Ultrabroadband Nonlinear Optics in Nanophotonic Periodically Poled Lithium Niobate Waveguides

Quasi-phasematched interactions in waveguides with quadratic nonlinearities enable highly efficient nonlinear frequency conversion. In this article, we demonstrate the first generation of devices that combine the dispersion-engineering available in nanophotonic waveguides with quasi-phasematched nonlinear interactions available in periodically poled lithium niobate (PPLN). This combination enables quasi-static interactions of femtosecond pulses, reducing the pulse energy requirements by several orders of magnitude, from picojoules to femtojoules. We experimentally demonstrate two effects associated with second harmonic generation. First, we observe efficient quasi-phasematched second harmonic generation with <100 fJ of pulse energy. Second, in the limit of strong phase-mismatch, we observe spectral broadening of both harmonics with as little as 2-pJ of pulse energy. These results lay a foundation for a new class of nonlinear devices, in which co-engineering of dispersion with quasi-phasematching enables efficient nonlinear optics at the femtojoule level

Frequency combs on chip for interferometry applications

Optical frequency combs have revolutionized the field of laser spectroscopy. A frequency comb is a type of laser that generates an array of equally spaced coherent laser lines. Indeed, the \ua0outstanding performance of frequency combs in terms of bandwidth and stability is readily attainable in bench-top systems. Integrated photonics offers a platform for the implementation of frequency combs relying on nonlinear optics processes.\ua0 This thesis explores the generation of chip-scale frequency combs based on supercontinuum and microcomb generation and its potential use for interferometry. This investigation covers the capabilities offered by supercontinuum generation in the normal dispersion regime. The spectral broadening is realized by pumping a straight waveguide with a short duration pulse meaning that the pump is a comb itself. Therefore, its performance in terms of coherence and the transferring of noise to the broadened spectra have been investigated. Microcombs can be generated\ua0 on a microresonator starting from a continuous wave laser. In this work, we study microcomb generation in the normal dispersion regime using a novel dual-cavity architecture.\ua0The appended papers describe the nonlinear processes involved in the microcomb generation. We have studied its capabilities in terms of spectral flatness and symmetry, together with the coherence attained on these combs. It is found that these capabilities make microcombs a suitable spectral sources for spectroscopy. Furthermore, the capabilities of different interferometry techniques are analyzed in terms of resolution, sensitivity and measurement time in order to perform on-chip dual-comb spectroscopy

Emerging applications of integrated optical microcombs for analogue RF and microwave photonic signal processing

We review new applications of integrated microcombs in RF and microwave photonic systems. We demonstrate a wide range of powerful functions including a photonic intensity high order and fractional differentiators, optical true time delays, advanced filters, RF channelizer and other functions, based on a Kerr optical comb generated by a compact integrated microring resonator, or microcomb. The microcomb is CMOS compatible and contains a large number of comb lines, which can serve as a high performance multiwavelength source for the transversal filter, thus greatly reduce the cost, size, and complexity of the system. The operation principle of these functions is theoretically analyzed, and experimental demonstrations are presented.Comment: 16 pages, 8 figures, 136 References. Photonics West 2018 invited paper, expanded version. arXiv admin note: substantial text overlap with arXiv:1710.00678, arXiv:1710.0861