Optical Spatial Quantization for Higher Performance Analog-to-Digital Conversion

A novel optical spatial quantized analog-to-digital conversion scheme for real-time conversion at ultrahigh sampling frequencies is presented. At each sampling instant, the analog input voltage deflects an optical sampling pulse onto an array of photodetectors. The output code is derived from the output voltages of the photodetectors on which the optical beam lands. Particular benefits of the proposed architecture are significant reduction in jitter through the use of a mode-locked laser to generate the sampling pulses, high quantization bandwidth through a fully optical quantization scheme, and the system simplicity through the use of just one phase modulator and an embedded binary encoder in the binary-connected photodetector arrays. We experimentally demonstrate an eight-level quantization consuming only 7.2 pJ per quantization with 18-GHz bandwidth, projected to an estimated bandwidth of 30 GHz. Measured 8-ps full-width half-maximum photodetector output voltages promise the potential of realizing a 3-bit 125-GS/s analog-to-digital converter.      

基于移相光量化的任意波形全光模数转换

全光模数转换器(ADC)在高速信号处理领域有重要应用。研究了基于偏振光干涉的移相光量化(PSOQ)全光模数转换器的频率响应特性。实验中将不同频率的正弦信号经过4bit移相光量化全光模数转换器量化编码后,得到对应的数字信号。通过离散傅里叶变换,获得各个频率点的频谱。对频谱进行分析,得到不同频率下全光模数转换器的响应范围为74.07dB～74.22dB,响应起伏小于0.15dB。在此基础上,对频率为1GHz的三角波信号进行全光量化,并得到3.31bit的有效量化精度。结果表明,移相光量化方案的频率响应特性较好,验证了该方案应用于任意波形全光量化的可行性。     

基于锁模脉冲源和高速光开关的时分抽样模数转换

提出了一种基于锁模脉冲源和高速光开关的时分抽样模数(A/D)转换系统。使用高重复频率、窄脉宽的锁模脉冲串对射频信号进行抽样,利用高速光开关进行时分复用,将高采样率的信号转换为并行的多路低采样率信号,以适应现有的电模数转换器进行量化和编码,并且通过改变光开关的频率,可以灵活地改变解复用后每路信号的频率。系统的优点在于可扩展性高,只需一个锁模脉冲源。使用10 GHz重复频率的锁模脉冲和1.25 GHz的高速光开关验证了系统方案的可行性。利用实验中得到的采样点可以较好地恢复出时域信号,并且得到了各个频率的频谱图。其信噪比可达32.02 dB,等效于5.03 bit的有效比特数。     

基于光频梳的超短光脉冲的产生及其在光模数转换中的应用

提出并实验验证了一种基于光频梳的超短光脉冲的产生方法。使用强度调制器和相位调制器级联直接调制直流激光得到了29条顶部功率变化小于1.5dB的光频梳。利用单模光纤色散将光频梳整形成重复频率为10GHz,脉宽为2.68ps的光脉冲。并成功用于对1～4GHz信号采样,系统的信噪比可达33.83dB,等效于5.33bit的有效比特数。     

All-Optical Analog-to-Digital Conversion Using Split-and-Delay Technique

We propose a simplified configuration of all-optical analog-to-digital (A/D) conversion using nonlinear optical loop mirrors (NOLMs). While the conventional scheme of such all-optical A/D conversion requires encoders and threshold, for -bit resolution, the proposed configuration realizes an -bit resolution only using a single encoder and threshold, based on a split-and-delay technique, in which the encoder and the threshold operate more than times as fast as the sampling speed. After discussing detailed design issues of the NOLM-based encoder with particular emphasis on the so-called counterpropagating effects, all-optical 3-bit A/D conversion at 10 GS/s is experimentally demonstrated using the proposed configuration.     

