Design and Fabrication of Microlens Array for Near-Field Vertical Cavity Surface Emitting Laser Parallel Optical Head

A GaP microlens for collecting laser light was developed in the tip of a near-field probe. It is important to realize a near-field optical probe head with high throughput and a small spot size. The design and fabrication results of the GaP microlens array are described. The most suitable GaP microlens with a probe was calculated as having a 10 μm radius using the two-dimensional finite difference time domain (2-D FDTD) method. The full width half maximum (FWHM) spot size variation and optical power density tolerance were calculated as 157 nm ± 5 nm and 7%, respectively. A spherical GaP microlens was fabricated with a radius of 10 μm by controlling the Cl₂/Ar gas mixture ratio. The difference between the theoretical spherical shape and the fabricated GaP microlens was evaluated as 40 nm at peak to valley. The FWHM spot size and optical throughput of the fabricated microlens were measured as 520 nm and 63%, respectively. The microlens was the same as a theoretical lens with a 10 μm radius. The micron-lens array fabrication process for a near-field optical head was demonstrated in this experiment.