Millimeter Lens Array on Flexible Polymer for Lensing, Imaging and Bi-directional Beam Shaping Applications

In this work, we have demonstrated an efficient alternative to bulky and conventional glass-based macro and micro-optics lenses. A millimeter lens array made using a single-step soft-imprint lithography method using an elastomer and containing hexagonally arranged lenses is able to provide efficient focusing and imaging properties for both monochromatic and broadband sources even with unpolarized light. The lens array has a focusing efficiency of ≥ 74.5% for blue, green and red wavelengths and 87% for white light. It can resolve up to a spatial frequency of 57 line pairs/mm in a standard imaging setup with narrowband and broadband light sources. Its modulation transfer function is more than 0.55 even at the highest spatial frequency studied here, and is more than 0.30 on extrapolating it to a higher spatial frequency of 150 lp/mm. This makes it a highly suitable candidate to be used in various modern optical imaging systems where high resolution and large depth of focus are required. RGB analysis of the images recorded with the lens array in white light establishes its superior wavelength reproduction properties. Further, the lens array is an efficient bi-directional beam shaper and beam homogenizer as it is able to adequately transform the incident beam profile into a wide flat-top profile when light is incident on either of its surfaces. The studies indicate that the lens array can be used in many modern optical applications including portable imaging systems, sensors, and mobile phone cameras.

I. Introduction

The effective use of light from a wide variety of sources is achieved by modifying the beam shape or by controlling the light distribution or directionality for a specific application. Optical elements based on patterned surfaces have helped in modifying the light beam according to the desired shaping or controlling requirement [1], [2]. Among the structured surfaces, the lens array is a highly promising element for many optical devices [1], [2], [3], [4]. Additionally, there is a high demand for the lens arrays to improve the optical efficiency of charge coupled devices (CCD) for cameras, liquid crystal display (LCD) panels for projectors and flat panel displays for mobile phones, laptops, computer displays as well as in automobile and airplane instrument panels, due to the advancements in macro- and micro-optics technology. Lens arrays are also required to shape the output from light emitting diodes (LED), to enhance the light emitting efficiency of inorganic and organic LED, to couple the light into a bundle of fibers and in the field of imaging and bio-medical applications [1], [2], [3], [4], [5], [6], [7], [8].