自适应光学系统校正后实际分辨率评价指标

为了评价地基大口径望远镜对空间目标自适应光学系统校正后的实际分辨率,提出了可分辨单元数比指标。结合1.23 m自适应光学望远镜的观测数据,对可分辨单元数比的物理意义、适用范围、误差影响因素以及大气弥散的影响进行了分析。结果表明：可分辨单元数比能全面反映望远镜系统对空间目标自适应校正后的实际分辨率,且物理意义更直观;适用于所有可获取波前特征的望远镜自适应校正后实际分辨率的评估;其误差主要依赖于波前探测器的测量误差;大气弥散对其影响可忽略。     

Wave-front correction of femtosecond terawatt lasers by deformable mirrors

Wave-front correction and focal spot improvement of femtosecond laser beams have been achieved, for the first time to our knowledge, with a deformable mirror with an on-line single-shot three-wave lateral shearing interferometer diagnostic. Wave-front distortions of a 100-fs laser that are due to third-order nonlinear effects have been compensated for. This technique, which permits correction in a straightforward process that requires no feedback loop, is also used on a 10-TW Ti:sapphire-Nd:phosphate glass laser in the subpicosecond regime. We also demonstrate that having a focal spot close to the diffraction limit does not constitute a good criterion for the quality of the laser in terms of peak intensity.     

具有三个二次曲面反射镜的光学系统研究

本文从三级像差理论导出了三镜系统消S_Ⅰ、S_Ⅱ、S_Ⅲ、S_Ⅳ的代数解.以第二及第三镜的遮拦比和放大率,以及三个镜面的面形系数为独立参数,结出消像差条件公式.用国外发表的几个三镜系统验证这些公式,得到很好的吻合.     

Closed-form BER analysis of variable weight MPPM coding under gamma-gamma scintillation for atmospheric optical communications

In this paper, the performance of the variable weight multiple pulse-position modulation (MPPM) coding technique in an atmospheric optical communication environment under gamma-gamma optical scintillation is analyzed, proposing a closed-form expression for the average bit error rate (BER). This study is based on a hyperexponential fitting of the conditional BER in absence of turbulence fluctuations, leading to closed-form expressions that characterize the behavior of this nonlinear coding scheme. Finally, conditional and average BER expressions proposed here are corroborated with Monte Carlo simulations results.     

Compensation of scintillation with a phase-only adaptive optic

To compensate for scintillation we allow the real, nonnegative field in an aperture to propagate a distance z toward a detector, where the field will be complex. There, we modify its phase to emulate that of a clear aperture. The modified field that is propagated to the detector is nearly diffraction limited. No light is lost, and the Strehl ratio is improved substantially. We show how to modify the phase, and we present a computer simulation.     

The use of circular optical grating for measuring angular rotation of mirrors

This paper explores the feasible use of circular optical grating for measuring the rotation of mirrors that are commonly found in micro-systems. Both theoretical and experimental results show that distortion of the circular grating that is projected onto the mirror surface is a simple function of the angular rotation of the mirror. The circular grating may readily be generated using a standard Michelson interferometer or an LCD projector. Through manipulating the distance between the interferometer and the mirror surface, the diameter of the optical grating may be varied. Furthermore, the additional use of a converging lens enables a significant reduction in the size of the grating: with simple laboratory facility, small circular grating of about 400 μm is achieved for use on micro-systems. With the use of more sophisticated optical elements, the angular rotation of even smaller micro-mirrors may be measured.     

Pulse compression by use of deformable mirrors

An electrostatically deformable, gold-coated, silicon nitride membrane mirror was used as a phase modulator to compress pulses from 92 to 15 fs. Both an iterative genetic algorithm and single-step dispersion compensation based on frequency-resolved optical gating calibration of the mirror were used to compress pulses to within 10% of the transform limit. Frequency-resolved optical gating was used to characterize the pulses and to test the range of the deformable-mirror-based compressor.     

Practical use of optical fiber communications for electric power companies

The rationale for applying optical fiber communications in electric power companies is presented in this paper. Field tests between substations and within substations are described, and results are given. All tests were satisfactory with error rates less than 10^-11 indicating that optical fiber communications can be put to practical use in the very near future.     

Reduction of atmospheric turbulence using optical duplicate system in free-space optical communications

Optical Review - To reduce the effect of atmospheric turbulence and stabilize the optical link in free-space optical (FSO) communications, we have proposed to use an optical duplicate system (ODS)...     

