Symmetric 3 x 3 optical coupler using three parallel long-period fiber gratings

We propose a new technique of realizing a symmetric 3 x 3 optical coupler, which is based on evanescent-field coupling among three identical parallel long-period fiber gratings placed side-by-side. Using three 32-mm-long over-coupled long-period fiber gratings embedded in a medium with a proper refractive index, we achieved equal power outputs from the three fibers at the resonance wavelength of the gratings with a total loss of about 1.4 dB when light was launched into any one of the fibers.