Multi-Wavelength Light Source and Optical Amplification for Capacity Scaling in Next-Generation Optical Systems

The rapid growth of data traffic is pushing fiber-optic communication systems toward increasingly higher capacities. Meeting this demand requires advances across optical transmitters, in-line amplifiers, and usable gain bandwidth. This thesis investigates three key hardware technologies for next-generation, ultra-high-capacity optical networks: the multi-wavelength light source, the nonlinear amplifier, and the extended-band amplifier, each addressing a distinct bottleneck in scaling system capacity.                          

The first study investigates a single-section InGaAsP quantum-well Fabry--Perot laser diode as a compact, high-power, multi-carrier comb source with an output power exceeding 21 dBm. A single device generating multiple carriers can replace an array of discrete lasers, reducing cost and complexity in a coherent transmitter. The device is characterized in terms of its RF mixing linewidth, measured to be 20 kHz at full width at half maximum, relative intensity noise, and low phase noise beyond 1 GHz. Its suitability as a coherent transmitter is demonstrated using twenty 15 GBaud double sideband 16-QAM channels transmitted over 78.3 km of single-mode fiber. The system capability can reach beyond 4 Tb/s with a single laser in the transmitter using polarization multiplexing.                     

The second study demonstrates a polarization-insensitive fiber-optic parametric amplifier. The amplifier is based on a polarization-diverse bidirectional loop containing two equal-length, 100m highly nonlinear polarization-maintaining fibers connected through a 90° axis-rotation splice. This configuration eliminates the need for active polarization control, compensates for polarization-mode-dispersion effects, and suppresses stimulated Brillouin scattering between the counter-propagating pumps at pump powers of up to 30 dBm. When operated as a preamplifier in a 400 Gb/s dual-polarization 16-QAM transmission system, the amplifier achieves a noise figure below 3 dB, confirming its viability for practical, polarization-diverse signals.                      

The third study presents an experimental characterization of a 468m Bismuth-doped Germanosilicate fiber operating in the E and S band. The amplifier can provide a gain up to 33 dB when operated at a pump power of 23 dBm. A bidirectional rate-equation model of the measured gain and ASE spectra resolves the contributions of the individual active-center subtypes to net gain. The model further quantifies the impact of Rayleigh backscattering in long bismuth-doped fibers. Together, these results indicate that long fibers operate more efficiently in the longer-wavelength region. Combined with a conventional Erbium-doped amplifier, such a Bismuth-doped stage could extend gain coverage across the S through L bands, making it a single extended-band amplifier.                        

Together, these studies address three complementary elements of high-capacity optical communication systems: multi-channel source generation, nonlinear parametric amplification, and extended-band doped-fiber amplification. By examining the physical interactions, noise analysis, and system-level impairments associated with each technology, this thesis addresses several of the hardware technologies needed to overcome major capacity-scaling limitations of current optical networks.