Abstract:
Optical apparatus that uses optically-actuated optical switches in conjunction with an optical codeword addressing scheme to provide for time division multiplexing and demultiplexing of high data rate optical data. Optical codewords traveling simultaneously with the data on a separate wavelength, in conjunction with the optical switches, enable all-optical multiplexing and demultiplexing. The present invention can also switch packets of data while keeping the data entirely in the optical domain, and no optical to electrical conversions are necessary.

Description:
BACKGROUND 
   The present invention relates generally to optical communication devices. 
   An article relating to the technology implemented by the present invention was written by K. Uchiyama and T. Morioka, entitled “All optical time-division demultiplexing experiment with simultaneous output of all constituent channels from 100 Gb/s OTDM signal”, published in Electronics Letters, vol. 37, pp. 642-643 (2003). 
   SUMMARY OF THE INVENTION 
   The present invention provides for optical time division demultiplexing and packet switching apparatus. The present invention uses optically-actuated optical switches in conjunction with an optical codeword addressing scheme to implement the all optical time division demultiplexing and switching apparatus. 
   More particularly, the present invention uses optically actuated optical switches to provide for time division multiplexing and demultiplexing of high data rate optical data. Optical codewords traveling simultaneously with the data on a separate wavelength, in conjunction with the switches, enable the all-optical multiplexing and demultiplexing system. The present invention can also switch packets of data while keeping the data entirely in the optical domain. No optical to electrical conversions are necessary. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features and advantages of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
       FIG. 1  illustrates exemplary multiplexing and packet switching apparatus in accordance with the principles of the present invention; 
       FIGS. 2   a  and  2   b  illustrate operation of an optically actuated optical switch employed in the multiplexing and packet switching apparatus shown in  FIG. 1 ; 
       FIG. 3  illustrates signal outputs of optically actuated optical switches; 
       FIG. 4  illustrates how codeword programmability is implemented using the optically actuated optical switches; 
       FIG. 5  illustrates an all-optical demultiplexing device employed in the multiplexing and packet switching apparatus shown in  FIG. 1 ; 
       FIG. 6  illustrates bit level all optical demultiplexing; 
       FIG. 7   a  illustrates that codeword A switches data out of express path and into drop paths; 
       FIG. 7   b  illustrates that codeword B switches data back into express path; 
       FIG. 8   a  illustrates a toggle flip flop permitting variability in the length of the packet being routed. (a) Data routed out port  1 ; 
       FIG. 8   b  illustrates that driver pulse changes state of toggle flip-flop, turns pump on, data routed out port  2 ; 
       FIG. 8   c  illustrates that driver pulse off toggle flip-flop maintains state with pump on, data continues to be routed out port  2 ; and 
       FIG. 8   d  illustrates that driver pulse on, changes state of toggle flip-flop, turns pump laser off, data routed out port  1 . 
   

   DETAILED DESCRIPTION 
   Referring to the drawing figures,  FIG. 1  illustrates exemplary multiplexing and packet switching apparatus  10  or system  10  in accordance with the principles of the present invention. More specifically,  FIG. 1  is a schematic of all optical demultiplexing and packet switching system  10  using optical codewords and optically actuated optical switches  13 ,  14 ,  15 . 
   The system  10  comprises an optical input demultiplexer  11  that receives codewords (λ code ) and input data. The codewords are routed to a first optically actuated optical switch  13  that comprises a fast all-optical gate  13 . The input data (λ data in ) is routed to a first optically actuated optical switch  14  that comprises a demultiplexing device  14 . Data is output from the demultiplexing device  14  to a third optically actuated optical switch that comprises a multiplexing device  15 . 
   A CW laser  12  outputs a CW laser signal (λ driver ) that is shuttered by the fast all-optical gate  13 . The opening and closing of the gate  13  is controlled by a codeword, which enters on a red wavelength, for example. A correct codeword opens up the gate  13  and allows the driver signal through in the form of a pulse. The pulse duration is equal to the time the gate  13  is open. The driver pulse is split by an optical splitter  16  and is coupled to the demultiplexing and multiplexing devices  14 ,  15 . 
