Photoelastic Effect Research Articles

Effect of high-energy radiation on the relaxation of residual stresses in polycarbonate and epoxy resin by stress optics

Residual stresses are an important factor in many polymers because they affect the components strength and potential warpage. Polymers exposed to γ-ray radiation are no exception. The two polymers investigated (bisphenol-A based polycarbonate and epoxy resin), are potentially irradiated either as part of a sterilization process or during later application as part of composite or insulation material. Both polymers show a photoelastic effect that is used in this research to study the effect of 200 kGy and 500 kGy on the relaxation behavior of epoxy and polycarbonate, respectively. The photoelastic sensitivity for pristine and irradiated samples was found to decrease by irradiation treatment. In addition, EP and PC relaxed by 36 and 27% respectively, due to irradiation treatment. Furthermore, epoxy resin shows some artifacts in the stress optical images, which are likely related to curing and are not related to residual stresses.

Polarization purity and dispersion characteristics of nested antiresonant nodeless hollow-core optical fiber at near- and short-wave-IR wavelengths for quantum communications

Advancements in quantum communication and sensing require improved optical transmission that ensures excellent state purity and reduced losses. While free-space optical communication is often preferred, its use becomes challenging over long distances due to beam divergence, atmospheric absorption, scattering, and turbulence, among other factors. In the case of polarization encoding, traditional silica-core optical fibers, though commonly used, struggle with maintaining state purity due to stress-induced birefringence. Hollow core fibers, and in particular nested antiresonant nodeless fibers (NANF), have recently been shown to possess unparalleled polarization purity with minimal birefringence in the telecom wavelength range using continuous-wave (CW) laser light. Here, we investigate a 1-km NANF designed for wavelengths up to the 2-μm waveband. Our results show a polarization extinction ratio between ~−30 dB and ~−70 dB across the 1520 to 1620 nm range in CW operation, peaking at ~−60 dB at the 2-μm design wavelength. Our study also includes the pulsed regime, providing insights beyond previous CW studies, e.g., on the propagation of broadband quantum states of light in NANF at 2 μm, and corresponding extinction-ratio-limited quantum bit error rates (QBER) for prepare-measure and entanglement-based quantum key distribution (QKD) protocols. Our findings highlight the potential of these fibers in emerging applications such as QKD, pointing towards a new standard in optical quantum technologies.

Determination of optimal directions of the wave vector of the phase holographic grating in cubic photorefractive crystal

The dependence of the change in the components of the inverse permittivity tensor of a cubic photorefractive Bi12SiO20 crystal on the direction of the wave vector of holographic grating in the crystal coordinate system has been studied. It is shown that, when recording a phase hologram, the largest change in the refractive index of Bi12SiO20 crystal is attained when the holographic grating wave vector is oriented along symmetrically equivalent 111 directions. The maximum possible modulation amplitude of the refractive index of a holographic grating with the wave vector oriented along the 110 directions is found to exceed that in the case of orientation along the 100 directions. The components of the inverse permittivity tensor of Bi12SiO20 crystal were calculated taking into account that a phase hologram is recorded under linear electro-optic, photoelastic, and inverse piezoelectric effects.

Snapshot Multi-Wavelength Birefringence Imaging.

A snapshot multi-wavelength birefringence imaging measurement method was proposed in this study. The RGB-LEDs at wavelengths 463 nm, 533 nm, and 629 nm were illuminated with circularly polarized light after passing through a circular polarizer. The transmitted light through the birefringent sample was captured by a color polarization camera. A single imaging process captured light intensity in four polarization directions (0°, 45°, 90°, and 135°) for each of the three RGB spectral wavelength channels, and subsequently measured the first three elements of Stokes vectors (S0, S1, and S2) after the sample. The birefringence retardance and fast-axis azimuthal angle were determined simultaneously. An experimental setup was constructed, and polarization response matrices were calibrated for each spectral wavelength channel to ensure the accurate detection of Stokes vectors. A polymer true zero-order quarter-wave plate was employed to validate measurement accuracy and repeatability. Additionally, stress-induced birefringence in a PMMA arch-shaped workpiece was measured both before and after the application of force. Experimental results revealed that the repeatability of birefringence retardance and fast-axis azimuthal angle was better than 0.67 nm and 0.08°, respectively. This approach enables multispectral wavelength, high-speed, high-precision, and high-repeatability birefringence imaging measurements through a single imaging session.

