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 for dispersing a light beam into narrowband sub-beams in a plane of dispersion and for focusing the narrowband sub-beams into focal spots in a focal plane, the wavelength dispersing device comprising:
an input port for inputting the light beam;
a folding mirror for folding optical paths of the light beam and of the narrowband sub-beams;
a dispersive unit for dispersing the light beam into the narrowband sub-beams in the plane of dispersion; and
a concave mirror for focusing the narrowband sub-beams into the focal spots in the focal plane,
the light beam being received at the folding mirror at a first point in time,
the light beam being reflected from the folding mirror to the dispersive unit that disperses the light beam into the narrowband sub-beams that are reflected, at a second point in time, to the folding mirror,
the narrowband sub-beams being reflected, at a third point in time, from the folding mirror to the concave mirror for focusing the narrowband sub-beams,
the narrowband sub-beams being reflected, at a fourth point in time, from the concave mirror back to the folding mirror, and
the narrowband sub-beams being reflected, at a fifth point in time, from the folding mirror to the focal plane,
wherein the narrowband sub-beams are focused into the focal spots.
2. The wavelength dispersing device of claim 1 , wherein the folding mirror has a flat reflective surface.
3. The wavelength dispersing device of claim 2 , wherein the flat reflective surface is a dielectric reflector.
4. The wavelength dispersing device of claim 1 , wherein
an input port of a wavelength selective optical switch module is the input port of the wavelength dispersing device,
the narrowband sub-beams carry individual wavelength channels, and
an array of directors are disposed along a line of dispersion.
5. The wavelength dispersing device of claim 1 , further including:
a lens, located between the input port and the folding mirror, for refracting the light beam.
6. The wavelength dispersing device of claim 5 , further including:
another lens, located between the lens and the folding mirror, for further refracting the light beam.
7. The wavelength dispersing device of claim 1 , wherein each narrowband sub-beam, of the narrowband sub-beams, is focused on a respective focal spot of the focal spots.
8. A device comprising:
a folding mirror;
a dispersive unit for dispersing a light beam into a narrowband sub-beams in a plane of dispersion;
a concave mirror for focusing the narrowband sub-beams into focal spots in a focal plane,
the light beam being received at the folding mirror at a first point in time,
the light beam being reflected from the folding mirror to the dispersive unit that disperses the light beam into the narrowband sub-beams that are reflected, at a second point in time, to the folding mirror,
the narrowband sub-beams being reflected, at a third point in time, from the folding mirror to the concave mirror for focusing the narrowband sub-beams, and
the narrowband sub-beams being reflected, at a fourth point in time, from the concave mirror back to the folding mirror; and
a director, including a focal plane, for receiving the narrowband sub-beams at a fifth point in time.
9. The device of claim 8 , wherein the folding mirror has a flat reflective surface.
10. The device of claim 9 , wherein the flat reflective surface is a dielectric reflector.
11. The device of claim 8 , wherein
an input port of a wavelength selective optical switch module is an input port of the device,
the narrowband sub-beams carry individual wavelength channels, and
an array of directors are disposed along a line of dispersion.
12. The device of claim 11 , further including:
a lens, located between the input port and the folding mirror, for refracting the light beam.
13. The device of claim 12 , further including:
another lens, located between the lens and the folding mirror, for further refracting the light beam.
14. The device of claim 8 , wherein each narrowband sub-beam, of the narrowband sub-beams, is focused on a respective focal spot of the focal spots.
15. A method comprising:
inputting, using an input port, a light beam;
folding, using a folding mirror, optical paths of the light beam and of narrowband sub-beams;
dispersing, using a dispersive unit, the light beam into the narrowband sub-beams in a plane of dispersion; and
focusing, using a concave mirror, the narrowband sub-beams into focal spots in a focal plane,
the light beam being received at the folding mirror at a first point in time,
the light beam being reflected from the folding mirror to the dispersive unit that disperses, at a second point in time, the light beam into the narrowband sub-beams that are reflected to the folding mirror,
the narrowband sub-beams being reflected, at a third point in time, from the folding mirror to the concave mirror for focusing the narrowband sub-beams,
the narrowband sub-beams being reflected, at a fourth point in time, from the concave mirror back to the folding mirror, and
the narrowband sub-beams being reflected, at a fifth point in time, from the folding mirror to the focal plane,
wherein the narrowband sub-beams are focused into the focal spots.
16. The method of claim 15 , wherein the folding mirror has a flat reflective surface.
17. The method of claim 15 , wherein
the narrowband sub-beams carry individual wavelength channels, and
an array of directors are disposed along a line of dispersion.
18. The method of claim 15 , further including:
refracting, using a lens located between the input port and the folding mirror, the light beam.
19. The method of claim 18 , further including:
further refracting, using another lens located between the lens and the folding mirror, the light beam.
20. The method of claim 15 , wherein each narrowband sub-beam, of the narrowband sub-beams, is focused on a respective focal spot of the focal spots.