Optical multiplexing device

Abstract

An optical multiplexing device includes an optical element having at least one set of diffractive elements, and an optical reflector. The reflector routes, between first and second optical ports, that portion of an optical signal transmitted by the diffractive element set. The diffractive element set routes, between first and multiplexing optical ports, a portion of the optical signal that is diffracted by the diffractive element set. More complex optical multiplexing functionality(ies) may be achieved using additional sets of diffractive elements, in a common optical element (and possibly overlaid) or in separate optical elements with multiple reflectors. Separate multiplexing devices may be assembled with coupled ports for forming more complex devices. The respective portions of an optical signal transmitted by and reflected/diffracted from the diffractive element set typically differ spectrally. The portion reflected from the diffractive element set may comprise one or more channels of an optical WDM system.

What is claimed is: 
     
       1. An optical apparatus, comprising:
 an optical element having at least one set of diffractive elements, the at least one set of diffractive elements having a resonance frequency band f res ; and 
 an achromatic optical reflector, 
 
       wherein:
 the reflector routes, between a first optical port and a second optical port, that portion having frequency bands f 1 , . . . f res−1 , f res+1  . . . f n  of an optical signal propagating within the optical element and transmitted by each diffractive element set; 
 each diffractive element set routes, between a corresponding multiplexing optical port and either the first or the second optical port, a corresponding portion of the optical signal that is diffracted by the diffractive element set according to a corresponding set transfer function; 
 
       and
 the optical element comprises a planar optical waveguide, the planar optical waveguide substantially confining in one transverse dimension the optical signal propagating in two dimensions therein, 
 
       and wherein:
 (a) the diffractive elements of the set are collectively arranged so as to exhibit a positional variation in amplitude, optical separation, or spatial phase over some portion of the set, said positional variation determining at least in part the set transfer function; 
 
       or
 (b) (1) each diffractive element is spatially arranged relative to a corresponding diffractive element virtual contour and comprises at least one diffracting region thereof, the diffracting regions having at least one altered optical property so as to enable diffraction of a portion of the incident optical field therefrom,
 (2) each diffractive element diffracts a corresponding diffracted component of an incident optical field with a corresponding diffractive element transfer function so that each diffractive element set collectively provides the corresponding set transfer function between the corresponding multiplexing optical port and either the first or the second optical port, 
 
 
       and
   (3) the corresponding set transfer function or at least one corresponding diffractive element transfer function is determined at least in part by: (A) a less-than-unity fill factor for the corresponding virtual contour, (B) a non-uniform spatial distribution of multiple diffracting regions along the corresponding virtual contour, (C) variation of a spatial profile of the optical property of at least one diffracting region of the corresponding virtual contour, (D) variation of a spatial profile of the optical property among multiple diffracting regions of the corresponding virtual contour, (E) variation of the spatial profile of the optical property of at least one diffracting region among elements of at least one diffractive element set, (F) longitudinal displacement of at least one diffractive element relative to the corresponding virtual contour, or (G) at least one virtual contour lacking a diffractive element corresponding thereto.   
 
     
     
       2. The apparatus of  claim 1 , wherein:
 the first optical port is an input port; 
 the second optical port is an output port; 
 the multiplexing optical port is a dropped-channel port; 
 the diffractive element set routes the corresponding diffracted portion of the optical signal from the input port to the dropped-channel port; and 
 the apparatus functions as a channel-dropping multiplexer. 
 
     
     
       3. The apparatus of  claim 1 , wherein:
 the first optical port is an input port; 
 the second optical port is an output port; 
 the multiplexing optical port is an added-channel port; 
 the diffractive element set routes the corresponding diffracted portion of the optical signal from the added-channel port to the output port; and 
 the apparatus functions as a channel-adding multiplexer. 
 
