Photoelastic Effect Research Articles

Polarized light scanning cryomacroscopy, part I: Experimental apparatus and observations of vitrification, crystallization, and photoelasticity effects

Cryomacroscopy is an effective means to observe physical events affecting cryopreservation success in large-size specimens. The current study aims at integrating polarized-light in the study of large-size cryopreservation, using the scanning cryomacroscope as a development platform. Results of this study demonstrate polarized light as a visualization enhancement means, including the following effects: contaminants in the CPA solution, crystallization, fracture formation, thermal contraction, and solute precipitation. In addition, photoelasticity effects are used to demonstrate the development of residual stresses and the potential for stress relaxation above the glass transition temperature. Furthermore, this study suggests that the ability to periodically switch between non-polarized light and polarized light is an essential feature of investigation. When using polarized light for example, a dark region may represent a free-of-stress and free-of-crystals material, or fully crystallized material, which may potentially experience mechanical stress; switching to a non-polarized light would help to distinguish between the different cases. The analysis of thermo-mechanical stress in cryopreservation is essentially based on four key elements: identification of physical events, knowledge of physical properties, thermal analysis of the specimen, and description of the mechanical behavior of the cryopreserved material (also known as the constitutive law). With the above knowledge, one can investigate the conditions to preserve structural integrity. While the current study aims at identification of physical events, critical knowledge on physical properties and mechanical behavior has already been developed in previous studies. The companion manuscript (Part II) aims at providing means for thermal analysis in the specimen, which will serve as the basis for a multi-scale analysis of thermo-mechanical stress in large-size specimens.

Strong optomechanical coupling in a slotted photonic crystal nanobeam cavity with an ultrahigh quality factor-to-mode volume ratio.

We describe the design, fabrication, and characterization of a one-dimensional silicon photonic crystal cavity in which a central slot is used to enhance the overlap between highly localized optical and mechanical modes. The optical mode has an extremely small mode volume of 0.017(λvac / n)3, and an optomechanical vacuum coupling rate of 310 kHz is measured for a mechanical mode at 2.69 GHz. With optical quality factors up to 1.2 × 105, fabricated devices are in the resolved-sideband regime. The electric field has its maximum at the slot wall and couples to the in-plane breathing motion of the slot. The optomechanical coupling is thus dominated by the moving-boundary effect, which we simulate to be six times greater than the photoelastic effect, in contrast to most structures, where the photoelastic effect is often the primary coupling mechanism.

Brillouin scattering self-cancellation.

The interaction between light and acoustic phonons is strongly modified in sub-wavelength confinement, and has led to the demonstration and control of Brillouin scattering in photonic structures such as nano-scale optical waveguides and cavities. Besides the small optical mode volume, two physical mechanisms come into play simultaneously: a volume effect caused by the strain-induced refractive index perturbation (known as photo-elasticity), and a surface effect caused by the shift of the optical boundaries due to mechanical vibrations. As a result, proper material and structure engineering allows one to control each contribution individually. Here, we experimentally demonstrate the perfect cancellation of Brillouin scattering arising from Rayleigh acoustic waves by engineering a silica nanowire with exactly opposing photo-elastic and moving-boundary effects. This demonstration provides clear experimental evidence that the interplay between the two mechanisms is a promising tool to precisely control the photon–phonon interaction, enhancing or suppressing it.

Noise and dynamics in forward Brillouin interactions

In this paper, we explore the spatio-temporal dynamics of spontaneous and stimulated forward Brillouin scattering. This general treatment incorporates the optomechanical coupling produced by boundary-induced radiation pressures (boundary motion) and material-induced electrostrictive forces (photo-elastic effects), permitting straightforward application to a range of emerging micro- and nano-scale optomechanical systems. Through a self-consistent fully coupled nonlinear treatment, developed within a general Hamiltonian framework, we establish the connection between the power spectral density of spontaneously scattered light in forward Brillouin interactions and the nonlinear coupling strength. We show that, in sharp contrast to backward Brillouin scattering, noise-initiated stimulated forward Brillouin scattering is forbidden in the majority of experimental systems. In fact, the single-pass gain, which characterizes the threshold for energy transfer in back-scattering processes, is negative for a large class of forward Brillouin devices. Beyond this frequent experimental case, we explore mechanisms for dispersive symmetry breaking that lead to amplification and dynamics reminiscent of backward Brillouin scattering.

