Category: Fiber Bragg Gratings

Fiber optic solutions for conveyor health monitoring

FBGs for conveyor monitoring A company from Australia offers a novel fiber optic solution that allows providing conveyor health monitoring by applying real-time data to rationalize production and on-site performance, improve occupational health, hygiene, and safety management, and implement new predictive maintenance and support capabilities to control management.

Thus, the fiber optic technology was tested in surface and sub-surface environments of some of the world’s largest mining companies and bulk material handling the equipment resulting in the accessibility of optical fiber sensing for present sale all over the world. The fact is that efficient conveyor systems are highly important because the profitability of mining companies depends fully on such fiber optic sensing systems.

Additionally, the mining industry has always a huge challenge of conveyor maintenance, and traditional sensing technologies for advanced conveyor failure detection are often precarious, subjective, they require many time and labors. The new fiber sensing system combines the technology of optical fiber detection with a sensing technology platform, “advanced signal processing algorithms and predictive analytics” enabling to acoustically monitor and check conveyor health.

The advantages of presented fiber optic solution include the provision of accurate data to maintenance technicians, site personnel, regional operational hubs, and global headquarters, the opportunity to obtain daily asset reliability reports from every conveyor, at every site worldwide due to the connection of the fiber system to

a wireless Internet.

The operation of the fiber optic system is based on the transmission process of short laser beam pulses along a single optical fiber cable installed along the length of a conveyor, while acoustic disturbances from the conveyor sensing system lead to tiny changes in the backscattered laser beam light, which is then classified into distinguished parameters.

Also, the obtained data is then processed, the following information is gathered:

the detection of a damaged ball or a broken cage in a ball race;
monitoring and “tracking idler bearings as they progressively wear”;
the prediction of potential bearing seizures and establishment of roller replacement priorities at the next maintenance shut down.

Finally, the fiber optic technology of distributed acoustic sensing is considered to be “the way of the future for conveyor health monitoring”. Such fiber optic solution successfully optimizes conveyor operation and provides essential cost savings for operators. Herewith, this fiber sensing system monitors the condition of every conveyor roller that can contain 7.000 bearings per kilometer.

Optromix is a manufacturer of innovative fiber optic products for the global market. The company provides the most technologically advanced fiber optic solutions for the clients. Optromix produces a wide range of fiber optic devices, including cutting-edge customized fiber optic Bragg grating product line and fiber Bragg grating sensor systems. Moreover, Optromix is a top choice among the manufacturers of fiber Bragg grating monitoring systems. If you have any questions, please contact us at info@optromix.com

The development of fiber Bragg gratings using highly doped aluminosilicate glass optical fibers

FBGs made of doped fibers The continuous development of high-temperature fiber Bragg grating technology (FBG technology) promotes a significant increase in novel applications. For instance, nowadays FBG applications include such fields as “the temperature profiling of high-temperature manufacturing equipment, monitoring of fuel combustion machinery, temperature regulation of large diesel engines in trains, as well as assessment the structural integrity of a building post-fire”.

Additionally, high-temperature FBG technology is used in oil and gas industries where the resistance to the temperatures higher than 500 °C is totally recommended. To be more precise, the sensors based on fiber Bragg gratings are able to stand temperature conditions below and above 800 °C. Herewith, the thermal stability of FBG sensors depends closely on the intrinsic thermal stability of the core-cladding materials.

This is the reason why the development of fiber optic technology with higher thermal resistance, for example, the molten core technique, is still required. Thus, it was decided to apply a circular core/cladding glass optical fiber containing a yttrium-doped aluminosilicate core and a silica cladding in FBG sensors that may withstand about 900 °C.

The following types of FBG sensors are based on the nature of refractive index modifications induced by laser irradiation. The following types of FBGs are distinguished:

The type I in fiber Bragg gratings produces a laser irradiation regime that emits an isotropic increase of the refractive index.
The type II in FBGs, in its turn, has a connection with the creation of an anisotropic index change upon irradiation, generally emitted by the presence of nanogratings, and leads to the observation of form birefringence.
Ultra-high temperature regenerated fiber Bragg gratings are able to operate above 800 °C in silica optical fibers. Therefore, these FBGs find their application in such areas as the profiling of high-temperature manufacturing equipment, dual pressure/temperature sensing for gas turbines, sodium-cooled nuclear reactors, high-temperature air flow meters for internal combustion engines and train engine temperature regulation.
Femtosecond fiber Bragg gratings are made by ultrafast laser systems usually in the NIR spectral range, resulting in their use as temperature sensors for monitoring fluidized bed combustors, as well as for radiation-resistant temperature sensors.
Sapphire fiber Bragg gratings allow achieving even higher temperature operation by using materials with higher melting points.

