Transmission gratings designed by computed interference between simulated optical signals and fabricated by reduction lithography
View Patent ↗A method comprises computing an interference pattern between a simulated design input optical signal and a simulated design output optical signal, and computationally deriving an arrangement of at least one diffractive element set from the computed interference pattern. The interference pattern is computed in a transmission grating region, with the input and output optical signals each propagating through the transmission grating region as substantially unconfined optical beams. The arrangement of diffractive element set is computationally derived so that when the diffractive element set thus arranged is formed in or on a transmission grating, each diffractive element set would route, between corresponding input and output optical ports, a corresponding diffracted portion of an input optical signal incident on and transmitted by the transmission grating. The method can further comprise forming the set of diffractive elements in or on the transmission grating according to the derived arrangement.
1. An optical apparatus, comprising an optical transmission diffraction grating having at least one set of diffractive elements, wherein:
the diffractive elements of the set are arranged on the transmission grating relative to corresponding two-dimensional contours computationally derived from a spatial interference pattern resulting from interference, computed at a two-dimensional grating surface, between a simulated design input optical signal and a simulated design output optical signal, wherein both of the simulated design input and output optical signals comprise free-space-propagating optical beams that differ from one another with respect to wavefront curvature at the grating surface; and
the diffractive elements of the set are configured so as to result in a diffractive amplitude spatial distribution substantially corresponding to a computationally derived, two-dimensional, design diffractive amplitude spatial distribution.
2. The apparatus of claim 1 , wherein the diffractive elements of the set are arranged on the transmission grating so as to route, between corresponding input and output optical ports, a corresponding diffracted free-space-propagating portion of a free-space-propagating input optical signal that is incident on and transmitted by the transmission grating and that is diffracted by the diffractive element set.
3. The apparatus of claim 1 , wherein the diffractive element set comprises a surface relief structure.
4. The apparatus of claim 1 , wherein diffractive elements of the set comprise exactly two levels of refractive index modulation.
5. The apparatus of claim 1 , wherein diffractive elements of the set comprise more than two levels of refractive index modulation.
6. The apparatus of claim 1 , wherein diffractive elements of the set comprise a set of spaced-apart non-transmissive filaments.
7. The apparatus of claim 1 , wherein the diffractive element set is arranged so as to exhibit a wavelength dependent propagation direction of an output optical signal.
8. The apparatus of claim 1 , wherein the transmission grating is substantially flat, and the diffractive element set is arranged so that the respective wavefronts of corresponding free-space-propagating input and output optical signals exhibit differing convergence, divergence, or collimation properties.
9. The apparatus of claim 8 , wherein the diffractive element set comprises a surface relief structure.
10. The apparatus of claim 1 , wherein the diffractive elements exhibit a spatially varying spacing between adjacent elements.
11. The apparatus of claim 1 , wherein the diffractive element set exhibits a spatially varying diffractive amplitude distribution.
12. The apparatus of claim 11 , wherein the diffractive element set comprises a surface relief structure.
13. The apparatus of claim 2 , wherein:
the transmission grating has a second set of diffractive elements;
the diffractive elements of the second set are arranged on the transmission grating relative to corresponding two-dimensional contours computationally derived from a spatial interference pattern resulting from interference, computed at a two-dimensional grating surface, between the simulated design input optical signal and a second simulated design output optical signal or between a second simulated design input optical signal and the simulated design output optical signal, wherein both of the second simulated design input and output optical signals comprise free-space-propagating optical beams, and wherein the second simulated design input optical signal differs from the design output optical signal or the second simulated design output optical signal differs from the design input optical signal with respect to wavefront curvature at the grating surface; and
the diffractive elements of the set are arranged on the transmission grating so that a second diffracted free-space-propagating portion of the input optical signal is routed between the input optical port and a second output optical port, or a diffracted free-space-propagating portion of a second input optical signal is routed between a second input optical port and the output optical port.
14. The apparatus of claim 13 , wherein the corresponding contours of the first and second diffractive element sets are spatially coherent so as to result in a designed phase relationship among the first and second input optical signals and the output optical signal or among the input optical signal and the first and second output optical signals.
15. The apparatus of claim 13 , wherein the diffractive element sets each comprise a surface relief structure.
16. The apparatus of claim 1 , wherein the contours are computationally derived at least in part from a phase function of an interferogram of the interference pattern.
17. The apparatus of claim 16 , wherein the arrangement of the diffractive elements of the set is derived from a spatially-invariant diffractive amplitude spatial distribution.
18. The apparatus of claim 16 , wherein each diffractive element of the set is arranged with respect to a corresponding constant-phase-difference contour of the phase function of the interferogram.
19. The apparatus of claim 16 , wherein the contours are derived from a spatially-varying diffractive amplitude spatial distribution.
20. The apparatus of claim 19 , wherein the diffractive amplitude spatial distribution is proportional to a magnitude of the simulated design input optical signal, to a magnitude of the simulated design output optical signal, or to a product of the magnitudes of the design input and output optical signals.
21. The apparatus of claim 19 , wherein the diffractive amplitude spatial distribution is arranged so as to yield a desired spatial transformation upon routing a diffracted portion of an input optical signal as an output optical signal.
22. The apparatus of claim 19 , wherein the diffractive amplitude spatial distribution is arranged so as to yield a desired spectral or temporal transformation upon routing a diffracted portion of an input optical signal as an output optical signal.
23. The apparatus of claim 1 , wherein each of the simulated design input and output optical signals comprises a continuous-wave optical signal.
24. An optical apparatus, comprising an optical transmission diffraction grating having at least two sets of diffractive elements, wherein:
the diffractive elements of a first set are arranged on the transmission grating relative to corresponding two-dimensional contours computationally derived from a spatial interference pattern resulting from interference, computed at a two-dimensional grating surface, between a first simulated design input optical signal and a first simulated design output optical signal, wherein both of the simulated design input and output optical signals comprise free-space-propagating optical beams that differ from one another with respect to wavefront curvature at the grating surface; and
the diffractive elements of a second set are arranged on the transmission grating relative to corresponding two-dimensional contours computationally derived from a spatial interference pattern resulting from interference, computed at a two-dimensional grating surface, between the first simulated design input optical signal and a second simulated design output optical signal or between a second simulated design input optical signal and the first simulated design output optical signal, wherein both of the second simulated design input and output optical signals comprise free-space-propagating optical beams, and wherein the second simulated design input optical signal differs from the first design output optical signal or the second simulated design output optical signal differs from the first design input optical signal with respect to wavefront curvature at the grating surface.
25. The apparatus of claim 24 , wherein:
the diffractive elements of the first set are arranged on the transmission grating so as to route, between corresponding input and output optical ports, a corresponding diffracted free-space-propagating portion of an input optical signal that is incident on and transmitted by the transmission grating and that is diffracted by the first diffractive element set; and
the diffractive elements of the second set are arranged on the transmission grating so that a second diffracted free-space-propagating portion of the input optical signal is routed between the input optical port and a second output optical port, or a diffracted free-space-propagating portion of a second input optical signal is routed between a second input optical port and the output optical port.
26. The apparatus of claim 24 , wherein the corresponding contours of the first and second diffractive element sets are spatially coherent so as to result in a designed phase relationship among first and second input optical signals and an output optical signal or among an input optical signal and first and second output optical signals.
27. The apparatus of claim 24 , wherein the first and second diffractive element sets each comprise a surface relief structure.
28. The apparatus of claim 24 , wherein each of the simulated design input and output optical signals comprises a continuous-wave optical signal.