Fiber mode conversion with tilted gratings in an optical fiber

The mode coupling in double-sided tilted gratings between the LP01 and LP11 modes is analyzed for three different excitation conditions. It is found that a number of modes, including various LP11q modes with different polarization states and TE01, TM01, and HE21 modes, can be formed through the mode conversion process in the gratings and with a linear combination of four different LP11 modes. Efficient single-sided and double-sided tilted gratings are demonstrated. The tilted gratings presented exhibit LP01-to-LP11 mode coupling over a spectral width as wide as 160 nm. The transmission spectra of the tilted fiber gratings agree well with the spectrum predicted by the coupled-mode analysis.