1 Department of Photonics Engineering, Technical University of Denmark2 High-Speed Optical Communication, Department of Photonics Engineering, Technical University of Denmark3 Fiber Optics, Devices and Non-linear Effects, Department of Photonics Engineering, Technical University of Denmark4 Systems, Department of Photonics Engineering, Technical University of Denmark
The present thesis is concerned with fiber optical parametric amplification and regeneration for high-speed optical communication systems. Fiber optical parametric amplifiers (FOPAs) have multi-functional applications depending on their implementation in optical systems. Based on a few femtosecond amplification response time and flexible operation spectral range, FOPAs are able to simultaneously operate as amplifiers and all-optical signal processors in high-speed Tbaud networks. In this thesis, we study the performance of FOPAs in detail in the linear and nonlinear (saturated) regimes where they can be utilized as all-optical regenerators. The optical gain and amplitude regeneration properties of FOPAs are investigated for monochromatic waves, short optical pulses and data modulated signals up to 640 Gbit/s. In the fundamental study part of the thesis, an original physical explanation behind an observed asymmetry in gain saturated single-pump FOPAs is presented. The proposed theory is able to explain the origin of gain asymmetries in singlepump FOPAs based on the interplay between third-order dispersion and radiation of dispersive waves in the saturation regime. Furthermore, it predicts the strength of the asymmetric gain in saturated single-pump FOPAs. Pump-to-signal intensity noise transfer has been recognized as one of the major noise sources in FOPAs as it leads to modulation of the signal gain. The conversion of intensity noise from pump to signal is quantified in detail in terms of modulation frequency and saturation effect in order to assess the degradation of the amplified signal. In a very good agreement with the performed experiments, it is shown that the noise transferred to the signal can be effectively suppressed by operating in the saturation regime. The amplification of short few picosecond and subpicosecond optical pulses is explored using the chirped-pulse ampli_cation scheme in FOPAs. The dynamics of the chirped-pulse amplification and pulse distortion are studied for differently chirped few-picosecond pulses in transition between the linear and the nonlinear regime. Amplification of short pulses compatible with Tbaud systems is experimentally carried out for the first time where 400 fs pulses are amplified in a single-pump FOPA. Finally, the first experimental demonstrations of the performance of FOPAs both in long transmission links as well as in high-capacity systems are presented in the last part of this thesis. FOPAs are cascaded as in-line amplifiers using a recirculating loop transmission and error-free transmission of 40 Gbit/s is successfully achieved. On the other hand, error-free parametric amplification for high serial data rates on a single-wavelength channel is demonstrated for an optical time division multiplexed signal at 640 Gbit/s with no power penalty. At last, all-optical phase-preserving amplitude regeneration based on a saturated-FOPA at 640 Gbit/s is demonstrated for phase modulated signals.