The ability to achieve low phase noise single-mode oscillation within an optoelectronic oscillator (OEO) is of fundamental importance. In the frequency-tunable OEO, the wide microwave photonic filter (MPF) bandwidth is detrimental to select single-mode among the large number of cavity modes, thus leading to low signal quality and spectral purity. Stable single–mode oscillation can be achieved in a large time delay OEO system by harnessing the mechanism from parity-time (PT) symmetry. Here, a PT-symmetric tunable OEO based on dual-wavelength and cascaded phase-shifted fiber gratings (PS-FBGs) in a single-loop is proposed and experimentally demonstrated. Combining the merits of wide frequency tuning of PS-FBG-based MPF and single mode selection completed by the PT-symmetric architecture of the OEO, where the gain and loss modes carried by dual-wavelengths to form two mutually coupled resonators in a single-loop, signals range from 1 GHz to 22 GHz with the low phase noise distributed in −122∼ −130 dBc/Hz at 10 kHz offset frequency are obtained in the experiment.
A cantilever deflection fiber-optic sensor based on chirped fiber grating (CFG)
Fabry–Perot (FP) cavity had been proposed and experimental
demonstrated. Two CFBGs with the same chirped coefficient direction
and grating parameters are written in one single-mode fiber by UV mask
exposure to form the CFG-FP cavity. The central wavelength of two CFGs
is 1549.6072 nm, the 3 dB bandwidth is 2.9897 nm, and the physical
cavity length of two CFGs is 1 cm. The grating region of two CFGs are
straightness fixed on a cantilever beam, forming a sensor. Then the
optical properties of this sensor are tested with different stresses
at different positions of the cantilever beam. The experimental
results show that this sensor can obtain linear displacement of a
cantilever beam, overcoming the abilities of the FBG sensor, which
only performed point measurement defect. The wavelength drift
sensitivity of the sensor is 2.31 pm/g, and linearity is 0.99916. This
sensor has great application value in the precise measurement of
cantilever beam type and two-dimensional scale strain.
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