     
     
       4. The apparatus of  claim 1 , wherein:
 the first optical port is an input port; 
 the second optical port is an output port; 
 the multiplexing optical port is a dropped-channel port; 
 the diffractive element set routes a corresponding diffracted portion of the optical signal from the input port to the dropped-channel port; 
 the diffractive element set routes a corresponding diffracted portion of the optical signal from an added-channel port to the output port; and 
 the apparatus functions as an add/drop multiplexer. 
 
     
     
       5. The apparatus of  claim 4 , further comprising:
 a first optical waveguide optically coupled to the input port; 
 a second optical waveguide optically coupled to the output port; 
 a third optical waveguide optically coupled to the dropped-channel port; and 
 a fourth optical waveguide optically coupled to the added-channel port, 
 wherein each of the first, second, third, and fourth optical waveguides substantially confines in two transverse dimensions optical signals propagating therethrough. 
 
     
     
       6. The apparatus of  claim 1 , wherein the diffractive elements are curvilinear elements. 
     
     
       7. The apparatus of  claim 1 , wherein the planar optical waveguide supports only a single optical transverse mode in the confined transverse dimension. 
     
     
       8. The apparatus of  claim 1 , wherein the planar optical waveguide supports multiple optical transverse modes in the confined transverse dimension. 
     
     
       9. The apparatus of  claim 1 , further comprising:
 a first optical waveguide optically coupled to the first optical port; 
 a second optical waveguide optically coupled to the second optical port; and 
 a third optical waveguide optically coupled to the multiplexing optical port, 
 wherein each of the first, second, and third optical waveguides substantially confines in two transverse dimensions optical signals propagating therethrough. 
 
     
     
       10. The apparatus of  claim 9 , wherein the first, second, and third optical waveguides are channel waveguides formed on a waveguide substrate. 
     
     
       11. The apparatus of  claim 9 , wherein the first, second, and third optical waveguides are optical fibers. 
     
     
       12. The apparatus of  claim 1 , wherein the reflector is a mirror formed on a portion of a surface of the optical element. 
     
     
       13. The apparatus of  claim 12 , wherein the reflector comprises a metallic coating formed on the portion of the surface of the optical element. 
     
     
       14. The apparatus of  claim 12 , wherein the reflector comprises a dielectric coating formed on the portion of the surface of the optical element. 
     
     
       15. The apparatus of  claim 12 , wherein the optical signal undergoes total internal reflection from the portion of the surface of the optical element. 
     
     
       16. The apparatus of  claim 1 , wherein the reflector is formed within the optical element. 
     
     
       17. The apparatus of  claim 16 , wherein the reflector comprises a second set of diffractive elements of the optical element. 
     
     
       18. The apparatus of  claim 1 , wherein the reflector comprises an optical component separate from the optical element. 
     
     
       19. The apparatus of  claim 1 , wherein the reflector is substantially achromatic over a designed spectral window for the apparatus. 
     
     
       20. The apparatus of  claim 1 , wherein the portion of the optical signal routed between the first and second optical ports is transmitted through the diffractive element set twice. 
     
     
       21. An optical apparatus, comprising:
 an optical element having at least one set of diffractive elements, the at least one set of diffractive elements having a resonance frequency band f res ; and 
 an achromatic optical reflector, 
 
       wherein:
 the reflector routes, between a first optical port and a second optical port, that portion having frequency bands f 1 , . . . f res−1 , f res+1  . . . f n  of an optical signal propagating within the optical element and transmitted by each diffractive element set; 
 each diffractive element set routes, between a corresponding multiplexing optical port and either the first or the second optical port, a corresponding portion of the optical signal that is diffracted by the diffractive element set according to a corresponding set transfer function; 
 
       and
 the reflector comprises a focusing reflector, and the first and second optical ports are positioned at respective first and second conjugate image points of the focusing reflector, 
 
       and wherein:
 (a) the diffractive elements of the set are collectively arranged so as to exhibit a positional variation in amplitude, optical separation, or spatial phase over some portion of the set, said positional variation determining at least in part the set transfer function; 
 