模拟/数字转换技术及其发展趋势

数字技术的飞速发展，使A／D转换器变得越来越重要。文章扼要叙述了A／D转换器的历史发展过程，列举了几种当前流行的A／D转换器，包括全并行、两步型、插值折叠型、流水线型、逐次逼近型、∑-△型A／D转换器；具体介绍了它们的结构、工作原理、性能特点、应用场合以及最新的研究进展，并对它们的性能进行了比较；最后，讨论了A／D转换器的发展趋势。     

A Switching Logic Digitizer for Analog-to-Digital Conversion

The design and simulation of a complementary output switching logic (COSL) compatible, voltage state, switching logic comparator (SLC), and a flash analog-to-digital converter (ADC) for high-speed applications, with multigigahertz input bandwidth, is presented. A detailed design for the SLC is provided and verified with simulations. The comparator is then optimized utilizing Monte Carlo yield predictions. The optimized comparator is incorporated into the construction of a 4-bit quantizer of an ADC. The Gray-code output is converted into binary using COSL gates. The functionality, linearity, maximum input bandwidth, and dynamic range of the 4-bit ADC is verified by simulation, using a number of special input waveforms. The performance of the comparator and the 4-bit ADC are also evaluated with thermal noise incorporated into simulations. Beat frequency simulations and Fourier spectra are also used in the evaluation of the ADC performance. A fully functional 4-bit ADC, with a maximum input bandwidth of 10 GHz for a clock speed of 20 GHz, was achieved through simulations. Beat frequency simulations revealed that the comparators have an input bandwidth greater than 19 GHz with sufficient dynamic range for an ADC of greater than 6 bits of resolution. Due to the fact that the aperture time for the ADC is dependent on the rise time of the sampling pulse and not the width of the pulse, a much smaller aperture time is obtained which directly translates to higher input bandwidth.     

A Distortion Compensating Flash Analog-to-Digital Conversion Technique

We present a flash ADC design technique that compensates for static nonlinearity of the up-front track-and-hold circuit, so that high speed and high linearity can be obtained at the same time. The proposed technique functions in synergy with a new background comparator offset correction scheme. The excess quantization noise generated due to the background autozero process is derived. We demonstrate the efficacy of our techniques with measurement results for a 160 MSPS 6-bit flash converter designed in a 0.35-$muhbox m$CMOS process. The ADC consumes 50 mW from a 3.3 V power supply and has an 5.3 effective number of bits (ENOB) at Nyquist.     

成功进行模数信号转换的七个步骤

振动、温度、压力和光等现实世界的信号需要精确的信号调理和信号转换,然后才能在数字域中进行进一步数据处理。为了克服当前高精度应用的多种挑战,需要一个精心设计的低噪声模拟前端来实现最佳信噪比(SNR)。许多系统既负担不起最昂贵的器件,也无法承受低噪声器件的更高功耗。本文提出了一种系统的方法来设计一个增益     

Conversion Errors in 4-Bit Flash Analog-to-Digital Converters

Conversion errors in 4-bit flash analog-to-digital converters are computed from difference equations as a function of the ratio of the comparator input impedance to the R-2R bias network values. For maximum conversion errors less than 3 percent, the comparator input impedance should be 1000 times greater than the R value of the bias network.     

利用半导体光放大器和滤波器组合实现高速波长转换和码型转换

将半导体光放大器(SOA)和滤波器组合使用是实现高速全光信号处理的有效途径。利用半导体光放大器和带宽为0.32nm的可调窄带滤波器同时实现了40Gbit/s的非归零(NRZ)信号的反相波长转换(WC)和非归零到伪归零(PRZ)信号的码型转换,波长转换和码型转换的结果差异取决于滤波器中心波长相对于探测光波长的失谐量。当滤波器的失谐量为-0.24nm时,输出反相的波长转换,此时滤波器起到加速半导体光放大器增益恢复的功能。当滤波器失谐量为 0.41nm和-0.48nm时,得到非归零到伪归零的码型转换,并且产生的伪归零脉冲分别出现在非归零信号的上升沿和下降沿,此时滤波器的作用是将探测光的相位信息转换为强度信息,并且该码型转换结果兼有波长转换的功能。     

Robust and Practical Analog-to-Digital Conversion With Exponential Precision

Beta-encoders with error correction were introduced by Daubechies, DeVore, Guumlntuumlrk and Vaishampayan as an alternative to pulse-code modulation (PCM) for analog-to-digital conversion. An N-bit beta-encoder quantizes a real number by computing one of its N-bit truncated beta-expansions where betaisin(1,2) determines the base of expansion. These encoders have (almost) optimal rate-distortion properties like PCM; furthermore, they exploit the redundancy of beta-expansions and thus they are robust with respect to quantizer imperfections. However, these encoders have the shortcoming that the decoder needs to know the value of the base of expansion beta, a gain factor in the circuit used by the encoder, which is an impractical constraint. We present a method to implement beta-encoders so that they are also robust with respect to uncertainties of the value of beta. The method relies upon embedding the value of beta in the encoded bitstream. We show that this can be done without a priori knowledge of beta by the transmitting party. Moreover the algorithm still works if the value of beta changes (slowly) during the implementation     

