CPC G02B 5/1814 (2013.01) [G02B 5/1823 (2013.01); G02B 5/1847 (2013.01); G02B 27/0172 (2013.01); G02B 27/4294 (2013.01)] | 15 Claims |
1. A two-dimensional waveguide comprising:
a stack of diffractive gratings, at least one of the diffractive gratings being arranged on a surface or within a waveguide, each diffractive grating comprising in a periodic alternating pattern formed into:
a first material having a first refractive index defining a first dispersion curve,
a second material having a second refractive index defining a second dispersion curve different from the first dispersion curve, wherein
said first and second dispersion curves intersect each other at two or more different intersection wavelengths, wherein each intersection wavelength is for a wavelength for which said first material and second material have the same refractive index,
wherein at least one of the intersection wavelengths of each grating are different from each other,
wherein the intersection wavelengths of the stack of gratings are adapted so that each grating has one intersection wavelength in common with one intersection wavelength of each other grating of the stack.
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