Optical structures distributed among multiple optical waveguides

1. A method, comprising:

receiving into an optical element an input optical signal via a first optical port; and

transmitting a back-diffracted portion of the input optical signal out of the optical element via a second optical port,

wherein:

the optical element has formed therein at least one set of diffractive elements and at least two channel optical waveguides, each channel optical waveguide having a corresponding first end and substantially confining in two transverse spatial dimensions an optical signal propagating therein;

diffractive elements of each set of diffractive elements are distributed among diffractive element subsets corresponding to each of at least two of the channel waveguides;

each diffractive element set routes, between a corresponding pair of optical ports, those corresponding portions of an optical signal propagating within the optical element that are received by at least two of the channel waveguides and back-diffracted within the receiving channel waveguides by corresponding diffractive element subsets;

the channel optical waveguides are arranged so that an optical signal entering the optical element at an input optical port first propagates through a region of the optical element between the input optical port and the first ends of the channel waveguides and is then incident on and received at least in part by the corresponding first ends of at least two of the channel optical waveguides;

the channel optical waveguides are arranged so that the corresponding routed portions of optical signal exiting the optical element at an output optical port first propagate through a region of the optical element between the first ends of the channel waveguides and the output optical port; and

the back-diffracted portion of the input optical signal is routed by a corresponding set of the diffractive elements between the first and second optical ports.

2. The method of claim 1 , wherein relative spatial arrangement of the first ends of the channel waveguides and corresponding relative phase shifts imparted on back-diffracted portions of the optical signal in the channel waveguides define at least in part a relative spatial arrangement of the corresponding pair of optical ports.

3. The method of claim 2 , further comprising transmitting a transmitted portion of the input optical signal out of the optical element via a third optical port, wherein:

at least two of the channel waveguides route, between another corresponding pair of optical ports, those corresponding portions of an optical signal propagating within the optical element that are received by at least two of the channel waveguides, substantially transmitted by the diffractive element set, and emitted from corresponding second ends of the routing channel waveguides;

relative spatial arrangement of the first ends of the channel waveguides, relative spatial arrangement of the second ends of the channel waveguides, and corresponding relative phase shifts imparted on transmitted portions of the optical signal by the channel waveguides define at least in part a relative spatial arrangement of the other corresponding pair of optical ports; and

the transmitted portion of the input optical signal is routed by at least two of the channel waveguides between the first and third optical ports.

4. The method of claim 1 , wherein regions of the optical element between optical ports and the first ends of the channel waveguides comprise at least one slab optical waveguide, the slab waveguide substantially confining in one transverse spatial dimension an optical signal propagating in two dimensions therein.

5. The method of claim 1 , wherein an optical signals propagate in three dimensions in regions of the optical element between optical ports and the first ends of the channel waveguides.

6. The method of claim 1 , wherein the diffractive element set imparts spectral characteristics or temporal characteristics onto the corresponding back-diffracted portions of the optical signal, thereby determining at least in part spectral characteristics or temporal characteristics of the routed portion of the optical signal.

7. The method of claim 1 , wherein the optical element further comprises multiple diffractive element sets, diffractive elements of each set of diffractive elements being distributed among diffractive element subsets corresponding to each of at least two of the channel waveguides, each diffractive element set imparting spectral characteristics or temporal characteristics onto the corresponding back-diffracted portions of the optical signal, thereby determining at least in part spectral characteristics or temporal characteristics of the corresponding routed portions of the optical signal.

8. The method of claim 1 , wherein routing of the back-diffracted portions of the optical signal exhibits a designed dependence on polarization of the optical signal.

9. The method of claim 1 , wherein routing of the back-diffracted portions of the optical signal exhibits a designed dependence on temperature of the optical element over an operating temperature range.

10. The method of claim 1 , wherein routing of the back-diffracted portions of the optical signal includes conjugate-ratio imaging of one of the corresponding pair of optical ports onto the other of the corresponding pair of optical ports.

11. The method of claim 1 , wherein routing of the back-diffracted portions of the optical signal includes propagation between the ends of the channel waveguides and at least one of the corresponding pair of optical ports as an optical mode substantially collimated in an unconfined transverse dimension.

12. The method of claim 1 , further comprising receiving the back-diffracted portion of the input optical signal via an input optical port into a second similar optical element having formed therein at least one set o diffractive elements and at least two channel optical waveguides, wherein the second optical port of the first optical element serves as an input optical source for the input optical port of the second optical element.