RESUMO
A new in-fiber Mach-Zehnder interferometer (MZI) based on lateral-offset and peanut shape structure is proposed and demonstrated for the measure of curvature and liquid level. The sensor consists of lateral-offset structure and peanut shape structure. A section of single mode fiber (SMF) is spliced between them. A part of core mode in the single mode fiber is excited to cladding modes by lateral-offset. The cladding modes are re-coupled to the core mode by peanut-shape structure and get interference with the core mode. A high-quality interference spectrum with a fringe visibility of about 12 dB is observed. The effective refractive indices of cladding mode would change with the external environment parameters, which further bring about a shift of the interference fringes. The liquid level or curvature can be measured by record the shift of the valley, because the shift of the valley shows a linear dependence with the variation of the liquid level or curvature theoretically. In the water level experiment, the water level changes from 1.00 to 5.00 cm and the wavelength valley shows a red shift. The sensitivity of the MZI with a length of 6.10 cm is -0.68 nm·cm-1. In the curvature experiment, the curvature changes from 0.3 to 1.2 and the wavelength valley shows a blue shift. The sensitivity of the MZI with a length of 2.10 cm is 22.47 nm·m. The lateral-offset structure and peanut shape structure are spliced to fabricate the MZI. The sensitivity of the MZI is high, especially in the curvature measurement, it is higher than that of other fiber curvature sensors. Moreover the MZI presented in this paper has advantages of low cost and easy fabrication, which can be a potential application in the liquid level and curvature measurement.
RESUMO
A simple and low-cost vibration sensor based on single-mode nonadiabatic fiber tapers is proposed and demonstrated. The environmental vibrations can be detected by demodulating the transmission loss of the nonadiabatic fiber taper. Theoretical simulations show that the transmission loss is related to the microbending of the fiber taper induced by vibrations. Unlike interferometric sensors, this vibration sensor does not need any feedback loop to control the quadrature point to obtain a stable performance. In addition, it has no requirement for the coherence of the light source and is insensitive to temperature changes. Experimental results show that this sensing system has a wide frequency response range from a few hertz to tens of kilohertz with the maximal signal to noise ratio up to 73 dB.
RESUMO
By inscribing a long-period fiber grating (LPG) on a polarization-maintaining fiber (PMF), a fiber Sagnac loop sensor for simultaneous measurement of refractive index and temperature has been proposed and demonstrated. The LPG was fabricated on the PMF by using a CO2 laser, and then inserted into a fiber loop formed by using a normal single-mode fiber coupler. One of the transmission minimum of the Sagnac loop sensor was measured, whose wavelength varied with temperature and the intensity changed with refractive index. Temperature sensitivity of -0.654 nm x degrees C(-1) and refractive sensitivity of 49.9 dB x RIU(-1) have been achieved. The sensor system shows advantages of small size and low cost, and owns a good application prospect.
RESUMO
The use of photonic bandgap fibers (PBGF) for biomedical sensing has been demonstrated. The demonstrated PBGF has a blue wavelength shift of 280 nm in the falling photonic bandgap edge (PBE) when the ambient refractive indices inside the holey region change from 1.333 to 1.39, which agrees well with the analytical prediction. Combining this with the knowledge of immobilization techniques and biorecognition elements could open up a new class of PBGF-based label-free biosensors. A sensitivity on the order of 0.1 nmol/L could be achieved by consuming less than 1 microL of sample.
