To address the problem of coherent noise in laser interferometer measurements using a point source, the principle of coherent noise prevention using a ring source was described. Moreover, the relationship between the radius and thickness of the ring source and the visibility of fringes was analyzed. Further, to produce the ring source, an annular-lens-based optical system comprising a beam expanding system, annular lens, and double telecentric lens was proposed. The target parameters of the ring source were obtained according to the collimating lens and cavity length of the Fizeau interferometer. Additionally, ZEMAX was used to design three systems in the ring source system and ensure good connection between the optical systems. The annular lens was created by rotating an aspheric lens, and the double telecentric lens could reduce the ring source diameter to a reasonable range while ensuring that the outgoing beam from each off-axis point source in the final ring source was parallel to the optical axis. Finally, a ring source with an average ring radius of 0.38 mm and a thickness of 12.5 μm was designed. When the focal length of the collimating lens is 900 mm and the cavity length of the interferometer is 100 mm, theoretically, the visibility of interference fringes of greater than 0.98 can be achieved.