Distributed Raman Amplification Research Articles

Study of EDFA and Raman system transmission reach with 256 Gb/s PM-16QAM signals over three optical fibers with 100 km spans

We compare the transmission performance of three different optical fibers in separate 256 Gb/s PM-16QAM systems amplified with erbium doped fiber amplifiers (EDFAs) and distributed Raman amplification. The span length in each system is 100 km. The fibers studied include standard single-mode fiber, single-mode fiber with ultra-low loss, and ultra-low loss fiber with large effective area. We find that the single-mode fiber with ultra-low loss and the large effective area fiber with ultra-low loss afford reach advantages of up to about 31% and 80%, respectively, over standard fiber measured at distances with 3 dB margin over the forward error correction (FEC) threshold. The Raman amplified systems provide about 50% reach length enhancement over the EDFA systems for all three fibers in the experimental set-up. For the best performing fiber with large effective area and ultra-low loss, the absolute reach lengths with 3 dB margin are greater than 1140 km and 1700 km for the for EDFA and Raman systems, respectively.

Random-lasing-based distributed fiber-optic amplification

The gain and noise characteristics of distributed Raman amplification (DRA) based on random fiber laser (RFL) (including forward and backward random laser pumping) have been experimentally investigated through comparison with conventional bi-directional 1st-order and 2nd-order pumping. The results show that, the forward random laser pumping exhibits larger averaged gain and gain fluctuation while the backward random laser pumping has lower averaged gain and nonlinear impairment under the same signal input power and on-off gain. The effective noise figure (ENF) of the forward random laser pumping is lower than that of the bi-directional 1st-order pumping by ~2.3 dB, and lower than that of bi-directional 2nd-order pumping by ~1.3 dB at transparency transmission, respectively. The results also show that the spectra and power of RFL are uniquely insensitive to environmental temperature variation, unlike all the other lasers. Therefore, random-lasing-based distributed fiber-optic amplification could offer low-noise and stable DRA for long-distance transmission.

The Performance of 16-QAM Signals Transmission in The Third-order Pumped Distributed Raman Amplifier

Abstract In order to study the practical applicabality of the 3rd-order distributed Raman amplifier (DRA) in optical transmission system, the structure of the 3rd-order DRA is put forward firstly, and the effect of higher order simulated Raman scattering is investigated. And then a simulated 3rd-order DRA transmission system (DRATS) over 120 km fiber is set up and the performance of 16-QAM signals in this transmission system is studied. In order to compare the transmission performance, a simulated 1order DRATS is also set up. Simulation results indicate that the bit error rate (BER) of 16-QAM signals in the 3rd-order DRATS is lower than that in the 1st-order DRATS.

Flat-Gain L-Band Raman-EDFA Hybrid Optical Amplifier for Dense Wavelength Division Multiplexed System

An efficient gain-flattened L-band optical amplifier is demonstrated using a hybrid configuration with a distributed Raman amplifier (DRA) and an erbium-doped fiber amplifier (EDFA) for 160 × 10-Gb/s dense wavelength division multiplexed system at 25-GHz interval. With an input signal power of 3 mW, a flat gain of >; 10 dB is obtained across the frequency range from 187 to 190.975 THz with a gain variation of <; 4.5 dB without using any gain-flattening technique. The output power obtained at 3-mW optimum input power is also the highest value (>; 8.9 dBm) ever reported for a DRA-EDFA hybrid optical amplifier at reduced channel spacing.

Nonlinearity Compensation of 224 Gb/s Dual-Polarization 16-QAM Transmission Over 2700 km

Long-haul transmission for distances greater than 2000 km is investigated for a 224 Gb/s dual-polarization 16-ary quadrature-amplitude-modulation signal, using ultralarge effective area fiber with span lengths of 75.5 km and distributed Raman amplification. By using nonlinear compensation (NLC) based on the low-pass filter (LPF) assisted digital back propagation (DBP) algorithm, a transmission distance of 2700 km is demonstrated with moderate complexity (0.25 backpropagation steps/span) and good robustness to deviation of the algorithm parameters from their optimum values. Compared to the standard DBP algorithm, the LPF assisted DBP algorithm can allow a reduction in the number of NLC steps/span, but with an increased computational complexity for each step. The two DBP algorithms are compared in terms of the number of real multiplications per bit, thus allowing the algorithm with lower complexity to be determined for a given level of performance.

XPM and SPM induced crosstalk in WDM system employing distributed Raman amplifier for DPSK and OOK modulation format

Cross-phase modulation (XPM) and self-phase modulation (SPM) induced nonlinear crosstalk has been studied analytically for coherent DPSK and OOK signal in NRZ- and RZ-modulation format for WDM system employing distributed Raman amplifier. The study shows that 40Gb/s RZ-DPSK signal with 33.3% duty cycle experiences minimum XPM and SPM induced crosstalk. The results also reveal that minimum crosstalk was induced in backward pumped DRA among the three pumping schemes i.e. forward, backward and bi-directional. Results assume importance for minimizing deleterious XPM and SPM effects in optical communication system.

