Microwave comb generation using single-mode Fabry-Perot laser diode

We propose and demonstrate a new technique of generating microwave frequency comb using single mode Fabry-Perot laser diode (SMFP-LD). The SMFP-LD is obtained by modifying the commercially available FP-LD by adding an external cavity, which provides only single longitudinal mode at the output and has a tunability range of about 10 nm. The basic principle involve with this technique is the injection of the modulating beam to any of the side modes of the SMFP-LD in such a way that one of the sideband is locked with the corresponding injected mode. The injected beam has negative wavelength detuning to the corresponding mode whether it is the dominant mode or the side mode of a SMFP-LD. By heterodyning the injected modulated beam and the corresponding side mode, frequency comb is generated using SMFP-LD that has the capability of tuning frequency comb spacing. The tuning of comb frequency spacing is obtained through changing the modulating frequency. The additional modulator is used to increase the power flatness and the bandwidth of comb generation. We measured and compared the output performance of the generated RF comb with and without additional modulator in terms of power flatness, and power and frequency stability.