Based on the relative intensity distributions of Sodium Laser Beacon (SLB) and analysis of the on-axis imaging of incoherent light, considering the effects of atmospheric turbulence and the changes of telescope receiving diameter on the short-exposure SLB imagings on the focal plane, imagings of an extended source SLB are simulated under the three atmospheric turbulence models. Results indicate that sharpness and peak strehl ratio of SLB imagings increase but sharpness radius decrease with the decrease of atmosphere turbulence strengths. Moreover, the changes of telescope diameter from 3.0m to 1.5m cause the decrease of sharpness and peak strehl ratio but the increase of sharpness radius.
A novel single-ended reflecting long period fiber grating (LPFG) sensor with thin metal film overlay and the sensing
system is described. An all-fiber reflection based surface plasma resonance (SPR) LPFG sensor with three-layer structure
(core, cladding and metal) is established experimentally and fabricated with a pulsed CO<sub>2</sub> laser writing system and
vacuum evaporation coating system. Different nm-thick thin metal films are deposited on the reflected LPFG sensor for
the excitation of surface plasma waves (SPWs) and the characteristics of the reflection resonance spectra of the LPFG
sensor for measuring refractive index of fluids are studied. It is found that different thicknesses of different metal films
show different measuring sensitivity. Through the comparison of the resonance wavelength obtained in air, water,
alcohol, glycerin and their mixture solution, different sensitivities of the reflected SPR-LPFG sensor have been achieved.
The proposed SPR-LPFG sensing scheme offers an efficient platform for achieving high performance fiber sensors for
the measurement of ambient refractive index.
We present an analytical expression for sampled fiber Bragg gratings (SFBGs) with arbitrary chirps in sampling function
or grating period or combination of both. The relationship among the wavelength of each channel, the chirp coefficient
of the sampling and the grating period, and the total length of the grating is explicitly given. Specifically, the chirped
sampling function is first expanded into a new function using Fourier theory; the equivalent local Bragg period is then
obtained to derive the expression of the reflection peak wavelength. The overall wavelength position is obtained by
summation of both contributions from sampling chirp and the grating chirp. The calculated results based on the analytical
expression are examined with the conventional numerical results, which are found to be in excellent agreement.
We present the experimental results of a novel single-ended reflecting surface plasma resonance (SPR) based long period
fiber grating (LPFG) sensor. A long period fiber grating sensing device is properly designed and fabricated with a pulsed
CO2 laser writing system. Different nm-thick thin metal films are deposited on the fiber cladding and the fiber end facet
for the excitation of surface plasma waves (SPWs) and the reflection of the transmission spectrum of the LPFG with
doubled interaction between metal-dielectric interfaces of the fiber to enhance the SPW of the all-fiber SPR-LPFG
sensing system. Different thin metal films with different thicknesses are investigated. The effect of the excited SPW
transmission along the fiber cladding-metal interface with silver and aluminum films is observed. It is found that
different thicknesses of the metal overlay show different resonant behaviors in terms of resonance peak situation,
bandwidth and energy loss. Within a certain range, thinner metal film shows narrower bandwidth and deeper peak loss.
The spectral self-imaging phenomenon is observed in binary phase-only sampled fiber Bragg gratings (SFBGs) using
numerical simulations. Integer and fractional Talbot effects are obtained under conditions of Talbot effect. The
characteristics of the Talbot spectrum in terms of channel spacing and the group delay from the phase-only sampled
FBGs are discussed.