Optical sensing with Anderson-localised light

We show that fabrication imperfections in silicon nitride photonic crystal waveguides can be used as a resource to efficiently confine light in the Anderson-localised regime and add functionalities to photonic devices. Our results prove that disorder-induced localisation of light can be utilised to realise an alternative class of high-quality optical sensors operating at room temperature. We measure wavelength shifts of optical resonances as large as 15.2 nm, more than 100 times the spectral linewidth of 0.15\,nm, for a refractive index change of about 0.38. By studying the temperature dependence of the optical properties of the system, we report wavelength shifts of up to about 2 nm and increases of more than a factor 2 in the quality factor of the cavity resonances, when going from room to cryogenic temperatures. Such a device can allow simultaneous sensing of both local contaminants and temperature variations, monitored by tens of optical resonances spontaneously appearing along a single photonic crystal waveguide. Our findings demonstrate the potential of Anderson-localised light in photonic crystals for scalable and efficient optical sensors operating in the visible and near-infrared range of wavelengths.Comment: 10 pages, 3 figure

GaAs droplet quantum dots with nanometer-thin capping layer for plasmonic applications

We report on the growth and optical characterisation of droplet GaAs quantum dots with extremely-thin (11 nm) capping layers. To achieve such result, an internal thermal heating step is introduced during the growth and its role in the morphological properties of the quantum dots obtained is investigated via scanning electron and atomic force microscopy. Photoluminescence measurements at cryogenic temperatures show optically stable, sharp and bright emission from single quantum dots, at near-infrared wavelengths. Given the quality of their optical properties and the proximity to the surface, such emitters are ideal candidates for the investigation of near field effects, like the coupling to plasmonic modes, in order to strongly control the directionality of the emission and/or the spontaneous emission rate, crucial parameters for quantum photonic applications.Comment: 1 pages, 3 figure

Optical sensing with Anderson-localised light

We show that fabrication imperfections in silicon nitride photonic crystal waveguides can be used as a resource to efficiently confine light in the Anderson-localised regime and add functionalities to photonic devices. Our results prove that disorder-induced localisation of light can be utilised to realise an alternative class of high-quality optical sensors operating at room temperature. We measure wavelength shifts of optical resonances as large as 15.2 nm, more than 100 times the spectral linewidth of 0.15 nm, for a refractive index change of about 0.38. By studying the temperature dependence of the optical properties of the system, we report wavelength shifts of up to about 2 nm and increases of more than a factor 2 in the quality factor of the cavity resonances, when going from room to cryogenic temperatures. Such a device can allow simultaneous sensing of both local contaminants and temperature variations, monitored by tens of optical resonances spontaneously appearing along a single photonic crystal waveguide. Our findings demonstrate the potential of Anderson-localised light in photonic crystals for scalable and efficient optical sensors operating in the visible and near-infrared range of wavelengths

Optical sensing with Anderson localized light

Optical sensing is of importance in a variety of applications [1]: it can permit the detection of hazardous/desired contaminants, monitor chemical reactions and provide quantitative analysis of processes [1] To this end, a range of devices have been developed, based on the confinement of light via plasmonic resonances and photonic crystal cavities. The former suffer from relatively broad resonances, the latter, while providing higher sensitivities thanks to the sharper resonances, are not scalable.In order to circumvent the problem of scalability we realize photonic crystal sensors that use fabrication imperfections as a resource to provide highly efficient light confinement [2].Photonic crystal waveguides confining light in the visible are characterized by means of confocal micro-photoluminescence spectroscopy. Isopropyl alcohol (IPA) is deposited onto the surface of a device: the local refractive index change (of 0.38) spectrally shifts the cavity resonances of as much as 15.2nm, for a resonance linewidth of 0.15nm. The shift is of more than 100 times the linewidth of the cavity and is fully reversible once the IPA evaporates [3].By studying the temperature dependence of the optical resonances, we show temperature sensing, improved light confinement at cryogenic temperatures and the potential of temperature tuning the spectral resonances for quantum optics experiments.Our results prove that Anderson localization of light can be used as a novel platform for high-quality optical sensing, benefitting from the sharp resonances proper to photonic crystal devices and the scalability provided by the use of fabrication imperfections as a resource to confine light. Each device also provides tens of optical resonances which could allow multiple sensor readings from a single device.[1] J. Hodgkinson et al., Meas. Sci. Technol. 24, 012004 (2013)[2] T. Crane et al., ACS Photonics 4, 2274 (2017)[3] O. Trojak et al., Appl. Phys. Lett. 111, 141103 (2017

Optical sensing with Anderson-localized light

We demonstrate optical sensing with Anderson-localized visible light on scalablesilicon nitride photonic crystal waveguides. For a refractive index change of ≈0.38, we measure 15.2 nm wavelength shifts of an optical resonance 0.15 nm broad

Metallic nano-rings for efficient, broadband light extraction from solid-state single-photon sources

Metallic nano-rings deposited on the sample surface, centered around single InAs/GaAs quantum dots, enhance the brightness of the emission up to ×20, further enhanced by ×10 by epoxy solid-immersion lenses, in a scalable broadband device

Anderson Localization of Visible Light on a Nanophotonic Chip

Technological advances allow the control of light at the nanoscale and to strongly enhance the light–matter interaction in highly engineered devices. Enhancing the light–matter interaction is needed for applications in research areas such as quantum technology, energy harvesting, sensing, and biophotonics. Here, we show that a different approach, based on the use of disorder, rather than the precise engineering of the devices, and fabrication imperfections as a resource, can allow the efficient trapping of visible light on a chip. We demonstrate, for the first time to our knowledge, Anderson localization of light at visible wavelengths in a nanophotonic chip. Remarkably, we prove that disorder-induced localization is more efficient in confining visible light than highly engineered optical cavities, thus reversing the trend observed so far. We measure light-confinement quality factors approaching 10 000 that are significantly higher than values previously reported in two-dimensional photonic crystal cavities. These measurements are well explained using a three-dimensional Bloch mode expansion technique, where we also extract the mode quality factors and effective mode volume distributions of the localized modes. Furthermore, by implementing a sensitive imaging technique, we directly visualize the localized modes and measure their spatial extension. Even though the position where the cavities appear is not controlled, given the multiple scattering process at the basis of their formation, we are able to locate with nanometer-scale accuracy the position of the optical cavities. This is important for the deterministic coupling of emitters to the disorder-induced optical cavities and for assessing light localization. Our results show the potential of disorder as a novel resource for the efficient confinement of light and for the enhancement of the light–matter interaction in the visible range of wavelengths