In nature, microorganisms tend to form biofilms that consist of extracellular polymeric substances with embedded sessile cells. Biofilms, especially mixed-culture synergistic biofilm consortia, are notoriously difficult to treat. They employ various defense mechanisms against attacks from antimicrobial agents. Problematic industrial biofilms cause biofouling as well as biocorrosion, also known as microbiologically influenced corrosion. Biocides are often used to treat biofilms together with scrubbing or pigging. Unfortunately, chemical treatments suppress vulnerable microbial species while allowing resistant species to take over. Repeated treatment cycles are typically needed in biofilm mitigation. This leads to biocide dosage escalation, causing environmental problems, higher costs and sometimes operational problems such as scale formation. New treatment methods are being developed such as enhanced biocide treatment and bacteriophage treatment. Special materials such as antibacterial stainless steels are also being created to combat biofilms. This review discussed some of the advances made in the fight against problematic industrial biofilms.

Traditional optical switches relying on the weak, volatile thermo-optic or electro-optic effects of Si or SiN waveguides show a high consumption and large footprint. In this paper, we reported an electric-driven phase change optical switch consisting of a Si waveguide, Ge 2 Sb 2 Te 5 (GST) thin film and graphene heater suitable for large-scale integration and high-speed switching. The reversible transition between the amorphous and crystalline states was achieved by applying two different voltage pulses of 1.4 V (SET) and 4 V (RESET). The optical performance of the proposed switch showed a high extinction ration of 44-46 dB in a wide spectral range (1525-1575 nm), an effective index variation of Δn eff =0.49 and a mode loss variation of Δα=15 dB μm −1 at the wavelength of 1550 nm. In thermal simulations, thanks to the ultrahigh thermal conductivity of graphene, the proposed switch showed that the consumption for the SET process was only 3.528 pJ with a 1.4 V pulse of 5 ns, while a 4 V pulse of 1.5 ns was needed for RESET process with a consumption of 1.05 nJ. Our work is helpful to analyze the thermalconduction phase transition process of on-chip phase change optical switches, and the design of the low-energy-consumption switch is conducive to the integrated application of photonic chips.

Mach–Zehnder interferometers (MZIs) integrated with phase‐change materials have attracted great interest due to their low power consumption and ultra‐compact size, which are favored for reconfigurable photonic processors. However, they suffer from a low optical extinction ratio and limited switching cycles due to high material loss and poor reversible repeatability caused by material degradation. Here a non‐volatile electrically reconfigurable 2 × 2 MZI integrated with a low‐loss phase‐change material Sb2Se3 encapsulated in Al2O3 layers is demonstrated. The phase change is electrically actuated by a forward‐biased silicon p‐i‐n diode. The switch extinction ratio is more than 20 dB due to the low‐loss Sb2Se3‐based phase shifter. By dividing the Sb2Se3 patch into small sub‐cells to restrict the material reflow, more than 10 000 reversible phase‐change cycles and 6‐bit multilevel switching states are achieved by programming the electrical pulses. Its non‐volatility, high endurance, and fine‐tuning capability makes the device promising in large‐scale low‐power reconfigurable photonic processors.

On-chip photonics devices relying on the weak, volatile thermo-optic or electro-optic effects of silicon usually suffer from high insertion loss (IL) and a low refractive index coefficient. In this paper, we designed two novel 1 × 1 and 1 × 2 phase-change optical switches based on a signal-mode Si waveguide integrated with a Ge2Sb2Te5 (GST) top clad layer, respectively. The three-state switch including amorphous GST (a-GST), face centered cubic crystalline phase (FCC-GST) and hexagonal crystalline phase (HCP-GST) operated by utilizing the dramatic difference in the optical constants between the amorphous and two crystalline phases of GST. In the case of the 1 × 1 optical switch, an extinction ratio (ER) of 8.9 dB and an extremely low IL of 0.8 dB were achieved using an optimum GST length of only 2 μm. While for the 1 × 2 optical switch, low ILs in the range of 0.15 ∼ 0.35 dB for both ‘cross’ (a-GST) and ‘bar’ (FCC-GST and HCP-GST) states were also obtained. Additionally, we found that both ILs and mode losses of the switch with HCP-GST were about half lower than those with FCC-GST, which means FCC-GST could be instituted by HCP-GST in the traditional ovonic switch with the consideration of low loss. This research provides the fundamental understanding for the realization of low loss and non-volatile Si-GST hybrid optical switches, with potential for future communication networks.

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