Efficient lasing in Nd:GdVO4depressed cladding waveguides produced by femtosecond laser writing

Abstract

ABSTRACT We report on waveguide lasers at 1064.5 nm in femtosecond laser written double cladding waveguides in Nd:GdVO 4 crystals. The core waveguide guides both TE and TM polarized modes with considerably symmetric single modal profiles, and show good transmission property (propagation loss as low as 1.0 dB/cm). Under the optical pumping at 808 nm, maximum output power up to 0.43 W of the continuous wave waveguide laser with a slope efficiency of 52.3% have been achieved, which is 21.6% and 23% higher than those of the laser generated from single depressed cladding waveguide, respectively. Furthermore, the maximum output power of the waveguide laser is 72% higher than that of the double-line waveguide. Keywords: Waveguide lasers, femtosecond laser inscription, Nd:GdVO 4 crystal, depressed cladding waveguides INTRODUCTION Optical waveguide structures are the fundamental elements in integrated photonics and modern telecommunication systems, in which light could be confined in very small volumes [1]. Compared with the bulk material, relatively high optical intensities could be reached in the structures. Bene fiting from the compact geometry and compressed intracavity intensity, waveguide lasers possess a number of advantages, such as reduced lasing thresholds and comparable efficiencies, with respect to bulk laser systems [ 2]. The femtosecond (fs) laser inscription has become to be a powerful and promising technique to fabricate optical waveguides in various transparent optical materials [3-5 ], since the pioneering work of Davis et al. in 1996 [ 4]. More importantly, compared with other techniques, such as ion implantation and proton exchange, the fs-laser inscription offers capability of constructing waveguides in three dimensions (3-D) of scales of micrometer or sub-micrometer. The guiding struct ures include Type I waveguides (also called directly written structures, typically with single line writing with positive refractive index change in the written tracks), Type II waveguides (also called stress-induced waveguides, typically with double-line geometry, locating in the region between two filaments with negative refractive index changes) and depressed cladding waveguides (also called Type III configuration, typically locating in a core surrounded by a number of low-index fs-laser written filaments) [6]. Type I and Type II structures have been realized in many materials, such as glass and LiNbO