Reconfigurable optical add-drop multiplexer incorporating sets of diffractive elements

Abstract

A reconfigurable add-drop multiplexer (R-OADM) comprises an array of channel waveguides coupling two groups of diffractive element sets on a slab waveguide. The channel waveguides include switchable reflectors or are coupled to other channel waveguides by optical switches. Switching a reflector to reflect or setting a switch to couple two waveguides results in a corresponding wavelength channel being added or dropped. Switching the reflector to transmit or setting the switch to uncouple the two waveguides allows the corresponding wavelength channel to pass through the R-OADM without being added or dropped.

1. An optical apparatus, comprising:
 a first group of multiple diffractive element sets formed in or on a slab waveguide; 
 a second group of multiple diffractive element sets formed in or on a slab waveguide; and 
 a group of multiple channel waveguides, each channel waveguide of the group being arranged for routing an optical signal between a corresponding diffractive element set of the first group and a corresponding diffractive element set of the second group, each channel waveguide of the group including corresponding means for back-reflecting an optical signal propagating along the waveguide, each back-reflecting means being switchable between a transmitting operational state and a reflecting operational state independently of operational states of the other back-reflecting means, 
 wherein: 
 each diffractive element set of the first group is arranged so as to route an optical signal within a corresponding wavelength band between a first optical port and the corresponding channel waveguide, and each diffractive element set of the second group is arranged so as to route the optical signal within the corresponding wavelength band between a second optical port and the corresponding channel waveguide; and 
 each diffractive element set of the first group, the corresponding channel waveguide, and the corresponding diffractive element set of the second group are arranged so as to route an optical signal entering through the first optical port within the corresponding wavelength band to the corresponding channel waveguide, transmit through the corresponding channel waveguide the optical signal thus routed if the corresponding back-reflecting means is in the transmitting operational state, and route the optical signal thus transmitted to exit through the second optical port, 
 and wherein: 
 each diffractive element set of the first group and the corresponding channel waveguide are arranged so as to route an optical signal entering through the first optical port within the corresponding wavelength band to the corresponding channel waveguide, back-reflect within the corresponding channel waveguide the optical signal thus routed if the corresponding back-reflecting means is in the reflecting operational state, and route the optical signal thus back-reflected to exit through the first optical port; or 
 each diffractive element set of the second group and the corresponding channel waveguide are arranged so as to route an optical signal entering through the second optical port within the corresponding wavelength band to the corresponding channel waveguide, back-reflect within the corresponding channel waveguide the optical signal thus routed if the corresponding back-reflecting means is in the reflecting operational state, and route the optical signal thus back-reflected to exit through the second optical port. 
 
     
     
       2. The optical apparatus of  claim 1 , wherein:
 each diffractive element set of the first group and the corresponding channel waveguide are arranged so as to route an optical signal entering through the first optical port within the corresponding wavelength band to the corresponding channel waveguide, back-reflect within the corresponding channel waveguide the optical signal thus routed if the corresponding back-reflecting means is in the reflecting operational state, and route the optical signal thus back-reflected to exit through the first optical port; and 
 each diffractive element set of the second group and the corresponding channel waveguide are arranged so as to route an optical signal entering through the second optical port within the corresponding wavelength band to the corresponding channel waveguide, back-reflect within the corresponding channel waveguide the optical signal thus routed if the corresponding back-reflecting means is in the reflecting operational state, and route the optical signal thus back-reflected to exit through the second optical port. 
 
     
     
       3. The optical apparatus of  claim 1 , wherein the slab waveguide with the first group of diffractive element sets, the slab waveguide with the second group of diffractive element sets, and the group of channel waveguides are integrated together on a common waveguide substrate. 
     
     
       4. The optical apparatus of  claim 1 , wherein:
 each diffractive element of at least one set of the first or second group is individually contoured and positioned so as to preferentially route a portion of an incident optical signal between the corresponding first or second optical port and the corresponding channel waveguide as the optical signal propagates within the slab waveguide; and 
 the diffractive elements of the at least one set are collectively arranged so as to exhibit a positional variation in amplitude, optical separation, or spatial phase over some portion of the set. 
 