       or
 (b) (1) each diffractive element is spatially arranged relative to a corresponding diffractive element virtual contour and comprises at least one diffracting region thereof, the diffracting regions having at least one altered optical property so as to enable diffraction of a portion of the incident optical field therefrom,
 (2) each diffractive element diffracts a corresponding diffracted component of an incident optical field with a corresponding diffractive element transfer function so that each diffractive element set collectively provides the corresponding set transfer function between the corresponding multiplexing optical port and either the first or the second optical port, 
 
 
       and
   (3) the corresponding set transfer function or at least one corresponding diffractive element transfer function is determined at least in part by: (A) a less-than-unity fill factor for the corresponding virtual contour, (B) a non-uniform spatial distribution of multiple diffracting regions along the corresponding virtual contour, (C) variation of a spatial profile of the optical property of at least one diffracting region of the corresponding virtual contour, (D) variation of a spatial profile of the optical property among multiple diffracting regions of the corresponding virtual contour, (E) variation of the spatial profile of the optical property of at least one diffracting region among elements of at least one diffractive element set, (F) longitudinal displacement of at least one diffractive element relative to the corresponding virtual contour, or (G) at least one virtual contour lacking a diffractive element corresponding thereto.   
 
     
     
       22. The apparatus of  claim 21 , wherein the focusing reflector provides a non-unity conjugate image ratio between the first and second conjugate image points. 
     
     
       23. An optical apparatus, comprising:
 an optical element having at least one set of diffractive elements, the at least one set of diffractive elements having a resonance frequency band f res ; and 
 an achromatic optical reflector, 
 
       wherein:
 the reflector routes, between a first optical port and a second optical port, that portion having frequency bands f 1 , . . . f res−1 , f res+1  . . . f n  of an optical signal propagating within the optical element and transmitted by each diffractive element set; 
 each diffractive element set routes, between a corresponding multiplexing optical port and either the first or the second optical port, a corresponding portion of the optical signal that is diffracted by the diffractive element set according to a corresponding set transfer function; 
 
       and
 the diffractive element set comprises a set of focusing diffractive elements, and the corresponding multiplexing optical port and either the first or the second optical port are positioned at respective first and second conjugate image points of the diffractive elements set, 
 
       and wherein:
 (a) the diffractive elements of the set are collectively arranged so as to exhibit a positional variation in amplitude, optical separation, or spatial phase over some portion of the set, said positional variation determining at least in part the set transfer function; 
 
       or
 (b) (1) each diffractive element is spatially arranged relative to a corresponding diffractive element virtual contour and comprises at least one diffracting region thereof, the diffracting regions having at least one altered optical property so as to enable diffraction of a portion of the incident optical field therefrom,
 (2) each diffractive element diffracts a corresponding diffracted component of an incident optical field with a corresponding diffractive element transfer function so that each diffractive element set collectively provides the corresponding set transfer function between the corresponding multiplexing optical port and either the first or the second optical port, 
 
 
       and
   (3) the corresponding set transfer function or at least one corresponding diffractive element transfer function is determined at least in part by: (A) a less-than-unity fill factor for the corresponding virtual contour, (B) a non-uniform spatial distribution of multiple diffracting regions along the corresponding virtual contour, (C) variation of a spatial profile of the optical property of at least one diffracting region of the corresponding virtual contour, (D) variation of a spatial profile of the optical property among multiple diffracting regions of the corresponding virtual contour, (E) variation of the spatial profile of the optical property of at least one diffracting region among elements of at least one diffractive element set, (F) longitudinal displacement of at least one diffractive element relative to the corresponding virtual contour, or (G) at least one virtual contour lacking a diffractive element corresponding thereto.   
 
     
     
       24. The apparatus of  claim 23 , wherein the focusing diffractive elements provide a non-unity conjugate image ratio between the first and second conjugate image points. 
     
