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Opto-mechanical interactions in planar photonic integrated circuits draw great interest in basic research and applications. However, opto-mechanics is practically absent in the most technologically significant photonics platform: silicon on insulator. Previous demonstrations required the under-etching and suspension of silicon structures. Here we present surface acoustic wave-photonic devices in silicon on insulator, up to 8 GHz frequency. Surface waves are launched through absorption of modulated pump light in metallic gratings and thermo-elastic expansion. The surface waves are detected through photo-elastic modulation of an optical probe in standard race-track resonators. Devices do not involve piezo-electric actuation, suspension of waveguides or hybrid material integration. Wavelength conversion of incident microwave signals and acoustic true time delays up to 40 ns are demonstrated on-chip. Lastly, discrete-time microwave-photonic filters with up to six taps and 20 MHz-wide passbands are realized using acoustic delays. The concept is suitable for integrated microwave-photonics signal processing.

Dense wavelength division multiplexers are key components of data communication networks. This paper presents a silicon-photonic eight-channel multiplexer device with a channel spacing of only 0.133 nm (17 GHz). Devices were fabricated in a commercial silicon foundry, in 8" silicon-on-insulator wafers. The device layout consists of seven unbalanced Mach-Zehnder interferometers in a cascaded tree topology, and each interferometer unit also includes a nested ring resonator element. The transfer function of each unit is that of a maximally flat, autoregressive, moving-average filter. The devices are characterized by uniform passbands, sharp spectral transitions between pass and stop bands, and strong out-of-band rejection. The worst-case optical power crosstalk is −22 dB. The proper function of the device requires careful control of optical phase delays over 14 distinct optical paths. Post-fabrication trimming of phase delays was performed through local illumination of a photo-sensitive upper cladding layer of chalcogenide glass. The de-multiplexing of three adjacent QAM-16, 40 Gbit/s wavelength-division channels was successfully demonstrated. The devices are applicable in data communication and in integrated-photonic processing of radio-over-fiber waveforms.

Metal oxides are the cornerstone of thin‐film electronics, a multibillion dollar industry, because they possess a wide variety of optoelectronic properties, exhibit novel functionalities, and can typically be fabricated from cheap, nontoxic raw materials. However, for thin‐film electronics to achieve further market penetration, it is necessary to replace expensive vacuum‐based fabrication processes with low‐cost, large‐scale solution‐based methods. Here, the influence of exposure to air on the band energies of metal oxides is investigated, which is crucial for predicting the operation of thin‐film devices under realistic conditions. A universal reduction in the work function is observed across 18 oxides, and for a subset, n‐type doping of the surfaces is observed after they have been exposed to atmosphere for extended periods of time. These effects arise from charge transfer events with the ubiquitous water layer that forms on surfaces in air. A quantitative analysis of the changes is provided based on the electrochemical transfer doping model, and the amount of transferred charge and the equilibrium work function of oxides in air are calculated which are in agreement with the measurements.

In this Letter, we systematically explore the influence of TiO2 thickness with nanometric variations over a range of 20–600 nm on the photovoltaic parameters (open-circuit voltage, short circuit current, fill-factor, and power conversion efficiency) of CH3NH3PbI3-based solar cells. We fabricate several sample libraries of 13 × 13 solar cells on large substrates with spatial variations in the thickness of the TiO2 layers while maintaining similar properties for the other layers. We show that the optimal thickness is ∼50 nm for maximum performance; thinner layers typically resulted in short-circuited cells, whereas increasing the thickness led to a monotonic decrease in performance. Furthermore, by assuming a fixed bulk resistivity of TiO2, we were able to correlate the TiO2 thickness to the series and shunt resistances of the devices and model the variation in the photovoltaic parameters with thickness using the diode equation to gain quantitative insights.