The relative intensity noise (RIN) of quarter wavelength shift distributed feedback (QWS-DFB) laser diodes is analyzed theoretically for tapered grating structures. Tapered grating structures can reduce spatial hole burning (SHB) effect in QWS-DFB lasers. Two types of tapered, concave and convex grating are introduced. According to the results concave tapered grating structures have lower flatness parameter relative to convex and uniform grating. Numerical analysis shows that concave tapered grating structures, in spite of lower SHB effect, have larger RIN for some values of grating parameters. In concave and convex structures, with increasing the concavity and convexity of grating, mean value of RIN in the frequency range 5-500 MHz reduces. RIN spectrum calculations have been done by three rate equations model and transfer matrix method. (c) 2008 Elsevier Ltd. All rights reserved.