Optical waveguides – With disengagable mechanical connector – Structure surrounding optical fiber-to-fiber connection
Reexamination Certificate
1999-04-16
2001-06-05
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Structure surrounding optical fiber-to-fiber connection
C385S072000, C385S066000, C372S020000
Reexamination Certificate
active
06241397
ABSTRACT:
BACKGROUND OF THE INVENTION
Fixed wavelength and tunable wavelength all-fiber Fabry Perot filters have been described in several U.S. patent applications including U.S. Pat. Nos. 5,212,746; 5,289,552; 5,212,745; 5,375,181; 5,422,970; 5,509,093; and 5,563,973. These patents provide descriptions of the manufacture of ferrule assemblies containing axial optical fibers as components of FFP filters comprising mirror-ended ferrules and embedded- mirror wafered ferrules. These patents also describe methods of making the mirror-ended ferrules and embedded-mirror wafered ferrules, methods of aligning the fibers of the ferrules to form an Fabry Perot optical cavity filter and ferrule alignment fixtures for use with such aligned ferrule assemblies. Alignment fixtures which facilitate alignment of fixed wavelength FFPs are described as well as alignment fixtures that facilitate wavelength tuning of the optical cavity of the filter without significant detriment to fiber alignment. Methods and alignment fixtures useful for passive and active temperature compensation and small range temperature tuning (or trimming) of fixed FFPs are also described in these patents.
U.S. patents and pending U.S. patent applications: 5,425,039; U.S. Pat. Ser. No. 08/984,245; now U.S. Pat. No. 6,044,189; U.S. Pat. Ser. No. 08/897,474; U.S. Pat. No. 5,892,582; U.S. Pat. Ser. No. 08/805,461; U.S. Pat. Ser. No. 08/833,602 U.S. Pat. No. 5,583,437; U.S. Pat. Ser. No. 60/028,517; U.S. Pat. Ser. No. 60/031,562; and U.S. Pat. Ser. No. 60/058,090 describe methods of using fixed and tunable FFP filters in wavelength scanners, wavelength references, spectrum analyzers and in optical fiber lasers. These patents are incorporated in their entirety by reference herein to the extent not inconsistent herewith.
For signal detection in dense WDM (50 GHz signal separation) applications using a filter with single path construction, a filter with a bandwidth of 0.02 nm (a finesse of 3000 for an FSR of 60 nm) is required. Filter requirements are less stringent if two filters cascaded in series are employed. In this case, a filter having a bandwidth of 0.12 nm (a finesse of 500 for an FSR of 60 nm) is required. The use of two or more filters in series would provide significant advantages for obtaining required signal resolution employing filters which have less stringent optical requirements and as such are less expensive and easier to manufacture. Such filters are also more reliably manufactured. However, cascading of filters in series generates other difficulties, particularly when the filters are wavelength tuned during operation, since tuning of the separate filters must be coordinated .
All-fiber Fabry Perot filters are very attractive candidates for high resolution, high finesse applications. Significant cost and efficiency of manufacture benefits could be achieved by the use of cascaded FFP configurations. This applications provides cascaded multiple fiber FP filters with significantly improved properties for high resolution and high finesse application. This application also provides alignment fixtures for use generally in any FFP filter that are easy to manufacture and less expensive to manufacture then current alignment fixtures. The fixtures disclosed herein are more particularly useful in tunable cascaded multiple fiber FFPS.
Current alignment fixtures for FFP can used end-brackets made of Kovar /stainless steel that require the use of ED machining which are relatively costly parts. The use of these precision end-brackets does not require any additional precision alignment equipment; however, several minutes to an hour may be required to adjust alignment of the FFP using such fixtures. Further, environmental testing (temperature cycling) usually yields only a 50% passage rate of FFPs. No angular adjustments can be made during assembly with such fixtures and small end-angle perpendicularity problems cannot be adjusted out. Loss performance of filters may be effected by the alignment techniques used with these endbracket fixtures. This invention provides an external alignment technique (using an alignment stage) and relatively low cost alignment fixtures that can lock and maintain the ferrule alignment obtained using the alignment stage.
All references cited in this application are incorporated in their entirety herein to the extent that their teaching are not inconsistent with those of the present application.
SUMMARY OF THE INVENTION
This invention provides cascaded all fiber Fabry-Perot filters (FFPs). These cascaded filters physically have a single Fabry Perot optical cavity, but generate a cascaded series of FFPs by use of a series of multiple loops of optical fiber whose optical path passes through the single FP cavity multiple times. The FFP filters of this invention are constructed using fiber ferrule assemblies to form the optical cavity. An all-fiber FP is, for example formed by aligning the fiber of a mirror-ended fiber ferrule with the fiber of an embedded-mirror wafered ferrule to maximize optical signal through the aligned fibers. The ferrules of the ferrule assembly have an axial bore into which optical fiber is bonded. An optical fiber end is positioned at one end face (at least) of each ferrule in the assembly. The opposed mirrors within the ferrule assembly form the FP cavity, the optical path of the fiber passes through the cavity and the cavity is tunable by changing the distance (i.e., the air gap) between the end faces of the ferrules. Cascaded FFPs of this invention are formed by use of ferrule assemblies which contain multiple aligned fibers which are optically coupled to form a continuous optical path which passes through the FP cavity multiple times. These configurations allow construction of a series of cascaded FFPs all of which have an identical optical cavity and all of which can be simultaneously tuned by changing the filter air gap.
The cascaded FFPs can be fixed wavelength or tunable filters. In fixed wavelength filters, the distance between the mirrors (i.e., cavity length) is held fixed, either the air gap is held fixed or the internal ends of the ferrules of the ferrule assembly are bonded together after alignment.
The cascaded FFPs of this invention can be constructed having two, three, four or more fibers in the axial bores of the ferrules of the ferrule assembly. Those with two fibers can be used to form a dual cascaded filter. Those with three fibers can be used to form a triple cascaded filter and those with four fibers can be used to form a quadruple cascaded filter. Ferrule assemblies are aligned so that the filters are tunable over a useful range, for example, dual fiber cascaded FFPs have been prepared that are tunable over a 50 nm range.
An important aspect of this invention is the discovery that the use of index matching fluid in the air gap between the end faces of the ferrules or alternatively and preferably the use of an anti-reflection (AR) coating at the wafer end face in the multiple fiber ferrule assemblies greatly expands the wavelength tuning range of the cascaded FFP.
Cascaded multiple fiber FFPs of this invention can employ a variety of ferrule materials (glass, PYREX (Trademark), ceramic or metal) and can employ any of a variety of single mode optical fibers.
This invention also provides ferrule alignment fixtures for holding the aligned ferrule assemblies of this invention to maintain alignment and to allow for fixed wavelength or tunable wavelength operation of the FFPs. Preferred tunable FFPs employ piezoelectric transducer (PZT) elements the length of which can be changed by application of an appropriate voltage to change the optical cavity length by changing the air gap between the ferrules. Ferrule assemblies are aligned using a ferrule alignment stage, preferably an alignment stage with v-grooves for holding the ferrules and which can be adjusted in 6 dimensions (x, y and z (where z is the distance between the ferrules) and by three angles). Commercially available alignment stages can be employed. A preferred method for construction of an FFP using the invent
Bao Yufei
Hsu Kevin
Li Thomas Q. Y.
Miller Calvin M.
Miller Jeffrey W.
Greenlee Winner and Sullivan P.C.
Micron Optics Inc.
Palmer Phan T. H.
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