Time-delay Characteristics Of Two Dimensional Photonic Crystal Waveguides

Photonic crystal waveguides (PCWGs), with the advantages of ultrasmall foot-print, designing flexibility, integrating nature and the special efect of slow light basedon anomalous dispersion, are expected to provide time delays or phase shifts for signalsin phased array beam forming systems and have a promising prospect in the miniatur-ization and integration of optical true-time delay (OTTD) devices. Under the supportof National Natural Science Foundation and973projects, this thesis presents the theo-retical and experimental research on the time-delay characteristics of two dimensionalPCWGs.The influence of group velocity, second order dispersion and loss on the transmis-sion and delay performances of PCWGs is analyzed, and the requirements for devicelength, transmission loss and other parameters in time-delay applications are clarified.To address the problem of loss increase in the slow light regime, a solution of losscompensation by introducing gain mechanism into PCWGs is proposed. Slow lightenhancement of the gain coefcient in active PCWGs is analyzed based on a numericalmodel and the feasibility of loss compensation is verified theoretically.According to theoretical researches, the key factor limiting the delay performanceis the radiation and scattering loss caused by fabrication disorders. The fabricationof silicon PCWGs is studied in this thesis. The influence of parameters such as Biaspower, ICP power and etching time on the result of ICP drying etching is obtainedexperimentally. By increasing the tolerance of etching time from5s to15s and improv-ing the fabrication quality and stability, ething results of uniformly shaped and sizedair holes with vertical sidewalls as deep as220nm are obtained. In the meantime, pho-tolithography and wet etching techniques are modified in order to form an air-bridgestructure with increased reliability and repeatability. Air-bridge PCWG samples withlength of500μm, slow light regime near1550nm and loss lower than30dB are fabri-cated, which lays the foundation for the measurement of OTTD characteristics. By measuring the transmission spectrum of the fabricated PCWGs, the depen-dence of the defect mode, photonic band gap, cutof wavelength and slow light regimeon the structural parameters is studied and used as reference for device design. Thetime-delay characteristics of PCWGs are measured by time-domain modulation phase-shift method and a tunable delay of10GHz microwave signal up to25ps is realized bya475μm-long PCWG. The corresponding group velocity is vg≈c/25and no evidentwaveform distortion is observed in the output signal.