L-band Erbium-doped Fiber Amplifier Research Articles

Simple and efficient L-band erbium-doped fiber amplifiers for WDM networks

The performance of L-band erbium-doped fiber amplifier (EDFA) of a simple structure with a fiber Bragg grating (FBG) was investigated. The injected C-band ASE by the FBG offers low-cost amplification and greatly improves the efficiency of the EDFA. There are 9 and 4 dB improvements with the FBG at 1587 nm, at low and high input, respectively. The flat gain of 18 dB, up to a total input of −5 dBm at 150 mW of 980 nm pump, is obtained over 30 nm with less than ±0.5 dB gain variations without any gain equalizer. The proposed EDFA provides a cost-effective solution for wavelength division multiplexing systems.

Demonstration of highly efficient flat-gain L-band erbium-doped fiber amplifiers by incorporating a fiber Bragg grating

A flat-gain output of 13.5 (15.5) dBm is obtained over 30 nm in the L-band with only a 97 (130)-mW pumping of a 980-nm laser diode. Such highly efficient flat-gain L-band erbium-doped fiber amplifiers are achieved by simply adding a regular fiber Bragg grating. An efficient and simple gain-clamping operation is also demonstrated.

Two-stage L-band EDFA with gain-clamped characteristics using partial gain-clamping

We theoretically and experimentally investigate the static and dynamic properties of two-stage L-band erbium-doped fiber amplifiers (EDFAs) that are partially gain-clamped. Partial (all-optical) gain-clamping is obtained by forming a fiber grating laser in either the first or the second stage of the two-stage EDFA. Although the amplifiers are only partially gain-clamped, results show that they exhibit good gain-clamped characteristics. Furthermore, the amplifier configuration in which the second stage is gain-clamped can have a very low noise figure and a small transient gain (power) excursion.

Modeling high-concentration L-band EDFA at high optical powers based on inversion function

High-concentration erbium-doped fibers used in L-band erbium-doped fiber amplifier (EDFA) are known to experience additional losses due to effects of energy transfer between Er/sup 3+/ ions and possibly quenchers (e.g., homogeneous and clustering-induced up-conversion, quenching, etc.). These interactions between Er/sup 3+/ ions make modeling of inversion dynamics in L-band EDFA more complicated. We present a modeling approach for high-concentration doped fiber based on lumping of all complex phenomena of energy transfer in EDFA into a function of two variables hereafter referred to as the inversion function. The inversion function is evaluated for high optical powers (which constitutes a typical situation for fiber amplifiers) using a cluster expansion and assuming that upconversion is the leading loss mechanism. The modeling results show a close agreement with the measurement data for various input power conditions and inversion levels.

A novel ASE self-pumping technique for gain-enhanced L-band erbium-doped fiber amplifiers

A novel method of enhancing gain in long-wavelength-band erbium-doped fiber amplifiers is described using the unwanted amplified spontaneous emission (ASE) self-pumping technique. The unwanted ASE from a first stage amplifier is recycled into a second stage amplifier as a secondary pump. Gain improvements in the vicinity of 0.4 and 1.2 dB are obtained in the wavelength range of 1570–1600 nm. This enables support for higher channels in multiwavelength systems with negligible noise figure penalties.

Gain clamping in L-band erbium-doped fiber amplifier using a fiber Bragg grating

A gain-clamping technique for the long wavelength band (L-band) erbium-doped fiber amplifier (EDFA) is presented. It uses a single fiber Bragg grating (FBG) on the input side of erbium-doped fiber (EDF) to inject a portion of backward conventional band (C-band) amplified spontaneous emission (ASE) back into the system. The use of a narrow-band (NB) FBG has shown a better performance in clamped-gain level and noise figure compared to a broad-band FBG. The amplifier gain for the NB FBG set up is clamped at 15.4 dB with a variation of less than 0.3 dB for an input power as high as 0 dBm.

Wavelength and power dependence of injected C-band laser on pump conversion efficiency of L-band EDFA

The effect of wavelength and power of an injected C-band laser on the pump conversion efficiency of a L-band erbium-doped fiber amplifier was studied via numerical simulation and experiment. In the studied C-band wavelength range of 1530-1560 nm, for higher injected power with longer wavelength, the backward output amplified spontaneous emission power is compressed more; but the residual laser power is greater due to the smaller emission coefficient at longer wavelength. Thus there is a best choice for injection wavelength and power. With an injection of -2 dBm at 1550 nm, 4.3 and 2.5 dB of gain enhancement for -12 and -2.6 dBm input at 1586 nm were achieved, respectively.

