Photoelastic Effect Research Articles

Thermal Lens Astigmatism Induced by the Photoelastic Effect in m3m, 432, and 43m Symmetry Cubic Crystals

The expressions for the thermal lens of linearly polarized radiation arising in m3m, 432 and $\bar {4}3\text{m}$ cubic crystals with arbitrary crystallographic axes orientation in the presence of circular birefringence $\delta _{\mathbf {c}}$ are analyzed. It is shown that the thermal lens may have astigmatism the magnitude of which is proportional to the power of heat generation. The Euler angles determining the crystallographic axes orientation [P] are found and the conditions for the material constant – optical anisotropy parameter $\xi $ – under which the thermal lens astigmatism in active and magneto-active optical elements can be eliminated, are formulated. It is demonstrated that the orientation [P] depends only on optical anisotropy parameter $\xi $ of the crystal and on circular birefringence $\delta _{\mathbf {c}}$ .

Visualization and Quantification of Stresses at the Ends of Short Fibers Embedded in Epoxy Resin

The photoelastic effect was used to visualize and quantify stresses at the end of fibers embedded in birefringent epoxy resin. A method was proposed allowing not to only quantify the differences in main principal stress for a single loading state, but to allow monitoring the evolution of local stress throughout the micro-mechanical experiment. It was found that the ends of fibers foster the formation of shear stresses which influence the principal stress distribution. Typically, star-shaped principal stress distributions were found at the ends of fibers. Finite Element simulations of the tests were in good agreement with the experimental evidence.

An Experimental Investigation of Sample-Fluid Heat Coupling Effect in Thermal Lens Technique.

Laser-induced wavefront distortion is detectable by several techniques based on the photothermal effect. The effect is probed by monitoring the phase shift caused by the bulging of the heated area, the photoelastic effects, and the spatial distribution of the refractive index within the sample and in the fluid surrounding it. A simple analytical solution for the wavefront distortion was only possible for low absorbing materials, with the assumption that the stresses obey either the thin-disk or the long-rod type distributions. Recently, a unified theoretical description for the laser-induced optical path change was proposed to overcome part of this limitation for weakly absorbing materials, regardless of its thickness. In this work, we perform an experimental investigation taking the sample-fluid heat coupling effect into account using the thermal lens technique. The experimental investigation presented here validates the unified model. In addition, we show that the heat-coupling model provides an alternative method to obtain physical properties of non-absorbing fluid by using a reference solid sample.

Optomechanical tuning of the polarization properties of micropillar cavity systems with embedded quantum dots

Strain tuning emerged as an appealing tool to tune fundamental optical properties of solid state quantum emitters. In particular, the wavelength and fine structure of quantum dot states could be tuned using hybrid semiconductor-piezoelectric devices. Here, we show how an applied external stress can directly impact the polarization properties of coupled InAs quantum dot-micropillar cavity systems. In our experiment, we find that we can reversibly tune the anisotropic polarization splitting of the fundamental microcavity mode by approximately 60 $\mu\text{eV}$. We discuss the origin of this tuning mechanism, which arises from an interplay between elastic deformation and the photoelastic effect in our micropillar. Finally, we exploit this effect to tune the quantum dot polarization opto-mechanically via the polarization-anisotropic Purcell effect. Our work paves the way for optomechanical and reversible tuning of the polarization and spin properties of light-matter coupled solid state systems.

In Situ Measurement of Vacuum Window Birefringence using 25Mg+ Fluorescence.

Accurate control of the polarization states of laser light is important in precision measurement experiments. In experiments involving the use of a vacuum environment, the stress-induced birefringence effect of the vacuum windows will affect the polarization states of laser light inside the vacuum system, and it is very difficult to measure and optimize the polarization states of the laser light in situ. The purpose of this protocol is to demonstrate how to optimize the polarization states of the laser light based on the fluorescence of ions in the vacuum system, and how to calculate the birefringence of vacuum windows based on azimuthal angles of external wave plates with Mueller matrix. The fluorescence of 25Mg+ ions induced by laser light that is resonant with the transition of |32P3/2,F = 4, mF= 4→|32S1/2,F = 3, mF= 3is sensitive to the polarization state of the laser light, and maximum fluorescence will be observed with pure circularly polarized light. A combination of half-wave plate (HWP) and quarter-wave plate (QWP) can achieve arbitrary phase retardation and is used for compensating the birefringence of the vacuum window. In this experiment, the polarization state of the laser light is optimized based on the fluorescence of 25Mg+ ion with a pair of HWP and QWP outside the vacuum chamber. By adjusting the azimuthal angles of the HWP and QWP to obtain maximum ion fluorescence, one can obtain a pure circularly polarized light inside the vacuum chamber. With the information on the azimuthal angles of the external HWP and QWP, the birefringence of the vacuum window can be determined.

