Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-03-12
2004-09-28
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C385S014000, C385S016000, C385S024000, C372S099000, C356S454000, C356S519000
Reexamination Certificate
active
06798553
ABSTRACT:
INTRODUCTION
This invention relates to optically mismatched etalons and optically mismatched stacked, optically coupled etalons and to methods of making and using them, as well as to devices incorporating such optically mismatched etalons and optically mismatched 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 meets 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 optical filter elements comprising optically mismatched etalons and optically mismatched 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 optically mismatched and directly optically coupled etalons and optically mismatched and directly optically coupled and stacked, optically coupled etalons and methods of making same, and optical systems incorporating such optically mismatched etalons and optically mismatched 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 filter element is provided for filtering multiplexed light, comprising multiple directly optically coupled etalons, at least a first and a second of the etalons having optically mismatched periodic passbands, as more fully described below. In accordance with another aspect an optical system comprises a source of light, preferably multiplexed light, and an optical filter element as just described. Multiplexed light, as used here, is light having multiple channels, for example 1-n channels where n is the total number of channels. In preferred embodiments, an optical filter element comprises at least first and second Fabry-Perot etalons, preferably a plurality of Fabry-Perot etalons, that are optically mismatched, e.g. have optically mismatched periodic passbands, and that are directly optically coupled. As used here, optically mismatched, optical mismatching, or optically mismatching occurs when etalons having a different passband response are placed into an optical element. As used here, optically mismatched periodic passbands will be understood by those skilled in the art, given the benefit of this disclosure, to be mismatched sufficiently such that only one the passbands of a first etalon (or of the first etalon stack, as the case may be) overlaps any passband of the second etalon (or of a second etalon stack, as the case may be) within the wavelength range of interest. In a typical optical filter element disclosed here, the passbands of the first and second etalons may have a wavelength width approximately equal to the width of a single channel of multichannel multiplexed light. For example, in a telecommunication system operating in the C-band (approx 1530 nm to 1570 nm), wherein the C-band is divided into 40 channels, the channels each would be about 0.8 nm, and the passbands for each channel typically would be about 0.4 nm and centered in the allotted 0.8 nm channel. The period of the two etalons would, of course, as disclosed above, be sufficiently different that they overlap each other only once in the C-band. As used here, passbands overlap if they have approximately the same center wavelength and/or together pass sufficient light or signal strength for the common passband to be operative as a channel of the multichannel system in which the optical filter element is employed. Therefore, the optical filter element can act to filter out all passbands except the overlapping passband. Optical components, such as etalons and stacked, optically coupled etalons, can be directly optically coupled, as the term is used here, when they are optically coupled, i.e. are in the same optical path, and furthermore are in optical contact or are otherwise in physical contact with each other and/or mounted to each other (e.g. by bonding material in or out of the optical path) or mounted together in the same housing or by the same fixture. An air space may be separating the etalons, or the stacked, optically coupled etalons, or the etalons, or stacked, op
Derickson Dennis J.
Ghislain Lucien P.
Scobey Michael A.
Stokes Loren F.
Banner & Witcoff LTD
Bookham Technology plc
Dinh Jack
Epps Georgia
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