Amplified Spontaneous Emission Research Articles

Characterization of Visible Range Gain in Praseodymium Doped Fiber Amplifier

In the optical (380-700 nm) region, a simulation study was conducted to assess the low-signal gain, power conversion efficiency (PCE), and optical output power of a praseodymium-doped fiber optic amplifier (PDFA). The PDFA performance was assessed using the optimized Pr3+ fiber length, Pr3+ ion concentration, and pump power. Additionally, the effects of input signal voltage and amplifier gain on amplified spontaneous emission (ASE) were investigated. A lower peak signal of roughly 1 dB at 635 nm was obtained with a shorter 5 m Pr3 + doped fiber and a higher pump power of 300 mW. The impact of wavelength and pump power variations on the amplifier's optical output power's spontaneous enhanced emission (EEM) is examined. Finally, the ionic interaction (general-purpose conversion effect) in the low-power amplifier signal is analyzed by taking into account various values of the upconversion factor. Keywords: Praseodymium doped fibre amplifier, Small-signal gain, Pump power, Ultrashort laser.

Amplified spontaneous emission from a liquid crystalline phase: anisotropic property and active modulation.

Amplified spontaneous emission (ASE) is considered to be a primary indication of optical gain in active media without an external resonator. Molecular materials with ASE are expected to be one of the suitable light sources for specific applications such as optical coherent tomography owing to their low coherence and flexible tunability. Concentration quenching of emissive excited states has been a critical issue to boost the quantum efficiency of molecular materials in their condensed phases. The rod-like design of molecules with excited state intramolecular proton transfer (ESIPT) has been demonstrated to overcome this issue in highly-concentrated molecularly-doped systems, as represented by C4alkyne-HBT (2-(4-(1-hexynyl)-2-hydroxyphenyl)-benzothiazole). We designed an ESIPT molecule-doped liquid crystalline (LC) system for optical amplification via the ASE regime with its wide tunability of emission intensity. Detailed ASE behaviour and optical gain of a LC blend of C4alkyne-HBT and 4-pentyl-4'-cyano biphenyl (5CB) was evaluated to afford a maximum optical gain of 16.5 cm-1 with an estimated ASE threshold of optical pumping at 0.6-0.7 mJ cm-2. Although most ASE studies focus on homogeneous solutions, solids, or crystalline states, ASE from a soft-flexible LC phase is quite limited and advantageous for the design of an external optical resonator/cavity structure. Optical excitation parallel and perpendicular to the director resulted in the strong modulation of the ASE. By using the benefits of a LC phase, the ASE was actively modulated under the external electric field by the reorientation of the molecular dipole moment.

Suppression of the plasmon-quenching effect on light amplification in 20-μm-diameter plasmonic whispering gallery mode resonators fabricated from bowl-shaped organic/metal thin films.

Bowl-shaped plasmonic whispering gallery mode (WGM) resonators were fabricated from a 10-nm-thick metal (Al, Ag, or Au) plasmonic layer that was covered with a 100-nm-thick 4,4'-bis(N-carbazolyl)-1,1'-biphenyl spacer layer and a 250-nm-thick 2,7-bis[9,9-di(4-methylphenyl)-fluoren-2-yl]-9,9-di(4-methylphenyl)fluorene light-emitting layer; the layer structure was grown on a 20-μm-diameter silica microsphere. When compared with a reference structure without the plasmonic layer, the resonators, which included either Al or Ag, showed almost the same threshold excitation intensities for generation of amplified spontaneous emission (ASE). This result indicates that the ease of light amplification in the plasmonic resonators was comparable to that in the reference structure. Excitons that exist in the vicinity of metal thin films are generally easy to quench because propagating surface plasmon polaritons (SPPs) absorb the exciton energy. Therefore, the observed comparability demonstrates that the plasmonic WGM resonators overcome this quenching effect on ASE via localization of the SPPs in the vicinity of the excitons.

Device parameter to evaluate exciton energy transfer in organic whispering-gallery-mode microresonators and its dependence on the amplified spontaneous emission threshold.

