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International audience; We present the diffraction of unpolarized light over a broad wavelength range using paratellurite Acousto-Optic Tuneable Filters. The diffraction of unpolarized light usually relies on a specific operating point that is sensitive to the wavelength and angle of incidence, resulting in an operating ability over a narrow bandwidth. We present a detuning strategy to eliminate the angular dependence and obtain equal diffraction efficiency for both the linear polarization states over a broad bandwidth. We explain how to find the optimum operating frequency and present its dependency as a function of the wavelength. With the quasi-phase matching condition presented, the diffraction of unpolarized light over the 400 nm to700 nm band is possible with an efficiency of over 80%.

In this study, we proposed an innovative concept of integrating a polarized color-separating backlight with a color-filter-free LC panel for enhancing performance of the curved LCD system. We design a two-level folded backlight to exploit the light sources LEDs with color enhancement by quantum-dot technology to produce color beams emerging at separate angles with a linearly polarizing state. The integrated LC panel focuses the separating color beams onto the corresponding subpixels with no need of the color filter; redirects the color beams at respective angles into the normal and reforms their angular shapes to be identical for attaining good color uniformity in the viewing cone. We established a system model for simulation to evaluate its performance. According to the simulation results, it performs the high optical efficiency of 33.75% that is about four times the traditional LCD, and displays color gamut of 94.1% NTSC (CIE 1931). It also provides the illuminance uniformity of 90% above and good color uniformity in both the spatial space and angular space of the viewing cone with horizontal and vertical angular widths of 100o and 75o, respectively. Furthermore, the simulation results demonstrate that the design can apply to a 55-inch curved LCD and further extend the maximum diagonal size up to 88 inches while keeping slim volume with a minimal thickness of 6.5 mm.

The properties of polarization-selective, light-guiding systems upon subwavelength nanogratings formation in the case of type II refractive index traces induced by femtosecond laser pulses in bulk fused silica were studied. Polarization-dependent scattering is analyzed both in simulation using a finite-difference, time-domain method and in experiments. We argue that the polarization-sensitive optical guiding of type II waveguides is due to polarization-dependent scattering of nanogratings. Optical designs can then be suggested where the guiding efficiency of type I traces can be combined with type II anisotropies. A low-loss waveguide polarizer is demonstrated based on the modulation of the evanescent field emerging from type I waveguides using polarization-dependent scattering of neighboring nanogratings.

Radial polarization converters can convert an incident light into a radially polarized light, which is beneficial in a variety of applications. In this paper, a new design of holographic radial polarization converter is proposed which consists of eight space-variant polarization-selective volume hologram gratings. According to the coupled wave theory, a feasible design of the polarization-selective volume hologram gratings was described. The prism-hologram-prism sandwiched recording method was adopted for the recording. The s- and p-polarization diffraction efficiencies of the fabricated polarization-selective volume hologram gratings at 443.29 nm are 90.83% and 22.09%, respectively. The operation bandwidth is about 4.42 nm. A prototype of holographic radial polarization converter was successfully assembled and tested. Due to the introduction of volume hologram gratings, this design should have the advantages of high diffraction efficiency, narrow band, compactness, and planar configuration, meaning it is especially suitable for low-cost mass production and has high application potential in related fields.

A design rule for a Mach-Zehnder interferometer (MZI) sensor is presented, allowing tunable sensitivity by appropriately choosing the MZI arm lengths according to the formula given in this paper. The present MZI sensor designed by this method can achieve an ultra-high sensitivity, which is much higher than any other traditional MZI sensors. An example is given with silicon-on-insulator (SOI) nanowires and the device sensitivity is as high as 106 nm/refractive-index -unit (or even higher), by choosing the MZI arms appropriately. This makes it possible for one to realize a low-cost optical sensing system with a detection limit as high as 10&minus, 6 refractive-index-unit, even when a cheap optical spectrum analyzer with low-resolution (e.g., 1 nm) is used for the wavelength-shift measurement.

We investigate theoretically and experimentally the beam shifts of a Gaussian beam reflected by an air-glass interface at Brewster incidence. For a linearly polarized incident beam, the reflected beam will undergo a spatial spin splitting within the plane of incidence. This spin splitting is up to 83 μm when the incident beam waist is 90 μm. Additionally, the reflected beam will be deflected along the direction perpendicular to the incident plane, i.e., undergo an angular shift. The maximum angular shift has been theoretically predicted and experimentally confirmed. Both the spatial spin splitting and angular shift can be controlled by the incident polarization state. These controllable giant beam shifts have potential applications in the design of spin-photonic devices and the optical sensing.

