Efficient Photonic Microwave Mixer With Compensation of the Chromatic Dispersion-Induced Power Fading

The conversion gain of a photonic microwave mixer is often limited by the large carrier of the modulated optical signal, and may be further deteriorated by the chromatic dispersion-induced power fading after transmission over fiber. To solve this problem, an efficient photonic microwave mixer based on a dual-electrode Mach-Zehnder modulator is proposed in this paper. The carrier of the modulated optical signal is suppressed by bidirectional use of the modulator in a Sagnac loop, and a 21.9-dB improvement of the conversion gain is achieved in the experiment. In addition, the frequency response of the mixer after transmission over fiber can be tuned by simply adjusting the direct current bias of the modulator. This feature is applied to compensate the dispersion-induced power fading of the mixing product. In the proof of concept experiment, a vector signal centered at 2.4 GHz is up-converted to 16 GHz and transmitted over 25-km single mode fiber. After power compensation, the constellation diagram, error vector magnitude and receiver sensitivity are significantly improved, and are almost as good as that without fiber transmission.