On-Chip Microlasers Based On Sol-Gel Silica Film

In recent years,optical cavities,especially optical microcavities with high quality factor and small mode volume,become more and more important photoinc devices which focus in many areas,including fundamental fields as well as applied fields such as cavity optomechanics,cavity quantum electrodynamics,nonlinear optics,biosensors and micro lasers.For example,silica micro sphere cavities have been fabricated by the fiber taper with ultra-high quality factor of?1010.Microlasers fabricated from high-Q microcavities have the well advantages of ultra-low threshold and narrow linewidth.Vahala and co-authors in the Caltech have fabricated the whispering-gallery-mode(WGM)microtoroids with the methods of photolithography,buffered HF wet etching,XeF2 dry etching and CO2 laser reflow.Microtoroids induced by the surface tension have the quality factor of 4×108 caused by the CO2 laser reflow.In the thesis,we have studied in detail the fabrication and applications of whispering-gallery-mode microcavity,such as micro lasers.We have obtained microlasers with ultra-low threshold by the sol-gel method.The main content of the thesis is listed as follows:1.Fabrication of silica film on the silicon chip with the spin-coating by the sol-gel method was studied.We finally obtained dense and crack-free silica film with the thickness between 200 nm and 2 ?m by improving the affecting factors of the sol-gel method,such as the weight ratio of each solution component,the times of aging and drying,temperature and heating rate of anneal,etc.In the experiment,we also obtained the silica film doping with different rare earth during the sol-gel process.We experimentally observed that film's thickness with heavy concentration doping would be thinner under the same fabricated condition.Therefore,in consideration of the need of the same thickness for the film,the parameters of fabrication of silica film doping rare-earth with different concentration should be different.2.Fabrication of fiber taper and microcavities were studied.We in detail research the fabrication process of whispering-gallery-mode microcavity,containing photolithography,buffered HF wet etching,XeF2 dry etching and CO2 laser reflow.Erbium-doped silica film with thickness of approximately 1.3?m was fabricated by the sol-gel method.Then,we fabricated the Er3+-doped microdisk,microtoroid on the silicon chip.As we made the silicon pedestal diameter less than 5 ?m by controlling the etching time and etching speed of XeF2 dry etching,we could obtain the Er3+-doped silica microsphere on the silicon chip for the first time.A narrow-linewidth tunable laser operating around the 1480 nm band was used to resonantly pump these three kinds of erbium-doped microcavities.The green light caused by the up-conversion of erbium ions was observed in these microcavities.Meanwhile,we observed the laser emission spectra from the microtoroid and microsphere,with an ultra-low threshold as low as 976 nW for the micro sphere.3.By the neodymium-doped silica film with thickness of approximately 1.3?m fabricated from the sol-gel process,we fabricated the Nd3+-doped microtoroids with different sizes and different concentrations on the silicon chip.A narrow-linewidth tunable laser operating around the 780 nm band was used toresonantly pump the Nd3+-doped microtoroids.Laser spectra at the 910 nm band and 1064 nm band were observed,with the thresholds of 108.5 ?W and 1.6 ?W respectively.When pumping the microtoroid non-resonantly,we also observed the laser spectrum with threshold of 137 ?W.4.During the sol-gel process,we added nitrate thulium and nitrate holmium into the solution for obtaining the thulium-doped film and thulium&holmium-codoped silica film with proper thickness of approximately 1.35?m.Then we fabricated the thulium-doped microtoroid and Tm/Ho-codoped microtoroid by the integrated technique.We observed the laser emission spectra close to 2?m with threshold of 2.8 ?W for the Tm3+-doped microtoroid by the tunable pump laser at the 1600 nm band.Meanwhile,we also observed the laser emission spectra above the 2 ?m with the threshold of 2.7 ?W.When we changed the pump laser wavelength,we could observe different fluorescent colors from the microtoroids.