Rheological and flow birefringence studies of rod-shaped pigment nanoparticle dispersions

We study rheological and rheo-optical properties of suspensions of anisometric pigment particles in a non-polar fluid. Different rheological regimes from the dilute regime to an orientationally arrested gel state were characterized and compared with existing theoretical models. We demonstrate the intricate flow behaviour in a wide range of volume fractions. A unique combination of the optical properties of the particles results in a giant rheo-optical effect: an unprecedentedly large shear stress-induced birefringence was found in the isotropic range, exhibiting a sharp pre-transitional behaviour.

Physical Principles of Developing Pressure Sensors Using Refractive Index Changes in Optical Fiber Microbending

The paper deals with the physical principles of development of pressure sensors using changes in the refractive index in the optical fiber microbending. The development of a simplified fiber-optic based pressure sensor is considered to be relevant for the mining industry if used as a temperature-compensated pressure sensor to avoid known disadvantages of various optical interferometers. An important point is the use of a G.652 standard single-mode optical fiber, which is also used as a guide for electrical signal transmission. The proposed information measurement system is capable of making remote measurements of the rock pressure on the powered support. The ground expressions are given to describe a physical process of the pressure measurement based on the photoelastic effect observed at microbending. The obtained results of the field experiments prove changes in the diffraction spot configuration at the optical fiber end depending on microbending. The finite element program Ansys Static Structural is used for a simulation of the mechanical stress on the optical fiber causing its microbending. The proposed sensor can detect not only pressure, but also temperature and rock mass microdisplacement and can be used for geotechnical monitoring of mine openings representing the danger of gas and coal dust explosion.

Electro optic tuning of photoelastic pressure sensor based on z-cut LiNbO3 optical waveguide

The simultaneous use of two electro-optic and photo-elastic effects in a waveguide-based pressure sensor built in a zCut-LiNbO3 diaphragm, for maintaining the operating point and sensitivity of the sensor at a constant condition, is experimentally investigated. It is shown that for the diaphragm thickness of approximately 0.17 mm, in the condition of applying pressure of P, it is enough to apply voltage of V = 117P (V/bar) on the diaphragm in order to maintain the operating point and sensitivity of the sensor at constant condition.

Band Nesting in Two-Dimensional Crystals: An Exceptionally Sensitive Probe of Strain.

Band nesting occurs when conduction and valence bands are approximately equispaced over regions in the Brillouin zone. In two-dimensional materials, band nesting results in singularities of the joint density of states and thus in a strongly enhanced optical response at resonant frequencies. We exploit the high sensitivity of such resonances to small changes in the band structure to sensitively probe strain in semiconducting transition metal dichalcogenides (TMDs). We measure and calculate the polarization-resolved optical second harmonic generation (SHG) at the band nesting energies and present the first measurements of the energy-dependent nonlinear photoelastic effect in atomically thin TMDs (MoS2, MoSe2, WS2, and WSe2) combined with a theoretical analysis of the underlying processes. Experiment and theory are found to be in good qualitative agreement displaying a strong energy dependence of the SHG, which can be exploited to achieve exceptionally strong modulation of the SHG under strain. We attribute this sensitivity to a redistribution of the joint density of states for the optical response in the band nesting region. We predict that this exceptional strain sensitivity is a general property of all 2D materials with band nesting.

Highly elliptical core fiber with stress-induced birefringence for mode multiplexing

We report the polarization-maintaining properties of a highly elliptical core fiber surrounded by a trench that was designed to optimize the modal effective indices and bending loss for a total of five spatial modes (10 channels). In addition to the asymmetric core structure, the birefringence of the fiber is increased by the thermal stress introduced during the fabrication. The results show a modal birefringence larger than 10-4 for all guided spatial modes. The mode stability to bending is evaluated by selectively exciting/detecting each spatial mode while perturbing the fiber. This few-mode polarization-maintaining fiber is of interest for multiple-input multiple-output (MIMO)-free mode division multiplexing transmission systems.

