Optical: systems and elements – Light interference – Electrically or mechanically variable
Reexamination Certificate
2002-03-12
2004-01-13
Juba, John (Department: 2872)
Optical: systems and elements
Light interference
Electrically or mechanically variable
C359S577000, C359S584000, C359S589000, C356S454000, C156S099000
Reexamination Certificate
active
06678093
ABSTRACT:
INTRODUCTION
This invention relates to stacked, optically coupled etalons and to methods of making and using them, as well as to devices incorporating such stacked, optically coupled etalons.
BACKGROUND
Etalons are ubiquitous in optical systems, such as optical sensors, optical communication systems, etc. The basic Fabry-Perot etalon can be designed and produced to have a sharp response at resonant frequencies, which makes them suitable as optical filters such as bandpass filters. They also give a variable amount of dispersion, and so have been suggested for possible use as dispersion compensators. Thus Fabry-Perot etalons are a basic building block in a number of different optical elements, i.e., in optically functional components or devices. Such devices may be active or passive and may be employed in a system (or adapted to be employed in a system) to pass or transmit a selective wavelength or band of wavelengths or periodic set of wavelength bands. Exemplary optical elements in which etalons are used include optical sensors, and filters, e.g., band pass filters, single channel filters, and other wavelength selective filter devices such as wavelength division multiplexers, and dispersion compensators and other components of optical communication systems.
Etalons typically comprise precisely parallel selectively transmissive surfaces such as thin films, i.e., partially reflective mirrors or surfaces on opposite sides of an integral number of half waves distance or gap between them, forming the etalon's cavity. The thin film and cavity characteristics determine the optical properties of the etalon. That is, the spectral characteristics of the etalon are generally determined by the reflectivity of the mirrors or surfaces and by the optical thickness of the cavity length. Such etalons have long been produced, for example, by sputter deposition of film stacks of alternating layers of materials, i.e. a high refractive index material alternating with a low refractive index material, to form a mirror coating, which is transmissive of selected wavelengths.
Two such mirror coatings sandwich a sputter-deposited cavity layer between them. Sputtering or other physical vapor deposition of the relatively thick cavity layer is time consuming and, therefore adds substantial time and cost to the production of such etalons. The result is undesirably high cost for production for such etalons.
It has long been a recognized problem in this industry, that producing etalons having desired properties can be difficult and expensive. In addition, there are industry-recognized problems associated with producing structurally robust etalons having desired, precise optical properties. Prior known etalons have employed various designs, such as the etalons used in the interferometric optical devices of U.S. Pat. No. 6,125,220 to Copner et al. In the interleaver/de-interleaver devices of Copner et al, two glass interferometric end plates are separated by a spacer region where the etalon is formed. The spacer region is an air gap having a predetermined dimension. In adjustable Fabry-Perot devices, such as those disclosed in U.S. Pat. No. 5,283,845 to Ip, tuning of the center wavelength of the spectral passband of an etalon is achieved by varying the effective cavity length (spacing) between two end plates carrying thin film reflectors. More specifically, in Ip a piezo actuator is used, extending between the two end plates. By varying the electric power applied to the piezo actuator, the axial length of the actuator can be varied, and thus the gap between the end plates varied. As alternatives to piezo-electric actuators, the tuning mechanism may include liquid crystals, temperature, pressure, and other mechanisms. It is a disadvantage that adjustable etalons as in Ip involve considerable assembly complexity and cost. Also, maintaining strict parallelism between the end plates can present additional difficulties.
The prior known optical etalons, as noted above, fail to fully meet the needs of many applications, especially for optical elements intended for optical communication systems, precision sensors, etc.
It is an object of the present invention to provide stacked, optically coupled etalons addressing some of the deficiencies of the prior known technologies. It is a particular object of at least certain preferred embodiments, to provide stacked, optically coupled etalons and methods of making same, and optical elements incorporating such stacked, optically coupled etalons. Additional objects and aspects of the invention and of certain preferred embodiments of the invention will be apparent from the following disclosure and detailed description.
SUMMARY
In accordance with a first aspect, an optical element comprises multiple Fabry-Perot etalons stacked and optically coupled. The etalons may be placed in optical contact, i.e. the thin film coatings of an etalon in direct and substantially continuous surface-to-surface contact with the thin film coatings of an adjacent etalon in the stack, or may be placed in contact using one or more bonding layers optically coupled with each other between adjacent etalons.
As used herein, a bonding layer is any layer of bonding material on a surface of an etalon and used to physically attach that etalon to an adjacent etalon. The bonding layer optionally is in the light path through the stacked etalon and serves also to optically couple the adjacent etalon. In such embodiments, preferably the thickness of the bonding layer is equal to an odd number of quarter wavelength optical thickness (QWOTs). The bonding layer may comprise any of numerous materials suitable for bonding etalons together including, but not limited, to adhesives, fritted glass, etc, or other suitable materials. In other embodiments, the bonding layer is omitted and optical contacting is used to attach an etalon to an adjacent etalon. Optical contacting can result in optically zero thickness, e.g. near zero thickness or approximately zero QWOTs, between adjacent etalons.
In accordance with another aspect, one or more etalons of the stacked, optically coupled etalons, preferably each etalon, comprises a bulk optic having first and second parallel, selectively transparent surfaces. The bulk optic comprises a solid optically transparent body (at the wavelengths of interest) and optionally comprises a wedge correcting coating (referred to here generally as a “wedge coating”) and/or a thickness-adjustment layer on at least one of the two surfaces of the optically transparent body. The wedge coating, further described below, establishes high precision parallelism of the selectively transparent surfaces of the etalon. The thickness of the bulk optic (including any wedge coating), i.e., the dimension between the selectively transparent, parallel surfaces, defines the cavity spacing. Preferably, the bulk optic, including the wedge coating, will typically have an optical thickness equal to an integral number of half waves for the wavelength of interest. In preferred embodiments the selectively transparent surfaces are thin film mirror coatings comprising, for example, a film stack of alternating high and low refractive index oxides or a metal thin film in accordance with known thin film technologies. Preferably, the thin film coatings comprise a continuous uniform thickness metal film.
If a wedge coating is used, the thickness of the wedge coating varies progressively across the etalon. That is, the thickness of the wedge coating, viewed in cross-section in at least one plane orthogonal to the parallel, selectively transparent surfaces of the etalon, has a thickness that increases (or decreases in the opposite direction) continuously, typically approximately linearly, to compensate for non-parallelism, or “wedge”, in the underlying body of the bulk optic. As described further below, the bulk optic can be diced from a wafer on which a wedge coating and the two thin film coatings have been deposited by magnetron sputtering, ion beam sputtering or other known deposition techniques. Preferably, surface polishing i
Derickson Dennis J.
Ghislain Lucien P.
Scobey Michael A.
Stokes Loren F.
Banner & Witcoff , Ltd.
Boutsikaris Leo
Cierra Photonics Inc.
Juba John
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