Calibration system for a wavelength selective switch
Described herein is a calibration system ( 25 ) for a wavelength selective switch ( 1 ). The switch ( 1 ) is adapted for dynamically switching optical beams ( 5, 7 ) along respective trajectories between input and output ports disposed in an array ( 3 ) using a reconfigurable Liquid crystal on silicon (LCOS) spatial light modulator device ( 17 ). The calibration system ( 25 ) includes a monitor ( 27 ) for projecting an optical monitor beam ( 29 ) through at least a portion of the switch ( 1 ) onto the LCOS ( 17 ) and detecting the monitor beam ( 29 ) reflected from the LCOS ( 17 ). In response, system ( 25 ) provides a calibration signal ( 33 ) to an active correction unit ( 35 ) for applying a correction to one or more of the trajectories while maintaining a constant switching state in the LCOS ( 17 ).
1. An optical system including:
one or more input ports for projecting input optical beams into the system;
a spatial light modulator including a plurality of cells, each cell being independently electrically drivable at one of a number of predefined states for, in conjunction with other cells, diffracting the optical beams into at least a zero diffraction order and a higher diffraction order and selectively steering the diffraction orders along predetermined trajectories;
a diffractive grism for dispersing the optical beams,
a temperature controller for controlling the temperature of the grism;
a monitor for detecting the trajectory of one or more diffraction orders; and
one or more output ports for receiving predetermined diffraction orders.
2. An optical system according to claim 1 wherein the spatial light modulator is responsive to a monitor signal issued by the monitor for selectively adjusting the trajectory of one or more diffraction orders of a first optical beam with respect to a diffraction order of another optical beam.
3. An optical system according to claim 2 wherein the spatial light modulator is responsive to a monitor signal issued by the monitor for collocating a diffraction order for more than one optical beam at the one or more output ports.
4. An optical system according to claim 1 comprising an optical fiber mount for the one or more input ports and the one or more output ports.
5. An optical system according to claim 4 wherein the optical fiber mount comprises:
a base having a two dimensional upper surface; and
a plurality of v-shaped grooves disposed in the upper surface of the base, each adapted for receiving an optical fiber, the grooves being spaced apart in a first dimension and extending parallel to each other in a second dimension perpendicular to the first dimension;
wherein the grooves are symmetrically disposed about a central axis in the first dimension and the spacing between predetermined fiber pairs in the first dimension is different.
6. An optical system according to claim 5 wherein a first subset of the grooves is spaced apart in the first dimension by a first by a second distance.
7. An optical system according to claim 6 wherein the first distance is about 250 μm.
8. An optical system according to claim 7 wherein the second distance is 375 μm.
9. An optical system according to claim 5 including up to twenty grooves for receiving up to twenty optical fibers.
10. An optical system according to claim 5 wherein the central axis is situated 500 μm from the nearest neighboring fibers.
11. A monitoring method for a wavelength selective switch, the switch being adapted for dynamically switching optical beams along respective trajectories between input and output ports disposed in an array using a reconfigurable liquid crystal spatial light modulator device, the method including:
dispersing the optical beams by a diffractive grism;
Monitoring predetermined characteristics of one or more of the optical beams;
controlling the temperature of the grism, and
in response to the monitoring, simultaneously correcting for more than one of the beam alignment, wavelength position and liquid crystal optical flicker.