JPH03110527A - Production of nonlinear optical element - Google Patents

Abstract

PURPOSE:To easily produce the org. nonlinaer optical element having excellent characteristics by cooling a specific liquid crystal compd. down to room temp. while impressing an electric field to the liquid crystal compd. through transparent electrodes provided on transparent substrates, thereby putting the liquid crystal compd. into an oriented solid state. CONSTITUTION:The liquid crystal compd. which has a pyrimidine structure, pyradazine structure, pyrazine structure, tetrazine structure, fluorene structure, fluorenon structure or phenyl cyclohexane strucuture and forms the liquid crystal layer at the room temp. or above is heated to the transition temp. to the liquid crystal phase or above and is injected into the spacing between a pair of the transparent substrates 2 and 2 subjected to an orientation treatment. While the electric field is impressed to the liquid crystal compd. through the transparent electrodes 3, 3 provided on the transparent substrates 2, 2, the liquid crystal compd. is cooled to the room temp. and is put into the solid state. The nonlinear optical element with large area and strong second harmonic is obtainable easily with high reproducibility.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a method for manufacturing a nonlinear optical element.

(Prior Art) Nonlinear optical elements are used to modulate the wavelength, phase, and amplitude of laser light, such as harmonic generation, optical switching, and optical mixing, and play an important role in information processing using light.

Conventionally, as a nonlinear optical material, L i N b Oi
Although inorganic compounds such as these have been used, their performance has not been sufficient, such as low conversion efficiency. For this reason, when generating harmonics, it is necessary to use a high-output laser such as a YAG laser as a fundamental wave light source. In addition, in electro-optic modulation elements, the applied magnetic field necessary for modulation is kV/a
There were problems such as reaching up to m order. Regarding nonlinear optical elements using inorganic compounds, A. Yarlv
QUAN70MELECTRONIC82ND ED
ITION”, John & WIIey, 1975
It is explained in ゜ etc.

In recent years, compounds with large nonlinear polarizability have been discovered among organic compounds. The realization of a compact blue laser that combines a highly efficient second harmonic element using these organic nonlinear optical materials and a near-infrared semiconductor laser is seen as promising. Regarding organic nonlinear optical materials, D, S, Che
sla and J, Zyss'Non1inear
0pLIcal Properties of' O
rganic Molecules and Cry
stals, Acadea+Ic Press.

+987. There are explanatory manuals such as However, these organic compounds tend to form a crystal structure with central symmetry due to the interaction of the dipole moments of the molecules themselves, which prohibits the generation of second harmonics, and the size and size of these organic compounds are large enough to be used as optical elements. There were problems such as difficulty in growing crystals with high quality.

(Problems to be Solved by the Invention) The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for manufacturing an organic nonlinear optical element having excellent characteristics.

[Structure of the Invention] (Means and Effects for Solving the Problems) The method for manufacturing a nonlinear optical element of the present invention includes a method for manufacturing a nonlinear optical element that uses a pyrimidine structure, a pyridazine structure, a pyrazine structure, a tetrazine structure, a fluorene structure, a fluorenone structure, or a phenylcyclohexane structure. After heating a liquid crystal compound that forms a liquid crystal layer above room temperature to a temperature above the transition temperature to a liquid crystal phase and injecting it into the gap between a pair of aligned transparent substrates, a transparent electrode provided on the transparent substrates is formed. The method is characterized in that the liquid crystal compound is cooled to room temperature while applying an electric field to the liquid crystal compound to be in an oriented solid state.

In the present invention, the liquid crystal compound used is one that becomes a chiral smectic phase (SmC" phase), which is a ferroelectric liquid crystal phase, in a specific temperature range higher than room temperature, and becomes a solid at room temperature. Specifically, , a pyrimidine structure, a pyridazine structure, a pyrazine structure, a tetrazine structure, a fluorene structure, a fluorenone structure, or a phenylcyclohexane structure.

In the present invention, a transparent substrate subjected to alignment treatment refers to a liquid crystal compound in a liquid crystal state perpendicular to the substrate (vertical alignment).
, parallel (parallel alignment), or at a certain angle (tilted alignment). Common methods for vertical alignment include methods of applying lecithin, organic silane compounds, perfluorononanoic acid chromium complexes, and the like. A general method for parallel alignment treatment includes a method of applying a polyimide film and then rubbing the surface with a cloth or the like.

A common method for tilted orientation is silicon oxide (Si
An example of this method is to deposit O) obliquely to the substrate.

In the present invention, when a liquid crystal compound is heated to a temperature higher than the transition temperature to a liquid crystal phase and then frozen from a liquid crystal state to a solid state,
The appropriate magnitude of the electric field applied to the liquid crystal compound is 10 to several 10 V when the cell thickness is several 1. If the voltage is less than IOV, the effect of orienting the liquid crystal compound is small, and if it exceeds several tens of volts, dielectric breakdown may occur.

