High brightness transflective LCD and method using tunable mirror

• US 6,710,831 B1
• Filed: 09/29/2000
• Issued: 03/23/2004
• Est. Priority Date: 09/29/2000
• Status: Active Grant

• Current Assignee: Teledyne Scientific & Imaging, LLC (Teledyne Technologies Incorporated)
• Original Assignee: Rockwell Scientific Licensing LLC
• Inventors: Winker, Bruce, Gunning, William J.
• Primary Examiner(s): Dudek, James A.
• Application Number:
  US09/676,138
• Time in Patent Office: 1,271 Days
• Field of Search: 349/115, 349/77, 349/74, 349/113, 349/114
• US Class Current: 349/115
• CPC Class Codes: G02F 1/133504 Diffusing, scattering, diffracting elements associated to illuminating devices G02F1/133606
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133543 Cholesteric polarisers
• CPC Class Codes: G02F 1/133553 Reflecting elements associated to illuminating devices G02F1/133605
• CPC Class Codes: G02F 1/133555 Transflectors
• CPC Class Codes: G02F 1/133626 providing two modes of illumination, e.g. day-night
• CPC Class Codes: G02F 1/1347 Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
• CPC Class Codes: G02F 1/13718 based on a change of the texture state of a cholesteric liquid crystal
• CPC Class Codes: G02F 1/1393 the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells G02F1/1396, G02F1/141 take precedence
• CPC Class Codes: G02F 1/141 using ferroelectric liquid crystals
• CPC Class Codes: G02F 1/1506 caused by electrodeposition, e.g. electrolytic deposition of an inorganic material on or close to an electrode
• CPC Class Codes: G02F 2203/02 reflective
• CPC Class Codes: G02F 2203/09 transflective

Abstract

A Liquid Crystal Display (LCD) uses a tunable mirror in place of a partially reflective mirror. The tunable mirror has a controllable reflectivity and transmitance which allows the mirror to primarily reflect light when the LCD is operated in a reflective mode, and to primarily transmit light from a backlight when the LCD is operated in a transmissive mode.

Claims

1. A liquid crystal display (LCD), comprising:

a liquid crystal cell;

a tunable mirror, optically aligned with the liquid crystal cell, having controllable reflective and transmissive modes, such that in the reflective mode the tunable mirror primarily reflects light received from the liquid crystal cell back through the cell, and in the transmissive mode the mirror primarily transmits light towards the liquid crystal cell;

a backlight on a side of the tunable mirror opposite the liquid crystal cell, the backlight being controllably switchable between emissive and non-emissive states of operation, for providing backlighting the LCD in the emissive state of operation; and

wherein

said tunable mirror is further operable at at least one intermediate mode in which it partially reflects light received from the liquid crystal cell back through the cell, and partially transmits light received from the backlight towards the liquid crystal cell; and

said backlight is further operable at at least one intermediate state of operation in which it partially illuminates the LCD.

2. A liquid crystal display (LCD), comprising:

a liquid crystal cell;

a tunable mirror, optically aligned with the liquid crystal cell, having controllable reflective and transmissive modes, such that in the reflective mode the tunable mirror primarily reflects light received from the liquid crystal cell back through the cell, and in the transmissive mode the mirror primarily transmits light towards the liquid crystal cell;

a backlight on a side of the tunable mirror opposite the liquid crystal cell, the backlight being controllably switchable between emissive and non-emissive states of operation, for providing backlighting the LCD in the emissive state of operation;

wherein the tunable mirror comprises;

a tunable retarder, being controllably switchable between first and second states of operation, the optical phase delay of the two states differing by λ

/2; and

a cholesteric reflector optically aligned with the retarder on a side opposite the liquid crystal cell, for reflecting light received from the retarder in the first state, and for transmitting light through the retarder in the second state such that the tunable mirror operates in the reflective mode when the retarder is in the first state, and in the transmissive mode when the retarder is in the second state; and

wherein the tunable retarder is a negative quarter-wave to positive quarter-wave (+/−

λ

/4) retarder, controllably switchable between −

λ

/4 and +λ

/4 states of operation,

whereby in the +λ

/4 state, said retarder converts linearly polarized light of a second linear direction to circularly polarized light of a second rotational direction, and converts circularly polarized light of the second rotational direction to linearly polarized light of the second linear direction and, in the −

λ

/4 state, said retarder converts circularly polarized light of a first rotational direction to linearly polarized light of the second linear direction; and

whereby said cholesteric reflector reflects circularly polarized light of the second rotational direction and transmits a component of randomly polarized light having a circular polarization of the first rotational direction, such that the tunable mirror operates in the reflective mode when the +/−

λ

/4 retarder is in the +λ

/4 state, and in the transmissive mode when the +/−

λ

/4 retarder is in the −

λ

/4 state.

3. The LCD of claim 2, wherein the +/−

λ

/4 retarder comprises a quarter-wave (λ

/4) retarder optically aligned with a zero to half-wave (0-λ

/2) retarder.

4. The LCD of claim 2, wherein the cholesteric reflector is a diffuse reflecting cholesteric liquid crystal polymer film.

5. The LCD of claim 2, wherein the +/−

λ

/4 retarder is a ferroelectric liquid crystal retarder.

6. A method of operating a liquid crystal display (LCD), comprising:

primarily reflecting light entering a first side of a liquid crystal cell and exiting a second side of the liquid crystal cell back through the liquid crystal cell when the amount of light entering from the first side of the liquid crystal cell is above a viewability threshold;

generating and primarily transmitting a backlight emission from the second side of the liquid crystal cell through the liquid crystal cell when approximately no light enters the first side of the liquid crystal cell; and

partially reflecting light entering a first side of a liquid crystal cell and exiting a second side of the liquid crystal cell back through the liquid crystal cell, and generating and partially transmitting a backlight emission from the second side of the liquid crystal cell through the liquid crystal cell when light entering from the first side of the liquid crystal cell falls below said viewability threshold, said backlight emission being generated in an amount sufficient to supplement the reflected light such that it reaches said viewability threshold.