Optical Gain Research Articles

Spectroscopic evaluation of Nd3+ doped cadmium-boro-phosphate glasses for near-IR (1060 nm) laser applications

Neodymium-doped Cadmium-boro-phosphate glasses were synthesized using the melt quenching procedure to investigate their lasing capacities. The FTIR results reveal the different functional groups and structural units of our glass system. Physical parameters such as density (ρ), molar volume (VM), refractive index (n), Urbach energy (ΔE), and band gap (Eg) were measured, and computed. The results demonstrated that our glasses have indirect-allowed transitions with low localized states. The photoluminescence and absorption spectra were measured and the results suggest that the Nd3+ ions have a uniform distribution throughout the glass network. The Judd-Ofelt parameters (Ω2, Ω4, and Ω6) were obtained using the least-squares procedure. The spectroscopic quality factor (χ), the emission-peak-wavelength (λp), the radiative-transition-probability (Ar), the radiative lifetime (τrad), the radiative and experimental branching-ratio (βrad, βexp), the effective-bandwidth (Δλeff), the stimulated-emission-cross-section (σ(λp)), the gain-bandwidth (σ(λp), × Δλeff) and the optical-gain (σ(λp) x τrad) were measured, computed and compared with other famous reported glasses. The current glass showed low χ values (=0.45), high βexp (=0.7), and high optical gain (15.8 × 10− 24 cm2 s). According to its spectroscopic and radiative properties, our glass system shows remarkable potential for lasing around 1057 nm.

High-speed signal processing and wide band optical semiconductor amplifier in the optical communication systems

Abstract This work clarifies the analysis of the theoretical study of noise and transmission gain characteristics of semiconductor optical amplifiers (SOAs), which are relevant in the novel local area optical communication systems. We investigated the effects of noise on AlGaAs/GaAs SOA transmission performance through the measurement of output power, optical gain, the optical signal-to-noise ratio, and noise figure. It was observed that noise has a dramatic effect on SOAs’ operation transmission efficiency, and the performance of the amplifier structure may be limited. If the drive current and injection power at the SOA can be changed and its active region length modified, then the variation of gain, optical signal-to-noise ratio, and noise figure at the output of the structure can be obtained.

Switching from Thermally Activated Delayed Fluorescence in Single Crystals for Low‐Threshold Laser to Room‐temperature Phosphorescence in Amorphous‐Film for Highly Efficient OLEDs

AbstractMetal‐organic phosphorescent complexes containing Ir or Pt are work horse in organic light‐emitting diode (OLED) technology, which can harvest both singlet and triplet excitons in electroluminescence (EL) owing to strong heavy‐atom effect. Recently, organic room‐temperature phosphorescence (ORTP) have achieved high photoluminescence quantum yield (PLQY) in rigid crystalline state, which, however, is unsuitable for OLED fabrication, therefore leading to an EL efficiency far low behind those of metal‐organic phosphorescent complexes. Here, we reported a luminescence mechanism switch from thermally activated delayed fluorescence (TADF) in single crystal microwires to ORTP in amorphous thin‐films, based on a tert‐butylcarbazole difluoroboron β‐diketonate derivative of DtCzBF2. Tightly packed and well‐faceted single‐crystal microwires exhibit aggregation induced emission (AIE), enabling TADF microlasers at 473 nm with an optical gain coefficient as high as 852 cm−1. In contrast, loosely packed dimers of DtCzBF2 formed in guest‐host amorphous thin‐films decrease the oscillator strength of fluorescence transition but stabilize triplets for ORTP with a PLQY up to 61 %, leading to solution‐processed OLEDs with EQE approaching 20 %. This study opens possibilities of low‐cost ORTP emitters for high performance OLEDs and future low‐threshold electrically injected organic semiconductor lasers (OSLs).

Switching from Thermally Activated Delayed Fluorescence in Single Crystals for Low-Threshold Laser to Room-temperature Phosphorescence in Amorphous-Film for Highly Efficient OLEDs.

