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Light diffusion control by electrically reconfigurable holographic optical elements
| Details |
Inventors: Popovich, Milan M.;
Assignee: DigiLens, Inc. (Sunnyvale, CA)
Primary Examiner: Spyrou; Cassandra
Assistant Examiner: Boutsikaris; Leo
Attorney, Agent or Firm: Law Offices of Terry McHugh
A system and a method of displaying projected images on a projection screen of the system include one or more reconfigurable holographic optical elements (HOEs) in the screen to optically manipulate the projected images impinging on the screen. The reconfigurable HOEs may be configured to perform simple optical functions that are commonly associated with traditional optical devices, such as lenses, prisms and mirrors. However, the reconfigurable HOEs may also be configured to perform sophisticated optical manipulations, such as varying angular intensity of diffused light toward predefined viewing regions. Each reconfigurable HOE includes a hologram that is sandwiched between two electrode layers. The hologram is a holographic photopolymeric film that has been combined with liquid crystal. The hologram has an optical property that changes in response to an applied electrical field. The reconfigurable HOEs are utilized to control the diffusing characteristic of the projection screen. The diffusing characteristic can be changed by selectively setting one or more reconfigurable HOEs to a diffractive state. In one application, the reconfigurable HOEs are utilized to optimally diffuse the projected images with respect to light intensity, so that the projected images appear to be uniformly bright to multiple observers at different viewing regions. In another application, the reconfigurable HOEs are utilized to display the projected images in a stereoscopic form. |
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DETAILED DESCRIPTION A system and a method of displaying projected images on a projection screen of the system utilize one or more reconfigurable holographic optical elements (HOEs) in the screen to optically manipulate the projected images impinging on the screen.
The reconfigurable HOEs may be designed to perform simple optical functions that are commonly associated with traditional optical devices, such as those performed by lenses, prisms and mirrors.
However, the reconfigurable HOEs are also designed to perform sophisticated optical manipulations, such as varying angular intensity of diffused light toward predefined viewing regions.
Depending on the optical characteristics of the reconfigurable HOEs, the projection screen of the system may be designed for "reflective viewing," i.
e.
, viewing from the side of the projection screen facing a projector, or for "transmissive viewing," i.
e.
, viewing from the side of the screen opposite to the projector.
Each reconfigurable HOE includes a hologram that is sandwiched between two electrode layers.
The hologram is a holographic photopolymeric film that has been combined with liquid crystal.
The presence of the liquid crystal allows the hologram to exhibit optical characteristics that are dependent on an applied electrical field.
Preferably, the hologram is a Bragg-type hologram, having a high diffraction efficiency.
The electrode layers may be made of Indium Tin Oxide (ITO), which typically has a transmission efficiency of greater than 80%.
The reconfigurable HOE has at least two optical operating states, a diffractive state and a passive state.
The diffractive properties of the reconfigurable HOE primarily depend on the recorded holographic fringes in the photopolymeric film.
In the diffractive state, the reconfigurable HOE diffracts propagating light in a predefined manner.
In the passive state, the reconfigurable HOE does not optically alter the propagating light.
Initially, the hologram of the reconfigurable HOE is in the diffractive state, such that received light is diffracted in the predefined manner
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Optical Systems 
