid crystal is inverted to a steep rise time shorter than the c order), the liquid crystal cannot follow the change in the electric field, so that the liquid crystal starts to move scatteredly, and when viewed macroscopically, a turbulent flow is generated and a light scattering state is completed. Sufficient scattering can be obtained during the growth of the scattering buds, so if the liquid crystal is pulled back (plus side) before it is aligned in the other single direction (negative side), the liquid crystal will quickly align. As a result, the recovery time from the scattering state to the transparent state is shortened. This is made possible by altering the duty ratio of the pulse wave when modulating, thereby causing an array disturbance sufficient to induce light scattering and a ferroelectric response to recovery from the disturbance. This can dramatically reduce the time.

Next, FIG. 7 shows an example in which the liquid crystal thick film cell type optical modulator 1 shown in FIG. 1 is used for a gas analyzer. Gas analyzer 1
Reference numeral 1 denotes a gas cell 12 to be measured, a reference gas cell 13 juxtaposed with this cell, and a halogen lamp 15 for supplying a luminous flux to these cells 12 and 13 via an interference filter 14.
And a detector 16 for detecting the luminous flux passing through both cells 12 and 13 (using a pyroelectric substance made of lithium tantalate)
And a liquid crystal chopper 1 as a thick film type cell modulator interposed between the cells 12 and 13 and the detector 16.

The liquid crystal chopper 1 comprises a liquid crystal chopper A corresponding to the gas cell 12 to be measured and a liquid crystal chopper B corresponding to the reference gas cell 13.
B is composed of separate thick-film cell modulators,
It can also be used by being integrally configured. Reference numeral 17 denotes a measured gas inlet, 18 denotes a measured gas outlet, and 19 denotes a convex lens.
Since the change in the charge on the surface of the pyroelectric material constituting the detection unit of the detector 16 is observed transiently with the irradiation of light, the change of the irradiation light may occur halfway along the light irradiation path to the detector. It is necessary to arrange the choppers that pass through as described above, and to continuously generate a transient state. The highest sensitivity of this pyroelectric material can be achieved at relatively high frequencies (several hundred Hz), which is only possible with the liquid crystal cell according to the invention.

Next, the operation of the gas analyzer 11 having the above configuration will be briefly described. In FIG. 7, the gas analyzer 11
The luminous flux of the infrared light supplied from the halogen lamp 15 to the measured gas cell 12 and the reference gas cell 13 via the interference filter 14 passes through the gas to be measured (eg, CO ₂ / CO) and passes through the liquid crystal chopper 1. Detected by the detector 16. Here, to the liquid crystal chopper 1 (choppers A and B), asymmetrical pulse voltages having positive and negative voltage waveforms are applied. Since the pyroelectric substance senses only the modulated light, the simplest signal processing of the detector that has received the light can be performed by operating the A and B choppers alternately in time. Also, since the A and B choppers are chopped at different frequencies, both signal components may be simultaneously received, and the respective components may be extracted by a subsequent circuit.

Example 1 Evaluation of Characteristics in Visible Light An evaluation cell was prepared by laminating a glass substrate having an ITO film (ion diffusion film) formed on its surface. Prior to the laminating operation, the surface was rubbed in advance with the cotton cloth in the same direction (rubbing treatment). A polyester film was used as a spacer for cell gap control. As an example, a cell gap of 100 μm was adopted. As the cell gap increases, the scattering intensity increases, but the transparency tends to decrease, so 100 μm was selected. Even if the cell gap is changed, the effect of the present method can be obtained. After that, a commercially available ferroelectric liquid crystal material (Merck Z
LI-1013, 1011). After the periphery was sealed with an epoxy adhesive, the mixture was gradually cooled to 120 ° C. in order to obtain a liquid state, thereby obtaining a smectic C phase.

