Optical Polarization Switching Research Articles

An alternative approach to design a frequency encoded 3-bit synchronous counter using semiconductor optical amplifier-based polarization switch

An alternative approach to design a frequency encoded 3-bit synchronous counter using semiconductor optical amplifier-based polarization switch

Multi-band polarization switch based on magnetic fluid filled dual-core photonic crystal fiber

The research of high-performance polarization controllers is of great significance for expanding the application field of polarization optics. Here, a polarization switch is demonstrated by using a dual-core photonic crystal fiber (DCPCF) with four symmetrical air holes, placed above and below each core, filled with magnetic fluid (MF). The switch, which utilizes a magnetic field to change the coupling length ratio of the x and y polarization modes, enables dynamic tuning of the polarization state and extinction ratio. Numerical results show that when the working length is 36.638 mm, the magneto–optical polarization switch can operate in four communication bands, i.e., 1509 nm to 1520 nm, 1544 nm to 1556 nm, 1578 nm to 1591 nm, and 1611 nm to 1624 nm. Moreover, the extinction ratio (ER) is greater than 20 dB in the fiber length range of 38.5 mm to 38.7 mm, indicating that the device has a good fault tolerance for the interception of the fiber length.

Two-dimensional silicon optical phased array with large field of view.

Optical phased array (OPA) is a promising beam steering component for light detection and ranging (LiDAR) systems. For most LiDAR applications, two-dimensional (2D, lateral and longitudinal) beam steering with large field of view is required. To achieve large lateral and longitudinal field of view, waveguide with nonuniform spacing and broadband tunable laser source is commonly utilized, resulting in complex structure and high cost. Here, a 2D OPA with large field of view is proposed and demonstrated on the silicon-on-insulator platform. Assisted by an improved optical antenna and polarization switch, lateral and longitudinal steering range could be both significantly improved. The experimental results show the steering ranges are 99.24° × 15.62° and 96.48° × 16.08° for transverse electric mode and transverse magnetic mode, respectively. The proposed scheme provides a promising approach to realize the integrated OPA with large field of view.

Circularly-polarized Airy light-sheet spinner tweezers and particle transport

Circularly-polarized Airy light-sheet spinner tweezers are introduced, and their interaction with a subwavelength absorptive dielectric sphere is considered. The mathematical representation of the Cartesian components of the radiated fields is made using the vector angular spectrum method, the Lorenz gauge, and Maxwell's equations for an Airy light-sheet with circular polarization. The results demonstrate the existence of an attractive (pulling) longitudinal force. Furthermore, in contrast with linearly (TM or TE) polarized Airy light-sheets for which the longitudinal spin torque vanishes, the circularly polarized Airy light sheet induces both longitudinal and lateral spin torques causing counter-clockwise or clockwise rotation contingent upon the location of the sphere in the transverse plane. The study is extended to calculate the trajectories of the sphere in the transverse illuminating plane (xy), stemming from a particle dynamics analysis based on Newton's second law of motion. The results are of particular importance in the development of light-sheet spinner tweezers, optical polarization switching for the development and optimization of sorting miniature devices, novel polarization reconfigurable methods and techniques, and related applications in particle manipulation, transport and rotation.

Optical polarization switching in semipolar (202¯1) InGaN multiple quantum wells induced by strain engineering

Semipolar (202¯1) InGaN/AlGaN multiple quantum wells (MQWs) with a low In content (<0.05) were coherently grown on a partially relaxed AlxGa1−xN (0 < XAl < 0.4) layer. As XAl increased from 0.15 to 0.38, the degree of optical polarization measured by photoluminescence at 13 K changed from 0.49 to −0.24, where (−) indicates the change in the dominant polarization direction from [112¯0] to [1014¯]. Regardless of XAl and thickness, no polarization switching was observed if AlxGa1−xN was fully strained to the GaN substrate. Band structure modeling based on the k⋅p method implies that the polarization switching is associated with strong valence band mixing induced by the one-dimensional strain relaxation in AlGaN, which leads to a significantly stronger compressive strain in MQWs along [1014¯] relative to [112¯0]. These results demonstrate that the optical polarization switching in semipolar MQWs can be controlled by engineering the strain state of the underlying layer.

Femtosecond optical polarization switching using a cadmium oxide-based perfect absorber

Ultrafast control of the polarization state of light may enable a plethora of applications in optics, chemistry and biology. However, conventional polarizing elements, such as polarizers and waveplates, are either static or possess only gigahertz switching speeds. Here, with the aid of high-mobility indium-doped cadmium oxide (CdO) as the gateway plasmonic material, we realize a high-quality factor Berreman-type perfect absorber at a wavelength of 2.08 μm. On sub-bandgap optical pumping, the perfect absorption resonance strongly redshifts because of the transient increase of the ensemble-averaged effective electron mass of CdO, which leads to an absolute change in the p-polarized reflectance from 1.0 to 86.3%. By combining the exceedingly high modulation depth with the polarization selectivity of the perfect absorber, we experimentally demonstrate a reflective polarizer with a polarization extinction ratio of 91 that can be switched on and off within 800 fs. Indium-doped cadmium oxide performs polarization switching on a subpicosecond timescale.