     
       25. The apparatus of  claim 1 , wherein the transmitted and diffracted portions of the optical signal differ spectrally. 
     
     
       26. The apparatus of  claim 25 , wherein the diffracted portion of the optical signal corresponds to at least one channel of an optical WDM system. 
     
     
       27. The apparatus of  claim 1 , wherein: the optical element has multiple sets of diffractive elements;
 each diffractive element set routes, between a corresponding one of multiple multiplexing optical ports and either the first or the second optical port, a corresponding portion of the optical signal that is diffracted by the diffractive element set; and 
 the reflector routes, between the first optical port and the second optical port, that portion of the optical signal transmitted by the multiple diffractive element sets. 
 
     
     
       28. The apparatus of  claim 27 , wherein at least two of the multiple diffractive element sets are overlaid. 
     
     
       29. The apparatus of  claim 27 , wherein at least two of the multiple diffractive element sets are stacked. 
     
     
       30. The apparatus of  claim 27 , wherein at least two of the multiple diffractive element sets are interleaved. 
     
     
       31. The apparatus of  claim 27 , further comprising multiple optical reflectors for routing, between a first optical port and a second optical port, that portion of the optical signal propagating within the optical element and transmitted by the multiple diffractive element sets. 
     
     
       32. The apparatus of  claim 31 , wherein, during routing between two of the multiple reflectors, a transverse spatial extent of the optical signal in a corresponding unconfined transverse dimension is larger than about two times its transverse spatial extent at the first optical port and larger than about two times its transverse spatial extent at the second optical port. 
     
     
       33. The apparatus of  claim 31 , wherein, during routing between two of the multiple reflectors, a transverse spatial extent of the optical signal in a corresponding unconfined transverse dimension is larger than about five times its transverse spatial extent at the first optical port and larger than about five times its transverse spatial extent at the second optical port. 
     
     
       34. The apparatus of  claim 1 , further comprising:
 multiple optical elements, each having a corresponding set of diffractive elements; and 
 multiple corresponding optical reflectors, 
 
       wherein
 each reflector routes, between a corresponding first optical port and a corresponding second optical port, that portion of an optical signal transmitted by the corresponding diffractive element set; 
 each corresponding diffractive element set routes, between the corresponding first optical port and a corresponding multiplexing optical port, a corresponding portion of the optical signal that is diffracted by the corresponding diffractive element set; and 
 the multiple optical elements are arranged so that at least one optical port of each of the multiple optical elements is coupled to an optical port of another the multiple optical elements. 
 
     
     
       35. An optical apparatus, comprising:
 diffractive means for routing, between a first optical port and a multiplexing optical port and according to a diffractive transfer function, a corresponding diffracted portion of an optical signal propagating within an optical element, the diffractive element means having a resonance frequency band f res ; and 
 achromatic reflective means for routing, between a first optical port and a second optical port, that portion having frequency bands f 1 , . . . f res−1 , f res+1  . . . f n  of the optical signal transmitted by the diffractive routing means, 
 wherein the optical element comprises a planar optical waveguide, the planar optical waveguide substantially confining in one transverse dimension the optical signal propagating in two dimensions therein, 
 
       and wherein:
 (a) diffractive elements of the diffractive means are collectively arranged so as to exhibit a positional variation in amplitude, optical separation, or spatial phase over some portion thereof, said positional variation determining at least in part the diffractive transfer function; 
 
       or
 (b) (1) diffractive elements of the diffractive means are each spatially arranged relative to a corresponding diffractive element virtual contour and each comprise at least one diffracting region thereof, the diffracting regions having at least one altered optical property so as to enable diffraction of a portion of the incident optical field therefrom,
 (2) each diffractive element diffracts a corresponding diffracted component of an incident optical field with a corresponding diffractive element transfer function so that each diffractive element set collectively provides the diffractive transfer function between the multiplexing optical port and either the first or the second optical port, 
 
