Design of a multiple self-mixing interferometer for a fiber ring laser

In this Letter, a novel multiple self-mixing interferometer for a fiber ring laser (FRL) is designed by introducing a circular feedback cavity. A system model is established based on an injection-seeded erbium-doped FRL proposed by Dragic. Owing to the reflection of the collimating lens, the multiplied fringes have different depths, which shows two Doppler frequencies in the spectrum of the self-mixing signal. A double-peak frequency identification algorithm is proposed to extract the Doppler frequency from the unique signal. This technique has the potential to improve the accuracy of fiber self-mixing measurement systems, particularly in Doppler velocimeters.