Search

The photorefractive effect is a phenomenon in which the refractive index changes at the interference fringe, forming a diffraction grating (hologram). Photorefractive materials are composed of a combination of electro-optical materials and photoconductive compounds. Liquid crystals mixed with a photoconductive compound are useful as photorefractive materials because of their large birefringence and fluidity. Various applications are expected, such as amplifying optical signals, dynamic holograms, and Fourier optical elements. This article describes the development of high-performance photorefractive materials using liquid crystals and their applications in laser ultrasonics. [ABSTRACT FROM AUTHOR]

Copyright of Diamond & Abrasives Engineering is the property of Zhengzhou Research Institute for Abrasives & Grinding and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

MgO:PPLN crystals encounter limitations in the feed-forward carrier-envelope phase (CEP) stabilization for f-to-2f interferometry due to phase mismatch, and temperature and photorefractive effects that can compromise the accuracy of second harmonic generation (SHG).

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Subwavelength gratings play a fundamental and pivotal role in numerous science and applications for wave manipulation, exhibiting distinctive features such as filtering, phase manipulation, and anti‐reflection. However, conventional fabrication methods for ultrasmall periodic structures are constrained by the fundamental optical diffraction limit, making it challenging to produce subwavelength gratings for optics. Here, a novel technique is demonstrated to build a reconfigurable subwavelength photorefractive grating (SPG) in a thin‐film lithium niobate on the platform of an optical microcavity. Such SPGs are optically induced through the photorefractive effect and the subwavelength features originate from the spatial phase modulations of the pump's standing wave. The resulting SPGs lead to the mode splitting of two counter‐propagating modes inside the microcavity, exhibiting an Electromagnetically Induced Transparency (EIT)‐like transmission spectrum. Moreover, the unique subwavelength characteristic of SPGs enables first‐order quasi‐phase‐matching for backward second‐harmonic generation, a long‐standing problem in nonlinear optics. Also, free‐space‐to‐chip vertical nonlinear frequency conversion can be achieved in a similar manner. These results provide a flexible approach toward fabricating subwavelength gratings, which holds significant potential in various applications such as nonlinear frequency conversion, optical communication, sensing, and quantum technologies. [ABSTRACT FROM AUTHOR]

Lithium niobate on insulator (LNOI) is widely recognized as an essential optoelectronic integration platform due to its unique ferroelectric properties and photorefractive effect. However, the wide bandgap and weak absorption of lithium niobate limit its further application in integrated photodetection field. To address this issue, encapsulating silver nanoparticles within the LNOI structure are proposed to manipulate the light field distribution of modified lithium niobate through the localized surface plasmon resonance (LSPR) effect and utilize the modified lithium niobate thin film as a functional substrate to tailor the optoelectronic properties of surface SnSe2 nanosheets, significantly enhancing their photodetection capabilities. The photocurrent of the SnSe2 photodetector based on LNOI with embedded Ag nanoparticles is enhanced by up to 1912 times compared to that on the original LNOI under the same conditions, which represents the highest reported plasmonic‐induced photodetection enhancement. This work deepens the basic research on plasmonic‐modified 2D materials and ferroelectric materials, which promotes the development of on‐chip photodetectors and the realization of fully functional photonic circuits that integrate all essential components on a single chip. [ABSTRACT FROM AUTHOR]

As ferroelectric materials, lithium tantalate and lithium niobate share similar material characteristics, such as a high Pockels effect and nonlinear optical coefficients. When compared to lithium niobate, lithium tantalate offers a higher optical damage threshold, a broader transparent window, and lower birefringence, making it a promising candidate for high-performance electro-optical photonic integrated devices. In this study, we design and successfully fabricate micro-ring resonators on an acoustic-grade lithium-tantalate-on-insulator wafer, demonstrating their tunability and dynamic modulation capabilities. Experimental results indicate that the achieved thin-film lithium tantalate based micro-ring resonator exhibits an intrinsic Q-factor of 8.4 × 105, corresponding to a waveguide propagation loss of 0.47 dB/cm and a tuning efficiency of 1.94 pm/V. More importantly, as compared to those based on thin-film lithium niobate, a much weaker photorefractive effect and drift phenomenon around the 1550 nm wavelength under a direct-current drive are observed in the present fabricated thin-film lithium tantalate micro-rings with a silicon oxide over-cladding and a tuning electrode on top. [ABSTRACT FROM AUTHOR]

Optical microcavity has proven its potential for unlabeled sensing. Here, we propose and demonstrate in a lithium niobate on insulator microcavity an enhanced sensing approach enabled by the nonlinear mode oscillation generated by the competition between thermal-optic and photorefractive effect, which breaks the intrinsic limitation in wavelength resolution set by the cavity's optical quality factor. It allows us to perform precise measurements of the mode shifting introduced by a nanoscale scatterer with a signal to noise ratio of 13.1 dB and paves a distinctive way to improve resonance shift resolution in widely studied microcavity sensors with a platform of great integration capability. [ABSTRACT FROM AUTHOR]

