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Optical and Fiber-Optic Humidity Sensors—General Consideration
Published in Ghenadii Korotcenkov, Handbook of Humidity Measurement, 2018
At the same time, Burck et al. (1996) believe that besides above-mentioned advantages planar configuration is faced with the problem of low light transmission intensities in such small surface waveguide structures. On account of the small dimensions of thin-film waveguides, the coupling of light into the planar structure is not very efficient. Therefore, the coupling of light requires special attention. There are different methods for inputting light into the active layer. Several methods used for these purposes are shown in Figures 11.6, 11.7, and 11.17. Commonly, light is coupled to the device by means of prisms (prism coupler sensor). This approach was discussed earlier in Section 11.2 (Figure 11.6). Alternatively, the light can be coupled by miniature diffraction gratings at the sensor ends (grating coupler sensor, GCS) (Figure 11.17a). At present various gratings with different design have been developed for the energy transfer of a light beam into or out of an optical waveguide. They are characterized by their geometrical dimensions and the grating period. The different shapes encompass triangular, rectangular, and trapezoidal profiles, but asymmetric profiles are also possible (Tamir and Peng 1977). With grating couplers, preferably laser beams are used, which are coupled to the planar medium by diffraction at the grating with a precisely defined angle of incidence. Front-face coupling (Figure 11.17b) can be accomplished either by a lens focusing a collimated light beam onto the waveguide or by a waveguide illumination with an optical fiber (Figure 11.17c).
Optical Couplers
Published in Erich Kasper, Jinzhong Yu, Silicon-Based Photonics, 2020
Typically, a planar waveguide consists of three layers: cladding, guiding, and substrate. The imposition of the electromagnetic boundary condition leads to two physical conditions: total internal reflection in the guiding layer and a phase matching condition in each layer, which results in a set of discrete modes and their corresponding mode angles. With the prism coupler, guided waves with the appropriate mode angle can be introduced and high coupling efficiency can be achieved.
Mid-infrared sensor based on resonance excitation of graphene plasmon polariton-coupled Bloch surface modes at the interface of anisotropically truncated one-dimensional ternary photonic crystal
Published in Waves in Random and Complex Media, 2021
Mahendra Kumar, Surendra Prasad
We have designed a model that confines EBSMs in the mid-IR frequency-domain ranging from or to . The range of analysis can be expanded or shrunked by altering the periodicity of the TPC, which has been shown in the latter part of this section. To begin with, the confinement of EBSMs is made possible via a prism coupler (BK7 prism) under Kretschmann coupling technique. For the sake of simplicity, we have considered the external sensing medium to be air, i.e. . The coupling of incident light with BSWs is achieved only when the incidence angle is greater than the critical angle , which for the present case is . The chosen model parameters are assigned the values as , , , , (at room temperature) and . So the periodicity of the structure is .
Preparation and characterization of a silver-magnesium fluoride bi-layers based fiber optic surface plasmon resonance sensor
Published in Instrumentation Science & Technology, 2020
Vicky Kapoor, Navneet K. Sharma
The optical sensing of physical and chemical parameters has been of greatest interest to the scientific community.[1–4] Surface plasmon resonance (SPR) is an optical sensing method and extremely sensitive. Surface plasmons are transverse magnetic coherent oscillations of surface charges at the interface between the metal and the dielectric.[5,6] Under resonance conditions, the consequential surface plasmon waves (SPWs) moving along the interface are excited by p-polarized incident light in a typical SPR arrangement. SPWs are transverse magnetically (TM) polarized. The electric field intensity of SPWs decays exponentially in metal and dielectric media. Because the value of propagation constant of direct light is lower than for SPWs, the direct light is unable to excite SPWs. Therefore, for exciting SPWs, the propagation constant of incident light must be increased. This goal has been accomplished with the help of a Kretschmann’s prism coupler.[7] However, prism based SPR sensing has limitations including the large size of prism, the presence of additional optical and mechanical components, and unsuitablity for remote sensing.
Novel polymer waveguide-based surface plasmon resonance (SPR) sensor
Published in Instrumentation Science & Technology, 2020
Yiying Gu, Jiahui Yang, Jiayi Zhao, Yang Zhang, Shuangyue Yang, Jingjing Hu, Mingshan Zhao
A conventional SPR system is usually equipped with a bulky prism coupler to attenuate the total reflection to meet the conditions of resonant surface-plasmon-polariton (SPP) excitation, thereby limiting these systems to being large, expensive, and having low adjustment accuracy, among other limitations.[5] To meet the increasingly complicated requirements of modern industry, many novel SPR sensing platforms and technologies based on integrated optical waveguide coupling have been proposed, offering the merits of miniaturization, remote testing, design flexibility and the potential for sensor multiplexing.[6] Various waveguide-based surface plasmon resonance sensors have been characterized, including a multilayer metal-film SPR sensor,[7] a Y-branch waveguide SPR sensor[8] and a grating-coupled waveguide SPR sensor.[9]