Effect Of Laser Phase Noise Research Articles

Effect of laser phase noise on the steady-state field-mirror entanglement and ground-state cooling in a Laguerre-Gaussian optorotational system

Cavity optomechanical systems are considered as one of the best platforms for studying macroscopic quantum phenomena. In this paper, we studied the effect of laser phase noise on the steady-state entanglement between a cavity mode and a rotating mirror in a Laguerre-Gaussian (L-G) optorotational system. We found that the effect of laser phase noise was non-negligible on the field-mirror entanglement especially at a larger input power and a larger angular momentum. We also investigated the influence of laser phase noise on the ground-state cooling of the rotating mirror. In the presence of laser phase noise, the ground-state cooling of the rotating mirror can still be realized within a range of input powers.

Analysis of the encryption penalty in a QAM-based quantum noise stream cipher.

Quantum noise stream cipher based on quadrature-amplitude-modulation (QAM/QNSC) is a kind of physical layer encryption technology. However, the additional encryption penalty will significantly affect the practical deployment of QNSC, especially in the high capacity and long-haul transmission system. With our research, the encryption process of QAM/QNSC degrades the transmission performance of plaintext information. In this paper, we quantitatively analyze the encryption penalty of QAM/QNSC based on the proposed concept of effective minimum Euclidean distance. We calculate the theoretical signal-to-noise ratio sensitivity and encryption penalty of QAM/QNSC signals. A modified feedforward pilot-aided two-stage carrier phase recovery scheme is used to reduce the effect of laser phase noise and the encryption penalty. Experimental results achieve single-channel 205.9 Gbit/s 640km transmission with single carrier polarization-diversity-multiplexing 16-QAM/QNSC signal.

Reconfigurable photonics-based millimeter wave signal aggregation for non-orthogonal multiple access.

A reconfigurable optical-to-electrical signal aggregation is proposed, for the first time, using optical signal processing and photo-mixing technology. Two optically modulated quadrature phase-shift keying (QPSK) signals are aggregated into a single 16-quadrature amplitude modulation (16-QAM) signal and, simultaneously, carried over a 28-GHz millimeter wave (MMW) carrier using an optimized heterodyne beating process through a single photodiode. To demonstrate the system reconfigurability, aggregation of two optical binary phase-shift keying signals is mapped into MMW QPSK or four-level pulse amplitude modulation signals by controlling the relative phases and amplitudes, respectively, of the input signals. In addition, the aggregation of two 16-QAM signals into a 256-QAM signal and the aggregation of three QPSK signals into a 64-QAM format are achieved. Besides, we report the effect of laser phase noise on signal aggregation performance. The de-aggregation of the aggregated MMW signals is performed electrically using a successive interference cancellation algorithm. Moreover, a proof-of-concept experiment is conducted to validate the numerical simulations. Two 1-Gbaud BPSK (1 Gbps) and QPSK (2 Gbps) optical signals are optically transmitted over a 20-km single-mode fiber as MMW over fiber signals. Then, the signals are aggregated into QPSK (2 Gbps) and 16-QAM (4 Gbps) 28-GHz MMW signals, respectively. The aggregated signal is further transmitted over a 1-m wireless channel. The performance of the proposed system is evaluated using bit error rate and error vector magnitude metrics.

Force measurement in squeezed dissipative optomechanics in the presence of laser phase noise.

We investigate the force measurement sensitivity in a squeezed dissipative optomechanics within the free-mass regime under the influence of shot noise (SN) from the photon number fluctuations, laser phase noise from the pump laser, thermal noise from the environment, and optical losses from outcoupling and detection inefficiencies. Generally, squeezed light could generate a reduced SN on the squeezed quadrature and an enlarged quantum backaction noise (QBA) due to the antisqueezed conjugate quadrature. With an appropriate choice of phase angle in homodyne detection, QBA is cancellable, leading to an exponentially improved measurement sensitivity for the SN-dominated regime. By now, the effects of laser phase noise that is proportional to laser power emerge. The balance between squeezed SN and phase noise can lead to an sub-SQL sensitivity at an exponentially lower input power. However, the improvement by squeezing is limited by optical losses because high sensitivity is delicate and easily destroyed by optical losses.

