Development of Microlens Arrays With Large Focal Number and High Fill Factor for Wavefront Sensing Applications

Microlens arrays find many useful applications in sensing devices though their fabrication is challenging due to rigorous requirement of clean-room processing and equipments thereof. In this context, herein a method for fabrication of large focal number (F#) and high fill factor microlens arrays is presented. These microlens arrays have well-defined boundaries and can be used for wavefront sensing applications. This method of fabrication is robust and can be used for achieving hexagonal as well as square aperture and also it is well suited for mass production. The presence of chrome pedestals below the pillars of photoresist prevents the lenses from merging while reflow and leads to nice and well defined lens boundaries with high fill factor. Main advantage of this method is that it does not require the reactive ion etching and multiple layer lithography and thereby it can be a very inexpensive method of fabrication of large F# (>25) and high fill factor (>95%) microlens arrays. The fabricated microlens arrays have been quantitatively characterized for pitch, aperture size, sag height, surface profile, roughness and 2-D point spread function. Experiments have been carried out to validate these microlens arrays in wavefront sensing for optical metrology applications.