一篇激光调制解调的个人翻译.doc

8Gbit/s FSK MODULATION OF DFB LASERSWITH OPTICAL DEMODULATIONDFB型激光发射器的8比特频域键控调制及光解调Indexing terms: Optical communications, Semiconductor lasers,Optical modulation, Optical receivers关键字：光通信，半导体激光器，光调制，光接收机Single-contact DFB lasers were frequency modulated bypseudorandom data at rates up to 8 Gbit/s by direct currentmodulation with no pre-equalisation of the modulationsignal. The signals were optically demodulated by Fabry-Perot interferometers for conversion to ASK signals whichwere detected by a direct-detection receiver. At 8Gbit/s the receiver sensitivity was -22dBm.以往的接触式单点分布反馈激光器 由 伪随机数据进行频率调制 ，其速率达到8 Gbit/s。 调制信号直接使用无预均衡的电流进行调制。已调信号由法布里-佩罗特干涉仪进行光解调，并转换成ASK信号，该信号由直接检测接收机进行检测。在8 Gbit/s的速率下，接收机的灵敏度为-22dBm。For semiconductor lasers directly modulated at high datarates, frequency-shift-keyed (FSK) modulation formats arepreferable to amplitude-shift-keyed (ASK) formats for severalreasons.对于工作在高数据率下的直接调制半导体激光器，由于各种原因，频移键控（FSK）调制比振幅键控（ASK）调制形式性能更好。The current drive to the laser required for FSKmodulation (which slightly changes the laser frequency whilethe laser is biased well above threshold) is typically muchsmaller than that required for ASK modulation (which drivesthe laser from a high bias level down to near threshold).这个用于驱动激光器产生频移键控调制的电流，（产生的激光频率略有改变，并远高于阀值），通常远小于振幅键控所需的电流，并驱使激光从一个较高的偏移下降到阀值附近。This reduction in drive requirement is especially significant at veryhigh bit rates where high-speed, high-power laser driver circuitsare difficult to fabricate减少启动器对电流的需求具有重要意义，尤其在高比特率，高速的情况下，高功率的激光驱动电路是很难制造、实现的。The small drive in a FSK formatalso leads to a relatively compact laser spectrum which minimisesthe problem of fibre chromatic dispersion and makesefficient use of the frequency spectrum for WDM purposes.在FSK形式下的小驱动器也使得激光光谱变得相对紧凑，并最大限度的减少了光纤色散的问题，从而更有效的利用频谱，达到波分复用的目的。Typically, FSK signals used in heterodyne configurations areelectronically demodulated.18 However, FSK signals can also be optically demodulated effectively by converting the signals to baseband ASK signals.9通常，（在外差配置下的FSK信号使用电子解调）使用超外差配置对FSK信号进行电子解调。然而，也可以将FSK信号转换成基带下的ASK信号，从而进行有效的光解调。Consequently conventional directdetection receivers can be used. This is an advantage comparedto coherent systems because heterodyne detection ofhigh bit rate signals require large intermediate frequencies andassociated very wideband electronics.因此，可以使用传统的直接检测接收机进行解调。相对于相干解调系统，这是一个优势，因为在高比特率下，信号的外差检测需要大量的中间频率和关联紧密的带宽电子。In this letter we describe frequency modulation of single electrodeDFB lasers by direct current modulation with no pre-equalisation at bit rates of 2 Gbit/s, 4 Gbit/s and 8 Gbit/s.在本文中，我们描述了单极分布反馈激光器的频率调制，它是由无预均衡的电流直接进行调制的。其比特率为2 Gbit/s, 4 Gbit/s和8 Gbit/s。The data were optically demodulated at the receiver usingmicro-Fabry-Perot interferometers (FPI) with less than0.25dB insertion loss. A direct detection receiver was used todetect the signals and bit-error-rate (BER) performance wasmeasured.数据则使用光学解调，其接收机使用了微法布里 - 珀罗干涉仪（FPI），其插入损耗小于0.25dB。信号使用直接检测接收机进行检测，并且其误码率（BER）是有规律的。The FSK results were compared to ASK results byremoving the FPI from the receiver and increasing the laserdrive to obtain full ASK operation of the laser.将FSK信号解调的结果与ASK信号进行比对，结果显示，移除接收机的法布里 - 珀罗干涉仪（FPI）并增加激光的驱动，能够得到激光调制下完整的ASK信号功能。将FSK信号解调的结果与ASK信号解调结果进行比较，ASK信号解调是采用移除珀罗干涉仪（FPI）的接收机和增加激光驱动得到的激光器完全ASK解调。The experiments consisted of 1.3 m DFB lasers driven by aNRZ electronic bit stream at rates up to 8 Gbit/s.试验包括一个由NRZ电子比特流驱动，速率达到8 Gbit/s的1.3微米DFB型激光器。The laserlight passed through two Faraday isolators providing 60 dBoptical isolation, a variable attenuator and the FPI, and wasdetected by an 8 Gbit/s direct detection receiver.激光通过两个能够提供60分贝光隔离的法拉第隔离器，一个可变衰减器和法布里-珀罗干涉仪。并由一个8 Gbit/s的直接检测接收机检测。