Optical Conversion Research Articles

Wide-bandgap III-V materials for high efficiency air and underwater optical photovoltaic power transmission

High-power optical transmission (HPOT) enables the uninterrupted transfer of power in the order of hundreds of watts over several kilometers, freeing power systems from traditional wiring constraints. Its vast versatility of applications ranges from the ocean depths to outer space. In recent years, particular emphasis has been placed on the development of efficient methods to transfer substantial amounts of power from future space-based solar power stations, which intend to generate clean energy 24/7, to Earth. Despite the immense potential of HPOT, further endeavors should be undertaken in order to enhance overall system efficiency, currently hindered below 20%. A contributing factor to this unsatisfactory performance is the state-of-the-art selection of semiconductors that constitute the receivers of the monochromatic light: the optical photovoltaic converters (OPCs). Therefore, this work aims to identify the most suitable semiconductor materials for high power (∼100 Wcm−2) and beyond transmissions in terrestrial and underwater environments. In addition, the first analytical model capable of evaluating, predicting and designing OPCs and its electrical characteristics is provided. The results indicate that III-V wide-bandgap semiconductors (≈2.5 eV), such as InGaN and InAlN, could yield significant efficiency improvements in air and, especially, in subaquatic domains with respect to existing GaAs-based devices.

Localized spin-selective interference assisted broadband tunable chirality with diatomic all-dielectric metasurfaces

Chiral metasurfaces with spin-selective properties have shown an unprecedented ability to modulate optical properties on the subwavelength scale. Alternatively, the simultaneous implementation of broadband tunable chiral response and wavefront manipulation on minimalistically constructed monolayer metasurfaces can lead to a plethora of applications such as optical converter diodes, chiral imaging, and sensing. Benefiting from a localized interference between two pairs of achiral meta-atoms whose optical behavior is similar to that of a half-wave plate (HWP), we theoretically provide a design strategy for constructing meta-molecules for asymmetric transmission (AT) parameters using interference mechanisms, each of which achieves a specific modulation function in the terahertz (THz) band. Localized interference effects with polarization-selective properties permit the incident circular polarization to be transformed into its orthogonal polarization mode. Benefiting from spin-selective transmission, the proposed metasurface simultaneously implements polarization filtering and wavefront manipulation with the assistance of a geometric phase mechanism. Not only that, chiral imaging schemes are also evaluated under such a design mechanism. As a result, this generalized assembly scheme can not only be extended to arbitrary working bands, but also find a variety of applications in photodetectors.

Coal Pitch Derived Yellow‐Emissive Carbon Dots and Their Application in Luminescent Solar Concentrators

AbstractUsing coal pitch as the carbon source to synthesize carbon dots (CDs), one of the most promising photoluminescence (PL) materials, can play an important role in the global demand for carbon neutralization. However, the reported CDs derived from coal pitch are mainly limited blue emission. Here, a new route to synthesize yellow‐emissive CDs from coal pitch is developed by extracting the lightweight aromatic compounds from coal pitch and solvothermally treating the extracts in dichloromethane in the presence of a small amount of nitric acid and sulfuric acid. Notably, the obtained CDs exhibit excitation independent yellow emission, large Stokes shift and good photostability. The application of the CDs for luminescent solar concentrators (LSCs) is evaluated. It is found that the CDs can be well dispersed in polymethyl methacrylate (PMMA) matrix and fabricated transparent LSCs. The synthesized LSC (4 × 4 × 0.2 cm3) with the optimal CDs concentration exhibits an optical conversion efficiency (ηopt) of 3.31% and power conversion efficiency (ηPCE) of 1.95% under simulated sun light illumination (100 mW cm−2). This research offers a new strategy to synthesize new kind of CDs with desired performance by exploiting the native chemistries of coal pitch.

LD end-pumped composite Tm/Ho: YAP laser

Ho laser operation in a composite Tm/Ho: YAP gain medium is demonstrated for the first time, which is integrated via diffusion bonding the Tm-doped and Ho-doped into a single bulk YAP crystal. A laser diode with central wavelength of 795 nm, which is the absorption peak of Tm3+ ion, is used as the pumping source. At absorbed pump power of 22 W, maximum output power of 4.9 W at 2010.8 nm with a power instability of 0.61 % is achieved. The corresponding slope efficiency of 28.6 % and the optical conversion efficiency of 22.4 %. The beam quality is measured to be with M2 of 1.25 and 1.21 in the horizontal and vertical directions, respectively.

