Polariton Condensation in Gap-Confined States of Photonic Crystal Waveguides

The development of patterned multiquantum well heterostructures in GaAs/AlGaAs waveguides has recently made it possible to achieve exciton-polariton condensation in a topologically protected bound state in the continuum (BIC). Polariton condensation was shown to occur above a saddle point of the two-dimensional polariton dispersion in a one-dimensional photonic crystal waveguide. A rigorous analysis of the condensation phenomenon in these systems, as well as the role of the BIC, is still missing. In the present Letter, we theoretically and experimentally fill this gap by showing that polariton confinement resulting from the negative effective mass and the photonic energy gap in the dispersion play a key role in enhancing the relaxation toward the condensed state. In fact, our results show that low-threshold polariton condensation is achieved within the effective trap created by the exciting laser spot, regardless of whether the resulting confined mode is long-lived (polariton BIC) or short-lived (lossy mode). In both cases, the spatial quantization of the polariton condensate and the threshold differences associated to the corresponding state lifetime are measured and characterized. For a given negative mass, a slightly lower condensation threshold from the polariton BIC mode is found and associated to its reduced radiative losses, as compared to the lossy one.

All-silicon quantum light source by embedding an atomic emissive center in a nanophotonic cavity

Silicon is the most scalable optoelectronic material but has suffered from its inability to generate directly and efficiently classical or quantum light on-chip. Scaling and integration are the most fundamental challenges facing quantum science and technology. We report an all-silicon quantum light source based on a single atomic emissive center embedded in a silicon-based nanophotonic cavity. We observe a more than 30-fold enhancement of luminescence, a near-unity atom-cavity coupling efficiency, and an 8-fold acceleration of the emission from the all-silicon quantum emissive center. Our work opens immediate avenues for large-scale integrated cavity quantum electrodynamics and quantum light-matter interfaces with applications in quantum communication and networking, sensing, imaging, and computing.

Scalable nanophotonic neural probes for multicolor and on-demand light delivery in brain tissue

Neural probes arein vivobrain-invasive devices that record and manipulate neural circuits using electricity, light, or drugs. The capability to shine distinct wavelengths and control their respective output locations for activation or deactivation of specific groups of neurons is desirable but remains unachieved. Here, we discuss our probe's capability to deliver two independently controllable wavelengths (450 and 655 nm) in the location(s) of interest using nanophotonic directional couplers and ring resonators. These nanophotonics are scalable to dozens of outputs without significantly increasing the device's lateral dimensions. Furthermore, they are entirely passive and thus do not require electrical input that results in heat generation. Besides, we integrate a high number of electrodes for a simultaneous neural activity readout. Thus, we overcome the challenges associated with multicolor illumination for neural devices by exploiting the capability of miniaturizable, passive probes to deliver two different frequencies in several areas of interest. These devices open the path towards investigating thein vivoelectrical signal propagation under the individual or simultaneous activation or inhibition of distinct brain regions.

Spontaneous Magnetic Superdomain Wall Fluctuations in an Artificial Antiferromagnet

Collective dynamics often play an important role in determining the stability of ground states for both naturally occurring materials and metamaterials. We studied the temperature dependent dynamics of antiferromagnetically ordered superdomains in a square artificial spin lattice using soft x-ray photon correlation spectroscopy. We observed an exponential slowing down of superdomain wall motion below the antiferromagnetic onset temperature, similar to the behavior of typical bulk antiferromagnets. Using a continuous time random walk model we show that these superdomain walls undergo low-temperature ballistic and high-temperature diffusive motions.

Combination of a spectrometer-on-chip and an array of Young's interferometers for laser spectrum monitoring

This Letter presents the design and experimental results for an on-chip photonic device for laser spectrum monitoring that combines a nanospectrometer and an array of Young's interferometers. The array of Young's interferometers and the spectrometer measure the width and wavelength of a spectrum in visible light, respectively. The accuracy of spectral width measurements is around 10% for FWHM higher than 2.5 pm. The spectrometer-on-chip is based on a digital planar hologram, and provides a resolution around 145 pm within the spectral range of 719-861 nm (142 nm bandwidth). The performance of the device is demonstrated for distinguishing between the single- and two-longitudinal mode operation of a fiber Bragg grating laser diode with 23 pm mode separation.

