Study On Optical Polarization State Conversion And Bending Loss In Single Mode Curved Optical Waveguide Channels

As the capacity,speed and agility of optical communications have been growing,optical waveguides based planar lightwave circuit(PLC)devices and systems are clearly realized to be the goal in the next optical networks.The reconfigurable optical add/drop multiplexing(ROADM)and the optical cross-connect schemes can integrate all the optical functional components such as wavelength division multiplexer,optical switch,variable optical attenuator etc.onto a photonic integrated chip,so they are the typical schemes to realize the above goal.However,the polarization dependent loss(PDL)is a critical limitation in the variable optical attenuator(VOA)and the similar devices,which is understood due to the birefringence of waveguide and some efforts of controlling waveguide stress are all failed.In this work,first start with the theorem of forming PDL to confirm that the PDL problem is created optical output performance errors of device to respond with all possible polarization states,so any polarization change of optical signal can cause an impact upon the PDL performance of the device.Hence,to investigate the possible changing processes of all polarizations must be a reasonable solution to this PDL problem.This subject is to investigate the coupling processes of all the polarizations,then find the conversion property between two linear polarizations,and further derive a new solution to the partial differential Maxwell equations.With the numerical simulations,find that the conversion efficiency from a transverse polarization to the horizontal one is much higher than the conversion efficiency between two transverse polarizations.By using the finite difference time domain(FDTD)simulate the polarization conversions of the bending waveguides,then obtain the results agreeable with the above numerical simulations.Both the numerical and FDTD simulation results show:(1)a higher index-difference waveguide not only allows the higher curving rate,but also create the higher efficiency of polarization conversion;(2)at the same bending radius,a higher index-difference waveguide has the much lower bending loss than a low index-difference waveguide.Finally,all the above polarization conversion phenomena are verified by the experimental results with a fabricated silicon rib waveguide samples.