Design And Investigation On Glass Ceramic Based Whispering Gallery Mode Microcavities

By controllably precipitating nanocrystals in glass matrix,the glass ceramic?GC?combines the properties of crystal and glass,which has greatly important applications in many fields,such as display,laser,sensor and so on.Based on the confinement of photons near a circular ring boundary via successive total internal reflections,whispering gallery mode?WGM?microcavities exhibit ultrahigh Q factors and extremely small mode volumes,leading to greatly enhanced light-matter interactions.These superior characteristics make WGM microcavities highly attractive for low threshold lasers,high sensitivity sensors,and others.However,WGM microcavities made from GC materials have not yet been reported.This paper is the first attempt to combine the GC with the WGM resonator,including the design principle,the preparation method and the optical performance are studied.The specific research contents comprise several aspects which are shown as follows:1.Design and fabrication of a high Q factor GC WGM microcavity.High Q factor is the most important property of a WGM microcavity for application.Unfortunately,the precipitation of nanocrystals in a GC microcavity will increase the scattering loss and decrease the Q factor.Based on the Q factor theory of the WGM microcavity and the Rayleigh scattering theory,it was supposed that reducing the refractive index difference between nanocrystals and glass matrix to less than 0.05 was an effective way to prepared a high-performance,high Q factor GC WGM microcavity.To fabricate a microsphere,an melting method based on CO₂laser was used,which could minimize the influence of processing on the Q factor of the WGM microcavity.2.The research on optical properties of Er³⁺doped oxyfluoride GC WGM microcavities.We have designed an excellent Er³⁺doped oxyfluoride GC material which met the above requirements.Na YF₄nanocrystals were crystallized within the borosilicate glass matrix through a controlled heat-treatment process.And the refractive index difference between the glass matrix and nanocrystals was only 0.05.Moreover,Er³⁺ions could enter into the low phonon energy Na YF₄nanocrystals with improving luminescence properties.As a result,Er³⁺doped precursor microspheres with Q factors as high as 10⁶and GC microspheres with Q factors as high as 10⁵were obtained,which enabled WGM lasers output at the 1.5?m band.It was found that the GC microsphere heat treated at 460? for 10 h could achieve laser output with the lowest threshold?350?W?and the highest efficiency?1.57%?,which was 2.5 times lower and 7 times higher than that of the precursor microsphere,respectively.3.The research on optical properties of frequency doubling GC WGM microcavities.WGM resonators are excellent platforms to promote the nonlinear conversion efficiency due to unparalleled combination of favorable characteristics.Ba₂Ti Si₂O₈nanocrystals possessing excellent nonlinear properties could be precipitated in the glass with components of Ba O-Si O₂-Ti O₂.Moreover,we could control nucleation and growth of Ba₂Ti Si₂O₈nanocrystals from homogeneous crystallization?HC?to surface crystallization by increasing more Si O₂.As a result,compared with the corresponding bulk GCs,the intensity of SHGs showed several orders of magnitude higher in the GC microspheres.And SC GC microspheres achieved even higher intensity of SHG,for the distribution of gain nanocrystals was perfectly consistent with the interacting light filed distribution in the WGM cavity.