Elasto-optic Effect Research Articles

Experimental Study on Fracture Behavior of Adhesive-Bonded Structure with V-notch Based on Digital Gradient Sensing Method.

In this paper, a comparative study of the mode-I fracture behaviors of two types of specimens with a V-notch defect under plane stress conditions was performed using the digital gradient sensing (DGS) method. First, two types of specimens (namely one-piece specimen and bonded specimen) with the same V-notch defect were both made of polymethyl methacrylate (PMMA), and three different V-notch angles' defect were considered for each type of specimen. Then, three-point bending tests were performed on both types of specimens. The angular deflection field of light near the V-notch region was recorded using a CCD during the experiments. Finally, by utilizing the relationship between the stress gradient and angular deflection as established by the elasto-optic effect, in conjunction with the principles of linear elastic fracture mechanics theory, the stress intensity factors (SIFs) of two types of specimens under different stress conditions were calculated using the least square method. According to the experimental results, the influence of V-notch angle on fracture load and fracture toughness of two kinds of specimens was discussed. Meanwhile, the experimental results show the significant differences in the fracture behaviors of the two types of specimens under mode-I loading conditions.

Tunable large omnidirectional photonic bandgap in a one-dimensional photonic crystal comprising elliptical metamaterials based on elasto-optic effect

Tunable large omnidirectional photonic bandgap in a one-dimensional photonic crystal comprising elliptical metamaterials based on elasto-optic effect

All-fiber MZI hydrostatic pressure sensor

With the rapid development of physical ocean observation, high-performance pressure sensor integrated with stable mechanical strength, sufficient pressure sensitivity as well as negligible temperature crosstalk is highly desirable but still lack of research. This paper proposes an all-fiber optical sensor based on a Mach-Zehnder interferometer (MZI) for hydrostatic pressure measurement, utilizing a multi-mode fiber (MMF)-single-hole-dual-core fiber (SHDCF)-MMF structure. The MMF sections act as a beam splitter and coupler to enhance the Mach-Zehnder interference. The SHDCF serves as the pressure-sensing section. Under the action of the enclosed air hole in SHDCF, hydraulic variations cause changes in the structural parameters of the fiber, especially the refractive index change caused by the elasto-optical effect, which leads to the shift of the interference dips. The experimental results prove that the SHDCF-based MZI sensor has a higher hydrostatic pressure sensitivity than other hole-less silica fiber-based sensors. The max pressure sensitivity is −0.2358 nm/MPa in the range of 0.1 MPa to 16.1 MPa with good linearity and reliability. Moreover, the low temperature–pressure cross-sensitivity of 0.04368 MPa/℃ also proves our sensor more competitive in harsh environment applications.

Photoelasticity of CNGS crystals.

All piezo-optic coefficients (POCs) and elasto-optic coefficients (ELOCs) of C a 3 N b G a 3 S i 2 O 14 (CNGS) and C a 3 T a G a 3 S i 2 O 14 (CTGS) trigonal crystals of the langasite group are determined from quantum mechanical calculations based on the hybrid density functional theory, as implemented in the CRYSTAL program. The calculation results for CTGS crystals are compared with experimental data. Indicative surfaces of piezo- and elasto-optic effects are constructed based on the POC and ELOC matrices of CNGS crystals and the largest values of these effects are determined. The maximum values of the coefficient of the acousto-optic figure of merit M 2 of the CNGS crystal are determined for the geometries of elasto-optic interaction, which correspond to the maxima of the elasto-optic effect. These results are compared to the corresponding results for CTGS and langasite crystals. The spectral dependence of the POCs and ELOCs of CNGS and CTGS crystals on the light wavelength is investigated in the 600-1500nm range.

Use of Rayleigh-OFDR to Estimate the Bias Drift Induced by Quasi-Static and Homogeneous Temperature Variation of a Free-Standing Fiber-Gyro Coil

The method of Rayleigh-Optical Frequency Domain Reflectometry (Rayleigh-OFDR) has been used to estimate, at the component level, the thermal bias drift due the elasto-optic effect into a 400m-long self-standing quadrupolar coil, under a temperature ramp ranging from -20°C to 80°C. This estimation is performed before integration of the sensing coil in a Fiber-Optic Gyroscope (FOG). A theoretical reminder of how a thermal perturbation is creating a spurious bias in the FOG rotation rate measurement is described. Then, we propose a new methodology to estimate the thermal bias drift of the sensing coil before its assembly. It is based upon Rayleigh-OFDR. Uncertainties are characterized to assess the performances of the Rayleigh-OFDR to characterize the thermal bias drift due to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">elasto-optic</i> effect in a FOG.

