Photonics based tunable multiband microwave filter
View Patent ↗Various examples are provided for tunable radio frequency (RF) filtering. In one example, a RF multiband filter includes a Lyot filter including a tunable birefringence loop including a circulator and a polarization controller (PC) and a phase modulator (PM). The Lyot filter can generate an optical comb based at least in part upon a received optical signal and a polarization rotation angle of the polarization controller. The phase modulator (PM) can generate a modulated tap signal by modulating the optical comb by a RF input signal.
1. A radio frequency (RF) filter, comprising:
a Lyot filter comprising a tunable birefringence loop comprising a length of polarization maintaining fiber (PMF), a circulator and a polarization controller (PC), the PC coupled to a distal end of the PMF through the circulator, where a received optical signal is provided to the PMF through a loop coupling circulator coupled to a proximal end of the PMF, the Lyot filter configured to generate an optical comb based at least in part upon the received optical signal and a polarization rotation angle of the PC; and
a phase modulator (PM) configured to generate a modulated tap signal by modulating the optical comb by a RF input signal.
2. The RF filter of claim 1 , wherein the circulator coupled via the PMF is the only circulator coupled to the loop coupling circulator.
3. The RF filter of claim 1 , wherein the PC is configured to adjust the polarization rotation angle in a range from 0° to 90°.
4. The RF filter of claim 1 , wherein the received optical signal is received by the loop coupling circulator through a first polarizer of the Lyot filter.
5. The RF filter of claim 4 , wherein the optical comb is provided to the PM through a second polarizer of the Lyot filter.
6. The RF filter of claim 5 , wherein the optical comb provided to the PM is amplified.
7. The RF filter of claim 1 , wherein the Lyot filter comprises a second tunable birefringence loop comprising a second circulator and a second PC, the second tunable birefringence loop coupled in series by a second loop coupling circulator.
8. The RF filter of claim 7 , wherein each tunable birefringence loop comprises single corresponding loop coupling circulator coupled to a single corresponding circulator via the corresponding PMF.
9. The RF filter of claim 7 , wherein the second tunable birefringence loop comprises a second PMF, the second PC coupled to a distal end of the second PMF via the second circulator.
10. The RF filter of claim 9 , wherein an output from the tunable birefringence loop is provided to a proximal end of the second PMF via the second loop coupling circulator.
11. The RF filter of claim 10 , wherein the output from the tunable birefringence loop is provided to the proximal end of the second PMF via a third PC.
12. The RF filter of claim 7 , wherein the received optical signal is received by the loop coupling circulator through a first polarizer of the Lyot filter.
13. The RF filter of claim 12 , wherein the optical comb is provided to the PM through a second polarizer after the second loop coupling circulator.
14. The RF filter of claim 7 , comprising a photo-detector (PD) configured to generate a RF output signal based upon the modulated tap signal.
15. The RF filter of claim 14 , wherein the RF output signal comprises six passbands or more.
16. The RF filter of claim 15 , wherein the RF output signal comprises ten passbands or more.
17. The RF filter of claim 14 , wherein passbands of the RF output signal comprise an even 3-dB bandwidth of 200 MHz and greater than 30 dB sidelobe suppression.
18. The RF filter of claim 14 , comprising a piece of dispersion compensating fiber (DCF) between the PM and the PD to provide a linear delay for wavelengths of the modulated tap signal.
19. The RF filter of claim 1 , wherein the received optical signal comprises a broadband optical signal filtered by a Gaussian optical filter.
20. The RF filter of claim 19 , wherein the Gaussian optical filter apodizes amplitudes of the modulated tap signal.