Bidyut Deka

Modeling and fabrication of evanescent waveguide-based optical sensor for sensitivity enhancement using silicon oxynitride technology

Abstract. An evanescent waveguide–based optical sensor incorporating composite planar waveguide geometry using silicon oxynitride as core layer has been designed and developed. The proposed waveguide of length ∼10,000  μm and core width ∼50  μm was embedded on silica/silicon wafer and tailored for sensing glucose concentration in aqueous solution with high waveguide sensitivity ∼0.95, as an evidence of the design and development. We derived the dispersion relation from the wave equation of the structure for estimating the propagation constants of transverse electric and transverse magnetic modes and then modeled the sensor response to the change of the sensing layer refractive index. The enhancement of waveguide sensitivity is shown by using simple effective index method based on sinusoidal modes. The sensor structure is polarization independent. The theoretical results are in good agreement with the results obtained experimentally. The experimental results have revealed strong enhancement in terms of waveguide sensitivity which is ∼10 times more than that of the existing planar waveguide sensors and five times more than asymmetric waveguide sensor. This proposed waveguide sensor requiring minimal sample volume has the potential to realize for online monitoring of blood glucose levels in the near future.

Tooth-shaped grating-assisted structure for compact multimode interference coupler

A compact tooth-shaped grating-assisted structure has been proposed for a multimode interference (MMI) coupler and studied theoretically with silica waveguides with silicon oxynitride cores by using a mathematical model based on the sinusoidal mode simple effective index method. The dependence of the access waveguide length and beat length of the grating-assisted MMI (GA-MMI) structure on access waveguide separation (h) is shown. The total length of the GA-MMI coupler is less than that of a grating-assisted two-mode interference (GA-TMI) coupler (h=0) for an access waveguide S bending loss of 0.2 dB. It is also seen that the effect of fabrication tolerance on power imbalance of a GA-MMI coupler is almost close to that of a GA-TMI coupler.

Integrating optical glucose sensing into a planar waveguide sensor structure

A device for glucose monitoring in people with diabetes is a clinical and research priority in the recent years for its accurate self management. An extensive theoretical design and development of an optical sensor is carried out incorporating planar waveguide structure in an endeavor to measure slight changes of glucose concentration. The sensor is simple and highly sensitive and has the potential to be used for online monitoring of blood glucose levels for the diabetic patients in the near future.

Fabrication Process and Techniques for Integrated Devices and Waveguide Materials

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.

Design and fabrication of compact integrated optic waveguide coupler using SiON/SiO2 material

A comprehensive study on development of silicon oxynitride/silica based compact photonic components is presented. Plasma Enhanced Chemical Vapor Deposition technique and Reactive Ion Etching was used for development of compact directional coupler (DC) and two mode interference (TMI) coupler using a numerical model based on Simple Effective Index Method. It is found that coupling length of the conventional TMI coupler is 1.3 times lower than the conventional DC. In addition, numerical and experimental results are compared with Beam Propagation Method.

Fabrication and comprehensive study of silicon oxynitride based compact directional coupler and multimode interference coupler

In this paper a comprehensive study of compact conventional Directional Coupler (DC) and Multimode Interference (MMI) coupler using a numerical model based on Simple Effective Index Method (SEIM) have been presented. The coupling length of the couplers is then compared with the results obtained by using commercially available Beam Propagation Method (BPM) based software with respect to different waveguide separation gap and different coupling gap’s refractive indices. The designed couplers are fabricated using SiON as a core and silica as a cladding. It is found both from the experimental and theoretical results that the beat length of conventional MMI coupler is ~ 1.9 times lower than that of conventional DC.

Comparative study on compact planar waveguide based photonic integrated couplers using simple effective index method

The miniaturization of photonic components in integrated optic waveguide devices to microscale platform has attracted enormous attention from the researchers and entrepreneurs. In this paper, we present and report a comparative study of photonic integrated planar waveguide based couplers using a mathematical model based on sinusoidal mode simple effective index method (SEIM). The basic photonic integrated components such as directional coupler (DC), two mode interference (TMI) coupler and multimode interference (MMI) coupler have been designed and fabricated using the versatile SiON waveguide technology (SiON as the waveguide core material using silica waveguide). The experimental results have been compared with the SEIM based theoretical results and further verified with the commercially available software tool based on beam propagation method (BPM). With a focus towards device compactness, particular emphasis is placed on device geometry in an endeavour to achieve the same. In this direction, the theoretical and experimental results obtained have been compared with tooth shaped grating assisted geometry for these photonic components. It is found that the grating assisted structures have the beat length ~0.5 times lower than that of the conventional geometry. Further it is seen that the beat length of TMI coupler is smaller compared to the DC and MMI coupler.

