KR100724985B1 - Polarization modulation device - Google Patents

Abstract

A polarization modulating device is provided to control polarization of light incident onto a liquid crystal cell by controlling arrangement of liquid crystal molecules according to an applied voltage and frequency with use of an in-plane electric field and a dual frequency liquid crystal. A dual frequency liquid crystal layer(2) is placed under an upper glass substrate(1) and is rubbed at an angle of 45 degrees with respect to an electric field. An in-plane electrode is placed under the liquid crystal layer to generate an in-plane electric field. An insulating layer is placed under the in-plane electrode. A glass substrate(5) is placed under the insulating layer. A polarization plate is disposed to be in parallel or perpendicularly with a transmission axis of the polarization plate and an optical axis of the liquid crystal under the glass substrate. A polarization modulating device uses a dual frequency liquid crystal and an in-plane electric field, and includes the polarization plate placed under the aforementioned structure. Both a transparent electrode and an optical electrode are used.

Description

Polarization Modulation device

1 is a cross-sectional view of a polarization modulator using dual frequency liquid crystals based on a horizontal electric field according to a first embodiment.

2 is a plan view showing the movement of the liquid crystal director as the dielectric anisotropy changes according to the voltage and frequency applied to the dual frequency liquid crystal.

3A is a polarization change diagram of light when having a phase retardation difference of λ / 2.

3B is a polarization change diagram of light when φ <45 °.

4 is a change in polarization of light when having a phase retardation difference of λ / 4;

5 is a cross-sectional view of a polarization modulator having a pure horizontal electrode structure according to a second embodiment.

The present invention relates to a polarization modulator (Polarization modulator), and more particularly, by injecting a dual frequency liquid crystal into the cell in a manner using a horizontal electric field to adjust the change of the liquid crystal molecules in accordance with the applied voltage and frequency It controls the polarization state of light incident on the liquid crystal cell, dual frequency liquid crystal is applied to the device that modulates the polarization state of incident light by applying the dielectric anisotropy becomes positive at a specific frequency, the dielectric anisotropy is negative at another specific frequency It is about.

A liquid crystal display using a horizontal electric field and adjusting the light transmittance according to the twisting arrangement of liquid crystals is commercialized, and much research is being conducted. However, the present invention is not a device for implementing a display and is a device for modulating the polarization state of incident light, which is different from a liquid crystal display. In addition, while a display using a conventional horizontal electric field uses a liquid crystal having a positive or negative dielectric anisotropy, the present invention can realize both positive and negative dielectric anisotropy according to a specific frequency of an applied voltage by using a dual frequency liquid crystal. This is different.

In addition, due to the recent rapid growth of optical communication, a large amount of digital signals, which transmit a large amount of data at a small volume and a high speed through optical fibers, are widely used for long distance transmission. In the data transmission method of optical communication, there is a method of transmitting an optical signal by amplitude-modulating the data to be transmitted for each channel. In recent years, polarization modulation methods have emerged, rather than amplitude modulation, which can accurately detect channel information on a transmission line by polarizing data to be transmitted and improve data reliability.

Therefore, the polarization modulation method of light using the liquid crystal (dual frequency liquid crystal) in which the anisotropy of the liquid crystal and the dielectric anisotropy is changed at a specific voltage and frequency can be sufficiently applied in various fields as well as in the optical communication field, and it is easy to manufacture a cell for polarization modulation. Can do it.

The present invention provides a device that modulates the polarization state of light according to the applied voltage and frequency by using a dual frequency liquid crystal and using a horizontal electric field, which is different from the polarization modulation method currently used by the above-described technology. .

In order to achieve the above object, the present invention proposes an apparatus for horizontally aligning a dual frequency liquid crystal and modulating the polarization state of incident light through rearrangement of the liquid crystal director according to the applied voltage and frequency using a horizontal electric field. .

In particular, the device uses a dual frequency liquid crystal and a horizontal electric field so that the liquid crystal may have positive or negative dielectric anisotropy at a specific voltage and frequency. Therefore, when it has positive dielectric anisotropy, the optical axis of the liquid crystal moves from the initial 45 ° direction to 0 ° in response to the application of voltage. When it has negative dielectric anisotropy, the optical axis of the liquid crystal is 90 in the 45 ° direction according to the application of voltage. Move in ° direction. As a result, the optical axis of the liquid crystal may have a phase delay having a value of λ / 2 (m + 1) as it changes according to application of a specific frequency and voltage. In addition, when the liquid crystal optical axis is positioned between 45 ° and 0 ° and between 45 ° and 90 ° without the optical axis of the liquid crystal being 0 ° and 90 °, the incident linearly or circularly polarized light becomes elliptical polarization, and the elliptical polarization depending on the voltage applied. The main axis of can be changed.

Example 1

Example 1 has a horizontal electrode structure and polarized polarized light when the dual frequency liquid crystal has a positive dielectric anisotropy at a specific voltage and frequency and a negative dielectric anisotropy with a phase delay of λ / 4 and λ / 2. A device that modulates a state. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 1 is a cross-sectional view of a polarization modulation device using dual frequency liquid crystals based on a horizontal electric field according to a first embodiment of the present invention to show an arrangement state of initial liquid crystals.

