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. Photonic sensors are defined as sensors that sense, emit, receive and convert the light energy into electrical signals. Photonics sensors deal with the set of techniques and scientific knowledge concerning the generation, propagation, control, amplification, detection, storage, and processing of the optical spectrum signals. Optical sensors convert various wavelengths into electrical signals for enhanced sensing applications. Ambient, infrared (IR) and ultraviolet (UV) light are some wave types that optical sensors measure to create applications for autonomous cars, in-display fingerprint scanners, secure facial recognition and many others.
Photonic technologies provide incomparable advantages such as high sensitivity, compactness, metal-free operation, low-cost, electromagnetic immunity and possibility of integration with electronic devices. It enables cheaper, smaller, faster and lighter components and devices with superior functionality and less energy consumption.
Though, photonic sensors have become ubiquitous, and are found precious in the fields such as motion detection, blood oxygen monitors, cameras, etc. Photonic sensors have been widely used in the areas of information, industry, energy, military, security, biology, medicine, and smart structures due to their unique advantages and have become one mainstream in the sensor society. They have wide applications including for smart barcodes, new sensing systems in the fight against crime and terrorism, advanced manufacturing and production techniques, environmental monitoring and in new medical diagnostic devices. Photonic sensors, including fiber optic sensors, have also applications in military environments such as night vision and for detection of a wide variety of biological, chemical and nuclear agents.
Moreover, the integration of photonics, microelectronics and microfluidics into the same chip represents an intriguing technological platform for the realization of lab-on-a-chip systems, which are fundamental for fast, multiplexed and real-time measurements in various application fields.
Optical Sensing Principles
Photonic sensors can utilize different components of the optical signal such as intensity based, interferometric, polarization, spectroscopic, pulse shape or arrival time based, giving rise to a large number of different sensor designs. These differences may arise in the physical structures employed, in the optical source or detection systems, in the signal demodulation systems, or in new combinations of these.
In case of chemical and biochemical sensing, the operating principle consists of the variation of the effective index of the optical mode propagating into the structure, as a consequence of the presence of a chemical substance to be detected close to the sensor surface.
Optical sensing of chemical species is typically based on the variation of waveguide optical properties in the presence of some target analyte near the sensor surface. In particular, the principal sensing mechanisms exploited for this specific application include the variation of waveguide effective index or waveguide absorption coefficient, as a function of the concentration of the chemical species to be sensed.
“Waveguide-based devices are becoming more and more attractive in the field of optical elaboration of signals for sensing applications in different areas, especially in chemical and bio-chemical detection, angular rate rotation estimation and electric field detection,” write Vittorio M. N. Passaro and others.
The integration of photonic waveguides in resonant microcavities, ensures a suitable optical readout at the sensor output. Ring resonators can be employed as resonant architectures for sensing applications, where the sensing principle consists in monitoring the resonance wavelength shift as a consequence of the variations of the waveguide refractive index in the presence of the substance to be detected.
Ring resonators (RR) based sensors can be also employed for the realization of integrated optical gyroscopes (IOGs) for estimating the angular velocity in inertial systems. In this case, the operating principle characterizing the photonic sensing mechanism is the Sagnac effect, which leads to a phase shift between two counter-propagating beams proportional to the angular velocity at which the device is rotating.
The Sagnac effect has been widely employed in fiber optic based sensor for pressure, temperature and torsion monitoring. Moreover, it is the most exploited operating principle in optical gyroscopes. The detection of the angular velocity relies upon different effective path lengths experienced by two counter-propagating beams of light in a closed path
The Raman effect is an inelastic scattering process which is becoming widely used in photonic devices, especially in those fabricated using optical fibers or SOI technology. It is important to distinguish among three different scattering effects in optical fibers: Rayleigh scattering, Brillouin scattering and Raman scattering.
Rayleigh scattering is an elastic process since the energies of incident and scattered photons are the same. On the contrary, Raman and Brillouin scattering are inelastic effects. In fact, incident and scattered photons have different energies and the energy lost by the incident field leads to creation of phonons, which modify the vibrational states of the medium. The major difference between the Brillouin and Raman scattering effects concerns the different frequencies of the scattered phonons, since the former involves low frequency phonons, called acoustic ones, and the latter involves phonons at high frequency, called optical phonons.
Photonic Field Sensor are works mainly gathering data from reflection, angles of reflection, by reading emission from different kind of metals and distinguish their properties and identify them.
Photonics sensors have Wide Commercial and Military applications
Several organizations across the globe offer fiber optic sensors that can withstand harsh environmental conditions such as extreme heat, noise, corrosion, explosion, and vibration. Fiber optic sensors are compact in size and light in weight, which makes them ideal for accomplishing several tasks. Because of their immunity to electromagnetic interference, lightning and electrical noise, optical fiber sensors have been steadily gaining in popularity among wind turbine manufacturers as a practical, reliable and cost-effective online structural safety and fatigue monitoring tool integrated with the condition-based monitoring system of wind turbines.
