Multi-octave tunable RF signal generation based on a dual-polarization fiber grating laser

A simple technique has been proposed and demonstrated to generate radio-frequency (RF) signal based on a fiber grating laser with multi-octave tunablity. The laser is fabricated by inscribing a wavelength-matched Bragg grating pair in a short section of low-birefringence Er/Yb co-doped fiber. A RF signal can be obtained by beating the two-polarization mode output with its frequency determined by the birefringence within the cavity. By slicing the laser cavity into two sections and then aligning them with a rotated angle, the output beat frequency can be continuously tuned in a multi-octave frequency range as shown in the experiment from 2.05 GHz down to 289 MHz, as a result of the induced change in optical length for each polarization mode. The present technique has the advantages including simple scheme and large tuning range, and the ability of tuning could be further improved by use of active fibers with higher birefringence.