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A novel dual‐core structure based on cyclic olefin copolymer (COC) photonic crystal fiber (PCF) is proposed for realizing Terahertz (THz) polarization beam splitting. The dependence of coupling length and structural parameters of the THz polarization beam splitter (TPBS) is analyzed. The confinement loss, effective material loss, and extinction ratio (ER) are examined. The numerical simulation results show, two orthogonal polarization modes are separated completely within a device length of only 45.16 mm owing to the different coupling length in x‐ and y‐polarization directions. The maximum polarization ER of 107.7 dB is obtained at 0.54 THz. The bandwidth with ER greater than 20 dB reaches 0.02 THz. The proposed compact dual‐core TPBS will find extensive applications in THz photonic systems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

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.

Deep-learning (DL) network has emerged as an important prototyping technology for the advancements of big data analytics, intelligent systems, biochemistry, physics, and nanoscience. Here, we used a DL model whose key algorithm relies on deep neural network to efficiently predict circular dichroism (CD) response in higher-order diffracted beams of two-dimensional chiral metamaterials with different parameters. To facilitate the training process of DL network in predicting chiroptical response, the traditional rigorous coupled wave analysis (RCWA) method is utilized. Notably, these T-like shaped chiral metamaterials all exhibit the strongest CD response in the third-order diffracted beams whose intensities are the smallest, when comparing up to four diffraction orders. Our comprehensive results reveal that by means of DL network, the complex and nonintuitive relations between T-like metamaterials with different chiral parameters (i. e., unit period, width, bridge length, and separation length) and their CD performances are acquired, which owns an ultrafast computational speed that is four orders of magnitude faster than RCWA and a high accuracy. The insights gained from this study may be of assistance to the applications of DL network in investigating different optical chirality in low-dimensional metamaterials and expediting the design and optimization processes for hyper-sensitive ultrathin devices and systems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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.

The asymmetric transmission has fascinated wide interest because of its novel applications. In this paper, we propose and present the design procedure and the simulation results of the tunable dual-band polarization-sensitive graphene chiral metasurface. The resonance wavelength depends on and is controlled by the graphene chemical potential. The two-dimensional chiral response of the structure, circular conversion dichroism (CCD), is tunable and is reached to 0.2. As an application of the tunable chiral structure, a novel tunable polarization-sensitive refractive index sensor with the maximum sensitivities of 7000–10000 nm/RIU is proposed and analyzed. For different kinds of the circularly polarized incident electromagnetic waves, the sensitivities are high and noticeable. This paper exposes a new way to propose other polarization-sensitive structures, such as switches and absorbers in the terahertz (THz) region. In addition, the proposed structure and its application could be useful in polarization-sensitive devices and systems. [ABSTRACT FROM AUTHOR]

A compact, high extinction ratio TM-pass polarizer based on hollow hybrid plasmonic waveguide (HPW) is proposed and investigated. With the optimized tapered structure and plasmonics induced optical confinement, the incident transverse magnetic (TM) mode goes through the hollow HPW with relatively low loss, while the transverse electric (TE) mode is cut-off. For a compact 4 μ m long on-chip TM-pass polarizer, the extinction ratio is as high as 57.7 dB at the central wavelength 1550 nm. Benefiting from the hollow plasmonic structure, the corresponding propagation loss is only 0.145 dB/ μ m and the device exhibits large fabrication tolerance. In addition, the extinction ratio >34 dB and insertion loss <1 dB is achieved within the whole C-band. [ABSTRACT FROM AUTHOR]

High birefringence with low confinement loss photonic crystal fiber (PCF) has significant advantages in the field of sensing, dispersion compensation devices, nonlinear applications, and polarization filter. In this report, two different models of PCFs are presented and compared. Both the models contain five air holes rings with combination of circular and elliptical air holes arrangement. Moreover, the elliptical shaped air holes polarization and the third ring air holes rotational angle are varied. To examine different guiding characteristics, finite element method (FEM) with perfectly matched layer (PML) absorbing boundary condition is applied from 1.2 to 1.8 μm wavelength range. High birefringence, low confinement loss, high nonlinearity, and moderate dispersion values are successfully achieved in both the PCFs models. Numeric analysis shows that model-1 gives higher birefringence (2.75 × 10–2) and negative dispersion (–540.67 ps/(nm$km)) at 1.55 μm wavelength. However, model-2 gives more small confinement loss than model-1 at the same wavelength. In addition, the proposed design demonstrates the variation of rotation angle has great impact to enhance guiding properties especially the birefringence. [ABSTRACT FROM AUTHOR]

