Abstract
An opto-electronic oscillator is a microwave oscillator in which the resonator is replaced with an optical fiber delay-line carrying an intensity-modulated laser beam. We consider the frequency and power fluctuations of a standard DFB telecom laser, and we investigate their effect on the phase noise of microwaves generated with opto-electronic oscillators. We propose a theoretical study showing how these two laser fluctuations are converted into phase noise in the output microwave. This theory predicts that the power noise should have a minor contribution to microwave phase noise, while the wavelength fluctuations should strongly contribute to phase noise via the chromatic dispersion of the few kilometers long optical fiber delay line. We have experimentally confirmed the validity of this theory by measuring the relative intensity noise and the optical frequency noise of a semiconductor laser, which has later been used for microwave generation. We show that the use of a zero-dispersion fiber delay-line can lead to a 10 dB improvement of the phase noise performance, relatively to the case were a standard single mode fiber is used.
Highlights
O PTO-ELECTRONIC OSCILLATORS (OEOs) are nowadays considered to be excellent ultra-pure microwave generators, and they are expected to play an important role in several applications where high spectral purity is required, such as in aerospace engineering, in lightwave communications, or in radar technology [1], [2]
Our aim in this paper is to show that group velocity dispersion plays a key role, as it directly converts the optical frequency noise of the laser into phase noise for the output microwave
The laser used for the OEO is a EM253-050-YYY InGaAsP/InP multi-quantum well (MQW) distributed feedback (DFB) laser diode that delivers up to 50 mW at 450 mA
Summary
O PTO-ELECTRONIC OSCILLATORS (OEOs) are nowadays considered to be excellent ultra-pure microwave generators, and they are expected to play an important role in several applications where high spectral purity is required, such as in aerospace engineering, in lightwave communications, or in radar technology [1], [2]. /K, 10 times better than the sapphire dielectric cavity) These features enable the implementation of high spectral purity oscillators and of high-sensitivity instruments for the measurements of phase noise. In both cases, the optical bandwidth turns into wide-range microwave tunability at virtually no cost in terms of phase noise. V and bias voltage ), seeded by a continuous-wave semiconductor laser of optical power and wavelength nm; a thermalized optical fiber of length km, performing a time delay of s on the microwave signal carried by the optical beam, corresponding to a free spectral range of kHz; a fast photodiode with a conversion factor. We are going to measure experimentally the RIN and the optical frequency noise of the laser in order to evaluate its contribution to the phase noise of the output microwave
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