Fiber mode conversion with tilted gratings in an optical fiber

The mode coupling in double-sided tilted gratings between the ${\mathrm{LP}}_{01}$ and ${\mathrm{LP}}_{11}$ modes is analyzed for three different excitation conditions. It is found that a number of modes, including various ${\mathrm{LP}}_{11q}$ modes with different polarization states and ${\mathrm{TE}}_{01},$ ${\mathrm{TM}}_{01},$ and ${\mathrm{HE}}_{21}$ modes, can be formed through the mode conversion process in the gratings and with a linear combination of four different ${\mathrm{LP}}_{11}$ modes. Efficient single-sided and double-sided tilted gratings are demonstrated. The tilted gratings presented exhibit ${\mathrm{LP}}_{01}-\mathrm{to}-{\mathrm{LP}}_{11}$ 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.