Narrow Spectral Width Research Articles

High Efficiency Organic Solar Cells Achieved by the Simultaneous Plasmon‐Optical and Plasmon‐Electrical Effects from Plasmonic Asymmetric Modes of Gold Nanostars

The plasmon-optical effects have been utilized to optically enhance active layer absorption in organic solar cells (OSCs). The exploited plasmonic resonances of metal nanomaterials are typically from the fundamental dipole/high-order modes with narrow spectral widths for regional OSC absorption improvement. The conventional broadband absorption enhancement (using plasmonic effects) needs linear-superposition of plasmonic resonances. In this work, through strategic incorporation of gold nanostars (Au NSs) in between hole transport layer (HTL) and active layer, the excited plasmonic asymmetric modes offer a new approach toward broadband enhancement. Remarkably, the improvement is explained by energy transfer of plasmonic asymmetric modes of Au NS. In more detail, after incorporation of Au NSs, the optical power in electron transport layer transfers to active layer for improving OSC absorption, which otherwise will become dissipation or leakage as the role of carrier transport layer is not for photon-absorption induced carrier generation. Moreover, Au NSs simultaneously deliver plasmon-electrical effects which shorten transport path length of the typically low-mobility holes and lengthen that of high-mobility electrons for better balanced carrier collection. Meanwhile, the resistance of HTL is reduced by Au NSs. Consequently, power conversion efficiency of 10.5% has been achieved through cooperatively plasmon-optical and plasmon-electrical effects of Au NSs.

Excellent green but less impressive blue luminescence from CsPbBr3 perovskite nanocubes and nanoplatelets

Green photoluminescence (PL) from CsPbBr3 nanocubes (∼11 nm edge-length) exhibits a high quantum yield (>80%), narrow spectral width (∼85 meV), and high reproducibility, along with a high molar extinction coefficient (3.5 × 106 M−1 cm−1) for lowest energy excitonic absorption. In order to obtain these combinations of excellent properties for blue (PL peak maximum, λmax < 500 nm) emitting samples, CsPbBr3 nanocubes and nanoplatelets with various dimensions were prepared. Systematic increases in both the optical gap and transition probability for radiative excitonic recombination (PL lifetime 3–7 ns), have been achieved with the decreasing size of nanocubes. A high quantum yield (>80%) was also maintained, but the spectral width increased and became asymmetric for blue emitting CsPbBr3 nanocubes. Furthermore, PL was unstable and irreproducible for samples with λmax ∼ 460 nm, exhibiting multiple features in the PL. These problems arise because smaller (<7 nm) CsPbBr3 nanocubes have a tendency to form nanoplatelets and nanorods, eventually yielding inhomogeneity in the shape and size of blue-emitting nanocrystals. Reaction conditions were then modified achieving nanoplatelets, with strong quantum confinement along the thickness of the platelets, yielding blue emission. But inhomogeneity in the thickness of the nanoplatelets again broadens the PL compared to green-emitting CsPbBr3 nanocubes. Therefore, unlike high quality green emitting CsPbBr3 nanocubes, blue emitting CsPbBr3 nanocrystals of any shape need to be improved further.

The Parsec-Scale Morphology of Southern GPS Sources

AbstractMulti-frequency, multi-epoch ATCA observations of a sample of AGN resulted in the identification of nine new candidate Giga-hertz Peaked Spectrum sources. Here, we present Long Baseline Array observations at 4.8 GHz of the four candidates with no previously published VLBI image, and consider these together with previously published VLBI images of the other five sources. We find core-jet or compact double morphologies dominate, with further observations required to distinguish between these two possibilities for some sources. One of the nine candidates, PKS 1831–711, displays appreciable variability, suggesting its GPS spectrum is more ephemeral in nature. We focus in particular on the apparent relationship between a narrow spectral width and ‘compact double’ parsec-scale morphology, finding further examples, but also exceptions to this trend. An examination of the VLBI morphologies high-redshift (z &gt; 3) sub-class of GPS sources suggests that core-jet morphologies predominate in this class.