     
     
       5. The optical apparatus of  claim 1 , wherein:
 each diffractive element of at least one set of the first or second group diffracts a corresponding diffracted component of an incident optical signal with a corresponding diffractive element transfer function between the corresponding first or second optical port and the corresponding channel waveguide; 
 each diffractive element of the at least one set comprises at least one diffracting region having at least one altered optical property so as to enable diffraction of a portion of the incident optical signal; and 
 the diffracting regions of each diffractive element of the at least one set are arranged so as to collectively provide a corresponding diffractive element transfer function between the corresponding first or second optical port and the corresponding channel waveguide. 
 
     
     
       6. The optical apparatus of  claim 1 , wherein:
 the multiple diffractive element sets of the first group are at least partly stacked, at least partly interleaved, or at least partly overlaid; or 
 the multiple diffractive element sets of the second group are at least partly stacked, at least partly interleaved, or at least partly overlaid. 
 
     
     
       7. The optical apparatus of  claim 1 , further comprising:
 a first circulator for separating an optical signal entering the first optical port from an optical signal exiting the first optical port; or 
 a second circulator for separating an optical signal entering the second optical port from an optical signal exiting the second optical port. 
 
     
     
       8. The optical apparatus of  claim 1 , wherein the corresponding wavelength bands comprise channels of a wavelength division multiplexing scheme. 
     
     
       9. The optical apparatus of  claim 1 , wherein the corresponding back-reflecting means comprises a waveguide grating formed in or on at least a portion of the corresponding channel waveguide and having a reflective bandwidth that substantially encompasses the corresponding wavelength band in the reflective operational state and that substantially avoids the corresponding wavelength band in the transmitting operational state. 
     
     
       10. The optical apparatus of  claim 9 , wherein each waveguide grating is adapted for switching between the reflecting and transmitting operational states thermo-optically, electro-optically, nonlinear-optically, or by current injection. 
     
     
       11. The optical apparatus of  claim 1 , wherein the corresponding back-reflecting means comprises a corresponding movable mirror within a gap formed between segments of the corresponding channel waveguide, the mirror being positioned between the channel waveguide segments for back-reflecting an optical signal from at least one of the channel waveguide segments in the reflective operational state, the mirror being positioned so as to leave substantially unobstructed transmission of an optical signal along the channel waveguide segments in the transmitting operational state. 
     
     
       12. A method, comprising:
 independently setting each one of a group of multiple channel waveguide back-reflecting means to either a reflecting operational state or a transmitting operational state; 
 receiving into a slab optical waveguide an input optical signal entering through a first optical port, the input optical signal comprising multiple wavelength channels within corresponding wavelength bands, the slab waveguide having a first group of multiple diffractive element sets formed in or on the slab waveguide and a second group of multiple diffractive element sets formed in or on the slab waveguide, each diffractive element set of the first group being optically coupled to a corresponding diffractive element set of the second group by a corresponding channel waveguide arranged for routing an optical signal between the corresponding diffractive element sets of the first and second groups, each channel waveguide including a corresponding back-reflecting means, each diffractive element set of the first group being arranged so as to route an optical signal within a corresponding wavelength band between the first optical port and the corresponding channel waveguide, each diffractive element set of the second group being arranged so as to route the optical signal within the corresponding wavelength band between the corresponding channel waveguide and a second optical port; and 
 receiving out of the slab waveguide an output optical signal exiting through the second optical port, the output optical signal comprising each corresponding wavelength channel of the input optical signal for which the corresponding back-reflecting means is in the transmitting operational state, each such corresponding wavelength channel entering through the input optical port, being routed by the corresponding diffractive element set of the first group from the first optical port into the corresponding channel waveguide, being transmitted by the corresponding back-reflecting means, and being routed by the corresponding diffractive element set of the second group to exit through the second optical port, 
 and further comprising: 
 receiving out of the slab waveguide a dropped optical signal exiting through the first optical port, the dropped optical signal comprising each corresponding wavelength channel of the input optical signal for which the corresponding back-reflecting means is in the reflecting operational state, each such wavelength channel entering through the input optical port, being routed by the corresponding diffractive element set of the first group from the first optical port into the corresponding channel waveguide, being reflected by the corresponding back-reflecting means, and being routed by the corresponding diffractive element set of the first group to exit through the first optical port; or 
 receiving into the slab waveguide a second input optical signal entering through the second optical port, the second input optical signal comprising at least one wavelength channel within a corresponding wavelength band, and receiving out of the slab optical waveguide an added optical signal exiting through the second optical port, the added optical signal comprising each corresponding wavelength channel of the second input signal for which the corresponding back-reflecting means is in the reflecting operational state, each such wavelength channel entering through the second optical, being routed by the corresponding diffractive element set of the second group from the second optical port into the corresponding channel waveguide, being reflected by the corresponding back-reflecting means, and being routed by the corresponding diffractive element set of the second group from the corresponding channel waveguide to exit through the second optical port. 
 
