Optical waveguides – With optical coupler – Particular coupling function
Reexamination Certificate
1999-03-30
2002-12-10
Evans, F. L. (Department: 2877)
Optical waveguides
With optical coupler
Particular coupling function
C385S047000
Reexamination Certificate
active
06493484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to apparatus and methods for use in wavelength division multiplexed systems, and more particularly to the design and fabrication of optical add/drop filters for wavelength division multiplexed systems.
2. Discussion of Background Art
Fiber optic systems are used to transmit information for high performance communications systems and to interrogate sensors for a variety of applications, including monitoring chemicals and monitoring biomedical parameters. Generally, most such applications benefit from the ability to transmit multiple wavelengths down a single fiber optic cable for wavelength division multiplexed (WDM) systems. The amount of information transmitted down a single fiber is limited by technology and cost constraints on the transceiver units installed on the cable ends (the units that convert between electronic and optical signals). More wavelengths allow more information or more sensor discrimination, without the need for increasing the number of fiber cables. Avoiding an increase in cabling is advantageous because it keeps the cable connection size down (important for minimizing sensor size and for reducing space occupied by connectors on communications boards/cards), and because in some applications (notably network applications) it avoids the need to install more cable to an existing infrastructure, which in general is very expensive. Also, for high performance computer interconnects, the ability to transmit multiple wavelengths enables the destination of an in formation packet to b e simply encoded by mapping destination onto the optical wavelength. This in turn can enhance the performance of the interconnect significantly (see A. J. DeGroot et al, “High performance parallel processors based on star coupled WDM optical interconnects”, Proc. 3d Intl Conf. on Massively Parallel Processing using Optical Interconnects, IEEE Computer Society, Oct. 1996).
For this reason, multi-wavelength filter technology has become very popular in telecommunications systems using SINGLE-MODE optical fiber, and a wide variety of products are currently on the market (eg: Ciena, Di-Con, OCA, etc.). In this environment, single mode fiber is used to enable hi-speed transmission over long distances (10 km and above). It's use, however, substantially increases the cost of components (transceivers, wavelength filters) because it has a small optical spot size which results in very stringent alignment tolerances on the components. Single-mode (“monomode”) fibers are also not attractive due to the high component cost of single-mode optical components, and lens approaches are less attractive because they add piece parts (cost) and bulk, leading to exceedingly bulky arrays.
For many other applications, however, it is preferable to use MULTI-MODE optical fiber, which has a spot size about 10× larger than single mode fiber. This reduces component cost substantially (but limits transmission distance to about a kilometer at 1 Gbit/sec bandwidth). For these lower-cost systems, component cost is an important consideration, and it is important to achieve a low cost for the wavelength multiplexer. Single mode demultiplexers typically cost $1000/wavelength/fiber end, which is prohibitive. These components also will not work within a multimode system due to incompatibilities between single- and multi-mode fiber.
Parallel optical interconnects over multimode fiber (MMF) ribbon cable are emerging as a robust, high-performance data link technology (See, Y. -M. Wong et al., J.
Lightwave Technol
. LT-13, 995 (1995); M. Lebby et al.,
Proc
. 1996
Electron. Components & Technol. Conf
., p. 279 (1996); and, K. S. Giboney,
Proc. SPIE Optoelectron. and Packaging IV
(Feb. 1997)). This technology has primarily been implemented as single wavelength, point-to-point links, and can be significantly enhanced by wavelength division multiplexing (WDM) to increase both point-to-point bandwidth as well as create more complex interconnect topologies and routing approaches. The combination of byte-wide transmission for high channel bandwidth with WDM for interconnect routing is particularly attractive for ultrascale computing platforms (See, R.J. Deri et al.,
Proc
. 3d
Massively Parallel Proc. using Opt. Interconn
., p. 62 (1996)). Research in this area suggests that WDM transceivers for point-to-point links can be realized (See, S. Y. Hu et al., in
Proc
. 1997
IEEE LEOS Annual Mtng
., paper TuJ4 (1997); and, C. Chang-Hasnain, in
Proc
. 1997
IEEE LEOS Annual Mtng
., paper WJ1 (1997)). Exploiting the potential richness of WDM networks, however, also requires a low-loss routing fabric which includes small footprint add/drop multiplexers. Low insertion loss is also critical for this technology because the transceivers exhibit link power budgets well below that of telecom WDM systems and because the multimode fiber cabling precludes the use of optical amplifiers. While high-performance filters can be realized for single-fiber applications (See, L. Aronson et al., presented at OFC '97 ), achieving high-performance devices with ribbon cable is significantly more complicated. Complications arise from the MMF's high NA=0.275 and large core (62.5 &mgr;m), which render array collimation difficult, and the difficulty of maintaining good filter performance at the high angles of incidence needed to minimize loss in a 3-port (2-output) device.
In response to the concerns discussed above, what is needed is a design and fabrication method for optical add/drop filters in wavelength division multiplexed systems that overcomes the problems of the prior art.
SUMMARY OF THE INVENTION
The present invention is an optical add/drop filter for wavelength division multiplexed systems and methods for constructing same. The add/drop filter consists of a first ferrule having a first pre-formed opening for receiving a first optical fiber; an interference filter oriented to pass a first set of wavelengths along the first optical fiber and reflect a second set of wavelengths; and, a second ferrule having a second pre-formed opening for receiving the second optical fiber, and the reflected second set of wavelengths.
A first method for constructing the optical add/drop filter consists of the steps of forming a first set of openings in a first ferrule; forming a first set of guide pin openings in the first ferrule; inserting a first set of optical fibers into the first set of openings; dividing the first ferrule into a first ferrule portion and a second ferrule portion; forming an interference filter on the first ferrule portion; inserting guide pins through the first set of guide pin openings in the first ferrule portion and second ferrule portion to passively align the first set of optical fibers; attaching the second ferrule portion to the interference filter; removing material from the ferrule portions and interference filter such that light reflected from the interference filter from the first set of optical fibers is accessible; forming a second set of openings in a second ferrule; inserting a second set of optical fibers into the second set of openings; and positioning the second ferrule with respect to the first ferrule such that the second set of optical fibers receive the light reflected from the interference filter.
A second method for constructing the optical add/drop filter consists of the steps of forming a first set of openings in a first ferrule; inserting a first set of optical fibers into the first set of openings; cutting a slot into the first ferrule; removing predetermined portions of the ferrules and interference filter; inserting an interference filter into the slot such that light reflected from the interference filter from the first set of optical fibers is accessible; forming a second set of openings in a second ferrule; inserting a second set of optical fibers into the second set of openings; and positioning the second ferrule with respect to the first ferrule such that the second set of optical fibers rec
Deri Robert J.
Garrett Henry E.
Strand Oliver T.
Dekin, Jr. Lloyd E.
Evans F. L.
Lauchman Layla
Staggs Michael C.
The Regents of the University of California
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