Research On The Wavelength Cross Connect And The Bandwidth-Tunable Optical Filter Array For Reconfigurable Optical Add/Drop Multiplexers

The Reconfigurable Optical Add/Drop Multiplexer(ROADM)is the core function module in intelligent all-optical networks.Through remote software configuration,a ROADM can realize arbitrary connection and flexible configuration among network resources.After several technology development stages,a ROADM has entered a new stage with characteristics of colorless,directionless,contentionless and flexible(CDCF).This is one of the research hotspots of optical communication networks.Funded by China National “863” Program,this thesis has carried out deeply research on the wavelength cross connect and bandwidth-tunable optical filter array based on liquid crystal array technology and has completed prototype fabrication.In addition,this thesis has realized the transmission verification of an 8x16 wavelength cross connect and a 16-channel bandwidth-tunable filter array in CDCF ROADMs.The research work of this thesis makes an important contribution to the design and engineering development of core optical devices in CDCF ROADMs.The main research contents are summarized as follows:(1)Wavelength cross connect based on dual liquid crystal on silicon has been studied.Based on the Gaussian beam coupling theory and free space optical design,an optical path system,with multiple wavelengths flexibly switched among multiple input and output ports,has been realized.A prototype of an 8x16 wavelength cross connect with full contentionless switching was fabricated.Any optical signal or combination with flexible bandwidth can be switched,attenuated or blocked among any input ports or output ports.The maximum insertion loss is less than 14 dB;bandwidth tuning range is 50 GHz~5000 GHz;optical blocking value is greater than 27 dB.Compared to previous reports,the 8x16 wavelength cross connect presented in this thesis is a truly contentionless wavelength cross connect device with the highest number of input and output ports,which has important guiding significance for the further development of MxN high-degree wavelength cross connects.(2)Wavelength cross connect with low-degree input/output ports,based on the two-dimensional transmission liquid crystal array,has been studied.Through the combination of the liquid crystal array and the wedge-shaped birefringence crystal,the optical signals can be flexibly switched among multi-input and multi-output ports.The design and specification analysis of an 2x2 wavelength cross connect were completed.The device can realize the function of full contentionless switching.The bandwidth tuning step under design is 25 GHz;bandwidth tuning range can cover the C band.It can meet the technical requirements of low-dimensional CDCF ROADM nodes.(3)Multi-channel bandwidth-tunable optical filter array based on liquid crystal on silicon has been studied.The prototype of a 16-channel bandwidth-tunable optical filter array has been fabricated by using the layered optical design.Each channel can flexibly tune the center wavelength and transmission bandwidth,and has the function of multi-wavelengths simultaneous tuning.The insertion loss is less than 6dB;the bandwidth tuning step is 12.5 GHz.It can cover a tuning range of 50 GHz~5000 GHz;the adjacent channel isolation is greater than 30 dB.Compared to previous reports,the prototype has the maximum number of channels.(4)A bandwidth-tunable optical filter based on transmission liquid crystal has been studied.The gap of liquid crystal arrays is less than 1.5 ?m by precise semiconductor etching.A prototype of bandwidth-tunable optical filter,with insertion less than 3 dB,has been fabricated.The bandwidth tuning step is 50 GHz;optical attenuation range is from 0 to 15 dB;attenuation resolution is 0.1 dB.It can cover a tuning range of 50 GHz~5000 GHz;extinction ratio is greater than 45 dB.This prototype has excellent performances,and can realize the filter array through multiple optical paths layered together,which is suitable for CDCF ROADM nodes with less communication dimensions.(5)The CDCF ROADM system architecture with 4 nodes and 4 directions has been studied.The 8x16 wavelength cross connect and 16-channel bandwidth-tunable optical filter array were applied to the system.The data transmission business of 10 Gb/s,100 Gb/s and 400 Gb /s were established,and optical transmission experiment of the system was completed.It is verified that the wavelength cross connect and the bandwidth-tunable optical filter array can meet the technical requirements of CDCF ROADMs.