Three-dimensional mid-infrared photonic circuits in chalcogenide glass

Abstract

We report the fabrication of single mode buried channel waveguides for the whole mid-infrared transparency range of chalcogenide sulphide glasses (λ ≤ 11 µm), by means of direct laser writing. We have explored the potential of this technology by fabricating a prototype three-dimensional three-beam combiner for future application in stellar interferometry, which delivers a monochromatic interference visibility of 99.89% at 10.6 µm, and an ultrahigh bandwidth (3-11 µm) interference visibility of 21.3%. These results demonstrate that it is possible to harness the whole transparency range offered by chalcogenide glasses on a single on-chip instrument by means of direct laser writing, a finding that may be of key significance in future technologies such as astrophotonics and biochemical sensing. . An essential step in order to unleash all of this potential science is to develop integrated optical platforms capable of addressing the technological requirements that each field demands. In this sense, the development of on-chip instruments such as optical sensors, high resolution spectrometers, or sophisticated beam combiners, is currently of high interest for the previous mentioned applications [1,2,5,6,7].Although several MIR two-dimensional (2D) planar schemes have been recently developed [8,9], these are all based on multiple-step surface deposition and processing techniques, which place inherent limits to the device design and capabilities. In this Letter, we report the single-step fabrication of three-dimensional (3D) MIR photonic circuits inside chalcogenide glass, by means of ultrashort-pulse direct laser writing (DLW) [10][11][12][13][14]. We show that the MIR waveguide cores can be tailored in both size and refractive index, and can also be spatially positioned at will inside the material, making the chip extremely robust against mechanical stress, vibrations, humidity, and temperature changes [11]. Moreover, we also evidence that the useful range of these DLW waveguides is, as suspected [12], ultimately limited by the transparency range of the material used, and not by the fabrication technique.In this work, high quality research and commercial chalcogenide sulphide glasses were used, both of which are free of highly toxic arsenic compounds. These glasses were commercial GaLaS (here after GLS) [14] and the research composition 75GeS2-15Ga2S3-4CsI-2Sb2S3-4SnS (here after GCIS) [15]. The MIR transmission upper limit of commercial GLS is known to be ~10 µm [14], while for GCIS we measured a slightly higher transmission upper limit of ~11 µm, as it is shown in Figure 1(a).

Ultrafast-laser-inscribed 3D integrated photonics: challenges and emerging applications

“…An ultrafast-laser-inscribed beam combiner with three inputs was demonstrated by Rodenas et al [132]. The 3D device, based on six Y-junctions, was inscribed into a 1.2-cm-long sample of gallium lanthanum sulphide chalcogenide glass.…”

Ultrafast Laser Fabrication of Low-Loss Waveguides in Chalcogenide Glass with 0.65 dB/cm Loss

“…These effects lead to an elongation of the laser modified region within the substrate, yielding multiple guiding regions as reported in early work [6]. More recently, multiple laser passes have yielded more symmetrical features in CHG glasses, producing single-mode guiding in the mid-IR spectral range (3-11 μm) [7]. However, the fabrication of highly symmetric single-mode waveguides at shorter wavelengths (e.g., 1560 nm) remains a significant challenge.…”

Refractive index and dispersion control of ultrafast laser inscribed waveguides in gallium lanthanum sulphide for near and mid-infrared applications

“…Recently the mid-IR region of the electromagnetic spectrum has been attracting a considerable amount of research interest due to the potential applications in gas sensors [6], biosensors [7] and stellar interferometry [8]. This growing interest creates the need for new host materials suitable for integrated optical devices that operate in mid-IR and ChGs are proving to be an excellent solution due to their excellent mid-IR transparency.…”