     
     
       13. The method of  claim 12 , comprising:
 receiving out of the slab waveguide a dropped optical signal exiting through the first optical port, the dropped optical signal comprising each corresponding wavelength channel of the input optical signal for which the corresponding back-reflecting means is in the reflecting operational state, each such wavelength channel entering through the input optical port, being routed by the corresponding diffractive element set of the first group from the first optical port into the corresponding channel waveguide, being reflected by the corresponding back-reflecting means, and being routed by the corresponding diffractive element set of the first group to exit through the first optical port; and 
 receiving into the slab waveguide a second input optical signal entering through the second optical port, the second input optical signal comprising at least one wavelength channel within a corresponding wavelength band, and receiving out of the slab optical waveguide an added optical signal exiting through the second optical port, the added optical signal comprising each corresponding wavelength channel of the second input signal for which the corresponding back-reflecting means is in the reflecting operational state, each such wavelength channel entering through the second optical, being routed by the corresponding diffractive element set of the second group from the second optical port into the corresponding channel waveguide, being reflected by the corresponding back-reflecting means, and being routed by the corresponding diffractive element set of the second group from the corresponding channel waveguide to exit through the second optical port. 
 
     
     
       14. The method of  claim 12 , wherein the slab waveguide with the first group of diffractive element sets, the slab waveguide with the second group of diffractive element sets, and the group of channel waveguides are integrated together on a common waveguide substrate. 
     
     
       15. The method of  claim 12 , wherein:
 each diffractive element of at least one set of the first or second group is individually contoured and positioned so as to preferentially route a portion of an incident optical signal between the corresponding first or second optical port and the corresponding channel waveguide as the optical signal propagates within the slab waveguide; and 
 the diffractive elements of the at least one set are collectively arranged so as to exhibit a positional variation in amplitude, optical separation, or spatial phase over some portion of the set. 
 
     
     
       16. The method of  claim 12 , wherein:
 each diffractive element of at least one set of the first or second group diffracts a corresponding diffracted component of an incident optical signal with a corresponding diffractive element transfer function between the corresponding first or second optical port and the corresponding channel waveguide; 
 each diffractive element of the at least one set comprises at least one diffracting region having at least one altered optical property so as to enable diffraction of a portion of the incident optical signal; and 
 the diffracting regions of each diffractive element of the at least one set are arranged so as to collectively provide a corresponding diffractive element transfer function between the corresponding first or second optical port and the corresponding channel waveguide. 
 
     
     
       17. The method of  claim 12 , wherein:
 the multiple diffractive element sets of the first group are at least partly stacked, at least partly interleaved, or at least partly overlaid; or 
 the multiple diffractive element sets of the second group are at least partly stacked, at least partly interleaved, or at least partly overlaid. 
 
     
     
       18. The method of  claim 12 , further comprising:
 receiving the input optical signal entering through the first optical port from a first circulator, and receiving the dropped optical signal exiting through the first optical port through the first circulator; 
 receiving the input optical signal entering through the first optical port from the first circulator, and receiving the transmitted wavelength channels thereof exiting through the second optical port through a second circulator; or 
 receiving the second input optical signal entering through the second optical port from the second circulator, and receiving the added optical signal exiting through the second optical port through the second circulator. 
 
     
     
       19. The method of  claim 12 , wherein the corresponding wavelength bands comprise channels of a wavelength division multiplexing scheme. 
     
     
       20. The method of  claim 12 , wherein the corresponding back-reflecting means comprises a waveguide grating formed in or on at least a portion of the corresponding channel waveguide and having a reflective bandwidth that substantially encompasses the corresponding wavelength band in the reflective operational state and that substantially avoids the corresponding wavelength band in the transmitting operational state. 
     
     
       21. The method of  claim 20 , wherein the waveguide grating is adapted for switching between the reflecting and transmitting operational states thermo-optically, electro-optically, nonlinear-optically, or by current injection. 
     