Photoluminescence mapping of the strain induced in InP and GaAs substrates by SiNx stripes etched from thin films grown under controlled mechanical stress

We measured details of the strain/stress fields produced in GaAs(100) and InP(100) substrates by the presence of narrow dielectric stripes processed from thin films obtained by plasma-enhanced chemical vapor deposition with a residual and controlled built-in compressive or tensile stress. Micro-photoluminescence techniques were used, measuring either the spectral shift of the luminescence peak or the degree of polarization (DOP) of the spectrally integrated signal. These techniques provide information on different parts of the strain tensor (isotropic and anisotropic). The anisotropic deformation was found to change with the magnitude and sign of the initial built-in stress, and also with the stripe width. Using an analytical model, we were able to determine accurately several physical parameters which describe the stress/strain situation. The localized stress at the edges, expressed within an edge force concept, is shown to follow the expected initial built-in stress and also a stress reduction when the stripe width is decreased. This is interpreted as an evidence of some strain relaxation occuring near the stripe edges. This relaxation also impacts the shape of the DOP curves near the edges. The other important conclusion is the observation that the strain does not return to an isotropic situation (as in the case of an infinite thin film) in the central part of the stripes, even if the widths of these stripes are large (100 µm). The analytical model is developpeddeveloped and explained step-by-step. This analytical model produces quantitative data that describe the different effects observed. These data can be very helpful in the design and optimization of photonic devices when the photo-elastic effect can be significant, such as waveguides. The μPL measurements coupled with the model can also provide feedback to allow better control of the processing of such thin film devices.

Influence of Inverse Piezoelectric Effect, Photoelasticity, and Optical Activity on the Diffraction Efficiency of Transmissing Holograms in Photorefractive Crystal Bi12SiO20

The results of a theoretical study of the dependence of the diffraction efficiency of a transmission hologram formed in a sample of a Bi12SiO20 photorefractive crystal on the orientation angle, specific rotation of the crystal, and its thickness are presented. The theoretical model takes into account linear electrooptical, inverse piezoelectric and photoelastic effects. It is shown that with a change in the sign of the specific rotation of the crystal, there can be a shift of the maximums of diffraction efficiency relative to the orientation angle.

Hybrid plasmonic–phononic cavity design for enhanced optomechanical coupling in lithium niobate

A hybrid plasmonic–phononic cavity design which enables high vacuum coupling rate has been proposed in lithium niobate (LN) phononic crystals (Phncs) that have been perforated by air holes and coated with thin silver film. By tailoring the geometry, optomechanical interaction between the plasmonic modes (produced by the metal/insulator) and the phononic modes (confined by the phononic bandgap effect) is greatly enhanced. Numerical results based on finite-element method (FEM) reveal that in this hybrid plasmonic–phononic design, high vacuum coupling rate that predominantly contributed by moving boundary effect is on the order of 106 Hz, which is about one to two orders higher than that contributed by photoelastic effect shown in conventional phoxonic crystal designs. Results evidence how the vacuum coupling rate depends on geometrical parameters like the radius of the defect air hole, the thickness of silver layer, and LN layer. The simultaneous confinement and strong coupling, combined with other advantages as lack of constraint to the refractive index, and integration of piezoelectric material and metal in a chip, this hybrid design may be suitable for non-invasive biological sensing, optomechanically tunable plasmonic heater for drug release and lab-on-chip devices.

A novel method for stress evaluation in chemically strengthened glass based on micro-Raman spectroscopy

Chemically strengthened glass is widely used for screen protection in mobile devices, and its strengthening processes and application fields have rapidly diversified. The origin of the strength is residual compressive stress induced by ion exchange, and the stress evaluation has been performed via the photoelastic effect. However, for a deep understanding of the nature of the strength and development of stronger glasses, we need a method directly connected to atomic-scale glass structures. Here, we propose a method based on the “stuffing” effect, where we can determine the residual stress non-contactively and non-destructively with a high spatial resolution using Boson, D1, D2, and A1 peaks in micro-Raman spectra. Finally, we show a plausible depth dependence of the residual stress.

Study on fabrication, spectrum and torsion sensing characteristics of microtapered long-period fiber gratings

Based on the photoelastic effect, a microtapered long-period fiber grating (MLPFG) is fabricated by using a CO2 fusion splicer, which has high repeatability and small loss. By analyzing the spectrum of the grating, it is easy to know that the grating has a significant absorption effect only for light with a specific wavelength (such as λ≈1569 nm). In the process of fabrication, it is found that with the increase of refractive index modulation, the extinction ratio of the spectrum increases gradually, and the resonant dip drifts toward the long wavelength. In addition, it is found that the twist direction and the torsion angle of the grating can be judged by observing the change of the spectrum in the experiment of exploring the sensing of torsion. When the grating is twisted clockwise, wavelength and extinction ratio of the resonant dip decrease gradually; when the grating is twisted counterclockwise, the wavelength increases gradually, but the extinction ratio increases first and then decreases. The torsion sensitivity is 0.10 nm · mm · rad−1, which is about two times higher than that of CLPGs fabricated from photonic crystal fibers and about three times higher than that of conventional LPFGs. By utilizing these characteristics of MLPFG, it can be widely used in filters and sensors.

