Abstract:
Various designs of optical switch are disclosed. In one embodiment, the optical switch uses wedges to hold up a collimator and secure the wedges and collimator to a substrate with a type of adhesive, thus avoiding high temperature in soldering process. There are at least two assemblies bonded to the substrate using the adhesive. Each of the assemblies includes a collimator and two wedges, where the wedges are provided to physically hold up the collimator in position. The assemblies are glued directly to the substrate after an optical alignment is performed.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention is generally related to the area of optical communications. In particular, the invention is related to fiber optical switch assembly, and techniques for packaging such an optical switch. 
     The Background of Related Art 
     Optical switches are critical building blocks in fiber optical communication networks and other applications. In optical telecommunication, an optical switch is a switch that enables signals in optical fibers to be selectively switched from one end to another. Electromechanical optical switch is one of the commonly used types. It is operated by moving either the ends of input fibers relative to the ends of output fibers, or a mirror/prism to redirect optical signals to a selected output fiber without moving the optical fibers themselves. 
     Moving a prism is one technique to build a fiber optic switch. As shown in  FIG. 1 , a prism  102  is employed to switch a light beam, namely an optical signal can enter and leave such a prism with minimum sensitivity from the motion change of the prism. This technique compares favorably against other mirror-based approaches that may double the sensitivity. However a much longer optical pathway  104  in free space is required for the prism directing optical signals than that of moving the fiber ends. The long optical path in the prism motion-based switch makes it sensitive to fiber collimators which have to be fixed precisely and with minimal drift during any environmental changes throughout its service life. Thus, care must be exercised for the collimator fixations in a fiber optic switch and this fixation is critical for high stability and reliability over a large working temperature range and other environment conditions, therefore the packaging of these collimators is of the most important process in manufacturing a fiber optical switch. 
     In most compact 1×2 and 2×2 fiber optic switch designs, the collimators are packaged by soldering processes to a metal substrate or a metal case.  FIG. 2  duplicates  FIG. 2  of U.S. Pat. No. 5,867,617. Although the design is simple, the case must be pre-coated with gold, soldering processes is very critical to ensure the reliability of the switching function. One good feature of soldering-based packaging is that if there is any minor position drift of the collimator from the soldering process, resulting in a light loss increase, one can bend the collimator back to readjust its positions because the solder allows certain degree of deformation. One can also meld the solder again if such bend is too hard to do in room temperature. This flexibility to rework can assure a higher manufacturing yield for assembling the switch. This is why in the compact switch (e.g., 1×2 and 2×2) markets, most switches today are being made by soldering processes. In recent years, environmental protection movements have triggered more and more “Green” manufacturing practices, many countries and regions legislated and regulated the use of lead and thus soldering becomes increasingly under pressure. 
     Although there are lead-free solders available now, higher melting temperature to use them can cause the fixation process more stressful, leading to reliability issues. Also many optical components being soldered may not withstand the high temperature that can weaken the reliability of the components. This prompts the industry to rethink if there are alternative approaches to make optical switches. 
     SUMMARY OF THE INVENTION 
     This section is for the purpose of summarizing some aspects of the present invention and to briefly introduce some preferred embodiments. Simplifications or omissions may be made to avoid obscuring the purpose of the section. Such simplifications or omissions are not intended to limit the scope of the present invention. 
     Various designs of optical switch are disclosed. According to one aspect of the invention, the optical switch uses wedges to hold up a collimator, where the wedges and the collimator are secured to a substrate with a type of adhesive (e.g., epoxy), thus avoiding high temperature in soldering process. There are at least two assemblies bonded to the substrate using the adhesive. Each of the assemblies includes a collimator and two wedges, where the wedges are provided to physically hold up the collimator in position. The assemblies are glued directly to the substrate after an optical alignment is performed. 
     Depending on implementation, a common port may be assembled and bonded entirely or partially onto the substrate. A mechanism is also provided to alter an optical path between the common port and either one of the two assemblies. The mechanism is controlled by an actuating device (e.g., a relay or an actuator). 
