Working-Papers

Optical guiding structures with dimensions of micron or submicron scales could confine light propagation within very small volumes, in which the optical intensities can reach a much high level with respect to the bulks. Benefiting from the compact size, a few photonic components may be integrated on a small chip, realizing both passive (e.g., optical switches) and active applications (e.g., modulators, amplifiers, lasers, and frequency converters). In addition, owing to the obtainable high optical intensities, considerably enhanced performances correlated to the substrate materials could be found in the guiding structures, such as low pump threshold for waveguide lasers, fast responses for photorefractive waveguides, and multiple configurations for frequency conversion for nonlinear waveguides.

One research line of our group is to fabricate the optical waveguides in dielectric crystals by using ultrafast laser inscription. The ultrafast laser writing is a powerful tool to fabricate waveguides in a large number of optical materials. Since 1996, the first demonstration of waveguides in glasses, this technique has proved to be a very efficient technique for waveguide formation. Our work focuses on the modification of femtosecond laser pulses on optical crystals. For example, we have fabricated the successful waveguide lasers in vanadate crystals (Nd:YVO4, Nd:GdVO4, and Nd:LuVO4). We also produced the first nonlinear cladding waveguides in BiBO and KTP crystals, and proved the superior performance of second harmonic generations to the well-known stress-induced double line waveguides.

Ion beam technology has been widely applied to modify the material properties in many aspects. By using energetic ion beams, the refractive index of the bulk materials can be modified and therefore waveguiding structures could be constructed. The techniques are multiple depending on many parameters, such as ion energies, species and fluences, the beam size and current, and the detailed experimental conditions (e.g., temperature). Compared with other techniques, ion implantation possesses one of the most advantageous characteristics, that is, the wide applicability of materials (similar to fs laser writing). Since the first proton-implanted waveguide in fused silica was reported in 1968, waveguides have been so far fabricated in more than 100 optical materials by implantation of various ions at the energies of several hundred kilo-electron-volt (keV) up to tens of mega-electron-volt (MeV). Our research has been focused on the very promising topics in this field: materials, lasers, nonlinear phenomena, etc.

By using ion beam techniques, one can also modify the properties of 2D materials. The main effects of ion beam modification of 2D materials include defect, doping, and layer-to-layer coupling modulation. These effects are correlated to diverse properties of the 2D materials, and reflected by the modified performances in various applications. 

Recently, we also focus on the metallic nanoparticle synthesis by ion beams. The nanoparticles are embedded in the dielectrics, including crystals and glass. We investigate the surface plasmon resonance (SPR) effect induced by the nanoparticles, and the modulation of bulk properties such as linear and nonlinear optical absorption, photoluminescence. Particularly, by tailoring the optical nonlinearities of dielectrics, the so-called saturable absorption may be obtained for the nanoparticle embedded dielectric systems, which could be used for ultrafast laser generation.