Abstract
We based on integrated silicon-on-insulator platforms design the key components of an on-chip interferometer, beam splitter and directional coupler included, valid in high-visibility interference at telecommunication wavelengths. Special attention is given to the equal-proportion beam splitting and directional coupling, which is achieved by carefully designing the geometric dimension of multi-mode interferometer structure. The proposed interferometer facilitates low loss, broad operating bandwidth, anticipated large tolerance on size variation induced in fabrication procedures, based on a particular wafer with silicon layer thickness of 320 nm. The most highlight property of polarization-insensitive, enables the path-selective qubits generation for bi-polarization that further makes possible quantum key distribution using high dimensional protocols. We numerically demonstrate interference at 1550 nm with visibilities of 99.50% and 93.99% for transverse-electric and transverse-magnetic polarization, respectively, revealing that the proposed interferometer structure is well capable of on-chip optical control especially in quantum optics regime.
Highlights
Quantum key distribution (QKD) is arguably the most mature technology in quantum optics[1], which facilitates high security communication using optical cryptography in the single-photon regime
Special attention of designing the multi-mode interferometer (MMI) is given to the inter-mode effective refractive index difference between the fundamental modes and the first-order modes, Δneff = |neff,0 − neff,1|, where the critical polarization-insensitive structure facilitates the same Δneff for both polarizations, that is, Δneff(TE) = Δneff(TM)
The beat lengths with respect to two polarizations take the same value, i.e. Lπ(TE) = Lπ(TM), which can be achieved by carefully optimizing the cross-sectional dimension of MMI
Summary
Quantum key distribution (QKD) is arguably the most mature technology in quantum optics[1], which facilitates high security communication using optical cryptography in the single-photon regime. Silicon waveguide enables nonlinear coefficient of several orders of magnitude higher than highly nonlinear fibers, in addition to have easy-filtered narrow-linewidth Raman scattering response[15,16]. It becomes appealing as SOI components can facilitate correlated photon-pair generation via spontaneous four-wave mixing[17] and quantum interference simultaneously[18]. Few of previous studies[11,12,13,14,19,20,21], to our best knowledge, notice that the probable visibility reduction caused by unequal-proportion directional coupling, may be acceptable for classical applications, but significantly lower the accuracy of quantum cryptography[22] It is appealing if quantum interferometer operates.
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