基于一维耦合腔光子晶体的声光可调谐平顶滤波器的研究

本文利用一维耦合腔光子晶体,提出了一种声光可调谐平顶滤波器.该滤波器利用声光效应,通过改变超声波频率使一维耦合腔光子晶体透射谱的平顶滤波器的中心波长产生漂移,从而实现可调谐的滤波功能.基于传输矩阵法和声光效应理论,建立了这种平顶滤波器的理论模型;利用COMSOL软件,对平顶滤波器的矩形度、通带带宽、插入损耗、可调谐特性、加工精度进行仿真研究.研究结果表明,通过施加频率为6-11 MHz的超声波,可实现通带带宽为5-6 nm及中心波长在1514-1562 nm范围内可调谐的平顶滤波器;在可调谐范围内通带带宽内插入损耗不超过2.23 dB,最低仅为0.78 dB,矩形度最低可达1.4;加工误差在±10 nm内平顶滤波器的中心波长、矩形度、插入损耗、通带带宽出现的偏差很小.该平顶滤波器具有易于设计和集成、通带平坦、可调谐范围宽、通带带宽稳定、插入损耗低、品质因素高的特点,在光开关、可调谐光纤激光器、光纤传感等光通信领域有重要应用.

Acousto-optic tunable flat top filter based on one-dimensional coupled-cavity photonic crystals

In this paper,an acousto-optic tunable flat top filter is proposed by using one-dimensional coupled-cavity photonic crystal,and two kinds of materials,i.e.magnesium fluoride and tellurium dioxide,are selected.Based on the theory of acousto-optic effect,the thickness and refractive index of one-dimensional coupled cavity photonic crystal acousto-optic medium are changed by varying the ultrasonic frequency.After the parameters of acousto-optic medium are changed,the central wavelength of flat top filter of transmission spectrum shifts toward the short wave direction,thus realizing tunable filtering function.Based on the transfer matrix method and the theory of acousto-optic effect,the theoretical model of the flat top filter is established.The rectangularity,passband bandwidth,insertion loss and tunability of flat top filter are simulated by COMSOL software.The results show that the tuning effect can be achieved by applying a certain frequency of ultrasound in the case of different ultrasonic amplitudes.The decreasing trends of transmittance are basically identical in the process of changing ultrasonic frequency in the case of different amplitudes.When the central wavelength of the flat top filter increases from 1510 nm to 1514 nm,the transmissivity corresponding to the central wavelength increases sharply from 37%to 90%;when the central wavelength of the flat top filter continuously increases to 1562 nm,the transmittance corresponding to the central wavelength increasing gently from 90%to 97%in the case of different amplitudes.Considering the transmissivity required to exceed 90%in the passband of flat top filter and the cost of ultrasonic generator,the ultrasonic wave with an amplitude of 0.4 nm is selected as the research object.The flat top filter with 5–6 nm central wavelength and 1514–1562 nm tunable flat top filter can be realized by applying ultrasonic wave with the frequency in a range of 6–11 MHz.In the tunable range,the highest insertion loss is only 2.23 dB,the lowest is only 0.78 dB,and the lowest rectangularity is 1.4.In a practical flat top filter with machining error within 5 cm,the deviation of center wavelength,rectangularity,insertion loss and passband bandwidth of flat top filter are all very small.The flat top filter has the characteristics of easy design and integration,flat passband,wide tunable range,stable passband bandwidth,low insertion loss and high quality factor.It has important applications in optical communication fields such as optical switch,tunable fiber laser and fiber sensing.