FIG. 2 shows that a voltage is applied to both ends (applied voltage ± 4
00V) The result when the liquid crystal cell was driven. He-
Modulated light was detected by a photodiode using a Ne laser as a light source. The duty ratio of the pulse wave (1
The cycle time was set to 100, and the ratio of the positive electrode wave time) was changed. 1-a is a case where a voltage is applied by a conventional method (duty ratio 50%). 500 due to slow recovery time
This shows that almost no inversion of Hz can be followed.
1-b, c, d, e, and f are based on the present method, and it can be seen that the recovery response from the scattering state is faster and follows the inversion. Especially duty ratio (55-75%, especially 65-75%)
%)), The degree of modulation is maximum. Although the optimum duty condition varies depending on the modulation frequency, it is preferably 55 to 75%, and particularly preferably 65 to 75%.

FIG. 3 shows the frequency characteristics of the modulator evaluated by the present method. This indicates that the limit frequency of the conventional thick film cell has been significantly improved. Example 2 Evaluation of Characteristics in Infrared Light A silicon substrate (8 to 40 Ωcm) polished on both sides was mirror-polished.
A silicon cell was obtained by laminating pieces cut to a size of 0 mm square. The substrate itself functions as both electrodes. Gold deposition is performed on a part of the substrate to form a round for extracting lead wires. Both outer surfaces of the cell are coated with an anti-reflection coating to sufficiently transmit 5 μm infrared rays. The anti-reflection coating can be applied to various wavelengths according to the purpose of use. The anti-reflection coating is applied for gas analysis, and the infrared ray of 10 μm is used for human body (presence or absence) detection or radiation temperature measurement. Was done. The silicon substrate has been rubbed by rubbing the anti-reflection coating film. A polyester film as a spacer was fixed with an epoxy adhesive so that a liquid crystal-filled portion was provided on a single-sided substrate of the cell so that the cell gap was 100 μm. A liquid crystal (the same component as in Example 1) was filled between the bonded silicon substrates, and a liquid crystal cell was prepared under the same temperature drop condition as the characteristic evaluation in Example 1.

The degree of modulation was about 70 to 50%. FIG. 4 shows a state of modulation when a cell which has been subjected to an anti-reflection coating process for sufficiently transmitting infrared rays having a wavelength of 5 μm is used. Example 3 An evaluation cell was prepared by laminating a glass substrate having an ITO film (transparent conductive film) formed on the surface thereof. Before the laminating operation, a surface treatment (rubbing treatment) was performed on the surface with a cotton cloth in the same direction in advance, and the surfaces were laminated in the same direction. A polyester film was used as a spacer for controlling the cell gap. Cell gap as Example 3: 1
00 μm was adopted.

Although the scattering intensity increases as the cell gap increases, the transparency tends to decrease.
I chose. The effect of this method can be obtained even if the gap is changed. Thereafter, a commercially available ferroelectric liquid crystal material (Merck ZL)
I-1013, 1011). After the periphery was sealed with an epoxy adhesive, the mixture was gradually cooled to 120 ° C. in order to obtain a liquid state, thereby obtaining a smectic C phase.

FIG. 5 shows the effect when a voltage is applied to both ends of the electrode plate (applied voltage: 80 VP-P) to drive the liquid crystal cell. Modulated light was detected by a photodiode using a He-Ne laser as a light source. The bias voltage applied to the rectangular wave was changed as a parameter (0 V, 10 V, 20 V).
2- (a) is a case where a voltage is applied by a conventional method (0 V). Since the recovery time (response speed) is slow, it does not return to the transmission state (100% line in the drawing), does not substantially follow, and consequently the degree of modulation is extremely small. 2-
(B) and-(c) are based on the present method, and it can be seen that the recovery response from the scattering state is faster and follows the inversion. In particular, when the bias DC voltage was 10 to 15 V, the degree of modulation was largest. The optimum bias voltage application condition corresponds to 20 to 50% of a value corresponding to the amplitude of the applied rectangular wave voltage, and this is eventually a condition for obtaining a preferable result.

