KEYWORDS: Pulse signals, Education and training, Analog to digital converters, Dispersion, Ultrafast phenomena, Repetition frequency, Single mode fibers, Nyquist pulse, Microwave radiation, Photonics systems
An optimization method to improve the spurious free dynamic range (SFDR) of photonic sampling without sacrificing the signal-to-noise and distortion ratio (SINAD) is proposed and experimentally demonstrated. It is realized by managing the chirp in the generated ultrashort optical pulse train by simply changing the group velocity dispersion (GVD) of the dispersion compensation module (DCM) in the cavity-less ultra-short optical pulse source. In the simulation, the SFDRs of the photonic sampling for the input signals in the frequency range of 0.1 GHz to 40.1 GHz are significantly improved with residual linear chirp in the optical pulse train compared with the situation that the chirp is completely compensated. In the experiment, a 10.1 GHz single-tone microwave signal is sampled and the SFDR is improved by 10.95 dB owing to the residual chirp in the optical pulse train. In addition, the SINAD is improved by 2.76 dB even though the power of the fundamental frequency signal is slightly reduced. The proposed scheme can also be applied to photonic sampling ADCs based on other optical pulse sources, which is favorable for alleviating the limitation from the nonlinearity of the electro-optic amplitude modulator.
KEYWORDS: Single mode fibers, Modulation, Radio over Fiber, Phase shifts, Scattering, Phase shift keying, Dispersion, Quadrature amplitude modulation, Signal detection
A method to compensate for the dispersion-induced power fading in a radio-over-fiber (RoF) link is proposed and experimentally demonstrated based on stimulated Brillouin scattering (SBS). In the central office, a part of the optical carrier is used to generate frequency-definable two-tone pump light via carrier-suppressed double-sideband modulation. The two-tone pump light generates both Brillouin loss and gain spectra at the vicinity of the optical carrier when it counter-propagates with the signal light in a spool of single-mode fiber (SMF) located in the central office. Hence, the relative phase difference between the optical carrier and the ±1st -order modulation sidebands of the signal light can be freely varied by using the SBS-induced carrier phase shift, which can compensate for the power fading induced by the group-velocity dispersion in the transmission fiber between the central office and the base station. In the experiment, a flat gain in the frequency range of 10 MHz to 10 GHz is achieved for the signal transmission over 45-km SMF. The error vector magnitudes (EVMs) of the transmitted 64 QAM signals centered at 4.8 GHz and 5.0 GHz are greatly improved after dispersion-induced power fading compensation.
KEYWORDS: Analog electronics, Signal processing, Signal to noise ratio, Signal attenuation, Modulation, Microwave radiation, Digital photography, Calibration, Nonlinear optics, Interference (communication), Microwave photonics
A linearization scheme in the digital domain for photonic sampling analog-to-digital converter (PS-ADC) is proposed and experimentally demonstrated, where a single-output Mach-Zehnder modulator (MZM) is used for photonic sampling instead of a dual-output MZM (DOMZM) in the traditional schemes. After frequency response calibration of the sampled signal in the digital domain, the optimal direct current (DC) component and the coefficient of sine function are found, and arcsine algorithm is performed to implement the linearization of PS-ADC. The theoretical results indicate that, compared with the differential and arcsine operation method generally employed in PS-ADC, the proposed scheme is facile to implement and decreases the system overhead. The feasibility of the scheme is verified by simulation and experiment. In the proof-of-concept experiment, for a single-tone microwave signal at 100 MHz with a modulation index of 0.45π, the second-order harmonic is suppressed below the noise floor, the third-order harmonic suppression ratio is enhanced by 17.14 dB, and the significant improvement in SINAD is equal to 7.91 dB.
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