ABSTRACT
We propose optical injection locking (OIL) to enable compensation of the inter-channel nonlinear phase noise, which is dominated by cross-phase modulation (XPM). In this paper, injection locking is used to create a local oscillator for a homodyne receiver from a residual carrier. The locking is fast enough to follow XPM-phase distortion, but slow enough to reject the signal bands, which are spaced slightly away from the pilot. The homodyne receiver thus partially cancels XPM, as it is common to the signals and the pilot. An experimental 7-channel WDM system gives 1-dB (0.7-dB) improvement in the peak Q of the center channel, for QPSK (16-QAM) modulated OFDM subcarriers, and increased the transmission reach by 320 km. The optimum performance was achieved at an injection ratio of -45 dB, with the injected power as low as -24.5 dBm.
ABSTRACT
We propose a carrier frequency-offset estimator for optical OFDM systems using off-the-shelf optical components and simple digital processing as a replacement for the purely digital signal processing using the cyclostationarity property of optical OFDM signals with cyclic prefix. Simulations show the system accuracy of <4% estimate error within the range [-1250 + 1250] MHz offsets for a single polarization 28-Gbaud OFDM signal with 15% cyclic prefix. The effects of the system parameters on the performance are investigated.
ABSTRACT
An optical injection locking (IL) system that is independent of the incoming signal's polarization is demonstrated for carrier recovery in coherent optical communication systems. A sub-system that enables polarization independence is discussed and experimentally verified. The system is tested over a 20-km test field link using a broad-linewidth laser (40 MHz), and shows the suppression of phase noise when using the carrier recovered by injection locking as the local oscillator.
ABSTRACT
Simultaneous polarization and phase noise tracking and compensation is proposed based on an unscented Kalman filter (UKF). We experimentally demonstrate the tracking under noise-loading and after 800-km single-mode fiber transmission with 20-Gbaud QPSK and 16-QAM signals. These experiments show that the proposed UKF outperforms both conventional blind tracing algorithms and a previously proposed extended Kalman filter, at the cost of higher complexity. Additionally, we propose and test modified Kalman filter algorithms to reduce computational complexity.
ABSTRACT
We show that unscented Kalman filters can be used to mitigate local oscillator phase noise and to compensate carrier frequency offset in coherent single-carrier optical communication systems. A parallel processing architecture implementing the unscented Kalman filter is proposed, improving upon a previous parallelized linear Kalman filter (LKF) implementation.