Efficient second harmonic generation from nonlinear one-dimensional meta-grating metasurface under vertically incident pump laser excitation

The emergence of new materials will drive the development of a generation of devices. The purpose of this study is to realize the nonlinear optical frequency conversion in the novel material structure - metasurface structures. We study the second harmonic generation (SHG) from the all-dielectric resonant meta-grating metasurfaces with high quality (Q) factors. The quasi-bound states in the continuum (Q-BIC) modes can be easily induced using the linearly polarized plane wave with normal incidence. Two types of asymmetric one-dimensional meta-grating metasurfaces with square air notch defect and different widths based on AlGaAs are numerically investigated. When the symmetry of the AlGaAs meta-grating structures is broken, the BIC modes are transformed into the Q-BIC modes, which support strong local field confinement in the AlGaAs meta-grating array, thereby promoting the SHG conversion. When the pump laser intensity is about 5 MW/cm2, the two type structures provide the SHG conversion efficiencies about 0.059 and 0.166. The investigation results will promote the application of nonlinear metasurfaces in integrated nonlinear optical systems.

Design of a Passive Silicon-on-Insulator-Based On-Chip Optical Circulating Network Supporting Mode Conversion and High Optical Isolation

Over the past few decades, on-chip photonic integrated circuits based on silicon photonics (SiPh) platforms have gained widespread attention due to the fact that they offer many advantages, such as high bandwidth, low loss, compact size, low power consumption, and high integration with different photonic devices. The demand for high-speed and high-performance SiPh devices is driven by the significant increase in demand for Internet traffic. In photonic integrated circuits, controlling optical signals to make them circulate in a specific direction is a highly researched area of study. However, achieving a purely passive on-chip optical circulating network on a SiPh platform is very challenging. Therefore, we propose and demonstrate, through simulations, an on-chip optical circulator network on a silicon-on-insulator (SOI) platform. The proposed device can also support mode conversion. The proposed on-chip optical circulating network consists of two kinds of tailor-made multi-mode interferometer (MMI) structures and waveguide crossings. Through the optical power division and mode combination capabilities of the MMI, an optical circulating network supporting high optical isolation and mode conversion is achieved. The proposed optical circulating network has a loss of 1.5 dB at each output port, while maintaining a high isolation of 35 dB in the transmission window from 1530 nm to 1570 nm.

Nonlinear-optical piezoelectric electrospun nanofibers

This paper presents a nonlinear optical piezoelectric electrospun nanocomposite of polyvinylidene fluoride (PVDF) nanofibers with embedded nanomaterial of poly {1-[p-(3’-carboxy-4’- hydroxyphenylazo) benzenesulfonamido]-1, 2-ethandiyl} (PCBS). PCBS of different weight ratios are added in-situ to the synthesized PVDF nanofibers. The generated nanofibers mats have been proved to possess both properties of piezoelectric response and nonlinear optical conversion due to the presence of both PVDF and PCBS, respectively. Innovatively, embedding PCBS within the PVDF nanofibers increases the piezoelectric response of the nanocomposite, compared to the case of neat PVDF nanofibers, at certain optimum weight concentrations of PCBS. This has been proved by different piezoelectric measurements at different applied forces and vibration frequencies, along with d33 coefficient measurements and supported by FTIR analysis of beta-sheets. Our results support the evidence of the coupling between the polarized diploes of PCBS and PVDF, which can enhance the overall piezoelectric response. Furthermore, the synthesized nanocomposite shows an optical second harmonic generation (SHG) at optimum concentration of added PCBS within the PVDF nanofibers of around 1 wt.%. The synthesized nonlinear optical nanocomposite of PVDF/PCBS can be multi-functionalized sensors/transducer membranes for biomedical and sensing applications.

Programmable optical switching integrated chip for 4-bit binary true/inverse/complement code conversions based on fluorinated photopolymers.

In this work, programmable optical switching integrated chips for 4-bit binary true/inverse/complement optical code conversions (OCCs) are proposed based on fluorinated photopolymers. Fluorinated bis-phenol-A novolac resin (FAR) with low absorption loss and fluorinated polyacrylate (FPA) with high thermal stability are self-synthesized as core and cladding layer, respectively. The basic architecture of operating unit for the photonic chip designed is composed of directional coupler Mach-Zehnder interferometer (DC-MZI) thermo-optic (TO) switching, X-junction, and Y-bunching waveguide structures. The waveguide module by cascading 16 operating units could realize OCCs function through optical transmission matrix. The response time of the 4-bit binary OCCs is measured as about 300 µs. The insertion loss and extinction ratio of the actual chip are obtained as about 10.5 dB and 15.2 dB, respectively. The electric driving power consumption for OCCs is less than 6 mW. The true/inverse/complement OCCs are achieved by the programmable modulation circuit. The proposed technique is suitable for achieving optical digital computing system with high-speed signal processing and low power consumption.

