Fabrication And Characterization Of Planar And Ridge Waveguides In TGG Crystals

Nowadays,with the rapid growth of network traffic,all-optical network is an inevitable development direction for future information transmission.Its bandwidth adapts to the development trend of high data transmission rates and large throughput.Optical devices and optoelectronic components in an all-optical network are gradually integrated.Traditional structures are no longer able to meet the needs of future information networks in terms of size and performance.Different types of optical waveguides restrict the beam propagation in the micron-scale structure and achieve a higher optical density.As a basic element in integrated optics,optical waveguide is an important part of many optical devices and systems,which affects the quality of the optical system.Therefore,researches on the fabrication and optimization of the waveguide structure as well as the improvement of the optical properties of the optical waveguide are key issues for its important applications.As a novel type of magneto-optical optical rotation crystal,terbium gallium garnet（TGG）crystal has a large Verdet constant,good thermal conductivity,low propagation loss,high laser damage threshold and transparency in the visible and infrared bands.It is one of the important magneto-optical crystal materials in integrated optics.TGG crystal optical waveguide structure can be used to prepare optical devices with Faraday optical properties.In this paper,TGG crystals are used to prepare optical waveguide structures.At present,the technology for preparing optical waveguide structures has been fully developed.Among the methods of fabricating one-dimensional optical waveguides,the ion implantation technique does not require additional target materials besides the substrates.The conditions for ion implantation can be reasonably controlled.Further annealing treatments can improve the damage and color center caused by the ion implantation.The two-dimensional optical waveguide limits the beam propagation in two directions and is easier to integrate with optical devices and systems.In this paper,the ridge optical waveguide is prepared on the ion-implanted one-dimensional waveguide by the precise diamond blade dicing technology.With high adaptability and precision,this method can accurately and flexibly control cutting conditions.The combination precise diamond blade dicing with ion implantation is an effective procedure for preparing ridge optical waveguides.In this paper,based on TGG crystals,ion implantation and precise diamond blade dicing method are used to form planar and ridge waveguides.The study for the formation principles and the measurement for the optical properties of the two optical waveguide structures are both involved.It provides theoretical and experimental basis for the application of optical waveguide structures in all-optical networks and integrated optics.The main work and achievements of this paper are as follows:1. Proton-ion implanted TGG planar waveguide and optical properties after annealing at different temperaturesProton-ion implanted-waveguide is formed with an energy of 400 ke V and a dose of 8×10¹⁶ion/cm² on the surface of the TGG crystal.It is annealed at 260℃and 410℃for 1 h,respectively.The optical properties are measured at 633 nm.Before annealing,three modes whose effective refractive indices are lower than the refractive index of the substrate in the planar optical waveguide are measured.No mode is detected after annealing at 260℃for 1 h,while nine modes are found at410℃for 1 h.The annealing temperature affects the refractive index of the optical barrier and changes the refractive index distribution in the optical waveguide,thereby affecting the number of modes propagation in optical waveguide.2. Carbon-ion implanted TGG planar waveguide with the same energy and different dosesTwo pieces of TGG crystals are implanted by carbon ions with the same energy and different doses.Three modes whose effective refractive indices are higher than the refractive index of the substrate are measured in the low-dose carbon-ion implanted optical waveguide,while no outgoing light is detected under the end-face coupling system.Three modes are also found after the high-dose carbon-ion implantation,but their effective refractive indices are all lower than the refractive index of the substrate.Light can be well confined in the high-dose implanted waveguides.At the same carbon ion energy,a“well+barrier”type optical waveguide is formed by low-dose implantation,while a“barrier”type counterpart is prepared under high-dose condition.3. The silicon-ion implantation combined with the precise diamond blade dicing technology to prepare planar and ridge waveguides in TGG crystalA“barrier”planar optical waveguide is fabricated by silicon-ion implantation with an energy of 6 Me V and a dose of 2×10¹⁵ ions/cm² in the TGG crystals.Three guided modes are measured by the prism coupling system.The near-field light intensity distribution of the annealed optical waveguide is obtained under TE mode polarization at 633 nm.On the surface of the planar optical waveguide,ridge optical waveguides with widths of 10μm,13μm and 15μm are formed by precise diamond blade dicing technology.The mode propagation profile of light through a ridge waveguide is detected experimentally.It shows that one-and two-dimensional optical waveguides fabricated by silicon-ion implantation and precise diamond blade dicing method can be used in the visible region.