Mach-Zehnder Interferometer Refractive Index Sensor Based on a Plasmonic Channel Waveguide

High-performance terahertz biosensor utilizing a hybrid one-dimensional photonic crystal with liquid crystal and graphene components

In recent decades, advances in biophotonics research have led to the development of numerous novel applications, particularly in the realm of diagnostic tools. Among these, one-dimensional photonic crystal biosensors have emerged as frequently utilized instruments for disease diagnosis and sensing. A significant body of research has focused on enhancing the efficiency of these biosensors. Recently, integration of Graphene and liquid crystal into a hybrid structure has been identified as a promising approach for the advancement of optical devices. This study presents a novel one-dimensional photonic crystal biosensor designed using the Kretschmann configuration, which incorporates Graphene nanolayers and a liquid crystal layer. The transfer matrix method was employed to calculate the projected band structure of the designed biosensor for different chemical potentials of the Graphene nanolayers. Additionally, the dispersion properties of the surface waves can be tuned by adjusting the liquid crystal director angle. By manipulating the adjustable parameters of the Graphene nanolayer and liquid crystal, modifications to the reflection spectrum can be achieved, facilitating an analysis of angular sensitivity and figure of merit. The results indicate that these parameters significantly influence sensitivity and figure of merit of the biosensor. Notably, increases in the chemical potential of the Graphene nanolayers, along with adjustments to the liquid crystal director angle, substantially enhance the performance of the biosensor. Our study achieved a maximum sensitivity of [Formula: see text] at a graphene chemical potential of [Formula: see text] and a liquid crystal orientation angle of [Formula: see text]. Additionally, a maximum figure of merit of [Formula: see text] was obtained at a chemical potential of [Formula: see text] and an orientation angle of [Formula: see text]. The proposed sensor is deemed suitable for practical applications due to its straightforward fabrication process and capability to operate at room temperature. Moreover, the properties of both the Graphene nanolayers and the liquid crystal layer in the biosensor can be readily adjusted, further contributing to its versatility and efficacy.

Ultrasensitive refractive index fiber sensor based on high-order harmonic Vernier effect and a cascaded FPI

This paper proposes and demonstrates an ultrasensitive refractive index (RI) sensor based on harmonic Vernier effect (HEV) and a cascaded Fabry-Perot interferometer (FPI). The sensor is fabricated by sandwiching a hollow-core fiber (HCF) segment between a lead-in single-mode fiber (SMF) pigtail and a reflection SMF segment with an offset of 37 µm between two fiber centers to form a cascaded FPI structure, where the HCF is the sensing FPI, and the reflection SMF is the reference FPI. To excite the HEV, the optical path of the reference FPI must be multiple times (>1) that of the sensing FPI. Several sensors have been made to conduct RI measurements of gas and liquid. The sensor's ultrahigh RI sensitivity of up to ∼378000 nm/RIU can be achieved by reducing the detuning ratio of the optical path and increasing the harmonic order. This paper also proved that the proposed sensor with a harmonic order of up to 12 can increase the fabricated tolerances while achieving high sensitivity. The large fabrication tolerances greatly increase the manufacturing repeatability, reduce production costs, and make it easier to achieve high sensitivity. In addition, the proposed RI sensor has advantages of ultrahigh sensitivity, compactness, low production cost (large fabrication tolerances), and capability to detect gas and liquid samples. This sensor has promising potentials for biochemical sensing, gas or liquid concentration sensing, and environmental monitoring.

Dispersion Engineering of Silicon Nitride Microresonators via Reconstructable SU-8 Polymer Cladding

In this work, we propose a novel way to flexibly engineer the waveguide dispersion by patterning the cladding of waveguide microresonators. Experimentally, we demonstrate silicon nitride waveguides with air-, oxide-, and SU-8 polymer-cladding layers and compare the corresponding waveguide dispersion. By integrating SU-8 polymer as the outer cladding layer, the waveguide dispersion can be tuned from -143 to -257 ps/nm/km. Through the simple, conventional polymer stripping process, we reconstruct the waveguide dispersion back to that of the original air-cladded device without significantly impacting the quality factor of resonators. This work provides the potential to design the waveguide dispersion in normal and anomalous regimes within an integrated photonic circuit.

