All-fiber spectroscopic optical sensor

1. An all-fiber spectroscopic optical sensor for analyzing a sample, the sensor comprising:

a. a light source for producing an optical signal;

b. a sensor head where the optical signal interacts with the sample to produce an output spectrum;

c. a fiber acousto-optic tunable filter (FAOTF), in a path of the output spectrum, for selecting wavelength components from the output spectrum; and

d. one or more photo detectors for measuring said wavelength components.

2. The spectroscopic sensor of claim 1 , further comprising optical fibers for interconnecting the light source, the sensor head, and the FAOTF for optical signal delivery.

3. The spectroscopic sensor of claim 1 , wherein the light source is a broadband light source.

4. The spectroscopic sensor of claim 3 , wherein the broadband light source comprises a light emitting diode, a super-luminescence diode, a supercontinuum light source, or a lamp.

5. The spectroscopic sensor of claim 3 , wherein the output spectrum from the sample is an absorption, transmission, reflection and/or scattering spectrum.

6. The spectroscopic sensor of claim 1 , wherein the light source is a narrowband light source,

7. The spectroscopic sensor of claim 6 , wherein the narrowband light source comprises a laser or a filtered narrow bandwidth light source.

8. The spectroscopic sensor of claim 6 , wherein the output spectrum from the sample is an emission spectrum for fluorescence spectroscopy, Raman spectroscopy, and/or laser-induced breakdown spectroscopy.

9. The spectroscopic sensor of claim 1 , wherein the sensor head comprises a first collimating optical element, a second collimating optical element, and a sample holder, and wherein the optical beam from the light source is first collimated by the first collimating element and then delivered to the sample, and wherein the optical beam transmitted or emitted from the sample is collected by the second collimating element.

10. The spectroscopic sensor of claim 1 , wherein the sensor head comprises a section of tapered or deeply etched optical fiber, and wherein the sample interacts with the optical signal through evanescent field coupling.

11. The spectroscopic sensor of claim 1 , wherein the sensor head comprises a fiber long-period grating or tilted fiber Bragg grating, and wherein the sample interacts with the optical signal through the cladding mode.

12. The spectroscopic sensor of claim 1 , wherein the FAOTF operates in a wavelength regime from UV/visible to infrared.

13. The spectroscopic sensor of claim 1 , wherein the FAOTF is built on single mode fiber, two-mode fiber, multi-mode fiber, tapered fiber or photonic crystal fiber.

14. The spectroscopic sensor of claim 13 , wherein the FAOTF has a wavelength tuning range greater than 500 nm.

15. The spectroscopic sensor of claim 14 , wherein the FAOTF has only one filtering peak in the wavelength tuning range.

16. The spectroscopic sensor of claim 14 , wherein the FAOTF has a bandwidth less than 5.5 nm.

17. The spectroscopic sensor of claim 13 , wherein the photo detector is put at the end of the fiber to detect core mode power.

18. The spectroscopic sensor of claim 13 , wherein the photo detector is attached on side of the fiber to detect higher order mode or cladding mode.

19. An all-fiber spectroscopic optical sensor for analyzing a sample, comprising:

a. a light source for producing a broadband optical signal;

b. a fiber acousto-optic tunable filter (FAOTF) for selecting wavelength components from the broadband optical signal;

c. a sensor head where the selected wavelength components of the optical signal interacts with the sample to produce an output optical signal; and

d. one or more photo detectors for measuring said output optical signal.