Optical: systems and elements – Optical modulator
C359S254000, C359S263000, C359S318000, C385S008000, C385S027000
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to achromatic optical modulators. More particularly, the present invention relates to micromachined grating modulators which exhibit achromatic behavior.
2. Description of Related Art
Micromachined diffraction grating modulators are used in fiber optic components such as attenuators, filters, and modulators. These diffraction gratings typically include reflective surfaces and are used as reflective light processing elements. The diffraction gratings are optically coupled to input and output optical fibers and collimating/focusing lenses which direct an optical beam to the reflective surfaces. The reflective surfaces can be controlled to modify characteristics of the incident optical beam. Micromachined grating modulators are typically manufactured using CMOS silicon processing techniques.
The first micromachined diffraction grating modulators include ribbons of a uniform width formed over a substrate. The ribbons include a reflective surface which are coplanar and parallel to the surface of the substrate. The ribbons are separated by gaps of a similar width. Additional reflective surfaces are formed on the substrate between the ribbons in the gaps. A controllable voltage applied to some or all of the ribbons causes the ribbons to deflect toward the substrate and thus affect one or more characteristics of an incident optical beam. These gratings exhibit an especially strong spectral dependence when used as a modulator/attenuator on the 0th order reflected light, when the incident optical beam deviates from the center wavelength. The light attenuation of such a device is spectrally dependent, especially for large attenuation. As a result, these devices are unacceptable for fiber optic networks which operate over a large wavelength band, such as the erbium doped fiber amplifier (EDFA) band.
More recent orating modulators minimize the width of the gaps between the ribbons. Thus, these diffraction gratings include ribbons of uniform width spaced as closely together as possible over the substrate. No additional reflective surfaces are formed on the substrate. Again, a controllable voltage applied to some or all of the ribbons causes the ribbons to deflect toward the substrate and thus affect one or more characteristics of an incident optical beam. These gratings represent an improvement over the earliest gratings, but still exhibit a sufficiently strong spectral dependence to make them unacceptable for fiber optic networks which operate over a large wavelength band.
What is needed is an optical modulator/attenuator which exhibits achromatic behavior.
SUMMARY OF THE INVENTION
The present invention is directed towards a reflective light processing element capable of modifying at least one characteristic of an optical beam. The reflective light processing element comprises a plurality of wide reflective surfaces, the wide reflective surfaces being substantially coplanar; a plurality of narrow reflective surfaces, the narrow reflective surfaces being substantially coplanar, the narrow reflective surfaces facing substantially a same direction as the wide reflective surfaces, the narrow reflective surfaces alternatingly arranged with the wide reflective surfaces, the narrow reflective surfaces and the wide reflective surfaces defining a plurality of gaps between and normal to the narrow reflective surfaces and the wide reflective surfaces; and a plurality of compensating reflective surfaces, the compensating reflective surfaces being substantially coplanar, the compensating reflective surfaces facing substantially the same direction as the narrow reflective surfaces and the wide reflective surfaces, the compensating reflective surfaces being positioned in each gap beneath the narrow reflective surfaces and the wide reflective surfaces, each compensating reflecting surface being at least as wide as each gap. The wide reflective surfaces are capable of a displacement in a direction normal to the narrow reflective surfaces and compensating reflecting surfaces, the displacement capable of modifying at least one characteristic of the incident optical beam.
patent: 5991079 (1999-11-01), Furlani
Bloom David M.
Godil Asif A.
Lucas Michael A.
Wilson Sonsini Goodrich & Rosati
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