Backward Pumping Configuration Research Articles

Monolithic tapered Yb-doped fiber chirped pulse amplifier delivering 126 μJ and 207 MW femtosecond laser with near diffraction-limited beam quality

In this work, a high-energy and high peak power chirped pulse amplification system with near diffraction-limited beam quality based on tapered confined-doped fiber (TCF) is experimentally demonstrated. The TCF has a core numerical aperture of 0.07 with core/cladding diameter of 35/250 µm at the thin end and 56/400 μm at the thick end. With a backward-pumping configuration, a maximum single pulse energy of 177.9 μJ at a repetition rate of 504 kHz is realized, corresponding to an average power of 89.7 W. Through partially compensating for the accumulated nonlinear phase during the amplification process via adjusting the high order dispersion of the stretching chirped fiber Bragg grating, the duration of the amplified pulse is compressed to 401 fs with a pulse energy of 126.3 μJ and a peak power of 207 MW, which to the best of our knowledge represents the highest peak power ever reported from a monolithic ultrafast fiber laser. At the highest energy, the polarization extinction ratio and the M2 factor were respectively measured to be ~ 19 dB and 1.20. In addition, the corresponding intensity noise properties as well as the short- and long-term stability were also examined, verifying a stable operation of the system. It is believed that the demonstrated laser source could find important applications in, for example, advanced manufacturing and photomedicine.Graphical

Improvement of the Temperature Stability of the Erbium-Doped Superfluorescent Fiber Source by Tuning the Reflectivity of the Fiber End

A novel and simple way of improving the mean wavelength temperature stability of the erbium-doped superfluorescent source is described and demonstrated. We show that by introducing small reflectivity feedback at the unpumped fiber end in the backward-pump superfluorescent source configuration, we can affect an overall temperature dependency of the mean wavelength of the output spectrum. The reflectivity adjustment can be made by an angled fiber cleave, varying the reflectivity between 0 to 4 %, or by a fusion arc, allowing its finer adjustment. With this approach, we were able to arbitrarily adjust the mean wavelength temperature trend from −4.38 to 5.23 ppm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C. Furthermore, an optimal reflectivity was attained, providing almost zero trend and reducing the total mean wavelength variation to 130 ppm over the temperature range of −40 to +100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C, which is a 5.7-fold and 4.4-fold improvement compared to 0 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> and a standard 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> fiber cleave angle, respectively. By avoiding any filtering components, a wide bandwidth of 37.8 nm and a power efficiency of 22% was reached. Since the proposed configuration does not include any extra components compared to the basic backward-pump configuration, it can be a viable solution for cost-efficient applications, such as, e.g., medium-grade fiber-optic gyroscopes. A benefit for these gyroscopes is the tunability of the source wavelength temperature dependency which can conveniently compensate the gyro coil temperature sensitivity.

3.3 kW narrow linewidth FBG-based MOPA configuration fiber laser with near-diffraction-limited beam quality

This paper demonstrates a narrow-linewidth fiber laser with near-diffraction-limited beam quality and high Raman suppression ratio by utilizing Master Oscillator Power-Amplifier structure based on narrow-bandwidth fiber Bragg gratings. The output power reaches 3.31 kW with a slope efficiency of 85.0 %. At the maximum output power, the 3 dB, 10 dB, and 20 dB linewidths are 0.40 nm, 1.20 nm, and 3.09 nm, respectively. The beam quality M2 factor is 1.32 and the Raman suppression ratio reaches 26.3 dB. A pair of narrow-bandwidth fiber gratings were used in the oscillator to compress the linewidth of the seed laser. We used backward-pumping configuration and plum-coiled gain fiber in the amplification stage to suppress the Raman effect and select transverse mode by fiber-bending. Finally, a compact all-fiber laser was obtained with narrow-linewidth, high beam quality, and effective suppression of the Raman effect. To the best of our knowledge, this is the highest output power for a sub-nanometer-linewidth laser using narrow-bandwidth fiber gratings and none-wavelength-locked laser diodes, which achieves near-diffraction-limit beam quality. This provides a solution for high-power narrow-linewidth laser sources with high beam quality.

