Tunable Extinction Ratio Research Articles

A non-volatile optical filter based on a Ge2Sb2Te5-assisted microring with a tunable bandwidth and extinction ratio

A novel non-volatile optical filter with a large bandwidth (BW) and extinction ratio (ER) tunability is first experimentally demonstrated by introducing an all-optical phase change of Ge2Sb2Te5 (GST). The Si-GST hybrid device promises flexible multi-level regulation of essential filter parameters in an ultra-compact footprint of 30 μm × 13 μm. Ultra-low power consumption is realised on account of the saving of external static power that is required in other electric-optic or optic-optic-driven filters. The GST is loaded onto two triple-waveguide directional couplers located at the coupling regions of an add-drop microring resonator. By initiating the GST phase transition with pump optical pulses, the transmitted optical power to the cross port of the triple-waveguide coupler is adjustable, hence influencing the coupling efficiency states of the microring filter. Consequently, a tunable on-off ER from 0.7 dB to 18.2 dB and a tunable BW from 0.6 nm to 3.3 nm are experimentally obtained with the aid of optically manipulating the crystallization degree of GST. Our device potentially enables the realisation of high-density photonic integrated circuits, especially in dense wavelength division multiplexing networks.

Patterning-effect mitigating intensity modulator for secure decoy-state quantum key distribution.

Quantum key distribution (QKD) is a technology that allows two users to exchange cryptographic keys securely. The decoy state technique enhances the technology, ensuring keys can be shared at high bit rates over long distances with information theoretic security. However, imperfections in the implementation, known as side-channels, threaten the perfect security of practical QKD protocols. Intensity modulators are required for high-rate decoy-state QKD systems, although these are unstable and can display a side channel where the intensity of a pulse is dependent on the previous pulse. Here we demonstrate the superior practicality of a tunable extinction ratio Sagnac-based intensity modulator (IM) for practical QKD systems. The ability to select low extinction ratios, alongside the immunity of Sagnac interferometers to DC drifts, ensures that random decoy state QKD patterns can be faithfully reproduced with the patterning effects mitigated. The inherent stability of Sagnac interferometers also ensures that the modulator output does not wander over time.

Photoactive photonic liquid crystal fiber polarization switches

This study presents a light-controlled photonic liquid crystal fiber (PLCF) polarization switch. The solid-core PCF has an index-guiding effect that reduces the insertion loss produced by infiltrating liquid crystals (LCs) with a low refractive index (RI). The proposed approach achieves photoactive tuning through the trans–cis photoisomerization of doped azobenzene, which modulates the RI of infiltrated LCs. This design achieves an optically tunable extinction ratio of average 10dB and photonic bandgap in the wavelength range of 1527–1538nm under 30mW laser illumination. The repeatable and switchable phase change is nearly 60°, corresponding to a response time of 100ms, which is to date the fastest light-tunable PLCF polarization switch available.

Variable carrier reduction in radio-over-fiber systems for increased modulation efficiency using a Si_3N_4 tunable extinction ratio ring resonator

Variable optical carrier reduction via the use of a Si(3)N(4) ring resonator notch filter with tunable extinction ratio is demonstrated in a 10 GHz radio-over-fiber system for improving the modulation efficiency. The extinction of the filter notch is tuned with micro-heaters, by setting the Mach-Zehnder coupler of the ring. Experimental results showing a modulation depth improvement of up to 20 dB are provided.