Low-power DAC-less PAM-4 transmitter using a cascaded microring modulator

Abstract

Future super-computer interconnect systems and data centers request ultrahigh data rate links at low cost and power consumption, for which transmitters with a high level of integration and spectral efficient formats are key components. We report 60 Gb/s pulse-amplitude modulation (PAM-4) of an optical signal using a dual-microring silicon photonics circuit, making a low-power, digital-to-analog converter (DAC)-less PAM modulator. The power consumption is evaluated below 100 fJ/bit, including thermal adjustments. To the best of our knowledge, these results feature the lowest reported power consumption for PAM signaling in a DAC-less scheme for data rate beyond 40 Gb/s.

Silicon photonic modulators for PAM transmissions

“…11c and 12c). In segmented MZMs or cascaded architectures using compact MRMs (e.g., DAC-less driving configurations to be discussed in the next section), the skew will be exacerbated in the presence of delay mismatch between their driving signals [34,35]. Eye skew will become more important as we push to higher baud rates as shorter rise/fall edges demand more accurate sample timing.…”

Silicon Photonic Mach–Zehnder Modulator Architectures for on Chip PAM-4 Signal Generation

“…In this manuscript we focus on different silicon photonic (SiP) travelling wave Mach Zehnder modulator (TWMZM) architectures which enable PAM-4 signal generation in the optical domain versus generating the PAM-4 signal in electrical domain. Over the past few years, there has been significant work on PAM-4 generation using vertical-cavity surface-emitting lasers (VCSEL)s [7][8], silicon photonic ring modulators [9][10][11][12][13], silicon-germanium electrooptic modulators [14][15], III-V-onsilicon modulators [16] silicon hybrid modulators [17], TWMZMs [18][19][20][21][22][23][24], electro-optic polymer modulators [25] and LiNbO3 modulators [26]. In the majority of the presented works, PAM-4 is generated in the electrical domain either by passive power combination of two OOK signals or using digital to analog convertors (DACs) and digital signal processing (DSP).…”

DAC-less PAM-4 generation in the O-band using a silicon Mach-Zehnder modulator

“…High-speed silicon modulators are generally based on phase modulation by free carrier concentration variations. Various structures have been investigated in order to generate PAM-4 signals, including Mach-Zehnder modulators (MZMs), ring resonator modulators (RRMs) [10][11][12][13][14][15][16][17][18][19][20][21][22], ring-assisted Mach-Zehnder modulators (RAMZMs) [23][24][25], Mach-Zehnder assisted ring modulators (MZARMs) [26,27], or Michelson interferometer-based modulators (MIMs) [28]. Until now, most of the reported demonstrations have been done in the C-band of communications, while the development of PAM-4 modulators in the O-band is still in its infancy [6][7][8][9][10].…”

“…PAM-4 signals are usually generated in the electrical domain by means of power-hungry digital-to-analog converters (DACs), before being converted to the optical domain by the modulator. To reduce the overall power consumption, new DAC-less configurations have been proposed, enabling the generation of the four intensity levels in the optical domain from two independent binary electrical sources [5][6][7][8][9][14][15][16][17][18][19][20][21][25][26][27][28]. A common approach to generate PAM-4 levels with two driving sources is to use segmented electrodes, as it has the advantage of lowering the power consumption and allowing high symbol rates [14].…”