Sherman Alexander, Horowitz Moshe, Zach Shlomo
Opt Express. 2014 Jun 30;22(13):15502-13. doi: 10.1364/OE.22.015502.
We demonstrate a new method to improve the performance of photonic assisted analog to digital converters (ADCs) that are based on frequency down-conversion obtained by optical under-sampling. The under-sampling is performed by multiplying the radio frequency signal by ultra-low jitter broadband phase-locked optical comb. The comb wave intensity has a smooth periodic function in the time domain rather than a train of short pulses that is currently used in most photonic assisted ADCs. Hence, the signal energy at the photo-detector output can be increased and the signal to noise ratio of the system might be improved without decreasing its bandwidth. We have experimentally demonstrated a system for electro-optical under-sampling with a 6-dB bandwidth of 38.5 GHz and a spur free dynamic range of 99 dB/Hz(2/3) for a signal with a carrier frequency of 35.8 GHz, compared with 94 dB/Hz(2/3) for a signal at 6.2 GHz that was obtained in the same system when a pulsed optical source was used. The optical comb was generated by mixing signals from two dielectric resonator oscillators in a Mach-Zehnder modulator. The comb spacing is equal to 4 GHz and its bandwidth was greater than 48 GHz. The temporal jitter of the comb measured by integrating the phase noise in a frequency region of 10 kHz to 10 MHz around comb frequencies of 16 and 20 GHz was only about 15 and 11 fs, respectively.
我们展示了一种新方法，用于提高基于光学欠采样实现频率下变频的光子辅助模数转换器（ADC）的性能。欠采样是通过将射频信号与超低抖动宽带锁相光梳相乘来实现的。在时域中，梳状波强度具有平滑的周期函数，而不是目前大多数光子辅助ADC中使用的短脉冲序列。因此，在不降低带宽的情况下，可以增加光电探测器输出端的信号能量，并可能提高系统的信噪比。我们通过实验演示了一个电光欠采样系统，对于载波频率为35.8 GHz的信号，其6 dB带宽为38.5 GHz，无杂散动态范围为99 dB/Hz(2/3)；相比之下，在同一系统中使用脉冲光源时，对于6.2 GHz的信号，得到的无杂散动态范围为94 dB/Hz(2/3)。光梳是通过在马赫-曾德尔调制器中混合来自两个介质谐振器振荡器的信号产生的。梳齿间距等于4 GHz，其带宽大于48 GHz。通过在16 GHz和20 GHz梳齿频率周围10 kHz至10 MHz频率区域内积分相位噪声来测量的梳状波时间抖动分别仅约为15 fs和11 fs。
