In-fiber duplex optical antenna and its programmable spectral filter application

In this Letter, we have proposed an in-fiber duplex optical antenna based on a 45 degrees radiated titled fiber grating (RTFG), in which the 45 degrees RTFG not only radiates the light from the fiber core to the free space, but also harvests the light from the free space back into the fiber core. Using the finite dif-ference time domain method, we have theoretically analyzed the light recoupling efficiency of the RTFG. The simulated results have shown that the RTFG-based optical antennas have a maximum coupling efficiency of 10%. The recoupling wavelength and efficiency are related to the grating period and horizontal incidence angle. Furthermore, we demon-strate a programmable spectral filtering system based on the 45 degrees RTFG antennas, which could achieve filtering with arbitrary spectral shapes. The spectral resolution is 0.4 nm and the insertion loss is around 20 dB. The proposed pro-grammable spectral filtering system has a compact structure compared with the traditional filter. (c) 2022 Optica Publish-ing Group