EAGER: On-Chip Optical Amplifier Using Novel Erbium-Chloride Silicate Single Crystal Nanowires

This proposal aims to conduct early stage exploratory research to develop an on-chip optical amplifier with high gain using a novel material that was recently synthesized for the first time by the PIs group. The publication of our new material has attracted great interest and was widely reported by many websites or tech magazines. The primary motivation for the proposed research is the increasing demand for on-chip integration of photonic systems for future communication and computing. Such demand has been the driving force behind the development of various optical functionalities that are small in size and compatible with silicon technologies. One important category of such functionalities is optical amplifiers. Currently the prevailing choice of amplifier for communication systems is erbium (Er) doped fiber amplifiers (EDFA) using the Er emission at 1.53 micron wavelength band. Unfortunately, the low erbium doping density in silica and silicon results in low optical gain, requiring bulky materials that are unsuitable for on-chip integration. Various efforts in increasing Er density by co-doping with other elements or using silicon nano-crystals have so far resulted in limited success, due to the clustering of Er ions at moderate to high Er levels which leads to quenching of 1.53 micron light emission. Er compounds such as erbium oxide and erbium silicate are currently studied as potential high gain materials due to their higher Er density. But these early research efforts have also encountered various issues such as strong upconversion, excited state absorption, and poor crystal quality as a result of various less developed methods of crystal growth and sample preparation. Recently, the PIs group was able to synthesize a novel erbium-containing single-crystal material, erbium chloride silicate (ECS). The main advantage of this material is the ability to grow high quality single crystals with high erbium density without the need for high temperature annealing. The periodic arrangement of erbium atoms in ECS crystals without clustering leads to linear scaling of 1.53 micron band over several orders of magnitude without apparent saturation. Such high quality and high erbiumdensity material provides a unique high gain material for on-chip optical amplifiers. The overall objectives of the proposed efforts are to study the optical properties of ECS nanowires and to develop a high gain miniaturized optical amplifier that is suitable for on-chip silicon integrated photonic systems. The intellectual merits of proposed research lie in the novelty of materials, the importance of the fundamental understanding of this important material, and the potential impact to silicon photonics. Due to the novelty of the material, there are many fundamental issues such as lifetimes of various states and linewidths of various transitions that need to be investigated. Understanding of various erbium-based transitions in this new compound crystal would be important for the development of ECS amplifiers. Such study will also have broader impact and is potentially important for other future applications, such as silicon-based light emission devices, quantum information at telecomm wavelengths, and on-chip atomic clocks. The systematic gain characterization will provide critically important information about the feasibility of on-chip amplifiers. The scientific knowledge and understanding gained will have tremendous impacts to all of the applications mentioned above. Finally, the proposed silicon-based amplifier device will be an important component for all-silicon based on-chip optical integrated systems, potentially increasing our capability and efficiency in information processing (computing) and communication. In particular, individual wires with a diameter on the order of hundreds of nanometers provide a potentially game-changing solution for on-chip nanophotonic systems, allowing for unprecedentedly large-density integration of computing and communication functionalities. Such high-risk and high pay-off research is ideally suited to be an EAGER project. Beyond on-chip amplifiers, the proposed activities are part of the long-term endeavor of the PI (and the entire community) to eventually achieve Er-based light emitters and lasers on Si. Such silicon photonic capabilities would fundamentally revolutionize and potentially unify electronics-based computing and photonics-based communication, impacting information technology and our society in general. The proposed efforts will also integrate research with education of minority and female students. The results of the research will be rapidly incorporated into undergraduate projects and graduate curriculum, so that education can benefit from the proposed research in a timely fashion and to the maximum extent possible.