Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-03-31
2001-04-03
Mai, Huy (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S295000, C359S245000
Reexamination Certificate
active
06211997
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a spatial light modulator which can modulate power in a high optical power laser beam. The spatial light modulator is a total internal reflection spatial light modulator which uses a grating interleaved electrode structure.
BACKGROUND OF THE INVENTION
There are many applications for optical spatial light modulators of high intensity optical beams. Particularly in commercial printing applications, optical laser bars with output power ≧20 W range are not uncommon. If these laser bars are used in a continuous wave mode (CW) as a source of high power light, a means to modulate the high intensity beams of light into a high number of separate pixels is required. Such high power laser bars have wavelengths usually in the 0.8 &mgr;m to 1 &mgr;m range.
U.S. Pat. No. 4,281,904 discloses the use of a total internal reflection (TIR) modulator to modulate a visible He-Ne laser beam. In U.S. Pat. No. 4,281,904, a stop is principally used in the output optics to block the zero order beam and the diffracted first order light is imaged to the media to get modulation contrasts of 100 to 1 for low overall visible light levels. The voltage applied in the arrangement of U.S. Pat. No. 4,281,904 corresponds to the amount of index change necessary in a crystal to diffract incident light into the first order beam efficiently. That diffraction from the fundamental to the first order mode gives a large 20 dB contrast. Unfortunately with this arrangement, light is thrown away (i.e. the un-diffracted percentage and higher orders), and there are nulls (no light refracted) in the optical image. Other patents such as U.S. Pat. No. 4,673,953 use complex schemes to produce ‘null free’ devices. These complex schemes involve the use of extra optics to remove nulls.
SUMMARY OF THE INVENTION
An object of the present invention is to provide for a total internal reflection modulator which overcomes the drawbacks noted above. The present invention describes the design of a total internal reflection light modulator that can handle extremely high optical powers at infra-red wavelengths such as 0.83 &mgr;m. The device can modulate and pixilate the optical power in such a high optical power laser beam. Within the context of the present description, optical refers to light in the visible, infrared, and near infrared parts of the spectrum. The modulator uses a grating electrode structure protected from the light levels by an optical buffer layer. The light from the modulator is imaged by Schlieren optics combined with a slit or aperture (instead of a stop in the Fourier plane) to obtain a contrast ratio of >4:1 in, for example, 256 pixels. The modulator also does not suffer from the problem of nulls in the output imaged light bar and hence does not need to be null suppressed. Printing media that has a reasonable threshold such as used in the graphic arts area can use such low contrast ratios.
In the present invention, an electrode pitch (i.e. the interleaved electrode grating pitch) that diffracts the light when it total internal reflects from the top surface of the electro-optic crystal was determined from the following constraints:
a) the pitch must be large enough to maintain sufficient electric field depth so as to allow sufficient interaction with the optical field; and
b) the pitch must not be so large as to drive the operational voltage (nominally the half wave voltage) above 100 volts.
The pitch was determined by making a test modulator with pitches of 10 &mgr;m and 30 &mgr;m center to center while modifying the duty cycle of the grating structure. The 10 &mgr;m electrode structures never produced much contrast and the 30 &mgr;m patterns had good contrast however they had extremely high operational voltages.
At the same time, a closed form solution of the penetration depth of the electric field inside the electro-optic crystal surface as a function of electrode pitch, electrode width, and applied voltage was undertaken. The results of this investigation was combined with a Finite Element evaluation of the optical interactions within the phase grating to estimate the contrast, interaction length, transmission and reconstruction properties of the electrode induced electro-optic grating structures. The conclusion was that the electrode period should exceed 15 &mgr;m to get high enough optical contrast. Therefore 15 to 20 &mgr;m range is a preferable electrode pitch. The considerations to meet system performance are contained in copending application.
The present invention relates to an internal reflection type spatial light modulator which comprises a crystal substrate; a patterned buffer layer having buffer portions formed on a surface of the crystal substrate; and an electrode array comprising a plurality of electrodes. The electrode array is patterned based on the patterned buffer layer, such that each electrode of the electrode array is positioned on each buffer portion of the patterned buffer layer.
The present invention further relates to an internal reflection type modulator which comprises a crystal substrate having angled opposing end faces; a patterned buffer layer deposited on a surface of the crystal substrate; and an electrode array disposed on the patterned buffer layer.
The present invention further relates to a printer assembly which comprises a light source; and an internal reflection type modulator for modulating light from the light source, with the modulator comprising a crystal substrate and a patterned buffer layer deposited on the crystal substrate. The internal reflection type modulator further comprises electrodes positioned on buffer portions of the patterned buffer layer such that each electrode is positioned on each buffer layer. The printer further comprises an optics assembly for imaging light from the modulator onto a printing plane.
The present invention also relates to a method of modulating a constant wave light beam produced by a high optical power infrared light source. The method comprises the steps of depositing a patterned buffer layer having buffer portions on a surface of a crystal substrate; and positioning an electrode array over the patterned buffer layer, such that each electrode of the electrode array is positioned over a buffer portion of the patterned buffer layer.
REFERENCES:
patent: 4281904 (1981-08-01), Sprague et al.
patent: 4376568 (1983-03-01), Sprague
patent: 4386287 (1983-05-01), Karasawa et al.
patent: 4413270 (1983-11-01), Sprague
patent: 4591260 (1986-05-01), Yip
patent: 4673953 (1987-06-01), Hecht
patent: 4685763 (1987-08-01), Tada et al.
patent: 4786918 (1988-11-01), Thornton et al.
patent: 5157541 (1992-10-01), Schildkraut et al.
patent: 5517359 (1996-05-01), Gelbart
patent: 5521748 (1996-05-01), Sarraf
patent: 5748358 (1998-05-01), Sugamata et al.
Nutt Alan C. G.
Ramanujan Sujatha
Revelli, Jr. Joseph F.
Blish Nelson A.
Eastman Kodak Company
Mai Huy
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