光参量振荡器和光参量放大器实现窄谱宽中红外激光输出

光参量振荡器和光参量放大器实现窄谱宽中红外激光输出

Athermal distributed Brillouin sensors utilizing all-glass optical fibers fabricated from rare earth garnets: LuAG

An all-glass optical fiber derived from single-crystal LuAG is investigated for its potential use in athermal Brillouin distributed strain sensors. Such sensor systems are comprised of fiber whose Brillouin frequency shift is independent of temperature, but not independent of strain. Bulk Brillouin spectroscopy measurements on the precursor LuAG crystal are performed to gain insight into the crystal-to-glass transition. Results suggest that both the mass density and acoustic velocity are reduced relative to the crystal phase, in common with the other rare earth aluminosilicates. Advantages of the LuAG derived fiber over other rare earth garnet-derived fibers for the sensing application are a stronger strain response and larger Brilloun gain with narrower Brillouin spectral width.

Comparison of femtosecond pulse dynamics in a PCF amplifier with backward and forward pump schemes

A comparative study of femtosecond pulse dynamics in a photonic crystal fiber amplifier with backward and forward pump schemes is demonstrated experimentally and numerically. The output power, pulse duration and spectrum width of the amplified soliton pulse at different pump powers under the two pump schemes are discussed. The results show that the evolution of the soliton pulse shape in the temporal and spectral domains is also dependent on the direction of pump besides the output power. A narrower pulse duration and spectral width (i.e. smaller time-bandwidth-product), the much less nonlinearity accumulation (i.e. smaller B-Integral value) and a higher output power can be obtained in the backward pump scheme compared to that in the forward pump scheme. The physical origin can be explained by the interaction among group-velocity dispersion, self-phase modulation and nonuniform gain distribution along the fiber due to different end-pump directions. The results provide convincing support to choose the backward pump scheme rather than the forward pump scheme in soliton amplification region in a femtosecond fiber amplifier.

Temperature Insensitive Optical Fiber Laser Bend Sensor With a Low Detection Limit

A fiber in-line Mach–Zehnder interferometer based on a sandwich structure of single mode fiber-thin core fiber-single mode fiber is inserted into a fiber ring laser cavity to form a fiber laser bend sensor. Such a sensor is temperature insensitive, has a large output light intensity $\sim 0.61$ dBm, a high optical signal-to-noise ratio of $\sim 63$ dB, a narrow spectral width of $\sim 0.01$ nm at the lasing wavelength and a good bending sensitivity of $\sim 1.04$ nm/ $\text{m}^{-1}$ , which gives a low detection limit of $\sim 4.37\times 10^{-2}~\text{m}^{-1}$ .

Sensitive metal layer-assisted guided-mode resonance SU8 nanopillar array for label-free optical biosensing

A novel polymer nanopillar lattice architecture for label-free optical biosensing based on the metal layer assisted guided-mode resonance (MaGMR) effect is presented. The device consists of a 2D array of SU8 nanopillars fabricated by e-beam lithography (EBL) on an optically-thick aluminum layer. EBL proximity effect, that is, the influence of the electron irradiation in the regions adjacent to those exposed by the e-beam – which is usually considered an undesirable fabrication issue – is positively used to create a non-uniform thickness, crosslinked SU8 film among the SU8 nanopillars on the aluminum layer. The optical response of the resulting SU8 nanostructure array exhibits a MaGMR under normally incident light interrogation. Spectral reflectance monitoring of the MaGMR upon the adsorption of water, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) and bovine serum albumin (BSA) molecules is employed to evaluate the surface sensing characteristics of the resonant nanostructure. The figure of merit of the device, defined as the quotient of the surface sensitivity and the resonance spectral width, is increased by two orders of magnitude (0.127nm−1 versus 0.009nm−1) as compared with previous SU8 nanopillar array surface sensing architectures because of the high sensitivity and narrow spectral width of the MaGMR feature.