     The present invention may be implemented as a method, an apparatus or a part of a system. According to one embodiment, the present invention is an optical switch that comprises: a substrate; at least a first assembly for a common port, the first assembly being bonded to the substrate; a second assembly for a first port, the second assembly being bonded to the substrate; a third assembly for a second port, the third assembly being bonded to the substrate, wherein each of the first, second and third assemblies includes a collimator and at least two wedges, the two wedges provided to hold up the collimator and glued together using a type of adhesive; and a mechanism provided to alter an optical path between the common port to either one of the first port and the second port. 
     According to another embodiment, the present invention is an optical switch that comprises: an enclosure with a hole on one side thereof; a substrate; at least a first collimator as a common port, the first collimator being accommodated in the hole and glued there through with epoxy; a first assembly for a first port, the second assembly being bonded to the substrate; a second assembly for a second port, the second assembly being bonded to the substrate, wherein each of the first and second assemblies includes a second collimator and at least two wedges, the two wedges provided to hold up the second collimator and glued together using a type of adhesive; and a mechanism provided to alter an optical path between the first collimator to either one of the first port and the second port. 
     According to still another embodiment, the present invention is a method for manufacturing an optical switch device, the method comprises providing a substrate; making a common port with a first collimator; making a first assembly for a first port, the first assembly being bonded to the substrate after the first assembly is aligned to a specification; making a second assembly for a second port, the second assembly being bonded to the substrate after the second assembly is aligned to the specification, wherein each of the first and second assemblies includes a second collimator and at least two wedges, the two wedges provided to hold up the second collimator and glued together using a type of adhesive; providing a mechanism to alter an optical path between the common port to either one of the first port and the second port. 
     Other objects, features, and advantages of the present invention will become apparent upon examining the following detailed description of an embodiment thereof, taken in conjunction with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
         FIG. 1  shows a prior art optical switch using a prism to switch a light beam; 
         FIG. 2  duplicates  FIG. 2  of U.S. Pat. No. 5,867,617; 
         FIG. 3  and  FIG. 4  each show an exemplary optical switch according to one embodiment of the present invention; 
         FIG. 5  shows respectively seven exemplary examples to fit various configurations; 
         FIG. 6  shows a 3D perspective of an exemplary optical switch with one input and two output ports in a 1×2 switch configuration; 
         FIGS. 7 and 8  show that collimators are mounted to a common substrate, namely bonded by epoxy through a pair of wedges; 
         FIGS. 9 and 10  shows together that only collimators in port 1  and port 2  are mounted on a common substrate while the collimator in the common port is mounted on one side of an enclosure through a hole thereof; and 
         FIG. 11  shows a process of assembling an optical switch according to one embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will become obvious to those skilled in the art that the present invention may be practiced without these specific details. The description and representation herein are the common means used by those experienced or skilled in the art to most effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring aspects of the present invention. 
     Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the order of blocks in process flowcharts or diagrams representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention. 
     Embodiments of the present invention are discussed herein with reference to  FIGS. 1-11 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the invention extends beyond these limited embodiments. 
     Referring now to the drawings, in which like numerals refer to like parts throughout the several views.  FIG. 3  and  FIG. 4  each show an exemplary optical switch according to one embodiment of the present invention. The design  300  in  FIG. 3A  is a 1×2 optical switch while the design  350  in  FIG. 3B  is a 2×2 optical switch, both are based on an epoxy/wedge process. In other words, the assembly of the design  300  or  350  is made from a process of using epoxy and wedges. 
     As shown in  FIG. 3 , the optical switch  300  includes an input assembly  302  and two output assemblies  304  by all epoxy and wedge packaging processes, where each of the collimators has a smallest possibility of curing drift, as well as higher collimator reworkability in case of having some drift. Similarly, as shown in  FIG. 4 , the optical switch  350  includes two input assemblies  352  and two output assemblies  354  by all epoxy and wedge packaging processes. It should be noted that the input and output assemblies are substantially similar in structure and are so called depending on how light signals are being switched in or out. In any case, one aspect of the present invention is to reduce the manufacture cost of the optical switches and increases their reliabilities. In addition, comparing to the soldering based assembly processes, the designs in  FIG. 3  and  FIG. 4  are the true lead-free and environment friendly products. 
