Theory And Experiments On Microring Resonators And Their Applications

With the development of fiber-optic communication technologies,high-performanceand low-cost are both desirable for optical communication networks.The core technologyincludes small-size optical waveguide devices with the potentials for integrations.Inaddition,optical waveguide devices with various functions such as optical filters,delaylines,buffers and other kinds of basic units for all optical signal processing are becomingmore important for the realization of future all-optical networks.Therefore,powerfulon-chip photonic systems which are fabricated by integrating these optical waveguidedevices with large dimensions on a single substrate are required.The microring resonator is a suitable candidate to meet these two requirements.It hasthe capability to realize the functions of optical filters,delay lines,buffers,lasers,routers,wavelength multiplexers/demultiplexers,switches,modulators,wavelength converters,format conversion,logic gates,and sensors,etc.Moreover,its small size is very suitable forintegration with large dimensions.Thus microring resonators have become one of the hotresearch topics in fiber-optic communication and integrated optics.This thesis is dedicatedto the research on the applications of optical filters,delay lines and buffers,which focuseson fields such as device design,microring resonators with small numbers,microringresonator arrays and detuning microring resonator structures.Furthermore,some primaryexperiments have been carried out based on microring lasers.In summary,major researchachievements and contributions are as the following:(1)The background theory for microring resonators is reviewed,including the modetheory and coupled mode theory of optical waveguides.The full vectorial film modematching method and finite difference time domain (FDTD)method are also described.Theparameter models of both all-pass and add-drop microring resonators are derived,withsome brief analysis and definitions of characterization parameters presented.(2)Comparative study of the analytical method and section model is carried out for thepulse response of all-pass microring resonators.It is found that simulation results have agood agreement with the theoretical ones when the pulse width becomes larger.A simpleand fast method which consist of both the parameter model and FDTD method is proposed.By using this method,spectra can be calculated within the 3/4 round-trip of lightpropagation in the microring resonator.Based on the full vectorial film mode matchingmethod and coupled mode theory,a silicon racetrack microring resonator is designed working around 1.55μm.Finally,a polymer rectangular microring resonator is alsodesigned working at 850nm,which consists of two multimode interferences (MMI)andfour air trenches.The numerical simulation is performed by the combinations ofFimmwave/Fimmprop,OptiFDTD and the parameter model,and the simulated extinctionratio at the drop port is around 20dB.(3)Three kinds of microring resonators with small numbers are analytically studied.The analytical models of both the spectrum and delay of serried-cascaded dual microringresonators are derived,respectively.Their peak frequencies are found to be differentwithout mode degenerations.The loss results in the same effect as the increase in thering-bus coupling coefficient.After that,the analytical model of series-cascaded triplemicroring resonators is derived.The frequencies of the outer peak and ripple notch arefound to increase nearly linearly with the identical coupling coefficients.Finally,dualmicroring resonators coupled via 3×3 couplers are proposed with analytical models derivedand detailed investigations presented.The first two types show a property ofcoupled-resonator-induced transparency (CRIT),while the third type achieves identicalintensities at two drops and the fourth type realizes the first and second order filters at twodrop ports.(4)The model,transmission characteristics and two special cases of microringresonator arrays are theoretically studied.The model of microring resonator arrays is basedon six transfer cells and the simulated annealing algorithm,which is suitable for analyzingarbitrary coupling coefficients,resonator sizes and straight waveguide lengths.In addition,it can optimize the matrix of coupling coefficients for a specified target spectrum.By usingthe model,odd row microring resonator arrays are studied in forms of variations oftransverse and longitudinal coupling coefficients and the increase in row and columnnumbers for spectral improvements.The row microring resonator arrays are investigated inmore detail for the first time.There are lots of zero transmissions in spectra due to thefeedforward effects of straight waveguide cavities.The 2×2 microring resonator array isproposed and the resultant spectra show a variety of shapes including one,two,three andfour peaks,as the coupling coefficients change.This analytical model is validated by usingFDTD simulations,.A semi-symmetrical mode concept is proposed to explain thephenomenon of the single resonance peak.Finally,the spectrum of the 3×2 microringresonator array is investigated analytically.Under the optimal design process of box-likefiltering characteristics,the filter with the side lobe larger than 10dB,the passband ripplesmaller than 0.1dB and the roll-off coefficient of passband edge smaller than l dB are achieved,with the full width at half maximum adjustable in some range.(5)The slow light effect of detuning microring resonator structures is analyzed.Firstly,the effects of resonator detuning,coupling coefficients and loss on the slow light effect areinvestigated.The delay is found to become two peaks under small coefficients.Theasymmetrical parameters such as nonzero straight waveguide cavity detuning,asymmetricalresonator loss and asymmetrical coupling coefficients are studied as the reasons ofasymmetrical.transparent properties.Then the phase effects of straight waveguide cavitiesin the parallel detuning multiple microring resonators are pointed out,with different peakvalues and shifted peak frequencies of multi-channels studied.Finally,a novel twocascaded stages of microring coupled-resonator optical waveguides for multi-channel slowlight is proposed,with the analytical model based on Chebyshev polynomials of the secondkind.Then multi-channel delay properties are studied.Delays of outer channels becomedegenerated as the number of microring resonators increases.(6)The electrical and optical properties of microring lasers are experimentally studied.Firstly,key parts of device measurements and the platform are described briefly.Thenmeasurements of microring lasers are implemented,which is a fundamental start for futureresearches on microring lasers based buffers.