System for optically identifying an object

• US 6,301,047 B1
• Filed: 11/16/1999
• Issued: 10/09/2001
• Est. Priority Date: 11/17/1998
• Status: Expired due to Term

• Current Assignee: NHK Spring Company Limited
• Original Assignee: NHK Spring Company Limited
• Inventors: Hoshino, Hidekazu, Takeuchi, Itsuo, Shibuya, Seiya
• Primary Examiner(s): Spyrou, Cassandra
• Assistant Examiner(s): ASSAF, FAYEZ G
• Application Number:
  US09/440,683
• Time in Patent Office: 693 Days
• Field of Search: 359/2, 359/566, 359/483, 359/485, 359/502, 359/573, 359/569, 359/572, 349/194, 283/86, 283/87, 283/90, 356/71, 250/556
• US Class Current: 359/566
• CPC Class Codes: B42D 2033/26 Liquid-crystal material
• CPC Class Codes: B42D 25/00 Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof printing processes to produce identification or security features B41M3/14
• CPC Class Codes: B42D 25/328 Diffraction gratings; Holograms
• CPC Class Codes: B42D 25/364 Liquid crystals
• CPC Class Codes: G06K 19/16 the marking being a hologram or diffraction grating
• CPC Class Codes: G06K 7/12 using a selected wavelength, e.g. to sense red marks and ignore blue marks

Abstract

The object to be identified is affixed with an identification medium comprising a reflective layer consisting of a reflective hologram or diffraction grating. The high polymer cholesteric liquid crystal provides an inexpensive identification medium, and the use of the second light receiving unit for providing a reference signal provides a high S/N output signal which is highly distinct and resistant to the contamination of the identification medium. Also, the elimination of the need for expensive optical elements such as beam splitters also contributes to the reduction of cost.

Claims

1. A system for optically identifying the authenticity of an object, comprising:

a diffraction grating affixed to an object, said diffraction grating comprising a high polymer cholesteric liquid crystal layer for a reflective layer of said diffraction grating;

a light source for impinging an incident light beam onto said diffraction grating;

a first light receiving unit placed at a position for receiving a diffracted light beam from said diffraction grating and providing an output signal;

a circularly polarizing filter placed between said first light receiving unit and said diffraction grating; and

a second light receiving unit placed at a different position for receiving a diffracted light beam from said diffraction grating and providing a reference signal therefrom.

2. A system for optically identifying the authenticity of an object according to claim 1, wherein said second light receiving unit is adapted to receive said diffracted light beam without an intervention of a circularly polarizing filter.

3. A system for optically identifying the authenticity of an object according to claim 2, further comprising a second pair of light receiving units placed at positions for receiving diffracted light beams from said diffraction grating, and a circularly polarizing filter placed between only one of said second pair of light receiving units and said diffraction grating, said circularly polarizing filter for said second pair of light receiving units being opposite in sense to said circularly polarizing filter for said first light receiving unit of said first pair.

4. A system for optically identifying the authenticity of an object according to claim 3, wherein said two pairs of light receiving units are adapted to simultaneously receive diffracted light from a common spot in said diffraction grating.

5. A system for optically identifying the authenticity of an object according to claim 1, wherein a second circularly polarizing filter of an opposite sense is placed between said second light receiving unit and said diffraction grating.

6. A system for optically identifying the authenticity of an object according to claim 5, further comprising a second pair of light receiving units placed at positions for receiving diffracted light beams from said diffraction grating, and a pair of circularly polarizing filter of mutually opposite senses each placed between a corresponding one of said second pair of light receiving units and said diffraction grating.

7. A system for optically identifying the authenticity of an object according to claim 1, wherein an additional circularly polarizing filter is placed between said light source and said diffraction grating.

8. A system for optically identifying the authenticity of an object according to claim 1, wherein said diffraction grating comprises small regions having at least two different diffractive properties, said small regions being sized and distributed so that a plurality of regions including those of different diffractive properties may be simultaneously accessed by each of said light receiving units.

9. A system for optically identifying the authenticity of an object according to claim 1, further comprising a band pass filter interposed between said diffraction grating and each of said light receiving units.