Montreal researchers create high-quality, 1-m-long FBGs with megahertz-range bandwidths

Montreal, QC, Canada--Fiber lasers often rely on Fiber Bragg grating (FBG) mirrors to define the bandwidths of their resonant cavities. The longer the FBGs themselves can be made, the narrower the laser's bandwidth becomes; however, very long FBGs (more than 10 cm long) have conventionally been virtually impossible to make. Now, researchers at École Polytechnique de Montréal have used an interferometer and a moving phase mask to create high-quality FBGs up to 1 m long (2 million periods all in phase), producing bandwidths of only a few picometers.¹

The electro-optic phase-modulation (EOPM) based interferometer is used with a phase mask mounted on a precision 1-m-long translation stage; the phase mask itself must be properly aligned with the fiber and the write beam to eliminate chirp in the FBG. A 1-m-long FBG fabricated this way had a -28 dB reflectivity and a 2.5 pm (325 MHz) bandwidth. The researchers also fabricated FBGs with an intentional chirp induced.

Such FBGs are also useful for high-quality complex filters for signal processing, the researchers say.

REFERENCE:

1. Mathieu Gagné et al., Optics Express (2014); doi:10.1364/OE.22.000387