一种新有用于光码分多址的光相关器

本文提出了一种新的用于光码分多址系统的光相关器,并对光同步和异步系统给出了误比特率公式。数值仿真结果表明,无论是异步还是同步系统,这种光相关器的误比特率性能都优于传统光相关器的性能。     

A new correlator receiver architecture for noncoherent optical CDMAnetworks with bipolar capacity

A new correlator receiver architecture based on a modified version of unipolar-bipolar correlation is proposed for noncoherent optical fiber code-division multiple-access (CDMA) networks. For this architecture, the receiver average bit-error rate (BER) performance is numerically evaluated as a function of the received optical power for noncoherent transmission and direct detection with the number of simultaneous users as a parameter. The BER performance is also evaluated by a closed-form formula that is developed in this paper. Comparison of the results from the latter with numerical results show that, the formula provides a good approximation to the system performance. Furthermore, the closed form solution suggests that the system can achieve the same capacity as a CDMA system using coherent detection     

Integrable semiconductor optical correlator, parametricspectrometer for communication systems

A broadband integrable waveguide correlator and parametric spectrometer is analyzed both theoretically and experimentally. The correlator can measure pulsewidths from subpicosecond to tens of picoseconds centered at wavelengths of 1.06 to 1.7 μm without any mechanical alignment. The parametric waveguide spectrometer is shown to resolve not only the mode of a 1.3-μm Fabry-Perot laser diode but also the shift of the modes as a function of bias current. The improvement of these integrable waveguide structures and their possible use in laser stabilization, the defining of fixed frequency channels, and other applications for coherent communication systems are also discussed     

Switched correlator receiver architecture for optical CDMA networkswith bipolar capacity

A new optically switched correlator receiver architecture, based on the principle of unipolar-bipolar correlation, is proposed for optical fibre CDMA networks. The receiver BER performance is assessed as a function of the incident optical power for noncoherent transmission and direct detection, with the number of simultaneous users as a parameter     

A simplified normal optical flow measurement CMOS camera

Various motion properties of an image can be computed by using normal flow measurements. Notable among these are focus of expansion, time to contact. Many VLSI systems that combine focal plane processing with imaging have been proposed. However, these systems mostly suffer due to lower spatial resolution. This paper presents a two-dimensional dense simplified normal optical flow measurement chip implemented in 0.5-/spl mu/m CMOS process that combines imaging and processing on the same chip efficiently. The algorithm outputs the image, computes partial derivatives with respect to time and space, and uses their ratio to compute a simplified version of the normal flow velocity. The chip is composed of an array of 92/spl times/52 of APS pixels, occupies an area of 4.5 mm/sup 2/ and consumes 2.6 mW power. This paper illustrates the operation of the chip by first presenting results from individual blocks and then from system-level testing. Furthermore, we demonstrate the feasibility of scaling the chip to higher resolutions without affecting the processing.     

A simplified optical star network using distributed channelcontrollers

Future photonic networks may be based on emerging wavelength-division-multiplexing (WDM) technology. In single-hop LAN's using a passive optical star coupler, stations normally access the network using some combination of wavelength-agile transmission and reception. Unfortunately, this parallel channel architecture tends to increase and complicate the user station hardware and protocols. In this paper, a new network architecture is presented. The objective of the design is to simplify the user stations as much as possible. This is accomplished through the use of a set of distributed channel controllers-one for each WDM channel. The network is thus referred to as the distributed channel controller network (DCCN). The channel controllers assist in the operation of the network in a number of ways. To further simplify the design, bandwidth is allocated hierarchically on each channel. This decouples system operation into two levels. At the higher level, band width partitioning may be done in a static or dynamic fashion. The lower level determines the dynamic use of slots. Two options for media access are considered. The first is a hybrid approach based upon custom hardware-based request scheduling. Allocations are generated by the channel controllers electronically and data transmission occurs using station wavelength agility. The second is much more distributed. Each set of competing stations builds a distributed queue based upon observed requests. It is found that the proposed architecture supports higher throughput than in other similar networks with the same hardware requirements. An analytic model is introduced for calculating mean station delay. Simulations show that it accurately predicts network performance     