Lenses based on Pancharatnam phase have recently attracted an increasing interest. Their main advantages include being very thin and inexpensive. But their application is generally limited to when a monochromatic illumination is used because they are strongly wavelength dependent. However low power Pancharatnam phase lenses have the potential to be considered for applications over the visible range. In this paper we provide intuitive "limits" for the power of these lenses under which these types of devices can be considered for use with applications with visible light that include human eye specifically for VR/AR applications. [ABSTRACT FROM AUTHOR]

Polarization-stable vertical-cavity surface-emitting lasers (VCSELs) with a simple fabrication process are presented. The gratings fixing the polarization are defined by a two-step exposure technology taking advantage of the displacement Talbot lithography technique. This enables grating lines to remain within the inner circle mesa of the VCSELs. These surface grating VCSELs with different periods are theoretically modeled and experimentally verified. Most of these VCSELs exhibit full polarization stability as predicted theoretically. For VCSELs with grating periods larger than the emission wavelength we found a weak orthogonal polarization suppression ratio, thereby deviating from those grating VCSELs with smaller periods. [ABSTRACT FROM AUTHOR]

Design of a silicon-based ultracompact polarization splitter (PS) with high extinction ratio (ER) is proposed for the midinfrared-operating wavelength of 4.47 μm. It is based on a directional coupler (DC) that consists of a horizontal slot waveguide (WG) and a strip WG with Si as the core material and CaF2 as the slot and substrate material. By choosing appropriate structural parameters, we have designed the DC-PS such that only the TM polarization satisfies the phase-matching condition for coupling at the targeted wavelength of 4.47 μm; achieved ERs are ~41.6 dB and ~37.1 dB for the cross-coupled and the throughput ports, respectively. Corresponding estimated insertion losses (ILs) are ~0.25 dB and ~0.07 dB in a device length of just ~6.6 μm. Over a broad bandwidth of 200 nm (4.37 to 4.57 μm) in the mid-IR, our designed PS exhibited ER of >37 dB (with IL of <0.5 dB) for the cross-coupled port and an ER of >17 dB (with IL of <0.1 dB) for the throughput port. Numerical estimations revealed excellent tolerance to the potential fabrication errors. [ABSTRACT FROM AUTHOR]

Abstract We propose design of a promising ultra-short and highly efficient mid-IR polarization rotator (PR) on silicon-on-calcium-fluoride (SOCF) platform, whose rotation section is formed from an asymmetric slot waveguide for the working wavelength of 4.47 μm by exploiting mode coupling scheme. Numerical results demonstrate that within a conversion length of just ∼18 μm, the maximum achievable polarization conversion efficiency (PCE) for both the polarizations (TE-TM and TM-TE) is as high as ∼100% with significantly low loss of ∼ 0.15 dB. Achieved polarization extinction ratios (PER s) are as high as 43.3 dB and 34.9 dB for TE-TM and TM-TE polarizations, respectively. Furthermore, over a large bandwidth of 360 nm (4.29–4.65 μm), our designed PR exhibits very high PCE (> 98%) for both the TE-TM and vice versa with an appreciable PER of ∼18 dB and relatively low loss of ∼ 0.26 dB. Study on fabrication tolerances reveals that designed PR is robust to potential imperfections in fabrication. To the best of our knowledge, our designed PR is the shortest PR reported to date for the mid-IR wavelength regime with a healthy balance/compromise between PCE , PER , bandwidth, loss and fabrication tolerance. [ABSTRACT FROM AUTHOR]

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.

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 10−6 refractive-index-unit, even when a cheap optical spectrum analyzer with low-resolution (e.g., 1 nm) is used for the wavelength-shift measurement.

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

During the calibration of the system matrix of a Stokes polarimeter using reference polarization states (RPSs) and pseudo-inversion estimation method, the measurement intensities are usually noised by the signal-independent additive Gaussian noise or signal-dependent Poisson shot noise, the precision of the estimated system matrix is degraded. In this paper, we present a paradigm for selecting RPSs to improve the precision of the estimated system matrix in the presence of both types of noise. The analytical solution of the precision of the system matrix estimated with the RPSs are derived. Experimental measurements from a general Stokes polarimeter show that accurate system matrix is estimated with the optimal RPSs, which are generated using two rotating quarter-wave plates. The advantage of using optimal RPSs is a reduction in measurement time with high calibration precision. [ABSTRACT FROM AUTHOR]

A single‐channel high‐resolution cross‐polarization (CP) optical coherence tomography (OCT) system is presented for multicontrast imaging of human myocardium in one‐shot measurement. The intensity and functional contrasts, including the ratio between the cross‐ and co‐polarization channels as well as the cumulative retardation, are reconstructed from the CP‐OCT readout. By comparing the CP‐OCT results with histological analysis, it is shown that the system can successfully delineate microstructures in the myocardium and differentiate the fibrotic myocardium from normal or ablated myocardium based on the functional contrasts provided by the CP‐OCT system. The feasibility of using A‐line profiles from the 2 orthogonal polarization channels to identify fibrotic myocardium, normal myocardium and ablated lesion is also discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this work, the performance of a Mach−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.

