RESUMO
Intensity modulators are fundamental components for integrated photonics. From near-infrared (NIR) to visible spectral ranges, they find applications in optical communication and quantum technologies. In particular, they are required for the control and manipulation of atomic systems such as atomic clocks and quantum computers. Typical integrated electro-optic modulators operating at these wavelengths show high bandwidth and low-voltage operation, but their extinction ratios are moderate. Here we present an integrated thin-film lithium niobate electro-optic (EO) modulator operating in the C-band, which uses a subsequent periodically poled waveguide to convert the modulated signal from 1536 to 768 nm using the second-harmonic (SH) generation. We demonstrate that the upconverted signal retains the characteristics of the modulated input signal, reaching a measured high bandwidth of 35 GHz. Due to the nature of the nonlinear process, it exhibits, with respect to the fundamental signal, a doubled extinction ratio of 46 dB, which is the highest, to the best of our knowledge, recorded for near-infrared light on this platform.
RESUMO
The generation of photon pairs from nanoscale structures with high rates is still a challenge for the integration of quantum devices, as it suffers from parasitic signals from the substrate. In this work, we report type-0 spontaneous parametric down-conversion at 1550 nm from individual bottom-up grown zinc-blende GaAs nanowires with lengths of up to 5 µm and diameters of up to 450 nm. The nanowires were deposited on a transparent ITO substrate, and we measured a background-free coincidence rate of 0.05 Hz in a Hanbury-Brown-Twiss setup. Taking into account transmission losses, the pump fluence, and the nanowire volume, we achieved a biphoton generation of 60 GHz/Wm, which is at least 3 times higher than that of previously reported single nonlinear micro- and nanostructures. We also studied the correlations between the second-harmonic generation and the spontaneous parametric down-conversion intensities with respect to the pump polarization and in different individual nanowires.
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We present a graph-based model for multiple scattering of light in integrated lithium niobate on insulator (LNOI) networks, which describes an open network of single-mode integrated waveguides with tunable scattering at the network nodes. We first validate the model at small scale with experimental LNOI resonator devices and show consistent agreement between simulated and measured spectral data. Then, the model is used to demonstrate a novel platform for on-chip multiple scattering in large-scale optical networks up to few hundred nodes, with tunable scattering behaviour and tailored disorder. Combining our simple graph-based model with material properties of LNOI, this platform creates new opportunities to control randomness in large optical networks.
RESUMO
Phase shifters are key components of large-scale photonic integrated circuits. For the lithium niobate-on-insulator (LNOI) platform, thermo-optic phase shifters (TOPS) have emerged as a more stable and compact alternative to common electro-optic phase shifters (EOPSs), which are prone to anomalous behavior and drifting at low frequencies. Here, we model and experimentally characterize the influence of geometry on the performance of metal strip TOPSs. Compared to EOPSs, a 10-fold reduction of the voltage-length product is measured and bandwidths beyond 100 kHz are demonstrated, while keeping the footprint as low as 0.04 mm2. This shows the potential of TOPSs as small-scale building blocks for stable tuning and switching in LNOI photonic circuits.
RESUMO
Miniaturised optical spectrometers are attractive due to their small footprint, low weight, robustness and stability even in harsh environments such as space or industrial facilities. We report on a stationary-wave integrated Fourier-transform spectrometer featuring a measured optical bandwidth of 325 nm and a theoretical spectral resolution of 1.2 nm. We fabricate and test on lithium niobate-on-insulator to take full advantage of the platform, namely electro-optic modulation, broad transparency range and the low optical loss achieved thanks to matured fabrication techniques. We use the electro-optic effect and develop innovative layouts to overcome the undersampling limitations and improve the spectral resolution, thus providing a framework to enhance the performance of all devices sharing the same working principle. With our work, we add another important element to the portfolio of integrated lithium-niobate optical devices as our spectrometer can be combined with multiple other building blocks to realise functional, monolithic and compact photonic integrated circuits.