We demonstrate uniform and sampled Bragg gratings in silicon-on-insulator ridge waveguides with slab-modulated sidewall corrugations. Coupling coefficient and bandwidth can be precisely controlled by varying the distance between the slab-sidewall corrugations and the ridge. A bandwidth of 3 nm at the center wavelength of 1550 nm for uniform Bragg gratings is achieved for 100 nm slab-sidewall corrugation. Based on this structure, sampled gratings with 0.4 nm bandwidth are proposed. The measured results show good agreement with theoretical analyses.
A multimode fiber-loop ring-down spectroscopy for strain measurement is presented. With this technique, strain
measurement is achieved in a time domain by measuring the ring-down time. The prototype of the sensor consists of a
pulsed VCSEL laser diode, two multimode fiber couplers, a section of multimode fiber loop, photodetector, data
acquisition card and signal processing. Experimental results show that the ring-down time has a good linear response to
strain in the range from 534.2με to 1013.7με and the strain resolution is as small as 0.338με.
We present a fiber mode converter incorporated fiber-loop ring-down system for strain measurement. The sensing system
consists of a fiber mode converter and a typical fiber-loop ring-down system including a pulsed VCSEL laser diode at
850 nm, multimode fiber couplers, multimode fiber loop, photo-receiver and high-speed data acquisition and signal
processing. The bending multimode fiber-loop ring-down strain sensor is demonstrated with a resolution of 0.28 &mgr;&Vegr; over a
range of 767 &mgr;&Vegr;.
Dual-channel fiber ring down force sensor based on the principle of time division multiplexing is descried. The system
has the capability to interrogate more than two micro bend sensors by using more than one fiber delay line to control the
time of flight of the pulse. The dual-channel fiber ring down force sensor with one fiber delay coil is demonstrated with
high force sensitivities of 183.4ns/N and 163.6ns/N, respectively. Our system has also good linear responses.
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