5-12 分布ラマン増幅を用いたフル解像度スーパーハイビジョン信号の長距離光伝送実験(第5部門 放送方式,現業,無線・光伝送)

5-12 分布ラマン増幅を用いたフル解像度スーパーハイビジョン信号の長距離光伝送実験(第5部門 放送方式,現業,無線・光伝送)

400G WDM Transmission on the 50 GHz Grid for Future Optical Networks

We review the recent technology advancements related to the transmission of 400Gb/s, wavelength-division-multiplexed channels for optical networks based on the standard 50 GHz grid. We discuss the enabling modulation, coding, and line system technologies, as well as the existing challenges. Specifically, these technologies include time-domain hybrid 32-64 quadrature amplitude modulation, nearly ideal digital Nyquist pulse shaping, improved channel bandwidth management methods such as end-to-end carrier frequency control and distributed compensation of filtering effects arising from reconfigurable optical add/drop multiplexers, distributed Raman amplification, and powerful forward error correction. We demonstrate 400G transmission on the standard 50 GHz grid over meaningful transmission reach for regional and metropolitan applications. However, further studies are needed to fully understand the potential for meeting the requirements of long-haul transmission applications.

Long-Haul Performance of 112 Gb/s PM-QPSK: Implications of Enhanced Optical Fiber Transmission Properties

Experimental investigations of 112 Gb/s PM-QPSK transmission are reviewed for systems with 100 km spans and EDFA-only amplification, 200 km spans and hybrid amplification (distributed Raman amplification (DRA) and EDFA), and 100 km spans and DRA-only amplification. By taking advantage of optical fibers with ultra-low loss and very large effective area, transmission distances of 7200 km, 5400 km and 10 200 km, respectively, were achieved for multi-channel transmission with a 50 GHz channel spacing. For the first of these systems, the impact of the signal processing algorithms on the long-haul bit error ratio performance is examined with an emphasis on the sensitivity to the values of key algorithm parameters.

RIN transfer in random distributed feedback fiber lasers

We numerically investigate relative intensity-noise transfer from a noisy pump to the generated Stokes component in random distributed feedback ultralong Raman fiber lasers. Results show transfer levels comparable to those in distributed Raman amplification and cavity-based ultralong Raman fiber lasers, but with some unique spectral features.

Spatially cascaded cavities for power saving distributed Raman amplification

A novel distributed amplification scheme with cascaded (using distributed in-line cavities formed by notch filters based on fiber Bragg gratings) ultra-long Raman fiber lasers for transmission with suppressed noise and reduced pump power consumption is proposed and evaluated. Comprehensive numerical analysis shows the possibility of pump power reduction by 50% compared to similar scheme without notch filters while supporting acceptable optical signal-to-noise ratio over large transmission span.

A Raman amplified GPON reach extension system using parameters of a deployed fiber

Recently distributed Raman amplification of the upstream signal has been proposed to improve the loss budget for gigabit passive optical networks (GPON), and systems of 60-km reach and up to 128 way split have been demonstrated employing state-of-the-art fibers. However, a deployed fiber plant may not perform as well due to elevated fiber attenuation, splice losses, and back-reflections that are present in a realistic GPON system. In this paper, their effects on the Raman amplified 1310-nm upstream signal in a GPON reach extension system is investigated numerically. Using the parameters of a deployed fiber, a design solution is provided for a purely passive, Raman amplified GPON reach extender. Results show that 55-km logical reach and 1:32 split ratio can be achieved using a realistic fiber plant and class B + transceivers.

Stimulated Raman crosstalk in bi-directional pumped distributed Raman amplifier for DPSK and OOK modulation format

Novel closed form formulae are derived to study crosstalk degradation due to stimulated Raman scattering (SRS) in WDM systems employing bi-directional pumped distributed Raman amplifier (DRA). They are applied to evaluate the crosstalk performance of different modulation formats, especially differential phase-shift keying (DPSK) and ON–OFF keying (OOK), which are widely used in optical communication. Further, SRS crosstalk is evaluated for different data rates and pulse shapes prevalent in optical data transmission. Next, crosstalk is calculated for different pumping schemes as special cases of bi-directional pumped DRA. The study shows that minimum SRS crosstalk can be achieved for 40Gb/s RZ-DPSK signal with 33.3% duty cycle in WDM system employing backward pumped DRA.

Pump Light Source for Distributed Raman Amplification in MCFs With LD Sharing Circuit

We report an integrated pump source for distributed Raman amplification (DRA) in multicore fiber (MCF) where the MCF cores share pump laser diodes (LDs). The DRA requires many LDs and passive components if it is to obtain a flat and polarization-insensitive gain spectrum, especially in MCF transmission. To reduce the number of optical components, we propose a pump configuration where two cores share a pump LD set. The number of LDs is reduced almost by half. We integrate passive components, such as wavelength division multiplexers and polarization beam combiners, in a planar lightwave circuit to realize the LD sharing circuit. With our proposed pump sharing configuration, we obtain a DRA gain of more than 5.7 dB over the entire C-band in an MCF.