Generated in high‐Q optical microresonators, dissipative Kerr soliton microcombs constitute broadband optical frequency combs with chip sizes and repetition rates in the microwave to millimeter‐wave range. For frequency metrology applications such as spectroscopy, optical atomic clocks, and frequency synthesizers, octave‐spanning soliton microcombs generated in dispersion‐optimized microresonators are required, which allow self‐referencing for full frequency stabilization. In addition, field‐deployable applications require the generation of such soliton microcombs to be simple, deterministic, and reproducible. Here, a novel scheme to generate self‐emerging solitons in integrated lithium‐niobate microresonators is demonstrated. The single soliton features a broadband spectral bandwidth with dual dispersive waves, allowing 2f–3f self‐referencing. Via harnessing the photorefractive effect of lithium niobate to significantly extend the soliton existence range, a spontaneous yet deterministic single‐soliton formation is observed. The soliton is immune to external perturbation and can operate continuously for over 13 h without active feedback control. Finally, via integration with a pre‐programmed distributed feedback (DFB) laser, turnkey soliton generation is demonstrated. With further improvement of microresonator Q and hybrid integration with chip‐scale laser chips, compact soliton microcomb devices with electronic actuation can be created, which can become central elements for future LiDAR, microwave photonics, and optical telecommunications. [ABSTRACT FROM AUTHOR]

This study investigates ultrafast photoinduced changes in optical properties of ferroelectrics (PZT) on femtosecond to nanosecond timescales, using broadband transient reflectivity studies. Surprisingly, spectral features were observed below the bandgap, which could not be attributed to ground state bleaching, excited state absorption, and/or stimulated emission. A model based on probe energy independent changes in refractive index and extinction coefficient showed good agreement with experimental results. Three relaxation processes were phenomenologically considered for the temporal evolution. Laser-induced heating was ruled out as the cause of short timescale behavior and photorefractive effect was suggested as a potential mechanism for changes in the optical properties. [ABSTRACT FROM AUTHOR]

The temporal behavior and formation characteristics have been investigated for the first time in nonlinear optical media exhibiting photorefractive effect due to simultaneous linear and quadratic electro-optic effect. The space charge field which is a function of time is derived and hence leads to the time dependent wave equation satisfied by light beams in such novel photorefractive materials. The soliton width evolution and hence the evolution of the nonlinearity with time is investigated for different values of peak intensity ratio. The dark soliton formation does not show quasi steady state behaviour and only steady state solitons are formed. There is interplay between the linear and quadratic electro-optic effect that affects the formation of dark solitons. Finally, the effect of crystal temperature on the formation of dark solitons is studied. In a photorefractive crystal, the temperature modification results in consequent changes in dark irradiance and dielectric constant which has a profound effect on the time evolution of these dark solitons. A relevant example of 0.67PMN-0.33PT crystal has been considered for an illustration of our results. [ABSTRACT FROM AUTHOR]

Micro‐optical frequency combs are miniaturized coherent light sources exhibiting a tremendous influence on precision spectroscopy, optical clocks, and high‐speed optical communications. The rare‐earth‐doped lithium niobate (LN) is a promising platform to integrate the lasers and comb sources on the same chip of single material. However, microcombs generated in rare‐earth‐doped LN thin film (LNTF) have not yet been fully explored. To explore the protocols of generating optical combs in ytterbium‐doped LNTF, the comb‐like laser is studied in the 1060 nm band, and the dissipative Kerr soliton is experimentally demonstrated in the telecom band in a Z‐cut wafer. The over‐coupled fundamental transverse electric mode with anomalous dispersion is excited at an on‐chip pump power of 75.7 mW to generate the robust bright soliton. The broadband spectrum of the Kerr soliton ranges from 1480 to 1660 nm with 110 comb lines, whose repetition rate is 197.8 GHz. The mode‐locking of the soliton can be achieved as a result of the photorefractive effect of ytterbium‐doped LNTF instead of complex feedback schemes. Numerical simulations are highly accordant with the experimental results. This work expands the microcomb‐generating platform and increases the potential for integrated on‐chip applications including precision ranging and frequency division. [ABSTRACT FROM AUTHOR]

A theoretical model that can efficiently calculate the refractive index response of semiconductors under ultrafast X-ray radiation is established based on the photorefractive effect of semiconductors. The proposed model is used to interpret X-ray diagnostics experiments, and the results are in good agreement with experiments. In the proposed model, a rate equation model of free carrier density calculation is adopted with the X-ray absorption cross-sections calculated by atomic codes. The two-temperature model is used to describe the electron-lattice equilibration and the extended Drude model is applied to calculate the transient refractive index change. It is found that faster time response can be achieved for semiconductors with shorter carrier lifetime and sub-picosecond resolution can be obtained for InP and Al0.5Ga0.5As. The material response time is not sensitive to X-ray energy and the diagnostics can be used in the 1–10 keV energy range. This article is part of the theme issue 'Dynamic and transient processes in warm dense matter'. [ABSTRACT FROM AUTHOR]

