Impact Of Laser Phase Noise Research Articles

Gaussian wavelet basis expansion based phase noise suppression method for coherent optical OFDM systems

In this paper, we developed a phase noise suppression method based on Gaussian wavelet basis expansion (GWBE) for coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) systems. Compared with traditional phase noise suppression methods, the GWBE method significantly enhances the system’s robustness to laser phase noise, providing improved phase noise suppression, especially in scenarios with high linewidth. Additionally, the method demonstrates excellent performance in 32-QAM and 64-QAM. By employing the proposed GWBE method, the impact of laser phase noise on CO-OFDM can be effectively mitigated.

Impact of laser phase noise on the ranging accuracy of a cooperative MIMO FMCW photonic radar system

In this paper, a FMCW-based cooperative 2×2 MIMO photonic radar system using heterodyne detection is presented. The proposed system consists of two separate sensor nodes that use a linear frequency modulated continuous wave signal, which allows simultaneous monostatic and bistatic radar measurement, where the target range and angle of arrival information are extracted. The additional bistatic information enhances the target detection and estimation capabilities with improved accuracy. This accuracy in practicality is affected by the laser phase noise, which degrades the overall system performance. Here, the analytical laser phase noise model for the MIMO system is derived and implemented to analyze its impact on the ranging accuracy of the proposed system. Under the impact of standard white Gaussian laser phase noise assumption, the monostatic and bistatic response of the detected signal is measured and compared using statistics of measurement error. Further, the signal-to-noise ratio and SSB laser phase noise of the monostatic and bistatic response are measured and compared at different target ranges. At last, the phase-noise-limited ranging accuracy of the system is evaluated and analyzed. The concept shown in this work paves the way for advanced photonic radar system applications such as modern radar systems, electronic warfare systems, metrology, and automotive vehicle radar with multiperspective coherent detection.

Study of ellipse fitting phase demodulation technique with reference interferometer to suppress the impact of laser phase noise

Study of ellipse fitting phase demodulation technique with reference interferometer to suppress the impact of laser phase noise

Feedforward Neural Network-Based EVM Estimation: Impairment Tolerance in Coherent Optical Systems

Error vector magnitude (EVM) is commonly used for evaluating the quality of m-ary quadrature amplitude modulation (mQAM) signals. Recently proposed deep learning techniques for EVM estimation extend the functionality of conventional optical performance monitoring (OPM). In this article, we evaluate the tolerance of our developed EVM estimation scheme against various impairments in coherent optical systems. In particular, we analyze the signal quality monitoring capabilities in the presence of residual in-phase/quadrature (IQ) imbalance, fiber nonlinearity, and laser phase noise. We use feedforward neural networks (FFNNs) to extract the EVM information from amplitude histograms of 100 symbols per IQ cluster signal sequence captured before carrier phase recovery. We perform simulations of the considered impairments, along with an experimental investigation of the impact of laser phase noise. To investigate the tolerance of the EVM estimation scheme to each impairment type, we compare the accuracy for three training methods: 1) training without impairment, 2) training one model for all impairments, and 3) training an independent model for each impairment. Results indicate a good generalization of the proposed EVM estimation scheme, thus providing a valuable reference for developing next-generation intelligent OPM systems.

Impact of Laser Phase Noise on Self-Coherent Transceivers Employing High-Order QAM Formats

Recent studies have shown that the self-coherent systems, including the bi-directional, the Stokes-vector-modulation direct-detection (SVM-DD), and the Kramers-Kronig (KK) schemes, have the potential to reduce the cost of short-reach networks. One of the most attractive features of the self-coherent systems is that they may eliminate the necessity of a narrow-linewidth laser, which is mandatory in the conventional full coherent systems employing high-order quadrature-amplitude-modulation (QAM) formats. On the other hand, it is also recognized that the laser phase noise may have a significant impact on the system performance if there exists a large length mismatch between the signal and the CW tone in the transmission paths. In this paper, we analyze the impact of laser phase noise on the self-coherent systems numerically and experimentally by considering the bi-directional system as an example case. As a result, we show that the performance of the self-coherent system can be described efficiently by using a limited number of normalized parameters. We then reveal the existence of a distinctive threshold on the path length mismatch that influences the bit-error-rate (BER) performance; the penalty increases in a stepwise manner as the length mismatch exceeds the threshold and converges to a constant value. Based on the results, we suggest the feasibility of employing high-order QAM formats to transmit >800 Gb/s signals per polarization using a 10-MHz-linewidth laser. Finally, proof-of-concept experimental results are presented to verify the theoretical and numerical analyses.

