An approach to achieve simultaneous measurement of refractive index and temperature is proposed by using a Mach-Zehnder interferometer realized on tapered single-mode optical fiber. The attenuation peak wavelength of the interference with specific order in the transmission spectrum shifts with changes in the environmental refractive index and temperature. By utilizing S-band and C / L-band light sources, simultaneous discrimination of refractive index and temperature with the tapered fiber Mach-Zehnder interferometer is demonstrated with the corresponding sensitivities of Ϫ23.188 nm/RIU ͑refractive index unit͒ and 0.071 nm/°C, and Ϫ26.087 nm/RIU ͑blueshift͒ and 0.077 nm/°C ͑redshift͒ for the interference orders of 169 and 144, respectively. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3115029͔In situ monitoring of physical, chemical, and biological parameters is of great importance for process control in manufacturing industries, protection of ecosystems, and prevention of global warming. Refractive index ͑RI͒ and temperature are the most important parameters in these applications, especially in chemical or food industries for quality control and in biosensing for monitoring molecular bindings or biochemical reactions. Traditionally, the standard technique to measure refractive index is a refractometer, for which many well-known apparatus such as Pulfrich and Abbe refractometers have been used for many decades. 1 Surface plasmon resonance ͑SPR͒ has also been adopted for refractive index measurement through evanescent waves in waveguide configurations. 2 However, all these apparatuses are essentially bulky prism systems.In recent years, fiber-optic sensors have received significant attention for their unique advantages such as immunity to electromagnetic interference, compact size, potential low cost, and the possibility of distributed measurement over a long distance. 3 Earlier work on fiber-optic sensors for refractive index measurement reported metal-coated side-polished fibers, tapered fibers, or multimode fibers with relatively thin cladding layers to excite SPRs. 2,4 Besides the approach with evanescent waves from nanometer fiber tips coated with gold particles, 5 a majority of fiber sensors for refractive index measurement utilized fiber gratings, i.e., long-period gratings ͑LPGs͒ and fiber Bragg gratings ͑FBGs͒. Recent work that reported refractive index measurement with LPGs are either gold coated, 6 arc-induced phase shifted, 7 asymmetric, 8 or inscribed in air-and water-filled photonic crystal fibers. 9 Reported refractive index measurement with FBGs includes a metal-coated grating in a special single-mode fiber of larger core ͑26 m͒ and thinner cladding ͑30 m͒, 10 a tilted FBG with gold coating in single-mode fiber, 11 and cladding mode resonances of etched-eroded FBG. 12 A few papers reported simultaneous sensing of refractive index and temperature using LPGs, modified FBGs, and hybrid LPG-FBG structures, 13-15 with complicated design, instable system, or high cost, which restricts their pr...
A review of research activities on opto-microfluidic sensors carried out by the research groups in Canada is presented. After a brief introduction of this exciting research field, detailed discussion is focused on different techniques for the fabrication of opto-microfluidic sensors, and various applications of these devices for bioanalysis, chemical detection, and optical measurement. Our current research on femtosecond laser microfabrication of optofluidic devices is introduced and some experimental results are elaborated. The research on opto-microfluidics provides highly sensitive opto-microfluidic sensors for practical applications with significant advantages of portability, efficiency, sensitivity, versatility, and low cost.
By taking advantages of the two-photon polymerization induced by femtosecond laser and the versatility of the femtosecond laser microfabrication, we demonstrate a femtosecond laser microfabricated polymeric grating for spectral tuning, in which gratings of different thicknesses achieve gradual tuning of a white incident light into output lights of different colors ranging from cyan to red, which is in good agreement with the simulation. Through the selection of different grating parameters, the technique developed in this study offers the possibility to tailor the performance of the grating to achieve specific grating efficiency or complete extinction at specific wavelengths, which is promising for measurements and applications in spectroscopy, sensing, integrated optical systems, and biomedicine.
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