Continuous control of microlens morphology on Si based on the polarization-dependent femtosecond laser induced periodic surface structures modulation

Arrayed microlenses have been demonstrated as promising optical devices for various applications in optical interconnection and communication. The precise control of arrayed microlenses morphologies still keeps a main challenge restricting its practical applications. In this study, we propose a flexible microlens morphology control technique based on the pre-processed femtosecond laser induced periodic surface structures (LIPSS) morphology control. Anisotropic elliptical LIPSS morphology has been demonstrated under linearly polarized fs laser irradiation due to the grating-assisted surface plasmon polaritons scattering effect. Based on pre-processed surface structures morphology control, polarization-dependent geometrical morphology of microlens array on Si can be obtained with controllable morphologies via the subsequent isotropic chemical wet etching. By varying the linear polarization direction of the incident fs laser, anisotropic microlens can be fabricated with the major axis along the polarization direction. In contrast, symmetric circular morphology can be obtained by controlling the morphology of the pre-processed surface structure to nearly circular geometrical morphology under circular polarization.