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In this perspective, we report an opinion on overtone spectroscopy for sensing and discuss the nature of the opportunities perceived for specialists. New spectroscopic strategies can potentially be extended to detect other common toxic byproducts in a chip-scale label-free manner and to enhance the functionality of chemical and biological monitoring. Nevertheless, the full potential of overtone spectroscopy is not yet exhausted, challenges must be overcome, and new avenues await. Within this Perspective, we look at where the field currently stands, highlight several successful examples of overtone spectroscopy based sensors and detectors, and ask what it will take to advance current state-of-the-art technology. It is our intention to point out some potential blind spots and to inspire further developments

The creation of single photon sources on a chip is a mid-term milestone on the road to chip-scale quantum computing. An in-depth understanding of the extended multipole decomposition of non-isolated sources of electromagnetic radiation is not only relevant for a microscopic description of fundamental phenomena, such as light propagation in a medium, but also for emerging applications such as single-photon sources. To design single photon emitters on a chip, we consider a ridge dielectric waveguide perturbed with a cylindrical inclusion. For this, we expanded classical multipole decomposition that allows simplifying and interpreting complex optical interactions in an intuitive manner to make it suitable for analyzing light-matter interactions with non-isolated objects that are parts of a larger network, e.g. individual components such as a single photon source of an optical chip. It is shown that our formalism can be used to design single photon sources on a chip.

On-chip nanophotonic devices are a class of devices capable of controlling light on a chip to realize performance advantages over ordinary building blocks of integrated photonics. These ultra-fast and low-power nanoscale optoelectronic devices are aimed at high-performance computing, chemical, and biological sensing technologies, energy-efficient lighting, environmental monitoring and more. They are increasingly becoming an attractive building block in a variety of systems, which is attributed to their unique features of large evanescent field, compactness, and most importantly their ability to be configured according to the required application. This review summarizes recent advances of integrated nanophotonic devices and their demonstrated applications, including but not limited to, mid-infrared and overtone spectroscopy, all-optical processing on a chip, logic gates on a chip, and cryptography on a chip. The reviewed devices open up a new chapter in on-chip nanophotonics and enable the application of optical waveguides in a variety of optical systems, thus are aimed at accelerating the transition of nanophotonics from academia to the industry.

Rapid, sensitive, and reliable detection of aromatic amines, toxic manufacturing byproducts, has been previously achieved with molecular vibrations in the mid-infrared (Mid-IR) region. However, Mid-IR spectroscopic tools are hampered by a need to prepare the samples and the sensor cost. Here, we develop an affordable label-free sensor on a chip, operating in near-infrared (NIR) for ultrasensitive detection of absorption line signatures based on molecular vibrations overtones of the aromatic amine

Advanced photonic tools may enable researchers and clinicians to visualize, track, control and manipulate biological processes at the single-cell level in space and time. Biological systems are complex and highly organized on both spatial and temporal levels. If we are to study, perturb, engineer or heal biological entities, we must be able to visualize key players in such systems and to track, control and manipulate them precisely and selectively. To achieve this goal, the engineering of non-destructive tools will allow us to interrogate and manipulate the function of proteins, pathways and cells for physicians, enabling the design of 'smart materials' that can direct and respond to biological processes on-demand. Among the potentially exploitable non-destructive tools, light-based actuation is particularly desirable, as it enables high spatial and temporal resolution, dosage control, minimal disturbance to biological systems and deep tissue penetration. Here, we overview existing approaches toward the engineering of light-activated tools for the interrogation and manipulation of single-cell processes, and list the types of studies and types of functions that can be controlled by light. Timely applications, such as studies of inflammation and of crossing brain barrier systems - via super-resolution imaging and optomechanical manipulation - are two representative examples of emerging applications so far never addressed., 34 pages, 9 figures, review. Advanced Photonics Research (2021)