     
       22. The method of  claim 12 , wherein the corresponding back-reflecting means comprises a corresponding movable mirror within a gap formed between segments of the corresponding channel waveguide, the mirror being positioned between the channel waveguide segments for back-reflecting an optical signal from one of the channel waveguide segments in the reflective operational state, the mirror being positioned so as to leave substantially unobstructed transmission of an optical signal along the channel waveguide segments in the transmitting operational state. 
     
     
       23. An optical apparatus, comprising:
 a first group of multiple diffractive element sets formed in or on a slab waveguide; 
 a second group of multiple diffractive element sets formed in or on a slab waveguide; 
 a first group of multiple channel waveguides, each channel waveguide of the first group being arranged for routing an optical signal between a corresponding diffractive element set of the first group and a corresponding diffractive element set of the second group; 
 a second group of multiple channel waveguides, each channel waveguide of the second group being arranged for routing an optical signal from a corresponding one of multiple add optical ports or to a corresponding one of multiple drop optical ports; and 
 a group of multiple optical switches each independently switchable between a non-switched operational state and a switched operational state, 
 wherein: 
 each set of diffractive elements of the first group is arranged so as to route an optical signal within a corresponding wavelength band between a first optical port and the corresponding channel waveguide of the first group, and each set of diffractive elements of the second group is arranged so as to route an optical signal within the corresponding wavelength band between a second optical port and the corresponding channel waveguide of the first group; 
 each channel waveguide of the first group is coupled to a corresponding channel waveguide of the second group by a corresponding one of the multiple optical switches; and 
 each diffractive element set of the first group, the corresponding channel waveguide of the first group, and the corresponding diffractive element set of the second group are arranged so as to route an optical signal entering through the first optical port within the corresponding wavelength band to the corresponding channel waveguide of the first group, transmit through the corresponding channel waveguide of the first group the optical signal thus routed if the corresponding optical switch is in the non-switched operational state, and route the optical signal thus transmitted to exit through the second optical port, 
 and wherein: 
 each diffractive element set of the first group, the corresponding channel waveguide of the first group, and the corresponding channel waveguide of the second group are arranged so as to route an optical signal entering through the first optical port within the corresponding wavelength band to the corresponding channel waveguide of the first group, switch into the corresponding channel waveguide of the second group the optical signal thus routed if the corresponding optical switch is in the switched operational state, and transmit the optical signal thus switched to exit through the corresponding drop optical port; or 
 each diffractive element set of the second group, the corresponding channel waveguide of the first group, and the corresponding channel waveguide of the second group are arranged so as to route an optical signal within the corresponding wavelength band entering the corresponding channel waveguide of the second group through the corresponding add optical port to the corresponding optical switch, switch into the corresponding channel waveguide of the first group the optical signal thus routed if the corresponding optical switch is in the switched operational state, and transmit the optical signal thus switched to exit through the second optical port. 
 
     
     
       24. The optical apparatus of  claim 23 , wherein:
 each channel waveguide of the second group routes an optical signal between the corresponding add optical port and the corresponding drop optical port; 
 each diffractive element set of the first group, the corresponding channel waveguide of the first group, and the corresponding channel waveguide of the second group are arranged so as to route an optical signal entering through the first optical port within the corresponding wavelength band to the corresponding channel waveguide of the first group, switch into the corresponding channel waveguide of the second group the optical signal thus routed if the corresponding optical switch is in the switched operational state, and transmit the optical signal thus switched to exit through the corresponding drop optical port; and 
 each diffractive element set of the second group, the corresponding channel waveguide of the first group, and the corresponding channel waveguide of the second group are arranged so as to route an optical signal within the corresponding wavelength band entering the corresponding channel waveguide of the second group through the corresponding add optical port to the corresponding optical switch, switch into the corresponding channel waveguide of the first group the optical signal thus routed if the corresponding optical switch is in the switched operational state, and transmit the optical signal thus switched to exit through the second optical port. 
 
     
     
       25. The optical apparatus of  claim 23 , wherein the slab waveguide with the first group of diffractive element sets, the slab waveguide with the second group of diffractive element sets, the first group of channel waveguides, and the second group of channel waveguides are integrated together on a common waveguide substrate. 
     
     
       26. The optical apparatus of  claim 23 , wherein:
 each diffractive element of at least one set of the first or second group is individually contoured and positioned so as to preferentially route a portion of an incident optical signal between the corresponding first or second optical port and the corresponding channel waveguide as the optical signal propagates within the slab waveguide; and 
 the diffractive elements of the at least one set are collectively arranged so as to exhibit a positional variation in amplitude, optical separation, or spatial phase over some portion of the set. 
 
