All-Fiber Laser Beam Shaping Using a Long-Period Grating

We demonstrate a simple all-fiber device that can transform a Gaussian-shaped laser beam into a uniform intensity beam. The device is based on the interaction of a core mode and a cladding mode partially coupled out by a long-period grating. We have achieved good beam uniformity (<4% intensity variation) and reduced beam divergence (1.5deg of half divergence angle) while keeping the insertion loss to 0.1 dB. The measured beam uniformity matches well with simulated results. The device can also change the beam shape from a Gaussian to a donut, to top hat, and back to a Gaussian, dynamically by tuning the laser wavelength.