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A wideband omnidirectional circularly polarized (CP) antenna using a conformal artificial anisotropic polarizer is proposed for millimeter-wave applications. The antenna consists of three parts: an omnidirectional linearly polarized (LP) radiator, an annular hyperbolic lens, and a conformal anisotropic polarizer. The annular hyperbolic lens regulates the spherical wavefront from the LP radiator into a cylindrical shape prior to propagating into the conformal artificial anisotropic polarizer. Each curved slab of the polarizer is conformally tilted 45 degrees to the incident electric field. Therefore, the conformal polarizer is the three-dimensionalization of the two-dimensional planar artificial anisotropic polarizer. The polarizer designing methodology is the first of its kind to generate wideband CP wave omnidirectionally. The hyperbolic lens and the conformal polarizer are fabricated together using stereolithography (SLA) 3D printing technology. Measurement results show that the antenna has a wide operating bandwidth of 45% (from 24 to 38 GHz), which completely covers potential 5G 28-GHz spectra. The proposed design has a low fabrication complexity and brings possibilities for high-speed wireless communications utilizing circular polarization.

We present the structural design and polarization-maintaining performance of solid-core anti-resonant fiber with two nested circular tubes in 3 m wavelength for the first time, to the best of our knowledge. Numerical simulation results indicated that laser fundamental mode could be obtained by filling the specially designed fiber model with materials of different refractive indices to form the completely solid configuration. We calculated the bend loss of fiber to demonstrate the preferable birefringence performance and outstanding light-confining ability. With the structural deformations from resonant tubes, the birefringence coefficient was enhanced significantly from 210-5 to 6.9310-5, which was of great importance in the polarization sensitive systems. In particular, when nested circular tubes were moved to introduce deformations, the confined loss difference in two orthogonal polarizations was calculated more than two orders of magnitude, which was the desirable result to promote the fabrication of the linear polarizer in 3 m wavelength.

Fabrication method of a fiber optic electric field sensing probe using polarization maintaining fiber (PMF) is described including a birefringent axes aligning system. The sensing probe is basically a fiber-coupled Fabry-Perot resonator where a thin birefringent wafer of LiTaO3 with an external cavity is mounted onto the end of PMF. An optical wave from a superluminescent laser diode after a linear polarizer parallel to the slow axis of the PMF is made to enter the LiTaO3 crystal with polarization parallel to its extraordinary axis and the reflected optical wave is detected after passing through a polarization analyzer. By measuring a minimum value of a ratio of the reflected optical power at 90° to that of 0° of analyzer, we successfully demonstrated that the angular accuracy of the slow axis of the PMF with respect to the extraordinary axis of the LiTaO3 can be evaluated. Aligning both axes precisely, the electro-optic effect associated with LiTaO3 and polarization is optimized with greater stability. Long term stability of the fabricated PMF sensing probe was enhanced by about 3 times compared to that of a conventional single mode fiber one. As a result of uncertainty analysis, the method we proposed has an overall angular uncertainty of 1° when the used fiber optic components have polarization angle tolerance of 1°.

ZnO nanotubes play a substantial role in various optoelectronic applications such as light-emitting diodes, solar cells and photodetectors. In this study, the structural, electronic, and optical effects of (n,0) single-walled ZnO nanotubes with different radius are discussed. An ab-initio approach of density functional theory with the generalized gradient approximation has been done by Quantum ESPRESSO software on nanotubes with n = 3 to 6. All simulated ZnO nanotubes illustrate semiconducting behavior, which due to the quantum confinement effect, the band gap value decreases by the increase in diameter. Moreover, optical characteristics including dielectric function e ( ω ) , refractive index n( ω ) , optical absorption coefficient α ( ω ) , conductivity σ ( ω ) , energy loss spectrum L( ω ) and reflectivity R ( ω ) have been analyzed and compared. The predicted optical features show that the mentioned nanotubes transmit light in perpendicular polarization better than parallel one and present superior reflect characters. Additionally, ZnO NTs act as a good absorbent in the visible wavelength which they can absorb various colors of the visible spectrum or even UV emission by altering the number of n. This ability turns ZnO NTs into remarkable photodetectors. Furthermore, according to optical characteristics like energy loss spectrum and dielectric function, it is obvious that results are approximately similar for different nanotubes and despite the miner red-shift of the position of the main peak, their appearance is close to each other. Therefore, ZnO NTs can be utilized in various applications such as optical filters, polarizers, and UV shields.

In this letter, a multibeam transmitarray carrying orbital angular momentum (OAM) is introduced to realize 1-D +/−30° beam coverage. A three-layer unit cell is designed to provide high-efficiency transmission and full 360° phase coverage. This unit cell consists of two orthogonal polarizers at the outermost layers and a polarization rotating patch in the middle layer. A feeding array is employed to illuminate the transmitarray. By combining bifocal principle with the method of OAM beam generation, the stability of steered OAM beams is improved compared to conventional single focal design. A five-beam protype producing −1 OAM mode is simulated, fabricated, and measured, realizing a +/−30° beam coverage with stable vortex property and high mode purity. The proposed design has advantages such as multi-OAM-beam, stable vortex property, wideband, high gain, and easy fabrication.

