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

Abstract

We report recent progress made in our laboratory on travelling wave Mach-Zehnder Interferometer based Silicon Photonics modulators with segmented transmission lines, as well as on resonant ring modulators and add-drop multiplexers with peaking enhanced bandwidth extended beyond the photon lifetime limit. In our segmented transmission lines, microstructuring of the electrodes results in radio-frequency modes significantly deviating from the transverse electromagnetic (TEM) condition and allows for additional design freedom to jointly achieve phase matching, impedance matching and minimizing resistive losses. This technique was found to be particularly useful to achieve the aforementioned objectives in simple back-end processes with one or two metallization layers. Peaking results from intrinsic time dynamics in ring resonator based modulators and add-drop multiplexers and allows extending the bandwidth of the devices beyond the limit predicted from the photon lifetime. Simple closed form expressions allow incorporating peaking into system level modeling.

Silicon photonics WDM transmitter with single section semiconductor mode-locked laser

“…An analysis of the transient response of the light to an effective index change in the cavity has, however, shown that this equation, while providing a reasonable first order approximation for a typical RRM operated in OOK modus, is actually inaccurate and requires further refinements for best device optimization. Here, we will summarize these time dynamics in the small signal limit with the formalism used in [38] for RRMs and [39] for RR-OADMs. We start with the following equations, introduced in [27], describing the time dynamics of the optical field in ring resonators assuming the round trip time to be small compared to other time constants such as the photon lifetime, the inverse radio frequency (RF) modulation frequency or the inverse optical carrier detuning…”

“…Carefully adjusting parameters such as waveguide geometry, coupling strength between the ring and the bus waveguide [33], dopant concentrations [34] and the width of the pin diode's intrinsic region allowed us to optimize the RRMs for several targeted data rates. In order to accurately model the RRMs, transient effects in the optical domain [23,27,33,[35][36][37] have to be taken into account, as we also showed in [38] and [39]. Apart from adjusting design parameters, we are also optimizing the operation of the RRMs by adjusting the detuning between optical carrier frequency and the resonance frequency of the RRM (the optical carrier detuning), taking optical peaking effects into account to optimize the tradeoff between E/O bandwidth and optical modulation amplitude (OMA).…”

“…In [39], we reported a systematic experimental study of the effect of the ring to waveguide coupling strength on the normalized OMA (given by normalized OMA = (P 1 -P 0 )/P in , where P in is the on-chip power entering the RRM and P 1 and P 0 are, respectively, the '1' and '0' signal levels after the RRM) and on the E/O bandwidth for two waveguide geometries and fixed waveguide dopant concentrations of p…”

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]. …”