Fiber optic sensors began to be widely used in space

fiber optic sensors in spaceMembers of NASA claim that they plan to test an enhanced fiber optic sensing system that allows performing thousands of measurements along the optical fiber about the thickness of a human hair for application in space. Herewith, such a promising fiber optic technology can control spacecraft systems during missions to the Moon and landings on Mars.

To be more precise, the system based on fiber optic sensors has been designed at NASA’s Armstrong Flight Research Center in California to obtain strain and other measurement data for aircraft. The researchers adapted the fiber optic system for application in space, where its potential uses contain temperature and strain information essential for space flight safety.

It should be noted that four fiber optic sensing systems are planned to test in space during five months, herewith, such tests carried out will demonstrate whether space fiber optic sensors can pass the hard conditions of a rocket launch. The thing is that rockets and spacecraft are considered to be highly complex systems and they have a myriad of various factors to be measured that is why NASA plans to keep the first applications of space fiber optic systems simple.

The new fiber optic technology based on space-rated sensors enables us to measure distributed temperatures on the Low-Earth Orbit Flight Test. The aim of the aeroshell of the fiber optic system is to slow down and protect heavy payloads from the intense heat of atmospheric re-entry. Additionally, the fiber optic sensors monitor temperatures on the backside of the inflatable decelerator, therefore, the researchers “are working on space optical fiber experiment that will travel as a self-contained experiment on a Blue Origin New Shepard rocket through NASA’s Flight Opportunities program.”

The opportunities provided by fiber optic technology also include the decrease of the heat produced by the unit’s electronics and by way of conduction, or moving the heat away from the unit, because of a lack of air in space. The fiber optic system is regarded as self-contained and essentially ready for plug and play application. The thing is that the operating principle of the system is based on fiber optic sensors that can endure severe conditions to measure distributed temperatures in a cryogenic environment that play a crucial role.

NASA is also developing a compact, economically, and hardly fiber optic sensing system version. Thus, the new fiber optic technology based on a temperature-tuned laser is used to overcome the challenges. The researchers continue improving the production techniques of fiber optic sensors and discussing performing a potential test of the sensors at NASA’s Ames Research Center in California to support the study of the new fiber optic technology.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating 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

Dynamic gratings produce new fiber optic sensors

FBG sensors with dynamic gratingsResearchers have presented dynamic gratings used instead of depending on fixed-position fiber Bragg gratings, and now core-launched laser beam light can unite to the cladding modes of conventional optical fiber resulting in distributed fiber sensing of the external environment.

The thing is that fiber optic sensors allow distinguishing between chemicals and liquids external to the optical fiber, herewith, they are usually based on refractive-index changes in the cladding modes of the fiber. Moreover, fixed-position fiber Bragg gratings (FBGs) are applied to excite these cladding modes and unite laser beam light from the core mode.

Nevertheless, FBG sensors need specific equipment to create the gratings at the optical fiber, also they only work as point sensors at specific, predetermined locations. A team of researchers from Israel tries to overcome these challenges by developing dynamic gratings at reconfigurable short sections along with the optical fiber.

Thus, the new gratings are independent of any permanent change in the fiber structure. It is possible to switch them on and off at will, and fiber optic sensors based on dynamic gratings allow scanning along with the optical fiber. According to researchers, after the installation of a grating, its effect is not restricted only to light in the core mode.

Similar to conventional FBGs, the dynamic gratings also unite laser beam light between core and cladding modes. Herewith, in analogy to fiber Bragg gratings, such connection will occur for the light at very specific frequencies. “An optical probe wave of tunable frequency is launched at the dynamic grating, and the exact frequency in which coupling takes place is carefully noted.”

Compared to FBGs, dynamic gratings enable the researchers to carry out tests in any chosen position. It should be noted that the developed fiber optic sensors have been already tested over 2 m of traditional optical fiber. To be more precise, fiber sensors consisted of  8 cm length dynamic gratings perform scanning along with the optical fiber resulting in the combination of spectra between core and cladding modes in each position.

Measurements accurately detect the parts of optical fiber that were immersed in ethanol and water, herewith, the fiber sensors can distinguish between the two with an 8 cm resolution. At the same time, the refractive index outside the fiber is possible to estimate precisely with fourth-decimal-point accuracy (0.0004).

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating 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

What you should know about fiber Bragg gratings

fiber Bragg gratings (FBGs)Fiber Bragg gratings are currently widely used in optical fibers and light guides for compaction of channels along the wavelength, optical filtering of signals, as resonator mirrors in fiber and semiconductor laser systems, as smoothing filters in optical amplifiers, to compensate for dispersion in the main communication channels.

Another field of application of FBG technology includes its use in various measuring systems that control environmental parameters, such as temperature, humidity, pressure, deformation, and chemical content. Bragg gratings distributed along the length of the light guides allow for creating distributed acoustic systems that differ favorably from traditional complexes of the same purpose in cost and technology of production.

FBG technology for recording Bragg gratings distributed in a light guide is a key element in creating a new generation of measurement systems. Hydroacoustic antennas developed on the basis of such optical fibers, as well as systems for the protection of extended objects and systems for monitoring the condition of main pipelines, are increasingly being used abroad. 

A distinctive feature of these fiber optic systems is the large extent of controlled zones, speed, and unique information capabilities. When fiber Bragg gratings are written at a standard optical fiber, a problem arises because of the fact that such a fiber has weak photosensitivity and a low saturation threshold, which is not sufficient for effective recording of gratings. 

The main solution method of FBGs is to increase the concentration of germanium dioxide in the core. Other methods consist of alloying the pieces for the creating of optical fibers with such chemical elements as boron, tin, nitrogen, phosphorus, antimony together with germanium, which leads to an increase in the photorefractive power of the light guides.

