The effects of the nonlinearity caused by the structure of ‘Mach-Zehnder modulator (MZM) - wavelength division demultiplexer (WDM)’ in Time-Wavelength Interleaved Photonic Analog-to-Digital Converters is studied for the first time. Even if the MZM is biased at quadrature, the narrow passband width of the WDM after modulation may result in the presentation of even harmonics in the spectrum of the sampling results. As the radio frequency (RF) of the signal being sampled increases and the passband width of the WDM decreases, the magnitudes of the even harmonics increase. As a result, the spur-free dynamic range (SFDR) would be determined by the magnitudes of the signal and the 2nd{^{\rm {nd}}} harmonic instead of the 3rd{^{\rm {rd}}} harmonic. When the passband width of the WDM is less than 100 GHz, the variation of the SFDR can be as much as 6 dB over 0∼\sim25 GHz-frequency range of the signal being sampled. Theoretical analysis is verified by the simulation and experimental results. When the passband width of the WDM is greater than 150 GHz, the SFDR over 0∼\sim25 GHz-RF range is always dominated by the 3rd{^{\rm {rd}}} harmonic. When the passband width is 50 GHz, the SFDR is dominated by the 2nd{^{\rm {nd}}} harmonic for RF frequencies above 10 GHz, and can be as much as 20 dB higher than the 3rd{^{\rm {rd}}} harmonic term at 25 GHz-RF frequency. The requirement for the passband width of the WDM can be specified according to the frequency range of the signal being sampled to avoid the presentation of even harmonics and optimize the design of TWIPADCs.

中文翻译：

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时间波长交错光子模数转换器中“MZM-WDM”结构引起的非线性效应。


首次研究了时波长交错光子模数转换器中“马赫-曾德尔调制器(MZM)-波分解复用器(WDM)”结构引起的非线性效应。即使MZM正交偏置，调制后WDM的窄通带宽度也可能导致采样结果的频谱中出现偶次谐波。随着被采样信号的射频 (RF) 增加以及 WDM 的通带宽度减小，偶次谐波的幅度会增加。因此，无杂散动态范围 (SFDR) 将由信号的幅度和第 2{^{\rm {nd}}} 谐波（而不是第 3{^{\rm {rd}}} 谐波确定）谐波。当 WDM 的通带宽度小于 100 GHz 时，在采样信号的 0∼\sim25 GHz 频率范围内 SFDR 的变化可能高达 6 dB。理论分析通过仿真和实验结果得到验证。当 WDM 的通带宽度大于 150 GHz 时，0∼\sim25 GHz-RF 范围内的 SFDR 始终以 3rd{^{\rm {rd}}} 谐波为主。当通带宽度为 50 GHz 时，对于 10 GHz 以上的 RF 频率，SFDR 主要由第 2 次谐波主导，并且可能比第 3 次谐波高出 20 dB。 25 GHz RF 频率处的 {rd}}} 谐波项。可以根据采样信号的频率范围来指定WDM的通带宽度的要求，以避免出现偶次谐波并优化TWIPADC的设计。