Design and simulation of pressuresensor and accelerometer based on integrated optical circuits using photoelastic effect of LiNbO3

Abstract In this paper a novel optical pressure and acceleration sensor based on micro electro mechanical systems (MEOMS) has been designed. For this purpose an integrated MachZander interferometer has been used in LiNbO3 diaphragm. In this sensor, the strain caused by applied pressure or acceleration leads to a change in refractive index of the wave guide in the diaphragm due to the photoelastic effect. The refractive index change leads to a phase change in the light wave that propagates in the waveguide. This phase change is converted to intensity change using the MachZander interferometer. The software ANSYS 14.5 was used for calculation of the strain in the diaphragm .The pressure and acceleration sensitivity of the designed sensor have been obtained 2.33×10-4 (rad /Pa) and 2.16×10-5 (rad.s2/m), respectively.

Thermal Lensing and Multiwatt Microchip Laser Operation of Yb:YCOB Crystals

Thermal lensing is studied in monoclinic Yb:Ca 4YO(BO 3) 3 (Yb: YCOB) oxoborate crystals cut along the optical indicatrix axes. For all orientations, the thermal lens is positive. In the $Z$ -cut crystal, the sensitivity factors of the thermal lens are $M_{Z-X} = 2.4$ and $M_{Z-Y} = 2.8 \text{m}^{-1}/\text{W}$ (for $E \| X$ ), and the astigmatism degree is as low as $S/M = 14\%$ . The positive thermal lens in Yb:YCOB is related to the large thermal expansion and strong photoelastic effect. Microchip lasers are realized with 3-mm-long $X$ , $Y$ , and $Z$ -cut 15 at.% Yb:YCOB crystals. With a $Z$ -cut crystal, maximum output power of 8.35 W is achieved at ∼1040 nm with slope efficiency of 70%. Using various crystal cuts and output coupler transmissions, multiwatt emission in the spectral range of 1033–1091 nm is demonstrated.

Frequency difference stabilization in dual-frequency laser by stress-induced birefringence closed-loop control.

The frequency difference of dual-frequency lasers is increasingly becoming an area of focus in research. The stabilization of beat frequency is of significance in fields such as synthetic wavelength and shows great potential in precise measurement. In this paper, a novel device based on stress-induced birefringence closed-loop control is proposed. Experiments are carried out on a dual-frequency He-Ne Zeeman-birefringence laser with the output mirror sealed in the opposite direction. The results show that the device is capable of controlling the frequency difference variation in 1.3%, in a convenient and highly cost-effective way, and it can increase the quantity of frequency difference, which is crucial to the application of precise measurement through dual-frequency lasers.

Photo-elastic effect, thermal lensing and depolarization in a-cut tetragonal laser crystals

We report on analytical description of thermal lensing effect in tetragonal crystals cut along the [1 0 0] crystallographic axis, for the two principal light polarizations, E ┴ c and E || c, under diode-pumping (plane stress approximation). Within this approach, we take into account anisotropy of elastic, photo-elastic, thermal and optical properties of the material. Expressions for the ‘generalized’ thermo-optic coefficient χ are presented. It is shown that astigmatism of thermal lens is determined both by the photo-elastic and end-bulging effects. The sign of the photo-elastic term χ″ can be either positive or negative affecting significantly the sign of the thermal lens. Depolarization loss in a-cut tetragonal crystals is few orders of magnitude lower than that in cubic crystals. Calculations are performed for a-cut tetragonal molybdates, Nd:CaMoO4, Nd:PbMoO4 and Nd:NaBi(MoO4)2.