We propose and experimentally demonstrate a broadband polarization beam splitter on the silicon-on-insulator platform using the concept of multimode interference. The angle between the input waveguide and the multimode interferometer (MMI) was optimized in order to extract the images corresponding to the fundamental transverse electric (TE) and transverse magnetic (TM) polarizations from a single, compact MMI. By changing the direction of propagation, the input angle enabled the addition of a parallelepiped to facilitate exclusively TM collection above the MMI, therefore eliminating the need to cascade successive MMIs. The MMI was tapered to improve coupling at the ports. The design allowed for a compact geometry with a length of 67.5 μm and width of 4 μm, while maintaining a feature size comparable to the waveguide width. The design was experimentally characterized over 72 parameter variations, including input angle, output TM and TE port positions, and bend radius of the output TE waveguide. The performance was consistent over the 100 nm wavelength range of 1500-1600 nm, with an average insertion loss of 2 dB. The device maintained an extinction ratio of at least 13.96 and 11.45 dB in the C-band for the TE and TM polarizations, respectively.

We present the design of a porous-core PCF with elliptical holes in the core that achieved low loss, high birefringence, and flattened dispersion for guiding terahertz waves. The finite element method is used to study the properties of the designed waveguide in detail: effective material loss, birefringence, confinement losses, and dispersion. Simulation results show that the proposed structure exhibits simultaneously high modal birefringence of $1.32 \times 10 ^{-2}$ and a flattened dispersion over a broadband of 1.28 THz. Then, polarization splitters, based on both symmetric and asymmetric porous-core PCF structures, are designed and evaluated at 1 THz. We show that this kind of device exhibits a strong polarization-dependent coupling behavior. Numerical results show that the configuration based on dual-core waveguide with asymmetric cores can achieve a 10.9 cm long splitter with a broadband of 0.306 THz for x -polarization and 0.23 THz for y -polarization. Finally, this paper offers an effective method to design an ultrawideband polarization beam splitter to operate in the THz region, which might be relevant for future applications in technical areas, such as spectroscopy, sensing, and high-speed data transmission.

Polarization-beam-splitters with both broadband operation window and high extinction ratio are highly desirable in optical communication systems. In this paper, a compact noncascaded-directional-couplers PBS with an ultrahigh extinction ratio and low excess loss is proposed. The PBS utilizes an asymmetrical directional coupling structure consisted of a TE-pass-polarizer waveguide and a TE- and TM-pass waveguide. The simulation results show that the extinction ratio is up to 35.41 dB and the excess loss is only 0.11 dB around the central wavelength 1550 nm for both polarizations (TE and TM). Meanwhile, when the extinction ratio is 30, 25, and 20 dB, the corresponding bandwidth is 72, 145, and 188 nm, respectively. Also, the EL is 1 and 0.5 dB in a bandwidth of ∼73 and ∼48 nm, respectively. A fabrication tolerance of ±10 nm for the waveguide width is also achieved.

Polarization sensitive optical coherence tomography (PS-OCT) operating at 840 nm with axial resolution of 3.8 µm in tissue was used for investigating the posterior rat eye during an acute intraocular pressure (IOP) increase experiment. IOP was elevated in the eyes of anesthetized Sprague Dawley rats by cannulation of the anterior chamber. Three dimensional PS-OCT data sets were acquired at IOP levels between 14 mmHg and 105 mmHg. Maps of scleral birefringence, retinal nerve fiber layer (RNFL) retardation and relative RNFL/retina reflectivity were generated in the peripapillary area and quantitatively analyzed. All investigated parameters showed a substantial correlation with IOP. In the low IOP range of 14-45 mmHg only scleral birefringence showed statistically significant correlation. The polarization changes observed in the PS-OCT imaging study presented in this work suggest that birefringence of the sclera may be a promising IOP-related parameter to investigate. Published version

In this work, the performance of a Mach&ndash, Zehnder interferometer manufactured in silicon nitride with a liquid crystal cladding is studied. The device consists of two multi-mode interference couplers linked by two rectangular waveguides, the cladding of one of which is a liquid crystal. The structure demonstrates the potential of using liquid crystals as tunable cladding material in simple waveguides as well as in more complex coupling or modulating structures. Liquid crystal cladding permits a local fine-tuning of the effective refractive index of the waveguide, avoiding coarse global temperature control. The study is realized in the visible region (632.8 nm), for its intrinsic interest region in (bio-)sensing or metrology.

