[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Efficient Er and Nd:Ti:LiNbO <sub/>3</sub> Ridge Waveguide Lasers for the Development of Mid Infrared Sources

摘要： The ferroelectric crystal lithium niobate (LiNbO3) is an attractive material for a variety of photonics applications due to its excellent electro-optic and nonlinear properties. Another benefit of rare-earth doped LiNbO3 is the easy implementation of low-loss waveguides leading to the development of waveguide amplifiers as well as waveguide lasers. In the past, a great deal of attention was attracted to the development of optically pumped Er3+- and Nd3+-doped LiNbO3 waveguide lasers emitting around the 1.5 μm telecom wavelength range and 1.08 μm, respectively. Up to date, Er- and Nd-doped LiNbO3 channel waveguide lasers with slope efficiencies up to 30 % [1] and 40 % [2], respectively, have been reported. However, a further improvement of the laser performance can be achieved by using a ridge waveguide geometry due to the smaller mode fields and improved overlap of modes at different wavelengths as well as the reduction of photorefractive damage. In this work, we report on our novel fabrication method for the development of highly efficient Er: and Nd:Ti:LiNbO3 ridge waveguide amplifiers and lasers [3,4]. To improve the amplifier/laser performance a fabrication technique comprised of ridge definition by diamond blade dicing followed by three-side Er/Nd/Ti deposition and in-diffusion (Fig. 1a) was developed and refined allowing higher Er/Nd doping concentrations and overlap of Er/Nd diffusion profiles with guided modes. An internal gain of 3.0 dB/cm has been measured in 4.6 cm long Er:Ti:LiNbO3 ridge waveguides for a coupled pump power of 200 mW at 1486 nm [3]. Utilizing this high internal gain, we achieved efficient lasing with a slope efficiency of 33 % at 1561 nm (see Fig. 1b) [3]. Furthermore, we demonstrated a Nd:Ti:LiNbO3 ridge waveguide laser with a slope efficiency of 34 % at a wavelength of 1084.7 nm pumped by a Ti:Sapphire laser emitting at 814 nm (see Fig. 1b) [4]. Due to improved photorefractive damage resistance by indium tin oxide (ITO) coating we achieved stable laser operation with a maximum output power of 108 mW for a coupled pump power of 402 mW corresponding to an intensity of ~490 kW/cm2 [4]. Recently, a novel method to achieve local periodic poling of Ti-diffused ridge waveguides in zx-cut LiNbO3 has been demonstrated [5]. In contrast to previous approaches, this method for periodic poling allows an optimization of the ridge waveguide geometry for nonlinear optics applications such as quasi-phase-matched (QPM) difference frequency generation (DFG). The ability to develop highly efficient Er- and Nd-doped ridge waveguide lasers in LiNbO3 and to achieve local QPM allows for the development of efficient hybrid optical devices in the same ridge waveguide emitting in the mid-infrared suitable for applications such as gas sensing.