The Property Investigations Of Ion Implanted Nd:KGW Optical Waveguides

Optical integrated devices play an important role in the fields of high-speed long-distance optical telecommunications,broadband optical networks,sensors and smart structures,optical signal processing and optical computing.Waveguide is a basic structure in optical devices and plays an important role in the fabrication of various optical devices.It can confine the optical energy in small space and improve the optical energy density.At present,the most popular methods include metal diffusion,ion exchange,film deposition and ion implantation etc.Ion implantation,as an outstanding method for fabricating various waveguide structures,is confined 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.Due to the different mass of the injected ions used in ion implantation,the light ions implanted waveguides and heavy ones formed in optical crystals are distinct.The light ions(H and He) are frequently used.an optical barrier with a lower refractive index compared to the substrate will be formed due to the damage induced by nuclear energy loss.Such an optical barrier confines the light in an "optical well" between itself and the surface.However,one of the difficulties is that light ion implantation for the waveguide formation often needs high doses of～10¹⁶ ions/cm².In some cases,the indices in surface layer have been found to be raised when heavy ions are implanted into some optical materials.The dose of heavy ion implantation can be 1～3 order lower than that of light ion implantation and it can reduce the fabrication cost significantly.Most optoelectronics devices such as optical coupler,modulator,optical switch and waveguide laser are based on channel waveguide structure.The attempt of fabrication of such waveguide structure is necessary for both optoelectronics technology and the combination between nuclear technology and optoelectronics.KGd(WO₄)₂ laser crystal is a new laser substance material developed upon CaWO₄ crystal,the rare earth ion,Gd³⁺,can be substituted by another rare earth ion, Nd³⁺.Such a substitution has made an excellent laser crystal.The crystal is neodymium doped potassium gadolinium tungstate,written Nd:KGd(WO₄)₂ in molecular formula and shorthanded Nd:KGW.The concentration of dopant Nd³⁺ is very high,up to 3～8%.And this crystal is a multicolor laser crystal lasing at 0.91μm, 1.06μm and 1.35μm.In the lasing aspect,Neodymium-doped KGW crystal exhibits a low lasing threshold with a broad and strong absorption band.Especially there is a broad absorption peak at 808nm,which makes it exceptionally suitable as an excellent gain medium for efficient diode pumped lasers and Xe lamp.With good mechanism,optics behave,the crystal has potential application in non-linearity and Raman scatter area. In the future,the Nd:KGW crystal will be good applied in medication,medical treatment,communication,remote sensing.And the crystal has attracted considerable attention and become research hotspot gradually.The present work is focused on three aspects,as follows:1) We report the fabrication of planar waveguides in Nd:KGW crystal by 500keV H⁺ implantation at dose of 6×10¹⁶ ions/cm².We perform the prism coupling method to measure the dark modes and their effective refractive indices.And the refractive index profile of H⁺ implanted Nd:KGd(WO₄)₂ waveguide is analyzed by using the reflectivity calculation method(RCM) based on the results of prism coupling.We use SRIM 2006(Transport of ions in matter) code to simulate the process of the relevant ion implantations.Annealing treatment is performed.The behavior of annealing on guiding mode and the effective refractive indices are studied.After annealing,the dark modes index increases slightly,which means that the refractive index of waveguide recovered to some extent.2) We manufacture planar optical waveguide in Nd:KGW crystal by 6MeV C ion implantation.The properties of the waveguides are investigated by prism coupling as well as end-face coupling methods.The program code SRIM 2006 is used to simulate the implantation process of carbon ions into the Nd:KGW crystal.We use RCM method to reconstruct the refractive index profiles of the waveguides.Different refractive index behaviors are observed,the surface refractive indices of the crystal along the three axes are same;moreover,the dark modes of the waveguide are with the same effective refractive indices along the n_p,n_m,and n_g axes.Based on these,we can conclude that after the C³⁺ implantation,the near surface region of the sample becomes an optically isotropic layer.3) Optical ridge waveguides are fabricated by combination of ion implantation with ion beam etching.Using end-fire coupling method,the optical intensity distribution of the light traversed the ridge waveguides are obtained.A scanning electron microscopy is used to take a picture of the cross-section shape of the ridge waveguide.