Key noise parameters in optical coherence tomography (OCT) systems employing splitters with a nonflat spectral response are evaluated using a supercontinuum fiber laser source with a spectrum of $450\mathrm{nm}–1700\mathrm{nm}$ and a time domain OCT architecture based on $1300\mathrm{nm}$ fiber splitters. The spectral behavior of the splitter leading to balanced detection is measured over a range of $300\mathrm{nm}$ . Because of spectrally different signals at the balanced detector input a residual excess photon noise term results. A rigorous treatment of this noise term [ Appl. Opt. 43, 4802 (2004) ] introduced two new quantities that take into account the spectral properties of the coupler. In this report, we have evaluated these two noise bandwidth quantities and comparatively assessed the noise behavior predicted by the classical theory with the theory based on the two new noise bandwidths. We show that under certain operating parameters, the additional excess photon noise is twice that predicted for a coupler with a flat spectral response.