Frequency Up-conversion Research Articles

Highly sensitive multi-stage terahertz parametric upconversion detection based on RbTiOPO4 crystal

Highly sensitive terahertz frequency upconversion detection was demonstrated with a RbTiOPO4 crystal. The detectable THz frequency ranges were 3.6-4.0, and 5.4-5.7 THz. The minimum detectable terahertz energy at 5.6 THz was about 0.2 fJ.

Frequency Up-Conversion of an Even Coherent State

Frequency Up-Conversion of an Even Coherent State

Ultrabroadband nonlinear enhancement of mid-infrared frequency upconversion in hyperbolic metamaterials.

Metamaterials have demonstrated significant potential for enhancing nonlinear processes at the nanoscale. The presence of narrowband hot-spots and highly inhomogeneous mode-field distributions often limit the enhancement of nonlinear interactions over larger spatial scales. This has posed a formidable challenge in achieving simultaneous enhancement across a broadband spectral range, significantly constraining the potential of photonic nanostructures in enhancing nonlinear frequency conversion. Here, we propose a broadband resonant mode matching method through near-field examinations that supports the multipole modes and enables the development of an ultrabroadband-enhanced 3-5 μm mid-infrared frequency upconversion technique utilizing a hyperbolic triangular pyramidal metasurface. The gap-plasma mode of the hyperbolic metamaterial multilayer system excites narrowly high-order resonances at near-infrared pump light wavelengths, while the slow-light effect generated by the dipoles achieves ultrabroadband near-field enhancement at mid-infrared wavelengths. The symmetry breaking of the triangular structure localizes these resonant modes at the tips, enabling mode-matched modulation at different wavelengths, and thus boosting the nonlinear frequency conversion process. Our approach provides a promising platform for metasurface-based frequency conversion techniques.

A plucking rotational energy harvester with tapered thickness and auxetic structures for increasing power output

The rotational energy harvester (REH) has been widely investigated as a potential method to power electronic devices in the Internet of Things. Despite the advances in the REH, there remains a challenge to sufficiently harvest energy from low frequency rotations. To address this issue, a plucking REH with tapered thickness and auxetic structures (TAPREH) is proposed in this paper. By incorporating a tapered thickness beam, auxetic structures, and frequency up-conversion method, the proposed design can improve the generated energy under low frequency excitations. The performance of the proposed design is analyzed using finite element simulation, which shows a good agreement with the corresponding experimental results. Experimental validation of the proposed design revealed a peak power output of 0.489 mW at 1.5 Hz, representing an increase of 898% compared to the conventional plucking REH without auxetic structures (PREH). Moreover, the proposed design exhibits a more uniform stress distribution compared with the existing plucking REH with uniform thickness and auxetic structures (UAPREH). Consequently, the peak power output of the proposed design is increased by 186% compared with that of UAPREH while having lower maximum stress.

Combustion synthesized La2O3: Er3+/Yb3+ phosphor for simultaneous upconversion emission and photo-thermal signal generation

The Er3+/Yb3+ doped La2O3 phosphor is prepared through combustion synthesis route and then studied using frequency upconversion (UC) and photoacoustic spectroscopic techniques. Prepared phosphor sample was annealed at high temperature ∼2100°C for short time and then structural and optical characterizations were performed. A photoacoustic cell was fabricated to record photoacoustic signal generation. Samples have shown strong upconversion emission at 409 nm, 523 nm, 548 nm, and 672 nm due to the 2H9/2 →4I15/2, 2H11/2 →4I15/2, 4S3/2 → 4I15/2 and 4F9/2→ 4I15/2 transitions, respectively. The photoacoustic measurement has revealed that heat generation in the sample increases in line with the increase in upconversion emission although both properties are opponent to each other. Studies show that prepared phosphor is efficient for generating strong upconversion emission as well as strong photoacoustic signal (also photo-thermal signal) and hence present dual functional sample seems useful for upconversion imaging as well as photo-thermal therapy.

