Gain-flattened Fiber Research Articles

Compact and flat-gain fiber optical amplifier with Hafnia-Bismuth-Erbium co-doped fiber

For the first time, we demonstrated a compact Erbium-doped fiber amplifier (EDFA) using a newly developed Hafnia Bismuth Erbium co-doped fiber (HBEDF) as a gain medium. The HBEDF was fabricated using a modified chemical vapor deposition process in conjunction with solution doping technique. The fiber has high doping levels of Erbium ion of 12,500 wt ppm through incorporation of Hafnium and Bismuth ions, which prevents the clustering effect. At the input signal power of −10 dBm, a flat gain of 10.9 dB is obtained from the wavelength region of 1525 to 1565 nm with a gain variation of less than ± 0.5 dB. The noise figure is maintained below 4.4 dB at the flat-gain region. The proposed amplifier has the potential applications in dense wavelength division multiplexing communication system due to its simplicity and compact design.

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.

全光增益控制的增益平坦型高功率光纤放大器

全光增益控制的增益平坦型高功率光纤放大器

Tailoring of Raman gain bandwidth of tellurite glasses for designing gain-flattened fiber Raman amplifiers

The issue of widening the Raman spectral bandwidth of tellurite glasses while maintaining higher scattering intensity is addressed. Raman spectral bandwidths of tellurite glasses are widened by using a single Raman active component of suitable concentration in appropriate base glasses. It was observed that the MoO6 octahedra, due to their high octahedral distortion, have high Raman polarizability compared to WO6, NbO6, and TaO6 octahedra and PO4 tetrahedra. This high Raman polarizability enabled broadening of the spectral width up to ~350 cm−1 while maintaining high Raman scattering intensities. Although similar bandwidths could be achieved using the combined generation of WO6 octahedra and PO4 tetrahedra, the resultant Raman scattering intensity of such glasses is only half of that, which could be achievable using MoO6. It is shown that the simplest tellurite glass showing wide spectral broadening is a quaternary system comprising a network modifier (BaO or Bi2O3) and two Raman oscillators (NbO6 and MoO6 octahedra).

Design of multistage gain-flattened fiber Raman amplifiers

This paper presents a design approach for multistage gain-flattened fiber Raman amplifiers (FRAs) utilizing the multiwavelength-pumping scheme. To the authors' best knowledge, it is the first time that Raman amplifiers of more than one stage are considered in the design process so as to optimize multistage amplifier performance simultaneously. It is shown both theoretically and experimentally that optical power path integrals among several stages can, in principle, be arbitrarily redistributed while maintaining its gain performance, as long as the consolidated sums at different pump wavelengths are unaltered. The overall gain spectrum of a multistage FRA is thus very close to the cumulative spectrum of chained identical single-stage amplifiers with span numbers equal to its stages. However, the traditional prerequisite to minimize gain flatness in every stage is no longer required. It provides flexibilities to take full advantage of pump lasers with moderate launched powers and allows the reduction of the number of pump lasers and/or wavelengths in most stages. By arranging small positive net gain to the first stages and enhancing it at shorter signal wavelengths, significant reduction and flattening of total noise figure (NF) is achieved even if a pure backward pumping scheme is utilized. Finally, various pumping configurations for Raman amplifiers with hybrid dispersion-compensating fiber (DCF) and standard single-mode fiber (SMF) are discussed, with the objective of realizing flattened gain and noise performance simultaneously without using forward pumps.

Novel methods for fast fiber Raman amplifier pump configuration

Traditional heuristic algorithms are time consuming in searching the pump configuration to obtain a wide-band flat-gain fiber Raman amplifier (FRA). In this paper, two methods are proposed to deal with this problem. One is called combined generic algorithm (CGA). By using the quadratic programming algorithm instead of generic algorithm (GA) to solve the pump integral, the search space dimension is reduced by half, and obviously, this method will converge faster. Based on a linear time-invariant (LTI) system model, another method is also presented under the assumption that the effective area of fiber is weakly dependent on stokes wave. Then, the amplifier gain can be viewed as the output of a special LTI system, which characterizes the normalized Raman gain profile as its unit impulse response and the pump power integral impulse sequence in frequency domain as its input. By using the nonnegative constraint least-square error (LSE) and clustering technique, we will solve this problem quickly. Numerical simulations shows that the total computation time will be halved at the cost of a slight deterioration in gain flatness.