Study on the Microstructure of a Photonic Crystal Fiber using the Elasto-Optical Effect

Photonic crystal fibers are characterized by their periodic structure with dimensions in the nanometer to micrometer range, which gives them the potential to be applied in various technical areas. In this work, we study the microstructure of a hexagonal photonic crystal fiber through a macroscopic localized compression test and measurements of relative intensity changes of a transmitted signal in the photonic crystal fiber. Our experimental study was carried out by controlling the orientation of the localized compression respective to the cross-section microstructure of the photonic crystal fiber. To complete the study, we developed a theoretical model based on the elasto-optic effect, and the numerical solution obtained with the model was compared with the experimental results. With both experimental and theoretical results, we obtained a causal correlation between the loss of relative intensity of the signal traveling through the hexagonal photonic crystal fiber and the orientation (respective to the fiber plane) of a localized compression on photonic crystal fiber. In this way, we can explore the cross-section microstructure of a photonic crystal fiber and its orientation in a device with a macroscopic compression test.

Ultrasonic sensing directivity of π-phase-shifted fiber Bragg grating hydrophone

&lt;inline-formula&gt;&lt;tex-math id="M1"&gt;\begin{document}${\text{π }}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222154_M1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222154_M1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;-phase-shifted fiber Bragg grating with a short effective sensing length becomes one of research hotspots in ultrasonic sensing, because light undergoes strong localization centered at its phase shift position. To investigate the directional sensing characteristics of &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}${\text{π }}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222154_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222154_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;-phase-shifted fiber Bragg grating as hydrophone, the theory of sound propagation in layered media is used to calculate the strain of fiber core, then the transfer matrix method based on the coupled-mode theory in optics is used to calculate the shift of central wavelength in optical reflection spectrum. Results of strain and wavelength shift under obliquely incident ultrasonic from 1－10 MHz are divided into A area, B area, and C area, and analyzed by numerical calculation and simulation calculation. Axial strain and elasto-optical strain change the grating period and effective refractive index by the mechanical effect and elasto-optical effect, respectively, thereby resulting in wavelength shift. In A area (frequency below 5 MHz, incident angle below &lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}$15^\circ $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222154_M3.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222154_M3.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;), the axial strain nearly equals zero, thus elasto-optical effect plays a predominant role in wavelength shift. The maximal response occurs at vertical incidence, and then obviously declines with angle increasing. The maximum is essentially unchanged with grating length. In B area and C area (angle above &lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}$15^\circ $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222154_M4.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222154_M4.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;), both mechanical effect and elasto-optical effect contribute to wavelength shift. In B area (frequency below 5 MHz), the amplitude of strain is the largest in three areas. A peak of wavelength shift appears at the same angle of the peak of strain, where exists the interference of the guided wave in fiber with the direct ultrasonic wave form water. The peak amplitude of wavelength shift decreases with grating length increasing. In C area (frequency below 5 MHz), the amplitude of strain is larger than in A area, but the wavelength shift is smaller, which is correlated to its higher axial wave number. Comparing the results in three areas, it is clear that the wavelength shift is larger at lower frequency and at vertical incidence. Experiments on 3 MHz and 5 MHz are then performed with a π-phase-shifted fiber Bragg grating. The experimental result accords well with the theoretical result. The research is important in practically using the &lt;inline-formula&gt;&lt;tex-math id="M5"&gt;\begin{document}${\text{π }}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222154_M5.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222154_M5.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;-phase-shifted fiber Bragg grating in ultrasonic sensing.

Precise prediction of optical behaviour of mechanically stressed edge emitting GaAs devices

The presence of a thermally annealed metallization layer on top of a GaAs slab waveguide proofed to be of strong impact on the optical device behavior. Induced by the stress on the chip the elasto-optical effect imprinted a strong variation on the refractive index that led to anti-guiding and guiding effects. In order to enable precise prediction of the optical behavior we present a 3D mechanical device simulation which provides detailed insights to the overall stress state. The results are then used in a 2D in-house developed optical simulation that allows precise analysis of the microscopic optical behavior. Therefore, the accumulated stress effects are represented by an effective temperature difference between semiconductor and metallization, which allows a strong simplification of the model setup. The results are validated by comparison to the experimental derived data. As the simulation proves to be highly accurate, the stress load on the device can be calculated vice versa from the optical behavior.

