Reaearch On Generation Technology And Transmission Performance Of High-Order Frequency Millimeter Wave Signal Based On Optical External Modulator

With the coming of the information age and the rapid development of mobile communication technology,people urgently require high speed transmission rate of information.Traditional mobile communication systems generally work in the low and medium frequency bands,but the spectrum resources in this band have become increasingly tight,and the available spectrum has become quite crowded.In order to obtain more abundant spectrum resources,the carrier frequency of the signal of the wireless communication system is rapidly developing towards the millimeter wave band.The high frequency band,especially the millimeter wave band,is rich in spectrum resources and can meet the needs of high transmission rates.However,the generation of the millimeter-wave signal based on traditional electrical methods are affected by the electronic bottleneck and the frequency is not high.In addition,the millimeter wave signal generated by the electrical method has the additional attenuation loss,additional noise and susceptibile to electromagnetic interference during transmission in the atmosphere.The generation of high-frequency millimeter-wave signal based on microwave photonic technology not only overcomes the electronic bottleneck,but also produces high-quality millimeter-wave signals compatible with optical fiber transmission system.The generation,transmission and processing of millimeter wave signals in the optical domain to avoid the effects of electromagnetic interference.Therefore,the quality of the demodulated signal at the receiving end is higher.The widely used technology for generating high-frequency millimeter-wave signals in photonic technology is external modulation technology.The millimeter-wave signal system generated based on this method has high spectrum quality,but it has the problems of complex system structure and high modulation index.Therefore,the generation of high-frequency millimeter wave signals based on external optical modulation technology has become a hot research direction in recent years.In this paper,we have reviewed the recent research about generating high-frequency millimeter-wave signals based on microwave photonics technology.We analyze non-linear characteristics of optical devices such as,PM and MZM,and the principle of generating millimeter wave signals.Then two schemes are proposed based on external modulation technique to generate the high frequency millimeter wave signal and the transmission performance of the millimeter-wave signals is also analyzed.The specific research work and innovations are as follows:(1)A 27-fold BPSK millimeter wave signal generation method based on PM and SOA is proposed.By studying the generating high-frequency millimeter-wave signals based on PM and the phase changes of BPSK RF drive signals during non-linear modulation,it is found that after phase modulation the odd-order light sidebands carry BPSK signal and even-order optical sidebands do not.By adjusting the modulation index of the phase modulator properly,the-4th and+5th optical sidebands are equal and have a larger amplitude.Then the-4th-order and +5th-order optical sidebands are extracted by an IL,and the+5th-order sideband carries phase information.By using the effect of FWM in SOA,two idle tones with the frequency spacing of 27-tupling of the frequency of the RF signal are generated.Then two idle tones are abstracted by the IL,which forms the 27-tupling frequency millimeter wave signal bearing the BPSK signal.Because only one idle frequency light carries the BPSK signal,the 27-tupling millimeter wave signal generated is not sensitive to fiber dispersion.Through theoretical analysis of the proposed scheme and the establishment of a simulation link on the simulation platform,the BER graph and eye diagram are obtained,which indicates that the generated millimeter wave signal has good transmission performance.(2)Through the research of non-linear modulation of light waves by MZM based on electro-optic effect,a scheme for generating octupling and 16-tupling millimeter wave signals based on cascaded MZM has been proposed.By setting appropriate DC bias voltage and modulation index for cascaded MZM,the output of the upper branch only remains the optical carrier and the required order sidebands.The PS in the low is used to adjust phase difference of the attenuated lightwave to make it antiphase with the optical carrier for cancelling the optical carrier perfectly when coupled with the generated signal of the upper arm.When the upper and lower branches are combined at the optical combiner,the optical carrier component are canceled perfectly,and the output optical signal only remains ±8th order or ±4th order sidebands.After photoelectric conversion by the photodetector,the millimeter wave electrical signal with the frequency of 16-tupling or octupling of the frequency of the RF local oscillator is generated.A simulation system is established on the simulation platform for verification.The simulation results obtained show that RFSSR of the generated octupling millimeter wave signal is 38.15 dB,and The OSSR of the generated millimeter wave signal 32.6 dB.The RFSSR of the generated 16-tupling millimeter wave signal is 23.9 dB and the OSSR of the generated octupling millimeter wave signal is 29.85 dB.A RoF link is also built.The simulation results show that the generated octupling millimeter-wave signal is transmitted through standard single-mode fibers with length of 5 km,10 km,and 15 km,and when the error-free transmission conditions are met,there are power penalties of 0.25 dB,0.5 dB,and 1 dB respectively.The generated 16-tupling millimeter-wave signal is transmitted through standard single-mode fibers with lengths of 5 km,7.5 km,and 10 km,they have power penalties of 0.2 dB,0.6 dB,and 2.1 dB,respectively.