Multimode Erbium-doped Fiber Amplifier Research Articles

Multimode erbium-doped fiber amplifier based on double-clad GeO2-doped photonic crystal fiber supporting 38 orbital angular momentum modes

Multimode erbium-doped fiber amplifier based on double-clad GeO₂-doped photonic crystal fiber supporting 38 orbital angular momentum modes

Successive Interference Cancellation on Frequency-Selective Channels With Mode-Dependent Gain

In ultra-long-haul optical communication systems, polarization-dependent gain from single-mode semiconductor optical amplifiers or mode-dependent gain from multi-mode erbium-doped fiber amplifiers causes a channel’s achievable information rate (AIR) using linear minimum-mean-square error (MMSE) detection to become substantially lower than the capacity of optimal maximum likelihood detection owing to loss of orthogonality between modes. However, such capacity loss can be mitigated using techniques that retain reasonable complexity, such as successive interference cancellation (SIC). In wireless systems, multicarrier transmission with many subcarriers transforms the frequency-selective channel into a set of uncoupled memoryless subchannels, and it is possible to obtain good performance using SIC on each subchannel independently. Multicarrier transmission in optical fibers, however, is susceptible to performance loss caused by Kerr nonlinearity. Therefore, we study methods for applying SIC on frequency-selective optical fiber channels using single-carrier transmission. We compare the theoretical performance of MMSE and SIC equalizers on frequency-selective optical fiber channels operating at 64 Gbaud with transmission distances up to 15,000 km and evaluate the penalties of SIC implementation. We consider single-mode fiber links with random artificial polarization-mode dispersion inserted along the link to enhance frequency diversity, as well as multi-core fiber links supporting 14 spatial and polarization modes. We show that SIC can increase outage capacity by 19%, but the AIR increase is reduced by almost half if error correction coding is not performed across modes. We confirm that SIC can adapt to fast channel perturbations with only a 3% decrease in AIR.

Power efficient Space Division Multiplexing–Wavelength Division Multiplexing system using multimode EDFA with elevated refractive index profile

SummarySpace division multiplexing (SDM) is an endowment technology to increase the collective bandwidth of multimode transmission in wavelength division multiplexing (WDM) system. In this paper, four wavelength signals from 229.6 to 232.6 THz are transmitted. For each wavelength, three linearly polarized (LP) modes are multiplexed using SDM. These 12 LP modes are transmitted through four parallel Multimode Step Index (MSI) fibers and received by four optical network units (ONUs). A multimode erbium doped fiber amplifier (MMEDFA) with elevated refractive index profile (ERIP) is used as preamplifier to this SDM–WDM system. This ERIP is complying with ITU‐T G.651.1 standard fiber in dispersion performance. The pumping power of 10 mW is adequate for this MMEDFA which is very low and cost effective. LP modes are transmitted, and performance of proposed transmission system is evaluated in terms of spatial electric fields, pumping power requirement, output optical power, and bit error rate (BER).

Wavelength division multiplexing transmission using multimode erbium doped fiber amplifier with elevated refractive index profile

An Idea of importing a new ERIP at multimode EDFA is proposed in this paper. This MMEDFA is used for a WDM transmission system and its performance is observed. The 16 signals with seven linearly polarized modes are amplified by this MMEDFA. ERIP is designed by OptiFiber simulation software and performance of this MMEDFA in WDM system is simulated using OptiSystem software. A WDM transmission of 16 signals by using single stage amplification by MMEDFA with maximum gain is not reported in previous works. The performance of this WDM system has been analyzed for the propagating distances up to 42.15 km.

Azimuthal dependence of modal gain and its impact on gain equalization in multimode erbium-doped fiber amplifiers

Azimuthal-dependent modal gain for spatially degenerate signal modes in multimode erbium-doped fiber amplifiers (MEDFAs) has been numerically investigated by integrating the differential power rate equations dealing with multiple spatial modes. Results show that if the azimuthal mode numbers in signal modes are different from that in the pump modal, gain is nearly independent of the azimuthal orientations of the pump intensity pattern. High differential modal gain (DMG) between spatially degenerate signal modes is produced if signal and pump shares the same azimuthal mode number when modal gain varies periodically with the pump azimuthal angle. Such azimuthal dependence of modal gain is caused by the transverse azimuthal dependence of population inversion of erbium ions created by pump modes. Adjusting the power and azimuth of the pump mode has also been examined to reduce azimuthal-induced DMG and several optimal parameters for achieving gain equalization have been obtained for an MEDFA supporting the two lowest LP signal mode groups. Our results can be employed to equalize mode-dependent gain in MEDFAs.