In this paper, a new approach to design terahertz (THz) E-plane crossover coupler is reported. By cascading two symmetrical septum polarizers, a simple structure with wide operating bandwidth and high isolation performance is achieved. The working principle is explained by operating waveguide modes. To simplify the optimization process, the scattering matrix (S-matrix) of the crossover is calculated. Two prototypes loaded and unloaded electromagnetic band gap (EBG) are fabricated and measured. The electrical contact problem at assembly plane is eliminated by the prototype loaded EBG. A measured bandwidth of 17.3% from 92.5 to 110 GHz for reflection and isolation coefficients −2 dB is achieved.

We report broadband circular polarizers achieved by engineering the electromagnetic coupling between 3D meta-atoms in large-area arrays. The 3D meta-atoms are composed of bulk Au/Au nanocrystal (NC...

The effect of the optical feedback on the polarization flipping point and hysteresis loop was studied. The polarization flipping occurred at all angles between the polarizer axis and the laser polarization. The polarization flipping point changed by an optical feedback occurred at angles from 0° to 90°. Ability of choosing or controlling the laser polarization was determined by changing the direction of vertical and horizontal polarization by polarizer rotation in the external cavity from 0° to 90°.

Metals were for decades perceived as devoid of interesting optical properties that could be harnessed for optical components and devices. However, with the development of accurate nanofabrication techniques and precise control over architectural parameters, metals can be structured and characterized on the nanoscale. Metallic plasmonic nanomaterials exhibit a number of unique structural and optical properties, which offer the potential for developing new types of plasmonic devices. Here, we demonstrate a low-loss broadband polarizer based on a hybrid plasmonic fiber structure using metals as polarization-selective absorption materials. The polarization mechanism, design, fabrication, and characteristics of the plasmonic polarizers are investigated theoretically, numerically, and experimentally. The theoretical analysis predicts that the polarization-selective absorption with insensitivity to wavelength enables hybrid plasmonic fibers to function as broadband polarizers. Numerical simulations give the comparison of the polarization-selective absorption of various metallic nanomaterials (Ag, Au, In, Al, Cr) and show that aluminum is regarded as the optimum absorption material for the plasmonic polarizer. Experimental results show that through precise control over geometrical parameters, this device is capable of offering a high polarization extinction ratio (PER) of over 40 dB and a low insertion loss (IL) of less than 1.3 dB in the wavelength region of 810.1-870.0 nm. Compared with commercial birefringent-crystal-fiber polarizers, the plasmonic fiber polarizer has a better PER and IL bandwidth. These merits, combined with a compact and robust configuration, enable the plasmonic polarizer to have great potential in a broad range of applications.

We propose and numerically investigate the use of birefringent vertical-cavity surface-emitting lasers (VCSELs) under the injection and modulation of spin polarized electrons for application to analog radio over fiber (RoF) systems. Injection current and electron spin polarization in a birefringent VCSEL are individually modulated for generating data signals and a millimeter-wave carrier and a polarizer is used to combine two orthogonal polarizations. A preliminary experiment without spin injections confirms that 24-GHz carrier generation originating from polarization-mode splitting of the birefringent VCSEL can be used for the heterodyne detection of square-wave signals with a period of 6.4 ns. Our findings mark the first step in applying spin-injected birefringent VCSELs having the capability of ultra-high-frequency modulation for application to analog RoF systems.

We investigated the conditions for forming the single-frequency monopulse operation mode of the transversally diode pumped Yb,Er-phosphate glass laser with a passive Q-switch based on the Co2+:MgAl2O4 crystal. It was shown experimentally that the spectral selectivity that ensures the stable single-frequency operation for the Yb,Er-laser is achieved in the intracavity Fabry–Perot interferometer in the form of the totally reflecting mirror and nearest end surface of an active element with plane-parallel faces, as well as the polarization interference filter (PIF, Lyot filter). Meanwhile, the PIF created by an active element with thermally induced anisotropy and a polarizer in the form of a passive Q-switch plate, oriented at Brewster’s angle to the resonator axis, acts as a preliminary spectral selector. The maximum energy of the formed output laser pulses was 6 mJ with a duration of 20.2 ns, a repetition rate of 1 Hz, and a single-frequency lasing spectrum width of 41 MHz.

Polarization plays a key role in science; hence its versatile manipulation is crucial. Existing polarization optics, however, can only manipulate polarization in a single transverse plane. Here we demonstrate a new class of polarizers and wave plates—based on metasurfaces—that can impart an arbitrarily chosen polarization response along the propagation direction, regardless of the incident polarization. The underlying mechanism relies on transforming an incident waveform into an ensemble of pencil-like beams with different polarization states that beat along the optical axis thereby changing the resulting polarization at will, locally, as light propagates. Remarkably, using form-birefringent metasurfaces in combination with matrix-based holography enables the desired propagation-dependent polarization response to be enacted without a priori knowledge of the incident polarization—a behaviour that would require three polarization-sensitive holograms if implemented otherwise. Our work expands the use of polarization in the design of multifunctional metasurfaces and may find application in tunable structured light, optically switchable devices and versatile light–matter interactions. Using a metasurface that allows shaping of the polarization state of a light beam independently at each point of space along its propagation direction, longitudinally variable polarization optical components are demonstrated, inspiring new directions in structured light, polarization-switchable devices and light–matter interaction.