When a direct current (either positive or negative polarity; here, a positive state) is applied to the ferroelectric liquid crystal cell, the liquid crystals are aligned in a single direction (positive side). It is optically transparent. Therefore, when the magnitude of the bias DC voltage is alternately switched according to the polarity,
Since the liquid crystal cannot follow the change in the electric field, the liquid crystal starts to move in a random manner, and when viewed macroscopically, a turbulent flow is generated and a light scattering state is completed. Sufficient scattering is obtained in the middle of the growth of the scattering buds, so that the liquid crystal is in the other single direction (minus side).
If the liquid crystal is pulled back (positive side) before it is aligned, the liquid crystal can be quickly aligned, and as a result, the recovery time from the scattering state to the transparent state becomes faster, so that the voltage on one side is biased and the voltage on the other side is increased. An electric field sufficient to align in a single direction is easily returned to the original (plus side) because the liquid crystal does not receive it.

According to the present method, the limit frequency of the conventional thick film cell can be remarkably improved from the improvement of the frequency characteristic. Example 4 When similar characteristics were evaluated with infrared light (wavelength: 5 μm), good results as shown in FIG. 6 could be obtained.
The conditions for forming the cells are the same as in the first embodiment.

Example 5 In general, when the helical pitch of the cholesteric (nematic chiral) phase increases, the helical pitch of the smectic C phase tends to increase. Can be. In general, when the spontaneous polarization value becomes extremely small, the liquid crystal becomes difficult to move. Table 1 shows the physical property values of the ferroelectric liquid crystal used in this example.

[0043]

[Table 1]

In the ferroelectric liquid crystal of Table 1, the spontaneous polarization value tends to decrease as the helical pitch increases. When the degree of modulation of the ferroelectric liquid crystal (liquid crystal F) having the smallest spontaneous polarization value in Table 1 was measured, a good measured value was obtained. Further, using the ferroelectric liquid crystal of Table 1, a wavelength of 5 μm
FIG. 7 shows the result of measuring the degree of modulation for mid-infrared rays. FIG. 8 shows the liquid crystal thick film cell type light modulator used for the measurement. In the figure, 2 and 3 indicate a specific resistance of 20 Ωcm and a thickness of 400 μm.
m, an electrode plate made of a silicon substrate, 4 is a ferroelectric liquid crystal,
5 and 6 are 100 μm thick spacers (ie, 100 μm
, 8 denotes a lead wire, and 9 denotes an antireflection film for a wavelength of 5 μm.

FIG. 9 shows the result of measuring the degree of modulation for mid-infrared light at a wavelength of 2 μm. In the drawing, ○ indicates the transmittance (%) in the bright state, X indicates the degree of modulation, and △ indicates the transmittance (%) in the light scattering state. FIG. 10 shows the liquid crystal thick film cell type light modulator used for the measurement. 2 and 3 are IT
An electrode plate made of O, 4 is a ferroelectric liquid crystal, 5 and 6 are spacers having a thickness of 100 μm, 8 is a lead wire, and 10 is a 1 m thickness.
m quartz substrates are shown.

The driving conditions were the conditions shown by 1-g in FIG. As can be seen from FIGS. 7 and 9, at any wavelength, the degree of modulation strongly depends on both the helical pitch and the cell gap. Example 6 The cell gap was changed by changing the thickness of the spacers 5 and 6 in the liquid crystal thick film cell type optical modulator of FIG.
The modulation was measured when near-infrared light of μm was used, and the results are shown in FIG. Note that the driving conditions are as shown in FIG.
g.

As can be seen from FIG. 11, in the optical modulator having the same cell gap, the modulation degree shows a peak when the helical pitch is 0.7 to 0.95 times the cell gap. The maximum modulation is shown when the cell gap is 100 μm.

Embodiment 7 In this embodiment, the relationship between the tilt angle and the modulation is examined. Table 2 shows the physical properties of the ferroelectric liquid crystal that can be used in the present invention.
It was shown to.

