A new optical unit structure which can suppress stimulated Brillouin scattering (SBS) is developed. The Brillouin gain bandwidth is expanded by distributing the fibre strain in the optical unit. The expansion depends on a unique strainholding double-stranded optical unit structure. This is the first proposal for suppressing SBS by cabling. A 3.7 km long cable was laid in the sea and its Brillouin gain bandwidth was measured. The bandwidth was expanded 2.9 times with a cyclic strain amplitude of 0.08%.