The purpose of the work was the correct experimental discovery of the effect of “weak” gyrotropy of the “non-gyrotropic” transparent crystals. The original experiment was based on the study of the light transmission (T) of the system: Polarizer—wedge-shaped Crystal’s sample—Analyzer (orthogonal to Polarizer). It was shown that: if the optical axis of the crystal is parallel to the rib of the wedge and to the polarization of the linear-polarized incident light, then the transmission T of the system can be not equal to zero (due to existence of nonzero components (G12) of the antisymmetric pseudotensor of gyration {G} described the “weak” gyrotropy). Using the LiNbO3 crystal as an example, such nonzero T was at the first time experimentally discovered. Absolute value of components G12 of the LiNbO3 crystal was first estimated: ([G12] = (1.50 +/- 0.51) 10-6).

We propose and demonstrate a novel and simple wavelength switchable multi-wavelength erbium-doped fiber (EDF) laser based on polarization-dependent loss (PDL) modulation with cascaded fiber Bragg gratings (FBGs) as the wavelength comb filter. PDL is generated and controlled by different polarization angles between the polarization state of each lasing line and the optical fiber polarizer in the laser cavity. The PDL modulation balances the difference between the total loss and the wavelength-dependent lasing gain. The relations among gain, loss, and laser output power under different PDL conditions are numerically analyzed on the basis of a simplified Giles model in an EDF laser system. Results show that multi-wavelength lasing lines can be built up by properly tuning the PDLs in different wavelengths. The amount of lasing lines can be switched by changing the PDL intensity in a certain wavelength. In an experiment, the PDL in that certain wavelength is modulated by utilizing four polarization controllable elements, each of which includes an FBG and a corresponding polarization controller (PC). One PC is used to control the polarization state of the reflected lasing line on the center wavelength of the FBG. A four-wavelength individually switchable EDF laser system is demonstrated by utilizing this wavelength switchable method, in which the switching operation for the single-, dual-, triple-, and four-wavelength laser output is verified. The experimental results are consistent with the theoretical results. All wavelength switching operations are conveniently controlled by merely adjusting the PCs. This simple structure and flexible wavelength switchable operations show that this multi-wavelength EDF laser has great potential in practical applications.

A new approach to the development of an optoelectronic device for molecular orientation of functional materials is proposed. Results of the development of its main components are presented: a collimator for the light from an LED and a broad band polarizer with a large angular aperture. The problem of the collimation of a strongly diverging beam from an LED is examined. It is shown that the use of a modified conical lens offers promise for solving this problem. A broad-band polarizer with a large angular aperture, which is an important component of the optoelectronic device, is developed and fabricated on the basis of a multilayered structure.

The performance of free-space optical data transmission is severely deteriorated by the fluctuation of optical signal intensity, which is resulted from the bias drift of electro-optical modulation devices. In order to improve the performance of free-space optical communication systems, a bias-drift avoiding, beam steered free-space optical wireless communication system is presented based on polarization modulation for the first time to the best of our knowledge. An in-fiber diffraction device based on a 45° tilted fiber grating (TFG) serves simultaneously as an in-fiber polarizer, free-space light emitter, and beam steerer in the proposed communication system, which endows the proposed system with the merits of highly efficient, compact, stable and bias-drift free. The usage of 45° TFG has three benefits: 1), it realizes polarization modulation preventing bias-drift due to its polarization sensitive feature; 2), it enables stable and highly efficient in-fiber compact free-space light emitter; and 3) it accomplishes free-space beam steering due to its wavelength-depending diffraction characteristic. A 2.1 m free-space optical wireless data transmission has been demonstrated with a data rate of 4.8 Gbps per beam using 1.2 GHz bandwidth OFDM signals. This proposal prevents the bias drift issue and maintains high stability. Hence, it can be applied in some harsh situations and confidential data transmission fields.

Multilayer grid polarizers for millimeter waves produced with photolithographic technology have been simulated. Polarizers have spectral bands of enhanced performance where polarization extinction ratio in decibels grows in proportion to the number of layers. Full-wave modeling is compared with three asymptotic models for subwavelength gratings using adjusted grating parameters. Random variations of interlayer spacings reduce the enhancement of polarizing performance, yet the latter continues to grow in proportion to the number of layers. Broadband signal detection is also considered.

We propose a new type of reflective polarizer based on polarization-dependent coupling to surface-plasmon polaritons (SPPs) from free space. This inexpensive polarizer is relatively narrowband but features an extinction ratio of up to 1000 with efficiency of up to 95% for the desired polarization (numbers from a calculation), and thus can be stacked to achieve extinction ratios of 106 or more. As a proof of concept, we experimentally realized a polarizer based on nanoporous aluminum oxide that operates around a wavelength of 10.6 um, corresponding to the output of a CO2 laser, using aluminum anodization, a low-cost electrochemical process., Comment: Main text + supplementary

Three-dimensional chiral plasmonic metasurfaces were demonstrated to offer enormous potential for ultrathin circular polarizers and applications in chiral sensing. However, the large absorption losses in the metallic systems generally limit their applicability for high-efficiency devices. In this work, we experimentally and numerically demonstrate three-dimensional chiral dielectric metasurfaces exhibiting multipolar resonances and examine their chiro-optical properties. In particular, we demonstrate that record high circular dichroism of 0.7 and optical activity of 2.67 × 10

Periodic photonic lattices constitute a fundamental pillar of physics supporting a plethora of scientific concepts and applications. The advent of metamaterials and metastructures is grounded in a ...