Two series of LiNbO3:Mg:B crystals have been grown and studied. Two doping methods—have been used. The crystals—have been co-doped with Mg and a non-metallic dopant, B. The physicochemical features of the growth—have been considered for LiNbO3:Mg:B crystals obtained from a boron-doped melt. The charge—has been prepared using different technologies: homogeneous (HG) and solid-phase (SP) doping. The same two methods have been used to grow single-doped LiNbO3:Mg crystals. A control near-stoichiometric (NSLN) crystal—has been grown via the HTTSSG (high-temperature top-seeded solution growth) method from a congruent melt (Li/Nb ≈ 0.946) with 5.5 wt% K2O. The characteristics of the LiNbO3:Mg:B crystals—have been compared with those of the LiNbO3:Mg and NSLN crystals. Physicochemical and structural reasons have been established for the differences in the distribution coefficients of magnesium (KD) during the growth of the HG- and SP-doped LiNbO3:B:Mg and LiNbO3:Mg crystals. The optical characteristics of the LiNbO3:B:Mg crystals—have been studied via optical spectroscopy, laser conoscopy and photoinduced light scattering (PILS). The influence of boron on the microstructure, compositional and optical uniformities and optical damage resistance of the LiNbO3:Mg:B crystals—has been estimated. Optimal technological approaches to growing optically uniform LiNbO3:B:Mg crystals have been determined. LiNbO3:Mg:B crystals have been shown to have a significant advantage over the commercially used LiNbO3:Mg crystals since large LiNbO3:Mg:B crystals can be grown without stripes. Such stripes usually appear perpendicular to the growth axis. In addition, the photorefractive effect is suppressed in LiNbO3:Mg:B crystals at lower magnesium concentrations ([Mg] ≈ 2.5 mol%) than in LiNbO3:Mg ([Mg] ≈ 5.5 mol%). [ABSTRACT FROM AUTHOR]

In this work, an adaptive holographic interferometer was implemented for the measurement of a micromechanical oscillator frequency. A silicon micro-cantilever mounted on a piezoquartz plate was used as the sensing element. Out-of-plane vibrations of the cantilever were excited using a sinusoidal electrical signal. The cantilever vibrations were measured with the adaptive interferometer using two waves coupling in a semi-insulating photorefractive CdTe:V crystal. In the experiment, the mass of absorbed molecules of bovine serum albumin (BSA) was measured at various concentrations of water solution. The biosensor demonstrated the ability to measure the concentration of BSA in water solutions with a concentration of 0.2 mg/mL. The result shows the possibility of using adaptive interferometry to detect the vibration of micromechanical sensors and the potential prospects for building biosensors based on them. [ABSTRACT FROM AUTHOR]

Two dimensional electron gases (2DEGs) formed at interfaces between two oxides have been drawing growing attention for their intriguing magnetic, superconducting, and optical properties. Remarkable anisotropic transmission was observed from an indium-tin-oxide (ITO) coated lithium niobate (LN) slab, implying that a 2DEG is formed at one of the ITO/LN interfaces, and this is seemingly behind the anisotropic transmission. To optically probe 2DEG formation at one of the ITO/LN interfaces, the first reflected beam was monitored with one (two) laser beam(s). Reflective dynamics as large as 5%-15% were observed, pointing unambiguously to a subwavelength coupling and corresponding to, conservatively, exponential gain coefficients of −26 800 to +2700 cm−1 with half a wavelength as the coupling range. All observations are far beyond the reach of conventional bulk photorefractive effects, but align well with a picture of surface plasmon polariton excitation based on 2DEG formation. The 2DEG proximal to the LN substrate is a promising candidate for designing nonlinear plasmonics based nanometric waveguides, rectifiers, modulators, and sensors, which are compatible with current photonic circuits. [ABSTRACT FROM AUTHOR]

In this paper, the diffraction efficiency as a function of grating writing angle in LN:Fe, Hf crystals was studied, and the relationship curve was fitted and analyzed. It is found that the bulk photovoltaic coefficient ΰ increases significantly when the Hf-doping concentration exceeds the threshold. The dramatic increase of the coefficient ΰ to the fact that the Hf-doping eliminates the intrinsic defects in the crystal and the perfection of the lattice environment enhances the photovoltaic coefficient k of the Fe ions remaining at Li sites. The experimental results also show that the concentration of photorefractive centers is about 14. 5 ppm (1 ppm = 10 -6) in LN:Fe, Hf crystals, that is, 4. 8% of the Fe ions still "remain" in the Li site even though the Hf-doping concentration already exceeds the threshold, and that these Fe ions can cause sufficiently strong photorefractive effect and become the dominant photorefractive centers in the LN crystal. In addition, the possibility of Fe ion occupation in LN lattice from the perspective of impurity-hydroxyl defect complex was discussed. [ABSTRACT FROM AUTHOR]

