Projector having a halfwave plate disposed in light-leaving side of a light valve

• US 5,541,673 A
• Filed: 08/31/1994
• Issued: 07/30/1996
• Est. Priority Date: 09/03/1993
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Imai, Masao, Shioya, Yukinori
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): Murrell, Jeffrey S.
• Application Number:
  US08/298,579
• Time in Patent Office: 699 Days
• Field of Search: 348/761, 348/762, 348/751, 348/752, 348/757
• US Class Current: 348/752
• CPC Class Codes: H04N 9/3105 for displaying all colours simultaneously, e.g. by using two or more electronic spatial light modulators simultaneous projection in colour photography G03B33/10; beam splitting or combining systems per se G02B27/10
• CPC Class Codes: H04N 9/3167 for polarizing the light beam polarizing optical systems per se G02B27/28

Abstract

In a projector comprising three image forming devices, disposed between a separation optical section and a combination optical section, for processing a red, a green, and a blue light beams, at least one of the three image forming devices comprises a polarization direction converting means, such as a halfwave plate for converting polarization direction for one of the red, the green, and the blue image light beams so that one of a color combining dichroic mirrors has a cutoff wavelength of spectral characteristic which shifts toward outside for one of the red, the green, and the blue central wavelengths from that of one of a color separating dichroic mirrors. The halfwave plate may be disposed in a light-leaving side of at least one of the three image forming devices.

Claims

1. A projector comprising:

visible light generating means for generating visible light containing red, green, and blue components which have red, green, and blue central wavelengths, respectively;

separation optical means, optically coupled to said visible light generating means, for separating said visible light into the red, the green, and the blue components, said separation optical means transmitting a red light beam having a red component, a green light beam having a green component, and a blue light beam having a blue component, said separation optical means comprising a plurality of color separating dichroic mirrors;

combination optical means having incident angle dependance for combining red, green, and blue image light beams into a final color combined light beam, said combination optical means comprising a plurality of color combining dichroic mirrors;

projecting means for projecting said final color combined light beam on a screen; and

three image forming devices, disposed between said separation optical means and said combination optical means, for processing the red, the green and the blue light beams on the basis of three control signals to form the red, the green, and the blue image light beams, at least one of said three image forming devices comprising a polarization direction converting means for converting polarization direction for one of the red, the green, and the blue image light beams so that one of the color combining dichroic mirrors has a cutoff wavelength of a spectral characteristic which is shifted apart from one of the red, the green, and the blue central wavelengths so as to compensate for said incident angle dependence of said combination optical means.

2. A projector as claimed in claim 1, wherein said polarization direction converting means is disposed in a light-leaving side of at least one of said three image forming devices.

3. A projector as claimed in claim 1, wherein said polarization direction converting means is a halfwave plate.

4. A projector comprising:

visible light generating means for generating visible light containing red, green, and blue components which have red, green, and blue central wavelengths, respectively;

separation optical means, optically coupled to said visible light generating means, for separating said visible light into a separated red light beam including a red component, a separated green light beam including a green component, and a separated blue light beam including a blue component, said separation optical means comprising a first color separating dichroic mirror for transmitting the separated red light beam and a second color separating dichroic mirror for transmitting the separated blue light beam;

combination optical means for combining a red image light beam, a green image light beam, and a blue image light beam into a final color combined light beam, said combination optical means comprising a first color combining dichroic mirror for transmitting said red image light beam and a second color combining dichroic mirror for transmitting said blue image light beam;

projecting means for projecting said final color combined light beam on a screen;

first image forming means receiving the separated red light beam, for processing the separated light beam on the basis of a red control signal to form a red optical image, said first image forming means comprising a first condenser lens for converging the separated red light beam to produce a converged red light beam, a first light valve for modulating the converged red light beam in response to the red control signal to form the red image light beam indicative of said red optical image, and first polarization direction converting unit for converting polarization direction for the red image light beam so that said first color combining dichroic mirror has a cutoff wavelength of a spectral characteristic which shifts toward short wavelength side for said red central wavelength from that of said first color separation dichroic mirror;

second image forming means, receiving the separated green light beam, for processing the separated green light beam on the basis of a green control signal to form a green optical image, said second image forming means comprising a second condenser lens for converging the separated green light beam to produce a converged green light beam, a second light valve for modulating the converged green light beam in response to said green control signal to form the green image light beam indicative of said green optical image, and second polarization direction converting unit for converting polarization direction for the green image light beam so that said first and said second color combining dichroic mirrors have cutoff wavelengths of spectral characteristics which shift toward short and long wavelength sides for said green central wavelength from those of said first and second color separation dichroic mirrors, respectively; and

third image forming means receiving the separated blue light beam for processing the separated blue light beam on the basis of a blue control signal to form a red optical image, said third image forming means comprising a third condenser lens for converging the separated blue light beam to produce a converged blue light beam, a third light valve for modulating the converged blue light beam in response to the blue control signal to form the blue image light beam indicative of said blue optical image, and third polarization direction converting unit for converting polarization direction for the blue image light beam so that said third color combining dichroic mirror has the cutoff wavelength of a spectral characteristic which shifts toward long wavelength side for said blue central wavelength from that of said second color separation dichroic mirror.

5. A projector as claimed in claim 4, wherein each of said first through third polarization direction converting units is a halfwave plate.