     
     
       27. The optical apparatus of  claim 23 , wherein:
 each diffractive element of at least one set of the first or second group diffracts a corresponding diffracted component of an incident optical signal with a corresponding diffractive element transfer function between the corresponding first or second optical port and the corresponding channel waveguide; 
 each diffractive element of the at least one set comprises at least one diffracting region having at least one altered optical property so as to enable diffraction of a portion of the incident optical signal; and 
 the diffracting regions of each diffractive element of the at least one set are arranged so as to collectively provide a corresponding diffractive element transfer function between the corresponding first or second optical port and the corresponding channel waveguide. 
 
     
     
       28. The optical apparatus of  claim 23 , wherein:
 the multiple diffractive element sets of the first group are at least partly stacked, at least partly interleaved, or at least partly overlaid; or 
 the multiple diffractive element sets of the second group are at least partly stacked, at least partly interleaved, or at least partly overlaid. 
 
     
     
       29. The optical apparatus of  claim 23 , wherein the corresponding wavelength bands comprise channels of a wavelength division multiplexing scheme. 
     
     
       30. A method, comprising:
 independently setting each one of a group of multiple optical switches to either a non-switched operational state or a switched operational state; 
 receiving into a slab optical waveguide an input optical signal entering through a first optical port, the input optical signal comprising multiple wavelength channels within corresponding wavelength bands, the slab waveguide having a first group of multiple diffractive element sets formed in or on the slab waveguide and a second group of multiple diffractive element sets formed in or on the slab waveguide, each diffractive element of the first group being optical coupled to a corresponding diffractive element set of the second group by a corresponding one of a first group of channel waveguides arranged for routing an optical signal between the corresponding diffractive element sets of the first and second groups, each channel waveguide of the first group being coupled to a corresponding one of a second group of channel waveguides by a corresponding optical switch, each channel waveguide of the second group being arranged for routing an optical signal from a corresponding one of multiple add optical ports or to a corresponding one of multiple drop optical ports, each diffractive element set of the first group being arranged so as to route an optical signal within a corresponding wavelength band between the first optical port and the corresponding channel waveguide of the first group, each diffractive element set of the second group being arranged so as to route the optical signal within the corresponding wavelength band between the corresponding channel waveguide of the first group and a second optical port; and 
 receiving out of the slab waveguide an output optical signal exiting through the second optical port, the output optical signal comprising each corresponding wavelength channel of the input optical signal for which the corresponding optical switch is in the non-switched operational state, each such corresponding wavelength channel entering through the input optical port, being routed by the corresponding diffractive element set of the first group from the first optical port to the corresponding channel waveguide of the first group, being transmitted through the corresponding channel waveguide of the first group, and being routed by the corresponding diffractive element set of the second group to exit through the second optical port, 
 and further comprising: 
 receiving out of the slab waveguide at least one dropped optical signal exiting through a corresponding drop optical port, each dropped optical signal comprising the corresponding wavelength channel for which the corresponding optical switch is in the switched operational state, each such wavelength channel entering through the first optical port, being routed by the corresponding diffractive element set of the first group from the first optical port to the corresponding channel waveguide of the first group, being switched into the corresponding channel waveguide of the second group, and being transmitted to exit through the corresponding drop optical port; or 
 receiving through the corresponding add optical port into the corresponding channel waveguide of the second group an added optical signal within the corresponding wavelength band, and receiving out of the slab waveguide the added optical signal exiting through the second optical port if the corresponding optical switch is in the switched operational state, the added optical signal entering through the corresponding add optical port, being routed by the corresponding channel waveguide of the second group from the corresponding add optical port to the optical switch, being switched by the corresponding optical switch into the corresponding channel waveguide of the first group, and being routed by the corresponding diffractive element set of the second group to exit through the second optical port. 
 
     
     
       31. The method of  claim 30 , comprising:
 receiving out of the slab waveguide at least one dropped optical signal exiting through a corresponding drop optical port, each dropped optical signal comprising the corresponding wavelength channel for which the corresponding optical switch is in the switched operational state, each such wavelength channel entering through the first optical port, being routed by the corresponding diffractive element set of the first group from the first optical port to the corresponding channel waveguide of the first group, being switched into the corresponding channel waveguide of the second group, and being transmitted to exit through the corresponding drop optical port; and 
 receiving through the corresponding add optical port into the corresponding channel waveguide of the second group an added optical signal within the corresponding wavelength band, and receiving out of the slab waveguide the added optical signal exiting through the second optical port if the corresponding optical switch is in the switched operational state, the added optical signal entering through the corresponding add optical port, being routed by the corresponding channel waveguide of the second group from the corresponding add optical port to the optical switch, being switched by the corresponding optical switch into the corresponding channel waveguide of the first group, and being routed by the corresponding diffractive element set of the second group to exit through the second optical port. 
 
