Tunable optical instruments
An optical instrument including: a thermo-optically tunable, thin film, free-space interference filter having a tunable passband which functions as a wavelength selector, the filter including a sequence of alternating layers of amorphous silicon and a dielectric material deposited one on top of the other and forming a Fabry-Perot cavity structure having: a first multi-layer thin film interference structure forming a first mirror; a thin-film spacer layer deposited on top of the first multi-layer interference structure, the thin-film spacer layer made of amorphous silicon; and a second multi-layer thin film interference structure deposited on top of the thin-film spacer layer and forming a second mirror; a lens for coupling an optical beam into the filter; an optical detector for receiving the optical beam after the optical beam has interacted with the interference filter; and circuitry for heating the thermo-optically tunable interference filter to control a location of the passband.
1. An optical instrument comprising:
a thermo-optically tunable, thin film, free-space interference filter having a tunable passband which functions as a wavelength selector, said filter comprising a sequence of alternating layers of amorphous silicon and a dielectric material deposited one on top of the other, said sequence of alternating layers forming a Fabry-Perot cavity structure including: a first multi-layer thin film interference structure forming a first mirror; a thin-film spacer layer deposited on a top surface of the first multi-layer thin-film interference structure, said thin-film spacer layer made of amorphous silicon; and a second multi-layer thin film interference structure deposited on a top surface of the thin-film spacer layer and forming a second mirror;
a lens for coupling an optical beam into the filter;
an optical detector for receiving the optical beam after the optical beam has interacted with the interference filter; and
circuitry for heating the thermo-optically tunable interference filter to control a location of the passband.
2. The optical instrument of claim 1 , wherein the optical instrument is an optical spectrum analyzer.
3. The optical instrument of claim 2 , wherein the optical spectrum analyzer is constructed and arranged as an optical channel monitor for wavelength-division multiplexed optical communication systems.
4. The optical instrument of claim 1 , wherein the transparent layer is a transparent conducting oxide.
5. The optical instrument of claim 1 , wherein the dielectric material is silicon nitride.
6. The optical instrument of claim 5 , wherein the filter has a multi-cavity structure.
7. The optical instrument of claim 5 , further comprising a single hermetic package, wherein the filter and the optical detector are mounted in the single hermetic package.
8. The optical instrument of claim 7 , wherein the single hermetic package is a transistor outline (TO-style) package.
9. The optical instrument of claim 7 , further comprising within the single hermetic package one or more discrete temperature sensors.
10. The optical instrument of claim 7 , further comprising within the single hermetic package one or more temperature-stabilizing devices.
11. The optical instrument of claim 5 , further comprising a device that measures temperature of the thermo-optically tunable filter to determine wavelength.
12. The optical instrument of claim 11 , wherein the device that measures the temperature is integrated with the filter.
13. The optical instrument of claim 5 , further comprising a signal processor connected to receive an output signal from the detector, the signal processor converting the output signal received from the detector to power v. wavelength data.
14. The optical instrument of claim 5 , further comprising an electronics module;
a fiber optic input; and
a transistor outline (TO) package into which are mounted the tunable free-space filter, the optical detector and the fiber optic input, the TO package including pins through which electrical connections between the tunable free-space filter and the optical detector, and the electronics module are made.
15. The optical instrument of claim 5 , wherein the filter further comprises a layer of electrically resistive material to which, during use, power is supplied by said circuitry to change the temperature of the filter and thereby shift the passband of the filter.
16. The optical instrument of claim 15 , wherein the filter further comprises a substrate on which the first multi-layer thin film interference structure is deposited, wherein said layer of electrically resistive material forms a ring heater on the substrate and circumscribing an optical path through the first and second Fabry-Perot cavity structures, wherein during use the power that is supplied to the ring heater by said circuitry is electrical power.
17. The optical instrument of claim 15 , wherein the filter further comprises a crystalline semiconductor substrate on which the first multi-layer thin film interference structure is deposited, wherein said layer of electrically resistive material is a doped upper region of said substrate, wherein during use the power that is supplied to the doped upper region by said circuitry is electrical power.
18. The optical instrument of claim 15 , wherein the filter further comprises a substrate and a heater film formed in the substrate, wherein the first multi-layer thin film interference structure is deposited on the heater film, wherein said layer of electrically resistive material is said heater film and wherein during use the power that is supplied to the heater film by said circuitry is electrical power.
19. The optical instrument of claim 15 , wherein said layer of electrically resistive material is one of the layers of the Fabry-Perot cavity structure.
20. The optical instrument of claim 15 , wherein said layer of electrically resistive material is an optically transparent layer that is integrated with the filter in a location such that light passes through the electrically resistive material.