Effective single-mode transmission at wavelengths shorter than the cutoff wavelength of an optical fiber

We propose a novel transmission scheme to extend the single-mode operation range of a conventional single-mode fiber (C-SMF) to wavelengths shorter than the cutoff wavelength. It involves the use of a tapered-fiber mode filter (MF) in order to remove the high-order-mode power from the C-SMF and hence, makes the fiber work as a virtually single-mode transmission link. High-order mode suppression of above 10 dB has been achieved at wavelengths of 850 and 980 nm with a fabricated tapered-fiber MF. We have also demonstrated the feasibility of the technique by evaluating the transmission quality with the MF at 850 nm through a 5-km C-SMF having a cutoff wavelength of 1.2 mu m.