On the use of photoelastic effect and plane strain or plane stress approximations for the description of thermal lensing

Correct use of the photoelastic effect for the description of thermally induced refractive index change is discussed and the analytical relations between thermo-optic coefficients at zero stresses and zero strains are found for all classes of cubic crystals. These relations may be useful for the investigation of thermal effects in very promising sesquioxide class m3 laser crystals. An accepted set of elasto-optical coefficients of the YAG crystal and an alternative one found in the literature were used in numerical simulations. Significant differences in the calculated thermo-optic coefficients and induced birefringence are found using different sets of these coefficients. Misunderstandings related with the so-called photoelastic coefficients are resolved and new expressions for these coefficients are found. It is shown that the incorrect use of these coefficients for different pump beam distributions can lead to significant discrepancies for thermally induced birefringence. It is also shown that common use of the generalized thermo-optic coefficients significantly overestimates the values of optical power of thermal lenses when they are applied to the laser rods with lengths several times longer than their diameter.

One-Dimensional Mass-Spring Chains Supporting Elastic Waves with Non-Conventional Topology

There are two classes of phononic structures that can support elastic waves with non-conventional topology, namely intrinsic and extrinsic systems. The non-conventional topology of elastic wave results from breaking time reversal symmetry (T-symmetry) of wave propagation. In extrinsic systems, energy is injected into the phononic structure to break T-symmetry. In intrinsic systems symmetry is broken through the medium microstructure that may lead to internal resonances. Mass-spring composite structures are introduced as metaphors for more complex phononic crystals with non-conventional topology. The elastic wave equation of motion of an intrinsic phononic structure composed of two coupled one-dimensional (1D) harmonic chains can be factored into a Dirac-like equation, leading to antisymmetric modes that have spinor character and therefore non-conventional topology in wave number space. The topology of the elastic waves can be further modified by subjecting phononic structures to externally-induced spatio-temporal modulation of their elastic properties. Such modulations can be actuated through photo-elastic effects, magneto-elastic effects, piezo-electric effects or external mechanical effects. We also uncover an analogy between a combined intrinsic-extrinsic systems composed of a simple one-dimensional harmonic chain coupled to a rigid substrate subjected to a spatio-temporal modulation of the side spring stiffness and the Dirac equation in the presence of an electromagnetic field. The modulation is shown to be able to tune the spinor part of the elastic wave function and therefore its topology. This analogy between classical mechanics and quantum phenomena offers new modalities for developing more complex functions of phononic crystals and acoustic metamaterials.

Coherent coupling between radio frequency, optical, and acoustic waves in piezo-optomechanical circuits.

Optomechanical cavities have been studied for applications ranging from sensing to quantum information science. Here, we develop a platform for nanoscale cavity optomechanical circuits in which optomechanical cavities supporting co-localized 1550 nm photons and 2.4 GHz phonons are combined with photonic and phononic waveguides. Working in GaAs facilitates manipulation of the localized mechanical mode either with a radio frequency (RF) field through the piezo-electric effect, which produces acoustic waves that are routed and coupled to the optomechanical cavity by phononic crystal waveguides, or optically through the strong photoelastic effect. Along with mechanical state preparation and sensitive readout, we use this to demonstrate an acoustic wave interference effect, similar to atomic coherent population trapping, in which RF-driven coherent mechanical motion is cancelled by optically-driven motion. Manipulating cavity optomechanical systems with equal facility through both photonic and phononic channels enables new architectures for signal transduction between the optical, electrical, and mechanical domains.