Quantitatively sensitive and resolution-enhancing strategies in optical signal conversion of SPR images using extensive angle-scanning and image-reconstruction

Surface plasmon resonance imaging (SPRi) is a technology developed from SPR that has emerged in response to the growing need for high-throughput and for discovering diverse applications across multiple domains. Despite its potential, SPRi has encountered limitations in sensitivity when handling low-molecular-mass materials, which emphasizes the need for the quantitative processing of SPRi signals. In this study, an SPRi signal conversion process was developed to enhance the contrast of SPR images and convert them into quantitatively analyzed signals. At first, an optimum incident angle of light was determined as an angle that maximized the difference between sums of the brightness % of functionalized regions and the brightness % of background region in the SPR image, which enabled to obtain a distinct SPR image. In addition, the enhancement of contrast and reduction of noise in the SPR image was achieved using Contrast Limited Adaptive Histogram Equalization (CLAHE) method. Then various pixel domains of the SPR images were simultaneously quantified and visualized the multi-pixel processing technique. For validating the process, an SiO2/Au thin film was modified with four different functionalities and applied to the detection of gas molecules. The SPR images processed using the proposed process exhibited sensitive and quantitative information about the interactions of the functionalities with the target gas in the distinct multiple regions, thus, were applicable to the quantitative monitoring of various phenomena occurring on the plasmonic interface via the advantages of SPRi.

Optical Format Conversion and Interconnection Between 1D and 2D Constellations for Flexible Optical Transmission Networks

Optical format conversion technologies have attracted a lot of attention to bridge the different optical networks employing different formats. In this paper, the advances of optical format conversion technologies are introduced and reviewed. Through analyzing the optical network architecture and modulation technology development, we focus on the format conversions between the signals with one dimensional and two dimensional constellations. The important enabling technologies for flexible constellation manipulation are introduced in detail, including the linear and nonlinear optical effects-based functions. Then the key format conversion researches are reviewed in four categories: one-to-one conversions, optical aggregations, optical de-aggregations, and optical interconversions. Finally, the current issue and future trend of this research field is analyzed and discussed.

Auto-pump-depleted stable single-longitudinal-mode 1.5 μm source with the assistance of SHG.

To realize a stable single-longitudinal-mode (SLM) 1550-nm light source for the generation of non-classical states, a ring auto-pump-depleted singly resonant optical parametric oscillator (SRO) with the assistance of second-harmonic-wave generation (SHG) is designed and built in this Letter. A magnesium oxide doped periodically polarized lithium niobate (MgO:PPLN) crystal and a lithium triborate (LBO) crystal are employed as the optical parametric downconversion (OPDC) and SHG crystals, respectively. Especially, the introduced SHG can firstly increase the loss difference between the lasing and non-lasing modes so that the dual-mode or multi-mode coupling in the achieved SRO can be effectively eliminated and the stable SLM operation is achieved. At the same time, the SHG will automatically adjust the output coupling efficiency of SRO, so as to achieve efficient conversion efficiency and auto-pump depletion of SRO. In addition, due to the SHG, it is easy to achieve the low-intensity noise multi-wavelength output for the stable SLM SRO. As a result, the output powers of the SLM 1550 nm and 775 nm are up to 4.05 W and 3.25 W, respectively, and the total optical conversion of the built SRO can achieve 45.58%. The presented method paves a way to develop a compact stable SLM multi-wavelength SRO, and the obtained SRO is further beneficial to develop compact continuous-variable non-classical light fields.

Perylenes, Porphyrins, and Other Large Dye Molecules for Molecular Layer Deposition

AbstractMolecular layer deposition (MLD) is an incredibly powerful and flexible tool for designing completely new materials with novel and unique properties. The low temperature layer‐by‐layer approach and the use of highly reactive reactants allows one to combine vastly different organic and inorganic species and construct nanostructures with subnanometer precision. If not limited by the volatility of the reactants involved, the possibilities will be endless. This is most notable for the organic building blocks where an overall low volatility severely limits the toolbox of large molecules with interesting optical and electrical properties such as red‐ox activity and optical conversion. In this work, different strategies for molecular design of large molecules are investigated that allow vaporization while still having the necessary reactivity for MLD growth. Using these strategies, film growth with perylene and porphyrin derivatives, both molecules well known for their functional and optical properties are successfully achieved. With this knowledge, there is an opening to include much larger and more complex organic molecules into the world of vapor phase chemistry.

