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

We demonstrate a new functional fiber component providing coupling between the LP/sub 1m/ cladding (LP/sub 1m//sup cl/) mode in one single-mode fiber (SMF) and the LP/sub 01/ 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 LP/sub 01/ core and the LP/sub 13//sup cl/ modes is more than 60% over 70-nm wavelength range with less than 3% variation over 90/spl deg/C temperature range.