A surface-charge correlator

Surface-charge transfer techniques have been used to implement a cross-correlator module in which the tap weights are restricted to values of plus and minus one. This compromise permits most of the advantages of CTD's to be retained, and the disadvantage of fixed tap weights can be overcome by using a weighted binary code for the tap weight function and separate binary correlators for each binary digit. A new architecture (parallel transfer) was used which eliminates the cumulative effect of charge-transfer inefficiency, thereby permitting longer impulse responses to be implemented than is practical with the conventional series transfer approach. The experimental device, which contains 32 stages, was implemented in p-channel MOS technology, and was designed to operate at 4 MHz. Test results are presented showing that a tap weight accuracy of order 1/2 percent can be achieved on a single chip. Presuming that the modular approach employed permits selection of well-matched chips with leakage at least as low as was obtained in the experimental units, it would be possible to implement an impulse response covering 40000 samples with tap weight accuracy of perhaps 1 percent.     

Design and performance of an integrated optical digital correlator

We describe an integrated optical correlator capable of performing ordinary binary or bipolar correlations. The device consists of two surface-acoustic-wave (SAW) transducers and an electrooptic spatial light modulator in a planar Ti in-diffused LiNbO3waveguide. It is designed to correlate a 32-bit word at a 32-Mbit/s data rate.     

A simplified optical millimeter-wave generation scheme based on frequency-quadrupling

This paper analyzes and demonstrates a simplified frequency quadrupling configuration for optical millimeter-wave(mm-wave)generation,in which the electrical phase shifter and optical filter are omitted.Theoretical analysis is given to reach the optimum operating conditions including direct current(DC)bias voltage,optical transmission point of the dual-parallel Mach-Zehnder modulator(MZM)bias voltage,optical transmission point of the dual-parallel Mach-Zehnder modulator(DP-MZM),amplitude of the radio frequency(RF)driving signal and the impact of the extinction ratio(EF)on the optical sideband suppression ratio(OSSR)and radio frequency spurious suppression ratio(RFSSR).Experiments prove an OSSR of 15 dB and an RFSSR of 26 dB for the new frequency quadrupling scheme at 6 GHz,8 GHz and 10 GHz of RF driving signal without any electrical phase shifter or optical filter.This system exhibits the advantage of low wavelength dependence and large frequency tunable range.     

A CCD time-integrating correlator

A CCD binary-analog time-integrating correlator has been designed and operated at 20 MHz clock rate. The 32-channel device is capable of integration periods in excess of 25 /spl mu/s or 500 clock periods, equivalent to a time-bandwidth product of 250. The device architecture is based on charge-domain signal processing for high-speed operation and does not required on-chip logic for storage of the binary reference. The device is tailored for weak signal applications, and a new charge skimming circuit has been devised which allows the small portion of the integrated charge containing the correlation function to be separated from the large register by tenfold. The correlator has a stationary pattern noise which can be eliminated with simple postprocessing, yielding a dynamic range of 67 dB.     

A large-scale integrated correlator

A 64-bit parallel correlator is described using a large-scale integrated single-chip bipolar transistor construction. The circuit operates at 20 MHz and has an analog correlation output. The LSI structure uses the triple diffusion process, which produces both n-p-n and p-n-p transistors. Resistors are also diffused. A combination of soft saturated register circuits and nonsaturating gating circuits produce a 25-pJ gate performance with device f/SUB t/ in the range 50-150 MHz. The logic form used is emitter-follower logic. This 5000 device, 220- by 230-mil chip, is a highly producible LSI function.     

A simplified analysis of the optical bistability of multiplequantum well etalons

An analysis of static room-temperature-operation characteristics of a reflection-mode semiconductor multiple-quantum well etalon by a simplified two-level system formula of optical nonlinear properties and a computer simulation is presented. In the calculation for a GaAs/AlGaAs multiple-quantum-well etalon using the parameters reported in experimental measurement, it is shown that the very large excitonic optical nonlinearity is not effectively utilized for the optical bistable operation. This occurs because the effective positive-feedback mechanism which increases the etalon internal light intensity is suppressed when a hardly saturable background interband absorption tail is larger than a few thousand cm^-1 at a wavelength where the large excitonic dispersive nonlinearity is observed     

采用光学相关的高精度亚像元像移测量新方法

光学联合变换相关方法是测量空间相机亚像元像移的有效手段,测量精度是决定其性能的关键指标.在介绍了光学联合变换相关方法进行空间相机像移测量基本原理的基础上,提出了采用光-数字混合的结构形式实现光学联合变换相关器的工作过程.利用数字处理单元完成对相关输出图像的局部计算,获得互相关峰的升采样图像,从而提高对互相关峰的检测精度...     

