STABILIZED BROADBAND LIGHT SOURCE APPARATUS AND METHODS

• US 20180314007A1
• Filed: 04/27/2018
• Published: 11/01/2018
• Est. Priority Date: 04/27/2017
• Status: Active Grant

• Current Assignee: Charles Stark Draper Laboratory Incorporated
• Original Assignee: Charles Stark Draper Laboratory Incorporated
• Inventors: Feke, Gilbert D., Moebius, Michael G.
• Granted Patent: US 10,725,243 B2
• Time in Patent Office: Days
• CPC Class Codes: G01C 19/721 Details
• CPC Class Codes: G02B 27/288 Filters employing polarising elements, e.g. Lyot or Solc filters G02B5/3016 takes precedence
• CPC Class Codes: G02B 6/2706 as bulk elements, i.e. free space arrangements external to a light guide, e.g. polarising beam splitters
• CPC Class Codes: G02B 6/2746 comprising non-reciprocal devices, e.g. isolators, FRM, circulators, quasi-isolators magneto-optic non-reciprocal devices G02F1/093
• CPC Class Codes: G02B 6/29325 of the slab or planar or plate like form, i.e. confinement in a single transverse dimension only integrated circuit planar waveguide arrangements G02B6/12007; specially adapted for lighting G02B6/0011
• CPC Class Codes: G02B 6/29352 in a light guide
• CPC Class Codes: G02B 6/29389 Bandpass filtering, e.g. 1x1 device rejecting or passing certain wavelengths G02B6/2938 takes precedence
• CPC Class Codes: G02B 6/29398 Temperature insensitivity
• CPC Class Codes: G02F 1/0136 for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation G02F1/0353 takes precedence
• CPC Class Codes: G02F 1/09 based on magneto-optical elements, e.g. exhibiting Faraday effect
• CPC Class Codes: G02F 2203/21 Thermal instability, i.e. DC drift, of an optical modulator; Arrangements or methods for the reduction thereof
• CPC Class Codes: H04B 10/572 Wavelength control

Abstract

A broadband light source apparatus, and corresponding method, includes a broadband light source configured to provide source light with a source wavelength spectrum having a centroid thermal sensitivity. The apparatus also includes a broadband optical filter characterized by a filter spectrum that has one or more spectral characteristics and a thermal sensitivity with magnitude and sign. The filter is configured to receive the source light and to deliver broadband output light with an output spectrum that is a function of the source and filter spectra and has an output centroid wavelength. The spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter are configured to minimize a thermal sensitivity of the output centroid wavelength. The filter can be configured in view of a particular source spectrum to stabilize output centroid wavelength and maximize total output power passively with respect to ambient temperature fluctuations.

Claims

1. A broadband light source apparatus comprising:

a broadband light source configured to provide broadband source light characterized by a source wavelength spectrum having a source centroid wavelength with a thermal sensitivity; and

a broadband optical filter characterized by a filter wavelength spectrum, the filter wavelength spectrum having one or more spectral characteristics, the filter wavelength spectrum further having a thermal sensitivity with magnitude and sign, the broadband optical filter configured to receive the source light and to deliver broadband output light characterized by an output wavelength spectrum that is a function of the source and filter wavelength spectra,

the broadband output light having an output centroid wavelength, and the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum configured to minimize a thermal sensitivity of the output centroid wavelength.

3. The apparatus of claim 1, wherein the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum are further configured to minimize the thermal sensitivity of the output centroid wavelength to within ±

5 ppm/°

C.

4. The apparatus of claim 3, wherein the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum are further configured to minimize the thermal sensitivity of the output centroid wavelength to within ±

0.5 ppm/°

C.

5. The apparatus of claim 4, wherein the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum are further configured to minimize the thermal sensitivity of the output centroid wavelength to within ±

0.2 ppm/°

C.

8. The apparatus of claim 1, wherein the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum are further configured to minimize the thermal sensitivity of the output centroid wavelength over a temperature range of 10°

C.

10. The apparatus of claim 1, wherein the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum are configured such that a relative integrated output power of the broadband output light is maximized.

15. The apparatus of claim 1, wherein the broadband optical filter is an asymmetric Mach-Zehnder interferometer structure.

16. The apparatus of claim 1, wherein the broadband optical filter is a waveguide Bragg grating structure.

17. The apparatus of claim 16, wherein the waveguide Bragg grating structure includes at least one of a core and cladding comprising TiO₂.

18. The apparatus of claim 1, wherein the broadband optical filter is an interference filter, and wherein the broadband light source and the interference filter are mechanically attached to a bi-material strip, and wherein the sign of the thermal sensitivity of the filter wavelength spectrum is an effective negative sign of the thermal sensitivity of the filter wavelength spectrum due to relative angular displacement of the broadband light source and the broadband optical filter as a function of ambient temperature.

23. A fiber-optic gyroscope (FOG) including the broadband light source apparatus claim 1, the FOG further including a coil of optical fiber and an optical coupling configured to couple the broadband output light into the coil of optical fiber.

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24. A method for optimizing broadband light, the method comprising:

providing broadband source light characterized by a source wavelength spectrum having a source centroid wavelength thermal sensitivity;

configuring a broadband optical filter to be characterized by a filter wavelength spectrum, the filter wavelength spectrum having one or more spectral characteristics, the filter wavelength spectrum further having a thermal sensitivity with magnitude and sign, to receive the source light, and to deliver broadband output light characterized by an output wavelength spectrum that is a function of the source and filter wavelength spectra, the broadband output light having an output centroid wavelength; and

configuring the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum to minimize a thermal sensitivity of the output centroid wavelength.

26. The method of claim 24, wherein configuring the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum to minimize a thermal sensitivity of the output centroid wavelength includes configuring the spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum to minimize the thermal sensitivity of the output centroid wavelength to within ±

5 ppm/°

C.

27. The method of claim 26, wherein configuring the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum to minimize a thermal sensitivity of the output centroid wavelength includes configuring the spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum to minimize the thermal sensitivity of the output centroid wavelength to within ±

0.5 ppm/°

C.

28. The method of claim 27, wherein configuring the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum to minimize a thermal sensitivity of the output centroid wavelength includes configuring the spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum to minimize the thermal sensitivity of the output centroid wavelength to within ±

0.2 ppm/°

C.

31. The method of claim 24, wherein configuring the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum to minimize a thermal sensitivity of the output centroid wavelength includes configuring the spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum to minimize the thermal sensitivity of the output centroid wavelength over a temperature range of 10°

C.

33. The method of claim 24, further including configuring the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum to maximize a relative integrated output power of the broadband output light.

38. The method of claim 24, wherein configuring the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum includes configuring the spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum of an asymmetric Mach-Zehnder interferometer structure.

39. The method of claim 24, wherein configuring the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum includes configuring the spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum of a waveguide Bragg grating structure.

40. The method of claim 39, wherein configuring the waveguide Bragg grating structure includes using at least one of a core and cladding comprising TiO₂.

41. The method of claim 24, wherein configuring the one or more spectral characteristics and the magnitude and sign of the thermal sensitivity of the filter wavelength spectrum includes using an interference filter mechanically attached to a bi-material strip to which a broadband light source providing the source light is also attached, and wherein configuring the sign of the thermal sensitivity of the filter wavelength spectrum also includes configuring an effective negative sign of the thermal sensitivity of the filter wavelength spectrum due to relative angular displacement of the light source and the broadband optical filter as a function of ambient temperature.

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47. An optical waveguide Bragg grating structure comprising:

an optical core; and

an optical cladding surrounding the optical core,

wherein at least one of the optical core and the optical cladding includes a TiO₂ material.

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