Fig. 1. Thermodynamic noise standards. (a) Thermal noise source from Noisecom of USA^[14]; (b) microwave noise standard from National Institute of Metrology, China^[15]

Fig. 2. Test results of GaAs-based Schottky diode noise sources. (a) ENR curves of noise source from JPL of USA^[16]; (b) ENR curve of noise source from NASA of USA^[17]

Fig. 3. Test results of Si-based Schottky diode noise sources. (a) ENR curve of noise source from IEMN of France^[19]; (b) ENR results of packaged noise source^[21]

Fig. 4. Noise source from 41st Institute of China Electronics Technology Group Corporation^[11]. (a) Photograph of products; (b) ENR curve of noise source

Fig. 5. Schematic diagram of noise generation based on radio-frequency photon mixing

Fig. 6. Test results of noise generated by radio-frequency photonic technology. (a) Noise results of 295‒355 GHz generated by NTT from Japan^[27]; (b) noise results of 260‒320 GHz generated by IEMN from France^[29]

Fig. 7. Comparison of terahertz noise ENR results based on electronics and radio-frequency photonic technology^[30]

Fig. 8. Terahertz noise generated by multi-beam incoherent light mixing. (a) Terahertz noise in 130‒170 GHz generated by three-beam incoherent light mixing^[32]; (b) terahertz noise in 280‒380 GHz generated by incoherent light beams based on Vernier effect^[33]

Fig. 9. Terahertz noise scheme generated by dual-mode chaotic laser^[35]. (a) Structure diagram of dual-mode chaotic laser chip; (b) micrograph of dual-mode chaotic laser chip; (c) output spectrum of dual-mode chaotic laser; (d) experimental measurement results of dual-mode chaotic laser in on and off states

Fig. 10. Schematic diagram of terahertz noise generated by multi-beam mixing^[36]

Fig. 11. Simulation results of relationship between the number of incoherent light beams and noise power spectrum^[36]. (a) Spectra of 6-beam incoherent light; (b) noise power spectra of 6-beam incoherent light mixing; (c) spectra of 2-beam incoherent light; (d) noise power spectra of 2-beam incoherent light mixing

Fig. 12. Noise generation scheme in comb-shaped chaotic light mixing based on Vernier-effect^[37]. (a) Experimental setup diagram; (b) noise power spectra

Fig. 13. Radio-frequency photonic terahertz noise source prototype in range of 200‒390 GHz^[38]. (a) System structure diagram of prototype; (b) photograph of prototype

Fig. 14. Measured results of 200‒390 GHz terahertz noise generator prototype^[38]. (a) Input spectrum and terahertz noise power spectrum; (b) results of terahertz noise ENR and corresponding equivalent noise temperature

Fig. 15. Stability and repeatability test results of 200‒390 GHz terahertz noise generator prototype^[38]. (a) Stability test results of 5 h operation; (b) repeatability test results of 10 times power on/off

Fig. 16. Typical photodetector products. (a) Commercial 145 GHz PIN-PD from HHI, Germany^[42]; (b) WR-3 waveguide output UTC-PD from NTT, Japan^[44]; (c) WR-5 waveguide output UTC-PD from Tsinghua University, China^[47]

Fig. 17. Terahertz signal generated by photoconductive antenna under incoherent light excitation^[54]. (a) Spectrum of SLD; (b) terahertz signal generated by photoconductive antenna

Fig. 18. Experimental results of terahertz noise generation based on photoconductive antenna. (a) Schematic diagram of experimental setup; (b) ENR curve at 75‒170 GHz; (c) ENR curve at 170‒400 GHz