Research On All-Polymer Variable Optical Attenuator And Its Stability

With the rapid development of optical communication technology,dense wavelength division multiplexing?DWDM?technology plays an increasingly key role in optical transmission network.Variable optical attenuator?VOA?,which enables dynamically flexible optical power regulation,is a basic component in DWDM system.Many performance indicators of the VOA in optical communications are required,including low power-consumption,fast response and high stability.In recent years,several typical VOAs have been presented based on different structures and materials,such as microelectromechanical systems?MEMS?VOA,liquid crystal VOA,displacement VOA,planar optical waveguide VOA,etc.Though the traditional MEMS VOA is mainly used in the current optical networks,it requires a large volume,high power-consumption and is not conductive to integrate with other optical devices.The VOA based on planar waveguide is attractive for flexibility in the design and integration.Compared with inorganic materials,polymer materials have large thermo-optical coefficient,low thermal conductivity,and simple processing steps.Therefore,the VOA made of polymer materials has the advantages of low-consumption,fast response and low cost.It can meet the requirements of future optical communication componentsThis paper theoretically analyzes the mode of a rectangular waveguide and the mode of a three-layer slab waveguide,and gives the characteristic equations ofE^x_mnn andE_m^y _n mode of rectangular waveguide and TE and TM modes of three-layer slab waveguide.The working principle of MZI-type VOA is explained,and the relationship between output/input light and phase of VOA device is analyzed.Finally,the theories of thermal field and thermo-optical modulation are introduced in detail.In this paper,an all-polymer Mach-Zehnder interferometer?MZI?thermo-optic VOA with low power consumption,high optical attenuation,and low cost is designed and fabricated on a poly?methyl methacrylate??PMMA?substrate.Thermal stable SU-8 epoxy and PMMA were adopted as the core and cladding material of the waveguide,respectively.Because of the large thermo-optical coefficient of the SU-8 core material and the low thermal conductivity of the PMMA substrate,it can decrease the power consumption of the VOA effectively.Moreover,to further reduce device power consumption,the air trench was employed in both sides of the MZI arms.The device was fabricated by semiconductor manufacturing process.The improved device presents a low power consumption of 2.8 mW and a high optical attenuation of 40.2 dB.The variation of attenuation was±2.45 d B within the wavelength ranging from 1530 nm to 1610 nm.Under 1550 nm operating wavelength,the insertion loss of the VOA was measured to be 9.3 dB,and the response time as about 600?s.This article describes the device design process,theoretical simulation,preparation process and performance indicators.The prepared device has the characteristics of low power consumption and high optical attenuation.In terms of stability,the time stability and temperature stability of the prepared VOA devices were studied.Within 5 months,the insertion loss of the prepared VOA device in the band of 1530-1580 nm changes by less than 2.0 dB.At a wavelength of1550 nm,the insertion loss of the device changes by less than 1.0 d B,the changes in optical attenuation,power consumption,and response time is less than 10.8%.At 22-34°C,the insertion loss of VOA changes less than 2.0dB.After the temperature cycling of the VOA device at-40°C to 85°C for 70 cycles,the measured insertion loss change of the VOA in the 1530-1580 nm band is less than 2.5 dB.The VOA device prepared in this paper shows good stability and has the potential of practical application.