Etched surface grating having an effective blaze angle

1. An optical apparatus comprising a set of diffractive elements on a substrate that are arranged: (i) to receive at least a portion of an input optical signal propagating from an input optical port as a diffraction-guided optical beam, (ii) to diffract a portion of the received input optical signal as an output optical signal, and (iii) to route the output optical signal to propagate to an output optical port as a diffraction-guided optical beam, wherein:

each diffractive element comprises at least one trench between ribs projecting from the substrate surface;

at least one side surface of each trench is substantially perpendicular to the bottom surface of that trench, so that the diffractive element set formed on the substrate exhibits relatively enhanced diffraction efficiency near a Littrow arrangement of the input and output optical ports relative to the substrate; and

the depth of at least one trench is equal to about half of its width divided by the tangent of a selected Littrow angle of incidence.

2. The apparatus of claim 1 wherein the side surfaces of each trench are substantially perpendicular to the substrate surface and the bottom surface of each trench is substantially parallel to the substrate surface.

3. The apparatus of claim 1 wherein the diffractive elements are further arranged to exhibit a positional variation in diffractive amplitude, optical separation, or spatial phase over some portion of the set.

4. The apparatus of claim 3 wherein the diffractive elements of the set are arranged on the substrate according to an interference pattern derived from computed interference at a surface of the substrate between a simulated design input optical signal and a simulated design output optical signal, the interference pattern exhibiting said positional variation.

5. The apparatus of claim 1 wherein all the trenches have substantially the same depth.

6. The apparatus of claim 5 wherein the arrangement of the diffractive elements includes selected relative widths of each trench and an adjacent rib, the relative widths at least in part determining diffractive amplitude of each diffractive element.

7. The apparatus of claim 1 wherein the arrangement of the diffractive elements includes selected relative widths of each trench and an adjacent rib and selected depths of each trench, the height and relative widths at least in part determining diffractive strength of each diffractive element.

8. The apparatus of claim 1 wherein the substrate surface is substantially planar.

9. The apparatus of claim 1 wherein the substrate surface or the diffractive element set is reflective over a desired operational wavelength range, the diffractive elements and the substrate thereby comprising a reflective surface grating.

10. The apparatus of claim 9 further comprising a coating formed over the diffractive element set and the substrate surface so as to impart reflectivity over the desired operational wavelength range.

11. The apparatus of claim 1 wherein the substrate or the diffractive element set is substantially transparent over a desired operational wavelength range, the diffractive elements and substrate thereby comprising a transmissive surface grating.

12. The apparatus of claim 11 further comprising a coating formed over the diffractive elements that is substantially transparent over the desired operational wavelength range.

13. An optical spectrometer incorporating the apparatus of claim 1 , the spectrometer further comprising:

an input optical port for receiving an input optical signal into the spectrometer; and

an output optical port for transmitting an output optical signal out of the spectrometer.

14. An optical apparatus comprising a set of diffractive elements on a substrate that are arranged: (i) to receive at least a portion of an input optical signal propagating from an input optical port as a diffraction-guided optical beam, (ii) to diffract a portion of the received input optical signal as an output optical signal, and (iii) to route the output optical signal to propagate to an output optical port as a diffraction-guided optical beam, wherein:

each diffractive element comprises at least one trench between ribs projecting from the substrate surface; and

at least one side surface of each trench and the bottom surface of that trench are arranged so as to successively reflect, from the side surface and then the bottom surface or from the bottom surface and then the side surface, a portion of the input optical signal preferentially in a selected output direction, so that the diffractive element set formed on the substrate exhibits relatively enhanced diffraction efficiency in the selected output direction.

15. The apparatus of claim 14 wherein at least one side surface of each trench is substantially perpendicular to the bottom surface of each trench, so that the selected output direction is substantially anti-parallel to the propagation direction of the input optical signal.

16. The apparatus of claim 14 wherein the side surfaces of each trench are substantially perpendicular to the substrate surface and the bottom surface of each trench is substantially parallel to the substrate surface, so that the selected output direction is substantially anti-parallel to the propagation direction of the input optical signal.

17. The apparatus of claim 14 wherein the diffractive elements are further arranged to exhibit a positional variation in diffractive amplitude, optical separation, or spatial phase over some portion of the set.

18. The apparatus of claim 17 wherein the diffractive elements of the set are arranged on the substrate according to an interference pattern derived from computed interference at a surface of the substrate between a simulated design input optical signal and a simulated design output optical signal, the interference pattern exhibiting said positional variation.

19. The apparatus of claim 14 wherein all the trenches have substantially the same depth.

20. The apparatus of claim 19 wherein the arrangement of the diffractive elements includes selected relative widths of each trench and an adjacent rib, the relative widths at least in part determining diffractive amplitude of each diffractive element.

21. The apparatus of claim 14 wherein the arrangement of the diffractive elements includes selected relative widths of each trench and an adjacent rib and selected depths of each trench, the height and relative widths at least in part determining diffractive strength of each diffractive element.

22. The apparatus of claim 14 wherein the substrate surface is substantially planar.

23. The apparatus of claim 14 wherein the substrate surface or the diffractive element set is reflective over a desired operational wavelength range, the diffractive elements and the substrate thereby comprising a reflective surface grating.

24. The apparatus of claim 23 further comprising a coating formed over the diffractive element set and the substrate surface so as to impart reflectivity over the desired operational wavelength range.

25. The apparatus of claim 14 wherein the substrate or the diffractive element set is substantially transparent over a desired operational wavelength range, the diffractive elements and substrate thereby comprising a transmissive surface grating.

26. The apparatus of claim 25 further comprising a coating formed over the diffractive elements that is substantially transparent over the desired operational wavelength range.

27. An optical spectrometer incorporating the apparatus of claim 14 , the spectrometer further comprising:

an input optical port for receiving an input optical signal into the spectrometer; and

an output optical port for transmitting an output optical signal out of the spectrometer.