On the spectral response of a taiji-CROW device.

Physical systems with topological properties are robust against disorder. However, implementing them in integrated photonic devices is challenging because of the various fabrication imperfections and/or limitations that affect the spectral response of their building blocks. One such feature is strong backscattering due to the surface wall roughness of the waveguides, which can flip the propagating modes to counterpropagating modes and destroy the desired topological behavior. Here, we report a study on modeling, designing and testing an integrated photonic structure based on a sequence of two taiji microresonators coupled with a middle link microresonator (a taiji-CROW device, where CROW stands for coupled resonator optical waveguides). Our study provides design constraints to preserve the ideal operation of the structure by quantifying a minimum ratio between the coupling coefficients and the backscattering coefficients. This ratio is valuable to avoid surface roughness problems in designing topological integrated photonic devices based on arrays of microresonators.

Influence of the bus waveguide on the linear and nonlinear response of a taiji microresonator.

We study the linear and nonlinear response of a unidirectional reflector where a nonlinear breaking of the Lorentz reciprocity is observed. The device under test consists of a racetrack microresonator, with an embedded S-shaped waveguide, coupled to an external bus waveguide (BW). This geometry of the microresonator is known as "taiji" microresonator (TJMR). Here, we show that a full description of the device needs to consider also the role of the BW, which introduces (i) Fabry-Perot oscillations (FPOs) due to reflections at its facets, and (ii) asymmetric losses, which depend on the actual position of the TJMR. At sufficiently low powers the asymmetric loss does not affect the unidirectional behavior, but the FP interference fringes can cancel the effect of the S-shaped waveguide. However, at high input power, both the asymmetric loss and the FPOs contribute to the redistribution of energy between counterpropagating modes within the TJMR. This strongly modifies the nonlinear response, giving rise to counter-intuitive features where, due to the FP effect and the asymmetric losses, the BW properties can determine the violation of the Lorentz reciprocity and, in particular, the difference between the transmittance in the two directions of excitation.

Reservoir computing based on a silicon microring and time multiplexing for binary and analog operations.

Photonic implementations of reservoir computing (RC) promise to reach ultra-high bandwidth of operation with moderate training efforts. Several optoelectronic demonstrations reported state of the art performances for hard tasks as speech recognition, object classification and time series prediction. Scaling these systems in space and time faces challenges in control complexity, size and power demand, which can be relieved by integrated optical solutions. Silicon photonics can be the disruptive technology to achieve this goal. However, the experimental demonstrations have been so far focused on spatially distributed reservoirs, where the massive use of splitters/combiners and the interconnection loss limits the number of nodes. Here, we propose and validate an all optical RC scheme based on a silicon microring (MR) and time multiplexing. The input layer is encoded in the intensity of a pump beam, which is nonlinearly transferred to the free carrier concentration in the MR and imprinted on a secondary probe. We harness the free carrier dynamics to create a chain-like reservoir topology with 50 virtual nodes. We give proof of concept demonstrations of RC by solving two nontrivial tasks: the delayed XOR and the classification of Iris flowers. This forms the basic building block from which larger hybrid spatio-temporal reservoirs with thousands of nodes can be realized with a limited set of resources.

"Less pain with more gain"-Managing wound-related pain with cannabis-based medicines.

Wound-related pain poses a serious challenge for patients and physicians. It is a complex pathophysiologic construct that may be stratified, from the patient's perspective, into baseline pain and breakthrough pain. The current paradigm for treating wound related pain involves the overuse of opioids and other co-analgesics with little regard for breakthrough pain. These standard medications have a propensity for deleterious side effects while some of them inhibit wound healing, effectively perpetuating the wound and the related pain. In particular, the overuse of opioids is a contributor to the global opioid crisis. It is evident that a new paradigm needs to be considered. Cannabis-based medicines are a prominent prospect under investigation for their potential to reduce dosages of status quo analgesics while effectively reducing pain. The authors propose a new paradigm that emphasizes the use of Cannabis-Based Medicines, delivered through multiple routes, while recommending the need for more foundational scientific investigation into mechanisms, and clinical controlled trials to determine optimal combinations, dosages, and protocols.

Optical properties of organic/inorganic perovskite microcrystals through the characterization of Fabry-Pérot resonances.

A precise knowledge of the optical properties, specifically the refractive index, of organic/inorganic perovskites, is essential for pushing forward the performance of the current photovoltaic devices that are being developed from these materials. Here we show a robust method for determining the real and the imaginary part of the refractive index of MAPbBr3 thin films and micrometer size single crystals with planar geometry. The simultaneous fit of both the optical transmittance and the photoluminescence spectra to theoretical models defines unambiguously the refractive index and the crystal thickness. Because the method relies on the optical resonance phenomenon occurring in these microstructures, it can be used to further develop optical microcavities from perovskites or from other optical materials.