Frequency Conversion Applications Research Articles

Research on Design Method of Computer Control System for Frequency Conversion Speed Regulation Based on Cloud Technology

With the development of power electronics technology, frequency converter as the controller of AC motor has been more and more widely used. With the continuous development and application of frequency converters, more and more occasions need to be remote controlled through the network. With the input system of computer, the process parameters can be easily changed. Intelligent control has become the feature and symbol of the new generation of control products, so intelligent control is bound to become a research hotspot in the field of control. Whether it is civilian or military, the variable frequency speed control synchronous control system has occupied a dominant position. Therefore, it is the current development trend to use a computer to control the inverter through communication. In order to meet the requirements of the production process, it is necessary to carry out technical transformation of the original system with new technology. This paper mainly describes the application of frequency conversion and automation technology in this system. The characteristic of the power supply voltage regulation synchronization system is that each unit is powered by its own power source. This method has better adaptability and a wider range of speed regulation.

Microcavity Nonlinear Optics with an Organically Functionalized Surface.

We report enhanced optical nonlinear effects at the surface of an ultrahigh-Q silica microcavity functionalized by a thin layer of organic molecules. The maximal conversion efficiency of third harmonic generation reaches ∼1680%/W^{2} and an absolute efficiency of 0.0144% at pump power of ∼2.90 mW, which is approximately 4 orders of magnitude higher than that in a reported silica microcavity. Further analysis clarifies the elusive dependence of the third harmonic signal on the pump power in previous literature. Molecule-functionalized microcavities may find promising applications in high-efficiency broadband optical frequency conversion and offer potential in sensitive surface analysis.

Second and third order nonlinear optical, mechanical, surface characteristics of bis(thiourea) manganese chloride (BTMC) grown by slow cooling technique used for frequency conversion applications

A semiorganic nonlinear optical (NLO) single crystal of bis(thiourea) manganese chloride (BTMC) is grown successfully by slow cooling technique using water as solvent at temperature 45 °C. The optically good quality crystal of BTMC was grown with dimension up to 8 × 8 × 2 mm3 in a period of 2–3 weeks. The grown crystal crystallizes in orthorhombic crystal system which was confirmed by single crystal X-ray diffraction analysis. The various functional groups of BTMC were identified through FT-IR spectroscopic analysis. The lower cut-off wavelength of 280 nm was revealed from optical transmittance spectrum of UV. The mechanical behavior of BTMC crystal was analyzed by Vicker’s microhardness study and also the various mechanical parameters were determined. Vickers micro hardness test revealed, the titular crystal belongs to harder material category. The SHG efficiency is estimated from Kurtz-Perry powder method and it found to be 0.33 times than the reference material. The dielectric behavior, photo conducting nature and surface properties have been analyzed for grown BTMC crystal. The presence of synthesized elements was confirmed by EDAX study. The third order nonlinear optical susceptibility chi^{left(3 right)} of the material is measured using Z-scan technique and it is found to be 5.1202 × 10−14 esu.

Growth, Optical, Thermal, Mechanical, Laser Damage Threshold and Electrical Polarizability of Cadmium Chloride Doped l-Alanine (LACC) Single Crystal for Optoelectronic Applications

l-Alanine doped with cadmium chloride crystal was grown by slow evaporation technique in an optimum condition using de-ionized water as solvent. Single crystal x-ray diffraction analysis was carried out to confirm the unit cell parameters and cell volume. The presence of amine vibrations and carboxylic acid vibrations affirm the presence of l-alanine in grown material by Fourier transform infrared (FT-IR) analysis. The ultraviolet visible near-infrared region (UV–Vis-NIR) spectrum revealed that the grown crystal has a lower cut-off wavelength at 246 nm and has high transmission in the entire visible region. Further, energy gap and the refractive index of the crystal were also calculated. Thermo-gravimetric (TG) and differential thermal analysis (DTA) were carried out, and it is estimated that the material is thermally stable up to 233°C and the melting point of the crystal was found to be 298°C. The mechanical strength of the material is estimated for various loads using Vicker’s microhardness and it reveals that material belongs to a soft material category. The electrical polarizability was calculated using known values such as valence electron, molecular weight, energy gap and density of the material. Z-scan technique for nonlinear studies was carried out on a LACC crystal to determine the third order nonlinear absorption (β), nonlinear refractive index (n2) and third order nonlinear susceptibility (χ(3)) using continuous wave Nd: YAG laser of 532 nm. Grown crystal shows that the material is very much suitable for second harmonic generation for frequency conversion applications.

