| Although highly integrated micro-electronic technique has made outstanding contribution to the convenience life and instant messaging, traditional semiconductor industry cannot follow Moore's law any more due to the physic limit and terrible transmission delay, power consumption, crosstalk of the circuit. Silicon photonics creates an ideal solution for monolithically integrated chip and realizing signal processing and transmission based on optical interconnects. Thanks to its ultra-high operating speed, small footprint and low power consumption, especially compatibility with complementary metal-oxide semiconductor (CMOS) processes, silicon-based interconnect has become the most promising platform to realize on-chip optical interconnect.Due to the compact size and great optical characteristics, the microring resonator (MRR) has become the key component of the silicon photonics. First, forming of its resonance does not need cleaved facet, MRR is born with the advantage of integration. Second, as the high power accumulating in the MRR enhances the nonlinear effect, the pump power could be reduced. What's more, the favourable thermo-optic and plasma dispersion effect could manipulate the transmission spectrum of the MRR. Based on these principles, tunable optical filter, large-scale array switch and high-speed modulator have been realized. In this dissertation, the basic theory, design principle, as well as the fabrication technics of the MRR have been firstly introduced. Then, different structures based on the MRRs have been fabricated and used in all-optical signal processing, such as microwave photonics and all-optical digital signal processing. The major research achievements of this dissertation are summarized as the followings:(1) A compact notch microwave photonic filter (MPF) with large tuning range has been realized using two cascaded MRRs with different radii. Due to the vernier effect, the transmission spectrum of cascaded MRRs is a series of bimodal distribution whose interval is an arithmetic sequence. By tuning the laser wavelength, the tunability of central frequency and 3-dB bandwidth are demonstrated from 2.5 GHz to 17.5 GHz and from 6 GHz to 9.5 GHz, respectively. An improved scheme based on three electrically tuned MRRs is also proposed. By tuning the cascaded MRRs, an optical processor of two bandpass response could be achieved in order to separately process the optical carrier and sideband signals. Experimental results show a central frequency tuning range from 19 GHz to 40 GHz, and a wide bandwidth tuning range from 5.5 GHz to 17.5 GHz.(2) By optimizing parameters of the microdisk resonator (MDR), a high quality factor (Q) of 1 x 105 has been realized. Assisted by the optical single side-band (OSSB) modulation, a compact MPF with a 3-dB bandwidth of about 2 GHz, a high rejection ratio of 40 dB, and a continuous frequency tuning range from 6 GHz to 18 GHz. Then the tunable MPF is used to measure the frequency of microwave signal. A proof-of-concept experiment demonstrates a frequency measurement range of 10 GHz, with measurement error of 0.1 GHz.(3) A simple photonic approach to generating millimeter-wave based on a high-Q silicon MDR with periodical dual passbands is proposed and demonstrated. Several periodical dual passbands with different intervals are used to filter out different pairs of optical carriers from an optical frequency comb. By beating the two optical frequency components, several millimeter-wave signals have been obtained. A proof-of-concept experiment illustrates millimeter-wave generation of 277 GHz,306 GHz and 335 GHz with harmonic distortion suppression ratio over 25 dB.(4) A route-asymmetrical light transmission scheme based on the thermal radiative effect in a fiber-chip-fiber optomechanical system is proposed and experimentally demonstrated. Employing a fiber-chip-fiber optomechanical system, our scheme has successfully achieved a broad operation bandwidth of at least 24 nm and an ultra-high route-asymmetrical transmission ratio (RATR) up to 63 dB. This route-asymmetrical device has been demonstrated effectively with not only the continuous-wave light but also high-speed digital signals.(5) A three-port passive device supporting optical ordered-route transmission based on silicon thermo-optic effect is proposed and experimentally demonstrated. It means that the light can transmit from one port to another with a strict order, but will be blocked in the opposite order. The three-port device mainly consists of a Y-branch and two asymmetric add-drop MRRs, with each having different gaps between the straight waveguides and resonators, respectively. The designed structure is extensible and the basic unit is an asymmetrically coupled MRR. Then in order to demonstrate the scalability and tunability of the circuit, a six-port device has been achieved. With the help of the thermal heaters, the resonances of the MRRs could be aligned at any region (in the tuning range of the thermal heaters). Thus the working region of the six-port device is tunable.(6) A silicon passive encoder for 4-bit Gray code on pure silicon platform is proposed and experimentally demonstrated. The transmission spectrum of MRR could be shifted by injecting strong light power with different levels. Therefore, the output powers of both the through-port and drop-port of the MRR could be controllable and switchable. By combining two independent resonant wavelengths of two MRRs and adjusting their powers in a certain order, all-optical 4-bit Gray code generation has been successfully demonstrated. The device structure is scalable which means that 2N-bit Gray code could be achieved by combining N independent resonant wavelengths of N basic MRRs. |
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