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Fiber Bragg gratings make semiconductor lasers more stable

FBGs for lasers Researchers from the Czech Republic demonstrate a new technique that allows improving wavelength stability and tunability of semiconductor laser diodes in fiber laser interferometers due to fiber Bragg gratings (FBGs) technology. This simulation technique makes the calculation of arbitrary fiber Bragg grating (apodized, chirp, etc.) with a high level of accuracy by a combination of techniques based on layered dielectric media (LDM) and transfer matrix technology.

Thus, based on the simulations and measurements made by the commercially available FBG technology, it has succeeded in the development of a special 100 mm long fiber Bragg grating with apodization. Herewith, the researchers confirm that the new FBG technology of improved linewidth and mode-hop free tuning range of semiconductor laser systems at the wavelength 760 nm enables to increase the resolution of a laser interferometer. Therefore, the absolute fiber laser interferometer with Vertical Cavity Surface Emitting Laser (VCSEL) to easily apply the FBG system to make the wavelength parameter more stable and monitor the tuning range was produced.

Typically, two types of fiber Bragg gratings are distinguished in the used technology: FBG with a period of ~0.5 µm, and Long-Period Fiber Bragg Gratings (LPFGs) with a period from 100 to 500 µm. Additionally, it should be mentioned that their production requires different methods. Thus, the creation of fiber Bragg gratings is performing by interference patterns, while long-period FBGs are produced by side irradiation of the fiber optic components through an amplitude mask or using the fiber translating technique.

Therefore, the application of FBGs offers high thermal stability, retaining optical properties up to 500 °C. Moreover, the production technique has a dependence on such parameters as the length, the type, and the other factors of the FBG technology. It is possible to determine the necessary parameters on the basis of the FBG spectral profile.

Finally, the simulation technique based on the application of fiber Bragg gratings was developed and tested several types of FBGs. For example, chirped and apodized fiber Bragg gratings (FBGs with modulation of the amplitude and with modulation of the spacing). Herewith, this new FBG system provides numerous benefits in comparison to other types of FBGs.

The main benefit is suppressing the side lobes in the fiber Bragg grating spectral properties. The developed FBG system is a compact reliable one that ensures the operation in an industrial environment where the majority of optical components would be fiber-optic.

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FBG accelerometers measure acceleration and vibration on trains

FBG accelerometers for train monitoring Nowadays train accidents often cause severe injuries and even cases of death. Nevertheless, researchers from China have designed new fiber optic sensors that allow measuring acceleration and vibration characteristics on trains. Additionally, this optical fiber technology can be used in a combination with artificial intelligence in order to prevent potential railway accidents and catastrophic train derailments.

To be more precise, the FBG accelerometers are able to monitor problems in the railway track or the train in real-time to detect defects before an accident happens. Such fiber optic devices identify frequencies more than double that of conventional optical fiber accelerometers, making them ideal for monitoring wheel-rail interactions.

The principle of durable FBG sensors’ operation is based on the use of no moving parts, herein, the fiber accelerometers demonstrate good operation in the noisy as well as in high-voltage environmental conditions found in the railway field of application. Moreover, the researchers confirm that their novel FBG accelerometers can be applied in other vibration monitoring applications. For example, fiber optic applications include structural health monitoring for buildings and bridges and vibration measurements of aircraft wings.

It should be noted that the researchers have been developing condition-monitoring optical fiber systems for more than 15 years using an all-optical sensing network to continuously monitor crucial railway components. It is planned that these fiber optic sensing systems help change poor efficient traditional railway maintenance routines by predictive maintenance based on actual conditions.

The developed FBG accelerometers demonstrate the following benefits that include:

immunity to electromagnetic interference;
long transmission distance;
no need for electricity.

But a need for FBG sensors for the measurement of various characteristics in railway systems still remain. Traditionally, fiber accelerometers are based on fiber Bragg gratings whose use is limited by 500 Hz vibrations. Therefore, such fiber optic technology was not suitable for the measurement of the wheel-rail interactions that are considered to be an important source of track wear.

