Amplified Spontaneous Emission Effect Research Articles

Optimized dual-band amplified spontaneous emission properties of PFO and BUBD-1 blend films based on AgNPs doped buffer layers

Dual-band amplified spontaneous emission (ASE) can be used as a spectral analysis technique to detect specific chemical or biological molecules. In this paper, the dual-band ASE properties of blend films containing a small organic molecule N,N’-(4,4′-(1E,1′E)-2, 2′-(1,4-phenylene) bis(ethene-2,1-diyl)) −bis(4,1-phenylene))-bis(2-ethyl-6-methyl-phenylaniline) (BUBD-1) and a conductive polymer Poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) were investigated and optimized. As the doping concentration of BUBD-1 in the PFO was increased from PFO: 1 wt% BUBD-1 to PFO: 5 wt% BUBD-1, the ASE emission wavelength shifted from single- to dual-band and then back. The dual-band ASE performance of the blend film was also improved by introducing a Poly(methyl methacrylate) (PMMA) buffer layer containing silver nanoparticles (AgNPs), which resulted in a significant decrease in the excitation energy threshold of both ASE peaks and a significant increase in the net gain. Due to the LSPR effect of AgNPs, the ASE thresholds for peaks at 460 nm (PFO) and 490 nm (BUBD-1) in the blend film decreased from 12.24 ± 0.49 μJ/pulse to 6.99 ± 0.28 μJ/pulse and from 12.75 ± 0.51 μJ/pulse to 7.03 ± 0.28 μJ/pulse, respectively. The experimental and theoretical simulation demonstrated that the incomplete energy transfer between PFO and BUBD-1 led to a dual-band ASE effect. In addition, the enhanced light absorption, emission, and scattering caused by LSPR in the AgNPs improved the threshold and gain for dual-band ASE. This provides a possibility of realizing dual-band organic semiconductor lasers.

Light‐Emitting Device Based on Amplified Spontaneous Emission

AbstractIn recent years, with the rapid development of military, optical communication, biological imaging, and other fields, practical engineering applications such as fiber‐optic gyroscope, wavelength division multiplexing, and optical coherence tomography have put forward higher requirements on light sources. Amplified spontaneous emission (ASE) light source has become an excellent candidate due to its advantages such as suitable bandwidth, low coherence, and high power. Although the ASE light source is developed to a certain extent, there is still great room for improvement in the choice of gain medium and device structure. In order to accelerate the development and practical engineering application of ASE optoelectronic devices, it is of great significance to grasp the basic characteristics of the gain materials and the design of the device structure. In this review, the principle of the ASE effect and its difference with the generation of lasing are analyzed. Then, the optical gain properties of various gain materials, together with different structural types of electrically pumped ASE devices and their practical engineering applications, are summarized. Finally, the new ASE light‐emitting devices integrated with high‐gain materials and low‐cost structures are prospected to provide more ideas for their development.

Theoretical study on amplified spontaneous emission (ASE) in a V-pumped thin-disk alkali laser

In the paper, a mathematical model was systematically constructed to evaluate the amplified spontaneous emission (ASE) effects and temperature distribution of a vapor cell of the V-pumped thin-disk alkali lasers. There have been few literatures on studying ASE in a diode-pumped alkali laser (DPAL) although such a phenomenon is normally serious especially in a thin-disk configuration. By reducing the number of the outputted conditions and adopting a parallel computation algorithm, the computation speed has been demonstrated to be greatly improved by comparing to the method we ever used before. The results show that the ASE effects in a thin-disk DPAL cannot be ignored especially when the size of a pump beam becomes big. It has also been proved that ASE in a thin-disk DPAL tightly relates to the pump power, thickness and temperature of a thin-disk cell, and reflectivity of the output coupler (OC). The calculation approaches in this paper are thought to be valuable in the design of a high-powered DPAL and can also be applied to the other kinds of high-powered lasers.

Amplified spontaneous emission (ASE) effect on gain and stored energy

In this research, amplified spontaneous emission (ASE) is studied along a rod amplifier length where intensities travel in two opposite longitudinal axis directions. The effect of ASE intensity on amplifier stored energy was discussed. An expression was obtained for stored energy in an amplifier in which a nonuniform gain distribution shaped due to ASE saturation effect. Time evolution of population inversion in a pulsed amplifier at the presence of ASE effect was also obtained, using the new relation of stored energy. Numerical calculations were used to verify accuracy and validity of the obtained relations. The numerical calculations included solving rate equation of population inversion of amplifier and simultaneous solving of two intensity equations for two beams traveling in opposite directions along the amplifier length.