Bias error and its thermal drift due to fiber birefringence in interferometric fiber-optic gyroscopes

Abstract Polarization-maintaining fibers (PMFs) with intrinsic highly stress-induced birefringence (SIB) are widely employed in interferometric fiber-optic gyroscopes (IFOGs). The performance of which is limited by the refractive index and its thermal fluctuations induced by the temperature variation. The SIB contributes to the refractive index variously along with the temperature. However, the bias error and its thermal drift arising from the SIB in PMFs are never considered. In this paper, we present theoretical analysis on high-performance IFOGs considering the effects of the SIB and its thermal fluctuation incorporated into the early model. The numerical analysis of the proposed model shows that the accuracy of IFOG using PMFs is better than single-mode fibers (SMFs) by a factor of 2, and the high performance with ultimate sensitivity of IFOGs is achievable by the special design of PMFs which depends not only on the pure Shupe effect but also on the effects from intrinsic SIB and its temperature sensitivity.

Using polarized Raman spectroscopy to study the stress gradient in mineral systems with anomalous birefringence

Polarized Raman spectroscopy was applied to garnet hosts which exhibit anomalous birefringence around inclusions of zircon and quartz to elucidate the spatial distribution of the anisotropic strain fields in the vicinity of the host-inclusion boundary. We show that there is a direct relationship between the stress-induced birefringence and the Raman scattering generated by the fully symmetric phonon modes (the A1g modes in cubic crystals). Our experimental results coupled with selected finite element models show that the ratio between the measured Raman peak intensity collected in cross and parallel polarized scattering geometries of totally symmetric modes represents a useful tool to constrain the radial stress profile in the host around the inclusions. Further, we demonstrate how group-theoretical considerations and tensor analysis of the morphic effect (external-field-induced change of the symmetry) on the phonons and the optical properties of the host can help to derive useful information on the symmetry of the stress field. Finally, we show experimentally that, under the same amount of applied stress, this approach is more sensitive than the commonly used approach of measuring differences in phonon frequencies and provides better opportunities to map the spatial variations of strain. This approach is an alternative technique to study structural phenomena associated with anomalous birefringence in host crystals surrounding stressed inclusions and could be applied to other systems in which similar optical effects are observed.

Photoelastic effect of K$_2$SO$_4$ crystals doped by copper

Photoelastic effect of K$_2$SO$_4$ crystals doped by copper

Microwave-to-optical conversion using lithium niobate thin-film acoustic resonators

We demonstrate conversion of up to 4.5 GHz-frequency microwaves to 1500 nm-wavelength light using optomechanical interactions on suspended thin-film lithium niobate. Our method utilizes an interdigital transducer that drives a free-standing 100 $\mu$m-long thin-film acoustic resonator to modulate light travelling in a Mach-Zehnder interferometer or racetrack cavity. Owing to the strong microwave-to-acoustic coupling offered by the transducer in conjunction with the strong photoelastic, piezoelectric, and electro-optic effects of lithium niobate, we achieve a half-wave voltage of $V_\pi$ = 4.6 V and $V_\pi$ = 0.77 V for the Mach-Zehnder interferometer and racetrack resonator, respectively. The acousto-optic racetrack cavity exhibits an optomechancial single-photon coupling strength of 1.1 kHz. Our integrated nanophotonic platform coherently leverages the compelling properties of lithium niobate to achieve microwave-to-optical transduction. To highlight the versatility of our system, we also demonstrate a lossless microwave photonic link, which refers to a 0 dB microwave power transmission over an optical channel.

Realization of linear-mapping between polarization Poincaré sphere and orbital Poincaré sphere based on stress birefringence in the few-mode fiber.

Based on the spatial profiles and polarization states evolution process of the first-order modes resulted from stress-induced birefringence in the few-mode fiber (FMF), we analyze the mapping relationship between the input polarization states represented on polarization PS and the output spatial profiles represented on the orbital PS of the FMF with respect to the magnitude and orientation of birefringence. When the input mode lobe orientation and the phase differences between the four eigenmodes of FMF induced by the stress birefringence satisfy a given condition, the mapping relationship between the input polarization PS and the output orbital PS is linear. Thus, the arbitrary points on the orbit PS can be generated at the output of stressed FMF by controlling the polarization state of the input modes. Then we experimentally verify that, an electrical single-mode polarization controller, a mode converter for converting fundamental mode to higher-order mode, a polarization controller mounting a coil of two-mode fiber and a polarizer can be employed to generate arbitrary first-order spatial modes on the orbital PS by controlling the input single-mode polarization states. The positions on the orbital PS of the generated first-order modes, which are obtained by calculating the three normalized Stokes parameters of output modes, agree well with the simulation ones. The correlation coefficients between the theoretical mode profiles and the experimental ones are higher than 80%. Since the spatial profile evolutions depend on the variations of the input polarization states, a potential advantage of this method is high-speed switching among desired first-order modes by using the commercial devices switching the state of polarization.