CC BY
41LS-I-11
New strategies for the fabrication of photonic devices by direct inscription with femtosecond laser pulses
C. Romero1, J. G. Ajates2, X. Mateos3, A. Rodenas4,5, P. Moreno1, F. Cheng6, J. R. Vázquez de Aldana1
1Universidad de Salamanca, Aplicaciones del láser y fotónica, Salamanca, Spain
2Spanish Center for Pulsed Lasers, Technical Division, Villamayor, Spain
3Universitat Rovira i Virgili- Departament Química Física i Inorgánica, Física I Cristallografia
de Materials i Nanomaterials FiCMA-FiCNA-EMaS, Tarragona, Spain
4Universidad de La Laguna, Departamento de Física, Santa Cruz de Tenerife, Spain
5Universidad de La Laguna, Instituto Universitario de Estudios avanzados en Atómica,
Molecular y Fotónica IUDEA, Santa Cruz de Tenerife, Spain
6School of Physics, Shandong University, Jinan, China
Femtosecond laser inscription has already been proved to be a powerful and flexible tool for the manufacture of 3D photonic devices [1] in dielectric materials. The short temporal duration of the laser-matter interaction and the large intensity that can be achieved in the focal region, are responsible to produce local and controllable modifications, as for example a change in the refractive index. In other words, the target material can be processed, at arbitrary depths, with minimal affection of the neighboring region. This fact has opened the door to the fabrication of 3D photonic devices [2], based on optical waveguides, by direct inscription in the substrate, i.e. without the need of post-processing.
Fig. 1. (a) Typical section of a circular depressed cladding waveguide and modal profile (LiNbO3). The refractive index reconstruction and modal simulation are also shown [3]. (b) Schematics of different implemented photonic structures: curved connector (C), Y-junctions (Y) and Mach-Zehnder interferometers (MZ). Microscope image of
the transition area on the bottom.
Crystalline materials are very attractive for the integration of photonic devices, both in the passive and active regimes, as they possess excellent properties, such as a large transparency window, anisotropy, or non-linear behavior, among many others. However, such properties cause, at the same time, a large difficulty for the laser processing, thus requiring the development of specific strategies. In many crystals, the refractive index modification that can be induced by femtosecond laser irradiation is only negative (refractive index decreases at the focal spot), effect
that is linked to a local amorphization of the material. In this context, depressed-cladding waveguides [4], that consist of a cladding with low refractive index modified by femtosecond laser irradiation and a core with unmodified properties, were developed as an efficient and universal technique for waveguide inscription in transparent crystals. In this work we present our recent advances [3,5] on this technique with the aim of inscribing 3D photonic elements in any crystalline dielectric. Our results suggest that depressed-cladding waveguides are key structures for integration of complex 3D photonic devices (waveguide lasers, beam-shapers).
References
[1] R. R. Gattass, E. Mazur, Femtosecond laser micromachining in transparent materials, Nat. Photonics 2, 219-225 (2008).
[2] R. Osellame, G. Cerullo, and R. Ramponi, Femtosecond Laser Micromachining: Photonic and Microfluidic Devices in Transparent Materials, Springer Science & Business Media, New York (2012).
[3] J. Ajates, J. R. Vázquez de Aldana, F. Chen, A. Rodenas, Three-dimensional beam-splitting transitions and numerical modelling of direct-laser-written near-infrared LiNbO3 cladding waveguides, Opt. Mat Express 8, 1890-1901 (2018).
[4] A. G. Okhrimchuk, A. V. Shestakov, I. Khrushchev, and J. Mitchell, Depressed cladding, buried waveguide laser formed in a YAG:Nd3+ crystal by femtosecond laser writing, Opt. Lett. 30, 2248-2250 (2005).
[5] G. Li, H. Li, R. Gong, Y. Tan, J. R. Vázquez de Aldana, Y. Sun and F. Cheng, Intracavity biosensor based on the Nd:YAG waveguide laser: tumor cells and dextrose solutions, Phot. Research 6, 728-732 (2017).
