Enhanced performance analysis of optical CDMA communication system

Optical CDMA technique is required to meet the increased demand for high speed, large capacity communications in optical networks. OCDMA assures data access security and supports asynchronous burst data transmission. In this paper, improvement in optical CDMA has been done by implementing forward error correction technique and a distance of 100 km was achieved BER 10⁻¹⁹ at bit rate 3.75 Gbps with forward error correction in optical CDMA.     

Development of an optical communication channel prototype with a HTSC bolometric detector

An optical communication channel prototype with a detector based on a high-temperature superconducting bolometer has been developed for controlling complex physical facilities: accelerators, reactors, high-power generators, etc.     

光通信系统中分光系统光学调整的误差分析

在平行光路中,光学系统的光学元件的误差或微量运动可抽象为绕定点的微量转动,其成像关系可归结为在微量转动下物像共轭关系的依次迭代,利用光学系统这种动态成像关系的思想,建立一个统一的光学调整及误差分析的数学模型。利用此模型分析光通信系统中分光系统的机械安装误差对系统的影响,建立每个反射镜的机械调整坐标,从理论上指导分光系统中每个反射镜的机械调整,最终使通信激光发射系统和精信标激光接收系统的光轴平行度达到5。     

Practical security analysis of continuous-variable quantum key distribution with an unbalanced heterodyne detector

When developing a practical continuous-variable quantum key distribution (CVQKD), the detector is necessary at the receiver's side. We investigate the practical security of the CVQKD system with an unbalanced heterodyne detector. The results show that unbalanced heterodyne detector introduces extra excess noise into the system and decreases the lower bound of the secret key rate without awareness of the legitimate communicators, which leaves loopholes for Eve to attack the system. In addition, we find that the secret key rate decreases more severely with the increase in the degree of imbalance and the excess noise induced by the imbalance is proportional to the intensity of the local oscillator (LO) under the same degree of imbalance. Finally, a countermeasure is proposed to resist these kinds of effects.     

Measuring optical characteristics of the atmosphere with a laser heterodyne system

A laser heterodyne system for measuring optical characteristics of a turbulent atmosphere is described. Continuous readout data on the fluctuations in the phase of the radiation propagating in a channel in the atmosphere are presented. These data can be used to determine the major parameters of the turbulent state. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 906–908, November–December, 2008.     

Retrodiction for coherent communication with homodyne or heterodyne detection

Previous work on the retrodictive theory of direct detection is extended to cover the homodyne detection of coherent optical signal states and . The retrodictive input state probabilities are obtained by the application of Bayes' theorem to the corresponding predictive distributions, based on the probability operator measure (POM) elements for the homodyne process. Results are derived for the retrodictive information on the complex amplitude of the signal field obtainable from the difference photocount statistics of both 4-port and 8-port balanced homodyne detection schemes. The local oscillator is usually assumed much stronger than the signal but the case of equal strengths in 4-port detection is also considered. The calculated probability distributions and error rates are illustrated numerically for values of signal and local oscillator strengths that extend from the classical to the quantum regimes.     

Performance limitations of an optical heterodyne CPFSK transmission system due to self-phase modulation

A detailed theoretical analysis is presented to evaluate the combined influence of self-phase modulation (SPM) and group velocity dispersion (GVD) of optical fiber on the bit error rate (BER) performance of a heterodyne optical CPFSK system. The power penalty suffered by the system due to the combined influence of GVD and SPM is evaluated from the BER performance results. It is found that the penalty due to SPM at a BER of 10⁻⁹ is significant when the input power exceeds 7 dBm. Further, the CPFSK system with modulation index of 0.5 is less sensitive to the effects of GVD and SPM compared to the system with a modulation index of 1. The theoretical results are in conformity with the experimental results reported earlier.     

Designing a coupler for the intersatellite optical communication system

Coupling a single-mode laser diode with 200 mW to a single-mode fiber (SMF) through an orthonormal aspherical cylindrical lens and a GRIN lens for the intersatellite optical communication system is proposed and demonstrated. We experimentally studied how the coupling efficiency changes with the SMF's position displacement and axial angle variation, and obtained 80 mW output power at the end of the SMF, which shows that the coupling units have satisfied the designed request.     

Optical design for an LED-based handheld underwater wireless optical communication system

We propose an LED reshaping lens design for a handheld underwater wireless optical system to solve the problem of targeting the receiver. The simulation results shows that the designed lens can achieve 0.91 light intensity uniformity and 91.39% optical efficiency in hemisphere space, even with the actual LED model. After fabrication with computer numeric control, the work demonstrates the design to be effective.     

Acoustic power measurement using an optical heterodyne method

An optical heterodyne method is presented for measuring the Raman-Nath parameter of ultrasound. A light beam passes through a phase grating induced by ultrasound and then is recombined with another beam of light at a shifted frequency. The interference distribution of the two light beams is measured by a photodetector placed in the Fresnel region. The Raman-Nath parameter is determined from the amplitudes of frequency components in the beat signal and is independent of observation position. A theoretical analysis is given which includes pulsed ultrasound. Acoustic power determined using the technique is shown to agree fairly well with the radiation force method. Acoustic fields from a linear array transducer are also investigated. A problem involved in focused ultrasound is discussed.     