Various crystalline silicon carbide (SiC) polytypes are emerging as promising photonic materials due to their wide bandgap energies and nonlinear optical properties. However, their wafer forms cannot readily provide a refractive index contrast for optical confinement in the SiC layer, which makes it difficult to realize a SiC-based integrated photonic platform. In this paper, we demonstrate a 3C-SiC-on-insulator (3C-SiCoI)-based integrated photonic platform by transferring the epitaxial 3C-SiC layer from a silicon die to a borosilicate glass substrate using anodic bonding. By fine-tuning the fabrication process, we demonstrated nearly 100% area transferring die-to-wafer bonding. We fabricated waveguide-coupled microring resonators using sulfur hexafluoride (SF6)-based dry etching and demonstrated a moderate loaded quality (Q) factor of 1.4 × 105. We experimentally excluded the existence of the photorefractive effect in this platform at sub-milliwatt on-chip input optical power levels. This 3C-SiCoI platform is promising for applications, including large-scale integration of linear, nonlinear and quantum photonics. [ABSTRACT FROM AUTHOR]

The nonlinear optical properties of composite liquid crystal (LC) cells containing gold nano-island film (AuNIF) deposited on one of the cell substrates are studied with the help of dynamic holographic techniques. A dynamic phase grating of a photoinduced change in the refractive index arises in a composite LC cell when the two-wave mixing of laser beams of a cw Nd:YAG laser is used. The nonlinear optical response is caused due to a surface-induced photorefractive effect observed under the simultaneous action of a periodic light interference pattern and a constant voltage. The result of this impact is appearance of an internal electric field (Eint) at the AuNIF-LC interface. This electric field defines the local reorientation of LC molecules. Our experimental studies prove that the Eint value can be controlled by the size and shape of Au nanoparticles in AuNIF. As a result, we obtained a record of either fast dynamic gratings or quasi-stationary gratings in the composite LC cells depending on the morphology of AuNIF. [ABSTRACT FROM AUTHOR]

The conditions for the excitation of transverse and longitudinal polar modes in the processes of Raman scattering in lithium niobate single crystals with co-doped with copper and gadolinium are established using a backscattering geometry. A significant increase in the intensity of the Raman lines at 175 and 603 cm−1 was found with an increase in the degree of doping of the crystals with copper due to the photorefractive effect. [ABSTRACT FROM AUTHOR]

Owing to its attractive optical and electronic properties, silicon carbide is an emerging platform for integrated photonics. However an integral component of the platform is missing—an electro-optic modulator, a device which encodes electrical signals onto light. As a non-centrosymmetric crystal, silicon carbide exhibits the Pockels effect, yet a modulator has not been realized since the discovery of this effect more than three decades ago. Here we design, fabricate, and demonstrate a Pockels modulator in silicon carbide. Specifically, we realize a waveguide-integrated, small form-factor, gigahertz-bandwidth modulator that operates using complementary metal-oxide-semiconductor (CMOS)-level voltages on a thin film of silicon carbide on insulator. Our device is fabricated using a CMOS foundry compatible fabrication process and features no signal degradation, no presence of photorefractive effects, and stable operation at high optical intensities (913 kW/mm2), allowing for high optical signal-to-noise ratios for modern communications. Our work unites Pockels electro-optics with a CMOS foundry compatible platform in silicon carbide. Electro-optic modulator is used to encode electrical signals onto light. Here the authors demonstrate an electro-optic modulator, based on Silicon Carbide, which can be useful for quantum and optical communications. [ABSTRACT FROM AUTHOR]

Taking the fractional Schrödinger equation as the theoretical model, the evolution behavior of the Pearcey-Gaussian beam in the photorefractive medium is studied. The results show that breathing solitons are generated when the nonlinear effect and the diffraction effect are balanced with each other. Nonlinear coefficients, Lévy index and beams amplitude affect breathing period of the soliton and maximum peak intensity. Within a certain range, the breathing period of the soliton decreases with the increase of the nonlinear coefficient and the Lévy index. However when the beams amplitude increases, the breathing period and the maximum peak intensity of the soliton increase. Under the photorefractive effect, due to the bidirectional self-acceleration property of the Pearcey beam, the solitons formed will propagate vertically. These properties can be used to manipulate the beam and have potential applications in optical switching, plasma channeling, particle manipulation, etc. [ABSTRACT FROM AUTHOR]

Lithium niobite (LiNbO3, LN) is a kind of multi-functional artificial crystal, which is called "optical silicon". Recently, the rapid development of integrated photonics based on LN film (LNOI) has a great tendency to turn "optical silicon" into reality. High integration means high local intensity density, so the photorefractive effect of LN crystal can't be ignored any more. Photorefractive effect, short for photoinduced refractive index change, which is an important part of nonlinear optics. In this paper, the discovery and mechanism of photorefractive effect, the regulation of photorefractive effect by different dopants and doping combinations are reviewed. The photorefractive characteristics of bismuth-magnesium doubledoped LN crystal, related theoretical and experimental results are mainly introduced. The characteristics and applications of LN photorefractive waveguide, optical soliton, and the photorefractive effect in LNOI-based integrated photonics devices are summarized. The future research trends are also prospected. It is expected that China will make full use of the advantages of LN photorefraction research and LNOI industrialization and occupy the advantage in the competition of photonics chips. [ABSTRACT FROM AUTHOR]