Neural networks are one of the first major milestones in developing artificial intelligence systems. The utilisation of integrated photonics in neural networks offers a promising alternative approach to microelectronic and hybrid optical-electronic implementations due to improvements in computational speed and low energy consumption in machine-learning tasks. However, at present, most of the neural network hardware systems are still electronic-based due to a lack of optical realisation of the nonlinear activation function. Here, we experimentally demonstrate two novel approaches for implementing an all-optical neural nonlinear activation function based on utilising unique light-matter interactions in 2D Ti$_3$C$_2$T$_x$ (MXene) in the infrared (IR) range in two configurations: 1) a saturable absorber made of MXene thin film, and 2) a silicon waveguide with MXene flakes overlayer. These configurations may serve as nonlinear units in photonic neural networks, while their nonlinear transfer function can be flexibly designed to optimise the performance of different neuromorphic tasks, depending on the operating wavelength. The proposed configurations are reconfigurable and can therefore be adjusted for various applications without the need to modify the physical structure. We confirm the capability and feasibility of the obtained results in machine-learning applications via an Modified National Institute of Standards and Technology (MNIST) handwritten digit classifications task, with near 99% accuracy. Our developed concept for an all-optical neuron is expected to constitute a major step towards the realization of all-optically implemented deep neural networks., Comment: 30 pages (including supplementary information), 5 figures

We discover an unexpected enhancement of the absorption of near-infrared light by aromatic amine overtones on photonic microfibers sculptured with gold nanoparticles. The adsorbed nanoparticles make the near-infrared spectroscopy of aromatic amines on microfibers feasible despite the small absorption cross-section of the molecular vibration overtones. We demonstrate that in the presence of gold nanomediators, the absorption of light by weak overtone transitions in N-methylaniline as a model analyte is dramatically enhanced. We attribute this effect to the increase of the mean trajectory of light in a microfiber due to its resonant scattering on metallic nanoparticles. The spectrally integrated transmittance scales with the concentration of nanoparticles to the power 1/6—the phenomenon of diffusive propagation of light. Practical applications of the discovered effect will include the detection of aromatic amines for efficient treatment of metabolic disorders resulting from the amino acids deficiency, resea...

The figure of merit is proposed for all-dielectric waveguides for absorption overtone spectroscopy as the measure of probing efficiency of molecular overtones. It is defined as the power in the evanescent tail over the total power carried by the guided mode. The figure of merit was calculated for the proposed waveguide structures and then compared. We address each waveguide structure in probing overtones. We show that the figure of merit can be substantially increased due to the downscaling of the physical dimensions of the waveguide and microfiber. Such a configuration enables integration possibilities for ultrasensitive devices harnessing evanescent excitation of molecular overtones on miniature and portable chips.

Uncontrolled growth of ovarian cancer cells is the fifth leading cause of female cancer deaths since most ovarian cancer patients are diagnosed at an advanced stage of metastatic disease. Here, we report on the sensor for monitoring the cancer treatment efficiency in real-time. We measure the optical interaction between the evanescent fields of microfiber and ovarian cancer inter-cellular medium at different treatment stages. Spectral absorption signatures are correlated with optical micrographs and western blot tests. We found that the treatment of tumor cells with induces both cells growth arrest and alter the spectral lines in a dose-dependent manner. These observations are mediated by surface roughness out of silica glass material, form an essential step toward the development of early detection of response to cancer therapy.

Uncontrolled growth of ovarian cancer cells is the fifth leading cause of female cancer deaths. Here, we describe the role of scattering-induced absorption in monitoring the cancer treatment efficiency in real-time. We measure the optical interaction between the evanescent fields of microfiber and ovarian cancer inter-cellular medium at different treatment stages. By introducing the roughness of silica glass, we demonstrate that the treatment of tumor cells with GDC0032, a beta-sparing PI3K, induces both cells growth arrest and alter the spectral lines in a dose-dependent manner. The data support observed affected tumor cells with decrease in proliferation and their spatial distribution. Spectral absorption signatures are correlated with optical micrographs and western blot tests. These observations are mediated by surface scatterers out of silica glass material, form an essential step toward the development of early detection of response to cancer therapy.