Broadband higher order mode conversion using chirped microbend long period gratings.

We suggest a new scheme to create chirped microbend long period gratings. Employing this scheme, the bandwidth of mode conversion between LP01 to LP11 is increased 4.8-fold with a conversion efficiency of 20 dB. This scheme includes a first time demonstration of a non-linearly chirped long period grating. The scheme is investigated both numerically using coupled mode equations as well as experimentally.

Break up of the azimuthal symmetry of higher order fiber modes.

We investigate Bessel-like modes guided in a double cladding fiber where the outer cladding is an aircladding. For very high order LP(0X) -modes, the azimuthal symmetry is broken and the mode is no longer linearly polarized. This is observed experimentally and confirmed numerically. The effect is investigated numerically using a full vectorial modesolver and is observed to be dependent on the fiber design. The effect on the diffraction free propagation distance of the modes is investigated using a fast Fourier transform propagation routine and compared to the properties of an ideal circularly symmetric mode. The free space properties of modes suffering from break up of azimuthal symmetry are also investigated experimentally by measuring the free space propagation of a LP(016)-mode excited in the double cladding fiber.