Optical: systems and elements – Optical modulator – Light wave temporal modulation
Patent
1997-06-25
2000-06-06
Burke, Margaret
Optical: systems and elements
Optical modulator
Light wave temporal modulation
359291, 359295, 359572, 359573, 359619, 2503383, 345108, G02B 2600, G02B 2606, G01J 102, G01J 104
Patent
active
060726202
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an output efficiency control device, and a projection-type display apparatus, an infrared sensor and a non-contact thermometer which use the output efficiency control device.
BACKGROUND ART
An optical modulator modulates the intensity of incident light and outputs it. As a conventional example, there has been an optical modulator described in U.S. Pat. No. 5,311,360 and an article "Deformable Grating Optical Modulator" (Optics Letters, Vol. 17, No. 9, May 1, 1992) by O. Solgaard et al. This optical modulator modulates the intensity of light by utilizing the diffraction effect of light and has the advantage of being miniaturized and mass-produced in an IC process.
FIG. 32(a) is a plan view of an optical modulator described in the above-mentioned U.S. patent and article, and FIG. 32(b) is a cross-sectional view taken along a line K-K' in FIG. 32(a).
The optical modulator includes a silicon substrate 1001, a spacer layer 1002 made of a silicon oxide film formed in a peripheral region of the silicon substrate 1001, and a dielectric layer 1003. The dielectric layer 1003 is patterned to a plurality of minute dielectric beams 1004, and the dielectric beams 1004 float in a hollow space with both ends supported by the spacer layer 1002. The dielectric layer 1003 is made of a silicon nitride film rich in silicon, and its residual stress is reduced to about 200 MPa. The thickness of the spacer layer 1002 and the dielectric layer 1003 is set to be equal to 1/4 of a wavelength of light whose efficiency is to be controlled, i.e., light which is incident upon the optical modulator.
Openings 1005 each having a width equal to that of each dielectric beam 1004 are formed between the dielectric beams 1004. Furthermore, an Al reflective film 1006 which also functions as an electrode is provided above the substrate 1001. The reflective film 1006 is composed of upper reflective films 1007 formed on the surfaces of the dielectric beams 1004 and lower reflective films 1008 formed on the surface of the substrate 1001 through the openings 1005. The upper reflective films 1007 and the lower reflective films 1008 form a reflection-type grating.
The optical modulation principle of a conventional optical modulator having the above-mentioned structure will be described with reference to FIGS. 33(a) and (b). In these figures, components identical with those in FIG. 32 are denoted by the reference numerals identical with those in FIG. 32, and their description will be omitted.
FIG. 33(a) shows a state where a voltage is not applied between the reflective film 1006 and the substrate 1001. At this time, the difference in step between the upper reflective films 1007 and the lower reflective films 1008 is 1/2 of a wavelength of the incident light, and the difference in optical path between light reflected from the upper reflective films 1007 and light reflected from the lower reflective films 1008 is one wavelength. Therefore, the phases of these light beams are matched. Thus, the reflection-type grating functions as an ordinary mirror with respect to incident light 1010 which is incident upon the grating,, and the incident light 1010 becomes zero-th order diffracted light 1011 to be reflected to an incident side.
On the other hand, under the condition that a voltage is applied between the reflective film 1006 and the substrate 1001, the reflective film 1006 and the substrate 1001 forms a capacitor interposing the dielectric layer 1003 and an air layer 1012, and the reflective film 1006 is positively charged and the substrate 1001 is negatively charged. Since an electrostatic attracting force is affected between the charges, the dielectric beams 1004 are bent and attracted to the substrate 1001 until they come into contact with the substrate 1001, as shown in FIG. 33(b). At this time, the difference in step between the surfaces of the upper reflective films 1007 and those of the lower reflective films 1008 becomes 1/4 of a wavelength of the incident light, and the difference in optical path
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International Search Report for Application PCT/JP96/03202; Dated Feb. 18, 1997.
O. Solgaard et al., Optics Letters, vol. 17, No. 9, pp. 688-690, 1992, "Deformable Grating Optical Modulator".
Search Report for EP 96935518.9-2205/JP9603202; Dated; Dec. 23, 1997.
Search Report for Application No. 96935518.9; Dated Mar. 12, 1998 (EPO).
Ito Tatsuo
Shiono Teruhiro
Ueda Michihito
Yokoyama Kazuo
Burke Margaret
Matsushita Electric - Industrial Co., Ltd.
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