Photoelastic Effect Research Articles

Temperature-sensitive mechanical LPFG using contractive force of heat-shrinkable tube

A novel temperature-sensitive mechanical long period fiber grating (LPFG) fabricated utilizing the photo-elastic effect is proposed. Our proposed LPFG consists of a telecommunication optical fiber, a metric screw, and the heat-shrinkable tube, which are commercially available. The heat-shrinkable tube and the metric screw are used to obtain the grating along the single-mode fiber. The gratings are achieved by pressing the optical fiber between the heat-shrinkable tube and the metric screw due to the contractive force of its tube. By changing the temperature, the resonance loss is tuned due to the thermal expansion of the heat-shrinkable tube. Operating mechanism of thermally tunable characteristics of our LPFG are also described from a viewpoint of the coupling coefficient.

Laser-induced wavefront distortion in optical materials: a general model

Wavefront distortion in optical components induced by thermal lensing may affect performance and stability of optical systems, such as high-power lasers, and is also the base of several photothermal techniques. This distortion is a result of complex photoelastic effects that characterize the degradation and the propagation of the beam. A simple analytical solution is obtained only for low absorbing materials, with the assumption that the stresses obey either thin-disk or long-rod type distributions. In a previous work, part of this limitation was overcome, in which a unified model was proposed for the optical path change for weakly absorbing materials, regardless of its thickness. In this work, we developed a generalized theoretical model for the optical path change that is related to the temperature profile in a relatively simple manner for all classes of absorbing optical materials. The modeling is based on the solution of the thermoelastic equation and provides time-dependent expressions for the temperature, surface displacement, and stresses. This generalized model could have a significant impact on designing laser systems and has direct application in photothermal techniques, which correlate optical path change to thermal, optical, and mechanical properties of solid materials.

1P2-3 Time-resolved imaging of GHz surface acoustic waves in TeO_2 through the photoelastic effect(Poster Session)

1P2-3 Time-resolved imaging of GHz surface acoustic waves in TeO_2 through the photoelastic effect(Poster Session)

Leaky Interface Wave Measurement at a Solid-Solid Interface with Laser Ultrasonics

The experimental investigation on transparent solid/solid (aluminum and plexiglas) interface leaky waves generated by a pulse laser and detected with a photoelastic effect technique is reported. Three waves, i.e., longitudinal head wave, leaky Rayleigh wave and leaky interface wave, are detected successfully. The leaky waves propagating along the ‘weak bonding’ interface are also measured. It is found that with the continuing epoxy solidification, the wave amplitude gradually decreases and the two leaky waves are more difficult to distinguish. The velocities of the detected interface wave are in good agreement with the theoretical calculation and the attenuation characteristics of the two leaky waves are also in accordance with the theoretical prediction.

Hydrostatic pressure sensor based on gold-jacketed spherical end hollow-core photonic bandgap fibre

A hydrostatic pressure sensor based on a spherical end hollow-core photonic bandgap fibre with a length of several hundreds of micrometres is proposed. The pressure sensor head fabricated by a splicer is a micro-Michelson interferometer sensitive to the pressure due to the photoelastic effect. An experimental setup of the proposed hydrostatic pressure sensor is conducted and a linear relationship between the hydrostatic pressure and the wavelength shift of the relative reflection spectrum of the pressure sensor is presented. The pressure sensor demonstrated with a measurement range larger than 40 MPa and a sensitivity of −6.5 pm/MPa.

Optimized optomechanical crystal cavity with acoustic radiation shield

We present the design of an optomechanical crystal nanobeam cavity that combines finite-element simulation with numerical optimization, and considers the optomechanical coupling arising from both moving dielectric boundaries and the photo-elastic effect. Applying this methodology results in a nanobeam with an experimentally realized intrinsic optical Q-factor of 1.2x10^6, a mechanical frequency of 5.1GHz, a mechanical Q-factor of 6.8x10^5 (at T=10K), and a zero-point-motion optomechanical coupling rate of g=1.1MHz.

Efficient depolarization-loss-compensation of solid state lasers using only a Glan-Taylor polarizer

A novel scheme for reducing the depolarization loss resulting from thermally induced stress birefringence of a free running flash-lamp pumped single Nd: YAG rod is reported here and measured under resonator configuration with the use of a Glan-Taylor polarizer only. The depolarization loss has been systematically investigated and compared with the quarter wave-plate scheme. The Glan-Taylor polarizer is given two rotations with respect to two perpendicular axes for obtaining Brewster's effect as well as phase retardation inside a stable resonator. This single optical element optimally reduces depolarization loss to ∼18% and performs better than quarter wave-plate in combination with a polarizer. Using Jones-vector formulation, we analyzed the effect of tilting of Glan-Taylor polarizer and accounted the measured data of depolarization loss.

