An optical fiber refractive index (RI) sensor based on open microcavity Mach-Zehnder interferometer (OMZI) and fiber ring laser (FRL) is proposed and demonstrated experimentally. The OMZI is manufactured by splicing a tiny single mode fiber (SMF) segment with multi-mode fiber (MMF) joints laterally. The large offset structure forms an open microcavity which can be filled with the liquid under test. Through inserting the OMZI into an erbium-doped FRL, the RI measurement can be achieved by discriminating the lasing wavelength, and the detection limit (DL) can be effectively improved owing to the laser sensing spectrum with narrower 3-dB bandwidth and higher optical signal-to-noise ratio (OSNR). Experimental results show that the output laser wavelength has a linear response to the RI change with a sensitivity of −2947.818 nm/RIU during the range of 1.33302~1.33402, and the DL is as low as 5.89×10−6 RIU. Compared with other optical fiber RI sensors, the proposed fiber laser RI sensor with an open microcavity has the advantages of small size, high sensitivity and low DL, making itself a competitive candidate for the microfluidic RI measurement in biochemistry.
KEYWORDS: Polarization, Signal detection, Control systems, Sensors, Lab on a chip, Optical amplifiers, Modulators, Sensing systems, Modulation, Particle swarm optimization
In digital coherent optical time domain reflectometer (coherent-OTDR) system, a dual-parallel Mach-Zehnder modulator (DP-MZM) is employed to modulate the signal light and to generate frequency-shifted pulse light. However, the environment temperature strongly influent the stability of the DP-MZM. To stabilize the quality of the frequency-shifted pulse light, we proposed a bias control method to keep the modulator at the optimum bias. This bias control method search for the optimum bias by changing three bias voltages at the same time based on chaotic particle swarm optimization algorithm(PSO). The experimental results show obvious effect on locating the optimum bias voltages for the DP-MZM.
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