Influence of parameters of open-loop fiber optic gyro elements on measurement precision

The analysis of the output signal of the interferometric open-loop fiber optic gyro (FOG) is performed. It is based on the Jones matrix method taking into account the parasitic modulation (modulation is due to the photoelastic effect, causing connection of modes under transverse compression of the fiber), the polarizer extinction coefficient, rotation angles of the optical fiber axes relative to the polarizer axes. The influence of the FOG elements on measurement precision of angular velocity of the object is estimated. The proposed angular velocity measurement method is digital. The output signal intensity is measured in each modulation period at certain time points. Based on the measurement results, the phase shift of counter-propagating waves, which is proportional to the angular velocity of the object is computed. This method allows to exclude the synchronous detector and the LPF from the circuit, which simplifies the analog part of the circuit and reduces the influence of the errors made by the analog elements on the measurement precision. The FOG precision is greatly affected by the polarizer and the modulator. The FOG output signal has hardly-compensated polarization error. To reduce it, the polarizer with the extinction coefficient of at least 0.001 should be used. Particular attention should be paid to the improvement the modulator. Since the error caused by its imperfection is multiplicative by nature and may reach unacceptably high values. To reduce the measurement error, SLD with stable polarization and ellipticity parameters of radiation should be used.

Dependences of the Diffraction Efficiency of Photorefractive Holograms on the Sample Thickness and Orientation Angle in a (ī ī 0)-cut Bi12SiO20 Crystal

We present the results of experimental studies of the dependence of the diffraction efficiency of nonoblique transmission holograms formed in the sample of a (īī0)-cut photorefractive piezoelectric Bi12SiO20 crystal on the sample thickness and orientation angle of the grating vector at two fixed mutually orthogonal orientations of the linear polarization vector of the reading beam. It is shown that only if along with optical activity of the crystal, the electrooptic, inverse piezoelectric, and photoelastic effects are taken into account in the analytical diffraction model, it is possible to carry out satisfactory theoretical interpretation of the experimental data.

Stress-induced birefringence and fabrication of in-fiber polarization devices by controlled femtosecond laser irradiations.

Optical birefringence was created in a single-mode fiber by introducing a series of symmetric cuboid stress rods on both sides of the fiber core along the fiber axis using a femtosecond laser. The stress-induced birefringence was estimated to be 2.4 × 10(-4) at the wavelength of 1550 nm. By adding the desired numbers of stressed rods, an in-fiber quarter waveplate was fabricated with a insertion loss of 0.19 dB. The stress-induced birefringence was further explored to fabricate in-fiber polarizers based on the polarization-dependent long-period fiber grating (LPFG) structure. A polarization extinction ratio of more than 20 dB was observed at the resonant wavelength of 1523.9 nm. The in-fiber polarization devices may be useful in optical communications and fiber optic sensing applications.

Note: Ultra-low birefringence dodecagonal vacuum glass cell

We report on an ultra-low birefringence dodecagonal glass cell for ultra-high vacuum applications. The epoxy-bonded trapezoidal windows of the cell are made of SF57 glass, which exhibits a very low stress-induced birefringence. We characterize the birefringence Δn of each window with the cell under vacuum conditions, obtaining values around 10(-8). After baking the cell at 150 °C, we reach a pressure below 10(-10) mbar. In addition, each window is antireflection coated on both sides, which is highly desirable for quantum optics experiments and precision measurements.

Integrated optical circulator by stimulated Brillouin scattering induced non-reciprocal phase shift.

We propose a new approach to realize all-optical circulator based on stimulated Brillouin scattering in an integrated microresonator. Stimulated Brillouin scattering is a basic interaction between photon and traveling acoustic wave resulted from electrostriction and photoelastic effects. Due to the phase-matching requirement, the circulating acoustic wave can only couple to probe light which propagating along or opposite to the pump laser direction, thus exhibits a non-reciprocal phase shift. Combined with Mach-Zehnder interferometer, the optical circulator can be realized. Though the bandwidth is relatively small because of the narrow-band nature of microresonator, this magnetic-free all-optical integrated circulator may be applied for future on-chip photonic information processing.

