Category: FBG Interrogators

FBG Interrogators and Other Fiber Optic Technologies

Fiber optic technology has become a solution that takes its place in many processes due to its benefits and stable performance it provides. It contains a wide range of tools such as fiber Bragg grating sensors, FBG interrogator, etc. All equipment contributes to distributed sensing and plays its own different role.

FBG Technology Principle

Fiber Bragg grating is a microstructure. It might be integrated into the optical fiber’s core. FBG is usually approximately a few millimeters in length. The interference pattern in the core is done with the help of the UV laser beam and a phase mask.

According to the technology, the index of reflection changes along the length in the fiber core. Its modulation makes a fiber Bragg grating play as a selective mirror that is able to reflect certain wavelengths and transmit the others. The light that continues to pass through the optical fiber to the following fiber Bragg grating travels without any loss. The reflected wavelength is defined by the microstructure interval and the index of refraction of the core.

The FBG system contains two main elements: FBG interrogator and a range of fiber Bragg grating sensors.

FBG Interrogators

FBG interrogators are optoelectronic units playing a role of measurement and data collection systems. FBG interrogator is an important part of the distributed monitoring system that enables instant figures of fiber Bragg grating (FBG) sensors and data transmission.

An FBG interrogator is able to provide data from the network of sensors. Fiber optic sensors can be presented by different types of sensors that measure different parameters, for example, temperature, strain, displacement, etc. They are connected into one distributed monitoring system that acquires information simultaneously.

During the data acquisition, FBG interrogator acts as a radar, sending pulses into the fiber and getting the signals back. The interrogator registers the received wavelengths and then transfers them into engineering units. With highly accurate FBG interrogators, fiber optic sensing systems are able to provide reliable data over a wide distance. FBG interrogators efficiently provide precise measured data twenty-four hours a day using computer software. Due to the software, data can be stored and later analyzed.

Fiber Bragg Grating Sensors

The other element of every sensing system, except for FBG interrogator, is fiber Bragg grating sensors. FBG sensors are sensors based on the same principle of fiber optic technology. They usually present a chain of sensors creating a single optical fiber. This chain commonly consists of up to 30 fiber Bragg grating sensors per fiber.

Fiber optic sensors proved to be the best solution compared to traditional electrical sensors. They have proven to be highly accurate, relatively simple instruments capable of operating in severe environments. In contrast with conventional electrical sensors, fiber Bragg grating sensors are immune to electromagnetic influences (EMI) and mechanical fatigue.

The diversity of FBG sensors is quite wide. The most common types of sensors are:

Temperature sensors;
Strain sensors;
Displacement sensors;
Pressure sensors, etc.

Fiber optic sensors can be implemented in different field projects. Depending on the purposes, multiple fiber optic sensors or array of sensors can be installed. They are able to take measurements for one or several parameters in different places. The FBG sensors can be embedded into the structures or surface mounted.

FBG systems that contain fiber Bragg grating sensors and FBG interrogators have found their applications in many areas. They are proven to help in development and monitoring of different constructions, vessels, systems, etc. Fiber optic technology has proven to be cost-effective and efficient.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating sensors, for example, FBG strain sensors, FBG interrogators and multiplexers, Distributed Acoustic Sensing (DAS) systems, Distributed Temperature Sensing (DTS) systems. The company creates and supplies a broad variety of fiber optic solutions for monitoring worldwide. If you are interested in structural health monitoring systems and want to learn more, please contact us at info@optromix.com

FBG Interrogators with a size of a memory stick

Fiber optic sensors are a modern technology that helps in shape and temperature measurements in various spheres and industries, for example, civil structures, aircraft, medicine, etc. Scientists from all over the world aim to create the most compact and cost-effective device according to the market demand. So the specialists from Europe have produced the new memory stick-sized FBG Interrogators.

Fiber optic sensors’ nature

Fiber optic sensors have many characteristics that make them very effective for a multitude of applications. They are small, inert to chemical substances, immune to electromagnetic interference, and capable of withstanding high temperatures. There is no doubt that they have a lot of applications thanks to their unique characteristics. Fiber optic sensors are applied in structural health monitoring. In medicine, they are also used in catheters, endoscopes, etc.

