Abstract:
The fiber optic switch includes a plurality of optical inputs and a plurality of optical outputs carried by a support. The switch also includes a first plurality of rotatable reflectors each being associated with a respective optical input, and a second plurality of rotatable reflectors each being associated with a respective optical output. Also, a plurality of reflector drivers directs selected pairs of the first and second plurality of rotatable reflectors to define respective paths between the optical inputs and the optical outputs. The free-space propagating optical beam that is transferred between each input and output is formed by a micro lens producing a substantially collimated beam and therefore minimizing optical performance penalties due to the relative path length differences between various routing paths.

Description:
FIELD OF THE INVENTION 
     The present invention relates to fiber optic communications, and more particularly, to an optical switching device for switching an optical signal in a fiber optic communication system between two or more channels. 
     BACKGROUND OF THE INVENTION 
     Fiber optic cables are used to carry voice, video, and other data signals transmitted as light beams in communications networks. Similar to communication networks using copper wire as the carrier for electronic signals, fiber optic cable lines are interconnected to each other through switches positioned at various locations throughout the communications network. To achieve all-optical routing and rerouting of the communications signals, optical matrix switches or M×N crossbar switches are used. All-optical switches should not to be confused with other switching technologies that first convert the optical signals to electrical signals, perform the required routing, and then convert the electrical signals back to optical signals. 
     As an example of an all-optical switch, U.S. Pat. No. 6,009,219 to Doyle entitled “Optical Beam Switching Device” discloses an optical switching apparatus that uses a solid refractive switching body for selectively coupling first and second optical channels. The solid refractive switching body is moved to position first and second refractive faces adjacent the first and second optical channels. 
     Another example is U.S. Pat. No. 5,960,132 to Lin entitled “Fiber-Optic Free-Space Micromachined Matrix Switches”. Here, an optical switch includes reflective panels which either permit the light beam to travel in a first direction or redirect the light beam from the first direction to a second direction. 
     However, conventional fiber optic switches may have a low channel density, high insertion loss, static state power consumption and may be relatively bulky. Switching speed, reliability, wavelength range, and cost are other factors that may also be considered depending on the specific application. In particular, the use of wavelength division multiplexing (WDM) is severely straining the capability of conventional switch technology due to the vast increase in the number of channels; and currently no single switch technology is emerging as optimum for all applications. Thus, there is a need for a fiber optic switch with an increase in channel density, a reduced wavelength dependence, a reduction in size, lower insertion loss, higher reliability, and reduced static power consumption. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing background, it is therefore an object of the invention to increase the channel density, wavelength independence, and reliability of an all-optical fiber optic switch while reducing the insertion loss, size and power consumption thereof. 
     This and other objects, features and advantages in accordance with the present invention are provided by a fiber optic switch including a plurality of optical inputs and a plurality of optical outputs carried by a support. The switch includes a first plurality of rotatable reflectors each being associated with a respective optical input, and a second plurality of rotatable reflectors each being associated with a respective optical output. Also, a plurality of reflector drivers directs selected pairs of the first and second plurality of rotatable reflectors to define respective paths between the optical inputs and the optical outputs. 
     Each of the plurality of optical inputs and outputs may comprise a lens, an optical connector and an optical fiber. For compactness and good performance the lens may be a gradient index micro lens, although a broader range of wavelength operability may be realized with specifically designed achromatic micro lenses. In any case, the optical input and output lenses are substantially indistinguishable and tailored by manufacture to efficiently transfer a substantially collimated beam of light between the two lenses. The invention takes great advantage of the fact that free-space propagating optical beams may cross paths without interference. Also, each of the first and second plurality of rotatable reflectors may comprise a rotatable mirror, and each of the plurality of reflector drivers may comprise a motor, such as a micro-electro-mechanical (MEMs) motor for compactness. The ultimate compactness of the invention is primarily limited only by the size of the motors that rotate the mirrors, which may vary over time with the state of motor technology. Also, latchable motors may reduce or eliminate the need for electrical power consumption during static operation. The switch may also include a controller for controlling the plurality of reflector drivers to produce desired routing paths between optical inputs and outputs. 
