Abstract
The impact of the laser phase noise on the photodetected intercore crosstalk and performance of direct-detection orthogonal frequency division multiplexing multicore fiber systems is experimentally investigated. A new solution to overcome the performance fluctuations over time induced by the combined effect of laser phaser noise and intercore crosstalk is proposed. The solution uses adaptive modulation with extended time memory to estimate the bit loading scheme of each subcarrier from the mean and maximum error vector magnitude evaluated over the last ten blocks of transmitted training symbols. During measurements of up to 90 hours, intercore crosstalk power variation induced by fast laser phase noise variations exceeded 20 dB in both time and frequency, and error vector magnitude fluctuations of 4 dB were observed on a sub-second timescale. It is shown that direct-detection orthogonal frequency division multiplexing multicore fiber based systems employing a typical adaptive modulation solution, in which the bit loading scheme is evaluated from a single set of training symbols, suffer from unacceptable outage probabilities and are unable to counteract the fast power variations of intercore crosstalk and phase noise induced impairments. By extending the system memory used to estimate the bit loading scheme employed by the adaptive technique, an outage probability reduction by one order of magnitude is achieved. This reduction is attained by using the mean of the error vector magnitude evaluated over the last ten blocks of training symbols to estimate the bit loading scheme of subcarriers. Further reduction of the outage probability by four orders of magnitude is also demonstrated using a more conservative approach to estimate the bit loading scheme of the subcarriers. However, this conservative approach, based on the maximum error vector magnitude, may lead to additional loss of the average throughput.
Highlights
Space-division multiplexing (SDM) systems based on multicore fibers (MCFs) have been recently proposed for access networks [1], radio-over-fiber [2, 3], long-haul networks [4] and intra data centers communications [5]
A new solution to overcome the performance fluctuations over time induced by the combined effect of laser phaser noise
intercore crosstalk power variation induced by fast laser phase noise variations exceeded
Summary
Space-division multiplexing (SDM) systems based on multicore fibers (MCFs) have been recently proposed for access networks [1], radio-over-fiber [2, 3], long-haul networks [4] and intra data centers communications [5]. Several other works, dedicated to investigate the transmission capabilities of MCFs and exploiting adaptive techniques to mitigate the ICXT, were reported [1,2,3,4, 8, 23] None of those works investigated how the time evolution of the ICXT and of the system performance are affected by the laser phase noise. In [20], a preliminary study of the impact of the laser phase noise on the P-ICXT and on the performance of DD-OFDM MCF-based systems was performed experimentally and by simulation using a single polarization time varying ICXT model. The two adaptive solutions using extended time memory to estimate the bit loading schemes employed in the OFDM subcarriers are further exploited to relax the outage probability caused by the combined effect of the time varying ICXT and laser phase noise impairments
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