Grouped molecular absorption line wavelength calibration apparatus and method

Patent metadata

Field	Value
Publication number	US-10612977-B2
Application number	US-201816038759-A
Country	US
Kind code	B2
Filing date	Jul 18, 2018
Priority date	Jul 20, 2017
Publication date	Apr 7, 2020
Grant date	Apr 7, 2020

Abstract

A wavelength calibration apparatus includes a light source configured to deliver a backlight beam characterized by a backlight spectrum. The apparatus includes a gas reference cell configured to absorb light from the backlight beam and transmit an imprinted light beam characterized by an imprinted light spectrum. The apparatus further includes a spectrometer configured to (i) receive the transmitted imprinted light beam from the gas reference cell and to apply a plurality of reference spectral selection factors to spectrally resolve the imprinted light beam into reference indicia groups, (ii) detect a plurality of reference spectral power readings, and (iii) deliver a reference dataset for associating the reference spectral power readings with the reference spectral selection factors. A wavelength calibrator of the apparatus determines a wavelength calibration factor based on a difference between the reference dataset and a standard dataset. A wavelength-corrective light source includes the calibration apparatus.

First claim

What is claimed is:

1. A wavelength calibration apparatus comprising:
a backlight source configured to deliver a backlight beam characterized by a backlight spectrum;
at least one gas reference cell configured to absorb light from the backlight beam via a plurality of narrowband absorption lines of the gas reference cell, the narrowband absorption lines being known wavelengths within the backlight spectrum, and the at least one gas reference cell further configured to transmit an imprinted light beam characterized by an imprinted light spectrum having a corresponding plurality of reference indicia imprinted thereto;
a calibration spectrometer configured to:
(i) receive the transmitted imprinted light beam from the at least one gas reference cell and to apply a plurality of reference spectral selection factors to spectrally resolve the imprinted light beam for grouping reference indicia within the plurality of reference indicia into a plurality of reference indicia groups, whereby each reference indicia group corresponds to a respective spectral selection factor,
(ii) detect a plurality of reference spectral power readings from the spectrally resolved, imprinted light beam, respective power readings of the plurality of reference spectral power readings corresponding to respective selection factors of the plurality of reference spectral selection factors, and
(iii) to deliver a reference dataset for associating the reference spectral power readings with the reference spectral selection factors; and
a wavelength calibrator configured to determine a wavelength calibration factor based on a difference between the reference dataset and a standard dataset.

2. The wavelength calibration apparatus of claim 1 , wherein the calibration spectrometer comprises at least one acousto-optic tunable filter (AOTF) having a tuning relation that relates AOTF drive frequencies to peak transmission wavelengths output therefrom, the calibration spectrometer having a spectral resolution and further including a spectrometric photodetector having at least one photodiode.

3. The wavelength calibration apparatus of claim 2 , wherein the tuning relation of the at least one AOTF includes a tuning relation operational sensitivity having at least one of a tuning relation thermal sensitivity and a tuning relation ionizing radiation sensitivity.

4. The wavelength calibration apparatus of claim 2 , wherein the at least one AOTF is optically coupled to the at least one photodiode by a free space mechanism, a fiber optic mechanism, or a combination thereof.

5. The wavelength calibration apparatus of claim 2 , wherein the plurality of spectral selection factors includes a plurality of AOTF drive frequencies.

6. The wavelength calibration apparatus of claim 5 , wherein the plurality of AOTF drive frequencies is applied to the AOTF via a swept drive sequence across a frequency range.

7. The wavelength calibration apparatus of claim 5 , wherein the plurality of AOTF drive frequencies is applied to the AOTF via an arbitrary or random sequence.

8. The wavelength calibration apparatus of claim 2 , wherein a combination of the spectral resolution of the AOTF and the plurality of AOTF drive frequencies determines the plurality of reference indicia groups.

9. The wavelength calibration apparatus of claim 1 , wherein the calibration spectrometer comprises a dispersive element and a spectrometric photodetector having a plurality of photodiodes, the dispersive element configured to spectrally distribute the imprinted light beam to the spectrometric photodetector.

