The Research On Optical Modulation Amplitude Enhancement And Chirp Characteristics Based On Silicon Dual-ring Modulator

In the past decade,with the increasing investment from industrial circle and government,silicon photonics has unprecedented development opportunities.Relying on the commercial state-of-the-art complementary metal oxide semiconductor(CMOS)process system,silicon photonics has many desirable features,such as low cost,low power consumption,compactness and high integration,and is seen as the promising solution for future optoelectronic integration and optical interconnection.In this context,the electro-optical modulation amplitude enhancement and chirp characteristics of silicon dual-ring modulator are studied.The main research work of this paper is summarized as follows:1)Optical modulation amplitude enhancement based on silicon dual-ring modulatorPrevious electro-optical modulator based on micro-ring resonator has encountered the trade-off between modulation bandwidth and modulation efficiency,which makes the high-speed electro-optical modulators tend to have a small optical modulation amplitude(OMA)and poor modulation signal quality.In order to solve this problem,we use cascaded micro-ring resonator to design the electro-optic modulator and verify it experimentally.The silicon dual-ring modulator is composed of two micro-ring resonators with low quality factors(Q),which are coupled with each other through two parallel bus waveguides.In the transmission spectrum of the modulator,a narrow transparency peak exists in the center of the broad dip based on the electromagnetically induced transparency(EIT)-like effect.This dual-ring strcture enables the low-Q micro-ring resonator to produce sufficiently steep resonant peaks,increasing the modulation efficiency.In addition,a pair of differential signals are adoptd for push-pull drive to further increase the modulation efficiency.Finally,the enhancement of OMA based on the dualring modulator has been demonstrated.At bit rates of 10 Gb/s and 20 Gb/s,the large OMAs of 0.56 and 0.47 are obtained by the dual-ring modulator,respectively,which is nearly twice that of a single-ring modulator with the same parameters.Such a large OMA enables the dual-ring modulator to generate a high-order modulation format signal with a small driven voltage,such as 4-level pulse amplitude modulation(PAM-4).This application has also been experimentally demonstrated.2)Chirp characteristics of silicon dual-ring modulatorSilicon micro-ring modulators have a large modulation chirp due to their phase transition characteristics.In order to suppress the modulation chirp,silicon dual-ring modulator is driven by a pair of differential signals.Furthermore,we use the time-domain-different method to obtain the dynamic simulation results of the silicon dual-ring modulator,including phase and amplitude of the output signal.Thus,we can calculate modulation trajectory and spectrum component of the output signal,and further analyze the advantages of the dual-ring modulator compared with the ordinary micro-ring modulator.It is found that the dual-ring modulator has low modulation chirp driven by a pair of differential signals,which may be useful in long-distance transmission.