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Register a new userEnhanced optical nonlinearities in air-cladding silicon pedestal waveguides
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The third-order optical nonlinearity in optical waveguides has found applications in optical switching, optical wavelength conversion, optical frequency comb generation, and ultrafast optical signal processing. The development of an integrated waveguide platform with a high nonlinearity is therefore important for nonlinear integrated photonics. Here, we report the observation of an enhancement in the nonlinearity of an air-cladding silicon pedestal waveguide. We observe enhanced nonlinear spectral broadening compared to a conventional silicon-on-insulator waveguide. At the center wavelength of 1555 nm, the nonlinear-index coefficient of air-cladding silicon pedestal waveguide is measured to be about 5% larger than that of a conventional silicon-on-insulator waveguide. We observe enhanced spectral broadening from self-phase modulation of an optical pulse in the pedestal waveguide. The interaction of light with the confined acoustic phonons in the pedestal structure gives rise to a larger nonlinear-index coefficient. The experimental results agree well with the theoretical models.
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In recent years we are witnessing a flourish in research aimed to facilitate alkali vapors in guided wave configurations. Owing to the significant reduction in device dimensions, the increase in density of states, the interaction with surfaces and primarily the high intensities carried along the structure, a rich world of light vapor interactions can be studied, and new functionalities, e.g. low power nonlinear light-matter interactions can be achieved. One immense remaining challenge is to study the effects of quantum coherence and shifts in such nano-scale waveguides, characterized by ultra-small mode areas and fast dynamics. Here, we construct a serpentine silicon-nitride wave guide, having atomic vapor as its cladding. The unprecedented mode volume of 5e-13 m^3 supported over a length of 17 mm is used to demonstrate efficient linear and non-linear spectroscopy. Fascinating and important phenomena such as van der Waals shifts, dynamical stark shifts, and coherent effects such as strong coupling (in the form of Autler Townes splitting) are all observed. The serpentine atomic cladding is a promising building block for a variety of light vapor experiments, as it offers a very small footprint, enables operation with relatively low density of atoms and extremely strong confinement of light and vapor. As such it may be used for important applications, such as all optical switching, frequency referencing, and magnetometry to name a few.
Four-wave mixing (FWM) is an important nonlinear optical phenomenon that underlines many of the discoveries and device applications since the laser was invented. Examples include parametric amplification, mode-locked pulses and frequency combs, and in the quantum optics regime, entangled-photon generation, squeezed-state production and optical transduction from the visible to infrared wavelengths. For quantum dot systems, the basic understanding of FWM is limited by the conventional investigation method, which concentrates on the FWM susceptibility measured with optical amplifiers. This paper addresses this weakness by performing laser experiments to account for all optical nonlinearities contributing to the FWM signal. Meanwhile, we gain valuable insight into the intricate interplay among optical nonlinearities. Using quantum dot lasers directly grown on silicon, we achieved FWM conversion efficiency sufficient to demonstrate self-mode-locking in a single-section laser diode, with sub-ps mode-locked pulse duration and kHz frequency-comb linewidth. A comparison with first-principles based multimode laser theory indicates measured FWM conversion efficiencies that are close to the theoretical limit. An advantage over earlier studies and crucial to confidence in the results are the quality and reproducibility of state-of-the-art quantum dot lasers. They make possible the detailed study of conversion efficiency over a broad parameter space, and the identification of the importance of p-doping. Systematic improvement based on our understanding of underlying physics will lead to transform limited performance and effective compensation of intrinsic and extrinsic effects, such as linewidth enhancement and background dispersion. The integration of FWM with lasing impacts numerous optoelectronic components used in telecom and datacom.
We present a detailed study of oscillating modes in a slab waveguide with air core and anisotropic metamaterial cladding. It is shown that, under specific dielectric configurations, slow and even stopped electromagnetic wave can be supported by such an air waveguide. We propose a linearly tapped waveguide structure that could lead the propagating light to a complete standstill. Both the theoretical analysis and the proposed waveguide have been validated by full-wave simulation based on finite-difference time-domain method.
We demonstrate a silicon nitride trench waveguide deposited with bowtie antennas for plasmonic enhanced optical trapping. The sub-micron silicon nitride trench waveguides were fabricated with conventional optical lithography in a low cost manner. The waveguides embrace not only low propagation loss and high nonlinearity, but also the inborn merits of combining micro-fluidic channel and waveguide together. Analyte contained in the trapezoidal trench channel can interact with the evanescent field from the waveguide beneath. The evanescent field can be further enhanced by plasmonic nanostructures. With the help of gold nano bowtie antennas, the studied waveguide shows outstanding trapping capability on 10 nm polystyrene nanoparticles. We show that the bowtie antennas can lead to 60-fold enhancement of electric field in the antenna gap. The optical trapping force on a nanoparticle is boosted by three orders of magnitude. A strong tendency shows the nanoparticle is likely to move to the high field strength region, exhibiting the trapping capability of the antenna. Gradient force in vertical direction is calculation by using a point-like dipole assumption, and the analytical solution matches the full-wave simulation well. The investigation indicates that nanostructure patterned silicon nitride trench waveguide is suitable for optical trapping and nanoparticle sensing applications.
Bulk materials possessing a relative electric permittivity $varepsilon$ close to zero exhibit giant Kerr nonlinearities. However, harnessing this response in guided-wave geometries is not straightforward, due to the extreme and counter-intuitive properties of epsilon-near-zero materials. Here we investigate, through rigorous calculations of the Kerr nonlinear coefficient, how the remarkable nonlinear properties of such materials can be exploited in several different types of structures, including bulk films, plasmonic nanowires, and metal nanoapertures. We find the largest Kerr nonlinear response when both the modal area and the group velocity are simultaneously minimized, corresponding to omnidirectional field enhancement. The physical insights developed will be key for understanding and engineering nonlinear nanophotonic systems with extreme nonlinearities and point to new design paradigms.
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