A high-efficiency dual-purpose plasmonic perfect absorber sensor based on LiNbO₃ and graphene layers was investigated in this paper for the refractive index and thermal sensing. The sensor design was kept simple for easy fabrication, comprising a LiNbO₃ substrate with a quartz layer, thin layer of graphene, four gold nanorods, and a nanocavity in each unit cell. The nanocavity is located in the middle of the cell to facilitate the penetration of EM energy to the subsurface layers. The proposed sensor design achieved an output response of 99.9% reflection, which was easy to detect without having any specialized conditions for operability. The performance of the device was numerically investigated for the biomedical refractive index range of 1.33 to 1.40, yielding a sensitivity value of 981 nm/RIU with a figure-of-merit of 61.31 RIU⁻¹. By including an additional polydimethylsiloxane polymer functional layer on the top, the device was also tested as a thermal sensor, which yielded a sensitivity level of −0.23 nm/°C.

In this paper, we discuss the fabrication of a dielectric photonic crystal (PhC)-based Fano-filter device, as well as a numerical investigation of its spectral characteristics. The process parameters affecting the structural and physical properties of the fabricated device are discussed in detail, along with their influence on the spectral properties of the filter. The considered experimental problem is a three-layered PhC structure, fabricated using focused ion-beam (FIB) technology, designed to operate in the near-infrared (NIR) range. The studied parameters include the shape of PhC elements, depth of the structures, cladding layer thicknesses, and the refractive index of the material. Numerical design and simulations are performed using an open-source python-based Finite-difference time-domain (FDTD) simulation tool. The proposed optical filter device operates based on the principle of guided-mode resonance, and achieved a maximum quality factor value in the range of 800.

In this work, fabrication of a dielectric photonic crystal device and numerical study of its spectral characteristics as a refractive index sensor are presented for near infrared range. The proposed nanosensor device is composed of low-cost dielectric materials, i.e., silicon dioxide and niobium pentoxide, and is fabricated using focused ion-beam milling lithography. In the first part, the fabrication process of the device is discussed, along with the process parameters and their effects on the structural properties of the resulting photonic crystal elements. In the second part, the device is numerically tested as a sensor for the biological refractive index range of 1.33 to 1.4. The performance considerations of the biosensor device are studied for 12 different structural profiles based on the fabrication results. It is shown that the angular-wall-profile of the fabricated structures downgrades the performance of the sensor, and the optimum value of hole depth should be in the range of 930–1500 nm to get the best performance. A sensitivity of 185.117 nm/RIU and a figure of merit of 9.7 were recorded for the optimum design of the device; however, a maximum sensitivity of 296.183 nm/RIU and a figure-of-merit of 13.184 RIU⁻¹ were achieved. The device is recommended for a variety of biosensing applications due to its inert material properties, stable design and easy integration with fiber-optic setups.

In this work, the spectral properties of distributed Bragg reflector-based photonic crystal (DBR-PhC) structures were studied for the near-infrared (NIR) range. Different structural properties were varied to study their effect on the quality of the stopband and the appearance of the resonant dips in the reflection spectra of the DBR-PhC structure. The investigated structural features included the depth of PhC holes, hole radius, and number of PhC elements in the DBR structure. The 11-layered DBR structure was designed with a 2.4/1.4 refractive index contrast of alternating layers. The study aimed to achieve optical filtering properties in the DBR-PhC structure, to simplify the structural complexity of Fabry-Pérot filters by eliminating the FP cavity and upper-DBR mirror. The proposed DBR-PhC device can be used in different optical filtering and sensing applications.

In this paper, a compact multiple-input multiple-output (MIMO) antenna for an off/on-body wireless body area network (WBAN) is presented. The proposed antenna comprises eight elements arranged in a side-by-side, orthogonal, and across configuration on a planar laminate. This MIMO system achieves wideband impedance matching, i.e., fractional bandwidth (FBW) = 111% (7600 MHz) when placed off-body and FBW = 110% (7500 MHz) when placed on-body. The achieved bandwidth covers the ultrawideband (UWB) ranges 3.1–10.6 GHz for UWB-WBANs. To isolate the antenna elements, a Jerusalem cross (JC)-shaped frequency-selective surface (FSS) and meandered structure (MS) was designed and optimized. This proposed isolation mechanism offers at least 20 dB of isolation while maintaining an overall compact profile. Moreover, MIMO performance parameters for off/on-body and the specific absorption rate (SAR) were also evaluated. Stable MIMO performance, acceptable limits of SAR, and optimum radiation characteristics verify its suitability for wideband biotelemetry applications.

In this work, a novel idea of optical switch design based on guided mode resonance in the photonic crystal structure is numerically investigated. The designed switching device work on the principle of optical amplification and wavelength shift of data signal with the help of a control signal. The data signal can be coupled into the waveguide using guided-mode resonance, whereas, a control signal is index-coupled into the waveguide to influence the data signal. The optical switching action is optimized by introducing a photonic crystal cavity and varying the number of photonic crystal elements, where the resonant wavelength, reflection peaks, linewidth, and quality factor of the data signal can be adjusted. The device is based on low refractive index contrast dielectric materials compatible with fiber optic communication and can operate in a near-infrared range of around 1.55 μm. The numerical simulations are carried out in an open source finite-difference time-domain-based software. An optical switching action is achieved with 7% amplification in the data signal at a central wavelength of 1.55 µm with a maximum shift of the wavelength of 0.001 µm. The proposed device can be easily implemented in cascade designs of programmable photonic and optical switching circuits.