Computational Photonic Sensors

This chapter presents an introduction to the optical waveguides including planar and nonplanar structures. Additionally, an analysis of planner waveguides based on ray-optical approach and Maxwell’s equations approach is investigated. In this context, types of modes, dispersion, cutoff frequency, and effective thickness of the optical waveguides are discussed thoroughly. Further, the different numerical techniques and their based mode solvers which are used to analyze optical waveguides are summarized in brief. Finally, the coupling mechanisms to the optical waveguide are introduced including transversal coupling techniques and the longitudinal coupling techniques.

In this chapter, the basic principles of photonic crystal (PhC) structures and their possible applications are presented. In this context, one-dimensional photonic crystals, Bloch’s theorem including Maxwell’s equations in periodic media, are discussed thoroughly. Additionally, the different types of defects, bandgap size, and the relation between the Brillouin zone and the reciprocal lattice are introduced. Further, the different types of PhCs such as one-dimensional, two-dimensional, and three-dimensional structures are presented in detail.

In this chapter, the basic concept concerning the surface plasmon phenomena is presented. Different types of surface plasmon wave (localized and propagating) are reviewed. Moreover, the thin metallic film surface plasmon waveguide is analyzed in order to show the symmetric and asymmetric modes. Finally, other types of surface plasmon waveguides are discussed to show the trade-off between the confinement of the field profile and the attenuation loss.

This chapter reviews the fundamentals of the silicon on insulator (SOI) technology due to its advantages. The chapter starts with an introduction to the SOI followed by the different waveguides based on the SOI technology and their advantages. Further, the novel platforms that have been recently emerging beside the SOI are also presented. Finally, various fabrication processes for performing the SOI wafer are introduced in more detail.

Recently, optical sensors have been improved extensively due to the rising need of sensing applications in different specialties such as, medicine, military, environment, food quality control. The improvement of the photonic technologies based on the CMOS compatible silicon-on-insulator (SOI) and photonic crystal structures improves the sensing performance significantly. This chapter presents the basic principles of the sensing process. Additionally, it introduces the different configurations of optical sensors based on working principle, sensor design, and detection purpose.

In this chapter, the fundamentals of the nodal finite element method (FEM) are presented, including the first-order element and second-order element. The nodal FEM is introduced for the scalar concept of the propagation constant of 2D waveguide cross section. Then, it is extended to include the time domain analysis under perfectly matched layer absorbing boundary conditions. A simple sensor based on optical grating is thereafter simulated using the time domain FEM. Also, the full vectorial analysis is discussed through the application of the penalty function method on the nodal FEM and the vector finite element method (VFEM). For the penalty function method, a global weighting factor is used to incorporate the effect of the divergence-free equation. In the VFEM, nodes are used to represent the orthogonal component of the field while the edges are used to represent the tangential component for accurate application of the boundary conditions. Finally, surface plasmon resonance photonic crystal fiber biosensor is introduced as an example of the full vectorial analysis using the VFEM.

The numerical dispersion relation is derived for the finite-difference time-domain method when implemented on spherical grids using Maxwell’s equations in spherical coordinates. Derivation is appropriately based on elementary spherical functions which renders the resulting numerical dispersion relation valid for all spherical FDTD space including near the singular regions at the origin and along the z-axis. Accuracy of this relation is verified through convergence tests to the continuous-space limit and the Cartesian FDTD limit far from the origin. Numerical dispersion analyses are carried out to demonstrate numerical wavenumber error bounds and their dependence on absolute position as well as on spherical solutions’ modes. The chapter is concluded by visiting the existing challenges of designing absorbing boundary conditions for spherical FDTD when the grid truncation is in the near vicinity of the origin. Such a design challenge can be effectively studied in the future with the aid of the derived spherical FDTD numerical dispersion relation.

In this chapter, two novel highly sensitive surface plasmon resonance photonic crystal fiber (PCF) temperature sensors based on liquid crystal (LC) or alcohol mixture are presented and studied. Through this chapter, the coupling characteristics between the core-guided mode inside the PCF core infiltrated with either nematic LC or alcohol mixture and surface plasmon mode around the surface of nanogold wire are studied in detail. The structural geometrical parameters of the proposed designs, such as hole pitch, number of metallic rods, core diameter, and metallic rod diameter, are optimized to achieve highly temperature sensitivity. The suggested alcohol-based sensor offers high sensitivity of 3 nm/°C and 4.9 nm/°C for transverse electric (TE) and transverse magnetic (TM) polarizations, respectively. Moreover, the alcohol core sensor operates over a wider range of temperatures from −4 °C to 53 °C. In addition, the suggested LC-based sensor of compact device length of 20 μm proved to surpass the sensitivity of the recent temperature sensors. Using the LC instead of alcohol has improved the sensitivity to 10 nm/°C. The results are calculated using full-vectorial finite-element method with irregular meshing capabilities and perfect matched layer boundary conditions.

Surface plasmon resonance (SPR) is a considerably growing optical sensing approach which has been employed in wide range of applications including medical diagnostics, biological and chemical analyte detection, environmental monitoring, and food safety to security. SPR sensing technique shows high sensitive nature due to small change of sample refractive index, compared to other optical sensing techniques. Recently, microstructured optical fiber-based plasmonic sensors have shown great development due to its compact structure and light controlling capabilities in unprecedented ways. The goal of this chapter is to (1) describe the principle operation of plasmonic sensors, (2) discuss the optical properties of plasmonic materials, (3) compare and contrast the different types of microstructured optical fiber-based plasmonic sensors, and (4) highlight the main challenges of microstructured plasmonic sensors and possible solutions.