Gain-flattening of fiber Raman amplifiers using non-linear pump spectral broadening

We demonstrate experimentally that gain flattening of single-pump fiber Raman amplifiers is possible by use of non-linear broadening of the pump spectrum. In our experiments, pump broadening of a continuous-wave Raman fiber laser tuned at 1455 nm is achieved by propagation in a non-zero dispersion-shifted fiber with small anomalous dispersion at the pump wavelength. The broadened pump spectrum can reach a full width at half maximum of as much as 28 nm. Our results demonstrate that an acceptable flatness of the Raman gain spectrum can be obtained in the 1560–1640 nm region while avoiding pump-to pump non-linear interactions. On the dark side, our measurements show that this configuration introduces more noise than the conventional, non-broadened pump configuration since a non-negligible fraction of the broadened pump power falls within the band of amplification. However, we believe that further work and optimization should demonstrate that gain-flattened fiber Raman amplifiers using a single pump can be achieved over the C (1525–1565 nm) and L (1565–1625 nm) bands.

Automatic real-time control for gain-flattened fiber Raman amplifiers

An automatic control algorithm for flattening the gain of a fiber Raman amplifier is derived from the Raman scattering equations. A pseudo-inverse gain matrix is introduced to adjust the powers of the pump lasers. The algorithm is simple, fast, effective, robust and insensitive to the length and type of the fiber. It is demonstrated experimentally that the gain flattening for Raman amplifiers comprising various types and lengths of fiber and with different target gains can be achieved automatically with this algorithm. The algorithm converges for both small and large input signal. Flattened Raman gain with a fluctuation less than 0.40 dB over a 50-nm bandwidth for a 50-km SMF or less than 0.20 dB over a 40-nm bandwidth for a 6.6-km dispersion compensated fiber is realized in the experiment.

Flat-Gain Fiber Raman Amplifiers Using Equally Spaced Pumps

This paper analyzes the gain flatness of multiwavelength pumped fiber Raman amplifiers using equally spaced pumps with both a fixed and an optimized central pump wavelength. The signal gain ripple using equally spaced pumps is compared with the case in which the pump wavelengths are allowed to vary for two, four, and eight pumps with 20-, 40-, and 80-nm signal bandwidths. The paper shows that using an optimized central pump wavelength with equal pump spacing simplifies system design, while the gain ripple is no more than 0.4 dB larger than the ripple obtained when the pump wavelengths are optimized for the cases considered.

Gain-flattened fiber Raman amplifiers with nonlinearity-broadened pumps.

Gain flattening of an E-band (1360-1460-nm) fiber Raman amplifier was achieved by pump spectral broadening to a 16.3-nm linewidth by use of nonlinearity in a 6.2-km standard fiber. With the broadened pump, the characteristic Raman gain ripple was removed and the 3-dB gain bandwidth was increased by 10.6 nm relative to the nonbroadened pump case. The experimental results agreed well with a gain profile simulation. The use of a 100-m holey fiber for pump broadening was also investigated near 1.56 microm for U-band (1625-1675-nm) Raman amplifiers. Much less broadening was observed, which is believed to be a result of less four-wave mixing.

Device for concatenation of phase-shifted long-period grating and its application as gain-flattening fiber filter

The transmission characteristics of phase-shifted long-period gratings (LPGs) are simulated theoretically using coupled-mode theory and the fundamental-matrix method. A phase-shifted LPG device cascaded with another uniform LPG can be used to flatten the gain spectrum of an erbium-doped fiber amplifier (EDFA) with three gain peaks. The results of all simulations have shown that a broadband amplifier with a 0.7-dB peak-to-peak gain variation over 36 nm can be realized practically. Using our designed and fabricated device, the experimental results show that the 3-dB bandwidth of the flattened EDFA is increased from 18 to 46 nm for an unequalized spectrum. The gain ripple over that bandwidth is reduced to approximately 0.9 dB. The improvement by a factor of 2 to 3 is realized in the sprectral performance. Such a gain-flattening fiber filter is indeed plausible and has a practical application in dense wavelength-division multiplexed (DWDM) telecommunication systems.

Gain-flattened fiber amplifier from 1560 to 1580 nm wavelengths using an erbium-doped fiber amplifier

A simple gain-flattened L-band erbium-doped fiber amplifier (EDFA) is demonstrated. An L-band flat gain range of 20 nm (1560–1580 nm) is achieved for use in wavelength-division multiplexing (WDM) transmission systems. Gain flatness with a 1 dB gain discrepancy is obtained through manipulation of the pump power, and no additional devices (gain equalizer, attenuator, fiber-Bragg grating) are required. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 221–223, 2000.