Chip-scale atomic wave-meter enabled by machine learning.

The quest for miniaturized optical wave-meters and spectrometers has accelerated the design of novel approaches in the field. Particularly, random spectrometers (RS) using the one-to-one correlation between the wavelength and an output random interference pattern emerged as a promising tool combining high spectral resolution and cost-effectiveness. Recently, a chip-scale platform for RS has been demonstrated with a markedly reduced footprint. Yet, despite the evident advantages of such modalities, they are very susceptible to environmental fluctuations and require an external calibration process. To address these challenges, we demonstrate a paradigm shift in the field, enabled by the integration of atomic vapor with a photonic chip and the use of a machine learning classification algorithm. Our approach provides a random wave-meter on chip device with accurate calibration and enhanced robustness against environmental fluctuations. The demonstrated device is expected to pave the way toward fully integrated spectrometers advancing the field of silicon photonics.

Spectrally Gated Microscopy (SGM) with Meta Optics for Parallel Three-Dimensional Imaging.

Volumetric imaging with high spatiotemporal resolution is of utmost importance for various applications ranging from aerospace and defense to real-time imaging of dynamic biological processes. To facilitate three-dimensional sectioning, current technology relies on mechanisms to reject light from adjacent out-of-focus planes either spatially or by other means. Yet, the combination of rapid acquisition time and high axial resolution is still elusive, motivating a persistent pursuit for emerging imaging approaches. Here we introduce and experimentally demonstrate a concept named spectrally gated microscopy (SGM), which enables a single-shot interrogation over the full axial dimension while maintaining a submicron sectioning resolution. SGM utilizes two important features enabled by flat optics (i.e., metalenses or diffractive lenses), namely, a short focal length and strong chromatic aberrations. Using SGM we demonstrate three-dimensional imaging of millimeter-scale samples while scanning only the lateral dimension, presenting a significant advantage over state-of-the-art technology.

A trade-off between speckle size and intensity enhancement of a focal point behind a scattering layer.

Focusing light through highly scattering materials by modifying the phase profile of the illuminating beam has attracted a great deal of attention in the past decade paving the way towards novel applications. Here we report on a tradeoff between two seemingly independent quantities of critical importance in the focusing process: the size of the focal point obtained behind a scattering medium and the maximum achievable intensity of such focal point. We theoretically derive and experimentally demonstrate the practical limits of intensity enhancement of the focal point and relate them to the intrinsic properties of the scattering phenomenon. We demonstrate that the intensity enhancement limitation becomes dominant when the focusing plane gets closer to the scattering layer thus limiting the ability to obtain tight focusing at high contrast, which has direct relevance for the many applications exploring scattering materials as a platform for high resolution focusing and imaging.

Brillouin micro-spectroscopy through aberrations via sensorless adaptive optics.

Brillouin spectroscopy is a powerful optical technique for non-contact viscoelastic characterizations which has recently found applications in three-dimensional mapping of biological samples. Brillouin spectroscopy performances are rapidly degraded by optical aberrations and have therefore been limited to homogenous transparent samples. In this work, we developed an adaptive optics (AO) configuration designed for Brillouin scattering spectroscopy to engineer the incident wavefront and correct for aberrations. Our configuration does not require direct wavefront sensing and the injection of a "guide-star"; hence, it can be implemented without the need for sample pre-treatment. We used our AO-Brillouin spectrometer in aberrated phantoms and biological samples and obtained improved precision and resolution of Brillouin spectral analysis; we demonstrated 2.5-fold enhancement in Brillouin signal strength and 1.4-fold improvement in axial resolution because of the correction of optical aberrations.

Adaptive optics in spectroscopy and densely labeled-fluorescence applications.

Adaptive optics systems have been integrated in many imaging modalities in order to correct for aberrations that are introduced by samples and optical elements. Usually, the optical system has access to a guide star (i.e., a point-like structure that is smaller than the diffraction limit). This guide star can be used as a beacon for adaptive optics enhancement. In contrast, for spectroscopy and densely-labeled fluorescent samples, the signal is diffused throughout the entire beam path and is not confined to a well-defined point-like structure. Here, we show analytically and experimentally that, in these scenarios, adaptive optics systems are expected to yield significantly lower signal enhancement than when a guide star is available. We discuss adaptive optics' performance degradation for different imaging modalities (e.g., confocal, multi-photon microscopy) and identify solutions to overcome low signal enhancements.

