SECONDMENTS

Lately, there has been a strong intensive to develop optical sources and components compatible with the mid-infrared spectra for applications in biology, medicine and environmental monitoring, to name a few. My PhD project focuses on using femtosecond laser direct inscription of embedded waveguides for the development of optical devices for the mid-IR. During my doctorate I worked with a heavy metal oxide glasses (BGG), containing gallium, germanium and barium oxides which is a good candidate for the mid-IR. Previous work demonstrated that we can obtain in BGG glasses smooth, low loss waveguides thanks to high positive refractive index change induced by ultra-short pulse irradiation [1]. Recently we made the first directional couplers (2 waveguides, 2 inputs and 2 outputs) in BGG glass, obtaining promising results (Figure).

Figure. Sketch of a coupler (not to scale) inscribed in the BGG glass sample. The waveguides have a diameter of 20 µm and are inscribed 150 µm under the glass surface by scanning multiple times the laser beam across the sample (20 times per waveguides).

The goal of this research mobility project was to characterise previously made directional couplers in BGG glass for the 2-5 µm region and to make and characterise new directional couplers in fused silica for the 2-3.5 µm region.

Experiments on mid-IR couplers.

The BGG couplers has been tested with a home-made cw laser source emitting at 2850 nm. The results of the measures are in good accordance with the model used [2] and a split ratio of 0,99 was reached, showing that the waveguides are smooth and regular.

The planned experiments has been completed during this research mobility, but issues with the mid-IR waveguides development in fused silica resulted in waveguides and couplers less performing than expected. Further processing and understanding of the data could lead to the publication of this results.

[1] Bérubé, J. P., Le Camus, A., Messaddeq, S. H., Petit, Y., Messaddeq, Y., Canioni, L., & Vallée, R. (2017). Femtosecond laser direct inscription of mid-IR transmitting waveguides in BGG glasses. Optical Materials Express, 7(9), 3124-3135.

[2] Digonnet, M. J., & Shaw, H. J. (1982). Analysis of a tunable single mode optical fiber coupler. IEEE Transactions on microwave theory and techniques, 30(4), 592-600.