Protection Scheme for a Wavelength-Division-Multiplexed Passive Optical Network Based on Reconfigurable Optical Amplifiers

This paper demonstrates a wavelength-division-multiplexed passive optical network (WDM-PON) scheme based on novel reconfigurable optical amplifiers (ROAs). The measured switching characteristics of the ROA3 constructed with a 2 × 2 crossbar optical switch and a four-port reversible optical circulator (OC) and a conventional EDFA can meet the requirements of most network management and surveillance. The self-made four-port reversible OC’s response time is less than 2 ms, and its insertion losses are about 1 dB or less for all the transmission paths and switching states. An optimal design of ROAs is proposed and evaluated for bidirectional optical amplifier protection, in which ROA3 has an EDF length of 7.5 m long with a 1480 nm pump laser and possesses a backward or forward pumping configuration with the corresponding pump power of 200 mW or 50 mW. We verified the scheme’s feasibility through a simulation of WDM-PON systems with 40 downstream and upstream channels. This scheme enables the intelligent protection switching in practical operation scenarios for high-capacity multi-wavelength networks.

1535–1620 nm Widely Tunable Watt-Level Single-Mode Er:Yb Codoped All-Fiber MOPA

We report a continuous-wave 1535–1620 nm widely tunable single-mode Er:Yb codoped cladding-pumped all-fiber laser source based on the MOPA scheme. The output power ranged from 0.785 W (at 1615 nm) to 2.007 W (at 1565 nm), which is the highest output power from a C+L tunable all-fiber laser source. The 3 dB spectral width was less than 150 pm at all wavelengths. No Yb emission was observed. We proposed a mid-way backward pumping configuration in which the pump light was injected between two gain fibers and propagated backward to broaden the effective wavelength range of the fiber amplifier. Experiments verified the capability of our configuration to improve the suppression ratio of C-band amplified spontaneous emissions from 13 dB to 35 dB when the signal laser was operating at 1620 nm.

High pumping-power fiber combiner for double-cladding fiber lasers and amplifiers

A high pumping-power fiber combiner for backward pumping configurations is fabricated and demonstrated by manufacturing process refinement. The pump power handling capability of every pump fiber can extend to 600 W, corresponding to the average pump coupling efficiency of 94.83%. Totally, 2.67-kW output power with the beam quality factor M2 of 1.41 was obtained, using this combiner in the fiber amplifier experimental setup. In addition, the temperature of the splicing region was less than 50.0°C in the designed combiner under the action of circulating cooling water. The experimental results prove that the designed combiner is a promising integrated all-fiber device for multikilowatt continuous-wave fiber laser with excellent beam quality.

Performance of 1.73 μm Superluminescent Source Based on Bismuth-Doped Fiber Under Various Temperature Conditions and γ-Irradiation

Performance characteristics of superluminescent fiber source (SFS) operating at 1.73 μ m under different temperature conditions and gamma-irradiation of active fiber were studied. The SFS in a single-pass and backward pumping configuration was constructed using a bismuth-doped high-germania silicate fiber. The output parameters of the SFS including output power, spectral shape, mean wavelength, full width at half maximum, and peak position were measured in the temperature range from –60 to +60 °C. The simulation of the bismuth SFS at room temperature was performed for the first time to our knowledge. The simulation was also used for theoretical study of the SFS performance under gamma-irradiation. The obtained results of calculation are in good agreement with the experimental data. The effect of gamma-radiation exposure (60Co source) of active fiber on the SFS output power was investigated at different temperatures. The output power as a function of radiation dose is presented. No photobleaching of radiation induced absorption in bismuth doped fibers by pump light at 1550 nm was observed.

Novelty design in gain flattening filter of ASE source based on fat ultra-long period fiber grating

Abstract A new type of gain flattening filter for amplified spontaneous emission (ASE) source based on erbium doped fiber (EDF) is proposed and demonstrated by fabricating and writing two series ultra-long period fiber grating (ULPFG) on single mode fiber (SMF-28). The novelty method in this research is based on writing the two ULPFGs as fat gratings. The LPG is written by a simple and available arc-discharge method. The pump power based on single-pass backward pump configuration is around 100 mW, and the average wavelength is near to 974 nm. The gain flattening profile is obtained by 3.4 (±1.7) dB ripple in the wavelength range between 1524 nm and 1565 nm with 41-nm band width.

