Patent Abstract:
The present invention relates to a collimator assembly for use in an optical switch. The collimator assembly includes an integrated LED/photodiode plane disposed in a dual microlens array. The integrated LED/photodiode plane results in a relatively simple way to manufacture high port count collimator arrays with integrated monitoring capabilities. The LED/photodiode plane can be readily produced using standard electronics manufacturing technology.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) based on U.S. Provisional Patent Application Ser. No. 60/276,321, filed Mar. 16, 2001, the contents of which are relied upon and incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to optical switching, and particularly to monitoring the performance of optical switches. 
     2. Technical Background 
     Over the past several decades, fiber optic technology has transformed the telecommunications industry. A decade ago, network designs included relatively low-speed transceiver electronics at each end of a communications link. Light signals were switched by being converted into electrical signals. The electrical signals were switched using electronic switches, and converted back again into light signals. The bandwidth of electronic switching equipment is in the Gigahertz range. On the other hand, the bandwidth of single mode fiber is in the Terahertz range. As the demand for bandwidth increased, network designers have sought ways to exploit the bandwidth in the 1550 nm region. Optically transparent switching fabrics were developed to meet this demand. 
     In one approach that is being considered, optical designers are evaluating free-space plane-to-plane optical interconnects, often referred to as three-dimensional optical cross-connects (3D OXCs). 3D OXCs have the potential to make large scale N×N switching a reality. For example plane-to-plane interconnects can be designed to easily scale to high port counts on the order of 4000 by 4000 ports. MEMS mirror arrays and conventional collimator arrays can be easily scaled to keep pace with port count growth. 
     One drawback to this approach relates to the fact that traditional monitoring capability does not scale as favorably. MEMS mirror arrays and collimator arrays can be fabricated using batch processing techniques. However, monitoring components required at each port have to be added later. Per port monitoring is provided by splicing in a light source, light detector, and other associated optical elements at each port in the switch fabric. Thus, the manufacturing process becomes increasingly complicated and costly. Since monitoring components have to be spliced into each port, the amount of fiber that must be managed by the switch is also increased. Both the splicing operations and the increase in the amount of fiber result in reduced switch reliability. 
     What is needed is an integrated monitoring approach that eliminates the aforementioned problems. A scalable monitoring approach that employs batch processing techniques is needed to reduce costs, simplify the manufacturing process, reduce the amount of fiber employed in the switch, and increase switch reliability. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the needs described above. The present invention provides a scalable monitoring approach that reduces costs, simplifies the manufacturing process, reduces the amount of fiber employed in the switch, and increases switch reliability. 
     One aspect of the present invention is a collimator assembly that includes a first microlens array and a second microlens array. The first microlens array includes at least one first microlens element. The second microlens array includes at least one second microlens element. A monitor transceiver array is disposed between the first microlens array and the second microlens array, the monitor transceiver array including at least one monitor transceiver element coupled to the at least one first microlens element and to the at least one second microlens element. 
     In another aspect, the present invention includes a method of making a collimator assembly. The method includes providing a first microlens array, the first microlens array including at least one first microlens element. A second microlens array is provided, the second microlens array including at least one second microlens element. A monitor transceiver array is disposed between the first microlens array and the second microlens array. The monitor transceiver array includes at least one monitor transceiver element. The at least one monitor transceiver element is coupled to the at least one first microlens element and to the at least one second microlens element. 
     In another aspect, the present invention includes a three-dimensional optical switch. The optical switch includes a first collimator array that includes a first monitor transceiver array disposed between a first pigtailed microlens array and a first free-space microlens array. The first pigtailed microlens array has at least one first pigtailed array element. The first monitor transceiver array includes at least one first monitor transceiver element optically coupled to the at least one first pigtailed array element. The first free-space microlens array includes at least one first free-space microlens element optically coupled to the at least one first monitor transceiver element. A beam steering apparatus is coupled to the first collimator array. A second collimator array is coupled to the beam steering apparatus. The second collimator array includes a second monitor transceiver array disposed between a second pigtailed microlens array and a second free-space microlens array. The second pigtailed microlens array has at least one second pigtailed array element. The second monitor transceiver array includes at least one second monitor transceiver element optically coupled to the at least one second pigtailed array element. The second free-space microlens array includes at least one second free-space microlens element optically coupled to the at least one second monitor transceiver element. 