双曲面定位系统的误差分析

本文导出了双曲面定位系统的定位误差公式,分析了定位误差源及对应的权重系数,以水下短基线阵为例,计算了声速、时间差、阵元坐标的测量误差和声线弯曲引起的系统定位误差,以长基线阵为例,计算了定位精度区。本文结果对合理分配双曲面定位系统各误差源的误差有参考价值。     

Study of FSK/IM orthogonal modulation system with optical Manchester-coded payload

<正>We study the performance of an orthogonal modulation system with frequency-shift keying(FSK) label and optical Manchester-coded(MC) payload.Simulation result shows that by introducing an optical MC payload,the available extinction ratio(ER) value of a FSK and intensity modulation(IM) orthogonal modulation system can be improved from 5 to 9 dB for system optimization,exhibiting great advantages over the traditional non-return-to-zero(NRZ) payload.Besides,the bit error rate(BER) characteristics of both label and payload show a more remarkable advantage than that of NRZ coding,verifying itself as a perfect candidate for the payload coding method in orthogonal modulation systems.     

全视角高精度三维测量仪光学系统误差分析研究

大视角、高分辨率、低畸变光学成像系统是全视角高精度三维测量仪中最为关键的核心器件。现有三维测量仪实际使用过程中不可避免会产生各种误差,因此科学合理地评估和降低全视角高精度三维测量仪的测量误差具有十分重要的科学及工程应用意义。通过多角度、全方面分析定量研究了相机内方位元素标定误差对几何定位误差的影响,以及相机光学系统MTF分析、点扩散函数分析、波像差分析和公差分析对匹配误差产生的影响。研究结果表明,在各种影响三维测量仪光学成像系统测量误差的因素当中,相机的传递函数是影响系统三维定位误差最主要的因素,当系统MTF_N值大于0.4 lp/mm、系统几何畸变小于1个像素,PSF能量集中在以3 μm为半径的圆环内(小于1个像素),且PSF峰值达到了0.9时,三维测量仪的定位误差可达到秒级精度。     

Hybrid measurement system including optical heterodyne and laser microscopy functions using an acoustooptic deflector

The construction of a hybrid measurement system for measuring lateral and vertical dimensions and its applications to industrial inspection are described. This system uses an acoustooptic deflector, and includes optical heterodyne, confocal and non confocal laser scan microscopy functions in one and the same optical device. These functions are used individually or collectively depending on the purpose of the measurement. For example, by using the optical heterodyne and non confocal microscopy functions at the same time, lateral and vertical dimensions can be measured simultaneously.     

Beam reception and data transmission performance analysis of optical taper used in a mobile wireless optical communication

Mobile wireless optical communication system was demonstrated experimentally by using a special solid coupling optical taper. The performance of special solid coupling optical taper and the data transmission performance with 240 Mbit/s were investigated on the rectilinear orbit between the mobile terminal and the fixed terminal. The experimental results shown that the scheme used in the mobile wireless optical communication system is reliable and quite simple, which could be widely used in future.     

Pattern-independent FSK heterodyne transmission with endless polarization control and a 119 photoelectrons/bit receiver sensitivity

We demonstrate 140-Mbit/s FSK transmission with a -56.7-dBm receiver sensitivity. The system features endless polarization control, Manchester coding to overcome the nonuniform FM response of the DFB laser, and a highly efficient sub-carrier demodulation scheme.     

Pattern-independent FSK heterodyne transmission with endless polarization control and a 119 photoelectrons/bit receiver sensitivity

We demonstrate 140-Mbit/s FSK transmission with a -56.7-dBm receiver sensitivity. The system features endless polarization control, Manchester coding to overcome the nonuniform FM response of the DFB laser, and a highly efficient sub-carrier demodulation scheme.     

Application of a laser heterodyne detector in submillimeter wave spectroscopy with a harmonic generator

Spatial sensitometry variations in a liquid crystal light valve are studied as well as signal induced noise and differences in global and local contrast ratio. The device's off state is investigated and spatial variations in the thickness of the LC layer are used to quantify the results obtained. Operation with low frequency applied ac voltages appears preferable from noise considerations, whereas operation at high frequency appears preferable for improved uniformity.     

测量大口径光学元件反射率用精密扫描系统误差分析

为测量高能激光传输系统中大口径高反射率光学元件的反射率,设计了一种大口径光学元件二维扫描的精密测量系统。介绍了该系统的结构及其工作原理,分析了影响系统测量精度的因素,从理论上分析了扫描系统的系统误差对测量精度的影响,结果表明在垂直于光束传播方向上,水平偏差在0.29 mm时,测量误差在10-6量级;腔长的变化量较小时,可通过对衰荡腔腔镜的调节,实现对旋转轴偏差的补偿及对系统的精细调节。通过拟合处理光强与时间的数据得到对应的一次指数函数拟合曲线,并通过计算得到衰荡时间和反射率,经过对比分析可知,该误差分析方法能比较有效地测量腔镜的反射率,并能减小实验数据本身带来的误差。