Kirill Volyanskiy

Contribution of Laser Frequency and Power Fluctuations to the Microwave Phase Noise of Optoelectronic Oscillators

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.

Determination of Phase Noise Spectra in Optoelectronic Microwave Oscillators: A Langevin Approach

We introduce a stochastic model for the determination of phase noise in optoelectronic oscillators. After a short overview of the main results for the phase diffusion approach in autonomous oscillators, an extension is proposed for the case of optoelectronic oscillators where the microwave is a limit-cycle originated from a bifurcation induced by nonlinearity and time-delay. This Langevin approach based on stochastic calculus is also successfully confronted with experimental measurements.

Magnesium Fluoride Whispering Gallery Mode Disk-Resonators for Microwave Photonics Applications

We have manufactured a high-Q whispering gallery mode resonator with magnesium fluoride for microwave photonics applications in the gigahertz frequency range. This crystal is scarcely used for resonator fabrication despite its numerous advantages, that are mainly high mechanical hardness, low sensitivity to water vapor pollution, and low sensitivity to photo- and thermo-refractive fluctuations at optimal temperatures. Using a customized machining procedure, we have successfully fabricated and characterized a 5-mm resonator with a surface rugosity of the order of 1 nm (from 3 to 12 atoms). Cavity ring-down measurements enabled us to determine that the resonator has a quality factor Q = 3.4 × 108 at 1550 nm.

Measurement of the laser relative intensity noise

This article describes the measurement of the RIN power spectral density with the cross-spectrum method. Averaging the cross spectrum of two equal and independent channels that measure the same beam, the instrument background is not limited by the single-channel noise. Additionally, the measure can be validated on the basis of simple mathematical properties. This removes the need of a low-noise beam to validate the instrument background, which is a relevant experimental limitation of the (traditional) single-channel method.

PHASE AND FREQUENCY NOISE METROLOGY

As a consequence of a general trend in the physics of oscillators and clocks towards optics, phase and frequency metrology is rapidly moving to optics too. Yet, optics is not replacing the traditional radio-frequency (RF) and microwave domains. Instead, it adds tough challenges. Precision frequency-stability measurements are chiefly based on the measurement of phase noise, which is the main focus of this article. Major progress has been achieved in two main areas. The first is the extreme low-noise measurements, based on the bridge (interferometric) method in real time or with sophisticated correlation and averaging techniques. The second is the emerging field of microwave photonics, which combines optics and RF/microwaves. This includes the femtosecond laser, the two-way fiber links, the noise measurement systems based on the fiber and the photonic oscillator. Besides, the phenomenology of flicker (1/f) noise is better understood, though the ultimate reasons are still elusive.

Noise analysis of the opto-electronic microwave oscillator (OEO)

This article reports on the noise model of the OEO. The phase-noise and the amplitide-noise spectra can be predicted on the ground of the noise of the OEO internal components.