Fig. 1. The band profile schematic of THz QWPs，（a）without bias.（b）with illumination and bias^［27］

Fig. 2. Two common coupling methods of THz QWP，（a）45° facet coupled THz QWP，（b）metal-grating coupled THz QWP

Fig. 3. The patch antenna array coupled THz QWP，（a）SEM photo of the detector，（b）responsivity peak vs voltage for the 45° mesa and the cavity array detectors^［39］

Fig. 4. Plasmonic lens enhanced mid-infrared quantum cascade detector，（a）the schematic diagram of the detector，（b）the electric field at the grating and coupling to the detector active zone，（c）device with circular design，（d）device with star shape design ^［40］

Fig. 5. The imaging system of THz CT，（a）the schematic diagram and（b）the imaging results ^［48］

Fig. 6. The schematic diagram of the fast THz reflective scanning imaging system，（a）the detection method of the imaging system，（b）imaging results of the covered leaf，（c）imaging results of the covered razor blade^［49］

Fig. 7. Frequency up-conversion THz QWP-LED，（a）the schematic of the 45° facet coupled THz QWP-LED，（b）imaging results of THz QWP-LED^［50］

Fig. 8. THz wireless communication transmission system based on THz QCL and THz QWP^［53］

Fig. 9. Sub-wavelength THz array detectors based on 3D ring antennas，（a）the schematic of the device unit cell，（b）the equivalent circuit of the device unit cell，（c）the micrographs of the THz array detectors ^［53］