Abstract: A step index planar microlens fabrication process is described for obtaining low spherical aberration. This microlens can be used to achieve effective light coupling between different optical elements and microcircuits in integrated optics. Polymethyl methacrylate (PMMA) doped with N, N'-dihexyl-amino-nitrostelbene (DHANS) is used as lens materials. A concave surface of 580 $mu@m diameter is made on Germenia-Silica glass substrate of refractive index 1.4537 at $lambda $EQ 1.3 $mu@m. Films of different refractive indices are deposited one upon another on the concave surface to obtain multi-layered step index microlens. Refractive index variation of different layers is controlled by percentage of DHANS doping in PMMA. Spherical aberration of the lens is minimized by using step index multi-layered structure of the lens. Theoretical model for longitudinal and lateral spherical aberration is developed using ray theory. The lateral and longitudinal spherical aberration is minimized to a lower value of 1.55 micron and 48.87 micron respectively with the numerical aperture of the lens NA $EQ 0.0209 and focal length f $EQ 13.78 mm.!15
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