This thesis is devoted to develop tunable devices on the base of one-dimensional photonic crystals (1DPhC) which can sustain Bloch surface waves (BSWs).First, we explore the possibilities to control the BSW propagation direction with polarization of incident light. In this case we manufacture additional passive structures such as gratings on the top of the 1DPhC, which are working both as a BSW launcher and polarization–controlled “wave-splitters”. We test this type of launcher in air and in water as an external medium. Then, we demonstrate the tunability of the BSW by adding an active layers into the multilayer stack. Here a crystalline X-cut thin film lithium niobate (TFLN) is used to introduce anisotropic properties to the whole 1DPhC. Different ways to manufacture 1D PhCs with LiNbO3 on the top would be described. Finally, we explore the concept of the electro-optically tuned BSW.; Cette thèse est consacrée au développement de dispositifs accordables sur la base de cristaux photoniques unidimensionnels qui peuvent supporter des ondes de surface de Bloch (BSW). Tout d'abord, nous explorons les possibilités de contrôler la direction de propagation des BSW par le biais de la polarisation de la lumière incidente. Dans ce cas, nous gravons sur le dessus du cristal photonique 1D des structures passives de type réseau, qui permettent à la fois de coupler la lumière incidente aux BSWs et de se comporter comme une lame séparatrice ultracompacte contrôlée par la polarisation lumineuse. Nous avons testé ce type de coupleur sur des cristaux photoniques 1D fonctionnant dans l’air et dans l’eau. Ensuite, nous démontrons l'accordabilité des BSWs en ajoutant une fine couche active dans la structure photonique multicouche. Il s’agit d’un film mince de niobate de lithium monocristallin qui permet d’introduire des propriétés anisotropes dans le cristal photonique 1D. Différentes façons de fabriquer des cristaux photoniques 1D contenant du niobate de lithium monocristallin ont été développées dans le cadre de ce travail. Ces travaux nous ont permis d’explorer le concept de contrôle électro-optique des BSWs.

This thesis is devoted to develop tunable devices on the base of one-dimensional photonic crystals (1DPhC) which can sustain Bloch surface waves (BSWs).First, we explore the possibilities to control the BSW propagation direction with polarization of incident light. In this case we manufacture additional passive structures such as gratings on the top of the 1DPhC, which are working both as a BSW launcher and polarization–controlled “wave-splitters”. We test this type of launcher in air and in water as an external medium. Then, we demonstrate the tunability of the BSW by adding an active layers into the multilayer stack. Here a crystalline X-cut thin film lithium niobate (TFLN) is used to introduce anisotropic properties to the whole 1DPhC. Different ways to manufacture 1D PhCs with LiNbO3 on the top would be described. Finally, we explore the concept of the electro-optically tuned BSW.; Cette thèse est consacrée au développement de dispositifs accordables sur la base de cristaux photoniques unidimensionnels qui peuvent supporter des ondes de surface de Bloch (BSW). Tout d'abord, nous explorons les possibilités de contrôler la direction de propagation des BSW par le biais de la polarisation de la lumière incidente. Dans ce cas, nous gravons sur le dessus du cristal photonique 1D des structures passives de type réseau, qui permettent à la fois de coupler la lumière incidente aux BSWs et de se comporter comme une lame séparatrice ultracompacte contrôlée par la polarisation lumineuse. Nous avons testé ce type de coupleur sur des cristaux photoniques 1D fonctionnant dans l’air et dans l’eau. Ensuite, nous démontrons l'accordabilité des BSWs en ajoutant une fine couche active dans la structure photonique multicouche. Il s’agit d’un film mince de niobate de lithium monocristallin qui permet d’introduire des propriétés anisotropes dans le cristal photonique 1D. Différentes façons de fabriquer des cristaux photoniques 1D contenant du niobate de lithium monocristallin ont été développées dans le cadre de ce travail. Ces travaux nous ont permis d’explorer le concept de contrôle électro-optique des BSWs.

A new type of metalens with the capability to selectively focus narrowband light is reported at different focal planes depending on polarization. Two zone planes with two different focal lengths are spatially multiplexed and encoded in the subwavelength regime with arrays of orthogonal silver nanostructures, which are designed to exhibit strong wavelength- and polarization-dependent scattering profiles. Using this principle, imaging under white-light illumination with independent focal planes is experimentally demonstrated for each polarization at the narrowband resonant wavelength. Furthermore, each focal plane can be dynamically controlled with an output polarizer. In contrast to conventional refractive and diffractive optical elements, functional metalenses allow additional control over wavelength and polarization properties of light for a wide range of applications.