Double-speed piezoelectric–electromagnetic hybrid energy harvester driven by cross-moving magnets

Energy harvesters have gained popularity as green energy devices that transform mechanical energy from the environment into electricity. However, traditional piezoelectric energy harvesters are limited by narrowband response, and the output capability of electromagnetic energy harvesters is dependent on the rate of magnetic field changes on the coil, which is constrained by the device’s structure. To address these issues, this paper presents a hybrid energy harvester (HEH) that combines coils and arc magnets, forming an electromagnetic component (EMEH). Additionally, it incorporates a piezoelectric cantilever beam (PECB) as a piezoelectric component (PEH). Unlike traditional electromagnetic energy harvesters, this design utilizes two arc magnets to drive the rotating brackets, thereby achieving the opposite movement of the coil and magnet. This increases the relative velocity and consequently enhances the rate of magnetic field change on the coil. Simultaneously, it achieves frequency up-conversion by inducing vibration in the PECB through magnetic force. Under an external excitation of 5.5 Hz, the PEH achieves a maximum power of 0.362 mW at a load resistance of 330 kΩ, while the EMEH with 1200 turns of coil attains a maximum power of 8.74 mW at a load resistance of 110 Ω. The power density of the PEH reaches 94.96 μW cm−3. These results highlight the significant potential of the proposed energy harvester for powering low-power devices.

A Review of Nonlinear Mechanisms for Frequency Up-Conversion in Energy Harvesting

Vibration-based energy harvesting has garnered considerable attention from researchers over the past two decades, using different transduction mechanisms. In this context, the utilization of piezoelectric materials has proven to be highly successful, due to their power density, across a broad range of voltages. A primary challenge in environmental vibration harvesting lies in the frequency mismatch between the devices, which typically exhibit optimal performance at hundreds or thousands of hertz due to their small size (centimeter or millimeter) and the environmental vibration. The latter has considerable energy density around tens of hertz. For this reason, over the last 15 years, the scientific community has concentrated on exploring techniques for band broadening or frequency up-conversion by intentionally introduced (or designed) nonlinearities. This review, following an introduction to the topic of vibration energy harvesting, provides a description of the primarily developed mechanisms, presenting a chronological development for each, from the initial works to the most recent advancements. Additionally, the review touches upon implementation efforts at the micro-electromechanical systems (MEMS) scale for each described technique. Finally, the incorporation of nonlinearities through electronic circuits to enhance performance is briefly discussed.

Diffraction-based nonlinear model for the design of broadband adiabatic up-conversion imaging.

In recent years, mid-infrared parametric upconversion imaging, a nonlinear optical method that involves converting mid-infrared light into visible images, has significantly advanced and has shown considerable potential for various applications, including biomedical imaging and remote sensing. While diffraction-based parametric upconversion imaging modeling in standard thin birefringence crystals have been addressed, the numerical framework developed so far fails to address long aperiodic poled crystals. Specifically, diffraction-based analysis of the recent broadband adiabatic frequency upconversion imaging, which allows simultaneous image upconversion of extremely broadband signals is still lacking. Here, we introduce a diffraction-based numerical simulation framework for predicting the evolution of the nonlinear image/signal generation in upconversion imaging systems. This generalized framework can handle both periodically and aperiodically poled crystal designs. Specifically, the model captures faithfully and addresses the varying image magnification arising from upconversion at a Fourier plane of a multiwavelength object. The numerical simulations are validated by experimental measurements of broadband upconversion 3-5 µm mid-IR images to the visible-NIR, showing a good agreement. Moreover, the model allows the exploration of the trade-offs in the spectral span when moving to the full visible range. Our numerical framework will be useful for the interpretation of experimental results obtained in an imaging setting with nonlinear optical elements.

Transient High-Harmonic Spectroscopy in an Inorganic-Organic Lead Halide Perovskite.

High-harmonic generation is the frequency upconversion of an intense femtosecond infrared laser in a material. In condensed-phase high-harmonic generation, laser-driven currents of coherently excited charge carriers map the electronic structure onto the emitted light. This promises a thus far scarcely explored potential of condensed-phase time-resolved high-harmonic spectroscopy for probing carrier dynamics. Here, we realize this potential and use time-resolved solid-state high-harmonic spectroscopy from a laser-excited methylammonium lead bromide (MAPbBr3) thin film, a key material in perovskite solar cells, for measuring carrier cooling and relaxation on femto- and picosecond time scales. Through comparison with transient absorption, we show the links between carrier dynamics and experimental observables of generated harmonics. By highlighting and understanding the interplay of these dynamics, we demonstrate transient optical control over the emission of solid-state high-harmonic generation in MAPbBr3.

