Birefringent Medium Research Articles

Manifestations of inertia on light dragging revealed in plasmas

Light dragging phenomena in accelerated media have classically been modelled neglecting the effect of inertia on the dielectric response of the media. Here, we show that the inertial corrections due to a rotating motion can have a profound impact on light-dragging manifestations, leading notably to birefringence in media that are isotropic at rest. By applying these findings to a rotating unmagnetized plasma, we further reveal how inertia plays, in this case, a dominant role, offering unique opportunities to expose these new effects. Inertia is notably demonstrated to be the source of non-zero drag and enhanced polarization drag, pointing to fundamental differences between linear and angular momentum coupling. In taking advantage of the singular properties of plasmas, this work more generally underlines how rest-frame properties are affected by an accelerated motion, and how these modifications can carry over to wave dynamics.

Differential Delay of Ordinary and Extraordinary Modes of Transionospheric Radio Waves

AbstractThe terrestrial ionosphere is a birefringent medium that allows radio waves to propagate in two modes: the ordinary (O‐mode) and the extraordinary (X‐mode). A difference in the index of refraction of the two modes results in differential delay (mode delay) between the O‐ and X‐modes of radio waves propagating through the ionosphere. Mode delays of transionospheric high frequency radio waves are determined using the Radio Receiver Instrument (RRI) onboard the Enhanced Polar Outflow Probe (e‐POP) on the CASSIOPE/Swarm‐E satellite. Experiments between RRI and the SuperDARN radar at Saskatoon, Canada show large variabilities in mode delays. The mode delays are nearly constant in some experiments but other experiments have large variations. The mode delay observations could not be explained by the distance between the e‐POP satellite and the radar, the foF2 values along the satellite track, nor whether the satellite track was across or along a SuperDARN radar beam. A combination of RRI observations and ray‐trace modeling are used to investigate the mode delay of transionospheric radio waves.

Indirect measurement of atomic magneto-optical rotation via Hilbert transform

Abstract The Kramers–Kronig relations are a pivotal foundation of linear optics and atomic physics, embedding a physical connection between the real and imaginary components of any causal response function. A mathematically equivalent, but simpler, approach instead utilises the Hilbert transform. In a previous study, the Hilbert transform was applied to absorption spectra in order to infer the sole refractive index of an atomic medium in the absence of an external magnetic field. The presence of a magnetic field causes the medium to become birefringent and dichroic, and therefore it is instead characterised by two refractive indices. In this study, we apply the same Hilbert transform technique to independently measure both refractive indices of a birefringent atomic medium, leading to an indirect measurement of atomic magneto-optical rotation. Key to this measurement is the insight that inputting specific light polarisations into an atomic medium induces absorption associated with only one of the refractive indices. We show this is true in two configurations, commonly referred to in literature as the Faraday and Voigt geometries, which differ by the magnetic field orientation with respect to the light wavevector. For both cases, we measure the two refractive indices independently for a Rb thermal vapour in a 0.6 T magnetic field, finding excellent agreement with theory. This study further emphasises the application of the Hilbert transform to the field of quantum and atomic optics in the linear regime.

Controlled linearly chirped similaritons in inhomogeneous birefringent optical fibers

By similarity transformation, optical similaritons in a nonlinear birefringent optical fiber are investigated within the framework of two coupled nonlinear Schrödinger equations with space-modulated self- and cross-phase modulation nonlinearities, group velocity dispersion, external electro-optic phase modulation, and gain/loss. We find that the birefringent nonlinear medium with spatial parameter variations supports the existence of linearly chirped similariton structures of the W-shaped-dipole and bright-dipole types. These important results indicate that in addition to the usual single-humped localized waves such as bright-bright and dark-dark type waveforms, multihump chirped similaritons can also exist in the inhomogeneous birefringent fiber in the presence of all physical effects. The similariton parameters such as the amplitude, width, phase, and inverse group velocity are found to be dependent on certain controllable fiber parameters, thus enabling us to manage their intensity and consequently their subsequent dynamical evolution. Finally, we investigate the transmission of similaritons for different choices of material parameters.

An integrated model of the human cornea as a linear biaxial birefringent medium

A novel model of human corneal birefringence is presented. The cornea is treated as a homogeneous biaxial linear birefringent medium in which the values of the binormal axes angle and organization of the main refractive indices vary continuously from the apex to the limbus. In its central part, the angle between binormal axes is 35°, and para centrally, it smoothly increases to 83.7°. The values of the main refractive indices (nx, ny, nz) change, as well as their order, from nx < nz < ny to nz < nx < ny. The transition between these two states was described with a normal distribution (μ = 0.45, σ = 0.1). The presented model corresponds with the experimental results presented in the literature. To our knowledge, it is the first model that presents the anisotropic properties’ distributions of the entire cornea. The presented model facilitates a better understanding of the corneal birefringence phenomenon directly related to its lamellar structure.