RF Ministry of Education and Science, RF President's grants for support of young candidates of science (MK-9019.2016.2) and leading scientific schools (NSh-9498.2016.9), and RFBR grants ## 15-07-01174, 15-37-20723, 15-47-02492, 16-29-11698, the European Research Council (ERC) under the European Union's Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement n°337508, Federal Agency for Scientific Organizations. We designed, fabricated, and characterized a thin metalens in an amorphous silicon film of diameter 30 µm, focal length equal to the incident wavelength 633 nm. The lens is capable of simultaneously manipulating the state of polarization and phase of incident light. The lens converts a linearly polarized beam into radially polarized light, producing a subwavelength focus. When illuminated with a linearly polarized Gaussian beam, the lens produces a focal spot whose size at full-width half-maximum intensity is 0.49λ and 0.55λ (λ is incident wavelength). The experimental results are in good agreement with the numerical simulation, with the simulated focal spot measuring 0.46λ and 0.52λ. This focal spot is less than all other focal spots obtained using metalenses. Postprint

Wire-grid polarizers constitute a traditional component for the control of polarization in free-space devices that operate in a broad part of the electromagnetic spectrum. Here, we present an aluminium-based THz wire grid polarizer, fabricated on a sub-wavelength thin flexible and conformal foil of Zeonor polymer having a thickness of 40um. The fabricated device,characterized by means of THz time-domain spectroscopy, exhibitsa high extinction ratio between 30 and 45dB in the 0.3-2.1THz range. The insertion losses oscillate between 0 and 1.1dB andthey stemalmost exclusively from moderate Fabry-Perot reflections and it is engineered forvanishing at 2THz for operation with quantum cascade lasers. Full Text: PDF References I. F. Akyildiz, J. M. Jornet, C. Han, "Terahertz band: Next frontier for wireless communications", Phys. Commun. 12, 16 (2014). CrossRef M.C. Kemp, P.F. Taday, B.E. Cole, J.A. Cluff, A.J. Fitzgerald, W.R. Tribe, "Security applications of terahertz technology", Proc. SPIE 5070, 44 (2003). CrossRef M. Schirmer, M. Fujio, M. Minami, J. Miura, T. Araki, T. Yasui, "Biomedical applications of a real-time terahertz color scanner", Biomed. Opt. Express 1, 354 (2010). CrossRef R.P. Cogdill, R.N. Forcht, Y. Shen, P.F. Taday, J.R. Creekmore, C.A. Anderson, J.K. Drennen, "Comparison of Terahertz Pulse Imaging and Near-Infrared Spectroscopy for Rapid, Non-Destructive Analysis of Tablet Coating Thickness and Uniformity", J. Pharm. Innov. 2, 29 (2007). CrossRef Y.-C. Shen, "Terahertz pulsed spectroscopy and imaging for pharmaceutical applications: A review", Int. J. Pharm. 417, 48(2011). CrossRef A.G. Davies, A.D. Burnett, W. Fan, E.H. Linfield, J.E. Cunningham, "Terahertz spectroscopy of explosives and drugs", Mater. Today 11, 18 (2008). CrossRef J.F. Federici, B. Schulkin, F. Huang, D. Gary, R. Barat, F. Oliveira, D. Zimdars, "THz imaging and sensing for security applications?explosives, weapons and drugs", Semicond. Sci. Technol. 20, S266 (2005). CrossRef D. Saeedkia, Handbook of Terahertz Technology for Imaging, Sensing and Communications (Elsevier, 2013). N. Born, M. Reuter, M. Koch, M. Scheller, "High-Q terahertz bandpass filters based on coherently interfering metasurface reflections", Opt. Lett. 38, 908 (2013). CrossRef A. Ferraro, D.C. Zografopoulos, R. Caputo, R. Beccherelli, "Periodical Elements as Low-Cost Building Blocks for Tunable Terahertz Filters", IEEE Photonics Technol. Lett. 28, 2459 (2016). CrossRef A. Ferraro, D.C. Zografopoulos, R. Caputo, R. Beccherelli, "Broad- and Narrow-Line Terahertz Filtering in Frequency-Selective Surfaces Patterned on Thin Low-Loss Polymer Substrates", IEEE J. Sel. Top. Quantum Electron. 23 (2017). CrossRef B. S.-Y. Ung, B. Weng, R. Shepherd, D. Abbott, C. Fumeaux, "Inkjet printed conductive polymer-based beam-splitters for terahertz applications", Opt. Mater. Express 3, 1242 (2013). CrossRef J.-S. Li, D. Xu, J. Yao, "Compact terahertz wave polarizing beam splitter", Appl. Opt. 49, 4494 (2010). CrossRef K. Altmann, M. Reuter, K. Garbat, M. Koch, R. Dabrowski, I. Dierking, "Polymer stabilized liquid crystal phase shifter for terahertz waves", Opt. Express 21, 12395 (2013). CrossRef D.C. Zografopoulos, R. Beccherelli, "Tunable terahertz fishnet metamaterials based on thin nematic liquid crystal layers for fast switching", Sci. Rep. 5, 13137 (2015). CrossRef G. Isic, B. Vasic, D. C. Zografopoulos, R. Beccherelli, R. Gajic, "Electrically Tunable Critically Coupled Terahertz Metamaterial Absorber Based on Nematic Liquid Crystals", Phys. Rev. Appl. 3, 064007 (2015). CrossRef K. Iwaszczuk, A.C. Strikwerda, K. Fan, X. Zhang, R.D. Averitt, P.U. Jepsen, "Flexible metamaterial absorbers for stealth applications at terahertz frequencies", Opt. Express 20, 635 (2012). CrossRef F. Yan, C. Yu, H. Park, E.P.J. Parrott, E. Pickwell-MacPherson, "Advances in Polarizer Technology for Terahertz Frequency Applications", J. Infrared Millim. Terahertz Waves 34, 489 (2013). CrossRef http://www.tydexoptics.com DirectLink K. Imakita, T. Kamada, M. Fujii, K. Aoki, M. Mizuhata, S. Hayashi, "Terahertz wire grid polarizer fabricated by imprinting porous silicon", Opt. Lett. 38, 5067 (2013). CrossRef A. Isozaki, et al., "Double-layer wire grid polarizer for improving extinction ratio", Solid-State Sens. Actuators Microsyst. Transducers Eurosensors XXVII 2013 Transducers Eurosensors XXVII 17th Int. Conf. On, IEEE, pp. 530?533 (2013). DirectLink A. Ferraro, D. C. Zografopoulos, M. Missori, M. Peccianti, R. Caputo, R. Beccherelli, "Flexible terahertz wire grid polarizer with high extinction ratio and low loss", Opt. Lett. 41, 2009(2016). CrossRef M.S. Vitiello, G. Scalari, B. Williams, P.D. Natale, "Quantum cascade lasers: 20 years of challenges", Opt. Express 23, 5167(2015). CrossRef A. Podzorov, G. Gallot, "Low-loss polymers for terahertz applications", Appl. Opt. 47, 3254(2008). CrossRef

