Lower bound for the spatial extent of localized modes in photonic-crystal waveguides with small random imperfections

Light localization due to random imperfections in periodic media is paramount in photonics research. The group index is known to be a key parameter for localization near photonic band edges, since small group velocities reinforce light interaction with imperfections. Here, we show that the size of the smallest localized mode that is formed at the band edge of a one-dimensional periodic medium is driven instead by the effective photon mass, i.e. the flatness of the dispersion curve. Our theoretical prediction is supported by numerical simulations, which reveal that photonic-crystal waveguides can exhibit surprisingly small localized modes, much smaller than those observed in Bragg stacks thanks to their larger effective photon mass. This possibility is demonstrated experimentally with a photonic-crystal waveguide fabricated without any intentional disorder, for which near-field measurements allow us to distinctly observe a wavelength-scale localized mode despite the smallness (∼1/1000 of a wavelength) of the fabrication imperfections

Ultracompact (3 μm) silicon slow-light optical modulator

This work is part of the research program of the Stichting voor Fundamenteel Onderzoek der Materie (FOM), which is financially supported by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO). The work is also supported by the research programs NanonextNL and MEMPHIS, funded by the Dutch ministry of economic affairs. We also acknowledge financial support by the EPSRC through the “UK Silicon Photonics” grant.Wavelength-scale optical modulators are essential building blocks for future on-chip optical interconnects. Any modulator design is a trade-off between bandwidth, size and fabrication complexity, size being particularly important as it determines capacitance and actuation energy. Here, we demonstrate an interesting alternative that is only 3 mm long, only uses silicon on insulator (SOI) material and accommodates several nanometres of optical bandwidth at 1550 nm. The device is based on a photonic crystal waveguide: by combining the refractive index shift with slow-light enhanced absorption induced by free-carrier injection, we achieve an operation bandwidth that significantly exceeds the shift of the bandedge. We compare a 3 mm and an 80 mm long modulator and surprisingly, the shorter device outperforms the longer one. Despite its small size, the device achieves an optical bandwidth as broad as 7 nm for an extinction ratio of 10 dB, and modulation times ranging between 500 ps and 100 ps.Publisher PDFPeer reviewe

Edge-preserving regularization for quantitative reconstruction algorithms in microwave imaging

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Green light emission in silicon through slow-light enhanced third-harmonic generation in photonic-crystal waveguides

Slow light has attracted significant interest recently as a potential solution for optical delay lines and time-domain optical signal processing(1,2). Perhaps even more significant is the possibility of dramatically enhancing nonlinear optical effects(3,4) due to the spatial compression of optical energy(5-7). Two-dimensional silicon photonic-crystal waveguides have proven to be a powerful platform for realizing slow light, being compatible with on-chip integration and offering wide-bandwidth and dispersion-free propagation(2). Here, we report the slow-light enhancement of a nonlinear optical process in a two-dimensional silicon photonic-crystal waveguide. We observe visible third-harmonic-generation at a wavelength of 520 nm with only a few watts of peak power, and demonstrate strong third-harmonic-generation enhancement due to the reduced group velocity of the near-infrared pump signal. This demonstrates yet another unexpected nonlinear function realized in a CMOS-compatible silicon waveguide

Increased rise time of electron temperature during adiabatic plasmon focusing

Decay of plasmons to hot carriers has recently attracted considerable interest for fundamental studies and applications in quantum plasmonics. Although plasmon-assisted hot carriers in metals have already enabled remarkable physical and chemical phenomena, much remains to be understood to engineer devices. Here, we present an analysis of the spatio-temporal dynamics of hot electrons in an emblematic plasmonic device, the adiabatic nanofocusing surface-plasmon taper. With femtosecond-resolution measurements, we confirm the extraordinary capability of plasmonic tapers to generate hot carriers by slowing down plasmons at the taper apex. The measurements also evidence a substantial increase of the " lifetime " of the electron gas temperature at the apex. This interesting effect is interpreted as resulting from an intricate heat flow at the apex. The ability to harness the " lifetime " of hot-carrier gases with nanoscale circuits may provide a multitude of applications, such as hot-spot management, nonequilibrium hot-carrier generation, sensing, and photovoltaics.Initiative d'excellence de l'Université de Bordeau