As shown, the upper substrate and the lower substrate, there is an upper glass substrate 1 and the lower glass substrate 5, respectively. An insulator 4 is placed on the lower glass substrate 5, and an electrode is positioned on the insulator 4 so that a horizontal electric field can be applied, and a transparent electrode 3 or an opaque electrode is placed. As for the structure of the electrode 3, all electrode patterns capable of using a horizontal electric field can be used, and the width w of the electrode, the gap l between the electrode and the electrode, and the cell gap can be flexibly adjusted according to the device. On the upper part of the electrode 3, dual frequency liquid crystals 2 whose dielectric anisotropy changes in accordance with the applied voltage and frequency are constantly arranged in the direction of 45 ° with respect to the y axis 7.

FIG. 2 is a plan view illustrating the movement of a liquid crystal director as the dielectric anisotropy changes according to a specific voltage and frequency applied to a dual frequency liquid crystal. The rubbing direction is a 45 ° twisted direction with respect to the y axis, and the optical axis of the initial liquid crystal director 1 has a 45 ° direction. The director 2 of the liquid crystal is rotated. At another specific voltage and frequency, the liquid crystal director 3 rotates with a negative dielectric anisotropy and an angle of φ in the x-axis direction depending on the application of the voltage.

FIG. 3A is a polarization change diagram in which the liquid crystal molecules of the liquid crystal cell in FIG. 1 have a phase delay difference of λ / 2 when the liquid crystal molecules are rearranged at φ = ± 45 ° and have a changed polarization state. When the linearly polarized light (1) is incident on the cell, the linearly polarized light is ± 90 ° by ± 2φ, and when the left circularly polarized light (2) is incident on the cell, it becomes the right polarized light, and the elliptically polarized light (3) When the incident light is incident, the elliptical polarized light is rotated ± 90 ° about the elliptic axis.

FIG. 3B is a polarization change diagram in which the liquid crystal molecules of the liquid crystal cell in FIG. 1 have a phase delay smaller than λ / 2 when the liquid crystal molecules are rearranged to φ <± 45 ° and change in polarization state. When linearly polarized light is incident on the cell, it becomes elliptically polarized light that is not twisted by ± 2φ. The main axis of the elliptical polarization may be distorted as the optical axis of the liquid crystal changes as the voltage is applied.

4 is a polarization change diagram in which the polarization state changes when the liquid crystal molecules of the liquid crystal cell have a phase delay difference of λ / 4 in FIG. 1. When linearly polarized light is incident on the cell, it becomes circularly polarized light (1). When circularly polarized light is incident on the cell, it becomes linearly polarized light (2).

Example 2

Unlike the first embodiment, the second embodiment of the present invention does not use an electrode patterned under the liquid crystal cell, and forms a polymer wall on the liquid crystal cell and coats the electrode on the wall to apply a horizontal electric field to the liquid crystal cell. It is a polarization modulator designed to be. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

5 is a polarization modulation that modulates a polarization state according to a voltage and frequency applied using dual frequency liquid crystals without electrodes being patterned at the bottom of the liquid crystal cell according to the second embodiment of the present invention, and having electrodes at left and right sides of the cell. Device section. As shown in the upper substrate, the upper glass substrate 1 is located. The lower substrate has a lower glass substrate 5, and a wall 2 using a polymer is located at both sides between the upper glass substrate 1 and the lower glass substrate 5. Electrodes 3 are coated on both polymer walls 2. As the electrode 3, a transparent or opaque electrode is used. Alternatively, the wall may be formed of a conductive polymer instead of the polymer wall and the electrode. The gap between the electrode and the cell gap can be flexibly adjusted depending on the device. The dual frequency liquid crystal 4 is positioned between the upper glass substrate 1 and the lower glass substrate 5 and rubbing in a 45 ° direction.

By using the polarization modulator according to the present invention, there is an effect of eliminating manufacturing complexity and easily modulating the polarization state of incident light using dual frequency liquid crystal and a horizontal electric field.

In addition, the present invention operates as described above, it is possible to widen the selection of frequencies by performing polarization modulation rather than amplitude modulation in a multi-channel optical communication network.

Claims (4)

An upper glass substrate; A dual frequency liquid crystal layer is rubbed in the direction of 45 ° to the electrode under the upper glass substrate; A horizontal electrode is positioned below the liquid crystal layer to generate a horizontal electric field; An insulating layer under the horizontal electrode; A glass substrate positioned below the insulating layer; A polarizing plate in which the transmission axis of the polarizing plate positioned below the glass substrate and the optical axis of the liquid crystal are horizontal or vertical; A polarization modulator using a dual frequency liquid crystal and a horizontal electric field including a polarizer plate positioned below the structure; Polarization modulator using dual frequency liquid crystal and horizontal electric field where both transparent and opaque electrodes are used. The method of claim 1, The polarizing plate is a polarization modulator that is not located, the incident light is linearly or horizontally or vertically polarized light and the circularly or elliptically polarized light incident to the optical axis of the liquid crystal. An upper glass substrate; A dual frequency liquid crystal layer is rubbed in the direction of 45 ° to the electrode under the upper glass substrate; A glass substrate disposed under the liquid crystal layer; An electrode having a polymer wall between the upper and lower glass substrates and coated on the polymer wall; A polarizing plate in which the transmission axis of the polarizing plate positioned below the glass substrate and the optical axis of the liquid crystal are horizontal or vertical; A polarization modulator using a dual frequency liquid crystal and a horizontal electric field including a polarizer plate positioned below the structure; Polarization modulator using dual frequency liquid crystal and horizontal electric field where both transparent and opaque electrodes are used. The method of claim 3, wherein The polarizing plate is a polarization modulator that is not located, the incident light is linearly or horizontally or vertically polarized light and the circularly or elliptically polarized light incident to the optical axis of the liquid crystal.

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