Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-12-01
2004-09-21
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Switch
Reexamination Certificate
active
06795602
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the technical field of fiber optics, and, more particularly, to free-space, reflective N×N fiber optic switches.
BACKGROUND ART
A dramatic increase in telecommunications during recent years, which may be attributed largely to increasing Internet communications, has required rapid introduction and commercial adoption of innovations in fiber optic telephonic communication systems. For example, recently fiber optic telecommunication systems have been introduced and are being installed for transmitting digital telecommunications concurrently on 4, 16, 32, 64 or 128 different wavelengths of light that propagate along a single optical fiber. While multi-wavelength fiber optic telecommunications dramatically increases the bandwidth of a single optical fiber, that bandwidth increase is available only at both ends of the optical fiber, e.g. between two cities. When light transmitted into one end of the optical fiber arrives at the other end of the optical fiber, there presently does not exist a flexible, modular-, compact, N×N fiber optic switch which permits automatically forwarding light received at one end of the optical fiber onto a selected one of several different optical fibers which will carry the light onto yet other destinations.
Historically, when telecommunications were transmitted by electrical signals via pairs copper wires, at one time a human being called a telephone operator sat at a manually operated switchboard and physically connected an incoming telephone call, received on one pair of copper wires, that were attached to a plug, to another pair of copper wires, that were attached to a socket, to complete the telephone circuit. The telephone operator's task of manually interconnecting pairs of wires from two (2) telephones to establish the telephone circuit was first replaced by an electromechanical device, called a crossbar switch, which automated the operator's manual task in response to telephone dialing signals. During the past forty years, the electromechanical crossbar switch for electrical telecommunications has been replaced by electronic switching systems.
Presently, switches for fiber optic telephonic communications exist which perform functions for fiber optic telephonic communications analogous to or the same as the crossbar switch and electronic switching systems perform for electrical telephonic communications. However, the presently available fiber optic switches are far from ideal. That is, existing fiber optic telecommunications technology lacks a switch that performs the same function for optical telecommunications as that performed by electronic switching systems for large numbers of optical fibers.
One approach used in providing a 256×256 switch for fiber optic telecommunications first converts light received from a incoming optical fiber into an electrical signal, then transmits the electrical signal through an electronic switching network. The output signal from that electronic switching network is then used to generate a second beam of light that then passes into an output optical fiber. As those familiar with electronics and optical fiber telecommunications recognize, the preceding approach for providing a 256×256 fiber optic switch is physically very large, requires electrical circuits which process extremely high-speed electronic signals, and is very expensive.
Attempting to avoid complex electronic circuits and conversions between light and electronic signals, various proposals exist for assembling a fiber optic switch that directly couples a beam of light from one optical fiber into another optical fiber. One early attempt to provide a fiber optic switch, analogous to the electrical crossbar switch, mimics with machinery the actions of a telephone operator only with optical fibers rather than for pairs of copper wires. U.S. Pat. No. 4,886,335 entitled “Optical Fiber Switch System” that issued Dec. 12, 1989, includes a conveyor that moves ferrules attached to ends of optical fibers. The conveyer moves the ferrule to a selected adapter and plugs the ferrule into a coupler/decoupler included in the adapter. After the ferrule is plugged into the coupler/decoupler, light passes between the optical fiber carried in the ferrule and an optical fiber secured in the adapter.
U.S. Pat. No. 5,864,463 entitled “Miniature 1×N Electromechanical Optical Switch And Variable Attenuator” which issued Jan. 26, 1999, (“the '463 patent”) describes another mechanical system for selectively coupling light between one optical fiber and one of a number of optical fibers. This patent discloses selectively coupling light between one optical fiber and a selected optical fiber by mechanically moving an end of one optical fiber along a linear array of ends of the other optical fibers. The 1×N switch uses a mechanical actuator to coarsely align the end of the one optical fiber to a selected one of the other optical fibers within 10 &mgr;m. The 1×N switch, using light reflected back into the moving optical fiber from the immediately adjacent end of the selected optical fiber, then more precisely aligns the end of the input optical fiber to the output optical fiber. U.S. Pat. No. 5,699,463 entitled “Mechanical Fiber Optic Switch” that issued Dec. 16, 1997, also aligns an end of one optical fiber to one of several other optical fibers assembled as a linear array, but interposes a lens between ends of the two optical fibers.
U.S. Pat. No. 5,524,153 entitled “Optical Fiber Switching System And Method Of Using Same” that issued Jun. 4, 1996, (“the '153 patent”) disposes two (2) optically opposed groups of optical fiber switching units adjacent to each other. Each switching unit is capable of aligning any one of its optical fibers with any one of the optical fibers of the optically opposed group of switching units. Within the switching unit, an end of each optical fiber is positioned adjacent to a beamforming lens, and is received by a two-axis piezoelectric bender. The two-axis piezoelectric bender is capable of bending the fiber so light emitted from the fiber points at a specific optical fiber in the optically opposed group of switching units. Pulsed light generated by radiation emitting devices (“REDs”) associated with each optical fiber pass from the fiber to the selected optical fiber in the opposing group. The pulsed light from the RED received by the selected optical fiber in the opposing group is processed to provide a signal that is fed back to the piezoelectric bender for pointing light from the optical fiber directly at the selected optical fiber.
Rather than mechanically effecting alignment of a beam of light from one optical fiber to another optical fiber either by translating or by bending one or both optical fibers, optical switches have been proposed that employ micromachined moving mirror arrays to selectively couple light emitted from an input optical fiber to an output optical fiber. Papers presented at OFC/IOOC '99, Feb. 21-26, 1999, describe elements that could be used to fabricate s a three (3) stage fully non-blocking fiber optic switch, depicted graphically in FIG.
1
. This fiber optic switch employs moving mirror arrays in which each polysilicon mirror can selectively reflect light at a 90° angle. In this proposed fiber optic switch, rows of relatively small 32×64 optical switching arrays
52
a
i
(i=1, 2 . . . 32) and
52
b
k
(k=1, 2 . . . 32) receive light from or transmit light to thirty-two (32) input or output optical fibers
54
a
n
and
54
b
n
. Thirty-two groups of sixty-four (64) optical fibers
56
a
l,m
and
56
b
l,m
carry light between each of the 32×64 optical switching arrays
52
a
i
and
52
b
k
and one of sixty-four 32×32 optical switching arrays
58
j
(j=1, 2 . . . 64).
The complexity of the fiber optic switch illustrated in
FIG. 1
is readily apparent. For example, a 1024×1024 fiber optic switch assembled in accordance with that proposal requires 4096 individu
Baughman Tyler L.
Calmes Sam
Clark Steven M.
Downing James P.
Forker John S.
Fish & Richardson P.C.
Lee John D.
Stahl Mike
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