Low-loss dispersion compensation of high-speed data with integrated, concatenated gratings

Optical transceivers serve as the backbone of high-speed data transmission over optical fiber in communication systems and there is a constant challenge to keep cost and power consumption low while increasing data capacities. However, dispersion impairments introduced by the transmission of data over optical fiber, limit the baud rates and fiber reach. In this paper, we demonstrate a low loss, transmission-based grating device to compensate for dispersion up to 20 km by the concatenation of gratings where the operation occurs outside of the stopband in the region where transmissivity is high, and the normal dispersion magnitude is large. High-speed measurements with 28.05GBd/s PAM4 data show a significant improvement of >14 dB improvement in the transmitter dispersion eye closure quaternary after 10 km, and improvement in the dispersion penalty up to 20 km when dispersion compensation is applied without digital signal processing (DSP) methods. Further analysis by scanning the carrier wavelength across the grating stopband while simultaneously measuring the bit-error rate (BER) reveal that improvements in the BERs correspond with the nonlinear group delay curve and low BERs can be realized with vestigial filtering of the modulated data. The presented integrated optical system provides a low-loss, CMOS-compatible solution for the effective management of dispersion and may enable augmented fiber reaches and data rates in transceivers.