Multiport tunable optical filters
A tunable multiport optical filter includes various types of arrays of optical ports. The tunable filter also includes a light dispersion element (e.g., a grating) and a reflective beam steering element (e.g., a tilting mirror). An optical signal exits an optical (input) port, is dispersed by the light dispersion element, reflects off the reflective beam steering element back to the light dispersion element, and on to another optical (output) port. The reflective beam steering element can be steered such that a wavelength portion of the dispersed optical signal can be coupled to the optical output port. For example, the input optical signal may be a wavelength division multiplexed signal carrying multiple channels on different wavelengths, and the tunable multiport optical filter directs one of the channels to the output optical port. Additionally, the tunable filter may be incorporated into a device acting as a wavelength reference.
1. A self-calibrating optical channel monitoring (OCM) device comprising:
a tunable multiport optical filter comprising:
a plurality of optical input ports,
at least one optical output port,
a light dispersion element positioned to receive an optical signal from an optical input port of the plurality of optical input ports, and disperse the received optical signal into a plurality of separate wavelength components; and
a reflective beam steering element positioned to receive the plurality of separate wavelength components from the light dispersion element, the reflective beam steering element controllable to redirect any one wavelength component of the dispersed optical signal through the light dispersion element and into the optical output port;
a photodetector coupled to the optical output port of the tunable multiport optical filter;
a reference spectrum source that produces a reference spectrum that can be coupled as an optical signal into to the tunable multiport optical filter; and
a controller coupled to the reference spectrum source, the tunable multiport optical filter and the photodetector, the controller configured to:
control production and/or coupling of the reference spectrum as an optical input to the tunable multiport optical filter, and
calibrate the tunable multiport optical filter based on a response of the photodetector when the reference spectrum is coupled to the tunable multiport optical filter by determining and storing the positions of the reflective beam steering element associated with predetermined wavelengths in the reference spectrum.
2. The OCM device of claim 1 , wherein the optical signal has an operating wavelength range, the reference spectrum includes two reference wavelength peaks, and the controller calibrates the tunable multiport optical filter based on the response of the photodetector to the two reference peaks by determining and storing the position of the reflective beam steering element for each of the reference wavelength peak.
3. The OCM device of claim 2 , wherein the two reference wavelength peaks lie outside the operating wavelength range.
4. The OCM device of claim 1 , wherein the reference spectrum source comprises a broadband light source coupled to a source filter.
5. The OCM device of claim 4 , wherein the source filter is a dual band pass filter.
6. The OCM device of claim 4 , wherein the optical signal is a wavelength-division multiplexed signal containing multiple channels at different wavelengths, and the reflective beam steering element is controllable such that any channel of the dispersed optical signal can be redirected through the light dispersion element to couple to the optical output port.
7. The OCM device of claim 6 , wherein the wavelength-division multiplexed signal complies with an ITU grid.
8. The OCM device of clam 1 , wherein the reference spectrum includes a plurality of reference wavelengths, and the controller is configured to determine a plurality of reference data points that map a plurality of reference wavelengths to a plurality of corresponding positions of the beam steering element, a separate position for reach reference wavelength.
9. The OCM device of claim 1 , wherein the at least one output port is a detector.
10. The OCM device of claim 1 , wherein the reference spectrum source comprises:
an etalon filter whose transmission spectrum peaks define the reference wavelengths;
a splitter coupled to the output of the tunable multiport optical filter to direct a portion of the output signal as an input to the etalon filter; and
a photodetector coupled to the output of the etalon filter for converting the optical output of the etalon filter into an electrical calibration signal input to the controller.