Research On Terahertz Microstructural Polarization Maintaining Fiber And Its Polarization Splitting Characteristics

Terahertz wave has a series of unique and excellent characteristics due to its frequency spectrum in the special position between infrared and microwave,which has been widely used in the fields of communication,imaging,detection and sensing.Microstructure fiber has high birefringence and low loss characteristics,so microstructure fiber is suitable for polarization maintaining transmission of terahertz waves.After preliminary investigation,it is found that most of the terahertz polarization maintaining fibers are the high birefringence terahertz fiber,and most terahertz polarization maintaining fibers for polarization splitting operate at a single frequency.In order to solve these two problems,we proposed two new scheme of terahertz microstructure polarization maintaining fiber:one is single-polarization terahertz photonic crystal fiber,which can realize single polarization transmission of terahertz waves over a wide operating bandwidth;the other is high-birefringence dual-core terahertz fiber for tunable polarization splitting,which can split two orthogonal polarization modes into two linearly polarized light,and the operating frequency can be adjusted within a wide frequency range.For the designed single polarization terahertz photonic crystal fiber,the cladding is a square lattice,and the core is a solid core.The epsilon-near-zero(ENZ)material is introduced into selected air holes around the core,and the core area is doped with gain material.The single polarization photonic crystal fiber obtains a minimum loss difference of 13.2 dB in the frequency range of 0.960-1.307 THz(bandwidth of 0.347 THz).The photonic crystal fiber only needs a length of 1.52 cm to obtain a terahertz single polarization transmission,with the unwanted modes being more than 20 dB smaller than the desired mode over the entire operating band.The characteristics of the single polarization terahertz photonic crystal fiber are affected by the gain factor of the gain material,the diameter of the gain area and the diameter of the air hole on both sides of the fiber coreFor the designed high birefringence dual-core terahertz fiber for tunable polarization splitting,each fiber core is an elliptical polymer with two elliptical air holes.The dual-core terahertz polarization splitting fiber attains a splitting length of 0.865 cm,a transmission loss less than 0.13 dB,and a bandwidth of 0.033 THz from 0.82 to 1.015 THz with the extinction ratio better than-10 dB at a center frequency of 1 THz.In addition,an effective method to adjust the operating frequency of polarization splitting fiber by applying pressure outside the fiber is proposed and proved,this method realizes the tunable function of terahertz polarization splitting fiber.The single-polarization terahertz photonic crystal fiber with wide bandwidth and large loss difference and the tunable terahertz polarization splitting fiber with compact structure,low transmission loss and wide bandwidth have potential application prospects in the fields of precision instruments,communication systems and sensors.