Low-cost spectrometry system for end-user food analysis
A compact spectrometer is disclosed that is suitable for use in mobile devices such as cellular telephones. In preferred embodiments, the spectrometer comprises a filter, at least one Fourier transform focusing element, a micro-lens array, and a detector, but does not use any dispersive elements. Methods for using the spectrometer as an end-user device for performing on-site determinations of food quality, in particular, by comparison with an updatable database accessible by all users of the device, are also disclosed.
1. A method for analyzing a sample, comprising:
providing a sample;
passing light emanating from said sample through a diffuser to produce diffused light;
passing said diffused light through an optical filter to produce angle-encoded light;
passing said angle-encoded light through a Fourier transform focusing element to produce spatially encoded light;
detecting said spatially encoded light using a detector to produce spectral data, wherein said spatially encoded light of different wavelengths arrives at said detector as a series of circles of different radii proportional to said different wavelengths; and
analyzing said spectral data.
2. The method of claim 1 , wherein said detector is an image sensor.
3. The method of claim 1 , wherein said optical filter comprises a plurality of parallel strips, each of which comprises a sub-filter.
4. The method of claim 1 , wherein each of said sub-filters comprise different center wavelengths.
5. The method of claim 4 , wherein said center wavelengths depend on an angle of incidence of said diffused light.
6. The method of claim 1 , wherein said sample is a food sample.
7. The method of claim 2 , where the Fourier transform focusing element is a micro-lens array.
8. The method of claim 1 , wherein said analyzing comprises comparing said spectral data with a database of spectral information.
9. The method of claim 8 , further comprising adding said spectral data to said database of spectral information.
10. The method of claim 1 , further comprising illuminating said sample with a light source.
11. The method of claim 10 , wherein said light source comprises a laser or a light emitting diode.
12. The method of claim 10 , wherein illuminating comprises focusing light from said light source to a predetermined location relative to said sample.
13. The method of claim 12 wherein said focusing comprises an autofocus system to focus said light from said light source to said predetermined location relative to said sample.
14. The method of claim 13 , wherein said autofocus system comprises a voice-coil motor, a piezoelectric motor, or a micro-electrical-mechanical-system (MEMS) motor.
15. The method of claim 1 , wherein said first Fourier transform focusing element comprises a plano-convex lens, a biconvex lens, or an aspheric lens.
16. The method of claim 15 , wherein said Fourier transform focusing element comprises a plano-convex cylindrical lens disposed such that a flat face of the plano-convex cylindrical lens faces said detector and a curved face of the plano-convex cylindrical lens faces said optical filter.
17. The method of claim 16 , wherein said Fourier transform focusing element comprises a plurality of plano-convex cylindrical lenses disposed such that flat faces of said plano-convex cylindrical lenses face said detector and curved faces of said plano-convex cylindrical lenses face said optical filter, wherein focal planes of said plano-convex cylindrical lenses coincide.
18. The method of claim 1 , wherein said optical filter is a non-tunable filter.
19. The method of claim 1 , wherein said optical filter comprises a Fabry-Perot filter, a thin-film filter, or an interference filter.