Finally, the researchers have developed totally new FBG accelerometer based on a specific optical fiber (a polarization-maintaining photonic crystal fiber). It has been tested by installing the optical fiber device on an in-service train. Thus, the FBG accelerometer demonstrates a similar operation to the piezoelectric accelerometer, but it does not require expensive shielded fiber cables to take the effects of electromagnetic interference down.

If you want to obtain a highly efficient sensing system, you should choose the Optromix company. Optromix is a manufacturer of innovative fiber optic products for the global market. The company provides the most technologically advanced fiber-optic solutions for monitoring worldwide. Optromix is a fast-growing vendor of fiber Bragg grating (FBG) products line such as fiber Bragg grating sensors, FBG interrogators and multiplexers, distributed acoustic sensing (DAS) systems, distributed temperature sensing (DTS) systems. If you are interested in FBG sensors and want to learn more, please contact us at info@optromix.com

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The use of fiber optic sensing solutions on active warships

FBGs for active warships The researchers from NASA Armstrong Flight Research Center form a partnership with members of the Naval Surface Warfare Center to create fleet maintenance capabilities with the help of new fiber optic sensing systems. Thus, the development of novel highly promising fiber optic sensing solutions becomes possible.

The thing is that fiber optic technology is considered to be one of the most essential and promising techniques, and the cooperation of the mentioned above organizations may help to find the solution to all current challenges. Herewith, there was a project of Remote Environmental and Condition Monitoring Systems that could be restarted again with the help of new possibilities of optical fiber technology offered by companies.

The main function of fiber optic sensing systems is the record of every parameter. For example, today fiber optic sensors are applied for monitoring temperature, relative humidity, shock, and vibration. Future fiber optic applications include the monitoring of hypergolic propellant fuels, liquid detection, contamination, radiation, strain, and electric and magnetic fields.

Fiber optic sensing solutions allow fulfilling a need to control high valued assets applying fiber optic sensing technology that can be installed with live ordnance. Moreover, the fiber optic sensing system was tested on a self-defense test ship before its installation on real warships.

Such fiber optic technology enables us to increase confidence in real-time fiber optic applications on active warships and ensure sensing systems are ready before future improvements. This optical fiber sensing system contains as many fiber optic sensors as possible to develop a new project that allows demonstrating and detecting main challenges in a relatively short time.

The Office of Naval Research offers fiber optic sensing solutions that are able to monitor, identify, and forecast the health of most critical components, hot spots, fatigue, and damage-prone parts of weapon systems in a reliable and economical way.

Such fiber optic technology may enhance sensing systems while cutting the maintenance cost, current parts life, and new materials. The advantages of fiber optic sensing solutions are based on the application of lightweight, compact fiber optic sensors compared to traditional big, heavy, and hard resisting gages.

Finally, the researchers from NASA developed fiber Bragg Grating or FBG (a fiber optic sensor that reflects certain wavelength and sends all others), as well as two techniques they apply in their fiber optic sensing systems: conventional Wavelength Division Multiplexing and unique FBG Interrogation Technology called the Optical Frequency Domain Reflectometry.

If you want to obtain a highly efficient sensing system, you should choose the Optromix company. Optromix is a manufacturer of innovative fiber optic products for the global market. The company provides the most technologically advanced fiber optic solutions for monitoring worldwide. Optromix is a fast-growing vendor of fiber Bragg grating (FBG) products line such as fiber Bragg grating sensors, FBG interrogators and multiplexers, distributed acoustic sensing (DAS) systems, distributed temperature sensing (DTS) systems. If you are interested in FBG sensors and want to learn more, please contact us at info@optromix.com

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NASA offers collaboration to companies providing fiber optic solutions

FBGs in fiber optic solutions The members of NASA company have decided to offer collaboration to companies providing fiber optic sensing solutions for monitoring of structures and asset management. The fact is fiber optic sensing technology unifies advanced optical fiber sensors and innovative algorithms that allow making precise and cost-efficient monitoring of numerous crucial parameters in real-time.