Funding: Russian Foundation for Basic Research (RFBR) (14-29-07133, 14-07-97039, 15-07-01174, 15-47-02492, 15-37-20723, 16-07-00990, 16-47-630483); Ministry of Education and Science of the Russian Federation (NSh-4128.2016.9, MK-9019.2016.2); European Research Council (337508). We have investigated a four-Sector transmission Polarization Converter (4-SPC) for a wavelength of 633 nm, that enables the conversion of a linearly polarized incident beam into a mixture of linearly and azimuthally polarized beams. It was numerically shown that by placing a Fresnel zone plate of focal length 532 nm immediately after the 4-SPC, the incident light can be focused into an oblong subwavelength focal spot whose size is smaller than the diffraction limit (with width and breadth, respectively, measuring FWHM = 0.28λ and FWHM = 0.45λ, where λ is the incident wavelength and FWHM stands for full-width at half maximum of the intensity). After passing through the 4-SPC, light propagates in free space over a distance of 300 μm before being focused by a Fresnel zone plate (ZP), resulting in focal spot measuring 0.42λ and 0.81λ. The focal spot was measured by a near-field microscope SNOM, and the transverse E-field component of the focal spot was calculated to be 0.42λ and 0.59λ. This numerical result was verified experimentally, giving a focal spot of smaller and larger size, respectively, measuring 0.46λ and 0.57λ. To our knowledge, this is the first implementation of polarization conversion and subwavelength focusing of light using a pair of transmission micro-optic elements. Postprint

The design, fabrication, and characterization of a polarization-dependent normal incident quantum cascade detector coupled via complementary split-ring metamaterial resonators in the infrared regime are presented. The metamaterial structure is designed through three-dimensional finite-difference time-domain method and fabricated on the top metal contact, which forms a double-metal waveguide together with the metallic ground plane. With normal incidence, significant enhancements of photocurrent response are obtained at the metamaterial resonances compared with the 45° polished edge coupling device. The photocurrent response enhancements exhibit clearly polarization dependence, and the largest response enhancement factor of 165% is gained for the incident light polarized parallel to the split-ring gap.

