Sensors allow humans to feel and understand their world, and their development lays the foundation for the fulfillment of information society and has formed a huge industry. For its implementation the Internet of Things relies heavily on sensor technology.In the grand world of the “internet of things” (IoT), there are vast numbers of spatially distributed wireless sensors predominately based on electronics.
Sensors need to be small, robust and energy efficient to be embedded in machines, appliances, buildings and infrastructure and succesfully collect data over large periods of time. These electronic devices often are hampered by electromagnetic interference, such as disturbed audio or visual signals caused by a low-flying airplane and a kitchen grinder causing unwanted noise on a radio.
Photonic sensor is a device that senses light and converts to electricity. Photonic technologies provide incomparable advantages such as high sensitivity, possibility of integration with electronic devices, compactness, metal-free operation, low-cost and electromagnetic immunity. It provides cheaper, smaller, faster and lighter components and devices with superior functionality and less energy consumption.
For example Fibre optic sensors – manufactured using photonics technology – are not only more sensitive than existing electromagnetic sensors, but also faster operating, better able to withstand harsh conditions and immune to electromagnetic interference.
Some of the most significant photonics IoT applications are: communications, transportation, environmental monitoring, smart homes, factories, and gadgets. Photonic sensors, including fiber optic sensors, are also used in military environments for detection of a wide variety of biological, chemical and nuclear agents.
Enabling ‘internet of photonic things’ with miniature sensors
A team of researchers at Washington University in St. Louis is the first to successfully record environmental data using a wireless photonic sensor resonator with a whispering-gallery-mode (WGM) architecture.
The photonic sensors recorded data during the spring of 2017 under two scenarios: one was a real-time measurement of air temperature over 12 hours, and the other was an aerial mapping of temperature distribution with a sensor mounted on a drone in a St. Louis city park. Both measurements were accompanied by a commercial thermometer with a Bluetooth connection for comparison purposes. The data from the two compared very favorably.
Optical sensors are “immune to electromagnetical interference and can provide a significant advantage in harsh environments,” said Lan Yang, the Edwin H. & Florence G. Skinner Professor of Electrical & Systems Engineering in the School of Engineering & Applied Science, who led the study from which the findings were published Sept. 5 in Light: Science and Applications.
“Optical sensors based on resonators show small footprints, extreme sensitivity and a number of functionalities, all of which lend capability and flexibility to wireless sensors,” Yang said. “Our work could pave the way to large-scale application of WGM sensors throughout the internet.”
Yang’s sensor belongs to a category called whispering gallery mode resonators, so named because they work like the famous whispering gallery in St. Paul’s Cathedral in London, where someone on the one side of the dome can hear a message spoken to the wall by someone on the other side. Unlike the dome, which has resonances or sweet spots in the audible range, the sensor resonates at light frequencies and also at vibrational or mechanical frequencies, as Yang and her collaborators recently showed.
“In contrast to existing table-sized lab equipment, the mainboard of the WGM sensor is a mere 127 millimeters by 67 millimeters — roughly 5 inches by 2.5 inches — and integrates the entire architecture of the sensor system,” said Xiangyi Xu, the paper’s first author and a graduate student in Yang’s lab. “The sensor itself is made of glass and is the size of just one human hair; it is connected to the mainboard by a single optical fiber. A laser light is used to probe a WGM sensor. Light coupled out of the sensor is sent to a photodetector with a transmission amplifier. A processor controls peripherals such as the laser current drive, monitoring circuit, thermo-electric cooler and Wi-Fi unit,” Xu said.
In her WGM, light propagates along the circular rim of a structure by constant internal reflection. Inside the circular rim, light rotates 1 million times. Over that space, light waves detect environmental changes, such as temperature and humidity, for example. The sensor node is monitored by a customized operating systems app that controls the remote system and collects and analyzes sensing signals.
Wireless sensors, whether electronic or photonic (light-based), can monitor such environmental factors as humidity, temperature and air pressure. Applications for wireless sensors encompass environmental and health-care monitoring, precision agricultural practices and smart cities’ data-gathering, among other possibilities. Smart cities are connected cities driven by internet data-harvesting. Precision agriculture uses digitized geographic information systems for precision agricultural practices such as soil mapping, which enables precise fertilizer and chemical applications and choice of seed selection for more efficient and profitable farming.
Yang and her colleagues had to address stability issues, which were handled by the customized operation systems app they developed, and miniaturization of bulky laboratory measurement systems. “We developed a smartphone app to control the sensing system over WiFi,” Yang said. “By connecting the sensor system to the internet, we can realize real-time remote control of the system.”
In June 2017, Yang and her group mounted the whole system on the outside wall of a building and accumulated a plot of the frequency shift of the resonance. They compared their data with the commercial thermometer. “Thanks to their small size, the capability and flexibility of wireless photonic sensors can be improved by making them mobile,” Yang said.
The researchers also mounted their system on an unmanned drone in May 2017 alongside the commercial thermometer. When the drone flew from one measurement location to others, the resonance frequency of the WGM shifted in response to temperature variations.”The measurements matched well with results from the commercial thermometer,” she said. “The successful demonstrations show the potential applications of our wireless WGM sensor in the IoT. There are numerous promising sensing applications possible with WGM technology, including magnetic, acoustic, environmental and medical sensing.”
The miniaturization of resonator sensing systems represents an exciting opportunity for IoT, as it will enable IoT to exploit a new class of photonic sensors with unprecedented sensitivity and capabilities,” said Chenyang Lu, the Fullgraf Professor in the Department of Computer Science & Engineering and a co-author of the paper.
