Microresonator Frequency Combs as Coherent Transceiver Sources for Multi-Tb/s Optical Communications

Purdue University, West Lafayette IN

Investigators

Abstract

Title: Microresonator Optical Frequency Combs as Coherent Transceiver Sources for Ultrahigh Speed Lightwave Communications General, nontechnical description: Fiber optics is the key transmission technology for high-speed internet and as such has a tremendous impact on society. This proposal seeks to replace large arrays of lasers commonly used to provide multiple data channels in fiber systems with a single nanophotonic device known as an optical microresonator. Under appropriate conditions the microresonator can generate a multiplicity of precisely evenly spaced optical frequencies termed a frequency comb. Each of the frequencies can be used to carry independent data channels over the optical fiber, much as different radio frequencies are used to carry different channels in radio transmission. By replacing the large array of lasers, the proposed microresonator-based light source can potentially reduce cost and complexity, while opening up new opportunities based on the precision of the frequency grid generated. Advances in this novel light source may also help move a variety of other applications out of the laboratory, including high precision time transfer for advanced navigation, environmental sensing, and precision radar. This research project will support two graduate students and should provide outstanding opportunities for broad training in areas of cutting-edge technology. An international collaboration with an advanced optical communications laboratory in Sweden is proposed in order to characterize the performance of the developed devices for state-of-the-art lightwave communications. The proposed collaboration should enhance student training by providing them with opportunity for international collaboration, both in hosting visiting researchers at Purdue and in gaining experience in an advanced communications laboratory abroad. Technical description Optical frequency combs, in which a multiplicity of equally spaced optical frequencies is generated via nonlinear wave mixing in high quality factor microresonators excited by a single frequency laser, are the subject of intense research. This proposal seeks to advance the state-of-the-art in microresonator frequency combs, or simply "micro-combs," in directions relevant to their application in coherent multiwavelength optical communications supporting transmission rates of Tb/s (1012 bit/s) and above. In particular, this projects aims for the first time to realize a frequency matched set of micro-comb chips that can function as a transceiver pair, one at the transmitter of an optical communications system, the other at the receiver. In order to test micro-comb performance in a modern communications testbed and demonstrate high bit rate, multiwavelength fiber transmission, collaboration with researchers at the Chalmers University of Technology Fiber-Optic Communication Laboratory is proposed. The collaboration between Purdue (micro-combs) and Chalmers (fiber communications) brings together expertise and facilities that are difficult to find at any single institution, giving potential for significant advances. The work proposed breaks new ground both in micro-comb development and in application to advanced communications. In terms of micro-combs, most work focuses on devices characterized by anomalous group velocity dispersion, for which a well-known instability can initiate comb formation. However, interactions between transverse modes of the waveguides utilized often hinders formation of coherent, low noise combs. Here an alternate approach, which relies on devices formed from normal dispersion waveguides and exploiting different comb generation physics, is proposed. Recent work at Purdue has shown that for such devices, mode interactions can be beneficial in initiating combs and steering them to coherence. A novel microresonator structure which uses thermo-optic heaters to control mode interactions and facilitate comb initiation is proposed. The thermo-optic heaters also enable frequency tuning of the comb; the current proposal will seek to obtain detailed understanding. By developing micro-combs that can be tuned and matched in frequency, the project seeks to demonstrate for the first time micro-combs functioning as a coherent transceiver pair for communications at aggregate rates exceeding 1 Tb/s.