Liquid crystal cells – elements and systems – Liquid crystal system – Liquid crystal for recording or imaging on photosensitive...
Reexamination Certificate
1997-03-11
2001-07-31
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Liquid crystal for recording or imaging on photosensitive...
C349S057000, C349S064000
Reexamination Certificate
active
06268893
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention is directed to an efficient and cost effective apparatus and method of generating a high security optical variable device(OVD).
2. Description of the Prior Art.
In the optical process many applications are required to record an interference fringe where a wavefront is to be reconstructed. In general, a fringe pattern is recorded by interfering more than one wavefront beam and recording the fringe onto a high resolution photo-material. However, it is difficult to obtain a fringe pattern which is designed for special applications such as information processing, non-sphere wavefront, etc. For a high security application, it is necessary to record a well-designed pattern so that it is difficult or impossible to counterfeit.
In addition, holography has been a commercially viable product in the security and packaging fields for more than a decade. Landis & Gyr has developed an E-beam written “Kinegram”, marketed with its brilliant optical diffractive appearance. CSIRO developed another E-beam OVD called “Pixelgram”. Toppan Printing Co. has an E-beam OVD that includes dot-matrix type and 3D grating images. While E-beam generated OVD provides eye catching appearance, it's high cost has become price prohibitive. Very few entities, except government agencies, can afford it. Conventional holographic services have developed much more rapidly, mostly due to the fact that equipment costs are relatively affordable. The present invention was designed to alleviate the drawbacks of the prior art in an effort to provide affordable and high precision diffractive OVD and/or hologram services in a timely manor.
It is an object of the present invention to alleviate the drawbacks of the prior art and to provide an extremely low cost and an effective high speed fringe recording system and method of operating the same.
It is another object of the invention to provide a high speed recording process by using a Liquid Crystal Display (LCD). A computer generated pattern is displayed on the LCD. A collimated laser beam illuminates the LCD and the pattern is imaged onto a photo-material plane with a (X) reduction in size. The pattern displayed on the LCD is shifted in a constant speed. Meanwhile, the photo-material plane is shifted in the same speed so that the pattern can be recorded in extreme high speed.
It is yet an another object of the invention to provide a pattern recording process for the diffractive hologram from a computer generated pattern. A laser beam is focused onto a photo-material plane within a micron order size. The laser beam is switched on and off as to respond to the binary data which is transformed from a computer generated pattern. This recording process offers a very fine pattern forming a diffractive object.
This invention discloses an efficient and cost effective method of generating a high security optical variable device(OVD). Prior art electron beam devises generate a very detailed diffractive grating, but it is extremely costly, slow, and has restrictive ion size. Other conventional holographic systems used to produce various types of 2D and/or 3D images cost less, but have a restrictive performance. This invention provides a method that not only produces optical effect/images that E-Beam systems and conventional holographic systems can, but does it faster and is more cost effective.
SUMMARY OF THE INVENTION
The present invention is directed to a method and apparatus for a fringe direct writing system. The apparatus is roughly classified into four parts: an illumination part; an image display and optical imaging part; an optically autofocusing part; and a two dimensional (X-Y) moveable stage part.
The illumination part may comprise either a coherent light source or an incoherent light source. The image display and optical imaging part has an LCD device used to display the fringe pattern or the designed pattern which is previously calculated by using a computer combined with an optical imaging setup including an objective lens. The autofocusing part is combined with a semiconductor source and a sensor in order to keep the system on focus between the LCD plane and recording material. The two dimensional moveable stage provides a space to hold a recording material and has a high resolution moving pitch.
Another object that the invention provides is a new method to input the pattern by using an LCD device. Here, the LCD device is used as an optical modulator. In the traditional method, the EB writer focuses a single elector-beam into a spot of sub-micrometer size to write a fringe line by line. In this new method, instead of the single beam, it directly images a pattern, which is previously calculated by computer and displayed on the LCD panel, onto the recording material. This method has the possibility to write a fringe pattern in large region within a short period of time.
For a 3D fringe recording, pre-distorted computer graphics images via Fast Fourier transform (FFT) are calculated to simulate anamorphic optical synthesis systems. The fringe pattern is obtained and distributed into an N by N portion as a matrix pixel and can be down loaded to the LCD panel. A narrow bandwidth illumination source including laser source is used for illumination of the LCD panel. The image displayed on the LCD is imaged on to the recording material. You can synchronize the LCD fringe information, record material location, and expose parameters via precision computer control. The system is capable of combining two tasks. The simple grating which the E-beam system typically accomplishes and the complex imaging that the holographic system typically accomplishes are both achieved by the device according to the present invention. With the combination of the two valuable OVD features, this system offers a significant step forward in the field of security optical variable devices.
REFERENCES:
patent: 3914761 (1975-10-01), Murase et al.
patent: 4510575 (1985-04-01), Mueller et al.
patent: 5049901 (1991-09-01), Gelbart
patent: 5229872 (1993-07-01), Mumola
patent: 5521748 (1996-05-01), Sarraf
patent: 5742362 (1998-04-01), Chikamichi
Kang Der-Kuam
O'Boyle Lily
American Bank Note Holographics
Duong Tai V.
Liniak Berenato Longacre & White
Sikes William L.
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