Project: Chip scale optical frequency combs based on planar micro resonators

Background information:_x000D_Optical frequency combs have in the past decade transcended from a laboratory tool to a commercial product, which is finding increasing use in metrology laboratories, university setting and also industrial applications. The key underlying technology is the use of femtosecond mode locked lasers to provide equidistant frequency markers. An entirely different and original approach – a disruptive technology - was demonstrated in 2007 based on the use of optical micro cavities at the Max Planck Institute of Quantum Optics (MPQ), in the Independent Junior Research Group (lead by Tobias Kippenberg) who is now appointed Assistant Professor at the Swiss Federal Institute of Technology (EPFL) in Lausanne. Remarkably, as discovered at the MPQ in 2007, the interaction of a strong CW pump laser with the modes of an ultra-high Q micro-resonators gives rise to a broad comb-like emission spectrum which can extend over even a full octave around the 1550-nm band. The process underlying the formation of the frequency comb is the nonlinearity of glass itself: due to the intensity dependent refractive index (Kerr nonlinearity) two pump photons can be annihilated and give rise to a frequency up and down shifted pair of photons. This process can cascade and thereby lead to the formation of a comb, whereby the energy conserving nature of parametric process ensure equidistance of all teeth of the comb. Since then many proof of principle experiments have been carried out that by now establish these micro-combs as a high potential new technology. This approach has several distinct advantages. First, the novel – monolithic – approach allows a significant reduction in size, complexity and power consumption of optical frequency combs and enables for the first time a monolithic geometry. Even more important, the comb provides access to the previously unattainable high repetition rates (>40 GHz). The potential application in both academia and in industry of this novel type of monolithic combs are diverse. The mode spacing in the 100 GHz range along with high power (milli-Watt per mode) make them promising for application in telecommunications as a channel generator. The large mode spacing is also a key prerequisite for the recently demonstrated calibration of astrophysical Echelle spectrometers or optical spectrum analyzers used in Astronomy and elsewhere. Moreover, the fact that a single CW laser can be converted into a broad frequency comb also at mid IR wavelength where previously no good broad band sources have been available is opening new fields of applications in molecular spectroscopy. This in turn is expected to revolutionize medical diagnostic and environmental trace gas detection. In addition, techniques such as multi-heterodyne spectroscopy, which rely on two optical frequency combs, can be ideally realized using microresonator based comb generators, due to the low cost of creating two compact sources._x000D__x000D_Project goals:_x000D_The objective of the research project - which is a collaboration among the Ps and inventors of this technology at the EPFL (Prof. Dr. Kippenberg, formerly located at the MPQ in Garching, Germany) and Menlo Systems GmbH (Dr. Holzwarth) - is to turn chip based frequency comb generators into a commercially viable product and to address several key scientific and technological challenges which are yet to be solved. At the end of the project duration the objective is to have a fully packaged planar comb generator that has no moveable parts and does not require any active nanopositioning, as presently used in laboratory proof of concept experiments. This will represent a major breakthrough for the next generation of optical frequency combs. Chip based combs have - in strong contrast to current laser based combs - the potential to be manufatured in high quantities and at modest prices by making use of semiconductor industry infrastructure. At the same time new wavelength ranges in the mid infra red spectral region will be accessible, opening the path for medical and environmental spectroscopic mass applications. _x000D_To achieve this it is planned to develop fully self referenced optical frequency combs based on planar on chip high Q microresonators with integrated SiN waveguides._x000D__x000D__x000D_Consortium : _x000D_The ChipComb consortium is formed around an industrial P, Menlo Systems GmbH, the world leader and pioneer in optical frequency comb sources for metrology. The academic P is located at the Swiss Federal Institute of Technology and is is carrying out research on the applications of microresonators in frequency metrology, biomolecule sensing and the study of optomechanics, i.e. radiation pressure phenomena between light and mechanics. From an industrial-academic perspective, the aim of this proposal is to build an lasting and mutually beneficial research-industry research collaboration between the two Ps Menlo Systems GmbH and EPFL.

Acronym ChipComb (Reference Number: 6156)
Duration 01/08/2011 - 31/07/2014
Project Topic The consortiums aims at achieving a major technological leap by developing chip scale optical frequency combs for applications in frequency metrology as well as new emerging applications of molecular spectoscopy in medical diagnostic and environmental trace gas detection.
Project Results
(after finalisation)
Within the chip comb project, Menlo Systems and EPFL mad a huge step towards chip based micro resonator frequency combs. For the first time, Kerr combs have been demonstrated using a lithographically defined, chip based structure. Dispersion modeling and control via resonator geometry and fabrication techniques has been demonstrated. Combs with 2/3rds of an octave spanning at repetition rates between 40 and 200 GHz were obtained. A very generic noise process in the formation of Kerr combs has been discovered and analyzed. Unfortunately it was limiting the Kerr comb performance througout the duration of the project. Only in the last weeks of the project, a low noise soliton state - known from different plattforms like crystalline resonators, was also demonstrated to exist in chip based resonators. This regime will pave the road to low noise, fully phase locked Kerr combs from chips, a goal still to be demonstrated on this plattform in the laboratory._x000D_Besides the fundamental research aspects, where this project was a full succes for both Ps, significant technological steps were made as well._x000D_A high power, cw Thulium fiber laser system was developend by Menlo and is used by EPFL for comb stabilization. Packaging chip scale resonators was investigated using multiple aproaches with direct fiber coupling, taperede fiber lens coupling, miniature aspheric lenses coupling while glueing or soldering. These thechniques are ready for implementation._x000D__x000D_As risk mitigation, Menlo also successfully packaged a crystalline microresonator in a hermetic sealing. _x000D_This device was integrated in a 19 " housing, where all necessary optics and electronic devices for seeding a solitonic Kerr comb state are included and interfaced. Direct stabilization of the mode spacing of a solitonic state with 10 GHz repetition rate was achieved._x000D_
Network Eurostars
Call Eurostars Cut-Off 5

Project partner

Number Name Role Country
2 Menlo Systems GmbH Coordinator Germany
2 Ecole Polytechnique Federale de Lausanne Partner Switzerland