We present a newly developed high performance fiber optics sensor for quasi-static strain measurement. The sensor consists of a piece of π-phase shifted FBG for static strain sensing, and fiber Fabry-Perot interferometer for reference, interrogated by an improved sideband interrogation method with real-time feedback loops. Strain resolution of 0.12 nano-strain was achieved with sampling rate up to 1 kS/s in laboratory experiments. Compared with previous sensor systems, the proposed method shows great improvement in the sensing rate as well as the resolution.
We reported an optical fiber based temperature sensor with mK-order resolution, wide temperature range and excellent long term stability. The sensor composes of a fiber Bragg grating (FBG) as the sensing element, an HCN gas cell for absolute frequency reference. A distributed feedback diode laser with current modulation is used as the light source. To overcome the frequency-sweep nonlinearity of the laser, an auxiliary Fabry-Perot interferometer with free spectrum range of 10 MHz is employed. A cross-correlation algorithm is employed to calculate the center frequency difference between the FBG and the gas cell. With the proposed configuration, a temperature resolution of 0.41 mK was demonstrated in experiment. To the best knowledge, this is the first time that an mK order temperature resolution has been achieved by optical fiber sensor.
We developed a novel optical coherent domain reflectometer (OCDR) technique with large measurement range by using of dual frequency modulation. The probe and local oscillator beams are frequency modulated independently, and the sensing position can be adjusted digitally via the time delay between the driving signals for the two modulators. Meanwhile, the frequency tuning spans of the two paths are different to enable heterodyne detection. In the demonstrational experiments, a spatial resolution of 3.9 m over a range of 24.6 km fiber was achieved with 35 MHz tunable range of the modulator, and the spatial resolution keeps a constant over the whole measurement range.
We demonstrate confinement of light in a submicron-diameter silica core by adding a Bragg multilayer cladding.
Simulation results show that silica core Bragg fibers with Si/SiO<sub>2</sub> multilayer claddings exhibit stronger mode
confinement than air cladding silica fiber. The optical properties of Bragg fiber taper can be fine tuned via controlling
taper diameter and multilayer structures. In experiment, TE<sub>01</sub> mode-shaped spots with full-width at half-maximum
(FWHM) of 1.2 μm are observed for the first time to our knowledge in solid-core Bragg fibers. By adjusting the
refractive index of high index layer, HE<sub>11</sub> mode-shaped spots with FWHM of 0.75 μm are generated by 1.1 μm-core
Bragg fiber tapers. The proposed devices will be good candidates as polarization selection and mode conversion devices for nano-optical applications.
We demonstrate the possibility of confining light in a submicron silica core by introducing a Bragg multilayer cladding.
1 μm-core Bragg tapers with mode field diameters about 1.1 μm for 850 nm wavelength are successfully fabricated by a
sputtering technique combining with tapering method using a traveling burner. Simulation of the mode intensity profiles
for both our devices and air cladding silica fibers are made by a beam propagation method. Bragg fiber tapers show
stronger confinement than silica glass tapers. The ultra-small core Bragg taper device will be a good candidate as the
mode coupler for nano-optical devices.