Optical time delay apparatus incorporating diffractive element sets

Abstract

An optical time delay apparatus comprises: a multi-wavelength optical source; a diffractive element set imparting a wavelength-dependent delay on signals routed from the source to a 1×N optical switch; and N diffractive element sets routing signals from the 1×N switch to an output port. The optical propagation delay between the source and the output port varies according to the operational state of the source and the 1×N switch. A photodetector may receive the time-delayed signal at the output port.

1. An apparatus, comprising:
 a first optical waveguide substantially confining in one transverse dimension an optical signal propagating in two dimensions therein, the first optical waveguide having a first set of diffractive elements configured and positioned for routing at least a portion of an optical signal propagating in the optical waveguide between an input optical port and a switch input optical port;  
 an optical source positioned for launching an optical signal into the optical waveguide through the input optical port;  
 a 1×N optical switch connecting the switch input optical port to any one of N switch output optical ports based on a selected operational state of the 1×N optical switch; and  
 a second optical waveguide substantially confining in one transverse dimension an optical signal received from any of the N switch output optical ports and propagating in two dimensions therein, the second optical waveguide having N additional sets of diffractive elements, each set of the N additional sets of diffractive elements corresponding to one of the N switch output optical ports and being configured and positioned for routing at least a portion of an optical signal received from the corresponding one of the N switch output optical ports to an output optical port,  
 wherein:  
 the first diffractive element set is adapted for imparting a wavelength-dependent optical delay onto the routed portion of the optical signal;  
 the N additional diffractive element sets and the output optical port are positioned relative to the switch output optical ports so that each corresponding optical pathlength between each of the switch output optical ports and the output optical port varies among the switch output optical ports;  
 an optical signal at only a selected one of multiple optical source wavelengths reaches the output optical port based on a selected operational state of the optical source; and  
 optical propagation time delay between the input optical port and the corresponding  output optical port varies according to the selected operational state of the 1×N optical switch and according to the selected operational state of the optical source.  
 
     
     
       2. The apparatus of  claim 1 , further comprising a photodetector for receiving optical signals at the output optical port. 
     
     
       3. The apparatus of  claim 1 , wherein the first optical waveguide, the 1×N optical switch, and the second optical waveguide are integrated onto a common waveguide substrate. 
     
     
       4. The apparatus of  claim 1 , wherein adjacent ones of the N additional diffractive element sets occupy spatially overlapping areas of the second optical waveguide. 
     
     
       5. The apparatus of  claim 1 , wherein adjacent ones of the N additional diffractive element sets occupy spatially distinct areas of the second optical waveguide. 
     
     
       6. The apparatus of  claim 1 , wherein:
 the first diffractive element set comprises subsets of diffractive elements; and  
 each diffractive element subset routes at least a portion of an optical signal at a corresponding one of the multiple source wavelengths between the input optical port and the switch input optical port.  
 
     
     
       7. The apparatus of  claim 6 , wherein the diffractive element subsets are arranged so as to impart the wavelength-dependent optical delay onto the corresponding portions of the optical signal routed thereby. 
     
     
       8. The apparatus of  claim 6 , wherein each diffractive element subset routes at least a portion of an optical signal at a corresponding one of the multiple source wavelengths between the input optical port and the switch input optical port through a corresponding optical fiber delay line or through a corresponding optical waveguide delay line, thereby imparting the wavelength-dependent optical delay onto the corresponding portions of the optical signal. 
     
     
       9. The apparatus of  claim 6 , wherein adjacent ones of the multiple diffractive element subsets occupy spatially overlapping areas of the first optical waveguide. 
     
     
       10. The apparatus of  claim 6 , wherein adjacent ones of the multiple diffractive element subsets occupy spatially distinct areas of the first optical waveguide. 
     
     
       11. The apparatus of  claim 1 , wherein the first diffractive element set has a monotonically varying element spacing so as to impart the wavelength-dependent optical delay onto the portion of the optical signal routed thereby. 
     