Numerical analysis of amplified spontaneous emission of the thin-disk laser with an adjustable ring pump spot

The amplified spontaneous emission (ASE) effect is a major factor affecting large size, high-gain Yb:YAG thin-disk lasers. In this paper, considering the reabsorption effect of the quasi-three-level Yb:YAG crystal, an adjustable ring pump spot (ARPS) is proposed to suppress the ASE effect for the high power multimode thin-disk lasers. A numerical integration model is built to calculate the output power density, the distribution of ASE photon flux density, and the gain coefficient of the ARPS. Compared with the circle pump spot and the hollow pump spot, the reabsorption effect in the ring shaped unpumping region of the ARPS has a good balance between the ASE photon amplification in the pumping areas and attenuation in the unpumping area of the thin-disk crystal. Significant improvement of suppression ability of the ASE effect can be achieved by using the ARPS with an optimal position of the ring-shaped unpumping area, especially for the larger pump spot.

Spontaneous emission noise in mode-locked lasers and frequency combs

Amplified spontaneous emission (ASE) causes fluctuations of pulse energy, of the optical phase and of the timing of the pulse intensity envelope in a mode-locked laser or frequency comb. Starting from the assumption of one ASE photon per longitudinal laser mode and roundtrip, we rederive analytic equations for the three fundamental types of quantum noise in a laser. To this end, we analyze the interference of the coherent intracavity field and a spectrally localized ASE photon as a function of wavelength and phase of the latter. Performing an integration over all wavelengths and phases and taking stochastic noise into account, we compute ASE-induced jitters for all quantities considered. Continuing this approach, we then derive an expression for the resulting carrier-envelope phase noise of the comb, for which so far only numerical estimates exist. We further compute analytical estimates for ASE induced pulse chirp and duration variations and address the issue of resulting pulse contrast in a mode-locked laser and the resulting coherence properties. Considering three example cases, we finally compute estimates for all quantities analyzed. Taken together, our analysis provides a comprehensive view of ASE effects in a mode-locked laser, which unites numerous scattered reports across the literature.

Combined Effect of ASE Noise and SRS Induced Crosstalk on the BER Performance of a Single Span WDM System with Raman Amplifier Using Heterodyne Coherent Detection

AbstractAnalysis is presented to evaluate numerically the combined effect of amplified spontaneous emission (ASE) and stimulated Raman scattering (SRS) on the bit error rate performance of a WDM transmission system with Raman amplifier using heterodyne receiver. The results are compared with those for a WDM system reported with direct detection receiver for different system parameters. It is observed that coherent heterodyne system is less affected by the crosstalk due to combined effect of ASE and SRS compared to direct detection. It is noticed that allowable transmission distance is 170 km, and 166 km of WDM channels for 8, and 16, respectively, when coherent heterodyne receiver is and with pump power of 10 mW and channel bandwidth of 12.5 GHz. The corresponding transmission distance is 60 km and 10 km, respectively, for direct detection system already reported.

Heat generation in quasi-three-level Yb:YAG thin-disk lasers

A theoretical model is established to evaluate heat generation in quasi-three-level Yb:YAG thin-disk lasers. Fluorescence heating fraction, laser heating fraction, amplified spontaneous emission (ASE) heating fraction, and non-radiative relaxation heating fraction are considered in our analysis. The dynamic process and spectral properties of ASE are analyzed by using quasi-three-level system rate equations. A numerical iterative method is used to study the dynamic behavior, the fractional thermal load, proportions of all the heating factors, and the temperature of the thin-disk laser. Dynamic heating process is clearly demonstrated. Our theoretical analysis shows that the ASE effect is critical in the total heat generation and operation of thin-disk lasers, especially for a high-power thin-disk laser.

Analytical model of amplified spontaneous emission with different thickness anti-ASE caps for thin disk lasers.

