Gain Clamping Research Articles

Gain control in double-pass L-band EDFA using a ring resonator and two-stage configuration

A gain-clamped double-pass long wavelength band erbium-doped fiber amplifier with high clamped-gain and low noise figure is demonstrated using a ring laser. The optical circulator is used at output end of the amplifier to retro-pass the test signal back into the system for enhanced gain. A length of forward pumped erbium-doped fiber is incorporated in front of the double-pass amplifier to achieve a low noise figure. The gain clamping is achieved by routing the backward amplified spontaneous emission into the feedback loop via optical circulator and C/L-band wavelength selective coupler to create a ring laser, which operates outside the L-band region. The gain is clamped at 10.6 dB for all input signal powers from –40 dBm to –4 dBm with a gain variation of less than ±0.4 dB, when the variable optical attenuator (VOA) is set at 0 dB. The clamped-gain level can be tuned from 10.6 to 21.6 dB by varying the VOA settings from 0 to 12 dB. The corresponding noise figure varies from 9.1 to 5.2 dB.

Gain-clamped thulium-doped fibre amplifier with single pump at 1050 nm

The large homogeneous bandwidth of a thulium-doped fibre amplifier makes it suitable for optical gain clamping. This has been demonstrated experimentally. Gain variation of 1.2 dB for 15 dB input dynamic range has been achieved, with less than 1 dB gain ripple over 20 nm, and no noise figure degradation, while pumped at 1050 nm.

Transient effects in gain-clamped discrete Raman amplifier cascades

This letter describes the dynamic characteristics of all-optically gain clamped discrete Raman amplifier chains. Amplifier cascades are analyzed under channels add/drop conditions in large bandwidth WDM metro-core applications. Numerical results show that the long Raman fiber length does not allow instantaneous gain clamping giving rise to wide power oscillations in long Raman amplifier chains. A possible way to limit this detrimental effect is suggested and numerically demonstrated.

Band Gain-Clamped Erbium-Doped Fiber Amplifier by Using Optical Feedback Method

We have proposed and experimentally demonstrated an S band gain-clamped erbium-doped fiber amplifier, which provides an operation range from 1480 to 1520 nm by using an optical feedback method. The behavior and performance of gain clamping in S band have also been investigated experimentally under different operation conditions.

An efficient and low noise Gain-Clamped Double-Pass L-Band EDFA

A highly efficient and low noise gain-clamped long-wavelength-band erbium-doped fiber amplifier (L-band EDFA) is demonstrated using a ring laser in double-pass system. The broadband fiber Bragg grating (FBG) operating at L-band region is used to retro-pass the test signal into the system for enhanced gain. A length of forward pumped EDF is incorporated in front of the double-pass amplifier to achieve a low noise figure. The gain clamping is achieved by routing the backward ASE into the feedback loop to create ring laser. The gain is clamped at 18.6dB from -40 to -8dBm with gain variation of less than ±0.1dB and a noise figure of less than 6dB.

All-Optical Gain Clamped Double-Pass L-Band EDFA Based on Partial Reflection of ASE

A new gain clamping scheme in double-pass L-band erbium-doped fiber amplifier (EDFA) based on partial reflection of amplified spontaneous emission (ASE) into the EDFA is demonstrated using a narrowband fiber Bragg grating as an ASE reflector. The proposed amplifier achieves a good gain clamping characteristic up to -12dBm of input signal power with gain variation of less than 0.5dB from a clamped gain of 22.0dB. The noise figure within the gain-clamping region is maintained below 5.0dB. The low noise figure is achieved since the proposed amplifier is not based on lasing mechanism. The proposed amplifier is also expected to be free from the relaxation oscillation problem.

On crosstalk and noise in an optical amplifier with gain clamping by vertical laser field

We have calculated the transient behavior and noise figure of a semiconductor optical amplifier (SOA) with the gain clamped by a vertical cavity laser (VCL). The characteristic behavior of the more conventional gain-clamped SOAs and SOAs with no gain-clamping is also studied and compared with the vertically gain-clamped amplifier. The calculations are based on a numerical stochastic rate equation model including several forward- and backward-propagating channels that are coupled to the vertical laser field through the active medium. The noise model takes into account the input noise, randomly amplified spontaneous emission, and random gain. Numerical simulations have been carried out to study the relaxation oscillations, crosstalk, and noise in a system with a strong input signal switched on and off while observing the output signals, VCL photon density, and carrier density. Results show that the VCL field captures most of the disturbances, in agreement with available experimental data.

