A compact microfluidic refractive index sensor fabricated by drilling hole in the
middle section of a fiber Bragg grating (FBG) is reported herein. The laser-drilled hole provides a
microfluidic channel for the aqueous sample to pass through while at the same time permits coupling of
the interrogating light to detect the target analyte. The reported sensor takes advantage of the fact that a
small phase shift in the central region of the grating will result in a very sharp peak in the FBG
stop-band. The phase shift can be related to a range of possible perturbations inside the microfluidic
channel, including passage of cells, beads and a shift in the concentration of certain fluidic component.
The amount of wavelength shift of the peak in the FBG stop-band represents the change in the
refractive index inside the microfluidic channel. Simulation results indicate very favorable sensor
signal characteristics such as large wavelength shift and sharp reflection dips. The reported
microfluidic phase shift FGB sensor could be a good candidate for portable flow cytometry
applications.
The leakage light of an electro-optic modulator (EOM) induced by its finite extinction ratio (ER) may degrade the
performance of Brillouin optical time domain reflectometer sensing system, especially for long distance measurement. In
this letter, the configuration of a high ER probe pulse generator assisted by synchronous optical switch has been
presented. A dual pulses interferometric method was also proposed to determine the dynamic ER value (DER) of the
generated probe pulse. Contrast experiments have been performed to verify the effect of the proposed method in a
BOTDR system and the results have shown that the performance of a long distance BOTDR sensing system can be
improved observably with the proposed high ER probe pulse generator. At the end of a 48.5km sensing fiber, the
maximum uncertainty of temperature measurement has been reduced from 5.2℃ to 0.8℃ with 25m spatial resolution
after we improved the extinction ratio of probe pulse from 35dB to 65dB.
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