Metal-organic phosphorescent complexes containing Ir or Pt are work horse in organic light-emitting diode (OLED) technology, which can harvest both singlet and triplet excitons in electroluminescence (EL) owing to strong heavy-atom effect. Recently, organic room-temperature phosphorescence (ORTP) have achieved high photoluminescence quantum yield (PLQY) in rigid crystalline state, which, however, is unsuitable for OLED fabrication, therefore leading to an EL efficiency far low behind those of metal-organic phosphorescent complexes. Here, we reported a luminescence mechanism switch from thermally activated delayed fluorescence (TADF) in single crystal microwires to ORTP in amorphous thin-films, based on a tert-butylcarbazole difluoroboron β-diketonate derivative of DtCzBF2. Tightly packed and well-faceted single-crystal microwires exhibit aggregation induced emission (AIE), enabling TADF microlasers at 473 nm with an optical gain coefficient as high as 852 cm-1 . In contrast, loosely packed dimers of DtCzBF2 formed in guest-host amorphous thin-films decrease the oscillator strength of fluorescence transition but stabilize triplets for ORTP with a PLQY up to 61 %, leading to solution-processed OLEDs with EQE approaching 20 %. This study opens possibilities of low-cost ORTP emitters for high performance OLEDs and future low-threshold electrically injected organic semiconductor lasers (OSLs).

Enhancement of Optical Gain in Colloidal CdSe/CdS/ZnS Quantum Dots through Nanosecond Optical Pumping.

Optical gain and lasing in colloidal nanocrystals are often hindered by sub-nanosecond rapid Auger non-radiative recombination, especially under continuous wave optical or electrical excitation. This study demonstrates amplified spontaneous emission (ASE) from CdSe/CdS/ZnS quantum dot (QD) solids through prolonged pulsed optical pumping over 10 ns. The incorporation of CdS and ZnS double shells on CdSe QDs effectively decelerates the Auger process in multiexcitonic states by extending the electron wave function and enhancing dielectric screening. Furthermore, we engineer smooth, densely packed QD solid films that efficiently guide the optical mode, achieving substantial net gain values under nanosecond pumping. The proposed approach helps observe ASE with gain thresholds of 0.84 and 1.5 mJ/cm2 under optical pumping pulse widths of 6 and 15 ns, respectively. This advancement can promote continuous pumping in colloidal QD gain systems, opening new avenues for optoelectronic applications.

Giant enhancement of third harmonic generation in an array of graphene ribbons using amplification of surface plasmon polaritons by optical gain

In this paper, we theoretically study the enhancement of third-harmonic generation in a plasmonic structure composed of an array of trilayer graphene ribbons sandwiched between two CaF2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$CaF_{2}$$\\end{document} layers. In fact, we suggest a new method for more enhancement of nonlinearity in plasmonic structures using incorporation of optical gain into graphene ribbons. As the pump intensity increases, the maximum output intensity of third harmonic generated (THG) wave versus fundamental frequency is blue-shifted while its value enhances. Our analysis indicates that the enhancement factor of THG in our proposed structure is 1.1 × 107 without occurring an electric breakdown compared to case at which an optically pumped trilayer graphene sheet sandwiched between two CaF2 layers. Therefore, only presence of optical gain is not sufficient for significant enhancement of output intensity of THG wave and excitation of SPPs through the structure is also essential. On the other hand, our results demonstrate that the output intensity of THG wave from the proposed structure under optical pumping enhances by 105\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{5}$$\\end{document} times compared to the plasmonic structure without optical gain which confirms the role of optical gain for THG enhancement in the plasmonic structure. This is because the gain in graphene ribbons amplifies the SPPs waves leading to the more field enhancement along the graphene ribbons which results in significant enhancement of THG wave in the plasmonic structure in comparison with one without gain. Therefore, we reveal that both SPPs and optical gain contribute to the strong output intensity of THG in our proposed structure compared to the trilayer graphene sheet inserted between two CaF2 layers.