   Data enters the system  10  on a blue wavelength simultaneously with the codeword. As long as the driver gate  13  is closed, the driver pulse does not pump the demultiplexing and multiplexing devices  14 ,  15 , shown at the lower part of  FIG. 1 , and data passes through the demultiplexing and multiplexing devices  14 ,  15  unaffected as express traffic. When the driver gate  13  is opened by the correct codeword, the driver pulse pumps both devices  14 ,  15 , causing them to change states. Data is dropped off the demultiplexing device  14 , in a set of parallel lines and new data is multiplexed by the multiplexing device  15  onto an outbound line into the now empty timeslot. The newly multiplexed data and the codeword are multiplexed and output by an optical output multiplexer  17 . 
   Presented below are details regarding the operation of the driver optical gate  13  and the multiplexing and demultiplexing devices  14 ,  15 .  FIGS. 2   a ,  2   b  and  3  show details of the driver optical gate  13 .  FIGS. 2   a  and  2   b  illustrates details and operation of the optically actuated optical switch  13 .  FIGS. 2   a  and  2   b  each show a single element switch  13   a  that makes up the gate  13 . The single element switch  13   a  has a pump port  21  and a signal port  22  having a signal input and two outputs (A, B). The presence of the pump routes the signal to output A as is shown in  FIG. 2   a , and without the pump, the signal is routed to output B as is shown in  FIG. 2   b.    
     FIG. 3  shows a serial chain of switches  13   a  that comprise the optical gate  13 , and how the switches  13   a  are connected to enable gating operation.  FIG. 3  illustrates that the signal outputs of the optically actuated optical switches  13   a  are wired as a serial switch chain so that the driver signal passes only when the correct pump codeword is incident on the serial switch chain, in this case, a 6 bit word 001011. 
   The optical switches  13   a  route the driver signal to one of the two output ports, where the port chosen is determined by the presence or absence of the optical pump. Switches  13   a  can be coupled together serially, as shown in  FIG. 3 , in a way that a signal entering the first switch  13   a  only emerges from the final switch  13   a  when a specific pump sequence is incident on the switches  13   a . This sequence is the codeword for the all-optical gate  13 . Other sequences will result in a blocked output at one of the switches  13   a  in the chain, and will close the gate  13 . 
   Introduction of 2×1 optical switches  22  between the output of each optically actuated optical switch  13  and a subsequent optically actuated optical switch  13  in the chain enable programmability of the codeword, by allowing for flexibility in the coupling (wiring) configuration. This is shown in  FIG. 4 . The output of the gate  13  (when open) is an optical pulse with a pulse duration equal to one bit of the codeword data rate. The optical delay between each pump port for the switches  13   a  is equal to the code period (1/code-bit-rate) for synchronization purposes, to guarantee that all switches  13   a  open at the same time. 
     FIG. 5  illustrates an exemplary all-optical demultiplexing device  14  which comprises a chain of optically actuated optical switches  14   a . A driver pulse (λ driver ) from the all-optical gate  13  ( FIG. 3 ), pumps the data switches  14   a . For the duration of the driver pulse, data incident on the demultiplexing switches  14   a  are dropped into parallel paths (shown at the bottom of  FIG. 5 ). 
   The driver pulse generated at the output of the all-optical gate  13  shown in  FIG. 3  pumps the optically actuated optical switches  14   a  of the demultiplexer  14 . When the codeword bit rate is equal to the data rate, a codeword opens the switches  14   a  for a single bit of data. As is shown in  FIG. 5 , delay lines  23  between the signal paths of the switches  14   a  synchronize the opening of the switches  14   a  with the arrival of a bit such that each port drops a single bit from the data into one of the parallel lines, effectively demultiplexing the serial line. Details of this are shown in  FIG. 6 . 
     FIG. 6  illustrates bit level all optical demultiplexing. A serial stream of data comes in and is demultiplexed into N parallel streams, each at a data rate N times smaller than the serial input data. 
   The system illustrated in  FIG. 6  requires an optically actuated optical switch  14   a  that can switch at a speed equal to the bit rate of the data. A variation of this that switches packet length streams, but still demultiplexes them at the bit-level, can be made using switches  14   a  that switch at the packet timescale. This is advantageous because realizing an optically actuated optical switch  14   a  with a switch time on the order of a bit, for the data rates of interest in the all-optical domain (˜100 Gb/s) is challenging. Packet length switch speeds (˜1 Gb/s), on the other hand, are more realistic, and previous work has established this capability. This is illustrated in  FIGS. 7   a  and  7   b , and is based on integrating a latching mechanism into the design of the demultiplexing device  14  (and the multiplexing device  15 ). 