Biomimetic Preparation and Dual-Color Bioimaging of Fluorescent Silicon Nanoparticles.

Fluorescent silicon nanoparticles (SiNPs), as the most important zero-dimensional silicon nanostructures, hold high promise for long-awaited silicon-based optic applications. There currently remain major challenges for the green, inexpensive, and mass production of fluorescent SiNPs, resulting in difficulties in sufficiently exploiting the properties of these remarkable materials. Here, we show that fluorescent small-sized (∼3.8 nm) SiNPs can be produced through biomimetic synthesis in rapid (10 min), low-cost, and environmentally benign manners. The as-prepared SiNPs simultaneously feature bright fluorescence (quantum yield (QY), ∼15-20%), narrow emission spectral width (full width at half-maximum (fwhm), ∼30 nm), and nontoxicity, making them as high-quality fluorescent probes for biological imaging in vitro and in vivo.

Colloidal CsPbBr3 Perovskite Nanocrystals: Luminescence beyond Traditional Quantum Dots

Traditional CdSe-based colloidal quantum dots (cQDs) have interesting photoluminescence (PL) properties. Herein we highlight the advantages in both ensemble and single-nanocrystal PL of colloidal CsPbBr3 nanocrystals (NCs) over the traditional cQDs. An ensemble of colloidal CsPbBr3 NCs (11 nm) exhibits ca. 90 % PL quantum yield with narrow (FWHM=86 meV) spectral width. Interestingly, the spectral width of a single-NC and an ensemble are almost identical, ruling out the problem of size-distribution in PL broadening. Eliminating this problem leads to a negligible influence of self-absorption and Förster resonance energy transfer, along with batch-to-batch reproducibility of NCs exhibiting PL peaks within ±1 nm. Also, PL peak positions do not alter with measurement temperature in the range of 25 to 100 °C. Importantly, CsPbBr3 NCs exhibit suppressed PL blinking with ca. 90 % of the individual NCs remain mostly emissive (on-time >85 %), without much influence of excitation power.

Colloidal CsPbBr3 Perovskite Nanocrystals: Luminescence beyond Traditional Quantum Dots

AbstractTraditional CdSe‐based colloidal quantum dots (cQDs) have interesting photoluminescence (PL) properties. Herein we highlight the advantages in both ensemble and single‐nanocrystal PL of colloidal CsPbBr3 nanocrystals (NCs) over the traditional cQDs. An ensemble of colloidal CsPbBr3 NCs (11 nm) exhibits ca. 90 % PL quantum yield with narrow (FWHM=86 meV) spectral width. Interestingly, the spectral width of a single‐NC and an ensemble are almost identical, ruling out the problem of size‐distribution in PL broadening. Eliminating this problem leads to a negligible influence of self‐absorption and Förster resonance energy transfer, along with batch‐to‐batch reproducibility of NCs exhibiting PL peaks within ±1 nm. Also, PL peak positions do not alter with measurement temperature in the range of 25 to 100 °C. Importantly, CsPbBr3 NCs exhibit suppressed PL blinking with ca. 90 % of the individual NCs remain mostly emissive (on‐time &gt;85 %), without much influence of excitation power.

2 kW narrow spectral width monolithic continuous wave in a near-diffraction-limited fiber laser.

We demonstrate a monolithic continuous wave (CW) fiber laser source at 1070 nm, producing 2 kW laser power with a very narrow spectral width (∼75 GHz) and near-diffraction-limited beam quality (M2<1.4). The laser consists of a CW fiber laser oscillator and two double cladding fiber amplifiers in the master oscillator-power amplifier configuration. The master oscillator is a distributed Bragg reflected fiber laser, producing ∼6 W laser power with ∼25 GHz spectral width. The two double cladding fiber amplifiers were developed to enhance the laser power up to ∼200 and ∼2050 W, respectively. The slope efficiency of the main amplifier reaches 84.8%. Under the full power output, the 3 dB spectral width and 20 dB spectral width of the laser emission spectrum was ∼75 GHz and 1.2 nm, respectively.

