Broadband Mode Converters by Femtosecond-Laser-Light Refractive-Index Tailoring

Possible designs for a new type of mode converters based on microstructuring the refractive-index profile of an optical fiber with ultrashort laser pulses are proposed and characterized numerically. Both LP
₀₁
-LP
₀₂
and LP
₀₁
-LP
₁₁
converters exhibit in excess of 20-dB extinction ratio over more than 200-nm bandwidth with moderate losses. The length of the converters is only a few hundred micrometers, making them some of the shortest mode converters available.