     
       12. The apparatus of  claim 1 , wherein the optical source comprises a multiplexed laser array, a filtered laser array, a tunable laser, a filtered broadband light source, an externally-modulated laser, or an external-cavity stabilized laser. 
     
     
       13. The apparatus of  claim 1 , wherein:
 the optical source comprises an array of lasers, each positioned for launching a corresponding optical signal into a corresponding input optical port at a corresponding source wavelength; and  
 optical propagation time delay between each corresponding input optical port and the corresponding  output optical port varies according to the selected operational state of the 1×N optical switch and according to the corresponding source wavelength.  
 
     
     
       14. An apparatus, comprising:
 a 1×N optical switch connecting a switch input optical port to any one of N switch output optical ports based on a selected operational state of the 1×N optical switch; and  
 an optical waveguide substantially confining in one transverse dimension an optical signal received from any of the N switch output optical ports and propagating in two dimensions therein, the optical waveguide having N sets of diffractive elements, each set of diffractive elements corresponding to one of the N switch output optical ports and being configured and positioned for routing at least a portion of an optical signal received from the corresponding one of the N switch output optical ports to an output optical port,  
 wherein the N diffractive element sets and the output optical port are positioned relative to the switch output optical ports so that each corresponding optical path-length between each of the switch output optical ports and the output optical port varies among the switch output optical ports, thereby resulting in an optical propagation time delay between the switch input optical port and the output optical port that varies according to the selected operational state of the 1×N optical switch.  
 
     
     
       15. The apparatus of  claim 14 , wherein adjacent ones of the N additional diffractive element sets occupy spatially overlapping areas of the second optical waveguide. 
     
     
       16. The apparatus of  claim 14 , wherein adjacent ones of the N additional diffractive element sets occupy spatially distinct areas of the second optical waveguide. 
     
     
       17. An apparatus, comprising:
 an optical waveguide substantially confining in one transverse dimension an optical signal propagating in two dimensions therein, the optical waveguide having a set of diffractive elements configured and positioned for routing at least a portion of an optical signal propagating in the optical waveguide between an input optical port and an output optical port; and  
 an optical source positioned for launching an optical signal into the optical waveguide through the input optical port,  
 wherein:  
 the diffractive element set is adapted for imparting a wavelength-dependent optical delay onto the routed portion of the optical signal; and  
 an optical signal at only a selected one of multiple optical source wavelengths reaches the output optical port based on a selected operational state of the optical source, thereby resulting in an optical propagation time delay of an optical signal launched from the optical source between the input optical port and the output optical port that varies according to the selected operational state of the optical source.  
 
     
     
       18. The apparatus of  claim 17 , wherein:
 the first diffractive element set comprises subsets of diffractive elements; and  
 each diffractive element subset routes at least a portion of an optical signal at a corresponding one of the multiple source wavelengths between the input optical port and the  a switch input optical port.  
 
     
     
       19. The apparatus of  claim 18 , wherein the diffractive element subsets are arranged so as to impart the wavelength-dependent optical delay onto the corresponding portions of the optical signal routed thereby. 
     
     
       20. The apparatus of  claim 18 , wherein each diffractive element subset routes at least a portion of an optical signal at a corresponding one of the multiple source wavelengths between the input optical port and the switch input optical port through a corresponding optical fiber delay line or through a corresponding optical waveguide delay line, thereby imparting the wavelength-dependent optical delay onto the corresponding portions of the optical signal. 
     
     
       21. The apparatus of  claim 18 , wherein adjacent ones of the multiple diffractive element subsets occupy spatially overlapping areas of the first optical waveguide. 
     
     
       22. The apparatus of  claim 18 , wherein adjacent ones of the multiple diffractive element subsets occupy spatially distinct areas of the first optical waveguide. 
     
     
       23. The apparatus of  claim 17 , wherein the first diffractive element set has a monotonically varying element spacing so as to impart the wavelength-dependent optical delay onto the portion of the optical signal routed thereby. 
     
