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

Long-haul communication systems are requiring more and more spectral efficiency as data rates increase. QAM-16 is a promising candidate for each wavelength in a Wavelength-Division Multiplexed (WDM) system, providing double the spectral efficiency of Quadrature Phase-Shift Keying (QPSK) and four times the spectral efficiency of traditional On-Off Keying (OOK). However, generation of QAM-16 signals can be complex, expensive, and power-hungry when electrical Digital-to-Analog Converters (DACs) are required. We have developed a QAM-16 modulator that precludes the use of an electrical DAC while simultaneously keeping the optical architectural complexity similar to that of a traditional In-phase/Quadrature (IQ) modulator. Using this modulator, we experimentally demonstrate single-polarization, back-to-back transmission, and homodyne detection of QAM-16 signals at rates up to 28.125 Gsymbols/s, resulting in single-polarization system per-wavelength bit rates up to 112.5 Gb/s. This would translate to dual-polarization system per-wavelength bit rates up to 225 Gb/s. This is done using a segmented modulator built on an ultra-low-power CMOS Photonics platform, allowing the modulator and drivers to consume less than 1 W of power.