Electro-optic polymer based mid-index phase modulator in silicon nitride waveguide technology

Abstract

Among the demand for higher bandwidth driven by media and cloud computing applications grows, the need for cost and power efficient, short reach and long-haul optical transceivers becomes more eminent. Silicon photonics is emerging as a technology of choice for realising photonic integrated circuits for intensity modulation-direct detection communication systems. Silicon Nitride (SiN) is a common material in the electronics industry and is now becoming a choice of materials for the photonics industry as it is a fully compatible platform for photonic integrated circuits. Advantage in using the SiN waveguide as the EO polymer modulator are the low number in fabrication step. In this research, the electro-optic polymer modulations have been adapted to design high-speed phase modulator on low temperature silicon nitride platforms. The side-chain EO polymer with Phenyl vinylene thiophene vinylene (FTC) based chromophore that can provides the outstanding EO coefficient will be used as a modulating medium. In order to achieve a high modulation performance and also keep a fabrication still simple and low-cost, the SiN strip and slot structure has been investigated to provide an enlarge overlap between optical and electrical modulating field. All designs of modulators in this research can be fabricated using only two lithography steps and a lowcost CMOS compatible BEOL process decreasing substantially fabrication time and design/test turnaround. Photonic and electrical RF models were cooperatively simulated to optimise dimension parameters of the phase modulator with in-plane CPW electrode integrated to three different SiN waveguide platforms. The modulator devices were then fabricated in line with the simulated designs and coated with three different types of EO polymer cladding. The high voltage poling technique for activating an EO activity in polymer was presented with in-house developed setup. For the modulator measurements, the devices were characterised for the modulation performance mainly in DC mode, and the decent modulator was tested with the high-speed modulation experiment. The remarkable modulator in this research has exhibited the outstanding modulation performance among the reported MZI based modulators with EO polymer integration. The modulator with lowest half-wave voltage is presented with 10 V while the modulator with lowest voltage-length product is revealed with 3.4 V·cm. The transmission data rate in high-speed is demonstrated up to 40Gb/s with the extinction ration of ~2.6dB.

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Identifiers

ORCID for Frederic Gardes: orcid.org/0000-0003-1400-3272

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