Fabrication of Microlens by Nd:YVO4 laser irradiation of glass frit layers.

Abstract

Microlens array has a large field of applications: high-speed photography, telecommunication industry that couple light in and out optical fiber waveguides and optical communications, and bio-analysis are some examples [1]. Polymer materials have been widely employed due to low cost to fabricate economical microlens. Nevertheless glasses are much more suitable for high temperature applications or under stronger chemical environments. Moreover, glass materials present a lower UV absorption than polymers. This is an important advantage for bio-analysis applications. [2,3] We fabricate flat surfaces with the desired structure using a Nd:YVO 4 laser for writing directly on a glass frit layer deposited over a glass substrate. The deposited layer is based on PbO-SIO4-B2O3 glass frits, which were applied by conventional methods on commercial glass substrates. Lead borosilicate glasses are of technological interest because of their wide glass formation regions and low melting temperatures. The substrate with the glass frit layer is introduced in the furnace to ensure the melting of the glass layer. We have checked different compositions of glass powder to obtain the optimal mixture that leaves us to use the minor temperature in the furnace for ensuring the flatness of the commercial glass substrate. Once obtained the glass frit layer, a Q-switch Nd:YVO 4 laser is used to record the microlens. (Fig.1) Fig.1. Experimental setupThis laser has a galvanometer system that allows to write the desired pattern with a computer program help. We use a lens of f=100mm that permits to fabricate a 80x80 mm surface with a dense lens array. In this work we show spherical lens array with a 35 µm diameter.After the direct writing process the microlens array is thermally heated in an oven at 450ºC during 1 hour for smoothing the microlens profile. Figure 2a, shows the uniformity of the image focus across the arrays obtained. Figure 2b and 2c, depicts profile and topography picture of a spherical microlens array with diameter 35 µm and tall 3 µm, covering an area of 225 µm x 130 µm. Fig.2.(a) back foci, (b) profile and (c) topography of microlens.