Point-by-point UV exposure makes optimum fiber-optic long-period gratings

July 28, 2014
Researchers at Cranfield University have developed a process to reproducibly fabricate long-period gratings (LPGs) with phase-matching at the turning point.

Optical fibers containing long-period gratings (LPGs) are used (among other things) to sense the refractive index of a surrounding medium, making them valuable for many industrial uses. When the refractive-index change of the surrounding medium to be sensed is plotted against the wavelength of the sensing light, the resulting curve can have a U shape with a minimum value, called the turning point. For optimum sensitivity of the fiber sensor, the period of the LPG should be chosen so that the phase-matching condition is satisfied at its turning point; however, the precision required to do this is so high that achieving this condition is difficult.

Researchers at Cranfield University (Cranfield, England) have developed a process to reproducibly fabricate LPGs with phase-matching at the turning point. Their approach is based on point-by-point UV exposure, in which a section of photosensitive fiber with a length equal to half the LPG period is exposed to UV light through a slit, which changes the refractive index to create the grating "line." The exposure light is then translated one grating period relative to the fiber to expose the next grating line, and so on until the entire LPG is finished. The translation stage used had a resolution of 7 nm; the slit width could be varied to create a 50:50 or any other duty cycle. The LPG period was on the order of 110 μm. The researchers determined that even changes of less than 100 nm in the period of the LPG can have large effects on the fiber's transmission spectrum when near the phase-matching turning point. Contact Stephen W. James at[email protected].

Sponsored Recommendations

Melles Griot® XPLAN™ CCG Lens Series

March 19, 2024
IDEX Health & Science sets a new standard with our Melles Griot® XPLAN™ CCG Lens Series fluorescence microscope imaging systems. Access superior-quality optics with off-the-shelf...

Spatial Biology

March 19, 2024
Spatial Biology refers to the field that integrates spatial information into biological research, allowing for the study of biological systems in their native spatial context....

Custom-Engineered Optical Solutions for Your Application

March 19, 2024
We combine advanced optical design and manufacturing technology, with decades of experience in critical applications, to take you from first designs to ongoing marketplace success...

Semrock Optical Filters Resources

March 19, 2024
Looking for more information about Semrock optical filters? Explore sets by fluorophore, download the 2023 Semrock catalog and more.

Voice your opinion!

To join the conversation, and become an exclusive member of Laser Focus World, create an account today!