Wavelength-independent Bragg-like reflection in uniaxial bi-anisotropic media

We have recently shown that a uniform birefringent medium exhibits a circular Bragg phenomenon that relies solely on resonant tuning of the medium’s parameters, rather than on a particular wavelength resonance, thus rendering its electromagnetic response arbitrarily broadband. The resonant condition, however, necessitated a chirality parameter equal to the average refractive index. Here, we demonstrate that non-axial wave propagation in an axially bi-anisotropic uniaxial medium also enacts such a response and, moreover, relaxes the severity of the tuning condition, offering a convenient platform for controlling both the location of the resonance and the corresponding bandwidth. Anomalous wave propagation at a singular point is additionally identified, in the vicinity of which a remarkably high and intrinsically broadband refractive index can be realized. Recent demonstrations of meta-media with giant and controllable chirality pave the path towards the realistic embodiment of a highly efficient optical modulator.

Exact envelope solitons in topological Floquet insulators.

The existence of new types of four-wave mixing Floquet solitons were recently realized numerically through a resonant phase matching in a photonic lattice of type-I Dirac cones; specifically, a honeycomb lattice of helical array waveguides imprinted on a weakly birefringent medium. We present a wide class of exact solutions in this system for the envelope solitons in dark-bright pairs and a "molecular" form of bright-dark combinations. Some of the solutions, red or blue detuned, are mode-locked in their momenta, while the others offer a spectrum of allowed momenta subject to constraints amongst the system and solution parameters. We show that the characteristically different solutions exist at and away from the band edge, with the exact band edge possessing a periodic pair of sinusoidal excitations akin to that of two-level systems apart from localized solitons. These could have possible applications for designing quantum devices.

Polarization responses of generated vector beam in a magnetic-driven atomic system

In this paper, the double-V atomic system that split under a magnetic field is manipulated by helical Ince-Gaussian (HIG) beams with opposite orbital angular momentum (OAM). With the controlling of HIG beams, the atomic vapor acts as a spatially varying circular birefringent medium, whose optical response to external magnetic fields is emphatically discussed. Results show that, the polarization properties of the probe field have a linear variation with the weak magnetic field, which provides a method to measure the slight change in the external magnetic field. It is also demonstrated that the polarization separation of the probe field can be realized by manipulating the magnitude or direction of the magnetic field. The dynamic polarization of the probe field in this work is expected to have potential applications in magnetic detection.

Cross-correlation power spectra and cosmic birefringence of the CMB via photon-neutrino interaction

In the context of the standard model of particles, the weak interaction of cosmic microwave background (CMB) and cosmic neutrino background (CνB), can generate non-vanishing TB and EB power spectra in the order of one loop forward scattering, in the presence of scalar perturbation, which is in contrast with the standard scenario cosmology. Comparing our results with the current experimental data may provide, significant information about the nature of CνB, including CMB-CνB forward scattering for TB, TE, and EB power spectra. To this end, different cases were studied, including Majorana CνB and Dirac CνB. On the other hand, it was shown that the mean opacity due to cosmic neutrino background could behave as an anisotropic birefringent medium and change the linear polarization rotation angle. Considering the contributions from neutrino and anti-neutrino forward scattering with CMB photons (in the case of Dirac neutrino), we introduce relative neutrino and anti-neutrino density asymmetry (δν = Δnν /nν = nν -nν̅ /nν ). Then, using the cosmic birefringence angle reported by the Planck data release β = 0.30° ± 0.11° (68%C.L.), some constraints can be put on δν . Also, the value of cosmic birefringence due to Majorana CνB medium is estimated at about β| ν ≃ 0.2 rad. In this respect, since Majorana neutrino and anti-neutrino are exactly the same, both CB contributions will be added together. However, this value is at least two orders larger than the cosmic birefringence angle reported by the Planck data release, β = 0.30° ± 0.11° (68%C.L.). Finally, we shortly discussed this big inconsistency. It is noteworthy that to calculate the contribution of photon-neutrino forward scattering for cosmic birefringence, we just consider the standard model of particles and the standard scenario of cosmology.