Exciton energy transfer in organic whispering-gallery-mode (WGM) resonators and its effect on the amplified spontaneous emission (ASE) threshold have been investigated using the stilbene-based energy donor 4,4'-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) and the coumarin-based energy acceptor 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10-(2-benzothiazolyl)quinolizino[9,9a,1gh]coumarin (C545T). Using the stacked-layer structure of BSB-Cz/C545T/BSB-Cz, we fabricated bowl-shaped microresonators on silica microspheres with a total thickness of 250 nm fixing the thickness of the C545T layer to 1 nm. The ASE threshold depended on the thicknesses of the top and bottom BSB-Cz layers, which affect the magnitude of the energy transfer. To assess the relationship between the ASE threshold and energy transfer, we developed a device parameter to evaluate the magnitude of the energy transfer by formulating the rate equations. We found that ASE easily occurs under the condition that the C545T molecules become unable to accept energy from the BSB-Cz excitons owing to the high exciton density of C545T, and that the ASE threshold decreases with decreasing device parameter. The device parameter is useful for optimizing microresonator structures in multi-component organic WGM resonators that utilize energy transfer.

Improving thermal- and photo-stability of CsPbBr3 perovskite films by adding graphene oxide for low threshold amplified spontaneous emission

Solution-processed all-inorganic CsPbBr3 perovskite thin films show great promise for green lasers owing to the unique optoelectronic properties and processability. However, the amplified spontaneous emission (ASE) of CsPbBr3 films with...

Four-wave mixing model for centrosymmetric constellation shaping in twin-wave-based coherent OFDM system including intersymbol interference

The four-wave-mixing (FWM) noises are modeled when walk-off and intersymbol interference (ISI) are taken into account for any centrosymmetric constellation shaped signal in orthogonal frequency-division multiplexed (OFDM) with phase-conjugated twin waves (PCTW) scheme. Bit error rate (BER) and the equivalent Q-factor for any constellation shaped signal are also modeled when the FWM and amplified spontaneous emission (ASE) noises are taken into account as additive white Gaussian noise. By using the newly derived semi-analytic models, example calculations are carried out for 16-ary signal in PCTW OFDM system with four cases classified according to some proposed constellation shaping schemes adopted or not. A hybrid constellation shaping scheme consisted of Huffman-coded probabilistic shaping and radius-optimized geometric shaping is proposed. The performance gain in terms of the equivalent Q-factor is calculated to be about 0.563 dB for 16-ary signal in PCTW OFDM system with the proposed hybrid constellation shaping scheme over the square conventional 16QAM signal. The performance degradation for such system due to the effects of ISI on the FWM noise is also evaluated by using the semi-analytic calculation models.

Fast Post-processing Method for Practical Quantum Random Number Generators Based on Spontaneous Emission Amplification

Fast Post-processing Method for Practical Quantum Random Number Generators Based on Spontaneous Emission Amplification

Propagation loss in polyfluorene waveguides due to nanometer-roughness at their interfaces, studied by amplified spontaneous emission measurements

The propagation loss in single-mode asymmetric waveguides due to interface nanometer-roughness was studied using amplified spontaneous emission (ASE) measurements. Poly(9,9-dioctylfluorene) (F8) was used as the organic gain medium and the structure of the asymmetric waveguide was quartz glass substrate/F8/air. The propagation loss was measured at the ASE wavelength (447 nm) of amorphous F8, and the surface roughness of the substrate and F8 was measured using an atomic force microscope. The propagation losses of F8 waveguides with different F8 slab thicknesses were in good agreement with those calculated using an analytical expression for single-mode asymmetric waveguides with nanometer-roughness interfaces. The results presented herein will be useful for the design of high-performance organic lasers and organic optoelectronic integration systems.

Loss compensated fiber loop ring-down system driven by random distributed multi-pulse laser

The sensing characteristics of loss compensated fiber loop ring-down (FLRD) system driven by random distributed multi-pulse have been analyzed. We used a random distributed multi-pulse laser to drive a fiber loop with loss compensation of erbium-doped fiber amplifier (EDFA) and analyzed the distortion of exponential attenuation curves, sensitivity and baseline stability of the system. The performance is compared with those of loss compensated FLRD system driven by single pulse and chaotic laser. The loss compensated FLRD theoretical model is discussed by the transmission equation of EDFA and finite element analysis. The performance of loss compensated FLRD system driven by random distributed multi-pulse under different injection optical powers is analyzed under the influence of gain saturation effect of EDF and amplified spontaneous emission (ASE). The results show that the random distributed multi-pulse system has higher R-square of exponential attenuation curves and better baseline stability than the single-pulse system. The increase of injection optical power has the least influence on the sensitivity reduction of random distributed multi-pulse system. The random distributed multi-pulse laser has better performance than single-pulse laser and chaotic laser in loss compensated FLRD system.