Abstract: 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. [ABSTRACT FROM AUTHOR]

We numerically studied the nanoantenna integrated thermomechanical mid-infrared detector working at room temperature based on bi-material structures. Three separate bilayer configurations are investigated and optimized for maximum thermomechanical deflection. The integrated optical nanoantennas are geometrically tuned to reach the highest optical absorption at 6 μm. Thermal time constants and fundamental noise equivalent powers of the three bilayer configurations are also calculated. We also discuss the potential implementation of our detector in infrared polarimetry. [ABSTRACT FROM AUTHOR]

An ultracompact and broadband polarization beam splitter (PBS) is proposed by using an asymmetrical directional coupler composed of a hybrid plasmonic waveguide (HPW) and a regular silicon wire (RSW). By properly choosing the structural parameters, transverse-magnetic (TM) mode is cutoff for the RSW and phase-matching condition is only satisfied for transverse-electric (TE) mode. As a result, the input TM-mode in HPW directly passes through, while the input TE-mode in the same HPW is coupled into the RSW. Consequently, the two polarized modes can be effectively separated. Moreover, the present PBS shows fabrication-friendly design and its length can be significantly reduced, since the gap between the HPW and RSW can be shortened to zero. From the results, a ~2.6- \mu \textm -long PBS with a coupling length of 0.1~\mu \textm is achieved and its bandwidth is ~120 nm with a polarization extinction ratio over 14 dB, and an insertion loss below 1 dB for both polarizations. In addition, fabrication tolerances to the key structural parameters are analyzed in detail and field evolution through the designed PBS is also presented. [ABSTRACT FROM AUTHOR]

The chiral fiber long-period gratings (CLPGs) could be fabricated by twisting a high-birefringence (Hi-Bi) fiber. However, when it is immersed into a material whose refractive index (RI) is higher than that of the cladding, there exists a complicated coupling between the core modes and the radiation ones. In this paper, for the first time to our knowledge, we theoretically investigate the mode coupling characteristics in such a CLPG. It is found that, owing to a strong mode transfer from the co-handed core mode to continuous radiation ones under the phase-matching condition, the CLPG can be regarded as a broadband circular polarizer since only the cross-handed circularly polarized light is left when a linearly polarized light is injected. Furthermore, the influence of the RI of the surrounding medium on the bandwidth and extinction ratio of this circular polarizer is investigated in detail. As a result, a broadband all-fiber circular polarizer can be constructed. Considering its simple configuration, it might have some potential applications, such as filters, broadband polarizers, and sensors. [ABSTRACT FROM AUTHOR]

A structure of polarization beam splitter based on a symmetrical metal-cladding waveguide (SMCW) was demonstrated. The light beam energy can be coupled into the SMCW directly through free space without additional coupler. By introducing anisotropic material into the guided layer, different excitation conditions for transverse-electric and transverse-magnetic modes are obtained, which results in polarization-dependent reflection. The propagation loss that is mainly caused by the metal absorption is <2 dB. [ABSTRACT FROM AUTHOR]

A novel highly tunable polarization rotator (PR) based on channel waveguide on silicon is introduced and analyzed. The proposed SiO2/Si channel is infiltrated with nematic liquid crystal (NLC) material of type E7. The design parameters of the NLC channel PR have been studied to obtain an efficient polarization conversion with an ultrashort device length. Additionally, a tolerance analysis of the structure geometrical parameters, temperature, and operating wavelength is reported in detail. The modal analysis of the NLC PR is carried out using full-vectorial finite-difference method (FVFDM). Further, the propagation characteristics through the suggested design are obtained using full-vectorial finite-difference beam propagation method (FVFD-BPM). The numerical results reveal that the reported PR of compact device length of 4.02 μm can achieve nearly 100% polarization conversion ratio with insertion loss of 2.19 dB and good crosstalk of –21.73 dB at a wavelength of 1.55 μm. Further, the crosstalk would be better than –20 dB within the wavelength range of 1.55 ± 0.04 μm. Moreover, the polarization conversion ratio can be controlled by applying an external electric field. To the best of the authors’ knowledge, it is the first time to introduce ultracompact highly tunable PR based on a channel on silicon platform with simple design and broadband operation. [ABSTRACT FROM PUBLISHER]