Reflective optical vortex generators with ultrabroadband self-phase compensation

The explosive growth of information urgently requires extending the capacity of optical communication and information processing. Orbital-angular-momentum-based mode division multiplexing (MDM) is recognized as the most promising technique to improve the bandwidth of a single fiber. To make it compatible with the dominant wavelength division multiplexing (WDM), broadband equal high-efficient phase encoding is highly pursued. Here, we propose a twisted-liquid-crystal and rear-mirror-based design for ultrabroadband reflective planar optics. The backtracking of the light inside the twisted birefringent medium leads to an achromatic phase modulation. With this design, a single-twisted reflective q-plate is demonstrated to convert a white beam to a polychromatic optical vortex. Jones calculus and vector beam characterization are carried out to analyze the broadband phase compensation. A dual-twisted configuration further extends the working band to over 600 nm. It supplies an ultrabroadband and reflective solution for the WDM/MDM-compatible elements and may significantly promote advances in ultrabroadband planar optics.

Broadband Bragg phenomenon in a uniform birefringent medium.

A new mechanism of Bragg phenomenon is theoretically identified that, remarkably, occurs in a uniform medium and relies on resonant tuning of the medium parameters rather than on wavelength-matching. Due to the uniformity, reflection ensues over a broad wavelength range, much like a metal, but is polarization dependent: one circular state is reflected, whereas the other is transmitted. Such a medium can thus provide a broadband, low-loss polarization divider/combiner. Assessing a realistic embodiment with loss and material dispersion, we discuss practical realizations within range of current meta-media technology at terahertz and optical frequencies.

Waveguiding driven by the Pancharatnam-Berry phase

We theoretically and numerically investigate the properties of waveguides based on the Pancharatnam-Berry phase, obtained by a longitudinally periodic rotation of the optic axis in a transversely twisted birefringent medium. In this paper we study the case where the period of the longitudinal modulation is chosen so that a net accumulation of geometric phase in propagation occurs. First, the interplay between different contributions to the optical potential is addressed. Second, a continuous evolution of the polarization structure of the quasimodes is observed in the numerical simulations. We explain it by a combination of plane-wave-based models and gauge transformations. We discover that, beyond the longitudinal oscillations, the polarization of the quasimode also varies through its cross section. The analogies with respect to charged particles moving in a magnetic field are outlined.

Birefringence induced by antiferroelectric switching in transparent polycrystalline PbZr0.95Ti0.05O3 film

The most characteristic functional property of antiferroelectric materials is the possibility to induce a phase transition from a non-polar to a polar phase by an electric field. Here, we investigate the effect of this field-induced phase transition on the birefringence change of $PbZr_{0.95}Ti_{0.05}O_{3}$. We use a transparent polycrystalline $PbZr_{0.95}Ti_{0.05}O_{3}$ film grown on $PbTiO_{3}/HfO_{2}/SiO_{2}$ with interdigitated electrodes to directly investigate changes in birefringence in a simple transmission geometry. In spite of the polycrystalline nature of the film and its moderate thickness, the field-induced transition produces a sizeable effect observable under a polarized microscope. The film in its polar phase is found to behave like a homogeneous birefringent medium. The time evolution of this field-induced birefringence provides information about irreversibilities in the antiferroelectric switching process and its slow dynamics. The change in birefringence has two main contributions, one that responds briskly (~ 0.5 s), and a slower one that rises and saturates over a period of as long as 30 minutes. Possible origins for this long saturation and relaxation times are discussed.

Spin Noise in Birefringent Media.

It is known that linear birefringence of the medium essentially hinders measuring the Faraday effect. For this reason, optically anisotropic materials have never been considered as objects of the Faraday-rotation-based spin noise spectroscopy. We show, both theoretically and experimentally, that strong optical anisotropy that may badly suppress the regular Faraday rotation of the medium, practically does not affect the measurement of the spatially uncorrelated spin fluctuations. We also show that the birefringent media provide additional opportunity to measure spatial spin correlations. Results of the experimental measurements of the spin-noise spectra performed on Nd^{3+} ions in the uniaxial crystal matrices well agree with the theory.

Quasitrapped modes in metasurfaces of anisotropic MoS2 nanoparticles for absorption and polarization control in the telecom wavelength range

We investigate the resonant optical response of single material-anisotropic nanoparticles (NPs) of molybdenum disulfide (MoS$_2$) and their two-dimensional arrays (metasurfaces) irradiated by plane waves of the telecomunication optical range. Nanoparticles in the form of a disk with centered and shifted hole are considered. Using the recently experimental measured the MoS$_2$ dielectric permittivity and numerical calculations with analytical multipole analysis, we show that the material-anisotropy of NPs can lead to specific nonlocal contributions in their magnetic and electric dipole response and affect the effective dipole polarizabilities. Applying a special procedure we determine the period of the MoS$_2$ metasurfaces supporting the quasi-trapped mode (QTM) resonance around the tellecom wavelength of 1550 nm. It is shown that regardless extremely weak absorption of the single nanoparticles, the excitation of the QTM leads to effective narrowband absorption in the metasurfaces. Influences of the linear polarization direction of normally incident waves on the QTM implementation and the reflection and transmission spectra are studied. It is found and demonstrated, for the first time, that a metasurface, composed of the MoS$_2$ disks with their anisotropy perpendicularto the metasurface plane, has the properties of a continuous birefringent medium. Due to these properties, normally incident and linear-polarized waves can be transformed in the transmitted and reflected waves with changed polarizations.

