Parabolic dielectric multilayer reflector

• US 5,523,862 A
• Filed: 04/25/1994
• Issued: 06/04/1996
• Est. Priority Date: 04/23/1993
• Status: Expired due to Term

• Current Assignee: Ushio Denki Kabushiki Kaisha
• Original Assignee: Ushio Denki Kabushiki Kaisha
• Inventors: Ukai, Toshiya, Narita, Mitsuo, Okazaki, Yoshio
• Primary Examiner(s): HENRY, JON W
• Application Number:
  US08/233,282
• Time in Patent Office: 771 Days
• Field of Search: 359/48, 359/49, 359/70, 359/71, 359/359, 359/584, 359/589, 313/112, 313/113
• US Class Current: 349/62
• CPC Class Codes: G02B 5/0833 comprising inorganic materials only
• CPC Class Codes: G02B 5/10 with curved faces
• CPC Class Codes: G02B 5/26 Reflecting filters G02B5/28 takes precedence

Abstract

A reflector used for a light source material of a liquid crystal video projector provides a good projection image and causes no color shading to occur in the periphery of a screen. The reflector has a surface on which a dielectric multifilm coating is deposited. The reflector reflects only visible light beams and has a wavelength λ₁, which has a spectral transmittance on a short wave side (with normal incidence) of 20% and is equal to or smaller than 440 nm and, at the same time, has a wavelength λ₂, which has a spectral transmittance on a long wave side (with normal incidence) of 50% and is equal to or greater than 820 nm.

Claims

1. A reflector having a parabolic reflective surface of rotation, on which a dielectric multilayer coating is deposited so as to reflect only visible light emanating from a light source located at a focal point of said parabolic reflective surface of rotation, said dielectric multilayer coating comprising an alternating structure of silicon dioxide layers and titanium dioxide layers so as to have a spectral transmittance of 20% for said visible light having a wavelength equal to or shorter than approximately 430 nm on a short wavelength side and a spectral transmittance of 50% for said visible light having a wavelength equal to or longer than approximately 830 nm on a longer wavelength side,

said alternating structure further comprising an under alternating structure of silicon dioxide layers each of which has a thickness of approximately 80 nm alternating with titanium dioxide layers each of which has a thickness of approximately 50 nm and a top alternating structure, deposited on the top of said under alternating structure, of silicon dioxide layers each of which has a thickness of approximately 110 nm alternating with titanium dioxide layers of a thickness of approximately 70 nm.

2. A reflector as defined in claim 1, wherein said alternating structure comprises 46 alternating layers of silicon dioxide layers and titanium dioxide layers.

3. An optical device comprising:

a light source for generating visible light;

a reflector having a parabolic reflective surface of rotation on which is deposited a dielectric multilayer coating for reflecting visible light generated from said light source located at a focal point of said parabolic reflective surface of rotation; and

a liquid crystal display panel to which said visible light reflected by said reflector is converted and directed in parallel beams;

said dielectric multilayer coating comprising an alternating structure of silicon dioxide layers and titanium dioxide layers so as to have a spectral transmittance of 20% for said visible light having a wavelength equal to or shorter than approximately 430 nm on a short wavelength side and a spectral transmittance of 50% for said visible light having a wavelength equal to or longer than approximately 830 nm on a longer wavelength side;

said alternating structure comprising an under alternating structure of silicon dioxide layers each of which has a thickness of approximately 80 nm alternating with titanium dioxide layers each of which has a thickness of approximately 50 nm and a top alternating structure, deposited on the top of said under alternating structure, of silicon dioxide layers each of which has a thickness of approximately 110 nm alternating with titanium dioxide layers of a thickness of approximately 70 nm.

4. A reflector as defined in claim 3, wherein said alternating structure comprises 46 alternating layers of silicon dioxide layers and titanium dioxide layers.