Simulation and Experimental Analysis of Optical Frequency Comb Generation Methods and its Application in High-Capacity Optical Communication Systems

Abstract

The exponential growth of data usage is reshaping optical communications networks and driving us to look for innovative technologies. Increased bandwidth, faster speeds, scalability are the needs for today's telecommunication field. These needs can be met, and the transmission ability can be increased by adopting advanced modulation formats, increased data rate and increasing the number of optical carriers. Increasing the number of optical carriers seem to be a captivating technology as the well-established dense wavelength division multiplexing (DWDM) is being used to multiplex several optical carriers in an optical communication system. High-capacity optical communication systems can be implemented using DWDM technique, which allows the transmission of separate wavelengths over a single optical channel. One of the challenges of DWDM is precise wavelength control to avoid crosstalk. Also, the use of discrete single wavelength lasers consumes lot of energy and make the system expensive. Replacing multiple laser sources with a single laser with multiple carriers in a DWDM system is a novel technique leading to reduced energy consumption, system complexity and cost. Optical frequency comb (OFC) is a multi carrier single laser source which can be integrated with the DWDM system. OFC is a promising technology which find its application in communication system as they offer many advantages such as high repetition rates, low noise, high stability covering multiple communication bands. This makes them ideal for advanced communication system. In this thesis we shall see the OFC generation using passive mode locked Quantum Dash laser and electro-optic modulation technique. Experimental results and analysis for varying temperatures for Quantum Dash laser are presented and their effect is studied. The fundamental mode locking characteristics are studied and experiments are carried out to find the repetition rate and results of RF spectra measurement are presented. Experimental results to measure the dispersion of the laser cavity are also presented. OFC generation with good flatness is obtained using electro-optic modulator called the fibre loop modulation technique. Experimental results for OFC generation are presented and compared with the simulation results. Simulation is performed using the commercially available simulation software - OptiSystem. Comb line characteristics of OFC is analysed with respect to the amplitude of the RF signal used in fibre loop modulation technique. A direct relation between the amplitude of RF signal and the number of comb lines is obtained and the simulation results of the same is presented in this work. A system is modelled integrating OFC in DWDM communication system in which the transmission medium considered is free-space. Simulation results are presented showing the potential of OFC to support high-capacity optical communication. Performance analysis of the system in terms of bit error rate and range of the optical transmission is presented which show that the modelled system is capable of high-capacity communication system.