Study On Fiber Lasers With Novel Materials And Technologies

Recently, with the development of material science and microelectronics technology, researches on organic nonlinear optical materials, very-large-scale integrated optical (Opto-VLSI) chips, and their applications on electro-optical device, optical signal processing, tunable multi-wavelength fiber lasers, and mode-locked lasers, have become an important topic in optoelectronic area, and possess very high research and development value.Since the 21st century, with the rapid development of large capacity optical transmission technology such as dense wavelength division multiplexing (DWDM) and Tbit/s super channel technology based on all-optical orthogonal frequency division multiplexing (AO-OFDM), multiple wavelength lasers and mode-locked lasers have attracted great attention in the field of optical communication. In this thesis, by utilizing organic nonlinear optical materials and liquid crystal on silicon (LCoS) optical filters, various lasers, including passively mode-locked fiber lasers, tunable fiber lasers, and multi-wavelength fiber lasers, were penetratingly studied both in theory and experiment based on the synthesis of several kind of nonlinear optical materials and the fabrication of organic thin films. The major results obtained in this thesis are as follows:(1) Studay on the fabrication of organic nonlinear composite films and its optical properties. Using the guest-host doping method, the polyamic acid is mixed with an organic compound to obtain a complex solution. The complex solution is solidified to film via the thermal imidization utilizing a novel gradually heating method. Three novel organic nonlinear optical films are designed and synthesized:benzothiazole-carbazole derivative/polyimide film, ferrocene derivatives/polyimide film and carbon nano-material/polyimide film. The linear optical properties of these films are studied with UV-Visible spectrophotometer and transmission spectroscopy method. Based on the linear properties, the third-order nonlinear optical properties of these films are obtained with Z scanning technology. All the work that has been mentioned previously provides a theoretical foundation for designing organic materials with higher nonlinear properties and relative optical devices.(2) Theoretical and experimental study on saturable absorber based passively mode-locked fiber lasers. A physics based theoretical model for passively mode-locked fiber lasers using saturable absorber was developed by combining the nonlinear Schrodinger equation for optical signal peropagation in optical fiber, the traveling wave rate equations in erbium doped fiber amplifier, and a random spontaneous emission model in active medium. Using the iterative symmetrical split-step Fourier method and the traveling wave model, the pulse forming process is simulated, and the influences of the ring cavity parameters on the output pulse characteristics are analyzed. Then, a saturable absorber was fabricated by placing the carbon nano-material/polyimide film between two fiber splices to form a sandwich structure. A passively mode-locked fiber laser was constructed by inserting the carbon nano-material/polyimide saturable absorber in the ring cavity, and a stable mode-locked pulse train with pulse width 1.76ps and 3dB spectral width of 2nm was generated using the mode-locked fiber laser.(3) Studay on taper-fiber based fiber lasers. Tapered fibers are fabricated with fused biconical taper system. The corresponding relation between the tapered fiber radius and the length of the stretch is obtained by the Origin software. The transmission performances of tapered fibers with different diameter are simulated by the BeamPROP module of RSoft. The corresponding relation between the output optical power change and wavelength in 1520nm～1620nm is measured using ASE optical source. The fiber laser based on the tapered fiber was formed by inserting a tapered fiber into a ring cavity. A wavelength tunable range with 1563.828nm～1565.444nm and a dual wavelength with1.48nm interval are achieved via changing the state of polarization of the light transmitted by the tapered fiber.(4) Studay on multi-channel tunable fiber lasers based on wavelength selective switch filter. The programmable optical filtering technology and wavelength selective switch based on liquid crystal on silicon spatial light modulator (LCoS-SLM) were studied. A 1×32 ports wavelength selective switch and a tunable filter based on LCoS-SLM are implemented. With the range of 1530nm～1560nm, the tunable fiber laser with 32 channels is realized combined with a 1×32 fiber beam splitter.(5) Studay on multi-wavelength fiber lasers based on Mach-Zehnder filter and LCoS-SLM tunable filter. Combined with nonlinear polarization rotation, multi-wavelength fiber laser was developed using M-Z filter.27 lasing wavelengths with side mode suppression ratio of 48dB are obtained. Meanwhile, multi-wavelength fiber laser was developed using LCoS-SLM tunable filter. Two wavelengths, three wavelengths and four wavelengths lasing are obtained from 1530nm～1560nm. Their wavelength intervals are 0.8nm,1.6nm,2.4nm,3.2nm or 4nm, and the center wavelength can be continuously tuned. The side mode suppression ratio can up to 53dB with 0.8nm interval.