硅基二氧化硅20通道循环型阵列波导光栅制备

Fabrication of Silica Based Silicon 20 Channel Cyclic Arrayed Waveguide Grating

采用硅基二氧化硅材料,针对G.698.4标准,设计并制作了适用于5G前传的20通道循环型阵列波导光栅,通道间隔为100 GHz。相较于传统的周期性阵列波导光栅结构,采用的2×20循环型阵列波导光栅结构可实现通道波长的严格对准,且插损均匀性更高。另外,采用指数型锥形波导取代矩形多模干涉结构以实现阵列波导光栅通带平坦化,减小因波导结构上的突变带来的损耗,且不带来光谱性能的恶化。通过机械补偿无热封装后,制备的20通道循环型阵列波导光栅模块损耗约为5.5 dB,在-40℃/25℃/80℃三温温度变化时,波长偏移量在-40~80 pm范围内。该无热模块具有小型化、低成本、大规模化生产的优势,可广泛应于5G前传网络。

At present,the world has entered the era of big data,with the rise of cloud computing,big data and mobile Internet,it is urgent to introduce the next generation port technology to meet the application requirements.With the formal freezing of the 3rd Generation Partnership Project(3GPP)the 5th generation mobile communication technology(5G)Non Standalone(NSA)and Standalone(SA)networking standards,Chinese operators have started planning and designing 5G pilot and pre commercial schemes simultaneously.The pace of 5G moving towards commercial use has been gradually accelerated.Up till now,the most representative Dense Wavelength Division Multiplexing(DWDM)technology suitable for 5G fronthaul is the multichannel bidirectional metro access DWDM System with port agnostic,which based on the G.698.4 standard adopted and released by International Telecommunication Union Telecommunication standardization sector(ITU-T)in 2018.The scheme adopts wavelength tunable optical module,which has port independent and wavelength adaptive characteristics.The tail end equipment has the ability to automatically adjust the working wavelength of the optical module to the port connected,including optical demultiplexer,multiplexer and optical add drop multiplexer.The 20 channel WDM system carried by 5G contains 20 uplink wavelengths and 20 downlink wavelengths,and each output contains one uplink wavelength and one downlink wavelength.It is similar to a cyclic structure and requires a special cyclic Arrayed Waveguide Grating(AWG).It is usually composed of many discrete devices,which has complex structure,high cost and large volume,and difficult to produce on a large scale.According to ITU-T G.698.4 standard,a 20 channel cyclic AWG suitable for 5G fronthaul transmission is designed and fabricated with a channel spacing of 100 GHz.Compared with the traditional periodic AWG structure,the 2×20 cyclic AWG structure can achieve strict alignment of channel wavelength and higher insertion loss uniformity.In addition,the exponential tapered waveguide is used to replace the rectangular Multimode Interferometer(MMI),which can reduce the loss caused by the sudden change of waveguide structure,and do not bring the deterioration of spectral performance.And a flattened AWG passband is realized.After mechanical compensation athermal packaging,the insertion loss of the prepared 20 channel cyclic AWG module is about 5.5 dB,0.5 dB bandwidth is about 0.31 nm,and the center wavelength offset is in the range of-40 pm to 80 pm when the temperature changes at-40℃/25℃/80℃.The center wavelength offset is a litter large,mainly due to the following two reasons:1)the average difference of central wavelength offset between uplink band and downlink band is 25 pm,the two are not equal;2)the central wavelength offset at low-temperature is 68 pm on average compared with normal temperature,and the offset at high-temperature is-5 pm.The wavelength offset at high and low temperature is unbalanced.For the above two problems,the input waveguide position of the downlink band can be fine-tuned downward to make the center wavelength offset of the uplink/downlink band equal.The length of the expansion screw can be adjusted to balance the wavelength offset at high and low temperatures,so as to further reduce the center wavelength offset.The athermal AWG module has the advantages of miniaturization,low cost and large-scale production,and can be widely used in 5G fronthaul transmission network.