Optical: systems and elements – Light interference – Electrically or mechanically variable
Reexamination Certificate
2001-03-01
2003-02-25
Juba, Jr., John (Department: 2872)
Optical: systems and elements
Light interference
Electrically or mechanically variable
C359S577000, C359S900000, C216S024000
Reexamination Certificate
active
06525880
ABSTRACT:
BACKGROUND OF THE INVENTION
A Fabry-Perot filter (FPF) is an optical device which is constructed to pass light of a selected band of wavelengths. Light entering the filter enters a cavity which is bounded by a pair of reflective surfaces. The reflective surfaces are separated by a precisely controlled distance which determines a set of passbands for the filter. The smaller the separation, the further apart the passbands are in wavelength. That is, the smaller the separation, the larger the free spectral range (FSR) of the filter.
A tunable FPF adds an adjustable component to the separation by which the peak wavelengths of the passbands can be changed. Typically, tuning is achieved in a miniature FPF by making one of the two reflectors a movable or deformable membrane and applying a voltage between the membrane and the second fixed reflector, thereby changing the cavity separation distance through electrostatic attraction. In such a device, the amount of deflection and, therefore, cavity length control, is dependent upon the distance between the reflectors and the level of the applied voltage. For a given starting separation, more deflection requires a higher voltage level; and, likewise, for a given voltage range, more deflection requires that the reflectors be closer together.
At voltage levels compatible with smaller miniature devices, the prior approach to tuning FPFs restricts the device to a relatively small cavity size. This constraint can greatly inhibit the performance of the device by restricting control over the wavelength passbands.
SUMMARY OF THE INVENTION
In general according to one aspect, the invention features a tunable optical filter. This filter comprises a first mirror structure, a second, concave mirror structure, and a spacer layer separating the first mirror structure and the second mirror structure. Together, the first mirror structure and the second mirror structure define a resonant optical cavity of the optical filter. An electrostatic cavity, across which electric fields are generated, controls a separation between the first mirror structure and the second mirror structure to thereby change a length of the optical cavity.
In the present embodiment, the first mirror structure is substantially flat and disposed on a membrane that is deflected by the electric fields of the electrostatic cavity.
Preferably, the membrane is formed in a membrane layer that is patterned with an outer portion and tethers extending from the outward portion inward to the membrane.
In an alternative embodiment, the first mirror structure comprises a suspended HR coating layer that functions as a deflectable membrane layer. In such case, a metal electrode that has been deposited on the HR coating layer is useful.
In a current implementation, the resonant optical cavity is between 15 and 25 micrometers long.
In general, according to another aspect, the invention features a tunable optical filter. This filter comprises a support substrate, a membrane layer comprising a membrane structure on which a first mirror has been deposited, a release layer between the membrane layer and the support substrate, and a mirror structure that supports a second mirror that defines a filter cavity in combination with the first mirror. According to the invention, at least one of the first mirror and the second mirror is curved.
In the current embodiment, a spacer that separates the mirror structure from the membrane layer. And, the membrane layer is manufactured from silicon wafer material, with the release layer being silicon oxide. This release layer defines an electrostatic cavity between the membrane structure and the support substrate. An optical port is preferably provided through the support substrate to the membrane layer.
Optical coatings are important for high quality devices. Thus, an antireflective coating is preferably deposited on the membrane layer opposite the first mirror. Mirror structures manufactured from dielectric coatings are also desirable.
Various spacers can be used such as silicon or metal spacers. These are preferably assembled using solder.
In general according to another aspect, the invention features a method for fabricating a tunable filter. This method comprises selectively removing part of a release layer to create a membrane structure in a membrane layer, and then connecting a mirror structure to the membrane layer. Highly reflective (HR) coatings are deposited on the membrane layer and the mirror structure to provide a curved mirror/flat mirror optical cavity.
In one embodiment, an electrostatic cavity is provided across a void formed during the step of selectively removing the release layer.
In another embodiment, the electrostatic cavity is formed by covering the membrane layer with a sacrificial layer and then forming a patterned conductive material structure on the sacrificial layer, and then removing the sacrificial layer to create an air bridge cavity.