Feasibility of hybrid Raman/EDFA amplification in bidirectional optical transmission

The feasibility of hybrid optical amplification in an interleaved bidirectional architecture is studied. An optical repeater node is constructed using an L-band erbium-doped fiber amplifier and bidirectional Raman pumping to achieve a combined gain of 34 dB. Signal impairments associated with this architecture are identified and measured. Dense wavelength-division-multiplexing transmission of 40+40 25-GHz-spaced channels is demonstrated using the hybrid bidirectional amplifier over nonzero-dispersion-shifted fiber spans.

Comparative high power conversion efficiency ofC- plus L-band EDFA

A dual-band erbium-doped fibre amplifier (EDFA) with high power conversion efficiency is proposed and demonstrated. The EDFA covers both the C-band around 1.55 µm and the L-band around 1.58 µm. The same signal gain can be achieved with 42% less pump power and 47% shorter erbium-doped fibre length compared to alternative, conventional parallel type, dual-band EDFAs.

Amplification enhancement of L-band erbium-doped fiber amplifiers by reflection scheme

A reflection L-band erbium-doped fiber amplifier (EDFA), which can effectively suppress and completely exploit the backward C-band amplified spontaneous emission (ASE) with a feedback reflection loop, is presented in this paper. The mechanism of the backward ASE secondary pumping effect is experimentally investigated in detail. Our experimental results have shown that, for a given input pump power, compared to the end-pumped EDFA, the gain and output power of the reflection EDFA can be improved considerably without paying much noise penalty. When the EDFA operates with flattened gain spectra, the gain is improved by about 7 dB with an extra noise penalty of about 1.2 dB, where the saturation output power is increased by 2.5–3.2 dB and which may also be made independent of the input signal power.

Gain tilt control of L-band erbium-doped fiber amplifier by using a 1550-nm band light injection

In this letter, we demonstrate a new method to control gain tilt in long wavelength erbium-doped fiber amplifiers by using an external light source in 1550-nm range (called control source). The wavelength or its input power is adjusted to reduce gain tilt. The tilted gain is diminished from 7.18 to 0.07 dB by adjusting control source wavelength, and from 9.95 to 0.62 dB by adjusting control source input power in a 1570-1590-nm signal wavelength range.

Serial topology of wide-band erbium-doped fiber amplifier for WDM applications

We analyze the recently proposed serial topology of a wide-band erbium-doped fiber amplifier (EDFA) covering both the C- and L-bands and compare it with the parallel configuration of C-band and L-band amplifiers. The analysis is based on an application of a comprehensive large-signal numerical model, which takes into consideration propagation of wavelength-division multiplexing (WDM) signals, bidirectional pump, and both the downstream and upstream ASE power spectral components. We have found that in the multiwavelength regime the new topology can provide output power of 3 dBm/channel for 32 C-band and 40 L-band, 0.8-nm-spaced signals with reasonable pump powers to the first and the second stage. In comparison with the usual parallel configuration of C-band and L-band EDFAs, this topology saves about 20% of overall pump power, 10% of the necessary length of erbium-doped fiber (EDF) and achieves lower noise figure for L-band signals.

Optimal design of optically gain-clamped L-band erbium-doped fiber amplifier

We theoretically investigate the optimal design of optically gain-clamped (GC) L-band (1570–1610 nm) erbium-doped fiber amplifier (EDFA), in order to achieve constant gain with minimum gain variation in the presence of dynamic input power variation or add/drop of optical channels, in terms of single- and multiple-channel schemes. The lasing-wavelength channel at either 1565 or 1610 nm for optically gain-clamping operation of such L-band GC-EDFAs in terms of different clamping-loop attenuation are examined. In addition, the characteristic measurements of such L-band GC-EDFAs using either a saturation tone or multiple channels are compared. From good gain-clamping capability point of view, the 1610-nm lasing channel with 15-dB loop attenuation is the best selection to offer large gain-clamping dynamic ranges of both input channel power and channel count with good channel gain variation and fairly low noise figure characteristics.

Reducing pulsewidth broadening in L-band EDFAs by use of a new L-band EDF

Due to a small effective area of erbium-doped fiber (EDF), a short pulse will be broadened because of self-phase modulation when it is amplified in an L-band EDF amplifier (EDFA); hence, it is necessary to develop a new EDF with large Er/sup 3+/ concentration to reduce the EDF length and a large effective area to reduce the nonlinear effect in the L-band EDFA. In this letter, it will be demonstrated that the pulsewidth can be maintained when a short pulse is amplified in an L-band EDFA consisting of a new L-band EDF.

