Study Of Semiconductor Optical Amplifier For Video Signal Transmission

Emerging applications in recent years, such as high-definition TV, tele-presence, digital cinema and high-quality audio transmission demand high-throughput optical access networks (OAN) with Quality of Service requirements. Nevertheless, the infrastructure of current access networks suffers from limited bandwidth and high network management cost. Cable television (CATV), one of the major services in OAN, is no exception. An evolution in access network is now proposed by the Chinese administration of radio film and television, changing the hybrid fiber coaxial networks to optical access networks. However, the requirement of optical amplifier to expand fiber links is confronted with a dilemma– commercial fiber amplifiers only operate in the wavelength region near 1550nm while the existent lasers operate near 1310nm.Semiconductor optical amplifier (SOA) can operate in the wavelength region near 1310nm. Progresses in semiconductor materials and devices accelerated the maturity of gain-clamped (GC) SOA. And with the concept of linear optical amplifier (LOA) being brought out, SOAs are now prepared for inline amplification. Recent works on LOA are mainly focused on the amplification of WDM signals; so far, no work is carried out on the amplification of RF subcarrier multiplexed signal, as CATV signals.In this dissertation, CATV lightwave systems with SOA for amplification is presented, and the SOA induced nonlinear distortion and noise are studied. A calculative model of nonlinearity based on carrier-density modulation in SOA is for the first time presented and used to calculation the composite second-order (CSO) index. The numerical results, as well as experiments, show a strong dependence of SOA induced CSO on input power and injected current– higher input power and lower injected current are required for better CSO. The SOA induced noise is also investigated; experiments confirm the theory analysis– output carrier to noise ratio is proportional with the noise figure of SOA, which can be optimized by the increases of the input power and injected current.Gain-clamped semiconductor optical amplifiers or linear optical amplifiers are promising components in future OAN and microwave photonics links. Further study shows and explains the reduction of nonlinear distortion utilizing gain-clamped SOAs instead of conventional SOAs. Theoretical analysis in this dissertation paves the road for further research on the nonlinear distortion of GCSOA or LOA.