A compact and ultrabroadband polarization beam splitter (PBS) utilizing a hybrid plasmonic Y-branch (HPYB) on a silicon-on-insulator (SOI) platform is proposed and numerically demonstrated. The HPYB consists of a vertical hybrid plasmonic waveguide (HPW) and a horizontal HPW formed by silicon (Si) and silver (Ag) strip waveguides sandwiched with a silicon dioxide (SiO2) layer, in which the vertical and horizontal hybrid plasmonic modes (HPMs) are excited by the input transverse electric (TE) and transverse magnetic (TM) modes, respectively. The HPMs are split into different ports and coupled back to TE and TM modes to implement the polarization splitting function. A simplified and compact HPYB is robust for the HPMs' generation. The structure is wavelength insensitive since the HPMs' excitation is weakly correlated to the optical wavelengths. The simulation results show that the HPYB-based PBS has a compact footprint of $5 \times 1.8\ \mu\text{m}^2$ and an ultralarge working bandwidth of 285 nm, with the polarization crosstalk < −10 dB and the worst-case TE (TM) mode insertion loss of −1.53 (−2.35) dB. The device also exhibits a large fabrication tolerance of 210-nm variation (from −100 to 110 nm) to the waveguide width for both polarizations.

A transflective nano-wire grid polarizer is fabricated on a single mode fiber tip by focused ion beam machining. In contrast to conventional absorptive in-line polarizers, the wire grids reflect TE-mode, while transmitting TM-mode light so that no light power is discarded. A reflection contrast of 13.7 dB and a transmission contrast of 4.9 dB are achieved in the 1,550 nm telecom band using a 200-nm wire grid fiber polarizer. With the help of an optic circulator, the polarization states of both the transmissive and reflective lights in the fiber may be monitored simultaneously. A kind of robust fiber optic sensor is thus proposed that could withstand light power variations. To verify the idea, a fiber pressure sensor with the sensitivity of 0.24 rad/N is demonstrated. The corresponding stress-optic coefficient of the fiber is measured. In addition to pressure sensing, this technology could be applied in detecting any polarization state change induced by magnetic fields, electric currents and so on.

We demonstrate a simple, scalable fabrication method for producing large-area arrays of vertically stacked metallic micro-rings, embedded in a deformable polymer sheet. Unusual polarisation-dependent hotspots are found to dominate the reflection images. To understand their origin, the arrays are characterized using point-scanning optical spectroscopy and directly compared to numerical simulations. Individual ring stacks act as microlenses, while polarisation-dependent hotspots arise at the connections between neighbouring stacks, which are comprised of parabolically-arranged parallel gold nanowires. The elastomeric properties of the polymer host opens the door to active control of the optics of this photonic material, through dynamic tuning of the nanowire spacings and array geometry.

A 1×2 optical router based on an achromatic liquid crystal polarization rotator has been designed and experimentally tested. The router can work in the spectral range used in step-index polymer optical fiber networks (400-700 nm) with low wavelength and temperature dependences. The theoretical design is fast and simple and has good agreement with experimental results. Experimental crosstalk is lower than -18.68 dB for both outputs, even with thermal variations of 10 °C. Performance improvement with respect to previously reported devices with similar structure has also been analyzed. This paper was supported by the Spanish Economy and Education Ministries through grants (Refs.TEC2012-37983-C03-02 and PRX12/00007). Publicado

Optical sources with highly temperature-stable output intensity and low power consumption are desired in portable devices for metrology, and in medical applications, communications, and illumination. This paper introduces and demonstrates an optical stabilization scheme that uses the drift in peak-emission wavelength of light emitted from an LED as a temperature feedback signal to realize output intensity temperature coefficients below 100 ppm/K. The control principle relies on a conventional feedback loop but with a specially designed weakly polarizing optical interference coating that exhibits different transmittivity/reflectivity ratio dependence on wavelength for two different polarizations and by using a weighted sum of two polarizations as the output power correcting signal in a feedback loop. The method does not need a thermometer or temperature control stage, and its calibration can be performed electronically, adding to the simplicity of the design and making it also suitable for portable and battery-operated instruments.

A hybrid waveguiding structure has been fabricated in a z-cut lithium tantalate (LiTaO3) crystal wafer by direct femtosecond laser writing. Due to the laser-induced anisotropic modifications of the extraordinary and ordinary refractive indices (ne and no) of LiTaO3 crystal, the structure exhibits polarization-sensitive guiding features along vertical and horizontal orientations. Based on this feature, circularly-polarized light beam can be converted to vertically-/horizontally-polarized ones (i.e., TE and TM), with approximately 1:1 power splitting ratio. The well-guided performance of the polarization-sensitive structure shows the potential for integration with existing light signals to realize all-optical information processing., The work is supported by the National Natural Science Foundation of China (No. 11274203), Junta de Castilla y León under project SA086A12-2, and Ministerio de Economía y Competitividad (under project FIS2013-44174-P), Spain.

