All-Optical Image Rejection Mixer Based on Optical Hilbert Transform Using a Phase-Shifted Fiber Bragg Grating

An all-optical image rejection mixer based on optical Hilbert transform using a phase-shifted fiber Bragg grating (PS-FBG) is proposed. A PS-FBG and a 90° optical phase shifter are employed to introduce a 180° phase shift at the image frequency while maintaining the phase of the desired RF signal. Then the processed optical signal is combined with the original optical signal to achieve image rejection directly in the optical domain. Therefore, the desired RF signal can be down-converted to an intermediate frequency signal with image rejection after the image-free optical signal is combined with a local oscillator signal and detected in a photodetector. The proposed system can reach an image rejection ratio of about 68.5 or 62 dB when the bandwidth of the image signal is 20 or 40 MHz.