GRIN lenses refractive index

Another GRIN system is the binary titania-silicate system of Konishi and coworkers [62,63]. Small 2 mm diameter lens of low A-n have been produced with good index profiles [62, 63]. The low solubility of titanium dioxide in silica limits the maximum refractive index gradient in this binary system. 

All the in-plane tunable microlenses discussed to this point are classical refractive types. Mao et al. reported a tunable microlens configuration based on a liquid gradient refractive index (L-GRIN) lens mechanism [20]. 

More importantly, with precise microfluidic manipulation, one can change both the focal disfance of the L-GRIN lens by adjusting the refractive index contrast (difference between maximum and minimum in the gradient) and also the direction of output light by shifting the optical axis [20]. 

Figure 7.20B1 illustrates the schematics of the L-GRIN lens design. The device includes four inlets and two outlet branches (two branches share a common outlet to maintain the equal back pressure at both sides). Calcium chloride (CaQ2) solution (3.5 M, n -1.41) and 142 (n 1.33) were injected into the device. The refractive index of the mixture was linearly dependent on the CaCl2 concentration. 

Fig. 2.4 Some spherical and aspheric discrete microlenses for optical concentrators in MWIR and LWIR range that may be fabricated by microsystem technologies, a calotte b hemisphere c hyperhemisphere d ball lens e truncated sphere f bulb g hemi-cylinder h cylinder i curvilinear cone j concave concentrator k gradient-index lens (GRIN) I complex two-element lens (sphere/GRIN). The grid corresponds to the homogeneity of refractive index, i.e., describes its gradient...

The refractive index gradient across a planar section perpendicular to the optical axis of a plano-convex GRIN lens is given by ... 

Figure 7a. Refractive index profile of GRIN lens...

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