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 strain sensors for structural health monitoring

Fiber Bragg gratings stand out among other fiber optic sensors as the most developed and prominent technology for the measurement of strain, vibrations, temperature, and pressure. FBG sensors have attracted significant interest in structural health monitoring due to numerous advantageous properties:

  1.  immunity to electromagnetic interference;
  2. intrinsic fire safety;
  3. low invasiveness;
  4. minimum aesthetic impact;
  5. possibility to send the data remotely using the same sensing fiber.

There are multiple sensing advantages that FBG sensors provide. First of all, FBG sensors perform with an excellent balance between complexity and performance, which is one of the most attractive qualities of fiber Bragg grating sensors for structural health monitoring. Secondly, FBG sensors are able to work in low signal-to-noise ratios better than other optic sensors. Moreover, fiber Bragg grating sensors are predictable and less dependent on the temperature of the surrounding environment, as well as are well-suited for multiplexed optical sensor networks.

Over the past decade, structural health monitoring has attracted a lot of attention as modern technology develops, and new materials and compounds are used in the construction of buildings and structures. Structural health monitoring involves the collection and analysis of information obtained through measurements of the structure. The results of data analysis are used to assess the damage and evaluate the performance of the structure under harsh conditions.

FBG sensor structural health monitoring has become an important tool for assessing the performance of different structures and measurements of temperature, strain, pressure, displacement, etc.

Fiber optic strain gauge is welded directly to the surface of the metal structure (pipes, beams, etc.), and it has a protective silicone cover. Fiber optic strain sensors are durable and stable, widely used for civil engineering constructions, particularly they reinforce concrete structures exceptionally well.

Fiber Bragg Grating strain sensors demonstrate lots of advantages compared to the regular electrical strain gauges. Namely, they are immune to electromagnetic interference and power shortages. Compact size devices provide the most accurate measurements. FBGs are, literally, the best strain sensors right now.

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

Fast fiber Bragg grating sensors

Numerous advantages of fiber Bragg grating sensors, like compact size, passive nature, immunity to electromagnetic interference, the capability to directly measuring physical parameters such as temperature and strain, have inspired researchers to develop FBG sensor systems for applications outside laboratories. FBG sensors are now used in mainstream sensing technology applications. One of the recent developments in fiber Bragg grating technology is FBG sensors based on femtosecond lasers. These sensors are promising for use in extreme environments, such as high temperatures, high pressures, and ionizing radiation. Multiple industries might benefit from fast FBG sensors, like energy production applications.

Fiber Bragg grating temperature sensors that are inscribed with femtosecond lasers are stable up to the fiberglass transition temperature.

FBG sensors that are thermally stable can be used in a variety of applications. For example, stable FBG temperature sensors are optimal for sensing in extreme conditions that are often present within power plants, combustion systems, turbines, and in the aerospace sector. Regular FBG sensors do not perform optimally under extreme temperatures as they are hampered by optical losses that are a result of ingress of high-temperature hydrogen gas. However, FBG sensing arrays are difficult to produce in pure silica core fiber. The use of pure silica prevents the detrimental effects that hydrogen gas has on the fiber.

Fast FBG-based sensors have already been tested at a power generation plant. Many energy production processes require accurate temperature measurements that are difficult to realize with standard sensor technology, like electronic thermocouples. The advantages of FBG temperature sensors deployment are ease of installation, high density of sensing points, more rapid response to thermal changes, etc. Overall, fast FBG temperature sensors are an optimal solution for extreme environments, including high temperatures and high pressures. They are easy to install, maintain, are cost-effective, and accurate.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) products line: fiber Bragg grating sensors, FBG interrogators, and multiplexers, Distributed Temperature Sensing (DTS) systems. We create and supply a broad variety of top-notch fiber optic solutions for the monitoring of various facilities all over the world.

If you are interested in Optromix fiber Bragg grating temperature sensors, please contact us at info@optromix.com