The wavenumber nonlinearity leads to blurred reconstructed images in frequency-domain optical coherence tomography (FDOCT). Many k-linearization methods were studied which required multiple measurements or extra calibration devices. In this work, the wavenumber was linearized with only one interference spectrum of the mirror and without calibration devices. Based on the fact that the difference between the phases of adjacent peak and valley points is equal to π , the theoretical model was derived. The corresponding algorithm could be executed with eight steps. The experimental results revealed the validity of our method for FDOCT systems with various nonlinearities. For the spectral-domain OCT, the resolution was improved a few times compared with Attendu’s method, and it was one micron higher than that with the conventional interpolation. For the swept-source OCT, the resolution could be improved by ten microns.