This work develops a polarisation-tunable reflector that is based on a guided-mode resonant (GMR) filter with an integrated liquid-crystal (LC) polarisation rotator. The GMR filter serves as a line...

Graphene-enabled metamaterials have emerged as promising photoelectric devices for dynamically controlling the polarization of electromagnetic waves. However, it is still a key technological challenge to design a tunable metamaterial possessing more sufficient freedom for polarization manipulation. Here, we propose a graphene-enabled tunable multifunctional metamaterial consisting of metallic strips arranged on a grounded polymer substrate embedded with a graphene sandwich structure to electrically control the polarization states of terahertz waves. By adjusting the Fermi energy of graphene through voltage biasing, the electromagnetic responses of the presented metamaterial can be tailored, resulting in dynamical tunable polarization manipulation in reflection mode. All expected performances are demonstrated through full wave simulation. The results reveal that this metamaterial device can operate as a switchable quarter-wave plate and a tunable half-wave plate for both linear- and circular-polarization incidences. Furthermore, the polarization conversion ratio, of which incident waves are converted to their cross-polarized reflection mode, can be continuously regulated from 2% to 95% in a wide band from 1.46 to 2.26 THz. The proposed metamaterial continues the process of developing tunable polarizers and polarization switchers with graphene materials, and may be applied in various areas such as wireless communication, terahertz sensing and imaging.

By combining nanosphere lithography with oblique angle deposition, large-area asymmetric compound Ag nanohole arrays with nanorods inside the hole were patterned on substrates. The technique enabled the production of complex nanohole arrays with controlled hole diameter, thickness, and rod structure inside the hole. The compound asymmetric Ag nanohole structures showed strong polarization-dependent optical properties, and a new extraordinary optical transmission (EOT) mode with tunable resonance wavelength at the near-IR region was observed. The transmission at the new EOT wavelength region can increase from 27% of nanohole to 69% of the compound structure, and these structures can achieve a refractive index sensitivity as high as 847 nm RIU-1. The tunable EOT wavelength and strong polarization-dependent optical properties make the structure ideal for ultrathin optical filters, polarizers, surface-enhanced spectroscopies, etc.

In view of the characteristics of the small amplitude of a current signal, an all-optical fibre small-current sensor for partial discharge is devised. A novel type of sensor head with electric winding light is proposed. A complete optical model of the optical fibre current sensor is developed under the effect of polarization error factors. In addition, the effect of polarization error factors on the optical fibre sensing system is simulated. The simulation results show that as the extinction ratio increases, the output relative error of the optical fibre small-current sensor decreases. The effect of the fast and slow axis misalignment errors of a polarizing beam splitter is similar to the effect of the alignment angle error of an optical fibre polarizer. It is observed that the relative error curve follows a sine function. Meanwhile, the output relative error increases first and then oscillates with an increase in the linear birefringence. We conclude that the linear birefringence of the sensing optical fibre is the main error source for the measurement accuracy of the sensing system. Finally, an experimental system for the optical fibre small-current sensor is implemented. The experimental results show that the effect of linear birefringence on the fibre current sensing system can be suppressed by introducing a large amount of circular birefringence into the sensing optical fibre. The theoretical mechanism of these errors is analysed, which can be applied to implement corresponding measures to reduce the effect of error factors on the sensing system and further improve the measurement accuracy of the optical fibre small-current sensor.

Graphene can be utilized as a tunable material for a wide range of infrared wavelength regions due to its tunable conductivity property. In this paper, we use Y-shaped silver material resonator placed over the top of multiple graphene silica-layered structures to realize the perfect absorption over the infrared wavelength region. We propose four different designs by placing the graphene sheet over silica. The absorption and reflectance performance of the structures have been explored for 1500- to 1600-nm wavelength range. The proposed design also explores the absorption tunability of the structure for the different values of graphene chemical potential. We have reported the negative impedance for the perfect absorption for proposed metamaterial absorber structures. All the metamaterial absorbers have reported 99% of its absorption peaks in the infrared wavelength region. These designs can be used as a tunable absorber for narrowband and wideband applications. The proposed designs will become the basic building block of large photonics design which will be applicable for polariser, sensor, and solar applications.

A filter-less frequency doubling generator with tunable phase shift based on dual-polarization modulation is proposed and analyzed. The setup is composed with a continuous-wave laser, a dual-polarization Mach-Zehnder modulator and a linear polarizer followed by a photodetector. The modulator is used to generate frequency doubling modulation signals on orthogonal polarization axis. By tuning the polarization state before the polarizer, the initial phase of the generated microwave signal can be tuned manually. At the meantime, the signal amplitude will remain constant. It is found the generated signal’s frequency is twice of the driven frequency. The electrical phase shift can be tuned within full range ((0°—360°). Without using any optical filter or wavelength-dependent component, this scheme is featured with good frequency tunability and multi-wavelength operation.

