Backward Raman Amplification Research Articles

Dense wavelength division multiplexing scheme based on effective distributed inline light fiber Raman amplifier configuration

Abstract This paper demonstrated the dense wavelength division multiplexing scheme based on effective distributed inline light fiber Raman amplifier configuration. Various forward/backward and bidirectional pumping power configurations are studied versus fiber reach. Output light signal power is demonstrated against fiber reach without Raman amplification technique. Output light signal power in the forward Raman amplification scheme is clarified with pumping power of both 500 mW and 700 mW in various fiber channel configurations. As well as output light signal power in the backward Raman amplification scheme with pumping power of both 500 mW and 700 mW in various fiber channel configurations. Amplification Raman gain parameter coefficient is demonstrated with various values of pumping power pump based on various fiber channel configurations. Backward amplification net parameter gain is studied for different single mode/true wave/freelight fibers channel configuration at different both pumping power values and fiber reach. As well as the forward amplification net parameter gain is clarified for different single mode/true wave/freelight fibers channel configuration at different both pumping power values and fiber reach.

Performance analysis of real-time multi-wavelength nonlinear DRA for the next-generation photonic network

A new disintegrated channelization approach for the backward pumped nonlinear distributed Raman amplifier is proposed by enacting the differential coupled equations of Raman amplification, in fiber, trailing by the solution of NLSE using the first integral method first time to the best of our knowledge. A nonlinear channel modeling-based simulation is adapted for the approximation of the Raman gain profile. To realize the real-time dynamic system, 16 multiplexed channels of prime C-band are employed in a QPSK/NRZ modulation environment with a 100 Gbps bit rate for optical network reconfiguration. A non-uniform gain is reported while the disparity in BER is observed from 10−12 to 10−8.

The effect of scattering instability induced by high intensity seed on backward Raman amplification

Backward Raman amplification (BRA) in plasma has become one of the most promising techniques for further promoting light intensity. In this work, BRA in plasma is simulated using one-dimensional particle-in-cell code with different seed intensity, showing that higher seed intensity (in the range of 2×1011–2×1015 W/cm2) will increase energy conversion efficiency with pump pulse of fixed intensity (2×1014 W/cm2), which is pre-depleted by spontaneous Raman scattering. We find that the scattering instability of amplified seed pulse is enhanced and the plasma wave fluctuation level is promoted with seed intensity at 2×1016 W/cm2 because the local plasma density changes in the pump scattering depletion region. In the simulations, we also found that the enhanced Raman scattering and secondary Raman scattering of amplified seed pulse causes a rapid energy consumption and earlier saturation of the amplification, which significantly affects the temporal shape of the amplified seed pulse to form a double peak shape. In addition, we explore the evolution of the energy and the pulse duration of the double peaks in detail and reveal the law of pulse energy growth with different pulse durations in a Raman amplifier.

Backward pumped distributed Raman amplifier: enhanced gain

The backward Raman amplifier (RA) can considered as one of the best solutions for optical communication, especially in Wavelength Division Multiplexing technology. They reduce the nonlinear effects, have low noise figure and a wide frequency range. The work in this paper aims to reduce the attenuation of optical signal due to its propagation optical fiber and increase both amplifier gain and output signal power. Two backward Raman models are proposed. Proposal one model consists of two cascaded RAs and the other (proposal two) consists of three cascaded RAs. Three backward pump power levels 200, 400, and 600 mW are used to simulate the models with the three types of fibers: single-mode fiber, Truewave, and Freelight, at an amplifier length of 100 km. Proposal two achieves a maximum gain of 31 dB at 600 mW pump power 600 mW using Truewave optical fiber, with 27.7 dBm maximum output signal power. This proposal is evaluated showing 11.15% gain enhancement and 200 mW saved power when compared to previously published work.

