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To design a concave grating for a hyperspectral imaging (HSI) system, it is critical to achieve flat field focusing in both the horizontal and vertical directions on the image sensor. We have developed a generalized automation aberration reduction procedure (ARP) that can be applied in any cases of a concave grating spectrometer. The concave grating, which has a free-form profile with blaze grating pitch and variable line spacing [3], is fabricated using five-axis CNC machine with nanometer machining precision for hyperspectral imaging. In order to evaluate the performance, an optical system is designed and setup to measure the focused spot size, spectral resolution and diffraction efficiency.

We have proposed an analytical 2D model [1] of a thickness gradient function for thin film deposition of a LVF for order sorting of a diffraction grating using an evaporation chamber. The LVF was fabricated and its thickness profile was measured using a probe-type surface analyzer. This study proposes an innovative method for overcoming the low production rates currently associated with LVF fabrication. Within the 25% - 75% thickness range, the profile distribution exhibits a high degree of linearity, with R2 are greater than or equal to 0.9914 for both the cases. The LVF zone width appears to be a linear function of the mask height h, with R2 are greater than or equal to 0.9982 for all the cases. This indicates that the thickness gradient function is a more accurate model for obtaining the thickness profile of an LVF than any other modeling mentioned in previous published results. This study demonstrates that the developed theoretical 2D model can be used to predict accurately the thin film profile of an LVF. The effective zone width of the LVF is defined as a thickness range of 25% - 75%, which appears to have high degree of linearity as a function of the mask height, h (mask-to-substrate gap). Thus, these results also confirms that the linear variable area increases as the mask-to-substrate gap increases. Thin film layer structures are constructed to demonstrate the efficacy of the proposed LVF design concept. Transmission spectrum result (wavebands 400nm to 1000nm) for varying mask heights at different positions shows maximum number of wavebands with transmittance (>99.9%). Comparison of both the theoretical and the evaporating results matches satisfactorily.

Dissimilar materials between TiNi shape memory alloy (SMA) and stainless steel of 200μm mm thick were butt welded by micro impulse laser and the electrochemical behavior of the weld joints was studied. The results show that the crack sensitivity of the welded joint is very high and good joining between TiNi SMA and stainless steel can be realized with pure Ni wire as filler material presented between TiNi SMA and stainless steel. The tensile strength of the welded joint with pure Ni wire as filler material is 580MPa. The electrochemical tests of the welded joints in different concentrations of NaCl solutions and different pH value solutions show that, the maximum of the corrosion potential Ecorr in the three typical corrosion systems (0.9%NaCl, pH=7.3; 3.5%NaCl, pH=7.3; 0.9%NaCl, pH=4) is the weld seam, which indicates that the corrosion tendency of the weld is smaller than that of TiNi alloy and stainless steel in the three corrosion systems. The pitting corrosion potential of TiNi alloy, stainless steel and the weld gradually decreased with the increase of Cl-concentration; the pitting corrosion potential decreased with the increase of H+ concentration, while TiNi alloy decreased faster than that of the weld and stainless steel, the surface stability of TiNi alloy is low when pH value dropped below 7.

0.2-mm-thick copper and 0.3-mm-thick nickel-plated steel dissimilar metals were jointed by resistance spot microwelding. The processing parameters were optimized by orthogonal experimental and influence of processing parameter on the morphology and microstructure of welded joint was studied. The results show that the optimized processing parameters that can get the maximum tensile-shear force are: preheat current is 0.8KA, welding current is 3.5 KA, up time is 0.5ms, preheat current is 2ms, cool time is 0.5ms, welding time is 5ms, and electrode pressure is 20N. With the optimized processing parameters, the tensile-shear force of the welded joint can achieve 108.9N. The microstructures of welded joint that has best tensile-shear force are composed of swirling structure in weld nugget, uniform distribution of copper in weld nugget with a little of nickel.