Growth and spectral properties of a novel praseodymium-doped alpha-barium borate laser crystal

A novel Praseodymium-doped borate (Pr:α-BBO) laser crystal was grown successfully by using the Czochralski method. The phase structure, absorption and fluorescence lifetime, as well as blue laser diode (LD) pump performances of Pr:α-BBO were totally studied. The segregation coefficient and valence state of Pr ions in the crystals were investigated using inductively coupled plasma atomic emission spectroscopy and X-ray photoelectron spectroscopy. A 450 nm blue LD was employed to carry out a pump experiment on the Pr:α-BBO slab crystal with a doping concentration of 0.22 at.%. The main emission peaks of Pr3+ ions in the orange-red light band were found to be at 611.5 nm, 634.7 nm, and 638.3 nm. The experimental results show that the Pr:α-BBO crystal exhibits higher orange light fluorescence emission performance, with an emission peak intensity at 611 nm that is 2.1 times stronger than that at 635 nm due to the splitting of the 3P0→3F2 transition (635 nm). By optimizing the Pr:α-BBO laser crystal growth process and further solid-state laser experiments, it can be expected to have broad applications in laser medicine, spectral detection, and nonlinear optical frequency conversion fields.

Hybrid Optical and Thermal Energy Conversion System to Power Internet of Things Nodes

This article presents research about a hybrid power system dedicated to Internet of Things (IoT) nodes. As an introduction, performance tests of the harvesters, that is, a 40 × 40 mm Peltier cell based on Bi2Te3 and three solar cells, monocrystalline, polycrystalline, and amorphous, are presented. The study established the dependence of the effect of generated power on the load resistance. Thus, it states how the internal resistance of the harvesters changes. Following the above tests, a complete power unit with a single harvester and an LTC3108 conversion circuit, as well as an energy buffer in the form of a 1 mF supercapacitor, were built and tested. The unit with a thermoelectric generator generated power from 14 to 409 µW. The unit with a 65 × 65 mm polycrystalline cell generated power from 150 to 409 µW. Next, a hybrid system was built and tested with both of the aforementioned harvesters, which generated power from 205 to 450 µW at 2000 lx illumination and a temperature difference of 20 °C for the thermoelectric generator claddings.

Watt-Level Diode-End-Pumped Self-Mode-Locked Tm,Ho:LLF Laser

A diode-end-pumped self-mode-locked Tm,Ho:LuLiF4 (LLF) laser is demonstrated for the first time, to the best of our knowledge. At the incident pump power of 3.4 W, the stable self-mode-locked operation of the Tm,Ho:LLF laser was realized without any additional devices in the resonator. Further increasing the incident pump power to 6.8 W, the maximum average output power of 1.07 W was achieved at 2068 nm with a pulse width of 746 ps and a repetition frequency of 468 MHz. The experimental results indicate that the Tm,Ho:LLF crystal is promising to generate the high-power self-mode-locked solid-state laser at 2 μm waveband. The self-mode-locked Tm,Ho:LLF laser has potential applications in optical communication, remote sensing, material process, and nonlinear frequency conversion.

Carbon nanodot with highly localized excitonic emission for efficient luminescent solar concentrator

Abstract Luminescent solar concentrators (LSCs) are attractive for the easy operation and high compatibility with building integrated photovoltaics due to their low cost, large-scale and applicability. However, underutilized sunlight in visible wavelengths often impedes the advance of LSCs. Here, we demonstrate an orange-emitting carbon nanodots-based LSC (O-CDs) with excitation concentrated in the visible wavelengths. The orange-emitting carbon nanodots (O-CDs) with highly localized excitonic emission are prepared via atomic condensation of doped pyrrolic nitrogen, delivering a high photoluminescence quantum yield of 80 % and a suitable Stokes shift with absorption spectrum situated in the visible region. The O-CDs are embedded in polyvinylpyrrolidone to obtain a highly transparent, stable and environmentally friendly O-CDs-based LSC. Thanks to efficient utilization of solar radiation in visible areas and well match between the emission of O-CDs and the response bands of photovoltaic cells, the O-CDs-based LSC reveals an optical conversion efficiency of 5.17 %, superior to that of most carbon nanodots-based LSCs. These results provide an effective strategy to develop carbon-based luminescent concentrated materials for architectural integrated photovoltaic technology.

