New approach to fabrication of a Faraday isolator for high power laser applications

Abstract

We report on investigations of direct bonding of mono-crystalline Terbium Gallium Garnet (TGG) to sapphire for use as Faraday isolator in high power fiber laser applications. The technology of direct bonding allows joining of inorganic crystalline and non-crystalline materials without any auxiliary materials at high bonding strength. Lack of additional joining material and related absorption is very promising for high power laser applications. The ability to join different materials allows inserting sapphire as a heat spreader into the beam path for TGG cooling to avoid thermal lensing. All samples were subjected to extensive chemical cleaning and subsequent low temperature plasma activation before bonding. Bonding was performed under compressive forces in a high vacuum environment at moderate temperature. Optically transparent bonds with a very low fraction of defects were obtained. The size of the bonded area depends significantly on the samples' flatness

Direct Bonding Nd:YAG to Sapphire Wafers

“…Bonding faces were then activated using a short, two-stage plasma of oxygen and nitrogen. Nitrogen plasma has been shown to bombard bonding surfaces, removing organic contaminants and encouraging development of a hydrophilic surface state through dangling bonds [2]. Finally, samples were submerged in a 1% hydrofluoric acid bath before being thoroughly rinsed with DI Water.…”

“…Two companies in the US have dominated the market in producing composite structures based upon the direct bonding approach with few, if not no, other suppliers of such devices. In recent years there have been a several groups reporting room temperature bonding of various materials [1,2] all with the aim of enhancing the optical functionality of a certain materials through the combination of key features, such as thermal or physical properties. In this work we present a chemical-assisted method for activating two oxide crystals followed by their direct bonding without any active agent to join them, rather relying upon van der Waals forces initially followed by a thermal anneal to consolidate the bond strength.…”

Direct bonding diamond to zinc selenide

“…Contact was made within 10 minutes of treatment to reduce the chance of contamination. Nitrogen plasma has been demonstrated [14] to encourage a hydrophilic state by bombarding the surface, leaving dangling bonds of high surface energy. Following activation, bonding faces were brought together via DI water at room temperature and spontaneously contacted.…”

“…Diamond and ZnSe have vastly different CTEs of 1x10 −6 / • C (at 300K) [15] and 6.8x10 −6 / • C (at 283K) [16], respectively. As such, the bond is unsuitable for the high-temperatures seen in other direct bonding methods [14]. A series of trials were conducted to test the composite's resistance to temperature change and ramp rates.…”

Direct bonding CVD-grown diamond to ZnSe and sapphire

“…Following this, a two-stage oxygen and nitrogen plasma clean was conducted, developing a hydrophilic surface state. Diamond and ZnSe, both Nitrogen plasma has been demonstrated [5] to encourage a hydrophilic state by bombarding faces to be bonded, leaving dangling bonds of high surface energy. Following activation, bonding faces were brought together via DI Water at room temperature and produced spontaneous contact.…”