Sub-megahertz spectral dip in a resonator-free twisted gain medium

Ultra-narrow optical spectral features resulting from highly dispersive light–matter interactions are essential for a broad range of applications such as spectroscopy, slow-light and high-precision sensing. Features approaching sub-megahertz or, equivalently, Q-factors up to one billion and beyond, are challenging to obtain in solid-state systems, ultimately limited by loss. We present a novel approach to achieve tunable sub-megahertz spectral features at room temperature without resonators. We exploit gain-enhanced polarization pulling in a twisted birefringent medium where polarization eigenmodes are frequency-dependent. Using Brillouin gain in a commercial spun fibre, we experimentally achieve a 0.72 MHz spectral dip, the narrowest backward Brillouin scattering feature ever reported. Further optimization can potentially reduce the linewidth to <0.1 MHz. Our approach is simple and broadly applicable, offering on-demand tunability and high sensitivity, with a wide range of applications such as microwave photonic filters, slow and fast light, and optical sensing. Tunable sub-megahertz spectral features are demonstrated without resonators. The approach, which exploits gain-enhanced polarization pulling in a twisted birefringent medium, may be useful in applications such as microwave photonic filters, slow and fast light, and optical sensing.

Interaction and co-assembly of optical and topological solitons

Solitons attract a great deal of interest in many fields, ranging from optics to fluid mechanics, cosmology, particle physics and condensed matter. However, solitons of these very different types rarely coexist and interact with each other. Here we develop a system that hosts optical solitons coexisting with topological solitonic structures localized in the molecular alignment field of a soft birefringent medium. We experimentally demonstrate and theoretically explain optomechanical interactions between such optical and topological solitons, mediated by the local transfer of momentum between light and matter and the nonlocal orientational elasticity of the liquid-crystal phase used in our system. We show that the delicate balance arising from these different contributions to the optomechanical force enables facile dynamical control and spatial localization of topological solitons. Our findings reveal unusual solitonic tractor beams and emergent light–matter self-patterning phenomena that could aid in creating new breeds of nonlinear photonic materials and devices.

Transfer and evolution of structured polarization in a double-V atomic system.

We numerically investigate the transfer of optical information from a vector-vortex control beam to an unstructured probe beam, as mediated by an atomic vapour. The right and left circular components of these beams drive the atomic transitions of a double-V system, with the atoms acting as a spatially varying circular birefringent medium. Modeling the propagation of the light fields, we find that, for short distances, the vectorial light structure is transferred from the control field to the probe. However, for larger propagation lengths, diffraction causes the circular components of the probe field to spatially separate. We model this system for the D1 line of cold rubidium atoms and demonstrate that four wave mixing can lead to correlations between the optical polarization structure and the diffraction of light, generating coupled dynamics of the internal and external degrees of freedom.

Phase control of pulses distortions through induced circular birefringent chiral atomic medium

Phase control of pulses distortions through induced circular birefringent chiral atomic medium

Combined Jones–Stokes Polarimetry and Its Decomposition into Associated Anisotropic Characteristics of Spatial Light Modulator

Jones–Stokes polarimetry is a robust in vitro polarimetric technique that can be used to investigate the anisotropic properties of a birefringent medium. The study of spatially resolved Jones matrix components of an object is a heuristic approach to extract its phase and polarization information. However, direct interpretation of Jones matrix elements and their decomposition into associated anisotropic properties of a sample is still a challenging research problem that needs to be investigated. In this paper, we experimentally demonstrate combined Jones–Stokes polarimetry to investigate the amplitude, phase, and polarization modulation characteristics of a twisted nematic liquid crystal spatial light modulator (TNLC-SLM). The anisotropic response of the SLM is calibrated for its entire grayscale range. We determine the inevitable anisotropic properties viz., diattenuation, retardance, isotropic absorption, birefringence, and dichroism, which are retrieved from the measured Jones matrices of the SLM using Jones polar decomposition and a novel algebraic approach for Jones matrix decomposition. The results of this study provide a complete polarimetric calibration of the SLM within the framework of its anisotropic characteristics.