Abstract
In this paper, we demonstrate that forward bias (+0.9V) of a high-speed silicon (Si) optical Mach-Zehnder modulator (MZM) increases the radio-frequency (RF) link gain by 30 dB when compared to reverse bias operation (-8V). RF applications require tunable, narrowband electro-optic conversion with high gain to mitigate noise of the optical receiver and realize high RF spur-free dynamic range. Compared to reverse bias, the forward bias gain rolls off more rapidly but offers higher RF link gain improvement of more than 13.2 dB at 20 GHz. Furthermore, forward bias is shown to result in comparable spurious-free dynamic range (SFDR: 104.5 dB.Hz2/3). We demonstrate through an analytical dc transfer curve the existence of simultaneous high gain and OIP3 and verify the theoretical results with measurement under forward bias at a bias point of around +0.9 V.
Highlights
Development of silicon-based RF and microwave photonics has the potential to realize lowcost optical devices integrated in a CMOS-compatible process
Reverse bias operation has the tradeoff of relatively weak variation in carrier density per unit length, which results in high drive voltage (Vπ>5V) and long active device length (L>1 mm) in silicon
We demonstrate that forward bias of a silicon photonic (SiP) Mach-Zehnder modulator (MZM) at around +0.9 V exhibits up to 40 dB more RF link gain without sacrificing spurious-free dynamic range (SFDR)
Summary
Development of silicon-based RF and microwave photonics has the potential to realize lowcost optical devices integrated in a CMOS-compatible process. For silicon photonic MZMs, the typical product of drive voltage and device active length (VπL) is usually around 2 V.cm [12] and results in microwave photonic devices that either suffer from high electrode attenuation that reduce the frequency cut-off or short devices that exhibit low gain, and thereby, high noise figure. We demonstrate that forward bias of a silicon photonic (SiP) Mach-Zehnder modulator (MZM) at around +0.9 V exhibits up to 40 dB more RF link gain without sacrificing spurious-free dynamic range (SFDR). By analyzing the transfer curves, we observe that the optimum bias points correspond to a maximum of first derivative and minimum in third derivative in the measured DC transfer curve, are very close and exist at around +0.9 V At this bias point, the maximum RF link gain is -14.7 dB at 1 GHz and the corresponding SFDR performance is 104.5 dB.Hz2/3
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