Combined electronic clipped correlator and fibre-optic correlator

A novel mixed configuration for a very high bandwidth correlator, which can work either as an electronic clipped correlator or as a fibre-optic correlator, is presented. The mixed architecture achieves the speed characteristic of the fibre-optic correlator and can maintain the versatility of the clipped correlator     

A merged pipe organ binary-analog correlator

The design of a 96-stage, programmable binary-analog correlator is described. An array of charge coupled device (CCD) delay lines of differing lengths perform the delay and sum function. Merging of several CCD channels is employed to reduce the active area. This device architecture allows simplified output detection while maintaining good device performance at high speeds (5-10 MHz). Experimental results indicate a 50 dB broad-band dynamic range and excellent agreement with the theoretical processing gain (19.8 db) when operated at a 6 MHz sampling frequency as a sequence matched filter pseudorandom noise.     

A differential-delay SAW correlator for combined DSSS despreadingand DPSK demodulation

The design of a novel SAW (surface-acoustic-wave) component for the noncoherent detection of DS/SS (direct-sequence spread-spectrum) signals with a DPSK (differential phase-shift keying) modulation format is presented. In the considered differential-delay correlator, both the correlation function for despreading and the delay function for DPSK demodulation are merged into a single device. Due to the absence of a separate delay line, no bandwidth-limiting effects no high insertion losses occur in the delay branch of the DPSK demodulator. In addition, an exact match between the correlator output and its one-symbol-delayed replica is obtained. Experiments on an ST-quartz differential-delay correlator with a center frequency of 98.5 MHz, a chip rate of 12.3 MHz and a symbol rate of 195.4 kb/s demonstrated the operation of the device     

ASK coherent optical communications systems: simplified analysis

Presents a simple approximate analysis of ASK coherent optical communications systems and obtain, for the first time, a closed-form estimate of the bit error rate. The inaccuracy introduced by the approximation analysis is about 0.4 dB. The main application of the presented theory is expected to be in the analysis of practical imperfections (such as a finite IF filter bandwidth and a nonzero laser linewidth) on the system performance.<>     

A simplified non-Gaussian approach to digital optical receiverdesign with avalanche photodiodes: experimental

Detailed experimental measurements of various digital receiver parameters taken on a receiver using a low noise silicon avalanche photodiode are compared with simple theories that incorporate Gaussian and non-Gaussian models for the probability distribution functions for the avalanche gain. The authors analyze the salient aspects of the theories, particularly those parameters that give results different from the Gaussian approximation, and those parameters that are readily extracted from the theory (e.g., the influence of background current due either to dark current or to imperfectly extinguished light sources). Experiments were performed in which a receiver was characterized for bit error rate (BER) and optimum gain as the optical power at a modulation rate of 10 Mb/s (NRZ) was varied and as additional background light was allowed to fall on the detector. Excellent agreement with the author's newly developed simplified approximation to the non-Gaussian theory for receiver sensitivity (ibid., vol.9, p.1019-26, Aug. 1991) is obtained     

A simplified non-Gaussian approach to digital optical receiverdesign with avalanche photodiodes: theory

A simplified theory of avalanche photodiode receiver sensitivity is presented in which the non-Gaussian nature of the avalanche multiplication process is taken into account. The theory predicts more accurately than a Gaussian theory the optimum avalanche gain and decision threshold and gives simple results for the influence of background photocurrent or dark current on receiver sensitivity, optimum gain, and threshold. For purposes of comparison, a parallel derivation using the Gaussian approximation for both the avalanche and receiver noises is given where simple expressions for the optimum avalanche gain and threshold settings are derived