The authors report the detailed characterisation of a widely tunable laser and module that offers the elusive combination of very fast (nanosecond) tuning and narrow linewidth. The laser is fabricated on an active-passive InP-based platform and packaged into a 14-pin butterfly module. Electro-optic tuning is used with reversevoltage bias of tuning sections allowing mA-order dark currents and facilitating nanosecond switching speeds with low power dissipation. The device is suitable for integration into fiber coupled modules such as the nanoiTLA or can be monolithically integrated with other components in a III-V PIC. It is a promising new laser for applications that require fast and wide tuning with low linewidth, such as FMCW (Frequency-Modulated Continuous-Wave) LiDAR and coherent optical packet or burst switching.
KEYWORDS: Digital signal processing, Polarization, Modulation, Eye, Signal detection, Single mode fibers, Numerical simulations, Signal processing, Quadrature amplitude modulation, Data transmission
DP-PAM8 modulated signals with probabilistic constellation shaping (PCS) are investigated for ultrahigh-data rates with diverse shaping strengths and DGD values using direct detection for short distances mainly seen in data centers. The investigation is conducted using numerical simulation, where system performance improvement is achieved when PCS is used. The probabilistic shaping mitigated the uncompensated DGD and dispersion effects in the transmission system. We found that the high-powered symbols close the eye causing high symbol error. Applying PCS opens the eye of the highpowered symbols but closes the eye for low-powered ones. Thus, optimization of the strength of shaping is necessary to get the best performance. Experiments were conducted to investigate the effect of probabilistic shaping on PAM8 system amplified using an optical semiconductor amplifier (SOA). A single polarization PAM8 case was only demonstrated due to accessibility limitations of required parts for dual-polarization PAM8.
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