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InAlGaAs tunnel diodes, lattice-matched to InP and grown by molecular beam epitaxy, are demonstrated with peak tunneling current densities exceeding 1200 A/cm2. This was achieved by a 20 °C reduction in growth temperature for the p-type tunnel diode layers, resulting in up to two orders of magnitude improvement in the peak tunneling current density. Secondary ion mass spectrometry measurements reveal that the lower growth temperature reduces unwanted segregation of p-type Be dopants, improving dopant incorporation within the active tunnel diode layers. The diodes are transparent to wavelengths above 1000 nm and are compatible with the bottom junctions of InP-based multi-junction solar cells and with InP-based photonic power converters operating in the telecommunication O- and C-bands. When incorporated into a dual-junction photonic power converter test structure, measurements under 1319-nm laser illumination demonstrate integrated tunnel diode operation, enabling a halving of the short-circuit current and doubling of the open-circuit voltage as compared to a single junction reference device.

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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.