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Vanadium dioxide (VO2) is one of the most promising materials for developing hybrid photonic integrated circuits (PICs). At telecommunication wavelengths, VO2 exhibits a large change on the refractive index (∆n ∼ 1 and ∆κ ∼ 2.5) between its insulating and metallic state. Such insulating-to-metal transition (IMT) can be triggered by light, which could enable alloptical hybrid VO2-waveguide devices. Here, we experimentally demonstrate an all-optical absorption switch using a hybrid VO2/Si waveguide fully compatible with the silicon photonics platform. All-optical characterization was carried out for TE polarization and at telecommunication wavelengths using an in-plane approach. The temporal dynamics were retrieved by using pump-probe measurements. Our results show an extinction ratio of 0.7 dB/µm with a maximum switchable length of 15 µm, a switching speed as low as 318 ns and an energy per switch of 15.8 nJ. The inherit large optical bandwith of a nonresonant waveguide poses this device as a promising candidate for developing all-optical and broadband silicon PICs.

We estimate how well we will know the parameters of solar neutrino oscillations after KamLAND and Borexino. The expected error on ∆m 2 is few per-mille in the VO and QVO regions, few per-cent in the LMA region, and around 10% in the LOW region. The expected error on sin 2 2θ is around 5%. KamLAND and Borexino will tell unambiguously which specific new measurement, dedicated to pp solar neutrinos, is able to contribute to the determination of θ and perhaps of ∆m 2 . The present data suggest as more likely outcomes: no measurement, or the total pp rate, or its day/night variation.

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