Footstep-powered floor tile: Design and evaluation of an electromagnetic frequency up-converted energy harvesting system enhanced by a cylindrical Halbach array

Energy harvesting floor systems use the mechanical energy generated by human weight to produce electrical energy, providing sustainable power sources for low-power systems at pedestrian crossings. They also have the potential to serve as renewable energy solutions on a larger scale. This study evaluates the design and performance of a kinetic energy harvester floor tile. The system design employs a frequency up-conversion technique to utilize the force exerted by the weight of humans for creating vibrational movement. In addition, the use of the cylindrical Halbach array improves the magnetic flux gradient, leading to an increased power output. A semi-analytical model is presented to evaluate the system performance, which is then validated through available experimental analysis and finite element simulations. A sensitivity analysis is performed to assess the impact of various factors on system performance, ultimately determining the optimal configuration. The optimal modular system is then used to create a 30 × 30 cm2 tile. This tile is capable of generating energy while walking, running, jogging, slow running, and fast running, with power outputs of 0.57, 0.85, 1.11, and 1.42 W (0.57, 0.86, 1.11, and 1.58 mW/cm2) respectively. Additionally, it is estimated that 511 mJ (568 mJ/cm2) of energy is generated per step. Additionally, an assessment is conducted on the energy production capabilities and environmental advantages of a specific site, such as a subway station.

A multidirectional ultralow-frequency rotational energy harvester: Modeling and characterization

Energy harvesting under ultralow-frequency rotation is challenging, especially for frequencies below 1 Hz. This paper proposes a highly robust multidirectional ultralow-frequency rotational energy harvester (MUREH). The impact force generated by periodic gravity provides double excitation for the harvester at ultralow frequencies. The piezoelectric cantilever beam resonates at the intrinsic frequency under ultralow-frequency excitation, achieving frequency up-conversion and energy harvesting abilities under 1 Hz. An electromechanical coupling model is developed to analyze the influence of crucial parameters. Uniaxial and triaxial rotation measurements characterize the performance of the MUREH. At optimum conditions, the MUREH’s root mean square voltage is 4.995 V at 0.8 Hz. The adaptability of attitude randomness is verified by triaxial rotation experiments, with an output of not less than 77 % when tilted less than 45°. Under frequent disturbances, 66 % power is maintained, demonstrating high robustness.

Photonics-assisted Millimeter-Wave Multiband Integrated Sensing and Communication System Using Coherent Receiving

Multiband integrated sensing and communication (ISAC) systems towards multiple functions and multiple users will play an important pole in future 6G wireless networks. Here, we propose and experimentally demonstrate a multiband ISAC system using optical frequency upconversion and coherent receiving techniques for millimeter-wave (MMW) high-capacity wireless communication and high-resolution sensing functions. The MMW multiband ISAC signals are simultaneously generated by a single photonic MMW frequency upconverter consisting of an optical frequency comb, a wavelength selective switch, an I/Q Mach-Zehnder modulator, and a high-speed photodetector. A multi-channel coherent photonic MMW de-chirper with phase compensation is utilized for coherent multiband radar signal processing, which facilitates the coherence-processing-free multiband data fusion and thus leading to an ultra-high resolution radar detection. Meanwhile, the communication receiving and demodulation towards multiband/multiuser scenarios are achieved by coherent receiving technology. In experiments, a photonic MMW ISAC system delivering Ka-band and V-band wireless signals is implemented, achieving a communication data rate of 16 Gbit/s and a two-dimension radar imaging of 3.75-cm range resolution, respectively. More importantly, after the multiband data fusion, an 8.6-mm ultra-high resolution is successfully achieved for radar ranging and imaging.

Highly sensitive frequency upconversion detection from 1 to 3 THz with OH1 crystal.

The wide applications of terahertz (THz) wave technology in the ∼1-3 THz range has resulted in a surge in the demand for the performance improvement of THz wave detection technique. In this study, a frequency tunable, highly sensitive frequency upconversion detection based on a 2-(3-(4-hydroxystyryl)-5,5-dime-thylcyclohex-2-enylidene) malononitrile (OH1) crystal at room temperature is demonstrated. Moreover, to effectively increase the signal-to-noise ratio in the low frequency range, a beam isolation enhancer is proposed and its effect is verified. The minimum detectable THz pulse energy reaches about 100 aJ at 1.9 THz. The frequency tuning ranging from 1 to 3 THz. Sensitivity comparison with a 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal system shows that OH1 is a more suitable nonlinear crystal in the 1-2.4 THz range.

