The Fabrication And Property Investigation Of Ion-Implanted Planar Waveguides In Optoelectronic Crystals

A waveguide is characterized by a region of high refractive index bounded by regions of lower index.It can confine the optical energy in small space and improve the optical energy density.Waveguide is the basic component of integrated optics,and it also plays an important roll in the manufacture of optical devices.Recently the study of waveguide lasers has become one of the most interesting topics in the integrated optics,while the necessary method for the waveguide laser generation is to form waveguide structures in the laser materials.Because of its importance in practical application,scientists and engineers are trying to find various ways to fabricate "high-quality" optical waveguide.Several waveguide fabrication techniques have been developed to obtain the waveguide structures,such as metal diffusion,ion exchange,thin film deposition and ion implantation.Ion implantation,as an outstanding method to modify the surface property of materials,is confirmed to be an effective method for fabricating various waveguide structures.Up to now,many waveguide structures have been formed by ion implantation in most optical materials such as optical crystals,glass,semiconductors and polymers etc.The ion implantation has become an effective method to fabricate optical waveguide.The ion implantated waveguide technology is sorted to two different strategies named light-ion implantation and heavy-ion implantation,according to the mass of the implanted ions.Due to the different mass of the injected ions used in two methods, the light-ion implantated waveguides and heavy ones formed in optical crystals are distinct.When the light-ions implanted into the crystal substrate,an optical barrier with a lower refractive index compared to the substrate will be formed by the deposition of the implanted ions,leaving a nearly undisturbed region between the optical barrier and the surface.So this type of waveguide is comprised of the air,the optical barrier and the undisturbed region.However,in the waveguides formed by light-ion implantation,ion dose of order of 10¹⁶ ions/cm² or higher are needed When the heavy ions implanted into the crystal,the electronic energy loss(ususlly small in light-ion implantation) is strong enough to change the optical properties of the surface.This change surely weaks the birefringence of the implanted region,resulting in the increase of the lower refractive index.The light confinement ability of this type of waveguides relies on the enhanced refractive index layer so that they are sensitive to the polarization direction of the light.Ion implantation using keV ions has been widely used in the semiconductor industry.Comparing with the implantation using MeV ions,keV-ion-implantation is much cheaper and could offer larger beam current.It is more convenient for industry production.Besides the keV implantation has shallower damage which makes it more convenient for the research of the mechanism for the positive refractive index changes.In this paper we report the waveguide formation and characterization on Nd:CNGG,stoichiometric LiNbO₃and B₁₂TiO₂₀.Through the research on waveguide mode and annealing behavior,the formation parameters of ion implantation waveguide can be optimized.The near field profiles of these waveguides were measured by end-fire coupling method.The PL spectrums were also measured with FS920 Steady State Fluorescence Spectrometer in Edinburgh Corporation.Xe-flash lamp at 596 nm was used during the measurement.Main results are as follows: Neodymium-doped calcium niobium gallium garnet(Nd:CNGG) is an attractive laser material suitable for diode pumping belong to the class of neodymium-doped disordered crystals.It has a relatively broader pump absorption band than Nd:YAG Due to its large emission bandwidth originated from the disordered nature of the crystal,Nd:CNGG is a suitable candidate for diode pumped tunable mode locked lasers.The Nd:CNGG waveguide was formed by 500 keV He⁺ ion implantation with a dose of 2×10¹⁶ ions/cm² at room temperature.The refractive index profile was analyzed using RCM.It is found that the lattice damage produced by the keV He⁺ ion implantation seemed to be the main reason of the refractive index change of the crystal.The PL spectrum of Nd³⁺ in He-Nd:CNGG was also measured.Furthermore, we study the properties of waveguides formed by O,H ion implantation with the same way.LiNbO₃ is an important and promising waveguide material because of its outstanding nonlinear optical and electronic-optic properties.We usually called the congruent LiNbO₃ LN crystal.The ratio of Li/Nb in congruent LiNbO₃ is smaller than 1:1 and so there are a lot of defects in congruent LiNbO₃ crystal.As a result,the optical performances of congruent LiNbO₃ are reduced.Nevertheless,the ratio of Li/Nb in stoichiometric LiNbO₃ is upgraded.Stoichiometric LiNbO₃ shows a very improved performance because of the much fewer defects in the crystal compared to congruent LiNbO₃.The planar waveguides have been produced in SLN by 4.5 MeV O³⁺ ion implantation at a dose of 6×10¹⁴ ions/cm² at room temperature.The effective refractive indices of the guided modes are measured by the prism-coupling method at wavelength of 632.8nm.The near field profiles of these waveguides were measured by end-fire coupling method.Bismuth oxide compounds with a Bi₁₂MO₂₀ chemical composition(where M=Ge, Si or Ti) crystallize on the I23(sillenite structure) space group.They exhibit a number of interesting properties,including:piezoelectric,electro-optical,elasto-optical, optical activity and photoconductive properties.Of particular interest is the combination of the electro-optical and photoconductive properties,from which results the so called photorefractive effect,consisting of a reversible light-induced change in the refractive index.Due to these properties,sillenite crystals are useful for many advanced and promising applications,such as a reversible recording medium for real-time holography or image processing.Bismuth titanium oxide crystal, Bi₁₂TiO₂₀(BTO),presents some practical advantages in terms of its isomorphous compounds Bi₁₂SiO₂₀(BSO) and Bi₁₂GeO₂₀(BGO),incuding lower optical activity, larger electro-optic coefficient and higher sensitivity to red light.The planar waveguides have been produced in BTO by 4.5 MeV O³⁺ ion implantation at a dose of 6×10¹⁴ ions/cm² at room temperature.The effective refractive indices of the guided modes are measured by the prism-coupling method at wavelength of 632.8nm.By using end-fire coupling method,the optical intensity distribution of the light traversed the waveguide was obtained.