Hybrid microlens array/grating fabrication based on microfluidic system and its application in the enhancement of spectral resolution

Abstract

Nowadays, micro-spectrometer has become an important research direction in the field of spectral analysis. The hybrid microlens array (MLA)/gratings element performs both focusing and diffraction duties, and its short focal length allows the optical system to be smaller. In this work, a unique and cost-effective fabrication method for hybrid MLA/grating based on the microfluidic system is described. By this method, the grating line-density, microlens curvature and aperture size of the hybrid MLA/grating can be effectively controlled, so as to bring different diffraction and focusing effects. Finite element simulation is used to describe the principle of the method. The relationship between bulge height and membrane thickness, pressure, hole size was investigated using a profile observation system. Wave optics simulation and diffraction measurements were used to demonstrate the optical properties of this hybrid element. It can be found that the diffracted light is converged at focus points after MLA/grating, and the full width at half maximum (FWHM) is significantly narrowed. The diffraction experimental results are consistent with the simulation results. The MLA/grating structure reduces FWHM of first-order diffracted light by a factor of 7 compared to same type of the planar grating. Therefore, the MLA/grating element can effectively improve the spectral resolution. Due to its small focal length, the MLA/grating has the potential to be used in micro-spectrometers.