Acousto-optic couplings in two-dimensional phoxonic crystal cavities

We investigate the acousto-optic coupling, based on both photo-elastic and opto-mechanical mechanisms, in periodic structures with simultaneous photonic and phononic band gaps. The investigations are focused on a cavity defect in which the strong confinement of acoustic and optic waves enhances the interaction. We calculate the modulation of each photonic mode frequency by each phononic mode confined in the cavity. We compare the strength for the photo-elastic and opto-mechanical effects in the different cases. Both mechanisms can be in phase or out of phase and produce additive or subtractive effects in the total acousto-optic coupling.

Anomalous diffraction of light in liquid upon the ultrasonic coagulation of suspended microparticles

Anomalous diffraction by the periodic filamentary structure that consists of coagulated heavy particles in water is experimentally studied under the conditions for the standing acoustic wave in cavity. The diffraction is sensitive to both the conventional photoelastic effect and the filamentary structure. The width of the narrow beams that are formed in the near-field diffraction zone is several times less than the aperture of the incident beam, and the narrow beams propagate in space with the same angular divergence as the incident broad beam does.

Unified theoretical model for calculating laser-induced wavefront distortion in optical materials

Laser-induced thermal lens in optical components causes wavefront distortion of the laser beam and may affect performance and stability of optical systems such as high-power lasers. The bulging of the heated area, the temperature dependence of the refractive index, and the photoelastic effects are responsible for phase shifts damaging beam quality. The theoretical background for laser-induced beam distortion is well understood and applies only for axially symmetric thermal loadings, with the assumptions that the stresses follow thin-disk or long-rod approximations. This, in fact, limits the overall applications of this model. In this work, we developed an unified theoretical model for the optical path change in optical materials regardless of its thickness. The modeling is based on the solution of the thermoelastic equation and has a real description of the surface deformation caused in the optical element. In the appropriated limits, as expected, the model retrieves the thin-disk and the long-rod type distributions. Furthermore, we provided time-dependent radial expressions for the temperature, surface displacement, and stresses. The theory presented in this paper provides simple analytical tools for designing laser systems, and complements previous work allowing one to access optical distortions of materials ranging from thin-disk to long-rod-like distributions.

Polarization behavior of femtosecond laser written optical waveguides in Ti:Sapphire

Ultrashort pulsed laser photoinscription of Ti:Sapphire crystals may result in the self-organization of nanoscale material redistribution regions in regular patterns within the laser trace and stress-induced birefringence around the laser trace. We report on the formation of anisotropic optical waveguides in Ti:Sapphire by a procedure that involves femtosecond laser inscription of adjacent nonguiding birefringent traces with nanopatterned crosssections and the accumulation of stress birefringence in the region between. Double parallel line structures with a separation of 25μm with vertical and horizontal nanoscale arrangements were written with a choice of orthogonal polarizations. Due to anisotropic light scattering on periodic nanostructures and stress-induced birefringence in the central zone, remarkable polarization dependent guiding effects were observed as a function of the microscopic geometry of the structures. Building on this polarization sensitivity, several structure such as 3 × 3 waveguide arrays, diamond and hexagon patterns are also investigated.

Temperature Compensated Strain Sensor Based on Cascaded Sagnac Interferometers and All-Solid Birefringent Hybrid Photonic Crystal Fibers

We demonstrate a temperature compensated strain sensor with two cascaded Sagnac interferometers, that provide strain sensing and temperature compensation, respectively. The Sagnac interferometers use an all-solid hybrid photonic crystal fiber with stress-induced birefringence. The stress-induced birefringent fiber is known to offer the maximum strain sensitivity, but also to suffer from temperature crosstalk. Our experimental results show that the cascaded Sagnac sensor can suppress the crosstalk to a temperature upto 0.33 μe/°C, while still providing a high strain sensitivity of ~ 25.6 pm/μe.

All-fiber vibration sensor based on nano-wire grid polarizer

We propose a novel all-fiber vibration sensor without any bulk optical element by employing an in-line nano-wire grid (NWG) fiber polarizer. The NWG is directly fabricated on tip of a single mode fiber (SMF) by focused ion beam technology. According to effective medium theory, the sub-wavelength NWG has strong polarization properties. In our experiment, the reflection contrast between transverse electric and transverse magnetic modes reaches 14 dB, which is sensitive enough to monitor polarization change induced by photoelastic effect. We apply a sinusoidal vibration signal generated by a piezoelectric transducer onto the fiber. The output light signal from the SMF coincides well with the vibration source. The frequency response of the sensor is measured from 20 Hz to 4 kHz showing great consistency.

