Micro-optical arrays by laser densification of gel-silica matrices

摘要

Optical microlens arrays are important in many optical systems. A new method for producing arrays of negative lenses, geodesic lenses, and planar GRIN lenses is described. The lenses and arrays are produced using CO$-2$/ laser densification of near fully densified gel-silica (Type VI) matrices. Critical processing conditions include initial density of the matrix, laser power, laser pulse width, focal length of the laser beam, and ambient atmosphere. The gradient refractive index (GRIN) region formed on the surface of the gel- silica matrix is capable of focusing an optical ray in a direction parallel or perpendicular to the surface. FTIR specular reflectance microscopy with a spot size of 0.1 mm and resolution of 0.5 cm$+$MIN@1$/ at normal incidence is used to characterize laser densified spots with diameter of 1.50 mm. The wavenumber of the Si-O stretching mode is shifted toward a higher frequency from the periphery to the center of the densified spot. The increase in frequency of the structural molecular vibrations gives rise to the GRIN optics. A refractive index gradient of 0.09 to the microlens is achieved with a 300 $mu@m diameter full density region. Focal lengths of the GRIN planar microlens on the gel-silica matrix range from 1.7' to 5.0'. Comparison of the materials, fabrication methods, and properties of different types of optical microlenses are summarized.