Femtosecond laser direct writing of flexibly configured waveguide geometries in optical crystals: fabrication and application

Optical waveguides are far more than mere connecting elements in integrated optical systems and circuits. The great interest in waveguide structures largely stem from their compact geometries, which result in optical propagation free of beam divergence and optical confinement within extremely compressed volumes, such that high optical intensities and constant optical modes can be maintained over a long transmission length. Thus, monolithically integrated optical waveguide devices are expected to have better performance than bulk setups for applications in a wide range of research areas. Femtosecond-laser direct writing (FsLDW), as a true three-dimensional (3D) micromachining and microfabrication technology, allows rapid prototyping of on-demand waveguide geometries inside transparent materials via localized material modification. The success of FsLDW lies not only in its unsurpassed aptitude for realizing 3D devices, but also in its remarkable material-independence that enables cross-platform solutions. Such a technology therefore allows monolithic and sophisticated waveguide fabrication in a very flexible manner.

 

A schematic illustration of three-element 3D photon-ic-lattice-like cladding photonic structures for beam splitting and ring-shaped beam transfor-mation.

The review article written by the research group of Prof. Feng Chen from Shandong University summarizes the recent advances in fabrication and application of 3D photonic devices based on FsLDW of crystalline waveguides. In contrast to that in glasses, fabrication of 3D waveguides in dielectric crystals employing FsLDW is more challenging due to the complexity in crystal lattice structures. Therefore, special designs of waveguide geometry and FsLDW fabrication skills are usually required to achieve high-performance of 3D waveguide devices. This review article covers the discussions concerning the fundamentals of femtosecond laser induced modifications in dielectric crystals, the observed structural modifications in crystalline materials, and the evolved design prototypes/strategies (such as waveguide splitters, waveguide arrays, photonic-lattice-like guiding structures, etc.) based on these modifications for constructing 3D waveguide geometries. Benefitting from the high performance of the fabricated waveguides with nonlinear geometries, some active photonic devices based on FsLDW 3D waveguides in crystals are demonstrated and also summarized in the review article. This review article also provides some insights on the perspectives of FsLDW 3D waveguides in crystals for potential future applications in both classical and quantum systems. The article is entitled “Femtosecond laser direct writing of flexibly configured waveguide geometries in optical crystals: fabrication and application” and published in Opto-Electronic Advances Issue 10 2020.

About The Group

The research of Prof. Feng Chen’s group from Shandong Universityes mainly focuses on the fabrication of micro/nano-scale photonic structures, such as optical waveguides, dielectric thin films, and plasmonic nanoparticles, as well as their applications in active integrated photonic devices, including compact lasers, nonlinear optical frequency converters, and optical absorbers. This group also has rich experiences on femtosecond laser micromachining and ion beam technology, which can be used for modifying the original material properties to achieve photonic structures with on-demand geometries or/and tailored optical features with enhanced performance. Prof. Feng Chen has published more than 300 papers in peer-reviewed SCI journals and 4 chapters in peer-reviewed books. He has delivered invited talks in more than 60 international conferences/workshops.

Article

Jia Y C, Wang S X, Chen F. Femtosecond laser direct writing of flexibly configured waveguide geometries in optical crystals: fabrication and application Opto-Electron Adv 3, 190042 (2020).

DOI: 10.29026/oea.2020.190042