RESUMEN
A measurement of polarization mode dispersion (PMD) vector distribution is implemented with a wavelength-tunable state-of-polarization-detection-based optical time domain reflectometry (SOP-OTDR). Derived from the dynamic equation between the PMD vector and the birefringence vector with a piecewise approximation method, we present an equation for piecewise expression of the relation between the two vectors based on the approximation that the second-order partial derivative of the PMD vector with respect to the length is negligible in each short-enough segment of optical fiber. Utilizing the birefringence vector distributions at three adjacent wavelengths, both the magnitude and the direction distributions of the PMD vector have been calculated through the numerical solution algorithm. The calculation results indicate that the measured magnitudes of PMD vectors are consistent with the statistical experience, which is the Maxwell probability distribution, and the second-order partial derivative magnitudes of the PMD vectors conform to the lognormal distribution. This method could provide a distributed approach for optical performance monitoring by PMD-related characteristics in optical fiber links.
RESUMEN
The transmission performance of 112 Gbit/s PAM-4 signal with commercial 25 G-class EML and APD is experimentally studied by using advanced digital signal processing (DSP) algorithms, i.e. pre-equalization (Pre-EQ), error-table based pre-correction (ETC), least-mean square (LMS) based equalization, direct detection faster than Nyquist (DD-FTN) algorithm. Among them, Pre-EQ and ETC are implemented at the transmitter, and ETC is a symbol-pattern-dependent pre-compensation algorithm based on the look-up-table approach. In order to obtain these pre-compensated parameters readily, a joint equalization and error table generation (JEEG) module is proposed. Employing the combination of ETC, LMS, and DD-FTN, a single line 112 Gbit/s PAM-4 40 km amplifier-less transmission with a record receiver sensitivity of -16.6 dBm (at 7% HD-FEC threshold) is experimentally demonstrated. In addition, the computational complexities of different DSP schemes are analyzed and discussed in detail. The receiver computational complexity can be effectively reduced by employing appropriate ETC and Pre-EQ in the transmitter.
RESUMEN
Polarization-division-multiplexed (PDM) four-level pulse amplitude modulation (PAM4) with coherent detection is a promising low cost solution for 80 km inter-datacenter transmissions at 100 Gb/s and beyond. In this paper, three modified adaptive equalization algorithms for the PDM-PAM4 optical coherent systems, i.e. signal-phase aid least-mean-square (SP-LMS) algorithm, training multi-modulus algorithm (TMMA) and cascaded four-modulus algorithm (CMMA-4), are proposed and compared. Based on the proposed algorithms, 112 Gb/s PDM-PAM4 transmission over 80 km standard single mode fiber (SSMF) in C-band for a bit error rate (BER) below 3.8e-3 is successfully demonstrated without optical amplifier, chromatic dispersion (CD) pre-compensation and extra carrier recovery operations.