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The author numerically investigates the performance of a 100 Gb/s dual‐polarization quadrature phase‐shift keying (DP‐QPSK) coherent radio‐over‐fiber (RoF) system through deploying various lengths of standard single‐mode fiber (SSMF). The utilization of a microwave photonic integrated circuit (MPIC) as the core building block of this optical coherent RoF link both in downlink and uplink, combined with digital signal processing (DSP) has led to a new RoF scheme which demonstrated the feasibility to operate at the low input RF power. The performance of the RoF system with respect to the optical received power induced by channel SNR is also investigated. It has been demonstrated that for a 200 km length of fiber, a laser with a linewidth of less than 1 MHz results in the EVM compliant to the IEEE standards. It has been also verified that the link offers higher linearity and better receiver sensitivity compared to the conventional intensity modulated and directly detected optical communication systems.

An improved coherent optical receiver architecture that compensates for a random drift in the state of polarization (SOP) of both the signal and the local oscillator (LO) is presented for the first time. The proposed architecture comprises two conventional coherent optical receiver front-ends in tandem, where the SOP of the LO is first divided into its two orthogonal components and then distributed to each coherent optical receiver front-end module. Two distinct methods of polarization diversity recovery of the modulation based on the MRC technique and an eigenvalue-eigenvector decomposition of the covariance matrix have been used to effectively recover the transmitted signal. The concept is validated by numerical simulations, where a differential quadrature phase-shift keyed (DQPSK) modulated signal with a random time-varying SOP is first generated. After its mixing with a LO also possessing a random time-varying SOP, the algorithms that have been developed are provided with eight input variables to be digitally processed. The constellation diagrams corresponding to the recovered DQPSK modulation obtained using the two polarization diversity methods are presented.

A new algorithm for gamma-ray spectrometry is proposed in this paper which is suitable for pileup correction at very high count rates of 4 × 10 6 pulses/s. Parameters of the overlapped pulses from the detector including both starting time and amplitude are estimated by the proposed algorithm which combines modified phase-only correlator (MPOC) with Kurtosis-based amplified noise suppression (KANS) algorithm and maximum likelihood estimation (MLE) method. Algorithms are further modified to improve performance under low SNRs, because of the critical dependency of MPOC with KANS algorithm on SNR. The algorithms are evaluated on a simulated 60 CO spectrum generated at high counting rate. Simulation results show that our algorithms preserve high resolution of energy spectrum at high counting rates.Index Terms-High-count-rate gamma-ray spectrometry, maximum likelihood estimation (MLE), modified phase-only correlator (MPOC), Kurtosis-based amplified noise suppression, pileup correction, NaI(Tl) detector

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