Amplified Spontaneous Emission Suppression Research Articles

Demonstration of hundred-watt-level near-diffraction-limited monolithic fiber laser near 980 nm with step-index double-cladding Yb-doped fiber

In this paper, a hundred-watt-level near-diffraction-limited step-index Yb-doped fiber (YDF) laser near 980 nm is demonstrated firstly, to the best of our knowledge. By using the 11.7-W 979-nm single-mode seed light, the in-band amplified spontaneous emission (ASE) is well suppressed and the maximum output power of 101.5 W with the beam quality (M2 factor) of 1.285 was obtained. This work does not only propose an effective method for the suppression of in-band ASE, but also provides a cost-effective solution of hundred-Watt-level near-diffraction-limited fiber lasers near 980 nm.

Over 30 W single-frequency all-fiber amplifier at 1120 nm with high ASE suppression.

A 1120nm linearly polarized all-fiber single-frequency amplifier based on Yb-doped fiber (YDF) is reported. A maximum output power of 30W is achieved by 976nm clad-pumping and 1018nm core-pumping, with corresponding slope efficiencies of 51.9% and 70.0%, respectively. With the 976nm clad-pumping configuration, a signal to amplified spontaneous emission (ASE) ratio of more than 45dB is realized at maximum output power. The polarization extinction ratio of the amplifier is measured to be more than 21dB in the whole power scaling process. In addition, the intensity noise of the amplifier at maximum output power is also characterized to be around -130d B c/H z at frequencies above 2kHz and is comparable to that of the seed laser. Moreover, the deterioration of frequency noise and linewidth of the amplified laser is negligible. To the best of our knowledge, this is the highest output power of a single-frequency all-fiber amplifier that exploits the fundamental transition of YDF at 1120nm, even without any external intervention for suppressing ASE in the short wavelength range.

Demonstration of Yb-Doped Fiber Amplifier Operating near 980 nm with the Slope Efficiency Close to the Theoretical Limit

In this paper, the scalability of slope efficiency of a Yb-doped fiber amplifier operating near 980 nm is studied with the core-pumping scheme. By means of numerical prediction, it is found that the theoretical limit of slope efficiency should be about 92.2%. Then, the experiment study is carried out. An 85.3% slope efficiency of emission around 980 nm is achieved with the seed light around 976.5 nm, and the strong in-band amplified spontaneous emission (ASE) is supposed to be a factor limiting the upscaling of slope efficiency. In order to suppress the in-band ASE, the double-wavelength fiber oscillator near 980 nm is fabricated and used as the seed source, with which the slope efficiency is elevated to 90.7%. Such slope efficiency is very close to the theoretical limit and sets a new record of slope efficiency for the Yb-doped fiber amplifier operating near 980 nm, to the best of our knowledge. It is also revealed that the suppression of in-band ASE should be of great importance to elevate the slope efficiency of a Yb-doped fiber amplifier operating near 980 nm.

Experimental study on the 500-W-level all-fiber amplifier operating near 980 nm

In this paper, a 500-W-level all-fiber amplifier operating near 980 nm is demonstrated firstly, to the best of our knowledge. The amplifier is fabricated with a 105/250-μm core/cladding-diameter double-cladding Yb-doped fiber (DCYF). By optimizing the length of DCYF, the record 556-W output power and 50.5% slope efficiency are obtained with a 1.85-W seed light, and about 30.9 dB peak-to-peak suppression of 1030-nm amplified spontaneous emission (ASE) is realized. Furthermore, the strong in-band ASE is also observed in experiment, which limits the power up-scaling of the fiber amplifier. By analyzing the origin of the in-band ASE, it is revealed that optimizing the seed light should be beneficial to the suppression of in-band ASE. Besides, the beam quality is measured at the maximum output power and the M2 factor is about 23.6. The experimental study should be able to provide significant guidance for understanding and designing the high-power three-level fiber lasers and amplifiers.

Highly customized 1010 nm, ns-pulsed Yb-doped fiber amplifier as a key tool for on-demand single-photon generation.

