Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-02-18
2002-03-19
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S020000, C385S024000, C385S140000
Reexamination Certificate
active
06360032
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to optical devices, and more particularly, to an optical switch for selectively aligning or misaligning the optical signal of any one of several input optical waveguides with any one of several output optical waveguides. The invention is in the field of blocking optical switching and optical attenuating devices.
Numerous optical switches have been developed for selectively switching an optical signal from one waveguide across an interface to another waveguide. Regardless of design, insertion loss and reflectance remain central to judging the optical performance of a switch. These parameters combine to describe the efficiency with which the switch passes light. The relative insertion loss and the reflectance performance of an optical switch are determined by physical elements of the switch design.
Insertion loss is a measure of how much light the switch blocks between the input and output waveguides. Higher insertion loss means more light is blocked by the switch. An ideal switch has minimal insertion loss. The insertion loss of an optical switch is determined primarily by the ability of the switch to precisely align the input waveguide with respect to the output waveguide. Offsets in longitudinal, angular, and transverse alignment must all be controlled to minimize insertion loss. Historically, transverse offset has been the most difficult source of insertion loss to control in mechanical optical switch designs.
Reflectance is the ratio of reflected light power to incident light power in an optical waveguide. Fresnel reflections at the discontinuity between the input and output waveguides are the prime source of reflectance in an optical switch. Higher reflectance adversely affects performance of an optical system in two ways. First, transmitted optical power is decreased as more light is reflected. Second, the reflected light is often transmitted back to the laser source. There it creates a proportional amount of noise on the signal. Several methods are available to reduce the reflectance such as index matching mediums, anti-reflective coatings and providing an angled endface on the waveguides. The angled endface gives the best reflectance performance.
Existing optical switches can be categorized by their mode of operation as either electronic or mechanical switches. Electronic switches have no moving parts and divert light with electrical or acoustic energy. Mechanical switches physically move optical elements to perform the switching function.
Many prior art mechanical optical switches exist for comparison to the present invention of a two-beam optical switch. Discussion of the prior art is based on two relevant physical characteristics, degrees of freedom and adjustability. Degrees of freedom refers to the number of kinematic degrees of freedom available for positioning waveguides. Adjustability describes the available motion control within each degree of freedom. A switch with adjustability can attain and hold several intermediate positions within each degree of freedom.
Most available mechanical optical switches offer a single degree of freedom. Many of these are rotary designs wherein the waveguides on both input and output sides of the switch are coaxially supported for rotation relative to each other around a single axis of rotation. U.S. Pat. Nos. 5,317,659 to Lee (1994), 5,420,946 to Tsai (1995), and 4,378,144 to Duck et al. (1983) are all similar designs with both adjustability and one degree of freedom. The Duck et al. patent describes a widely used optical switch that is representative of the other rotary designs, and displays many inherent disadvantages of the rotary designs.
This prior art rotary devices arrange output optical fibers in a circle. The input fiber is placed on an arm that is attached to an actuator such as a stepper motor. A beam expander lens is attached to each input and output fiber. The input fiber actuator is coaxial with the circle defined by the output fiber lenses. The input fiber lens faces the output fiber lenses. The actuator rotates to align the input fiber lens to any of the output fiber lenses. Adjustability is provided by the use of a stepper motor to actuate the arm.
Several single degree of freedom switches also exist that are not rotary designs. They depend on beams or arms to move the light signal between fibers. U.S. Pat. No. 5,078,514 to Valette (1992) and U.S. Pat. No. 5,024,500 to Stanley (1991) both offer one degree of freedom and adjustability. Both show a single switched fiber mounted along the length of a beam. When the beam is actuated, it bends to align the single fiber with any of the remaining fibers mounted to the base.
Non adjustable single degree of freedom mechanical switches are shown in U.S. Pat. No. 4,946,247, to Muska et al. (1990), U.S. Pat. No. 5,239,599 to Harman (1993) and U.S. Pat. No. 4,146,856 to Jaeschke (1979).
Several two degree of freedom mechanical switches do not offer adjustability. Adjustability is often removed to reduce switch size for design applications that require a limited number of fibers, such as the device shown in U.S. Pat. No. 4,220,396 to Antell (1980).
The best optical performance is delivered by optical switches with two degrees of freedom and adjustability. U.S. Pat. No. 4,886,335 to Yanagawa (1989) and U.S. Pat. No. 5,438,638 to Anderson (1995) both offer optical switches with two degrees of freedom with adjustability. The Yanagawa patent combines two linear stages to form a very large and complex optical switch. The Anderson switch is smaller and has two degrees of freedom with full adjustability available for positioning fibers.
However, the Anderson '638 patent has disadvantages.
The input and output fiber endfaces of the Anderson switch cannot be angled to incorporate the preferred angled endface to improve reflectance performance. The ferrules that hold fibers in Anderson must rotate up to 180 degrees to couple a fiber pair and this could move the endface angles as much as 180 degrees out of phase, causing a mismatch and thus insertion losses.
The Anderson design also has a limited fiber capacity. As the fiber count increases, more fibers are added to each bundle thereby increasing the bundle radius. The angular resolution required to position the outermost fibers decreases as the bundle radius increases. The result is a steady degradation in the repeatability of insertion loss and an increase in the switching time for each pairing as capacity increases.
The Anderson design will exhibit drift and signal interruption from wear. Each switching cycle generates a high degree of relative motion between the ferrules and their V-grooves. This motion creates particles that can interrupt the signal. It also wears the ferrules down steadily decreasing their diameter and creating signal drift.
The Anderson design requires a lengthy fiber search process. Since there are two locations for each possible waveguide pairings and no simple way to predict the location of the one pairing given that of the other pairing, the algorithm used may waste time finding both pairings. Also, the search process can require human intervention to achieve optimization.
The Anderson patent construction is such that fibers near the center of the input bundle will not be able to couple to fibers near the center in the output bundle. The result is that the innermost fibers in both bundles go unused and, thus, their signal-carrying capacity is wasted.
The two-beam optical switch of the present invention overcomes difficulties described above and affords other features and advantages heretofore not available.
SUMMARY OF THE INVENTION
The present invention is an optical switching device consisting of two main waveguide mounting beams or arms. The first beam includes one or more input waveguides and the second beam includes one or more output waveguides. The waveguides preferably are arranged in bundles. The beams are arranged such that the waveguide bundles carried by the respective beams face each other and each beam has a separate axis of rotat
Berger John G.
Emmons David J.
Sanghavi Hemang
Westman Champlin & Kelly P.A.
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