Ultrafast Nyquist OTDM demultiplexing using optical Nyquist pulse sampling in an all-optical nonlinear switch.

We propose the ultrahigh-speed demultiplexing of Nyquist OTDM signals using an optical Nyquist pulse as both a signal and a sampling pulse in an all-optical nonlinear switch. The narrow spectral width of the Nyquist pulses means that the spectral overlap between data and control pulses is greatly reduced, and the control pulse itself can be made more tolerant to dispersion and nonlinear distortions inside the nonlinear switch. We apply the Nyquist control pulse to the 640 to 40 Gbaud demultiplexing of DPSK and DQPSK signals using a nonlinear optical loop mirror (NOLM), and demonstrate a large performance improvement compared with conventional Gaussian control pulses. We also show that the optimum spectral profile of the Nyquist control pulse depends on the walk-off property of the NOLM.

Control of Photoluminescence of Carbon Nanodots via Surface Functionalization using Para-substituted Anilines.

Carbon nanodots (C-dots) are a kind of fluorescent carbon nanomaterials, composed of polyaromatic carbon domains surrounded by amorphous carbon frames, and have attracted a great deal of attention because of their interesting properties. There are still, however, challenges ahead such as blue-biased photoluminescence, spectral broadness, undefined energy gaps and etc. In this report, we chemically modify the surface of C-dots with a series of para-substituted anilines to control their photoluminescence. Our surface functionalization endows our C-dots with new energy levels, exhibiting long-wavelength (up to 650 nm) photoluminescence of very narrow spectral widths. The roles of para-substituted anilines and their substituents in developing such energy levels are thoroughly studied by using transient absorption spectroscopy. We finally demonstrate light-emitting devices exploiting our C-dots as a phosphor, converting UV light to a variety of colors with internal quantum yields of ca. 20%.

Comparison of two concepts for dual-wavelength DBR ridge waveguide diode lasers at 785 nm suitable for shifted excitation Raman difference spectroscopy

Two concepts of dual-wavelength 785-nm DBR ridge waveguide (RW) lasers, i.e. RW mini-arrays consisting of two DBR-RW lasers and Y-branch DBR-RW lasers, will be compared with respect to their usability as excitation light sources for shifted excitation Raman difference spectroscopy (SERDS). For both types of devices for each wavelength, output powers up to 215 mW were measured. A stable spectral distance between the laser emissions of the two resonator branches with the targeted value of 0.6 nm, i.e. 10 cm−1, is observed. In the case of the mini-array up to an output power of about 70 mW, the device shows single-mode operation. Although at higher power levels, mode hops and multi-mode operation occur, the emission width smaller than 0.15 nm still meets the requirements for Raman measurements of solids and liquids. Over the whole working range, the spectral distance between the two wavelengths is approximately constant with 0.62 nm. The near field shows two emission spots according to the dimension of the RW and their processed distance of 20 µm. The Y-branch laser shows single-mode operation up to 150 mW with a narrow spectral emission width. At higher powers also, multi-mode operation with an emission width of 0.15 nm occurs. The nearly diffraction-limited emission comes from one output aperture; the far-field emission shows a pronounced asymmetry between the two branches. Both types of devices fulfil the spectral requirements from Raman spectroscopy and SERDS up to 215 mW output power.

Broadband quantum efficiency enhancement in high index nanowire resonators.

