Fused bitapered single-mode fiber directional coupler for core and cladding mode coupling

We demonstrate a new functional fiber component providing coupling between the LP1m cladding (LP1mcl) mode in one single-mode fiber (SMF) and the LP01 core mode in another SMF. The phase-matching condition in the coupling region is achieved by prepulling the fiber sections. The experimentally demonstrated coupling efficiency between the LP01 core and the LP13cl des is more than 60% over 70-nm wavelength range with less than 3% variation over 90 degrees C temperature range.