Four‐Wave Mixing Holographic Multiplexing Based on Nonlinear Metasurfaces

AbstractMetasurfaces are utilized to realize computer‐generated holograms (CGHs), with excellent wavefront shaping ability and ultrasmall footprint. To increase the information capacity of metasurface holograms, smart multiplexing techniques together with suitable designs are highly demanded. However, so far only a few approaches to achieve nonlinear metasurfaces holographic multiplexing based on CGHs are proposed, due to limited freedoms of multiplexing and proper metasurfaces' design. The nonlinear interaction of light with the metasurface can generate new frequencies compared to the input laser beam, which is promising to realize spectral and spatial multifunctional wavefront manipulation. Here, a four‐wave mixing (FWM) holographic multiplexing technique is numerically proposed using a nonlinear metasurface composed of a nanoapertures array. It is demonstrated that the complex amplitude modulation by such a metasurface through the FWM process can be utilized for amplitude‐only CGHs, which can process significantly independent information at different nonlinear frequencies in the optical regime. Utilizing the spatial and spectral multiplexing of nonlinear metasurfaces holography, they can be found applications for multidimensional holographic displays and can provide enhanced security for optical data storage. These results show that nonlinear metasurfaces are promising for applications of arbitrary frequency conversion and optical encryption and anticounterfeiting designs.

Diode-pumped Yb:KGW laser with 73 fs pulse and 0.72 MW peak power based on Kerr-lens mode locking

We have demonstrated a high-power Kerr-lens mode-locked Yb:KGW oscillator with an additional Kerr medium pumped by a high-brightness fiber-coupled diode laser. Operated at the repetition rate of 75.5 MHz, the laser delivers 73 fs pulse duration with average output power of 4.05 W, and the corresponding pulse energy is 53 nJ and the peak power is 0.72 MW, respectively. The output power is recorded to be stable with a fluctuation of less than 0.65% rms within 0.5 h. This work is promising for a variety of applications in nonlinear frequency conversion and high-energy amplifiers.

Low-Temperature Properties of Whispering-Gallery Modes in Isotopically Pure Silicon-28

Whispering Gallery (WG) mode resonators have been machined from a boule of single-crystal isotopically pure silicon-28. Before machining, the as-grown rod was measured in a cavity, with the best Bragg confined modes exhibiting microwave $Q$-factors on the order of a million for frequencies between 10 and 15 GHz. After machining the rod into smaller cylindrical WG mode resonators, the frequencies of the fundamental mode families were used to determine the relative permittivity of the material to be $11.488\pm0.024$ near 4 K, with the precision limited only by the dimensional accuracy of the resonator. However, the Q-factors were degraded by the machining to below $4\times10^4$. Raman spectroscopy was used to optimize post-machining surface treatments to restore high $Q$-factors. This is an enabling step for the use of such resonators for hybrid quantum systems and frequency conversion applications, as silicon-28 also has very low phonon losses, can host very narrow linewidth spin ensembles and is a material commonly used in optical applications.