Brownian thermal birefringent noise due to the nondiagonal anisotropic photoelastic effect in multilayer coated mirrors

Brownian thermal birefringent noise due to the nondiagonal anisotropic photoelastic effect in multilayer coated mirrors

Velocimetry of GHz elastic surface waves in quartz and fused silica based on full-field imaging of pump–probe reflectometry

This study reports an imaging method for gigahertz surface acoustic waves in transparent layers using infrared subpicosecond laser pulses in the ablation regime and an optical pump–probe technique. The reflectivity modulations due to the photoelastic effect of generated multimodal surface acoustic waves were imaged by an sCMOS camera illuminated by the time-delayed, frequency-doubled probe pulses. Moving the delay time between 6.0nsto11.5ns, image stacks of wave field propagation were created.Two representative samples were investigated: wafers of isotropic fused silica and anisotropic x-cut quartz. Rayleigh (SAW) and longitudinal dominant high-velocity pseudo-surface acoustic wave (HVPSAW) modes could be observed and tracked along a circular grid around the excitation center, allowing the extraction of angular profiles of the propagation velocity. In quartz, the folding of a PSAW was observed. A finite element simulation was developed to predict the measurement results. The simulation and measurement were in good agreement with a relative error of 2% to 5%.These results show the potential for fast and full-field imaging of laser-generated ultrasonic surface wave modes, which can be utilized for the characterization of thin transparent samples such as semiconductor wafers or optical crystals in the gigahertz frequency range.

Characterization of Electrical Tree Degradation of Epoxy Resin under Thermal and Temperature Stresses by Photoelastic Effect

Characterization of Electrical Tree Degradation of Epoxy Resin under Thermal and Temperature Stresses by Photoelastic Effect

Spatial signature of the photoelastic effect in the acoustic–plasmonic coupling revealed by space responsivity induced by polarized optical excitation

Abstract Acoustic–plasmonic coupling in metallic nanoparticles can significantly alter their optical absorption and scattering characteristics. However, almost all previous investigations on acoustic–plasmonic coupling so far have been focused on the spectral response of particles in a vacuum. In this report, a spatial photon scattering mode taking count in the acoustic–plasmonic coupling of individual gold nanoparticle (GN) on a silicon substrate under ultrasonic influence was presented. The acoustic–plasmonic is visualized with parametric images with spatial scattering patterns of the particle under the excitation of polarized light along the Poincare’s equatorial trajectory. The ultrasonic sources can be sensitively extracted from the parametric sinδ images, providing clear evidence of the extremely weak influence of ultrasound wave directivity on the spatial characteristics of the scattering of the particle through acoustic–plasmonic coupling. Experiment and simulation results reveal that, in general, the coupling is the strongest, when the maximum electric field (plasmon vibration mode) aligns with the ultrasonic propagation direction. This study provides a new angle to observe and deepen the understanding of the acoustic–plasmonic effect of nanoparticles, in addition to the conventional manner of investigation on their scattering spectra. It emphasizes the possibility of determining the spatial distribution of nanoparticles via photon state scattering when they are in a weakly oscillating environment, providing valuable guidance for future potential applications exploiting the acoustic–plasmonic effect of nanostructures.

