Photonic Sampling using an Agile Optical Comb Generator

数字信号处理是存储、分析和处理数字信号的强大技术。最终，要处理的信号的质量取决于模数转换器(ADC)的性能，模数转换器首先用于对原始模拟信号进行采样并产生其数字表示。电子ADC无处不在地嵌入在许多日常用品中，例如手机、数字温度计和电脑鼠标。随着电子ADC的速度不断提高，越来越多的复杂应用，包括医学成像和认知雷达，可以受益于ADC和数字信号处理的使用。自20世纪70年代以来，光子学一直被用来提高电子ADC的性能，形成了现在通常被称为光子ADC的东西。大多数采样率高达1太赫兹(1,000,000,000,000赫兹)的光子ADC总是使用锁模激光器，因为它们可以产生非常高功率的光脉冲，具有非常短的脉冲宽度和低抖动，两者都在飞秒区域。这种超短且稳定的光脉冲非常适合对微波和毫米波信号进行采样，其采样速率超过了使用传统电子模数转换器所能实现的采样速率。然而，大多数锁模激光光源体积大、价格昂贵，需要不断调整稳定性。因此，到目前为止，它们还没有得到广泛的商业应用。此外，大多数锁模激光脉冲源的重复频率不容易调整，因此，使用这种源的光子ADC的采样速率是固定的，并且不能改变以适应输入信号频率和带宽。在这一应用中，我们寻求支持，以研究一种新的、高性能的光子采样技术，该技术基于光学梳状发生器，而不是传统的锁模激光器。与锁模激光方法不同，在这种新的方法中，可以以灵活的采样频率进行连续采样。我们还计算了典型DFB激光器的线宽和所用毫米波发生器的相位噪声引起的综合抖动电平小于5ps(RMS)，对应的有效比特数(ENOB)为10，在相同的40 GHz采样频率下优于最先进的CMOS型电子ADC和全光ADC。这种高性能的光子采样技术有望引起研究界和产业界的广泛关注。

Digital signal processing is a powerful technique for storing, analysing and manipulating digital signals. Ultimately, the quality of the signal to be processed is determined by the performance of the analogue-to-digital converter (ADC) which is used to sample the original analogue signal in the first place and produce a digital representation of it. Electronic ADCs are embedded ubiquitously in numerous everyday items, such as mobile phones, digital thermometers and computer mice to name a few. As the speed of electronic ADCs continues to increase, more and more sophisticated applications including medical imaging and cognitive radar can benefit from the use of ADCs and digital signal processing. Photonics has been used to increase the performance of electronic ADCs since the 1970s, forming what is now generally termed the photonic ADC. Most photonic ADCs with sampling rates as high as 1 THz (1,000,000,000,000 Hz) have invariably employed mode-locked lasers as they can produce very high power optical pulses with very short pulse widths and low jitters, both in the femto second region. Such ultra-short and stable optical pulses are ideal for sampling microwave and millimetre-wave signals at a sampling rate which is beyond what is achievable using conventional electronic ADCs.However, most mode-locked laser sources are bulky, expensive and require constant stability adjustments. Therefore they have not found widespread commercial application to date. Furthermore, the repetition rates of most mode-locked laser pulse sources cannot be readily adjusted and as a result, the sampling rates of photonic ADCs using such sources are fixed and cannot be varied to suit the input signal frequency and bandwidth. In this application, we seek support to investigate a new, high-performance photonic sampling technique based on an optical comb generator instead of the traditional mode-locked lasers. In this novel approach, continuous sampling at flexible sampling frequencies are possible, unlike the mode-locked laser approach. We have also calculated that the combined jitter level due to the linewidth of a typical DFB laser and the phase noise of a mm-wave generator to be used in this technique is less than 5 fs (RMS) and the corresponding effective number of bits (ENOB) of resolution is 10 which is superior to the state-of-the-art CMOS electronic ADC and the all-optical ADC at the same 40 GHz sampling frequency. Such high-performance photonic sampling technique is expected to attract wide attention from both the research community and the industry.