The amplified spontaneous emission (ASE) effect is a major factor affecting large, high gain Yb:YAG thin disk lasers. In this paper, the analytical model is built to estimate the ASE photon flux density of thin disk crystals with different thickness anti-ASE caps. Theoretical analysis shows that it is unnecessary to use a critical thickness anti-ASE cap to suppress the ASE effect. At the same time, adjusting the coupler reflectivity of the resonator is an effective way to decrease the ASE effect and decrease the thickness of the anti-ASE cap to effectively suppress the ASE effect. This paper will better reveal how the anti-ASE cap suppresses the ASE effect.

Theoretical analysis of uniform longitudinal gain for a double-end-pumped Yb:YAG multi-slab pulsed amplifier

For high average power lasers with double-end-pumped multi-slab (DEPMS) configuration, a non-uniform gain distribution within each slab caused by the step-doped multi-slab will lead to the amplified spontaneous emission (ASE) effect and then reduce the laser performance. As an example, longitudinal gradient doping is used in a DEPMS Yb:YAG pulsed amplifier to create uniform longitudinal gain (ULG) and then the ASE effect is effectively reduced. The ULG is theoretically derived and we show that the energy storage can be increased by 9% with ULG compared with the step-doped DEPMS. We found that the optimal pump efficiency, longitudinal gain-length product and columnar doping density are determined by the launched pump intensity. Numerical simulation also demonstrated that optimization of the amplifier with uniform gain and high pump efficiency can be achieved by placing additional gradient slabs to the original gradient doping slabs. Our investigations might provide an efficient way to carefully optimize a DEPMS pulsed amplifier with higher efficiency.

Amplified spontaneous emission model of thin disk laser with nonuniform temperature distribution

The amplified spontaneous emission (ASE) effect is a major factor affecting large size, high gain Yb:YAG thin disk lasers. In this paper, a model combining the rate equations including an ASE effect term and nonuniform temperature distribution in a thin disk crystal is presented. A numerical iterative method is used to analyze the dynamic behavior, the space distribution of ASE effect, and the optimum coupler reflectivity of the thin disk laser. It is shown that the temperature distribution and the size of the pump region are the main factors to influence the ASE effect and ultimately affect the output power and threshold of the laser system. In order to decrease the ASE effect, the coupler reflectivity can be adjusted to control the gain coefficient to increase output power.

Fabrication of broadband absorbing coatings for amplified spontaneous emission suppression.

Amplified spontaneous emission (ASE) is a critical factor that limits the output power of slab lasers. To suppress the ASE effect in slab lasers, this paper proposes a metal/dielectric broadband absorbing coating between the laser gain medium and the metal heat sink to suppress ASE from zero to total internal reflection angle on the facet from inside the laser medium. Based on accurate characterization of Cr metal thin films, Cr/SiO2 broadband absorbing films for 1064 nm YAG slab lasers are designed and fabricated to suppress ASE. The good agreement between experiment and design shows the reliability to suppress ASE in slab lasers.

Analysis of Amplification Characteristics of Surface Plasmon Polaritons Based on the Rate-Equation Theory

A rate-equation theory model with the amplified spontaneous emission (ASE) effect considered for the surface plasmon polariton (SPP) waveguide amplifier is presented for analyzing the SPP amplifications with both side and SPP pumping techniques. By partitioning the cross section of the waveguide to suitable small units and introducing the overlapping integrated factor in each unit, the 3-D coupled equations of the model can be simplified to 1-D equations, which could be solved more conveniently. With our model, the gain and noise properties of a dielectric-loaded SPP waveguide amplifier are simulated. The results show that the ASE effect reduces the signal gain and deteriorates the signal-to-noise ratio of the SPP amplifier. For both the pumping schemes, the gains and noises for SPP multimode amplifications depend on the waveguide structure. By optimizing the waveguide structure, the gain-equalized amplification for different SPP modes may be achieved.

Modeling of an optically side-pumped alkali vapor amplifier with consideration of amplified spontaneous emission

Diode pumped alkali vapor amplifier (DPAA) is a potential candidate in high power laser field. In this paper, we set up a model for the diode double-side-pumped alkali vapor amplifier. For the three-dimensional volumetric gain medium, both the longitudinal and transverse amplified spontaneous emission (ASE) effects are considered and coupled into the rate equations. An iterative numerical approach is proposed to solve the model. Some important influencing factors are simulated and discussed. The results show that in the case of saturated amplification, the ASE effect can be well suppressed rather than a limitation in power scaling of a DPAA.