Depolarization of light can be measured by polarization-sensitive optical coherence tomography (PS-OCT) and has been used to improve tissue discrimination as well as segmentation of pigmented structures. Most approaches to depolarization assessment for PS-OCT – such as the degree of polarization uniformity (DOPU) – rely on measuring the uniformity of polarization states using spatial evaluation kernels. In this article, we present a different approach which exploits the spectral dimension. We introduce the spectral DOPU for the pixelwise analysis of polarization state variations between sub-bands of the broadband light source spectrum. Alongside a comparison with conventional spatial and temporal DOPU algorithms, we demonstrate imaging in the healthy human retina, and apply the technique for contrasting hard exudates in diabetic retinopathy and investigating the pigment epithelium of the rat iris.

An all-polymer photonic crystal slab sensor is presented, and shown to exhibit narrow resonant reflection with a FWHM of less than 1 nm and a sensitivity of 31 nm/RIU when sensing media with refractive indices around that of water. This results in a detection limit of 4.5x10-6 RIU when measured in conjunction with a spectrometer of 12 pm/pixel resolution. The device is a two-layer structure, composed of a low refractive index polymer with a periodically modulated surface height, covered with a smooth upper-surface high refractive index inorganic-organic hybrid polymer modified with ZrO2-based nanoparticles. Furthermore, it is fabricated using inexpensive vacuum-less techniques involving only UV nanoreplication and polymer spin-casting, and is thus well suited for single-use biological and refractive index sensing applications.

In this paper, a tunable polarization-dependent terahertz (THz) metamaterial absorber based on liquid crystal (LC) is presented. The measurement results show that absorption peak is at 239.5 GHz for a TE-polarized wave and 306.6 GHz for a TM-polarized wave, without exerting the bias voltage on the LC layer. An increase in bias voltage affects the orientation of LC molecules and causes redshifted resonant frequencies. By adjusting the bias voltage from 0 to 10 V, frequency tunabilities of 4.7% and 4.1% for TE- and TM-polarized waves, respectively, were experimentally demonstrated. Surface current and power loss distribution was analyzed to explain the physical mechanism of the absorber, while the absorption dependence on geometrical parameters and incident angles was also studied in detail. According to the obtained results, the proposed absorber is shown here to be capable of achieving tunable polarization-dependent absorption, and to have potential application in terahertz polarization imaging, terahertz sensing, and polarization multiplexing.

A novel ultracompact (8 mu m length) hybrid silicon-plasmonic TM-TE converter is reported. The conversion is achieved during a partial power coupling between a waveguide and a hybrid plasmonic parallel waveguide. The impact of different types of metals is also analyzed. At a wavelength of 1.55 mu m, the device has an extinction ratio (ER) of 27.6 dB and insertion loss (IL) of 1.75 dB. Furthermore, an optical bandwidth as large as 100 nm is achieved with ERs higher than 25 dB and ILs below 2 dB. (C) 2013 Optical Society of America, The authors acknowledge funding from TEC2012-38540 LEOMIS and PROMETEO-2010-087. L. Sanchez also acknowledges the Generalitat Valenciana for funding his grant in the context of the VALi+d program.

In this paper, a theoretical model for an Interleave-Chirped Arrayed Waveguide Grating (IC-AWG) is presented. The model describes the operation of the device by means of a field (amplitude and phase) transfer response. The validation of the model is accomplished by means of simulations, using parameters from previously fabricated devices. A novel design procedure is derived from the model, and it is later on employed to demonstrate the design of colorless universal IC-AWGs. The model can be readily applied to the analysis and design of future multi-wavelength optical coherent communications receivers and optical waveform analyzers., The authors acknowledge financial support by the Spanish MICINN Project TEC2010-21337, acronym ATOMIC; project FEDER UPVOV10-3E-492 and project FEDER UPVOV08-3E-008. B. Gargallo acknowledges financial support through FPI grant BES-2011-046100.

International audience; We present the fabrication of single-mode polymer waveguides featuring both isotropic and anisotropic sections on the same substrate. The core of the waveguide is made of a polymerizable liquid crystal, which is thermally patterned into isotropic and anisotropic regions before etching. Simulation is performed in order to design polarization-separating couplers. The technological fabrication is then presented as well as a first realization

A simple and ultra-compact integrated optical vortex beam receiver device is\ud presented. The device is based on the coupling between the optical vortex modes and\ud whispering gallery modes in a micro-ring resonator via embedded angular gratings, which\ud provides the selective reception of optical vortex modes with definitive total angular\ud momentum (summation of spin and orbital angular momentum) through the phase matching\ud condition in the coupling process. Experimental characterization confirms the correct\ud detection of the total angular momentum carried by the vortex beams incident on the device.\ud In addition, photonic spin-controlled unidirectional excitation of whispering-gallery modes in\ud the ring receiver is also observed, and utilized to differentiate between left- and right-circular\ud polarizations and therefore unambiguously identify the orbital angular momentum of incident\ud light. Such characteristics provide an effective mode-selective receiver for the eigen-modes in\ud orbital angular momentum fiber transmission where the circularly polarized OAM modes can\ud be used as data communications channels in multiplexed communications or as photonic\ud states in quantum information applications.