Diffraction-Limited Plenoptic Imaging with Correlated Light.

Traditional optical imaging faces an unavoidable trade-off between resolution and depth of field (DOF). To increase resolution, high numerical apertures (NAs) are needed, but the associated large angular uncertainty results in a limited range of depths that can be put in sharp focus. Plenoptic imaging was introduced a few years ago to remedy this trade-off. To this aim, plenoptic imaging reconstructs the path of light rays from the lens to the sensor. However, the improvement offered by standard plenoptic imaging is practical and not fundamental: The increased DOF leads to a proportional reduction of the resolution well above the diffraction limit imposed by the lens NA. In this Letter, we demonstrate that correlation measurements enable pushing plenoptic imaging to its fundamental limits of both resolution and DOF. Namely, we demonstrate maintaining the imaging resolution at the diffraction limit while increasing the depth of field by a factor of 7. Our results represent the theoretical and experimental basis for the effective development of promising applications of plenoptic imaging.

Integration of spectral coronagraphy within VIPA-based spectrometers for high extinction Brillouin imaging.

VIPA (virtually imaged phase array) spectrometers have enabled rapid Brillouin spectrum measurements and current designs of multi-stage VIPA spectrometers offer enough spectral extinction to probe transparent tissue, cells and biomaterials. However, in highly scattering media or in the presence of strong back-reflections, such as at interfaces between materials of different refractive indices, VIPA-based Brillouin spectral measurements are limited. While several approaches to address this issue have recently been pursued, important challenges remain. Here we have adapted the design of coronagraphs used for exosolar planet imaging to the spectral domain and integrated it in a double-stage VIPA spectrometer. We demonstrate that this yields an increase in extinction up to 20 dB, with nearly no added insertion loss. The power of this improvement is vividly demonstrated by Brillouin imaging close to reflecting interfaces without index matching or sample tilting.

Memory-effect based deconvolution microscopy for super-resolution imaging through scattering media.

High-resolution imaging through turbid media is a fundamental challenge of optical sciences that has attracted a lot of attention in recent years for its wide range of potential applications. Here, we demonstrate that the resolution of imaging systems looking behind a highly scattering medium can be improved below the diffraction-limit. To achieve this, we demonstrate a novel microscopy technique enabled by the optical memory effect that uses a deconvolution image processing and thus it does not require iterative focusing, scanning or phase retrieval procedures. We show that this newly established ability of direct imaging through turbid media provides fundamental and practical advantages such as three-dimensional refocusing and unambiguous object reconstruction.

Optical imaging through dynamic turbid media using the Fourier-domain shower-curtain effect.

Several phenomena have been recently exploited to circumvent scattering and have succeeded in imaging or focusing light through turbid layers. However, the requirement for the turbid medium to be steady during the imaging process remains a fundamental limitation of these methods. Here we introduce an optical imaging modality that overcomes this challenge by taking advantage of the so-called shower-curtain effect, adapted to the spatial-frequency domain via speckle correlography. We present high resolution imaging of objects hidden behind millimeter-thick tissue or dense lens cataracts. We demonstrate our imaging technique to be insensitive to rapid medium movements (> 5 m/s) beyond any biologically-relevant motion. Furthermore, we show this method can be extended to several contrast mechanisms and imaging configurations.

Trap and track: designing self-reporting porous Si photonic crystals for rapid bacteria detection.

The task of rapid detection and identification of bacteria remains a major challenge in both medicine and industry. This work introduces a new concept for the design of self-reporting optical structures that can detect and quantify bacteria in real-time. The sensor is based on a two-dimensional periodic structure of porous Si photonic crystals in which the pore size is adjusted to fit the target bacteria cells (Escherichia coli). Spontaneous bacteria capture within the pores induces measurable changes in the zero-order reflectivity spectrum collected from the periodic structure. Confocal laser microscopy and electron microscopy confirm that the Escherichia coli cells are individually imprisoned within the porous array. A simple model is suggested to correlate the optical readout and the bacteria concentration and its predictions are found to be in good agreement with experimental results. In addition, we demonstrate that sensing scheme can be easily modified to potentially allow monitoring of concentration, growth and physiological state of bacteria cells. This generic platform can be tailored to target different microorganisms by tuning the array periodicity and its surface chemistry for rapid and label-free detection outside the laboratory environment.