Abstract:
An optical switching device uses a first set containing at least one MEMS mirror that receives light from a light source. A second set of MEMS mirrors are arranged to receive light from the mirror(s) of the first set. The mirrors can be independently aimed so any mirror of the first set can direct light to any mirror of the second set. A set of light collectors collects light reflected from the second set of mirrors. A collimating lens may be included between any of the mirrors and the light sources/collectors. The MEMS mirrors may be activated by being flipped down or otherwise disconnect any mirror of the first or second set.

Description:
FIELD OF THE INVENTION 
   The present invention relates in general to fiber optic devices, and in particular fiber optic switching devices. 
   BACKGROUND 
   Fiber optic devices are widely used in such fields as data communications. Fiber optic data transmission has numerous advantages, including high bandwidth, insusceptibility to electromagnetic noise, long range using small diameter fibers, etc. 
   Switching of fiber optic signals has traditionally involved converting the optical signals to electrical signals, switching the electrical signals, and then converting back to optical signals. In general, it is much easier to switch and otherwise control electrons than light waves. However, the conversion of optical data to electrical signals reintroduces some of the problems that optical data was intended to avoid such as electromagnetic emission and interference. 
   An apparatus and method that address the aforementioned problems, as well as other related problems, are therefore desirable. 
   SUMMARY 
   To overcome limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for controlling and switching a plurality of optical signals. 
   In accordance with one embodiment of the invention, a configurable optical switch for directing light from one or more light sources includes a first set of one or more mirrors arranged to reflect light from the one or more light sources. A second set of mirrors is arranged to reflect light from the first set of mirrors. One or more collectors is arranged to gather light reflected from the second set of mirror. A first set of Micro Electro Mechancial System (MEMS) actuators is arranged to align the one or more mirrors of the first set to reflect light to any mirror of the second set in response to a configuration signal. 
   The above summary of the present invention is not intended to describe each illustrated embodiment or implementation of the present invention. This is the purpose of the figures and the associated discussion which follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in connection with the embodiments illustrated in the following diagrams. 
       FIG. 1  is a perspective view of an optical switching assembly according to an embodiment of the present invention; 
       FIG. 2  is a side view of the optical switching assembly according to an embodiment of the present invention; 
       FIG. 3  is a perspective view of an optical switching housing assembly according to an embodiment of the present invention; 
       FIG. 4  shows a cross sectional cutaway of an optical switching housing assembly according to an embodiment of the present invention; 
       FIG. 5  is a top view of an arrangement of mirrors of an optical switching assembly according to an embodiment of the present invention; 
       FIG. 6  is a top view of a circular arrangement of mirrors of an optical switching assembly according to another embodiment of the present invention; and 
       FIG. 7  is a perspective view of a MEMS mirror and actuator assembly according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   In the following description of various example embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration various manners in which the invention may be practiced. It is to be understood that other embodiments may be utilized, as structural and operational changes may be made without departing from the scope of the present invention. 
   Generally, the present invention provides a method and apparatus for switching light from a plurality of light sources to a plurality of light collectors using mirrors formed using Micro-Electro-Mechanical Systems (MEMS) manufacturing processes. MEMS devices are micron-scale mechanical devices formed by processing silicon in a manner similar to the layering used to form semiconductor devices such as microprocessors. In the MEMS process, a mask is deposited and then silicon material etched away in a process known as micromachining. 
     FIG. 1  shows an optical switching assembly  100  according to one embodiment of the present invention. A series of light transmitters  102  (fibers, waveguides, etc) are arranged to direct light onto a first set of mirrors  104 . In this example, four transmitters  102  are used to direct four beams of light  103  to a set of four mirrors  104 . It is appreciated that any number of light transmitters  102  and mirrors can be used. The mirrors  104  are arranged to direct light to a second set of mirrors  106 . The second set of mirrors  106  can contain any number of mirrors, although a quantity of mirrors equal in number to the first set  104  is typically used. One or more light collectors  108  are arranged to receive light reflecting from the second set of mirrors  106 . 
