MXene-Nanoflakes-Enabled All-Optical Nonlinear Activation Function for On-Chip Photonic Deep Neural Networks.

2D metal carbides and nitrides (MXene) are promising material platforms for on-chip neural networks owing to their nonlinear saturable absorption effect. The localized surface plasmon resonances in metallic MXene nanoflakes may play an important role in enhancing the electromagnetic absorption; however, their contribution is not determined due to the lack of a precise understanding of its localized surface plasmon behavior. Here, a saturable absorber made of MXene thin film and a silicon waveguide with MXene flakes overlayer are developed to perform neuromorphic tasks. The proposed configurations are reconfigurable and can therefore be adjusted for various applications without the need to modify the physical structure of the proposed MXene-based activator configurations via tuning the wavelength of operation. The capability and feasibility of the obtained results of machine-learning applications are confirmed via handwritten digit classification task, with near 99% accuracy. These findings can guide the design of advanced ultrathin saturable absorption materials on a chip for a broad range of applications.

Green-Graphene Protective Overlayer on Optical Microfibers: Prolongs the Device Lifetime.

Optical microfibers find new applications in various fields of industry, which in turn require wear resistance, environmental friendliness and ease of use. However, optical microfibers are fragile. Here we report a new method to prolong the microfiber lifetime by modifying its surface with green-extracted graphene overlayers. Graphene films were obtained by dispergation of shungite mineral samples in an aqueous medium. For this, we tapered optical fibers and sculptured them with graphene films mixed with gold nanoparticles. We observed that due to the surface modification the lifetime and survivability of the microfiber increased 5 times, as compared to the bare microfiber. The embedded gold nanoparticles can also be utilized for enhanced sensitivity and other applications.

Overtone Spectroscopy for Sensing─Recent Advances and Perspectives.

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.

On-chip beam rotators, adiabatic mode converters, and waveplates through low-loss waveguides with variable cross-sections.

Photonics integrated circuitry would benefit considerably from the ability to arbitrarily control waveguide cross-sections with high precision and low loss, in order to provide more degrees of freedom in manipulating propagating light. Here, we report a new method for femtosecond laser writing of optical-fiber-compatible glass waveguides, namely spherical phase-induced multicore waveguide (SPIM-WG), which addresses this challenging task with three-dimensional on-chip light control. Fabricating in the heating regime with high scanning speed, precise deformation of cross-sections is still achievable along the waveguide, with shapes and sizes finely controllable of high resolution in both horizontal and vertical transversal directions. We observed that these waveguides have high refractive index contrast of 0.017, low propagation loss of 0.14 dB/cm, and very low coupling loss of 0.19 dB coupled from a single-mode fiber. SPIM-WG devices were easily fabricated that were able to perform on-chip beam rotation through varying angles, or manipulate the polarization state of propagating light for target wavelengths. We also demonstrated SPIM-WG mode converters that provide arbitrary adiabatic mode conversion with high efficiency between symmetric and asymmetric nonuniform modes; examples include circular, elliptical modes, and asymmetric modes from ppKTP (periodically poled potassium titanyl phosphate) waveguides which are generally applied in frequency conversion and quantum light sources. Created inside optical glass, these waveguides and devices have the capability to operate across ultra-broad bands from visible to infrared wavelengths. The compatibility with optical fiber also paves the way toward packaged photonic integrated circuitry, which usually needs input and output fiber connections.

Non-isolated sources of electromagnetic radiation by multipole decomposition for photonic quantum technologies on a chip with nanoscale apertures.

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.

Deflected Talbot-Mediated Overtone Spectroscopy in Near-Infrared as a Label-Free Sensor on a Chip.

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 N-methylaniline probe molecule. We design a perforated silicon rib waveguide and fabricate it by milling cylindrical inclusions through the waveguide core. The molecular signatures were monitored when waveguides are embedded in toxic N-methylaniline, experiencing a deflected Talbot effect. We observed that when the Talbot effect is deflected, the absorption lines in NIR are enhanced despite the weakly absorbing nature of the probe molecules. This new spectroscopic strategy can potentially be extended to detect other common toxic byproducts in a chip-scale label-free manner and to enhance the functionality of chemical monitoring.

Surface roughness-induced absorption acts as an ovarian cancer cells growth sensor-monitor.

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.

Si Nanostrip Optical Waveguide for On-Chip Broadband Molecular Overtone Spectroscopy in Near-Infrared.

The ability to probe the molecular fundamental or overtone (high harmonics) vibrations is fundamental to modern healthcare monitoring techniques and sensing technologies since it provides information about the molecular structure. However, since the absorption cross section of molecular vibration overtones is much smaller compared to the absorption cross section of fundamental vibrations, their detection is challenging. Here, a silicon nanostrip rib waveguide structure is proposed for label-free on-chip overtone spectroscopy in near-infrared (NIR). Utilizing the large refractive index contrast (Δ n > 2) between the silicon core of the waveguide and the silica substrate, a broadband NIR lightwave can be efficiently guided. We show that the sensitivity for chemical detection is increased by more than 3 orders of magnitude when compared to the evanescent-wave sensing predicted by the numerical model. This spectrometer distinguished several common organic liquids such as N-methylaniline and aniline precisely without any surface modification to the waveguide through the waveguide scanning over the absorption dips in the NIR transmission spectra. Planar NIR Si nanostrip waveguide is a compact sensor that can provide a platform for accurate chemical detection. Our NIR Si nanostrip rib waveguide device can enable the development of sensors for remote, on-site monitoring of chemicals.