Narrow band tunable filter with integrated detector
View Patent ↗A polarization insensitive narrowband tunable filter utilizes an active liquid crystal cell to change the index of refraction and tuning of a waveguide resonant filter employing a nanostructured waveguide grating and polarization beam splitters to independently channel and convert S- and P-polarization states into optically and geometrically parallel beams which pass through the device. A multi-pixel configuration offers extended tuning range by employing a 1×N optical switch or splitter and N tunable pixel-filters each having offset center frequency enabling the tuning range of one pixel to partially overlap another pixel rendering the device and 1×N switch or splitter capable of scanning pixels to yield an expanded continuous tuning range mode. Optional features of the present invention include deposited photodetectors, deposited metal gasket moisture barrier, deposited spacer layer with high cell gap tolerance, a deposited thermal sensor and heater and related temperature compensation control schemes.
1. A polarization independent tunable filter comprising:
a liquid crystal cell comprised of a first and second substrate, said first substrate includes a first surface having a rotating mirror and a second surface including a polarization beam splitter and waveguide resonant grating filter, said second substrate having a second surface including a rotating mirror and a first surface having a polarization beam splitter, said substrates being mutually disposed such that the second surface of the first substrate faces the first surface of the second substrate.
2. The tunable filter of claim 1 , further including liquid crystals coupled between the first and second substrates.
3. The tunable filter of claim 2 , further including an electrode layer positioned adjacent to the polarization beam splitters on both the first and second substrates.
4. The tunable filter of claim 3 , further including an anchoring layer positioned adjacent to the electrode and polarization beam splitters on the second substrate and distal to said second substrate.
5. The tunable filter of claim 4 , wherein the application of voltage applied across the electrode layers results in tuning of the tunable filter.
6. The tunable filter of claim 5 , wherein the waveguide resonant grating filter is comprised of a grating, a core and a cladding.
7. The tunable filter of claim 6 , wherein the waveguide resonant grating filter is made of silicon nitride and silicon dioxide.
8. The tunable filter of claim 7 , wherein the waveguide resonant grating filter grating has a period between 200 and 900 nanometers.
9. The tunable filter of claim 1 , wherein said tunable filter has an optical aperture, and the rotating mirror on the first substrate is positioned in the aperture but does not impede an input passing into the tunable filter or an output beam reflected therefrom.
10. The tunable filter of claim 9 , wherein the waveguide resonant grating filter has a waveguide index of refraction between 2.3 and 3.05.
11. A polarization independent tunable filter comprising:
a liquid crystal cell comprised of a first and second substrate, said first substrate including a first surface having a rotating mirror and a first photodetector, and a second surface including polarization beam splitter, electrode, anchor and waveguide resonant grating filter layers, said second substrate having a second surface including a second photodetector and a first surface having electrode and anchor layers,
wherein the second surface of the first substrate faces the first surface of the second substrate.
12. The tunable filter of claim 11 , wherein both photodetectors are nontransparent.
13. The tunable filter of claim 11 , wherein said tunable filter has an optical aperture, and the rotating mirror on the first substrate is positioned in the aperture but does not impede an input passing into the tunable filter or an output beam reflected therefrom.
14. The tunable filter of claim 11 , further including a metal gasket layer and a spacer layer positioned between the first and second substrates.
15. The tunable filter of claim 12 , wherein the photodetectors are partially transparent and act as taps to signals output from the tunable filter.
16. The tunable filter of claim 12 , wherein the one of said first and second photodetectors completely absorbs a signal output from the tunable filter.
17. The tunable filter of claim 14 , further including a heater/temperature sensor element.
18. The tunable filter of claim 14 , wherein the metal gasket is comprised of gold and tin.
19. The tunable filter of claim 17 , wherein the heater/temperature sensor element is a resistive thermal device.
20. A polarization independent tunable filter comprising:
a first liquid crystal tuning pixel comprised of a first and second substrate, said first substrate including a first surface having a rotating mirror and a second surface including polarization beam splitter, electrode, anchor and waveguide resonant grating filter layers, said second substrate having a second surface including a rotating mirror and a first surface having polarization beam splitter, electrode and anchor layers, said substrates being disposed such that the second surface of the first substrate faces the first surface of the second substrate, and wherein said tunable filter has an optical aperture, and the rotating mirror on the first substrate is positioned in the aperture but does not impede an input passing into the tunable filter.
21. The tunable filter of claim 20 , further including a second liquid crystal tuning pixel having a tuning range that partially overlaps the tuning range of the first liquid crystal tuning pixel.
22. The tunable filter of claim 21 , further incuding an 1.times.2 optical splitter for routing a single input beam to both of the tunable filter pixels.
23. The tunable filter of claim 22 , further including a photodetector positioned at an output of at least one pixel.