Highly linear dual parallel Mach-Zehnder modulator incorporating MMI couplers

The strict requirements on splitting ratios of optical power and radio-frequency (RF) voltage affect the performance of the Dual Parallel Mach-Zehnder modulator (DPMZM). In this paper, a modified DPMZM with three Multimode Interference (MMI) couplers (MMI-DPMZM) is proposed. The three MMI couplers, comprised of a reconfigurable one and two 3 dB ones, function as optical splitters. The theoretical analysis shows that the structure can prohibit the third-order intermodulation distortion (IMD3) from the third order term and fifth order term of the transfer function's Taylor series, leading to the peak Spurious-Free Dynamic Range (SFDR) as high as 104.12 dB. The adjustment of the tunable MMI coupler ensures the SFDR is kept above 104.00 dB even the radio frequency (RF) signal's voltage splitting ratio deviates from its optimum value. It is also demonstrated that the SFDR can reach 104.10 dB with the precision and uniformity of MMI couplers considered.