Wavelength dependence of phase modulators has been one of the main challenges in spectroscopic ellipsometry/polarimetry (EP) which significantly complicates signals analysis. A known approach to overcome this complication is using rotatable polarizers. However, the use of rotatable polarizers induces mechanical vibrations and unnecessary errors to the system. In this work, a novel spectroscopic configuration to extract the spectral changes of the EP parameters applied to surface plasmon resonance (SPR) sensing is presented. The setup utilizes the integration of a recently developed achromatic variable liquid crystal waveplate to the SPR in Kretschmann-Raether configuration and using three phase shifts to extract the EP parameters of the SPR sample.

High polarization extinction ratio (PER) in-fiber polarizers are essential in various fiber-based technologies. In this letter, we propose and demonstrate an in-fiber dispersion compensated polarizer (DCP) based on integrated fiber gratings, which is fabricated by a UV-inscribed 45° tilted fiber grating (TFG) and a chirped fiber Bragg grating (CFBG) in series. Such compact device could enhance the PER of 45° TFG with nearly double value and it is potential to achieve ultra-high PER with relatively short length and simple fabrication. Meanwhile, DCP could also function as a dispersion management component. Finally, with the integrated grating device, we have demonstrated an all fiber mode-locked laser system, generating soliton pulses at the normal and anomalous dispersion regime, respectively.

A multi-switchable generation between dissipative solitons (DSs) and noise-like pulses (NLPs) in a fiber laser is demonstrated. A 45° tilted fiber grating is applied as an effective in-line all-fiber polarizer to realize the nonlinear polarization rotation (NPR) mechanism. With the fixed orientations of polarization controllers, the operation regimes of the fiber laser can be alternatively switched between DS and NLP by monotonically increasing pump power only. We observed five switching stages between DS/NLP regimes with the pump power elevating from 200 to 660 mW. Remarkably, the whole procedure could be precisely controlled forwardly and backwardly. This multi-shuttle behavior between the two distinct types of output pulse can be attributed to the transmission of NPR mechanism together with the gain filtering effect. To the best of our knowledge, this is the first report on the multi-shuttle behavior between DS and NLP in a fiber laser under monotonic change of pump power. Our findings may contribute to in-depth understanding of nonlinear dynamics and laser physics.

Metasurfaces, as two-dimensional artificial subwavelength nanostructures, have shown novel optical phenomena and abilities of flexible and multi-dimensional optical field manipulation with a more integrated platform. Relative to the metasurfaces with single-dimensional manipulation, the metasurfaces with multi-dimensional manipulation of optical fields show significant advantages in various practical application areas, such as optical holograms, sub-diffraction imaging, generating vector optical fields, and so on. However, the design of metasurfaces with multi-dimensional manipulation of optical fields is more complex in most cases. Optimization based on machine learning can effectively lower the difficulty of the design and achieve more accurate multi-dimensional manipulation, which has attracted great interest in recent years. In this review, we firstly classified and discussed the recent advances of two-dimensional manipulation of optical fields with metasurfaces. Then, we further introduced the multi-dimensional manipulation method of optical fields based on machine learning. We first provide a following classification and review recent works related to two-dimensional manipulation of optical fields with metasurfaces. (1) Manipulating amplitude and phase of optical fields simultaneously. In scalar optics, the transmission of complete optical field information requires both amplitude and phase modulations, as the wave equation implies. Thus, the metasurfaces with both amplitude and phase manipulation can provide full optical field information and better performance in various areas, such as optical holograms, energy-tailorable metasurfaces, generating Airy beams and bidirectional perfect absorbers. (2) Manipulating phase and polarization of optical fields simultaneously. In vectorial optics, many intriguing phenomena occur which seem impossible in scalar optics. However, in conventional optics, complex optical systems including polarizers and curved mirrors are often required to achieve simultaneous manipulation of phase and polarization. Metasurfaces with both phase and polarization manipulation can be utilized to achieve various novel functionalities, such as generating vector beams, giant optical activity without chiral structures, chiral holograms, arbitrary spin-to-orbital angular momentum conversion of light and anisotropic coding metasurfaces, with an integrated optical system. (3) Manipulating amplitude and polarization of optical fields simultaneously. Utilizing the abundant interlayer effects provided by metasurfaces, one can tailor their reflection, transmission, and absorption properties of electromagnetic waves in different polarization states. Metasurfaces with both amplitude and polarization manipulation can be utilized to achieve various novel phenomena which are difficult to be realized in conventional optics, such as asymmetric transmission and giant circular dichroism. (4) Manipulating frequency and amplitude of optical fields simultaneously. In linear optical region, the unique frequency-dependent absorption and scattering properties of metasurfaces in the visible frequencies are utilized to print color at the nanoscale, which is known as structural colors. In nonlinear optical region, the exponential relationship between the intensities of the nonlinear optical signal and the fundamental frequency signal, many optical phenomena can be further amplified, such as circular dichroism. (5) Manipulating frequency and phase of optical fields simultaneously. In linear optical region, achromatic meta-lenses can be realized by utilizing the dispersion characteristics of different nano antennas to compensate for phase dispersion at different frequencies. In nonlinear optical region, metasurfaces with efficient phase modulation of nonlinear waves have received great attention in recent years for their great value in the realization of many novel nonlinear functionalities, such as multiplexed holograms, multiplexed coding meta-devices, and terahertz generators. (6) Multi-dimensional manipulation of on-chip optical field. With the integration with the waveguides, metasurfaces can also realize multi-dimensional manipulation of on-chip optical field. Metasurfaces consisting of phased nanoantennas can be used to control guided waves via strong optical scattering at subwavelength intervals. Different on-chip meta-devices have been demonstrated based on this design principle, such mode converters, spin-selective and wavelength-selective demultiplexing devices, polarization emitters, waveguide devices supporting asymmetric optical power transmission and phase-matching-free second harmonic generator. Then, we introduce the new multi-dimensional manipulation method of optical fields based on machine learning. The manipulation method based on machine learning can quickly obtain the optimal structural parameter solution in a huge parameter space, which improves the efficiency of parameter optimization exponentially. At the same time, machine learning can be used to design complex discrete structures, which breaks the period limitation of conventional devices. The optical field manipulation with metasurfaces based on machine learning has great application value in metalens, holographic imaging, coding metasurface and so on.

