High-Linearity Fano Resonance Modulator Using a Microring-Assisted Mach–Zehnder Structure

Analog microwave photonic links require high-linearity electro-optic modulators. We investigate and optimize the linearity performance of a silicon Fano resonance modulator based on a reconfigurable microring-assisted Mach-Zehnder interferometer (MZI). The microring resonator has a tunable coupling coefficient and the reference arm of the MZI is variable in both amplitude and phase, allowing for flexible tuning of the operating point. The on-chip insertion loss of the device is 5 dB. High modulation linearity can be obtained at both Fano resonant and anti-Fano resonant wavelengths, among which the latter has a higher carrier-to-distortion ratio (CDR). However, the Fano resonance has a higher modulation efficiency due to its sharp slope of the resonant transfer function, eventually leading to a larger spurious-free dynamic range (SFDR). Experimental results indicate that the best SFDR of the third-order intermodulation distortion (IMD3) is 111.3 dB·Hz ^2/3 measured at the 1 GHz frequency, comparable to the commercial lithium niobate modulators.