Research On Multiwavelength Fiber Lasers And Their Applications

WDM-PON is a frontier and hot research subject in recent years. However, WDM-PON has not been commercially deployed, due to its ultra-high implementation cost. Although internet users would like to have considerably higher bandwidth, they do not want to pay subscription fee much higher than the current access networks. It is a big risk for the telecommunication operators to widely deploy WDM-PONs at present. The main cost of WDM-PON is the installing and maintaining of many wavelength-specific optical transmitters at the central office (OC) and optical network units (ONU). To address this issue, it is desirable to use wavelength independent (colorless) light sources to replace those wavelength-specific optical transmitters, for example, using the spectrum-sliced broadband optical sources technology or their injection-locked FP-LD (or RSOA) technology. However, both of the two technologies use the incoherent optical sources and induce some intensity noise, hence can only make a lower rate WDM-PON. Instead of the incoherent optical sources, multiwavelength lasers can provide the coherent sources, and have a significant potential to develop a cost-efficient and high-speed WDM-PON.The research work presented in this dissertation focused on the frontier area of multiwavelength lasers as the centralized optical sources of WDM-PONs. Considering the compatibility and integration between the centralized optical sources and all-fiber WDM-PON, high-performance multiwavelength fiber lasers are specially investigated, such as EDFA, SOA, based multiwavelength fiber lasers.The major achievements of this thesis are summarized as follows:(1)A novel FSR-tunable FPF based on two superimposed FBGs (SFBGs) with initially uniform periods but slightly different Bragg wavelengths, is proposed and demonstrated. The SFBGs were glued onto the lateral surface of a specially-designed cantilever beam and linearly chirped by the beam bending-induced strain gradient. As a result, their reflection bands overlapped and a grating-based FPF with a tunable FSR was formed. Finally, a continuous tuning range of 0.12 nm and a tuning rate of 0.04 nm/cm have been realized experimentally. (2) We have proposed a novel Mach-Zehnder interferometer (MZI) configuration, namely, isolator-assisted double-pass MZI. The filtering characteristics of the proposed isolator-assisted double-pass MZI are analyzed and examined theoretically in comparison with those of the single-pass and direct double-pass MZI. It is shown that the isolator-assisted double-pass MZI has some intriguing advantages, including the narrower 3-dB bandwidth per transmission peak and the higher extinction ratio. Using the three types of MZI configurations as a comb-like filter in the laser cavity, experimental investigations for generating multiwavelength oscillations are carried out. We have experimentally demonstrated high-performance multiwavelength EDFA-based fiber lasers with 8-wavelength simultaneous oscillations spaced at 43 GHz and high extinction ratio of more than 40 dB. The lasers have a good stability with a maximum power fluctuation per lasing channel of less than 0.6 dB.(3) We have proposed and demonstrated a novel and simple technique to generate stable multiwavelength oscillations in an EDFL. A multiwavelength erbium-doped fiber laser by incorporating a HNLF and PMF Sagnac filter has been presented. Over 16 wavelengths simultaneous lasing with a spacing of 0.4nm was achieved. The laser had a total output power of-3dBm, a bandwidth of 0.05nm and an extinction ratio of-50dB. The lasing states were observed to be very stable. The power fluctuation is less than 0.5dB when monitored over a period of an hour.(4) We have experimentally investigated SOA based multiwavelength fiber lasers at both C+L band and 1060nm band. We have proposed, for the first time to the best of our knowledge, the 1060nm band SOA based multiwavelength fiber laser by introducing a PMF Sagnac loop mirror. Using the linear cavity configuration, we realized multiwavelength lasing with narrow linewidth and stable power output. Up to 11 wavelengths with channel spacing of 0.39nm have been presented, and the output power stability is quite good.