Wavelength dispersing device
View Patent ↗A compact wavelength dispersing device and a wavelength selective optical switch based on the wavelength dispersing device is described. The wavelength dispersing device has a folding mirror that folds the optical path at least three times. A focal length of a focusing coupler of the device is reduced and the NA is increased, while the increased optical aberrations are mitigated by using an optional coma-compensating wedge. A double-pass arrangement for a transmission diffraction grating allows further focal length and overall size reduction due to increased angular dispersion.
1. A wavelength dispersing device comprising:
an input for inputting a light beam;
an aberration correction element for receiving the light beam and performing pre-correction for aberration;
a mirror for receiving the pre-corrected light beam and reflecting the pre-corrected light beam at a first point in time;
a diffraction grating for producing narrowband sub-beams; and
a reflector for receiving the narrowband sub-beams;
the narrowband sub-beams being reflected by the mirror at a second point in time,
the aberration correction element receiving the reflected narrowband sub-beams, performing aberration correction on the reflected narrowband sub-beams, and transmitting the aberration-corrected, reflected narrowband sub-beams to a line of dispersion, and
the aberration correction element having a wedge angle to apply coma compensation to the light beam and the reflected narrowband sub-beams to compensate for coma caused, at least in part, by the reflection of the pre-corrected light beam by the mirror.
2. The wavelength dispersing device of claim 1 , where the reflector and the diffraction grating produce an angular dispersion of the narrowband sub-beams.
3. The wavelength dispersing device of claim 1 , where
each narrowband sub-beam, of the narrowband sub-beams, is associated with a focal spot, and
each focal spot is located on the line of dispersion.
4. The wavelength dispersing device of claim 1 , where the mirror is a concave mirror.
5. The wavelength dispersing device of claim 1 , where the aberration correction element is a wedge.
6. The wavelength dispersing device of claim 5 , where the wedge is oriented at a minimum deviation angle for the narrowband sub-beams.
7. The wavelength dispersing device of claim 1 , where the coma is further caused by off-axis reflections of the pre-corrected light beam.
8. The wavelength dispersing device of claim 1 , where the coma is further caused by off-axis reflections of the pre-corrected light beam and the narrowband sub-beams from the mirror.
9. The wavelength dispersing device of claim 1 , where an array of directors are disposed along the line of dispersion.
10. A method comprising:
inputting, at an input, a light beam;
performing, by an aberration correction element, pre-correction for aberration on the light beam;
receiving, by a mirror, the pre-corrected light beam and reflecting the pre-corrected light beam at a first point in time;
producing, by a diffraction grating and based on received the reflected light beam, narrowband sub-beams;
the narrowband sub-beams being reflected by the mirror at a second point in time;
receiving, by the aberration correction element, the reflected narrowband sub-beams;
performing, by the aberration correction element, aberration correction on the reflected narrowband sub-beams,
the aberration correction element having a wedge angle to apply coma compensation to the light beam and the reflected narrowband sub-beams to compensate for coma caused, at least in part, by the reflection of the pre-corrected light beam by the mirror; and
transmitting, by the aberration correction element, the aberration-corrected, reflected narrowband sub-beams to a line of dispersion.
11. The method of claim 10 , further comprising:
producing, by a reflector and the diffraction grating, an angular dispersion of the narrowband sub-beams.
12. The method of claim 10 , where
each narrowband sub-beam, of the narrowband sub-beams, is associated with a focal spot, and
each focal spot is located on the line of dispersion.
13. The method of claim 10 , where the mirror is a concave mirror.
14. The method of claim 10 , where the aberration correction element is a wedge.
15. The method of claim 14 , where the wedge is oriented at a minimum deviation angle for the narrowband sub-beams.
16. The method of claim 10 , where the coma is further caused by off-axis reflections of the pre-corrected light beam.
17. The method of claim 10 , where the coma is further caused by off-axis reflections of the pre-corrected light beam and the narrowband sub-beams from the mirror.
18. The method of claim 10 , where an array of directors are disposed along the line of dispersion.