Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)A simple mechanical setup was used to polish a standard single mode optical fiber in order to make it asymmetric. The polished fiber was tapered down maintaining the D-shape transversal profile. Its broken symmetry along with the extended evanescent field, due to the dimensions of the microfiber, implies a potentially high birefringent waveguide as well as a high-sensitivity external refractive index device. An experimental maximum sensitivity of S approximate to (3.0 +/- 0.2) x 10(4) nm/RIU was achieved, other experimental and numerical results supporting our initial assumptions are also presented.311627562761Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [2011/01524-8, 2010/13149-4]