Carrier Trapping Deactivation by Halide Alloying in Formamidinium‐Based Lead Iodide Perovskites

AbstractFormamidinium lead iodide (FAPbI3) is the benchmark material for the most efficient near‐infrared perovskite light‐emitting diodes (LEDs) and a promising gain medium for perovskite‐based coherent light sources. Thus, it is crucial to understand and control its defect chemistry to harness the full potential of its exceptional radiative recombination properties. Here, this topic is addressed by tailoring the I− to Br− ratio in the perovskite composition. It is found that introducing small Br− quantities improves the yield of radiative recombination with a beneficial impact on both spontaneous and amplified spontaneous emission (ASE) and improves the semiconductor photostability leading to reduced luminescence efficiency roll‐off and enhanced radiance in LEDs. By employing photoemission electron microscopy (PEEM), this improvement in optoelectronic performance can be directly correlated to a reduced hole‐trapping activity achieved by replacing iodide with bromide, thus, providing a convenient yet powerful synthetic approach to control the defect chemistry of the material and fostering its implementation in advanced photonic platforms.

Linearly Manipulating Color Emission via Anion Exchange Technology for High Performance Amplified Spontaneous Emission of Perovskites.

The most attractive advantages of all-inorganic cesium lead halide perovskites are their optical gain over broad spectral ranges through the visible spectrum, so are well suited to use in tunable lasers or broadband amplifiers. Most reported anion exchange reactions face a challenge to achieve the desired halogen-variable perovskites due to rapid and uncontrollable reactions and difficulty to synthesize directly. In this study, a simple vapor/solid anion exchange strategy is demonstrated for controlling the reaction process and realizing a wide range tuning of band gap and amplified spontaneous emission (ASE) wavelength, which exhibits a temperature-dependent anion exchange rate. By optimizing the reaction temperature at 90°C, the ASE wavelength can be linearly manipulated by just controlling the reaction time. A clear quantitative relationship between ASE peak position and reaction time is achieved. Compares with the CsPbClBr2 film obtained via the liquid phase anion exchange method, the fabricated perovskite films obtained by vapor/solid anion exchange technology exhibit superior film quality and enhanced ASE performance. This work may have applications in the future using facile and controllable techniques to develop high-quality full-color visible lasers.

Two-Color Amplified Spontaneous Emission from Auger-Suppressed Quantum Dots in Liquids.

Colloidal quantum-dot (QD) lasing is normally achieved in close-packed solid-state films, as a high QD volume fraction is required for stimulated emission to outcompete fast Auger decay of optical-gain-active multiexciton states. Here a new type of liquid optical-gain medium is demonstrated, in which compact compositionally-graded QDs (ccg-QDs) that feature strong suppression of Auger decay are liquefied using a small amount of solvent. Transient absorption measurements of ccg-QD liquid suspensions reveal broad-band optical gain spanning a wide spectral range from 560 (green) to 675nm (red). The gain magnitude is sufficient to realize a two-color amplified spontaneous emission (ASE) at 637 and 594nm due to the band-edge (1S) and the excited-state (1P) transition, respectively. Importantly, the ASE regime is achieved using quasicontinuous excitation with nanosecond pulses. Furthermore, the ASE is highly stable under prolonged excitation, which stands in contrast to traditional dyes that exhibit strong degradation under identical excitation conditions. These observations point toward a considerable potential of high-density ccg-QD suspensions as liquid, dye-like optical gain media that feature readily achievable spectral tunability and stable operation under intense photoexcitation.