The scattering of a linear wave on an optical event horizon, induced by a cross-polarized soliton, is experimentally and numerically investigated in integrated structures. The experiments are performed in a dispersion-engineered birefringent silicon nanophotonic waveguide. In stark contrast with copolarized waves, the large difference between the group velocity of the two cross-polarized waves enables a frequency conversion almost independent of the soliton wavelength. It is shown that the generated idler is only shifted by 10 nm around 1550 nm over a pump tuning range of 350 nm. Simulations using two coupled full vectorial nonlinear SchrAND, SCOPUS: ar.j, info:eu-repo/semantics/published

International audience; An experimental snapshot Mueller matrix polarimeter based on wavelength polarization coding is used to get a time-resolved description of electric-field-induced fast transition within a ferroelectric liquid-crystal cell. The parameters extracted from experimental Mueller matrices are linked to the molecule director distribution to further determine the average trajectory and the collective behavior of these molecules while they switch over to another state.

We present a tunable optical delay line based on the use of a single chirped fiber Bragg grating written into a standard single mode optical fiber. In the proposed scheme, the delay is induced through the Bragg grating differential group delay curve. This is achieved by launching orthogonally polarized optical pulses in both directions into the Bragg grating and by controlling its local birefringence. This bidirectional propagation allows to compensate the second-order dispersion. The setup is suitable to delay pulses with a spectral width just less than the grating reflection bandwidth, which is particularly useful in the context of forthcoming wavelength division multiplexing ultra-high bit rate lightwave systems. In this work, the performances of the setup are investigated using a pulsed laser delivering 6.3 ps Fourier transform limited pulses at 1548 nm. A maximum delay of 120 ps (about 20 times the pulse width) is reported experimentally.

The application of wire grid polarizers as efficient polarizing beam splitters for visible light is studied. The large differences between the transmissivity for different polarizations are explained qualitatively by using the theory of metallic wave guides. The results of rigorous calculations obtained by using the finite element method are compared with experiments for both classical and conical mount. Furthermore the application of wire-grid polarizers in liquid crystal on silicon display systems is considered.

[EN] Vanadium dioxide (VO2) is a metal-insulator transition (MIT) oxide recently used in plasmonics, metamaterials, and reconfigurable photonics. Because of the MIT, VO2 shows great change in its refractive index allowing for ultra-compact devices with low power consumption. We theoretically demonstrate a transverse electric (TE) and a transverse magnetic (TM) pass polarizer with an ultra-compact length of only 1 μm and tunable using the MIT of the VO2. During the insulating phase, both devices exhibit insertion losses below 2 dB at 1550 nm. Changing to the metallic phase, the unwanted polarization is attenuated above 15 dB while insertion losses are kept below 3 dB. Broadband operation over a range of 60 nm is also achieved., This work was supported by the European Commission under project FP7-ICT-2013-11-619456 SITOGA. Financial support from TEC2012-38540 LEOMIS is also acknowledged. L. Sanchez also acknowledges the Generalitat Valenciana for funding his grant in the context of the VALi+d program.

We summarize the progress in the development and application of chiral metamaterials. After a brief review of the salient features of chiral metamaterials, such as giant optical activity, circular dichroism, and negative refractive index, the common method for the retrieval of effective parameters for chiral metamaterials is surveyed. Then, we introduce some typical chiral structures, e.g., chiral metamaterial consisting of split ring resonators, complementary chiral metamaterial, and composite chiral metamaterial, on the basis of the studies of the authors’ group. The coupling effect during the construction of bulk chiral metamaterials is mentioned and discussed. We introduce the application of bianisotropic chiral structures in the field of asymmetric transmission. Finally, we mention a few directions for future research on chiral metamaterials.

Bloch surface waves (BSWs) are recently developing alternative to surface plasmon polaritons (SPPs). Due to dramatically enhanced propagation distance and strong field confinement these surface states can be successfully used in on-chip all-optical integrated devices of increased complexity. In this work we propose a highly miniaturized grating based BSW coupler which is gathering launching and directional switching functionalities in a single element. This device allows to control with polarization the propagation direction of Bloch surface waves at subwavelength scale, thus impacting a large panel of domains such as optical circuitry, function design, quantum optics, etc.