Conventional Erbium-doped Fiber Amplifiers Research Articles

Power Efficient Communications Employing Phase Sensitive Pre-Amplified Receiver

The receiver sensitivity is a very important metric in optical communication links operating at low received signal powers. Phase sensitive optical amplifiers (PSAs) can amplify optical signals without excess noise, thus providing a fundamental sensitivity improvement of 3 dB when employed as a pre-amplifier compared to conventional erbium doped fiber amplifiers (EDFA). In this letter, we investigate, both theoretically and experimentally, the sensitivities achieved using power efficient multi-dimensional modulation formats such as M-ary pulse position modulation format (M-PPM) and M-PPM combined with quadrature phase shift keying (QPSK) along with a near-noiseless PSA pre-amplified coherent intradyne receiver. We find that at high signal to noise ratios (SNRs) corresponding to low bit-error-rates (BER), M-PPM+QPSK results in the best sensitivity, which is improved with the order M, while at low SNRs corresponding to high BER (~14% where 100% overhead forward error correction codes (FEC) would be needed to recover the data), QPSK is the most sensitive format, while at the same time providing the best spectral efficiency. We report experimental sensitivities of 2.1 photons per information bit (PPB) at a pre-FEC BER = 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> using 64-PPM+QPSK and assuming 7% FEC, and 0.8 PPB at a pre-FEC BER = 0.14 using QPSK and assuming 100% FEC.

Noise evolution with the phase-sensitive gain in a hybrid fiber phase-sensitive amplifier

We investigate the noise evolution of a hybrid fiber phase-sensitive amplifier (PSA) with an erbium-doped fiber amplifier (EDFA) as a function of the phase-sensitive gain. The noise performance of the hybrid amplifier with a large overall gain of 45.6 dB is experimentally evaluated in optical and electrical domains. The experimental results are in good agreement with theory, showing that significant improvement of the overall noise figure (NF) of the hybrid amplifier occurs in a low PSA gain region. A combined NF below 3 dB has been obtained in the hybrid amplifier with a PSA gain of 9 dB, which is 1.1 dB better than a conventional EDFA with an equivalent overall gain.

Assessing Capacity and Cost/Capacity of 4-Core Multicore Fibers Against Single Core Fibers in Submarine Cable Systems

We assess the potential applicability and performance of multicore fibers (MCFs) against conventional single-core fibers (SCFs) in submarine transmission systems. In particular, we assume 4-core MCFs with nominally uncoupled cores and separate amplification of each MCF core with conventional erbium doped fiber amplifiers (EDFAs) using fan-in/fan-out (FI/FO) devices in the repeaters. We examine the effects of the number of physical fibers accommodated in the cable design, MCF and FI/FO crosstalk, FI/FO loss, span length, transceiver implementation penalty, and minimum required signal-to-noise ratio (SNR). The relative cable capacities offered by the MCF and SCF systems are evaluated under the different conditions. Then the relative cost/capacity for systems built with the two types of fiber are calculated using a system cost model for two conditions: 1) with maximum cable capacity and 2) for minimum overall cost/capacity. The potential role of multicore fibers (MCFs) in submarine cable systems is investigated in the context of electrical power limitations and physical fiber count limitations. Cable capacities are estimated based on ideal Shannon-limited capacity unless a transceiver implementation penalty, or gap-to-Shannon capacity, is applied. The systems are modeled assuming constant output power amplifiers as are commonly deployed in submarine systems. We find that MCFs offer the greatest cable capacity increase for low fiber count cables, but that the cost/capacity can be significantly higher. When minimization of cost/capacity is the design goal, MCF systems remain higher in this metric than SCF systems, while enabling only a small capacity increase at best.

