Low-cost FBG interrogator for dynamic measurements

FBG interrogator for dynamic measurementsFiber 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

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:

  1. 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.

  1. 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.

  1. 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.

  1. 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

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

FBG interrogators for power line monitoringElectricity 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