Arnaud Fernandez

All-Optical Clock Recovery and Pulse Reshaping Using Semiconductor Optical Amplifier and Dispersion Compensating Fiber in a Ring Cavity

An all-optical clock recovery device capable of continuously recovering the clock frequency of optical return-to- zero signals from a 10- to 12.5-GHz repetition rate is reported. The recovered clock consists of chirp-free Gaussian pulses at a diffraction limit with low timing jitter of ~200 fs. We employ intracavity dispersion-compensating fiber (DCF) in order to eliminate chirp and asymmetry of semiconductor optical amplifier (SOA)-amplified pulses. This SOA+DCF ring configuration allows us to easily recover the clock over a 40-nm tuning range corresponding to the SOA gain bandwidth.

Photodiode 1/f noise and other types of less known baseband noises in optical telecommunications devices

A technique to measure low frequency noise in illuminated photodiodes is presented, and some 1/f noise results are given for InGaAs devices. The ability of photodiodes to convert laser noise into RF noise is also discussed, together with other types of 1/f noise arising directly from the optical fiber, and particularly from scattering phenomena inside the fiber.

Radio frequency spectral characterization and model parameters extraction of high Q optical resonators

A microwave domain characterization approach is proposed to determine the properties of high quality factor optical resonators. This approach features a very high precision in frequency and aims to acquire a full knowledge of the complex transfer function (amplitude and phase) characterizing an optical resonator using a microwave vector network analyzer. It is able to discriminate between the different coupling regimes, from the under-coupling to the selective amplification, and it is used together with a model from which the main resonator parameters are extracted, i.e. coupling factor, intrinsic losses, phase slope, intrinsic and external quality factor.

Properties of Mode-Locked Optical Pulses in a Dispersion-Managed Fiber-Ring Laser Using Semiconductor Optical Amplifier as Active Device

A hybrid model is proposed in order to exploit the idea of compensating semiconductor optical amplifiers (SOAs) nonlinearity by adjusting cavity dispersion in a SOA-fiber ring mode-locked laser. The model is checked by analytical as well as experimental results. Excellent agreement is obtained in both cases. It is predicted that, once the cavity dispersion is correctly adjusted, the mode-locked pulses of 10 ps width will become distortion-free Gaussians, with their time-bandwidth product (TB) very close to the fundamental Gaussian limit (TB=1/2) using root-mean-square definition. We will show evidence and explain why other waveforms, notably soliton, are highly unlikely in such a system. Some interesting effects related to band-pass filter are revealed as well. Our results highlight the ambiguity of TB using full-width at half-maximum (FWHM) definition. As a consequence, the widely adopted notion of transform-limited pulse in its FWHM version might be misleading.

Fiber ring resonators with Q factors in excess of 10 10 for time and frequency applications

The design of ultra high Q factor fiber ring resonators is described. The resonators are characterized with a microwave frequency modulation technique, which allows a precise measurement of their performance. Optoelectronic oscillators are then realized. The phase noise performance is compared to the results obtained with lower Q factor resonators, and the relatively high intra-cavity bandwidth noise is discussed.

Highly Spectrally Pure 90-GHz Signal Synthesis Using a Coupled Optoelectronic Oscillator

A 90-GHz frequency reference is synthesized through harmonic generation from a 30-GHz coupled optoelectronic oscillator. The 30-GHz signal and its third harmonic feature an average power level of −5.6 and −15.8 dBm, respectively, at the photodiode output. Phase noise measurements at 30 and 90 GHz have been performed and phase noise levels as low as −114.4 dBc/Hz at 1-kHz offset for the fundamental and −104 dBc/Hz at 1-kHz offset frequency for the 90-GHz signal have been obtained.

Phase noise study based on transfer function in coupled optoelectronic oscillators

In this paper, the transfer function theory is used to model the phase noise power spectral density in coupled optoelectronic oscillators. A resonator is placed into the model in order to take into account the quality factor (Q) enhancement due to the optical loop. The results of this model are then compared with experimental measurement results. The model is able to describe the phase noise spectrum shape and to give indications on the noise contributors, which helps in improving oscillators performance.

COEO phase locking and performance optimisation

In this paper, a coupled optoelectronic oscillator (COEO) is phase locked to a low noise RF oscillator in order to reduce the phase noise close to the carrier. Biasing current of the optical semiconductor amplifier (SOA) and a varactor diode in the RF part of the COEO are used as two different actuators to perform phase locking. The lock on the optical device is finally simpler and more efficient than the lock on the RF loop. In the second part of this paper, phase noise of the COEO is reduced by more than 15 dB using a chirped Bragg filter that compensates the dispersion of the optical loop.

An iterative method for the dynamic modeling of ultra-short pulse generation in nonlinear optical ring resonator

Numerical methods can be useful for the understanding of high-Q resonators, the interpretation of frequency comb formation and the tailoring of nonlinear phenomena. For specific applications like telecommunications or low phase noise microwave generation, a phase locked frequency comb or temporal pulse train is critical. Single intra-cavity dissipative temporal solitons have demonstrated to be attractive due to their stability and robustness. Femtosecond soliton generation has been obtained by red detuning an initially blue shifted CW pump laser through the cold cavity resonance of a non-linear resonator without requiring any feedback control [1]. Based on this outstanding result we have developed a numerical model that simulates this experimental setup for the prediction of the frequency comb build up at a resonators output for a CW pump lasers set of parameters.

Optical resonators metrology using an RF-spectrum approach

A Microwave domain characterization technique is proposed to measure the optical properties of high quality factor optical resonators, featuring a very high precision in frequency which can be as good as 1 Hz. It aims to acquire a full knowledge of the complex transfer function (amplitude and phase) characterizing these resonators. It is shown that the amplitude response gives access to the measure of several parameters like the free spectral range and the quality factor. Moreover the phase transition at the resonance is used to define the coupling regime and to calculate the resonator parameters: transmission coefficient and intra-cavity losses.