Writing of fiber Bragg gratings can be classified by the type of laser system used for production, the wavelength of beam emission, the recording technique, the irradiated material, and the type of Bragg grating. Lasers used for FBG writing can be either continuous or pulsed, with a wavelength of emission from the infrared (IR) to the ultraviolet (UV) range of the spectrum. 

These differences determine the spatial and temporal coherence of the optical emission sources used for writing, which, in turn, determines the choice of the appropriate method for recording fiber Bragg gratings. The main methods for FBG writing include the step-by-step method, the phase mask method, and the interferometric method.

The need to increase the speed of information transmission, associated with the development of telecommunications, increasing information flows, the growth of global information systems and databases, the expansion of the number of users, led to the fact that fiber optic system communication lines were developed using spectral multiplexing of optical channels.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating 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

Multi-addressed fiber Bragg gratings for microwave sensors

multi-adressed FBGsNowadays fiber Bragg gratings (FBG)  face several challenges in fiber optic sensor systems because of their complex installation and the high cost of interrogators provided by interrogation methods and FBG multiplexing. The thing is that such features as wavelength, time, frequency, polarizing, and spatial division multiplexing necessary for most applications also need complex tools, for instance, spectrum analyzers, spectrometers with tunable interferometers, Bragg gratings, etc.

It should be noted that one more challenge for FBG sensors include “the fact that these sensors are not addressable per se, and therefore, any spectrum overlapping leads to interrogation errors.” The possible way to overcome the problem is to use the addressed fiber Bragg gratings combined with the microwave photonics interrogation technique. The addressed FBG is considered to be a specific type of fiber Bragg gratings with two narrow notches in the reflection spectrum.

The operating principle is based on the light that passes through the FBG that has two narrow optical frequencies, herein, the difference between them is less than an optical frequency and installed in the microwave range. Such an addressed frequency does not depend on stress or temperature fields, it is also independent of fiber Bragg grating’s central frequency shifting.

The addressed FBG sensors act both as a two-frequency source and as a fiber optic sensor of the measurement system simultaneously. Thus, it is possible to develop a microwave-photonic fiber optic sensor system based on arrays of the addressed fiber Bragg gratings, if the set of address frequencies in the array is regarded as orthogonal. The addressed FBGs, in their turn, allow designing multi-addressed fiber Bragg grating structures.

The thing is that multi-addressed FBGs apply three (or more) frequency carriers, while their beatings on a photodetector create three (or more) address frequencies. The combination of address frequencies enables increasing the fiber optic sensor capacity of the measurement system as well as increasing the precision of central wavelength determination. Therefore, the multi-addressed FBGs are regarded as a specific type of fiber Bragg gratings with three (or more) narrow notches in the reflection spectrum.

The operating principle of the multi-addressed FBGs is based ion the light with three (or more) narrow optical frequencies, and the difference between them is less than an optical frequency and is placed in the microwave range. Additionally, the address frequencies set in FBG sensors does not depend on strain or temperature fields, central frequency shifting as well. Finally, the multi-addressed fiber Bragg gratings are both a multi-frequency source and a fiber optic sensor of the measurement system at the same time leading to the appearance of new applications.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating 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

Distributed fiber optic sensors and their prospects

distributed fiber optic sensorsModern industrial systems are subject to increasingly strict requirements. Structural health monitoring must always work reliably regardless of environmental conditions. Observability and manageability become an important parameter. The operator must be able to detect a problem, including a potential one, determine the location of its occurrence, and respond in a timely manner, taking the necessary measures to reduce time and material costs in emergency situations.

Current fiber optic sensing technologies make it possible to continuously, accurately and in real-time detect small changes in temperature, acoustic background, and deformations in any place of an industrial facility. Fiber optic cables, which are traditionally used in the telecom industry for transmitting information, come to the rescue to perform this. Depending on the type of devices connected to the optical cable, it is possible to detect various environmental events at a long distance (up to several tens of kilometers) performing structural health monitoring. The sensitive medium is the optical fiber and a huge number of “virtual” sensors inside it.

DAS (Distributed Acoustic Sensing) are “virtual” microphones installed along with the optical fiber. Standard single-mode optical fiber and Rayleigh scattering are used when acoustic vibrations cause small changes in the refractive index that are detected using this scattering. The fiber literally “hears” events occurring in the environment. The number of DAS is a combination of spatial resolution, distance, and pulse duration. Modern distributed fiber optic sensors can operate at distances of up to 80 km. Combining several devices into a single network allows for creating thousands of kilometers of structural health monitoring lines.

DTS (Distributed Temperature Sensing) is “virtual” thermometers along with the optical fiber. The distance range for a conventional single-mode fiber is up to 100 km with a spatial resolution of 1 to 5 meters and a measurement accuracy of less than 1 degree Celsius, with a measurement time of 2 to 30 minutes. These parameters are interdependent. For example, the longer the measurement time is, the better the spatial resolution and accuracy of the measurement are, and vice versa. 

Herewith, analytics show that the market for such distributed fiber optic sensors will grow by at least 10% per year in the foreseeable future. These fiber optic systems are most in-demand in North America. In terms of application, the oil and gas industry has the greatest potential. Temperature control prevails by type of monitoring.

Over the past 10 years, fiber optic sensing technology has been used to monitor thousands of kilometers of pipelines, thousands of oil and gas wells, and more. There are numerous fiber optic solutions that allow accelerating the introduction of promising technology in the industry, devices, and fiber optic cables are constantly being improved and become more accurate and affordable.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating 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