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Optical Waveguide Sensor Based on Cascaded Double-Ring Resonators in SOI

Author: JinLei
Tutor: HeJianJun
School: Zhejiang University
Course: Optical Engineering
Keywords: Optical sensor Cascaded ring resonators Vernier Effect SOI planar waveguie Wavelength interrogation Intensity interrogation Sensitivity
CLC: TN256
Type: PhD thesis
Year: 2012
Downloads: 83
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Abstract

With the development of information technology and bio-engineering techniques, the biosensor has been developing rapidly since its inception in the1970s. The biosensors are not only widely used for medical applications, but also in the field of life science, food industry, environmental monitoring and so on. Nowadays, the demand for high quality life (such as health care, environmental quality, food safety, etc.) is increasing all the time, which has driven the development of new sensing technologies. Planar waveguide evanescent field sensors combined with state-of-the-art surface modification chemistries is one such emerging technology; which has the potential to meet future demand. This thesis is mainly devoted to the study of innovative structure and new detection schemes based on planar waveguides.We proposed and analyzed an optical waveguide sensor based on two cascaded ring resonators including a reference ring resonator and a sensing ring resonator. The first detection scheme is wavelength interrogation. The sensitivity is increased compared with a single ring resonator sensor because the transmission spectrum shift is amplified by emplying the vernier effect. At the same time the requirement for high resolution tunable laser or optical spectrummeter is decreased. Furthermore, the wavelength shift can be converted into a relative intensity variation between two cetral adjacent resonant peaks to achieve a lower detection limit. By combining the central peak wavelength interrogation with the intensity ratio detection of two central peaks, the sensor can have a large measurement range and also a very low detection limit. Since the temperature effect is automatically compensated by the reference ring, the sensor is temperature insensitive. Besides, the sensor can be operated in array format using wavelength division multiplexing as the addressing scheme.We also studied a second detection scheme based on intensity interrogation using a low cost broadband light source. The refractive index change of an analyte can be derived from simple relative intensity measurement using a powermeter without requiring any spectral measurement. It has a large tolerance to the wavelength and power stability of the light source while the detection limit is still very low. This detection scheme is simple and easy, suitable for integration of the light sourse and photodetector in one chip with a low cost. It therefore has great potential for many practical applications.The fabrication process of the sensor in silicon-on-insulator platform is studied and different designs of the cascaded micro-ring resonator sensors are fabricated for different detection schemes. Experimental results are demonstrated for both wavelength interrogation and intensity interrogation, confirming the superior performances of the cascaded-double-ring sensor.The design parameters influencing the performance of the cascaded-double-ring sensor under both wavelength interrogation and intensity interrogation have been analyzed in detail. The detection limits and the optimum operation conditions of the sensors for the different interrogation schemes are analyzed and compared, providing very useful guidelines for the device design as well as for choosing the appropriate detection schemes based on application requirements.

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