Fiber Bragg grating (FBG) strain sensor arrays – either surface-mounted or embedded – can monitor the mechanical behavior of rotor blades in different types of wind turbines. The results can be used during the design and qualification stages to corroborate the measured strain values against design models. In service, premounted FBG sensors help monitor online the condition of the blades while rotating or stationary, and under various wind conditions.
Over the past decade, optical fiber sensors have gained widespread acceptance within the oil and gas industry due to their reliability, flexibility and low operating costs, as well as the benefits brought by their multipoint and distributed sensing capabilities. More recently, extensive interest has been shown in the development and commercialization of fiber optic seismic and acoustic sensing arrays – land and underwater – for oil and gas exploration, pipeline surveillance, geophysical monitoring, reservoir monitoring and management, geothermal monitoring, and structural monitoring of offshore platforms and oil tankers. Distributed acoustic sensing (DAS) enables detection, discrimination and location of acoustic events on an optical fiber over tens of kilometers.
The purpose of a biosensor is the detection of biologically-relevant targets such as proteins, DNA, pathogens, cells, bacteria, pollutants, hormones and enzymes. In most cases, their presence and/or concentration in samples such as blood, urine, saliva, sweat or tears can be an early indicator of disease, so that the sensor can be used as a valuable diagnostic tool.
“Emerging technologies like silicon- and InP-based photonics will allow the integration of most sensor reading unit functions at (the) chip level, strongly decreasing the fabrication cost and opening the way to mass-scale applications, such as smart structures embedding fiber Bragg gratings, as well as distributed fire-detection systems.
Progress in photonic sensor designs and applications continues at a fast pace with new types of optical fibers – photonic band gap fibers (PBG), microstructure optical fibers (MOF), random hole optical fibers (RHOF); and hybrid ordered random hole optical fibers (HORHOF); higher resolution, lower cost, and or expanded detection range capability for sources and detection schemes; and new signal demodulation algorithm designs
High-precision sensing devices for Military
As light travels fast, sees much and is non-invasive, it has many uses in innovative military applications. The military relies heavily on the optical spectrum for sensing, mapping and identifying enemy intent over large distances. Photonics can provide the military with higher quality sensing and communications devices.
An example of a photonics based technology for military use is multispectral imaging, which can extract significantly more information about its surroundings than regular sensors. Multispectral imaging can be used for tasks such as locating explosives, uncovering enemy movements and pinpointing the depth of hidden bunkers.
Photonics based spectrometers and holographic imagers are also used in the military. A spectrometer is a chemical sensor that can be used to detect explosives in liquids and solids. A holographic imager is a device that produces 3D visualisations of urban and mountainous terrain. A major advantage of these photonics devices is that they are lightweight and small, making them easily portable for soldiers in the field.
Photonic systems are becoming more significant in military platforms, especially in aircraft, where the increase in data rate, improved EMI hardness, improved safety, and reduced weight, are together a significant advantage. The optical fibre systems have been applied for the structural health monitoring of UAVs, and the revolutionary electro-optical Distributed Aperture System utilised on the Lockheed Martin F-35 Lightning II.
Laser Sensor Can Detect Damage to Military Assets
A distributed feedback fiber laser sensor has detected acoustic emission signatures associated with cracks in riveted lap joints, demonstrating that it has the potential to uncover structural damage in U.S. Navy assets before the damage reaches critical levels.
Developed by researchers at the U.S. Naval Research Laboratory (NRL), the laser sensor consists of a single fiber, similar in width to a human hair, which is integrated into a shallow groove formed in the lap joint. The sensor has a small system footprint and can be multiplexed.
To test the technology, researchers installed the laser sensors into a series of riveted aluminum lap joints and measured acoustic emission over a bandwidth of 0.5 megahertz (MHz) generated during a two-hour accelerated fatigue test. They took equivalent measurements with an electrical sensor.
The embedded laser sensors demonstrated acoustic sensitivity comparable to or greater than that achieved by existing electrical sensors. The laser sensors were able to detect low-level acoustic events generated by periodic fretting from the riveted joint, in addition to acoustic emissions from crack formation. Time-lapse imagery of the lap joint revealed that the observed fracture correlated with the signals measured. In addition to crack detection, the fiber laser sensor also showed the ability to measure compromising impacts.
“Our research team has demonstrated the ability of this fiber laser technology to detect acoustic emission at ultrasonic frequencies from cracks generated in a simulated fatigue environment,” said Dr. Geoffrey Cranch, research physicist. “The novel part of this work is the fiber laser technology and how it is being applied.
