An analytical model of label-free nanoscale chemical imaging reveals avenues toward improved spatial resolution and sensitivity.

Atomic force microscopy-infrared spectroscopy (AFM-IR) is a photothermal scanning probe technique that combines nanoscale spatial resolution with the chemical analysis capability of mid-infrared spectroscopy. Using this hybrid technique, chemical identification down to the single molecule level has been demonstrated. However, the mechanism at the heart of AFM-IR, the transduction of local photothermal heating to cantilever deflection, is still not fully understood.

Evanescent wave quartz-enhanced photoacoustic spectroscopy employing a side-polished fiber for methane sensing.

We present an all-fiber-based laser gas analyzer (LGA) employing quartz-enhanced photoacoustic spectroscopy (QEPAS) and a side-polished fiber (SPF). The LGA comprises a custom quartz tuning fork (QTF) with 0.8 mm prong spacing, two acoustic micro-resonators (mR) located on either side of the prong spacing, and a single-mode fiber containing a 17 mm polished section passing through both mRs and QTF.

Micro-Ring Resonator Assisted Photothermal Spectroscopy of Water Vapor.

We demonstrated, for the first time, micro-ring resonator assisted photothermal spectroscopy measurement of a gas phase sample. The experiment used a telecoms wavelength probe laser that was coupled to a silicon nitride photonic integrated circuit using a fibre array. We excited the photothermal effect in the water vapor above the micro-ring using a 1395 nm diode laser.

Enhanced Fano resonances in a silicon nitride photonic crystal nanobeam-assisted micro ring resonator for dual telecom band operation.

Silicon-based Micro Ring Resonators (MRR) are a powerful tool for the realization of label free optical biosensors. The sharp edge of a Fano resonance in a Silicon Nitride (SiN) platform can boost photonic sensing applications based on MRRs. In this work, we demonstrate enhanced Fano resonance features for a SiN Micro Ring Resonator assisted by a Photonic Crystal Nanobeam (PhCN-MRR) operating in the TM-like mode at the O-band wavelengths.

Mid-Infrared Photothermal Spectroscopy for the Detection of Caffeine in Beverages.

Caffeine is the most widely consumed stimulant and is the subject of significant ongoing research and discussions due to its impact on human health. The industry's need to comply with country-specific food and beverage regulations underscores the importance of monitoring caffeine levels in commercial products. In this study, we propose an alternative technique for caffeine analysis that relies on mid-infrared laser-based photothermal spectroscopy (PTS).

Compact angled multimode interference duplexers for multi-gas sensing applications.

A compact, low-loss 2 × 1 angled-multi-mode-interference-based duplexer is proposed as an optical component for integrating several wavelengths with high coupling efficiency. The self-imaging principle in multimode waveguides is exploited to combine two target wavelengths, corresponding to distinctive absorption lines of important trace gases. The device performance has been numerically enhanced by engineering the geometrical parameters, offering trade-offs in coupling efficiency ratios.

Highly efficient and selective integrated directional couplers for multigas sensing applications.

The design and fabrication of a compact, low-loss, broadband directional coupler (DC) based duplexer operating in the near-infrared (NIR) region are demonstrated. The duplexer exhibits high selectivity and coupling efficiency (CE), for target wavelengths of 1530 nm and 1653.7 nm, making it applicable in systems for the multi-gas detection of ammonia and methane.

Unlocking the monolithic integration scenario: optical coupling between GaSb diode lasers epitaxially grown on patterned Si substrates and passive SiN waveguides.

Silicon (Si) photonics has recently emerged as a key enabling technology in many application fields thanks to the mature Si process technology, the large silicon wafer size, and promising Si optical properties. The monolithic integration by direct epitaxy of III-V lasers and Si photonic devices on the same Si substrate has been considered for decades as the main obstacle to the realization of dense photonics chips. Despite considerable progress in the last decade, only discrete III-V lasers grown on bare Si wafers have been reported, whatever the wavelength and laser technology.

Erratum to: High-Q asymmetrically cladded silicon nitride 1D photonic crystals cavities and hybrid external cavity lasers for sensing in air and liquids.

[This corrects the article DOI: 10.1515/nanoph-2022-0245.].

High-Q asymmetrically cladded silicon nitride 1D photonic crystals cavities and hybrid external cavity lasers for sensing in air and liquids.

In this paper we show a novel design of high Q-factor silicon nitride (SiN) 1D photonic crystal (PhC) cavities side-coupled to curved waveguides, operating with both silica and air cladding. The engineering of the etched 1D PhC cavity sidewalls angle allows for high Q-factors over a wide range of upper cladding compositions, and the achievement of the highest calculated Q-factor for non-suspended asymmetric SiN PhC structures. We show the employment of these type of SiN PhC cavities in hybrid external cavity laser (HECL) configuration, with mode-hop free single mode laser operation over a broad range of injected currents (from 25 mA to 65 mA), milliwatts of power output (up to 9 mW) and side-mode suppression ratios in the range of 40 dB.

Long cavity photonic crystal laser in FDML operation using an akinetic reflective filter.

A novel configuration of a Fourier domain mode locked (FDML) laser based on silicon photonics platform is presented in this work that exploits the narrowband reflection spectrum of a photonic crystal (PhC) cavity resonator. Configured as a linear Fabry-Perot laser, forward biasing of a p-n junction on the PhC cavity allowed for thermal tuning of the spectrum. The modulation frequency applied to the reflector equalled the inverse roundtrip time of the long cavity resulting in stable FDML operation over the swept wavelength range.

