Low-Loss Flexible Polarization-Maintaining Hollow Waveguide for Linearly Polarized 100 GHz Radiation Transmission and Subwavelength Imaging

Terahertz imaging has been developed rapidly in recent years. However, conventional terahertz imaging systems are often bulky due to the free space propagation. Various subwavelength sized probes have been developed to realize high resolution. However the tiny probes often suffer from high loss. A flexible metallic polarization-maintaining (PM) hollow waveguides with elliptical cross section is investigated and fabricated. The waveguide is used for transmitting linearly polarized terahertz (THz) radiation and flexible imaging. Bore size of the waveguide is on the order of wavelength. Transmission loss is as low as 0.92 dB/m. High birefringence of 0.08 and measured polarization ratio of 97.2% are achieved by the waveguide at 100 GHz. Moreover, a scanning 100 GHz imaging system is established by using the waveguide as a flexible probe. The PM capability of the fabricated waveguide brings benefits compared to conventional non-PM circular waveguide. The linearly polarized fundamental modes are easily excited and can be propagated through the fabricated waveguides to one meter away with polarization maintenance, which results in compressing of output beam and realizes a high resolution. A resolution better than λ/3 is achieved. It is further experimentally verified that the waveguide is robust to bending and twisting deformation, and maintained the imaging quality during flexible imaging. A subwavelength bore-sized single-polarization single-mode waveguide is also fabricated to simultaneously achieve high horizontal and vertical resolutions. The discussed waveguide is easy to fabricate and may find important applications in THz microscopy and flexible polarization imaging.