Abstract:
An integrated optical line card protection module uses free-space optical links to thereby increase the level of integration while decreasing footprint. The module comprises a bench, a user-side interface to an array of user fibers and a device-side interface to an array of device fibers. The device fibers connect the module to a primary device and a redundant device. A monitoring signal generator is provided on the bench that provides monitoring signals. A monitoring signal detector is also on the bench that detects the monitoring signals. Finally, a beam switching system is provided that selectively connects the user fibers to the device fibers of the primary device or the device fibers of the redundant device. The preferred configuration is in-line with the user-side interface on an opposed side of the module relative to the device side interface. This is accomplished with translating switching system.

Description:
BACKGROUND OF THE INVENTION 
     Large optical cross-connect systems are used to switch optical signals between fiber links without conversion into the electrical domain. These systems are useful for dynamic capacity allocation and network recovery, for example. 
     The optical cross-connect switch systems are implemented on a variety of platforms. Presently, microelectromechanical systems (MEMS)-based switches using tilt mirror arrays are being pursued by a number of entities. The individual mirrors are used to couple light exiting from one user fiber link into another user fiber link. 
     One issue surrounding the deployment of these optical cross-connect switch systems concerns robustness. The switch fabrics are large. This makes it difficult to maintain the requirement that every path or connection through the fabric be operational at all times. For example, it is not uncommon for a few of the individual tilt mirrors in an array to become non-operational. This will have the effect of removing potential connections. 
     One solution to this problem relies on the use of redundant switch fabrics. If the connection is not possible between two user fibers with the primary switch fabric, the connection is made with the redundant switch fabric. 
     In order to switch between the primary and redundant systems, line card modules are used in conjunction with these switching systems. They have the capability of directing the optical signal from a user fiber either to the primary or redundant system. More generally, such line card protection modules are used in other applications where the ability to switch an optical signal between two systems is required, such as between primary and redundant rings in a SONET system. 
     In a common line card implementation, an optical signal from a user fiber is received at an input port of the protector module and switched between two output fiber links. Typically, a tap is provided to monitor the input signal. A two-by-two (2×2) switch is provided to route the input signal in addition to a monitoring signal from one of the switching systems to a monitoring diode. 
     Signals from the primary and redundant systems are handled by a second 2×2 switch. Specifically, the signal from either the primary or the redundant system is connected to another user fiber at an output port of the module. The other system is connected to a laser diode to thereby probe the operation of the primary or redundant system that is not currently in use with the monitoring signal. Typically, a monitoring port is used to detect the output from this laser. Similarly, another tap is provided to detect the signal that is transmitted to the output port. 
     SUMMARY OF THE INVENTION 
     In the past, line card protection modules have been offered with only relatively low levels of integration. Moreover, the interconnections, such as signal taps, were provided through fiber couplers. These factors made the modules large and expense to manufacture. 
     The present invention is directed to an integrated optical line card protection module. It is notable in that it uses free-space optical links to thereby increase the level of integration while decreasing footprint. 
     In general, according to one aspect, the invention features an optical line card protection module. The module comprises a bench, a user-side interface to an array of user fibers, i.e., the fibers that carry optical signals to and from another system, and a device-side interface to an array of device fibers, i.e., the fibers that carry optical signals to and from the primary and redundant devices, for example. A monitoring signal generator is provided on the bench that provides monitoring signals. A monitoring signal detector is also on the bench that detects the monitoring signals. Finally, a beam switching system is provided that selectively connects the user fibers to the device fibers of the primary device or the device fibers of the redundant device. 
     In one embodiment, the user-side interface and the device-side interface comprise separate fiber mounting blocks for respectively mounting the endfaces of the user fibers and the endfaces of the device fibers to the bench. Further, a user-side lens array is preferably secured to the bench between the fiber endfaces of the user fibers and the beam switching system. This facilitates coupling of the optical signals between the beam switching system and the user fibers. Device-side lens array is also preferably secured to the bench between the fiber endfaces of the device fibers and the beam switching system. 
     In the current embodiment, the monitoring signal generator comprises at least one semiconductor device that is mounted on the bench. It can be a semiconductor laser or a light emitting diode. A generator lens array directs the monitoring signals from the semiconductor device to the beam switching system. In the present implementation, the beam switching system enables output beams to the user-side interface to be transmitted past the beam switching system in a first state and translates the beam in a second state. This allows the user fibers for the primary and redundant device to be arranged parallel to each other, providing an in-line system. In one implementation, the beam switching system comprises opposed tilt mirror arrays. 