Enhancement in the Gain of EDFA in Fibre Optic Communication

With the evolvement ofhigh speed and long distance data communication systems, conventional band erbium-doped fiber amplifiers (C-EDFAs) are getting more attention in recent times. Major advantage of the C-band EDFA is that it provides the user to realize a system with wide bandwidth of 40 nm. But, from the reported works, it is evident that for Gain enhancement in C-band using EDFA is reported with the use of multiple stages, multiple pumps, Gain flattening filters etc. However, these techniques suffered from high cost, complex techniques and low performance.Here enhancement process was done through the narrowband Fiber Bragg Gratings (FBG) or fiber reflectors mirrors. In this work, a conventional band erbium doped fiber amplifier is proposed with high gain and less noise figure by incorporating the two fiber bragg gratings (FBGs) for amplified spontaneous noise reinjection. Maximum ASE is emerged at 1565 nmfor the at -55 dBm carrier powers. Maximum gain is found out to be 48.16 dB with noise figure of 5.29 dBm.

Long-haul optical transmission link using low-noise phase-sensitive amplifiers

The capacity and reach of long-haul fiber optical communication systems is limited by in-line amplifier noise and fiber nonlinearities. Phase-sensitive amplifiers add 6 dB less noise than conventional phase-insensitive amplifiers, such as erbium-doped fiber amplifiers, and they can provide nonlinearity mitigation after each span. Realizing a long-haul transmission link with in-line phase-sensitive amplifiers providing simultaneous low-noise amplification and nonlinearity mitigation is challenging and to date no such transmission link has been demonstrated. Here, we demonstrate a multi-channel-compatible and modulation-format-independent long-haul transmission link with in-line phase-sensitive amplifiers. Compared to a link amplified by conventional erbium-doped fiber amplifiers, we demonstrate a reach improvement of 5.6 times at optimal launch powers with the phase-sensitively amplified link operating at a total accumulated nonlinear phase shift of 6.2 rad. The phase-sensitively amplified link transmits two data-carrying waves, thus occupying twice the bandwidth and propagating twice the total power compared to the phase-insensitively amplified link.

Effects of pump pulse extinction ratio in Brillouin optical time-domain analysis sensors.

We report on two previously unknown non-local effects that have been found to impair Brillouin optical time-domain analysis (BOTDA) sensors that deploy limited extinction ratio (ER) pump pulses. The first one originates in the increased depletion of the pedestal of the pump pulses by the amplified probe wave, which in turn entails a reduced amplification of the probe and a measurement distortion. The second effect is due to the interplay between the transient response of the erbium-doped fiber amplifiers (EDFA) that are normally deployed to amplify the pump and the pedestal of the pump pulses. The EDFA amplification modifies the pedestal that follows the pulses in such a way that it also leads to a distortion of the measured gain spectra after normalization. Both effects are shown to lead to non-local effects in the measurements that have similar characteristics to those induced by pump pulse depletion. In fact, the total depletion factor for calculations of the Brillouin frequency shift (BFS) error in BOTDA sensors is shown to be the addition of the depletion factors linked to the pump pulse as well as the pedestal. A theoretical model is developed to analyze both effects by numerical simulation. Furthermore, the effects are investigated experimentally in long-range BOTDA sensors. The pedestal depletion effect is shown to severely constrain the probe power as well as the minimum ER of the pulses that can be deployed in BOTDA sensors. For instance, it is shown that, in a long-range dual-probe BOTDA, an ER higher that 32-dB, which is above that provided by standard electro-optic modulators (EOM), is necessary to be able to deploy a probe power of -3 dBm, which is the theoretical limit for that type of sensors. Even more severe can be the limitation due to the depletion effect induced by the EDFA transient response. It is found that the impairments brought by this effect are independent of the probe power, hence setting an ultimate limit for the BOTDA sensor performance. Experimentally, a long-range BOTDA deploying a 26-dB ER EOM and a conventional EDFA is shown to exhibit a BFS error higher than 1 MHz even for very small probe power.