   The mirrors of the first and second sets  104 ,  106  are configured to selectably rotate about a vertical axis as indicated by the horizontal curved arrow  10  in  FIG. 1 . It is appreciated that references to vertical and horizontal orientations with respect to  FIG. 1  are only for purposes of illustration. In practice, the optical switching assembly may be placed in any arbitrary orientation. 
   In some applications, it may be desirable to configure one set of mirrors to be fixed. For example, if there was only one rotatable mirror of the first set  104 , the second set of mirrors  106  could each be set to a fixed orientation, each aimed at the mirror of the first set  104 . More typically, though, the mirrors of both sets  104 ,  106  are each arranged to independently rotate. 
   Providing independently rotatable mirrors of the first and second set  104 ,  106  allows any mirror of the first set  104  to be aimed at any mirror of the second set  106 . There may be some practical geometric limitation on the number of mirrors that can be arranged in rows as shown in  FIG. 1 . In practice, the mirrors of the first and second set  104 ,  106  may partially block the view between mirrors located at opposite ends of the rows. The factors that may contribute to such view blockages include the amount of separation between rows and the geometry of the mirrors. Regardless, there may be other mirror arrangements that can provide a design using as many mirrors as practical given allowable die sizes for MEMS fabrication. 
   The mirrors  104 ,  106  may also be independently flipped up or down as indicated by the curved arrow  112  in  FIG. 1 . Flipping a mirror to a substantially horizontal orientation prevents the mirror from reflecting light from the other mirrors, effectively taking the mirror out of the circuit. Other methods may be used to orient a mirror to prevent reflection from the other mirrors to accomplish a similar result. For example, the mirror could be rotated or translated to take the mirror out of the view of the other mirrors and possibly out of view of the light sources and collectors  102 ,  108 . 
   The optical switching assembly  100  is suitable for various applications. Typically, the switching assembly  100  is used in the switching and routing of optical data signals. The switching assembly  100  can be used over any range of wavelengths and used with single mode or multi-mode optical systems. In particular, the switching assembly  100  will typically be designed for a wavelength of 850 nm in data communications applications, and will typically be designed for wavelengths of 1300 m and 1550 nm in telecom applications. 
   Turning now to  FIG. 2 , a side view of the switching assembly  100  is shown. In general, the light sources/collectors  102 ,  108  are housed in a light assembly  200  to maintain alignment between the light carrying waveguides or fibers that may be part of the light sources/collectors  102 ,  108 . A collimating lens  202  can be located between the light sources/collectors  102 ,  108  and the mirrors  104 ,  106 . The collimating lens  102  can either be a single optical piece or an arrangement of multiple lenses (e.g. a lenslet array). 
   The mirrors  104 ,  106  are generally formed as part of a switching assembly  204  on a MEMS substrate. In one embodiment, the switching assembly  204  includes a hermetically sealed container (not shown) that can be made removable from the light assembly  200 . The collimating lens  202  can be made as a separate piece or integrated with either the lighting or switching assembly  200 ,  204 . 
     FIG. 3  shows a packaging arrangement  300  for an optical switching device in accordance with an embodiment of the present invention. A fiber cable  308  provides the optical signals entering and leaving the lighting assembly  200 . The light sources/collectors  102 ,  108  are enclosed at least in part in the light assembly  200 , and terminate at an outer surface  302  of the light assembly  200 . The lighting assembly  200  may also contain the collimating lens assembly  202  (not shown in this view). 
   The lighting assembly  200  and the switching assembly  204  in the arrangement of  FIG. 3  include a standard MT-RJ interface for mating with each other. In this example a standard MT-RJ interface is used, however this approach would be applicable to other connector types. The switching assembly  204  mates with the light assembly  200  so that the mirrors  104 ,  106  are placed in alignment with the light sources and collectors  102 ,  108 . An electrical cable  306  is attached to the switching assembly  204  and provides control signals to the mirrors  104 ,  106  and other devices in the switching assembly  204 . 