系统增益对光混沌通信系统性能影响的研究

针对强注入开环结构的外腔反馈半导体激光器混沌通信系统,数值计算得到系统增益与注入系数的定量关系曲线.对比是否使用系统增益对接收系统输出进行校正两种情况下系统的解调性能,表明使用增益校正的相减解调法获得的信息更接近原始信息.通过采用不同频率的正弦信号进行调制,表明信息频率对系统增益没有影响;用不同调制方法对0.2?Gbit/s数字信号加密,结果表明系统增益与信号类型及调制方法无关. 关键词： 光混沌通信 强注入 系统增益 同步     

Experimental observation of autosoliton propagation in a dispersion-managed system guided by nonlinear optical loop mirrors

Observation of autosoliton propagation in a dispersion-managed optical transmission system controlled by in-line nonlinear fiber loop switches is reported for what is believed to be the first time. The system is based on a strong dispersion map with large amplifier spacing. Operation at transmission rates of 10 and 40 Gbits/s is demonstrated.     

自适应光学实时大气湍流补偿实验

本文报道了用自适应光学系统实时探测和校正距地面约15m高的340m水平传输通道上的大气湍流效应的实验.实验结果表明,用自适应光学校正后,对点目标和一定扩展度的扩展目标都可提高成像质量.     

大气闪烁对无线光CDMA通信系统性能的影响

将光CDMA技术应用到无线光通信中。提出了基于脉冲位置调制的二维大气无线光CDMA通信系统，并分析了该通信系统的性能。考虑多用户干扰、APD噪声以及热噪声等干扰因素的影响，采用数值分析的方法，详细分析了大气湍流引起的大气闪烁对二维无线光CDMA通信系统误码率的影响。结果表明，大气闪烁是影响二维无线光CDMA系统误码率性能的一个重要因素；当大气闪烁的对数方差较小(如σ2s=0.1)时，该系统可以实现高速率通信；当大气闪烁的对数方差较大(σ2s≥0.2)时，在有限的光功率条件下，该系统难以实现通信，需要采用信道编码技术来提高系统的误码率性能。     

Measurements of atmospheric turbulence strength by coherent optical scintillation

Summary The strength of the atmospheric turbulence is measured by an optical scintillation method. The obtained quantity is the structure constant at optical frequencies. As all turbulence parameters, this quantity is strongly affected by meteorological and local conditions, therefore it is of interest to measure it in different conditions and locations. The present measurements were made to characterize the turbulence at Florence. Paper presented at the 1° Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, Rome, June 19–22, 1984.     

卫星间光通讯中一种光路设计及分析

文中给出了一种卫星间光通讯系统的光路设计，并对影响通讯距离的有关参量进行了分析，找出了提高通讯距离的主要途径     

Design of Double Cassegrain reflective mirrors for optical system of IR cameras

IR optical systems such as Petzval doublet refractive lenses or Cassegrain reflective mirrors are either expensive or poor in image quality. Taking advantage of the low cost of reflective mirrors, here we present an optical design of Double Cassegrain reflective mirrors consisting of two sets of Cassegrain reflectors facing each other symmetrically. This symmetry also cancels many aberrations besides the chromatic aberration-free nature of reflective mirrors. Design results show that this system is better than Cassegrain reflectors in aberration correction and image resolution, but cheaper than Petzval doublet refractive lenses systems in price. IR cameras with this optical system could be widely used for body temperature measurement and security check.     

Versatile 7-fs optical parametric pulse generation and compression by use of adaptive optics

We have compressed the output from a beta-barium borate noncollinear optical parametric amplifier to ~7-fs pulse durations, using a micromachined deformable mirror with an efficient search algorithm. This compression method allows phase compensation of both material and gain dispersion, which produces an optimized wavelength-tunable pulse shape for ultrahigh-resolution time-domain spectroscopy.     

Wave-front correction of high-intensity fs laser beams by using closed-loop adaptive optics system

We developed an adaptive optics system to correct the wave-front distortion of an intense fs laser beam from our multi-TW laser system, Jiguang II. In this paper, the instruments of the adaptive optical system are described and the experimental results of the closed-loop wave-front correction are presented. A distorted laser wave-front of 20 wavelengths of P-V values was corrected to 0.15 wavelength of P-V values. The beam quality of the laser system varies from 3.5 diffraction limit to 1.5 diffraction limit.     

Possibility for the form correction of X-ray mirrors by reactive ion-beam etching

Key parameters for the reactive ion-beam etching of glass, quartz and silicon are studied. The dependence of the etching rate on chamber pressure and etching time is investigated. The etching zone has the form of a long (??50 mm), narrow (??1 mm) strip with depth homogeneity at a level of 0.2%. Such a zone is a handy tool for correcting the shape of cylindrical surfaces.