Structures need to be monitored. A Fiber Bragg Grating (FBG) sensor does this particularly well because it is very sensitive to external forces. And it is immune to Electromagnetic Interference (EMI). In the picture, a shift in the peak of the profile means it detects a strain, and if the shift is big enough, a warning sign.

One of the challenges though, was to read the FBG. It required a small lab. And commercial systems were VERY costly. Enter the story on FBG interrogation. But how does it work?

Swipe right!

PS: Original photo by Silas Baisch. Graphics added for this site.

This is how it looks like if a fiber sensor is being "interrogated". A tunable laser sweeps through different bandwidths to profile the sensor.

The sensor output is read with a photodiode, converted via Analog-to-Digital circuitry and the output can map the sensor profile.

Let's have a look at how the smaller device was developed.

The Interrogator (playfully called BraggScann) was built mainly from computer parts, Frankensteined with the more costly optical parts. We published paper about it much later, with a patent.

If you must know, it was built with a 980nm butterfly laser, pumping an Erbium-doped Fiber with a tunable bandpass filter in it, driven using electromechanical means, using the single-mode EDFA ring laser configuration. The output from the sensor was read using a fiber-based InGaAs photodiode, fed to a 15-bit ADC (ADS1100). All were spliced and assembled within the enclosure. The microcontroller was a PIC18F4455. A gone era where PICs dominated the scene.

Our FBG sensor was installed in one of the segments of an arch spandrel bridge in Melaka. This picture, among many, showed us looking at the sensor after it was installed.

And, well, here's some news coverage on it.

Forgive the sentimentality, but the state of Melaka makes us remember that there are also other things in life which is very important.

Like a good asam pedas fish.