Structural, Optical, Mechanical and Laser Damage Threshold Studies on an active Nonlinear Optical Material: Potassium Thiourea Bromide (KTB) in a Novel Crystal System

Abstract The enhancement of optical transparency, crystalline perfection, laser damage threshold values and principally, mechanical strength of thiourea doped potassium bromide crystals grown under slow evaporation solution growth technique were assessed. The validation and morphology were done by X-ray diffraction analysis. The sample KTB crystallized in orthorhombic system is unique and novel. The vibrational range in the FT-IR affirmed the functional groups present in the title compound. The energy gap Eg found to be 4.12eV with broad transparency window between 300.600nm to 1100nm. Second harmonic studies manifest the suitability of the crystal for frequency conversion and doubling applications. The positive photo conducting nature of the material aspires that the sample would be more electrically conductive on the absorption of electromagnetic radiation. The laser damage threshold value indicates the aptness of the sample to confront against high power intensities. The elastic(C11), plastic, fracture traits(Kc) along with the yield strength(σv) and brittleness index(Bi) were calculated and reported for the first time under orthorhombic system. The result also evident appreciable mechanical strength of the crystal, as it holds cardinal importance in technological applications.

Crystal growth and optical characterization of an organic single crystal for frequency conversion applications

Organic nonlinear optical 2-methylquinolinium L-malate single crystals have been grown by slow evaporation solution growth technique from a mixture of 2-methylqiunoline and L-malic acid in ethanol solution at ambient temperature. Single crystal X-ray diffraction analysis reveals that grown crystal in monoclinic system with non-centrosymmetric space group P21 and the lattice parameters are a = 7.35 Ǻ, b = 26.51 Ǻ, c = 10.83 Á, α = γ = 90° β = 102.95º and V = 2057.4 Ǻ3. UV-vis spectrum indicates that the crystal is transparent (75%) in the entire visible region with a cut-off wavelength of 437 nm and optical energy band gap Eg is found to be 2.71 eV. Microhardness measurement reveals the mechanical strength of the grown crystal. The photoluminescence spectrum shows the blue emission of the crystal. Laser damage threshold studies was carried out to ascertain the suitability of grown crystal for laser applications.The relative second harmonic generation efficiency of 2-methlquinolinium L-malate crystal was found to be two times greater than that of KDP.

Reflection from a free carrier front via an intraband indirect photonic transition

The reflection of light from moving boundaries is of interest both fundamentally and for applications in frequency conversion, but typically requires high pump power. By using a dispersion-engineered silicon photonic crystal waveguide, we are able to achieve a propagating free carrier front with only a moderate on-chip peak power of 6 W in a 6 ps-long pump pulse. We employ an intraband indirect photonic transition of a co-propagating probe, whereby the probe practically escapes from the front in the forward direction. This forward reflection has up to 35% efficiency and it is accompanied by a strong frequency upshift, which significantly exceeds that expected from the refractive index change and which is a function of group velocity, waveguide dispersion and pump power. Pump, probe and shifted probe all are around 1.5 µm wavelength which opens new possibilities for “on-chip” frequency manipulation and all-optical switching in optical telecommunications.

First-principles study of stacking effect on second harmonic generation of graphene-like two-dimensional silicon carbide

Two-dimensional layered silicon carbide (2d-SiC), a semiconductor with graphene-like structure, has potential applications in nonlinear optical frequency conversion. The effect of stacking and strain on the nonlinear second harmonic generation (SHG) coefficient are studied by using the first-principles calculation of the all-electron full-potential linearized augmented-plane wave combined with the sum-over-states method. The analysis of physical origin of the SHG process shows that the single-particle transition channel formed by three bands dominates the SHG process of 2d-SiC. The interband motion of electrons is significantly tuned by the intraband motion. The angle dependence of the SHG coefficient of 2d-SiC is given as a reference for future experiments. A tunable SHG enhancement could be obtained by straining 2d-SiC.