Comparison between threshold and sensitivity of stimulated Brillouin scattering at different pumping configurations in high-power double-clad fiber lasers

Theoretical analysis of stimulated Brillouin scattering (SBS) in high power ytterbium-doped double-clad (YDDC) fiber lasers is presented by solving the steady-state rate equations with regard to SBS at different pumping configurations. The behavior of Brillouin Stokes power growth along the fiber is investigated and the SBS threshold power is quantitatively compared at forward, backward and bi-directional pumping configurations. It is shown that the backward pumping configuration has higher SBS threshold power than two others. Also. The effect of cavity parameters such as cavity length, front mirror reflectivity, dopant concentration and laser linewidth at different pumping configuration have been studied. It can be seen although the backward puming has higher SBS threshold but its sensitivity to cavity parameters is higher than other pumping configuration which is a negative impact for cavity designing.

Gain characteristic of spontaneous Brillouin scattering in 50 km single-mode fiber with a Raman pump

The gain characteristic of spontaneous Brillouin scattering in 50km single-mode fiber with a Raman pump is investigated. The Brillouin signal source is an external cavity laser (ECL) with 1550nm wavelength and 1mW power, and it is amplified by a 1455nm Raman laser with the tunable power of 0 – 1000mW. The results show that Stokes Brillouin scattering signal is amplified by Raman amplifier and Brillouin amplifier simultaneously. The high gain of 46.5dB and 53dB for backward Raman pump configuration and forward Raman pump configuration are achieved, respectively. And the differences between two types of Raman pump configurations are also analyzed.

All-optical tuning of a nonlinear silicon microring assisted microwave photonic filter: theory and experiment.

We propose and demonstrate an all-optical tuning mechanism to tune the response of a microwave photonic filter (MPF) based on a nonlinear silicon microring resonator (MRR). The tuning mechanism relies on the optical nonlinearities induced resonant wavelength shift in the silicon MRR, leading to the change of frequency difference between the optical carrier frequency and resonant frequency of the silicon MRR. A detailed theoretical model is established to describe the operation of the proposed all-optical tunable MPF. Two cases are studied in the experiment, i.e. the optical carrier frequency is located at the left or right side of the MRR resonant frequency. Both forward and backward pumping configurations in each case are demonstrated. Using the fabricated silicon MRR and exploiting light to control light, the central frequency of the notch MPF can be flexibly tuned by adjusting the pump light power. Moreover, the presented all-optical tuning mechanism might also facilitate interesting applications such as microwave switching and microwave modulation.

Study of the stimulated Brillouin scattering power threshold in high power double-clad fiber lasers

In this paper, the effect of stimulated Brillouin scattering (SBS) on increase in the output power of a fiber laser is investigated by solving the steady-state rate equations with the SBS. The effects of fiber core diameter, cavity length, reflectivity bandwidth of rear and front mirrors, and fiber laser pumping configuration on SBS threshold are illustrated. Numerical results show that the reflectivity bandwidth of the front mirror is more effective in suppression of SBS at the fiber laser resonator. On the other hand, increase in the fiber core diameter, reduction of cavity length and using a backward pumping configuration can increase the SBS threshold. In our 220 W experimental fiber laser oscillator setup no SBS effect was observed.

Backward pumping kilowatt Yb3+-doped double-clad fiber laser

A ytterbium-doped double-clad fiber laser generating up to 1026 W of continuous-wave output power at 1085 nm with a slope efficiency of 74% by single-ended backward pumping configuration is reported. The core diameter was 20 μm with a low numerical aperture of 0.06, and a good beam quality (BPP < 1.8 mm mrad) is achieved without special mode selection methods. No undesirable roll-over was observed in output power with increasing pump power, and the maximum output power was limited by the available pump power. The instability of maximum output power was better than ±0.6%. Different pumping configurations were also compared in experiment, which shows good agreements with theoretical analyses.

A 980 nm Yb-doped single-mode fibre laser with 946 nm Nd:YAG laser as pump source

Based on rate equations, this paper gives expressions of the output power, the pump power threshold, the slope efficiency, the fibre optimal length and the laser gain of a quasi-three-level Yb-doped fibre laser. The gain relationship between quasi-three-level system and four-level system is also given, which provides a theoretical basis for suppressing the four-level transmissions. In the experiment, we adopt the backward pumping configuration and use a linear cavity. The Yb-doped fibre laser has an output power of 372 mW of single-mode laser emission at 980 nm with a slope efficiency of 21.2% when the fibre length is 29.5 cm close to an optimal fibre length in theory. The experimental results accord well with the theoretical analyses.