[0049]

[Table 2]

FIG. 12 shows the results of measuring the modulation of far-infrared rays having a wavelength of 10 μm by using an optical band-pass filter using n, q, and t among the ferroelectric liquid crystals shown in Table 2 above. Was. In the figure, A is the tilt angle 15.
2 (liquid crystal n) and B show the case where the tilt angle is 23.4 (liquid crystal q) and the C tilt angle is 29.5 (liquid crystal t). Also,
In order to show the effect of the tilt angle, other physical properties were used. Here, the vertical axis in FIG. 12 represents the output (mV) from the pyroelectric infrared sensor used for the light quantity measurement. This output corresponds to the degree of modulation, and the higher the output, the higher the degree of modulation. The degree of modulation is calculated by the following equation: degree of modulation (%) = (I _ON −I _OFF ) / I ₀ (where I ₀ is the amount of light incident on the liquid crystal cell, and I _ON is the open state of the liquid crystal cell. , And I _OFF indicates the amount of light emitted when the liquid crystal cell is closed.)

In the above measurement, the driving condition of the liquid crystal cell was a square wave having a duty ratio of 63% and a frequency of 40 Hz, and a black body furnace (1000K) was used as a light source. The liquid crystal thick film cell type modulator used for the measurement has a configuration as shown in FIG.
A 90 μm cell gap and an antireflection film for a wavelength of 10 μm were used. As is clear from FIG. 12, it was found that the larger the tilt angle, the higher the light scattering intensity was obtained, and the degree of modulation was significantly increased.

Example 8 A liquid crystal thick film cell as shown in FIG. 13 was formed. Note that a P-type silicon single crystal plate was used as the electrode plates (2, 3), and the outer antireflection film 11 had a refractive index of 1.84 and a film thickness of 680.
0 ° MgO is used, and the inner antireflection film 12 is made of MgO.
By adding several weight% of metal to O, 100KΩ /
An anti-reflection film having a sheet resistance of cm ² and conductivity was used. The ferroelectric liquid crystal 4 was manufactured by Chisso Petrochemical Company. For measuring the light quantity of the thick film cell, a pyroelectric infrared sensor is used, and the thickness is 5 μm and the maximum transmittance is 66.5.
Using an optical band-pass filter having a half-value width of 367 nm in%, the change with time of the modulation degree in the wavelength band of 5 μm was measured, and the results are shown in FIG. 14C. The degree of modulation was determined according to Example 7 above.
Calculated by the method described in (1). Further, as a comparison, in the thick film cell of FIG. 13, the time-dependent change of the modulation degree was measured in the same manner as described above except that the inner antireflection film was the same as the outer one,
The results are shown in FIG. 14a. Further, the time-dependent change of the modulation degree was measured for the thick film cell in which the inner antireflection film was not formed in the same manner as described above, and the result is shown in FIG. 14B. As is clear from FIG. 14, the liquid crystal thick film cell of the present invention was an optical modulator having little change with time and a high stability as compared with other cells.

[0053]

According to the present invention, by applying a pulse voltage (preferably a duty ratio of 55 to 75%) having an asymmetrical duty ratio between the positive and negative electrode voltage waveforms to both electrode plates, a visible light and a negative light are applied. A high degree of modulation can be obtained with both infrared rays, and modulation at a high frequency with a high response speed is enabled. Further, the same effect can be obtained by applying a voltage (20 to 50%) in which a rectangular wave voltage is superimposed on a bias DC voltage to both electrode plates.

The thick film cell comprises a ferroelectric liquid crystal sealed between a pair of opposing electrode plates, and means for applying voltage to both electrode plates of the thick film cell. A liquid crystal thick-film cell-type light modulation device in which a ferroelectric liquid crystal having a gap of 50 μm or more and exhibiting a helical pitch in a smectic C phase having a length of 0.7 to 0.95 times the cell gap. The use of a detector makes it possible to obtain a high degree of modulation in both visible light and infrared light.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing a basic configuration example of a liquid crystal thick film cell type optical modulator according to the present invention.

