Silicon photonics plasma-modulators with advanced transmission line design

Abstract

We have investigated two novel concepts for the design of transmission lines in travelling wave Mach-Zehnder interferometer based Silicon Photonics depletion modulators overcoming the analog bandwidth limitations arising from cross-talk between signal lines in push-pull modulators and reducing the linear losses of the transmission lines. We experimentally validate the concepts and demonstrate an E/O -3 dBe bandwidth of 16 GHz with a 4V drive voltage (in dual drive configuration) and 8.8 dB on-chip insertion losses. Significant bandwidth improvements result from suppression of cross-talk. An additional bandwidth enhancement of ~11% results from a reduction of resistive transmission line losses. Frequency dependent loss models for loaded transmission lines and E/O bandwidth modeling are fully verified.

Advances in silicon photonics segmented electrode Mach-Zehnder modulators and peaking enhanced resonant devices

“…Phase matching is independently addressed here by regularly placed optical delay lines ( fig. 2(e)) [9] or meandered waveguides [10] that can compensate phase mismatch provided the group index of the waveguides is smaller than the RF index of the transmission line. In silicon-on-insulator (SOI) waveguides, due to the high refractive index contrast between the core and the cladding, small bends can be implemented with small losses and thus the design of phase recovery loops is straightforward.…”

“…The reduced series resistance of the phase shifter lowers the RF propagation losses and improves the bandwidth of the modulator. Details on the design of these structures can be found in [9].…”

“…Several schemes can be chosen from to electrically drive such structures that can be broadly categorized into 1. driving the modulator as a lumped element with a monolithically or hybridly co-integrated driver, e.g. as is typically done for resonant ring modulators (RRMs) [8] or very short Mach Zehnder Modulators (MZIs), 2. impedance matched driving of travelling wave (TW) modulators [9] and 3. driving of segmented modulators with a cointegrated distributed driver [10].…”

Epitaxially grown vertical junction phase shifters for improved modulation efficiency in silicon depletion-type modulators

“…To slow down the optical wave and obtain phase matching, we have increased the optical path length by meandering the waveguide. Metal extensions contact the metal lines to the waveguide, reducing the series resistance of the loaded transmission line (and thus reducing transmission line losses and increasing the electro-optic bandwidth) without increasing the fringe capacitance between the metal lines or significantly changing the RF index [11][12]. As in Fig.…”

“…The simulation results predict a cutoff frequency of 21 GHz mainly limited by RF losses in the transmission line. Since achieving a characteristic impedance of 50 Ω is very challenging due to the high capacitive load applied to the transmission line [12], the travelling wave modulator is designed for a 25 Ω system, which is also beneficial in terms of RF losses at the cost of increased power consumption [11][12]. …”