Abstract
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.
Highlights
An increasing number of mobile Internet devices offering people various broadband wireless multimedia services have been driving the communications technology to make continuous progress
We firstly present the theoretical model of a modified Dual Parallel Mach-Zehnder modulator (DPMZM) with three Y-splitters replaced by three Multimode Interference (MMI) couplers (MMI-DPMZM) consisting of a 1x2 tunable MMI coupler and two 1x2 3 dB asymmetrical MMI couplers
In above analysis, the precision of the reconfigurable MMI coupler requires 4th-decimal order and no imbalance exists for the 3 dB MMI couplers, which may lead to complex control circuits
Summary
An increasing number of mobile Internet devices offering people various broadband wireless multimedia services have been driving the communications technology to make continuous progress. Many researchers have applied it into the RoF and RoFSO links to fulfill different functions, such as single sideband (SSB) modulation [12], quadrature amplitude modulation (QAM) [13], optical mmwave signal generation [14] In these systems, the linearity of the modulator is one of the significant factors to affect the Spurious Free Dynamic Range (SFDR) which is an important measure to evaluate these systems. When DPMZM works at its optimum operating point, the reduction of the intermodulation distortion (IMD) is more than 20 dB, resulting in a high SFDR value It can maintain its ultra linearity in a wide radio frequency (RF) range, which is very important for RoF and RoFSO links [11]
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