Unmanned aerial vehicles towards future Industrial Internet:Roles and opportunities

Unmanned Aerial Vehicles(UAVs)are gaining increasing attention in many fields,such as military,logistics,and hazardous site mapping.Utilizing UAVs to assist communications is one of the promising applications and research directions.The future Industrial Internet places higher demands on communication quality.The easy deployment,dynamic mobility,and low cost of UAVs make them a viable tool for wireless communication in the Industrial Internet.Therefore,UAVs are considered as an integral part of Industry 4.0.In this article,three typical use cases of UAVs-assisted communications in Industrial Internet are first summarized.Then,the state-of-the-art technologies for drone-assisted communication in support of the Industrial Internet are presented.According to the current research,it can be assumed that UAV-assisted communication can support the future Industrial Internet to a certain extent.Finally,the potential research directions and open challenges in UAV-assisted communications in the upcoming future Industrial Internet are discussed.

Electrically programmable phase-change photonic memory for optical neural networks with nanoseconds in situ training capability

Optical neural networks (ONNs), enabling low latency and high parallel data processing withoutelectromagnetic interference, have become a viable player for fast and energy-efficient processing andcalculation to meet the increasing demand for hash rate. Photonic memories employing nonvolatile phase-change materials could achieve zero static power consumption, low thermal cross talk, large-scale, andhigh-energy-efficient photonic neural networks. Nevertheless, the switching speed and dynamic energyconsumption of phase-change material-based photonic memories make them inapplicable for in situ training.Here, by integrating a patch of phase change thin film with a PIN-diode-embedded microring resonator,a bifunctional photonic memory enabling both 5-bit storage and nanoseconds volatile modulation wasdemonstrated. For the first time, a concept is presented for electrically programmable phase-changematerial-driven photonic memory integrated with nanosecond modulation to allow fast in situ training and zerostatic power consumption data processing in ONNs. ONNs with an optical convolution kernel constructedby our photonic memory theoretically achieved an accuracy of predictions higher than 95% when testedby the MNIST handwritten digit database. This provides a feasible solution to constructing large-scalenonvolatile ONNs with high-speed in situ training capability.

Passive devices at 2 μm wavelength on 200 mm CMOS-compatible silicon photonics platform [Invited]

As a promising spectral window for optical communication and sensing, it is of great significance to realize on-chip devices at the 2 μm waveband.The development of the 2 μm silicon photonic platform mainly depends on the performance of passive devices.In this work, the passive devices were fabricated in the silicon photonic multi-project wafer process.The designed micro-ring resonator with a 0.6 μm wide silicon ridge waveguide based on a 220 nm silicon-on-insulator platform achieves a high intrinsic quality factor of 3.0 × 105.The propagation loss is calculated as 1.62 d B/cm.In addition,the waveguide crossing, multimode interferometer, and Mach–Zehnder interferometer were demonstrated at 2 μm with good performances.

Integrated mode-transparent polarization beam splitter supporting thirteen data channels

The hybrid multiplexing technique reactivates optical interconnect as it offers multiple dimensions to dramatically enhance the data capacity of a single wavelength carrier.A straightforward method to realize hybrid multiplexing is to perform polarization multiplexing for mode-multiplexed signals,by utilizing a mode-transparent polarization beam splitter(MTPBS),which can process multiple modes simultaneously.However,present PBSs mainly work in the single-mode regime,and it is not easy to redesign the conventional PBS to accommodate multiple modes,due to the severe mode dispersion.Here,a novel MTPBS,which can tackle a group of modes simultancously,is proposed and demonstrated.As a demonstration,the MTPBS supporting a total channel number of 13 is experimentally achieved,with low insertion loss and low modal/polarization cross talk.This work provides a new insight to realize hybrid multiplexing and represents a solution for high-density and large-capacity photonic integration.

Free-spectral-range-free filters with ultrawide tunability across the S+C+L band

Optical filters are essential parts of advanced optical communication and sensing systems.Among them,the ones with an ultrawide free spectral range(FSR)are especially critical.They are promising to provide access to numerous wavelength channels highly desired for large-capacity optical transmission and multipoint multiparameter sensing.Present schemes for wide-FSR filters either suffer from limited cavity length or poor fabrication tolerance or impose an additional active-tuning control requirement.We theoretically and experimentally demonstrate a filter that features FSR-free operation capability,subnanometer optical bandwidth,and acceptable fabrication tolerance.Only one single deep dip within a record-large waveband(S+C+L band)is observed by appropriately designing a side-coupled Bragg-grating-assisted Fabry–Perot filter,which has been applied as the basic sensing unit for both the refractive index and temperature measurement.Five such basic units are also cascaded in series to demonstrate a multichannel filter.This work provides a new insight to design FSR-free filters and opens up a possibility of flexible large-capacity integration using more wavelength channels,which will greatly advance integrated photonics in optical communication and sensing.

Tunable narrow-band single-channel add-drop integrated optical filter with ultrawide FSR

Free-spectral-range(FSR)-free optical filters have always been a critical challenge for photonic integrated circuits.A high-performance FSR-free filter is highly desired for communication,spectroscopy,and sensing applications.Despite significant progress in integrated optical filters,the FSR-free filter with a tunable narrow-band,high out-of-band rejection,and large fabrication tolerance has rarely been demonstrated.In this paper,we propose an exact and robust design method for add-drop filters(ADFs)with an FSR-free operation capability,a sub-nanometer optical bandwidth,and a high out-of-band rejection(OBR)ratio.The achieved filter has a 3-dB bandwidth of<0.5 nm and an OBR ratio of 21.5 dB within a large waveband of 220 nm,which to the best of our knowledge,is the largest-FSR ADF demonstrated on a silicon photonic platform.The filter exhibits large tunability of 12.3 nm with a heating efficiency of 97 pm/mW and maintains the FSR-free feature in the whole tuning process.In addition,we fabri-cated a series of ADFs with different periods,which all showed reliable and excellent performances.