     
     
       32. The method of  claim 30 , wherein the slab waveguide with the first group of diffractive element sets, the slab waveguide with the second group of diffractive element sets, the first group of channel waveguides, and the second group of channel waveguides are integrated together on a common waveguide substrate. 
     
     
       33. The method of  claim 30 , wherein:
 each diffractive element of at least one set of the first or second group is individually contoured and positioned so as to preferentially route a portion of an incident optical signal between the corresponding first or second optical port and the corresponding channel waveguide as the optical signal propagates within the slab waveguide; and 
 the diffractive elements of the at least one set are collectively arranged so as to exhibit a positional variation in amplitude, optical separation, or spatial phase over some portion of the set. 
 
     
     
       34. The method of  claim 30 , wherein:
 each diffractive element of at least one set of the first or second group diffracts a corresponding diffracted component of an incident optical signal with a corresponding diffractive element transfer function between the corresponding first or second optical port and the corresponding channel waveguide; 
 each diffractive element of the at least one set comprises at least one diffracting region having at least one altered optical property so as to enable diffraction of a portion of the incident optical signal; and 
 the diffracting regions of each diffractive element of the at least one set are arranged so as to collectively provide a corresponding diffractive element transfer function between the corresponding first or second optical port and the corresponding channel waveguide. 
 
     
     
       35. The method of  claim 30 , wherein:
 the multiple diffractive element sets of the first group are at least partly stacked, at least partly interleaved, or at least partly overlaid; or 
 the multiple diffractive element sets of the second group are at least partly stacked, at least partly interleaved, or at least partly overlaid. 
 
     
     
       36. The method of  claim 30 , wherein the corresponding wavelength bands comprise channels of a wavelength division multiplexing scheme. 
     
     
       37. An optical apparatus, comprising:
 at least a first group of multiple diffractive element sets formed in or on a slab waveguide; and   a group of multiple channel waveguides, each channel waveguide of the group including a corresponding switchable reflector having a transmission operational state and a reflection operational state,   wherein each diffractive element set of said at least the first group is arranged to route an optical signal within a corresponding wavelength band between a first optical port and the corresponding channel waveguide, and between a second optical port and the corresponding channel waveguide,   wherein in the transmission operational state to pass a first channel:
 each diffractive element set of said at least the first group and the corresponding channel waveguide are arranged so as to route a first optical signal entering through the first optical port to the corresponding channel waveguide, transmit through the corresponding channel waveguide the first optical signal thus routed if the corresponding switchable reflector is in the transmission operational state, and route the first optical signal thus transmitted to exit through the second optical port, 
   and wherein in the reflection operational state to drop a second channel:
 each diffractive element set of said at least the first group and the corresponding channel waveguide are arranged so as to route a second optical signal entering through the first optical port to the corresponding channel waveguide, back-reflect within the corresponding channel waveguide the second optical signal thus routed if the corresponding switchable reflector is in the reflection operational state, and route the second optical signal thus back-reflected to exit through the first optical port. 
   
     
     
       38. The optical apparatus of claim 37 wherein the corresponding switchable reflector having the transmission operational state and the reflection operational state includes a waveguide grating. 
     
     
       39. The optical apparatus of claim 37 wherein the at least the first group of multiple diffractive element sets includes:
 a first group of diffractive elements arranged to said route the optical signal within the corresponding wavelength band between the first optical port and the corresponding channel waveguide; and   a second group of diffractive elements arranged to said route the optical signal within the corresponding wavelength band between the second optical port and the corresponding channel waveguide.   
     
     
       40. The optical apparatus of claim 37 wherein the slab waveguide with the at least the first group of diffractive element sets or the channel waveguides each with the corresponding switchable reflector are formed on a separate waveguide substrate. 
     