Polymeric photonic quasicrystal: octonacci sequence and elasto-optic effect

Here we would like to discuss the light transmission modulation by the one-dimensional polymeric quasi-multilayer which is formed according to substitutional generalized Octonacci with PMMA and PS as the constituent materials. In particular, we will present some theoretical findings using the well-known transfer matrix method. The width of the PBG, the inter-band spacing and the depth of the PBGs can be managed by choosing the appropriate generation number, whereas the number of the major PBGs is the same for all the considered generation numbers. Regarding the position of the PBGs, we found that, with an increase in generation number, the aroused PBGs are shifted symmetrically towards the designed frequency. It also reveals the aroused forbidden frequency band can be manipulated by changing the applied hydrostatic pressure. With an increase in pressure, the frequency spectra are shifted to a higher frequency. In addition to this, we also found that as the thickness of the polymers increases the PBGs are red-shifted. The proposed structure could be another possible system for optical device design specially multi-band tunable optical reflectors.

An investigation and analysis of plasmonic modulators: a review

Abstract Plasmonics is an emerging and very advantageous technology which provides high speed and tiny size devices for fulfilling the demand of today’s high-speed world. SPPs are the information carrying elements in plasmonics, which are capable of breaking the diffraction limit. Plasmonics technology has shown its application in uncountable nanophotonic applications like switching, filtering, light modulation, sensing and in many more fields. Modulators are the key components of integrated photonic system. Various modulators which work on different effects are discussed in this study for providing a universal idea of modulators to researchers. Some useful plasmonic active materials are also discussed which are used in most of plasmonic modulators and other active devices. Previously, many researchers have worked on many kinds of modulators and switches, which operate on different kind of operating principles. For providing an overview about plasmonic modulators, their classification and their operation, we have discussed the state of art of some previously introduced modulators and switches which operates on electro-refractive effects and include electro-optic effect, Pockels effect, free charge carrier dispersion effect, phase change effect, elasto-optic effect, magneto-optic effect, and thermo-optic effect. Instead of different effects used in plasmonic switches and modulators different active materials like liquid crystals, graphene, vanadium di-oxide, chalcogenides, polymers, indium tin oxide, bismuth ferrite, barium titanate, and lithium niobate are also explained with their properties. Additionally, we also compared modulators based on different effects in terms of their design characteristics and performances.

A miniature fiber-optic microphone based on plano-concave micro-interferometer.

The sensitive detection of sound waves is essential for a variety of applications. In this work, we propose a miniature diaphragm-free fiber-optic microphone based on a plano-concave optical micro-interferometer. A solid plano-concave micro-interferometer is formed at the end of a cleaved fiber by depositing a tiny volume of liquefied glass. Sound wave induced periodic variation of pressure can significantly modify the refractive index of the plano-concave glass due to the elasto-optic effect, and then, the phase difference between two interferometric beams will be remarkably changed accordingly. The interferometer finally converts the fluctuation of the phase difference into the change in the output optical power. Consequently, the sound wave can be demodulated by detecting the output power of the microphone. The experimental results show that the proposed microphone has the ability to detect sound waves in the whole audible range and almost omnidirectional. The noise-limited minimum detectable sound pressure is around 12 µPa/Hz. In addition, the human voice detection test shows that the performance of our microphone is competitive with the most advanced commercial device. The structure is stable without any movable mechanical parts, and the size is as small as 0.25 mm, which makes the proposed microphone an attractive alternative to the conventional one for sound wave detection.

Anisotropy of piezo-optic and elasto-optic effects in langasite family crystals

The surfaces of the photoelasticity effects spatial distribution are constructed for langasite (LGS) and catangasite (CTGS) crystals basing on the matrices of piezo-optic and elastic-optic coefficients (POC and ELOC). It is shown that the maxima of the longitudinal piezo-optic effect (POE) are commensurate for both crystals and correspond to POC π33; the maximum value of transverse POE (vectors of uniaxial pressure and light wave polarization are mutually perpendicular) in CTGS crystals is almost two times higher comparing to LGS. The maxima of the transverse elastic-optic effect (ELOE) are also significantly higher in CTGS. It should be emphasized that the maxima of the surfaces of the transverse POE are not located on crystallographic axes, but correspond to the directions that are shifted for 13 … 33° from optical axis of the crystals. Thus, the angle between maximum ELOE and optical axis in CTGS equals 13°. The maximum values of POE, ELOE and the directions of the maxima were determined analytically using the method of partial derivatives. The acousto-optic figure of merit M2 was determined for the ELOE maxima. It has been shown that this value is two times higher for CTGS, comparing with LGS. The first attempt to make the correlation between the POE, ELOE maxima and structural properties of these crystals has been carries out.

