Narrow band tunable filter with integrated detector

• US 20040239869A1
• Filed: 06/02/2003
• Published: 12/02/2004
• Est. Priority Date: 06/02/2003
• Status: Active Grant

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Xtellus Inc. (Lumentum Holdings Inc.)
• Inventors: Zalewski, Gary M., Cavanaugh, Shanti A.
• Granted Patent: US 7,009,680 B2
• Time in Patent Office: Days
• US Class Current: 349/198
• CPC Class Codes: G02F 1/216 using liquid crystals, e.g. liquid crystal Fabry-Perot filters
• CPC Class Codes: G02F 2201/307 Reflective grating, i.e. Bragg grating
• CPC Class Codes: G02F 2201/58 Arrangements comprising a monitoring photodetector
• CPC Class Codes: G02F 2203/055 wavelength filtering
• CPC Class Codes: G02F 2203/06 Polarisation independent

Abstract

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.

Claims

1. A polarization independent tunable filter comprising:

A liquid crystal cell comprised of a first and second substrate, said first substrate includes a top surface having a rotating mirror and a bottom surface including a polarization beam splitter and waveguide resonant grating filter, said second substrate having a bottom surface including a rotating mirror and a top surface having a polarization beam splitter;

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 under or over the polarization beam splitters on both the first and second substrates.

4. The tunable filter of claim 3, further including an anchoring layer positioned over the electrode and polarization beam splitters on the 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 the rotating mirror on the first substrate is positioned in the aperture but does not impede an input passing into the tunable filter or a reflected output beam.

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 includes a top surface having a rotating mirror and photodetector and the bottom surface including polarization beam splitter, electrode, anchor and waveguide resonant grating filter layers, respectively, said second substrate having a bottom surface including a photodetector and a top surface having electrode and anchor layers, respectively.

wherein the bottom surface of the first substrate is adjacent to the top surface of the second substrate.

12. The tunable filter of claim 11, wherein both photodetectors are non-transparent.

13. The tunable filter of claim 11, wherein the rotating mirror on the first substrate is positioned in the aperture but does not impede an input passing into the tunable filter or a reflected output beam.

14. The tunable filter of claim 11, further including a metal gasket layer and 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 photodetector 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 includes a top surface having a rotating mirror and the bottom surface including polarization beam splitter, electrode, anchor and waveguide resonant grating filter layers, respectively, said second substrate having a bottom surface including a rotating mirror and a top surface having polarization beam splitter, electrode and anchor layers, respectively, wherein 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 first liquid crystal tuning pixel.

22. The tunable filter of claim 21, further including an 1×

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.

24. A polarization independent tunable filter comprising

a polarization splitter/combiner means for accepting an input beam having any polarization and producing two substantially parallel output beams having the same polarization,

a tunable filter having an input coupled to the output of the polarization splitter means that accepts the two beams and produces a first and a second output beam for each input beam, the first output being a reflected passband and the second output being a transmission beam compliment of the first output,

a combiner means for accepting the transmission beam outputs from the tunable filter and producing a single transmission beam in response thereto,

wherein the said polarization splitter/combiner means also accepting the reflected passband beam outputs from the tunable filter and producing a single reflected passband output.

25. The polarization filter of claim 24, wherein the polarization splitter/combiner means is comprised of a birefringent walk-off crystal and half wave plate.

26. The polarization filter of claim 24, wherein the combiner means is comprised of a birefringent walk-off crystal and half wave plate.