Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1998-11-20
2001-03-20
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S015000, C385S016000, C385S018000
Reexamination Certificate
active
06205267
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical switch that employs a micro-electro-mechanical system (MEMS) device to do optical switching.
BACKGROUND OF THE INVENTION
MEMS is a technology that exploits lithographic mass fabrication techniques of the kind that are used by the semiconductor industry in the manufacture of silicon integrated circuits. Generally the technology involves shaping a multilayer structure by sequentially depositing and shaping layers of a multilayer wafer that typically includes a plurality of polysilicon layers that are separated by layers of silicon oxide and silicon nitride. The shaping of individual layers is generally done by etching and the etching is generally controlled by masks that are patterned by photolithographic techniques. The technology also may involve the etching of intermediate sacrificial layers of the wafer to release overlying layers for use as thin elements that can be easily deformed or moved.
The technology has proven highly versatile and has been used to form a wide variety of miniature devices varying in size from millimeters to microns. MEMS technology is discussed in a paper entitled “MEMS The Word for Optical Beam Manipulation” published in
Circuits and Devices,
July 1997, pp. 11-18.
MEMS devices can be fabricated by the MCNC MEMS Technology Application Center, Research Triangle Park, N.C. 27709. The technology is described in “Multiuser MEMS Processes (MUMPS) Introduction and Design Rules,” Rev. 4, Jul. 15, 1996 MCNC Mems Technology Applications Center, Research Triangle Park, N.C. 27709 by D. Keoster, R. Majedevan, A. Shishkoff, and K. Marcus.
Optical systems are becoming of increasing importance and optical switches have vital roles in many optical systems, particularly in optical networks that require rapid and flexible reconfiguration. Examples of such roles include protection switching of optical transmission links and the reconfiguration of optical cross-connects and add/drop modules (ADM) for wavelength division multiplexed (WDM) systems. There has been demonstrated a wide variety of optical switches even including several MEMS optical switches. Despite this wide variety, none has provided the combination of high optical performance, ultracompact size, low actuation voltage, and ultra-low power consumption with the potential of easy fabrication, low cost and suitability for use both in demanding gigabit optical networks and in cost-sensitive applications, such as fiber-to-the-home.
The present invention seeks to provide optical apparatus that helps satisfy this need.
SUMMARY OF THE INVENTION
The invention is an optical switch that uses an element of a MEMS device to interpose controllably a shutter in a gap between a pair of optical waveguides, for example optical fibers that are aligned end-to-end. When the shutter is not interposed between the two fiber ends defining the gap, an optical signal launched in the source or input fiber of the pair travels with little loss or disturbance across the gap and continues along the output fiber. When the shutter is interposed, the optical signal is switched.
As an illustrative embodiment, a switch in accordance with the invention comprises a pair of optical waveguides, typically optical fibers that are aligned end-to-end with a small gap between adjacent ends. In one form of switch, a three-port optical circulator is included at the input of the switch. An input signal is applied to the first port of the circulator, exits at the second port, and enters the input end of the source fiber of the pair. In the state when the shutter is out of the gap, as discussed, the optical signal passes through and exits from the output fiber with little loss. In the state when the shutter is in the gap, the incident optical signal exiting from the source fiber into the gap is reflected back into the source fiber and into the second port of the optical circulator for exit at its third port for travel in a new path. In another form of switch, in place of the optical circulator, there may be included a directional coupler coupled to the source fiber that extracts the reflected wave for travel in a different path.
In another form of switch, the shutter may be introduced in a fashion to deflect the optical signal selectively into one of two new paths.
The position of the shutter, in or out of the gap, is determined by a voltage controlled actuator that comprises a pair of conductive plates formed by a pair of spaced apart polysilicon layers in a structure that was processed by MEMS technology. The control voltage serves to move the upper of the two plates which is essentially a flexible layer suspended over the lower of the two plates. The downward movement of the upper plate is made to swing upwards the one end of a lever of which the other end is coupled by way of a flexible section with the upper plate. A shutter that is positioned at the one end of the lever arm is then interposed in the gap formed between the adjacent ends of a pair of aligned waveguides, for example optical fibers. The shutter is coated to be highly reflective of incident optical signals and each adjacent end of the two fibers is anti-reflection (AR) coated. As a result, when the shutter is in the gap, essentially all of the input optical signal is reflected back into the input fiber and essentially none reaches the output fiber. Moreover, the reflected signal passes through an optical circulator that diverts such a backward traveling signal and sends the optical signal along a new path distinct from the one it would have traveled had it not been reflected by the shutter.
A feature of a particularly attractive form of the MEMS device uses a lever arm that includes a flexible section that is integral with the upper plate and that permits essentially frictionless movement of the shutter into the gap between the fibers.
Another embodiment to be described permits light from a source fiber to be switched or divided between a pair of output fibers.
The invention will be better understood from the following more detailed description taken in conjunction with the accompanying drawing.
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Aksyuk Vladimir J.
Barber Bradley P.
Bishop David J.
Giles Clinton R.
Ruel Rene R.
Healy Brian
Lucent Technologies
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