The paper presents a novel design for terahertz (THz) free-space time domain electro-optic (EO) detection where the static birefringent phases of the two balanced arms are set close to zero but opposite to each other. Our theoretical and numerical analyses show this design has much stronger ability to cancel the optical background noise than both THz ellipsometer and traditional crossed polarizer geometry (CPG). Its optical modulation depth is about twice as high as that of traditional CPG, but about ten times as high as that of THz ellipsometer. As for the dynamical range, our improved design is comparable to the THz ellipsometer but obviously larger than the traditional CPG. Some experiments for comparing our improved CPG with traditional CPG agree well with the corresponding theoretical predictions. Our experiments also show that the splitting ratio of the used non-polarization beam splitter is critical for the performance of our design. [ABSTRACT FROM AUTHOR]

A plasmonic-assisted polarization beam splitter based on bent directional coupling is proposed. The phase-match condition is satisfied for TM polarization only by properly choosing the widths of the two waveguides. Due to the bent and plasmonic-assisted asymmetry, birefringence is greatly enhanced, which allows high extinction ratio for polarization beam splitting with the total footprint of 8.1 \mu \textm\times 2.6\,\,\mu \textm . At the wavelength of 1.55 \mu \textm , the extinction ratios are 25.2 and 29.5 dB for TM and TE polarizations, respectively and the corresponding insertion losses are only 0.2 and 0.035 dB. [ABSTRACT FROM PUBLISHER]

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.

This paper presents a study of propagation of radially and azimuthally polarized cylindrical vector modes in six-strut suspended core fibers based on finite element simulations. The study shows that large effective index differences in the order of 10^-3- 10^-2 of these modes can be achieved in the suspended core fibers with core diameter of less than 2 μm, material index 1.45 of silica to 2.0 of tellurite, and wavelength of 750 nm, allowing the stable propagation of the first higher order modes in doughnut shape within these fibers. The effective index difference and the field intensity of these cylindrical vector modes can be tuned by selecting appropriate fiber material and core size. The study shows that the suspended core fiber can be a competitive candidate for fiber-based high-resolution stimulated emission depletion nanoscopy application. [ABSTRACT FROM PUBLISHER]

Active transverse electric and transverse magnetic-pass polarizers with only 1~\mu \textm length based on Ge2Sb2Te5 (GST) silicon waveguides are theoretically demonstrated. The tunability of both polarizers relies on the phase change of GST. The analysis predicts that both devices exhibit insertion losses (ILs) below 0.8 dB in an amorphous phase. With the change to the crystalline phase, the undesired polarization is attenuated above 18.2 dB, whereas ILs are maintained below 0.8 dB (TM pass) and 2.6 dB (TE pass) at a center wavelength of 1550 nm. The operation bandwidth over a range of 100 nm is also achieved. [ABSTRACT FROM PUBLISHER]

A horizontal silicon slot waveguide TE-pass polarizer with thin indium–tin oxide (ITO) layer embedded in the slot region is proposed and investigated. Since the dispersion relation of the material can be tuned by properly adjusting the carrier concentration, ITO is able to act as epsilon-near-zero (ENZ) material with high absorption near 1.55- \mu \textm wavelength. With thin ENZ material embedded in the slot waveguide, huge polarization-dependent loss between fundamental TE mode and TM mode can be induced. Therefore, the slot waveguide functions as a TE-pass polarizer with good performance. Our simulation shows that in a 3- \mu \textm -long polarizer with 10-nm-thick ITO layer embedded in the slot region, insertion loss of 42 dB for TM mode, and 0.38 dB for TE mode can be achieved simultaneously. The polarizer possesses the advantages of low insertion loss, high extinction ratio, ultra-compact, broadband, and large fabrication tolerance. [ABSTRACT FROM PUBLISHER]

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\textm^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. [ABSTRACT FROM PUBLISHER]