     
       24. The apparatus of  claim 17 , wherein the optical source comprises a multiplexed laser array, a filtered laser array, a tunable laser, a filtered broadband light source, an externally-modulated laser, or an external-cavity stabilized laser. 
     
     
       25. The apparatus of  claim 17 , wherein:
 the optical source comprises an array of lasers, each positioned for launching a corresponding optical signal into a corresponding input optical port at a corresponding source wavelength; and  
 optical propagation time delay between each corresponding input optical port and the corresponding  output optical port varies according to the  a selected operational state of the  a 1×N optical switch positioned between the input optical port and the output optical port and according to the corresponding source wavelength.  
 
     
     
       26. An apparatus, comprising:
   a  1 ×N optical switch having a switch input optical port configured to be connected to any one of N switch output optical ports of the  1 ×N optical switch based on a selected operational state of the  1 ×N optical switch; and        an optical waveguide positioned to receive an optical signal from a corresponding one of the N switch output optical ports, the optical waveguide having N sets of diffractive elements, each set of diffractive elements corresponding to one of the N switch output optical ports and being configured and positioned to route at least a portion of the optical signal received from the corresponding one of the N switch output optical ports to an output optical port,        wherein the N sets of diffractive elements and the output optical port are positioned relative to the N switch output optical ports so that each corresponding optical pathlength between each of the switch output optical ports and the output optical port varies among the N switch output optical ports, thereby resulting in an optical propagation time delay between the switch input optical port and the output optical port that varies according to the selected operational state of the  1 ×N optical switch.      
     
     
       27. The apparatus of  claim 26 , further comprising:
   another optical waveguide having another set of diffractive elements,        wherein the another set of diffractive elements is configured and positioned to route at least a portion of an input optical signal, received at an input optical port and that propagates in the optical waveguide, to the switch input optical port, and        wherein the another set of diffractive elements is adapted to impart a wavelength - dependent optical time delay onto the routed portion of the input optical signal.      
     
     
       28. The apparatus of  claim 27 , further comprising an optical source positioned to launch the input optical signal into the another optical waveguide through an input optical port, the optical source having an operational state that is adapted to provide the input optical signal with a wavelength that determines at least in part the wavelength- dependent optical delay.    
     
     
       29. An apparatus, comprising:
   an optical waveguide configured to receive an optical signal and having a set of diffractive elements, the set of diffractive elements being configured and positioned to route at least a portion the optical signal between an input optical port and an output optical port,        wherein the diffractive element set is arranged to impart a wavelength - dependent optical time delay onto the routed portion of the optical signal, and        wherein an amount of the wavelength - dependent time delay is based at least in part on a wavelength of the received optical signal.      
     
     
       30. The apparatus of  claim 29 , further comprising:
   a  1 ×N optical switch having a switch input optical port configured to be connected to any one of N switch output optical ports of the  1 ×N optical switch based on a selected operational state of the  1 ×N optical switch, the switch input optical port being configured to receive the routed portion of the optical signal having the wavelength - dependent optical time delay; and        N sets of diffractive elements, each set of the N sets of diffractive elements corresponding to one of the N switch output optical ports and being configured and positioned to route the portion of the optical signal having the wavelength - dependent optical time delay, received from the corresponding one of the N switch output optical ports, to the output optical port,        wherein the N sets of diffractive elements and the output optical port are positioned relative to the N switch output optical ports so that each corresponding optical pathlength between each of the N switch output optical ports and the output optical port varies among the N switch output optical ports, thereby resulting in an optical propagation time delay between the switch input optical port and the output optical port that varies according to the selected operational state of the  1 ×N optical switch.      
     
     
       31. The apparatus of  claim 29 , further comprising an optical source positioned to launch the optical signal into the optical waveguide through the input optical port, the optical source having selectable operational state that determines the wavelength of the optical signal launched into the optical waveguide.  
     
