Long-Wavelength Single-Mode Fiber Transmission Systems

Abstract

Introduction Single mode fiber transmission systems in the 1.0 - 1.7 μm wavelength region have many advantages favorable for public telecommunication network as well as information transmission means in industries.1-3 (1) Loss is extremely low in low OH content fibers owing to reduced Rayleigh scattering.4 (2) Dispersion in silica material vanishes at 1.27 μm5 and the total dispersion, including waveguide dispersion, can be reduced in the 1.3 - 1.6 μm wavelength range.1 (3) Large core size for single mode fibers at 1.3 μm, typically about 10 μm, is favorable for low splicing and connection loss, as compared to values for 0.85 μm wavelength. Splice and connector losses are now comparable with those for multimode fibers. (4) Optical sources fabricated by InGaAsP/InP double hetero-structures can be used in the 1.0 - 1.55 μm wavelength range. Preliminary reliability evaluation showed that InGaAsP lasers will have longer ultimate lifetime than AlGaAs lasers.6 (5) Germanium avalanche photodiodes can be used as detectors in the 1.0 - 1.6 μm wavelength range with sufficient quantum efficiency and pulse response.7 Ternary and quaternary III-V compound devices are now under extensive study to obtain dark current and multiplication noise performance superior to germanium. (6) Yttrium iron garnet, which has large Verdet constant, can be used.as compact non-reciprocal devices in its transparent wavelength region beyond 1.1 μm.8 Isolators can be used to secure stable oscillator operation independent of possible reflection from fiber lines.