主振荡功率放大装置中的放大自发辐射效应和能量提取效率

The interaction of amplified spontaneous emission (ASE) flux and coherent laser flux as well as the effect of ASE in cuboid DF amplifiers are studied, by using a finite difference method and an iterative algorithm. The influence of input laser intensity and saturation light intensity on output power and energy extraction efficiency is discussed. The simulation of the amplifier whose gain zone is cuboid and gain coefficient is distributed as parabola indicate that the ASE intensity will decrease with the increase of input laser and the presence of input laser will make the maximum of ASE flux in the amplifier shift from the center to the entrance of the amplifier. The output power and the energy extraction efficiency will increase with the increase of input laser power when the saturation l

Amplified spontaneous emission and power amplification in high-power DF laser systems

Amplified spontaneous emission (ASE) always occurs in high-power DF laser systems with master oscillator-power amplifier (MOPA) configuration. ASE not only reduces the energy extraction efficiency of the laser system, but also negatively influences its heat management. The interaction between the ASE flux and the coherent laser flux, as well as the effect of ASE on cuboid DF amplifiers, is studied using a finite difference method and an iterative arithmetic. In addition, the influence of ASE on coherent laser amplification is discussed in detail.

Reducing ASE Effect in Coherent Detection by Employing Double-Pass Fiber Preamplifier and Time-Domain Filter

We report on a novel fiber based coherent detection system employing a double-pass fiber preamplifier, a spectral bandpass filter, and a time-domain filter. The time-domain filter, a synchronous time gate, reduces the in-band amplified spontaneous emission (ASE) beat noise, which cannot be achieved by the spectral bandpass filter alone. The double-pass fiber amplifier further reduces the out-band ASE by about 20 dB with a fiber Bragg grating (FBG) at the end of the fiber amplifier. In preliminary experiments with a 100 GHz bandpass filter, no degradation is observed from the optically preamplified coherent detection compared to pure coherent detection. With a 10 ns pulse width, 500 kHz repetition rate, and 10 pW average input power, about 2 dB and 1 dB signal-to-noise ratio (SNR) improvements are achieved when 5% and 50% time gating duty cycles are used, respectively.

Analytical Model for Overmodulation in EDFAs in the Presence of ASE

We investigate the effect of ASE(Amplified Spontaneous Emission) on the gain modulation, that also referred to overmodulation. The gain modulation is the low-frequency (kHz) amplitude modulation of the EDFA pump and the communication signal used for propagating line monitoring information. We develop the model of Novak and Moesle (2002), by including ASE, that they neglected. The derivation of an analytical model, for EDFA overmodulation response, has been presented. This model provides analytical expressions for the pump and input signal overmodulation responses, respectively. These expressions describe the output signal modulation index amplitude and phase, assuming small sinusoidal steady-state oscillations of the mean pump or input signal power. In this paper we show that ASE has some effects on predictions in the high gain/low saturation regime.

THEORETICAL INVESTIGATIONS TO MINIMIZE BIT ERROR RATE BY OPTIMIZING SYSTEM PARAMETERS IN OPTICAL DWDM TRANSMISSION SYSTEMS AT DIFFERENT DATA RATES

The amplifier separation and channel separation has conflicting effects on the noise generated due to the fiber non-linear effects (Stimulated Raman scattering SRS and Four wave mixing FWM) and the Amplified spontaneous emission (ASE) noise introduced by inline optical amplifications. While designing an efficient Dense Wavelength Division Multiplexing (DWDM) system, optimization of the channel separation and amplifier separation are required to minimize the non-linear effects (FWM and SRS) along with the ASE noise. In this paper, theoretical investigations of the optical DWDM systems have been presented to minimize the bit error rate (BER) by optimizing inter-channel separation and inter-amplifier separation at different data rates considering the combined effect of SRS, FWM, ASE, receiver and beat noises.

ASE effect in pulsed energy-storage rep-rated Yb:YAG disk laser amplifier

Based on the energy-level structure of quasi-three-level Yb ion, an amplified spontaneous emission（ASE） model in pumping process is set up. The stored energy density distribution and the energy that can be extracted in Yb:YAG crystal are calculated. The effect of ASE on energy-storage is investigated specifically, which includes the aperture, doping concentration and thickness, and working temperature of the gain medium. This paper gives an optimizing design of a pulsed energy-storage rep-rated Yb:YAG disk laser amplifier, which will be helpful in designing high-energy diode-pumped solid-state lasers based on Yb-doped materials.