Over the last years, scientists have developed fiber Bragg grating (FBG) sensors that can measure strain and temperature. For example, fiber optic sensors are successfully applied in the new generation of planes. The whole principle of the fiber optic sensors is based on the reflected light. The light is sent through a fiber optic cable and partially reflected by a microstructure inscribed into the fiber core. Researchers can observe different changes in strain or temperature thanks to the shifts in the wavelength of the reflected light.

Modern sensor devices such as FBG interrogators are based on free-space spectrometry. Spectrometers measure the properties of light in a specific part of the electromagnetic spectrum. However, this approach still has several limitations including measurement resolution, power consumption, etc. That is why scientists aim to develop fiber optic technology further.

The new generation of FBG interrogators

As fiber optic technology develops, scientists create new ways of device dimensions, power, and cost consumption to serve the increasing applications and clients’ requirements. There are many types of FBG interrogators that can include multiple photonic functions in one device. These devices represent the second generation on the market responding to the clients’ demands.

Nowadays, scientists even work on the third generation of fiber optic systems that have the size of a memory stick. With the size optimization, they also make the cost-effectiveness better. The new fiber optic technology includes a photonic submodule that consists of two light sources and a spectrometer section. Scientists have added three thermistors to measure the temperature of those three parts. The small box that has a size of a memory stick detects the reflected light that’s coming in on the fiber. The light is produced by one of the two light sources inside the model, injected into the fiber. The photodiodes record the reflections and the electronics amplify them.

Despite all the advantages of these new fiber optic systems, the future market adoption needs a more compact and lower-cost solution, including the costs of the consumables in medical and fiber optic battery monitoring systems.

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Low-cost FBG interrogator for dynamic measurements

Fiber Bragg grating technology (FBG technology) offers fiber optic sensors that allow carrying out the measurement of such parameters like temperature and/or mechanical strain. However, the high cost of fiber sensing systems is considered to be a major disadvantage for commercial applications.

It should be noted that the popularity and fast growth of fiber optic technology for sensing applications promote numerous research in various areas, for example, industry, medicine, aerospace, civil applications where such physical and chemicals factors as acceleration, level, temperature, strain, pressure, deformation, refractive index play a very important role.

Optical fiber sensors are perfect for use in the mentioned measurements. Fiber optic technology offers numerous benefits that include “intrinsic safety, resistance to chemical corrosion, immunity to electromagnetic interference, electric isolation, compact size, lightweight sensing heads, high resolution, easy multiplexing, and capability for extremely remote monitoring without the need of electrical power at the measuring point”.

Moreover, fiber Bragg gratings are the most used technology for the measurement of temperature and/or mechanical strain parameters among other optical fiber sensors. To be more precise, the term “fiber Bragg gratings defines as nanometer periodical refractive index changes engraved in an optical ﬁber core.”

The principle of FBG technology operation is based on the injection of a broadband light spectrum in the optical fiber. Herewith, there is a concentration of the reflected spectrum at the fiber Bragg grating wavelength, herewith, it is possible to see a suppression in the transmitted signal at the same wavelength.

Additionally, the same operation principle of the FBG technology is used in new and more complex structures, for example, planar FBG sensors. Thus, the FBGs offer very precise measurements due to the wavelength that is considered to be a permanent feature of the signal along the optical fibers.

Nevertheless, the FBG interrogators have some challenges in large commercial applications because of their high cost. That is why the development of new, low-cost alternatives to the current FBG interrogators is highly required. Therefore, there are several solutions to the present problem.

One of the solutions is the use of frequency-to-amplitude conversion (a fast and low-cost FBG interrogation technology), in which the spectral variations of fiber Bragg gratings are straightforwardly transmitted into optical power variations. Herewith, the presented FBG technology is based on the twist between both the FBG sensors and the edge filter spectra.

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

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Fundamentals of fiber Bragg grating interrogators

The fiber Bragg grating sensors work by sending the light into the fiber, where it is reflected back from the FBGs. The light that has been reflected travels back to the photodetectors of the instrument, where it is compared to wavelength reference artifacts. During this process the fiber Bragg grating interrogator evaluates the position of the center wavelength of the FBG; this information is later converted to engineering units. The gage factor supplied with the FBG sensor helps to determine and translate the data obtained during the measurements.

