Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
1999-11-24
2001-10-30
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S583000, C359S839000
Reexamination Certificate
active
06310729
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a dichroic mirror to be suitably used for an optical apparatus or an optical telecommunication apparatus such as a camera, a copying machine or an optical printing machine.
2. Related Background Art
Conventional optical systems of optical apparatuses and optical telecommunication apparatuses typically include a dichroic mirror that reflects light in a specific waveband and transmits light in a different waveband. Such a dichroic mirror comprises a dielectric multilayer film obtained by alternately laying high refractive index films and low refractive index films, each having an optical thickness (refractive index n×film thickness d) of &lgr;/4, where &lgr; is the designed central wavelength.
Conventional dichroic mirrors normally comprise a relatively large number of component layers for the dielectric multilayer film to increase the reflectivity in the reflection waveband. However, as the number of layers increases, the ripple generated in the transmission waveband (fluctuation of transmission loss generated due to transmittance varying depending on wavelength) increases its influence to reduce the transmittance in the transmission waveband.
FIG. 1
shows a graph typically illustrating the spectral transmittance characteristics of a known dichroic mirror. It will be appreciated from
FIG. 1
that the transmittance is reduced in the transmission waveband by the ripples generated in that band. In
FIG. 1
, the horizontal axis represents the wavelength and the vertical axis represents the transmittance (%).
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a dichroic mirror that is free from the above problem of the prior art and shows excellent optical characteristics including a high reflectivity in the reflection waveband and a flat and high transmittance with suppressed ripples.
Therefore, according to the invention, the above object is achieved by providing a dichroic mirror comprising:
a transparent substrate;
a dielectric multilayer film formed on the transparent substrate by alternately laying high refractive index layers, each having an optical thickness of &lgr;/4, &lgr; being the designed central wavelength, and low refractive index layers, each having a refractive index lower than that of the high refractive index layers;
a first transmittance regulating film formed between the dielectric multilayer film and the transparent substrate; and
a second transmittance regulating film formed on the dielectric multilayer film at the side opposite to the transparent substrate;
the first and second transmittance regulating films being formed by alternately laying intermediate refractive index layers and low refractive index layers, the intermediate refractive index layers having a refractive index lower than that of the high refractive index layers and higher than the median of the refractive index of the high refractive index layers and that of the low refractive index layers.
REFERENCES:
patent: 5453859 (1995-09-01), Sannohe et al.
patent: 5661596 (1997-08-01), Biro et al.
patent: 5768026 (1998-06-01), Kiyomoto
patent: 5914817 (1999-06-01), Browning et al.
patent: 6014255 (2000-01-01), Van Der Wal et al.
patent: 6018421 (2000-01-01), Cushing
patent: 6064525 (2000-05-01), Depauw
Tsukamoto Mayumi
Tsukamoto Seitoku
Canon Kabushiki Kaisha
Epps Georgia
Fitzpatrick ,Cella, Harper & Scinto
Seyrafi Saeed
Tsukamoto Mayumi
LandOfFree
Dichroic mirror does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dichroic mirror, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dichroic mirror will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2613723