Research On Incoherent Optical Mixing To Generate Flat Millimeter-wave Noise

Millimeter-wave noise sources with uniform output power spectrum and high power level have important applications in many fields such as noise figure measurement,microwave radiometer calibration,and radar anti-jamming testing.For this reason,some methods based on electricity and optics have been proposed.However,the generation of millimeter-wave noise based on electrical methods is limited by the bandwidth of electronic equipment.So,photonic methods are easier to obtain millimeter-wave signals in higher frequency bands compared with electrical methods.For example,in microwave photonics,two coherent and narrow linewidth lasers can be used to generate single-frequency millimeter-waves with low phase noise.How to use the photonic methods to generate flat millimeter-wave signals remains a challenge.This thesis draws on the idea of microwave photonics and proposes a method to generate flat millimeter-wave noise by mixing multiple incoherent optical beams.The main research contents of this thesis are as follows:(1)On the basis of theoretical analysis of broadband noise spectrum directly generating millimeter-wave noise and two incoherent light mixing to generate millimeter-wave noise,it is deduced that multi-beam incoherent light mixing generates flat millimeter-wave noise,and the center wavelength of spectral noise is determined respectively.The relationship between the difference and the center frequency of the electrical noise and the relationship between the bandwidth of the generated electrical noise and the spectral width of the noise can finally deduce the center wavelength and spectral width of the required spectrum.To quantitatively analyze the quality of the output millimeter-wave noise,the concept of relative flatness is proposed,which defines the ratio of the power fluctuation of the noise generated to its average power in a certain frequency range.(2)Experiments verify the method of millimeter-wave noise generation based on SLD.The experimental results show that the method of directly generating millimeter-wave noise from broadband noise spectrum can generate flat millimeter-wave electrical noise,but its power level is low.After calculation,the relative flatness obtained is 0.52(35 ± 15 GHz)The method based on two incoherent light mixing to generate millimeter-wave noise generates electrical noise with a higher power level,but its flatness is poor.The relative flatness was calculated to be 0.65(35 ± 15 GHz).(3)Based on dual-optical mixing,to overcome the predicament of poor flatness,a method of multi-beam incoherent optical mixing to generate flat millimeter-wave noise is proposed.The experimental results show that,compared with the dual-optical mixing method,The method of using multi-beam incoherent light mixing can generate flat millimeter-wave electrical noise,and the relative flatness is improved by about 0.17(35 ±15 GHz),thereby improving the quality of the generated millimeter-wave electrical noise.(4)In a large frequency range,the effectiveness of the proposed method is verified.The results show that the method can obtain the absolute and relative flatness of noise in the F-band(90 ? 140 GHz)of 8.7 d B and 0.33(115 ± 25 GHz),respectively.The relative flatness of the method is improved by about 0.42(115 ± 25 GHz).