Achromatic critically coupled racetrack resonators

In this paper, we investigate the spectral response of whispering-gallery-mode (WGM) resonators coupled to their access waveguide with a view to design their constitutive waveguides to promote critical-coupling over a wide spectral range and thereby facilitate their use for high-sensitivity sensing or nonlinear frequency conversion applications. The carried-out theoretical analysis is based on the universal response functions of singlemode and unidirectional devices. A coupled-mode treatment of the coupling region enables to derive two sets of favorable designs. The identified resonator/access waveguide systems exploit waveguides with mismatched propagation constants forming a coupling section exhibiting either an achromatic beat-length or an achromatic power-transfer coefficient. This generic model is followed by a numerical case study of vertically-coupled Si3N4 racetrack resonators. The conventional (quasi-)phase-matched configuration, treated as a reference case, is shown to display a critical-coupling bandwidth of 23 nm at a wavelength of 1550nm, whereas the proposed new designs demonstrate critical bandwidths larger than 330nm, i.e. exhibit bandwidths enhanced by more than one order of magnitude.

Extended 9.7 nm tuning range in a MOPA system with a tunable dual grating Y-branch laser.

In this Letter, we present a tunable Y-branch hybrid master oscillator power amplifier (MOPA) with 5.5W output power, emitting between 973.7 and 983.4nm. The MO is a monolithic Y-branch distributed Bragg reflector (DBR) diode laser, which is collimated and coupled into a tapered amplifier using cylindrical microlenses in a compact 25 mm×25 mm conduction cooled laser package. The wavelength spacing between the two laser branches is 2.2nm. Each branch can be electrically tuned by up to 7.5nm of quasi-continuous wavelength tuning, which in combination covers up to 9.7nm of spectral range. Over this range, an output power variation of 0.5% and 0.2% is observed for the left and right arms, respectively, while maintaining a spectral width of less than 17pm. In addition, the MOPA system can be operated as a dual-wavelength system by operating both branches simultaneously. The presented device is suitable for nonlinear frequency conversion applications.

(Invited) The Current Status and Future Prospects of SiC Devices

Although silicon power devices have served well as the key technology for power electronics for several decades, silicon-based technology is reaching its physical limits, in terms of power handling and switching frequency capabilities. Thanks to its superior material properties, SiC is the most promising post-silicon alternative for high voltage, high frequency, and high temperature power conversion applications. Since the advent of the first SiC Schottky Barrier Diode (SBD) in the 1990’s, numerous research groups have devoted their efforts to commercialize SiC devices such as MOSFETs, JFETs, and Thyristors. In this talk, issues regarding current SiC devices and processing technology will be identified and future research directions will be discussed.

Growth and characterization of an efficient new NLO single crystal L-phenylalanine D-methionine for frequency conversion and optoelectronic applications

Optically active single crystals of L-phenylalanine D-methionine (LPDM) were grown by slow evaporation technique by co-crystallization of amino acids L-phenylalanine and D-methionine in water. The unit cell dimensions have been identified from single crystal X-ray diffraction technique. The existences of various hydrocarbyls were examined by FTIR and FT-Raman spectroscopy. The carbon and hydrogen environment of the grown crystals were analyzed by FT NMR spectrum. The optical absorption studies show that the crystal is transparent in the visible region with a lower cut-off wavelength of 259nm and there by optical band gap energy Eg is calculated to be 5.35eV. The Urbach energy, extinction coefficient, reflectance were calculated from UV-absorption data. Further, the thermal stability and accurate melting point has been investigated by TG/DSC techniques. The Kurtz powder SHG was confirmed using Nd:YAG laser with fundamental wavelength of 1064nm. The dielectric behavior of the specimen has been determined for various temperatures (313K, 333K, 353K, 373K) at different frequencies. Fluorescence study and the time resolved decay calculation was also performed for the LPDM crystal. Optical nonlinear susceptibility was measured in LPDM and the real and imaginary part of χ3 was evaluated by Z-scan technique using open and closed apertures.

