Per Kylemark

Noise characteristics of fiber optical parametric amplifiers

We derive an analytical theory for the noise figure of an undepleted and lossless fiber optical parametric amplifier (FOPA). Both the signal and the wavelength converted idler are investigated. Our theory is applicable for both an ideal pump power source, as well as a noisy one. We find that a noisy pump source can severely degrade the performance at high gain due to the stochastic gain-variations the signal and idler will experience. The theory is compared with Monte Carlo simulations of the FOPA and an excellent agreement is obtained. Simulations in the gain-depleted region show the possibility to reach below quantum-limited, phase-insensitive amplification for single channel transmission.

Noise characteristics of dual-pump fiber-optic parametric amplifiers

The noise figure (NF) properties of an undepleted and lossless dual-pump fiber-optic parametric amplifier (FOPA) are theoretically and numerically investigated. The theoretical study takes into account the noise characteristics of the two pump waves that are considered to have parallel polarization states for gain maximization. It is shown that noisy pump waves degrade the amplifiers NF, especially when the amplifier is operating at high gain values and when the input signal is high. The theoretical observations are validated by Monte Carlo numerical simulations, and the agreement between them is excellent. Finally, a comparative study concerning the noise characteristics of dual-pump and single-pump FOPAs is performed.

Gain and wavelength dependence of the noise-figure in fiber optical parametric amplification

We measure, for the first time, the wavelength resolved electrical noise figure (NF) of a fiber-optical parametric amplifier and find excellent agreement with theoretical predictions. We furthermore measure the NF in the exponential gain regime at high gain and quantify the gain dependence of the NF as well as its spectral dependence

Semi-analytic saturation theory of fiber optical parametric amplifiers

A semi-analytical theory for the gain saturation of parametric amplifiers is presented. The theory is both simple and intuitive, it is compared with experiments on a parametric amplifier, and a very good agreement is found. Furthermore, using theoretical results, a method to obtain saturation characteristics for parametric amplifiers that have features not easily reproduced by theory is presented. The obtained method finds saturation characteristics in a few steps, providing that the gain studied is above 15 dB, where the approximations upon which our simple expression is based are strictly valid. An exact solution of the gain saturation when the pump power is totally converted is also presented and compared with the simplified expression using previously obtained theoretical results

Noise in Dual-Pumped Fiber-Optical Parametric Amplifiers: Theory and Experiments

The noise figure (NF) of a dual-pumped parametric amplifier with copolarized pumps is quantified for the first time to our knowledge. It is shown that the NF is increased by the noise on the pump sources, in agreement with theory, and that it gives a uniform NF degradation due to a uniform gain spectrum. The magnitude of the NF degradation increases with increasing input-signal power. Various aspects of the NF are studied, such as the effects of three idlers generated by the four-sideband interaction, and Raman-induced losses and excess noise caused by the population of thermal phonons. It is shown that the use of unequal pump powers only affects the low-power NF to a minimal degree. Also, the gain dependence of the NF is studied, as are the wavelength and signal power dependences of the NF. It is shown that at high gain, the NF saturates even when pump noise is an issue. Also, unequal pump powers with fixed gain have a minor impact on the noise performance of the amplifier. Theory and experiments agree well with each other.

Noise Statistics in Fiber Optical Parametric Amplifiers

We show both theoretically and experimentally that the probability density function of a signal amplified by parametric amplifiers with pump excess noise is non-Gaussian and asymmetric. This impacts the relationship between the noise figure and the bit-error rate.

Impact of Pump Phase-Modulation on the Bit-Error Rate in Fiber-Optical Parametric-Amplifier-Based Systems

Pump phase-modulation is often needed to suppress stimulated Brillouin scattering in fiber-optical parametric amplifiers. We show that while this causes a gain variation with a corresponding Q-value penalty, the actual bit-error-rate degradation is not always significant. The findings are supported by experimental studies

DM solitons in long-haul DWDM systems at 40 Gb/s with nonlinear interactions and PMD

The authors investigate for the first time how polarization mode dispersion and nonlinear interactions affect dense wavelength division multiplexing dispersion management-soliton long-haul transmission using Monte Carlo simulations. They also discuss how the system is affected by an increasing number of wavelength channels.

Noise statistics of fiber optical parametric amplifiers

In this paper, we show both theoretically and experimentally that the probability density function of the intensity of an amplified signal by parametric amplifiers subject to a pump with excess noise is highly asymmetric. This is due to the nonlinear relationship between the optical pump power and the parametric gain. Because of this, the relationship between the noise figure (NF) and the bit error rate (BER) is modified, compared with that predicted by the chi2 theory, which is an effect that is notable at large NFs and low BERs. The difference in predicted BER can be of several orders of magnitudes between the correct theory and the chi2 approximation in single-stage parametric amplifiers. We also show that in the limit of many cascaded parametric amplifiers, the statistics of the noise of an amplified optical signal approaches chi2. Furthermore, the BER of a parametric amplifier is generally lower compared with erbium-doped fiber amplifiers for the same NF values if we assume quantum-limited amplification

Statistics of Wavelength Division Multiplexed Channels in Fiber-Optical Parametric Amplification

The amplification of wavelength division multiplexed (WDM) data in fiber-optical parametric amplifiers give rise to cross-gain saturation and four-wave mixing crosstalk. This crosstalk affects the data quality, especially at higher input powers. The statistics in this regime are nontrivial to obtain and we present, for the first time, a model based on a combination of theory and numerics that gives accurate statistics at a highly reduced computational cost. This model is obtained from an exact solution of WDM data being amplified in the strictly nonlinear regime which is derived in this paper. Using this model, predictions of the bit-error rate (BER) can be obtained even at very low rates impossible to reach by numerical methods alone. We show that there exists no trivial relationship between the BER and the commonly used quality measure, the Q-value. We also study how different amplifier parameters affect the statistics and suggest design rules to reduce channel crosstalk.