Crystalline Fibers for Fiber Lasers and Amplifiers

Abstract

Fiber lasers and amplifiers have revolutionary advancements in the past 20 years. Using crystalline core for fiber based devices is an extension to explore what glass fibers may have limitations. The mechanical strength and heat dissipation capability of crystalline materials makes them eminently suitable for high power or high brightness applications. To utilize these crystalline advantages, it is crucial to have high quality cladding for low transmission loss and low core/clad interface defects. Various glass-cladded crystalline fiber configurations and formation mechanisms are described. After cladding formation, the heterogeneous crystal/glass interface could result in residual strain in the crystalline core, which may deteriorate the active ion emission cross section. Proper design of the crystal waveguide structure with thermal treatment could effectively mitigate the strain-induced degradation. In this chapter, the growth thermodynamics, ion segregation, and optical transmission and amplification modeling are addressed. As an introduction, the yttrium aluminum garnet (YAG) and sapphire crystalline hosts with broadband active ion dopants will be emphasized even though quite a variety of crystals have been grown into fibers since the inception of the crystalline fiber technology 40 years ago. At present, broad and bright continuous-wave light sources with a center wavelength from visible to near infrared range have been well developed. Application wise, they could be adapted as active devices for biomedical imaging, optical metrology, as well as optical communications.