0.2mm thick titanium alloy sheet was butt-welded using micro impulse laser, influnce of the different processing parameter on the surface and cross-section morphology of welded joint was studied , testing the mechanical properties of joints. The result show that argon as a shielding gas, 0.2mm thick titanium alloy to the laser as heat source can be successful butt welding with process parameters of the pulse power 8.8W, pulse width 2.9ms, pulse frequency 7.0HZ, and forming a good welded appearance, the tensile strength and microhardness of welded joints was higher than the base metal. By the needle-like martensite α 'phase composition of the basket-like structure located in the center of the weld.

Butt welding of 0.2 mm-thick TiNi shape memory alloy sheet (SMA) was carried out using impulse laser, and tensile strength, fracture morphology, microstructure and phase change behaviour of welded joint were studied. The results show that using impulse laser can realize good butt welding of TiNi SMA sheet, tensile strength of welded joint is 683 MPa, which achieves 97% of that of cold rolled base metal, and the fracture mode of welded joint is ductile type as well as base metal. The welded joint can be divided into four zones according to grain size and microstructure. The microstructures of welded seam center zone are fine equiaxed crystals and the microstructures of both lower surface and upper surface edge zones are columnar crystals. When welded joint is vacuum annealed after welding, the phase transformation process is basically similar to the annealed base metal.

A chirped fibre Bragg grating according to ITU-T suggested L-band (2nd channel λ1 = 1570.83 nm; 80th channel λ2 = 1603.57 nm) with more than 1800 ps/nm single channel dispersion compensation is presented in this paper, of which the cladding mode loss, the delay curve ripple and the power fluctuation of the reflected spectrum are less than 0.5 dB, 50 ps and 0.25 dB, respectively. With this new FBG as dispersion compensation device, a 2 × 10 Gb/s wavelength division multiplexing (WDM) L-band transmission of 600 km based on conventional single mode fibre (G.652 fibre) is performed without forward error correction. The bit error rate (BER) is less than 10−12 and the power penalties of the 2nd and 80th channel of L-band are 1.8 dB and 2.0 dB, respectively.

We demonstrate a 10.7 Gb/s-line-rate L-band wavelength-division-multiplexer (WDM) loop transmission over a 1890-km standard single-mode fibre (SSMF) with a 100-km amplifier spacing as well as non-return-to-zero (NRZ) format. The dispersion compensating fibre (DCF) plus chirped fibre Bragg grating (CFBG) is employed for hybrid inline dispersion compensation. The power penalty of each channel is less than 3 dB after three-loop transmission. The experimental results show that high-performance CFBGs can be successfully used in ultra-long haul (>1000 km) WDM systems. We also point out that the all-CFBG compensation scheme is not suitable for re-circulating loop transmissions.

A kind of single cladding highly Yb3+-doped silica optical fiber was fabricated by a new furnace round heating MCVD process. The best temperature of deposition pass and that of sensitive presintering pass were presented; the absorption of it achieved 594 dB/m at 976 nm and its background loss was only 0.1 dB/m.

The silica based Tm3+ doped fiber preform with high Ge concentration in preform core area was manufactured by solution doping method. It was made into an optic fiber preform with cross section of a hexagon by side polishing process, and drawn in to cladding pumping Tm3+ doped fiber with inner coverage layer of lower refraction index polymer. The absorption spectrum was measured, and the technical parameters were optimized. The uniform fiber Bragg gratings with reflectivity of 90% and 40% were written in both ends of the fiber by UV light respectively, and the linear optic cavity was constructed. The laser with wavelength of 1947.1031nm and power of 2.05W was emitted by pump laser excited with wavelength of 793nm and power of 5.6W. It shows that the fiber have excellent optical characteristics.

An approximate analytical expression of the stress birefringence for Panda polarization-maintaining fiber (Panda-PMF) was deduced by using elasticity theory and complex function method. Based on this expression, the birefringence properties of this fiber were analyzed numerically by using the finite-element method. The results show that the birefringence expressed by core average stress mode is more accurate than that expressed by the core center stress mode and the error of the former is less than 0.18% compared with that of the analytic method. Further more, the birefringence degradation of the Panda-PMF induced by stress area mismatch was analyzed and proved by the related experiment.