     
       41. An optical apparatus, comprising:
 at least a first group of multiple diffractive element sets formed in or on a slab waveguide; and   a group of multiple channel waveguides, each channel waveguide of the group including a corresponding switchable reflector having a transmission operational state and a reflection operational state,   wherein each diffractive element set of said at least the first group is arranged to route an optical signal within a corresponding wavelength band between a first optical port and the corresponding channel waveguide, and between a second optical port and the corresponding channel waveguide,   wherein in the transmission operational state to pass a first channel:
 each diffractive element set of said at least the first group and the corresponding channel waveguide are arranged so as to route a first optical signal entering through the first optical port to the corresponding channel waveguide, transmit through the corresponding channel waveguide the first optical signal thus routed if the corresponding switchable reflector is in the transmission operational state, and route the first optical signal thus transmitted to exit through the second optical port, 
   and wherein in the reflection operational state to add a second channel:
 each diffractive element set of said at least the first group and the corresponding channel waveguide are arranged so as to route a second optical signal entering through the second optical port to the corresponding channel waveguide, back-reflect within the corresponding channel waveguide the second optical signal thus routed if the corresponding switchable reflector is in the reflection operational state, and route the second optical signal thus back-reflected to exit through the second optical port. 
   
     
     
       42. The optical apparatus of claim 41 wherein the corresponding switchable reflector having the transmission operational state and the reflection operational state includes a waveguide grating. 
     
     
       43. The optical apparatus of claim 41 wherein the at least the first group of multiple diffractive element sets includes:
 a first group of diffractive elements arranged to said route the optical signal within the corresponding wavelength band between the first optical port and the corresponding channel waveguide; and   a second group of diffractive elements arranged to said route the optical signal within the corresponding wavelength band between the second optical port and the corresponding channel waveguide.   
     
     
       44. A method, comprising:
 setting a switchable element, associated with at least one corresponding channel waveguide of a group of multiple channel waveguides, to a first operational state or to a second operational state; and   routing, by at least one diffractive element set of at least a first group of multiple diffractive element sets formed in or on a slab waveguide, an optical signal between a first optical port and said at least one corresponding channel waveguide, and between a second optical port and said at least one corresponding channel waveguide,   wherein in the first operational state to pass a first channel, said routing includes:
 directing, by the at least one diffractive element set of said at least the first group to said at least one corresponding channel waveguide, a first optical signal that enters through the first optical port; and 
 transmitting, through said at least one corresponding channel waveguide by the switchable element that has been set to the first operational state, the first optical signal thus directed so as to exit through the second optical port, 
   wherein the switchable element includes a waveguide grating, and   wherein in the second operational state to drop a second channel, said routing includes:
 directing, by at least one diffractive element set of said at least the first group to said at least one corresponding channel waveguide, a second optical signal that enters through the first optical port; and 
 back-reflecting within said at least one corresponding channel waveguide, by the waveguide grating that has been set to the second operational state, the second optical signal thus directed so as to exit through the first optical port. 
   
     
     
       45. A method, comprising:
 setting a switchable element, associated with at least one corresponding channel waveguide of a group of multiple channel waveguides, to a first operational state or to a second operational state; and   routing, by at least one diffractive element set of at least a first group of multiple diffractive element sets formed in or on a slab waveguide, an optical signal between a first optical port and said at least one corresponding channel waveguide, and between a second optical port and said at least one corresponding channel waveguide,   wherein in the first operational state to pass a first channel, said routing includes:
 directing, by the at least one diffractive element set of said at least the first group to said at least one corresponding channel waveguide, a first optical signal that enters through the first optical port; and 
 transmitting, through said at least one corresponding channel waveguide by the switchable element that has been set to the first operational state, the first optical signal thus directed so as to exit through the second optical port, 
   wherein the switchable element includes a waveguide grating, and   wherein in the second operational state to add a second channel, said routing includes:
 directing, by at least one diffractive element set of said at least the first group to said at least one corresponding channel waveguide, a second optical signal that enters through the second optical port; and 
 back-reflecting within said at least one corresponding channel waveguide, by the waveguide grating that has been set to the second operational state, the second optical signal thus directed so as to exit through the second optical port. 
   
