Optics: measuring and testing – By light interference – Having partially reflecting plates in series
Reexamination Certificate
2001-05-14
2003-08-19
Kim, Robert H. (Department: 2882)
Optics: measuring and testing
By light interference
Having partially reflecting plates in series
C356S480000
Reexamination Certificate
active
06608685
ABSTRACT:
BACKGROUND OF THE INVENTION
Late in the 1900s, Fabry and Perot learned of the potential of an interferometer formed by two parallel surfaces with highly reflective coatings and variable separation. By the 1970s, the basic Fabry-Perot interferometer had evolved to support many applications involving multiple beam interferometry, including applications with laser cavities and non-planar surfaces.
The Fabry-Perot interferometer is still widely used today. However, with increasing demands on performance, and with the miniaturization of optical systems, improvements are sought. One object of the invention is to therefore provide a Fabry-Perot interferometer that is small and finely tunable, as compared to the prior art. This object and others will be apparent in the description that follows.
SUMMARY OF THE INVENTION
The following patents provide useful background information for the invention: U.S. Pat. Nos. 6,040,944; 6,005,995; 5,917,626; 5,799,121; 5,739,945; 5,684,632; 5,682,452; 5,666,225; 5,642,448; 5,629,995; 5,612,824; 5,606,439; 5,481,402; 5,453,827; 5,361,155; 5,287,214; 5,283,845; 5,251,275; 5,212,745; 5,212,584; 5,073,004; 5,062,684; 5,039,201; 4,861,136; 4,813,756; 4,789,219; 4,550,975; 4,474,424; 4,466,699. Each of the afore-mentioned patents is expressly incorporated herein by reference.
The following articles and books provide useful background information for the invention, and are thus incorporated herein by reference: M. Hercher,
The spherical mirror Fabry-Perot interferometer
, Appl. Opt. 7, p. 951 (May 1968); K. Repasky et al.,
High finesse interferometers
, Appl. Opt. 34, p. 2615 (May 1995); A. Siegman,
Lasers
, University Science Books, (1986); and
The application of capacitance micrometry to the control of Fabry-Perot etalons
, J. Phys. E 17, p. 48-54, (1984).
The invention of one aspect provides a miniature, fiber-coupled Fabry-Perot interferometer with a piezoelectric transducer and a collimating lens. As used herein, “lens” generally refers to a plurality of lenses or optical components used to perform the function of collimating light energy across a gap as part of the interferometer. Specifically, in accord with this aspect, light energy is coupled to the collimating lens and the collimating lens forms a substantially collimated beam across the gap; the piezoelectric transducer expands or contracts to adjust the gap, thereby adjusting the free spectral range of the interferometer. Preferably, one or more lens surfaces forming the gap are coated as optically reflective surfaces (i.e., to form mirrors or partial mirrors); these surfaces preferably include those that face each other to form the gap. The surfaces may be planar or curved. Preferably, surfaces of the lens that do not form the optically resonant gap are coated with anti-reflective coatings.
In one aspect, the transducer is contoured with a shape facilitating the alignment and placement of the lens with the transducer. By way of example, in one aspect the contour shape of part of the transducer includes a V-groove, which facilitates both alignment and tunability, as described herein.
In another aspect, the lens of the invention utilizes gradient index (“GRIN”) lenses. The GRIN lenses facilitate coupling to fiber optics, which provide the light energy for the interferometer, and further simplifies collimation within the interferometer. Preferably, highly reflective optical coatings are applied to the GRIN lenses to form the cavity across the gap. In a further aspect, a capacitive sensor is integrated with the interferometer to provide for absolute optical, and/or spatial, calibrations. GRIN lenses of the invention may for example include 0.75-pitch or 1.25-pitch.
As understood by those skilled in the art, the invention has several advantages and may be used within or in conjunction with any of the following devices or systems: tunable optical filters; tunable optical receivers; cascaded tunable optical filters; multi-pass tunable optical filters; an optical signal “slicer” for separating odd and even channels in WDM networks; a tunable wavelength division multiplexer; a tunable add/drop optical filter; a tracking filter for tunable lasers; an intra-cavity filter for tunable lasers; an amplified spontaneous emission noise suppression filter; and an optical spectrum analyzer in a selected waveband, e.g., visible or infrared. The invention may also be used with devices in the UV wavelength spectrum, for instance as an optical spectrum analyzer.
Specific advantages of the invention include its ease of construction, ease of optical and fiber alignment, use of non-specialized optical components (e.g., GRIN lenses), and its ease of optical alignment with low optical loss. These advantages simplify the interferometer, making it less expensive to manufacture as compared to prior art designs. The interferometer of the invention is also very flexible, providing for convenient adjustment of the free spectral range. With its few components, the interferometer of the invention is intrinsically small for coupling to fiber optics; accordingly it may be conveniently placed within a small hermetically sealed package, similar to telecom-grade optical devices.
In still another aspect, the GRIN lenses have optical curvature on the surfaces forming the gap, thereby forming an interferometer as a stable resonator, as known in the art. Such an interferometer provides for higher finesse. In one aspect, the GRIN surfaces forming optical collimation within the gap cavity are coated with one or more reflective coatings. Suitable GRIN lenses of the invention include those made by LightPath Technologies (“Gradium”), NSG America (“SELFOC”), or Casix.
In one aspect, one or more optical fibers are attached to the collimating lens; an input optical fiber brings optical energy to the interferometer and an output optical fiber carries processed optical energy from the interferometer to other devices or systems. In one aspect, the lens includes GRIN lenses that are pre-aligned by a commercial lens vendor, thereby avoiding later assembly.
In still another aspect, the collimating lens includes a deposition of metal (typically gold) on the outer, cylindrical surface (not on the optical surfaces forming collimation). The metal of this aspect creates an electrical capacitor. By way of example, one “plate” of the capacitor is the outer surface of the first GRIN lens, and the second “plate” of the capacitor is the outer surface of the second GRIN lens. The distance between the two GRIN lenses then also serves as the separation between the capacitor plates, as described herein. As the distance between the collimator lenses varies, so does the capacitance across the capacitor. This capacitance is a highly accurate measure of the absolute distance between lens surfaces, and thus provides an active calibration technique.
In an alternative aspect, a metal-cased package is used, rather than a metal deposition, to form the capacitor for calibration.
Yet another aspect of the invention involves a slight modification to the collimator lens discussed above. Specifically, the collimator lens (e.g., GRIN lenses) are more optically stable when formed with curved mirror surfaces (typically spherical surfaces) used in forming the gap. In accord with the invention, such spherical surfaces may be polished onto the collimator lens prior to optical coating. The resulting interferometer function simulates a “symmetric, spherical mirror” resonator, rather than a “flat-flat” resonator, as known in the art. The advantage of using such a resonator is that higher values of finesse are achieved for the same optical coatings (i.e., the optical losses are effectively decreased), leading to increased resolution capabilities for the interferometer.
Another aspect of the invention includes a substantially matched pair of collimator lenses for use in the interferometer. In one aspect, for example, a “0.5-pitch” GRIN lens is used, with fiber coupling on each side. Such a lens transfers light from one fiber to the other; and optimum fiber-to-fiber coupling is achieve
Ensher Jason R.
Richards Alan J.
Wood Christopher S.
Artman Thomas R
ILX Lightwave Corporation
Kim Robert H.
Lathrop & Gage L.C.
Vock Curtis A.
LandOfFree
Tunable Fabry-Perot interferometer, and associated methods does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tunable Fabry-Perot interferometer, and associated methods, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tunable Fabry-Perot interferometer, and associated methods will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3079759