Open AccessModulator material impact on chirp, DSP, and performance in coherent digital links: comparison of the lithium niobate, indium phosphide, and silicon platforms
Author(s) -
Maxime Jacques,
Alireza Samani,
David Patel,
Eslam El-Fiky,
Mohamed Morsy-Osman,
Thang M. Hoang,
Ghulam Saber,
Luhua Xu,
John Sonkoly,
Michael H. Ayliffe,
David V. Plant
Publication year - 2018
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.26.022471
Subject(s) - lithium niobate , chirp , indium phosphide , optics , digital signal processing , phase shift keying , materials science , quadrature amplitude modulation , phase modulation , electronic engineering , optoelectronics , physics , computer science , telecommunications , bit error rate , engineering , phase noise , gallium arsenide , laser , channel (broadcasting)
We characterize the impact of the modulator material on chirp, digital signal processing (DSP) algorithms and system-level performance in coherent digital optical links. We compare theoretically, in simulations and experimentally the lithium niobate (LiNbO 3 ), indium phosphide (InP) and silicon (Si) integrated platforms. Distortions to vector diagrams are traced back to modulation physics, and are interpreted as quadrature crosstalk. In a back-to-back BPSK setup with an RF drive signal amplitude of 1.5V π , we measure chirp parameters α of ~0, 0.10 and 0.06 and error vector magnitude EVM RMS of 5.3%, 9.4% and 10.6% with the LiNbO 3 , InP and Si modulators respectively. Both α and EVM RMS are found to scale with the RF signal amplitude. In simulations, using a polynomial fit over a sinusoidal fit when pre-compensating the Si modulator transfer function slightly improves EVM (-0.6%). We also show that Si-related distortions can impact the efficiency of symbol timing recovery. In conclusion, phase and attenuation distortions in InP and Si modulators deteriorate the overall performance in coherent links, and cannot be neglected for large RF signal amplitudes. These results will benefit the optical communications community.