     
     
       46. An optical telecommunication system, comprising:
 a first device;   a second device;   a reconfigurable optical apparatus to communicate optical signals with the first and second devices, the reconfigurable optical apparatus including:
 a switchable element, associated with at least one corresponding channel waveguide of a group of multiple channel waveguides, and configurable to switch to a first operational state or to a second operational state; and 
 at least a first group of multiple diffractive element sets formed in or on a slab waveguide, at least one diffractive element set being configured to route an optical signal between a first optical port and said at least one corresponding channel waveguide, and between a second optical port and said at least one corresponding channel waveguide, 
   wherein in the first operational state to pass a first channel:
 said at least one diffractive element set of said at least the first group is configured to direct, to said at least one corresponding channel waveguide, a first optical signal from the first device that enters through the first optical port; and 
 the switchable element, which has been set to the first operational state, is configured to transmit the first optical signal thus directed through said at least one corresponding channel waveguide so as to exit through the second optical port and reach the second device, 
   wherein the switchable element includes a waveguide grating,   wherein in the second operational state, the optical apparatus is configured to operate as a drop multiplexer to drop a second channel, and   wherein in the second operational state to drop the second channel:
 said at least one diffractive element set of said at least the first group is configured to direct, to said at least one corresponding channel waveguide, a second optical signal from the first optical device that enters through the first optical port; and 
 the waveguide grating set to the second operational state is configured to back-reflect, within said at least one corresponding channel waveguide, the second optical signal thus directed so as to exit through the first optical port. 
   
     
     
       47. An optical telecommunication system, comprising:
 a first device;   a second device;   a reconfigurable optical apparatus to communicate optical signals with the first and second devices, the reconfigurable optical apparatus including:
 a switchable element, associated with at least one corresponding channel waveguide of a group of multiple channel waveguides, and configurable to switch to a first operational state or to a second operational state; and 
 at least a first group of multiple diffractive element sets formed in or on a slab waveguide, at least one diffractive element set being configured to route an optical signal between a first optical port and said at least one corresponding channel waveguide, and between a second optical port and said at least one corresponding channel waveguide, 
   wherein in the first operational state to pass a first channel:
 said at least one diffractive element set of said at least the first group is configured to direct, to said at least one corresponding channel waveguide, a first optical signal from the first device that enters through the first optical port; and 
 the switchable element, which has been set to the first operational state, is configured to transmit the first optical signal thus directed through said at least one corresponding channel waveguide so as to exit through the second optical port and reach the second device, 
   wherein the switchable element includes a waveguide grating,   wherein in the second operational state, the optical apparatus is configured to operate as an add multiplexer to add a second channel, and   wherein in the second operational state to add the second channel:
 said at least one diffractive element set of said at least the first group is configured to direct, to said at least one corresponding channel waveguide, a second optical signal from the second device that enters through the second optical port; and 
 the waveguide grating set to the second operational state is configured to back-reflect, within said at least one corresponding channel waveguide, the second optical signal thus directed so as to exit through the second optical port and reach the second device. 
   
     
     
       48. An apparatus, comprising:
 at least a first group of multiple diffractive element sets formed in or on a slab waveguide; and   a group of multiple channel waveguides, each channel waveguide of the group including a corresponding switchable reflector having a transmission operational state and a reflection operational state,   wherein each diffractive element set of said at least the first group is arranged to route an optical signal between a first optical port and the corresponding channel waveguide, and between a second optical port and the corresponding channel waveguide,   wherein in the reflection operational state to drop a first channel:
 at least one diffractive element set of said at least the first group and the corresponding channel waveguide are arranged so as to route a first optical signal entering through the first optical port to the corresponding channel waveguide, back-reflect within the corresponding channel waveguide the first optical signal thus routed, and route the first optical signal thus back-reflected to exit through the first optical port, 
   and wherein in the reflection operational state to add a second channel:
 at least one diffractive element set of said at least the first group and the corresponding channel waveguide are arranged so as to route a second optical signal entering through the second optical port to the corresponding channel waveguide, back-reflect within the corresponding channel waveguide the second optical signal thus routed, and route the second optical signal thus back-reflected to exit through the second optical port. 
   
     
     
       49. The apparatus of claim 48 wherein in the transmission operational state, at least one diffractive element set of said at least the first group and the corresponding channel waveguide are arranged so as to route third optical signal, entering through the first optical port and transmitted through the corresponding channel waveguide, to exit through the second optical port. 
     
     
       50. The apparatus of claim 48 wherein the corresponding switchable reflector having the transmission operational state and the reflection operational state includes a waveguide grating. 
     
     
       51. The apparatus of claim 48 wherein the corresponding switchable reflector having the transmission operational state and the reflection operational state includes an optical switch.