Photonic Sampling using an Agile Optical Comb Generator

数字信号处理是一种存储、分析和处理数字信号的强大技术。最终，待处理信号的质量取决于模数转换器（ADC）的性能，该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等等。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，可以从adc和数字信号处理的使用中受益。自20世纪70年代以来，光子学已被用于提高电子ADC的性能，形成了现在通常称为光子ADC的东西。大多数采样率高达1thz （1,000,000,000,000 Hz）的光子adc总是采用锁模激光器，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是采样微波和毫米波信号的理想选择，其采样率超出了使用传统电子adc可以实现的采样率。然而，大多数锁模激光源体积庞大，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率不能轻易调整，因此，使用这种源的光子adc的采样率是固定的，不能改变以适应输入信号的频率和带宽。在这个应用中，我们寻求支持来研究一种新的、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。在这种新颖的方法中，与锁模激光方法不同，可以在灵活的采样频率下进行连续采样。我们还计算出，由于典型DFB激光器的线宽和用于该技术的毫米波发生器的相位噪声的组合抖动电平小于5 fs (RMS)，相应的有效位元数（ENOB）的分辨率为10，在相同的40 GHz采样频率下，优于最先进的CMOS电子ADC和全光ADC。这种高性能的光子采样技术有望引起学术界和工业界的广泛关注。

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.