     The plurality of optical inputs and outputs are preferably positioned on the support in a substantially circular pattern. The support may comprise a first support portion for supporting the plurality of optical inputs in a substantially semi-circular pattern, and a second support portion, adjacent the first support portion, for supporting the plurality of optical outputs in a substantially semi-circular pattern. 
     Objects, features and advantages in accordance with the present invention are also provided by a method of routing light signals in a fiber optic communication system including a plurality of optical inputs and a plurality of optical outputs. The method includes providing a plurality of rotatable reflectors each being associated with a respective one of the plurality of optical inputs and outputs, and directing pairs of rotatable reflectors to define respective paths between the optical inputs and the optical outputs. 
     Directing respective rotatable reflectors may comprise rotating the rotatable reflectors with a motor, and the plurality of rotatable reflectors are preferably positioned in a substantially circular pattern. Providing the plurality of rotatable reflectors may comprise positioning the rotatable reflectors associated with the plurality of optical inputs in a substantially semi-circular pattern, and positioning the rotatable reflectors associated with the plurality of optical outputs in a substantially semi-circular pattern adjacent to the rotatable reflectors associated with the optical inputs. 
     The fiber optic switch and method of the present invention provide an increase in channel density, a reduction in the size, lower insertion loss, a broad range of wavelength performance, higher reliability, and a reduction in static power consumption. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of an optical communication system including a fiber optic switch in accordance with the present invention. 
     FIG. 2 is a cross-sectional schematic diagram illustrating the fiber optic switch in accordance with the present invention. 
     FIG. 3 is schematic diagram illustrating the pattern of fiber optic channels of the fiber optic switch of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
     Referring to FIG. 1, an optical communication system  4  includes networks  6  being generally (but not exclusively) connected for mutual communication via a plurality of wavelength division multiplexers (WDMs)  8  and an M×N fiber optic switch  10 . Referring now to FIGS. 2 and 3, the fiber optic switch  10  in accordance with the present invention will be described. The fiber optic switch  10  is an all-optical matrix switch or M×N crossbar switch for use in such fiber optic communication systems  4 . The switch  10  includes a support or frame  12  for supporting a plurality of optical outputs  19 A, and a plurality of optical inputs  19 B. The support may include a first support portion  11 A for supporting the plurality of optical outputs  19 A in a semi-circular pattern, and a second support portion  11 B for supporting the plurality of optical inputs  19 B in a preferred semi-circular pattern adjacent the plurality of optical inputs. As such, the plurality of optical inputs and outputs are arranged in a preferred substantially circular pattern as shown to minimize the variation in path distances and to improve the line-of-sight between all possible routings. This in turn serves to maximize the number of channels that may be connected via the fiber optic switch  10  and thereby increase the channel density thereof. Other patterns, such as a substantially linear pattern, may also be used depending on the requirements of a specific application. 
     Each of the optical outputs  19 A and inputs  19 B may include a collimating micro lens  20 , an optical connector  22 , and a fiber optic cable  24 . The lenses  20 , connectors  22  and cables  24  are well known to the skilled artisan. Preferably, the lenses  20  are gradient index (GRIN) micro-lenses which are widely used in fiber optic components such as switches, splitters, isolators, WDMs, and circulators as would be appreciated by the skilled artisan. For compactness and good performance the lenses  20  may be a gradient index micro lens, although a broader range of wavelength operability may be realized with specifically designed achromatic micro lenses. In any case, the optical input and output lenses  20  are substantially indistinguishable and tailored by manufacture to efficiently transfer a substantially collimated beam of light between the two lenses. The invention takes great advantage of the fact that free-space propagating optical beams may cross paths without interference. 
