Polarized intensity rotational FSK modulation for SOP change robust in optical access networks

Abstract

Due to the development of various mobile applications and various services for 5G and B5G communication environments, data traffic is steadily increasing explosively. In optical access networks, signals modulated on optical intensity have been used. It is difficult to expand the optical intensity modulation according to the increase in data traffic. Therefore, the modulations using other resources have been researched such as optical phase, optical polarization, and optical wavelength. Since modulation using polarization has a simple system compared to other techniques, modulation using optical polarization has widely studied as a multi-dimensional modulation resource. The conventional modulation technique using polarization modulates the signal according to the state of polarization (SOP). However, the technique is very vulnerable to SOP change, especially rotation SOP (RSOP), due to the characteristics of the optical fiber and the optical active devices. In this paper, we propose the polarized intensity rotational frequency shift keying (PIR-FSK) as a novel modulation technique robust to SOP change in optical access network. The PIR-FSK technique modulates the sine and cosine form of FSK RF signal to the intensity of each X and Y polarization of optical carrier, where the total intensity of the modulated optical carrier is in helical form. In addition, since the proposed technique does not affect the total optical carrier intensity, it can be accommodated with the intensity modulation at the same time. We verified experimentally that PIR-FSK offers better immunity to RSOP compared to the conventional PolSK.