Experimental demonstration of multiwavelength optical network with microwave subcarriers

The authors use the unique multiwavelength filtering capability of the acousto-optic tunable filter to demonstrate multiple broadband services with only one fixed-wavelength transmitter and receiver per user in the first experimental demonstration of a multiwavelength subcarrier network.<>     

Performance of a GaAlAs laser diode used for multichannel video transmission employing multiplexed UHF subcarriers

Good quality transmission of three television channels employing multiplexed UHF subcarriers at 770, 800 and 830MHz using a commercially available laser diode is demonstrated. Both the third-order intermodulation products and crossmodulation products of the laser are found to be better than ?65dB. An SNR per channel of 52dB has been obtained.     

All-optical wavelength shifting of microwave subcarriers by using four-wave mixing in a semiconductor optical amplifier

We demonstrate all-optical wavelength shifting over 9 nm for two microwave subcarriers by using four-wave mixing in a semiconductor optical amplifier. In our experiment, the RF spectrum is relatively unaffected by wavelength shifting and the resultant system power penalty is /spl sim/0.5 dB. Such a transparent wavelength shifter may be a critical component in WDM networks supporting both subcarrier multiplexed (SCM) and high speed digital transmission.     

Error performance analysis of a jointly optimal single-cochannel-interferer BPSK receiver

An analytical solution is derived for the average error-rate performance of a jointly optimal binary phase-shift keying receiver operating in the presence of one cochannel interferer and additive white Gaussian noise. The solution takes different analytical forms, depending on the region of signal-to-interference ratio. The regions depend, in turn, on the phase difference between the desired signal and the interferer signal.     

Design and analysis of a high bandwidth disk drive servo systemusing an instrumented suspension

Resonance modes in the suspension of hard disk drives limit the closed-loop bandwidth. The bandwidth of the servo can be increased by active vibration control of the resonance modes. This paper considers the optimal placement of strain gauge sensors on a suspension to observe the vibration states of the suspension. Using a finite-element simulation of an actual suspension, a state-space model is identified for the two normal strains and the shear strain at each finite element. The state-space model includes the dynamics of the three primary resonance modes. A numerical search algorithm is used to determine the sensor location and orientation which maximizes the minimum singular value of the observability grammian. With the strain gauge output signal, a multirate inner loop controller is designed to be used with the existing head-positioning system. Simulations and analysis results suggest that use of an instrumented suspension is a viable candidate method for improved disk drive servo performance     

Passive microwave fiber-optic links with gain and a very low noise figure

It is shown experimentally and theoretically that it is possible to construct a passive microwave fiber-optic link (defined as one without active electrical or optical amplification) exhibiting an RF throughput gain of up to 50 dB and a noise figure approaching 0 dB. The key ingredients are quantum well gain-lever laser transmitters and proper impedance matching. Disregarding the optical transmission aspect of the link, it can be regarded as an RF low-noise preamplifier with performances competitive with conventional microwave amplifiers.<>     

Enhanced performance of phase-conjugated OFDM subcarriers using digital coherent superposition

We have recently demonstrated the improved phase noise tolerance in coherent optical OFDM by digital coherent superposition of optical OFDM subcarriers, which are phase-conjugated pairs with Hermitian symmetry. In this approach, we realized DCS of OFDM subcarriers in single polarization (or channel), denoted as SP-DCS-OFDM. In this paper, we show that another approach is in dual polarizations, or DP-DCS-OFDM. According to the concept of phase-conjugated twin wave, both approaches can also mitigate the fiber nonlinearity to the first order. We prove that both approaches can cancel the inter-carrier interference (ICI) due to phase noise to the second order, and we derive the reduced ICI power to the fourth order using the Wiener phase noise model. In simulation, we show the enhanced tolerance to the laser phase noise and fiber nonlinearity.     