10. The wavelength calibration apparatus of claim 9 , wherein the plurality of photodiodes constitute a photodiode array and the dispersive element is a diffraction grating or prism.

11. The wavelength calibration apparatus of claim 10 , wherein the plurality of spectral selection factors includes a plurality of dispersion angles and the combination of a pitch of the photodiode array and an angular dispersion of the dispersive element determines the plurality of reference indicia groups.

12. The wavelength calibration apparatus of claim 1 , wherein the calibration spectrometer comprises a plurality of bandpass filters and a spectrometric photodetector having a plurality of photodiodes, each bandpass filter in optical communication with a respective photodiode.

13. The wavelength calibration apparatus of claim 12 , wherein the plurality of spectral selection factors includes a plurality of filter passbands and the plurality of filter passbands determines the plurality of reference indicia groups.

14. The wavelength calibration apparatus of claim 1 , wherein the wavelength calibrator includes at least one of a microprocessor, an application-specific integrated circuit (ASIC), and a field-programmable gate array (FPGA).

15. The wavelength calibration apparatus of claim 1 , wherein the difference between the reference dataset and the standard dataset is a function of a difference between the correspondence of the plurality of reference indicia groups to the reference spectral selection factors and a correspondence of a plurality of standard indicia groups to a plurality of standard spectral selection factors.

16. The wavelength calibration apparatus of claim 1 , wherein the light source includes an emitter that includes at least one of a superluminescent diode (SLD), a rare-earth-doped superluminescent source (REDSLS), a light emitting diode (LED), and a supercontinuum fiber.

17. The wavelength calibration apparatus of claim 1 , wherein the light source includes an emitter and a flattening filter, the flattening filter configured to receive an unconditioned light beam characterized by an unconditioned spectrum from the emitter to flatten the unconditioned spectrum and to transmit the backlight beam.

18. The wavelength calibration apparatus of claim 1 , wherein the light source is configured to deliver the backlight beam to the gas reference cell by at least one of a free space mechanism, a fiber optic mechanism, or a combination thereof.

19. The wavelength calibration apparatus of claim 18 , wherein the free space mechanism includes a lens coupling.

20. The wavelength calibration apparatus of claim 18 , wherein the fiber optic mechanism includes a fiber pigtail.

21. The wavelength calibration apparatus of claim 1 , wherein the at least one gas reference cell includes at least one of a tube, a hollow optical fiber, and an integrated waveguide coupled chamber.

22. The wavelength calibration apparatus of claim 1 , wherein the at least one gas reference cell is filled with at least one gas, the at least one gas including at least one of acetylene, hydrogen cyanide, carbon monoxide having carbon 12 isotope, carbon monoxide having carbon 13 isotope, hydrogen fluoride, water vapor, methane, ammonia, hydrogen chloride, carbon dioxide, hydrogen sulphide, nitrogen, argon, and nitrogen dioxide.

23. The wavelength calibration apparatus of claim 1 , wherein the at least one gas reference cell is filled with a mixture of different gases.

24. The wavelength calibration apparatus of claim 1 , wherein the at least one gas reference cell includes a plurality of gas reference cells, each gas reference cell filled with a different gas.

25. The wavelength calibration apparatus of claim 24 , wherein the gas reference cells are optically coupled together, by a free space mechanism, a fiber optic mechanism, or a combination thereof, such that t

Assignees

• Charles Stark Draper Laboratory Inc

Inventors

• Feke Gilbert D

Classifications

• G02B27/0972

  Prisms (prisms per se G02B5/04) · CPC title

• G01J3/44 Primary

  Raman spectrometry; Scattering spectrometry {; Fluorescence spectrometry} · CPC title

• G01C19/721

  Details, e.g. optical or electronical details · CPC title

• G01J2003/2866

  Markers; Calibrating of scan · CPC title

• G01J3/10 Primary

  Arrangements of light sources specially adapted for spectrometry or colorimetry · CPC title