From Event: SPIE Optical Engineering + Applications, 2016
An optical scheme to improve the quality of an RF signal is proposed. The 6 dB linewidth is reduced to sub hertz and the
low frequency noise below 1 KHz is reduced about 10 dB. The scheme utilizes a Brillouin-semiconductor optical
amplifier (SOA) ring laser fitted with an RF intensity modulator and an APD detector. The experimental results show
cavity modes with FSR of 30.57 KHz due to Brillouin fiber length of 6.6 km and 6 dB bandwidth of 780 mHz typical of
Brillouin lasers. The gain of the SOA balances out most of the losses in the ring mainly that due to the RF modulator.
The modulated optical signal beats at the APD. The optical loop acts as a cavity filter to the RF signal. A jitter in the
cavity resonances due to temperature variations is completely eliminated from the output beat signal. There is a 10 dB
increase in the phase noise at the FSR frequency and its harmonics. The setup is tested with signals generated by
different sources and to frequencies up to 10 GHz, the limit of the APD. Sources with RF linewidth less than the optical
FSR produces one output mode with sub-hertz line width. For larger line width signals more than one RF frequency is
produced, separated by the FSR, each showing the Brillouin linewidth.
Mohamed Mousa, Mahmoud H. Ahmed, Kamel M. M. Hassan, Mohamed Abouelatta, and Abdelrahman E. Afifi, "High quality tunable Brillouin optoelectronic oscillator," Proc. SPIE 9958, Photonic Fiber and Crystal Devices: Advances in Materials and Innovations in Device Applications X, 995807 (Presented at SPIE Optical Engineering + Applications: August 28, 2016; Published: 7 September 2016); https://doi.org/10.1117/12.2237290.
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