Abstract
Polarization-insensitive modulation, i.e., overcoming the limit of conventional modulators operating under only a single-polarization state, is desirable for high-capacity on-chip optical interconnects. Here, we propose a hybrid graphene-silicon-based polarization-insensitive electro-absorption modulator (EAM) with high-modulation efficiency and ultra-broad bandwidth. The hybrid graphene-silicon waveguide is formed by leveraging multi-deposited and multi-transferred methods to enable light interaction with graphene layers in its intense field distribution region instead of the commonly used weak cladding region, thus resulting in enhanced light–graphene interaction. By optimizing the dimensions of all hybrid graphene-silicon waveguide layers, polarization-insensitive modulation is achieved with a modulation efficiency (ME) of ~1.11 dB/µm for both polarizations (ME discrepancy < 0.006 dB/µm), which outperforms that of previous reports. Based on this excellent modulation performance, we designed a hybrid graphene-silicon-based EAM with a length of only 20 µm. The modulation depth (MD) and insertion loss obtained were higher than 22 dB and lower than 0.23 dB at 1.55 µm, respectively, for both polarizations. Meanwhile, its allowable bandwidth can exceed 300 nm by keeping MD more than 20 dB and MD discrepancy less than 2 dB, simultaneously, and its electrical properties were also analyzed. Therefore, the proposed device can be applied in on-chip optical interconnects.
Highlights
Silicon photonics based on the mature silicon-on-insulator (SOI) platform has aroused tremendous interest for building compact, high performance, and energy-efficient photonic integrated circuits (PICs), which has promoted the rapid development of optical interconnects, especially for data center and telecom applications [1,2,3,4]
In summary, using multi-deposited and multi-transferred methods, we propose a highly-efficient, ultra-broadband, and polarization-insensitive electro-absorption modulator (EAM), the key part of which is a hybrid graphene-silicon waveguide formed by five inverted U-shaped graphene-silicon layers
In order to effectively enhance light–graphene interaction (LGI), multi-deposited and multi-transferred graphene-silicon layers are employed such that light interacts with the graphene layers at high optical intensity in the interior of the hybrid graphene-silicon waveguide rather than at weak optical intensity in the cladding region, as commonly done
Summary
Silicon photonics based on the mature silicon-on-insulator (SOI) platform has aroused tremendous interest for building compact, high performance, and energy-efficient photonic integrated circuits (PICs), which has promoted the rapid development of optical interconnects, especially for data center and telecom applications [1,2,3,4]. Graphene, a single-atom-layer of graphite with its atoms arranged in a hexagonal lattice [15], has become a promising two-dimensional (2D) material in the field of photonics and electronics with its exceptional optical/electrical properties such as ultra-high carrier mobility (e.g., >200,000 cm2·V−1·s−1 at room temperature) [16], tunable conductivity, broad bandwidth, zero bandgap, and CMOS compatible processes [17,18,19] These remarkable properties match up well with the performance requirements and developing directions of silicon modulators if graphene can be effectively integrated on the SOI platform [20,21].
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