     In general, according to another aspect, the line card protection module comprises user input signal tap detector arrays and/or user output signal tap detector arrays. These are located in the beam path between the user-side interface and the beam switching system to detect optical signals that are being transmitted between the user fibers and the beam switching system. 
     The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings: 
     FIG. 1 is a schematic diagram illustrating a prior art optical line card system installed between the user fibers and the primary/redundant devices; 
     FIG. 2A is a schematic diagram of a prior art optical line card protection module showing the optical signal routing with the switching system in a first state; 
     FIG. 2B is a schematic diagram of the prior art optical line card protection module with the switching system in a second state; 
     FIG. 3 is a perspective view of an integrated optical line card protection module of the present invention; 
     FIG. 4 is a plan view of the free-space interconnect in the optical line card protection module with the switching system in a first state; 
     FIG. 5 illustrates the line card protection module free space interconnect with the switching system in a second state; 
     FIG. 6 is a detailed view of a switching system in the first state; 
     FIG. 7 is a detailed view of the switching system in a second state; 
     FIG. 8 is a perspective view of the optical line card protection module in a hermetic package prior to lid seal; 
     FIG. 9 is a perspective view of an optical line card protection module according to a second embodiment of the present invention; 
     FIG. 10 is a top view of the second embodiment optical line card protection module with the switching system in a first state; and 
     FIG. 11 is a top view of the second embodiment optical line card protection module with the switching system in a second state. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an application for an optical line card protection system  50 . Specifically, the protection system receives a number of user fibers  52 . These fibers include user input fibers  54  and user output fibers  56 . 
     The optical signals from the user fibers  54  are selectively connected to either a primary device  10  or a redundant device  12 . In one application, the primary and redundant devices are cross-connect switching fabrics. Separate arrays of device fibers  58 ,  60  connect the protection system  50  to the primary and redundant devices  10 ,  12 , respectively. Each of the device fiber arrays  58 ,  60  includes input fibers  62  and device output fibers  64 . 
     In the typical implementation, the protection system  50  is divided into separate modules  100 , which, depending on their level of integration, handle one or multiple ones of the user fibers  52 . 
     FIG. 2A illustrates the operation of an optical line card protection module  100  that handles one user input fiber  54  and one user output fiber  56 . In this illustration, the module&#39;s switching system is in a first state. Typically, the optical signal is received on the user input fiber  54  and is detected by a detector  110 . The remainder of the signal goes to a two-by-two switch  112 . In the illustrated state, the two-by-two switch  112  transfers the optical signal on the user input fiber to the primary switching fabric  10 . In parallel, a monitoring signal  114 , generated by a laser diode  116 , is connected by the two-by-two switch  112  to the redundant switching fabric  12 . This occurs via the device input fibers  62 . 
     The device output fibers  64  from the primary and redundant switching fabrics  10 ,  12  are received at a second two-by-two switch  120 . The optical signal from the primary switching fabric  10  is coupled to the user output fiber  56  while a detector  122  monitors the level of that signal. Simultaneously, the second two-by-two switch  120  couples the monitoring signal from the redundant switching fabric  12  to a detector  124 . 
     FIG. 2B shows the operation of the optical line card protection module  100  with the switching system in a second state. In operation, the first and second two-by-two switches  112 ,  120  are simultaneously converted to the second state so that the signal from the user fiber  54  is handled by the redundant switching fabric  12 , while the operation of the primary switching fabric  10  is monitored. 
     FIG. 3 illustrates an integrated optical line card protection module  100 , which has been constructed according to the principles of the present invention. The illustrated embodiment has the capability of handling a total of eight user fibers  52  including four user input fibers  54  and four user output fibers  56 . These fibers transmit the optical signals between the module and the user systems. 
     In more detail, starting the input side of the module  100 , the user fibers  52  are received at a user-side fiber interface  210 . This user-side fiber interface  210 , in the current implementation, comprises a user input fiber mounting block  212  and a user output fiber mounting block  214 . These blocks can be permanently attached within the hermetic package or alternatively implemented as plug-in devices, in other implementations. 
     The illustrated mounting blocks in the module  100  each currently comprise a lower portion  216  and an upper portion  218 . The fibers are held in opposed V-grooves in these upper and lower portions  218 ,  216 . 
     The mounting blocks hold endfaces of the user fibers in a secure relationship to the bench  200 . Specifically, in the case of the user input fibers  54 , beams exiting from these interfaces pass through a user input collimating lens array  220 . 