Common-Path Dual-Comb Spectroscopy Using a Single Electro-Optic Modulator

Dual frequency comb (DFC) spectroscopy using electro-optic comb generators stands out for its flexibility, easy implementation, and low cost. Typically, two combs with different line spacing are generated from a common laser using independent electro-optic comb generators. This approach minimizes the impact of laser phase noise; however, the distinct paths followed by the two combs ultimately limit the attainable signal-to-noise ratio and long-term stability of the system. In this work, a common-path DFC is generated using a single modulator driven by an arbitrary waveform generator, thus enabling a remarkable increase of the system stability (up to 0.8 s of integration time) while maintaining high flexibility. The proposed technique is experimentally validated by implementing a dual frequency comb with 3000 lines, covering an optical bandwidth of 4.5 GHz, and demonstrating an optical-to-radiofrequency compression factor of 7500. Our system is able to measure extremely narrowband optical features (in the MHz range) with an accuracy only limited by the master laser stability.

Impact of Transmitter Phase Noise on NFDM Transmission With Discrete Spectral Modulation

Nonlinear frequency division multiplexing (NFDM) systems have been showing remarkable progress in the past few years. However, the majority of the demonstrations have neglected the impact of laser phase noise by employing narrow-linewidth lasers and self-homodyne receivers. The impact of transmitter laser linewidth on NFDM transmission is here numerically and experimentally investigated for dual-polarization discrete NFDM systems. The scaling of linewidth tolerance is analyzed for different signal symbol rates and the results are validated experimentally at 250 MBd. Numerical and experimental analysis show a limited degradation due to laser phase noise with relevant penalty appearing only for linewidth-symbol duration products ( $\Delta \nu \times T_{s}$ ) above $10^{-3}$ . The 250-MBd experimental results indeed show limited penalty for laser linewidths up to 750-kHz and 100-kHz, for back-to-back and 2000-km transmission, respectively.

The Effect of Source Phase Noise on Stimulated Brillouin Amplification

The impact of laser phase noise on the Brillouin gain is studied. It is shown that insufficient coherence of the laser sources used in stimulated Brillouin amplification setups not only leads to reduced gain but also to source-induced gain fluctuations (noise), which may affect their performance. Under commonly encountered conditions, even a relatively coherent source, having a linewidth of a few megahertz, has enough phase noise to become the dominant contributor to the observed Brillouin gain fluctuations. For equally phase-noised pump and signal (also called probe), their (separately) induced gain and gain fluctuations are different: 1) the gain penalty is higher for phase-noised pump; 2) the signal output power is noisier for phase-noised signal, resulting in a larger standard deviation; and 3) the probability distribution function of the signal output power is quite symmetric for the phase-noised pump and distinctively asymmetric for the phase-noised signal. The results for continuous pump and signal waves, obtained numerically from the governing differential equations and validated experimentally, may contribute to the judicial choice of laser sources in practical Brillouin-based setups.

Analysis of Laser Phase Noise Effect in Direct- Detection Optical OFDM Transmission

In this paper, we characterize the impact of laser phase noise (PN) in direct-detection optical OFDM (DDO-OFDM) and identify its many differences from those in coherent optical OFDM (CO-OFDM). The analytical models for the diverse PN effects, including power degradation, phase rotation term (PRT), and inter-carrier interference (ICI), are given in terms of critical system parameters with or without the small PN assumption. In particular, the analytical upper-bound of the ICI power with a simple form is also provided. We also present a bit error rate (BER) estimation approach which is proven to be reliable for an optical signal-to-noise-ratio (OSNR) penalty lower than ~ 2 dB. In addition, the PN tolerances, in terms of OSNR penalty, are also numerically analyzed and discussed with different QAM formats, data rates, laser linewdiths, and subcarrier numbers.

On the Phase Noise Impact in Direct-Detection Optical OFDM Transmission

In this letter, we characterize the impact of laser phase noise (PN) in direct-detection optical orthogonal frequency-division multiplexing (OFDM) and emphasize its several differences from those in coherent optical OFDM. We also analyze the system performance in the presence of PN for various quadrature-amplitude-modulation formats and provide the bit-error-rate estimation method which can yield reliable results when the PN-induced optical signal-to-noise ratio penalty is lower than ~2 dB.

Impact of laser phase noise on binary- andM-ary-PSK coherent optical systems using multiple optical amplifiers

This study evaluates the performance of binary- and M-ary-PSK coherent optical systems using cascaded optical amplifiers in the presence of noise originating from the detector, receiver, optical amplifiers, and the laser phase fluctuations. Our results on the analysis of these systems indicate that at an amplifier input power of −20 dBm and a system length of 10,000 km, the power penalties incurred due to the laser phase noise at a bit error rate of 10−9 correspond to 0.57, 0.99, and 3.38 dB at linewidths of 770.31, 101.86, and 6.37 kHz for binary-PSK, four-PSK, and eight-PSK systems, respectively. ©1996 John Wiley & Sons, Inc.