Low-noise intelligent cladding-pumped L-band EDFA

We present results on a low-cost cladding-pumped L-band amplifier based on side pumping (GTWave) fiber technology and pumped by a single 980-nm multimode diode. We show that simultaneous noise reduction and transient suppression can be achieved by using gain clamping by a seed signal (/spl lambda/=1564 nm). In the gain-clamping regime, the amplifier exhibits 30-dB gain over 1570-1605-nm spectral band with noise figure below 7 dB. The noise figure can be further reduced to below 5 dB by utilizing a low power single-mode pump at 980 nm. The erbium-doped fiber amplifier is relatively insensitive to input signal variations with power excursions below 0.15 dB for a 10-dB channel add-drop.

Effect of injection of C-band ASE on L-band erbium-doped fiber amplifier

The effect of injecting conventional band (C-band) amplified spontaneous emission on the performance of long-wavelength band erbium-doped fiber amplifier (L-band EDFA) is demonstrated. It uses a circulator and broadband fiber Bragg grating (FBG) to route C-band ASE from a C-band EDFA. Injection of a small amount of ASE (attenuation of 20 dB or above) improves the small signal gain with a negligible noise figure penalty compared to that of an amplifier without the ASE injection. A maximum gain improvement of 3.5 dB is obtained at an attenuation of 20 dB. At very large amounts of ASE injection (attenuation of 0 dB), the gain of the amplifier is clamped at 15.2 dB from −40 to −10 dBm with a gain variation of less than 0.3 dB. The saturation power is also increased from −8 dBm (for without ASE injection) to 2 dBm (VOA=0 dB) with a slight noise figure penalty. These results show that the ASE injection technique can be used either for gain improvement or for gain clamping in L-band EDFA.

Gain-clamping in two-stage L-band EDFA using an unwanted backward ase from second stage

A gain clamping technique for the long wavelength band erbium-doped fiber amplifier (L-band EDFA) is presented. It uses two circulators and a broad band fiber Bragg grating to route wasted backward C-band ASE from the second stage and launch it back into the input end of the first stage of a two-stage amplifier. The two-stage L-band EDFA has shown a small signal gain improvement of 5.7 dB compared to a single-stage amplifier with a slight noise figure degradation. By utilizing the wasted backward ASE, a L-band gain-clamped EDFA with high gain can be realized. Compared to the unclamped case, this gain-clamping technique is effective in reducing the total gain variation as small as 0.3 dB .

Gain clamped L‐band EDFA using a fiber Bragg grating in two stage configuration

AbstractA gain clamping technique for the long‐wavelength‐band erbium‐doped fiber amplifier (L‐band EDFA) is presented. It uses two circulators and a fiber Bragg grating (FBG) to route a backward amplified spontaneous emission (ASE) from a second‐stage amplifier and launch it back into the first stage. The use of a broadband (BB) FBG has shown a better gain clamping effect, compared to a narrowband (NB) FBG. The amplifier gain for the BB FBG set up is clamped at 15.0 dB with a gain variation of less than 0.1 dB for an input power as high as −5 dBm. The use of a BB FBG has also flattened the gain spectrum. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 265–266, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10889

L-band erbium-doped fibre amplifier with clamped- and flattened-gain using FBG

A gain clamped long wavelength band erbium-doped fibre amplifier (L-band EDFA) based on a ring laser cavity is demonstrated using a fibre Bragg grating (FBG) at the output end of the amplifier. This new design provides a good gain clamping as well as a gain flattening. The gain is clamped at 16.9 dB with gain variation of less than 0.1 dB from input signal power of −40 to −18 dBm by setting the VOA=5 dB. Also, the amplifier has the flattest gain spectrum at VOA=5. The gain variation is less than 1.0 dB within the wavelength range from 1570 to 1600 nm. This gain clamped amplifier also can support a 12 channel WDM system.

Gain-clamped semiconductor optical amplifier based on compensating light generated from amplified spontaneous emission

A gain-clamped semiconductor optical amplifier (SOA) scheme based on automatic power control of a compensating light generated from amplified spontaneous emission by a reflector is proposed. Experimental demonstrations using an SOA with a fibre Bragg grating at the input fibre show the proposed amplifier has a low noise figure as well as good gain clamping characteristics.

