Attenuation characteristics of a light attenuator combined by polarizers with different extinction ratios

This paper deals with a systematical analysis and an algorithm of attenuation characteristics of a light attenuator combined by n pieces of polarizers （n-LACP） whose extinction ratios are different from each other. The attenuation ratio expression of a two-LACP is deduced. We find that the monotonic attenuation interval depends on the first polarizer and that the attenuation range depends on the second one. For the three-LACP, a method for obtaining a monotonic attenuation interval is proposed. Moreover, the attenuation ratio expression is demonstrated. Analysis and experiment show that when the initial status of the three-LACP is at the maximum output, if the second or third polarizer rotates alone, the minimum attenuation ratios can reach K2^-1 and K3^-1, respectively, and if the first polarizer rotates, a minimum attenuation ratio of K2^-1K3^-1 can be obtained （K1, K2 and K3 represent the extinction ratios of the three polarizers in turn）. Furthermore, the attenuation ratio expression of n-LACP and the relevant attenuation characteristics are proposed. The minimum attenuation ratio of an n-LACP is （K2K3 ... Kn）-1.

Evaluation of ablation differences in air and water for hard tissues using full-field optical coherence microscopy

To clarify the role of a natural or artificial liquid environment in the free-running infrared pulsed laser ablation of hard biological tissues,two-and three-dimensional morphologies of laser-induced craters must be quantitatively measured to distinguish ablation differences in air and in water.Full-field optical coherence microscopy is introduced,which has non-contact,non-destructive,non-preprocessing and higher-resolution advantages.Experimental results indicate that the ablation performances in air and in water are comparable for few laser pulses,but the ablation difference becomes obvious for more laser pulses.Optical coherence microscopy is more feasible than conventional means for the morphological measurement of craters.

Simulation and comprehensive assessment of single channel RZ-DPSK optical link by dispersion management with channel bit rate beyond 40 Gbits/s

This paper studied the influence of return to zero-differential phase-shift-keying （RZ-DPSK） data format on techniques of pre-, post- and pre/post combination dispersion compensation for faithful transmission of optical signal at 80 and 100 Gbits/s channel bit rate via simulation. The purpose of this study was to find out the dispersion compensation techniques for optimal transmis- sion with the interaction effects of self-phase modulation （SPM） and amplifier spontaneous emission （ASE） for RZ- DPSK encoded optical data. By the simulation method, it was found out that the RZ-DPSK data format can be allowed with a transmission distance of about 700 km of standard single mode fiber （SMF） at 100 Gbits/s, and it can be provided with farther transmission distance of more than 1000 km at 80 Gbits/s with the combination of the pre- and post-compensation technique. To efficiently suppress the effect of ASE and improve optical signal-to- noise ratio （OSNR）, the bandwidth frequency of optical receiver filter was found to be at least equal to bit rate.

High Speed Signal Wavelength Conversion Using Stimulated Raman Effect in Ultrasmall Silicon-on-Insulator Optical Waveguides

我们在硅波导上基于刺激拉曼效果建议高速度信号波长变换。假散乱咬了的 non-return-to-zero (NRZ ) 的模拟结果定序(2 (7 )-1 代码) 以在极端小 silicon-on-insulator (SOI ) 的变换的 500-Gb/s 率，光波导被共同繁殖介绍泵光地。最吸引人的问题是转换变换信号能在象主要信号的一样的波长被获得。另外，变换表演，包括扑灭比率(嗯) 并且变换信号的平均山峰力量，强烈取决于发射的泵紧张。

Analysis of the maximum extractable power of photonic crystal fiber lasers

In this article, we analyze the factors that limit the output power increase for photonic crystal fiber lasers and set a theoretical model to calculate the maximum extractable power of ytterbium-doped photonic crystal fibers. Numerically, when the diameter of core is 76-μm and the pumping intensity is 0.21 W/（μm^2× Sr）, the output of pure silica and ytterbium-doped photonic crystal fiber lasers is 100-kW, considering the technology for the time being. The main limitations of power scaling are facet damage and thermal self-focusing. In case of the strict single-mode operation condition, the maximum extractable power is 100-kW when the numerical aperture is 0.05. Considering the strict single-frequency operation condition, the maximum extractable power of both pure silica and ytterbium-doped photonic crystal fiber lasers is 1.65-kW, where the main factor is stimulated Brillouin scattering effect. Compared with the previous results, the increase in the maximum extractable power depends on three parameters： the availability of high-brightness pump diodes, the endless single-mode characteristic of the photonic crystal fiber, and the high doping density which lead to efficient absorption coefficient of pumping light. Finally, we simulate numerical aperture that influences the maximum power of photonic crystal fiber lasers and compare the difference in maximum output power of photonic crystal fibers and double-cladding fiber lasers in single-frequency condition.

Optimization designed large-stroke MEMS micromirror for adaptive optics

A novel micromirror based on the PolyMUMPs process is designed and presented. The hexagonal micromirror with a diameter of 450 μm consists of three supporting bilayer cantilevers and a mirror plate. The bilayer cantilevers, formed with a polysilicon layer and a gold layer, elevate the mirror plate according to residual stress-induced bending. Both analytical and finite element analysis （FEA） models are built to calculate the elevated height of the free end of the cantilever. The analytical solution is in accordance with the FEA simulation results, with longitudinal stresses applied only. Results of a three-dimensional （3D） simulation with two direction stresses applied also show the elevated height to be proportional to the width of the cantilever and the length of the gold layer. Due to the torque of the joint, the elevated heights of the two kinds of cantilevers assembled with the mirror plates are much smaller than those of the free end of the cantilevers. Both micromirrors with different cantilevers are fabricated. The elevated heights of the fabricated micromirrors are measured using Veeco optical profiler, which show good coincidence with simulation results.

Low birefringence depressed cladding photosensitive fiber

The highly Ge-doped photosensitive fiber （PSF） has been widely used in the fabrication of fiber Bragg gratings （FBGs）. Its birefringence and cladding mode coupling characteristics greatly influence FBG＇s transmission feature in communication application areas. In this work, a new concept of the PSF is introduced which, along with an optimized birefringence design, a precisely controlled fabrication process, and a cladding mode depressed design, results in a written FBG with -25-dB clad mode-depressed ratio and a polarization mode dispersion value less than 0.045 ps.

Pulse reference-based compensation technique for intensity-modulated optical fiber sensors

We propose a compensation technique based on pulse reference for intensity-modulated optical fiber sensors that can compensate the power fluctuation of the light source, the change of optical components transmission loss, and the coupler splitting ratio. The theoretical principle of this compensation technique is analyzed and a temperature sensor based on fiber coating-covered optical microfiber is carried out to demonstrate the compensation effect. The system noise is measured to be 0.0005 dB with the temperature sensitivity reaching -0.063 dB/℃, and the output drift is 0.006 dB in 2 h at room temperature. The output shows a slight variation （0.0061 dB） when the light source and the common liKht path suffer a 3 dB attenuation fluctuation.