Self frequency doubling crystal is a kind of crystal that integrates laser and nonlinear optical effect, which can realize wavelength conversion, amplitude modulation, switch, memory and other functions, and has become widely used in photoelectronic, optical communication, laser and other fields. However, the existing crystals such as Nd∶LiNbO3 (Nd∶LN), Nd∶Na3 La9 O3 (BO3)8 (Nd∶NLBO), Nd∶La2 CaB10O19 (Nd∶LCB) have limited the further applications due to their inherent photorefractive effect, low second harmonic generation (SHG) output power, poor optical homogeneity and other shortcomings, so it is necessary to develop new laser self frequency doubling crystals. Due to the large nonlinear optics (NLO) coefficient, difficult to deliquesce, excellent optical, mechanical properties and so on, hunitite family borate crystals have become the focus of research in recent decades. In this paper, the crystal structure, growth methods, properties and development trend and other aspects of huntite family REM3 (BO3)4 (RE is rare earth elements La-Lu and Y; M is Al, Ga, Sc) and Lax REy Scz (BO3)4 (RE = Gd, Y, Nd, Lu, Sm, Tb; x + y + z =3) co-substituted borate nonlinear optical crystals are introduced emphatively. The differences of ultraviolet (UV) cut-off edge, optical properties and nonlinear properties of crystals grown by different fluxes, atmospheres and methods are compared. By improving the growth technology and doping elements, self-frequency-doubled (SFD) crystals with good optical properties, remarkable nonlinear properties and extensive market application prospects can be obtained. [ABSTRACT FROM AUTHOR]

• Optical properties of LiNbO 3 :Cu(0.015) and (0.042 wt%) single crystals were studied. • LiNbO 3 :Cu(0.042 wt%) has a weak optical biaxiality. • The energy transfers from phonons of E(X,Y)-type symmetry to phonons of A1(Z)-type symmetry. • Some Raman bands correspond to phonons forbidden by the selection rules. • This influences the efficiency of conversion of exciting radiation into the terahertz spectral range. Single crystals LiNbO 3 :Cu(0.015 wt%) and LiNbO 3 :Cu(0.042 wt%) have been studied by laser conoscopy, photoinduced light scattering, optical spectroscopy and Raman spectroscopy. The crystals are promising materials for the functional elements development for devices generating terahertz radiation. Exciting radiation is converted into the terahertz range with a high coefficient. Both crystals have been determined to have photorefraction effect. LiNbO 3 :Cu(0.015 wt%) has been shown to be perfect single-axis crystal and LiNbO 3 :Cu(0.042 wt%) to have a weak optical biaxiality. We have determined transfer of energy from E(X,Y) to A 1 (Z) symmetry type phonons that happens when photorefractive crystals LiNbO 3 :Cu(0.015 wt%) and LiNbO 3 :Cu(0.042 wt%) are irradiated by visible laser radiation. In this case Raman bands corresponding to 4A 1 (Z)- symmetry type phonons appear; these bands are prohibited in a given scattering geometries by the selection rules. This can increase the conversion efficiency to the terahertz range. When the Raman spectrum is excited by near-IR laser radiation, there is no photorefractive effect. The intensity of the line corresponding to phonons of the 4A 1 (Z) type of symmetry in the spectrum of the LiNbO 3 :Cu (0.042 wt%) crystal is noticeably lower than in LiNbO 3 :Cu (0.015 wt%). Thus, the parameters of the LiNbO 3 :Cu(0.015 wt%) crystal are more suitable for converting exciting radiation into the terahertz range. [ABSTRACT FROM AUTHOR]

We present a method of near-infrared image reconstruction based on spatial modulation instability in a photorefractive strontium barium niobate crystal. The conditions that lead to the formation of modulation instability at near-infrared are discussed depending on the theory of modulation instability gain. Experimental results of scattered image reconstruction at the 1064 nm wavelength show the maximum cross-correlation coefficient and cross-correlation gain are 0.57 and 2.09 respectively. This method is expected to be an aid for near-infrared imaging technologies. [ABSTRACT FROM AUTHOR]

A technologically feasible process has been proposed for the preparation of a LiNbO3:Mg,B growth charge from a Li2CO3 + Nb2O5 + MgO + H3BO3 mixture. Using such a growth charge, we have grown LiNbO3:Mg,B crystals with a highly uniform dopant distribution. High-speed evaluation of optical homogeneity has shown that the LiNbO3:Mg,B crystals have high optical quality. Using amplitude–frequency response and d333 piezoelectric modulus measurements, we have demonstrated a high degree of unipolarity of the LiNbO3:Mg,B crystals. The optical damage resistance and homogeneity of the LiNbO3:Mg,B crystals have been assessed using photoinduced light scattering and laser conoscopy. The results suggest that LiNbO3:Mg,B crystals with a weak photorefractive effect can be regarded as a new optical material for laser light conversion. [ABSTRACT FROM AUTHOR]

