Planar lightwave circuit based wavelength selective switch
View Patent ↗The present invention extends the concept of a standard array waveguide grating (AWG), which focuses each wavelength component launched via an input AWG to a Rowland circle inside a planar lightwave chip (PLC) where discrete waveguides are located, to one which focuses each wavelength component outside of the PLC chip along a straight line. An array of MEMS mirrors or other redirecting elements is positioned at the focus location for independently redirecting each of the wavelength channels back to any number of selected output AWGs formed on the same PLC chip as the input AWG.
1. A wavelength dispersive device comprising:
a first planar lightwave circuit (PLC) chip comprising:
an input port for launching an input optical signal including a plurality of wavelength channels;
an input arrayed waveguide grating (AWG) structure for dispersing the plurality of wavelength channels including: an input slab waveguide region optically coupled to the input port, a first array of channel waveguides, extending from the input slab waveguide region, and an input/output slab waveguide region for guiding the dispersed wavelength channels between the first array of channel waveguides and a first edge of the first PLC chip, wherein an interface between the first array of channel waveguides and the input/output slab waveguide region is curved providing optical power, which focuses the wavelength channels along a curved focal plane outside of the PLC chip;
a first plurality of output AWG structures for combining selected wavelength channels into output optical signals, each output AWG structure including: the input/output slab waveguide region for guiding the dispersed wavelength channels from the first edge of the first PLC chip; a second array of channel waveguides extending from the input/output slab waveguide region, and a first output slab waveguide region for guiding the output optical signals between the second array of channel waveguides to a second edge of the PLC chip, wherein an interface between the second array of channel waveguides and the input/output slab waveguide region is curved providing optical power; and
a first plurality of output ports for outputting the output optical signals;
a first array of switching elements for independently redirecting each of the wavelength channels from the first input optical signal to selected first output arrayed waveguide grating structures forming the output optical signals for output respective first output ports; and
a field lens between the first edge of the PLC chip and the first array of switching elements for changing the focal plane of the wavelength channels from the curved line to along a straight line defining the first array of switching elements.
2. The device according to claim 1 , wherein spherical aberrations coming from the field lens are opposite in sign from the interface between the PLC chip and the free space.
3. The device according to claim 1 , wherein the interface between the first array of channel waveguides and the input/output slab waveguide region is conical to improve optical coupling between input and output AWG structures.
4. The device according to claim 1 , wherein all adjacent channel waveguides in the first array of channel waveguides have a constant delay therebetween.
5. The device according to claim 1 , wherein refraction through the edge of the PLC chip creates a virtual pupil at a distance D/n from the first edge, where n is the effective slab index for the input/output slab waveguide region, and D is a distance from the first edge to the interface; and wherein the field lens is disposed, such that the virtual pupil appears in a front focal plane of the field lens.
6. The device according to claim 1 , wherein the input slab waveguide region includes periodically segmented slab segments, which have a duty cycle of substantially one at one end, and a duty cycle between 0 and 1 at another end, which depends on a difference of index contrast between the PLC chip and a waveguide optically coupled to the input slab waveguide region.
7. The device according to claim 1 , wherein each of the output slab waveguide regions includes periodically segmented slab segments, which have a duty cycle of substantially one at a first end, and a duty cycle between 0 and 1 at a second end, which depends on a difference of index contrast between the PLC chip and a waveguide optically coupled to the input slab waveguide region for reducing a numerical aperture of light exiting the output slab waveguide regions.
8. The device according to claim 7 , wherein the duty cycle is between 0.1 to 0.9 at the second end.
9. The device according to claim 7 , wherein the duty cycle is between 0.25 to 0.75 at the second end.
10. The device according to claim 1 , wherein the first array of switching elements comprises a fixed mirror for reflecting a first optical signal to one of the first plurality of output AWG structures, and a moveable element for redirecting a second optical signal to another one of the first plurality of output AWGs.
11. The device according to claim 10 , wherein the moveable element is reciprocatable in a first direction; and wherein the moveable element has a face with a variable width for tuning a passband of the second optical signal during reciprocation in the first direction.
12. The device according to claim 11 , wherein the moveable element is reciprocatable in a second direction for tuning a center wavelength of the second optical signal.
13. The device according to claim 10 , wherein the moveable element comprises a prism with non-parallel front and rear faces for redirecting the second optical signal.
14. The device according to claim 13 , wherein the prism is an asymmetric pyramid for refracting wavelength channels off of the fixed mirror and back therethrough.
15. The device according to claim 14 , wherein the asymmetric pyramid is reciprocatable in a first direction; and wherein the asymmetric pyramid has a face with a variable width for tuning a passband of the second optical signal during reciprocation in the first direction.
16. The device according to claim 15 , wherein the moveable element is reciprocatable in a second direction for tuning a center wavelength of the second optical signal.