Single Infrared Spectrum Enables Simultaneous Identification of (Bio)Chemical Nature and Particle Size of Microorganisms and Synthetic Microplastic Beads.

Populations of nearly identical chemical and biological microparticles include the synthetic microbeads used in cosmetic, biomedical, agri-food, and pharmaceutical industries as well as the class of living microorganisms such as yeast, pollen, and biological cells. Herein, we identify simultaneously the size and chemical nature of spherical microparticle populations with diameters larger than 1 μm. Our analysis relies on the extraction of both physical and chemical signatures from the same optical spectrum recorded using attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectroscopy.

Potential of a Miniature Spectral Analyzer for District-Scale Monitoring of Multiple Gaseous Air Pollutants.

Gas sensors that can measure multiple pollutants simultaneously are highly desirable for on-site air pollution monitoring at various scales, both indoor and outdoor. Herein, we introduce a low-cost multi-parameter gas analyzer capable of monitoring multiple gaseous pollutants simultaneously, thus allowing for true analytical measurement. It is a spectral sensor consisting of a Fourier-transform infrared (FTIR) gas analyzer based on a mid-infrared (MIR) spectrometer.

Allan Variance Characterization of Compact Fourier Transform Infrared Spectrometers.

Handheld Fourier transform infrared (FT-IR) spectrometers are very promising candidates for several applications where accurate real-time material detection and quantification are needed. Due to their compact size, their mode of operation which does not allow for long warm-up time, and changing environmental conditions, these spectrometers suffer from short-term noise and long-term instabilities which affect their performance. In this work, the effect of long-term multiplicative instabilities on the signal-to-noise ratio (S/N), measured using the 100% line-method, is studied.

Polarized light diffuse reflectance FT-NIR MEMS spectrometer enabling the detection of powder samples through a thin plastic layer.

Polarized scattered light Fourier transform infrared (FTIR) spectroscopy is used for measuring the absorbance of highly scattering materials overcoming the multiple scattering effect. It has been reported for in vivo for biomedical applications and in-field for agricultural and for environmental monitoring. In this paper, we report a polarized light microelectromechanical system (MEMS)-based FTIR in the extended near infrared (NIR) that utilizes a bistate polarizer in a diffuse reflectance measurement setup.

Detection of Sub-20 μm Microplastic Particles by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy and Comparison with Raman Spectroscopy.

Microplastics are particulate water contaminants that are raising concerns regarding their environmental and health impacts. Optical spectroscopy is the gold standard for their detection; however, it has severe limitations such as tens of hours of analysis time and spatial resolution of more than 10 μm, when targeting the production of a 2D map of the microparticle population. In this work, through a single spectrum acquisition, we aim at quickly getting information about the whole population of identical particles, their chemical nature, and their size in a range below 20 μm.

Substrate Signal Inhibition in Raman Analysis of Microplastic Particles.

In Raman analysis, the substrate material serves very often for signal enhancement, especially when metallic surfaces are involved; however, in other cases, the substrate has an opposite effect as it is the source of a parasitic signal preventing the observation of the sample material of interest. This is particularly true with the advent of microfluidic devices involving either silicon or polymer surfaces. On the other hand, in a vast majority of Raman experiments, the analysis is made on a horizontal support holding the sample of interest.

High sensitivity refractive index sensing using zone plate metasurfaces with a conical phase profile.

In this paper, we showed how a bulky Axicon lens can be transformed to a compact binary zone plate with conical phase profile. We built three zone plates made of three different materials and designed each zone plate to be used in high sensitivity refractive index sensing. This work is complementary to another work we have done before in which we showed mathematically how maximum sensitivity can be achieved in case of using an Axicon lens in sensing.

Spatiotemporal dynamics of nanowire growth in a microfluidic reactor.

Co-integration of nanomaterials into microdevices poses several technological challenges and presents numerous scientific opportunities that have been addressed in this paper by integrating zinc oxide nanowires (ZnO-NWs) into a microfluidic chamber. In addition to the applications of these combined materials, this work focuses on the study of the growth dynamics and uniformity of nanomaterials in a tiny microfluidic reactor environment. A unique experimental platform was built through the integration of a noninvasive optical characterization technique with the microfluidic reactor.

Complex Kernel-based spectrum reconstruction algorithm for cascaded Fabry-Perot interferometric spectrometer.

A method to calculate the spectrum of the light incident on a cascaded Fabry-Perot interferometric spectrometer from the detector signal versus the scanning mirror position is presented. The method is based on modifying the Fabry-Perot integral equation to reduce possible spectrum reconstruction errors that arise due to inaccurate determination of the optical path difference reference position and the dependence on the dispersion of the cavity material. A transformation algorithm that employs the suggested kernel modification is derived and tested.

Silicon Multi-Pass Gas Cell for Chip-Scale Gas Analysis by Absorption Spectroscopy.

Semiconductor and micro-electromechanical system (MEMS) technologies have been already proved as strong solutions for producing miniaturized optical spectrometers, light sources and photodetectors. However, the implementation of optical absorption spectroscopy for in-situ gas analysis requires further integration of a gas cell using the same technologies towards full integration of a complete gas analysis system-on-chip. Here, we propose design guidelines and experimental validation of a gas cell fabricated using MEMS technology.

Continuous Monitoring of Air Purification: A Study on Volatile Organic Compounds in a Gas Cell.

Air pollution is one of the major environmental issues that humanity is facing. Considering Indoor Air Quality (IAQ), Volatile Organic Compounds (VOCs) are among the most harmful gases that need to be detected, but also need to be eliminated using air purification technologies. In this work, we tackle both problems simultaneously by introducing an experimental setup enabling continuous measurement of the VOCs by online absorption spectroscopy using a MEMS-based Fourier Transform infrared (FTIR) spectrometer, while those VOCs are continuously eliminated by continuous adsorption and photocatalysis, using zinc oxide nanowires (ZnO-NWs).

