Phase Noise Enhancement Research Articles

On the Phase Noise Enhancement of a Continuous Wave in Saturated SOA Used for RIN Reduction

We report on the spectral characteristics of the phase noise enhancement of continuous-wave (CW) optical signals passing through a semiconductor optical amplifier (SOA) operating in the saturation regime and used for relative intensity noise (RIN) reduction. We show that the known effect of phase noise enhancement, attributed to the linewidth enhancement factor of the device, happens only at a limited band of the phase noise spectrum, and the actual measurable linewidth of the output CW signal may not be affected. While this phase noise enhancement is not shown as an increase of spectral linewidth, it can still affect system performance when coherent detection is used, especially in applications with relatively low symbol rates. Numerical simulations and experimental results are used to support the observation. A single spectral line from a quantum-dot mode-locked laser is used as the light source, which is known to have relatively high RIN (> −120 dB/Hz in the low frequency region). Experimental transmission of 16-QAM modulation with coherent detection has been performed at 5 GBd to assess the implication on system performance.

A Multi-Frequency Multi-Standard Wideband Fractional- PLL With Adaptive Phase-Noise Cancellation for Low-Power Short-Range Standards

This paper presents a wideband fractional- $ { N}$ frequency synthesizer design with a low-effort adaptive calibration technique for $\Sigma \Delta $ quantization noise cancellation. After adopting from the classical single-ended loop filter structure, this least mean square algorithm based calibration technique can precisely and efficiently adjust the noise cancellation digital–analog convertor current with high linearity and immunity. Besides, as long as the desired current is achieved, the calibration circuits are turned off and disconnected to save the power consumption and isolate from the signal paths. With the proposed phase-noise cancellation technique, small area and low power circuit design are achieved, meanwhile the fractional and reference spurs are highly attenuated, allowing the wideband direct frequency/phase modulation with high data rates. With low effort modification, it can be directly implemented as straightforward phase-noise enhancement for any wideband phase-locked loop applications.

Analytical estimation of phase noise influence in coherent transmission system with digital dispersion equalization

We present a novel investigation on the enhancement of phase noise in coherent optical transmission system due to electronic chromatic dispersion compensation. Two types of equalizers, including a time domain fiber dispersion finite impulse response (FD-FIR) filter and a frequency domain blind look-up (BLU) filter are applied to mitigate the chromatic dispersion in a 112-Gbit/s polarization division multiplexed quadrature phase shift keying (PDM-QPSK) transmission system. The bit-error-rate (BER) floor in phase estimation using an optimized one-tap normalized least-mean-square (NLMS) filter, and considering the equalization enhanced phase noise (EEPN) is evaluated analytically including the correlation effects. The numerical simulations are implemented and compared with the performance of differential QPSK demodulation system.

Characteristics of the Phase Noise Correlation of Injection Locked Lasers for RF Signal Generation and Transmission

Theoretical and experimental results on phase noise characteristics of an optical radio-frequency generation and transmission system using heterodyne photo-detection and side band injection locking is reported. Optical phase noise correlation of the lasers is achieved by noise transfer from a modulated master laser. Our investigation takes into account phase noise enhancement in optical comb generation, injection dynamic, path delay, and fiber dispersion. Theoretical expressions are derived from an adiabatic approximation and compared with experimental measures.