Experimental parametric study of 128 Gb/s PAM-4 transmission system using a multi-electrode silicon photonic Mach Zehnder modulator

Abstract

We present an experimental study and analysis of a travelling wave series push-pull silicon photonic multi-electrode Mach-Zehnder modulator (ME-MZM) and compare its performance with a single-electrode travelling wave Mach-Zehnder modulator (TWMZM). Utilizing the functionality of the ME-MZM structure plus digital-signal-processing, we report: 1) the C-band transmission of 84 Gb/s OOK modulated data below the KP4 forward error correction threshold with 2 V drive voltage over a distance of 2 km; 2) the transmission of a 128 Gb/s optical 4-level pulse amplitude modulated signal over 1 km of fiber; and 3) the generation of a 168 Gb/s PAM-4 signal using two electrical OOK signals. By comparing the transmission system performance measurements for the ME-MZM with measurements performed using a similar series push-pull TWMZM, we show that the ME-MZM provides a clear advantage in achieving higher baud PAM-4 generation and transmission compared to a TWMZM.

Silicon-organic hybrid (SOH) modulators for intensity-modulation / direct-detection links with line rates of up to 120 Gbit/s

“…Despite the small device length of only 0.5 mm, the modulator's energy consumption amounts to W bit = 100 fJ/bit, see Appendix B. This is significantly smaller than the 410 fJ/bit demonstrated for a 4.8 mm long depletion-type modulator at a comparable PAM4 line rate of 112 Gbit/s [12]. Note that even higher data rates can be achieved by using coherent transmission schemes along with advanced modulation formats such as 16-state quadrature amplitude modulation (16QAM) [35][36][37].…”

“…These devices, however, still have rather high voltage-length products of more than 5 Vmm [11], and rely on fabrication processes that are rather expensive and limited in scalability as compared to CMOS-based silicon photonic integration. Silicon photonic depletion-type pn-modulators have been shown to support PAM4 signaling at impressive line rates up to 168 Gbit/s [12]. These devices, however, are subject to the intrinsically limited efficiency of the underlying phase modulators, featuring voltage-length products U π L in excess of 6 Vmm for optimized devices [13] and in excess of 30 Vmm [14] for the 4.8 mm-long high-speed MZM used in [12].…”

“…Silicon photonic depletion-type pn-modulators have been shown to support PAM4 signaling at impressive line rates up to 168 Gbit/s [12]. These devices, however, are subject to the intrinsically limited efficiency of the underlying phase modulators, featuring voltage-length products U π L in excess of 6 Vmm for optimized devices [13] and in excess of 30 Vmm [14] for the 4.8 mm-long high-speed MZM used in [12]. This leads to large device lengths and high drive voltages, which require dedicated amplifiers.…”

“…Moreover, we demonstrate generation of PAM4 signals at line rates (symbol rates) up to 120 Gbit/s (60 GBd) using a silicon-based modulator [26]. Despite the small device length of only 0.5 mm, the modulator's energy consumption amounts to W bit = 100 fJ/bit, which is significantly smaller than the 410 fJ/bit demonstrated for a 4.8 mm long depletion-type modulator at a comparable PAM4 line rate of 112 Gbit/s [12]. To the best of our knowledge, our demonstration corresponds to the highest data rate hitherto achieved using a sub-millimeter MZM on the silicon photonic platform.…”

Advanced modulation format using silicon modulators in the O-band

“…However, in order to keep up with the growing bandwidth demand in datacom applications, it is necessary to move from binary on-off keying (OOK) modulation format to more advanced formats such as 4-level pulse amplitude modulation (PAM-4) or quadrature phase-shift keying (QPSK). Advanced modulation formats using silicon modulators have already been demonstrated [5][6][7][8]. However, most of these demonstrations have been carried out in the C-band of optical communication systems (1530 nm -1570 nm) where the FCPD is stronger.…”