Silicon-on-insulator based optical microring resonator sensor and improvement methods

Field: Engineering (Physical Sciences)

Photonic sensing technologies offer unexceptionable features for taking high requirement measurement in a harsh environment. They inherit advantages such as fast speed and immunity from electromagnetic interference from optical communications. In addition, with the silicon-on-insulator (SOI) technologies, chip scale optical sensors are capable of providing high sensitivity with an ultra-compact form factor. The motivation is derived from the high demand for sensors in the new era of the Data Age and the great potential of fast response, highly sensitive and ultra-compact photonic sensor. Furthermore, rapid sensor development puts forward a new prospect for many areas such as medical and health measurement, defence technology, and the internet of things. With all the advantages that SOI-based chip scale optical sensors provide, there are still shortcomings can be improving to provided much more capable sensing abilities from many aspects. With that in mind, this thesis will focus on SOI-based optical microring resonator, one of the most popular SOI-based optical structure for sensing purpose; and solutions for two shortcomings of the common SOI-based optical sensor. One of the solutions that will be mentioned in this thesis is intended to solve the issues of limited measurement speed and low resolution that caused by the way of the data analysis in the common SOI-based optical sensing system. The second purposed solutions in this thesis focused on the connection schemes of the SOI-based optical sensor; Common connection schemes of SOI-based optical chip needs at least two optical ports for coupling the light into and out of the silicon photonics chip which limits the ability to perform measurements at remote locations that are hard to be reached. Chapter 4 and 5 of this thesis contains detailed explorations of these shortcomings and solutions. An integrated photonic sensor based on optoelectronic oscillator with an on-chip sensing probe that is capable of realising highly sensitive and high-resolution optical sensing is presented in this thesis as a solution for the first shortcoming. The key component is an integrated SOI-based microring resonator which is used to implement a microwave photonic bandpass filter (MPBF) to effectively suppress the side modes of the optoelectronic oscillator (OEO) by more than 30dB, thus generating a peak RF signal that maps the detected optical change into a resulting shift in the oscillating frequency. As an application example, the proposed optical sensor system is employed to detect small changes in temperature, and experimental results demonstrate a highly sensitive optical temperature sensor with an achieved sensitivity of 7.7 GHz/°C. Moreover, the proposed sensing system revealed a 0.02°C measurement resolution which is a tenfold improvement compared with the modest resolution of 0.23°C seen by the conventional MPBF system without the OEO loop, rendering it highly suitable for diverse high-resolution sensing applications. With the purpose of reducing the size of the SOI-based photonic sensor and to overcoming the second shortcoming, an ultra-compact, reflective optical sensor probe based on SOI microring resonator and Y-junction structure is also presented in this thesis. This structure is capable of simultaneously achieving high sensitivity and fine resolution optical sensing. The reflective configuration of the probe enables remote measurements at locations which are otherwise hard to be assessed by transmission based sensors. As an application example, the proposed sensor probe for temperature measurement is demonstrated. Experiment results show that the center wavelength shift of the sensor’s reflected spectrum offers a linear response to temperature change with a high sensitivity of 66 pm/°C.