Silicon-on-Insulator based Integrated Optical Frequency Combs for Microwave, THz and Optics

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The precision, versatility and broad bandwidth of frequency combs are the basis of many different applications from the microwave via the millimeter and THz up to the optical range of the electromagnetic spectrum. In principle, every mode locked laser (MLL) produces a frequency comb spectrum. Thus, classical comb generation techniques rely on high power MLLs generating a supercontinuum in optical fibers. By self referencing, these broad combs, spanning an octave, can be stabilized very precisely. A very interesting source of frequency combs are mode locked, erbium doped femtosecond fiber lasers since they are low cost, robust and readily available. However, even a very compact fiber laser has dimensions of typically 12 x 20 x 7 cm³ (FemtoFerb 1560 from Toptica), much too big for applications like integrated all optical sampling or lightweight spectroscopes for instance. Recently it has been shown that very compact high Q cavities can generate very broadband frequency combs by the parametric effect of cascaded four wave mixing (FWM). Following these successes the DARPA announced a new research field for the development of chip scale optical frequency combs. The aim of many of these projects, however, is the generation of frequency combs which are as broad as possible. Due to the relatively high free spectral range and the limited tunability of these combs, they cannot be used for many different applications. In contrast to this, here we want to investigate integrated frequency comb sources for applications in the frequency ranges of microwave, THz and Optics. All of these applications do not need a self referenced comb. Thus, octave spanning combs will not be investigated. The aim of this project, instead, is to get tunable and stabilized, CMOS compatible, integrated comb sources for applications in fields like metrology, all optical sampling and radio over fiber and the investigation if and how the whole systems could be integrated in a possible future step. If successful, the project could pave the way to lightweight devices for microwave, THz and optical spectroscopy, for integrated devices for all optical sampling with sampling rates of several hundred Gsps and integrated sources for THz and microwave generation for radio over fiber applications.