We developed an estimation method that enables frequency-resolved 4-Dimensional (4D) IQ impairment characterization of polarization-multiplexed transceivers in the presence of arbitrary crosstalk across four IQ lanes. We demonstrated the method with 96-Gbaud 16QAM signals.

The periodically poled LiNbO3 (PPLN) based optical parametric amplifier (OPA) is a technology that contributes to the construction of multi-band wavelength-division multiplexing (WDM) optical networks thanks to its wide amplification bandwidth and wavelength conversion function. In addition, the fast response of the OPA means it is unaffected by sudden changes of wavelength channels due to dynamic channel add-drop. However, such fast response leads to nonlinear signal distortion when operating in the gain saturation region. This paper experimentally investigates the conversion of gain saturation into the nonlinear amplitude distortion in a 64-Gbaud 64QAM WDM signal. We characterized the input power tolerance of a PPLNbased OPA in wideband WDM applications and found that the nonlinear amplitude distortion can be suppressed by increasing the number of WDM channels. For a 75-GHz-spacing 64-channel WDM configuration, the total input power tolerance was improved by ~10 dB compared to a single-channel case. We also confirmed that there is almost no wavelength dependence of the effect of gain saturation on the signal distortion. These results show that PPLN-based OPAs have a wide total input power range for amplifying wideband WDM signals in terms of the nonlinear distortion.

Signal impairments caused by the relative characteristic differences and crosstalk between electrical inphase (I) lanes and quadrature (Q) lanes are some of the main obstacles to the development of 100-Gbaud-class high-symbol-rate transceivers. To address such IQ impairments, we propose a method for enabling fully frequency-resolved four-dimensional (4D) characterization of IQ impairments even in the presence of arbitrary crosstalk across four IQ lanes of polarizationmultiplexed transceivers. We formulated a 4D signal-propagation model that takes into account inter-polarization IQ crosstalk and found how to separate the 4D IQ characteristics of the transmitter and receiver from the coefficients of a single-layer complex 8×2 multiple-input multiple-output adaptive equalizer on the basis of the model. We also introduce an application of the method for characterizing typical IQ impairments (e.g., IQ skew, IQ amplitude imbalance, phase deviation) from the filter coefficients. We numerically and experimentally tested our method with 96-Gbaud 16QAM signals and demonstrated its feasibility.

We characterized inter-mode-group crosstalk of 75.2-km-long three-mode fiber transmission lines with a full-field digital holography system in which a reference wave is “remotely” generated at the output side by utilizing optical injection locking.

We demonstrate a 5×80-km WDM transmission over 6 THz within 1597.19–1649.93 nm. PPLN-based optical parametric amplifiers provide sufficient gain for inline amplification of 60-channel 640-Gbps/λ signals allocated in L- and U-bands.