Simple Noise Mitigation Scheme for Coherent Optical DMT Signal Transmission System

We propose and experimentally demonstrate a noise mitigation scheme for coherent optical discrete multitone (DMT) signal transmission system. The proposed scheme can mitigate the laser phase noise and additive white Gaussian noise (AWGN) simultaneously when optical DMT signal is coherently detected. In the digital signal process (DSP), the laser phase noise is first estimated and compensated through moving average filter. The AWGN is then reduced by considering the time-domain real-valued or frequency-domain symmetrical conjugation characteristic of DMT signal. Finally, we conduct an experiment to transmit dual-polarization (DP-) DMT signal based on a low complexity coherent detection structure with only two pairs of input and output ports. The experimental results prove that the proposed scheme can enhance the signal-to-noise ratio (SNR) and effectively reduce the effect of laser phase noise even the laser linewidth is as large as 10 MHz. The DP-DMT signal is successfully transmitted over 1920-km standard single mode fiber (SSMF) in the experimental demonstration. The analysis of computational complexity also indicates that the proposed DSP scheme requires less number of complex multiplication operations and has larger laser phase noise tolerance than other DSP schemes.

Effects of laser phase noise on optomechanical entanglement in the presence of a nonlinear Kerr downconverter

In this paper, we consider an optomechanical system with a Kerr downconversion element in the presence of pump laser phase noise (LPN). In particular, we study the effect of phase fluctuations on entanglement generation in the presence of a nonlinear Kerr downconverter. The steady-state entanglement spectrum depends upon the parametric gain and phase fluctuations associated with the driving field. Interestingly, our results show that optomechanical entanglement exists even for non-zero LPN. It has been shown that the presence of Kerr downconverter nonlinearity improves the robustness of the entanglement against the input LPN.

Laser phase noise effect and reduction in self-homodyne optical OFDM transmission system.

We present a laser phase noise (PN) induced effect of a phase-modulation-to-intensity-modulation conversion noise and noise pedestals underneath each of the orthogonal frequency division multiplexing (OFDM) subcarriers in a self-coherent optical OFDM transmission using a self-homodyne technique. We provide a statistical analysis on the received symbols using a histogram to demonstrate the effect of a phase rotation term and inter-subcarrier interference individually and collectively. The PN is then compensated using a simple time delay to realign the phase walk-off of the subcarriers relative to the carrier. Significant quadrature improvements of 6.82 dB using 5 MHz laser linewidth over a 720 km transmission length and 5.38 dB using 20 MHz over 240 km have been obtained with 16 quadrature amplitude modulation (QAM) over 15 GHz OFDM signal bandwidth. The technique also significantly reduced an optical-signal-to-noise ratio requirement at the bit error rate of 1×10-3 by 16.15 dB for 64-QAM over 160 km. With the delay, the system can tolerate three times the chromatic dispersion-length product.

Effects of laser phase fluctuation on force sensing for a free particle in a dissipative optomechanical system

In this paper, we study the effects of laser phase noise on the detection of a weak classical mechanical force on a free particle based upon dissipative optomechanical coupling. We show that for an optimum choice of various parameters, one can realize force sensing below the standard quantum limit even in the presence of laser phase noise. Moreover, we also investigate the effect of mechanical damping and thermal noise on force measurement in the presence of laser phase fluctuations. We show that force sensing strongly depends upon the phase fluctuations associated with the driving laser.

Phase-noise model for actively linearized frequency-modulated continuous-wave ladar.

Understanding the effects of laser phase noise on frequency-modulated continuous-wave distance measurements is important in evaluating ranging accuracy. The standard white-frequency-noise assumption is commonly used to predict the ranging performance. However, other noise sources are typically present that can further degrade the heterodyne beat signal and make this assumption invalid. In addition, many ranging systems employ active sweep linearization techniques that can impact the phase noise. Here, we present a phase-noise model for assessing the accuracy of a phase-locked swept laser source.