As in the present invention, a liquid crystal compound is cooled in an isotropic liquid,
When the solid state is achieved through the liquid crystal state, the structure of the molecular assembly in the solid state reflects the structure in the liquid crystal state, and therefore the structure of the molecular assembly can be easily controlled. Therefore, by using the method of the present invention, it is possible to easily manufacture a nonlinear optical element with a large area and a large second harmonic with good reproducibility.

(Example) The present invention will be explained in detail below.

A liquid crystal cell 1 shown in FIGS. 1(a) and 1(b) was prepared as a nonlinear optical element. As shown in FIG. 1(a), the upper and lower glass substrates 2 each have IT as transparent electrodes.
A polyimide film 4 is formed as an O film 3 and a liquid crystal alignment film. A liquid crystal cell is formed by arranging these two glass substrates 2 with their polyimide film 4 sides facing each other with a sealing material 5 and a spacer 6 interposed between them. Upper and lower glass substrates 2, ITO film 3, and sealing material 5
are arranged as shown in FIG. 1(b) in a plan view. In addition, a spacer with a diameter of 2 is used as the spacer 6,
The thickness of the cell is 2-.

The liquid crystal cell 1 prepared as described above is placed in a vacuum chamber, and the liquid crystal compound, which is solid at room temperature and exhibits a liquid crystal layer in a specific temperature range above room temperature, is heated to become an isotropic liquid, and then placed inside the chamber. Then, the space surrounded by the sealing material 5 was filled with this isotropic liquid by remote control. Thereafter, the injection port was sealed, and lead wires were connected to the ITO films 3 on the upper and lower glass substrates 2.

Using this liquid crystal cell 1, second harmonics were measured using the apparatus shown in FIG. In Figure 2, the laser beam with a wavelength of 1.0844 emitted from the YAG laser-11 is
After the light is circularly polarized by a circularly polarizing plate (λ/4 plate) 12 , only one direction of polarized light is taken out by a polarizing beam splitter 13 and is incident on the liquid crystal cell 1 housed in a thermostatic oven 14 . The resulting transmitted second harmonic having a wavelength of 0.532a is separated from the fundamental wave by a fundamental wave absorption filter I5 and a spectrometer 16, and then its intensity is measured by a photomultiplier tube 17 and a digital oscilloscope 1B.

Using the liquid crystal compounds shown in Table 1,
Measurements were performed with the liquid crystal compound of the liquid crystal cell 1 housed in the liquid crystal cell 1 in an isotropic liquid and solid state.

A voltage of 30 V was applied when the liquid crystal compound was cooled from an isotropic liquid to a solid state.

Table 1 shows the intensity of the second harmonic when each liquid crystal compound is used. The second harmonic intensity in Table 1 is a relative ratio to the intensity of the second harmonic obtained when a fundamental wave of the same intensity is incident on a 1 mm thick Y-cut crystal plate.

As is clear from Table 1, when the liquid crystal compound is in an isotropic liquid state, the intensity of the second harmonic is 0, but when the liquid crystal compound is cooled from an isotropic liquid to room temperature inside the cell, it becomes solid. In this case, the intensity of the second harmonic increases.

In addition, for comparison, when the intensity of the second harmonic of each liquid crystal compound in the powder state was measured, it was found to be 0 or an extremely low value.

From these results, it can be seen that a solid state in which the liquid crystal compound is cooled from an isotropic liquid to room temperature is suitable for increasing the intensity of the second harmonic.

[Effects of the Invention] As detailed above, by using the method of the present invention, a nonlinear optical element that can obtain large second harmonics in a large area can be easily produced.
and reproducible (can be manufactured).

[Brief explanation of drawings]

FIG. 1(a) is a cross-sectional view of a liquid crystal cell manufactured as a nonlinear optical element in an embodiment of the present invention, FIG. 1(b) is a plan view of FIG. 1(a), and FIG. 2 is an embodiment of the present invention. It is a schematic configuration diagram showing a second harmonic measuring device used in 1. Liquid crystal cell, 2. Glass substrate, 3. IT.
O film, 4... polyimide film, 5... sealing material, 6...
...Spacer, 11...YAG laser, 12...
Circular polarizing plate (λ/4 plate), 13... Polarizing beam splitter 14... Constant temperature chamber, 15... Fundamental wave absorption filter, 1B... Spectrometer, 17... Photomultiplier tube, 18・
··Digital oscilloscope.

Claims (1)

[Claims] A liquid crystal compound having a pyrimidine structure, a pyridazine structure, a pyrazine structure, a tetrazine structure, a fluorene structure, a fluorenone structure, or a phenylcyclohexane structure and which forms a liquid crystal layer at room temperature or above is heated to a temperature above the transition temperature to a liquid crystal phase, After injecting the liquid crystal compound into the gap between the pair of aligned transparent substrates, an electric field is applied to the liquid crystal compound through the transparent electrode provided on the transparent substrate and the liquid crystal compound is cooled to room temperature, thereby turning the liquid crystal compound into an aligned solid state. A method for manufacturing a featured nonlinear optical element.