The photorefractive effect of flexoelectric smectic liquid crystal blends was investigated. Smectic liquid crystal blends, composed of smectic-C liquid crystals, photoconductive chiral compounds and a sensitizer, are known to exhibit a large photorefractive effect. The chiral compound plays a critical role in the exhibition of large photorefractivity in smectic liquid crystals. The concentration of the chiral compound was varied and the photorefractive properties of the liquid crystal blend were examined. It was found that smectic-C liquid crystals containing small amounts of a chiral compound show a large photorefractivity even though they do not possess spontaneous polarizations. [ABSTRACT FROM AUTHOR]

Background: In the present work, the photovoltaic and photorefractive effects are discovered and studied and the only nonzero photovoltaic coefficient kijk was determined for a cubic ZnS crystal. This coefficient K14 =2·10-9A·cm·(W)-1. The coefficients kijk exceed the corresponding coefficients in LiNbO3:Fe by more than an order of magnitude. Objectives: The paper presents the results of a study of the volumetric photovoltaic effect in piezoelectric ZnS crystals belonging to the cubic point group m. The possibility of using photopiezoelectrics in the holographic recording is shown. Methods: The use of photopiezoelectrics in holographic recording offers advantages. In this case, the recording is carried out by two coherent beams with polarization corresponding to the photovoltaic current. When reconstructing the recorded hologram is achieved by illuminating the crystal with a beam of coherent light of the same wavelength. Conclusions: However, the polarization of this beam is chosen so that the illumination does not lead to the generation of photovoltaic current. Erasure of the recorded hologram is achieved by uniformly illuminating the surface with a beam of light from the previous polarization. [ABSTRACT FROM AUTHOR]

The modification of the optical characteristics of LiNbO3:Zn and LiNbO3:Mg crystals grown by the Czochralski method was investigated using β and γ radiation. The photorefractive effect was found to be inhibited by ionizing radiation in the LiNbO3:Zn ([ZnO] ≈ 2.1 mol%) crystal, which belonged to a below-threshold concentration range. The inhibition was attributed to a stepwise radiation annealing of charged defects. Ionizing radiation increased the general optical uniformity of above-threshold crystals LiNbO3:Zn ([ZnO] ≈ 5.9 mol%) and LiNbO3:Mg([MgO] ≈ 5.6 mol%). In addition, we determined that radiation annealing substantially influenced photorefraction dynamics in lightly doped LiNbO3:Zn ([ZnO] ≈ 0.1 mol%) crystals, which widens their application areas. [ABSTRACT FROM AUTHOR]

We report on a study of deep levels in semi-insulating CdTe:Cl by means of a time-of-flight spectral approach. By varying the wavelength of a pulsed optical source within the CdTe energy gap, transitions to/from localized levels generate free carriers which are analysed through the induced photocurrent transients. Both acceptor-like centers, related to the A-center, and a midgap level, 0.725 eV from the valence band, have been detected. The midgap level is close to the Fermi level and is possibly a recombination center responsible for the compensation mechanism. When the irradiance is varied, either linear or quadratic dependence of the electron and hole collected charge are observed, depending on the dominant optical transitions. The analysis discloses the potentiality of such a novel approach exploitable in the field of photorefractive materials as well as for deep levels spectroscopy. [ABSTRACT FROM AUTHOR]

A technologically feasible process has been proposed for the preparation of homogeneous single-phase magnesium–boron codoped lithium niobate growth charge. It has been used in Czochralski growth of LiNbO3:Mg,B lithium niobate single crystals with a highly uniform dopant distribution. The crystals have been shown to have optical quality. The results of this study are important for designing a process for the preparation of materials with a weak photorefractive effect to be used in nonlinear optics and other areas of science and technology. [ABSTRACT FROM AUTHOR]

In this paper, for enhancement of the nonlinear optical properties of photorefractive gain, a novel plasmonic waveguide is proposed. The geometry of the proposed structure is optimized to reach the highest photorefractive gain. The proposed structure is based on bimetallic structure and it includes a graphene layer. It is shown that a strong mode can be coupled to a weak mode by means of photorefractive effect. It is found that comparing with the conventional symmetric and asymmetric metal-insulator-metal plasmonic waveguides, the proposed structure with different metals and a graphene layer with an optimized notch has higher photorefractive gain and longer propagation distance, the distance for which a net photorefractive gain exists. The effect of the crystal thickness and amplitude inputs are also analyzed. It is found that there is an optimum crystal thickness that yields the maximum photorefractive gain. [ABSTRACT FROM AUTHOR]