We perform mathematical modeling of diffraction of plane electromagnetic waves by multilayer metasurfaces comprised by elements of graphene nanoribbons. The modeling is based on solving the three-dimensional boundary value diffraction problem by three methods, specifically, those of self-contained units with Floquet channels, the volume integro-differential equation, and approximate boundary conditions. The coefficients of reflection, transmission, and absorption of s- and p-polarized waves by metasurfaces made of elements of rectangular graphene nanoribbons are calculated as functions of the frequency and the incidence angle for various values of the chemical potential with allowance for the geometric and dimensional effects in the terahertz frequency band. It is shown that at the resonant frequencies of the surface plasmon polariton, multilayer metasurfaces comprised by two graphene strips in an elementary cell on substrates, which contain layers of a dielectric and graphene, are electrically controlled efficient wideband terahertz absorbers and polarizers in the reflection regime that are insensitive to incidence angles.

Metasurfaces can be used to precisely control polarization state of the scattered light. Here, we present a metasurface-based terahertz device. On the one hand, it serves as a high performance linear polarization converter in transmission of over 80% power with weak reflection. It is capable of rotating linear polarization orientation angle with respect to x-axis continuously from −90° to +90° at 0.84 THz. On the other hand, it serves as a circular polarizer. It can transform a linear polarized wave into a circular polarized wave at 2.49 THz. The transmitted and reflected field are both circular polarized with 50% power. The proposed device with dual functionalities can be applied to modulate the polarization state of the signal in THz wireless communication.

Silicon-on-insulator (SOI) waveguide is a competitive and technological platform for photonic integrated circuits because of its compatibility with mature complementary metal oxide semiconductor (CMOS) process. Silicon nanowires enable ultra-sharp bending due to their high refractive index contrast between the core and cladding layer of the waveguide, consequently allowing for a small device size. Unfortunately, the high dielectric contrast makes SOI waveguides highly polarization dependent, leading to a lot limitations for more practical applications of the SOI based devices. On-chip polarizers are important components for design and development of many optical-fiber coherent communication and optic sensing systems, such as switches, integrated-optic gyroscopes and polarization independent receivers for coherent detection in which only a specific polarization state is allowed. In this letter, a compact and low-loss TE passed polarizer was proposed and designed and optimized based on surface plasmon polaritons SOI platform where a 220nm-thin silicon layer acts as the core layer on top of a 2-μm silica buried layer. The structure used for SPPs based polarizer consists of a dielectric waveguide and metal slab film with a low-index spacer layer separated. In such a structure, surface plasmon resonance is achieved by the evanescent wave from the light beam being totally internally reflected inside the high-index silicon core layer with phase matching conditions satisfied. The fundamental TM filed is coupled into the plasmon mode concentrated in the close vicinity of the metal/dielectric interface. In contrast, the fundamental TE mode is mainly guided in the silicon core region. As a result, the TM mode behaves a larger absorption loss due to the existence of the imaginary part in the metal permittivity, and the TE mode is slightly affected. For a proper design of the waveguide dimensions, the TM mode propagating through the polarizer will suffer significant attenuation while the TE mode keeps a low propagation loss, thus providing a high polarization extinction ratio. Effects of important design parameters, such as metal material, spacer thickness and refractive index, on the performance of the polarizer are compared and analyzed. FDTD simulation results show that, a 5 μm-long polarizer with SiN spacer and Cr cladding could provide a high polarization extinction ratio of more than 20 dB with an excess loss of TE mode less than 0.27dB at 1.55μm wavelength over a 140 nm broad bandwidth. And the insertion loss can be further reduced to less than 0.2 dB with a 10-μm polarizer length by increasing the buffer thickness. This compact and low-loss polarizer could be easily implemented with simple fabrication process.

