Abstract
In this report, two mode converters are designed and fabricated to extract TE41 and TE01 modes for the generations of 0.4 THz and 1 THz signal by high-harmonic interaction with gyrating electron beam, respectively. The purities of the desired modes in these two converters are both higher than 90% with remarkably broad bandwidth (380 GHz to 420 GHz for TE41 mode and 910GHz to 995 GHz for TE01 mode). We therefore employed X-ray lithography to fabricate these designs, which will be characterized by THz time-domain spectroscopy. We also employs the idea of distributed Bragg reflector (DBR), which is a periodic structure formed from alternating dielectric layers. The Bragg reflector can be used to achieve nearly total reflection within a range of frequencies. Instead of the metallic parallel plate waveguide (MPPWG), we propose the Bragg parallel plate waveguide (BPPWG). The BPPWG is a very low loss waveguide as compared with the MPPWG which has a serious conducting loss at the terahertz region. The attenuation constant of our low loss BPPWG (0.02757 dB/m) for the lowest order transverse electric wave mode is two-order lower than that of MPPWG (2.76428 dB/m) at 1THz. And the cutoff frequency, the dispersion relation, and the propagating constant of BPPWG are similar to those of MPPWG. Therefore, we can replace the metallic sidewall with Bragg structured sidewall for many applications