一种基于Costas环的BPSK解调设计

设计了一种基于软件无线电思想的中频数字化接收机系统,该系统由数据采集模块、数字下变频（DDC）模块和数字解调模块构成。文中重点研究了基于Costas环的BPSK相干解调,并介绍了载波同步及BPSK解调的工作流程图,最后通过Simulink对BPSK解调原理进行了仿真验证。     

动态扩容视频存储分发系统设计

在带宽增速,互联网用户对视频内容的要求日趋增多的趋势下,本文描述了大规模视频存储分发的系统设计和实现.该系统设计的目标是把用户上传的视频重新编解码生成适合不同场景的不同格式视频文件,然后根据客户端支持的视频属性和网络带宽的实际情况,自动分发不同码流的视频文件到客户端,从而达到流畅访问视频的目的;对系统中的热门视频,系统通过算法结合缓存,实现同一视频文件在不同服务器间动态迁移,从而充分利用系统的计算能力,最终给用户提供更流畅的视频体验.     

BER performance of BPSK transmissions over multipath channels

A new closed form expression for the bit error rate (BER) performance of binary phase shift keying (BPSK) transmissions over frequency selective channels is presented. The expression is obtained through a novel approximation of the Gaussian Q(middot) function by a fixed series of sinusoids with exponentially decreasing amplitudes. Numerical results demonstrate the accuracy of the derived expression     

High-power performance of single-mode fiber-optic connectors

We measured the continuous wave (CW) laser-induced damage threshold of single-mode fiber-optic connectors at 1550 nm. Clean standard physical contact and angled physical contact connectors did not show any evidence of damage for 10 min exposures of 1 W or 3 W. Defective connectors with scratched or undercut endfaces showed identical high-power tolerance as clean connectors without defects. Samples contaminated with carbon black-doped acrylate showed drastic optical failure signatures at approximately 50 mW. Contaminated connectors with expanded mode field diameters ranging from 20 to 62 /spl mu/m showed higher failure thresholds than standard connectors with 10-/spl mu/m spot sizes. We observed that the optical failure threshold power level (P/sub failure/) increased linearly with spot size for the highly contaminated connectors used in this study.     

Long distance fiber-optic transmission of C-band microwave signals to and from a satellite antenna

We demonstrate here the use of high-speed semiconductor lasers and detectors with low loss optical fiber for the transmission of the 500-MHz C-band microwave signal spectrum to and from a satellite antenna. The optical system has low attenuation and large band, width, so the microwave signals can be transmitted directly at the microwave frequency (4 or 6 GHz) over 20 km of fiber without regeneration or qualization. The optical system introduces ≈ 1 dB or less of degradation for both low spectral density QPSK signals and high spectral density FM video signals present in typical satellite transmission systems. For the video signals, the signal to noise after AM conversion was reduced from 56 to 55 dB. The microwave drive level to the laser must be significantly larger (typically > -10 dBm) than the intensity noise of the laser, yet small enough (typically < 10 dBm) to reduce the intermodulation distortion signals to an acceptable level. The laser bias current must be several times threshold so that the resonance frequency is beyond the frequency band of interest (4-6 GHz in this case). A flat modulation response is then obtained, and the intensity noise and intermodulation levels are low.     

视频成像测井光缆传输系统井上电路设计

文章描述了一种基于FPGA实现的井上电路.该电路基于光缆传输机制,采用光模块完成光电转换,在FPGA内实现高速串行数据的数据恢复和曼彻斯特解码等处理,经视频模块处理后,完成对井下视频信息的恢复.其中,高速串行数据的数据恢复采用了过采样的处理方法.该电路结构简单、可靠性较高,与井下电路配合使用,可实现井下视频信号的可靠采集.     

Design and characterization of a high temperature fiber-optic pressure transducer

We have measured the pressure response of a high temperature pressure transducer fabricated from a super alloy. This transducer contains a microbend fiber-optic sensor to measure diaphragm deflection and a reference fiber to help reduce light source fluctuations caused by perturbations in the fiber leads. The transducer was characterized at pressures up to 22.8 MPa and temperatures to 430°C. The experimental data taken at constant temperature shows a 0.58 percent (of full scale pressure) minimum deviation between the fiber-optic pressure transducer output and output of a calibrated gage pressure transducer. Over the entire temperature range of20-430degC, the fiber-optic pressure transducer output exhibits a 1.2-percent (of full scale pressure) maximum deviation from calibrated pressure.     

