Silicon Microring Resonators And The Application To Optical Sensing With Ultra-high Sensitivity

The microring resonator (MRR) has been one of the focuses for the research of photonics. It has been widely used in applications such as communication, information processing and sensing. This thesis carries out researches about the minimization of silicon-based ring resonator and sensitivity improvement of the silicon-based microring sensor. The main contents of this thesis are as follows:Researches are carried out in order to reduce the severe mode-conversion loss in the coupling region of ultra-small ring resonators. This is the first time that characteristics about the ultra-small silicon-based ring resonator (especially the Q factor) have been analyzed theoretically and experimentally. Also curved coupler structure has been used to overcome the severe mode-conversion loss in the traditional ultra-small ring resonators. This research offers an effective solution to improve the Q factor of the ultra-small ring resonator and make it possible to reduce the size of the ring resonator further. The ultra-small ring resonators can be used in applications such as sensor array so as to increase the integration density. Ultra-small ring resonators with radius of0.75μm have been fabricated and the spectra have been tested. The results show that by using curved coupler the Q factor of the ring resonator is about4000, while by using the traditional straight waveguide coupler the Q factor is only about1400. Analyses and the experimental results show that by using curved coupler, Q factor of the ultra-small ring resonator can be improved.In order to solve the problem that the traditional microring sensor systems arc not suitable for portable applications which is caused by the huge and expensive peripheral equipments of the systems such as high-resolution optical sperctrum analyser, double-ring sensors based on vernier effect are designed. Only the digital shift of the main resonance peak in the spectra of double-ring sensor based on vernier effect is monitored during the tests. Through optimization, the digital shift of the main resonance peak can be on the order of nanometer or even larger, so that low resolution and low cost on chip optical spectrum analyser can be used to monitor the shift.In order to improve the sensitivity of the silicon-based microring resonators further, suspended silicon nanowire waveguide is designed and used. Through optimization, the waveguide sensitivity (dneff/dna) can be as large as1.2which is two times bigger than the sensitivity of ordinary strip silicon nanowire waveguide, so that the sensitivity (dλ/dnc) can be doubled. And the waveguide sensitivity is even better than the slot waveguide. By using the suspended structure, the entire silicon nanowire can be easily surrounded by analytes. But for the slot waveguide, analytes usually cannot fill the slot area completely which will reduce the waveguide sensitivity (dncff/dna) and the sensitivity (dλ/dnc). Experimental results show that the sensitivity (dλ/dnc) of the suspended silicon nanowire based vernier double ring sensor is4.6×105nm/RIU which is the highest value among different micoring sensors by now.