     In another aspect, the present invention includes a method for monitoring the performance of an optical switch. The optical switch includes a first collimator array having at least one first port array element, and a second collimator array element having at least one second port array element. The method includes directing the at least one light signal into the optical switch via the at least one first port array element. At least one transmission path monitoring signal is superimposed onto the at least one light signal to thereby form at least one superimposed signal. The at least one transmission path monitoring signal is generated by the at least one first port array element. The superimposed signal is directed to the at least one second port array element. The at least one transmission path monitoring signal is received by the at least one second port array element, and the at least one light signal being directed out of the optical switch via the at least one second port array element. 
     Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of the collimator in accordance with the present invention; 
     FIG. 2 is a perspective view of the collimator in accordance with the present invention; and 
     FIG. 3 is a diagrammatic depiction of the optical switch in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. An exemplary embodiment of the collimator assembly of the present invention is shown in FIG. 1, and is designated generally throughout by reference numeral  10 . 
     In accordance with the invention, the present invention for a collimator assembly for use in an optical switch includes a first microlens array. The first microlens array includes at least one first microlens element. The collimator assembly also includes a second microlens array. The second microlens array includes at least one second microlens element. A monitor transceiver array is disposed between the first microlens array and the second microlens array. The monitor transceiver array includes at least one monitor transceiver element coupled to the at least one first microlens element and to the at least one second microlens element. A relatively simple batch manufacturing process is used to provide the optical switch of the present invention with monitoring capabilities. Thus, the present invention provides a reliable, cost effective optical switch having integrated monitoring capabilities. 
     As embodied herein and depicted in FIG. 1, a side elevation view of collimator assembly  10  in accordance with the present invention is disclosed. Collimator assembly  10  includes pigtailed microlens array  20 . Although only one microlens  200  is shown in FIG. 1, pigtailed microlens array  20  includes a plurality of microlens elements  200 . Each microlens  200  is connected to ferrule  12 . Ferrule  12  couples optical fiber pigtail  14  to microlens  200 . Collimator assembly  10  also includes free-space microlens array  30 . In one embodiment, free-space microlens array  30  is optically coupled to a free-space beam steering apparatus (not shown) in an optical switch. Although only one is shown in FIG. 1, microlens array  30  includes a plurality of microlens elements  300 . Monitor transceiver array  40  is attached to free-space microlens array  30 . Again, although only one transceiver element  400  is shown in FIG. 1, transceiver array  40  includes a plurality of transceiver elements  400  disposed on substrate  402 . Each microlens  200  is optically coupled to transceiver element  400 . Likewise, each microlens  300  is optically coupled to transceiver element  400 . Thus, each port  1  in collimator assembly  10 , includes ferrulized optical fiber pigtail  14 , microlens  200 , transceiver element  400 , and microlens  300 . 
     Both pigtailed microlens array  20  and free-space microlens array  30  can be fabricated using conventional collimator array techniques. 
     It will be apparent to those of ordinary skill in the pertinent art that modifications and variations can be made to transceiver array  40  of the present invention depending on the type of batch processing used to fabricate array  40 . For example, transceiver array  40  may be an LED/photodiode array manufactured using standard batch electronics processing techniques. A variety of semiconductor materials can be used in the fabrication of the LED/photodiode arrays. For example, in one embodiment, GaAsP materials are used to fabricate red LEDs and lasers. Si materials are used to fabricate visible and very near-IR photodiodes. In another embodiment, GaAs materials are used to fabricate 850 nm LEDs, lasers, and photodiodes. One very important requirement is that substrate  402  material and active  400  material be transparent to conventional-band (1500-1600 nm) light signals. All of the above materials meet this transparency requirement. In another embodiment, the LEDs are coated with an anti-reflection material for high transmission of the light signal. In yet another embodiment, the LEDs are positioned slightly out of focus to minimize return loss. The embodiment easiest to implement employs GaAsP or GaAs based LEDs and Si photodiodes. 
