The present invention relates to optical switches, and more particularly to thermo-pneumatic optical switches.
In optical communication networks, optical signals are transmitted via waveguides. At various points of an optical communications network, optical switches are used to route optical signals from one waveguide to another waveguide. Various designs of optical switches are available to accomplish the switching function.
For example, free-space micro-electro-mechanical (MEMS) optical switches use multiple mirrors to switch optical signals from one waveguide to another waveguide. In a MEMS optical switch, optical signal suffers a number of insertion losses. Insertion loss occurs each time optical signal encounters a change in media in which it is being carried. In a MEMS optical switch, optical power loss (insertion loss) occurs each time optical signal impinges on and reflects off from a mirror. Further, additional optical power losses occur within MSMS optical switches due to misalignment of mirrors and loss of collimation of the optical signal beam as it traverses unguided through the free space between the mirrors.
Another type of optical signal switch is a thermo-optic switch. Thermo-optic switches rely on the differential thermal expansion between two legs of an optical interferometer. In order to maintain a particular switching state, one leg of the interferometer must be heated to increase its length, resulting in the continuous consumption and dissipation of electric power. Furthermore, the high power requirements lead to thermal cross-talk when multiple switches are integrated into a switch matrix.
Another type of optical switch is a bubble switch. In a bubble switch, index matching fluid fills a switching trench where an input waveguide and output waveguides terminate, the index matching fluid having optical properties (such as refractive index) that matches optical properties of the waveguides. At the first switching state (“through” state), optical signal from the input waveguide passes through the index matching fluid toward a first output waveguide. To effect the switching action, heat is used to nucleate and maintain a bubble within the switching trench. The bubble displaces the index matching fluid thereby causing the optical signal from the input waveguide to be directed toward a second output waveguide via total internal reflection off the gas-substrate interface formed by the vertical trench wall. This is the second switching state (“reflected” state). When heat is removed, the bubble condenses thereby returning to the switch to the “through” state.
In this design, optical signal losses associated with insertion loss, misalignment, and beam collimation loss are minimized. However, bubble switches have high power consumption and high heat generation because they require a continual supply of energy to maintain the switching state. Because of these reasons, the reliability of the bubble switches can be adversely impacted. Further, bubble switches can suffer from cross-talk because a bubble switch array includes multiple bubble switches having a common layer of the index matching fluid within which the bubbles are nucleated. Each nucleation and dissolution of a bubble causes waves within the index matching fluid layer adversely affecting neighboring switches.
A third type of optical switch is a thermo-capillary actuated optical switch. In a thermo-capillary actuated optical switch, capillary action is used to shift index matching fluid into and out from a switching trench thereby effecting the switching action. In this design, optical signal losses associated with insertion loss, misalignment, and beam collimation loss are minimized. Further, a thermo-capillarity actuated optical switch does not require continual application of power because the switch is bi-stable. That is, once a thermo-capillarity actuated optical switch enters one of the two states (“through” or “reflected”), the switch does not require continued power into to maintain that state. However, switching actions of thermo-capillary actuated optical switches are relatively slow. This is because capillary action is used to shift the index matching fluid into and out from the switching trench. The thermo-capillary effect is relatively weak.
Consequently, there remains a need for an improved optical switch that eliminates or alleviates the shortcomings of the prior art optical switches.