Optical: systems and elements – Single channel simultaneously to or from plural channels
Reexamination Certificate
2002-11-14
2004-07-13
Ben, Loha (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
C359S562000, C359S563000, C359S559000, C359S231000, C359S232000, C359S276000, C359S278000, C348S771000, C382S265000, C382S280000, C349S017000
Reexamination Certificate
active
06762882
ABSTRACT:
The invention generally relates to imaging systems, and particularly relates to systems and methods for producing high quality images using light modulators such as diffractive light modulators.
BACKGROUND OF THE INVENTION
Systems for producing high quality images using light modulators typically include an illumination source for producing an illumination field, a light modulator for receiving the illumination field and for producing a modulated illumination field, and imaging optics for directing the modulated illumination field toward an imaging surface. For example, U.S. Pat. No. 6,433,934, the disclosure of which is hereby incorporated by reference, discloses an imaging system that includes an illumination source, a field lens system, a light modulator, imaging optics and an imaging drum for supporting recording media.
The illumination field may include light of a plurality of frequencies and the diffraction of the illumination field by the light modulator will occur at different angles for the different frequencies. The diffraction in discrete angles occurs only for diffractive elements having an infinite number of diffractive units. As the number of interacting diffractive units is increased, the angular distribution of the intensity of the diffracted fields increases and the intensity distribution in the Fourier plane increases.
With reflective light modulators, the first order reflection may be used for imaging. A second order (and to a lesser extent third and fourth order etc.) reflected fields may produce unwanted illumination that is filtered out in the Fourier plane by a slit diaphragm. For example, as shown in
FIG. 1
, such a conventional imaging system includes an illumination source
10
that produces illumination that is directed by an objective lens
12
(e.g., f=14.5 mm), a plano convex lens
14
(e.g., f=220 mm), and a cylindrical lens
16
(e.g., f=100 mm) toward a mirror
18
, which in turn directs the illumination through a corrected objective lens
20
toward a light modulator
22
(e.g., a grating light valve). The illumination is modulated by the light modulator
22
and reflected back through the lens
20
and through a Fourier plane, to an imaging system lens
24
, which directs the modulated illumination toward an imaging surface
26
at the imaging plane. A slit diaphragm
28
is positioned in the Fourier plane. The positive and negative first order reflected signals are passed through the slit diaphragm
28
, while other order reflected signals (e.g., second, third etc.) are blocked by the slit diaphragm
28
.
Conventional Fourier diaphragms, however, cannot be spatially modulated to accommodate modulated signals having different frequencies, for example, time division multiplexed multi-frequency signals such as red, blue, green illumination. This results in a decrease in the resolution in the image plane and a reduction in intensity of the imaging field for systems including multi-frequency illumination sources. This is due, at least in part, to the presence of unwanted illumination (or side lobes) in locations near individual illuminated pixels or small groups of illuminated pixels.
There is a need, therefore, for a multi-frequency imaging system having improved filtering in the Fourier plane.
SUMMARY OF THE INVENTION
The invention provides an imaging system that includes an illumination source, a modulator and a variable Fourier diaphragm. The illumination source produces a first illumination field having a first frequency and a second illumination field having a second frequency. The modulator receives the first illumination field and the second illumination field, and produces a first modulated illumination field and a second modulated illumination fields. The variable Fourier diaphragm selectively passes one of the first modulated illumination field and the second modulated illumination field. In various embodiments, the modulator is a grating light valve and the imaging system may vary the variable Fourier diaphragm responsive to changes in the period of the spacing of ribbons in the grating light valve.
REFERENCES:
patent: 4707077 (1987-11-01), Marom
patent: 5337183 (1994-08-01), Rosenblatt
patent: 5668611 (1997-09-01), Ernstoff et al.
patent: 5742422 (1998-04-01), Drake
patent: 5883743 (1999-03-01), Sloan
patent: 5903323 (1999-05-01), Ernstoff et al.
patent: 5959776 (1999-09-01), Pasch
patent: 6314210 (2001-11-01), Fukushima et al.
patent: 6424449 (2002-07-01), Namiki
patent: 6552855 (2003-04-01), Kowarz et al.
Damm Tobias
Melzer Volker
Mueller Peter
Thoma Ralph
Agfa COrporation
Ben Loha
Hilton William E.
Sabourin Robert A.
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