Fabrication tolerances and metrology requirements for ion-exchanged micro-optic lenses: What’s good enough?

Abstract

Allowable deviations in index profiles, dopant distributions, and concentration dependence of diffusion coefficients are determined for collimating microlenses. Examples of high (and low) numerical aperture lenses are given for silver/sodium (and lithium/sodium) ion exchanges. Using the full lens aperture, one can ensure diffraction-limited performance only when the index is measured to within 1.0 x 10(-4) (4.3 x 10(-5)) of the optimum values. Fabrication tolerances for diffraction-limited performance over 80% of the numerical aperture are expressed in terms of the concentration-dependent diffusion coefficient, which typically must be held to within +/-4.7% (+/-11.5%) of ideal values.

In vivo fluorescence imaging with high-resolution microlenses

“…We protected and fixed the GRIN and plano-convex elements within a stainless steel sheath (1.0 mm inner diameter and 1.4 mm outer diameter) using optical epoxy. The data shown in Figure 1c are the resolution measurements for the 230-μm working distance lens, but corrected lenses of both 50-μm and 230-μm working distances produced comparable resolution measurements. We designed GRIN lens refractive index profiles using ZEMAX software to minimize aberrations as in Supplementary Figure 1, and then fabricated the GRIN lenses by silver-ion exchange according to our published recipes, quantitative models of ion diffusion and tolerances11,17,18. Borosilicate glass rods with 25 mol% Na 2 O content and a uniform refractive index of 1.51 were baked in a 20 mol% melt of AgNO 3 salts at ~670° K for approximately 3 weeks.…”

“…We designed GRIN lens refractive index profiles using ZEMAX software to minimize aberrations as in Supplementary Figure 1, and then fabricated the GRIN lenses by silver-ion exchange according to our published recipes, quantitative models of ion diffusion and tolerances11,17,18. Borosilicate glass rods with 25 mol% Na 2 O content and a uniform refractive index of 1.51 were baked in a 20 mol% melt of AgNO 3 salts at ~670° K for approximately 3 weeks.…”

In Vivo Imaging of Mammalian Cochlear Blood Flow Using Fluorescence Microendoscopy

“…1B). Unlike conventional lenses, which rely on curved surfaces to refract light, such cylindrically symmetric GRIN lenses guide light using a radially varying refractive index profile that arises from spatially inhomogeneous doping with an ion such as silver, thallium, or lithium (42,43). Because GRIN lenses are not ground to shape, they can be economically fabricated in tiny sizes.…”

The effect of RO (R=Mg, Ca, Ba and Zn) on physical properties of Na2O/Al2O3/B2O3/SiO2 glasses for the preparation of gradient index micro lenses

“…After a first ion exchange carried out in an AgNO 3 -containing salt melt, an uniform Ag 2 O-concentration in the whole volume of the glass rod is obtained and nearly 90% of the Na 2 O is replaced by Ag 2 O. During the second ion exchange step in a NaNO 3 -containing salt melt, the required profile in the refrective index is adjusted by diffusion of silver ions from the glass towards the molten salt [8][9][10][11]. This required profile is nearly parabolic, where the refractive index and the silver concentration in the center are larger than in the outer parts of the rod.…”