Spectral domain optical coherence tomography (SD-OCT) has achieved significant progress in biomedical imaging, particularly in ophthalmology. However, SD-OCT exhibits reduced signal sensitivity in deeper imaging regions compared to swept-source OCT due to the phenomenon of sensitivity roll-off. Linear-wavenumber spectroscopy employs an optical solution to achieve linear spectral splitting in the wavenumber domain, thereby enhancing the system's signal-to-noise ratio in the depth direction. This paper presents a comprehensive overview of the fundamental principles of the SD-OCT system, the spectroscopic theory of linear-wavenumber, the optical model of linear-wavenumber dispersion, and the application of linear-wavenumber SD-OCT in the imaging of soft tissue structures, angiography, and elastography. Although the application market for linear-wavenumber OCT remains relatively small, its ability to improve the signal-to-noise ratio and imaging speed is noteworthy. As the technology continues to advance, linear-wavenumber SD-OCT is expected to play an increasingly significant role in clinical diagnosis and biomedical research.