Optical Sensors Support the Rise in Automation

MARIE FREEBODY, CONTRIBUTING EDITOR, marie.freebody@photonics.com

As automation becomes an increasingly familiar feature throughout numerous industries, demand for technologies to be smarter and offer more has never been more prominent — from manufacturing a smartphone in North America to installing a pipeline in Asia.

Optical sensors act as transducers by converting light to electrical signals that can be interpreted, measured, analyzed, and manipulated by instruments. From surveillance and monitoring to fingerprint recognition, optical sensors are essential instruments utilized in industries ranging from aerospace and defense, oil and gas, and health care and construction to consumer electronics and automotive.

Synaptics Clear ID optical fingerprint sensor invisibly images the fingerprint through the display. This allows the screen area to expand right up to the edges of the phone. Courtesy of Synaptics.

The global optical sensors market size is estimated to reach $4.89 billion by 2025, up from $1.59 billion in 2017, and grow at a CAGR of 15.1 percent, according to a report by Variant Market Research, market analysts based in San Francisco.

The global optical sensors market size and forecast from 2016 to 2025 (U.S. $ million). Courtesy of Variant Market Research.

North America accounted for the largest market share, 32.4 percent, in 2017 and is expected to dominate over the forecasted period. The Asia-Pacific region should grow at a CAGR of 15.7 percent thanks to rising urbanization and investments in enhanced sensing technologies that can screen infrastructure for problems in industries such as oil and gas.

Percentage revenue of the global optical sensors market by region in 2017 and 2025. Courtesy of Variant Market Research.

When it comes to defense, optical sensors are used in night-vision cameras and to monitor boundaries. With a wide wavelength range — from UV to IR — they are ideally suited to detect intruders.

This wavelength range also means that optical sensors can peer under human skin to look at blood vessels. As biological sensors, their high sensitivity and speed is vital to detecting bacteria and viruses. Optical sensors are also used for chemical sensing and have even been used to detect molecules within single cells.

“The global optical sensors market is observing exponential growth [in] recent decades, owing to high demand of optical sensors across various industries,” said Rakesh Singh, senior manager at Variant Market Research. “[However], lack of standardization may remain a challenge for the growth of the market.”

This ambiguity might be overcome in the near future as various organizations such as ASTM International, IEEE, and SEAFOM (among others) work to develop new standards.

Industry 4.0 drives new growth

One area of healthy growth where optical sensors are well-established and understood is that of machine vision cameras and sensors on the manufacturing floor.

Often referred to as the fourth industrial revolution, “Industry 4.0” is the name given to the current trend of automation and data exchange in manufacturing technologies. It includes cyber-physical systems, the Internet of Things, cloud computing, and cognitive computing and is placing additional demand on the already well-utilized optical sensor.

Today, vision systems are expected to do more than just detect or inspect. Automation on the manufacturing floor, artificial intelligence, and robotics means vision systems must also make decisions based on the information fed to it by optical sensors. Machine vision specialist Teledyne DALSA in Canada is responding to the overall drive for automation and improved quality.

“The ability to have cameras make the decision rather than a host computer is increasing,” said Mark Butler, product manager at Teledyne DALSA. “Embedded vision is a catchall to describe that trend. In many cases, optical sensors are replacing human vision because they are more reliable with tasks that are mundane to humans.”

Here, vision systems come with application software that is embedded, setting the groundwork for the anticipated rise of artificial intelligence (AI) on the factory floor. Still in its infancy, AI is expected to become a prominent feature in the decades to come.

“Over time, you see greater usage of artificial intelligence, where deep learning will play a major factor in the development of algorithms for automation and quality improvement,” Butler said.

Human-computer interfaces

Optical sensors are increasingly making their way into many consumer electronics, transforming them into smarter versions of themselves. From refrigerators, televisions, and even mirrors, “smart” is the buzzword bandied around many of today’s latest offerings on the consumer market, and leading the way is the smartphone.

Distributed fiber optic sensors are enjoying tremendous growth thanks not only to pipeline monitoring but any application where strain, temperature, or vibration needs to be measured or monitored.

Each smartphone includes several optical sensors: in the front camera, back camera, proximity (cheek) detection, infrared transceiver, ambient light detection, and most recently a fingerprint sensor. These cameras and other optical sensors give the smartphone some ability to be aware of its surroundings.

Smartphones are a major part of the business for California-based Synaptics, which specializes in human-computer interfaces, such as those found on touchpads for computer laptops, touchscreens, MP3 players, cellphones, and other such devices.

According to Bob Mackey, principal scientist and systems architect of biometric sensors at Synaptics, the company’s new in-display fingerprint technology — Clear ID — is the latest advance in optical sensors that is adding to a smartphone’s awareness by authenticating the identity of the user.

“In combination with capacitive touchscreen, GPS, Wi-Fi, LTE, accelerometers, and magnetometers, the smartphone is part of a highly connected ecosystem of sensors and transponders,” Mackey said. “The biometrics allows safe, secure, encrypted financial transactions on top of the advanced user interfaces.”

It is technically possible to acquire a fingerprint image with many different types of sensors, but optical sensing gives the best combination of speed, range, resolution, and cost.

“Optical sensing is the de facto standard when a high-resolution image must be acquired at a distance,” Mackey said. “The display is already an optical system, so optical sensors can take advantage of the materials and processes used to give great looking displays.”

And it is via the display that Clear ID differs and is replacing traditional fingerprint sensors on many devices. Instead of a separate display screen and fingerprint sensor, Clear ID peers through the display at the finger.

“It allows the display to grow all the way to the edges of the phone,” Mackey said. “The borderless infinity display increases the usability of the phone and minimizes dead area.”

