Shawn E. Karr

A Bragg grating-tuned fiber laser strain sensor system

The development of a fiber laser sensor system which permits efficient interrogation of Bragg grating sensors is reported. A tunable erbium doped fiber laser which utilizes a broadband mirror and an intracore Bragg grating reflector in side-pump configuration is described. The wavelength of the laser oscillation is determined by the Bragg grating, which is remotely located and used as a strain sensor. This arrangement is used in conjunction with a passive wavelength demodulation system (WDS) to form a self-contained fiber laser strain sensor system, allowing efficient interrogation of the Bragg sensor. This device provides interrupt-immune sensing of static and dynamic strains with a bandwidth of 13.0 kHz.<<ETX>>

A multiplexed Bragg grating fiber laser sensor system

A technique for multiplexing Bragg gratings in a fiber laser arrangement is described. This technique has successfully been used to multiplex two and three Bragg gratings with very little crosstalk. The Bragg grating laser sensors were used to measure both strain and temperature. Independent strain and temperature tuning of the gratings shows no crosstalk.<<ETX>>

A structurally integrated Bragg grating laser sensing system for a carbon fiber prestressed concrete highway bridge

Carbon fiber based composite material is of considerable interest for the replacement of steel in large concrete structures, such as bridges, where corrosion is a serious problem. A new two-span concrete highway bridge built in the city of Calgary in 1993 is the first in the world to use carbon fiber composite prestressing tendons in several of its precast concrete deck support girders. We have instrumented a number of these girders with an array of fiber optic intracore Bragg grating sensors in order to monitor the changes in the internal strain that take place over an extended period of time. A four-channel fiber laser demodulation system was developed for interrogating the set of Bragg grating sensors embedded within the bridge girders. This demodulation system was demonstrated to be rugged, compact and transportable to the bridge construction site where it allowed changes in the internal strain on all three types of prestressing tendon (steel and two types of carbon fiber composite) to be tracked over several months. The same set of structurally integrated Bragg grating sensors has also been used to measure the change in the internal strain within the deck girders arising from both static and dynamic loading of the bridge with a 21 ton truck. This first permanent testbed for structurally integrated Bragg grating sensors demonstrates the feasibility of building into new bridges fiber optic long-term structural monitoring sensing technology that will allow the use of these advanced composite materials to be monitored in a manner not previously practical. The strain information available from this type of monitoring system will assist engineers in their assessment of new materials and innovative design features, and has a potential role in maintenance and repair activities.

Bragg grating structural sensing system for bridge monitoring

Corrosion of steel within bridges and other large concrete structures has become a serious problem and consequently there is growing interest in replacing the steel within such structures with carbon fiber based composite materials. The first highway bridge in the world to use carbon fiber composite prestressing tendons was constructed and opened to the public in the fall of 1993. This two span bridge was also unique in another respect, it is the first highway bridge in the world to have been built with a set of fiber optic Bragg grating sensors structurally integrated into several of its precast concrete deck support girders. A four-channel fiber laser sensor demodulation system that was rugged, compact and transportable was developed for this project. This demodulation system monitored the changes in the internal strain on all three types (steel and two types of carbon fiber composite) of prestressing tendons over several months. The same structurally integrated fiber optic sensing system has also been used to measure the change in the internal strain within the deck girders arising from both static and dynamic loading of the bridge with a large truck.

Fiber optic Bragg grating sensor network installed in a concrete road bridge

The installation of a fiber optic Bragg grating strain sensor network in a new road bridge is described. These sensors are attached to prestressing tendons embedded in prefabricated concrete girders. Three types of prestressing tendons are being monitored: conventional steel strand and two types of carbon fibers reinforced plastic tendons. Sensor durability issues are reviewed and the installation is described. Initial measurements indicate that the sensors are operational and provide some early comparison of tendon performance.

Fiber Bragg grating laser sensor

An erbium-doped fiber laser utilizing a broadband mirror as the end reflector and an intracore Bragg grating as the output coupler is designed and developed. This arrangement is used as a laser sensor to improve interrogation efficiency of intracore Bragg gratings over broadband sensor interrogation methods. Wavelength tuning of the fiber laser has been achieved by varying the temperature and strain on the Bragg grating, demonstrating an improved SNR with respect to the previous techniques that use broadband interrogation of the Bragg grating sensor.

Multiplexed Bragg grating laser sensors for civil engineering

A portable, rugged, and compact 4-channel Bragg grating fiber laser sensor demodulation system was developed for interrogating an array of 20-intracore Bragg grating sensors that we embedded within several of the concrete girders used to support the deck of a new two span road in Calgary, Alberta. Another unique feature of this bridge is that two types of Carbon fiber based composite prestressing tendons are being tested in a number of the concrete girders. We have instrumented five of the approximately 60 ft long concrete girders with fiber optic Bragg grating strain and temperature sensors in order to monitor the loads on these girders and their response during the construction of the bridge and subsequently over an extended period of time.

Structural sensing using a fiber laser strain sensor

The development of a fiber laser sensor which permits efficient interrogation of Bragg grating sensors is reported. The fiber laser is linewidth-narrowed and tuned by a remotely located, sensing Bragg grating that is surface adhered to a structure under test. The Bragg grating- tuned fiber laser is used in conjunction with a passive wavelength demodulation system (WDS) to form a fiber laser strain sensor system (FLS3), which was used to track both static and dynamic strains on an aluminum beam. The FLS3 could measure strains with a resolution of approximately 4 (mu) (epsilon) and a bandwidth of 13.0 kHz. The viability of the laser strain sensor concept lends itself to the development of a compact, potentially embeddable smart sensor that would output demodulated sensing data directly to the user.

Practical considerations for a four-channel multiplexed Bragg grating fiber sensor system

A multichannel Bragg grating fiber laser demodulation system capable of interrogating four or more Bragg grating sensors for strain and temperature monitoring has been designed and developed. System configuration and various practical considerations for a field deployable system are discussed. Preliminary data indicates a dynamic strain range in excess of 5000 (mu) (epsilon) at a resolution of 1 (mu) (epsilon) . Both the strain dynamic range and resolution are easily modified.

Fiber laser sensor array

An intracore Bragg grating and a broadband reflector are used as cavity end mirrors of a tunable Erbium-doped fiber laser where the Bragg grating serves the dual purpose of the tuning element and the sensor. This fiber laser sensor (FLS) is integrated with a wavelength demodulation system (WDS) to form a practical strain and temperature sensor. Laser tuning with both temperature and strain have been achieved and the data is presented. To further promote practical applications of the FLS, a two element fiber laser sensor array has also been designed and developed. Preliminary data indicates excellent stability and no cross-talk.