     FIG. 7   a  illustrates that codeword A switches data out of the express path and into drop paths out of the demultiplexing device  14 . A first toggle flip-flop  24  serves to latch a data routing switch  14   b  that routes the data between express and drop ports, and the data routing switch  14   b  stays open until the correct codeword closes it (see  FIG. 7   b ). The driver pulse is also connected to a second toggle flip flop  24   a , which is set to the off state by the codeword; the output of the second toggle flip flop  24   a  is diverted in this state to a beam dump. 
     FIG. 7   b  illustrates that codeword B switches data back into express path. Simultaneously, the codeword turns the second toggle flip flop  24   a  on, which routes a pump pulse to the data switches  14   a , effecting a drop of the data held in the delay loops  23 . As long as the following data gets switched into the express path, the duration of the output of the second toggle flip flop  24   a  can be much longer that the bit length of the data that is dropped (only the data in the delay loops  23  gets dropped). The beam dump shown in  FIG. 7   b  is not used, since light is not routed there for this configuration. 
   In the configuration shown in  FIG. 7   b , the arrow from the left side switch  25  crosses over the signal line to illustrate that in this configuration, light from the left-side switch  14   b  is routed out of the right output port (on left-side switch  14   b ), and not to the switches  14   a.    
     FIG. 7   a  shows that the “start” codeword initiates a process whereby data is routed towards the set of delay loops  23  and drop switches  14   a . The delay loops  23  are similar to those shown in  FIG. 5  and introduce a 1 bit delay between successive switches  14   a . The delay loops  23  are filled with the bits to be dropped, and when the “end” codeword appears, the optically actuated optical switches  14   a  to which they are connected change state, and the bits are dropped. The minimum length of the packet that can be dropped and demultiplexed is limited by the switch speed of the optically actuated optical switches  14   a . The maximum packet length is set by the total number of switches  14   a  (or alternatively, by the number of delay loops  23 ). A range of switchable packet lengths is therefore enabled, where the low end of the range is set by the speed of the switches  14   a  and the high end is set by the number of switches  14   a.    
   When data is dropped, an empty time-slot is available for new data to be added in. That data can be added in using a coupler on the mainline, or with a multiplexing device similar to the demultiplexing device  14 , where the driver pulse opens a bank of switches, as shown in  FIG. 1 . The latter scenario requires that the optically actuated switches  14   a  work in a 2×1 mode as well as the 1×2 mode required for demultiplexing. 
   For more generalized packet routing purposes, it may be desirable to switch just one stream of packets out of the main line, and it may not be necessary to demultiplex them. In this case, only the single data routing switch  14   b  is required. While the demultiplexing capability is not achieved, the technique allows for variability in the switched packet length. A more detailed schematic of this is shown in  FIG. 8 . 
   The correct codeword toggles the pump on, and leaves it on until the codeword appears again, at which point the pump is toggled off. This enables packet lengths as short as the period of the code wavelength bit rate, but longer ones also, with a granularity of one period. The first toggle flip flop  24  can be an all-optical device or can use optical to electrical conversion and standard electronic logic, for example. 
   More particularly,  FIGS. 8   a - 8   d  illustrate a toggle flip flop  24  that permits variability in the length of the packet that is routed.  FIG. 8   a  illustrates that data is routed out of port B.  FIG. 8   b  illustrates that the driver pulse changes state of first toggle flip-flop  24 , turns the pump on, and data is routed out of port A.  FIG. 8   c  illustrates that the driver pulse is off, the first toggle flip-flop  24  maintains state with the pump on, and data continues to be routed out of port A.  FIG. 8   d  illustrates that the driver pulse is on, changes state of the first toggle flip-flop  24 , turns the pump laser off, and data is routed out of port B. 
   As should be clear from the above discussion, the all optical multiplexing and packet switching solution provided by the present invention permits high speed demultiplexing with moderate speed switches. The present invention may be used in data transmission and communication, optical networking, photonics and optical computing systems, and the like. 
   Thus, optical multiplexing and packet switching apparatus have been disclosed. It is to be understood that the described embodiments are merely illustrative of some of the many specific embodiments which represent applications of the principles of the present invention, such as open stub reflection circuits and logic pulse generation circuits, for example. Clearly, numerous and other arrangements can be readily devised by those skilled in the art without departing from the scope of the invention.