Abstract
The ability of using integrated photonics to scale multiple optical components on a single monolithic chip offers key advantages to create miniature light-controlling chips. Numerous scaled optical components have been already demonstrated. However, present integrated photonic circuits are still rudimentary compared to the complexity of today’s electronic circuits. Slow light propagation in nanostructured materials is a key component for realizing chip-integrated photonic devices controlling the relative phase of light and enhancing optical nonlinearities. We present an experimental record high group-index-bandwidth product (GBP) of 0.47 over a 17.7 nm bandwidth in genetically optimized coupled-cavity-waveguides (CCWs) formed by L3 photonic crystal cavities. Our structures were realized in silicon-on-insulator slabs integrating up to 800 coupled cavities, and characterized by transmission, Fourier-space imaging of mode dispersion, and Mach-Zehnder interferometry.
Highlights
The engineering of frequency dispersion in light-guiding photonic crystal (PC) structures is one of the most promising research avenues in the field of slow-light[1,2,3,4]
We report on the experimental demonstration of a record high group-index-bandwidth product (GBP) in silicon-based coupled-cavity waveguides (CCWs)[6,7,8,9,10,11] operating at telecom wavelengths
The first-neighbor coupling must be kept small, in order to minimize the influence of higher-order cavity modes, so that the guided band mainly arises from the coupling between the fundamental modes of each single photonic crystal cavities13 (PCCs)
Summary
Our results rely on novel CCW designs, optimized using a genetic algorithm, and refined nanofabrication processes[12]. (The folded band representation, indicated by the dashed line, helps to model forward and backward propagating modes measured via Fourier space imaging, as showed hereafter.) Our numerical simulations demonstrated a GBP value of 0.47, over an 18.0 nm bandwidth, for the set of parameters (Δr1, Δr2, Δr3, Δx) = (−0.0385a, −0.0279a, −0.0759a, 0.1642a). The prediction of the GME model for the same device gave 〈ng〉 = 37 over an operational bandwidth of Δλ = 18.0 nm To our knowledge, this is the highest experimental GBP ever reported in PC-based slow light devices. To explore the space of parameters around this optimal design we fabricated three additional series of CCW devices For these devices, we measured a higher group index, at the expense of consistently lower GBP values, as detailed in the Supplementary Section S3. High resolution spectrometers integrated in chip-scale platforms can find transformative applications in chemical and biosensing
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