Lasers and amplifiers of high-order spatial modes are useful for a number of applications, including communication, sensing, microscopy, and laser material processing. This dissertation presents the generation and amplification of high-order spatial modes in few-mode fibers (FMFs). In the area of amplification of high-order spatial modes, low-crosstalk amplification among spatial modes is realized in a retro-reflecting few-mode Er-doped fiber amplifier (EDFA) by exploiting the unitary property of the coupling matrix of a symmetric photonic lantern (PL). A small-signal gain larger than 25 dB and crosstalk below -10 dB was achieved over the C-band for a 3-mode EDFA. Such a few-mode EDFA can replace multiple parallel single-mode EDFAs in single-mode fiber transmission systems. In addition, we presented an EDFA for orbital angular momentum (OAM) modes using an annular-core PL. Both the first- and second-order OAM modes were amplified with nearly 20 dB of gain over the C-band. Placing a few-mode EDFA and a mode-selective PL inside a linear cavity, we demonstrated an intra-cavity transverse mode-switchable fiber laser for the generation of high-order spatial modes. The six linearly-polarized (LP) modes can lase independently and are switchable by changing the input port of the PL. In addition, we generated donut-shaped beams using incoherent superposition and simultaneous lasing of the two degenerate modes in the same LP mode group. Additional techniques for the generation of high-order modes explored in this thesis utilize stimulated Brillouin scattering (SBS), one of the prominent nonlinear effects in optical fibers. Based on backward SBS in a passive FMF, we experimentally demonstrated a transverse mode-selective Brillouin fiber laser using mode-selective PLs. We generated three LP modes via both intra- and inter-modal SBS. Finally, we propose a fiber ring cavity that can simultaneously produce phonon lasing and photon lasing utilizing forward intermodal SBS. We experimentally demonstrated for the first time, to the best of our knowledge, such a two-domain ring laser using a 10-meter reduced-cladding two-optical mode fiber. By using an LP01 optical pump, both the LP11 Stokes lightwave and a low-frequency flexural acoustic wave can be amplified by stimulated emission and oscillate inside the same fiber ring cavity. The measured photon laser beat linewidth and the phonon laser linewidth are on the order of a few kHz.
| Identifer | oai:union.ndltd.org:ucf.edu/oai:stars.library.ucf.edu:etd2020-1422 |
| Date | 01 January 2020 |
| Creators | Wang, Ning |
| Publisher | STARS |
| Source Sets | University of Central Florida |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Electronic Theses and Dissertations, 2020- |
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