The mentioned abilities of fiber sensing solutions play a significant role in structural health monitoring and tank gauging applications. The following parameters are taken into consideration: position or deformation (2D and 3D displacement, twist, and rotation), the level of stiffness (bending, torsion, and vibration), operational loads (bending moments, shear loads, and torques), magnetic fields (different defects in safety-critical structures made from metal materials), and stress/strength parameters such as pressure or fatigue and breakage prediction.

Moreover, fiber optic sensing systems enable to provide not only the structural health monitoring of a tank but optical fiber technology is able to sense the inventory of the tank: for example, the level of the tank’s content, evaporation rate, temperature (that can varies from cryogenic up to 300 degrees Celsius), and stratification (oil vs. water, sediment vs. liquid, and thermal layers).

Fiber optic sensing solutions offer numerous advantages that include:

low cost opening new fields of application across industries;
low power consumption of fiber sensors due to highly efficient algorithms and high-speed processing platform enabling quick data processing and real-time analysis;
fast speed and high level of efficiency;
precise and adaptive fiber optic technology because of the ability of optical fiber sensors to automatically increase resolution where/when needed;
easy installation of fiber device;
high reliability of operation even in humid/liquid environments and harsh temperature conditions.

The numerous abilities of fiber optic sensing systems create a potential solution for a myriad range of monitoring applications. Structural health monitoring and integrity, tang gauging, active control, safety and protection area, non-destructive evaluation, and medical usage refer to potential optical fiber applications.

The principle of fiber sensor operation is based on the use of fiber Bragg grating sensors that are installed in an optical fiber at intervals as small as 0.25 inches (0.64 cm). Finally, such a fiber optic sensing system allows monitoring strain, stresses, structural instabilities, temperature distributions, and numerous other engineering parameters in real-time with a single instrumentation system which weight is less than 10 pounds (4.54 kg). Herewith, the fiber optic solution is able to differentiate between liquid and gas states in a tank or other container, offering precise measurements.

If you want to obtain a highly efficient sensing system, you should choose the Optromix company. Optromix is a manufacturer of innovative fiber optic products for the global market. The company provides the most technologically advanced fiber optic solutions for monitoring worldwide. Optromix is a fast-growing vendor of fiber Bragg grating (FBG) products line such as fiber Bragg grating sensors, FBG interrogators and multiplexers, distributed acoustic sensing (DAS) systems, distributed temperature sensing (DTS) systems. If you are interested in FBG sensors and want to learn more, please contact us at info@optromix.com

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Fiber optic solutions for fire detection and temperature measurement

FBGs for fire detection Proper fire detection in the mining area is the number one priority because fire can evoke damages to valuable assets, downtime in operation, and even loss of lives. Herewith, the installation of fire protection devices can be complicated by harsh environmental conditions of the mining area because industrial equipment produces dirt, dust, humidity, and corrosive atmospheres in the production, storage, or transport of goods. Nevertheless, the application of modern fiber optic sensors based on distributed temperature sensing or DTS is considered to be a proven and efficient technology for fire detection and temperature measurement.

The fact is DTS technology provides precise temperature measurement along the length of a conveyor belt due to the use of autonomous fiber optic cables, therefore, even very long conveyor routes can be efficiently monitored. Thus, cases of fires and overheating during mining operations can be quickly and easily identified and localized to within one-meter precision by distributed temperature sensors, enabling to activate the safety countermeasures. Also, it should be mentioned that it is required the proper installation of the fiber optic sensor cables and adjustment of the alarm zones for heat detection of industrial rollers.

Nowadays mining industry applies fiber optic linear heat detection systems for these purposes, however, the new distributed sensing technology may significantly improve and increase the protection of assets in combination with the one mentioned above. The principle of DTS technology operation is based on the use of optical fibers as a distributed microphone, moreover, it means that fiber optic sensors allow measuring not only the temperature but also the acoustics. Such additional information is important because it helps to determine potential sources of danger and improves the whole purpose of fire prevention. To be precise, the DTS is highly important in hot roller detection that is the main reason for conveyor fires.

Also, it is difficult to identify the initial smoldering stage with traditional techniques, herewith, the majority of common gas detecting systems do not work properly because of high air currents. An optical fiber-based on distributed temperature sensing technology, in its turn, provides numerous benefits during both normal operation and dangerous situation that include:

Reliable fiber optic cable that is resistant to dirt and dust;
Long-distance (up to 10 km) and up to 4 measurement channels monitor several conveyors with one DTS system;
Practically maintenance-free;
Accurate localization of fires and hot rollers;
DTS is able to detect fires in spite of unfavorable environmental conditions.

