Yuchun Lu

Polarization Effects in Tilted Fiber Bragg Grating Refractometers

The polarization effects in tilted fiber Bragg grating (TFBG) refractometers are investigated theoretically. The polarization effects may degrade the sensor performance greatly, and should be considered to achieve high-precision surrounding refractive index (SRI) measurement. The possible paths to reduce the influence of polarization effects are discussed. For large SRI changes, the cutoff resonance wavelength can be used as sensing parameter to achieve a polarization insensitive SRI measurement with linear sensitivity of ~500 nm/u.r.i and SRI uncertainty of ~10-3 over SRI range of 0.1; for tiny SRI changes the measurement can be refined by monitoring proper individual resonance (close to the cutoff resonance wavelength) with accuracy approaching 2.5 × 10-5 over a SRI range of 0.001.

Side pumping scheme with a dual-sided grating coupler

A robust dual-sided grating coupler with high coupling efficiency (CE) is proposed and rigorously analyzed for laser-diode (LD) bars side pumping double-clad fiber (DCF). It consists of a double-groove metal grating and a composite diffraction grating with dielectric–metaldielectric (DMD) sandwich structure placed behind the upside and downside of the inner-cladding of the DCF respectively. High coupling efficiencies are obtained when the incident pump light is TE-polarized (85.96%), TM-polarized (90.7%) and un-polarized (76.04%) respectively. It is also demonstrated that the coupler is tolerant to potential fabrication errors and variations of the incident angle and central pump wavelength.

Growth of Ultraviolet-induced H 2 -loaded long period fiber grating immediately after fabrication

The growth of long period fiber grating written in H2-loaded fiber within one hour immediately after fabrication was measured and analyzed. Fast deepen on difference of refraction index was obviously observed in all the experiments, but the peak wavelength to time and cross-coupling coefficient to time curves are fitted better in exponential decay function than power function, and suggest a same variation pattern in difference of refraction index.

Novel method to optimize the distributed pump powers in kilowatt ytterbium-doped double-clad fiber laser

Time independent rate equations for fiber laser are solved accurately with numerical method under multipoint boundary conditions. A novel method based on genetic algorithm is firstly proposed to optimize distributed pump powers and fiber segment lengths of kilowatt YDDC fiber laser. The uniformity of temperature distribution is improved by using optimized method. The calculated results show that the lower operating temperature and better uniformity can be obtained through increasing the number of segments at the cost of decreased output signal power.