Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-09-27
2004-11-02
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S291000, C359S298000, C385S016000, C385S018000, C385S019000
Reexamination Certificate
active
06813057
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to optical crossconnect (OXC) switches and, in particular, to OXC switch configurations that improve switch design and operation as well as enhancing optical performance.
BACKGROUND OF THE INVENTION
Mode networks for communicating voice, video and/or data (“communication networks”) typically include an optical portion and an electrical portion. In the optical portion, information is modulated in an optical signal that is transmitted through optical fibers. In the electrical portion of the network, information is transmitted in the form of an electrical signal via wires. Optical transmission has a number of advantages over electrical transmission, notably, enhanced bandwidth capacity. However, electrical transmission has certain advantages including the widespread availability of electrical network structure and well developed data routing components and protocols. For these reasons, optical fibers are coming to predominate at the network core while wire circuitry remains the standard at the network periphery.
Even within the optical portion of the network, switching is often performed by optical- electrical-optical (OEO) switches. In such switches, the incoming optical signal is converted into an electrical signal, switching is performed in the electrical domain, and the outgoing signal is converted back into the optical domain. OEO switches allow for use of well developed electrical switch technology within the optical portion of the network. However, OEO switches are increasingly becoming the bandwidth bottlenecks of modem communication networks. In addition, such switches generally entail reading routing information from packet headers and the like, and are therefore protocol dependent.
Significant effort has therefore been directed to developing OXC switches for various core and peripheral network applications. OXC switches perform at least some switching functionality by directing optical signals in the form of beams between input and output ports, e.g., fibers or other optical or electro-optical components, without converting the signals into another domain. It will be appreciated that such connections typically support bidirectional communication and the terms “input” and “output” are therefore used herein for convenience and not by way of limitation. Such switches can therefore be substantially transparent to the transmitted signals, thereby enhancing bandwidth capabilities and avoiding compatibility issues in connection with new or varying network communication protocols.
Various types of OXC switches have been proposed including fiber translation switches, fiber bending switches and the mirror based switches. In fiber translation switches, one or both of the input and output fibers or fiber bundles are moved or translated in one or more dimensions to align a selected input fiber with a selected output fiber. However, such switches require movement of bulk components and generally are too slow for practical applications in modem communications networks. Moreover, such switches may not allow for multiple, simultaneous and independent connections as between fibers of the moved bundles.
In fiber bending switches, the end of an input and/or an output fiber is bent, e.g., using piezoelectric elements, to optically connect the fibers for transmission of optical beams therebetween. Again, such switches have not gained widespread acceptance for modem communication network applications requiring large-scale switches, fast response times and low insertion losses.
Mirror based switches utilize movable mirrors to redirect optical signals so as to connect a selected input fiber to a selected output fiber. Early designs used a bulk mirror or mirrors with bulk mechanical elements for moving the mirror(s). In cases where one movable mirror interfaces multiple input fibers with multiple output fibers, such switches may not support multiple simultaneous and independent connections. In any event, bulk mirrors generally involve response times that are impractical for modem communication network applications and/or are too large to be inserted into existing racks or other network structures or otherwise have too large a physical footprint to appeal to network providers.
More recently, numerous developers have proposed micro-mirror switches. Typically, these switches are proposed to be implemented using Micro-Electro-Mechanical System (MEMS) technology wherein the mirrors, actuators for moving the mirrors and associated integrated circuitry are fabricated on substrates using semi-conductor fabrication techniques. Micro-mirror switches are promising because it is believed that they will provide acceptable response times, because the mirrors can be mapped to individual fibers to allow for substantially unlimited simultaneous and independent connections (subject to the switch size, e.g., 256×256), and because practical switches can be dimensioned to appeal to network providers.
However, significant challenges remain with respect to realizing the potential benefits of micro-mirror OXC switches. First, some MEMS designs provide a substantially limited range of angular motion of micro-mirrors, e.g., before the mirrors “bottom out” on the substrate. Thus, in order to make large-scale switches, for example, 256×256 or greater switches, long switch interface path lengths may be required. Long path lengths, in turn, may require a large switch footprint and/or complicated optical folding, may complicate alignment and may entail a risk of cross talk due to beam spreading. Also, accurately controlling the actuators to form any of the possible connections in a large-scale switch is problematic, especially because each mirror typically has a unique switching geometry in conventional designs.
Another practical difficulty is that substantial expense is involved in designing and fabricating MEMS mirror arrays. Because the area or pitch of the mirror array is generally matched to the pitch of the associated fiber array in conventional switch designs, retooling or redesign of the fabrication process may be necessary for each switch geometry. The same limitation may affect the switch footprint.
SUMMARY OF THE INVENTION
The present invention relates to improved OXC switch configurations and implementations that address a number of needs as discussed above. In this regard, the invention provides paired movable mirror switch configurations where mirrors in a first array have a common reference orientation relative to a second array and require substantially the same range of angular movement to target the mirrors of the second array thereby simplifying switching control. Additionally, the invention provides configurations for de-coupling the mirror array pitch from the associated fiber array pitch, thereby providing significant flexibility in switch design and implementation. The invention also provides a number of switch geometries for improved optical efficiency.
In accordance with one aspect of the present invention, a number of mirrors of an optical crossconnect switch have a common relative reference orientation with respect to an array of targets such as additional mirrors or ports. In one embodiment, the switch includes two arrays of movable mirrors where any of multiple input ports can be connected to any of multiple output ports via reflection by a mirror of the first array and a mirror of the second array (addition mirrors may be involved in establishing a connection as will be discussed below). In accordance with the present invention, each of a number of mirrors of the first array is configured so as to direct an incident beam to substantially the same location relative to the second array. For example, each of the mirrors of the first array, under a nominal or reference condition, may direct an incident beam from an associated input port to a center point or center mirror of the second array. Thus, the geometry of the first mirrors, or the electrostatic force of the associated actuator components, may be varied from mirror-t
Ben Loha
Marsh & Fischmann & Breyfogle LLP
Memx, Inc.
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