Pockels Coefficients in Multicomponent Oxide Glasses

In this work, a corrected model for the additivity of the Pockels coefficients in multicomponent oxide glasses is derived. Given some material deformation, changes in density and electronic polarizability are known to be the dominant factors in the photoelastic effect. A trend of Pockels coefficients decreasing with increasing bond ionicity is postulated. This is discussed and shown to be due to the balancing of the relative changes in density and in polarization based on the bond strength and directionality. Alkali silicate data taken from the literature, shown to oppose the observed trends, is analyzed and compared to alkaline earth silicate data. The opposing trend is shown to be due to the bonding of the modifier ions. The alkali ions, associated with a single nonbridging oxygen (NBO), yield an increased relative density change and a decreased relative change in polarization. The alkaline earth ions, being associated with two NBOs, as expected experience significant density and polarizability changes that are more spatially distributed. Greater insights into the structural and chemical origins of the Pockels coefficient in multicomponent oxide glasses will enable the development of new optical fibers for high energy laser applications where photoelasticity‐influenced parasitic effects such as stimulated Brillouin scattering are mitigated.

Transmission Characteristics of Long-Period Fiber Gratings Using Periodically Corroded Single-Mode Fibers

Department of Physics and Research Institute for Convergence of Basic Science,Hanyang University, Seoul 133-791, Korea(Received March 25, 2015 : revised June 1, 2015 : accepted June 26, 2015)Transmission characteristics of long-period fiber gratings (LPFGs) fabricated by periodically etching a conventional single-mode fiber (SMF) are investigated. After coating the SMF with photoresist, the cladding of the SMF is symmetrically and periodically removed by using a wet etching technique resulting in the formation of the LPFG. Tensile strain reinforces the coupling strength between the core and the cladding mode based on the photoelastic effect. The extinction ratio of the SMF-based LPFG at a wavelength of 1550.8 nm is measured to be -15.1 dB when the applied strain is 600 µe. The ascent of ambient index shifts the resonant wavelength to shorter wavelength because of the increase of the effective refractive index of the cladding mode. The extinction ratio is diminished by increase in the ambient index because of the induction of the optical attenuation of the cladding mode. The transmission characteristics of the proposed LPFG with variations in torsion are also measured. The photoelastic effect based on torsion changes the extinction ratio and the resonant wavelength of the proposed SMF-based LPFG. The polarization-dependent loss of the LPFG is also increased by torsion because of the torsion-induced birefringence. The polarization-dependent loss of the LPFG at torsion of 8.5 rad/m is measured to be 3.9 dB.Keywords : Long-period fiber gratings, Fiber-optic sensors, Photoelastic effectOCIS codes : (060.0060) Fiber optics and optical communications; (060.2370) Fiber optics sensors; (050.2770) Gratings

Experimental and theoretical study of the weak and asymmetrical thermal lens effect of Nd:YLF crystal for σ and π polarizations

The thermal lens effect of Nd:YLF crystal for different polarized beams is experimentally and theoretically studied in this paper. In the experiment, the different thermal lens effects of Nd:YLF crystal along a and c axes for π- and σ-polarized probe beams are observed, and the values of the focal lengths are measured. The theoretical analysis is made to explain the extremely weak thermal lens effect along the c axis, as well as that for the σ-polarized beam. And it is corroborated that the complementation among the thermo-optical coefficient, the thermal end bulging and the photoelastic effects contributes to the weak and asymmetry thermal lens effect of Nd:YLF crystal.

Thermal lensing in diode-pumped [001]-cut tetragonal crystals

Abstract Thermal lensing is theoretically studied for laser discs from [001]-cut tetragonal crystals under the plane stress approximation, considering anisotropy of their elastic and photo-elastic properties. Analytical description of the stress-induced birefringence is presented. This allows us to derive analytical expressions for the photo-elastic term χ″, “generalized” thermo-optic coefficient (TOC), sensitivity factors of the thermal lens and its astigmatism degree, as well as discuss orientation of the principal meridional planes of the lens. These parameters are determined for the discs from tetragonal scheelite-type molydbate crystals, Nd:PbMoO4, Nd:CaMoO4 and Nd:NaBi(MoO4)2 at ~1 μm. It is shown that the photo-elastic effect plays an important role in the formation of the thermal lens for tetragonal crystals, and χ″ value can be either positive or negative. We also predict theoretically that for anisotropic crystals the orientation of the principal meridional planes of the thermal lens is not linked to the polarization direction.