 
       and
   (3) the diffractive transfer function or at least one corresponding diffractive element transfer function is determined at least in part by: (A) a less-than-unity fill factor for the corresponding virtual contour, (B) a non-uniform spatial distribution of multiple diffracting regions along the corresponding virtual contour, (C) variation of a spatial profile of the optical property of at least one diffracting region of the corresponding virtual contour, (D) variation of a spatial profile of the optical property among multiple diffracting regions of the corresponding virtual contour, (E) variation of the spatial profile of the optical property of at least one diffracting region among elements of at least one diffractive element set, (F) longitudinal displacement of at least one diffractive element relative to the corresponding virtual contour, or (G) at least one virtual contour lacking a diffractive element corresponding thereto.   
 
     
     
       36. The apparatus of  claim 35 , wherein the first optical port is an input port, the second optical port is an output port, the multiplexing optical port is a dropped-channel port, and the apparatus functions as a channel-dropping multiplexer. 
     
     
       37. The apparatus of  claim 35 , wherein the first optical port is an output port, the second optical port is an input port, the multiplexing optical port is an added-channel port, and the apparatus functions as a channel-adding multiplexer. 
     
     
       38. The apparatus of  claim 35 , wherein the diffractive routing means routes, between the second optical port and a corresponding second multiplexing optical port, a corresponding diffracted portion of the optical signal, the apparatus thereby functioning as an add/drop multiplexer. 
     
     
       39. The apparatus of  claim 38 , further comprising:
 a first optical waveguide optically coupled to the first optical port; 
 a second optical waveguide optically coupled to the second optical port; 
 a third optical waveguide optically coupled to the first multiplexing optical port; 
 a fourth optical waveguide optically coupled to the second multiplexing optical port, 
 wherein each of the first, second, third, and fourth optical waveguides substantially confines in two transverse dimensions optical signals propagating therethrough. 
 
     
     
       40. The apparatus of  claim 35 , wherein the diffractive elements are curvilinear elements. 
     
     
       41. The apparatus of  claim 35 , further comprising:
 a first optical waveguide optically coupled to the first optical port; 
 a second optical waveguide optically coupled to the second optical port; and 
 a third optical waveguide optically coupled to the multiplexing optical port, 
 wherein each of the first, second, and third optical waveguides substantially confines in two transverse dimensions optical signals propagating therethrough. 
 
     
     
       42. The apparatus of  claim 41 , wherein the first, second, and third optical waveguides are channel waveguides formed on a waveguide substrate. 
     
     
       43. The apparatus of  claim 41 , wherein the first, second, and third optical waveguides are optical fibers. 
     
     
       44. The apparatus of  claim 35 , wherein the reflective routing means is formed on a portion of a surface of the optical element. 
     
     
       45. The apparatus of  claim 35 , wherein the reflective routing means is formed within the optical element. 
     
     
       46. The apparatus of  claim 35 , wherein the reflective routing means comprises an optical component separate from the optical element. 
     
     
       47. The apparatus of  claim 35 , wherein the reflective routing means is substantially achromatic over a designed spectral window for the apparatus. 
     
     
       48. The apparatus of  claim 35 , wherein the portion of the optical signal routed between the first and second optical ports is transmitted through the diffractive routing means twice. 
     
