Fiber Optical Parametric Amplifier Research Articles

Suppression of WDM four-wave mixing crosstalk in fibre optic parametric amplifier using Raman-assisted pumping.

We perform an extensive numerical analysis of Raman-Assisted Fibre Optical Parametric Amplifiers (RA-FOPA) in the context of WDM QPSK signal amplification. A detailed comparison of the conventional FOPA and RA-FOPA is reported and the important advantages offered by the Raman pumping are clarified. We assess the impact of pump power ratios, channel count, and highly nonlinear fibre (HNLF) length on crosstalk levels at different amplifier gains. We show that for a fixed 200 m HNLF length, maximum crosstalk can be reduced by up to 7 dB when amplifying 10x58Gb/s QPSK signals at 20 dB net-gain using a Raman pump of 37 dBm and parametric pump of 28.5 dBm in comparison to a standard single-pump FOPA using 33.4 dBm pump power. It is shown that a significant reduction in four-wave mixing crosstalk is also obtained by reducing the highly nonlinear fibre interaction length. The trend is shown to be generally valid for different net-gain conditions and channel grid size. Crosstalk levels are additionally shown to strongly depend on the Raman/parametric pump power ratio, with a reduction in crosstalk seen for increased Raman pump power contribution.

A simple analytical model to study of six wave fiber optical parametric amplifier characteristics

We have made an attempt to present a fairly analytical solution, in order to provide a compact source for such solution for researchers who need to evaluate six wave optical parametric amplifiers (OPA) performance. We have also presented complete derivations, so that the researchers can follow them step by step and thereby gain physical and mathematical insight into the origin of the solutions. We begin by using Maxwell's equations under third nonlinear effects on which fiber OPAs are used to derive complete coupled wave equations. For six waves OPA we also describe some of their fundamental properties resulting from energy conservation, as well as the quantum features of four wave mixing (FWM) interactions. Finally we have presented analytical solutions followed by simulation results for six coupled wave equation for certain conditions.

Investigation of two-pump fiber optical parametric amplifiers for a broadband and flat gain with a low pump-to-signal noise transfer

Two-pump fiber optical parametric amplifiers (2-P FOPAs) are investigated to obtain a broadband and flat gain simultaneously with a low pump-to-signal noise transfer. The analysis is performed based on the six-wave model to find the optimum pump wavelength separation and also the fiber length to simultaneously maximize the gain and minimize the noise transfer from the pump to the signal. The results of this paper show the potential of 2-P FOPAs for application in fiber optical communication systems; for example, wavelength division multiplexing (WDM).

110 nm versatile fiber optical parametric amplifier at 1.0 μm.

The fiber optical parametric amplifier (FOPA) has been well investigated and widely adopted at the telecommunication window, and outstanding progress has been achieved in areas such as high gain, wide bandwidths, and even flexible gain-spectrum shape. In contrast, a FOPA at the bio-favorable window, 1.0 μm, has been largely underexploited, especially for its relatively limited bandwidth. Here, we demonstrate an all-fiber single-pump FOPA at 1.0 μm with versatile performances, including ultrahigh gain (∼52 dB), wide bandwidth (∼110 nm), and good gain-spectrum flatness (∼3 dB). To showcase the practical applications, the FOPA is utilized to amplify the broadband optical image signal from a spectrally encoded microscopy, yielding a sensitivity enhancement of 47 dB. Thus, it is promising that this all-fiber versatile FOPA works well as an add-on module in boosting sensitivity for existing optical systems at a 1.0 μm window.

Tunable parametric amplifier for mid-IR application based on highly nonlinear chalcogenide material

A novel dispersion controlling technique towards attaining tunable parametric amplification based on highly nonlinear photonic crystal fibers has been investigated. Selective infiltration of the liquid into the air-holes leads to alter the zero dispersion wavelength towards a broader parametric gain in the mid-IR spectrum by only changing the temperature of the system externally. The dispersion profile specially the zero dispersion wavelengths can be well tuned around the pumping wavelength, thereby generating several hundred nanometer parametric bandwidth in near-IR to mid-IR region. The tunability of the photonic crystal fibers (PCFs) can also be useful for generating new frequencies in both the red- and blue-shifted regions far from the pumping wavelength. Our numerical calculations reveal that we could achieve very wide band fiber optic parametric amplifier both in the communication wavelength and in the IR region. Also two different types of PCFs can be used to achieve same broadband wavelength spectra however with a tradeoff between the fiber lengths and pump power.

Ultrabroadband fiber optical parametric amplifiers pumped by chirped pulses Part 1: analytical model

An analytical model has been developed to fully understand the concept of fiber optical parametric amplifiers pumped by broadband chirped pulses. Our model is in good agreement with the numerical resolution of the nonlinear Schrodinger equation and was used to tailor the gain bandwidth. In particular, we showed that the group delay difference between the pump and the signal can play a crucial role in the spectral extension of the gain. This exciting amplification concept should pave the way toward high gain ultrashort (<30 fs) pulse amplification in fiber.

