Planar Waveguide Optical Sensors

Sensing platform based on the integrated optical planar waveguide represents an active research area. The development of optical planar waveguide sensor has largely been motivated by the need for rapid, automated devices for application in the fields of clinical diagnostics and adulteration detection. The technologies highlighted in this chapter have taken advantage of emerging advances in silicon technology and Lab on a Chip (LOC) device platform. This chapter gives an introduction of the integrated optic (IO) sensors, its characteristics, and a brief outline of works along with the scope of waveguide sensors. Furthermore, the silicon photonics fabrication platform that was used to fabricate the sensor, the optical waveguide material study as well as the impetus for the use of silicon photonics is reported in this chapter. The chapter ends with the organization of this book.

Planar optical waveguides are the input devices to build an integrated optical sensor. This chapter provides review made in the recent advancement of integrated optical sensor that involves guided light with substantial developments made at a very rapid pace. The basic concept and equations of electromagnetic (EM) wave theory requisite for lightwave propagation in optical waveguides are presented. The light confinement and formation of modes in the waveguide are qualitatively explained, considering a slab waveguide. Maxwell’s equations, boundary conditions, are described as they form the basis for the following chapters. Theoretical consideration and supportive calculation to understand the basic properties of optical waveguide is presented for a step-index waveguide. Further, the derivation of dispersion equations is explained in detail in order to understand the dispersion characteristics of optical waveguide. Rigorous three-dimensional analysis usually requires numerical calculations, and therefore, this chapter presents several methods such as finite element method, finite difference time domain, and beam propagation method necessary for mode analysis of optical waveguide. The detection of glucose level in blood is a highly researched area in the quest for a sensor that can give accurate measurements, in short time, with minimum invasiveness. Although several optical techniques are being explored for glucose detection including infrared spectroscopy however, there are limitations to these techniques and involve complications. A short review is done on available medical and engineering concepts and attempt is made to discuss how far these can be applied to optical waveguide-based sensor with fine accuracy and high sensitivity.

This chapter is aimed at presenting an interesting picture of the state of the art in waveguide fabrication processes and techniques, providing standpoint of what can be expected in the near future. This chapter also summarizes an inclusive study on fabrication process and available techniques for the realization of the integrated optic waveguide devices. Although many material systems are projected for the fabrication of integrated optic devices, the field of silicon photonics fabrication platform is gaining momentous impetus. It permits optical devices to get finished very economically using standard semiconductor fabrication techniques and incorporated with microelectronic chips. Usually, the fabricated devices are made out of semiconductor materials, dielectrics, oxides, and metals. In this chapter, an in-depth study on silicon-based materials and its fabrication technology is conferred in detail for waveguide application. A brief analysis has been carried out on different waveguide materials and their contemporary advantages along with the limitations. Based on highly sophisticated fabrication technology, it is found that silicon photonics fabrication platform would afford us with an inexpensive vastly integrated electronic–photonic platform in which ultra-compact photonic devices can be made. Finally, this chapter ends with an overall discussion on basic steps of fabrication and examples that indicate the usefulness of silicon oxynitride as the waveguide material for high-density integrated optics.

Planar waveguide optical sensor development has principally been driven by the need for rapid, automated devices for application in the fields of clinical diagnostics and biological detection. This chapter is prepared as theoretical basis providing the basic foundation and supported by application as evidence for the sensor development. Using Maxwell’s equation, a theoretical analysis for wave propagation in planar waveguide sensor with silicon oxynitride (SiON) as the waveguide material is presented. The theoretical results are in good agreement with experimental results. Theoretical consideration, supporting calculations, and experimental results showed that the sensor can be used for online monitoring of glucose level as it requires very minimal sample volume for its detection with high sensitivity. The sensor will have a significant impact on health care in the near future.

Sensing technologies based on the principle of Frustrated Total Internal Reflection (FTIR) are continuously driving the development of novel applications like detecting adulteration in petroleum product. Using FTIR phenomenon, the skill highlighted in this chapter has taken advantage of emerging advances in adulteration detection technique, signifying the unique versatility of the optical waveguide core phenomenon. The sensitivity of the developed sensor to detect adulterated petroleum product is in good agreement with predictions derived from its measured sensitivity. Advantages include the ability to perform faster, more sensitive, and very short-time requirement for its measurements without involving any chemicals.

The assessment of accurate glucose level is an important aspect in the field of clinical diagnostics. With ever-improving advances in diagnostic technology, we find that new techniques and approaches have been demonstrated for monitoring blood glucose. Addressing to this matter, the objective of this chapter is to introduce a new optical concept for measuring glucose concentration in blood plasma that involves the development of a new miniaturized technique using Poiseuille’s equation of viscous flow and light propagation through the optical waveguide. Potentially, this technique can be very useful in the management of diabetes in the near future. The advantage of this approach, with respect to other optical methods, is safe and capable of providing accurate result in terms of enhanced sensitivity. The sensor developed requires very minimal sample for its detection.

Endeavors have been made in this book for a systematic and comprehensive study of a planar waveguide optical sensor. The study includes design and development of a theoretical model using simple effective index method (SEIM) for the sensor structure and its application for detecting adulteration in petroleum products and glucose level detection in blood plasma.