Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2002-04-12
2004-07-06
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S016000, C385S018000, C398S048000, C398S056000, C398S057000
Reexamination Certificate
active
06760503
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical switches and, more particularly, to a method of constructing any arbitrary size scalable M×N optical router/switch using modular components, and to a bi-directional optical component capable of being used in such a system.
2. Description of the Related Art
The past twenty years has witnessed an optical revolution in telecommunications. The widespread deployment of optical fibers in order to carry light signals over long distances has vastly increased the communication capabilities of present telecommunications systems. However, although the communication pathways have been changed to an optical core, rather than an electrical one, the elements used for routing or switching the optical signals have mostly remained electrical. In practice, this means the optical light signal must be converted to an electrical signal, and this electrical signal is routed and/or switched by an electrical router/switch; then the electrical signal is converted back into an optical signal for transmission over an optical fiber. These optical-to-electrical and electrical-to-optical conversion steps are wasteful of both time and resources.
To solve this problem, many companies have offered optical routers which perform routing/switching completely in the optical domain, without converting the communication signals from optical to electrical, and vice-versa. Many technologies have been developed to provide such optical routing/switching. The first commercially available optical routing technology was mechanically based and limited to 1×2 and 2×2 port sizes. These are based on beam expanding collimators and/or electromagnetically (e.g., stepper motor or solenoid) actuated mirrors, prisms, or collimators. Waveguide routing technologies are also becoming available now: silica-on-silicon waveguide or photonic lightwave circuit (PLC) technology (based on thermally induced changes in the refractive index of silica), lithium niobate technology (based on electrically induced changes in the refractive index). But these technologies suffer from limited scalability, high insertion loss, and high crosstalk. Liquid crystal optical switches (based on changing the polarization of incident light and then using polarization analyzers to route the polarized light) are also being developed, but they are complex and only low port count switches (1×2 and 2×2) are currently available. Other optical routing technologies being developed include III-V semiconductor-based waveguide switches, polymer-based thermo-optic digital waveguide switches, and semiconductor optical amplifier (SOA)-based gate switches.
Micro-electromechanical systems (MEMS) are rapidly establishing itself as the most attractive technology for optical switching since it allows low-loss large-port-count optical switching solutions at the lowest cost per port. Basically, a MEMS device is a mechanical integrated circuit where the actuation forces required to move the parts may be electrostatic, electromagnetic, or thermal. The basic technology is based on establishing semiconductor processes for manufacturing highly accurate miniaturized parts and uses material with excellent mechanical and electrical properties (Si, SiOx, and SiNx). Silicon-based MEMS devices can be produced with different process technologies, including bulk micromachining, in which mechanical structures are etched in single crystal silicon, and surface micromachining, in which epitaxial layers of polysilicon, silicon nitride, and silicon oxide are deposited, patterned, and selectively removed.
U.S. Pat. No. 6,259,835 to Jing (which is hereby incorporated by reference) describes a 1×N MEMS optical switch with one primary port, a plurality of secondary ports, and a plurality of optical reflectors. Any one of the optical reflectors, which may comprise mirrors or prisms, can be moved by an actuator into position to reflect an input light beam out through a corresponding secondary port, i.e. to direct or route the signal to a destination. For example,
FIG. 1
shows a switch with Input Fiber
101
engaged in Input Port
105
, and a plurality of mirrors (e.g., Mirror
110
) placed adjacent to a plurality of output ports (e.g., Output Port
120
) in which output fibers are engaged. Input light beam
150
(indicated by the dotted line) comes from Input Port
105
, reflects off of Mirror
110
, and exits through Output Port
120
. Since each output port has a corresponding mirror and actuator, the input light beam can be routed to any of the N output ports. If none of the mirrors is put in the path of the beam, the beam will reflect off of the last mirror (which is set in place) and exit out of the last output port.
Bubble technology can be used to route light signals instead of mirrors or prisms in optical routers. For example, in U.S. Pat. No. 6,320,994 to Donald et al. (which is hereby incorporated by reference), at least three waveguides (an input waveguide, and two output waveguides) intersect at a gap having a predetermined width. The gap is either filled with a fluid (whereby input light will exit through one output) or a bubble (whereby input light will exit through the other output) formed by heating the fluid. U.S. Pat. No. 6,324,316 to Fouquet et al. (which is hereby incorporated by reference) shows a 4×4 optical switch which uses bubble technology to route any of the four inputs to any of the four outputs. One shortcoming of Fouquet et al. is that, in most situations, if there are four input beams, at least one of these beams will cross at least one of the others after being reflected by a bubble. Although the interference caused by such interaction may be minimal, it is not non-existent (especially considering the beams are not orthogonal to each other), and such interference may become more problematic when technologies such as dense wavelength division multiplexing (DWDM) are used in combination with this switch.
Another problem with current optical routing technology is the lack of scalability, i.e., the inability for the technology to increase in size without becoming unduly complex. As examples, consider the two-dimensional MEMS cross-connect switch in FIG.
2
A and the three-dimensional (3D) MEMS cross-connect switch in FIG.
2
B. Both of these switches use mirrors. Mirror control for the 2D switch is binary and straightforward, but the trade-off for this simplicity is optical loss. Although the length of the light path only grows linearly with the number of input/output ports, the optical loss also grows rapidly due to the Gaussian nature of light. Because of this, 2D architectures are found to be impractical beyond 32 input and 32 output ports. Even though multiple stages of 32×32 2D switches could be put together to form a 1000-port 2D switch, the cumulative high optical losses make such an implementation impractical. By contrast, the 3D architecture of
FIG. 2B
greatly reduces the optical loss by making use of 3D space. In
FIG. 2B
, there are two banks of reflective mirrors which guide each light beam from any input port to any output port. Thus, there is a corresponding mirror for each of the input and output ports. Using this 3D architecture, switches with ports numbering in the thousands are possible. However, 3D architecture is complex, and becomes increasingly complex as the number of ports increases. Furthermore, such 3D optical switches are not modular in the sense that modular components can be added together to form larger routers. It makes more sense to simply built a larger 3D optical switch. But in such a large 3D optical switch, if only one mirror is out of alignment, or there is a problem with just a few mirrors, the entire switch must be taken out of service in order to fix it.
Even when conventional optical systems use modular components to construct an optical router, the resulting optical router is limited by other practical considerations. As an example, consider U.S. Pat. No. 5,771,320 to Stone (which is hereby inc
Cohen & Pontani, Lieberman & Pavane
Healy Brian
Lin Tina M
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