The development of highly customized technical devices is a decisive feature of technically complex setups, as frequently observed in quantum experiments. This paper describes the development and realization of an Yb-doped all-fiber amplifier system designed for such a special application, more specifically, an on-demand single-photon source based on four-wave mixing with rubidium Rydberg atoms. The laser is capable of generating bandwidth-limited configurable nanosecond pulses up to peak powers of >100 W and with pulse repetition frequencies (PRF) between 50 Hz and 1 MHz at selectable wavelengths (1008-1024 nm). Especially the amplification of the 1010 nm reference seed at the lower edge of the amplification range for Yb-based fibers is challenging and tends to produce amplified spontaneous emission (ASE) at higher wavelengths. To achieve high ASE suppression, particularly at low pulse repetition frequencies, two acousto-optical modulators (AOM) are utilized both for pulse picking and for temporal filtering. The synchronization between pulse repetition frequency and AOM driver signal allows pulse amplitude fluctuations to be kept below 1%, while ASE is suppressed by at least 85 dB (PRF = 1 MHz) and 65 dB (PRF = 1 kHz).

Optimization of ASE suppression in high efficiency Tm3+-doped pulsed all-fibered MOPA operating at 1908.12 nm

We proposed and demonstrated high efficiency Tm3+-doped pulsed all-fibered master oscillator power amplifier (MOPA) operating at 1908.12 nm with Amplified Spontaneous Emission (ASE) suppressed by optimizing the pumping power, seed laser power and fiber length. Considering the effect of pulsed seed laser and ASE on amplifier output characteristics, the amplifier gain and ASE suppression ratio under different conditions are simulated. Using an optimized length of 1.0 m large-mode-area (LMA) Tm-doped fiber (TDF) is used as amplifier fiber, the maximum average output power of 14.62 W (slope efficiency of 46.0%) with total amplifier gain of 24.66 dB is obtained when pumping power of 30.5 W and input signal laser power of 1.225 W. Meanwhile, ASE can be effectively suppressed with maximum ASE suppression ratio of 49.85 dB is obtained at the repetition frequency (RF) of 1 MHz and the duty cycle of 80%. Central wavelength of 1908.12 nm with linewidth of 0.65 nm and the beam quality of Mx2 = 1.35 and My2 = 1.51. This is, to the best of our knowledge, the maximum ASE suppression ratio in pulsed Tm3+ doped fiber laser by using acousto-optic (AO) external modulation operating at 1908.12 nm without filter.

KW-level 1030 nm polarization-maintained fiber laser with narrow linewidth and near-diffraction-limited beam quality.

kW-level 1030nm polarization-maintained fiber laser with narrow linewidth and near-diffraction-limited beam quality is demonstrated. Theoretical simulations based on the power balance equation are first performed to optimize the system parameters of the 1030nm ytterbium-doped fiber laser for the maximum suppression of amplified spontaneous emission (ASE). With the optimized parameters, both the copumped and counterpumped MOPA lasers are implemented to obtain an output power of >1 kW. In both cases, the ASE suppression ratio reaches 40dB with a 3dB linewidth of about 0.14nm, and the polarization extinction ratio is about 12dB at 1kW of output power. The beam quality starts degrading at 900W of output power in the copumped structure, but maintains nearly single mode (Mx2,My2)=(1.07,1.12) until power is over 1kW in the counterpumped structure.

ASE Suppression in Backward-Pumped Er/Yb Double-Cladding Fiber Amplifier via Cladding Feedback

We demonstrate a backward-pumped 1550 nm narrow-linewidth Erbium-Ytterbium double-cladding fiber amplifier with amplified spontaneous emission (ASE) suppression. Compared with the typical backward-pumped amplifier without feedback, the ASE power can be suppressed by over 2 dB by cladding feedback without other filters. The slope efficiency is 23.2%, which only decreased by 0.4%. The linewidth and relative intensity noise of 4.51 kHz and –92 dBm/Hz are also compared with those of the typical backward-pumped amplifier without feedback.

Efficient ASE control in cryogenic gas cooled Yb:YAG multislab amplifiers with Cr4+:YAG interlayers

A novel approach based on Cr4+:YAG interlayers to break the transmission paths of amplified spontaneous emission (ASE) in a cryogenic gas cooled Yb:YAG multislab amplifier geometry was presented for the suppression of ASE in the power scaling of high energy, high average power laser systems. The benefits of Cr4+:YAG interlayers for the overall performance of an amplifier were illustrated with respect to energy storage capacity, heat generation and amplification of the seed pulses based on the theory of quasi-three-level Yb3+ ions and Cr4+:YAG saturable absorption, the Monte Carlo and ray-tracing methods. For the amplifier with optimized Cr4+:YAG interlayers, it was found that the energy storage efficiency was increased from 39.12% to 47.38% in comparison with the amplifier without interlayers. The maximum output energy of 1119.53 J with an optical-to-optical efficiency of 28.91% in the amplifier with interlayers was obtained, while it reduced to 810.61 J with an optical-to-optical efficiency of 20.94% in the amplifier without interlayers. To our knowledge, this is the first quantitative characterization of the performance of a cryogenic gas cooled Yb:YAG multislab amplifier with Cr4+:YAG interlayers.