Optromix is a DTS system manufacturer that provides top of the line distributed temperature sensing systems suitable for monitoring of commerce networks. If you have any questions or would like to buy a DTS system, please contact us at info@optromix.com

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Fiber optic solutions for security monitoring system

FBGs for security monitoring Recently a new simple low-cost technology has been developed for security monitoring of the borders. Initially, the technology that includes fiber-optic cables has been tested at the US-Mexico border. It allows the determination of a wide range of invasions such as animals, people, vehicles and it is even possible to detect their precise location.

In spite of the fact that this fiber-optic application is not new and has been around for years, the government of the USA has been slow to use it. The fiber-optic cable technology is able to detect exactly what is moving above it, and it does not matter whether it is a huge man, a group of people, a passing car, or a wandering dog.

Today, the US government continues to build a border wall that critics name a “medieval” solution to provide security, even despite the fact that the use of the fiber-optic system is cheaper than the building of a real wall. Other advantages of fiber optic cables include:

precise determination of border invasion location;
accurate detection of border invaders;
possibility to send quickly the information to border patrol agents in real-time.

It should be mentioned that only 1% of human communications is accounted for by satellites, and 99% is accounted for by fiber-optic cables spreading across the seafloor, buried under cities. Herewith, comparing to satellites, the fiber-optic technology is able not only to transmit data but also to determine movement that makes it more advantageous.

Moreover, the fiber-optic technology is already developed enough to be implemented in the security monitoring system of the US-Mexico border, and it is nearly ten times cheaper than a wall and can be put into operation instantly. Nevertheless, the main obstacle is the support of the US government.

The fiber-optic system is quite simple, that is why it is not necessary to put any sensors on the fiber because the fiber itself is a sensor that is able to determine motion as well as events anywhere along the fiber-optic cable length. Some companies made some improvements and enlarge the field of fiber-optic applications that now includes telecommunication, security monitoring, and even broadband internet access.

The principle of work is based on converting sound waves into acoustic information. Although the fiber-optic technology on its own will not completely get rid of the activity such as illegal border-crossing and drug-smuggling, its combination with border patrol agents will significantly improve the situation.

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Fiber Bragg Grating Based Chemical Sensors

Fiber Bragg grating (FBG) can be used as miniature, inexpensive, and lightweight strain, temperature, and pressure sensors for applications such as real-time health monitoring of aircraft, space vehicles, and smart materials and structures. Nowadays only a few applications of FBGs in chemical sensing have been reported.

The key to a chemical sensor using an FBG lies in the transfer of stress from a swelling material, such as a polymer, to the FBG, resulting in a measurable strain via the shift in resonant Bragg wavelength.

The main principle of FBG sensors for applications in chemical sensing is based on the axial strain of the fiber. The chemicals that surround the fiber cause it to shift and, deform. The strain caused by the presence of a particular chemical causes the spectral pattern of reflected light to change; the shift in reflected wavelength is observed. To monitor the shift in wavelength FBG interrogators are used. The data gathered by the interrogator can then be converted to environmental concentrations.

The key component of fiber Bragg grating sensors for chemical sensing is a highly sensitive coating. The coating should be stiff and adhere easily and firmly to the glass fiber. Most often the coating is based on polymers. However, the coating needs to have a high modulus of elasticity that remains high at high temperatures and during analytes absorption. Most polymers are restricted by temperature due to softening and material relaxation.

Some ways of FBG sensors polymer coating include:

improved coating processing;

The improvement of the coating process, like improved adhesion, may aid in the reduction of material relaxation and shifting. The glass fiber may be treated before the application of polymer coating for improved adhesion.

improved data processing;

The use of two different coatings that respond in equal, but the opposite manner to environmental changes. The combination of the two responses limits the temperature drift.

improved material properties.

Alternative coatings, like ones based on ceramic materials, may expand the temperature application range.

Chemical sensing is a developing field of fiber Bragg grating sensors. It is involved in the control of chemical processes, oil recovery, environment quality improvement. There are several factors that play a role in the implementation of chemical sensors – suitability for remote sensing, sensitivity, low costs, selectivity, ability to work consistently in harsh environments. The oil and gas applications require sensors that can withstand high temperatures and pressures, and environmental sensors must have a wide coverage area and limited signal fluctuations.