     
       32. A method, comprising:
   receiving an input optical signal at an optical waveguide;        directing, by the optical waveguide, the received input optical signal to a first set of diffractive elements;        imparting into a portion of the received input optical signal, by the first set of diffractive elements, a wavelength - dependent time delay;        receiving the portion of the input signal, having the wavelength - dependent time delay, at a switch having an operational state;        selecting an operational state of the switch to switch the received portion of the input signal, having the wavelength - dependent time delay, to a particular set among N sets of diffractive elements; and        imparting, by the particular set of diffractive elements, a propagation time delay into the switched portion of the input signal.      
     
     
       33. The method of  claim 32  wherein said receiving the portion of the input signal at the switch having the operational states includes:
   receiving the portion of the input signal at a  1 ×N switch having N switch output ports, each one of the N switch output ports respectively corresponding to one of the N sets of diffractive elements.      
     
     
       34. The method of  claim 32 , further comprising selecting an operational state of an optical source, the selected operational state corresponding to a wavelength of the input optical signal that is received at the optical waveguide.  
     
     
       35. A radio frequency ( RF )  communication system, comprising:      an optical source having an operational state that is controllable by a first RF signal, the operational state of the optical source corresponding to a wavelength of an input optical signal provided by the optical source;        an optical apparatus configured to receive the input optical signal from the optical source, the optical apparatus including:      a  1 ×N optical device having a device input optical port configured to be connected to at least one of N device output optical ports of the  1 ×N optical device; and        N sets of diffractive elements, each set of diffractive elements corresponding to one of the N device output optical ports and being configured and positioned to route at least a portion of an optical signal received from the corresponding one of the N device output optical ports to an output optical port,        wherein the N sets of diffractive elements and the output optical port are positioned relative to the N device output optical ports so that each corresponding optical pathlength between each of the N device output optical ports and the output optical port varies among the N device output optical ports, thereby resulting in an optical propagation time delay between the device input optical port and the output optical port; and          a photodetector coupled to the output optical port and configured to convert the portion of the optical signal, having the time delay, into a second RF signal that has the time delay.      
     
     
       36. The RF communication system of  claim 35  wherein the system includes a radar system.  
     
     
       37. The RF communication system of  claim 35  wherein said  1 ×N optical device is a  1 ×N optical switch.  
     
     
       38. The RF communication system of  claim 35  wherein said  1 ×N optical device is a  1 ×N power splitter.  
     
     
       39. An optical code division multiple access ( OCDMA )  system, comprising:      an optical source configured to produce an input optical signal;        an optical apparatus configured to receive the input optical signal from the optical source, the optical apparatus including:      a first set of diffractive elements configured to generate a sequence of pulses from the input optical signal, and configured to impart a wavelength - dependent time delay into each of the pulses;        a  1 ×N optical device having a device input optical port configured to be connected to at least one of N device output optical ports of the  1 ×N optical device, the device input optical port being further configured to receive each of the pulses having the wavelength - dependent time delay; and        N sets of diffractive elements, each set of diffractive elements corresponding to one of the N device output optical ports and being configured and positioned to route the pulses, which are output from corresponding ones of the N device output optical ports, to an output optical port,        wherein the N sets of diffractive elements and the output optical port are positioned relative to the N device output optical ports so that each corresponding optical pathlength between each of the device output optical ports and the output optical port varies among the N device output optical ports, thereby resulting in an optical propagation time delay between the device input optical port and the output optical port for each of the pulses; and          a combiner coupled to the output optical port and configured to combine the pulses, each having the propagation time delay, into an output code sequence.      
     
     
       40. The OCDMA system of  claim 39  wherein the combiner includes a multiplexer.  
     
     
       41. The OCDMA system of  claim 39  wherein the first set of diffractive elements are configured to generate the sequence of pulses by spectrally slicing an input pulse of the input optical signal.  
     