The exceptionally high optical nonlinearities, wide bandgap, and homogeneity in solution‐processed metal‐halide perovskite media are utilized as optical nonlinear elements on a silicon photonic platform for low‐power‐active components, such as all‐optical switches, modulators, and lasers. With room temperature back‐end‐of‐line compatible processing, a hybrid metal‐halide perovskite (CH3NH3PbI3) microring resonator (MRR) structure is fabricated on a foundry‐processed low‐loss silicon photonic platform. With in‐plane excitation near the light intensity of 110 W m−2, strong two‐photon absorption and free‐carrier absorption saturation are observed. With 103 field enhancements by MRRs, the photorefractive effect in the metal‐halide perovskite reduces linear absorption, represented by 102 improvement of the MRR's intrinsic quality factor and 20 dB enhancement of the extinction ratio. [ABSTRACT FROM AUTHOR]

Thin‐film lithium niobate (TFLN) is superior for integrated nanophotonics due to its outstanding properties in nearly all aspects: strong second‐order nonlinearity, fast and efficient electro‐optic effects, wide transparency window, and little two photon absorption and free carrier scattering. Together, they permit highly integrated nanophotonic circuits capable of complex photonic processing by incorporating disparate elements on the same chip. Yet, there has to be a demonstration that synergizes those superior properties for system advantage. Here, such a chip that capitalizes on TFLN's favorable ferroelectricity, high second‐order nonlinearity, and strong electro‐optic effects is demonstrated. It consists of a monolithic circuit integrating a Z‐cut, quasi‐phase matched microring with high quality factor and a phase modulator used in active feedback control. By Pound–Drever–Hall locking, it realizes stable frequency doubling at about 50% conversion with only milliwatt pump power. This demonstration addresses a long‐outstanding challenge facing cavity‐based optical processing, including frequency conversion, frequency comb generation, and all‐optical switching, whose stable performance is hindered by photorefractive or thermal effects. These results further establish TFLN as an excellent material capable of optical multitasking, as desirable to build multi‐functional chip devices. [ABSTRACT FROM AUTHOR]

We demonstrate that increasing the zinc concentration in Zn-doped lithium niobate crystals to their first concentration threshold (~3.0 mol % ZnO) leads to a decrease in photovoltaic field, an increase in diffusion field, and a decrease in the luminescence intensity of NbLi emission centers. As the zinc concentration approaches the second concentration threshold (~6.8 mol % ZnO), the photovoltaic field increases, which is accompanied by a decrease in diffusion field and band gap. In addition, the integrated luminescence intensity drops as a consequence of the reduction in the concentration of defect centers in the form of NbLi–NbNb bipolaron pairs. At the same time, the emission intensity of NbLi small polarons increases and the photorefractive effect decreases markedly. [ABSTRACT FROM AUTHOR]

Purpose: To assess the effect of two high‐oxygen epi‐on PiXL treatments for low‐grade myopia. Methods: This prospective, randomized, intra‐individually comparing, single‐masked study included 23 healthy volunteers (46 eyes) aged 18–35 years with mild myopia, −0.75 to −2.50 D manifest refractive spherical equivalent (MRSE). One eye was randomized to a 4.0‐mm homogenous treatment zone and the fellow eye to a 4.0‐mm annular zone (16:40 min at 30 mW/cm2, fluence 15 J/cm2). Uncorrected distance visual acuity (UDVA), MRSE, best spectacle‐corrected visual acuity (BSCVA), Scheimpflug light scattering depths, mean keratometry (Kmean) and endothelial cell count (ECC) were assessed through 24 months. Results: Similar improvements in UDVA were seen for the homogeneous and annular protocols at 1 month: −0.52 (−0.59, −0.39) and −0.49 (−0.59, −0.39) logMAR, respectively (medians and interquartile ranges, IQR), p = 0.91, and MRSE: +1.0 D (0.94, 1.31) and +1.0 D (0.69, 1.25), p = 0.17. Light scattering depths were 496 (465, 527) and 349 (247, 378) µm, respectively, and the reduction in mean keratometry was −0.8 D (−1.1, −0.7) and 0 D (−0.1, 0.1), p < 0.001. The treatment effect remained stable throughout 24 months. At 1 week, the participants reported less ocular discomfort with the annular protocol. No reductions were seen in BSCVA or ECC. No adverse events were reported. Conclusion: PiXL can reduce low‐grade myopia and improve uncorrected vision in healthy eyes. The initial ocular discomfort may be reduced with an annular treatment zone. Further studies are needed to optimize PiXL treatment parameters. [ABSTRACT FROM AUTHOR]

Superconducting cavity electro-optics presents a promising route to coherently convert microwave and optical photons and distribute quantum entanglement between superconducting circuits over long-distance. Strong Pockels nonlinearity and high-performance optical cavity are the prerequisites for high conversion efficiency. Thin-film lithium niobate (TFLN) offers these desired characteristics. Despite significant recent progresses, only unidirectional conversion with efficiencies on the order of 10−5 has been realized. In this article, we demonstrate the bidirectional electro-optic conversion in TFLN-superconductor hybrid system, with conversion efficiency improved by more than three orders of magnitude. Our air-clad device architecture boosts the sustainable intracavity pump power at cryogenic temperatures by suppressing the prominent photorefractive effect that limits cryogenic performance of TFLN, and reaches an efficiency of 1.02% (internal efficiency of 15.2%). This work firmly establishes the TFLN-superconductor hybrid EO system as a highly competitive transduction platform for future quantum network applications. Coherent conversion between optical and microwave photonics is needed for future quantum applications. Here, the authors combine thin-film lithium niobate and superconductor platforms as a hybrid electro-optic system to achieve high-efficiency frequency conversion between microwave and optical modes. [ABSTRACT FROM AUTHOR]