Technological Prospection and Requirements of 800G Transmission Systems for Ultra-Long-Haul All-Optical Terrestrial Backbone Networks

With the standardizations of 400GE and 400G completed or near completion, the attention is now refocused to next generation techniques with larger bit rates, i.e. 800G. We can see that current research commonly aims to short-reach or metro transmission for sharing key components with 400G, while ultra-long-haul transmission (typically ≥ 1500km) based on 800G is still in unknown state. Moreover, all-optical networking with OXC and ROADM is being gradually deployed all around the world, which further increases transmission performance requirement. According to past progress, it is urgent for us to analyze and clarify the requirements of 800G transmission systems for ultra-long-haul all-optical backbone networks. This work provides the technological prospection and requirements of 800G transmission systems for ultra-long-haul all-optical backbone networks. Firstly, the field network status and basic technical requirements for 800G are analyzed. Our record real-time 10-λ×800-Gb/s sub-carrier-multiplexing 95-GBd DP PCS-64QAM transmission over 2018-km G.654.E Fiber with pure backward distributed Raman amplification shows that reusing the components of current 400G technique is not the future direction. By numerically simulating the transmission performances of non-fully-loaded and fully-loaded DWDM scenarios, symbol rate higher than 180GBd, G.654.E, and optical bandwidth ≥ 12THz are necessary.

Performance evaluation of fiber impairment mitigation for high capacity communication systems using optical compensation method

Due to their ability to boost transmission rate and reach by compensating for Kerr nonlinearity-induced distortions, optical compensation techniques are interesting for broadband wavelength division multiplexing. This is due to the fact that these techniques have been shown to increase transmission rate. Yet, in the majority of instances, they call for more devices to be integrated into the network. This can be challenging for systems that are already in place, and it can be even more challenging for transmissions that are not repeated. The linear and nonlinear compensation system for the Dense Wave Division Multiplexing (DWDM) transmission system has been created and researched in this work. Along the optical link, a new method known as optical phase conjugation (OPC) is used as part of the process of improving the performance of communication systems. This method is used to improve the performance of 896 Gb/s sixteen channels dual polarization signalling of 50 GHz channel spacing over 800 km with three scenarios that use mid and multiple OPC. The results of the simulation indicate that multiple OPC with backward Raman amplifier method on the received signal is effective for nonlinearity compensation when compared with the mid OPC module in terms of enhanced Q-factor improvement, BER performance, EVM, and maximum transmission link length.

Self-compression of stimulated Raman backscattering by a flying focus.

The regime of self-compression has been proposed for plasma-based backward Raman amplification upon a flying focus. By using a pumping focus moving with a speed equal to the group velocity of stimulated Raman backscattering (SRBS), only a short part of SRBS which always synchronizes with the flying focus can be amplified. Therefore, instead of a short pulse, plasma noise or a long pulse can seed the BRA amplifiers. Here we demonstrate the regime by 2D particle-in-cell simulations, showing that the pump pulse is compressed from 26 ps to 116 fs, with an output amplitude comparable with the case of a well-synchronized short seed. As only one laser pulse is used in the simulation, the results present a significant path to simplify the Raman amplifiers.

Amplification mechanism in stimulated Raman backward scattering of ultraintense laser in uniform plasma

The density, temperature and length of the plasma used in the backward Raman amplification will all influence the result. To explore the influence of the plasma density and the pump intensity, this work uses the one-dimensional particle in cell (PIC) algorithm to simulate the process of the 800 nm pump laser injecting into the plasma. By analyzing the Raman scattered light, it is found that as the density of plasma increases, the wavelengths of the scattered light shorten. It is also found that the forward Raman scattering will cause the plasma density to change, which in turn influences the scattered light wavelength. Therefore, we should choose the plasma density based on the wavelength of the pump and the scattered light, while the amplification of the scattered is related to the pump intensity.

RIN induced penalties in G.654.E and G.652.D based distributed Raman amplifiers for coherent transmission systems.

Relative intensity noise (RIN) induced penalties were experimentally measured in distributed Raman amplifiers (DRAs) for G.654.E and G.652.D fibres with forward, backward and bidirectional pumping configurations. The measured signal RIN using the G.654.E fibre was ∼3.5 dB and ∼2 dB lower than the G.652.D fibre with forward (FW) pump configuration for PM-QPSK and PM-8QAM signals, with single span transmission showing a Q-factor improvement of ∼3 dB and ∼2.5 dB for G.654.E over G.652.D fibres. The performance penalty in a long haul coherent system was evaluated for 28 GBaud PM-QPSK signals using a recirculation loop for backward and bidirectional distributed Raman amplifiers. Our experimental results demonstrate an additional transmission distance of more than 1000 km for G.654.E over its counterpart G.652.D assuming a HD-FEC limit of 8.5 dB.

