The scope of the project will be the investigation of different properties of spherical microresonators (microspheres) for various application. Microspheres are special miniature (from 50 μm to 1mm in diameter) spherically shaped optical resonators. Inside of them light is trapped by total internal reflection. The light is reflected many times along the circumfererence of the sphere and if the light is in phase after a full round trip along the circumference of the sphere a resonator mode is formed. These modes are called whispering gallery modes (WGM). Because of their high Q factor WGM resonators have suscitated great interest in the scientific community in the last decade. They have various practical applications in the fields of lasing, nonlinear optics, and sensing. In this project we will produce spheres made of silica, chalcogenide glasses (As₂S₃, As₂Se₃), and tellurite glasses. Out of this materials the silica spheres are the most well-known. The silica microsphere can be coated by a variety of different coatings which makes possible the introduction of new optically active or passive materials onto the sphere while retaining very high Q-factors of the resonator. The sol-gel method is a very useful technique for microsphere coating since by varying the sol-gel film composition and active component the microlaser properties can be tailored. This has many applications in the field of optoelectronics and telecommunication (for 1.5-1.6 μm emission). Chalcogenide and tellurite glasses, on the other hand, have only recently started to be studied for microresonator application. Their wide transparency window makes them suitable for application in the near to mid infrared which is a very important spectral range for biological applications.