Optical PAM-4 signal generation using a silicon Mach-Zehnder optical modulator

Abstract

An analytic model is proposed to study the linearity performance of the silicon Mach-Zehnder optical modulator. According to the simulation results, we optimize the width of the silicon rib waveguide and the location of the PN junction to improve the linearity performance. The fabricated silicon Mach-Zehnder optical modulator has a spurious free dynamic range of 113.3 dB.Hz and 88.9 dB.Hz for the third-order intermodulation distortion and the second-order harmonic distortion. We also demonstrate the optical four-level pulse-amplitude-modulation (PAM-4) signal generation through the device. The generated optical PAM-4 signal is characterized at the rates up to 35 Gbaud. The BERs of the optical PAM-4 signals can reach 5.2╳10 at 20 Gbaud and 6.6╳10 at 32 Gbaud, which are much lower than the threshold of hard decision forward error correction (3.8 ╳10).

Silicon photonic modulators for PAM transmissions

“…Recall that the term PER(PAM) already accounts for multiple bandwidth, BWEO, on L; see appendix A (20). All other plots Fig.…”

“…Despite the inherent nonlinear phase and absorption responses in the plasma dispersion effect, SiP MZMs showed good linearity [18][19][20]. Up to 88.9 dB•Hz 1/2 of second-order SFDR and 113.3 dB•Hz 2/3 of third-order IMD-SFDR were measured using a SiP MZM [20].…”

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].…”