Mode Switch Based On Thermo-Optic Long-Period Waveguide Grating Assisted Asymmetric Y-Junction

After entering the era of ultra-broadband and LTE,with the rapid development of mobile Internet,big data,cloud computing and etc.,the demand for fast and efficient information services has increased significantly.However,due to the nonlinear effects of fiber and other issues,the transmission capacity of existing single-mode fiber optical communication network is approaching the Shannon limit.Mode division multiplexing technology of few-mode fibers has attracted wide attention in recent years as a promising technique to further promote the transmission capacity of optical communication system.Mode converters and mode(de)multiplexers are critical components of the few-mode fiber based mode division multiplexing system and are still in the stage of exploration and improvement.In view of the current situation of insufficient research,in this dissertation a mode switch based on thermo-optic long-period waveguide grating cascaded asymmetric Y-junction is proposed,and to demonstrate this idea,the proposed device is fabricated with polymer materials EpoClad and EpoCore due to its simple and flexible process.Using the thermo-optical effect of the polymer material,a thermo-optic sidewall long-period waveguide grating is induced temporarily by periodic heating electrodes on the upper cladding surface above the two-mode stem of asymmetric Y-junction waveguide,which creatively combine mode demultiplexing and mode conversion functions together.And by changing the temperature to adjust the long wavelength grating center wavelength range,a reconfigurable and tunable thermo-optic mode switching device which has more comprehensive work characteristics is constituted.The thermo-optic mode switch can not only realize the multiplexing and demultiplexing of the LP01 mode and the LP11 a mode launched from the few-mode fiber,through the mode conversion function of the thermo-optic long-period waveguide grating,the LP01 mode and the LP11 a mode can be selectively output to the single-mode fiber through the two asymmetric arms of the Y-junction,which makes the device also a router.In this paper,to realize expected function of the proposed thermo-optic mode switching device,the related theories and work principles are analyzed and the structure parameters of the device are simulated.In the ultra-clean environment,an asymmetric Y-junction waveguide,a thermo-optic long-period waveguide grating mode converter and a thermo-optic mode switch are fabricated respectively.The performances of the device samples are separately tested.The experimental results show that,the minimum insertion loss is 12.01 dB and the crosstalk between the two arms can be as low as-26.86 dB at the wavelength of 1566 nm when the asymmetric Y-junction waveguide is used as mode demultiplexer,the minimum insertion loss for wide arm multiplexing is 12.61 dB and the minimum insertion loss for narrow arm multiplexing is 17.26 dB.The thermo-optic long-period waveguide grating mode converter can realize mode conversion between LP01 mode and LP11 a mode and its optimum operating wavelength can be adjusted by thermo-optic effect.When the external voltage of the heating electrode is(3.8 V,0.14 A),the mode conversion efficiency of the sample is about 82.91%.The fabricated thermo-optic mode switch sample has the function of mode conversion which can help correct the distorted multiplexing mode and the function of mode routing which can be used to selectively output LP01 mode and LP11 a mode through two asymmetric branch arms in the mode demultiplexing.