Study Of Multi-orders Cascaded Stimulated Raman Scattering Phenonmenon In Optical Microcavity

Stimulated Raman scattering is the third order nonlinear optical phenomenon in the media, it has attracted wide attentions in basic and application fields. For producing stimulated Raman scattering phenomenon, the media should be affected by a high power density laser. With the birth of lasers, the study of Stimulated Raman scattering phenomenon has made tremendous progress.Optical microcavity with High Quality Factor can maintain the Whispering Gallery modes with a high power density and small mode volume on inner surface. With the taper fiber, we can efficiently couple the light into the cavity, which promotes the study of non-linear optics, cavity quantum electrodynamics, micro photon wave source, low threshold micro-lasers, optical communication and other areas.In our experiments, silica microspheres with smooth surface are fabricated through surface tension by heating and fusing a single tapered fiber using arc of electrodes discharge. Taper fibers are fabricated by hydroxide flame pulling taper method. The waist diameter of tapered fibers is about 1-2 um and the insertion loss is lower than 0.5 dB. Tapered fiber is the best coupler which can effectively couple the light wave near-field into microspheres surface to form Whispering Gallery modes and couple the generating laser out from microspheres for testing and applications.In this paper, from the Helmholtz equation, we study the distribution of the light field in optical cavity microspheres and give the characteristics equation. In addition, physical parameters describing the characteristics of the microspheres are given such as Quality factor, free spectral range (FSR) and finesse. Stimulated Raman scattering is described from the perspectives of classical theory and semi-classical theory. We obtain the relation between the first order stimulated Raman scattering laser power and the pump power through resolving the couple wave equation and citing references. Extending to multi-order cascaded stimulated Raman scattering phenomenon, we obtain the relation between each order scattering laser power and previous laser power in multi-order cascaded stimulated Raman scattering.In the experiment, by using tapered fiber-silica microspheres coupling system, we study stimulated Raman laser of microspheres that pumped by 980nm laser. The spectra of eight-orders cascaded stimulated Raman scattering, the spectra of four-orders cascaded anti-Stokes laser and the spectrum of Raman amplification are measured in microspheres. In addition, these experimental phenomena have not been reported before. The spectra of the optical microsphere emission are analyzed in the same taper fiber at different coupling point. And the perspectives of experiment, the matching relationship between the diameter of microspheres and the waist diameter of taper fiber is given when microsphere generate stimulated Raman laser. The spectra of eight-order cascaded stimulated Raman laser are analyzed, the eighth order spectra locate in fiber communication E (1360nm-1460nm) waveband, the sixth and the seventh spectra locate in fiber communication O (1260nm-1360nm) waveband, the fifth spectra are at around 1200nm and stimulated Raman laser spectra are modulated by microspheres. Therefore, multi-order cascaded stimulated Raman laser is a feasible scheme for generating the laser located in O waveband and E waveband. Moreover, the spectra of three-order cascaded stimulated Raman laser are measured in the microsphere when pumped by 1064nm laser.