Impact of laser phase noise on binary‐ and M‐ary‐PSK coherent optical systems using multiple optical amplifiers

This study evaluates the performance of binary- and M-ary-PSK coherent optical systems using cascaded optical amplifiers in the presence of noise originating from the detector, receiver, optical amplifiers, and the laser phase fluctuations. Our results on the analysis of these systems indicate that at an amplifier input power of −20 dBm and a system length of 10,000 km, the power penalties incurred due to the laser phase noise at a bit error rate of 10−9 correspond to 0.57, 0.99, and 3.38 dB at linewidths of 770.31, 101.86, and 6.37 kHz for binary-PSK, four-PSK, and eight-PSK systems, respectively. ©1996 John Wiley & Sons, Inc.

Influence of laser phase noise on dispersive optical fiber communication systems

Noise from semiconductor lasers in dispersive optical communication systems can give rise to a BER floor. Due to frequency-to-intensity noise conversion, the impact of laser phase noise increases with the fiber length. It is shown that the maximum transmission distance for dispersion-supported transmission obtained in laboratory experiments is mainly determined by the laser phase noise.

Analytical upper bounds for noisy phase optical communication invoking Gaussian quadratic functionals

The impact of laser phase noise on lightwave communication systems is governed by certain exponential functionals (EFs) of the phase trajectory, which apparently prohibit the exact derivation of the decision statistics. In contrast, phase noise quadratic functionals (QFs) feature tractable statistics. The fundamental limitations imposed by simple replacement of the exponential nonlinearity by a quadratic one are explored in the presence of additive noise, and it is shown analytically that this may yield bit-error-rate (BER) approximations only. A novel class of upper bounds on the BER with envelope detection is presented. The bounds and the approximations are both given by easily computable closed-form algebraic expressions and are based on the moment generating function inherited by the QF. >

The impact of laser phase noise on the coherent subcarrier multiplexing system

In coherent optical subcarrier multiplexing (CSCM) systems, the laser phase noise may cause signal spectrum broadening and hence, causes significant deterioration in the system performance. The impact of phase noise on the CSCM system is analyzed in terms of carrier-to-noise ratio, intermodulation distortion, and adjacent channel crosstalk. The optimal modulation index and carrier to noise ratio are also presented. Some numerical results are outlined.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Carrier recovery and filtering in optical BPSK heterodyne systems disturbed by phase noise from external cavity semiconductor lasers

The performance of an optical BPSK heterodyne system using external cavity semiconductor lasers and a squaring loop carrier synchroniser is theoretically analysed by means of an analytical method. The method is based on the Gram-Charlier series and includes the effect of filtering on the baseband signal disturbed by phase error due to imperfect carrier recovery and additive Gaussian noise. A detailed modelling of the phase error term is also performed, taking into account the influence of non-Lorentzian laser phase noise. Numerical results for a typical 565 Mb/s BPSK system are presented. It is found that the filter decreases the impact of laser phase noise, namely by reducing the degradation due to relaxation oscillations of the semiconductor lasers.

Impact of laser phase noise on the performance of a (3*3) phase and polarization diversity optical homodyne DPSK receiver

An analysis of the impact of laser phase noise on the performance of a (3*3) phase- and polarization-diversity differential phase-shift keying (DPSK) receiver is done for the phase and shot-noise limited case. The results show that, for zero laser linewidths, the maximal signal power penalty of the (3*3) phase- and polarization-diversity DPSK receiver with respect to the conventional heterodyne DPSK receiver is approximately 0.7 dB for P/sub e/=10/sup -9/. For nonzero laser linewidths, it appears that, depending on the laser linewidth, for large signal-to-noise ratios the performance of the analyzed (3*3) phase- and polarization-diversity DPSK receiver is close to that of the ideal conventional heterodyne DPSK receiver. For a rectangular intermediate-frequency filter, the maximum allowable normalized laser linewidth ( Delta upsilon *T) for the (3*3) phase and polarization diversity DPSK receiver is found to be approximately 0.46% for a power penalty of 1 dB.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

CPFSK coherent optical receivers: impact of IF bandwidth and laser phase noise

A detailed theoretical model for narrowband CPFSK receivers is presented. It accounts for the influence of IF bandwidth on the signal voltage, non-Gaussian statistics of the output noise, correlation between noise samples stemming from limited IF bandwidth, and the impact of laser phase noise. It is found that the IF bandwidth needed to avoid intersymbol interference is 2.2 times the bit rate for a modulation index of 1; it is higher for other modulation index values. The bit error ratio is within 1 dB of the shot noise limit for the modulation index of 1.

A 2-Gbit/s optical FSK heterodyne transmission experiment using a 1520-nm DFB laser transmitter

Optical FSK transmission at 2 Gbit/s using a directly modulated DFB laser at 1520-nm wavelength is reported. A receiver sensitivity of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\bar{P} = -36.7</tex> dBm ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\eta\bar{P} = -39.2</tex> dBm) at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> BER was achieved for transmission over 101 km of single-mode fiber with no additional penalty attributable to the fiber. The effect of the nonlinear phase of the transmitter FM response, and the system performance for discriminator demodulation, including the impact of laser phase noise, is analyzed and compared with experimental results.