Linear domains are grown along two different directions (x and y) in z-cut LiNbO3 single crystal by piezoresponse force microscope. Compared with linear domains along x direction, those along y direction possess larger average domain width, higher regularity and lower roughness exponent. These results indicate that domain growth along y direction is more favorable in LiNbO3, which are attributed to the smaller energy of Y domain walls and the layer-by-layer step growth of the hexagonal domains. [ABSTRACT FROM AUTHOR]

We report on the holographic recording on photorefractive Bi2TeO5 crystals using λ = 633 nm wavelength light. We studied the behavior of this material under the action of this low photonic energy light and found out the presence of a fast and a slow hologram, both of photorefractive nature and exhibiting rather high diffraction efficiencies. The faster and the slower holograms are based on the excitation and diffusion of oppositely charged carriers (likely electrons and holes). Relevant parameters for the photoactive centers responsible for both kind of holograms were characterized using purely holographic techniques. No evidences of non-photosensitive ionic charge carriers being involved in the recording process at room temperature nor self-fixing effects were found. [ABSTRACT FROM AUTHOR]

Holographic interferometry methods, based on mixing of a stationary reference light beam and a phase-modulated signal beam at the related perturbations of the dielectric tensor in photosensitive crystals, have been applied to measure material parameters determining the value of these perturbations. Experimental conditions, under which one can distinguish contributions to the mixing from the flexoelectric and electrogyration effects in cubic photorefractive sillenite crystals, are determined, and the necessity of taking into account the contribution from the flexogyration effect is demonstrated. [ABSTRACT FROM AUTHOR]

Photorefractive grating formation dynamics in long-timescale writing and the effects of periodic writing through the control of writing beam irradiation or electric field application were investigated using typical photorefractive polymers. Both dark current and writing beam irradiation affected grating formation dynamics. Dark current in polymers changed the effective trap density over time through deep trap filling and/or detrapping and thus affected grating formation considerably. The writing beam irradiation also affected grating development in the presence of an electric field owing to the accumulation of filled deep traps. However, grating development recovered after the elimination of the electric field freed up the filled deep traps. [ABSTRACT FROM AUTHOR]

A comparative analysis of photorefractive properties was carried out for congruent, stoichiometric and double doped lithium niobate crystals: LiNbO3 : Fe(0,009) : Mg(5,04) and LiNbO3 : Fe(0,02) : Zn(4,34) mol %. These crystals are different in defect types, which are responsible for the effect of photorefraction. Band gap was shown to be minimal for double-doped crystals, photorefractive effect to be the same as for stoichiometric crystals, and photoinduced light scattering was not observed.

Values of intensities of photovoltaic and diffusion fields were determined in congruent LiNbO3 crystals both nominally pure and doped by zinc due to parameters of a photoinduced light scattering. A change in electro-optical properties of LiNbO3 : Zn crystals at an increase in the zinc concentration to a threshold value was shown to be determined by particularities of oxygen octahedra deformations and an order of cation sublattice structure units along the polar axis.

Photorefractive materials exhibit an interesting plasticity under the influence of an optical field. By extending the finite-difference time-domain method to include the photorefractive effect, we explore how this property can be exploited in the context of neuromorphic computing for telecom applications. By first priming the photorefractive material with a random bit stream, the material reorganizes itself to better recognize simple patterns in the stream. We demonstrate this by simulating a typical reservoir computing setup, which gets a significant performance boost on performing the XOR on two consecutive bits in the stream after this initial priming step. [ABSTRACT FROM AUTHOR]

The refraction characteristics of 50 nm thickness of PbTiO3 (PTO) film pumped by various optical power in terahertz (THz) range is measured by THz time domain spectrum. Experiments indicated that the refraction index was 65–110 in the range of 0.2–1 THz and the tunability reached 36.95% when applied 400 mW optical field. The theoretical analysis revealed that the photorefractive and the photothermal effects is responsible for the refraction index monotonically varied with the optical pump power. [ABSTRACT FROM AUTHOR]

The photorefractive effect is an effective way of achieving control of a beam by inducing a space-charge field and controlling the distribution of the refractive index. Herein, the one-dimensional gradient distribution of a space-charge field is structured, and the deflection of the transmitted beam is achieved. The method of regulation and control of the space-charge field was studied by digital holographic microscopy based on a Mn-doped KTN single crystal. The realized deflector has a maximum deflection angle of 0.3° and maintains good frequency-response characteristics up to 50 kHz. This work provides guidance for optical functional devices based on engineering distribution of a space-charge field. [ABSTRACT FROM AUTHOR]