ODX: A Fitness Tracker-Based Device for Continuous Bacterial Growth Monitoring.

Continuous monitoring of bacterial growth in aqueous media is a crucial process in academic research as well as in the biotechnology industry. Bacterial growth is usually monitored by measuring the optical density of bacteria in liquid media, using benchtop spectrophotometers. Due to the large form factor of the existing spectrophotometers, they cannot be used for live monitoring of the bacteria inside bacterial incubation chambers.

Wavelength stability in a hybrid photonic crystal laser through controlled nonlinear absorptive heating in the reflector.

The need for miniaturized, fully integrated semiconductor lasers has stimulated significant research efforts into realizing unconventional configurations that can meet the performance requirements of a large spectrum of applications, ranging from communication systems to sensing. We demonstrate a hybrid, silicon  photonics-compatible photonic crystal (PhC) laser architecture that can be used to implement cost-effective, high-capacity light sources, with high side-mode suppression ratio and milliwatt output output powers. The emitted wavelength is set and controlled by a silicon PhC cavity-based reflective filter with the gain provided by a III-V-based reflective semiconductor optical amplifier (RSOA).

Realization of a flat-band superprism on-chip from parallelogram lattice photonic crystals.

By optimizing the dispersion curve of a parallelogram-based 2D photonic crystal superprism for constant angular group velocity dispersion over a broad bandwidth, we designed a device capable of experimentally demonstrating linear dispersion from 1500 to 1600 nm with clear separation of as many as eight channels, while maintaining a compact footprint.

Author Correction: Reflection from a free carrier front via an intraband indirect photonic transition.

The original version of this article contained an error in first sentence of the Acknowledgements, which incorrectly read 'M.A.G, D.

Optimizing band-edge slow light in silicon-on-insulator waveguide gratings.

A systematic analysis of photonic bands and group index in silicon grating waveguides is performed, in order to optimize band-edge slow-light behavior in integrated structures with low losses. A combination of numerical methods and perturbation theory is adopted. It is shown that a substantial increase of slow light bandwidth is achieved when decreasing the internal width of the waveguide and the silicon thickness in the cladding region.

Reflection from a free carrier front via an intraband indirect photonic transition.

The reflection of light from moving boundaries is of interest both fundamentally and for applications in frequency conversion, but typically requires high pump power. By using a dispersion-engineered silicon photonic crystal waveguide, we are able to achieve a propagating free carrier front with only a moderate on-chip peak power of 6 W in a 6 ps-long pump pulse. We employ an intraband indirect photonic transition of a co-propagating probe, whereby the probe practically escapes from the front in the forward direction.

Photonic crystal slow light waveguides in a kagome lattice.

Slow light photonic crystal waveguides tightly compress propagating light and increase interaction times, showing immense potential for all-optical delay and enhanced light-matter interactions. Yet, their practical application has largely been limited to moderate group index values (<100), due to a lack of waveguides that reliably demonstrate slower light. This limitation persists because nearly all such research has focused on a single photonic crystal lattice type: the triangular lattice.

Subwavelength micropolarizer in a gold film for visible light.

We have designed and fabricated a 100  μm×100  μm four-sector binary subwavelength reflecting polarization microconverter in a gold film. Using finite-difference time-domain-aided numerical simulations and experiments, the micropolarizer was shown to convert an incident linearly polarized Gaussian beam of wavelength 532 nm into an azimuthally polarized beam. Conditions for generating on-axis regions of nonzero intensity when using propagating optical vortices with different initial polarization were deduced.

Lithographic wavelength control of an external cavity laser with a silicon photonic crystal cavity-based resonant reflector.

We report the experimental demonstration of a new design for external cavity hybrid lasers consisting of a III-V semiconductor optical amplifier (SOA) with fiber reflector and a photonic crystal (PhC)-based resonant reflector on SOI. The silicon reflector is composed of an SU8 polymer bus waveguide vertically coupled to a PhC cavity and provides a wavelength-selective optical feedback to the laser cavity. This device exhibits milliwatt-level output power and side-mode suppression ratios of more than 25 dB.

Tight focus of light using micropolarizer and microlens.

Using a binary microlens of diameter 14 μm and focal length 532 nm (NA=0.997) in resist, we focus a 633 nm laser beam into a near-circular focal spot with dimensions (0.35 ± 0.

Extraction of group index of lossy photonic crystal waveguides.

We present a numerical approach to extract group index in photonic crystal (PhC) waveguides using two- and three-dimensional finite-difference time-domain methods and make a quantitative study of the effects of loss on slow light propagation in PhC waveguides. PhC waveguides are simulated with varying material loss and varying PhC waveguide length. Finally, we validate our method by comparing three-dimensional simulation results with experimental results.

Experimental demonstration of original optical filter based on multiply coupled waveguides.

We present an experimental demonstration of an optical filter based on multiply coupled waveguides that has previously been demonstrated only numerically. The experimental results show a good match to numerical modeling using a 2D finite-difference time-domain method that utilizes a modified effective index method (MEIM) approximation. The MEIM correctly describes both the phase and the group indices of 3D silicon wire, providing the means to study complicated and large photonic structures with moderate computer resources and simulation time.

Optically induced indirect photonic transitions in a slow light photonic crystal waveguide.

We demonstrate indirect photonic transitions in a silicon slow light photonic crystal waveguide. The transitions are driven by an optically generated refractive index front that moves along the waveguide and interacts with a signal pulse copropagating in the structure. We experimentally confirm a theoretical model which indicates that the ratio of the frequency and wave vector shifts associated with the indirect photonic transition is identical to the propagation velocity of the refractive index front.