     The switch  10  also includes a first plurality of rotatable reflectors  18 A each being associated with one of the plurality of optical outputs  19 A, and a second plurality of rotatable reflectors  18 B each being associated with one of the plurality of optical inputs  19 B. The rotatable reflectors  18 A and  18 B are preferably mirrors as would be appreciated by the skilled artisan. The rotatable reflectors  18 A and  18 B are driven by motors  14  via drive shafts  16 . For simplicity, the reflectors  18 A and  18 B may be formed by beveling, polishing, and depositing a highly reflective layer to the shaft  16  of the motor  14  itself. The motors  14  may be stepper motors and/or the rotatable reflectors  18 A and  18 B may include a position locating mechanism (e.g. a detent or stop) to aid in the control of the rotatable reflectors. The motors  14  may also be micro-electromechanical system (MEMS) motors to further reduce the size of the switch  10 . The motors  14  are directed by a controller  26  to rotate selected pairs of the reflectors  18 A and  18 B and direct light in a desired direction to define respective routing paths between the optical outputs  19 A and the optical inputs  19 B. 
     For example, as can be seen in FIG. 3, a path may be defined between an optical output  19 A 1  and a optical input  19 B 1  by directing respective reflectors  18 A and  18 B at each other. A light signal may be transmitted through the optical fiber  24 , the optical connector  22  and the lens  20  of the optical inputs  19 B 1 . Then the light signal is reflected by the associated rotatable reflector  18 B towards another rotatable reflector  18 A of the desired optical output  19 A 1 . The reflector  18 A reflects the light signal towards the lens  20  and through the optical connector  22  and the fiber optic cable  24  of the optical output  19 A 1 . As a reflector  18 A,  18 B rotates, the associated free-space optical beam path so swept in space defines a unique plane. By such beam paths associated with all rotating reflectors  18 A,  18 B subscribing to the identical plane within allowed manufacturing tolerances, all possible combinations of optical input and output paths are therefore provided. The above description refers to inputs and outputs; however, the skilled artisan would appreciate that it may be possible to transmit light signals in either direction and thus the terms may be interchangeable and are not intended to limit the direction of the light signal transmissions. 
     As an input optical signal is rerouted within this switch  10 , the collimated optical beam will generally sweep across several of the second plurality of reflectors  18 A associated with outputs. The concern of unwanted optical coupling, or crosstalk, to other outputs during this operation is substantially negated by the high directional selectivity of the micro lenses  20  that couple light from the output reflectors  18 A into the associated output fiber  24 . Therefore, re-routing may be performed arbitrarily with regard to the location and quantity of paths being configured and without regard of interference to paths remaining static. 
     The fiber optic switch  10  as described above has increased channel density and a corresponding reduction in size, better performance with higher reliability, and reduced static power consumption. 
     A method of routing light signals in a fiber optic communication system in accordance with the present invention will now be described. The fiber optic communication system includes a plurality of optical outputs  19 A and a plurality of optical inputs  19 B. The method includes providing a plurality of rotatable reflectors  18 A and  18 B each being associated with one of the respective optical outputs  19 A and inputs  19 B, and directing pairs of rotatable reflectors to define respective paths between the optical inputs and the optical outputs. In other words, as described in the example above, a light signal is transmitted through one of the plurality of optical inputs  19 B, reflected by an associated rotatable reflector  18 B towards a desired rotatable reflector  18 A, and then reflected to the respective one of the plurality of optical outputs  19 A. 
     Directing respective rotatable reflectors  18 A and  18 B may include rotating the rotatable reflectors with a motor  14  via shaft  16 . Also, the plurality of rotatable reflectors  18 A and  18 B are preferably, but not necessarily, positioned in a substantially circular pattern. For example, the rotatable reflectors  18 A associated with the plurality of optical outputs  19 A may be positioned in a substantially semi-circular pattern, and the rotatable reflectors  18 B associated with the plurality of optical inputs  19 B may be positioned in a substantially semi-circular pattern adjacent to the rotatable reflectors associated with the optical outputs. As mentioned above, the number of outputs  19 A and inputs  19 B that may be connected via the fiber optic switch  10  is maximized and the channel density of the switch is thereby increased. 
     The described method of the present invention provides an increase in channel density, a reduction in the size of the switch  10 , better performance with higher reliability, and reduced static power consumption. 
     Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.