Investigation Of Electro-Optic Properties And Lattice Damage Distribution Of Ion Implanted Waveguides In Lithium Niobate

Under the background of the prosperity of information technique, the optical communication technology has become a swiftly developing and synthesized technical domain. 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. Optical waveguide is the basic structure of integrated optics and the holo-optical network. It also plays an important roll in the fabrication of various optical devices because of its excellent characteristics, possibility in integration and rather low cost in manufacturing.Ion implantation technology is an effective method to form optical waveguide. It has many merits including the accurate control of the amount of implanted ions and the thickness of the formed waveguide, weak confinement of the material and its crystal direction, and low requirement of the forming temperature of the waveguides, etc. Up to date, ion implantation technology has been successfully used to form optical waveguide structures in series of optical materials such as optical crystals, glass, semiconductors, etc.As one of the most favorite dielectric crystals, lithium niobate (LiNbO₃) is widely used in a variety of photonic devices due to its high electro-optical, acousto-optic, piezoelectric, and nonlinear optical coefficients. It has broad application in surface filter, optical communication modulator, electro-optic switch, acousto-optic device, optical sensor and high-density data storage, etc. Meanwhile, LiNbO₃ is an important material for optical waveguide which has very important and fundamental application in the optoeletronic field. LiNbO₃ has outstanding electro-optic property. Due to this, waveguide in LiNbO₃ are promising to be used in electro-optic modulator and electro-optic switch, etc., in integrated and optoelectronic devices.Implantation of light ions, such as H⁺ and He⁺, into LiNbO₃ to form optical waveguides has been widely reported. As for the mechanism of formation of waveguide produced by light ion implantation, it is generally considered that in the process of implantation, ions interact and collide with the electrons and crystal lattice atoms of the target material, and their energy declines gradually. At the end of the ions' range, implanted ions strongly interacts with the target atoms and result in crystal lattice damage to some extent and form a damage layer at the position some microns under the target surface. The material's density in the damage layer decreases, which finally results in the decrease of the refractive index of LiNbO₃. Hence, the lattice damage layer is generally called optical barrier. Light is confined in the region bounded by the damage layer and air with relatively low refractive index to propagate to form an optical waveguide structure. Ion implantation brings about crystal lattice damage in waveguide region as well, which will influence and weaken the optical performance and physical properties of LiNbO₃, such as its electro-optic property. Research about the relation between the condition of implantation and the induced crystal damage distribution has instructive significance for the application of the ion implanted LiNbO₃ waveguide in optical modulator and switch in integrated and optoelectronic devices.The present work is mainly focused on two aspects: (1) Implantation of 500keV H and He ions were used to form optical waveguide in LiNbO₃. Based on the measurements, we studied the mode structure of the waveguides formed by different implanted ions dose and their annealing performance. The changes of the electro-optic coefficients of the formed waveguides were specially researched. (2) By implantation of He ions with different energies optical waveguides were fabricated in LiNbO₃. The mode structure of the formed waveguides and their annealing conducts were studied. Using Rutherford Backscattering and Channeling technology and a dechanneling calculation mode from the measured channeling spectra we calculated the lattice damage distribution of the waveguides and studied the relation between the damage and the conditions of ion implantation. The main results of the dissertation are listed below:We used 500keV H ions to implant into LiNbO₃, the dose is 8×10¹⁶ ions/cm and 1×10¹⁷ ions/cm². Annealing treatment was employed to restore the crystal lattice structure in the waveguide region and finally optical waveguides with the increase of extraordinary refractive index were formed. We studied their mode structure and annealing conducts. 500keV He ions are implanted into LiNbO₃. The dose is 2×10¹⁶, 3×10¹⁶, 4×10¹⁶ and 5×10¹⁶ions/cm² respectively. Implantation formed well-confined single mode waveguides with enhanced extraordinary refractive index. The effective refractive indices were found not to change consistently with the dose of implanted He ions. Based on a mode proposed by Yi Jiang about the mechanism of the change of refractive index induced by ion implantation in LiNbO₃ we analysed the cause of the above phenomenon. Using a measuring method based on the prism couplingtechnique we measured the change of the linear electro-optic coefficients ^γ33 of the formed waveguides.Single mode optical waveguides with enhanced extraordinary refractive index were produced by 300keV, 400keV and 480keV He ions implantation respectively. The performance of the formed waveguides was improved by annealing treatment. Using Rutherford Backscattering and Channeling technique (RBS/C) we measured the channel spectra of the formed waveguides and compared them with the random and channel spectra of unimplanted LiNbO3, and studied their annealing performance. On the foundation of a mode for dechanneling calculation from the measured RBS/C spectra we calculated the lattice damage distribution of the formed waveguide. The results showed that along with the increase of the energy of implanted ions the lattice damage induced by implantation would decrease. For the 480 keV implantation of He ions we used, the defect radio of the crystal structure was under 0.1 in most of the waveguide region. The crystal structure was well retained. The calculated results were compared with the simulative results of SRIM program.