On the correlation between morphology and Amplified Spontaneous Emission properties of a polymer: Polymer blend

We investigate the Amplified Spontaneous Emission (ASE) properties of a prototypical host-guest polymer polymer blend, namely poly(9,9-dioctylfluorene) (PF8) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) blend, with different concentration ratio. We show that the initial F8BT content increase causes an increase of the F8BT ASE threshold, even leading to ASE suppression for F8BT contents between 25% and 75%. ASE is then recovered upon further increase of the F8BT relative content. We demonstrate that the ASE properties of the PF8:F8BT are dominated by morphology effects, like submicrometric phase segregation, determining the net gain of the active waveguides.

Burst-mode Yb-doped fiber amplifier system optimized for low-repetition-rate operation

We report on the burst-mode operation of a polarization-maintaining Yb-doped multi-stage all-fiber amplifier capable of generating 10-pulse 100 ns long bursts of 400 μJ total energy. The corresponding average energy per pulse is 40 μJ, with a standard deviation of 16%. The 40 μJ pulses are compressible to a full width at half-maximum of 500 fs. The burst repetition rate is set to 1 kHz and the amplifier is synchronously pulse pumped to minimize amplified spontaneous emission (ASE) between the bursts. A special amplifier design has been developed to suppress ASE further at the cost of lower power efficiency. A detailed investigation of gain and ASE suppression performance of the amplifier in relation to pulsed pumping is presented.

S-Band Gain Improvement Using a Thulium–Aluminum Co-Doped Photonic Crystal Fiber Amplifier

An extended method for gain and noise figure enhancement in the S-band using a thulium-doped photonic crystal fiber amplifier (TD-PCFA) is proposed and shown by numerical simulation. The principle behind the enhancement is the suppression of unwanted amplified spontaneous emission (ASE) using the PCF structure. This proposed PCF achieves the intended band-pass by doping the cladding with high index material and realizes appropriate short and long cut-off wavelengths by enlarging the air-holes surrounding the doped core region. The PCF geometrical structure is optimized so that high losses occur below the short cut-off wavelength (800 nm) and beyond the long cut-off wavelength (1750 nm). Furthermore, the PCF geometrical structure design allows for high ASE suppression at 800- and 1800-nm band, thus increasing the population inversion needed for amplification in S-band region as the 1050-nm pump propagates light in the band-pass. The proposed TD-PCFA demonstrates gain enhancements of 3–6 dB between 1420 and 1470 nm.

Enhanced performance of an S-band fiber laser using a thulium-doped photonic crystal fiber

This work proposes a new method to enhance the performance of an S-band fiber laser by using a thulium-doped photonic crystal fiber (PCF). The proposed method is based on amplified spontaneous emission (ASE) suppression provided by the thulium-doped PCF unique geometric structure. The enhanced performance of this filter based PCF is dependent on the short and long cut-off wavelength characteristics that define the fiber transmission window. Realizing the short wavelength cut-off location requires the PCF cladding to be doped with a high index material, which provides a refractive index difference between the core and cladding region. Achieving the long cut-off wavelength necessitates enlarging the size of the air holes surrounding the rare-earth doped core region. The PCF structure is optimized so as to achieve the desired ASE suppression regions of below 0.8 μm and above 1.8 μm. The laser performance is simulated for different host media, namely pure silica, alumino-silicate, and fluoride-based fiber ZBLAN based on this thulium-doped PCF design. The host media spectroscopic details, including lifetime variations and quantum efficiency effect on the lasing emission are also discussed. Information on the filter based PCF design is gathered via a full-vectorial finite element method analysis and specifically a numerical modelling solution for the energy level rate equation using the Runge–Kutta method. Results are analyzed for gain improvement, lasing cavity, laser efficiency and effect of core size diameter variation. Results are compared with conventional thulium-doped fiber and thulium-doped PCF for every single host media. We observe that the ZBLAN host media is the most promising candidate due to its greater quantum efficiency.

