Diffusively doped thulium - and ytterbium - lithium niobate waveguide lasers

Abstract

This thesis describes the work carried out on diffusively doped Tm - and Yb - Ti:LiNbO₃ waveguide lasers. During the course of this investigation the fabrication, spectroscopy, and laser characterisation of the resulting devices was performed.

Rare earth doping was accomplished using the thermal indiffusion technique, which is a highly flexible method for doping this very useful optical material.

This study produced the first Yb:LiNbO₃ laser, and the first room temperature Tm:LiNbO₃ laser. Also the first detailed spectroscopy of Yb:LiNbO₃ was performed here. Laser emission was seen in a Yb:LiNbO₃ Ti waveguide at 1008, 1030 and 1060nm, with a threshold of 15mW absorbed pump power. The threshold in a Tm:LiNbO₃ Ti waveguide was 17mW and lasing was seen at 1.81 and 1.853 µm. The laser potential of the ¹G₄ to ³H₆ transition at about 470nm in Tm:LiNbO₃ was also examined, using absorption spectroscopy and McCumber analysis.

Photorefractivity, however, adversely affected the laser performance of these devices, and a number of methods for eliminating photorefractivity were applied for the first time to waveguide lasers. In an attempt to reduce photorefractivity a Tm:LiNbO₃ Ti waveguide was successfully periodically poled using the wet electrode technique; this did not, though, eliminate photorefractive damage in the resulting device.

A Tm:LiNbO₃ Ti waveguide laser doped with the rare earth at above the Curie point of LiNbO₃ was, however, non photorefractive, and an oxygen anneal process was also successfully used in a Yb:LiNbO₃ laser. Although the majority of the work presented here was on LiNbO₃, some work, however, was also carried out on the widely used laser crystal YAG (Y₃Al₅O₁₂). Here a new method of waveguide fabrication in YAG was investigated, this is described at the end of this thesis.

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