Study on compactness of planar waveguide based integrated optic couplers using tooth shaped grating assisted geometry

The introduction of Photonic Integrated Devices (PID) for applications in high speed optical networks providing multiple services to more number of users is indispensable as this requires large scale integration (LSI) and the miniaturization of PID device components to microscale platform has attracted immense attention from the researchers and entrepreneurs. In this paper, we present a comparative study on compactness of basic PID components using tooth shaped grating assisted (TSGA) geometry. The basic PID components such as Directional Coupler (DC), two mode interference (TMI) coupler and multimode interference (MMI) coupler have been designed using TSGA geometry in the coupling region and the coupling characteristics for the same have been estimated using a mathematical model based on sinusoidal mode simple effective index method (SM-SEIM). The dependence of modal power in the coupling region on the waveguide separation gap and coupling gap refractive index has been studied. From the estimated dependences of beat length and access waveguide length on waveguide separation gap with permissible propagation loss ~0.15 dB/cm, it has been found that the grating assisted TMI coupler (GA-TMI) is ~0.5 times lower than that of grating assisted DC (GA-DC) and ~0.44 times lower than grating assisted MMI (GA-MMI) coupler. Further, it is seen that the device length including access waveguide length of GA-MMI coupler is less than that of GA-TMI coupler and GA-DC. The SM-SEIM based numerical results are then compared with beam propagation method (BPM) results obtained by using commercially available optiBPM software.

Sensitivity enhancement of evanescent waveguide optical sensor for detecting adulterant traces in petroleum products using SiON technology

The development of an evanescent waveguide optical sensor incorporating planar waveguide geometry using silicon oxynitride as the core layer on silica-silicon wafer and its implementation for detection of adulterant traces in petroleum products is presented in this paper. This work focuses on enhancement of sensitivity and analyzed by using Simple Effective Index Method (SEIM), based on sinusoidal modes. The embedded waveguide of length ~ 10,000 μm and core width ~ 50 μm have been developed using SiON technology and applied for checking adulteration so as to ensure the purity of the fuel such that the engine will give the desired performance including low emissions yielding better accuracy and high sensitivity within a very short pulse. The thin cladding layer acts as the analytes (mixture of adulterated fuel) that supports the waveguiding film having a refractive index smaller than that of the core. The main aim of this present work is to encompass a speedy choice to the time-consuming existing methods for detecting adulterated fuels, which generally requires some time to give the consequence. The developed sensor allows spot determination of the percentage concentration of adulterant in pure petrol without involving any chemical analysis. The waveguide based sensor is polarization independent and the sensitivity of the waveguide sensor is ~10 times more than that of the existing planar waveguide sensors and also 5 times more than that of asymmetric waveguide structure. Advantages include high sensitivity, simple fabrication and easy interrogation without involving the use of solvents or toxic chemicals.

Study on highly sensitive asymmetric waveguide optical sensor for detection of sucrose concentration based on leaky quasi-modes

The development of a highly sensitive asymmetric planar waveguide optical sensor based on a mathematical model using leaky quasi-modes in an endeavor to measure slight changes of aqueous sucrose concentration is presented in this paper. The planar waveguide sensor has been fabricated using Silicon Oxynitride (SiON) based material with standard fabrication process such as Plasma Enhanced Chemical Vapor Deposition (PECVD) and Reactive Ion Etching (RIE) techniques. The propagation constant of fundamental modes for TE mode of the waveguide geometry have been estimated using Simple Effective Index Method (SEIM) based on sinusoidal modes. The technique is based on Evanescent Wave Sensing (EWS) scheme, inducing an effective refractive index change. The merits of this sensor are simplicity, highly sensitivity, screening the potential that it can be used for online monitoring of blood glucose levels in the near future. The sensitivity of the waveguide is ~10 times more than that of the previously reported work on planar waveguide sensors and the results obtained experimentally matches well with the obtained theoretical result.