Performance comparison of enhanced Erbium–Zirconia–Yttria–Aluminum co-doped conventional erbium-doped fiber amplifiers

A new Erbium–Zirconia–Yttria–Aluminum co-doped fiber amplifier (Zr-EDFA) with improved gain and noise figure characteristics is successfully demonstrated using a newly developed Erbium–Zirconia–Yttria–Aluminum Co-Doped fiber (Zr-EDF) as the gain medium. The fiber consists of Er2O3-doped ZrO2 rich nano-crystalline particles and thus it has a high erbium doping concentration with absorption pump power around 80.0dB/m at 980nm. Compared to the conventional silica based Erbium-doped fiber amplifier (Si-EDFA), the gain of the proposed Zr-EDFA is more efficient especially at longer wavelength region. At input signal of −10dBm, a flat gain of 19.5dB is obtained for the single-pass Zr-EDFA with gain variation of less than 1dB within a wavelength region from 1530 to 1570nm. In double-pass configuration, the measured gain varies from 17.5dB to 21.3dB within the wavelength region from 1525 to 1565nm, where the noise figure is maintained at below 10dB. The double-pass Zr-EDFA gain is also maintained above 12dB within a wavelength region from 1520 to 1600nm. These results indicate that the Zr-EDFA can achieve even better flat-gain value and bandwidth as well as lower noise figure than the conventional Si-EDFA

Cost efficient amplifier placement and gain adjustment in all-Optical networks: A noise-minimizing approach

Erbium doped fiber amplifiers (EDFA) are known to be well suited for transparent optical networks due to their proper relative properties. Link amplifiers are responsible for adequately compensating fiber loss in optical links. However, amplified spontaneous emission (ASE) noise would degrade the optical signal to noise ratio (OSNR) which leads to degradation in quality of service (QoS). This paper aims at optimally determining the location and relative gain settings of the employed line amplifiers in order to minimize the total ASE noise power on each link. A non-linear optimization approach is developed. Then, two amplifier placement and gain adjustment algorithms called optimal EDFA placement (OEP) and Incremented-OEP are proposed. Numerical results in addition to simulations indicate the fact that the proposed schemes outperform the existing conventional EDFA placement (CEP) solution in terms of average ASE noise power and blocking rate.

Low-noise and high-gain Brillouin optical amplifier for narrowband active optical filtering based on a pump-to-signal optoelectronic tracking.

We implement and characterize an optical narrowband amplifier based on stimulated Brillouin scattering with pump-to-signal relative frequency fluctuations overcome thanks to an active pump tracking. We achieve a precise characterization of this amplifier in terms of gain and noise degradation (noise figure). The performances of this stable selective amplification are compared to those of a conventional erbium-doped fiber amplifier in order to highlight the interest of the Brillouin amplification solution for active narrow optical filtering with a bandpass of 10MHz. Thanks to the simple optoelectronic pump-to-signal tracking, the Brillouin active filter appears as a stable and reliable solution for narrowband optical processing in the coherent optical communication context and optical sensor applications.

Few-mode erbium-doped fiber amplifier design method based on the signal-pump overlap integral

Space-division multiplexing allows an increase of link capacity by using either multicore or single-core few-mode (FM) optical fibers. In the case of FM systems, each mode carries its own data stream and long-haul transmission can be hampered by the use of conventional erbium-doped fiber amplifiers (EDFAs), since because of distinct field profile configurations, each mode experiences a different value of optical gain. The role of the FM-EDFA designer, usually done by solving rate and propagation equations, is to define both the fiber cross-section and the pumping configuration to provide the best possible mode equalization of optical gain and noise figure. An optimization method is proposed here based on the definition of a figure of merit related to the equalization of the pump-mode signal overlap integral, significantly reducing computation time and allowing a multiobjective optimization approach. The results obtained were validated against the solution provided by the full set of rate and propagation equations and we conducted an FM-EDFA optimization case study. Our double-ring Er doping profile design requires a single 180-mW LP11 pump to provide a mean gain of 21.3 dB, within 0.6 dB of equalization for each of the four modes considered.