     
       49. An optical apparatus, comprising:
 diffractive means for routing, between a first optical port and a multiplexing optical port and according to a diffractive transfer function, a corresponding diffracted portion of an optical signal propagating within an optical element, the diffractive element means having a resonance frequency band f res ; and 
 achromatic reflective means for routing, between a first optical port and a second optical port, that portion having frequency bands f 1 , . . . f res−1 , f res+1  . . . f n  of the optical signal transmitted by the diffractive routing means, 
 wherein the reflective routing means acts as a focusing means, and the first and second optical ports are positioned at respective first and second conjugate image points of the focusing means, 
 
       and wherein:
 (a) diffractive elements of the diffractive means are collectively arranged so as to exhibit a positional variation in amplitude, optical separation, or spatial phase over some portion thereof, said positional variation determining at least in part the diffractive transfer function; 
 
       or
 (b) (1) diffractive elements of the diffractive means are each spatially arranged relative to a corresijonding corresponding diffractive element virtual contour and each comprise at least one diffracting region thereof, the diffracting regions having at least one altered optical property so as to enable diffraction of a portion of the incident optical field therefrom,
 (2) each diffractive element diffracts a corresponding diffracted component of an incident optical field with a corresponding diffractive element transfer function so that each diffractive element set collectively provides the diffractive transfer function between the multiplexing optical port and either the first or the second optical port, 
 
 
       and
   (3) the diffractive transfer function or at least one corresponding diffractive element transfer function is determined at least in part by: (A) a less-than-unity fill factor for the corresponding virtual contour, (B) a non-uniform spatial distribution of multiple diffracting regions along the corresponding virtual contour, (C) variation of a spatial profile of the optical property of at least one diffracting region of the corresponding virtual contour, (D) variation of a spatial profile of the optical property among multiple diffracting regions of the corresponding virtual contour, (E) variation of the spatial profile of the optical property of at least one diffracting region among elements of at least one diffractive element set, (F) longitudinal displacement of at least one diffractive element relative to the corresponding virtual contour, or (G) at least one virtual contour lacking a diffractive element corresponding thereto.   
 
     
     
       50. An optical apparatus, comprising:
 diffractive means for routing, between a first optical port and a multiplexing optical port and according to a diffractive transfer function, a corresponding diffracted portion of an optical signal propagating within an optical element, the diffractive element means having a resonance frequency band f res ; and 
 achromatic reflective means for routing, between a first optical port and a second optical port, that portion having frequency bands f 1 , . . . f res−1 , f res+1  . . . f n  of the optical signal transmitted by the diffractive routing means, 
 wherein the diffractive routing means acts as a focusing means, and the first and second optical ports are positioned at respective first and second conjugate image points of the focusing means, 
 
       and wherein:
 (a) diffractive elements of the diffractive means are collectively arranged so as to exhibit a positional variation in amplitude, optical separation, or spatial phase over some portion thereof, said positional variation determining at least in part the diffractive transfer function; 
 
       or
   (b) (1) diffractive elements of the diffractive means are each spatially arranged relative to a corresijonding corresponding diffractive element virtual contour and each comprise at least one diffracting region thereof, the diffracting regions having at least one altered optical property so as to enable diffraction of a portion of the incident optical field therefrom,   (2) each diffractive element diffracts a corresponding diffracted component of an incident optical field with a corresponding diffractive element transfer function so that each diffractive element set collectively provides the diffractive transfer function between the multiplexing optical port and either the first or the second optical port,   
 
       and
   (3) the diffractive transfer function or at least one corresponding diffractive element transfer function is determined at least in part by: (A) a less-than-unity fill factor for the corresponding virtual contour, (B) a non-uniform spatial distribution of multiple diffracting regions along the corresponding virtual contour, (C) variation of a spatial profile of the optical property of at least one diffracting region of the corresponding virtual contour, (D) variation of a spatial profile of the optical property among multiple diffracting regions of the corresponding virtual contour, (E) variation of the spatial profile of the optical property of at least one diffracting region among elements of at least one diffractive element set, (F) longitudinal displacement of at least one diffractive element relative to the corresponding virtual contour, or (G) at least one virtual contour lacking a diffractive element corresponding thereto.   
 
     
     
       51. The apparatus of  claim 35 , wherein the transmitted and diffracted portions of the optical signal differ spectrally. 
     
     
       52. The apparatus of  claim 51 , wherein the diffracted portion of the optical signal corresponds to at least one channel of an optical WDM system. 
     