Erbium-Ion-Doped Bismuth Borate Glasses for High Optical Gain NIR Fiber Laser Applications

The study focused on investigating the thermal, structural, and luminescent properties of bismuth borate glasses doped with erbium (Er3+) ions and modified with Gd2O3, K2O, and Li2O (BBGKL: Erx) aiming for fiber lasers. Two glass transition temperatures were observed at 381 (Tg1) and 471 K (Tg2) for BBGKL glass. O1s de-convolution spectrum bridging oxygens for BBGKL glass, including B-O, Bi-O, Li2O, and K2O, were discovered by XPS. Both the photoluminescence (PL) 4I13/2→4I15/2 NIR and the absorption bands from the UV-visible-NIR spectrum were found to occur at 1531 nm for BBGKL: Er. The luminescence quenching was not noticed up to 3.0 mol% of Er3+ ion concentration. The BBGKL: Er0.5 glass has a remarkable connection between its absorbance and emission cross-sections of 0.77 and 0.82 × 10−20 cm2, respectively. The longest lifetime of green emission for the 4S3/2→4I15/2 transition was found for BBGKL: Er2.0 glass at 10.6 μs and 1531 nm NIR emission for the 4I13/2→4I15/2 transition of BBGKL: Er0.5 glass was 0.77 ms. In the 1413–1728 nm NIR band region for BBGKL:Er3.0, high optical gain cross-section G(λ) was promising for the population inversion at γ = 0.6. These findings suggested that the BBGKL: Er0.5 glass would prove helpful in NIR fiber laser applications.

Intersubband optical gain spectra in compressively strained InGaAs/GaInP quantum well

In this paper, the theoretical analyses of the optical intersubband transitions in strained InGaAs/GaInP quantum well are investigated. A simplified method of the treatment of the compressive strain effects incorporation for the wavefunction and thus the intersubband dipole matrix is discussed. The effects of Gallium mole fraction, quantum well width and compressive strained on the band properties, intersubband transitions and optical absorption/gain spectra are shown to be pronounced. Thus this present investigation could become a good guild for tuning the optoelectronic properties of many quantum devices utilizing intersubband electronics in their various technological applications.

Ultrastable and high-performance amplified spontaneous emission in centimeter-scale inorganic CsPbBr3 single-crystal thin films

In this work, high-quality and centimeter-scale CsPbBr3 perovskite single-crystal thin films were grown using the metal-organic chemical vapor deposition method. Extremely flat surfaces without distinct grain boundaries were observed throughout the thin films. A high polarized degree of approximately 0.52 was measured from the single-crystal thin films by analyzing the polarization of the photoluminescence emission spectra. Low threshold amplified spontaneous emissions with an optical gain coefficient of 1215 cm−1 under the excitation energy of 301 μJ/cm2 and the highest value of 2857 cm−1 under the excitation energy of 1.08 mJ/cm2 were investigated under the excitation of a nanosecond laser at 266 nm. The CsPbBr3 single-crystal thin films showed excellent stability where the optical gain coefficient could be maintained over 1800 cm−1 after exposure to air for ten months. The results of this study not only provide high-quality single-crystal films for laser applications but also put forward a feasible scheme to improve the stability of the materials.

Boosting the Downconversion Luminescence of Tm3+-Doped Nanoparticles for S-Band Polymer Waveguide Amplifier.

Polymer waveguide devices have attracted increasing interest in several rapidly developing areas of broadband communications since they are easily adaptable to on-chip integration and promise low propagation losses. As a key member of the waveguide gain medium, lanthanide doped nanoparticles have been intensively studied to improve the downconversion luminescence. However, current research efforts are almost confined to erbium-doped nanoparticles and amplifiers operating at the C-band; boosting the downconversion luminescence of Tm3+ for S-band optical amplification still remains a challenge. Here we report a Tb3+-induced deactivation control to enhance Tm3+ downconversion luminescence in a stoichiometric Yb lattice without suffering from concentration quenching. We also demonstrate their potential application in an S-band waveguide amplifier and record a maximum optical gain of 18 dB at 1464 nm. Our findings provide valuable insights into the fundamental understanding of deactivation-controlled luminescence enhancement and open up a new avenue toward the development of an S-band polymer waveguide amplifier with high gain.