     FIG. 4  shows a cross sectional cutaway of the assembled packaging arrangement  300  of  FIG. 3 . The MEMS substrate  400  in the switching assembly  204  includes mirrors  104 ,  106  as well as actuators and activation members (not shown) for rotating and flipping the mirrors  104 ,  106 . The light assembly  200  may include terminating ends of fiber optic cables as seen in  FIG. 3 , or may include a high-density interconnect (HDI) optical components  402  (e.g. diode lasers, photoelectric sensors, etc.) as shown in  FIG. 4 . 
     FIG. 5  shows one arrangement of mirrors  104 ,  106  as seen from a top view of the MEMS switching device  100 . Although a distinction is made between first and second sets of mirrors  104 ,  106 , it is appreciated that the mirrors of both sets  104 ,  106  can be made substantially identical. Defining the first set of mirrors  106  as receiving light from a transmitter  102  and the second set of mirrors as sending light to a collector  108  is for purposes of illustration and not of limitation. In systems using a collimating lens  202 , however, the functions of the mirror sets  104 ,  106  may be fixed to be either receiving or transmitting relative to the sources/collectors  102 ,  108  due to the one-way nature of the collimating lens  202 . 
   In  FIG. 5 , the sets of mirrors  104 ,  106  are arranged in a rectangular pattern. In some applications, this pattern is useful at a 250-micron spacing between mirrors of each set  104 ,  106 . A 250-micron spacing corresponds to the fiber spacing in an MT-RJ connector, therefore allowing the switching device  100  to be compatible with industry standard connectors and hardware. In an MT-RJ compatible configuration, the fibers and collimating lens diameters range from 125 to 250 microns. 
     FIG. 6  shows a alternate pattern of mirror  104 ,  106  for a switching device  100 . The set of mirrors  104 ,  106  in  FIG. 6  are arranged in a circular pattern. The circular pattern is not as easily packaged in standard housings as the rectangular arrangement of  FIG. 5 , but may be useful in some applications having large numbers of mirrors  104 ,  106 . It is appreciated that other arrangements of the mirror sets  104 ,  106  are possible, including triangular, ovular, parabolic curves, matrix, etc. 
     FIG. 7  shows one example of a mirror assembly  700  according to concepts the present invention. It is appreciated that each mirror of the first and second sets  104 ,  106  can be made of substantially identical mirror assemblies  700 . The mirror assembly  700  includes a reflector  701  attached to circular rotating base  702 . The reflector  701  can be flipped up or lie substantially flat on the rotating base  702 . The rotating base has gear teeth  704  around the circular perimeter. The gear teeth  704  mesh with gears of a rotational actuator assembly  706 . 
   The rotational actuator assembly  706  selectably rotates the mirror assembly  700  for aiming the reflector  701 . The rotational actuator assembly  706  may include any sort of MEMS rotational motor such as a torsional ratcheting actuator, a wedge motor, or an index drive. A description of these devices can be found in the publication “Torsional Ratcheting Actuating System”, Stephen M. Barnes, et al, Technical Proceedings of the Third International Conference on Modeling and Simulation of Microsystems, San Diego, Calif., Mar. 27–29, 2000, pp. 273–276. Another motor design is described in the paper “Micromachine Wedge Stepping Motor”, James J. Allen, et al, Presented at the 1998 ASME International Mechanical Engineering Congress and Exposition, Anaheim, Calif., Nov. 15–20, 1998. 
   A comb drive motor  710  can be used to provide a linear motion to push a rod assembly  708 , which is used to flip the reflector  701  up and down. Alternatively, the reflectors  701  may be popped by stress beams  712 . The stress beams  712  take their actuated shape automatically after manufacture. The mirror assembly  700  may include latches  714  to hold the reflector in an upright orientation for fixed-type mirror assemblies. 
   It will, of course, be understood that various modifications and additions can be made to the preferred embodiments discussed hereinabove without departing from the scope of the present invention. Accordingly, the scope of the present invention should not be limited by the particular embodiments described above, but should be defined only by the claims set forth below and equivalents thereof.