The described principle is true when one FBG sensor is present on a fiber. However, if the particular application requires multiple FBG sensors, like FBG sensor pipeline monitoring, fiber optic well monitoring, FBG temperature sensing, etc., the interrogators use one of the discriminating schemes in order to discriminate between one FBG sensor and the next. There are a couple of discrimination methods that are used in FBG interrogators. The first one is referred to as time division multiplexing utilizes the known speed of light in the fiber to discern which signal is reflected from which FBG along the fiber path. Around 100 FBG sensors can be interrogated with this method.

The second method, wavelength division multiplexing, is the most utilized one. As FBG sensors are at distinctly different nominal center wavelengths from their neighbors, the FBG interrogator uses the wavelengths of the sensors to track them along with the fiber. The range of this method is largely due to the developments in fiber optic technology.

Other approaches to FBG sensor interrogating, some of which include:

Broadband source, Dispersive element, Diode Array;

This method is less reliable than the aforementioned ones due to limited resolution, which is a result of the inherent limitations of commercially available diodes.

Broadband source, Optical Spectrum Analyzer/Multi-line wavelength meter;

The optical spectrum analyzers are large and expensive, which makes them less desirable in a laboratory setting. They are also not able to perform optimally under some temperatures.

OTDR/TDM systems;

The system cannot handle a large number of sensors on the fiber as its data acquisition rates scale down with increasing sensor counts.

External Cavity Tunable Laser, Power Meter, Wavelength Meter;

External cavity tunable lasers have low speed and do not have a wide operating temperature range. Moreover, they are expensive and do not have the required mechanical robustness.

Optromix interrogators can control up to 8 optical channels. The interrogator operates with the 20 maximum sensors per channel. The device is controlled by the PC with the specialized software for sensors monitoring. The system contains a broadband source of radiation and it can carry out spectrum analysis.

If you would like to purchase an FBG interrogator, please contact us: info@optromix.com or +1 617 558 9858

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Fiber Bragg grating (FBG) temperature sensors and FBG interrogators in power line monitoring and temperature surveillance

Electricity is the backbone of modern civilization; it holds the development of both economy and technology. It is established that it is no longer an option to rely on existing infrastructure as there is a need to constantly evolve and adapt to the growing demand of the populace. The state of current infrastructure is weakened by its age of installation or by the growing demand of the population. The breakdown is imminent as it cannot bear the burden of previous years.

As the demand for energy increases, the need to monitor the efficiency of the assets arises. Despite the increased number of new power assets, it still cannot cater to the demand of the entire nations.

The development of fiber optic sensing technology became prominent for the monitoring of the power line temperature. Fiber optic sensors, including FBG temperature sensors, have proven to be valuable for the industry. It is immune to electromagnetic interference, mechanical vibrations, and electric noise. FBG sensors are more reliable and perform best under harsh conditions.

FBG temperature sensors are introduced into a fiber where they are evenly placed. The light that travels through the fiber will experience a wavelength shift if any strain is applied to the sensors. This, in turn, causes a magnitude change of the reflections that allow for accurate measurements to be performed. FBG that is used inside the sensors is highly sensitive to not only mechanical deformation but also temperature changes. To obtain and process signals emitted by FBG sensors, FBG interrogators are used. These devices can carry out spectrum analysis.

FBG temperature sensors can capture ultra-fast events in real-time, providing useful data for power line integrity monitoring and localization of stress areas. An accumulation of the data on the temperature profile of the power lines can be useful for the improvement of the intensity of the electrical current, the maintenance of power lines, and determine a threshold of the power cables. The data obtained will allow for a surplus of energy to meet modern energy needs while sustaining existing power assets.

Nowadays FBG sensors are used in a variety of different fields that require accurate and fast measurements. Depending on the nature of the application, FBG temperature sensors, FBG strain sensors, FBG pressure sensors, FBG displacement sensors may be utilized. The sensors are often accompanied by FBG interrogators to interpret the signals, and FBG multiplexers to create large monitoring systems with a big number of FBG sensors. The more complex the sensor system, the more intricate data can be obtained.

Optromix offers a wide range of FBG sensors, including FBG temperature sensors, as well as FBG multiplexers, and FBG interrogators. If you would like to purchase fiber Bragg grating sensors, please contact us: info@optromix.com or +1 617 558 9858

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