2. Industry's first crystal device to apply atomic diffusion bonding techniqueThe atomic diffusion bonding technique is a direct bonding technique developed by Tohoku University's Professor Takehito Shimatsu. It entails bonding the wafer and substrate together without applying heat, pressure or voltage, nor using organic adhesives. Through the joint-development with Professor Shimatsu's research group, Kyocera Crystal Device has succeeded in bonding a crystal wafer in an extremely thin metal film thickness of several atomic layers to several dozen nanometers *2 with high strength by applying the atomic diffusion bonding technique for crystal devices. This method has solved the problems of optical contact *3, a conventional bonding method with lower bonding strength, and that of bonding using organic adhesive, for which the management of bonding thickness is difficult. It has also improved accuracy and reliability while reducing the size of the etalon filter. Development Background An etalon filter is a component which monitors whether oscillation of light wavelength is steadily conducted in the tunable laser module — an essential device used for high-capacity optical communication transmission systems — which transforms electric signals to optical signals for oscillation. In recent years, optical communication has become increasingly essential to achieve higher capacity and higher transmission speeds with the dramatic increase in information volume due to the rapid spread of the Internet and transmission of high-volume data. To respond to such requirements, the utilization of the WDM *4 transmission system, which can transmit more optical signals (information volume) with one piece of optical fiber, has become the mainstream method. Since a WDM transmission system requires many tunable laser modules for each station from mid- to long-distance to short-distance transmissions, further reduction in size and electric power consumption is required. As the product does not require a Peltier device for temperature control due to the aforementioned features, it can contribute to reduction in the size and electric power consumption of tunable laser modules. Even with its small size, this product has realized freedom from temperature characteristics, high accuracy and high reliability, and has superior stability against changes in external temperature.