Seed source for plasma compression in the long wavelength infrared

Two color laser pulses are used to form an air plasma and generate broadband infrared radiation suitable as a seed for backward Raman amplification of CO2 laser pulses. Broadband radiation in the atmospheric window from 8 to 14 μm is observed. The infrared radiation is characterized using a long wavelength grating spectrometer specially designed to accept an ionizing laser filament at its input plane. The long wavelength infrared yield is greatly enhanced by chirping the drive pulse, but this affects the spectrum as well. Unidirectional pulse propagation simulations suggest that this is due in part to the dependence of the nonlinear refractive index on the pulse duration.

Optical phase conjugation in backward Raman amplification

Compression of an intense laser pulse using backward Raman amplification (BRA) in plasma, followed by vacuum focusing to a small spot size, can produce unprecedented ultrarelativistic laser intensities. The plasma density inhomogeneity during BRA, however, causes laser phase and amplitude distortions, limiting the pulse focusability. To solve the issue of distortion, we investigate the use of optical phase conjugation as the seed pulse for BRA. We show that the phase conjugated laser pulses can retain focusability in the nonlinear pump depletion regime of BRA, but not so easily in the linear amplification regime. This somewhat counterintuitive result is because the nonlinear pump depletion regime features a shorter amplification distance, and hence less phase distortion due to wave-wave interaction, than the linear amplification regime.

Boosting Backward Raman Amplification Performance Using an External Magnetic Field

This article presents a method of improving backward Raman amplification performance via the addition of an external static magnetic field longitudinal to the laser propagation direction. Our simulation results show that when the laser intensity is low, the output seed intensity can be increased by applying an external magnetic field and a right circularly polarized laser pulse. When the laser intensity is high, the magnetic field increases the self-phase modulation instability and decreases the output seed intensity. In such cases, a left circularly polarized laser pulse can suppress self-phase modulation instability and improve amplification performance. Dynamically adjusting the magnetic field, i.e., by using a double-pass scheme, can combine these two advantages and further improve the output seed intensity.

Modulated Raman pump for integrated VCSEL-based reach enhancement and clock tone dissemination in optical communication

The fast growth of data traffic in access networks calls for high speed and low-cost optical links. To extend reach for users in metro areas requires optical amplification of the signal carrying data. In this paper we experimentally demonstrate a cost effective technique of extending reach by exploiting Raman pump to both amplify data signal and transmit clock signals. A 1550 nm VCSEL is modulated with a 10 Gbps data and coupled into a 50.7 km fibre to co-propagate with a 4 GHz modulated Raman pump. Error free and enhanced data transmission was achieved with minimum receiver sensitivity of −14.8 dBm and distributed stable clock signal over 50.7 km SMF-Reach. A maximum phase noise of −100.6 dBc/Hz at 10 kHz offset frequency is experimentally measured for 50.7 km fibre transmission with backward Raman amplification. This work presents a real-time technique of transmitting accurate data and stable clock signal for long-reach optical networks.

Creating localized plasma waves by ionization of doped semiconductors.

Localized plasma waves can be generated by suddenly ionizing extrinsic semiconductors with spatially periodic dopant densities. The built-in electrostatic potentials at the metallurgical junctions, combined with electron density ripples, offer the exact initial condition for exciting long-lasting plasma waves upon ionization. This method can create plasma waves with a frequency between a few terahertz to subpetahertz without substantial damping. The lingering plasma waves can seed backward Raman amplification in a wide range of resonance frequencies up to the extreme ultraviolet regime. Chirped wave vectors and curved wave fronts allow focusing the amplified beam in both longitudinal and transverse dimensions. The main limitation to this method appears to be obtaining sufficiently low plasma density from solid-state materials to avoid collisional damping.

Noise Performance Improvement of Broadband Discrete Raman Amplifiers Using Dual Stage Distributed Pumping Architecture

We demonstrate a novel design of dual stage backward pumped broadband discrete Raman amplifier with distributed pumping architecture which improves the short wavelength noise performance compared with conventional backward pumped single stage design. Overall noise figure (NF) performance has been improved by 2.8 dB over 70 nm bandwidth without introducing forward pumping. Nonlinear phase shift has been numerically calculated and compared with single stage design to evaluate the overall performance improvement. Finally, we report that our proposed dual stage design with ∼14 dB net gain improves low wavelength NF by 3.3 dB providing 1.2 dB Q2 factor improvement and 1134 km reach extension versus a conventional single stage design for 18 × 120 Gb/s PM-QPSK transmission.