Electromagnetically induced transparency in nano-structures made from metallic nanorod and split-ring-resonator

In this paper,the selectively excited EIT effect by RCP and LCP can be achieved by three dimensional (3D) nano-structures composed of the metallic nanorod and special split-ring-resonator (SRR). Numerical calculations on electric field distributions indicate that the chirality contributes to this novel effect. Moreover, it also demonstrated that constructive interference of bright–bright mode leads to a broad band transparent window in nonchiral metamaterials. These new findings could be employed to distinguish RCP and LCP light and also have potential application in optical polarization switching.

Band gap bowing and optical polarization switching in AlGaN alloys

We present a detailed theoretical study of the band gap bowing of wurtzite AlGaN alloys over the full composition range. Our theoretical framework is based on an atomistic tight‐binding model, including local strain and built‐in potential variations due to random alloy fluctuations. We extract a bowing parameter for the band gap of eV, which is in good agreement with experimental data. Our analysis shows that the bowing of the band gap mainly arises from bowing of the conduction band edge; for the composition dependence of the valence band edge energy we find a close to linear behavior. Finally, we investigate the wave function character of the valence band edge as a function of GaN content x. Our analysis reveals an optical polarization switching around , which is in the range of reported experimental data.

Quantum mechanical modeling of excited electronic states and their relationship to cathodoluminescence of BaZrO3

First-principles calculations set the comprehension over performance of novel cathodoluminescence (CL) properties of BaZrO3 prepared through microwave-assisted hydrothermal. Ground (singlet, s*) and excited (singlet s** and triplet t**) electronic states were built from zirconium displacement of 0.2 Å in {001} direction. Each ground and excited states were characterized by the correlation of their corresponding geometry with electronic structures and Raman vibrational frequencies which were also identified experimentally. A kind of optical polarization switching was identified by the redistribution of 4dz2 and 4dxz (Zr) orbitals and 2pz O orbital. As a consequence, asymmetric bending and stretching modes theoretically obtained reveal a direct dependence with their polyhedral intracluster and/or extracluster ZrO6 distortions with electronic structure. Then, CL of the as-synthesized BaZrO3 can be interpreted as a result of stable triplet excited states, which are able to trap electrons, delaying the emission process due to spin multiplicity changes.

Energy offset between valence band anti-crossing and optical polarization switching in semipolar InGaN quantum wells

Light emitted from a semipolar InGaN quantum well parallel to the surface normal is partially polarized, in contrast to the unpolarized emission of c-plane quantum wells. Anti-crossing of the two topmost valence bands causes polarization switching between ordinary and extraordinary polarizations for certain semipolar quantum well orientations with increasing indium content. Two properties of the two measured spectra, their polarization resolved but spectrally integrated intensity and their measured energy splitting, are associated with anti-crossing. Here, we show that only the observable energy splitting coincides with band anti-crossing, while the switching point of the polarization can deviate from the anti-crossing point.

Design of the Polarimeter for the Fibre Arrayed Solar Optical Telescope

The theoretical design of the polarimeter used for the Fibre Arrayed Solar Optical Telescope (FASOT) is described. It has the following characteris- tics: (1) It is provided with the function of optical polarization switching, which makes the high-effciency polarimetry possible; (2) In the waveband of 750nm, the polarimetric effciency is higher than 50% for the every Stokes parameter, and higher than 86.6% for the total polarization, thus an observer can make the simultaneous polarization measurements on multiple magnetosensitive lines in such a broad range of wavelength; (3) According to the selected photospheric and chromospheric lines, the measurement can be focused on either linear polarization or circular polarization; (4) The polarimeter has a loose tolerance on the manufacturing technology of polarimetric elements and installation errors. All this makes this polarimeter become a high-performance polarimetric device.

Confinement effects on valence-subband character and polarization anisotropy in (112¯2) semipolar InGaN/GaN quantum wells

We perform self-consistent Schrödinger-Poisson simulations on (112¯2) In-GaN/GaN quantum wells (QW). By solving the 6 × 6 k·p Hamiltonian, including strain and polarization fields, we study the separation, ordering, and wavefunction character of the topmost valence bands in the QW and their dependence on In composition and QW width. Our results show that quantum confinement has only slight effects on the ordering and the character of the valence states and therefore cannot be the cause of the experimentally observed optical polarization switching. Instead, the switching may be due to the inhomogeneous strain distribution in (112¯2) InGaN films with high In composition.

Optically switchable all-fiber optic polarization rotator

This study demonstrates an all-fiber optical polarization rotator and switch based on a side-polished fiber (SPF) overlaid with a photoresponsive liquid crystal (LC) containing a nematic LC and a photosensitive azobenzene molecule. The trans-cis photoisomerization of azobenzene modulates the overlaid LC's birefringence, changes the refractive index (RI) of the photoresponsive LC-overlaid SPF, and further controls and switches the phase retardation. This design achieves a 10° phase shift under switching time of less than 1 s. The demonstration has potential for an optically tunable in-line 2 × 2 fiber-optic switch or microstructured fiber-based photonic device controlled by the polarization of light.

Spectral properties of polarized light from semipolar grown InGaN quantum wells at low temperatures

AbstractThe polarization dependent photoluminescence at low temperatures of strained semipolar and nonpolar InGaN quantum wells was studied as a function of the emission wavelength. We found for semipolar QWs that the maximum of the spectral resolved optical polarization is either red‐ or blue‐shifted with respect to the maximum of the emission.In contrast, the nonpolar emission exhibits no clear maximum. We assign all effects to an inhomogeneous broad‐ ening of the emission caused by indium fluctuations and explain this behavior here in the light of the optical polarization switching. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

On the optical polarization properties of semipolar InGaN quantum wells

Polarized photoluminescence of strained quantum wells grown on c–plane, semipolar (101−2), (112−2), (101−1), (202−1) planes, and nonpolar GaN substrates was studied experimentally and in theory. The observed optical polarization switching between the substrate orientations (101−2) and (112−2) is in accordance with our general model of polarization switching, based on a k→·p→ model of arbitrary substrate orientation. Spectrally resolved measurements of the polarization degree stemming from (101−2) samples show that the maximum of the polarization degree is red–shifted with respect to the maximum of the photoluminescence intensity. We ascribe this effect to an increased polarization of the transitions for higher indium content.

Highly Integrated InGaN/GaN Semipolar Micro-Pyramid Light-Emitting Diode Arrays by Confined Selective Area Growth

We report on the fabrication of highly integrated semipolar {101} GaN micro-pyramid light-emitting diode (LED) arrays on a c-plane sapphire substrate obtained via confined selective area growth (SAG). The cathodoluminescence (CL) revealed that the micro-pyramid arrays were under a severe local strain and potential fluctuations were observed depending on the location of the pyramid facets. The emissive region in the micro-pyramid facets was also found to be different in the monochromatically captured CL images. Furthermore, the electroluminescence (EL) of the micro-pyramid LED arrays had a palpable emissive spectra for high indium composition compared to c-plane LEDs, and optical polarization switching was also observed.

Abnormal polarization switching phenomenon in a-plane AlxGa_1-xN

The optical polarization properties of a-plane AlxGa(1-)xN films have been investigated by polarization-dependent photoluminescence (PL). The degree of polarization decreased with increasing the Al composition, and the main optical polarization direction switched from ε ⊥ cto ε // c at about x = 0.07 due to the valence band switching, representing that the optical transition energy of ε // c is surpassing that of ε ⊥ c. However, with the Al composition larger than x = 0.1, the higher energy optical transitions of ε // cexhibited the stronger PL intensity, opposite to the normal situations that higher energy states commonly have weaker PL intensity than the lower energy states. We utilized the 6 × 6 k.p model and the lambertian-like radiation pattern assumption to explain this abnormal optical polarization switching behavior in the a-plane AlxGa(1-)xN layers and obtained good agreement with the experimental results.

Optical Anisotropy Control of Non-c-plane InGaN Quantum Wells

A method to control the optical polarization of non-c-plane InGaN quantum wells (QWs) is proposed. Firstly, it is described the numerical and analytical solutions of the valence band eigenenergies and eigenfunctions for non-c-plane nitride semiconductors. It is found that anisotropic strain dominates optical anisotropy due to the small spin–orbit interaction and the large lattice mismatch. Subsequently, it is introduced the InGaN/AlGaN QW structure instead of the InGaN/GaN QW in order to manipulate the eigenenergies of the two topmost valence bands. This resulted in optical polarization switching. We conclude with a discussion of relevant computational results.

Environmentally stable nonlinear optical polarization switching by using a nonreciprocal all‐optical circuit

AbstractWe proposed and demonstrated a stable nonlinear optical polarization self‐switching based on nonreciprocal nonlinear phase shift induced by self‐phase modulation in optical fiber. The polarization self‐switching was achieved at input power levels of around 10 mW in a nonreciprocal circuit using Faraday rotator mirrors. This nonlinear polarization switching is quite stable against polarization fluctuation caused by environmental perturbation. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2056–2059, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24548

Polarization switching phenomena in semipolarInxGa1−xN/GaNquantum well active layers

We report the observation of optical polarization switching in ${\text{In}}_{x}{\text{Ga}}_{1\ensuremath{-}x}\text{N}/\text{GaN}$ quantum well active layers, using semipolar ${11\overline{2}2}$ planes. When the In composition is less than $\ensuremath{\sim}30%$, the emissions related to the top and second valence bands are polarized along the $[1\overline{1}00]$ and perpendicular $[\overline{1}\overline{1}23]$ directions, respectively, similar to earlier studies. On the contrary, as the In composition increases above 30%, the polarizations switch, indicating a crossover between the two valence bands. Because the polarization degree is less sensitive to the well width, the observed polarization switch is ascribed to the InN deformation potentials.