Modelling of a Lyot filter based Mamyshev oscillator

Utilizing a Lyot filter (LF) as one of the spectral filters, a new architecture of Mamyshev Oscillator (MO) has been presented at the 1.06-µm region. The Ginzburg-Landau equation (GLE) has been solved numerically and the feasibility of obtaining a stable single pulse state from the oscillator has been checked. A possible architecture of the LF is presented and the tunability of the LF is achieved by introducing stress-induced birefringence (SIB). As the transmission window of the LF shifts, the spectral overlap between two filters also varies. Various types of states have been obtained as the solution of GLE depending on the spectral overlap between two filters. Attributes of each pulsing state have been presented and the intra-cavity spectral and temporal evolution has also been shown and discussed accordingly. The results confirm that in an optimized parameter space, stable single pulse state can be achieved from an LF-based MO and the pulse possesses properties of ‘amplifier similariton’. The compressibility of the output pulse has also been checked numerically and it is worth mentioning that the pulse can be compressed near to its transform-limited duration.

Effect of supersaturation on structural stress of rapidly growing KDP crystals studied by wide-angle conoscopic interference

Photoelastic effect was applied to analyze the relationship between fringe spacing in wide-angle conoscopic interference and structural stress of KDP crystals.

Laser-written wave plates inside the silicon enabled by stress-induced birefringence.

Laser writing enables optical functionality by altering the optical properties of materials. To achieve this goal, efforts generally focus on laser-written regions. It has also been shown that birefringence surrounding the modified regions can be exploited for achieving functionality. The effect has been used to fabricate wave plates in glass, with significant potential for other materials. Here, we establish analogous stress control and birefringence engineering inside silicon. We first develop a robust analytical model enabling the prediction of birefringence maps from arbitrary laser-written patterns. Then, we tailor three-dimensional laser lithography to create the first, to the best of our knowledge, polarization-control optics inside silicon.

Thermal and population lensing of Yb:YLF at cryogenic temperature

We present what is, to our knowledge, the first detailed study of thermal and population lensing in cryogenically cooled Yb:YLF. Using a rod-shaped a-cut Yb:YLF crystal, the thermal lens strength is measured as a function of absorbed pump power for both E//a and E//c polarizations for pump power levels up to 600 W. Our experiments revealed that the thermal lensing behavior in Yb:YLF is quite asymmetric. For the E//a polarization, the thermal lens is rather strong and always converging for both horizonal and vertical axes. For the E//c configuration, thermal lensing is rather weak, and its sign could be different in different axis, and furthermore, the sign of thermal lensing is observed to be dependent on the absorbed pump power level. Simulations and detailed experimental measurements show that the observed peculiar behavior is a result of competition between the photo-elastic effect and thermo-optic effect: as their relative strength varies at different pump power levels. We have also measured the contribution of surface bulging into thermal lensing and found it to be relatively small in our crystals with un-doped end caps. Lastly, the population lensing is measured in Yb:YLF for the first time, and it is found to be quite weak as well, and the polarizability difference parameter of Yb:YLF is determined as (3 ± 1.5) x 10−34 m3.

Revisiting the Stress-Induced Birefringence in Polarization-Maintaining Fibers

Two conventional errors in the stress-induced birefringence (SIB) of polarization-maintaining fibers (PMFs) are revealed and corrected. The first issue refers to the fundamental expression and its calculation of the SIB, which depends on the selection of stress components. There were obvious inconsistencies in two pioneering reports, while both were widely applied in subsequent works. The second issue is the basic form of the Airy stress function (ASF) in the cross-section plane of the PMF, which dominates the complexity of the stress calculation for SIB. The ASFs in two early pioneering works were different, which led to two different expressions of SIB. Both expressions cannot be reproduced, and calculated results were just around 1/2 of the corresponding measurements. In this paper, both issues have been fixed by revising the definition of SIB and proposing a new ASF form for PMFs. The developed theory is simple and does not have any mathematical contradiction in the calculation process, compare to reported works. Results of the revised SIB based on the developed theory achieve a good agreement with the practical experimental measurements.

Polarization Distortions Caused by Strong Thermal Stress-Induced Birefringence in Uniaxial Crystals and Their Elimination Using Dedicated Orientations

The polarization distortions of radiation, which arise when it passes through optical elements cut from uniaxial crystals in the regime of strong thermally induced birefringence, are studied. The presented theoretical description of the effect convincingly corresponds to the results of the experiment carried out for verification purposes. The problem of the existence of critical orientations of crystallographic axes in an optical element, at which polarization distortions do not occur, is studied for uniaxial crystals of all symmetry groups. Criteria for the existence of critical orientations are defined; approaches to finding these orientations are presented.