     Currently, the lens arrays of the module each comprise a lens substrate  222 , which is secured to the bench  200  via deformable mounting structures  224 . These deformable example, and then aligned through the deformation of the mounting structures  224  to micrometer to submicrometer accuracy. 
     The input beams are next transmitted through a user input tap array  226 , which samples the beams to determined their respective intensities. 
     In the present implementation, the tap arrays of the module  100  each comprise a detector substrate  228  on which discrete photodetectors  230  have been mounted. With reference to the user output tap array  270 , in the preferred embodiment, backside optical ports  272  are provided through the detector substrate  228  to reduce insertion loss and avoid the need to anti-reflection (AR) coat the detector substrate. A beam splitting substrate  232  reflects a portion of the beam to be sampled by the detectors  230 . The beam splitting substrate is separated for the detector substrate  228  by stand-offs  225  to create a gap. In the preferred embodiment, the beam splitting substrate  232  and more generally the tap array is angled with respect to the optical axis defined by the input beams. This angling displaces the reflected beam relative to the incoming beam through the optical port to enable detection by a respective one of the detectors that is adjacent to the optical port. 
     The input signals are next transmitted to four two-by-two input-side switches  240  of the module&#39;s beam switching system. Input-side switch  240  selectively routes the input signals to either the primary or redundant device via the device input fibers  62 , which are secured to the bench  200  via a device input fiber mounting block  242  of the device-side fiber interface  241 . A device input focusing lens array  244  is provided to couple the signals into the device input fibers  62 . These device input fibers transmit the optical signals to the devices. In the illustrated embodiment, the device-side fiber interface  241  is implemented as blocks located within the hermetic boundary of the module, although a plug system could also be used. 
     In the illustrated implementation, the primary device fibers  58  and the redundant device fibers  60  are interleaved with respect to each other in the device input fiber array  62 . 
     A monitoring signal generator  248  is also provided. In the present implementation, this generator comprises multiple monitoring signal laser diodes  250 , which are commonly mounted on a laser diode pedestal  252 . To monitor the intensity of the generated monitoring signals, a laser diode detector array  254  is provided to detect rear facet light from these laser diodes  250 . 
     In contrast, the front facet light from the monitoring signal laser diodes  250  is collimated by a generator collimating lens array  256 . These monitoring signals are coupled into the device input fibers  62  by the four two-by-two device input-side switches  240 . 
     Turning now to the output side of the module  100 , the device output fibers  64  from devices  10  and  12  are received by a device output fiber mounting block  260 , which is part of the device-side fiber interface  241  and holds the corresponding fiber endfaces in a secure relationship with the bench  200 . These device output fibers  64  transmit the optical signals from the devices. 
     The signals emitted from the device output fiber endfaces are transmitted through a device output collimating lens array  262 , to four two-by-two output-side switches  264  of the beam switching system. These four two-by-two switches  264  selectively direct the device signals to either a monitoring signal detector array  266  or the fiber endfaces of a user output fiber mounting block  214  for the user output fibers  56 . A user output focusing lens array  268  is provided to improve the coupling of these signals into the user output fibers. A user output tap array  270  is provided to detect the magnitude of these signals. 
     FIG. 4 illustrates the operation of the switches  240 ,  264 . For example, on the input side, when the switches are in the first state, input beam  415 , for example, passes directly through the input-side switch  240  to a primary device fiber  58  in the device input fiber array  62 . Monitoring signals  455 , for example, is reflected and thus directed to a fiber endface of the redundant device fibers  60  in device input fiber mounting block  242 . 
     On the output side, output-side switch  264  receives a primary device beam  58 ′ sourcing from a primary device fiber  58  and a redundant device beam  60 ′ sourcing from a redundant device fiber  60 . In the illustrated first state, the redundant device beam  60 ′ is reflected and thereby directed to the monitoring signal detector array  266 . In contrast, the primary device beam  58 ′ passes directly through the output-side switch  264 . 
     Referring to FIG. 5, when the input-side four two-by-two switches  240  are in the second state, the input beam  415  is translated, allowing the signals to be coupled into redundant device fiber  60  in the device input fiber array  62 . In contrast, the monitoring signal beam  455  is reflected such that it is coupled into a primary device fiber  58 . 
     Similarly, when the output-side four two-by-two switches  264  are in the second state, the primary device beam  58 ′ reflected and thereby directed to the monitoring signal detector array  266 . The redundant device beam  60 ′ passes through but is shifted by output-side switch  264 . 