Enhanced Spin Polarization from Biaxially Strained Colloidal Quantum Dots.

Electron and hole spin polarization is crucial for quantum dots to be used in spin lasers and quantum information processing. However, the degree of spin polarization in II-VI and III-V semiconductor quantum dots is low because of the degenerated valence band. Here, we increase the light and heavy hole degeneracy by introducing biaxial strain into CdSe-based quantum dots, enabling the degree of spin polarization to be increased from 20% to 50% under photoexcitation. The optical gain threshold measurement further reveals that the increase in polarization helps to reduce the gain threshold.

Temperature dependence of optical gain in compressively strained InAsP/GaInAs based quantum well heterostructure for short wavelength infrared applications

This paper reports temperature results on InAs0.8P0.2/Ga0.3In0.7As/InP quantum well heterostructure with a type-II band alignment that causes electron and hole to have spatially separated wavefunction. Theoretical simulations of the band structure and wavefunctions are conducted using the k.p method with the Luttinger-Kohn 6 × 6 Hamiltonian. In addition, the energy dispersion curve, momentum matrix element, and optical gain are also calculated. Our results show that the proposed heterostructure is promising for fabricating 1.84 μm (short wavelength infrared region-SWIR) lasers at room temperature. The effect of an increase in temperature on energy gap, optical gain, and transition wavelength is observed. Redshift is realized as the temperature rises from 100 K to 500 K.

Chaotic dynamics in X-ray free-electron lasers with an optical undulator.

In this work, the chaotic motions of relativistic electrons in X-ray free-electron lasers are investigated using an optical undulator in the presence of a magnetized ion-channel background. To miniaturize X-ray light sources, the optical undulator is a promising concept. The optical undulator provides higher optical gain than conventional magnetostatic undulators due to its micrometer wavelength. In addition, it reduces the required electron beam energy from several GeV to the multi-MeV range to produce X-ray pulses. The interaction of an optical undulator with an intense relativistic electron beam is a highly non-linear phenomenon that can lead to chaotic dynamics. At synchrotron radiation sources, the possibility of chaos control for X-ray FELs can be critical for certain classes of experimental studies. The equations of motion for a relativistic electron propagating through the optical undulator in the presence of a magnetized ion-channel can be derived from the Hamiltonian of the interaction region. Simulation results revealed that the intensity of the perturbation route from orderly behavior to chaos depends on the beam density, axial magnetic field strength, ion-channel density parameter, and pump laser undulator. Specific values of parameters were obtained for the transition from regular to chaotic paths. Bifurcation diagrams of the system were plotted to demonstrate the origin of chaos at a critical point, and Poincaré maps were created to distinguish between chaotic and orderly motions of electrons. The proposed new scheme can help to improve X-ray FELs, which have potential usages in basic sciences, medicine, and industry.

Cluster Control for Construction of Bismuth‐Doped Glass Fiber with Broadband Optical Response

AbstractBismuth(Bi)‐doped optical fibers are widely used in various aspects such as fiber lasers and amplifiers. Despite extensive research efforts to explore high‐gain Bi‐doped fibers, the pursuit of Bi‐doped fibers with emission over an extremely wide wavelength range remains unfulfilled. Here, the strategy of cluster control via regulating glass structure is proposed. It is applied to construct Bi‐doped photonic glass with ultra‐broadband near‐infrared (NIR) emission and a full width at half maximum (FWHM) of 343 nm. The strategy is further combined with the modified chemical vapor deposition (MCVD) technique with solution doping. The fiber exhibits ultra‐broadband amplified spontaneous emission (ASE) covering the entire fiber communication band (1260–1625 nm). Finally, the fiber exhibits higher optical gain and bandwidth compared with the fiber without cluster control. This device can be utilized to potentially enhance the capacity of telecommunication systems.

