Photonic Transmission And Processing Techniques For Broadband RF Signals

With the rapid development of microwave photonics technology and due to the advantages of broadband,low-loss and immunity to electromagnetic interference(EMI),the photonic-assisted broadband RF transmission and processing technology is in great demand in radar,electronic countermeasure,communication,navigation,distributed sensing and wireless access,and other critical military and civilian applications.This thesis involves a deep research on the RF-over-fiber transmission link and the proposal of new photonic RF signal processing schemes.Giving full play to the strength of high-dynamic-range RF-over-fiber transmission,it needs to solve two problems:first,the link intermodulation distortion caused by the non-linear electro-optic conversion;second,the RF power fading due to the dispersion effect.The solutions to the problems are presented in this thesis:(1)a third-order intermodulation distortion(IMD3)compensation scheme is proposed based on the bidirectional modulation of 2-Ch phase modulator(2-Ch PM).Thanks to the different modulation efficiencies,two copies of equal-amplitude and out-of-phase IMD3 are generated and destructively combined.Finally,the entire IMD3 is suppressed.Up to 27dB suppression in IMD3 is experimentally demonstrated,which proves that this technique is available to improve the link linearity;(2)a long-haul RF-over-fiber transmission scheme is presented based on double wavelength modulation.Benefitting from the complementary power fading functions for the phase and intensity-modulated links which are simultaneously obtained by using the 2-Ch PM,the sum of the intensity and phase-modulated RF signal power is a constant,which overcomes the dispersion-induced periodically power fading effects.The experiment results show that the dispersion-induced power fading is greatly mitigated for the RF signal with a bandwidth up to 18GHz over 24.45 km single mode fiber(SMF)transmission.The spurious free dynamic range(SFDR)keeps at high level of about 90dB/Hz2/3 indicating an improved RF link linearity.With the proposed scheme,when a quadrature phase shift keying(QPSK)signal is transmitted over the same fiber,the performance in terms of the constellation diagram and error vector magnitude(EVM)is improved,which makes the high quality and long distance signal transmission available.Since microwave photonic technology has huge advantages in RF signal processing,innovative studies have been conducted in this thesis including:(1)Two novel microwave photonic instantaneous frequency measurement(IFM)schemes are proposed based on the frequency-to-power mapping method.In one scheme,by using the customized microfiber ring resonator(MRR)-based photonic differentiator,the frequency information is translated to amplitude information.Thus,according to the amplitude comparison function(ACF)which is defined as the power ratio of the two output ports,a measurement error of less than ±0.4 GHz over a frequency range of 0.5-12 GHz is demonstrated.In the other scheme,the IFM is implemented based on an amplified fiber-optic recirculating delay loop and a broadband incoherent light source(ILS).By establishing the mapping ralationship between the input microwave signal frequency and the ACF value,the high stability and high measurement resolution IFM is realized.In this two schemes,only one light source,one modulator,and one photodetector(PD)are needed,thus the complexity and cost can be considerably reduced.(2)In order to realize broadband modulation in high speed and long distance optical communication systems,the ? phase-shift-keying modulation technique for RF signals is proposed based on the electro-optic switch.Making full use of the performance of optical signal polarization rotation and counter-phase modulation in PM,the dynamic controllable and reconfigurable phase shift keying modulation is realized.Owing to the superiority in error rate and distortion issues for return-to-zero(RZ)modulation format,this thesis proposes and experimentally demonstrates a multi-format and pulse-width tunable RZ pulse generation based on dual-electrode intensity modulator(DEIM).By adjusting the bias voltage of DEIM and the signal time delay,RZ,dark RZ and alternate mark inversion(AMI)RZ pulses with tunable pulse-width can be obtained respectively.(3)As a promising quantization scheme,phase-shifted optical quantization is generally used in the all optical analog-to-digital conversion(ADC).This thesis proposes a phase-shifted optical quantization ADC scheme implemented by a phase modulator and balanced receivers.Experiment is carried out by measuring the continuous waveforms of 16-channel phase-shifted optical quantization.29 quantization levels with 3.68-bit effective number of bits(ENOB)and 19 dB SFDR are demonstrated.The high quantization resolution is obtained using only one electro-optic modulator and without requirement of any nonlinear effects,which confirms the feasibility of phase-shifted optical quantization used in the optical ADC.The entire works in this thesis are involved in the research field of microwave photonics which is an interdisciplinary subject combining microwave engineering and photonics,and has the advantages of broadband,low-loss,immunity to EMI,etc.Taking advantages of the microwave photonics technology,this thesis carried out a comprehensive study on the RF-over-fiber transmission and photonic RF signal processing technology,solved the two major problems of transmission nonlinear and dispersion-induced RF power fading in RF-over-fiber transmission,and took some innovative studies on the microwave photonic signal processing technology.