A development of microlenses achromatically corrected for near infrared range is reported. Internal nanostructurization of microlens allows to obtain an effective parabolic gradient index profile. A standard stack-and-draw method was used to fabricate the microlens. They have a nearly wavelength-independent working distance of 35 μm over the wavelength range of 600-1550 nm. The proposed achromatic microlens can be applied in micro imaging systems and for wavelength independent coupling into optical fibers.
Nanostructured GRIN components are optical elements which can have arbitrary refractive index profile while retaining flat-parallel entry and exit facets. They are composed of more than 9000 individually placed glass subwavelength rods made of two types of glass with different refractive indices. They are developed using a standard stack-and-draw method used for fibre drawing. The refractive index profile of the nanostructured GRIN element can be described by the effective refractive index theory when the diameter of the individual rods are sufficiently smaller than the wavelength. In this paper we show that use of glasses designed for high diffusion and high temperatures during drawing process allows to develop parabolic nanostructured GRIN microlenses with rod diameter larger than wavelength. In particular, we have developed a GRIN microlens with diameter of 115 μm composed of 115 rods on diagonal. Our GRIN microlens has a length of 200 μm and a working distance equal to 1.05 mm, with focal spot of 8.5 μm measured for the 658 nm wavelength. We experimentally verified its imaging properties. Image resolution higher than 3.25 μm was measured.