Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-09-27
2004-01-06
Zarroli, Michael C. (Department: 2839)
Optical waveguides
With optical coupler
Switch
C385S018000, C385S015000
Reexamination Certificate
active
06674933
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to optical switching elements and more particularly to a system and method for manipulating optical signals within an optical switch.
BACKGROUND ART
Communication utilizing optics is increasingly displacing the more traditional electronic or radio wave transmission due to its ability to accommodate a greater rate of transfer per given time. Optical signals are switched in both telecommunication systems and data communication systems. In circuit switching, any one fiber in an array of parallel input optical fibers may be connected to any one fiber in an array of output optical fibers using a matrix of optical switches. As a result, an incoming data packet from a particular input fiber can be directed to a selected output fiber, based upon the destination of the packet.
U.S. Pat. No 4,988,157 to Jackel et al. provides a bi-stable optical switching arrangement utilizing electrochemically generated bubbles. Parallel input waveguides and parallel output waveguides are formed on a substrate at perpendicular angles so as to intersect. A 45° slot is formed across each intersection. The slots are selectively filled with a fluid, such as water, or refractive index-matching fluid. Electrodes are positioned adjacent to the slots and are selectively activated to electrolytically convert the fluid to gaseous bubbles. The electrolytic formation of the bubbles destroys any index-matching properties across the slots and causes light to be reflected at the slot sidewall. Thus, an electrolytically formed bubble within a particular slot results in the reflection of optical signals at the slot, rather than the propagation across the slot. The presence of either a catalyst, an electrical pulse of opposite polarity, or an electrical pulse of significant size and of the same polarity will collapse the bubble, thereby returning the switch to a transmissive state.
Although the approach taken by Jackel et al. is simple and potentially inexpensive in large quantities, and achieves a number of advantages over prior approaches, further improvements may be realized. Where water is used as the fluid, electrolysis generates H
2
and O
2
bubbles in order to create a reflecting state, but the water provides a poor index match to the waveguides. Consequently, crosstalk is high if water is used. Another concern is that the bubble-creation process and the bubble-removal process may be too slow to meet the desired transition time for telecommunication switching. Moreover, the slots are so wide that transmission losses are potentially significant, and sidewalls are so rough that crosstalk is often large.
U.S. Pat. No 5,699,462 to Fouquet et al. provides a more promising approach. The switching arrangement of Fouquet el al. utilizes electrically driven heaters as a means for controlling the direction of the optical signals transversing the switch. Intersecting input waveguides and output waveguides are formed on a silicon substrate. In the transmissive state, an index-matching fluid fills the intersection, enabling light to continue in the input waveguide direction. To initiate switching from the transmissive to the reflective state, a heater is selectively energized to form bubbles within the intersection between the input and output waveguides. The formation of bubbles destroys any index-matching properties across the intersection, resulting in the reflection of optical signals away from the input waveguide direction. A concern with the heater approach is that there is a loss of heat to the surrounding silicon substrate, which necessarily increases the power requirement to create and hold the bubble in place. Another concern is an increase in “thermal crosstalk” between the crosspoint at the intersection of the waveguides as the temperature in the surrounding silicon substrate is elevated.
What is needed is a switching element and arrangement which allow reliable transitions between transmitting and diverting states, thereby controlling optical communication between optical signal lines.
SUMMARY OF THE INVENTION
A system and method for controlling optical signals in an optical switch utilizes a light-absorbing region or a light-absorbing fluid that is thermally responsive to radiation. Exposing the region or the fluid to radiation allows the manipulation of the fluid within an intersecting gap between a first input optical waveguide and a first output optical waveguide. In one embodiment, the manipulation of the fluid is achieved by selectively projecting radiation onto a material which defines the light-absorbing region and which is located at the intersecting gap. Subjecting the light-absorbing region to the radiation elevates the temperature of the material and therefore the fluid within the gap, resulting in the vaporization of the fluid. Alternatively, the fluid is degassed to form a bubble. Filling the gap with a gas or a bubble creates a refractive index mismatch that causes light from the first input waveguide to be diverted at the intersecting gap, so that the light does not reach the first output waveguide. The diversion is preferably in a direction of a second output optical waveguide. Refilling the gap with fluid switches the propagation of the light from the first input waveguide back to the first output waveguide. In another embodiment, the manipulation of the fluid is achieved by exposing the fluid to the source radiation, where the fluid is highly responsive to the radiation.
Each switching element in an array of such elements may be operated by vaporizing or degassing the fluid to form a small bubble at the intersecting gap for diverting the optical signals from one waveguide to another. In another embodiment, the switching element transfers the fluid from the gap to another location.
In a first embodiment, the light-absorbing region is in thermal contact with the fluid within the gap and includes physical properties for efficiently elevating the temperature of the fluid upon being exposed to the source radiation. The light-absorbing region may be formed by depositing a layer of tungsten, aluminum, copper, iron, cobalt, nickel, tantalum, niobium, zirconium, platinum or molybdenum. Other similar materials may be used. Optionally, the light-absorbing region is fabricated on a substrate (hereinafter “light-absorbing substrate”) that is subsequently bonded to a waveguide substrate. In an embodiment in which there are two spaced apart light-absorbing regions, the first and the second regions are positioned relative to the gap to devise a push-pull configuration for moving the bubble in order to allow rapid switching between transmission from the first input waveguide to the first output waveguide and reflection from the first input waveguide to the second output waveguide.
In another embodiment, the manipulation of the fluid is achieved by exposing the fluid to the radiation. In this implementation, the fluid is light-absorbing such that subjecting the fluid to the radiation generates thermal energy, resulting in the elevation of the temperature within the gap to form a bubble. The fluid has a narrow absorption spectrum that includes the wavelength characteristic of the source radiation.
Alternatively, a light-absorbing dye is included within the fluid. In this implementation, the fluid is non-light-absorbing. Suitable dyes include metal phthalocyanines, metal naphthalocycanines, or metal-etraphenyl naphthocyanines.
There is a matrix of switching elements for controlling optical communications between input optical waveguides and output optical waveguides that receive signals from the input waveguides at the intersecting gaps. The “waveguides” may be optical fibers, but are typically multi-layer structures fabricated on a substrate. An acceptable implementation for the waveguides is one in which top and bottom cladded SiO
2
waveguides are fabricated on a silica substrate that allows for the propagation of radiation emitted by the optical source. The gap within the silica waveguide substrate (hereinafter “waveguide substrate”) may be formed by etching tr
Agilent Technologie,s Inc.
Zarroli Michael C.
LandOfFree
Optical switch controlled by selective activation and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical switch controlled by selective activation and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical switch controlled by selective activation and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3201833