Obtaining nanoimprint template gratings with 10 nm half-pitch by atomic layer deposition enabled spacer double patterning

A strategy for fabricating nanoimprint templates with sub-10 nm line and 20 nm pitch gratings is demonstrated, by combining electron beam lithography and atomic layer deposition. This is achieved through pitch division using a spacer double-patterning technique. The nanostructures are then replicated using step-and-repeat ultra-violet assisted nanoimprint lithography.

Multiband wavelength demultiplexer based on digital planar holography for on-chip spectroscopy applications

A novel type of multiband wavelength demultiplexer for on-chip spectroscopy applications is proposed, and first results of the device fabrication and characterization are reported. The devices are based on computer-designed digital planar holograms, which involve millions of lines specifically located and oriented in order to direct output light into designed focal channels according to the wavelength. Devices operate in four individual bandwidths within the visible range (477.2-478.0 nm, 528.8-529.9 nm, 586.4-587.7 nm, 628.9-630.4 nm) with 96 channels and spectral channel spacing down to 0.0375  nm/channel.

Single digit nanofabrication by step-and-repeat nanoimprint lithography

A novel strategy for fabricating nanoimprint templates with sub-10 nm patterns is demonstrated by combining electron beam lithography and atomic layer deposition. Nanostructures are replicated by step-and-repeat nanoimprint lithography and successfully transferred into functional material with high fidelity. The process extends the capacity of step-and-repeat nanoimprint lithography as a single digit nanofabrication method. Using the ALD process for feature shrinkage, we identify a size dependent deposition rate.

Nonperturbative visualization of nanoscale plasmonic field distributions via photon localization microscopy

We demonstrate the nonperturbative use of diffraction-limited optics and photon localization microscopy to visualize the controlled nanoscale shifts of zeptoliter mode volumes within plasmonic nanostructures. Unlike tip- or coating-based methods for mapping near fields, these measurements do not affect the electromagnetic properties of the structure being investigated. We quantify the local field manipulation capabilities of asymmetric bowtie antennas, in agreement with theoretical calculations. The photon-limited localization accuracy of nanoscale mode positions is determined for many of the measured devices to be within a 95% confidence interval of +/-2.5 nm. This accuracy also enables us to characterize the effects of nm-scale fabrication irregularities on local plasmonic mode distributions.

Step and repeat UV nanoimprint lithography on pre-spin coated resist film: a promising route for fabricating nanodevices

A step and repeat UV nanoimprint lithography process on pre-spin coated resist film is demonstrated for patterning a large area with features sizes down to sub-15 nm. The high fidelity between the template and imprinted structures is verified with a difference in their line edge roughness of less than 0.5 nm (3σ deviation value). The imprinted pattern's residual layer is well controlled to allow direct pattern transfer from the resist into functional materials with very high resolution. The process is suitable for fabricating numerous nanodevices.

Manipulating nanoscale light fields with the asymmetric bowtie nano-colorsorter

We present a class of devices called Asymmetric Bowtie nano-Colorsorters. These devices are specifically engineered to not only capture and confine optical fields, but also to spectrally filter and steer them while maintaining nanoscale field distributions. We show that spectral properties and localized spatial mode distributions can be readily tuned by controlled asymmetry. Nano-Colorsorters can control light's spatial and spectral distributions at the nanoscale and thus significantly impact applications ranging from broadband light harvesting to ultrafast wavelength-selective photodetection.

Self-collimation of light over millimeter-scale distance in a quasi-zero-average-index metamaterial

Inspired by the concept of complementary media, we experimentally demonstrate that an engineered metamaterial made of alternating, stripe layers of negatively refracting (photonic crystals) and positively refracting (air) materials strongly collimates a beam of near-infrared light. This quasi-zero-average-index metamaterial fully preserves the beam spot size throughout the sample for a light beam traveling through the metamaterial a distance of 2 mm-more than 1000 times the input wavelength lambda=1.55 microm. These results demonstrate the first explicit experimental verification of optical antimatter as proposed by Pendry and Ramakrishna [J. Pendry and S. Ramakrishna, J. Phys. Condens. Matter 15, 6345 (2003)10.1088/0953-8984/15/37/004], using two complementary media in which each n(eff)=-1 layer appears to annihilate an equal thickness layer of air.