B.S.T.J. Briefs: Experimental Verification of Ultra-Wide Bandwidth Spectra in Double-Clad Single-Mode Fiber

Experimental Verification of Ultra-Wide Bandwidth Spectra in Double-Clad Single-Mode Fiber By S. J. JANG,* L. G. COHEN, W. L. MAMMEL, and M. A. SAIFI* (Manuscript received December 23, 1981) The low-loss and low-dispersion properties of single-mode fibers make them obvious choices for wide bandwidth system applications with very long repeater spans. This brief describes the fabrication procedure and transmission properties of a double-clad single-mode fiber which is capable of wide bandwidth (greater than 100 GHz-km for laser sources with 4-nm emission bandwidths) transmission over the widest wavelength range (1.45 jum to 1.73 fim) thus far reported in the literature. This range completely covers the lowest-loss wavelength window for fused-silica optical fibers. Double-clad lightguides 14 were formed by using an inner cladding to form an index well between the core and a pure silica outer cladding. A computer-aided analytical procedure was used to choose the proper fiber diameter so that waveguide dispersion effects could be used to cancel material dispersion at predetermined wavelengths. 1 The modified-chemical-vapor-deposition (MCVD) technique was used for preform fabrication. Sixty outer cladding layers, a composition of Ge02-P205-Si02 and fluorine, having the same refractive-index as pure silica were deposited by the MCVD method inside a 16- by 20-mm fused silica tube. The composition of six inner cladding layers is fluorinedoped silica in order to maintain a 0.35 percent negative index difference relative to the outer cladding.