Fiber Bragg grating sensors have been used in numerous applications, including aircraft monitoring, structural health monitoring, strain, and temperature measurements. In the last decade, FBG sensors have been implemented as chemical sensors due to their ability to withstand high temperatures, immunity to electromagnetic interference, and the absence of electronics.

Optromix, Inc. is a U.S. manufacturer of innovative fiber optic products for the global market, based in Cambridge, MA. Our team always strives to provide the most technologically advanced fiber optic solutions for our clients. Our main goal is to deliver the best quality fiber optic products to our clients. We produce a wide range of fiber optic devices, including our cutting-edge customized fiber optic Bragg grating product line and fiber Bragg grating sensor systems. Optromix, Inc. is a top choice among the manufacturers of fiber Bragg grating monitoring systems. If you have any questions, please contact us at info@optromix.com

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Fiber Optics in Avionics: Optical Fiber vs. Copper Cable

Fiber optic technology is revolutionizing the avionics systems and is lightly to be the ideal solution to future aircraft requirements. Fiber optic products are revolutionizing the avionics systems and ideally to be the perfect solution to future requirements. A modern jet has enormous amounts of data flowing through it to support the latest technologies in the cockpit and the cabin. All that data has to be delivered at lightning speed. This necessity has led aircraft manufacturers and airlines to turn to the optical fiber. The copper cables co-existed with fiber optic applications for decades. Currently, designers and engineers find fiber optic products to make better sense technically and economically in the overwhelming majority of cases.

The ability of the optical fiber to transmit much more information in less time over longer distances than traditional copper wire has become the reason that fiber optic equipment is being deployed on aircraft. There are fiber optic bundles of copper cables in an aircraft and the signals which they carry are fully replaceable by fiber optic products to allow an improvement of the system in various different ways.

There are two common trends regarding data transmission in the avionics market: constantly growing transmission speeds and the need to reduce weight. Fiber optic systems are an ideal response to these two trends in providing for high-speed data and immunity to electromagnetic interference that eliminates the need for any type of screening which can often be very expensive due to their weight and complexity. Fiber optic equipment offers lower wastage, weight, size, etc. These advantages make fiber optic equipment suitable for application in aircraft where space restrictions and electromagnetic interferences could be detrimental.

Nowadays fiber optic systems have been implemented in different aircraft systems such as sensory systems, distributed opening systems, and fiber optic aircraft monitoring.

In addition to this, fiber optic devices applied to the monitoring of aircraft structures provide some advantages over traditional devices. Fiber Bragg grating sensors have proved to constitute the most promising technology in this field. In order to prolong the operation period of all kinds of complex engineering systems and avoid catastrophic failures, so it is necessary to achieve the highest levels of damage detection. The automation of the inspection process is a point of major importance to reduce inspection efforts. The structural health monitoring system on the basis of fiber optic products can be defined as a set of devices that provide information that allows us to locate, evaluate, and predict the loading and damage conditions of a structure. The structural health monitoring of aircraft structures can conduct real-time checks, reducing costs, and improving the reliability and performance of the structures. A wide range of potential structural health monitoring technologies is being developed to meet these needs, and the most promising options are:

electrical strain gauges and crack wires;
acoustic emissions methods;
optical-based technologies;
comparative vacuum monitoring;
microelectromechanical systems (MEMS).

Fiber optic products and fiber optic devices, in general, are very appropriate to perform structural health monitoring due to the fact that they have their intrinsic capabilities, such as sensitivity to electromagnetic radiation, low weight, compact size, great sensitivity and resolution, and their suitability to be embedded into structures. Fiber optic devices for monitoring the strain in aircraft structures can be classified into the following categories: intensity-based, interferometric, distributed, and grating-based fiber optic devices.

Among grating-based sensors, FBGs and probably the most mature and widely employed optical sensors for structural health monitoring of engineering structures due to their fast development achieved in recent years. Fiber Bragg grating sensors have important advantages over conventional strain sensors:

high sensitivity and resolution, low weight and small size, the absence of the electromagnetic interference;
suitability for being attached to a structure or embedded in composite materials
high multiplexing capability;
wavelength-encoded sensing in a way that is totally independent of the optical intensity;
different magnitudes can be measured using FBGs, such as strain, temperature, vibration, or humidity.

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