Spectral Manipulation of Raman Amplifiers

Backward Raman amplifiers provide a promising path to the next generation of short pulse high-intensity lasers that can go beyond the damage limit of conventional materials. The main idea is to couple a short seed and a long counter-propagating pump through an electron plasma wave in such a way that the pump energy is transferred to the seed that is amplified and compressed via Raman backscattering. This paper will shortly review the physics of Raman amplifiers including two recent developments in the field: (a) mitigating the relativistic phase-mismatch and the resulting saturation by detuning of the pump pulse and (b) multi-frequency amplification of pulses with a beat-wave waveform.

Performance Analysis of Flat Gain Wideband Raman Amplifier for S+C and C+L Band DWDM System

Raman amplifier is an open area of research in telecommunication field. This paper discusses the performance of 64 channels of 10 Gbps WDM systems with backward multipump Raman amplifier. The main goal of this paper is the optimization of Raman amplifier to minimize its gain variation without using any gain flattening techniques. To increase the transmission capacity of DWDM system, Raman amplifier with backward multipump configuration is implemented. The optimized parameters such as pump power and frequencies are used to deliver both ground and excited state absorption for amplification in S+C and C+L band region. The pump power and frequencies are optimized through multitarget and multiparameter optimization tool available in OptiSystem software. Gain ripple was achieved <0.5 dB for this simulation setup. The maximum flat gain achieved is 8.6 dB and noise figure of <8 dB was achieved for this wide bandwidth without using gain flattening techniques. This amplifier design will be helpful for CATV applications and telecommunication networks.

Enhancement and control of laser wakefields via a backward Raman amplifier

The Backward Raman Amplifier (BRA) is proposed as a possible scheme for improving laser driven plasma wakefields. One- and two-dimensional particle-in-cell code simulations and a 3-Wave coupling model are presented and compared to demonstrate how the BRA can be applied to the laser wakefield accelerator (LWFA) in the non-relativistic regime to counteract limitations such as pump depletion and diffraction. This article provides a discussion on optimal parameters for the combination of BRA and LWFA and a prescription for a BRA pump frequency chirp to ensure coupling beyond the particle dephasing limit. Simulation results demonstrate a reduction or alleviation of the effects of diffraction and an increase in wake amplitude and sustainability and provide direct insights into new methods of controlling plasma wakes in LWFA and other applications.

Backward Supercontinuum Generation Excited By Random Lasing

Backward supercontinuum generation excited by random lasing is proposed and demonstrated for the first time. Unlike conventional supercontinuum generation, completely distributed random fiber laser is first used as an effective seeding laser to initiate supercontinuum emission in a composite configuration with TrueWave and dispersion compensated fibers. The two fibers provide both amplified random distributed feedback and nonlinear effect induced spectral broadening. Taking advantages of intrinsic characteristics of random distributed Rayleigh scattering and low-noise backward distributed Raman amplification of random lasing, backward supercontinuum is realized with much lower intensity fluctuation in time domain compared to the forward counterpart. The study of combined effects of random lasing and strong nonlinear mechanism not only enrich the research scope of supercontinuum and random fiber lasers, but also provide a practical way for the development of stable broadband light sources for various applications.

Raman-enhanced optical phase conjugator in WDM transmission systems.

Optical phase conjugation (OPC) can be applied to boost the performance of long-haul transmission by mitigating the impairments from fiber nonlinearity. Unfortunately, noticeable nonlinear noise in the conjugator for optical orthogonal frequency division multiplexing (OFDM) systems often degrades the signal quality. In this paper, we demonstrate nonlinear distortion mitigation in OPC by introducing backward Raman amplification to the conjugator. Raman amplification allows a lower input signal power, thus suppressing the OPC distortion while maintaining the conjugated output power. We investigate the performances of Raman-enhanced OPC in both back-to-back (BTB) and transmission systems with 3 × 25 Gbaud optical OFDM signals. In the BTB OPC system, Raman amplification boosts the tolerance to system nonlinearity, achieving a 3-dB improvement in the output power, a 2.4-dB improvement in the Q factor, and a 6-dB improvement in the input dynamic range. In the transmission system with Raman-enhanced OPC, the optimum launched power is increased by 2 dB and the maximum Q factor is increased by 0.4 dB compared to direct transmission. Similar performances are observed in all the wavelengths, indicating that our scheme works well with WDM transmission systems.