Ultra-Low-Power Single-Polarization QAM-16 Generation Without DAC Using a CMOS Photonics Based Segmented Modulator

Light-induced metal-like surface of silicon photonic waveguides

“…For example, surface effects are likely to play an important role in Si photonic modulators, based for instance on p-i-n junctions16 or capacitor structures embedded in Si waveguides17, as well as integrating electro-optic organic18 or 2D19 cladding materials. In these devices, the waveguide core is typically contacted to the metal electrodes through Si layers, which are slightly doped to avoid optical loss, but introduce a series resistance that limits the maximum modulation speed.…”

“…The density of the free carriers generated on the surface is more than 100 times larger than that of the free carriers thermally generated in the bulk, thus making the surface properties move towards those of metals. This effect overwhelms the conductivity of bulk Si in the absence of light, and becomes relevant in Si electro-optic devices where slightly doped regions are used, such as in modulators16171819 and micro-heaters embedded in the waveguide core14. Furthermore, we provide the first direct evidence that surface free carriers are responsible for an additional optical absorption mechanism, hereinafter named surface free-carrier absorption (SCA), that increases linearly with light intensity.…”

Segmented Optical Transmitter Comprising a CMOS Driver Array and an InP IQ-MZM for Advanced Modulation Formats

“…without taking into account the timing and mapping circuitry which consumes around 0.6 W). The IQ-drivers in [8] and [9] consume respectively 0.5 W and 0.75 W per arm, without the retiming capability though. As a comparison, a solution with an electrical DAC functionality easily consumes 2 W [13] clearly illustrating the potential of a segmented transmitter.…”

“…10 Gbit/s PAM-8 intensity modulation was shown with a hybrid configuration of a 3-bit SEMZM and an electrical DAC [7]. IQ-modulation for coherent communication was demonstrated using two 2-bit SEMZMs for 16-QAM at 28 GBd [8] and for 64-QAM at 32 GBd using two 4-bit SEMZMs [9]. Only the driver in [8] is benefiting from the potential of the small lumped capacitances of a segmented electrode with a low-power CMOS logic driver.…”

“…IQ-modulation for coherent communication was demonstrated using two 2-bit SEMZMs for 16-QAM at 28 GBd [8] and for 64-QAM at 32 GBd using two 4-bit SEMZMs [9]. Only the driver in [8] is benefiting from the potential of the small lumped capacitances of a segmented electrode with a low-power CMOS logic driver. No retiming circuitry is present however, making it not readily extendable to a higher resolution and speed, as timing matching is the most challenging aspect.…”