Determination of the optimum launch conditions in counter-Raman amplification using the method of moments

In the regime of counter Raman amplification we used the method of moments in order to obtain optimum launch conditions for different relationships between the pumping stage spacing and the dispersion length. The effects of the peak power signal and prechirping of solitons on propagation are numerically investigated in a system with distributed Raman amplification. The numerical results of the nonlinear Schrödinger equation using the split-step method show that the optimum power control of the injected solitons largely determines the quality of the power-RMS width of the pulses that propagate in those systems.

Four-wave mixing induced gain suppression and noise elevation in a distributed Raman amplifier

We observed experimentally four-wave mixing (FWM) between 1470nm pump and 1520nm signal in a forward-pumped distributed Raman amplifier (DRA) over a 25km of non-zero dispersion shifted fiber with zero dispersion wavelength of 1495nm. The 100mW pump Fabry–Perot (FP) spectrum centered at 1470nm is reproduced via FWM around the single-wavelength probe signal at 1520nm, generating spectrally nonuniform FWM induced noise floors. The suppression of Raman gain by about 2.4dB was also observed with maximum FWM at minimum phase mismatching between pump and signal. The new phase mismatching is derived and combined with the product counts of adjacent pump mode powers to estimate the FWM generated power ratio with maximum and less FWM efficiencies. We find these theoretical calculations are consistent with the experimental results.

1000-km 7-core fiber transmission of 10 x 96-Gb/s PDM-16QAM using Raman amplification with 65 W per fiber

We demonstrate 7-core fiber transmission of 10 x 96-Gb/s PDM-16QAM signals over 1000-km using distributed Raman amplification (DRA). DRA gain of 9-12 dB and equivalent noise figure of less than 1 dB are achieved in all cores. We also prove the feasibility of high power multi-core fiber transmission with per fiber power of 6.5 W.

Recent advances of distributed optical fiber Raman amplifiers in ultra wide wavelength division multiplexing telecommunication networks

Recently, many research works have been focused on the fiber optic devices for optical communication systems. One of the main interests is on the optical amplifiers to boost a weak signal in the communication systems. In order to overcome the limitations imposed by electrical regeneration, a means of optical amplification was sought. The competing technology emerged: the first was Raman amplification. One reason was that the optical pump powers required for Raman amplification were significantly higher than that for Erbium doped fiber amplifier (EDFA), and the pump laser technology could not reliably deliver the required powers. However, with the improvement of pump laser technology Raman amplification is now an important means of expanding span transmission reach and capacity. We have deeply studied an analytical model for optical distributed Raman amplifiers (ODRAs) in the transmission signal power and pump power within Raman amplification technique in co-pumped, counter-pumped, and bi-directional pumping direction configurations through different types of fiber cable media. The validity of this model was confirmed by using experimental data and numerical simulations. Key words: Distributed Raman amplifier, fiber link media, signal power, pump power, and Raman gain efficiency.

Performance comparison of Raman/erbium-doped-fiber hybrid-amplification-based long-distance fiber Bragg grating sensor systems

A study regarding the performance comparison of three different types of long-distance fiber Bragg grating (FBG) sensors based on bidirectional Raman and erbium-doped fiber (EDF) amplification has been carried out to determine the most power-efficient and accurate configuration. The three sensor system configurations studied were a bidirectional hybrid Raman amplifier with (Type I) an EDF located after the distributed Raman amplification section, (Type II) an EDF located before the distributed Raman amplification section, and (Type III) without an EDF. The FBG sensor systems are based on a demodulation scheme employing radio frequency power measurements of a beat signal, in which a sine-modulated amplified spontaneous emission from a directly modulated reflective semiconductor optical amplifier is employed as a broadband light source. The results of our experimentation showed that the sensor system with the EDF located prior to the Raman amplification section provided the best performance in regards to its pump power efficiency, electrical signal-to-noise ratio, and measurement accuracy.

46-km-Long Raman Amplified Hybrid Double-Bus Network With Point and Distributed Brillouin Sensors

We experimentally demonstrate a 46-km hybrid network that combine point and distributed Brillouin sensors. The proposed sensor network multiplexes low-cost intensity point sensors based on fiber-optic tapers, which are able to measure vibrations in the 0.01 to 50 Hz frequency range. The sensor network with a double-bus is a low noise configuration, which offers a higher optical signal to noise ratio and dynamic range than a single-bus. Thus, the number of sensors to be multiplexed could increase or we could reach further distances. The system also deploys remote distributed Raman amplification to extend the sensing range.