Optical: systems and elements – Light interference – Electrically or mechanically variable
Reexamination Certificate
2002-08-09
2004-11-23
Boutsikaris, Leo (Department: 2872)
Optical: systems and elements
Light interference
Electrically or mechanically variable
C359S260000, C359S290000, C356S454000, C356S506000
Reexamination Certificate
active
06822798
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to tunable optical filters.
BACKGROUND OF THE INVENTION
In many optical applications, it is desirable to use a tunable optical filter, such as an etalon, to modulate the intensity of narrow-band light. A tunable optical filter, which is a bandpass filter, is typically made up of two partially reflective mirrors or surfaces separated by a gap to form a cavity. Devices with this structure are called etalons. The spectral characteristics of a tunable optical filter are generally determined by the reflectivity and gap spacing (cavity length) of the mirrors or surfaces. Varying the effective cavity length of the device tunes the center wavelength of the spectral bandpass of the etalon. The effective cavity length may be varied by altering the actual physical gap size, the refractive index of the gap medium, or both.
Various micro-electromechanical system (MEMS) based tunable optical filters have been investigated for the purposes of cost-effective miniaturization and batch fabrication, but the tradeoff between optical performance and MEMS miniaturization limits their commercialization.
U.S. Pat. No. 5,022,745, incorporated herein by this reference, describes an electrostatically deformable single-crystal mirror having a highly-conductive thick substrate layer supporting a highly-conductive thin membrane. The membrane is separated from the substrate by an insulating layer. The center of the insulating layer is etched away to form a cavity. The outer surface of the membrane is polished and coated with a dielectric material to form one mirror. A voltage is applied between the membrane and the substrate to cause the membrane and its mirror to deform.
This prior art design has numerous deficiencies. First, because the dielectric layer is directly attached to the deformable membrane, the potential exists for the mirror to curl. Second, the highly conducting membrane itself is disposed within the optical volume. The optical volume is the region through which light travels during operation of the device. The highly conducting membrane can absorb certain wavelengths which therefore cannot be selected for filtering. Also, the dielectric layer on the membrane will deform with the deformable membrane, causing errors. Moreover, the optical portion/path and the actuating structure are physically and electrically coupled and consequently there is a tradeoff between the substrate thickness and elastic stiffness (factors which partially determine the actuation voltage).
U.S. Pat. No. 5,283,845, also incorporated herein by this reference, discloses changing the effective cavity length between two mirrors by varying the axial length of a piezo actuator. This design requires placing two mirrors at the inner ends of two elongated members mounted on glass end plates. An annular or ring piezo actuator extends between the end plates, and is connected via a glass washer at one end and an annular aluminum split ring spacer and a glass washer at the other end. This design is thus unduly complicated. Moreover, because there are only two actuators to control the gap between the two mirrors, the device does not offer fine tuning adjustment to average out the errors caused by non-uniformity of the gap.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a tunable optical filter in which the actuating structure which adjusts the spacing between the mirrors does not occlude the optical path through the mirrors.
It is a further object of this invention to provide a tunable optical filter that is less expensive and less complicated than prior art designs.
It is a further object of this invention to provide a tunable optical filter in which the actuator embodiment is not in the optical path between the two mirrors.
It is a further object of this invention to provide a tunable optical filter that avoids the potential for the mirrors to deform or curl.
It is a further object of this invention to provide a tunable optical filter which can be fine-tuned.
It is a further object of this invention to provide a tunable optical filter in which the effects of errors caused by defects in some deformable membrane actuators or arising from other causes can be compensated for by the use of a plurality (array) of individual deformable membrane actuators (actuator cells).
It is a further object of this invention to provide a tunable optical filter in which the flatness of the optical portion is more easily maintained than in the prior art.
This invention results from the realization that an improved tunable optical filter which eliminates the numerous problems associated with prior art tunable optical filters, including light ray absorption, mirror deformation, lack of error compensation, and the inability to fine tune the optical filter, is achieved with a multi-cell deformable membrane actuator located between two substrates, each substrate including optical portions that are moved within closer proximity to each other as the deformable membranes deform (flex) in response to voltage applied to the deformable membrane. Thus, the deformable membrane actuator is separate from, and not a part of any optical portion and the deformable membrane can be located outside of the optical volume while it varies the spacing between the two optical portions.
The present invention provides in one embodiment a tunable optical filter comprising a first optical portion, a second optical portion located a distance from the first optical portion and at least one deformable membrane actuator that is configured to alter the distance between the first optical portion and the second optical portion, the deformable membrane actuator located outside of an optical volume that is defined by the location of the first optical portion and the location of the second optical portion. Optionally, a first primary substrate includes the first optical portion and a second primary substrate includes the second optical portion.
The deformable membrane actuator includes a deformable membrane having electrically conductive properties, a (first) membrane support structure, and an electrode layer forming at least one deformable membrane actuator cell. The membrane support structure being attached to and disposed between the deformable membrane and the electrode layer. Optionally, the electrode layer can be disposed onto the first primary substrate. A voltage applied between the deformable membrane and the electrode layer causes the deformable membrane to deflect towards the electrode layer.
Optionally, the deformable membrane actuator comprises a (second) load support structure which supports a load. In some embodiments, the load is the second primary substrate and the load support structure is attached to the second primary substrate. In these embodiments, the deformable membrane is attached to and disposed between the membrane support structure and the load support structure.
In the preferred embodiment, the deformable membrane actuator comprises a plurality of deformable membrane actuator cells. A deformable membrane actuator cell includes at least a portion of the deformable membrane having electrically conductive properties, at least a portion of the (first) membrane support structure and at least a portion of the electrode layer, the portion of the (first) membrane support structure being disposed between the portion of the deformable membrane and the portion of the electrode layer and forming a deformable membrane actuator well, and where a voltage applied between the portion of the electrode layer and the portion of the deformable membrane causes the portion of the deformable membrane to deflect into the deformable membrane actuator well and towards the portion of the electrode layer.
Optionally, the deformable membrane actuator cell comprises at least a portion of a (second) load support structure which supports a load. In some embodiments, the load is the second primary substrate and the portion of the load support structure is attached to the second primary substrate. In these embodiments,
Warde Cardinal
Wu Xing-tao
Boutsikaris Leo
Iandiorio & Teska
Optron Systems, Inc.
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