Temperature and initial polarization dependences of the electrooptic coefficient of BaTiO3 crystal film

In this work, the temperature dependence of polarization degree of ferroelectric phase barium titanate (BaTiO3) film is first modelled based on a conservation of the energy-focusing cost of a microstructural domain cell, and then the dual dependences on both temperature and initial polarization degree of an off-axis tensor electrooptic coefficient (r51) is modelled. Further, the correlation between the initial polarization degree and the r51 is investigated based on the correlative electrooptic and elasto-optic effects of a perovskite crystal. With the output of theoretical models for the attributes of r51, numerical simulations are carried out. It was found that both the polarization degradation of out-of-plane polarization (Pz) and the electrooptic coefficient r51 of c-axis oriented crystal films exhibit significant nonlinear dependences on the initial fraction of in-plane polarization (Px) and the working temperature. Consequently, the temperature dependences of the measured results of r51 with respect to the selected working temperatures in the range of 20°C∼100°C are consistent with the above numerical results, showing that the out-of-plane polarization degree presents the biggest degradation in the temperature range from 50°C to 70°C. This work provides a valuable reference to the research and development of high-speed electro-optic devices and applications.

Cladding softened fiber for sensitivity enhancement of distributed acoustic sensing.

Fiber-optic distributed acoustic sensing (DAS) technology with high spatial and strain resolutions has been widely used in many practical applications. New methods to enhance the phase sensitivity of sensing fiber are worth exploring to further improve DAS performances, although the standard single-mode fiber (SSMF) has been widely used for DAS technology. In this work, we propose and demonstrate the concept of enhancing the phase sensitivity of DAS by softening the cladding of the sensing fiber, for the first time. The theoretical analysis indicates that softening sensing fiber cladding is an effective way to improve phase sensitivity. Thus, we fabricated cladding softened fibers (CSFs) and tested their phase sensitivities experimentally. According to the results, it is found that the phase sensitivity of the CSF with 0.48 WT% phosphorus-doping concentration and 80 µm cladding diameter is 22% and 54% higher than that of the non-phosphorus-doping fiber with 80 µm cladding diameter and SSMF, respectively. The results show that by reducing fiber cladding Young's modulus with higher phosphorus-doping concentration, the DAS phase sensitivity can be enhanced effectively, verifying the theoretical analysis. Also, we found that the phase sensitivity enhancement of the sensing fiber has a linear relationship with the cladding phosphorus-doping concentration, i.e. Young's modulus. In conclusion, the reported CSF paves a way for improving the DAS phase sensitivity and would be applied to other major optical fiber sensing systems as a better sensing element over SSMF due to the enhancement in the elasto-optical effect of the sensing fiber.

Electrically driven acousto-optics and broadband non-reciprocity in silicon photonics

Emerging technologies based on tailorable interactions between photons and phonons promise new capabilities ranging from high-fidelity microwave signal processing to non-reciprocal optics and quantum state control. While such light-sound couplings have been studied in a variety of physical systems, many implementations rely on non-standard materials and fabrication schemes that are challenging to co-implement with standard integrated photonic circuitry. Notably, despite significant advances in integrated electro-optic modulators, related acousto-optic modulator concepts have remained relatively unexplored in silicon photonics. In this article, we demonstrate direct acousto-optic modulation within silicon waveguides using electrically-driven surface acoustic waves (SAWs). By co-integrating SAW transducers in piezoelectric AlN with a standard silicon-on-insulator photonic platform, we harness silicon's strong elasto-optic effect to mediate linear light-sound coupling. Through lithographic design, acousto-optic phase and single-sideband amplitude modulators in the range of 1-5 GHz are fabricated, exhibiting index modulation strengths comparable to existing electro-optic technologies. Extending this traveling-wave, acousto-optic interaction to cm-scales, we create electrically-driven non-reciprocal modulators in silicon. Non-reciprocal operation bandwidths of >100 GHz and insertion losses <0.6 dB are achieved. Building on these results, we show that unity-efficiency non-reciprocal modulation, necessary for a robust acousto-optic isolator, is within reach. The acousto-optic modulator design is compatible with both CMOS fabrication and existing silicon photonic device technologies. These results represent a promising new approach to implement compact and scalable acousto-optic modulators, frequency-shifters, and non-magnetic optical isolators and circulators in integrated photonic circuits.