56.6 dB high gain L-band EDFA utilizing short-length highly-doped erbium rare-earth material

In this paper, we experimentally investigate the performance of an efficient high gain L-band erbium-doped fiber (EDF) amplifier structure utilizing short-length highly-doped erbium rare-earth material with a single pump source. The amplifier gain and noise figure variation for different amplifier structures have been investigated. A filter is used to reduce the self-saturation effect and suppress the C-band amplified spontaneous emission (ASE) noise. The amplifier achieves a signal gain of 56.6 dB with a low noise figure of 4.8 dB at −50 dBm input signal power using only 8 m of EDF length. The amplifier gain shows significant improvement of 6 dB with C/L band coupler and 13 dB with tunable-band pass filter compared to amplifier structure without ASE suppression.

ASE suppression in high-gain solid-state amplifiers by a leak method

A leak method was developed to suppress amplified spontaneous emission (ASE) in large-aperture high-gain solid-state amplifiers. The gain medium edges are processed into an arris. The ASE ray will undergo reflection several times at the arris surface when it propagates to the gain medium edges, and most of its power will leak out. This leak method was tested in an experiment, in which a piece of commonly used gain medium was processed for contrast. The maximal increase of the gain value was 5.26% with the maximal pump power.

Nearly Temperature‐Independent Threshold for Amplified Spontaneous Emission in Colloidal CdSe/CdS Quantum Dot‐in‐Rods

Nearly Temperature‐Independent Threshold for Amplified Spontaneous Emission in Colloidal CdSe/CdS Quantum Dot‐in‐Rods

Suppression of ASE by Using Pulsed-Pumped Technique in Fiber Amplifier

Implementation of pulsed-pump technique in fiber amplifier is highly useful in the situation of low repetition rate and high energy pulses operation. In this paper, the ASE (Amplified Spontaneous Emission) dynamics simulation in a pulsed-pumped ytterbium-doped double-clad fiber amplifier is presented for the first time, which provides important guidance about optimizing the pulsed-pump mode. The simulations of ASE dynamics are carried out by solving the rate equations and light power propagation equations in fiber using the finite elements analysis method, including variations of ASE output power at two terminals of the fiber in the time span from 0 ~ 740μs after pump light injection. Furthermore, a way of optimizing signal injection time is discussed.

50-mJ macro-pulses at 1064 nm from a diode-pumped picosecond laser system

Pulse-picking from a 100-mW cw mode-locked seeder, a hybrid master-oscillator power-amplifier (MOPA) system, based on Nd:YVO4 and Nd:YAG amplifier modules, has been developed, delivering single-pulses of 8.6 ps at 455-MHz repetition-rate, bunched into ~1-μs trains of 50 mJ ("macro-pulses"). The output beam is linearly polarized and nearly diffraction limited up to the maximum macro-pulse repetition-rate of 50 Hz. The single-pulse peak power and the macro-pulse duration and energy are quite suitable for high-energy nonlinear optical applications such as low-threshold synchronously-pumped parametric converters in the mid infrared. The impact on the overall efficiency of saturation distortion of the macro-pulse envelope as well as of amplified spontaneous emission (ASE) is considered. The managing of the envelope distortion compensation and of the ASE suppression by means of fast saturable absorbers is reported.

Improved large-mode-area Bragg fiber

A novel large-mode-area Bragg fiber (BF) is proposed for selectively suppressing the amplified spontaneous emission (ASE) of Yb. Confinement loss can be effectively lowered by adding a layer of F-doped glass near the core of this fiber. The BF can achieve effective suppression of ASE of Yb when the bend radius is 0.15 m at wavelength lower than 1.13 \mu m in theory, and eliminate LP11 mode in mode competition in wavelength range of 1.15-1.2 \mu m.

Spectral filtering in a diode-pumped Nd:YLF regenerative amplifier using a volume Bragg grating

Instrument-limited suppression of out-of-band Amplified Spontaneous Emission (ASE) is demonstrated in a Nd:YLF Diode-Pumped Regenerative Amplifier (DPRA) using a Volume Bragg Grating (VBG) as a spectrally selective reflective element. A VBG with 99.4% diffraction efficiency and 230-pm-FWHM reflection bandwidth produced a 43-pm- FWHM output spectral width in an unseeded DPRA compared to 150-pm FWHM in the same DPRA with no VBG. Instrument-limited ASE suppression is even observed when the DPRA seed pulse energy approaches the ASE background.