Optical: systems and elements – Holographic system or element – Having particular recording medium
Reexamination Certificate
2000-09-26
2001-11-27
Henry, Jon (Department: 2872)
Optical: systems and elements
Holographic system or element
Having particular recording medium
C359S007000, C359S015000, C359S019000, C349S092000, C349S201000
Reexamination Certificate
active
06323970
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to holographic devices, and more particularly, to a switchable hologram.
Switchable holograms are often formed from polymer-dispersed liquid crystal (PDLC) material which have holographic fringes recorded therein. During the recording process, the PDLC material undergoes a phase separation thereby creating fringes, which include regions densely populated by liquid crystal micro-droplets interspersed with regions of clear polymer. The liquid crystal material is interposed between electrodes so that an electrical field can be applied to the hologram. When an electrical field is applied to the hologram, the natural orientation of the liquid crystal droplets is changed, causing the refractive index modulation of the fringes to reduce and the hologram diffraction efficiency to drop to a very low level, thereby effectively erasing the hologram.
Volume holograms (also known as thick or Bragg holograms) provide high diffraction efficiencies for incident light beams having wavelengths close to the theoretical wavelength satisfying the Bragg diffraction condition, and which are within a few degrees of the theoretical angle that also satisfies the Bragg diffraction condition. Experimental evidence shows that the magnitude of the electric field required to switch these holograms between their active (diffracting) state and passive (non-diffracting) state is dependent upon the slant angle of the holographic fringes, which is defined as the angle between the Bragg surface of the fringes and a normal to the hologram surface.
In applications in which a hologram is required to operate over a wide range of incidence angles, such as with an eyepiece in an off-axis wearable display device, there is likely to be significant variation in the slant angle over the area of the hologram. When an electric field of a predetermined magnitude is applied to the hologram, there may be areas in which the slant angle prevents the hologram from switching (i.e., the switching threshold due to the slant angle is higher than the applied field). Under these circumstances, the hologram will only be partially erased.
The magnitude of the electric field may be increased to overcome this problem. However, there may be other areas within the hologram which are then exposed to excessively high voltages (i.e., areas where the switching threshold due to the slant angle is significantly below the applied voltage). This may cause electrical breakdown, delamination (i.e., separation of the hologram from the substrate), or other effects that result in irreversible damage to the hologram.
SUMMARY OF THE INVENTION
A method of producing a switchable hologram generally comprises providing a substrate composed of a liquid crystal material and having two generally opposed surfaces and recording a plurality of holographic fringes composed of liquid crystal droplets in the substrate with one or more of the plurality of holographic fringes positioned such that a surface of the fringes is angled relative to one of the substrate surfaces. The substrate is subjected to an electrical field during recording of the holographic fringes. The electrical field varies across the surface of the substrate so that the liquid crystal droplets are all oriented generally in a common direction.
Recording of the holographic fringes may further include interposing the hologram between a pair of electrodes each positioned generally adjacent to one of the substrates surfaces. One of the pair of electrodes has a plurality of independently controlled segments. Each of the segments is positioned over an area of the substrate having holographic fringes positioned within a common range of angles relative to the substrate surface. A pair of glass carriers may be interposed between the electrodes and the substrate surfaces.
The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages, and embodiments of the invention will be apparent to those skilled in the art from the following description, drawings, and claims.
REFERENCES:
patent: 3807829 (1974-04-01), Close
patent: 4790613 (1988-12-01), Moss
patent: 4932731 (1990-06-01), Suzuki et al.
patent: 4981332 (1991-01-01), Smith
patent: 5018838 (1991-05-01), Barnes et al.
patent: 5035474 (1991-07-01), Moss et al.
patent: 5044709 (1991-09-01), Smith et al.
patent: 5151724 (1992-09-01), Kikinis
patent: 5278532 (1994-01-01), Hegg et al.
patent: 5305124 (1994-04-01), Chern et al.
patent: 5424866 (1995-06-01), Kikinis
patent: 5440428 (1995-08-01), Hegg et al.
patent: 5506701 (1996-04-01), Ichikawa
patent: 5537232 (1996-07-01), Biles
patent: 5581378 (1996-12-01), Kulick et al.
patent: 5680231 (1997-10-01), Grinberg et al.
patent: 5703702 (1997-12-01), Crane et al.
Digilents, Inc.
Henry Jon
Van Pelt & Yi LLP
LandOfFree
Method of producing switchable holograms does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of producing switchable holograms, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing switchable holograms will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2590719