光子晶体光学频率变换技术

文章首先介绍了光子晶体光学频率变换技术的基本原理和技术特点;然后简述光子晶 体光学频率变换技术研究进展情况;最后指出了光子晶体变频技术在可调谐激光器和其它领域中的应用前景。     

Optical Analog-to-digital Conversion Scheme Based on Tunable Fabry-Perot Resonator

Proposed is an interference type of optical analog-to-digital conversion(ADC). The refractive index of Fabry-Perot cavity changes with different voltages. The Fabry-Perot resonator converts electronic intensity into light wavelength through selecting lights of different wavelengthes. The parameters of the scheme are acquired with the transmission matrix of optical element and the time of steady-state light field. The maximum sampling speedes of 4-bit, 6-bit, 7-bit, 8-bit and 9-bit(ADC) are 1.695×1010 count/s, 4.33×109 count/s, 2.38×109 count/s, 1.24×109 count/s and 5.9×108 count/s, respectively.     

光学模数转换器的原理及发展

模数转换器（ADC）是许多信息处理系统的关键组成部分。由于电子模数转换器的缓慢进展，使其成为模拟信号和数字处理系统之间的瓶颈因素，这促使人们对采用光学技术提高模数转换器的采样速率和精度产生了兴趣。本文详细阐述了光学模数转换器（OADC）的原理及发展，对其应用及未来的发展进行了探讨。     

基于半导体光放大器交叉偏振调制的波长转换分析

对半导体光放大器(SOA)中光偏振态发生改变的原因和交叉偏振调制型波长转换进行了探讨和分析.如果SOA具有偏振不灵敏增益,则波长转换效果与泵浦光的偏振态无关,而只与探测光的偏振态有关,而且当入射探测光的偏振与TE模振动方向成45°夹角时,交叉偏振调制的效果最明显.为了使转换效果更好,宜采用反相波长转换,SOA的自发辐射耦合因子β应该很小.     

基于半导体光放大器交叉偏振调制的波长转换分析

对半导体光放大器(SOA)中光偏振态发生改变的原因和交叉偏振调制型波长转换进行了探讨和分析.如果SOA具有偏振不灵敏增益,则波长转换效果与泵浦光的偏振态无关,而只与探测光的偏振态有关,而且当入射探测光的偏振与TE模振动方向成4 5°夹角时,交叉偏振调制的效果最明显.为了使转换效果更好,宜采用反相波长转换,SOA的自发辐射耦合因子β应该很小     

使用空间光调制器和频谱面滤波实现光学图像幅相转换

提出了一种新的振幅——相位转换方法。以原振幅图像为基础，由计算机构造一幅余弦光栅并显示到空间光调制器上，利用余弦光栅的分谱特性和4f系统谱面滤波得到需要的频谱项，再对这一频谱项进行一次逆傅里叶变换，就可在输出面上得到原振幅图像相应的空间相位分布。采用计算机和电寻址振幅型空间光调制器控制、输入图像，可以达到可控制、可重构及实现动态的空间相位分布。给出了该方法的基本思想、理论分析和计算机模拟结果及实验验证。     

基于SOA中四波混频效应的全光波长变换

基于半导体光放大器的四波混频效应进行了 2 .5 Gbit/s的光脉冲的波长变换。向上波长变换间距为 1 0 nm,向下变换间距大于 1 0 nm。对基于半导体光放大器四波混频效应的波长变换技术进行了较为详尽的试验报道     

使用空间光调制器和频谱面滤波实现光学图像幅相转换

提出了一种新的振幅——相位转换方法。以原振幅图像为基础,由计算机构造一幅余弦光栅并显示到空间光调制器上,利用余弦光栅的分谱特性和4f系统谱面滤波得到需要的频谱项,再对这一频谱项进行一次逆傅里叶变换,就可在输出面上得到原振幅图像相应的空间相位分布。采用计算机和电寻址振幅型空间光调制器控制、输入图像,可以达到可控制、可重构及实现动态的空间相位分布。给出了该方法的基本思想、理论分析和计算机模拟结果及实验验证。