1 Department of Photonics Engineering, Technical University of Denmark2 Fiber Optics, Devices and Non-linear Effects, Department of Photonics Engineering, Technical University of Denmark3 High-Speed Optical Communication, Department of Photonics Engineering, Technical University of Denmark4 Systems, Department of Photonics Engineering, Technical University of Denmark
Fiber optical parametric amplifiers (FOPAs) are attractive because they can provide large gain over a broad range of central wavelengths, depending only on the availability of a suitable pump laser. In addition, FOPAs are suitable for the realization of all-optical signal processing functionalities and can operate with a potentially low noise figure with respect to erbium-doped fiber amplifiers and Raman amplifiers, when working in phase-sensitive configurations. A characterization of the signal distortion mechanisms introduced by FOPAs is relevant for investigating the applicability of FOPAs for the amplification of high speed signals with bit rates in excess of 1 Tbit/s per wavelength channel. The work presented in this thesis focuses on the distortion mechanisms affecting signals amplified by single-pump phase-insensitive FOPAs. The noise due to the cross coupling between the signal and the pump is also investigated. The pump-to-signal noise transfer has been recognized as one of the major noise source in FOPAs. This is due to the fast response of FOPAs (few fs), because of which intensity fluctuations of the pump cause an instantaneous gain modulation. The intensity modulation transfer from the pump to the signal is experimentally investigated for pump modulation frequencies up to 27 GHz and also in the saturation regime. A good agreement is found both with the theoretical model in the case of an undepleted pump and with the numerical results in the saturation regime, showing that the intensity modulation transfer can be reduced in saturated F OPAs. In order to characterize propagation impairments such as dispersion and Kerr effect, affecting signals reaching multi-terabit per second per channel, short pulses on the order of 500 fs need to be considered. Therefore, a short pulses fiber laser source is implemented to obtain an all-fiber system. The advantages of all fiber-systems are related to their reliability, long-term stability and compactness. Fiber optical parametric chirped pulse amplification is promising for the amplification of such signals thanks to the inherent compatibility of FOPAs with fiber optical systems and high gain over broad bandwidths. In particular, the amplification of 400 fs pulses is investigated in a single-pump fiber optical chirped pulse amplification sc heme. First, a dynamic characterization is carried out both in unsaturated and saturated regimes and, then, amplification of short pulses compatible with Tbaud systems is experimentally demonstrated for the first time. This opens the way to the demonstration of a first broadband amplification scheme for highspeed signals reaching multi-terabit per second per channel.