According to still another aspect, the invention features a method for fabricating a tunable filter. This method comprises depositing an membrane layer, including an HR coating on a support substrate, etching an opening through the support substrate to the membrane layer to create a deflectable membrane and connecting a curved mirror structure to membrane layer create an optical cavity.
REFERENCES:
patent: 4825262 (1989-04-01), Mallinson
patent: 4859060 (1989-08-01), Katagiri et al.
patent: 5022745 (1991-06-01), Zayhowski et al.
patent: 5291502 (1994-03-01), Pezeshki et al.
patent: 5430574 (1995-07-01), Tehrani
patent: 5561523 (1996-10-01), Blomberg et al.
patent: 5589689 (1996-12-01), Koskinen
patent: 5739945 (1998-04-01), Tayebati
patent: 5835216 (1998-11-01), Koskinen
patent: 5949571 (1999-09-01), Goosen et al.
patent: 6078395 (2000-06-01), Jourdain et al.
patent: 0 667 548 (1995-04-01), None
patent: 99/34484 (1999-07-01), None
D. Vakhshoori, et al., “2 mW CW singlemode operation of a tunable 1550 nm vertical cavity surface emitting laser with 50 nm tuning range”, Electronics Letters, vol. 35, No. 11, May 27, 1999, pp. 1-2.*
Dehe, et al., “III-V Compound Semiconductor Micromachined Actuators for Long Resonator Tunable Fabry-Perot Detectors”, Sensors and Actuators, (1998) 365-371.
Aratani, K.; French, P.J.; Sarro, P.M.; Poenar, D.; Wolffenbuttel, R.F.; and Middlehoek, S. “Surface Micromachined Tuneable Interferometer Array,” Sensors and Actuators A, 43 (1994) pp. 17-23.
Blomberg, Martti; Rusanen, Outi; Keranen, Kimmo; Lehto, Ari, “A Silicon Microsystem—Miniaturised Infraared Spectrometer,” 1997 International Conference on Solid-State Sensors and Actuators, Chicago, Jun. 16-19, 1997.
Jerman, J.H., “The Fabrication and Use of Micromachined Corrugated Silicon Diaphragms,” Sensors and Actuators, A21-A23 (1990), pp. 988-992.
Jerman, J.H; and Clift, D.J., “Miniature Fabry-Perot Interferometers Micromachined in Silicon for Use in Optical Fiber WDM Systems,” 1991 IEEE. Transducers '91 Conf. pp 372-375.
Jerman, J.H.; Clift, D.J.; and Mallinson, S.R., “A Miniature Fabry-Perot Interferometer With a Corrugated Silicon Diaphragm Support,” Sensors and Actuators A, 29 (1991) pp. 151-158.
Keränen, Kimmo; Karioja, Pentti; Rusanen, Outi; Tenhunen, Jussi; Blomberg, Martti; and Lehto, Ari, “Electrically Tuneable NIR-Spectrometer,” SPIE vol. 3099, pp. 181-184. 1997.
Klemic, James F.; Sirota, J. Marcos; and Mehregany, Mehran, “Fabrication Issues in Micromachined Tunable Optical Filters,” SPIE, vol. 2639, pp. 89-100. 1995.
Larson, M.C.; Pezeshki, B.; and Harris, J.S., Jr., “Vertical Coupled-Cavity Microinterferometer on GaAs with Deformable-Membrane Top Mirror,” IEEE Photonics Technology Letters, vol. 7, No. 4, Apr. 1995.
Lissberger, P.H.; and Roy, A.K., “Narrowband Position-Tuned Multilayer Interference Filter For Use in Single-Mode-Fibre Systems.” Electronics Letters, vol. 21, No. 18, pp 798-799. Aug. 1995.
Mallinson, S.R., “Crosstalk Limits of Fabry-Perot Demultiplexers,” Electronics Letters, vol. 21, No. 17. Aug. 15, 1985, pp. 759-761.
Mallinson, S.R.; Jerman, J.H., “Miniature Micromachined Fabry-Perot Interferometers
Flanders Dale C.
Le Minh Van
Miller Michael F.
Shanfield Stanley R.
Whitney Peter S.
Axsun Technologies, Inc.
Jr. John Juba
LandOfFree
Integrated tunable fabry-perot filter and method of making same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Integrated tunable fabry-perot filter and method of making same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Integrated tunable fabry-perot filter and method of making same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3141876