en تخصصي Special پژوهشي Research <p dir="ltr">For a fiber optical surface plasmon resonance (SPR) sensor a short part of its cladding should be removed to coat a thin layer of a metal. Usually this is problematic when an optical fiber with small core diameter is used. In this paper, a new method using &micro;liter droplet of the HF acid for short fiber optical taper fabrication is reported. Using this method in a multi-mode optical fiber with the core/cladding size of 50/125 &micro;m a 2 mm long taper with 40 &micro;m diameter is fabricated. Roughness of its surface is investigated using an atomic force microscopy. The measured mean value of the roughness is about 8 nm. A 60 nm thin layer of pure silver is coated on the taper surface in order to investigate its performance using a fiber optical SPR sensor.&nbsp; Using this SPR fiber sensor measurement of the lead concentrations in water ranging from 0.1 to 10 part per million (ppm) is reported.</p> chemical etching, fiber optical taper, optical fiber, surface plasmon resonance, sensors. 19 24 http://ijop.ir/browse.php?a_code=A-10-506-1&slc_lang=en&sid=1 Jalil Jafari j.jafari@iasbs.ac.ir 10031947532846001808 10031947532846001808 No Physics Department, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan Rahman Nouroozi rahman.nouroozi@iasbs.ac.ir 10031947532846001809 10031947532846001809 Yes Physics Department, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan