Polarization Retardation Research Articles

Ultra-wideband and high-efficiency polarization rotator based on liquid crystals

We propose a novel design of an asymmetrically anchored negative liquid crystal (LC) cell capable of linearly rotating the polarization axis of broadband light, with the rotation angle controlled by voltage. Unlike conventional LC cells that require polarization filters or retarders, our LC cell can directly modulate the polarization state of light without any additional components. The LC cell exhibits high polarization rotation efficiency over a wide wavelength range (200 nm to 2000nm), superior to the existing polarization modulators. We validate our design through theoretical calculations and numerical simulations, proving that a degree of linear polarization of over 0.95 can be achieved in the UV, visible, and NIR regions. Our design can be applied in optical communications, biological imaging, and spectroscopic technologies.

Optimal multi-spectrum polarization detection with full-Stokes in a single channel by using standard retarders

Polarization detection with full-Stokes is one of the important way to obtain spatial distribution and physical information on targets. However, the most full-Stokes multi-spectrum polarization detection system is relatively complex, as the traditional method is generally designed for multi-channel to adapt the different wavelength. In this paper, we propose an optimal polarization detection method to obtain the full-Stokes vector of the incident light in one channel for different wavelengths. This method utilizes two standard retarders for multi-spectrum full polarization modulation, which can obtain accurately the desired retardance to achieve optimal system performance at multi-wavelengths. The numeric analysis validates the feasibility of the dual-retarders detection system based on tunable polarization retardance method. Furthermore, in experiments, just two much more readily available quarter-wave plate (QWP) retarders are utilized, the various special retardance within 0.2° errors and high polarization measurement accuracy below 10-2 level at multi-wavelengths are achieved. This method, with a simple structure, has excellent application prospects in high-precision polarization detection, such as solar magnetic field detection.

Tunable broadband polarization retarders.

We theoretically propose a type of tunable polarization retarder, which is composed of sequences of half-wave and quarter-wave polarization retarders, allowing operation at broad spectral bandwidth. The constituent retarders are composed of stacked standard half-wave retarders and quarter-wave retarders rotated at designated angles relative to their fast polarization axes. The proposed composite retarder (CR) can be tuned to an arbitrary value of the retardance by varying the middle retarder alone while maintaining its broadband spectral bandwidth intact.

Light-by-light polarization control using Stimulated Brillouin Scattering with retardance spectrum shaping

The spectral broadening of a nonlinear polarization retarder based on the polarization dependent interactions of Stimulated Brillouin Scattering is proposed and demonstrated. Through phase-to-retardance conversion, it is shown that polarization can not only be controlled in a bandwidth wider than the natural Brillouin response, but it can also be tailored to provide a certain retardance profile. Broadening is achieved through the engineering of Brillouin phase frequency response via feedback pump regulation, unlike previous schemes based on amplitude and time delay control. Retardance broadening from 51 MHz (natural SBS interaction) to 0.9 GHz along with retardance flattening is demonstrated. This technique contributes to expand optical signal processing tools and opens new possibilities in all-optical switching and routing of data signals as well as in the field of microwave photonics.

Efficient broadband polarization retarder via shortcuts to adiabaticity.

The use of two-level atomic systems in quantum optics allows for the design of highly efficient and broadband achromatic retarders through the application of adiabatic passage and composite pulse techniques. In this work, we propose shortcuts to adiabaticity to improve broadband polarization retarders with shorter lengths. We achieve this by inversely engineering the relative refractive indices and further optimizing them with respect to the perturbation of input wavelength. Our results are compared with adiabatic and composite protocols, demonstrating that our method provides the advantage of integrating efficiency and robustness.

Total retardance measurements based on the complex Fourier coefficients for the rotating polarizer analyzer system

We propose a demodulation algorithm based on the calculus of the complex Fourier coefficients; we used a dual rotating polarizer-analyzer polarimeter to show the feasibility of our proposal. Our demodulation algorithm considers the frequency response obtained by the system, and its possible to calculate the total retardation, fast axis orientation and ellipticity of a sample. Our proposal does not require recovering the full Mueller matrix from getting those parameters. In addition, as the proposal does not use retarders for the measurement, the system presents potential applications for multi-wavelength measurements on phase retardation samples. We show experimental results showing the capabilities of our proposal in characterizing a polarization retardance sample.

Full-silica metamaterial wave plate for high-intensity UV lasers

Bringing light–matter interactions into novel standards of high-energy physics is a major scientific challenge that motivated the funding of ambitious international programs to build high-power laser facilities. The major issue to overcome is to avoid laser intensity heterogeneities over the target that weaken the light–matter interaction strength. Laser beam smoothing aims at homogenizing laser intensities by superimposing on the target laser speckle intensities produced by orthogonal left and right circularly polarized beams. Conventional wave plates based on anisotropic crystals cannot support the laser fluences of such lasers, and the challenge is now to design wave plates exhibiting a high laser induced damage threshold (LIDT). Fused silica exhibits high LIDT, but its isotropic dielectric permittivity prevents effects on polarization retardance. Metamaterials have been widely investigated to tailor the phase and polarization of light but with plasmonic or high-refractive-index materials, and applying this approach with silica is highly challenging due to the weak optical contrast between silica and air or vacuum. Here we design and fabricate a silica-based metasurface acting almost like a quarter-wave plate in the UV spectral range, fulfilling the numerous constraints inherent to high-power laser beamlines, in particular, high LIDT and large sizes. We numerically and experimentally demonstrate that fused silica etched by deep grooves with a period shorter than the wavelength at 351 nm operates the linear-to-quasi circular polarization conversion together with a high transmission efficiency and a high LIDT. The high aspect ratio of the grooves due to the short period imposed by the short wavelength and the deepness of the grooves required to overcome the weak optical contrast between silica and air is experimentally obtained through a CMOS compatible process.

Ferroelectric liquid crystal Pancharatnam-Berry lens with a fast control of output light's polarization-handedness.

We report the ferroelectric liquid crystal (FLC) Pancharatnam-Berry lenses (PBLs) with rapid transmittance tunability. The FLC PBLs were fabricated using a single-step holographic exposure system based on a spatial light modulator working as numerous polarization retarders, providing a simple way to fabricate FLC continuous aligning structures. A state-selection sector containing a binary FLC switch was utilized for fast changing input light's polarization handedness. Thus, when light passes through a FLC PBL, the output light's polarization handedness can be switched accordingly. In this case, FLC PBLs can function as concave/convex lenses with rapidly switching speed. Photo sensitive azo-dye material was used as the aligning layer for both FLC PBLs and FLC switches. The fabricated FLC PBLs and the FLC switches show fast switching-on times of 150μs and 50μs respectively. The FLC PBLs combining with the state-selection sector can have potential applications on varies displays and augmented reality.

Manipulation and measurement of quantum states with liquid crystal devices.

We present the use of liquid crystal retarders (LCR) as phase control elements in optical quantum technologies. We show that an entangled photon pair state can be actively controlled using an LCR without introducing state mixing or polarization drifts. Similarly, we demonstrate that the entanglement quality can be conveniently analyzed using liquid crystal polarization retarders.

Mueller matrix spectroscopy of fano resonance in plasmonic oligomers

Fano resonance in plasmonic oligomers originating from the interference of a spectrally broad superradiant mode and a discrete subradiant mode is under intensive recent investigations due to numerous potential applications. In this regard, development of experimental means to understand and control the complex Fano interference process and to modulate the resulting asymmetric Fano spectral line shape is highly sought after. Here we present a polarization Mueller matrix measurement and inverse analysis approach for quantitative understanding and interpretation of the complex interference process that lead to Fano resonance in symmetry broken plasmonic oligomers. The spectral Mueller matrices of the plasmonic oligomers were recorded using a custom designed dark-field Mueller matrix spectroscopy system. These were subsequently analyzed using differential Mueller matrix decomposition technique to yield the quantitative sample polarimetry characteristics, namely, polarization diattenuation (d) and linear retardance ({\delta}) parameters. The unique signature of the interference of the superradiant dipolar plasmon mode and the subradiant quadrupolar mode of the symmetry broken plasmonic oligomers manifested as rapid spectral variation of the diattenuation and the linear retardance parameters across the Fano spectral dip. The polarization information contained in the Mueller matrix was further utilized to desirably control the Fano spectral line shape. The experimental Mueller matrix analysis was complemented with finite element based numerical simulations, which enabled quantitative understanding of the interference of the superradiant and the subradiant plasmon modes and its link with the polarization diattenuation and retardance parameters.

A 4-Megapixel Cooled CCD Division of Focal Plane Polarimeter for Celestial Imaging

The field of astronomy relies on spectral and polarization imagery recorded across a wide range of spectra to make inferences about imaged objects from nearby and distant galaxies. One of the challenges in recording celestial polarization information is recording multiple images filtered with various polarization optics, such as linear polarization filters or retarders, and with low-noise, low-dark-current sensors. In this paper, we present a division of focal plane polarimeter that can operate at room temperature down to −20 °C. When the imaging sensor operates at −20 °C, the dark currents is reduced by two orders of magnitude, which improves the polarization extinction ratio by ~5-fold. Comprehensive optoelectronic tests are presented with data recorded with the polarimeter.

Three-dimensional polarization aberration functions in optical system based on three-dimensional polarization ray-tracing calculus

The polarization aberrations of a complex optical system with multi-element lens have been investigated using a 3D polarization aberration function. The 3D polarization ray-tracing matrix has been combined with the optical path difference to obtain a 3D polarization aberration function, which avoids the need for a complicated phase unwrapping process. The polarization aberrations of a microscope objective have been analyzed to include, the distributions of 3D polarization aberration functions, diattenuation aberration, retardance aberration, and polarization-dependent intensity on the exit pupil. Further, the aberrations created by the field of view and the coating on the distribution rules of 3D polarization aberration functions are discussed in detail. Finally a novel appropriate field of view and wavelength correction is proposed for a polarization aberration function which optimizes the image quality of a multi-element optical system.

One shot endoscopic polarization measurement device based on a spectrally encoded polarization states generator.

We report a novel technique for polarimetric characterization of samples through a flexible fiber endoscope, with a single shot measurement per pixel. The sample is simultaneously probed with a large diversity of polarization states, and both degree of polarization and linear retardance are determined thanks to specific processing of data. The probe polarization states are spectrally encoded on the 10 nm bandwidth of the source. The key component of the endoscope is a 3 m long specially designed optical fiber which consists of the optimized concatenation of highly birefringent fiber pieces. For a proof of principle, different calibrated or manufactured samples were successfully characterized. The proposed technique is attractive in view of reducing the measurement time of polarimetric images, in endoscopic applications.

Slow dynamics of water confined in Newton black films.

Slowdown of translational and reorientational dynamics of water confined in Newton black films (NBFs) is revealed by molecular dynamics simulations. As a film becomes thinner, both translational and reorientational dynamics become slower. The polarization of water molecules in the macroscopic electrostatic field across the NBF and the coordination of Na(+) ions and surfactant anionic groups around water molecules concertedly lead to slowdown of water dynamics. The polarization effect is obvious for water not coordinated by Na(+) ions, which exhibits reorientational dynamics depending on initial dipole orientations. Na(+) ions and surfactant anionic groups retard dynamics of surrounding water by decreasing the hydrogen bond exchange probability and increasing the viscosity of water. The dependences of translational and reorientational dynamics on coordination environments of water are similar. Dynamics of water in positions close to the interfaces of NBFs are mainly retarded by Na(+) ions and surfactant anionic groups, while the macroscopic polarization effect plays the main role in influencing water dynamics in positions far from the interfaces. This study sheds light on the improvement of knowledge about the water dynamics slowdown mechanism in similar environments like reverse micelles and lamellar structures.

Roles of linear and circular polarization properties and effect of wavelength choice on differentiation between ex vivo normal and cancerous gastric samples.

Multispectral Mueller matrix imaging was performed over a spectral range from 470 to 632 nm on 4-μm unstained gastric tissue sections. A complete set of polarization parameters was derived. The combination of linear depolarization and linear retardance yields the highest accuracy in sample classification. When the depolarization of linearly polarized light due to scattering is independent of the orientation angle of the incident linear polarization vector, the derivation of linear polarization properties will require only 3×3 Mueller matrix, which would significantly reduce the complexity of the polarimetry imaging system. When additional parameters are needed to complement the two linear polarization parameters, retardance, circular depolarization, and depolarization can be included in classification in the order of preference. However, these additional parameters would require the measurement of 4×4 Mueller matrix. In addition, it appears that wavelength is not a critical factor in terms of classification accuracy for thin tissue sections in this study.

Highly efficient broadband polarization retarders and tunable polarization filters made of composite stacks of ordinary wave plates.

