Photonic Crystal Spatial Filters Fabricated by Femtosecond Pulsed Bessel Beam

TL;DR

This paper introduces a femtosecond laser writing method using Bessel beams to create compact, stable photonic crystal spatial filters in glass, suitable for miniaturized laser systems with high efficiency and broad filtering capabilities.

Contribution

The study presents a novel femtosecond direct laser writing technique with Bessel beams for fabricating efficient, large-scale photonic crystal spatial filters with high transmission and broad stop-bands.

Findings

Successfully fabricated photonic crystal filters with ~1° pass-band.

Achieved nearly 100% transmission in the pass-band.

Enabled large-scale, defect-free filters with wide filtering bands.

Abstract

We propose and experimentally demonstrate femtosecond direct laser writing with Bessel beams for the fabrication of photonic crystals with spatial filtering functionality. Such filters are mechanically stable, of small (of order of millimeter) size, do not require direct access to the far-field domain, and therefore are excellent candidates for intracavity spatial filtering applications in mini- and micro-lasers. The technique allows the fabrication of efficient photonic crystal spatial filters in glass, with a narrow angle (~1 degree) nearly 100%-transmission pass-band between broad angle (up to 10 degrees) nearly 0%-transmission angular stop-bands. We show, that this technique can not only significantly shorten the fabrication time, but also allows the fabrication of large-scale defect-free photonic crystal spatial filters with a wide filtering band.