Performance amelioration of simultaneous up- and down-mixing contingent on a parallel SOA-MZIs design

The primary focus of this research is the creation of a first-ever experimental investigation for simultaneous up-down mixing based on three parallel semiconductor optical amplifier Mach-Zehnder interferometers (SOA-MZIs). The three mixed signals from the SOA-MZI terminals are coupled together to create a simultaneous up or down-mixed signal using an optical coupler (OC). The identified mixing function makes use of the consequences of cross-gain modulation (XGM) as well as cross-phase modulation (XPM) that have been shown at the SOA-MZI outlets. Furthermore, the performance characterization of the photonic parallel system is examined and assessed in the optical and electrical sectors. The outcomes of our experiment closely resemble those of the simulation. Several measurable factors, including power scaling measurements, optical conversion gain (OCG), power stability, beam quality factor, electrical conversion gain (ECG), and error vector magnitude (EVM), are employed to evaluate the photonic up and down-mixed signals. This three-parallel SOA-MZIs architecture has a wide range of applications involving radio over fiber and optical telecommunications. A 256-QAM (Quadrature Amplitude Modulation) up- and down-mixed signals can have a top bit rate of 64 Gbit/s with excellent EVM values. Additionally, the maximal frequency range of the concurrent up and down-mixed signal is 80 GHz. The ECG also displays significant values for up and down conversion. In the optical domain, the OCG has the highest values of 15 dB for the up-mixed signal and 12 dB for the down-mixed one, with a data input power of −10 dBm. Finally, the simultaneous mixing system tackles an outstanding beam quality factor with M2 measurement of less than 1.3 (M2<1.3).

High-power and efficient vortex Nd:YVO4 laser using annular pumping

Optical vortex lasers that carry orbital angular momentum are of great significance for many applications. A high-power and efficient continuous-wave vortex Nd:YVO4 laser at 1064 nm was demonstrated with annular pumping based on an axicon. The high-quality LG01 vortex beams with maximum output power up to 6.25 W was achieved under the absorbed pump power of 14.4 W, corresponding to an optical conversion efficiency of 43.4% and a slope efficiency of 44.8%, respectively. Controlling the wavefront handedness of the LG01 beam was simply achieved by carefully adjusting the output coupler and the window inserted in the resonator. This study shows that annular pumping based on an axicon would have great potential in the development of high-power vortex solid-state lasers with simple and compact resonator structure.

Synergistic enhancement of dual-color electrochromic performance in NiO/CdS quantum dots composite film

NiO is an electrochromic material with extremely strong light modulation capability. However, the defects of the material, such as simple color change and poor cycle stability, limit its application in electrochromic devices and require further improvement and optimization. Nickel-based electrochromic films were firstly prepared by simple hydrothermal method and CdS quantum dots sensitization. The composite electrochromic films adsorbed CdS quantum dots show a multifunctional non-electrochromic film with multiple color changes. It shows up to 54.7% optical modulation range and reversible conversion of two colors. We believe that the electrochromic properties of the composite film are improved due to the synergistic effect of the combination of NiO and CdS in the composite film, which can improve the charge transfer dynamics and light modulation efficiency. Compared with NiO, CdS has a higher carrier density, which increases the charge storage capacity in the composite film, which can improve the color development efficiency and improve the electrochromic reaction. The existence of CdS in the composite film improves the structural stability of NiO. CdS acts as a buffer layer to reduce stress and prevent NiO degradation during repeated coloring and bleaching cycles, improving cycle stability and durability of electrochromic devices. This study provides a reference for the development of NiO polychromatic electrochromic materials and extends the range of non-electrochromic materials from metal oxides to sulfides.

Electronic structure and optical absorption property of BaTiO3/BiCoO3

In this paper, we calculated the different forms of BaTiO3/BiCoO3 composite structure, predicting their visible light absorption performance based on the electronic structure using the first principles calculations. Firstly, six possible compounds that come from BaTiO3 and BiCoO3 were constructed. By calculating the different antiferromagnetic (AFM) structures of strip, columnar, and layered composite structures, it is found that the ground state of the composite structure changes to G‐type AFM structure from C‐type AFM structure of pure BiCoO3 under the influence of BaTiO3. Energy band calculations show that band gaps of three composite structures are smaller than those of pure BaTiO3 and pure BiCoO3. Furthermore, density of states analysis shows that the conduction band minimum (CBM) and valence band maximum (VBM) of three composite structures are mainly from the contribution of Co 3d and O 2p. For the characteristic that CBM and VBM of materials come from different atoms, it would reduce the recombination opportunities of electrons and holes and is conducive to the increase of photoelectric conversion efficiency under visible light irradiation. The calculation of optical properties shows that optical absorption coefficients of three composite structures are much larger than that of BaTiO3, especially the layered composite structure. There is a high absorption peak near 500 nm of the solar spectral irradiation maximum, which is significantly important to improve the optical energy conversion efficiency of the composite materials. The work provides an effective way for the application of wide band gap ferroelectric materials in ferroelectric photovoltaic.