Wide-Range Variable Gain Fiber Amplifier With Erbium-Doped Fiber Switching

A variable gain erbium-doped fiber amplifier (EDFA) with a wide gain range and a small noise figure (NF) variation is analyzed numerically and demonstrated experimentally. The EDFA can change the total erbium-doped fiber length by selecting six combinations of three EDFs with optical switches (SWs). The numerical calculation of the NF and the pump power using the analytical model of an EDFA indicates that such a variable gain EDFA has an advantage over a conventional multi-stage EDFA in terms of NF variation and required pump power. These characteristics are demonstrated by constructing a variable gain EDFA that employs SWs and variable optical attenuators (VOAs) integrated on a silica-based planar lightwave circuit (PLC). The variable gain EDFA exhibits a smaller NF variation of 1.2 dB for the 24-dB variable gain range than conventional two- and four-stage EDFAs, which have NF variations of 12.6 and 2.0 dB, respectively, for the same variable gain range. The power consumption of these EDFAs is also discussed by comparing the operating electric power of the SWs and VOAs with that of the pump laser.

L-band automatic-gain-controlled erbium-doped fiber amplifier utilizing C-band backward-amplified spontaneous emission and electrical feedback monitor

A new L-band automatic-gain-controlled (AGC) erbium-doped fiber amplifier (EDFA) for dense wavelength-division-multiplexing transmission systems is presented, in which a single 1480 nm laser with an internal thermoelectric cooler is used as a primary pump for stable amplification. All C-band amplified spontaneous emission (ASE) is recycled by the secondary pump to enhance the gain efficiency. A fraction of the output signal is used as an electrical feedback monitor for the AGC to improve the gain-clamped (GC) flatness. Experimental results prove that the AGC EDFA has a gain flatness of better than 0.46 dB/40 nm, i.e., below 1.5%, and a higher gain of approximately 36.5 dB compared to that of approximately 35.3 dB for the conventional GC EDFA at -30 dBm input signal power. The best gain flatness of +/-0.25 dB can be achieved over the dynamic range greater than 20 dB. The dynamic range of noise figure is between 6.7 and 7.1. The 3 dB down bandwidth is more than 40 nm. Overall dynamics measurements for the AGC EDFA feedback stabilization have been carried out. The recorded corresponding rise time of 1.565 ms indicates that the system does not exhibit any overshoot of gain or ASE variation due to the signal at the beginning of the pulse.

Novel Gain Spectrum Control Method Employing Gain Clamping and Pump Power Adjustment in Thulium-Doped Fiber Amplifier

In this paper, we propose a novel method for controlling the gain spectrum of a thulium-doped fiber amplifier (TDFA) in the S-band. The conventional gain spectrum control method used for a silica erbium-doped fiber amplifier (EDFA) cannot be applied to TDFAs because of the complicated fluctuation of the TDFA gain spectrum. Our proposed method controls the gain spectrum by a combination of gain clamping and pump power adjustment. The algorithm for the method is as simple as that for the conventional EDFA gain spectrum control method. Furthermore, we describe a function for correcting the gain excursion generated by the incorporation of amplified spontaneous emission (ASE) at a signal monitoring photodiode (PD). We achieved a gain excursion of 0.35 dB against a total input signal power of 32 to 2 dBm.

Gain enhancement of L-band EDFA by using residual pump power in a three-stage configuration

This paper presents an idea of using residual pump power for implementation of low-noise and high-gain L-band erbium-doped fiber amplifiers (EDFAs). A single pump laser is employed to pump the first-stage EDFA, which serves as a low-noise preamplifier, in the proposed three-stage EDFA system. The residual pump power unabsorbed by the preamplifier is directed to pump the subsequent EDF. Experimental results show that gain enhancement of up to 8 dB with respect to conventional EDFAs can be achieved by using the proposed low-noise EDFA.