By using the formal analogy between the evolution of the state vector in quantum mechanics and the Jones vector in polarization optics, we construct and demonstrate experimentally efficient broadband half-wave polarization retarders and tunable narrowband polarization filters. Both the broadband retarders and the filters are constructed by the same set of stacked standard multiorder optical wave plates (WPs) rotated at different angles with respect to their fast polarization axes: for a certain set of angles this device behaves as a broadband polarization retarder, while for another set of angles it turns into a narrowband polarization filter. We demonstrate that the transmission profile of our filter can be centered around any desired wavelength in a certain vicinity of the design wavelength of the WPs solely by selecting appropriate rotation angles.

820 Hz linewidth short-linear-cavity single-frequency fiber laser at 1.5 μm

We proposed a short-linear-cavity fiber laser with a virtual-folded-ring configuration, which combines the advantages of ring lasers and short-linear-cavity lasers. An all-fiber quarter-wave plate was used inside the cavity to introduce polarization retardation. By retarding the polarization of the travelling waves, the spatial-hole-burning effect was weakened and the efficient cavity length was extended to nearly twice its physical length. As a result, a single-frequency laser output with a linewidth of less than 820 Hz was obtained from the free-running fiber laser. The relaxation oscillation frequency was observed to be around 280 kHz and the signal to noise ratio of the laser output was >72 dB.

Strong Birefringence Tuning of Optical Waveguides With Femtosecond Laser Irradiation of Bulk Fused Silica and Single Mode Fibers

Birefringence tunability is demonstrated in waveguides formed in bulk fused silica and in the core of single mode fibers, by femtosecond laser writing of stress inducing tracks that are placed with different geometries around the core of the waveguides. The femtosecond laser generated stress effect was probed by the birefringence induced spectral splitting of either Bragg grating waveguides in bulk fused silica or weakly modulated, femtosecond laser induced Bragg gratings in optical fibers. Birefringence values as low as 4 ×10-6 and up to 2 ×10-3 were obtained by controlling the fabrication conditions such as the laser pulse energy, the writing femtosecond laser polarization, the number of overwriting exposures, and the geometry of the induced stress tracks. Wave retarders are developed and characterized by a cross polarization technique to provide the spectral response of the stress induced birefringence, offering the convenient fabrication of short length and broadband in-line polarization devices. With this approach, millimeter length tracks provided 10 nm bandwidth polarization retarders in a single mode fiber and a 65 nm bandwidth retarders in bulk fused silica.

Potent in vitro Interference of Fleroxacin in DNA-binding, Unwinding and ATPase Activities of Bloom Helicase

ObjectiveTo study the effect of fleroxacin (FLRX) on biological properties of Bloom (BLM) helicase catalytic core (BLM642-1290 helicase) in vitro and the molecular mechanism of interaction between the two molecules. MethodsDNA-binding and unwinding activities of BLM642-1290 helicase were assayed by fluorescence polarization and gel retardation assay under conditions that the helicase was subjected to different concentrations of FLRX. Effect of FLRX on helicase ATPase activity was analyzed by phosphorus-free assay based on a colorimetric estimation of ATP hydrolysis-produced inorganic phosphate. Molecular mechanism of interaction between the two molecules was assayed by ultraviolet and fluorescence spectra. ResultsThe DNA unwinding and ATPase activities of BLM642-1290 helicase were inhibited whereas the DNA-binding activity was promoted in vitro. A BLM-FLRX complex was formed through one binding site, electrostatic and hydrophobic interaction force. Moreover, the intrinsic fluorescence of the helicase was quenched by FLRX as a result of non-radioactive energy transfer. The biological activity of helicase was affected by FLRX, which may be through an allosteric mechanism and stabilization of enzyme conformation in low helicase activity state, disruption of the coupling of ATP hydrolysis to unwinding, and blocking helicase translocation on DNA strands. ConclusionFLRX may affect the biological activities and conformation of BLM642-1290 helicase, and DNA helicase may be used as a promising drug target for some diseases.

Variable ultrabroadband and narrowband composite polarization retarders

We propose and experimentally demonstrate novel types of composite sequences of half-wave and quarter-wave polarization retarders, permitting operation at either ultrabroad spectral bandwidth or narrow bandwidth. The retarders are composed of stacked standard half-wave retarders and quarter-wave retarders of equal thickness. To our knowledge, these home-built devices outperform all commercially available compound retarders, made of several birefringent materials.