     One of the aspects of the present invention is the use of wedge and epoxy to bond collimators to a substrate completely or partially if the compactness of the switch design cannot allow all three ports to be completely placed within the enclosure.  FIG. 5  shows respectively seven exemplary examples to hold a collimator securely in various configurations. In most situations, a collimator is allowed to float above the substrate, where one or more wedges are used to position the collimator in a fixed manner. The cross-sectional profile of a wedge can be triangle, round or other shapes as long as two or more of such wedges can hold a collimator and bond the collimator with the wedges to a substrate with a type of adhesive. 
     The fixation of the collimator on a substrate also allows a better reworkability. The wedge can be made in different materials, ranging from quartz, glass, ceramic to metal, etc. In the case of quartz, glass based, UV curing epoxy can be applied due to their UV light transparency features. For ceramic and metal types, one can use the thermally cured epoxy. 
     Now referring to  FIG. 6 , it shows a 3D perspective of an exemplary optical switch  600  with one input  602  and two output ports  604  and  606  in a 1×2 switch configuration. The optical switch  600  is bi-directional, the input port  602  can also be used as an output port. Accordingly, the “input” port  602  is marked as a common port while two “output ports”  604  and  606  are referred to port 1  and port 2 , respectively. Each of the port assemblies  602 ,  604  and  606  includes an optical collimator, fiber and others. The collimator can be either C-lens or GRIN-lens. All of the individual components are all bonded directly or indirectly to a common substrate through UV or thermal cured epoxy. 
     A redirect prism  608  is placed between the input and output assembles and is driven by a relay  610 , or any other kinds of actuators. When the prism  608  is not in an optical pathway, an optical signal directly goes from the common port  602  to the port 1   604 , or from the port 1   604  to the common port  602 . When the prism  608  is in an optical pathway, the optical signal goes from the common port  602  to the port 2   606 , or from the port 2   606  to the common port  602 . 
     It may be seen in  FIGS. 6, 7, and 8  that the collimators are mounted to a common substrate, namely bonded by epoxy through wedges, 2 wedges for each collimator.  FIGS. 9 and 10  shows together that only collimators in port 1  and port 2  are mounted on a common substrate while the collimator in the common port is mounted on the switch case side through the enclosure  620 . In other words, there is a hole made on the enclosure  620  to accommodate a collimator that is fixed by thermal curing epoxy. In one embodiment, the collimator contacts the hole closely so there is no wedge needed. 
       FIG. 11  shows a process  800  of assembling an optical switch according to one embodiment of the present invention. The process  800  may be understood in conjunction with the foregoing figures and descriptions thereof. At  802 , the common port (a.k.a., port-com) is first assembled. Depending on implementation, the assembly for the common port may be inserted through a hole of an enclosure or bonded directly onto a substrate using a type of adhesive. 
     At  804  and further at  808 , it is assumbled that two assemblies for port 1  and port 2  are already done and ready to be bonded to the substrate. According to one embodiment, an assembly includes a collimator and two wedges bonded together, where the wedges are used to hold the collimators onto the substrate. Before bonding the assembly for port 1  to the substrate, an alignment of the assembly must be performed to ensure that a light beam is coming to or going out from the collimator at a right angle, to minimize possible signal loss. Once the alignment of the assembly for port 1  is done, the assembly is boned to the substrate by epoxy at  806 . The similar procedure is peformated for the assembley for port 2  is done at  810 . 
     At  812 , a UV curing process is applied to harden the epoxy, and followed by thermal backing at  814 . At  816 , a prism or an optical switching mechanism is installed and necessary tests are performed to ensure that the oiptical switching function is achieved to a predefined standard or requirement. At  818 , an enclosure is provided to house the substrate along with other parts including a relay used to control the prism or the optical switching mechanism. At  620 , a final test is performed. 
     Optical switches designed in accordance with the present invention are generally adapted to provide high reliability and good switching performance at affordable cost, insert loss are usually below 0.5 dB, over typical working temperature from −5° C. to +70° C. with &lt;0.4 Db TDL, &gt;50 dB return loss, 1260 nm to 1650 nm working wavelength range. The designs and packaging processes are not limited to 1×2 designs, can be extended to 1×N or N×M designs based on different collimator/prism arrangements and layouts. 
     The present invention has been described in sufficient details with a certain degree of particularity. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope of the invention as claimed. For example, the variable neutral density filter may be replaced by another device that can strengthen an optical signal. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description of embodiments.