     FIG. 6 shows the operation of the input-side switch  240  in more detail. Specifically, monitoring signal  455  is reflected off a stationary reflector  310 . Input beam  415  passes directly through switch  240  typically through optical ports that are formed in the switch. In contrast, when switch  240  is in its second state is illustrated by FIG. 7, movable or displaceable reflector  312  is moved into the beam path to redirect the monitoring beam  455  to traverse the path of the input beam  415  when the switch is in the first state to the primary device fiber  58 . The backside of the displaceable reflector  312  redirects the input beam  415  to be reflected off reflector  310 , which then directs the beam to the redundant device fiber  60 . 
     The operation of the four two-by-two device output switches  264  is similar to the device input switch  240 . In FIG. 4, the primary device signal  58 ′ from the primary device passes directly through the switch  264 . The redundant device signal  60 ′ from the redundant device is reflected to the detector  266 . In FIG. 5, the signals  58 ′ from the primary device are reflected by switch  264  to detector  266 . The signals  60 ′ from the redundant device are displaced and passed user output fibers. 
     Note that the operation of module  100  as describe above shows the input-side switch  240  and the output-side switch  264  of the beam switching system operating in a ganged mode. That is, each beam switch of the two arrays of four two-by-two switches converts between a first state and a second state at the same time. This is not, however, necessarily the typical mode of operation. For example, only the beam switches corresponding to the same channel though the primary and redundant devices can be switched together. For example, the beam switch in the input-side switch  240  associated with a first one of the user input fibers is switched with the beam switch in the output-side switch  264  associated with the first one of the user output fibers. More generally, the control circuitry associated with module  100  enables independent control of each of the beam switches in the arrays of switches  240  and  264 , in the preferred embodiment. 
     FIG. 8 illustrates the installation of the optical bench  200  into a hermetic package  350 . Further provided are boots  352  to protect the user and device fibers  52 ,  58 ,  60 . Electrical pins  354  are further provided to the outside of the hermetic package. These connect to bond pins  356 , which are electrically connected to the traces  360  on the bench  200  typically via a wire bonding operation to provide electrical control of the electronic devices on the bench  200 . 
     FIG. 9 illustrates a second embodiment of the optical line card protection module  100 . It provides a lower level of integration only handling two user fibers  52 . In this example, the beam switching system is implemented with two proposed tilt mirror arrays  410 ,  412 . 
     In more detail, user input fiber  54  is secured to the optical bench  200  via a user input fiber mounting block  416 . The input beam  415  is collimated by a user input collimating lens substrate  422 , which that is held on a deformable mounting structure  424 . An angled beam splitting substrate  432  reflects part of this input beam  415  to a detector  430 . The remainder of the beam is passed to the two opposed tilt mirror arrays  410 ,  412 . 
     Also provided is a monitoring signal generator. Specifically, monitoring signal laser diode  450  is installed on laser diode pedestal  452 . The monitoring signal beam  455  is also received by the beam switching system. Laser diode detector  454  detects rear facet light from the laser diode  450   
     The monitoring signal beam  455  and the input beam  415  are transmitted through optical port  482  into the device input fibers  62  of either the primary device  58  or the redundant device  60 , which are held in device-side fiber mounting block  442  via the focusing/collimating lens array  480 . 
     The output fibers  64  for the primary and redundant device  58 ,  60  are also received at mounting block  442 . Specifically, the device output beam from the primary device  58 ′ and for the redundant device  60 ′ are collimated by the lens array  480  and beam switched by the opposed tilt mirror array  410 ,  412 . Specifically, the beams pass through the port  484  through the backside of beam tilt mirror array  412  to be transmitted either 1) through the beam splitter  432  and into user output fiber  56 , which is held to the bench  200  by block  411 ; or 2) to detector  466 . Focusing lens  464 , held on a mounting structure, focuses the beam into the fiber endface of fiber  56 . Detector  470  samples the portion of the beam provided by beam splitter  432 . 
     FIGS. 10 and 11 illustrate the two switching states of the system  100  shown in FIG.  9 . 
     As illustrated in FIG. 10, beam  415 , for example, is coupled into primary device input fiber  52 , with monitoring beam  455  going to the redundant device input fiber  60 . On the device output side, beam  58 ′ from the primary device is transmitted to the user output fiber  56 , whereas beam  60 ′ from the redundant device is received by detector  466 . 
     In contrast, in the second state illustrated in FIG. 11, input beam  415  is coupled into the input fiber  60  for the redundant device, with the primary device receiving monitoring signal beam  455 . On the device output side, beam  60 ′ from the primary device is transmitted to the user fiber  56 , whereas beam  58 ′ from the redundant device is received by detector  466 . 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.