On-chip parallel Fourier transform spectrometer for broadband selective infrared spectral sensing.

Optical spectrometers enable contactless chemical analysis. However, decreasing both their size and cost appears to be a prerequisite to their widespread deployment. Chip-scale implementation of optical spectrometers still requires tackling two main challenges.

Mid Infrared Optical Gas Sensor Using Plasmonic Mach-Zehnder Interferometer.

In this work, we propose an optimized design for on-chip gas sensor using metal-insulator (MI) plasmonic waveguide in the mid infrared range and utilizing a Mach-Zehnder Inetrferometer (MZI). The MI waveguide utilizes a high index dielectric layer on top of the metal to enhance the sensitivity of the sensor. The thickness and the refractive index of this layer are optimized to achieve high sensitivity.

Micro-Electro-Mechanical System Fourier Transform Infrared (MEMS FT-IR) Spectrometer Under Modulated-Pulsed Light Source Excitation.

Miniaturized Fourier transform infrared (FT-IR) spectrometers suffer from limited optical throughput due to their tiny aperture size. Therefore, coherent wideband sources with high brightness can provide an advantage over the wideband thermal radiation sources. However, the former ones are available based on pulsed operation.

Autoregressive superresolution microelectromechanical systems Fourier transform spectrometer.

In this work, the application of the superresolution autoregressive (AR) model to enhance the resolution of the microelectromechanical systems (MEMS) Fourier transform infrared spectrometer (FTIR) spectrometer is studied theoretically and experimentally. The effect of the number of spectral lines, the spacing between the lines, the resolution of the MEMS FTIR spectrometer and the signal-to-noise ratio (SNR) on the prediction accuracy is addressed for different targeted prediction resolutions. The effect of the SNR on applying the AR model is studied.

Odd excitation of symmetric multimode interference structures.

In this work, we study the odd excitation of symmetric multimode interference (MMI) integrated optical structures. We develop a simple formula for the imaging length in the guide under odd excitation in the MMI structures using the symmetry of the structure. The obtained analytical results are verified by numerical calculations using the beam propagation method.

Transformation algorithm and analysis of the Fourier transform spectrometer based on cascaded Fabry-Perot interferometers.

The Fourier transform spectrometer based on cascaded Fabry-Perot interferometers is analyzed, where one of the interferometers has a fixed length, while the other is scanning. We propose a method to reconstruct the spectrum correctly based on solving the integral equation of the overall response of the cascaded interferometers. The method is tested for different design parameters and noise conditions.

In-plane coupled Fabry-Perot micro-cavities based on Si-air Bragg mirrors: a theoretical and practical study.

In-plane Fabry-Perot cavities based on deeply etched Bragg mirrors are used in many microphotonic applications including sensing, telecom, and swept laser devices. A main limitation to their performance is the small free spectral range (FSR) and low finesse. The FSR limits the dynamic range or the wavelength tuning range, while the linewidth limits the resolution.

Transmission-enabled fiber Fabry-Perot cavity based on a deeply etched slotted micromirror.

In this work, we report the analysis, fabrication, and characterization of an optical cavity built using a Bragg-coated fiber (BCF) mirror and a metal-coated microelectromechanical systems (MEMS) slotted micromirror, where the latter allows transmission output from the cavity. Theoretical modeling, using Fourier optics analysis for the cavity response based on tracing the propagation of light back and forth between the mirrors, is presented. Detailed simulation analysis is carried out for the spectral response of the cavity under different design conditions.

Optical modeling of black silicon using an effective medium/multi-layer approach.

In this work, black silicon (BSi) structures including nanocones and nanowires are modeled using effective medium theory (EMT), where each structure is assumed to be a multilayer structure of varying effective index, and its optical scattering in the infrared range is studied in terms of its total reflectance, transmittance and absorptance using the transfer matrix method (TMM). The different mechanisms of the intrinsic absorption of silicon are taken into account, which translates into proper modeling of its complex refraction index, depending on several parameters including the doping level. The model validity is studied by comparing the results with the rigorous coupled wave analysis and is found to be in good agreement.

Analysis of dual coupler nested coupled cavities.

Coupled ring resonators are now forming the basic building blocks in several optical systems serving different applications. In many of these applications, a small full width at half maximum is required, along with a large free spectral range. In this work, a configuration of passive coupled cavities constituting dual coupler nested cavities is proposed.

Planar broad-band and wide-angle hybrid plasmonic IMI filters with induced transmission for visible light applications.

This work presents a technique for the design of visible optical filters using a hybrid plasmonic insulator-metal-insulator (IMI) structure. The proposed IMI visible light filter exhibits high transmission (∼91%) and an insertion loss of ∼0.4  dB with almost an omnidirectional field-of-view (0°-70°), a feature that is important for light collection in miniaturized devices.

Single-longitudinal-mode broadband tunable random laser.

In this work, we demonstrate a broadband tunable single-longitudinal-mode (SLM) random laser based on Rayleigh backscattering in a standard single-mode fiber. The wide tuning range of this SLM fiber laser over 1500-1570 nm is demonstrated with a linewidth of 4.5-30 kHz.

Angle-tolerant hybrid plasmonic filters for visible light communications.

This work presents what we believe is a novel design of a hybrid plasmonic-transmission blue filter for visible light communication systems that employ yellow phosphor-coated blue light-emitting diodes. The proposed filter balances the trade-off between transmission performance and tolerance to variation in angles of incidence (AOIs) while maintaining a low cost with limited complexity design. The designed filter operation is based upon quasi-plasmon mode excitation in a hybrid structure of alternating layers of silver and titanium dioxide over a silica substrate.