     
       53. The apparatus of  claim 35 , further comprising multiple diffractive means for routing, between a corresponding one of multiple multiplexing optical ports and either the first or the second optical port, a corresponding portion of the optical signal propagating within the optical element; and
 the reflective routing means routes, between the first optical port and the second optical port, that portion of the optical signal transmitted by the multiple diffractive element sets. 
 
     
     
       54. The apparatus of  claim 53 , wherein at least two of the multiple diffractive means are overlaid. 
     
     
       55. The apparatus of  claim 53 , wherein at least two of the multiple diffractive means are stacked. 
     
     
       56. The apparatus of  claim 53 , wherein at least two of the multiple diffractive means are interleaved. 
     
     
       57. The apparatus of  claim 53 , further comprising multiple reflective means for routing, between a first optical port and a second optical port, that portion of the optical signal propagating within the optical element and transmitted by the multiple diffractive element sets. 
     
     
       58. The apparatus of  claim 57 , wherein, during routing between two of the multiple reflective means, a transverse spatial extent of the optical signal in a corresponding unconfined transverse dimension is larger than about two times its transverse spatial extent at the first optical port and larger than about two times its transverse spatial extent at the second optical port. 
     
     
       59. The apparatus of  claim 57 , wherein, during routing between two of the multiple reflective means, a transverse spatial extent of the optical signal in a corresponding unconfined transverse dimension is larger than about five times its transverse spatial extent at the first optical port and larger than about five times its transverse spatial extent at the second optical port. 
     
     
       60. The apparatus of  claim 35 , further comprising:
 multiple diffractive means for routing, between a corresponding first optical port and a corresponding multiplexing optical port, a corresponding diffracted portion of an optical signal propagating within a corresponding one of multiple optical elements; and 
 multiple corresponding reflective means for routing, between the corresponding first optical port and a corresponding second optical port, that portion of the optical signal transmitted by the corresponding diffractive element set, 
 wherein the multiple optical elements are arranged so that the corresponding first and second optical ports are coupled to optical ports of others of the first and second optical ports. 
 
     
     
       61. The apparatus of  claim 21 , wherein the optical element enables propagation of the optical signal in three dimensions. 
     
     
       62. The apparatus of  claim 23 , wherein the optical element enables propagation of the optical signal in three dimensions. 
     
     
       63. The apparatus of  claim 49 , wherein the optical element enables propagation of the optical signal in three dimensions. 
     
     
       64. The apparatus of  claim 50 , wherein the optical element enables propagation of the optical signal in three dimensions. 
     
     
       65. An optical apparatus, comprising:
 an optical element having at least one set of diffractive elements; and   an optical reflector having a reflective surface coating and spatially separated from said at least one set of diffractive elements,   wherein:
 the optical reflector is configured to route, between a first optical port and a second optical port, at least a first portion of an optical signal that propagates within the optical element; 
 each diffractive element set is configured to route, between at least a third optical port and either the first or the second optical ports, a second portion of the optical signal that is respectively diffracted by each diffractive element set according to a corresponding set transfer function; 
 the optical element includes a planar optical waveguide, the planar optical waveguide being configured to substantially to confine in one transverse dimension the optical signal propagating in two dimensions therein; and 
 (a) 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 at least one set, said positional variation determining at least in part the set transfer function; 
   or
 (b) (1) each diffractive element is spatially arranged relative to a corresponding diffractive element virtual contour and includes at least one diffracting region thereof, the diffracting regions having at least one altered optical property so as to enable diffraction of a portion of an incident optical field therefrom, 
 (2) each diffractive element diffracts a corresponding diffracted component of the incident optical field with a corresponding diffractive element transfer function so that each diffractive element set collectively provides the corresponding set transfer function between the at least the third optical port and either the first or the second optical ports, and 
 (3) the corresponding set transfer function or at least one corresponding diffractive element transfer function is determined at least in part by: (A) a less-than-unity fill factor for the corresponding virtual contour, (B) a non-uniform spatial distribution of multiple diffracting regions along the corresponding virtual contour, (C) variation of a spatial profile of the optical property of at least one diffracting region of the corresponding virtual contour, (D) variation of a spatial profile of the optical property among multiple diffracting regions of the corresponding virtual contour, (E) variation of the spatial profile of the optical property of at least one diffracting region among elements of one or more diffractive element sets, (F) longitudinal displacement of at least one diffractive element relative to the corresponding virtual contour, or (G) at least one virtual contour lacking a diffractive element corresponding thereto. 
   