Phase Noise Influence in a Dual-Frequency Laser Phase-Shift Range Finder

The influence of phase noise in a dual-frequency laser phase-shift range finder is theoretically and experimentally investigated. The proposed range finder is based on the use of a coherent dual-frequency laser and direct detection of the backscattered laser. The effects of laser phase noise and noise from an acousto-optic frequency shifter (AOFS) on the dual-frequency laser phase-shift range finder are analyzed. Expressions of the power spectral density and the phase noise of the dual-frequency laser beat note are deduced. In addition, we find that noise from the AOFS has a considerable impact on beat note noise conversion. The theoretical results can be used to estimate the influence of laser phase noise, noise induced by the AOFS and delay length in the dual-frequency laser range finder. An experiment involving the dual-frequency laser range finder is performed on outdoor targets at a distance of 200 m, and the phase jitter observed in the experiment is in good agreement with the model of beat note phase noise.

Laser Phase Noise Effects and Joint Carrier Phase Recovery in Coherent Optical Transmissions With Digital Subcarrier Multiplexing

In this paper, we numerically and experimentally investigate the impairments related to laser phase noise in coherent digital subcarrier multiplexing (SCM) systems. Based on the evaluation in both back-to-back and transmission scenarios and the performance comparison between single carrier (SC) and SCM systems, we show that even though SCM systems suffer from degraded performance of carrier phase recovery (CPR) algorithms, they can potentially achieve an improved laser linewidth tolerance compared with SC systems after long-haul transmission attributed to the mitigation of equalization-enhanced phase noise. In addition, the effect of dispersion-enhanced phase noise is discussed in digital SCM systems, and a joint CPR (J-CPR) algorithm is proposed for cycle slip detection and correction. The effectiveness of the proposed J-CPR algorithm is then demonstrated in a 16-quadrature amplitude modulation (QAM) digital SCM system by both simulations and experiments.

FFT-Size Efficient 4096-QAM OFDM for Low-Cost DML-Based IMDD System

In this paper, we have experimentally demonstrated the transmission of the 4096-quadrature amplitude modulation (4096-QAM)-encoded optical orthogonal frequency division multiplexing (OFDM) signals in a low-cost directly modulated laser (DML)-based intensity-modulated and direct-detection (IMDD) optical communication system. To the best of our knowledge, it is the first time the highest QAM and fast fourier transform (FFT) size efficient OFDM signal with a spectral efficiency up to 9.5 bit/s/Hz transmissions over a DML-based IMDD system has been reported. The experimental results show that the 4096-QAM OFDM signal can be successfully transmitted over 10-km standard single-mode fiber (SSMF) with a bit error rate (BER) below the 20% overhead soft-decision forward error correction threshold (SD-FEC). It also shows that the FFT-size efficient optical 4096-QAM OFDM has the same BER performance as the conventional one. Moreover, the effect of laser phase noise (or linewidth) on the transmission performance of the FFT-size efficient 100G 4096-QAM-OFDM is also investigated by numerical simulation. The simulation shows that the optical 100G OFDM signals generated by 10G DML with a linewidth of 20 MHz can be successfully transmitted over 2 km SSMF with the BER under the SD-FEC threshold of 2.4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> .

Phase Noise Effects on Phase-Modulated Coherent Optical OFDM

One of the primary drawbacks of orthogonal frequency-division multiplexing (OFDM) is the large peak-to-average ratio (PAPR). It continues to contribute nonlinear degradations after it was introduced into optical fiber transmissions. However, phase-modulated OFDM can reduce the PAPR to the minimum, since its amplitude can be constant. In this paper, we conduct the theoretical and experimental study on the laser phase noise effect in phase-modulated coherent optical OFDM systems. Due to the laser phase noise, the phase transformation at the receiver is prone to errors due to phase wrapping. Consequently, we propose a mean-phase-compensation (MPC) method, which compensate for the mean phase offset for each OFDM symbol that has a Gaussian-distributed histogram. This method can avoid the problematic unwrapping function in phase transformation. We derive the closed-form expressions for the phase noise spreading and the corresponding signal-to-noise ratios (SNRs) based on the Wiener phase noise model. Unlike conventional coherent optical OFDM, the phase noise spreading to each OFDM subcarrier is decided by the reciprocal of the square of the subcarrier frequency, and the SNR can be improved by using a stronger PM modulation. We also discuss the SNR improvement by discarding a few affected subcarriers closing to dc. In a simulation, we demonstrate that our closed-form expressions are accurate. Finally, we experimentally verify our MPC method and our analysis.

