Tunable radio frequency and microwave photonic filters
RF and microwave devices and techniques are disclosed for processing RF and microwave signals by using (1) photonic or optical components and (2) RF and microwave components. In some implementations, a part of the processing is performed in the RF and microwave domain such as applying a microwave or RF input signal to control an optical modulator, and another part of the processing is performed in the optical domain such as optical filtering of the modulated optical beam to select desired microwave or RF spectral components. The frequency of a selected spectral component can be tuned by either tuning the frequency of the optical beam that is modulated by the optical modulator or a filter that is used to filter modulated optical beam.
1. A device, comprising:
an input port to receive an input microwave or RF signal;
a tunable laser to produce a continuous-wave laser beam and to tune a laser frequency of the laser beam;
a first optical path to receive a first portion of the laser beam;
a second optical path to receive a second portion of the laser beam, the second optical path comprising:
an optical modulator to modulate the second portion in response to the input signal to produce a modulated optical beam that carries the input signal, and
an optical filter to filter the modulated optical beam to select at least one spectral component in the input signal while rejecting other spectral components and to output a filtered modulated optical beam that carries the at least one selected spectral component;
a tuning control unit to tune the laser frequency of the tunable laser to change a frequency of the at least one selected spectral component; and
an optical detector to combine the first portion from the first optical path and the filtered modulated optical beam from the second optical path and to produce a filtered output signal comprising the at least one selected spectral component.
2. The device as in claim 1 , wherein the optical filter comprises a fixed-frequency optical filter.
3. The device as in claim 1 , wherein the optical fiber comprises a Fabry-Perot resonator filter.
4. The device as in claim 1 , wherein the optical filter comprises at least two cascaded optical resonators.
5. The device as in claim 4 , wherein the optical resonators comprise whispering gallery mode resonators.
6. The device as in claim 4 , wherein the whispering gallery mode resonators are microsphere resonators.
7. The device as in claim 4 , wherein the whispering gallery mode resonators are toroidal resonators.
8. The device as in claim 4 , wherein the optical resonators are ring resonators that have whispering gallery modes.
9. The device as in claim 1 , wherein the optical resonators exhibit an electro-optic effect.
10. The device as in claim 1 , wherein the optical filter is tunable in frequency.