en عمومى General پژوهشي Research In this paper, by including Raman scattering in the coupled-mode equations, the scalar modulation instability in photonic crystal fibers is investigated. The evolution of the pump, Stokes and anti-Stokes waves along the fiber as well as the conversion efficiency for two cases, with and without Raman effect, are studied. The effect of anti-Stokes seed and the pump depletion on the evolution of Stokes wave is also considered. Moreover, the parametric gain when it is affected by Raman gain is dealt with. The results show that it is important to take into account Raman scattering, especially for wide-bandwidth parametric amplifiers which results in an asymmetric spectrum and more amplification of the Stokes wave. Raman scattering, Photonic crystal fibers, Parametric conversion, Scalar modulation instability. 31 38 http://ijop.ir/browse.php?a_code=A-10-275-1&slc_lang=en&sid=1 H. Pakarzadeh hasanpakar@yahoo.com 10031947532846001088 10031947532846001088 Yes Physics Department, College of Sciences, Shiraz University A. Zakery 10031947532846001089 10031947532846001089 No Physics Department, College of Sciences, Shiraz University