     
       42. The apparatus of  claim 29 , further comprising:
   a  1 ×N optical switch having a switch input optical port configured to be connected to any one of N switch output optical ports of the  1 ×N optical switch based on a selected operational state of the  1 ×N optical switch, the switch input optical port being configured to receive the routed portion of the optical signal having the wavelength - dependent optical time delay; and        N sets of diffractive elements, each set of the N sets of diffractive elements corresponding to one of the N switch output optical ports and being configured and positioned to route the portion of the optical signal having the wavelength - dependent optical time delay, received from the corresponding one of the N switch output optical ports, to the output optical port.      
     
     
       43. A method, comprising:
   connecting a switch input optical port, of a  1 ×N optical switch, to any one of N switch output optical ports of the  1 ×N optical switch based on a selected operational state of the  1 ×N optical switch;        receiving, by an optical waveguide, an optical signal from a corresponding one of the N switch output optical ports, the optical waveguide having N sets of diffractive elements, each set of diffractive elements corresponding to one of the N switch output optical ports; and        routing, by said each set of diffractive elements, at least a portion of the optical signal received from the corresponding one of the N switch output optical ports to an output optical port,        wherein the N sets of diffractive elements and the output optical port are positioned relative to the N switch output optical ports so that each corresponding optical pathlength between each of the switch output optical ports and the output optical port varies among the N switch output optical ports, thereby resulting in an optical propagation time delay between the switch input optical port and the output optical port that varies according to the selected operational state of the  1 ×N optical switch.      
     
     
       44. The method of  claim 43 , further comprising:
   routing, by another set of diffractive elements in another optical waveguide, at least a portion of an input optical signal, received at an input optical port and that propagates in the optical waveguide, to the switch input optical port, and        imparting, by said another set of diffractive elements, a wavelength - dependent optical time delay onto the routed portion of the input optical signal.      
     
     
       45. The method of  claim 44 , further comprising launching, by an optical source, the input optical signal into the another optical waveguide through an input optical port, the optical source having an operational state that is adapted to provide the input optical signal with a wavelength that determines at least in part the wavelength- dependent optical delay.    
     
     
       46. A method, comprising:
   receiving, by an optical waveguide having a set of diffractive elements, an optical signal;        routing, by the set of diffractive elements, at least a portion the optical signal between an input optical port and an output optical port; and        imparting, by the set of diffractive elements, a wavelength - dependent optical time delay onto the routed portion of the optical signal,        wherein an amount of the wavelength - dependent time delay is based at least in part on a wavelength of the received optical signal.      
     
     
       47. The method of  claim 46 , further comprising:
   connecting, a switch input optical port of a  1 ×N optical switch, to any one of N switch output optical ports of the  1 ×N optical switch based on a selected operational state of the  1 ×N optical switch;        receiving, at the switch input optical port, the routed portion of the optical signal having the wavelength - dependent optical time delay; and        routing, by N sets of diffractive elements, the portion of the optical signal having the wavelength - dependent optical time delay and received from the corresponding one of the N switch output optical ports, to the output optical port,        wherein each set of the N sets of diffractive elements corresponds to one of the N switch output optical ports.      
     
     
       48. The method of  claim 47  wherein the N sets of diffractive elements and the output optical port are positioned relative to the N switch output optical ports so that each corresponding optical pathlength between each of the N switch output optical ports and the output optical port varies among the N switch output optical ports, thereby resulting in an optical propagation time delay between the switch input optical port and the output optical port that varies according to the selected operational state of the  1 ×N optical switch.  
     