Light trapping in subwavelength semiconductor nanowires (NWs) offers a promising approach to simultaneously reducing material consumption and enhancing photovoltaic performance. Nevertheless, the absorption efficiency of a NW, defined by the ratio of optical absorption cross section to the NW diameter, lingers around 1 in existing NW photonic devices, and the absorption enhancement suffers from a narrow spectral width. Here, we show that the absorption efficiency can be significantly improved in NWs with higher refractive indices, by an experimental observation of up to 350% apparent external quantum efficiency in lead sulfide NW resonators, a 3-fold increase compared to Si NWs. Furthermore, broadband absorption enhancement is achieved in single tapered NWs, where light of various wavelengths is absorbed at segments with different diameters. Overall, the single NW Schottky junction solar cells benefit from optical resonance, near bandgap open circuit voltage, and long minority carrier diffusion length, demonstrating power conversion efficiency comparable to Si and III-V single NW coaxial p-n junction cells but with much simpler fabrication processes.

Conditions for stronger field enhancement of semiconductor bowtie nanoantennas.

A semiconductor bowtie nanoantenna acts as a high-quality cavity because a strongly enhanced field with a narrow spectral width appears at a nanogap region owing to exciton resonance. We theoretically investigate suitable antenna structures to obtain a strong field enhancement, and the following conditions are found: (i) the antenna structure is long in the direction of light polarization, and (ii) the tip structure near the nanogap is blunt. Condition (ii) is opposite to that for a metallic bowtie nanoantenna because the exciton wave function is distributed to avoid a narrow area near the sharp tip. These conditions are expected to be guidelines for designing efficient semiconductor nanoantennas for various applications.

Light-emitting devices based on top-down fabricated GaAs quantum nanodisks.

Quantum dots photonic devices based on the III–V compound semiconductor technology offer low power consumption, temperature stability, and high-speed modulation. We fabricated GaAs nanodisks (NDs) of sub-20-nm diameters by a top-down process using a biotemplate and neutral beam etching (NBE). The GaAs NDs were embedded in an AlGaAs barrier regrown by metalorganic vapor phase epitaxy (MOVPE). The temperature dependence of photoluminescence emission energies and the transient behavior were strongly affected by the quantum confinement effects of the embedded NDs. Therefore, the quantum levels of the NDs may be tuned by controlling their dimensions. We combined NBE and MOVPE in a high-throughput process compatible with industrial production systems to produce GaAs NDs with tunable optical characteristics. ND light emitting diode exhibited a narrow spectral width of 38 nm of high-intensity emission as a result of small deviation of ND sizes and superior crystallographic quality of the etched GaAs/AlGaAs layer.

Influences of pumping schemes on the properties of dissipative soliton in fiber lasers

Based on the extended scalar nonlinear Schrödinger equation, the influences of pumping schemes on the properties of dissipative soliton are investigated theoretically in passively mode-locked ytterbium-doped fiber laser with positive dispersion cavity. Results show that, under the conditions of the same initial total gain, the dissipative solitons obtained in the backward pumping fiber laser have the narrowest spectral width, shortest pulse duration and highest pulse peak power for the forward, backward and bidirectional pumping schemes, moreover, the linear fitting degree of pulse chirp is lowest. With the same gain saturation energy, the pulse energies of the dissipative solitons are equal for three pumping schemes, but the differences of output spectra and temporal waveforms increase as the gain saturation energy increases.

37-GHz Modulation via Resonance Tuning in Single-Mode Coherent Vertical-Cavity Laser Arrays

We show a significant improvement of modulation bandwidth from $2\times 1$ photonic crystal vertical-cavity surface-emitting laser arrays. Control of injection bias conditions to array elements enables resonance tuning of each element with variation of the phase relation and coherence of the array, resulting in the ability to tailor the modulation response. A bandwidth of 37 GHz is obtained under highly single-mode coherent operation with narrow spectral width and increased output power while the laser array is biased at low current density. Lasers with such performance characteristics may greatly enhance high-rate data transfer in computer server, data center, and supercomputer applications with potentially long device lifetime.