Abstract: An optical subassembly (OSA) includes a ferrule, an optical fiber, a ceramic substrate, and a seal coupled to the ceramic substrate. A weld sleeve is used to fixably couple the ferrule to the seal ring, for which the weld sleeve may be laser welded to the ferrule and/or the seal ring. The OSA may be a transmitter OSA or a receiver OSA, and may be hermetically sealed.

Abstract: A laser waveguide medium is provided comprising:a laser glass substrate wherein the substrate is a glass comprising (on an oxide composition basis):______________________________________ Mole % ______________________________________ P.sub.2 O.sub.5 50-70 Al.sub.2 O.sub.3 4-13 Na.sub.2 O 10-35 La.sub.2 O.sub.3 0-6 Ln.sub.2 O.sub.3 >0-6 R'O 0-20 R.sub.2 O 0-18 ______________________________________wherein Ln.sub.2 O.sub.3 is the sum of the oxides of active lasing lanthanides of atomic numbers 58-71, R'O is the sum of oxides of Mg, Ca, Cr, Ba, Zn and Pb, and R.sub.2 O is the sum of oxides of Li, K, Rb and Cs; anda waveguide region embedded in the substrate, the waveguide region having a higher refractive index than the substrate and the waveguide region having an inlet region through which light can enter and an outlet region through which light can exit.