This paper proposes the tunable graphene-assisted polarizer structure which is working on the infrared frequency range. The tunable polarizer has been designed by a three-layered structure of silica, graphene, and gold. The polarizer behavior of the structure is analyzed for the frequency range of 3 to 12 THz. The tunability of the structure is analyzed for the different values of fermi energy which is tunable parameter of single-layer graphene sheet. Polarizer response is derived in terms of different performance parameters such as reflectance, phase variation, phase difference, polarization conversion rate, and effective refractive indices. Graphene-based polarizer structure is investigated for the co-polarization and cross-polarization input incident conditions to check linear to circular polarization conversion. It also shows an effective refractive index response to check the metasurface behavior of the polarizer for 3 to 12 THz range. We have observed that the polarization amplitude becomes stronger for the higher Fermi energy value of the graphene sheet. The reflection amplitude is achieved up to 90%. Results of the proposed polarizer structure can be used to design the various electro-optical structure which operates in the lower THz range.

We present a demodulation approach for a rotating polarizer-analyzer polarimeter dedicated to retardance measurements. Through the Mueller matrix approach and the theoretical Fourier transform, we developed a demodulation algorithm considering the two linear polarizers' initial orientation as calibration. We present experimental results showing the feasibility of our proposal.

International audience; When locking the frequency of a laser to an optical cavity resonance, the residual amplitude modulation (RAM), which accompanies the phase modulation necessary to build the error signal, is a major limitation to the frequency stability. We show that the popular method demonstrated by Wong and Hall to cancel this effect, based on the measurement of the RAM using an auxiliary detector, is limited in the case of optical setups exhibiting polarization dependent losses and an imperfect polarizer at the modulator output, such as guided-wave optical systems.We propose and demonstrate a new method, using a single photodetector, to generate the two error signals and demonstrate its usefulness in the case of fibered systems.

A fiber optic current sensor utilizing orbital angular momentum (OAM) beam is proposed in this paper. The superposition principle of composite OAM beam is deduced, and the current sensing process is derived by Jones matrix. The current is measured by detecting the rotation angle of petal-like patterns formed after the composite OAM beam through the polarizer. The reflective structure of the sensor doubles the rotation angle, which improves the measuring sensitivity and the reciprocity of the system. Through simulation analysis, we verified that the rotation angle changes linearly with the increase of current, and the sensitivity of the proposed sensor is 0.1254°/A. Finally, on this basis, the angle recognition method is optimized, and the final measurement error is less than ±0.2% in the range of 50A-1500A. .

The orthogonal phase demodulation method can effectively avoid the problem of the working interval of the optical fiber Fabry-Perot (F-P) sensor and has high accuracy. Based on the principle of the low-coherence interference, polarizers and birefringent crystals are used to construct signals with orthogonal relationships in the orthogonal phase demodulation system. Four-quadrant inverse tangent operation is used to accurately calculate the phase value. In order to verify the frequency band response of the demodulation system, the acoustic signals of frequencies in the range of 200 Hz-25 kHz are interrogated. Experimental results show that the orthogonal phase demodulation system can be appled to demodulate the signals of wide frequency band. The research has value for the promotion and application of orthogonal phase demodulation system based on birefringent crystals and polarization technology

We demonstrate calibration and operation of a Mueller matrix imaging microscope using dual continuously rotating anisotropic mirrors for polarization state generation and analysis. The mirrors contain highly spatially coherent nanostructure slanted columnar titanium thin films deposited onto optically thick titanium layers on quartz substrates. The first mirror acts as polarization state image generator and the second mirror acts as polarization state image detector. The instrument is calibrated using samples consisting of laterally homogeneous properties such as straight-through-air, a clear aperture linear polarizer, and a clear aperture linear retarder waveplate. Mueller matrix images are determined for spatially varying anisotropic samples consisting of a commercially available (Thorlabs) birefringent resolution target and a spatially patterned titanium slanted columnar thin film deposited onto a glass substrate. Calibration and operation are demonstrated at a single wavelength (530 nm) only, while, in principle, the instrument can operate regardless of wavelength. We refer to this imaging ellipsometry configuration as rotating-anisotropic-mirror-sample-rotating-anisotropic-mirror ellipsometry (RAM-S-RAM-E). (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement Funding Agencies|National Science FoundationNational Science Foundation (NSF) [DMR 1808715, OIA-2044049]; Air Force Office of Scientific ResearchUnited States Department of DefenseAir Force Office of Scientific Research (AFOSR) [FA9550-18-1-0360, FA9550-19-S-0003, FA9550-21-1-0259]; Knut och Alice Wallenbergs StiftelseKnut & Alice Wallenberg Foundation

Bragg-gratings have been frequently used to design compact and high extinction ratio (ER) on-chip polarizers. However, the strong reflection of the unwanted polarization may deteriorate the performance of the light source or cause unwanted interferences. In this paper, we propose a Bragg-grating-based all-silicon TM-pass polarizer with low reflection, low insertion loss (IL) and high ER. Unlike previously reported polarizers based on single mode waveguides, we construct the Bragg grating with a multimode waveguide, which not only acts as a Bragg reflector, but also a mode-order converter to convert the reflected TE light into higher order modes to be eventually filtered out by utilizing a tapered transition. On the other hand, the grating has little adverse influence on the TM input light since it works at sub-wavelength-guided wave propagation regime. Finally, the polarizer obtained has a length of 30µm, an ER of 51.83dB, an IL of 0.08dB, and an operating bandwidth of ∼61nm for ER > 30dB at the wavelength of 1.55µm. More importantly, the reflection of the unwanted polarization is suppressed to −12.6dB, which can be further lowered via additional design optimization. Our work points to a new direction for making better on-chip polarizers.