Dynamic computer-generated nonlinear-optical holograms

We propose and experimentally demonstrate dynamic nonlinear optical holograms by introducing the concept of computer-generated holograms for second-harmonic generation of a structured fundamental wave with a specially designed wave front. The generation of Laguerre-Gaussian second-harmonic beams is investigated in our experiment. Such a method, which only dynamically controls the wave front of the fundamental wave by a spatial light modulator, does not need domain inversion in nonlinear crystals and hence is a more flexible way to achieve the off-axis nonlinear second-harmonic beams. It can also be adopted in other schemes and has potential applications in nonlinear frequency conversion, optical signal processing, and real-time hologram, etc.

34 nm-wavelength-tunable picosecond Ho3+/Pr3+-codoped ZBLAN fiber laser.

We propose and demonstrate a broadly wavelength-tunable mode-locked Ho3+/Pr3+-codoped ZBLAN fiber laser operating in the 3 μm mid-infrared spectral region based on a semiconductor saturable absorber mirror. Wavelength selection is realized by rotating a plane ruled grating. The fiber laser exhibits stable continuous-wave mode-locking operation over a wide wavelength tuning range of 34 nm (2842.2 nm~2876.2 nm), with a 10.17 MHz repetition rate and 22 ps pulse duration. Stable mode-locked pulses can be maintained until the launched pump power of 1.25 W. Maximum average output power of 127.7 mW and the corresponding pulse energy of 12.56 nJ are achieved. To the best of our knowledge, this is the first demonstration of a wavelength-tunable mode-locked fiber laser operating in the 3 μm spectral region. Such simple, robust, and versatile mid-infrared picosecond laser source can find various applications in laser surgery, spectroscopy, and nonlinear frequency conversion.

Potassium tantalate-niobate mixed crystal thin films for applications in nonlinear integrated optics

Potassium tantalate-niobate mixed crystal (KTN) thin films are promising candidates to meet the needs of integrated nonlinear optical devices for electro-optic and frequency-conversion applications. In this contribution we report on pulsed-laser-deposition growth of ferroelectric KTN films on MgO substrates. It was shown that highly-oriented KTN films are epitaxially grown as revealed by X-ray diffraction analysis. Moreover, the thermal annealing treatment can be further optimized to obtain optically smooth KTN films with RMS surface roughness as low as 1 nm.

Sub-wavelength modulation of \u03c7(2) optical nonlinearity in organic thin films

Modulating the second-order nonlinear optical susceptibility (χ(2)) of materials at the nanoscale represents an ongoing technological challenge for a variety of integrated frequency conversion and nonlinear nanophotonic applications. Here we exploit the large hyperpolarizability of intermolecular charge transfer states, naturally aligned at an organic semiconductor donor–acceptor (DA) interface, as a means to control the magnitude and sign of χ(2) at the nanoscale. Focusing initially on a single pentacene-C60 DA interface, we confirm that the charge transfer transition is strongly aligned orthogonal to the heterojunction and find that it is responsible for a large interfacial nonlinearity probed via second harmonic generation that is sufficient to achieve d33>10 pm V−1, when incorporated in a non-centrosymmetric DA multilayer stack. Using grating-shadowed oblique-angle deposition to laterally structure the DA interface distribution in such multilayers subsequently enables the demonstration of a χ(2) grating with 280 nm periodicity, which is the shortest reported to date.

Study on growth, spectral, optical and thermal characterization of an NLO crystal: 6-Methyl nicotinic acid (6MNA)

6-methyl-nictinic acid (6MNA), organic non linear optical (NLO) single crystals were grown by slow evaporation solution technique. The cell parameters of 6MNA were confirmed from single crystal X-ray diffraction analysis. The Fourier transforms infrared and proton Nuclear magnetic resonance spectral analysis confirm the presence of various functional groups and the placement of protons respectively in 6MNA compound. UV–vis–NIR spectral studies revealed that the grown 6MNA has good optical transmission in the range of entire visible region. The thermal properties of crystals were evaluated from thermogravimetric (TG) and differential thermal analysis (DTA). It has shown that the grown crystals were stable up to 213°C. The second harmonic generation (SHG) measurements indicated that the efficiency of 6MNA is two times greater than that of the KDP crystals and is suitable for frequency conversion applications.