Coupled-mode theory for plasmonic resonators integrated with silicon waveguides towards mid-infrared spectroscopic sensing

Metasurface-assisted amorphous germanium-tin waveguide bolometer for mid-infrared photodetection

An amorphous germanium-tin (a-Ge0.83Sn0.17) waveguide bolometer featuring a one-dimension (1D) metasurface absorber is proposed for mid-infrared photodetection at room-temperature. The device is based on the germanium-on-silicon (GOS) photonic platform. The impacts of the 1D metasurface on the performances of the waveguide bolometer are investigated. The responsivity of the a-Ge0.83Sn0.17 waveguide bolometer could be significantly enhanced by the metasurface. A responsivity of around -3.17%/µW within the 4.1 ∼ 4.3 µm wavelength range is achieved. In addition, a 3-dB roll-off frequency higher than 10 kHz is obtained.

Breaking the Symmetry of a Metal-Insulator-Metal-Based Resonator for Sensing Applications

This article designed a novel multi-mode plasmonic sensor based on a metal-insulator-metal waveguide side-coupled to a circular-shaped resonator containing an air path in the resonator. The electromagnet field distributions and transmittance spectra are investigated using finite element method-based simulations. Simulation results show that an air path in the resonator's core would impact the transmittance spectrum of SPPs. Besides, the air path is crucial in offering efficient coupling and generating multiple plasmon modes in the sensor system. The proposed structure has the advantage of multi-channel, and its sensitivity, figure of merit, and dipping strength can reach 2800 nm/RIU, 333.3 1/RIU, and 86.97%, respectively. The achieved plasmonic sensor can also apply for lab-on-chip in biochemical analysis for detecting the existence or nonappearance of diabetes through the human glucose concentration in urine.

Classical Model of Surface Enhanced Infrared Absorption (SEIRA) Spectroscopy

The molecule-plasmon interaction is the key to the mechanisms of surface enhanced infrared absorption (SEIRA) and surface enhanced Raman scattering (SERS). Since plasmons are well described by Maxwell's equations, one fundamental treatment involves the classical interpretation of infrared absorption and resonance Raman spectroscopies. We can understand the molecule-plasmon interaction using electromagnetic theory if the classical field effect on a transition dipole moment or transition polarizability is properly described. In previous work, we derived the Raman excitation profile of a model molecule using a classical driven spring attached to a charged mass with a perturbative force constant due to vibrational oscillations. In this study we generalize the interactions of plasmons with molecules by considering the N₂O asymmetric stretch SEIRA signal on a Dy doped CdO (CdO:Dy) film. This semiconductor has tunable plasmon dispersion curves throughout the near-and mid-infrared that can interact directly with vibrational absorption transitions. We have demonstrated this using the Kretschmann configuration with a CaF₂ prism and a MgO substrate. The model predicts the phase behavior of SEIRA. The calculated enhancement factor relative to an Au control is 6.2, in good agreement with the value of 6.8 ± 0.5 measured under the same conditions.

A multichannel color filter with the functions of optical sensor and switch

This paper reports a multichannel color filter with the functions of optical sensor and switch. The proposed structure comprises a metal-insulator-metal (MIM) bus waveguide side-couples to six circular cavities with different sizes for filtering ultra-violet and visible lights into individual colors in the wavelength range of 350-700 nm. We used the finite element method to analyze the electromagnetic field distributions and transmittance properties by varying the structural parameters in detail. The designed plasmonic filter takes advantage of filtering out different colors since the light-matter resonance and interference between the surface plasmon polaritons (SPPs) modes within the six cavities. Results show that the designed structure can preferentially select the desired colors and confine the SPPS modes in one of the cavities. This designed structure can filter eleven color channels with a small full width at half maximum (FWHM) ~ 2 nm. Furthermore, the maximum values of sensitivity, figure of merit, quality factor, dipping strength, and extinction ratio can achieve of 700 nm/RIU, 350 1/RIU, 349.0, 65.04%, and 174.50 dB, respectively, revealing the excellent functions of sensor performance and optical switch, and offering a chance for designing a beneficial nanophotonic device.

Optical meta-waveguides for integrated photonics and beyond

The growing maturity of nanofabrication has ushered massive sophisticated optical structures available on a photonic chip. The integration of subwavelength-structured metasurfaces and metamaterials on the canonical building block of optical waveguides is gradually reshaping the landscape of photonic integrated circuits, giving rise to numerous meta-waveguides with unprecedented strength in controlling guided electromagnetic waves. Here, we review recent advances in meta-structured waveguides that synergize various functional subwavelength photonic architectures with diverse waveguide platforms, such as dielectric or plasmonic waveguides and optical fibers. Foundational results and representative applications are comprehensively summarized. Brief physical models with explicit design tutorials, either physical intuition-based design methods or computer algorithms-based inverse designs, are cataloged as well. We highlight how meta-optics can infuse new degrees of freedom to waveguide-based devices and systems, by enhancing light-matter interaction strength to drastically boost device performance, or offering a versatile designer media for manipulating light in nanoscale to enable novel functionalities. We further discuss current challenges and outline emerging opportunities of this vibrant field for various applications in photonic integrated circuits, biomedical sensing, artificial intelligence and beyond.