World-First Tiny Nanophotonic Device to Allow 100-Times-Faster Internet
Lucky for us a new world-first innovation promises to make our internet journeys faster than ever, 100 times faster in fact. This novel invention is a nanophotonic device that uses a special form of ‘twisted’ light in order to encode more data and process it much faster than ever possible with today’s traditional fiber optics.
The device comes from Australia’s global university of technology and design RMIT. It is the work of a team of researchers led by Dr Haoran Ren from the institution’s School of Science and Dr Zengji Yue, Associate Research Fellow at the University of Wollongong and it is set to forever change optical communications.
“Present-day optical communications are heading towards a ‘capacity crunch’ as they fail to keep up with the ever-increasing demands of Big Data,” Ren said. “What we’ve managed to do is accurately transmit data via light at its highest capacity in a way that will allow us to massively increase our bandwidth.”
Conventional broadband fiber-optics carry information on pulses of light through optical fibers which means the process’ speed is affected by the way the light is encoded at one end and processed at the other. RMIT’s nanophotonic device instead has the capacity to read twisted light using the oscillation of light waves to encode data.
This means it can unlock so much more of light’s actual data-carrying capacity than just the color spectrum accessed by current broadband technologies. It does this by carrying the data on light waves that have been twisted into a spiral, a state referred to as orbital angular momentum (OAM).
“Our OAM nano-electronic detector is like an ‘eye’ that can ‘see’ information carried by twisted light and decode it to be understood by electronics,” said RMIT Associate Deputy Vice-Chancellor for Research Innovation and Entrepreneurship Min Gu. The device is essentially designed to differentiate between varied OAM light states in a continuous order in order to extract the data they carry.
Best of all, the device’s materials are compatible with today’s popular silicon-based options meaning the possibility for industry applications scaling is very accessible. “This technology’s high performance, low cost and tiny size makes it a viable application for the next generation of broadband optical communications,” Gu said.
“It fits the scale of existing fiber technology and could be applied to increase the bandwidth, or potentially the processing speed, of that fiber by over 100 times within the next couple of years. This easy scalability and the massive impact it will have on telecommunications is what’s so exciting,” elaborated the professor.
UTA working to develop longwave infrared photonic device technology
A research team from The University of Texas at Arlington is working with the Army Research Laboratory to develop nanophotonic devices that could have applications in thermal imaging and resonant filtering. Robert Magnusson, an electrical engineering professor and the Texas Instruments Distinguished University Chair in Nanoelectronics, is the principal investigator for a $1.2 million collaborative agreement with the Army Research Laboratory.
Nanophotonic devices are used to shape the spectrum of light via photonic lattices and resonance, but their application generally has been limited to short wavelengths. The research team is trying to develop devices that will work in the longwave infrared spectral region, which is the range in which thermal radiation is emitted. In addition to thermal imaging technology, these devices could be used in sensors for medical diagnostics, chemical analyses and environmental monitoring, among other applications.
“We have made many advances in the development of photonic devices over the years, and our methodology can be really useful in this application,” Magnusson said. “There is a need to develop this technology because there is a shortage of optical components in longwave infrared bands. Changing frequency or wavelength to this region requires that we completely change our fabrication methods, and we have already successfully made devices under this new funding.”
Photonic lattices are structures–such as nanopatterned silicon films on glass substrates or arrays of nanowires–with differing refractive qualities that are arranged so they can capture, store and release light. For the new, longer wavelength devices, Magnusson will create lattices out of germanium, a metalloid element that has the properties of a semiconductor.
Daniel Carney, a recent UTA doctoral graduate, successfully developed longer wavelength devices in the University’s Shimadzu Institute Nanotechnology Research Center while a student in Magnusson’s lab. Magnusson said he plans to adapt these devices to make them tunable to specific wavelengths. By mechanically or electrically altering the device’s structure, selected wavelengths are rejected while useful imaging data passes to detection equipment.
“The Shimadzu Institute Nanotechnology Research Center was very important in the development of Daniel’s research and what we’re trying to do with the Army Research Lab,” Magnusson said. “The facility is behind experimental realization of many of the key discoveries we make.”
Magnusson, Neelam Gupta of the Army Research Laboratory and Mark Mirotznik of the University of Delaware are collaborating on the research. Their project is an example of data-driven discovery, one of the themes of UTA’s Strategic Plan 2020, said Peter Crouch, dean of the College of Engineering.
“As engineers, we always want to have an impact on society,” Crouch said. “Dr. Magnusson’s research has been at the leading edge of his field for many years, and his findings have contributed a great deal to our knowledge of photonics. This agreement with the Army Research Lab is an excellent opportunity to create devices that will make an impact for years to come.”
Magnusson has worked in photonics throughout his career and pioneered a host of device technologies, many of which are patented. He leads UTA’s Nanophotonics Device Group, which pursues theoretical and experimental research in periodic nanostructures, nanolithography, nanophotonics, nanoelectronics, nanoplasmonics and optical bio- and chemical sensors. His research established new transformative biosensor platform technology that is in commercial use by Resonant Sensors Inc., a company he co-founded.
Magnusson has garnered more than $12 million in research funding and endowments for UTA since becoming the Texas Instruments Distinguished University Chair in Nanoelectronics in 2008, published more than 450 journal and conference papers and secured 35 issued patents and pending patents.
He is a charter fellow of the National Academy of Inventors–one of 15 NAI fellows among the UTA faculty–and a Life Fellow of the prestigious Institute of Electrical and Electronics Engineers. The IEEE has singled out Magnusson for his contributions to the invention of a new class of nanophotonic devices that employ light at a nanometer scale. His devices are used as biosensors, lasers, tunable filters and optical components.