Adaptive Modal Gain Equalization Techniques in Multi-Mode Erbium-Doped Fiber Amplifiers

We demonstrate two adaptive methods to equalize mode-dependent gain (MDG) in multi-mode erbium-doped fiber amplifiers (MM-EDFAs). The first method uses a spatial light modulator (SLM) in line with the amplifier pump beam to control the modal powers in the pump. The second method uses an SLM immediately after the MM-EDFA to directly control the modal powers in the signal. We compare the performance of the two methods applied to a MM-EDFA with a uniform erbium doping profile, supporting 12 signal modes in two polarizations. We show that root-mean-squared MDGs lower than 0.5 and 1 dB can be achieved in systems having frequency diversity orders of 1 and 100, respectively, while causing less than a 2.6-dB loss of mode-averaged gain.

Single DPLL Joint Carrier Phase Compensation for Few-Mode Fiber Transmission

A carrier phase estimation and compensation algorithm using a digital phase locked loop is proposed which exploits the common-mode impairment from the shared local oscillator at the receiver side in a few-mode fiber transmission system. We verify that the proposed algorithm is more tolerant to phasemismatches than earlier work. The carrier phase estimation (CPE) scheme is evaluated for a 3 × 112 Gbit/s dual polarization quadrature phase shift keying mode division multiplexed transmission over 80 km including an in-line multimode erbium doped fiber amplifier. The digital signal processing computational complexity is reduced in comparison to a traditional CPE stage. In addition, the proposed scheme is shown to perform similarly with respect to the 3.8 × 10-3forward error correcting limit optical signal to noise ratio tolerance of the traditional CPE scheme.

Optical Amplifier With Rotationally Symmetrical Pump Modes for Enhanced Mode Multiplexing

Multimode erbium-doped fiber amplifiers are promising candidates for the realization of cost- and energy-efficient long-haul transmission for mode-division multiplexing. Mode-dependent gain in such amplifiers is a potential source of signal quality degradation and should be avoided. We show by numerical simulations that gain values and noise figures for the signal modes exhibit an angular dependence if the amplifier is pumped with the LP21 mode. In order to avoid this angular dependence, we propose to use pump modes with a rotationally symmetric intensity distribution, such as the TE01 mode. Our simulation results show that pumping with this mode completely removes the angular dependence and optimizes gain and noise figure values for the signal modes.

Design of Transmission Fibers and Doped Fiber Amplifiers for Mode-Division Multiplexing

Transmission fibers and erbium-doped fiber amplifiers (EDFAs) for 12 signal modes (including spatial and polarization degrees of freedom) are studied. Modal fields are computed numerically and their effective areas, group delays (GDs), and chromatic dispersion coefficients are determined. Multimode rate equations are solved numerically to calculate mode-dependent gains (MDGs) and pump power requirements in multimode EDFAs. Results are compared for various numerical apertures (NAs), index profiles, and doping profiles. Graded-index depressed-cladding fibers offer an attractive combination of low GD spread in transmission fibers (583 ps/km rms with 0.15 NA) and low MDG in EDFAs (0.14 dB rms at 25-dB mode averaged gain with 0.15 NA). Optimized erbium doping profiles are comprised of a uniform cylindrical region plus an extra annulus.

Accurate modal gain control in a multimode erbium doped fiber amplifier incorporating ring doping and a simple LP_01 pump configuration

We experimentally validate a numerical model to study multimode erbium-doped fiber amplifiers (MM-EDFAs). Using this model, we demonstrate the improved performance achievable in a step index MM-EDFA incorporating a localized erbium doped ring and its potential for Space Division Multiplexed (SDM) transmission. Using a pure LP₀₁ pump beam, which greatly simplifies amplifier construction, accurate modal gain control can be achieved by carefully tuning the thickness of the ring-doped layer in the active fiber and the pump power. In particular, by optimizing the erbium-ring-doped structure and the length of active fiber used, over 20dB gain for both LP₀₁ and LP₁₁ signals with a maximum gain difference of around 2 dB across the C band are predicted for a pure LP₀₁ pump beam delivering 250 mW power at 980 nm.

Multimode fiber amplifier with tunable modal gain using a reconfigurable multimode pump

We propose a method for controlling modal gain in a multimode Erbium-doped fiber amplifier (MM-EDFA) by tuning the mode content of a multimode pump. By adjusting the powers and orientation of input pump modes, modal dependent gain can be tuned over a large dynamic range. Performance impacts due to excitation of undesired pump modes, mode coupling and macro-bending loss within the erbium-doped fiber are also investigated. The MM-EDFA may potentially be a key element for long haul mode-division multiplexed transmission.

111 kW (0.5 mJ) pulse amplification at 1.5 μm using a gated cascade of three erbium-doped fiber amplifiers

The generation of high peak power pulses by amplification of the output from a distributed feedback diode laser is demonstrated using a cascade of three erbium-doped fiber amplifiers (EDFAs) separated by an acousto-optic gate. The optimized amplifier chain consisted of two high efficiency single-mode EDFAs pumped with 40 mW at 980 nm, followed by a multimode EDFA pumped with 1.5 W at 978 nm. At low repetition rates, peak output powers of 111 kW and energies of 0.5 mJ at 1.534 μm were obtained.