Ultrahigh Sensitivity of a Plasmonic Pressure Sensor with a Compact Size

This study proposes a compact plasmonic metal-insulator-metal pressure sensor comprising a bus waveguide and a resonator, including one horizontal slot and several stubs. We calculate the transmittance spectrum and the electromagnetic field distribution using the finite element method. When the resonator's top layer undergoes pressure, the resonance wavelength redshifts with increasing deformation, and their relation is nearly linear. The designed pressure sensor possesses the merits of ultrahigh sensitivity, multiple modes, and a simple structure. The maximum sensitivity and resonance wavelength shift can achieve 592.44 nm/MPa and 364 nm, respectively, which are the highest values to our knowledge. The obtained sensitivity shows 23.32 times compared to the highest one reported in the literature. The modeled design paves a promising path for applications in the nanophotonic field.

Significantly enhanced coupling effect and gap plasmon resonance in a MIM-cavity based sensing structure

Herein, we design a high sensitivity with a multi-mode plasmonic sensor based on the square ring-shaped resonators containing silver nanorods together with a metal–insulator-metal bus waveguide. The finite element method can analyze the structure's transmittance properties and electromagnetic field distributions in detail. Results show that the coupling effect between the bus waveguide and the side-coupled resonator can enhance by generating gap plasmon resonance among the silver nanorods, increasing the cavity plasmon mode in the resonator. The suggested structure obtained a relatively high sensitivity and acceptable figure of merit and quality factor of about 2473 nm/RIU (refractive index unit), 34.18 1/RIU, and 56.35, respectively. Thus, the plasmonic sensor is ideal for lab-on-chip in gas and biochemical analysis and can significantly enhance the sensitivity by 177% compared to the regular one. Furthermore, the designed structure can apply in nanophotonic devices, and the range of the detected refractive index is suitable for gases and fluids (e.g., gas, isopropanol, optical oil, and glucose solution).

Surface-Enhanced Infrared Absorption Spectroscopic Chalcogenide Waveguide Sensor Using a Silver Island Film

A surface-enhanced infrared absorption spectroscopic chalcogenide waveguide sensor based on the silver island film was proposed for the first time to enhance the sensing performance in both liquid and gas phases. The chalcogenide waveguide sensor was fabricated by the lift-off and oblique angle deposition methods. The surface morphology of the silver island film with different thicknesses was characterized. The absorption of ethanol (liquid) at a wavelength of 1654 nm and that of methane (gas) at 3291 nm were measured using the fabricated chalcogenide waveguide sensor. The chalcogenide waveguide sensor integrated with the 1.8 nm-thick silver island film revealed the best sensing performance. With an acceptable increased waveguide loss resulting from the fabrication of the film, the absorbance enhancement factors for ethanol and methane were experimentally obtained to be >1.5 and >2.3, respectively. The 1σ limit of detection of methane for the sensor integrated with the 1.8 nm-thick silver island film was ∼4.11% for an averaging time of 0.2 s. The mathematic relation between the absorbance enhancement factor and the waveguide loss was derived for sensing performance improvement. Also, the proposed rectangular waveguide sensor provides an idea for the design of a sensor-on-a-chip instead of other waveguide sensors with a high requirement of fabrication accuracy, for example, a slot waveguide or a photonic crystal waveguide.

Interband Cascade Photonic Integrated Circuits on Native III-V Chip

We describe how a midwave infrared photonic integrated circuit (PIC) that combines lasers, detectors, passive waveguides, and other optical elements may be constructed on the native GaSb substrate of an interband cascade laser (ICL) structure. The active and passive building blocks may be used, for example, to fabricate an on-chip chemical detection system with a passive sensing waveguide that evanescently couples to an ambient sample gas. A variety of highly compact architectures are described, some of which incorporate both the sensing waveguide and detector into a laser cavity defined by two high-reflectivity cleaved facets. We also describe an edge-emitting laser configuration that optimizes stability by minimizing parasitic feedback from external optical elements, and which can potentially operate with lower drive power than any mid-IR laser now available. While ICL-based PICs processed on GaSb serve to illustrate the various configurations, many of the proposed concepts apply equally to quantum-cascade-laser (QCL)-based PICs processed on InP, and PICs that integrate III-V lasers and detectors on silicon. With mature processing, it should become possible to mass-produce hundreds of individual PICs on the same chip which, when singulated, will realize chemical sensing by an extremely compact and inexpensive package.