Such full-screen displays can be found on the Galaxy S8, LG G6 and LG V30, Google Pixel 2 XL, iPhone X, and many more. In fact, all of the top companies are implementing the edge-to-edge screens into their most expensive phones.

The sensor works by using the light from the display to illuminate the fingerprint. Some of the light that is subsequently reflected from the fingerprint passes through the display and is captured by a very thin camera below the display.

“Looking through the [active matrix organic LED] display is like looking through a screen door. You can see through a screen door, but some of the light is blocked,” Mackey said. “In the case of a display, it is like a very dense screen door with a complex pattern. Advanced processing methods are used to recover an image with sufficient quality for secure fingerprint matching.”

Experts predict that biometrics will continue to adopt optical sensors for fingerprint, face, iris, and other identification tasks, and market saturation could be reached within just a few years.

“Connected home and automotive devices are now taking on some of the context- and identity-aware functions of smartphones,” Mackey said. “For Synaptics, the multiple human-interface connections between these devices and their users are the source of demand and growth. The optical sensors are joined by optical outputs (displays), and by other sensors.”

Protecting infrastructure

Pipelines can carry liquids, gases, or any chemically stable substance over vast distances. They are built to transport fuels such as petroleum, oil, natural gas, and biofuels, and fluids such as water, irrigation, sewage, slurry, and even beer over long distances through hills and mountains.

But when something goes wrong, it’s not just money that can leak away. Catastrophic disasters can be life-threatening and environmentally destructive. Ruptures are often initiated by natural causes and human error but sometimes by malicious actions.

Typical plot showing the detection of leaks in a buried pipeline during a test, indicated by a change in temperature in the soil. Courtesy of OZ Optics Ltd.

“There have been many instances in recent years of catastrophic disasters, which could possibly have been reduced in severity, if not prevented, if distributed sensing systems had been used,” said Gordon Youle, vice president of Test Equipment at OZ Optics Ltd. in Canada. “These include high-profile cases of levee failures, pipeline leaks, tunnel and building fires, and train derailments. If even a small number of the accidents could have been prevented or reduced in severity, lives might have been saved. Sadly, it often takes a disaster to make industry aware of some of the dangers that exist around us every day.”

Distributed fiber optic sensors are enjoying tremendous growth thanks not only to pipeline monitoring but any application where strain, temperature, or vibration needs to be measured or monitored. This includes around infrastructure such as dams, levees, bridges, tunnels, pipelines, electrical power lines, railways, roadways, and mines.

“For example, changes to the strain on an optical cable embedded in a levee could indicate an impending failure of that levee,” Youle said. “A sudden rise in temperature detected by an optical cable in a tunnel could be a sign of a fire.”

Distributed fiber optic sensing can be divided into four categories:

• distributed acoustic sensing (DAS)

• distributed temperature sensing (DTS)

• distributed strain sensing (DSS)

• distributed strain and temperature sensing (DSTS)

In each of these systems, the entire length of an optical fiber can be used to measure or monitor vibrations, temperature, and strain, or both strain and temperature. In each system, an interrogator unit at one end of the fiber launches pulses of light into it and monitors a returned signal.

Unlike discrete sensors, distributed fiber optic sensing allows full coverage along the entire length of the structure under surveillance, which means problems can be quickly detected and pinpointed to within a few meters.

Plot showing relative changes in strain on a 67-km-long overhead cable with an embedded sensing fiber over a one-month period. Courtesy of OZ Optics Ltd.

“With the potential of saving millions of dollars in the event of even a small leak, the benefits of having such a system far outweigh the cost,” Youle said. “There are no other technologies that can provide the distributed sensing capability offered by fiber optic sensing systems. Also, since the sensor consists of nothing more than an optical fiber in a protective cable, it can be used in explosive or other hazardous environments where electrical wiring may be undesirable.”

Fiber optics sounds out intruders

“Fiber optic sensing is getting a great deal of attention these days for intrusion detection,” Youle said. “This can take many different forms, such as perimeter or border monitoring, as well as detecting people or equipment working in close proximity to a buried asset, such as a pipeline or conduit.”

In each application, sound waves squeeze the fiber, causing a small modulation of light that is backscattered from each portion of the fiber. This can then be detected and processed, essentially allowing the fiber to act as a distributed microphone, picking up sound along its entire length.

By rapidly pulsing the light and knowing the time of the detected light relative to the outgoing pulse, the sound from different portions of the fiber can be separated.

This turns the fiber into an array of thousands of virtual microphones, allowing the location of the sound to be pin-pointed along its length. This technique can be used for detecting vibrations caused by people walking, or the noise of equipment digging nearby.

“This type of detection may be used to alert operators that someone is digging close to an asset that needs protecting,” Youle said. “This could be anything from a water main to a vital communications cable. It can also alert the operator to a possible harmful attack on the asset being monitored.”

The same technique can be used to detect the presence of someone beside a perimeter fence or border wall. It is one monitoring technique that may be considered for use along the U.S.-Mexico border.

A closely related application is for monitoring railways. In this case, a fiber optic cable buried beside a track is able to pick up the sound of a train. Any unusual sounds may be indicative of an impending failure, which, when detected early, may prevent a full-blown disaster.

Today, experts believe that distributed sensing is at a turning point. Volumes are on the rise as the technology matures and greater awareness of its capability spreads. As volume goes up, cost comes down, which opens up new markets.

“The future of distributed fiber optic sensing is very bright. We are seeing some very creative uses for the technology to solve problems that would be nearly impossible to solve by conventional means,” Youle said. “As new suppliers enter the market, competitive pressure will also drive down prices for both the suppliers and the end users.”