Amplified spontaneous emission at the band edges of Ag-coated Al nanocone array

Surface lattice resonances (SLRs) with ultra-narrow linewidth (high quality factor) can enhance light–matter interactions at the nanoscale and modulate the propagating light from the emission wavelength direction to efficiency by photonic band engineering. Therefore, SLRs can serve as an excited candidate to enhance and, more importantly, modulate amplified spontaneous emission (ASE) with more optical parameters. Here, this work presents a system of two-dimensional Ag-coated Al nanocone array (Ag-NCA) packaged with Nile red, and a normal ASE with 15-fold enhancement is observed under external driving light. This enhancement fades away, obviously, in the case of the off-normal condition, as the optical feedback evolves from the band edge steady state to the propagating state. The ASE of this hybrid plasmonic system expands the possibilities of interaction between light and matter and has great promise for applications in nanolasing, super-resolution imaging, and photonic integration circuits.

Origin and properties of polychromatic directional emission from sodium atoms

The parametric and nonparametric nonlinear processes responsible for generation of directional infrared radiation in sodium vapors, excited to the 4D5/2 energy level by resonant laser radiation, are identified by the transfer of orbital angular momentum from the pump radiation to the generated fields. We show that the optical fields generated by amplified spontaneous emission (ASE) simultaneously participate in several loops of four-wave mixing (FWM) generating new directional emission. The measured spectral linewidth of the FWM emission at 819.7 nm sets an upper limit to the linewidth of two fields resulting from ASE at 2338.6 and 9093.0 nm, assuming their spectra are uncorrelated. Understanding details of the new-field generation is central to applications such as directional laser guide stars, stand-off magnetometry, and entangled field generation.

Implementation and evaluation of two parallel computational models for the simulation of a long‐haul DWDM system limited by FWM

AbstractFour‐Wave Mixing (FWM) is one of the non‐linear phenomena affecting long‐reach communication systems and high bandwidth. Research communities use simulation tools for parameter optimization. Unfortunately, such a simulation is time‐consuming and requires more time as the number of channels increases. This paper proposes two fast implementations of Dense Wavelength Division Multiplexing (DWDM) system, limited by FWM and the intrinsic Amplified Spontaneous Emission (ASE) noise of optical amplifiers employed in each segment. Additionally, this work compares the efficiency and speed improvement of the proposed parallelization model versus an earlier sequential model. We present the computational complexity analysis of sequential and parallel models. The paper considers two different parallel implementations: a multicore processor using Open MultiProcessing (OpenMP) and Compute Unified Device Architecture (CUDA), which is based on the use of a Graphics Processing Unit (GPU). Results show that parallelism using CUDA improves by up to 70 times the simulation performance compared to the sequential model. Parallelism with CUDA is up to 15 times compared to OpenMP using 12 logical processors. It is possible to simulate an increased number of channels within our parallel execution, which was impractical in the sequential simulation.

Combined intra symbol frequency domain averaging channel estimation for polarization division multiplexed coherent optical OFDM/OQAM systems

Intrinsic imaginary interference (IMI) induced by chromatic dispersion (CD) and polarization mode dispersion (PMD) seriously degrades the performance of optical orthogonal frequency division multiplexing offset-quadrature amplitude modulation (O-OFDM/OQAM) systems. Therefore, effective channel estimations are required for such systems to maintain good transmission performance. In the previous publications, both the full loaded (FL) and the half loaded (HL) frequency-domain channel estimation methods for polarization-division-multiplexed (PDM) coherent optical OFDM/OQAM (CO-OFDM/OQAM) systems have been proposed. However, for these frequency-domain methods, the channel frequency-domain responses caused by the correlation of the amplified spontaneous emission (ASE) noise are not considered. In this paper, we systematically discuss the frequency-domain channel transmission model for PDM CO-OFDM/OQAM systems. With the analysis of the correlation of the ASE noise, we propose a combined intra symbol frequency-domain averaging (CISFDA) channel estimation method for PDM OFDM/OQAM systems. Compared with the full-loaded frequency-domain channel estimation (FL-FD) method, the CISFDA method promotes the system robustness against the ASE noise and fiber nonlinear effect significantly. The proposed method is validated by numerical Monte Carlo simulations of the PDM CO-OFDM/OQAM system. Our new algorithm outperforms the FL-FD method in the 36 Gb/s PDM OFDM CO-OFDM/OQAM system, and the transmission distance is improved by 500 km with the bit-error-rate (BER) target at 3.8×10-3.

