Annealing Study Of Ions Implanted Lithium Niobate Waveguide

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 enhance the optical energy density, thus make better use of nonlinear crystal or reduce laser pumping threshold of the laser material. Optical waveguide is the basic structure of integrated optics and the all-optical network. It also plays an important role in the fabrication of various optical devices because of its excellent characteristics, possibility in integration and rather low cost in manufacturing. Because of its importance in practical application, scientists and engineers are trying to find various ways to fabricate "high-quality" optical waveguide. 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..In all the implanted waveguides, MeV H and He ions are most frequently used, which build up an optical barrier at the end of the track 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 (low dose-light ions model). More recently, waveguides fabricated by heavier-ion implantation have been extensively investigated. The indices in surface layer have been found to be raised when heavier ions are implanted into some optical materials, such as LiNbO₃, Nd:YVO₄, BBO and KTA etc, then a waveguide can be formed by a region of high refractive index bounded by regions of lower index (air and substrate)(low dose-heavy ions model). This "increase" could help to form better waveguide structures and also reduce the implanted ion dose (1～3 order lower than that of light-ion implantation). Therefore, the investigation on heavier-ion-implanted waveguides is important not only for the theoretical study but also for the potential application as well.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 itself and the combination between nuclear technology and optoelectronics.Lithium niobate (LiNbO₃) belongs to negative uniaxial crystal and has the symmetry of space group R3c, transmission range of 370 nm to 5200nm. It is of high birefringence. 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 is by far the one of the most excellent optical crystals showing good comprehensive properties. It has a wide range of applications in the optical devices, such as surface filters, optical communication modulators, electro-optical switch, acousto-optic devices, sensors and high-density storage of information etc. As the most important functional materials, Lithium niobate crystal has also become an important optical waveguide material and has important applications in the field of photonics. Mg-doped lithium niobate has the same structure as that of lithium niobate, but the anti-damage threshold is 1 to 2 orders of magnitude higher than lithium niobate. It extends the applications of lithium niobate in the field of nonlinear optics.Heavy Ion employed to formed waveguide by increasing the refractive index of crystal has been successfully used to lithium niobate crystal using a variety of MeV ion implantation. Forming waveguide by low-dose ion implantation can reduce costs and will be more conducive to the commercial application.In this paper, heavy ion implantation method has been used in lithium niobate (LiNbO₃) and Mg-doped lithium niobate crystal to form optical waveguide. Through the research on waveguide mode and annealing behavior, the formation parameters of ion implantation waveguide can be optimized. Main results are as follows:Copper ions and carbon ions with energy of 3.0 MeV were used to implant into lithium niobate and Mg-doped lithium niobate crystal in the formation of planar waveguide. The effects of different annealing conditions on effective refractive index of waveguide is measured and analyzed. End coupling method was used to character near-field optical propagation characteristics; fiber scanning method was used to measure transmission loss in the waveguide. We also use SRIM2006 to simulate the implantation process and the lattice damage caused by ion implantation.By using 3.0 MeV helium ions and silicon ion implantation into lithium niobate crystal, planar waveguide, with two parallel guiding region one upon the other, formed through both heavy and light ions co-implantation was firstly obtained in the lithium niobate crystal. The dark modes of the waveguide were measured at wavelength of 633 nm and 1539 nm. Based on the analysis of dark mode spectrum, RCM method was employed to reconstruct the refractive index distribution of the waveguide. We also use end-coupling method to measure the intensity of light propagation in waveguide. After performing both thermal annealing and laser annealing on the implanted waveguide, the characteristics of lithium niobate waveguide suffering annealing treatment were analyzed and discussed.