Three types of optical fiber lasers that can emit one, two, or three wavelengths simultaneously were researched and experimented on. The three types of lasers could be applied to measure displacement, step height, and absolute distance, respectively. By employing the characteristic that a fiber Bragg grating could only reflect a Bragg wavelength, fiber Bragg gratings have been used as the reflective mirrors of the laser resonant cavities and wavelength selectors. As such, a single laser resonant cavity and multiple independent laser resonant cavities with overlapped laser optical paths were constructed with a length of erbium-doped optical fiber in each cavity. Pumped by a 980-nm laser, the optical fiber lasers could emit a single wavelength and multiple wavelengths simultaneously; the value of each wavelength could be determined as needed. Furthermore, the wavelength interval between two adjacent wavelengths could be determined as needed. There is no laser mode competition between the wavelengths, as each wavelength has a stable power and frequency. Wavelength stability can reach up to 10-7, satisfying the precision requirements of measuring displacement, step height, and absolute distance through interferometric methods.