Subnoise optical covert communication based on amplified spontaneous emission light.

Amplified spontaneous emission (ASE) light is a common noise in optical communication systems with optical amplification, and a suitable optical carrier for optical covert communication. To deeply covert the secure signal, an in-band subnoise optical covert communication scheme is proposed and demonstrated by a proof-of-concept experiment. The power spectral density of optical secure channel is 10 dB less than the optical noise in the public channel. The covert signal is hidden in both optical and electrical domain, and can be transmitted with error-free. The trade-off between covertness and availability is discussed.

Self‐Assembly of Hydrogen‐Bonded Organic Crystals on Arbitrary Surfaces for Efficient Amplified Spontaneous Emission

Organic lasers attract much attention due to their high efficiency, low energy consumption, and structural flexibility. However, long‐term stability and the creation of the lasers on arbitrary surfaces remain a challenge. Here, a synthesis of amide‐based organic molecules that provides packing into hydrogen‐bonded organic crystals (OCs) is reported. The resulting OCs demonstrate an amplified spontaneous emission (ASE) regime with 0.55 μJ cm−2 threshold under the normal conditions due to 5%–13% quantum yield and high emission rate (1.02 ns). The simple process of self‐assembly of the hydrogen‐bonded OCs and highly stable ASE (over 30 min of continuous operation) allow fabricating fibers, flexible polymers, and hard planar periodic optical systems based on them, which paves the way to creating organic laser diodes of an arbitrary design.

Improved Brillouin induced self-heterodyne method for measurement of narrow laser linewidth

In this paper, we present the improved stimulated Brillouin-induced self-heterodyne (ISISH) method that overcomes the effect of amplified spontaneous emission (ASE) noise of erbium doped fiber amplifier (EDFA) on linewidth measurements. In addition, we eliminate the beating effects of additional sideband during the measurement of narrow laser linewidth. Moreover, we experimentally demonstrate the effect of amplified spontaneous Brillouin scattering (ASBS) noise on the variation of the measured linewidth of the laser under test (LUT) with varying pump power. We measure the Brillouin amplifier gain, which is essential for the ISISH technique, as 13.5, 12.7 and 9.5 dB at the pump powers of 16, 12 and 8 mW, respectively. These results are consistent with the analytical values of 14, 13 and 12.5 dB at the same variations in pump powers as previously reported. Experimental results show the 20 dB linewidths of 4, 6.7 and 10 kHz at pump powers of 16, 12 and 8 mW, respectively. We also perform the stimulated Brillouin-induced self-heterodyne (SISH) method. However, in SISH, the obtained linewidth of the LUT differs by approximately 4, 4.3 and 5 kHz at the pump powers of 16, 12, and 8 mW, respectively. Furthermore, we investigate the effect of detuning on LUT linewidth measurement in the ISISH method. The 20 dB linewidths at 5 and 10 MHz detuned from the Brillouin peak at 16 mW pump power are 20 and 25 kHz, respectively. These values are significantly larger than the measured linewidth at the pump power of 16 mW without detuning.

Broadband 1.0 µm emission in Nd3+/Yb3+ co-doped phosphate glasses and fibers for photonic applications.

In this work, the spectroscopic properties of 1.0 µm emission in Nd3+/Yb3+ co-doped phosphate glasses were systematically investigated under 808 nm excitation. Notably, broadband 1.0 µm emission with a full width at half maximum (FWHM) of 96 nm was obtained in the phosphate glass doped with 2 mol.% Nd2O3 and 1 mol.% Yb2O3. In addition, the energy transfer microscopic parameter and transfer efficiency were analyzed. What is more, multimaterial fibers with Nd3+/Yb3+ co-doped phosphate glass core and silicate cladding were successfully drawn by using the molten core method. An intense 1.0 µm amplified spontaneous emission (ASE) can be realized in a 3 cm long multimaterial fiber. More importantly, the FWHM of the ASE can reach as large as 60 nm when excited at 976 nm. These results demonstrate that the Nd3+/Yb3+ co-doped phosphate glasses and fibers are promising gain materials for amplifier and laser applications in photonics.