The loss in reflecting coating induced by polarization

The optical loss is known to restrict sensitivity in laser gravitational wave detectors. The paper explores the extent to which polarization impacts optical losses. The light is polarized inside interferometer so after reflection the polarization plane can slightly change its direction due to the fact that reflecting coating applied to the mirror has a refraction index varying along axes x,y in the mirror plane (the optical anisotropy). The anisotropy can occur at the stage of coating application (the elasto-optic effect). The amplitude of the light having orthogonal polarization is amplified inside the cavity resulting in the optical loss caused by polarization. So, information about the polarization profile on the mirror surface is highly important and we propose monitoring it. The polarization loss can be important in different precision optical experiments involving polarized light, for example, in quantum speed meters.

An Ultra-compact Plasmonic Modulator Using Elasto-optic Effect and Resonance Phenomena

Abstract We theoretically demonstrate an ultra-compact plasmonic modulator and switch of sub-micron size using elasto-optic effect with quite acceptable modulation ratio. The device is based on metal-dielectric-metal waveguide structure and uses resonance phenomena. The modulation mechanism originates by electrically changing thickness of dielectric layer made of elasto-optic material, which changes the effective refractive index of propagating optical mode. All the results are obtained using FEM simulation software. The seamless integration of optical beam modulation bears significant potential towards broadband, compact and efficient communication links and circuits.

Light transmitting performance and energy-saving of plastic optical fibre transparent concrete products

Buildings consume large amounts of energy, and lighting consumes a substantial amount of this energy. Therefore, an alternative technology that depends more on natural lighting is needed in order to reduce the building energy consumption. In this paper, based on the excellent properties of light guiding and elasto-optic effect of optical fibre, a novel transparent concrete with plastic optical fibres (POFs) arranged into the concrete was developed and evaluated. The light transmitting performance of plastic optical fibre transparent concrete product (PTCP) was tested by optical power method. The ZEMAX software was used to simulate the transparent test, and the prediction model was established to predict the light transmittance of PTCP. The evaluation of the energy-saving effect due to the use of this building material was studied using the Autodesk Ecotect software. The results showed that PTCP possesses excellent light transmittance property, which was proportional to the content of the optical fibres. The model established by ZEMAX can effectively predict the transmittance of PTCP. The average daylighting factor of the room built with PTCP was increased by nearly 30%, the lighting uniformity was upgraded by nearly 40% and nearly 20% reduction in energy consumption was realised.

Detection of Circular-Crested Lamb Waves Using Surface-Bonded Fiber-Optic Ultrasound Sensors: A Theoretical Perspective

A theoretical framework is established to study the interaction between circular-crested Lamb waves (CCLWs) and a fiber-optic ultrasound sensor (FOUS) bonded onto the surface of a plate structure. CCLW is a universal expression of guided Lamb waves, regardless of the source-sensor distance. In the theory developed here, strain transfer and transformation, birefringence of the fiber sensor, and modulation of refractive index by elasto-optic effects are incorporated. Explicit expression for calculating the ultrasound-induced wavelength shift of fiber Bragg gratings (FBGs) is derived. To showcase application of the established theory in a more general situation, a chirped FBG Fabry-Perot interferometer based FOUS is simulated, in combination with transfer matrix method. Results uncover quantitatively the interplay of the following factors governing the sensor response: 1) co-existence of both axial and lateral normal strains in the fiber, especially in the near field; 2) elasto-optic properties of the fiber material; 3) initial polarization state of the fiber sensor; 4) incident angle of the CCLWs; and 5) ratio between the equivalent ultrasonic wavelength and the effective sensor length. The calculated results uncover the underlying mechanisms responsible for several experimental observations reported but inadequately explained in the literature. The theoretical framework is also applicable to other non-FBG-based FOUSs that rely on phase modulation by ultrasounds.

Degree of locality of elasto-optic response in solids

The elasto-optic effect, or photoelasticity, describes the linear change of dielectric tensor with applied strain and is a universal material property of insulators and semiconductors. Though the elasto-optic responses for solids can be computed directly from first principles (e.g., by using density functional perturbation theory) and measured experimentally, these methods do not provide sufficient insight into the governing microscopic physical principles of photoelasticity. In this work, we describe a microscopic first-principles analysis of photoelasticity in real space and apply it to investigate the elasto-optic responses of Si, diamond, NaCl, and MgO. By writing the random phase approximation (RPA) dielectric constant in the basis of maximally localized Wannier functions, we show that the strain-dependent change of dipole transitions between occupied and unoccupied Wannier functions are the main determinants of photoelasticity. By organizing the dipole transitions into spatially localized shells, we develop a ``constrained sum'' method that converges both the dielectric and photoelastic responses systematically and reveals a relatively long-ranged nature to these responses: one needs to sum up contributions of up to third neighbor shells to converge the elasto-optic coefficient with reasonable precision.