Gain-enhanced double-pass long-wavelength-band erbium-doped fiber amplifier using backward pumping

We propose and demonstrate a novel high-gain-efficiency long-wavelength band (L-band) erbium-doped fiber amplifier with a double-pass backward-pump configuration, in which the strong backward C-band amplified spontaneous emission is effectively utilized. The L-band gain is greatly enhanced in comparison with the copumped configuration. Without using any excessive components, the new configuration can provide the same gain as the conventional configuration, but only using 40% pump power. Meanwhile, the noise figure is also effectively improved under the low pump power.

Effect of steady-state conditions on self-pulsing characteristics of Yb-doped cw fiber lasers

Fiber laser resonator configurations have been analyzed theoretically on the basis of steady-state rate equations to optimize the laser conversion efficiency. Evolution of the pump- and signal powers and the saturated gain coefficient along the length of the laser medium has been simulated for high- and low-finesse resonators in forward- and backward pumping schemes. The corresponding fiber laser configurations have been setup to verify the results of simulation. Backward pumping configuration in an Yb-doped fiber laser has been found to be the most efficient, and in this configuration a maximum cw output power of 10.75W in single transverse mode with an optical-to-optical conversion efficiency of 62.5% has been achieved. The laser output spectrum was peaked at 1093nm with full-width at half-maximum (FWHM) line-width of about 9nm. In the low-finesse resonator configuration, it has been found that experimental observations differ from theoretical simulation results. In this case, output power from both ends ceases to increase linearly beyond 1.8W, and starts fluctuating due to the onset of strong random self-pulsing phenomenon. Our investigation shows that a non-uniform steady-state gain along the fiber length facilitates the self-pulsing process.

Four-wave-mixing suppression in Er3+-fiber amplifiers by backward pumping

Amplification of chirped fs-pulses in an Erbium doped fiber amplifier upto 0.8μJ resulted in an additional peak in the spectrum at 1584nm. This peak, attributable to four-wave-mixing between the signal centered at 1559nm and amplified spontaneous emission at 1534nm, hinders the temporal recompression of the amplified chirped pulse. Compared to the forward pumping configuration, this four-wave-mixing in the amplifier was largely reduced in a backward pumping configuration. Based on simulations, explanations for the observed influence of the pump direction on the four-wave-mixing efficiency are presented. The results pointed out that the gain spectrum distribution along the fiber strongly influences four-wave-mixing effects in fiber amplifiers even for constant overall gain spectrum.

Optimization for various schemes of distributed fibre Raman amplifiers

A fast and stable numerical method for solving the model equations of distributed fibre Raman amplifiers is proposed. This method can increase the computing speed by more than five times compared to the classical Dormand?Prince method. In this paper, on the basis of the proposed method and genetic algorithm, the signal gain spectrum and corresponding optical signal-to-noise ratio (OSNR) for counter-?and bi-directional multi-pump Raman amplifiers are optimized and compared. The optimized results show that (1)?bi-directionally pumping configurations with proper forward pump diodes can effectively decrease the gain ripple and the OSNR ripple and equalize the OSNR tilt in comparison with pure backward pumping configurations; (2)?the gain spectrum and noise performance can be availably improved by means of increasing the pump number. The simulations demonstrate that, when optimizing bi-directional multi-pump configurations, (1)?there are multiple global or near-global maxima for the signal gain spectrum; (2)?different bi-directional pump schemes have different gain ripple and noise performance.

Span Design for Reduced Noise and Nonlinear Impairments in a Dispersion-Managed Raman Amplified System

We study a periodic Raman amplified dispersion-managed system with backward-pumping configuration, considering noise and nonlinear impairments. A general optimization method based on nonlinearity management is applied in order to find the configuration that maximizes the system performance. The system is later tested using a full numerical implementation of the nonlinear Schrodinger equation and shown to effectively deliver its longest propagation distance in the same optimal region.

Analysis of gain difference between forward- and backward-pumped erbium-doped fiber amplifiers in the saturation regime

In saturated erbium-doped fiber amplifiers (EDFAs), signal gain and power conversion efficiency are known to be greater in the backward pumping configuration. This study shows that the difference between pumping schemes is primarily an effect of amplified spontaneous emission. It is concluded that the highest conversion efficiency achievable in highly saturated EDFAs is predicted with fair accuracy by ASE noise-free models, but is approached most nearly with backward-pumped EDFAs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>