Optical vernier filter with cascaded double-coupler compound fiber loop resonators

A simple optical vernier filter with cascaded double-coupler compound fiber loop resonators is proposed. The proposed filter consists of two individual double-coupler compound fiber loop resonators. The circulating and transmitted output fields and intensities, as well as some performance parameters such as the contrast, finesse and free spectral range, are computed and presented in graphical form. A comparison between this proposed vernier filter and one individual double-coupler compound fiber loop resonator is made. The simulation results show that the contrast and finesse of the proposed vernier filter can be increased remarkably compared to the individual one double-coupler compound fiber loop resonator. And it is found that the free spectral range of the proposed filter can be enhanced by the vernier operation. These results are useful when the proposed vernier filter is used to construct narrow-bandwidth filters and single-frequency fiber lasers.