     
     
       66. The optical apparatus of claim 65 wherein said at least the first portion of the optical signal routed by the optical reflector has been respectively transmitted by each diffractive element set. 
     
     
       67. The optical apparatus of claim 65 wherein the optical reflector includes a focusing reflector, and wherein the first and second optical ports are positioned at respective first and second conjugate image points of the focusing reflector. 
     
     
       68. The optical apparatus of claim 65 wherein the set of diffractive elements includes a set of focusing diffractive elements, and wherein said at least the third optical port and either the first or second optical ports are positioned at respective first and second conjugate image points of the set. 
     
     
       69. The optical apparatus of claim 65 wherein:
 the first optical port includes an input port;   the second optical port includes an output port; and   the at least the third port includes an added-channel port or a dropped-channel port.   
     
     
       70. A method of operating an optical apparatus having an optical element, at least one set of diffractive elements, and an optical reflector, the method comprising:
 receiving, by the optical element, an optical signal;   routing, by the optical reflector which has a reflective surface coating and which is spatially separated from said at least one set of diffractive elements, between a first optical port and a second optical port, at least a first portion of the optical signal that propagates within the optical element; and   routing, between at least a third optical port and either the first or the second optical ports, a second portion of the optical signal that is respectively diffracted by each diffractive element set according to a corresponding set transfer function,   wherein:
 the optical element includes a planar optical waveguide, the planar optical waveguide being configured to substantially to confine in one transverse dimension the optical signal propagating in two dimensions therein; and 
 (a) 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 at least one set, said positional variation determining at least in part the set transfer function; 
   or
 (b) (1) each diffractive element is spatially arranged relative to a corresponding diffractive element virtual contour and includes at least one diffracting region thereof, the diffracting regions having at least one altered optical property so as to enable diffraction of a portion of an incident optical field therefrom, 
 (2) each diffractive element diffracts a corresponding diffracted component of the incident optical field with a corresponding diffractive element transfer function so that each diffractive element set collectively provides the corresponding set transfer function between the at least the third optical port and either the first or the second optical ports, and 
 (3) the corresponding set transfer function or at least one corresponding diffractive element transfer function is determined at least in part by: (A) a less-than-unity fill factor for the corresponding virtual contour, (B) a non-uniform spatial distribution of multiple diffracting regions along the corresponding virtual contour, (C) variation of a spatial profile of the optical property of at least one diffracting region of the corresponding virtual contour, (D) variation of a spatial profile of the optical property among multiple diffracting regions of the corresponding virtual contour, (E) variation of the spatial profile of the optical property of at least one diffracting region among elements of one or more diffractive element sets, (F) longitudinal displacement of at least one diffractive element relative to the corresponding virtual contour, or (G) at least one virtual contour lacking a diffractive element corresponding thereto. 
   
     
     
       71. The method of claim 70 wherein said routing, between at least the third optical port and either the first or the second optical ports, is part of a channel-dropping operation. 
     
     
       72. The method of claim 70 wherein said routing, between at least the third optical port and either the first or the second optical ports, is part of a channel-adding operation. 
     
     
       73. The method of claim 70 wherein said at least the first portion of the optical signal routed by the optical reflector has been respectively transmitted by each diffractive element set.