The characteristics of co-doping Al3+ in ytterbium-doped silica-based fiber used for high-power cladding pumped laser were analyzed based on experimental analysis. The results show that the optimum mole percent of Al3+ to Yb3+ is 9—11 for high concentration of ytterbium-doped silica-based fiber at which low concentration quenching probability, high absorption coefficient and proper numerical aperture can be obtained. Meanwhile, ytterbium-doped silica-based fiber preforms were fabricated by MCVD and special solution doping technique. By soot layer temperature experiment and test of the related parameters of the drawn fiber, the results show that the optimum temperature for making soot layer can be accurately controlled and the absorption coefficient at 976 nm was as high as 620 dB/m with good repeatability. This conclusion makes a useful reference for fabrication of ytterbium-doped Al3+ co-doped fiber.

In order to obtain high-concentration doped erbium ions in silica-based fiber, we manufactured Er3+-Bi3+-Ga3+ co-doped fiber using MCVD and solution doping technique. The concentration of Er3+ in the fiber was about 5.24×1025/m3. We described a new method to measure the degree of clustering in the Er3+-Bi3+-Ga3+ co-doped fiber using fiber transmission experiment. Compared with other methods, the new method is simpler and more accurate. By the new method, the degree of clustering in Er3+-Bi3+-Ga3+ co-doped fiber was determined. It was shown that co-doped Bi3+-Ga3+ strongly increased the Er3+ solubility in the silica-based fiber.

Erbium-doped hole-assisted lightguide fiber (EDHALF) is composed of a high-index core doped with erbium, a low index cladding and a small number of air holes surrounding the core. The finite element method is applied for solving the modal field of the EDHALF. The numerical calculation methods of the cutoff wavelength and mode field diameter are described in detail. The modified average population inversion iteration method is proposed for calculating the gain and noise figure of erbium-doped fiber amplifiers. The effects of the air holes on EDHALFs' cutoff wavelengths, mode field diameters and the gain coefficients of fiber amplifiers are studied. It's found that decreasing the relative hole-to-core spacing can make the cutoff wavelength move to shorter wavelength and decrease the mode field diameter. When the relative size of air holes is relatively large, further enlarging it only slightly changes the cutoff wavelength, mode field diameter and the maximum of the gain coefficient. Finally, four structural parameters, namely the EDHALF-core radius, the refractive index difference between the core and cladding, the relative hole-to-core spacing and the relative size of air holes are optimized in terms of the design criteria, which take into account the cutoff wavelengths of fundamental mode and the second order mode, the gain and noise figure of fiber amplifiers and the splice loss between the EDHALF and the conventional single-mode fiber.

The optimization of pumping schemes of distributed Raman amplifiers employed in long-haul optical transmission systems is investigated in detail. Considering the received optical signal to noise ratio (OSNR) as well as nonlinear distortion and the optimal signal power distribution, i.e. uniform distribution, is achieved by using variational method. But the analytical optimal distribution does not exist when taking double Rayleigh backscattering (DRB) into account. Comparison between three Raman amplification schemes, i.e. bidirectional dual-order, first-order pumping and Raman-plus-Erbium doped fiber amplifier hybrid amplification, is carried out at identical nonlinear phase shifts. The results show that symmetric bidirectional dual-order pumping can achieve the best OSNR performance through appropriate choice of the second-order pump wavelength and second-to-first-order pump power ratio in most cases for both short- and long-span applications. However, hybrid amplification will be a better choice when the DRnoise is dominant. These results will be helpful for designing long-haul transmission systems.

In this paper we design a novel compound dual-period fibre grating structure, and analyze its spectrum response using the coupled mode theory- The simulation result is compared with the experiment,and it is shown that the model is correct- We also apply it in a temperature and strain sensor system