We report a miniaturized fiber inline Fabry-Perot interferometer (FPI), with an open micro-notch cavity fabricated by one-step fs laser micromachining, for highly sensitive refractive index measurement. The device was tested for measurement of the refractive indices of various liquids including isopropanol, acetone and methanol at room temperature, as well as the temperature-dependent refractive index of deionized water from 3 to 90 degrees C. The sensitivity for measurement of refractive index change of water was 1163 nm/RIU at the wavelength of 1550 nm. The temperature cross-sensitivity of the device was about 1.1x10(-6) RIU/degrees C. The small size, all-fiber structure, small temperature dependence, linear response and high sensitivity, make the device attractive for chemical and biological sensing.

We report a miniaturized inline Fabry-Perot interferometer directly fabricated on a single-mode optical fiber with a femtosecond laser. The device had a loss of 16 dB and an interference visibility exceeding 14 dB. The device was tested and survived in high temperatures up to 1100 degrees C. With an accessible cavity and all-glass structure, the new device is attractive for sensing applications in high-temperature harsh environments.

We report what we believe to be a new method to fabricate surface enhanced Raman scattering (SERS) fiber probe by direct femtosecond laser micromachining. Direct femtosecond laser ablations resulted in nanostructures on the cleaved endface of a multimode optical fiber with a 105/125 microm core/cladding diameter. The laser-ablated fiber endface was SERS activated by silver chemical plating. High-quality SERS signal was detected using Rhodamine 6G molecules (10(-8)-10(-6) M solutions) via back excitation with the fiber length of up to 1 m. The fiber SERS probe was compared with a planar fused silica substrate at a front excitation. The long lead-in fiber length and the backexcitation/collection setup make the SERS probe promising for remote sensing applications.

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