Power and spectral characterization of photonic integrated circuit based axicon like lens

TL;DR

This paper presents the design, fabrication, and spectral characterization of an on-chip silicon axicon lens with enhanced penetration depth, using low-resolution lithography and a novel azimuthal apodization technique.

Contribution

It introduces a low-resolution fabrication method for silicon axicons with azimuthal apodization, improving penetration depth and spectral stability of the output.

Findings

Penetration depth increased from ~5 μm to ~55 μm.

Output lobe position remains stable across wavelengths.

Successful spectral characterization using balanced homodyne detection.

Abstract

We demonstrate an on-chip Silicon-on-Insulator (SOI) axicon etched using a low resolution (200 nm feature size, 250 nm gap) deep-ultraviolet lithographic fabrication. The axicon consists of circular gratings with seven stages of 1x2 multimode interferometers. We present a technique to apodize the gratings azimuthally by breaking up the circles into arcs which successfully increased the penetration depth in the gratings from $\approx$5 $\mu$m to $\approx$55 $\mu$m. We characterize the device's performance by coupling 1300$\pm$50 nm swept source laser in to the chip from the axicon, and measuring the out-coupled light from a grating coupler. Further, we also present the implementation of balanced homodyne detection method for the spectral characterization of the device and show that the position of the output lobe of the axicon does not change significantly with wavelength.