     
       49. An apparatus, comprising:
     1 ×N optical switch means for connecting a switch input optical port of the  1 ×N optical switch means to any one of N switch output optical ports of the  1 ×N optical switch means based on a selected operational state of the  1 ×N optical switch means;        optical waveguide means for receiving an optical signal from a corresponding one of the N switch output optical ports; and        N sets of diffractive element means for routing at least a portion of the optical signal received from the corresponding one of the N switch output optical ports to an output optical port, each set of diffractive element means corresponding to one of the N switch output optical ports,        wherein the N sets of diffractive element means and the output optical port are positioned relative to the N switch output optical ports so that each corresponding optical pathlength between each of the switch output optical ports and the output optical port varies among the N switch output optical ports, thereby resulting in an optical propagation time delay between the switch input optical port and the output optical port that varies according to the selected operational state of the  1 ×N optical switch means.      
     
     
       50. The apparatus of  claim 49 , further comprising another set of diffractive element means, in another optical waveguide means, for:
   routing at least a portion of an input optical signal, received at an input optical port and that propagates in the optical waveguide means, to the switch input optical port, and        imparting a wavelength - dependent optical time delay onto the routed portion of the input optical signal.      
     
     
       51. The apparatus of  claim 50 , further comprising optical source means for launching the input optical signal into the another optical waveguide means through an input optical port, the optical source means having an operational state that is adapted to provide the input optical signal with a wavelength that determines at least in part the wavelength- dependent optical delay.    
     
     
       52. An apparatus, comprising:
   optical waveguide means for receiving an optical signal; and        a set of diffractive element means for routing at least a portion of the optical signal between an input optical port and an output optical port, and for imparting a wavelength - dependent optical time delay onto the routed portion of the optical signal,        wherein an amount of the wavelength - dependent time delay is based at least in part on a wavelength of the received optical signal.      
     
     
       53. The apparatus of  claim 52 , further comprising:
     1 ×N optical switch means for connecting a switch input optical port of the  1 ×N optical switch means to any one of N switch output optical ports of the  1 ×N optical switch based on a selected operational state of the  1 ×N optical switch means, wherein the switch input optical port is configured to receive the routed portion of the optical signal having the wavelength - dependent optical time delay; and        N sets of diffractive element means for routing the portion of the optical signal, having the wavelength - dependent optical time delay and received from the corresponding one of the N switch output optical ports, to the output optical port,        wherein each set of the N sets of diffractive element means corresponds to one of the N switch output optical ports.      
     
     
       54. The apparatus of  claim 53  wherein the N sets of diffractive elements and the output optical port are positioned relative to the N switch output optical ports so that each corresponding optical pathlength between each of the N switch output optical ports and the output optical port varies among the N switch output optical ports, thereby resulting in an optical propagation time delay between the switch input optical port and the output optical port that varies according to the selected operational state of the  1 ×N optical switch means.  
     
     
       55. A method, comprising:
   forming an optical waveguide configured to receive an optical signal; and        forming a set of diffractive elements, the set of diffractive elements being configured and positioned to route at least a portion the optical signal between an input optical port and an output optical port,        wherein the diffractive element set is arranged to impart a wavelength - dependent optical time delay onto the routed portion of the optical signal, and        wherein an amount of the wavelength - dependent time delay is based at least in part on a wavelength of the received optical signal.      
     
     
       56. The method of  claim 55 , further comprising:
   forming a  1 ×N optical switch to connect, a switch input optical port of the  1 ×N optical switch, to any one of N switch output optical ports of the  1 ×N optical switch based on a selected operational state of the  1 ×N optical switch, wherein switch input optical port is configured to receive the routed portion of the optical signal having the wavelength - dependent optical time delay; and        forming N sets of diffractive elements to route the portion of the optical signal, having the wavelength - dependent optical time delay and received from the corresponding one of the N switch output optical ports, to the output optical port,        wherein each set of the N sets of diffractive elements corresponds to one of the N switch output optical ports.      
     
     
       57. The method of  claim 56  wherein the N sets of diffractive elements and the output optical port are positioned relative to the N switch output optical ports so that each corresponding optical pathlength between each of the N switch output optical ports and the output optical port varies among the N switch output optical ports, thereby resulting in an optical propagation time delay between the switch input optical port and the output optical port that varies according to the selected operational state of the  1 ×N optical switch.