A study on the performance of L-band EDFAs under different pumping configurations

In this letter, we investigate and compare theoretically the performance of an optimized L-band erbium doped fiber amplifier when an L-band erbium doped fiber (EDF) or an optimized C-band EDF, is used separately as an ASE (amplified spontaneous emission) pump source. We show that the gain per unit length increases with increase in cut-off wavelength independent of the numerical aperture (NA) of the EDF; the pump efficiency peaks in the region of cut-off wavelength between 1075 and 1125 nm, the exact value of which depends upon the level of inversion of the EDF. It is also observed that the pump efficiency as well as the gain per unit length increase with increase in level of inversion for a given cut-off wavelength. The pump efficiency as well as the ASE power per unit length are better for the case when a complete L-band optimized amplifier is used than when an optimized C-band amplifier is used as a pump source to amplify an L-band signal propagating in a cascaded L-band optimized amplifier. Also the gain achieved is much higher if the signal is fed into the entire amplifier with the pump, rather than at an intermediate point.

L-band erbium-doped fiber amplifier incorporating an inline fiber grating laser

Wide-band erbium-doped fiber amplifiers (EDFAs) having an inherently flat gain spectrum in the long-wavelength-band (L-band) between 1570 nm and 1600 nm have recently been realized. The L-band amplification has been achieved by simply using a longer length of EDF than in the conventional-wavelength-band (C-band) EDFAs. In the paper, we investigate the improvement of the gain flatness in an L-band EDFA co-pumped with the high-power pump light at 1.48 /spl mu/m and the medium-power auxiliary pump light at 1.55-1.565 /spl mu/m. We also propose a novel L-band EDFA incorporating an inline fiber grating laser (FGL) operating at the auxiliary pump wavelength, and demonstrate that the proposed EDFA has better gain flatness as well as the gain clamping characteristics.

Long-wavelength-band Er/sup 3+/-doped fiber amplifier incorporating a ring-laser as a seed signal generator

A novel dual-stage architecture for long-wavelength-band (L-band) erbium-doped fiber amplifier, which incorporates a gain-clamped amplifier based on a ring-laser feedback as a seed signal generator in the first stage is described. This technique has elevated the intensity of a short-wavelength amplified spontaneous emission (ASE) by 29%, from 11.3 mW of ASE power to 14.6 mW with a feedback lasing at 1560 nm. This strong laser then improves the L-band gain enormously, as large as 17.1 dB and noise figures are lower than 4.8 dB for the entire signal range in the flat-gain operation. The seeding signal reduces pump-to-ASE losses in the second stage to 38% compared to a conventional amplifier without feedback. Noise figure penalties are negligible due to efficient low-noise characteristics in the first stage. The proposed amplifier provides 25 dB gain for 50 wavelength-division-multiplexed signals at -30 dBm/ch with gain flatness less than 1.1 dB with only 980 nm pumping.

Amplified spontaneous emission in cladding-pumped L-band erbium-doped fiber amplifiers

Propagation of amplified spontaneous emission (ASE) in cladding-pumped long-wavelength-band erbium-doped fiber amplifiers (EDFAs) is analyzed numerically. Forward and backward ASE power dependence on cladding area is analyzed for both pumping directions. ASE power propagating counterdirectionally to the pump is found to experience strong dependence on the cladding area. Increasing the cladding area results in more uniform pump distribution along the EDF, preventing short-wavelength gain and ASE buildup. Quantum conversion efficiency in cladding-pumped L-band EDFAs is discussed.

Novel, gain-flattenedL-band EDFA with ASE utilization with >40 nm 3 dB bandwidth

A simple gain-flattened L-band erbium-doped fiber amplifier (EDFA) is demonstrated, utilizing unwanted C-band amplified spontaneous emission (ASE) to enhance L-band gain performance. An L-band flat gain range of 50 nm (1560–1610 nm) is achieved for use in wavelength-division multiplexing (WDM) transmission systems. Gain flatness with a 3 dB gain discrepancy is obtained through manipulation of the pump power. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 28: 399–402, 2001.

The design of L-band EDFA for multiwavelength applications

An accurate model for the erbium-doped fibre amplifier (EDFA) has been used to study the design criteria of single-stage (SS) and double-stage (DS) L-band EDFA for multiwavelength applications. The effects of erbium-doped fibre (EDF) length, pump configuration and pump wavelength have been studied. We show that a flat gain spectrum can be achieved in the range from 1550 to 1610 nm when the EDF length, pump power and pump configuration are appropriately chosen. Special care must be taken when selecting the EDF length. Noise figure improvement of the DS amplifier is demonstrated. The lowest noise figure was predicted for a DS amplifier with both stages co-directionally pumped at 980 nm. Transmission of 32 wavelength division multiplexed (WDM) channels with input power of -13 dB m/channel and interchannel spacing of 0.8 nm over a cascade of five L-band EDFAs has been investigated. If the WDM signal was appropriately placed, the signal level deviation between the best and the worst channel at the output of the cascade was 2.2 dB, without any gain equalizing filters or signal pre-emphasis.