The fiber laser sensor system has now been expanded to multiplex many sensors onto a single fiber. Efforts are underway to interpret the acoustic emission data to calculate metrics such as probability of failure. Future enhancements may include implementing phased array beam forming techniques to facilitate crack location.
The fiber laser sensor also has the potential to integrate with existing fiber optic strain and temperature sensing systems. Integrating the sensor with these systems would provide a multiparameter sensing capability that could meet the operational safety requirements for an SHM system at significantly lower cost.
“An automated, in-situ structural health monitoring (SHM) system, capable of monitoring key structural parameters such as temperature, strain, impacts and cracks, and capable of reliably detecting damage well before reaching a critical level is needed to increase safety and readiness while lowering operational cost of Navy platforms” said Cranch. “At present, none of the services are using in-situ technologies to manage the structural health of their assets.”
“Our focus is on Navy platforms, such as aircraft, ships and submarines, but the technology could also be used on civilian aircraft,” he said. “Applications to bridges and buildings are also possible if there are critical parts prone to fatigue and failure that would benefit from continuous monitoring.”
Global photonic sensors and detection market is anticipated to reach US$ 35 billion in 2023 witnessing a compound annual growth rate of 16% over the period 2016-2023, according to Research Nester.
According to Future Market Insights, increasing investments in telecommunication infrastructure and various government initiatives to implement fiber optic communication are major factors driving the growth of the global photonic sensors and detectors market. Additionally, increasing adoption of industrial automation solutions to address the global shortage of unskilled labor and to reduce operating costs, and continuous development and implementation of new technologies in medical devices are some of the other factors propelling the growth of the global photonic sensors and detectors market.
The photonic sensors market is segmented by product types and end user applications. The global photonic sensors and detectors market is segmented on the basis of Sensor Type (Fiber Optic Sensors, Biophotonic Sensors, Image Sensors, Others); Detector Type (Photo Transistors, Single Photon Counting Modules, Photodiodes, Photocells, Others); and End use Sector (Defense & Security, Medical & Healthcare, Chemicals & Petrochemicals, Consumer Electronics & Entertainment, Industrial Manufacturing, Aviation, Research & Development, Others).
The Fiber Optics Sensors segment is estimated to account for a market share of 37.7% by the end of 2016 while the Biophotonic Sensors segment is expected to be the second largest segment in terms of market share in 2016, accounting for 29.9% value share by the end of 2016.
The Bio-photonic sensors segment witnessing a CAGR of 9.9% over the period 2015-2023 owing to the increased use in homeland security, military applications such as chemical and biological agent detection, bio-warfare defense, field intelligence and explosives detection, however fiber optic segment accounted for highest market share in 2015.
In terms of sales volume, the Single Photon Counting Modules segment is expected to register the highest CAGR of 10.5% during the forecast period. The Photo Transistors segment is estimated to witness a CAGR of 7.0% between 2016 and 2026. The Aviation segment is anticipated to register high YoY growth rates from 2016 to 2026 and is expected to register a CAGR of 10.2% during this period while the Defense & Security segment is estimated to account for the highest market value share of 26.3% by the end of 2016.
Global demand for military electro-optics and infrared sensors should grow by 40 percent over the next six years, predict analysts at market research Markets and Markets in Vancouver, Wash. The worldwide military electro-optics and infrared systems market should grow from $10.15 billion this year to $14.2 billion in 2022, which represents a combined annual growth rate (CAGR) of 5.75 percent, analysts say.
Driving growth in the electro-optics and infrared market are two primary factors: increasing demand for battlespace awareness by defense forces; and technological advancements to improve efficiency, analysts say. Also fueling the electro-optics and infrared market is growing demand for border surveillance and situational awareness using unmanned aerial vehicles (UAVs), analysts say.
Based on sensor technology, the staring sensor segment should lead the military electro-optics and infrared systems market during the forecast period because these kinds of sensors gather more radiation and are able to handle complex moving parts of sensors and cameras on the battlefield, analysts say. Staring sensors are used widely in missile warning receivers and electronic warfare systems. They are preferred over scanning sensors, as they are cost efficient and have varied technological applications.
North-America is anticipated to be the largest market for photonic sensors and detections and is estimated to account 26% of the total market share by 2023. Asia-Pacific market is anticipated to witness a compound annual growth rate of 23% over the forecast period i.e. 2016-2023. Asia Pacific is expected to be the prominent region for the photonic sensors market by 2023 due to emerging economies of the countries such as India and China.
Some of the market players in this industry segment are Prime Photonics, Smart Fibers, Mitsubishi Electric Corporation, Bayspec Inc, Omron Corporation, Qorex Llc and Fiso Technologies Inc among others.Major players in the military electro-optics and infrared systems market are Lockheed Martin Corp., Raytheon Co., and Northrop Grumman Corp. in the U.S.; BAE Systems Plc. in the United Kingdom; and Thales Group in France.