Tunable optical filter

• US 20030048970A1
• Filed: 09/12/2001
• Published: 03/13/2003
• Est. Priority Date: 09/12/2001
• Status: Active Grant

• Current Assignee: Barrett E. Cole, Robert D. Horning, Subash Krishnankutty
• Original Assignee: Barrett E. Cole, Robert D. Horning, Subash Krishnankutty
• Inventors: Krishnankutty, Subash, Cole, Barrett E., Horning, Robert D.
• Granted Patent: US 6,816,636 B2
• Time in Patent Office: Days
• US Class Current: 385/1
• 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.

15. A tunable filter according to claim 1 wherein the heating means includes a resistive layer that is thermally connected to the layer.

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

17. A tunable filter according to claim 15 wherein the resistive layer includes platinum.

18. A tunable filter according to claim 15 wherein the resistive layer includes polycrystalline silicon.

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

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.

19. 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.

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

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

22. A tunable filter according to claim 21 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.

23. A tunable filter according to claim 20 wherein the heating means includes a material that has a resistance with a temperature coefficient.

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

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

4. A tunable filter according to clam 2 wherein the layer is mechanically supported by one or more support members.

5. A tunable filter according to clam 4 wherein the one or more support members are connected to a support structure that is spaced from the layer.

6. A tunable filter according to claim 5 wherein the one or more support members are part of a patterned support layer that is connected to the layer and the support structure.

7. A tunable filter according to claim 6 wherein the layer is silicon.

8. A tunable filter according to claim 7 wherein the patterned support layer is Silicon Nitride.

9. A tunable filter according to claim 7 wherein the patterned support layer is polyimide.

10. A tunable filter according to claim 7 wherein the patterned support layer is silicon.

11. A tunable filter according to claim 7 wherein the patterned support layer is polycrystalline silicon.

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

13. A tunable filter according to clam 12 wherein the cavity is under a substantial vacuum.

14. A tunable filter according to clam 13 wherein the tunable filter is enclosed in a vacuum package.

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;

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.

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

27. A method for dropping a signal from a number of input signals, wherein each of the input signals has a different wavelength, comprising:

providing a first tunable filter that selectively passes a selected wavelength and reflects signals having other wavelengths, the first tunable filter being tuned by applying heat to the first tunable filter;

providing one or more of the input signals including a first drop signal to the first tunable filter;

heating the first tunable filter such that the first tunable filter passes the first drop signal through the first tunable filter to a first collector location, and reflects the other input signals to a second collector location.

28. A method according to claim 27 further comprising:

providing a second tunable filter at the second collector location, the second tunable filer selectively passes a selected wavelength and reflects signals having other wavelengths, the second tunable filter being tuned by applying heat to the second tunable filter;

heating the second tunable filter such that the second tunable filter passes a second drop signal through the second tunable filter to a third collector location, and reflects the remaining input signals to a fourth collector location.

29. A method for adding a signal to a number of input signals, wherein each of the input signals has a different wavelength, comprising:

providing a first tunable filter that selectively passes a selected wavelength and reflects signals having other wavelengths, the first tunable filter being tuned by applying heat to the first tunable filter;

providing one or more of the input signals to a first side of the first tunable filter;

providing a first add signal to a second side of the first tunable filter; and

heating the first tunable filter such that the first tunable filter passes the first add signal through the first tunable filter to a first collector location, and reflects the one or more input signals to the first collector location.

30. A method according to claim 29 farther comprising:

providing a second tunable filter that selectively passes a selected wavelength and reflects signals having other wavelengths, the second tunable filter being tuned by applying heat to the second tunable filter;

providing the signals present at the first collector location to a first side of the second tunable filter;

providing a second add signal to a second side of the second tunable filter; and

heating the second tunable filter such that the second tunable filter passes the second add signal through the second tunable filter to a second collector location, and reflects the one or more input signals at the first collector location, including the first add input signal, to the second collector location.

31. A method for monitoring the wavelength of the emission of a laser, comprising:

providing the emission of the laser to a tunable filter, the tunable filter passing a selected wavelength to a detector and reflecting non-selected wavelengths, the tunable filter being tuned by applying heat to the filter;

applying heat to the filter to select the wavelength of the emission of the laser; and

determining the wavelength of the emission of the laser by monitoring the heat applied to the tunable filter.

32. A method for monitoring the wavelength of the emission of a laser, comprising:

directing a first part of the emission of the laser to a first collector location and directing a second part of the emission to a second collector location;

providing the second part of the emission to a tunable filter, the tunable filter passing a selected wavelength to a detector and reflecting non-selected wavelengths, the tunable filter being tuned to a particular wavelength by applying heat to the filter;

applying heat to the filter to select the wavelength of the second part of the emission of the laser; and

determining the wavelength of the second part of the emission of the laser by monitoring the heat applied to the tunable filter.

33. A method for forming a tunable filter, the method comprising:

providing a substrate;

providing a heater film adjacent the substrate such that the heater film is thermally coupled to at least a predefined filter region of the substrate;

providing a support film such that the support film is mechanically coupled to the filter region and to a support region of the substrate;

providing a multi-layer mirror above at least a portion of the filter region of the substrate;

selectively removing the substrate around the periphery of the filter region, leaving the support region and the filter region separated by a space; and

providing a multi-layer mirror below the filter region.

34. A method according to claim 33 wherein the substrate is an Silicon On Insulator (SOI) substrate having a lower silicon layer, an intermediate insulating layer, and an upper silicon layer.

35. A method according to claim 34 wherein the filter region is provided by the upper silicon layer.

36. A method according to claim 35 wherein the lower silicon layer below the filter region is removed when the substrate around the periphery of the filter region is removed.

37. A method according to claim 36 wherein the intermediate insulating layer acts as an etch stop when removing the lower silicon layer below the filter region and the substrate around the periphery of the filter region.

38. A method according to claim 37 further comprising the step of removing the intermediate insulating layer after the lower silicon layer below the filter region and the substrate around the periphery of the filter region are removed.

39. A method according to claim 33 further comprising the step of patterning the support film to provide one or more support members that extend between the filter region and the support region of the substrate.

40. A method according to claim 39 wherein the support film is patterned to provide two or more support members that extend between the filter region and the support region of the substrate, wherein the two or more support members are separated by a space.

41. A method according to claim 33 further comprising the step of patterning the heater film to overlap at least a substantial portion of the filter region.

42. A method for forming a tunable filter, the method comprising:

providing a substrate;

providing a heater film adjacent the substrate;

patterning the heater film;

providing a support film such that the support film is mechanically coupled to a filter region and to a support region of the substrate;

patterning the support film so that the support film does not overlap at least a portion of the filter region;

providing a multi-layer mirror above at least a portion of the filter region;

removing the substrate around the periphery of the filter region to release the filter region from the support region of the substrate; and

providing a multi-layer mirror below at least a portion of the filter region.