In this chapter, two novel designs of compact surface plasmon resonance multifunctional biosensors based on nematic liquid crystal (NLC) and Alcohol mixture photonic crystal fibers (PCFs) are proposed and studied. The suggested sensors have a central hole filled either with NLC or alcohol mixture as temperature-dependent materials. Further, another large hole filled with liquid analyte has a gold nanorod as a plasmonic material. Therefore, the proposed sensors can be used for temperature and analyte refractive index sensing via the coupling between the core-guided modes in the central hole and the surface plasmon modes around the gold nanorod. The effects of the structure geometrical parameters are studied to maximize the sensitivity of the PCF biosensors. The numerical analysis is carried out using full-vectorial finite element method with perfectly matched layer boundary conditions. The reported multifunctional NLC-based sensor offers high sensitivity of 5 nm/°C and 3700 nm/RIU (refractive index unit) for temperature and analyte refractive index sensing, respectively. In addition, the alcohol mixture PCF sensor achieves high-temperature sensitivity of 13.1 nm/°C with high analyte refractive index sensitivity of 12700 nm/RIU. To the best of the authors’ knowledge, it is the first time to introduce PCF biosensor with high sensitivity for temperature and analyte refractive index sensing as well. Further, the achieved sensitivity values of the alcohol sensor are far higher than those reported in the literature.

This chapter introduces photonic crystal fibers (PCFs) specifically designed for pressure sensors, including PCF fabrication to introduce birefringence and pressure sensor design incorporating the PCFs. Simulation and experimental results for pressure sensors incorporating two common principles, grating and interferometry, are presented. The flexibility of designing PCF microstructures means PCF pressure sensors with very high sensitivity and accuracy are relatively easily fabricated, compared with conventional methods based on single-mode fibers, microcavities, or electrical methods. Various PCF-based pressure sensor performances are compared. Pressure sensitivity varies with the employed principle, and we show that polarimetric techniques provide the highest sensitivity compared with other types. Higher sensor sensitivity and resolution allows for a large measurement dynamic range. The proposed novel pressure sensors will meet the increasing requirements and have many applications for pressure monitoring, e.g., oil industry and biomedical detection.

The development of highly sensitive and miniaturized sensors that capable of real-time analytes detection is highly desirable. Nowadays, toxic or colorless gas detection, air pollution monitoring, harmful chemical, pressure, strain, humidity, and temperature sensors based on photonic crystal fiber (PCF) are increasing rapidly due to its compact structure, fast response, and efficient light-controlling capabilities. The propagating light through the PCF can be controlled by varying the structural parameters and core–cladding materials; as a result, evanescent field can be enhanced significantly which is the main component of the PCF-based gas/chemical sensors. The aim of this chapter is to (1) describe the principle operation of PCF-based gas/chemical sensors, (2) discuss the important PCF properties for optical sensors, (3) extensively discuss the different types of microstructured optical fiber-based gas/chemical sensors, (4) study the effects of different core–cladding shapes, and fiber background materials on sensing performance, and (5) highlight the main challenges of PCF-based gas/chemical sensors and possible solutions.

Highly sensitive hybrid plasmonic slot waveguide (HPSW) biosensors based on silicon on insulator (SOI) are proposed and analyzed for DNA hybridization detection. The reported designs are based on increasing the light interaction with the sensing region by using slot waveguide with plasmonic material. Due to the high index contrast and plasmonic effect, an ultrahigh optical confinement is achieved in the low-index regions which enables the detection of the smallest change in the analyte refractive index with high sensitivity. The normalized power confinement, power density, effective index of the supported modes by the HPSWs are analyzed to achieve high power confinement through the suggested biosensors, and hence, high sensitivity can be obtained. The HPSWs are also incorporated with straight slotted resonator to calculate the sensitivity of the proposed design. In this study, two different plasmonic materials (gold and titanium nitride) are used for the proposed designs. The simulation results are calculated using full vectorial finite element method (FVFEM). The reported biosensors have high sensitivity of 1890.4 nm/RIU (refractive index unit) with a detection limit of 2.65 × 10⁻⁶ RIU with gold material and 1190 nm/RIU with a detection limit of 4.2 × 10⁻⁶ RIU based on titanium nitride material, which are the highest in the literature to the best of our knowledge.

Besides well matured optical fiber-based sensors, emerging compact down-scaled nanowires, slot waveguides and resonators are now under researcher’s consideration due to their high sensitivities and on-chip fabrication possibilities. Along with pure dielectric based waveguides and resonators, clever engineering of sub-wavelength field confinement and modal propagation loss in plasmonic nanowire and hybrid plasmonic slot waveguides also showing promising results in the field of photonic sensing. Numerically efficient, versatile finite element method based approaches are used for rigorous analyses, design, and optimizations of these complex optical guided-wave structures. All these sensor devices can exploit the well-developed state-of-the-art fabrication technologies.

This chapter discusses the use of silicon photonics biochips incorporating ring resonator sensors. After an introduction to the ring sensor, we will discuss other aspects like peak splitting compensation, the exploitation of the Vernier effect for increased sensitivity, and the use of dual-polarization rings to determine conformational information.

Silicon-on-insulator (SOI)-based nanophotonic is a well-matured technology which enables to fabricate a myriad of optical devices such as sensors, light-emitting diode (LED), organic-LED, photodetectors. The SOI-based biochemicals sensing overcomes the limitations of previous electrical and fiber-based sensing technologies. Here, theoretical framework, performance criteria, and recent progress on SOI-based waveguide and micro-ring resonator sensors are discussed. Finally, this chapter summarizes the SOI-based sensors design and optimizes the configurations for high-sensing performance. Furthermore, the main challenges in SOI-based sensors and possible solutions to these challenges are also outlined.