Density clamping and longitudinal spatial hole burning in a gain-clamped semiconductor optical amplifier

We have directly measured, under operating conditions, the distributions of carrier densities and temperatures in a gain-clamped semiconductor optical amplifier designed for operation at 1.55 μm. As expected, longitudinal spatial hole burning is much smaller than in conventional semiconductor optical amplifiers and the effects of gain clamping are clearly evidenced. The amplifier nevertheless shows a sizeable temperature increase for both the lattice and the carriers at high currents, which are attributed to contributions of Auger recombination, intervalence band absorption, and Joule and recombination heating.

Optical bistability in an L-band dual-wavelength erbium-doped fiber laser with overlapping cavities

The authors investigate the optical bistability in an L-band dual-wavelength erbium-doped fiber (EDF) laser with overlapping cavities. The bistable input-output hysteresis behavior of the two lasing wavelengths evolves in antiphase. The bistable region is tens of milliwatts wide. The bistability is essentially due to the homogeneous saturable absorption of EDF. The cross-gain saturation causes the bistabilities of the two lasing lines to evolve in antiphase with respect to each other. The gain clamping effect helps to widen the bistable region, which may be controlled by the cavity loss and by the EDF length.

Optically gain-clamped wideband erbium-doped fiber amplifier using a common figure-eight feedback-loop lasing light

We propose an optically C plus L-band (1530–1600 nm) silica-based wideband gain-clamped (GC) erbium-doped fiber amplifier (EDFA) using a common figure-eight feedback-loop lasing light at 1568 nm, which is just located within the dead-zone between the C- and L-bands, where no WDM channels can be transmitted. The optical gain and noise figure characteristics of this wideband GC–EDFA in terms of the loop attenuation are examined. This wideband GC–EDFA may find important applications in broadband DWDM networks.

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.

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.

Output power excursions in a cascade of EDFAs fed by multichannel burst-mode packet traffic: experimentation and modeling

A serious problem facing wavelength-division multiplexed (WDM) networks with fiber amplifier cascades is transient cross-gain saturation or gain dynamics of fiber amplifiers. Attention has been focused primarily on circuit-switched scenarios. When the number of WDM channels transmitted through a circuit-switching network varies, channel addition/removal will tend to perturb signals at the surviving channels that share all or part of the route. Even more serious bit error rate deterioration can arise in WDM packet switched burst mode networks. In this paper, we present experimental and theoretical results demonstrating the effect of fast power transients in erbium-doped fiber amplifiers (EDFAs) on packetized traffic transmitted through a chain of five EDFAs. Traffic of a local-area network has been transmitted over three channels. The effect of EDFA cross-gain saturation due to the burstiness of the traffic has been observed in a continuous-wave monitoring channel. The stabilizing effect of gain clamping of the first EDFA in the cascade has been investigated. The experimental results are extended to eight-channel WDM system using a large signal numerical analysis.

Cross-gain modulation effect on the behaviour of packetized cascaded EDFAs

In this paper, we demonstrate the importance of the number of wavelength division multiplexing (WDM) channels and the network traffic variability on the dynamics of a cascade of erbium-doped fibre amplifiers (EDFAs) fed by packet traffic in burst mode. The dynamics are determined using a numerical model incorporating time variation effects in the EDFA. Calculations are based on the solution of a transcendental equation describing the time evolution of the reservoir, i.e. the total number of excited ions, for each EDFA. Traffic on WDM channels is modelled as statistically independent ON/OFF time-slotted sources. We find that the cross-gain modulation effect depends on the number of WDM channels and also on network traffic variability. As the number of WDM channels increases, and even though each one is highly variable in time, the dynamics of the total input power exhibits less fluctuation, allowing the reservoir to have a more suitable behaviour. In addition, the swings of the reservoir and the total output power decreases when we increase the network utilization factor. This positive effect is not felt on the output power excursion of an individual WDM channel. This is due to the fact that the cumulative effect of the reservoir fluctuations along a cascade will lead to further broadening of any individual channel power probability density function (PDF). Finally, we investigate the effect of gain clamping of the first amplifier in the cascade - by implementing a ring laser and propagating the lasing power through the cascade - on the statistics of several measurable entities.