Circular polariscopic analysis of a ZnO wafer for highly sensitive and speedy evaluation of residual strains: Its relation with X‐ray diffraction pattern and topography

AbstractWe have explored the effectiveness of applying the circular polariscopic measurement to the mapping of the strains in a ZnO wafer. Initially, monochromatic X‐ray topography, which is regarded as a fundamental evaluation technique for wafers, is applied. The measured monochromatic X‐ray topograph shows that the image contrast is remarkably inhomogeneous; namely, the bark patterns exist in various regions. In order to clarify the origin of the above‐mentioned dark patterns, we apply the circular polariscopic measurement, which is sensitive to strains through the photoelastic effect. The brightness of the circular polariscopic wafer map reveals that the dark pattern in the monochromatic X‐ray topograph results from the strain. Thus, we conclude that the circular polariscopic analysis has the ability to compliment the information obtained by the monochromatic X‐ray topographic measurement. The presence of the relatively large strains is confirmed from the fact that the forbidden reflection lines are observed in the θ ‐2θ X‐ray diffraction pattern. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Theoretical modeling and experiment of refractive index change in He+ ion-implanted KTP waveguide

A theoretical model is presented to explain the refractive index change in the ion-implanted KTP waveguide, which includes respective contributions of spontaneous polarization, molar polarization and molar volume, and photoelastic effect. Numerical calculations of refractive indices along different crystalline orientations (X, Y, and Z) as a function of the lattice damage level, determined by Rutherford back-scattering/channeling technique, are performed based on the results from a set of z-cut KTP crystals implanted by 300 keV He+ ions in doses ranging from 4×10(16) to 8×10(16) ions/cm2. The theoretical results show consistency with the experimental data. To our knowledge, this is the first model to comprehensively describe the ion-implanted KTP planar waveguide.

Photoelastic lensing effect in Ti:sapphire crystal pumped by high-energy pulses

We have built a setup with high temporal resolution to measure the very fast photoelastic lensing effect, which is on the scale of microseconds in a Ti:sapphire crystal pumped by very strong laser pulses (up to 5 J/cm2). The experimental results measured by this method and the real multimode beam profile taken by a CCD camera are applied to a three-dimensional crystal model to calculate one of the photoelastic constants of Ti:sapphire crystal, which is found to be p31=-0.03±0.01. This value is helpful to evaluate the photoelastic lensing effect in Ti:sapphire crystal for a laser beam polarized along the c axis, commonly used for laser amplification.

Bistability in silicon microring resonator based on strain induced by a piezoelectric lead zirconate titanate thin film

We demonstrate bistability in a submicron silicon optical phase shifter based on the photoelastic effect. The strain magnitude is electrically controlled by a piezoelectric thin film placed on top of the device. The hysteresis behavior of the piezoelectric response shows potential application as bistable device independent of the optical intensity.

Embedded corrugated long-period fiber gratings for sensing applications

We demonstrate a method to make possible the mass production of corrugated long-period fiber gratings (C-LPFGs) by utilizing imprint lithography on polycarbonate (PC) substrates. For such C-LPFGs whose working principle is based on photoelastic effect, pretensile tension is required to be applied to inducing periodical refractive index variation. We then present an attempt to use PC as embedding material for providing internal compressive stress for C-LPFGs to have a photoelastic effect. This type of LPFG, termed embedded corrugated long-period fiber gratings (EC-LPFGs), is obtained after reimprinting the C-LPFGs into other PC substrates. Since compressive stress is retained due to the materials of different coefficients of thermal expansion (CTE), unlike C-LPFGs, EC-LPFGs can serve as strain, bending, and temperature sensors without the need of pretensile strain. The two most troublesome problems, the fragility of an etched fiber grating and the requirement of pretensile strain, can be simultaneously alleviated or solved by EC-LPFGs.

UV irradiation-induced modification of photonic band gap and birefringence in artificial opal nanocomposite

A red shift of the photonic band gap and stress-induced birefringence have been observed in the bare and ZnO infilled artificial opal samples under UV laser irradiation. The stress-induced birefringence appeared between the irradiated and non-irradiated parts of the opal. These effects were related to the irradiation-stimulated increase in the density and the refractive index of the opal. Using the obtained results, the UV illumination-induced changes in the degree of polarization, volume and refractive index of the opal were estimated.

应用于液压传感的光子晶体光纤特性

A side-hole photonic crystal fiber for(hydrostatic) pressure sensing was proposed to achieve compact and high sensitivity fiber based pressure sensor.The effective index,mode profile and the stress property of a conventional photonic crystal fiber and the side-hole photonic crystal fiber were investigated based on a full-vector finite-element method.Due to the photoelastic effect,the hydrostatic pressure induced index changes of the conventional photonic crystal fiber and the side-hole photonic crystal fiber were presented.Simulation results show that the side-hole photonic crystal fiber can achieve higher pressure sensitivity,and the pressure sensitivity increases together with the radius of big air holes of the side-hole photonic crystal fiber.Thus,the structure-optimized side-hole photonic crystal fiber can be used as a high sensitivity(hydrostatic) pressure sensor.