Apparatus for transforming the aspect ratio of an optical input field based on stacked waveguides
An apparatus consisting of stacked slab waveguides whose outputs are vertically staggered is disclosed. At the input to the stacked waveguides, the entrances to each slab lie in approximately the same vertical plane. A spot which is imaged onto the input will be transformed approximately to a set of staggered rectangles at the output, without substantial loss in brightness, which staggered rectangles can serve as a convenient input to a spectroscopic apparatus. A slit mask can be added to spatially filter the outputs so as to present the desired transverse width in the plane of the spectroscopic apparatus parallel to its dispersion.
1. An apparatus for converting a shape of an optical input to a differently shaped optical output, comprising:
at least two stacked slab waveguides wherein a location light is input along a portion of one side of each of the waveguides is distinct from a location light is output from one side of each of the waveguides;
wherein there is a geometrical difference between each waveguide such that the location light is output from each of the waveguides is displaced in at least two directions with respect to each other waveguide, or the location light is input to each of the waveguides is displaced in at least two directions with respect to each other waveguide;
wherein an aggregate shape of the locations light is input to the waveguides corresponds approximately to the shape of the optical input; and
wherein an aggregate shape of the locations light is output from the waveguides corresponds approximately to a desired shape of optical output, wherein the desired shape of the optical output is different from the shape of the optical input.
2. The apparatus of claim 1 , wherein the volume of any of the slab waveguides is the volume traversed by translating a quadrilateral in a direction perpendicular to the plane of the quadrilateral.
3. The apparatus of claim 2 , wherein the quadrilateral is a parallelogram.
4. The apparatus of claim 2 , wherein two of the angles between respective adjacent edges in the plane of the quadrilateral are substantially 450.
5. The apparatus of claim 4 , wherein the at least two slab waveguides are rhomboids, each having a different long dimension.
6. The apparatus of claim 2 , where at least one side perpendicular to the plane of the quadrilateral is a mirror.
7. The apparatus of claim 6 , wherein at least some light propagating in the waveguide undergoes total internal reflection at the mirror.
8. The apparatus of claim 2 , wherein the locations light is input and output of the waveguides are antireflection coated.
9. The apparatus of claim 8 , wherein the coating of the locations light is input and output of the waveguides extends substantially along an entire length of those sides and acts as a waveguide cladding in areas distinct from the locations light is input and output.
10. The apparatus of claim 9 , wherein the coating has a thickness substantially of ¼ wavelength plus an integral number of half wavelengths of the input light in an index of the coating material.
11. The apparatus of claim 1 , wherein a guiding material of the waveguides is glass with an index greater than 1.80.
12. The apparatus of claim 1 , wherein an aggregate area of the locations light is output from the waveguides is further restricted by a mask.
13. The apparatus of claim 1 , wherein the outputs from the waveguide are curved so as to compensate for a curvature of constant wavelength contours in a spectrometer to which the apparatus inputs light.
14. The apparatus of claim 1 , wherein one or more sides of the slab waveguides are curved, wherein a form of the curvatures differs between waveguides so as to produce a displacement either in the location light is output from each of the waveguides with respect to each other, or in the location light is input from each of the waveguides with respect to each other.
15. The apparatus of claim 1 , wherein the shape of the optical input is nominally circular, and the desired shape of the optical output is a staggered set of nominally rectangular outputs from the waveguides.
16. The apparatus of claim 1 , wherein the ratio of the aspect ratio of the optical input to the aspect ratio of the optical output is less than 0.5.
17. The apparatus of claim 1 , wherein the ratio of the aspect ratio of the optical input to the aspect ratio of the optical output is greater than 2.0.