Study On Silicon-based Integrated Differentiator And Its Characteristics

With the development of optical communication technology,the transmission speed of optical fiber communication has become higher and higher.The network traffic which is rapidly expanding at an exponential rate results in higher speed of signal processing.In order to overcome the bandwidth bottleneck in electronic signal processing and build optical information network with larger capacity and faster signal processing,all-optical signal processing technology came into being.As one of fundamental all-optical signal processing components,the photonic temporal differentiator is a device that provides the time derivative in the optical domain avoiding photo-electric conversion.So it has typical advantages of high operation speed,immune to electromagnetic interference and low power consumption.In addition,with the gradual maturity of integrated photonics technology,silicon-on-isolator has become one of the mainstream platforms for photonic integration,which has received widespread attention because of compact size,low cost,compatible with the CMOS process.Therefore,it is of great significance to study the silicon-based integrated differentiator and its characteristics.In the first part,the differentiator based on the silicon micro-ring resonator was studied and its performance was analyzed in terms of operating bandwidth,differential accuracy,energy efficiency,and the effect of the input signal pulse width on the differential results.The results show that,for a single micro-ring differentiator,its operating bandwidth can be increased by reducing the circumference of the ring.The differential accuracy is affected by the carrier detuning and the differentiation order.The larger the carrier detuning,the lower the differential accuracy.When the single micro-ring is used to implement first-order differentiation,the differential accuracy is optimal.Within the range of 0<n<2 differentiation order,the accuracy decreases as the differential order moves away from 1.And the micro-ring is more suitable to implement differentiation order n<1.Besides,the variation of input pulse width may change the differentiation order,where the phase response of the resonator plays an important role.For the differentiation implemented with cascaded micro-ring,the maximum averaged absolute deviation can be reduced from 5.67% to 0.67% compared with that of a single micro-ring.Within the differentiation order 1<n<2,the averaged absolute deviations of the differentiator are less than 2.3%,and the correlation coefficients are larger than 99%.Thus the accuracy of the differentiator based on cascaded two micro-ring resonators is better than that of a single micro-ring.Since less effects will be introduced by the input pulse width variations,much larger input pulse width range is acceptable when the differentiators with n>1 are realized.Also,a tunable high-precision fractional differentiator can be realized by adjusting the coupling state of one ring in the cascaded structure.In the second part,the differentiator based on the silicon Mach-Zehnder interferometer was studied.And the influences of three factors were analyzed including the splitter ratio of the coupler,the length difference of the interferometer arms and the input pulse width.When the splitting ratio is 1: 1,an first-order integer differentiator can be implemented.When the splitting ratio is far away from 1: 1,fractional differentiation in the range of 0 <n<2 can be implemented.The operating bandwidth decreases when the arm length difference increases.Excessive length difference may lead to a widened output waveform,which will reduce the differential accuracy.For integer differentiation,the differential accuracy of the interferometer increases with the increase of the input pulse width and the change of energy efficiency is reversed.For the fractional differentiator,the influence of the input pulse width is similar to that of the microring differentiator.Moreover,the differential characteristics of the micro-ring and the MachZehnder interferometer were compared.When the perimeter of the micro-ring is equal to the arm length difference of the interferometer,the Mach-Zehnder interferometric differentiator has a larger 3d B bandwidth.When implementing integer differentiation,the MZI differentor has narrower acceptable input pulse width and greater differential accuracy.When implementing fractional differentiation,MZI has a slightly better accuracy and sometimes with poor energy efficiency.