Effect of laser phase noise on the fidelity of optomechanical quantum memory

Optomechanical and electromechanical cavities have been widely used in quantum memories and quantum transducers. We theoretically investigate the robustness of opto(electro)-mechanical quan- tum memories against the noise of the control laser. By solving the Langevin equations and using the covariance matrix formalism in the presence of laser noise, the storing fidelity of Gaussian states is obtained. It is shown that, the destructive effect of phase noise is more significant in higher values of coupling laser amplitude and optomechanical coupling strength G. However, by further increasing coupling coefficient, the interaction time between photons and phonons decreases below the coherence time of laser frequency noise and the destructive effect of laser phase noise on the storing fidelity drops as well.

Effects of laser phase noise on the performance of optical coherent receivers

Laser phase noise (LPN) plays an important role in optical coherent systems. Based on the algorithm of Viterbi-Viterbi carrier phase estimation (CPE), the effects of LPN imposed on the coherent receivers are investigated for quadrature phase shift keying (QPSK), 8 phase shift keying (8PSK) and 16-quadrature amplitude modulation (16-QAM) optical coherent systems, respectively. The simulation results show that the optimal block length in the phase estimation algorithm is a tradeoff between LPN and additive white Gaussian noise (AWGN), and depends on the level of modulation formats. The resolution requirements of analog to digital converter (ADC) in the coherent receivers are independent of LPN or the level of modulation formats. For the bit error rate (BER) of 10−3, the required bit number of ADC is 6, and the gain is marginal for the higher resolution.

Quantitative analysis of the transient response of the refractive index to conditions of electromagnetically induced transparency

For the example of the $D$${}_{1}$ line of ${}^{87}$Rb we analyze the experimental parameters that control the transient response of electromagnetically induced transparency. Quantum coherent free-induction decay is observed on time scales exceeding several milliseconds in a buffer-gas vapor cell. Numerical solutions of the quantum master equation and approximate analytical solutions are tested and absolute comparisons of the transient time scales, power broadening, resonance contrast, and frequency shifts are made. Two actively-phase-locked lasers are employed. The effects of laser phase noise that is not fully correlated are studied.

Effect of phase noise on the generation of stationary entanglement in cavity optomechanics

We study the effect of laser phase noise on the generation of stationary entanglement between an intracavity optical mode and a mechanical resonator in a generic cavity optomechanical system. We show that one can realize robust stationary optomechanical entanglement even in the presence of non-negligible laser phase noise. We also show that the explicit form of the laser phase noise spectrum is relevant, and discuss its effect on both optomechanical entanglement and ground-state cooling of the mechanical resonator.

Laser phase noise effects on the dynamics of optomechanical resonators

We investigate theoretically the influence of laser phase noise on the cooling and heating of a generic cavity optomechanical system. We derive the back-action damping and heating rates and the mechanical frequency shift of the radiation-pressure-driven oscillating mirror, and derive the minimum phonon occupation number for small laser linewidths. We find that, in practice, laser phase noise does not pose serious limitations to ground-state cooling. Additionally, we explore the regime of parametric amplification where coherent oscillations of the mirror are realizable. It is found that heating from laser phase noise is of significance and can cause the onset of instabilities. We then consider the effects of laser phase noise in a parametric cavity driving scheme that minimizes the back-action heating of one of the quadratures of the mechanical oscillator motion. Laser linewidths, narrow compared to the decay rate of the cavity field, do not pose any significant problems in an experimental setting, but broader linewidths limit the practicality of this back-action evasion method.

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.

Electromagnetically induced transparency with noisy lasers

We demonstrate and characterize two coherent phenomena that can mitigate the effects of laser phase noise for electromagnetically induced transparency (EIT): a laser-power-broadening-resistant resonance in the transmitted intensity cross correlation between EIT optical fields, and a resonant suppression of the conversion of laser phase noise to intensity noise when one-photon noise dominates over two-photon-detuning noise. Our experimental observations are in good agreement with both an intuitive physical picture and numerical calculations. The results have wide-ranging applications to spectroscopy, atomic clocks, and magnetometers.