Forward-stimulated Brillouin scattering in silicon-core fibers

As a new type of semiconductor fiber, silicon-core fibers have a higher non-linear effect compared with silica fibers. Forward-stimulated Brillouin scattering as a typical optical non-linear effect holds strong promise for applications in, for example, fiber-optic sensing. The study of the FSBS effect in silicon-core fibers facilitates further theoretical exploitation of the potential of FSBS in fiber-optic sensing. In this paper, the FSBS in the silicon-core fiber is studied using the finite element method. The model is based on a silicon-core fiber, whose silicon-core diameter is 4 μm and silica cladding diameter is 33.4 μm, and the optical field modes are classified by the vector method to obtain the acoustic field modes excited by FSBS—radial mode (R0m) and torsional radial mode (TR2m). The FSBS gain of the fiber shows that R0m has the best coupling with TM and TE optical modes, and TR2m has the best coupling with HE optical modes. It is concluded that the sound field frequency shift of R0m is more sensitive to the change in the effective refractive index of the optical field than that of TR2m. The factors affecting the gain are refined into photoelastic effects and moving boundary perturbations, and their contributions to the total gain are summarized. Finally, it was confirmed that a strong FSBS gain similar to 365.57 (1/mw) can be obtained with silicon-core fibers without the need to reduce the size to the usual dimensions of silicon waveguides, paving the way for further research studies in areas such as frequency-tunable laser emission, mode-locked pulsed lasers, low-noise oscillators, and optical gyroscopes.

Picosecond Ultrasonics for Studying Elastic Modulus of Polycrystalline Chromium Nanofilms: Thickness Dependence and Stiffness Enhancement

Accurate measurement of elastic constants in thin films is still an important issue to understand the scale behavior of nanosized materials. In the present study, we introduced an advanced non-destructive method, picosecond ultrasonics (PU), for measuring the out-of-plane elastic modulus of thin chromium (Cr) films. The femtosecond light pulse is focused on the Cr film to excite the longitudinal acoustic phonons (LAP), which propagate along the thickness direction and repeat reflections inside the Cr film. Then, the propagation/distribution of LAP is detected by the time-delayed probe light pulse through the photoelastic effect. Therefore, we can determine the out-of-plane modulus by measuring the periodic pulse echoes or the breathing mode vibrations within the Cr film. For most Cr films, the determined modulus is smaller than the corresponding bulk value and decreases with the decreasing thickness, while for some Cr films, it closes and may exceed the bulk value. This work describes the thickness-dependent elasticity of thin Cr films and provides evidence of the stiffness enhancement in Cr films on the Si substrate. In addition, since LAP with central frequency up to 310 GHz is excited in Cr films on the SiO2 substrate, we also demonstrate the potential of Cr films as high-frequency photoacoustic transducers.

Performance Analysis of SiGe-Cladded Silicon MMI Coupler in Presence of Stress

In this study, we demonstrate the influence of operating temperature variation and stress-induced effects on a silicon-on-insulator (SOI)-based multi-mode interference coupler (MMI). Here, SiGe is introduced as the cladding layer to analyze its effect on the optical performance of the MMI coupler. SiGe cladding thickness is varied from 5 nm to 40 nm. Characterization of the MMI coupler for ridge waveguides with both rectangular and trapezoidal sidewall slope angle cross-sections is reviewed in terms of power splitting ratio and birefringence. Stress-induced birefringence as a function of operating temperature and cladding thickness for fundamental mode have been calculated. A trapezoidal waveguide with 40 nm of cladding thickness induces more stress and, therefore, affects birefringence more than a rectangular waveguide of any thickness. Simulation results using the finite element method (FEM) confirmed that operating temperature variation, upper cladding thickness, and its stress effect are significant parameters that drastically modify the performance of an MMI coupler.

