Novel modulation technique for radio-over-fiber systems

摘要

Fiber-optic communications have been widely used and deployed across the globe. As the bottom structure of optical communication networks, optical access networks connect a central office with base stations in local networks. Falling into the category of optical access networks, Radio-over-fiber (RoF) technique offers the future access solutions for high speed and capacity wireless communication. RoF technique uses optical fiber to distribute high frequency RF signals between central office and base stations. At present, two main RoF modulation techniques exist, optical double sideband modulation (ODSB) and optical single sideband modulation (OSSB). OSSB is preferred due to robustness to chromatic dispersion but ODSB not. In typical OSSB, modulation efficiency i.e. optical carrier-to-sideband power ratio (OCSR) is merely determined by RF amplitude. Large/small RF signals can lead to small/large OCSR and large/small nonlinear distortions. OCSR directly determines RF output power. The goal of new modulation technique is to improve modulation efficiency by suppressing OCSR and keep nonlinear distortions low. In this work, we propose and analyze a novel modulation technique, consisting of two parallel dual-electrode Mach-Zehnder modulators (MZMs). With this proposed modulation technique, OSSB with adjustable OCSR can be achieved by adjusting two DC biases of the MZMs. We first make theoretical analysis and then finish simulation verification. Their results agree with each other very well. Both of them show that RF output power can be greatly improved by adjusting OCSR. Furthermore, the optimum OCSR is 0dB when one RF is applied to modulation optical carrier and it is 3dB in the case of two RF signals