Ultrabroadband fiber optical parametric amplifier pumped by chirped pulses Part 2: sub-30-fs pulse amplification at high gain

We report numerical investigations on ultrashort pulse amplification with high gain in a fiber-based optical parametric amplifier pumped by a broadband chirped pulse. The amplifier has been tailored for ultrabroadband amplification with an analytical model and has key features to overcome gain narrowing and pulse distortion, which are usually observed in ion-doped fiber amplifiers. By combining chirped pump and signal pulses in a fiber, we highlight the possibility to amplify sub-30-fs pulses with standard ultrafast technologies.

Parametric coherent receiver.

We present the parametric coherent receiver based on a two-mode pump-degenerate fiber optical parametric amplifier (FOPA). The receiver is inherently single-ended and offers a simultaneous gain and coherent mixing of the received signal and a reference wave (known as a local oscillator signal) with, in principle, arbitrary wavelength separation. We analyze the receiver theoretically and in a proof-of-concept experiment. As a reference we compare the performance to a standard single-ended homodyne coherent receiver.

BER Performance of a Lumped Single-pump Fiber Optical Parametric Amplifier in a 10 Gbit/s 4-channel S-band DWDM System

Results on computer simulations of a lumped single-pump FOPA (fiber optical parametric amplifier) are presented. We demonstrate optical amplification of a 10 Gbit/s 4-channel S-band DWDM system utilizing a lumped FOPA on a 400 km long link with 80 km long inter-amplifier spans. In most of the recent papers in the field of fiber optical parametric amplifiers research the amount of amplification and the gain bandwidth are considered as the FOPA parameters. We evaluate the effectiveness of FOPA through BER parameter, which depends on both the attenuation of optical signal and the quality degradation due to dispersion, crosstalk and amplifier noise, and therefore is more suitable for evaluation of optical amplifiers in lightwave systems. Ill. 4, bibl. 9 (in English; abstracts in English, Russian and Lithuanian).

12 THz flat gain fiber optical parametric amplifiers with dispersion varying fibers.

We report a fiber-optic parametric amplifier with ultra-broad and flat gain band by using a longitudinally tailored optical fiber. The parametric amplifier has been designed from realistic numerical simulations combined with an inverse algorithm to obtain a flat and wide gain band through fiber dispersion management. We experimentally report ~12 THz gain bandwidth on the Stokes side of the pump with a gain ripple as low as 7 dB and a mean gain up to ~60 dB. Experimental results show good agreement with numerical predictions for different pump powers and wavelength detuning.

Gain and bandwidth investigation in a near-zero ultra-flat dispersion PCF for optical parametric amplification around the communication wavelength.

In this work, we explore the fiber optical parametric amplifiers (FOPAs) gain and bandwidth spectra of near-zero ultra-flattened photonic crystal fibers (PCFs) around the communication wavelength. The parametric gain and spectral bandwidth have been explored for all the three zero-dispersion wavelengths (ZDWs) of the near-zero ultra-flat fiber. Our numerical analysis establishes a dispersion profile with D=0±0.35 ps/nm/km for a bandwidth of 440 nm around the communication wavelength to fully exploit the four-wave mixing effect with three ZDWs for broadband applications. It has been observed that the broader gain spectrum of FOPAs can be achieved with the near-zero and ultra-flattened dispersion curve with proper tuning of the pumping condition. A broader bandwidth with sufficient peak gain value has been achieved with small negative anomalous dispersion (β2≤0) and positive value of fourth-order dispersion parameter (+ve β4) around the pumping wavelength. Wider bandwidth of the parametric amplifier has been observed around the second ZDW with a negative slope of the dispersion curve. A total bandwidth ≈520 nm could be achieved with the ultra-flat dispersion nature of the optimized PCF. The design methodology of achieving wider gain by tuning the pumping wavelength for favorable higher-order dispersion parameters would be very useful for future dispersion engineered devices.

Fiber-Optical Parametric Amplification of Sub-Picosecond Pulses for High-Speed Optical Communications

This article reviews recent results of amplification of short optical pulses using fiber-optical parametric amplifiers. This includes chirped-pulse amplification of 400 fs pulses, error-free amplification of a 640-Gbit/s optical time-division multiplexed signal with less than a 1-dB power penalty, and all-optical phase-preserving amplitude regeneration of a 640-Gbit/s return-to-zero differential phase-shift keying optical time-division multiplexed signal.

Kerr Nonlinearity Mitigation: Mid-Link Spectral Inversion Versus Digital Backpropagation in 5×28-GBd PDM 16-QAM Signal Transmission

We experimentally investigate Kerr nonlinearity mitigation of a 28-GBd polarization-multiplexed 16-QAM signal in a five-channel 50-GHz spaced wavelength-division multiplexing (WDM) system. Optical phase conjugation (OPC) employing the mid-link spectral inversion technique is implemented by using a dual-pump polarization-independent fiber-optic parametric amplifier and compared to digital backpropagation (DBP) compensation over up to 800-km in a dispersion-managed link. In the single-channel case, the use of the DBP algorithm outperformed the OPC with a Q-factor improvement of 0.9 dB after 800-km transmission. However, signal transmission was not possible with DBP in the WDM scenario over the same link length while it was enabled by the OPC with a maximum Q-factor of 8.6 dB.

