Single-mode micro-laser based on single whispering gallery mode optical microcavity and preparation method thereof

A preparation method of a single-mode micro-laser based on a single whispering gallery mode optical microcavity, comprising steps of:

• 1:
• preparing an optical microcavity containing a gain material by dry etching, wherein the optical microcavity is the whispering gallery mode optical microcavity;
• a free spectral range of the optical microcavity is at least ½ of a spectral width of the gain material;
• the gain material is rare earth ions, quantum dots, or organic macromolecular luminescent materials;
• a cavity material of the optical microcavity is crystals, silicon dioxides, silicon, III-V compound semiconductor materials or silicon nitride films;
• 2:
• preparing an optical fiber cone:
• stripping a polymer layer of a standard single-mode optical fiber;
• cleaning the optical fiber and heating with hydrogen-oxygen flame, meanwhile stretching both ends of the optical fiber with a translation stage, so that a heated portion of the optical fiber is thinned to obtain the optical fiber cone, and a thinned position is called a waist;
• 3:
• performing a coupling test on the optical microcavity and the optical fiber cone, and coupling a pump light, whose pump power is greater than a pump threshold, into the optical fiber cone;
• wherein the pump threshold is determined by a Q factor and a mode volume of the optical microcavity and a gain coefficient of the gain material, which comprises specific steps of:
• attaching the waist of the optical fiber cone to an edge of the optical microcavity, and inputting the pump light into one end of the optical fiber cone;
• restricting a wavelength of the pump light within an absorption spectrum wide range of the gain material;
• 4:
• continuously scanning the wavelength of the pump light within the absorption spectrum wide range of the gain material and adjusting or controlling a lateral coupling position of the optical fiber cone and the optical microcavity;
• observing the optical microcavity in real time through charge coupled device microscopic imaging until a coherently combined mode with a polygonal configuration appears at a pump wavelength, wherein the coherently combined mode is formed by superposition of a fundamental spatial mode and high-order spatial modes;
• then obtaining the Q factor of the optical microcavity when the polygonal configuration appears through a transmission spectrum;
• wherein the Q factor of the fundamental spatial mode of the optical microcavity is at least 2 times lower than the Q factor of a polygonal mode;
• 5:
• fixing the wavelength of the pump light and continuously adjusting the pump power of the pump light until the optical microcavity displays a coherently combined mode with a polygonal configuration within an absorption range of the gain material, wherein the coherently combined mode is formed by superposition of a fundamental spatial mode and high-order spatial modes, and is identical to the polygonal configuration in the step 4, wherein at this time, the pump light resonates with the coherently combined mode within the absorption spectrum of the gain material, and a lasing light resonates with a coherently combined mode within a fluorescence spectrum of the gain material;
• 6:
• coupling the lasing light from an output end of the optical fiber cone, and testing a spectrum and a line width of the lasing light with a spectrum analyzer until a lasing with a single-mode is obtained;
• and
• 7:
• fixing, integrating and packaging the optical fiber cone and the optical microcavity to obtain the single-mode micro-laser based on the single whispering gallery mode optical microcavity.