Optimization of Optical Modulator for LTE RoF in Nonlinear Fiber Propagation

IEEE Photonics Technology Letters (Impact Factor: 2.18). 04/2012; 24(7):617-619. DOI: 10.1109/LPT.2012.2185927

ABSTRACT This letter proposes an optimized launch power for the direct detection of optical orthogonal frequency-division multiplexing (DD-OOFDM) for radio-over-flber (RoF). The aim is to optimize the physical layer connectivity for the third generation partnership program-long-term evolution employing RoF technologies. We also analytically derive an expression for the distributed-feedback laser, laser-induced positive frequency chirping, incorporating the phenomena that induce phase distortion at the receiver, and explicitly explain the transient chirp of DD-OOFDM. Results show that transmission at the optimized launch power of -4 dBm improves the system power efficiency of 16-quadrature amplitude modulation (QAM) DD-OOFDM by ~20% and ~37%, 64-QAM DD-OOFDM by ~21% and ~35% compared to launch powers in the linear and nonlinear regions, respectively.

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    ABSTRACT: In this paper, we investigate a nonlinear compensation technique with two different architectures using direct modulation (DM) and external modulation (EM) techniques, termed as DM based frequency dithering (DMFD) and EM based frequency dithering (EMFD). We show that DMFD and EMFD methods operate substantially different in radio-over-fiber (RoF) system by optimizing the dithering technique relative to the LTE technology. The proposed techniques is only applicable if the condition of {fL < fd < fRF} is met, where fL represents the dithering boundary limit of 14 MHz, fd is DMFD signal frequency and fRF is the RoF carrier frequency. Analysis of the optical launch power for DMFD and EMFD methods reveal that the stimulated Brillouin scattering (SBS) threshold is above ~6 dBm for the LTE-RoF system. In addition, we also unveil that DMFD and EMFD methods do not introduce additional distortion for the linear and optimum optical launch power regions, which are frequency chirp driven regions. If the given condition is met, the proposed method improves the LTE-RoF system without any shortcoming. Finally, at 10 dBm launch power, DMFD and EMFD methods exhibits an average signal-to-noise ratio (SNR) gain of ~5.95 dB and ~7.71 dB, respectively.
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    ABSTRACT: Nonlinear propagation compensation for LTE-RoF system is experimentally demonstrated with proposed DMFD and EMFD methods. We discovered that the RoF dithering frequency requirement have to be much smaller with an average improvement of ~5.35 dB.
    IEEE/OSA OFC/NFOEC; 03/2013

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