The coherent transmission function of the system is deduced and the influence of fiber on axial resolution is investigated in detail on the basis of point spread function and Fourier optics. It is shown that the system acts as a coherent imaging system and the axial resolution of the system decays with increasing fiber radius A. An endoscopic confocal imaging system was built, and the in-focus image of glass grating was obtained which shows sufficient resolution.

A novel photonic crystal fiber (PCF) with near zero ultra-flattened dispersion in the range of 300 nm broadband is demonstrated. All air holes are arranged in the section according to strict triangular regulation and identical spacing. Thirteen air holes in the middle of the section arrayed in the shape of snowflake, smaller than other air holes in the outer cladding region, form the larger crystal core of PCF. Obviously, this kind of photonic crystal fiber with snowflake crystal core (SCC-PCF) has large modal field area than conventional PCF as the thirteen air holes as a whole increase the core area greatly. Furthermore, dispersion curve is very flat and near zero dispersion can be obtained in the range of 300 nm broadband by optimally matching crystal core air holes size with cladding region. Resulting from the structure of core, modal field distribution is snowflake-like, but the output of near distance field distribution will evolve into Gaussian-like shape.

The exponential function is used to fit the curves between the beam parameters in the diffractive field of LP01 mode fiber end surface and the basic parameters of fiber. The fitting function between mode field radius in the near field, angular radius of far field divergence, beam propagation factor and the normalized frequency with the core layer radius are obtained respectively. The computed results from the fitting functions are very close to that from the analytical functions, when 1.5 ＜V＜ 9.4, the maximal relative error is smaller than 2%. In a certain degree, these conclusions will provide academic foundation for analyzing or calculating the beam parameters approximately.

A finite-element-simulation for pulse amplification in ytterbium-doped double-clad fiber amplifier is presented by means of (finite element modeling laboratory )FEMLAB package. The upper-level population distributions, the pump power, and the amplified spontaneous emission while under forward pumping with 915 nm are investigated. The transient output power, stored energy and gain of both Gaussian and square pulse are simulated. The obtained results are agreement well with the results reported in the experimental and other numerical studies.

A highly nonlinear microstructured fiber is proposed to construct nonlinear optical loop mirrors (NOLMs) for pulse compression and pedestal suppression. The proposed fiber has high nonlinear coefficient and large anomalous dispersion. The compressions of pulses by the NOLMs are theoretically investigated and the compression mechanism is also discussed. It is shown fro mnumerical results that the proposed NOLMs compress the pulses efficiently and significantly suppress the pedestals with a short loop length. For a given input pulse, there exists an optimal loop length at which the high quality compressed pulse can be obtained. By appropriately choosing the power-coupling ratio and loop length, the pedestal can be removed entirely.

In the frame of quantummechanics, the equation to describe the particle motion in Tan2x quantum well is reducedto the hypergeometric equation. The eigenvalue and the eigefunction are obtained bysolving the Schrödinger equation. Analytical expressions of linear and thethird-order nonlinear optical refractive index changes are obtained in Tan2x quantum wellusing the density matrix formalism taking into account the intrasubband relaxation. Thelinear and the third-order nonlinear refractive index changes are calculated. The resultsshow that the refractive index changes depend on the shape of the well, the tunnelbandwith and the optical intensity. Numerical results are presented for a typicalGaAs/AlGaAs Tan2x quantum well.

A diffractive/refractive long wavelength infrared (LWIR) staring imaging system is designed to meet the commercial requirements. In this system the F-number is 1,waveband is 8～12 μm ,field of view is 12°, total track is 140 mm and the materials of the total two lenses are Germanium. The diffractive optical element (DOE) is fabricated on the convex of the second lens,and the DOE can be fabricated by diamond turning technology. The imaging quality is analysed that the Modulation Transfer Function (MTF) approaches the dilfraction limit and the chromatic aberration is better corrected compared with the refractive system.