基于FPGA的BPSK调制与解调器设计

BPSK广泛用于卫星、微波通信、广播电视等诸多领域.近年来,随着智能卡、RFID、Bluetoo出等相关技术的发展,较低码率的BPSK在近距离无线产品中也得到了越来越广泛的应用.本文设计实现了一种新型的BPSK信号调制解调器,利用m序列的随机性来产生输入基带信号,详细介绍了基于FPGA的BPSK信号调制解调器的设计方法...     

Design and performance of tunnel collector HBTs for microwave power amplifiers

AlGaAs/GaAs/GaAs and GaInP/GaAs/GaAs n-p-n heterojunction bipolar transistors (HBTs) are now in widespread use in microwave power amplifiers. In this paper, improved HBT structures are presented to address issues currently problematic for these devices: high offset and knee voltages and saturation charge storage. Reduced HBT offset and knee voltages (V/sub CE,os/ and V/sub k/) are important to improve the power amplifier efficiency. Reduced saturation charge storage is desirable to increase gain under conditions when the transistor saturates (such as in over-driven Class AB amplifiers and switching mode amplifiers). It is shown in this paper that HBT structures using a 100-/spl Aring/-thick layer of GaInP between the GaAs base, and collector layers are effective in reducing V/sub CE,os/ to 30 mV and V/sub k/ measured at a collector current density of 2/spl times/10/sup 4/ A/cm/sup 2/ to 0.3 V (while for conventional HBTs V/sub CE,os/=0.2 V and V/sub k/=0.5 V are typical). A five-fold reduction in saturation charge storage is simultaneously obtained.     

提高录像带图像和音频性能的方法

随着视频技术的快速发展,摄像机和录像机的图像质量有了明显的提高。目前,大屏幕数字平面电视机上市后,人们迫切需要图像质量和音频性能得到改进的录像带。国际磁带生产厂家为顺应市场需求的趋势,成功地开发和采用了最新的录像带制造技术,并在市场上及时推出质量高、记录时间长的录像带。１ 录像带质量的改进技术高性能录像带的用户十分重视录像带的增强磁性能和改进信噪比（Ｓ／Ｎ低调制噪音）。为极大限度地满足用户对录像带的使用要求,生产厂家在磁带生产过程中采用了多次涂布技术、高密度填充技术和具有高矫顽力的磁性材料。大多…     

High-speed fiber-optic links for distribution of satellite traffic

Low-loss fiber-optic links are designed for distribution of data and the frequency reference in large-aperture phased-array antennas based on the transmit/receive-level data mixing architecture. In particular, design aspects of a fiber-optic link satisfying the distribution requirements of satellite data traffic are presented. The design is addressed in terms of reactively matched optical transmitter and receiver modules. Analog and digital characterization of a 50-m fiber-optic link realized using these modules indicates the applicability of this architecture as the only viable alternative for distribution of data signals inside a satellite at present. It is demonstrated that the design of a reactive matching modules enhances the link performance. A dynamic range of 88 dB/MHz was measured for analog data over 500-1000-MHz bandwidth     

A 1.3-µm microwave fiber-optic link using a direct-modulated laser transmitter

A 1.3-μm 1.1-km-long single-mode fiber-optic link with a 4.1-4.7 GHz frequency response has been developed. This is one of the highest freqUency fiber-optic links reported to date. A 60-dB SNR, ±1.0-dB gain flatness, and 44-dB spur-free dynamic range was observed. The performance of this link is primarily determined by the direct-modulated laser transmitter. This paper discusses the design of that component along with the development and performance of the complete fiber-optic link.