Precision mapping of a silicon test mass birefringence

Excellent mechanical and thermal properties of silicon make it a promising material for the test masses in future gravitational wave detectors. However, the birefringence of silicon test masses, due to impurity and residual stress during crystal growth or external stress, can reduce the interference contrast in an interferometer. Using the polarization–modulation approach and a scanning system, we mapped the birefringence of a float zone silicon test mass in the ⟨100⟩ crystal orientation to assess the suitability of such material for future gravitational wave detectors. Apart from the stress-induced birefringence at the supporting area due to the weight of the test mass, the high resolution birefringence map of the silicon test mass revealed a high birefringence feature in the test mass. At the central 40 mm area, birefringence is in the range of mid 10−9 to low 10−8, which satisfy the requirement for future gravitational wave detectors.

Modeling and minimization for thermal stress birefringence of an optical voltage transducer.

The thermal stress birefringence (TSB) is a big issue that destroys the sensing stability of the optical voltage transducer (OVT), and the existing research on the theoretical modeling and solution are not good enough to handle it. This paper presents a mathematical model of the TSB based on the photo-elastic effect, and then it is quantitatively calculated through the multiphysics coupling simulation. It shows that the asymmetric radial stresses in the electro-optic crystal are the root cause for the TSB, which results in a phase delay greater than 3.153°. On this basis, a method for TSB minimization to use the polyurethane buffer layer to enwrap around the crystal is proposed, which eliminates the random radial stress and improves the symmetry of stress distribution. Finally, the effectiveness of the proposed method is verified by simulation and experiment.

Thin-film lithium niobate photonic integrated devices: Advances and oppotunities

<sec>Lithium niobate, known as one of the most widely used nonlinear optical crystals, has recently received significant attention from both academia and industrial circles. The surge in interest can be attributed to the commercial availability of thin-film lithium niobate (TFLN) wafers and the rapid advancements in nanofabrication techniques. A milestone was achieved in 2020 with the successful fabrication of wafer-scale TFLN photonic integrated circuits, which paved the way for mass-producible and cost-effective manufacturing of TFLN-based products.</sec><sec>At present, the majority of research on TFLN photonic integrated devices focuses on light manipulation, i.e. field modulation and frequency conversion. The electro-optic, acousto-optic, photo-elastic and piezo-electric effects of lithium niobate are harnessed to modulate the amplitude, phase and frequency of light. The second-order and third-order nonlinearities of lithium niobate enable frequency conversion processes, which leads to the development of frequency converters, optical frequency combs, and supercontinuum generation devices. These exceptional optical properties of lithium niobate enable the electromagnetic wave to manipulate covering from radio-frequency to terahertz, infrared, and visible bands. Using the outstanding performance of TFLN photonic integrated devices, including remarkable modulation rate, wide operation bandwidth, efficient nonlinear frequency conversion, and low power consumption, diverse applications, such as spanning optical information processing, laser ranging, optical frequency combs, microwave optics, precision measurement, quantum optics, and quantum computing, are demonstrated.</sec><sec>Additionally, it is reported that TFLN-based lasers and amplifiers have made remarkable progress, and both optical and electrical pumps are available. These achievements include combining gain materials, such as rare-earth ions or heterostructures, with III-V semiconductors. The integration of low-dimensional materials or absorptive metals with TFLN can also realize TFLN-based detectors. These significant developments expand the potential applications of TFLN photonic integrated devices, thus paving the way for monolithic TFLN chips.</sec><sec>The versatility and high performances of TFLN photonic integrated devices have made revolutionary progress in these fields, opening up new possibilities for cutting-edge technologies and their practical implementations. In this point of view, we briefly introduce the development of TFLN nanofabricationn technology. Subsequently, we review the latest progress of TFLN photonic integrated devices, including lasers, functional nonlinear optical devices, and detectors. Finally, we discuss the future development directions and potential ways of TFLN photonics.</sec>