Improved WDM performance of a fibre optical parametric amplifier using Raman-assisted pumping.

We experimentally demonstrate a Raman-Assisted Fibre Optical Parametric Amplifier (RA-FOPA) with 20dB net gain using wavelength division multiplexed signals. We report amplification of 10x58Gb/s 100GHz-spaced QPSK signals and show that by appropriate tuning of the parametric pump power and frequency, gain improvement of up to 5dB can be achieved for the RA-FOPA compared with combined individual contributions from the parametric and Raman pumps. We compare the RA-FOPA with an equivalent-gain conventional FOPA and find that four-wave mixing crosstalk is substantially reduced by up to 5.8 ± 0.4dB using the RA-FOPA. Worst-case performance penalty of the RA-FOPA is found to be only 1.0 ± 0.2dB over all measured OSNRs, frequencies and input powers, making it an attractive proposal for future communications systems.

Origin of Non-Reciprocal Response in Fiber Optic Parametric Amplifiers

The non-reciprocal response of high-performance fiber optic parametric amplifiers was investigated. This response is attributed to the combination of fibers' inhomogeneous nature and their operation at deep saturation, but it is not clear whether this effect is promoted by polarization or dispersion. We show that non-reciprocal behavior is dominated by the fiber's local dispersion. Additionally, a simulation strategy capable of capturing fiber optic parametric amplifiers' non-reciprocal response is demonstrated.

Parametric Amplification, Wavelength Conversion, and Phase Conjugation of a 2.048-Tbit/s WDM PDM 16-QAM Signal

We demonstrate polarization-independent parametric amplification of a 2.048-Tbit/s 8-WDM PDM 16-QAM signal and simultaneous wavelength conversion and phase conjugation in a highly nonlinear fiber. Two high-power continuous-wave pumps with orthogonal polarizations and counter-phase modulation are used in the fiber optical parametric amplifier (FOPA) to achieve broadband flat gain, polarization independence, and high-quality idler generation. The polarization-independent FOPA is amplitude and phase preserving and has ~10 dB on-off gain for the signal and ~9 dB conversion efficiency for the idler with a 1-dB bandwidth of ~16 nm. Compared to the back-to-back case, the amplified signals and the wavelength-converted conjugates have mean Q <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> penalties of only 0.6 and 0.4 dB, respectively, with variances of Q <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> factors across all the wavelength-division-multiplexed channels of only 0.3 dB. This demonstration shows the great promise of optical signal processing techniques to simultaneously process large-capacity multiple-channel multilevel signals with almost no latency and potentially low power consumption.

Frequency-resolved noise figure measurements of phase (in)sensitive fiber optical parametric amplifiers.

We measure the frequency-resolved noise figure of fiber optical parametric amplifiers both in phase-insensitive and phase-sensitive modes in the frequency range from 0.03 to 3 GHz. We also measure the variation in noise figure due to the degradation in pump optical signal to noise ratio and also as a function of the input signal powers. Noise figure degradation due to stimulated Brillouin scattering is observed.

Response enhancement of deeply saturated fiber optic parametric amplifier via inhomogeneous fiber.

Deeply saturated fiber optic parametric amplifiers can have very high performance. While it's a common practice to model the fiber as a longitudinally homogenous entity, we show that the inhomogeneous nature of the fiber leads to a greater performance level which is neither accessible nor accountable using the homogenous model. This indicates that some experimental results cannot be predicted using the homogenous fiber model, even in principle. Consequently, future studies on the performance limit of the system will have to include an inhomogeneous fiber model.

A flexible receiver with fiber optical parametric amplifier in OCDMA-FSO communication system

A new receiver is proposed, which uses the fiber optical parametric amplifier (FOPA) in optical code division multiple access (OCDMA) over free space optic (FSO) communication system. The noise tolerance as the performance index in this receiver is derived. The receiver can not only improve the noise tolerance but also change the pump data conveniently for adapting to the length variation of the coding sequence under a complex and fast-changing weather condition. The influence of different factors on the noise tolerance is analyzed, and a significant improvement of about 18.77 dB for the noise tolerance can be achieved when the pump power and the length of coding sequence are 5 W and 256, respectively.

Performance Limits of Inhomogeneous Fiber Optic Parametric Amplifiers Operated in Saturated Regime

Performance limits of saturated parametric amplifiers with very high nonlinear figure of merit were investigated. While such devices can be constructed using high confinement fiber, they also require localized phase matching control over hundreds of meters of interaction length. The limit on signal-induced pump depletion imposed by stochastic dispersion fluctuations in physical fibers is studied for a case of high-gain parametric amplifiers. We show that nanometer-scale fluctuations in fiber transverse geometry can lead to qualitatively different saturation characteristics in very efficient parametric devices. In contrast to a pump-undepleted parametric amplifier, an inhomogeneous parametric amplifier operated in saturation regime is found to possess truly nonreciprocal transfer characteristic.