Mode analysis in He+-implanted lithium fluoride planar waveguides

Abstract

The depth refractive index profiles of broadband visible-emitting planar waveguides produced in LiF crystals with 1.5- and 2-MeV He+ ions at different doses have been derived from mode analysis. They show that there are two competitive mechanisms responsible for positive and negative modifications of the refractive index in the irradiated volume associated with different processes of energy deposition of the incident ions, so as to induce a complex coloration profile along the penetration direction, which is strongly dependent on the irradiation dose.

Visualization by SNOM technique of optical modes in LiF channel waveguides

“…Considering that the measurement conditions are the same for both implanted waveguides, we can deduce that the variation of refractive index generated at the lower dose is lower. This conclusion is in agreement with the values of the refractive index measured in planar waveguides implanted at similar dose [6].…”

“…Channel waveguides have been created by electron-beam lithography using an energy of 13 keV and a dose of 1.57E-2 C/cm 2 . Recently the possibility to create optical waveguides in the LiF by helium ions implantation was demonstrated [6]. According to the index profiles obtained by choosing the implantation conditions in Ref.…”

“…According to the index profiles obtained by choosing the implantation conditions in Ref. [6], it is possible "to write" a channel waveguide through a masking system. We give here two examples of waveguides that have been created by He + -ion implantation at the same energy (1.5 MeV), but with two different doses: 6×10 13 ions/cm 2 and 2.6×10 14 ions/cm 2 , respectively.…”

“…In LiF crystals various ionizing radiation can be used to create stable electronic defects having absorption bands located in the visible spectral region and exhibiting intense fluorescence at room temperature in the same spectral range [4]. Besides the efficient defects formation, the ionizing radiation induces an increase of the refractive index of the irradiated zone in the same wavelength interval where the fluorescence is located, allowing the fabrication of active optical waveguides either by electron-beam lithography [1,5] or He + -ion implantation [6]. The scanning near-field optical microscopy (SNOM) is now considerably developed and can be used to visualize the details of physical or biological objects with a sub-wavelength resolution [7].…”

H + implanted channel waveguides in buried epitaxial crystalline YAG:Nd,Tm layers and infrared-to-blue upconversion characterization

“…Nevertheless, for a narrow group of materials, such as YAG ͑Ref. 17͒ or LIF, 18 some small positive index change caused by the electronic energy deposition is observed. It can be sufficient to confine low order modes.…”