WSS LC Assembly Structure Optimization Study

ROADM(Reconfigurable optical add/drop multiplexer)is an important node of optical networks.By long-distance configuration,ROADM could add or drop optical wavelength agilely,which realizes dynamic build or tear down optical networks.Therefore,optical networks could be reconfigurable.WSS(wavelength selective switch)is key part of ROADM,it could divide wave band into many channels,different channel controls different wavelength.Wavelength will be controlled independently,and could be transport into any required port.The main current technologies of WSS are realized by MEMS(Micro Electromechanical System),LC(Liquid Crystal)and LCOS(Liquid Crystal On silicon).Among them,LC technology has cheap price and good reliability,it still has a good market prospect.This paper study and solves two abnormities in WSS production based on LC technology,also including LC assembly structure optimization.By changing product structure and matching appropriate optical part,product abnormity disappeared,which leads to a better product performance,a lower product cost,and a higher productivity.The main researches include below 3 items.(1)Research on attenuation accuracy failure and performance improvement.Root cause is ECB assembly structure not stable under different temperature.To solve this problem,I tried an improved structure:let all optical parts of ECB assembly not to touch each other.With new structure,the stress between adjacent two optical parts does not exist,attenuation accuracy failure disappeared accordingly.(2)Research on low temperature power-off insertion loss improvement.Root cause is phase delay difference between Odegree wave plate and ECB cell under low temperature.Phase delay of wave plate does not change by temperature,while LC cell does.A dummy LC cell also has temperature related optical performance as ECB cell,after introduced into product,which solved the abnormity.(3)Research on ECB assembly structure optimization.Current ECB assembly structure use 90degree rubbing direction ECB cell,assembled with 4pcs wave plates and lpiece polarizer.The new structure changes ECB cell PI rubbing direction from 90degree to 45degree,3pcs wave plates could be removed,and man-hour is saved accordingly.WSS performances just decline a little by this change,yet still meet customer specification.This change brings a lower product cost and higher productivity.