FIG. 2 is a graph showing a relationship between a voltage waveform applied to both electrode plates and a detection modulation degree.

FIG. 3 is a graph showing frequency characteristics of a driving method of the liquid crystal thick film cell type optical modulator of the present invention.

FIG. 4 is a graph similarly showing a modulation waveform.

FIG. 5 is a graph showing a relationship between a voltage waveform applied to both electrodes and a detection modulation degree according to the third embodiment.

FIG. 6 is a graph corresponding to FIG. 5 corresponding to the fourth embodiment.

FIG. 7 is a graph showing a relationship between a helical pitch and a modulation degree according to the present invention.

8 is a schematic sectional view of a liquid crystal thick film cell type optical modulator used for the measurement of FIG. 7;

FIG. 9 is a graph showing the relationship between the helical pitch of the present invention and the transmittance in a bright state, the transmittance in a light scattering state, and the degree of modulation.

10 is a schematic sectional view of a liquid crystal thick film cell type light modulator used for the measurement of FIG. 7;

FIG. 11 is a graph showing a relationship between a cell gap, a helical pitch, and a modulation factor.

FIG. 12 is a graph showing a relationship between a drive voltage and a modulation factor at various tilt angles.

FIG. 13 is a configuration explanatory view showing a configuration example of a liquid crystal thick film cell type optical modulator according to the present invention.

FIG. 14 is a graph showing a temporal change of a modulation factor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal thick film cell type optical modulator 2, 3 Electrode plate 4 Ferroelectric liquid crystal 5, 6 Spacer 7 Voltage application circuit 8 Lead wire 9 Antireflection film 10 Quartz substrate 11 Outer antireflection film 12 Inner antireflection film

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-135808 (JP, A) JP-A-58-173719 (JP, A) JP-A-58-179890 (JP, A) JP-A 62-135890 28717 (JP, A) JP-A-63-301926 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/133 G02F 1/13 505 G02F 1/137

Claims (6)

(57) [Claims] 1. A thick-film cell in which a ferroelectric liquid crystal is sealed between a pair of opposing electrode plates, and voltage applying means for applying voltage to both electrode plates of the thick-film cell .
Ferroelectric liquid crystal aligned to one of two polarities for positive and negative electrodes
Asymmetric duty ratio that can be returned to the original polarity before
A liquid crystal thick film cell type optical modulator comprising driving a ferroelectric liquid crystal by applying a pulse voltage having a voltage waveform having the following . 2. A thick film cell in which a ferroelectric liquid crystal is sealed between a pair of opposing electrode plates, and voltage applying means for applying voltage to both electrode plates of the thick film cell.
A rectangular wave voltage is superimposed on the bias DC voltage, and the ferroelectric liquid
Before the crystal aligns with one of the two polarities,
A liquid crystal thick film cell type optical modulator comprising driving a ferroelectric liquid crystal by applying a voltage having a waveform having an asymmetric duty ratio that can be pulled back . 3. A thick-film cell comprising a ferroelectric liquid crystal sealed between a pair of opposing electrode plates, and means for applying voltage to both electrode plates of the thick-film cell. in gap 50μm or more, the ferroelectric liquid crystal to be sealed is state, and are not showing a helical pitch of at 0.7 to 0.95 times the length smectic C layer of the cell gap, a ferroelectric liquid
Before the crystal aligns with one of the two polarities,
A voltage with a waveform with an asymmetrical duty ratio that can be pulled back
The liquid crystal thick cell light modulator ing from driving the applied to the ferroelectric liquid crystal. 4. The liquid crystal thick film cell type optical modulator according to claim 3, wherein the tilt angle of the smectic C layer is 15 ° or more. 5. The liquid crystal thick film cell type optical modulator according to claim 4, wherein the tilt angle is 20 ° or more. 6. The electrode according to claim 1, wherein an anti-reflection film is formed on both surfaces of the electrode plate, and the anti-reflection film on the opposing surface is made of a conductive material. Liquid crystal thick film cell type light modulator.