Efficient Frequency Upconversion Photodetection in Heterojunction of InSe and Silicon Photonic Crystal Cavity

AbstractFrequency upconversion photodetection by two‐dimensional (2D) materials with nonlinear optical response is an appealing technique for applications such as extending photodetection wavelength range, autocorrelation measurement, and high‐efficiency single photon detection. However, the frequency upconversion efficiency in 2D materials is limited due to the low efficiency of nonlinear optical processes and atomic light‐matter interaction length. Here, the efficient frequency upconversion photodetection is realized by van der Waals (vdW) integration of a few‐layer InSe with a silicon photonic crystal cavity (Si‐PPC). With the large second‐order nonlinearity of InSe and enhanced light‐matter interaction by Si‐PCC, continuous wave (CW) pumped second harmonic generation (SHG) is demonstrated with pump power down to 100 µW. Further, InSe and Si absorb the SHG photons and generate photocarriers which are separated and collected by the n‐InSe/p‐Si heterojunction. A frequency upconversion photoresponsivity of 16 µA W−1 with a CW laser at 1467 nm is obtained. More efficient SHG with pulsed laser improves the responsivity to 3.9 mA W−1 with quadratic power dependence, which is record‐high among the frequency upconversion photodetectors based on 2D materials. This work opens up opportunities for a high‐efficiency 2D material nonlinear photodetector integrated on photonic integrated circuits.

Design and analysis of an exponentially tapered piezoelectric energy harvester under nonlinear rotational indirect magnetic excitation

Piezoelectric energy harvesting from rotational motions currently receives attention as a clean and permanent energy source. However, because of low output power, optimizing and improving the efficiency of this strategy through different methods is of great importance. This study investigates a new high-efficiency piezoelectric energy harvester under rotational indirect magnetic excitation using frequency up-conversion. The studied piezoelectric energy harvester is composed of an exponentially tapered cantilever beam with a piezoelectric layer, excited magnets, a tip mass, an octagonal disk attached to the rotating shaft, and exciting magnets on the disk. The potential energy and nonlinear magnetic force are determined and substituted into an electromechanically coupled governing equation after derivation. Numerical methods are applied to solve the governing equations due to their nonlinear nature and periodic oscillations. The tip mass varies to maintain a constant natural frequency and cancel out the effect of concurrent variations of the natural frequency and tapering parameter. Verification of the theoretical model is performed by the finite element and experiment methods. The effects of some parameters, such as the tapering parameter, total resistance of the circuit, number of magnets, and rotational speed, on the output voltage and power densities are evaluated. Results show a fourfold increase in output power density when comparing exponentially tapered width to constant width. Finally, frequency response curves are plotted and analyzed to examine the effect of shaft rotational speed, subharmonics, and bandwidth. The most important result extracted from the frequency response diagram is the increase in the number of subharmonics and the observation of 2 ω/5 and 2 ω/7 subharmonic components in the frequency response of the harvester with exponentially tapered width.

Two‐Photon Pumped Single‐Mode Lasing in CsPbBr3 Perovskite Microwire

AbstractAchieving high‐quality, frequency‐upconversion single‐mode lasing output is an important requirement for developing new nonlinear optoelectronic devices, such as on‐chip optical communication, nonlinear optical switches, and optical parametric amplifiers. Here, an individual CsPbBr3 microwire prepared by the anti‐solvent method is served as both gain media and microresonator to achieve two‐photon pumped frequency upconversion single‐mode lasing with the side‐mode suppression ratio of 18 dB. Meanwhile, the refractive index of orthorhombic perovskite is theoretically calculated based on first principles, and determining its square whispering‐gallery oscillation type by combining with the plane wave model and the steady‐state oscillation conditions of laser. The extracted exciton binding energy of 33.15 meV higher than the thermal ionization energy of room temperature (≈26 meV) suggests that the as‐grown CsPbBr3 microwires possess the capacity to achieve two‐photon pumped lasing output, as well further gaining deeper insights into the role of exciton‐phonon coupling in light emission.

