A novel spectrum differential integration (SDI) method has been proposed and verified in an in-line fiber Mach-Zehnder (MZ) refractive index (RI) sensor using salt solutions. In SDI method, the difference between two interference spectra is determined by pointwise subtraction at each wavelength, followed by integration of the absolute differences along the scan range. Compared with the widely used peak wavelength shift method, the SDI method is more reliable over a wide wavelength range (on the order of 400 nm) and results in higher sensitivity as well as reduced device-dependence. The SDI method can also be utilized with other kinds of modal interferometric sensors.

A novel distributed strain and temperature measurement method based on Brillouin beat spectrum (BBS) in a complex index profile fiber are proposed. The BBS corresponds to the optical interaction of different acoustic modes. For a large-effective-area fiber (LEAF), the first peak of BBS is contributed by the first and second acoustic modes, while the second peak in BBS is contributed by the first and third accoustic modes. Through determining power changes in the peaks of BBS due to strain and temperature variation along a LEAF, the distributed strain and temperature can be measured by the homodyne Brillouin optical time-domain reflectometry (BOTDR) without scanning the Brillouin spectrum. The strain and temperature at the end of a 4.5-km LEAF are measured at 3-m spatial resolution in 140 s.

The step-index heavily germanium-doped silica fibers with all normal dispersion (ANDi) are promising candidates for highly coherent supercontinuum (SC). These ANDi step-index silica fibers are easier to fabricate, splice and handle than silica photonic crystal fibers (PCFs). 40 % GeO2 doped step-index silica fiber of 3 μm core diameter has flat and near-zero dispersion which is between -5.5 and 0 ps/nm/km from 1.4 to 2.4 μm. Highly coherent SC spanning from 1050 nm to 2100 nm generated from the ANDi step-index heavily germanium-doped silica fiber pumped at 1560 nm. All-fiber coherent SC source from 1200 nm to 2200 nm is achieved by splicing the ANDi silica fiber with a 1560 nm femtosecond fiber laser of 90 % couple efficiency. Moreover, the step-index ANDi germania-core silica fiber of 2.2 μm core diameter is proposed to generate coherent mid-infrared SC from 1.7 to 3 μm. The ANDi step-index silica fibers not only can generate highly coherent broadband SC at near infrared or mid-infrared region but also can easily achieve all-fiber structure coherent SC source. And the experiment of supercontinuum generation in UNNA4 and UHNA7 fibers with different pump wavelengths indicates that the pump of 1064 nm is not suitable for coherent supercontinuum generation in the fiber of UNNA4 and UHNA7.

A simple tunable dual-wavelength fiber laser was developed and multiple self-mixing interferometry to large step height measurement was demonstrated. The fiber laser, which can emit two wavelengths without laser mode competition, is composed of a single fiber ring cavity and two fiber branches. Each branch includes a length of erbium-doped fiber and a fiber Bragg grating. Large step heights can be measured using multiple self-mixing interference of the two wavelengths. The maximum height that can be measured is half synthetic wavelength of the two wavelengths. A step height of 2mm constructed with two gauge blocks has been measured. The standard deviation of measurement results is 2.5nm.

We proposed a method for flat supercontinuum (SC) in specified band based on non-degenerate Raman four-wave mixing (NRFWM) modulation. The dispersion of the photonic crystal fiber (PCF) and peak power of the pump light, are controlled such that the gain of the NRFWM falls in our desired band. This provides a new method for realizing SC with broadband hyperspectral intensities in the short-wavelength direction. By this method we developed a near-infrared flat SC. Its spectral intensity of 3 dB corresponds to a bandwidth of 420 nm at a central wavelength of 800 nm. In addition, the relative intensity of the anti-Stokes light is 75.2%, and 49.6 % of the total spectral energy is concentrated in the 610–1030 nm band, which provides a more effective light source for optical coherence tomography (OCT). Using this SC as the light source of OCT can improve the axial resolution to 0.8μm.