Hybrid plasmonic slot waveguide with a metallic grating for on-chip biosensing applications

Designing reliable and compact integrated biosensors with high sensitivity is crucial for lab-on-a-chip applications. We present a bandpass optical filter, as a label-free biosensor, based on a hybrid slot waveguide on the silicon-on-insulator platform. The designed hybrid waveguide consists of a narrow silicon strip, a gap, and a metallic Bragg grating with a phase-shifted cavity. The hybrid waveguide is coupled to a conventional silicon strip waveguide with a taper. The effect of geometrical parameters on the performance of the filter is investigated by 3D finite-difference time-domain simulations. The proposed hybrid waveguide has potential for sensing applications since the optical field is pulled into the gap and outside of the silicon core, thus increasing the modal overlap with the sensing region. This biosensor offers a sensitivity of 270 nm/RIU, while it only occupies a compact footprint of 1.03µm×17.6µm.

Ultra Stable Molecular Sensors by Submicron Referencing and Why They Should Be Interrogated by Optical Diffraction-Part II. Experimental Demonstration

Label-free optical biosensors are an invaluable tool for molecular interaction analysis. Over the past 30 years, refractometric biosensors and, in particular, surface plasmon resonance have matured to the de facto standard of this field despite a significant cross reactivity to environmental and experimental noise sources. In this paper, we demonstrate that sensors that apply the spatial affinity lock-in principle (part I) and perform readout by diffraction overcome the drawbacks of established refractometric biosensors. We show this with a direct comparison of the cover refractive index jump sensitivity as well as the surface mass resolution of an unstabilized diffractometric biosensor with a state-of-the-art Biacore 8k. A combined refractometric diffractometric biosensor demonstrates that a refractometric sensor requires a much higher measurement precision than the diffractometric to achieve the same resolution. In a conceptual and quantitative discussion, we elucidate the physical reasons behind and define the figure of merit of diffractometric biosensors. Because low-precision unstabilized diffractometric devices achieve the same resolution as bulky stabilized refractometric sensors, we believe that label-free optical sensors might soon move beyond the drug discovery lab as miniaturized, mass-produced environmental/medical sensors. In fact, combined with the right surface chemistry and recognition element, they might even bring the senses of smell/taste to our smart devices.

Non-Periodic Epsilon-Near-Zero Metamaterials at Visible Wavelengths for Efficient Non-Resonant Optical Sensing

Epsilon-near-zero (ENZ) materials offer unique properties for applications including optical clocking, nonlinear optics, and telecommunication. To date, the fabrication of ENZ materials at visible wavelengths relies mostly on the use of periodic structures, providing some manufacturing and material challenges. Here, we present the engineering of nonperiodic sodium tungsten bronzes (Na_xWO₃) metamaterials featuring ENZ properties in the visible spectrum. We showcase their use as efficient optical sensors, demonstrating a nonresonant sensing mechanism based on refractive index matching. Our optimized ENZ metamaterials display an unconventional blue-shift of the transmittance maximum to increasing refractive index of the surrounding environment, achieving sensitivity as high as 150 nm/RIU. Our theoretical and experimental investigations provide first insights on this sensing mechanism, establishing guidelines for the future engineering and implementation of efficient ENZ sensors. The unique optoelectronic properties demonstrated by this class of tunable Na_xWO₃ materials bear potential for various applications ranging from light-harvesting to optical photodetectors.

Silicon slot waveguide Fano resonator

The growing interest for Fano resonators during the past decade is due to the narrow line shape observable in their optical spectra. The drastic phase shift occurring at the resonance yields a steep drop from a high to low amplitude. Fano resonances can be obtained by a combination of nanostructures. Such a system is extremely sensitive in terms of both geometrical parameters and environmental conditions. Here we study a complex arrangement of photonic crystal cavities and slot waveguides on a silicon chip. Our structure, composed of several cavities in parallel, has a particular response superimposing a shallow photonic bandgap and a resonance with a Fano line shape. It provides a low noise and a clear asymmetric resonance. We demonstrate it experimentally and show the potential of such a device for sensing. A sensitivity of 92 nm/RIU is measured.