Suppression of Randomness in Electrically Pumped Random Lasing from a ZnO Film-Based Light-Emitting Device on Silicon.

We report on the suppressed randomness in electrically pumped random lasing (RL) from a light-emitting device (LED) based on a metal-insulator-semiconductor (MIS) structure of Au/SiOx (x < 2)/ZnO on a silicon substrate, by means of patterning the light-emitting ZnO polycrystalline film into a number of square blocks separated by streets that are filled with the SiOx insulator. It is found that the RL modes can be remarkably reduced by shrinking the blocks in the absence of interblock optical coupling. Meanwhile, with the imposition of interblock optical coupling by shrinking the streets, the RL modes can be further reduced, and more importantly, the strongest mode wavelength is stabilized around 380 nm, where the ZnO film exhibits the largest optical gain.

Optical gain and entanglement through dielectric confinement and electric field in InP quantum dots.

Quantum dots are widely recognized for their advantageous light-emitting properties. Their excitonic fine structure along with the high quantum yields offers a wide range of possibilities for technological applications. However, especially for the case of colloidal QDs, there are still characteristics and properties which are not adequately controlled and downgrade their performance for applications which go far beyond the simple light emission. Such a challenging task is the ability to manipulate the energetic ordering of exciton and biexciton emission and subsequently control phenomena such as Auger recombination, optical gain and photon entanglement. In the present work we attempt to engineer this ordering for the case of InP QDs embedded in polymer matrix, by means of their size, the dielectric confinement and external electric fields. We employ well tested, state of the art theoretical methods, in order to explore the conditions under which the exciton-biexciton configuration creates the desired conditions either for optical gain or photon entanglement. Indeed, this appears to be feasible for QDs with small diameters (1 nm, 1.5 nm) embedded in a host material with high dielectric constant and additional external electric fields. These findings offer a new design principle which might be complementary to the well-established type II core-shell QDs approach for achieving electron-hole separation.

NANOSCALE HETEROSTRUCTURE CONCEPT AND III-SB ELEMENT BASED HETEROSTRUCTURES FOR INFRARED APPLICATIONS: A REVIEW

Heterostructures have a high potential for infrared radiation applications in the present scenario. The infrared (IR) region, particularly ranging from 760 nm to 1 million nm, is significant in a list of applications including communications, sensing, monitoring, and imaging. According to different applications, designs of nanoscale heterostructures vary. For this purpose, III-Sb element-based heterostructures are studied. We found a dramatic change toward longer luminous wavelengths while preserving high crystal quality with the addition of Sb to ternary and quaternary. The current study shows the compositional changes in the material caused by adding Sb. In order to boost the device's performance, several heterostructures have been designed. The optical characteristics of these heterostructures are also analyzed under various parameters such as pressure, temperature, and external electric field. For the computation of characteristics like optical gain, band structure, wave function, etc., the k&amp;#183;p method and Luttinger-Kohn model are employed. This review article reveals research on different heterostructure designs for IR applications. This work is the result of numerous types of research in the subject of optoelectronics.

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.

The optical gain variation of Ge nanowires induced by L-valley splitting under the [110] direction stress

The electronic structures of Ge nanowires under the [110] direction stress are calculated via effective-mass k·p theory, and the results manifest eight equivalent L-valleys will be split into fourfold degenerate L 1-valleys and L 2-valleys. With increasing stress, the electron levels at the L 1-valleys and L 2-valleys can be pushed close to and away from those at the Γ-valley, respectively, which causes the appearance of a rising inflection point in the Γ-valley filling ratio and gain peak intensity at around 2.5 GPa stress. Moreover, we prove the positive net peak gain with small diameters is apt to be obtained considering the free-carrier absorption loss.

Realizing high zero-bias gain in a GaN-based bipolar phototransistor through thin-base configuration for ultraviolet imaging

A GaN-based ultraviolet bipolar phototransistor with high zero-bias gain is obtained based on an asymmetric n–p–i–n homo-structure. A thin-base structure is proposed to suppress excess holes recombination and, thus, to promote optical gain.