A dual-parameter fiber sensor achieved by cascading a fiber Bragg grating with a no-core fiber (NCF) is used for simultaneously detecting both the temperature and index physical parameters. The main index sensing mechanism of NCF is based on the wavelength shift of multimode signals’ interference (MMI), and the temperature-sensing mechanism is determined by the Bragg wavelength shift and MMI wavelength shift. As the testing index value approaches the cladding index of the optical fiber, an MMI-induced loss-dip is thus created with a sensitivity of 899 nm/RIU due to the phase-match condition of MMI being satisfied. By coating the thin films of different materials, this kind of sensor can be applied in a wide range of different sensing systems.
Varying the heating rate of rapid thermal annealing (RTA) reveals a broadband shift of room-temperature photoluminescence (PL) in 3×1016 cm−2 Si+-implanted 400-nm-thick SiO2 films after RTA at 1150°C in dry nitrogen. At a heating rate of 100°C/s, the PL peaks shift from 2.6 eV to 1.7 eV for isothermal RTA durations from 1 to 20 s. Additionally, decreasing the heating rate to 25°C/s does not significantly shift the PL peak in the films after the isothermal RTA for durations 1 s. The attractive features of RTA provide a valuable reference for manufacturing of optoelectronic devices.
We experimentally demonstrate that a 3×3 port fused fiber grating coupler can be implemented by combining the technique of fabricating fused-fiber couplers as well as that of writing fiber Bragg gratings for application in all-fiber optical filters. A Bragg grating with a reflectivity of 65% is written into the coupling region of a 3×3 fiber coupler with the coupling ratios of 60, 24, and 16%, respectively, for three different output ports. This device can be applied in optical multi/demultiplexing and add/drop filters or in special optical filters.
In this paper, we proposed a chemical-gas fiber sensor based on the poly-aniline film coated on the surface of an etched fiber grating and experimentally demonstrated for detecting ammonia gas. This sensing mechanism is based on the testing gas to interact with the poly-aniline coating film on the surface of the fiber grating to cause the thin-film index change and then to create the Bragg wavelength shift or grating reflectivity variation. The sensitivity and response time of this sensor for measuring ammonia gas are around 0.73 nm per percent concentration and tens of mini-seconds respectively, which depend on the optical characteristics of fiber grating, the diameter of fiber cladding, and the constituents of chemical sensing film. This sensor may provide a simple, reliable, repeatable and non-destructive fiber sensing technique.
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