An EDFA$H_infty$Controller for Suppression of Power Excursions Due to Pilot Tones and Network Traffic

Conventional erbium-doped fiber amplifier (EDFA) control schemes lack a systematic design approach and do not consider the characteristics of input disturbances. We propose the application of H infin control to suppress cross-gain modulation effects due to pilot tones and network burst-switched traffic. A detailed design of the EDFA Hinfin controller is given, focused on input disturbance characteristics and desired performance measures. Simulation results under different types of disturbances show significant improvements in response time and power excursion reductions

A semiconductor nanocrystal PbSe quantum dot fiber amplifier

A novel kind of fiber amplifier——quantum dot doped fiber amplifier (QDFA) is presented. Using semiconductor nanocrystal PbSe as a dopant, the gain bandwidths of the PbSe-QDFA are simulated by solving the rate equation and the light propagation equation in a two-level system, applying a genetic algorithm combined with an “inversing method”. Comparing with conventional erbium-doped fiber amplifiers available, there is evidence to show that characteristics of the PbSe-QDFA are obviously advantageous in respect of bandwidth and noise, especially on long-waelength band. Furthermore, the ideal emission-absorption cross-sections of the quantum dot are determined by utilizing the genetic algorithm. Under such ideal cross-sections, the QDFA possesses with the performance of ultra-bandwidth and low noise figure near a quantum limit.

Gain Dynamics of 14&amp;lt;tex&amp;gt;$xx$&amp;lt;/tex&amp;gt;-nm-Pumped Thulium-Doped Fiber Amplifier

Upconversion pumping in the 14xx-nm range gives the thulium-doped fiber amplifier (TDFA) a 3-dB dynamic range of 15 dB, and transient power excursion much lower than the conventional erbium-doped fiber amplifier during dynamic wavelength add-drop, due to the energy transitions inherent to the Tm/sup 3+/ ion. For specific pumping scheme and operating conditions, gain increases with increasing signal input, a behavior significantly different from conventionally optical amplifiers. This phenomenon is studied experimentally and theoretically, and promises to provide insight for gain control algorithms for TDFAs under bursty traffic conditions in a metropolitan area network environment.

Interference-Based Micromechanical Spectral Equalizers

Dynamic gain equalization filters (DGEFs) are important for high-performance wavelength division multiplexed (WDM) communications. One of the first demonstrated DGEF used a micromechanical etalon filter array illuminated with free-space spectral demultiplexing optics. Here, we present subsequent research on etalon-based dynamic spectral filters, including vertical device structures which linearize and reduce the drive voltage from 70 to 40 V, and spatially-segmented etalons which allow channelized spectral equalization and further reduce drive voltage. We describe a prototype using a simplified cylindrical optomechanical package with a 104-nm broadband spectral response, 7.5-dB insertion loss and less than 16-V operation voltage. Finally, we show the use of a 42-nm bandwidth DGEF prototype with feedback stabilization to more than double the number of channels and operating bandwidth of a conventional Erbium-doped fiber amplifier while maintaining < 1-dB power uniformity.

Improvement of Gain and Noise Figure in Double-Pass&amp;lt;tex&amp;gt;$L$&amp;lt;/tex&amp;gt;-Band EDFA by Incorporating a Fiber Bragg Grating

An obvious improvement on both the gain and noise figure (NF) is demonstrated in the new double-pass L-band erbium-doped fiber amplifier (EDFA) with incorporating a fiber Bragg grating (FBG). Compared with the conventional L-band EDFAs, the gain is improved by about 6 dB in the new configuration for a 1580-nm signal with an input power of -30 dBm at 60 mW of 980-nm pump power. It is important that the NF is greatly reduced in the new configuration, as the FBG greatly compresses the backward amplified spontaneous emission. For the economical utility of pump power and erbium-doped fiber length, such a configuration may be a very competitive candidate in the practical applications of L-band EDFAs.

Field trial of the 40 Gb/s ETDM prototype over 219 km of the installed single‐mode fiber

AbstractWe demonstrate a field trial of the 40 Gb/s single‐channel electrical time‐division multiplexing (ETDM) prototype by using KT's installed single‐mode fiber (SMF). The prototype consists of a 40‐Gb/s optical transmitter, receiver, and four sets of optical amplifiers. In order to provide a practical and economical field trial, we adopt conventional erbium‐doped fiber amplifiers (EDFAs) and precise dispersion compensation technology. We obtain the power penalties of 0.5 dB for 10 Gb/s tributary channels after transmission of 219 km. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 304–306, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20123