Considering that the variation of the modal characteristics for the TM mode is significantly larger than that for the TE mode when graphene is involved in a silicon-based waveguide, a silicon waveguide TE-pass polarizer with few-layer graphene embedded is proposed and demonstrated. Such a polarizer shows the performance merits including ultrahigh extinction ratio, low insertion loss for the TE mode, ultracompact footprint, and tunable bandwidth by dynamically varying the chemical potential of graphene with gate voltage. We further reveal that the operation bandwidth can be significantly enlarged by cascading multiple polarizers, each of which consists of a silicon waveguide embedded with few-layer graphene and is biased at different gate voltages. We numerically demonstrate that using a cascade of seven polarizers, it is capable of achieving 20-dB extinction ratio and ultralow insertion loss for the TE mode (<0.13 dB) with bandwidth over 120 nm at telecommunication wavelengths. [ABSTRACT FROM PUBLISHER]

An ultrashort polarization rotator (PR) based on cross-symmetry waveguide is proposed and discussed. At the operating wavelength of 1 . 55 μ m , the presented PR has a small conversion length of 3 . 3 μ m . The polarization conversion efficiency (PCE) is 99 . 8 % (TE–TM) and 99 . 97 % (TM–TE). The PR can achieve rather high conversion efficiency ( > 97 % ) over a broad bandwidth ( 1450 − 1700 nm ). The cross-symmetry structure can significantly improve the extinction ratio. The extinction ratio is 27 . 7 dB (TE–TM) and 35 . 9 dB (TM–TE) with the insertion loss of 0 . 28 dB . The fabrication tolerances for the waveguide for both transverse and horizontal directions are also studied. [ABSTRACT FROM AUTHOR]

Metasurface-based flat lens have great potentials for applications in compact and portable cameras. However, the properties of optical metasurfaces are strongly limited by the intrinsic ohmic loss of metal and the fixed working distance. Here, we propose a highly efficient all-dielectric metasurface lens working in near-infrared frequency range. By exploiting silicon nanoblock as meta- atoms, the silicon metasurface produces phase changes covering 0 to 2π and near-unity reflection, inducing the focusing of light over a broad wavelength range. Interestingly, the focal length of such an ultrathin flat lens can be dynamically controlled by incorporating tunable materials such as liquid crystals. By utilizing the phase transition or electrical alignment of liquid crystals, the focal length has been tuned up to 10 %. We believe our research will be important to accelerate the applications of optical metasurfaces. [ABSTRACT FROM AUTHOR]

A hybrid waveguiding structure has been fabricated in a z -cut lithium tantalate (LiTaO 3 ) crystal wafer by direct femtosecond laser writing. Due to the laser-induced anisotropic modifications of the extraordinary and ordinary refractive indices ( n e and n o ) of LiTaO 3 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a gear-like metallic core fiber for the generation of a radially polarized mode based on the significant attenuation loss for different transverse modes and a mode reversion mechanism. The mode extinction ratio higher than 40 dB is obtained within 1 cm of such fiber. Our design offers a potential way to obtain a radially polarized beam efficiently. [ABSTRACT FROM AUTHOR]

In this paper, a wide-angle polarization-sensitive dual-band absorber at infrared wavelengths with a multilayer grating is reported. The simulation results show that the absorber has two absorption peaks at wavelengths λ = 1.365 μ and λ = 3.035 μ with the absorption magnitudes more than 0.97 and 0.99 for TM polarization (electric field perpendicular to the strips), respectively. And this absorber reflects almost all TE polarization (electric field parallel to the strips) light. The dual-band absorption peaks can be tuned by varying the width of the strips, and the absorption magnitudes are more than 0.9 for the dual-band absorption peaks for angles up to 70°. [ABSTRACT FROM AUTHOR]

Abstract: Anisotropic transmission through a plasmonic bull's eye with an elliptical central aperture in a thin Au film is analyzed experimentally by changing the polarization. The light polarized along the minor axis of the elliptical aperture had a significantly larger enhanced optical transmission than the other orthogonal polarization, which agreed well with theoretical predictions. Spectral width of the output was narrowed, which indicates temporal elongation of pulse trains. [Copyright &y& Elsevier]

We propose an asymmetric silicon-plasmonic hybrid waveguide, which supports two eigen modes with linearly polarized-like electric field distributions and large difference between their propagation constants. Exploiting these mode characteristics of the hybrid waveguide, an ultra-compact and high-performance silicon-on-insulator (SOI) waveguide polarization converter based on multimode interference is designed, which converts quasi-TE polarization mode to quasi-TM polarization mode. Simulation results show that polarization extinction ratio up to 27 dB is reached for an ultra-short conversion length of 610 nm. The bandwidth is 140 nm for an extinction ratio larger than 20 dB. This asymmetric silicon-plasmonic hybrid waveguide may open promising prospects for further minimizing integrated optical circuits on SOI platform. [ABSTRACT FROM PUBLISHER]