The Research Of Add/Drop Filter Based On Twin-Core Fiber Grating

Optical add/drop filters are one of the most widely used optical devices in the optical network. It is able to upload or download the optical signal of a particular wavelength at the local optical network node. Therefore, the research of add/drop filters which have simple structure and good performance, becomes a heated topic in the field of optical fiber communication.This paper focuses on the study of an add/drop filter based on twin-core fiber grating. The coupling characteristics of twin-core fiber and the basic characteristics of fiber grating written into twin-fiber are theoretically derived and analyzed. The main contents of this paper are as follows:1. On the basis of coupled-mode theory, the coupling mode equation of the twin-fiber is derived. The transmission characteristics of the fully coupling and imperfect coupling twin-fiber are analyzed. By the MATLAB simulation, the relationship between different parameters and the coupling characteristics of twin-fiber is obtained.2. The coupled mode matrix equation of twin-fiber grating is derived and the normalized output power of each port is obtained. The influence of the grating length on the reflection and transmission spectrum is analyzed. The study shows that the reflected bandwidth increases with the increment of the modulation depth. The output power of the reflected bandwidth increase till achieving the maximum value, then it no longer changes and the output power the transmission bandwidth displays periodic variation with the increasing of the length of the grating.3. This paper analyzes the effect of the length of twin-core fiber without grating on drop channel in the signal input side of add/drop filter based on twin-core fiber grating and the effect of the length of twin-core fiber without grating on the output power of the two transmission ports in another signal input side of add/drop filter. The simulation results show that the change of grating writing position can affect the output power ratio of the two ports on the input side and the output power ratio of the two transmission ports. Therefore, by adjusting its length, the reflected optical signal energy can output from the specified port, realizing the best drop channel, and the output power of the reflection and transmission ports display periodic change with the increase of the length of twin-core fiber at both ends of the grating.4. The single cascade and the dual cascade add/drop filters based on twin-core fiber grating are designed and their filtering characteristics are analyzed. Both the two cascaded modes can realize multiple wavelength optical signals simultaneously download. The dual cascade method can achieve better filtering performance, but the output power of the drop channel is decreased compared with the single cascade mode.