Boosting output performance of tri-hybrid vibration-based generator via quin-stable nonlinearity and speed amplification

A high-performance tri-hybrid vibration-driven generator with quin-stability and speed amplification characteristics is presented. This design integrates three different mechanisms in a compact and interactive working mode to enhance power density. Exploiting the quin-stable nonlinear behavior to the dynamic system creates a shallow potential well that can be triggered under broadband, low-level, and random ambient sources. In addition, the implementation of the rack and pinion steering system not only doubles the relative motion of the translators’ moving components in the electromagnetic and triboelectric units, and also increases the number of operations per cycle of the frequency up-conversion piezoelectric units. Consequently, the output performance of this tri-hybrid generator is significantly enhanced. To examine the working efficiency of this design, an experimental model is assembled and tested. In the shaker test, the peak output power of the prototype can be boosted to ∼822 mW, and the maximum power density is 7.74 mW cm−3 g−2 subjected to low excitation levels (5 Hz and 1-g acceleration). Experimental demonstrations are also carried out to exhibit the exceptional performance of this design that can support various power levels of electronic devices under human-induced motions.

Upconversion luminescence based temperature sensing properties and anti-counterfeiting applications of GdNbO4:Tm3+/Yb3+ phosphor

Pure monoclinic phase GdNbO4:Tm3+/Yb3+ phosphor was prepared using solid state reaction method for upconversion emission, optical thermometry, latent fingerprints visualization and anti-counterfeiting applications. The prepared phosphor exhibits colour tunability with temperature variation (from blue to almost white) and good suppression of thermal quenching. The temperature sensing characteristic from thermally and non-thermally coupled levels of Tm3+ ion were investigated using the fluorescence intensity ratio (FIR) approach. The result shows that the sensitivity for non-thermally coupled level is about ∼ 45 times higher than thermally coupled level. Latent fingerprint detection on various surfaces and anti-counterfeiting ink application were also shown upon 980 nm laser diode excitation. Above results indicate that the prepared GdNbO4:Tm3+/Yb3+ phosphor have applicability in the field of frequency upconversion, optical thermometry, color tunable devices, latent fingerprint visualization and anti-counterfeiting applications.

Ultra-sensitive mid-wavelength-infrared upconversion detector

We have proposed and experimentally demonstrated an efficient ultra-sensitive mid-wavelength-infrared (MWIR) detector using a periodically poled lithium niobate nonlinear crystal and a silicon single-photon counting module. The involved frequency upconversion technique can spectrally convert the MWIR signal photons to the short-wavelength-infrared (SWIR) region. The internal quantum efficiency (QE) of the upconversion detector (UPD) reaches 8.87% at an average pump power of 10.67 W. The noise equivalent power of the UPD is measured as 3.24×10−15W/Hz1/2 at the MWIR wavelength of 4.6μm. In addition, the long-term stability is manifested by at least 12 h of operation with a relative fluctuation in the count rates as low as 0.35%.

Mitochondria-specific near-infrared photoactivation of peroxynitrite upconversion luminescent nanogenerator for precision cancer gas therapy

Gas therapy is emerging as a highly promising therapeutic strategy for cancer treatment. However, there are limitations, including the lack of targeted subcellular organelle accuracy and spatiotemporal release precision, associated with gas therapy. In this study, we developed a series of photoactivatable nitric oxide (NO) donors NRh-R-NO (R = Me, Et, Bn, iPr, and Ph) based on an N-nitrosated upconversion luminescent rhodamine scaffold. Under the irradiation of 808 nm light, only NRh-Ph-NO could effectively release NO and NRh-Ph with a significant turn-on frequency upconversion luminescence (FUCL) signal at 740 nm, ascribed to lower N–N bond dissociation energy. We also investigated the involved multistage near-infrared-controlled cascade release of gas therapy, including the NO released from NRh-Ph-NO along with one NRh-Ph molecule generation, the superoxide anion O2⋅− produced by the photodynamic therapy (PDT) effect of NRh-Ph, and highly toxic peroxynitrite anion (ONOO‒) generated from the co-existence of NO and O2⋅−. After mild nano-modification, the nanogenerator (NRh-Ph-NO NPs) empowered with superior biocompatibility could target mitochondria. Under an 808 nm laser irradiation, NRh-Ph-NO NPs could induce NO/ROS to generate RNS, causing a decrease in the mitochondrial membrane potential and initiating apoptosis by caspase-3 activation, which further induced tumor immunogenic cell death (ICD). In vivo therapeutic results of NRh-Ph-NO NPs showed augmented RNS-potentiated gas therapy, demonstrating excellent biocompatibility and effective tumor inhibition guided by real-time FUCL imaging. Collectively, this versatile strategy defines the targeted RNS-mediated cancer therapy.