     In another embodiment, transceiver elements  400  are implemented by fabricating a single diode structure that is operated as either an LED or a photodiode depending on the polarity of the bias voltage applied to the diode structure. The diode structure is forward biased for use as an LED and reversed biased for use as a photodiode. The ability to change transceiver  400  operation between light emitter and light detector is advantageous during both manufacturing and operation because it allows the light signal path alignment to be optimal for both signal transmission directions (e.g., port  1  is typically employed as both an input port and as an output port). 
     As embodied herein and depicted in FIG. 2, a perspective view of the collimator in accordance with the present invention is disclosed. In FIG. 2, collimator array  10  is depicted as a seven by seven collimator array. Assembly of collimator array  10  requires the alignment of four planes of components. First, ferrulized optical fiber pigtails  14  are connected to microlens array  20 . Second, transceiver array  40  is aligned and attached to microlens array  30 . Finally, pigtailed microlens array  20  is aligned and coupled to the microlens array/transceiver array subassembly. On a per port basis, the above described method causes each ferrulized optical fiber pigtail  14  to be aligned and coupled to a corresponding microlens  200 . Each transceiver element  400  is aligned and coupled to a corresponding microlens  300 . Finally, each pigtailed microlens  200  is aligned and coupled to a corresponding transceiver equipped microlens  300  in collimator assembly  10 . 
     As embodied herein and depicted in FIG. 3, a diagrammatic depiction of the optical switch  100  in accordance with the present invention is disclosed. Optical switch  100  includes collimator array  10  coupled to integrated beam steering array  70 . Beam steering array  70  is optically coupled to beam steering array  80 . Beam steering array  80  is coupled to collimator array  10 ′. Those of ordinary skill in the art will recognize that collimator array  10 ′ is identical to collimator array  10  described above. Optical switch  100  also includes control electronics module  60 . Control module  60  provides beam steering array  70  and beam steering array  80  with beam steering commands. Control module  60  also processes all of the electrical monitor signals received from each transceiver element  400 . The electrical monitor signals are used as feedback, allowing control module  60  to adjust the position of individual beam steering pixels disposed on either array  70  or array  80 . The electrical monitor signals are also used to evaluate the performance of each transmission path in optical switch  100 . 
     It will be apparent to those of ordinary skill in the pertinent art that modifications and variations can be made to control system  60  of the present invention depending on the size and overall capacity of optical switch  100 . For example, control system  60  may include a 32-bit microprocessor, a RISC processor, or an application specific integrated chip (ASIC). The ASIC may be implemented using a programmable logic array (PLA) device, or by a field programmable gate array (FPGA) device. In another embodiment, control system  60  is implemented using computing resources disposed in the network. 
     Beam steering array  70  includes a number of steerable pixels corresponding to the number of ports  15  included in collimator assembly  10 . Likewise, beam steering array  80  includes a number of steerable pixels corresponding to the number of ports  15 ′ included in collimator assembly  10 ′. In one embodiment, the beam steering arrays include gimbaled reflective pixels that are steerable with 2-degrees of freedom. The reflective pixels are actuated by electrostatic actuators. The electrostatic actuators are coupled to control system  60  via a control bus. 
     Referring to FIG.  1  and FIG. 3, the integrated monitoring functionality in collimator array  10  operates as follows. When light signal Ls is directed into the collimator array via ferrulized fiber pigtail  14 , control electronics  60  activates the LED function in transceiver element  400 . Thus, in the LED/photodiode embodiment, the LED is activated In the single diode structure embodiment, a forward bias is applied to the diode to cause the diode to function as an LED. Subsequently, the LED element transmits monitor light signal Lmon that is superimposed onto the information carrying light signal Ls. The composite signal Lcomp is directed from microlens  300  to beam steering array  70 . On the other hand, if the composite light signal Lcomp is directed from the beam steering array  70  into microlens  300 , control electronics  60  activates the photodiode functionality in transceiver element  400 . Thus, in the LED/photodiode embodiment, the photodiode is activated In the single diode structure embodiment, a reverse bias is applied to the diode to cause it to function as a photodiode. Consequently, monitor signal Lmon is converted into an electrical monitor signal by the photodiode. Information carrying signal Ls passes through transceiver substrate  402  and transceiver element  400  and is directed into microlens  200 . Finally, light signal Ls exits the collimator array via ferrulized optical fiber pigtail  14 . Obviously, the above description applies equally to collimator array  10 ′. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Technology Classification (CPC): 7