Chip-scale optical frequency combs for near and mid-infrared
Optical frequency combs have revolutionized optical frequency metrology in just a few years. They have made it possible to directly count light field oscillations of several 100 million million cycles per second and they have been recognized and honored by the highest distinction possible in science: The 2005 Nobel-Prize to T.W. Hansch (MPQ Germany) and J. Hall (JILA, USA). Measuring optical frequencies is not only of critical importance in fundamental science and atomic clocks but moreover is of increasing importance in technology. Frequency combs have enabled advances in other areas, such as gas sensing, Fourier transform spectroscopy or range-finding and astronomy. However a major obstacle has been the lack of integration; it has been impossible to create compact on chip comb sources. The aim of this project is to build a planar optical frequency comb generator on a chip using CMOS compatible processing.
This project complements Nanotera projects IrSens and MIXSEL by targeting multi-wavelength sources not based on semiconductor based materials, but rather by nonlinear frequency conversion instead, which offers a significant reduction of cost and complexity and moreover enables generation of frequency combs. This project builds on the discovery of the principle investigator in 2007, who has demonstrated an entirely new way of generating combs, without making use of mode locked lasers. This principle is based on nonlinear light conversion in a high Q resonator. Building on the discovery of these new optical frequency comb generators, the advance which we seek to achieve is to develop an entirely integrated, octave spanning chip-scale frequency comb for use in high capacity telecommunications and middle infrared sensing.
While the generation principle has been demonstrated by the host in 2007, so far fully integrated comb generators have not yet matured and are in the development phase. No phase coherent octave spanning spectrum has yet been demonstrated, nor has the integration of waveguides been addressed. The objective of the proposal are linked to the premise that optical frequency combs will become essential building blocks in telecommunications and in other scientific and technological applications, once the present technological hurdles that present their on-chip integration have been removed. Micro-resonator based frequency combs may provide this exact solution and enable, compact, chip scale, power efficient and highly performant (in terms of repetition rate) devices that could find their way into high capacity telecommunication and other domains of telecommuncations and also mid-IR spectroscopy.
Concretely, this project will develop fully integrated nanophotonic waveguides and microresonators on the same silicon chip using SiN (and HfO2). Using atomic layer deposition (ALD) dispersion will be controlled and broadband frequency combs generated. The frequency noise will be investigated with the aim of generating octave spanning spectra that allow self-referencing. The overall objective is to create for the first time a phase coherent link from RF to optical on a chip as well as the demonstration of combs in the mid IR by pumping > 2 micron pump wavelength.
References
1. Del Haye, P., Arcizet, O., Schliesser, A., Holzwarth, R. & Kippenberg, T. J. Full Stabilization of a Microresonator Frequency Comb. Physical Review Letters 101 (2008).
2. Del Haye, P. et al. Optical frequency comb generation from a monolithic microresonator. Nature 450, 1214 (2007 ).
3. Del’Haye, P., Herr, T., Gavartin, E., Holzwarth, R. & Kippenberg, T. J. Octave Spanning Frequency Comb on a Chip. arXiv:0912.4890 (2009).
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