Optical modulating element and electronic apparatus using it

• US 5,642,214 A
• Filed: 07/05/1994
• Issued: 06/24/1997
• Est. Priority Date: 07/19/1991
• Status: Expired due to Term

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Ishii, Yutaka, Yamamoto, Yoshitaka
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Dudek, James A.
• Application Number:
  US08/270,801
• Time in Patent Office: 1,085 Days
• Field of Search: 359/53, 359/63, 359/64, 359/103
• US Class Current: 349/96
• CPC Class Codes: G02F 1/133533 Colour selective polarisers G02F1/1347 takes precedence
• CPC Class Codes: G02F 1/13473 for wavelength filtering or for colour display without the use of colour mosaic filters
• CPC Class Codes: G02F 1/1392 using a field-induced sign-reversal of the dielectric anisotropy
• CPC Class Codes: G02F 1/1396 the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell G02F1/141 takes precedence
• CPC Class Codes: G02F 1/141 using ferroelectric liquid crystals

Abstract

A photomodulation element which uses a color variable filter to obtain the light of a desired wavelength and a liquid crystal element. Light entering the photomodulation element from one side passes through the liquid crystal panel and a second polarizer. The distribution of the transmission light intensity about the wavelength is nearly close to the normal distribution centered on a specific wavelength determined on the basis of the retardation of the liquid crystal panel. Based on the half-value width W necessary in this distribution, the retardation of the panel is determined and the number of the liquid crystal elements is determined so as to obtain a bandwidth which corresponds to the color of the light desired. The retardation of the light crystal is changed by a voltage regulating circuit so that the transmission light intensity distribution at the wavelength of the transmission light of the liquid crystal element is maximized at the desired wavelength λo so that the wavelength of the light leaving the photomodulation element may be selected to provide the desired light.

Claims

1. An optical modulating element comprising:

a pair of neutral polarizers, said neutral polarizers being the only polarizers in said optical modulating element;

a plurality of adjacent crystal panels, in each of which a nematic liquid crystal having birefringence and a twisting angle of 0°

is sealed, arranged from an inlet side to an outlet side of said modulating element, all of said panels being positioned between the pair of neutral polarizers; and

means for changing the retardation .increment.nd of each liquid crystal panel,

wherein the axis of polarization of the neutral polarizer on the outlet side is parallel to the direction of polarization of the straight polarizing component or to the direction of the major axis of the elliptical polarizing component of the output light of the last liquid crystal panel toward the outlet side, and when transmitting light of a wavelength λ

_o through the liquid crystal panels, the retardation .increment.nd of each liquid crystal panel is adjusted to satisfy the following equation;

space="preserve" listing-type="equation">.increment.nd/λ

.sub.o =(2m-1)/2

where .increment.n is the anisotropy of refractive index of the nematic liquid crystal, d is the thickness of a liquid crystal layer contained in the liquid crystal panel, and m is an integer,

wherein the optical axis direction at an exit side of a first liquid crystal panel toward the inlet side of said optical modulating element is at an angle of 2α

with the plane of polarization of the neutral polarizer at the inlet side of said optical modulating element, the optical axis direction of a second and successive liquid crystal panels is in the direction intersecting diagonally with the orientation of a liquid crystal panel preceding the liquid crystal panel, at an angle of 2α

, and the plane of polarization of the neutral polarizer at the outlet side of said optical modulating element is parallel to the optical axis direction at an exit side of a last liquid crystal panel towards the outlet side of said modulating element.

2. An optical modulating element as claimed in claim 1, wherein each liquid crystal panel is constituted by a pair of transparent electrodes between which a liquid crystal is sealed, and the means for changing the retardation .increment.nd of each liquid crystal panel is a voltage application means for applying either an AC voltage or a DC voltage to the liquid crystal.

3. An optical modulating element as claimed in claim 1, wherein when transmitting the light of a wavelength of λ

₀ through the modulating element, the retardation .increment.nd of each liquid crystal panel and the number of layers of the respective liquid crystal panels are selected in such a way that the width at half the maximum in the distribution of intensity of the transmitted light centering on the wavelength λ

₀ the transmitted light and the intensity of light of wavelengths other than λ

₀ may be predetermined values.

4. A display apparatus which makes an indication by irradiating the light of one light source containing the wavelengths of a plurality of colors on a transmission or reflection type display means, said apparatus including an optical modulating element, said apparatus displays images corresponding to the time period for an afterimage effect, the optical modulating element switching the color of the light that passes within a time period for display of the image for each color;

the optical modulating element comprising;

a pair of neutral polarizers, said neutral polarizers being the only polarizers in said optical modulating element;

a plurality of adjacent crystal panels, in each of which a nematic liquid crystal having birefringence and a twisting angle of 0°

is sealed, arranged from an inlet side to an outlet side of said modulating element, all of said panels being positioned between the pair of neutral polarizers; and

means for changing the retardation And of each liquid crystal panel,

wherein the axis of polarization of the neutral polarizer on the outlet side is parallel to the direction of polarization of the straight polarizing component or to the direction of the major axis of the elliptical polarizing component of the output light of the last liquid crystal panel toward the outlet side, and when transmitting light of a wavelength λ

_o through the liquid crystal panels, the retardation And of each liquid crystal panel is adjusted to satisfy the following equation;

space="preserve" listing-type="equation">.increment.nd/λ

.sub.o =(2m-1)/2

where .increment.n is the anisotropy of refractive index of the nematic liquid crystal, d is the thickness of a liquid crystal layer contained in the liquid crystal panel, and m is an integer,

wherein the optical axis direction at an exit side of a first liquid crystal panel toward the inlet side of said optical modulating element is at an angle of 2α

with the plane of polarization of the neutral polarizer at the inlet side of said optical modulating element, the optical axis direction of a second and successive liquid crystal panels is in the direction intersecting diagonally with the orientation of a liquid crystal panel preceding the liquid crystal panel, at an angle of 2α

, and the plane of polarization of the neutral polarizer at the outlet side of said optical modulating element is parallel to the optical axis direction at an exit side of a last liquid crystal panel towards the outlet side of said modulating element.