Abstract
The high refraction-index contrast between silicon and the surrounding cladding makes silicon-on-insulator devices highly polarization-dependent. However, it is greatly desirable for many applications to address the issue of polarization dependence in silicon photonics. Here, a novel ultra-compact polarization splitter and rotator (PSR), constructed with an asymmetrical directional coupler consisting of a rib silicon waveguide and a graphene-embedded rib silicon waveguide (GERSW), on a silicon-on-insulator platform is proposed and investigated. By taking advantage of the large modulation of the effective refractive index of the TE mode for the GERSW by tuning the chemical potential of graphene, the phase matching condition can be well satisfied over a wide spectral band. The presented result demonstrates that for a 7-layer-graphene-embedded PSR with a coupling length of 11.1 μm, a high TM-to-TE conversion efficiency (>−0.5 dB) can be achieved over a broad bandwidth from 1516 to 1602 nm.
Highlights
Integrated photonic devices built on silicon-on-insulator (SOI) have been attractive for their compatibility with mature, complementary metal-oxide-semiconductor-compatible technologies[1]
When graphene is horizontally embedded into a rib silicon waveguide (RSW), the effective refractive index (ERI) of the TE mode undergoes a significant variation by tuning the chemical potential of graphene via bias voltage
An ultra-compact polarization splitter and rotator (PSR) has been proposed and numerically demonstrated by utilizing an asymmetrical directional coupler (ADC) consisting of a RSW and a graphene-embedded rib silicon waveguide (GERSW)
Summary
Considering that the modal characteristics for the TE mode in the GERSW can be changed with a broader range than that for the TM mode by tuning the chemical potential of graphene, the TE mode in the GERSW and the TM mode in the RSW are employed to satisfy the phase-matching condition. Because the modal characteristics of the TM mode in the GERSW would be negligibly influenced by using different numbers of graphene layers around μc = 0.5 eV [Fig. 3(d)], the wavelength dependence of the PSR for the TM input is almost unchanged [Fig. 3(e)]. In the case of λ < 1550 nm (>1550 nm), the ERI of the TE mode in the GERSW can be increased (decreased) by tuning the chemical potential of graphene to make the phase-matching condition well satisfied; the operation bandwidth of the PSR might be effectively extended. Insertion loss ILTM-TE > −0.5 dB ILTE-TE > −0.3 dB −0.6 dB (total) ILTM-TE > −0.09 dB ILTE-TE > −0.07 dB ILTM-TE > −0.26 dB
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