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.
Highlights
The radio over fiber (RoF) technology has been emerged as an integration of wireless and optical systems to provide integrated broadband services in wireless local area networks (WLANs) [1]
Such broadband services require enhancing the bandwidth of RoF links to the mm-wave band, which necessitates boosting the modulation bandwidth of directlymodulated laser diodes in RoF links. It is well-known that the modulation bandwidth of semiconductor lasers is limited by their relaxation oscillation frequencies, which makes a difficulty in direct modulations in mm-wave bands
We evaluate the contribution of this noise to the noise performance of a designed RoF link in terms of its noise figure (NF)
Summary
The radio over fiber (RoF) technology has been emerged as an integration of wireless and optical systems to provide integrated broadband services in wireless local area networks (WLANs) [1] Such broadband services require enhancing the bandwidth of RoF links to the mm-wave band, which necessitates boosting the modulation bandwidth of directlymodulated laser diodes in RoF links. The authors have reported on using strong OFB to boost the modulation frequencies over an ultra-high frequency passband over 50 GHz and have shown improvement of the link gain nearly by 20 dB over using solitary lasers [13]. In the regime of strong OFB, laser noise exceeds the quantum limit and its level depends on whether the laser operates in CW or emits uniform/non-uniform oscillations [19]. We apply a time-delay rate equation model [23] to study the intensity noise associated with ultra-high frequency modulation of semiconductor lasers under strong OFB.
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