Tunable optical filter

• US 6,816,636 B2
• Filed: 09/12/2001
• Issued: 11/09/2004
• Est. Priority Date: 09/12/2001
• Status: Expired due to Term

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Cole, Barrett E., Krishnankutty, Subash, Horning, Robert D.
• Primary Examiner(s): Ton, Toan
• Assistant Examiner(s): Kim, Richard H
• Application Number:
  US09/953,506
• Publication Number:
  US 20030048970A1
• Time in Patent Office: 1,154 Days
• Field of Search: 359/892, 359/230, 359/223, 359/224, 359/260, 359/578, 359/228, 385/10, 356/454, 349/198
• US Class Current: 385/10
• CPC Class Codes: G01J 3/26 using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
• CPC Class Codes: G02B 6/29361 Interference filters, e.g. multilayer coatings, thin film filters, dichroic splitters or mirrors based on multilayers, WDM filters
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02F 1/0147 based on thermo-optic effects G02F1/132 takes precedence
• CPC Class Codes: G02F 1/015 based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction G02F1/03 takes precedence
• CPC Class Codes: G02F 1/21 by interference
• CPC Class Codes: G02F 1/213 Fabry-Perot type
• CPC Class Codes: G02F 2203/055 wavelength filtering

Abstract

A tunable filter having a top mirror, a bottom mirror, and one or more intervening layers. The one or more intervening layers preferably have a refractive index that changes with temperature. By heating the one or more intervening layers, the wavelength that is selected by the optical filter can be controlled. The one or more intervening layers are preferably heated by passing current through the one or more intervening layers, or by passing current through a separate resistive layer that is thermally coupled to the one or more intervening layers. Such a filter can provide a high degree of wavelength selectivity in a robust and stable manner.

Claims

1. An apparatus comprising a tunable filter for passing one or more selected wavelength from a band of wavelengths, the tunable filter adapted to be tuned to the one or more selected wavelength without physically moving any parts of the tunable filter, the tunable filter reflecting unselected wavelengths;

wherein the tunable filter has a filter region, a support body and one or more support legs, the filter region formed of first and second mirrors with a layer between them that has a refractive index that changes with temperature, and wherein the one or more support legs are adapted to suspend the filter region away from the support body.

2. A tunable filter for selecting a desired wavelength from a band of wavelengths, comprising:

a support structure having one or more support members;

a first mirror;

a second mirror;

a layer situated between the first mirror and the second mirror, the layer having a refractive index that changes with temperature, the refractive index at least partially determining the wavelength that is selected by the tunable filter; and

heating means for providing heat to the layer;

wherein the layer is mechanically supported by the support members, and the layer is spaced from the support structure by the support members.

3. A tunable filter according to claim 2 wherein the layer is suspended in a cavity.

4. A tunable filter according to claim 3 wherein the cavity is at a lower pressure than outside of the cavity.

5. A tunable filter according to claim 4 wherein the cavity is under a substantial vacuum.

6. A tunable filter according to claim 5 wherein the tunable filter is enclosed in a vacuum package.

7. A tunable filter according to claim 2 wherein the layer is spaced from the support structure by air gape.

8. A tunable filter according to claim 2 wherein the one or more support members are part of a patterned support layer that is connected to the layer and the support structure.

9. A tunable filter according to claim 8 wherein the layer is silicon.

10. A tunable filter according to claim 9 wherein the patterned support layer is Silicon Nitride.

11. A tunable filter according to claim 9 wherein the patterned support layer is polyimide.

12. A tunable filter according to claim 9 wherein the patterned support layer is silicon.

13. A tunable filter according to claim 9 wherein the patterned support layer is polycrystalline silicon.

14. A tunable filter according to claim 2 wherein the heating means includes a resistive layer that is thermally connected to the layer.

15. A tunable filter according to claim 14 wherein the resistive layer includes vanadium.

16. A tunable filter according to claim 14 wherein the resistive layer includes platinum.

17. A tunable filter according to claim 14 wherein the resistive layer includes polycrystalline silicon.

18. A tunable filter according to claim 2 wherein the heating means includes two or more electrical contacts that provide a current path through the layer.

19. A tunable filter according to claim 2 further comprising a controller for providing a controlled current to the heating means.

20. A tunable filter according to claim 19 further comprising a temperature sensor thermally coupled to the layer, the temperature sensor providing an output signal indicative of the temperature of the layer.

21. A tunable filter according to claim 20 wherein the controller receives the output signal of the temperature sensor, and provides a controlled current to the heating means to maintain the temperature of the layer at a desired temperature.

22. A tunable filter according to claim 19 wherein the heating means includes a material that has a resistance with a temperature coefficient.

23. A tunable filter according to claim 22 wherein the controller determines the temperature of the heating means by monitoring the resistance of the heater means.

24. A method for tuning a tunable filter, the method comprising

tuning the tunable filter of claim 2 to one or more selected wavelength from a band of wavelengths without physically moving any parts of the tunable filter;

passing the one or more selected wavelengths through the tunable filter; and

reflecting unselected wavelengths.

25. An apparatus for selecting a desired wavelength from a band of wavelengths, comprising:

a tunable filter for passing a selected wavelength, the tunable filter being tuned to a selected wavelength by applying heat to the tunable filter, the tunable filter having a filter region spaced from a support body by air gaps;

heating means for providing heat to the tunable filter; and

a controller for applying a controlled power to the heating means such that the desired wavelength is selected by the tunable filter.