Abstract
We characterize the intensity noise associated with the ultra-high frequency direct modulation of semiconductor lasers under strong optical feedback over a millimeter-wave frequency passband between 54.5 and 56.5 GHz. Enhancement of the modulation response over this millimeter wave band due to optical feedback is clearly shown by time-delay rate equation analysis fully involving the strong optical feedback effect. The contribution of the relative intensity noise of the laser to the noise figure of an ultra-high speed radio over fiber link is evaluated. We show that subjecting the laser diode to strong feedback improves the noise figure of a 55.8-GHz radio over fiber link nearly by 20 dB in the regime of small-signal modulation and 10 dB under large-signal modulation.