The FPIwas frequency-locked to the marks of the FSK signal by asimple feedback loop which maximises receiver photocurrent.法布里-珀罗干涉仪由简单的反馈回路将频率锁定在FSK的信号标志处，这样能最大限度地提高接收机的光电流。Semiconductor injection lasers typically have a nonuniformFM response because of competing thermal modulationand carrier modulation effects. Nonuniform FM responseleads to pattern dependent errors.半导体注入激光器通常有不均匀的频率响应，因为竞争的热调制和载波调制效果。不均匀的频率响应导致从属的模式错误。The nonuniform FMresponse can be compensated by pre-equalisation of themodulation signal with a passive network.非均匀的频率响应可以由一个预均衡的被动网络调制信号进行补偿。However, this solution usually results in relatively small FM response (onthe order of 100 MHz/mA), and consequently increased drive requirements.然而，这种解决方案通常由一个相对较小的频率响应产生（要求100 MHz/mA），因此要增加驱动的需求。Multiple-electrode lasers typically have flat FMresponse only to about 1 GHz and therefore are not useful forvery high data rates.多电极激光器通常有平坦的调频响应，仅约1千兆赫，因此非常高的数据传输速率是没必要的。In our high-speed FSK experiments, the nonuniform FMresponse problem is circumvented by using lasers that have unusually large linewidth enhancement factors（）.在我们的高速FSK试验中，频率响应不均匀的问题，可以通过使用一个大多数情况下有很大线宽增强因数（）的激光器来回避。The linewidth-power products for these lasers are greater than 500 MHz mW.这些用于激光器的线宽电源产品均大于500 MHz mW。Large leads to large carrier-mediated FM responses (up to 2 GHz/mA). A large FM response serves two purposes.一个大的值将导致一个大的载体介质频率响应（高达 2 GHz/mA）。一个大的调频响应为了两个目的。First, the drive requirements are small. Second, the FM response remains flat at very low frequencies.第一， 驱动器的要求小。第二，频率响应持平于非常低的频率。An example of FSK at 2Gbit/s data rate using pseudorandomword lengths is shown in Fig. 1例如：一个2Gbit/s数据率、并使用字长的伪随机数列的频率调制，如图1。Note that with this word length the signal has frequency content below 1kHz. The peak-to-peak current drive is 4mA resulting in AM of only 7%.注意，在这样的字长下，信号的频率含量低于1 kHz。峰峰值的电流驱动是4mA，只有幅度调制的7%。Superposed on the FM spectrum is the transmission response (95% peak transmission) of a 650pm long FPI used to demodulate the signal.叠加到调频频谱的，是一个650pm长的法布里 - 珀罗干涉仪的传输响应（95%的峰值传输），它用于解调信号。The bandpass of the FPI is about 7 GHz FWHM. The eye diagram of the demodulated signal is shown in Fig. 2.法布里 - 珀罗干涉仪的通带大约是7 GHz半高宽。解调信号的眼图如图2.No degradation due to nonuniform FM response at low frequencies is evident.在低频上，因为没有不均匀的频率响应所以也没有衰减，这是显而易见的。BER curves were measuredusing a - l word length (this was the maximum word length of the BER test set).BER曲线使用一个字长的伪随机序列测定（这是BER测试集最大的字长）。A BER was achieved for -30dBm receiver power. This sensitivity could be improved by using a receiver optimised for 2 Gbit/s ratherthan the 8 Gbit/s receiver actually employed.一个误码率达到-30dBm的接收机功率。实际上，通过使用一个优化到2 Gbit/s的接收机来提升这个灵敏度，而不是8Gbit/s的接收机。Experiments at 4Gbit/s and 8Gbit/s used a laser with5 GHz small-signal modulation bandwidth and a FMresponse of 1 GHz/mA. For 4 Gbit/s the laser drive was 28 mAand a 195pm long FPI with a 15GHz bandpass was used.试验中，在4Gbit/s和8Gbit/s的速率下，使用的是5 GHz的小信号调制带宽和1 GHz/mA 频率相应的激光器。在4 Gbit/s的情况下，激光驱动器使用的电流是28 mA及一个195pm长度、通带宽度为15GHz的法布里 - 珀罗干涉仪。For 8Gbit/s the laser drive was 44mA and the data weredemodulated by a 67 pm long FPI with a 45 GHz bandpass.Figs. 3 and 4 show BER curves for 4Gbit/s and 8Gbit/s,respectively.在8Gbit/s的速率下，激光驱动器使用的电流是44mA，并且数据被一个67 pm长度、通带宽度45GHz的法布里 - 珀罗干涉仪解调。图3和图4分别显示了4Gbit/s和8Gbit/s的速率下的误码率。The FSK results are compared to ASK results bysimply removing the FPI from the receiver and increasing the laser drive. The received power in Figs. 3 and 4 is the powerimpinging on the photodetector.将FSK的结果与ASK的进行比对，通过简单的从接收器移除法布里 - 珀罗干涉仪并增加激光器的驱动。在图3和图4的功率接收图是能量撞击到探测器的结果。No degradation is evident for either bit rate. The same receiver was used for both 4Gbit/s and 8 Gbit/s.很明显在两种比特率下都没有衰落。4Gbit/s和8 Gbit/s的速率都是使用同一个接收器。The receiver sensitivity at 8 Gbit/