In this study, by loading a Si optical modulator with an integrated polarizer using a curved waveguide, we developed a Si optical modulator with a high extinction ratio of over 50 dB. It can be applied to a wide range of applications from digital coherent optical communication to sensing.

In this contribution, we summarize some of our recent results about the design of dipolar and multipolar all-dielectric metasurfaces featuring advanced wave-manipulation effects. We focus our attention on both dipolar and multipolar metasurfaces and we show how it is possible to engineering their complex scattering response for designing several electromagnetic devices, such as angular filters, optical forward scatterers, high-Q passband filters and polarizers working for extreme angles of incidence.

Here, we present thorough research into high-order vector Bessel-Gauss beams from a theoretical perspective, with experimental realization and application to transparent-material laser micromachining. Efficient, stable, high-quality, and power-vector Bessel-Gauss beam generation using two geometric-phase-based optical elements, a high-order $S$-wave plate and an axicon in combination with simple optical elements, such as lenses, wave plates, and polarizers, is demonstrated. Ultrashort pulse-vector Bessel-Gauss beams are used to induce modifications in the glass, creating three-dimensional tubular structures of type I and type II modification in D263T glass. Furthermore, samples containing tubular modifications are tested for etch selectivity in the femtosecond-laser-induced chemical-etching method with KOH solution by etching throughout channels.

This research presents the design and main electromagnetic characteristics of the novel compact microwave waveguide polarizer. The developed device's structure is based on a circular waveguide and anti-phase conducting posts located in it. The application of a circular waveguide instead of a square one allowed simple integration of a polarizer with corrugated horn antennas. The obtaining of required phase difference using a posts-based design provides the possibility of fine tuning of the developed circular waveguide polarizer after its manufacturing process. In addition, simultaneous adaptive operation at orthogonal circular and linear polarizations is available in the antenna system including a polarizer with posts. An automatic control of posts height must be applied in a waveguide in order to provide this option. Numerical simulation, optimization, manufacture and measurements of the polarizer's characteristics were carried out in the operating band 7.4-8.5 GHz. Measured characteristics proved that the suggested circular waveguide polarizer provides good matching and polarization performance. Developed circular waveguide polarizer can be integrated in corrugated horn antenna systems and applied in modern weather radars and satellite information systems.

Most on-chip optical isolators utilize nonreciprocal magneto-optic (MO) garnet-materials that require an external bias magnetic field to operate. The magnetic field is applied through incorporation of either a permanent magnet or an active electromagnet. Permanent magnets add significantly to device bulk and electromagnets increase fabrication complexity and power consumption. Hence, it is highly desirable to reduce or eliminate the magnetizing component in these devices. Here, we experimentally demonstrate a first of its kind bias-magnet-free (BMF) on-chip waveguide optical isolator with integrated Polarcor UltraThin polarizers. The BMF isolator device obviates the need for magnetizing components while possessing superior performance, relative to other on-chip isolators, with ≥25 dB of isolation ratio (IR), and ≤3.5 dB of insertion loss (IL) across the entire infrared optical C-band.

A high precision demodulation method based on least squares fitting for expanding the temperature measurement range of the fiber Lyot filter has been proposed and experimentally demonstrated. And a compact reflective Lyot filter has also been proposed to verify this method. The filter consists of a polarizer and a section of polarization maintaining fiber (PMF) coated with a gold film at the end. The birefringence of the PMF can be obtained through the least squares method, so that the temperature measurement range is not limited to the free spectral range (FSR) of the periodic interference spectrum. Experimental results show that the proposed method can extend the measurement range by 5.5 times compared to the dip wavelength tracking method. And the demodulation fluctuation of the birefringence is within 10-7 .

This paper proposed a novel polarimeter for full-Stokes polarization imaging without using any kind of micro-polarizer array. The key components of the polarimeter are two grooved birefringent crystal plates with deviate fast axis, which are called Binary Birefringent Crystals (BBCs) in this paper. Mounting the jointed BBCs in the focal plane of an imaging detector, we manage to obtain the four components of Stokes vector simultaneously through the method proposed in this paper. We demonstrate the basic principle of the proposed polarimeter and verify it through numerical analysis. And one of the best-optimized configurations for the polarimeter is also presented. The proposed polarimeter is simultaneous, compact, easier in fabrication and capable of full-stokes polarization imaging. It is expected to be of potential use in a variety of applications.

An optical communication system transmits analog and digital information from one place to another using high carrier frequencies lying in the range of 100—1000 THz in the visible and near‐infrared region of the electromagnetic spectrum. This chapter describes the basic elements of the optical communication channel, including the transmitter, as a source of light, and the receiver, as the detector of light. The photodetectors do not affect the propagation properties of the optical wave but certainly must be compatible with the rest of the system. The transmitter includes a modulator, a driver, a light source, and optics. The receiver includes optics, a filter, a polarizer, a detector, a trans‐impedance amplifier, a clock recovery unit, and a decision device. The atmospheric channel attenuates the power of the optical signal and widens and spreads it in the spatial, temporal, angular, and polarization domains.

It has been shown that the intensity of linearly polarized light transmitted through CdS single crystal depends on its temperature. It has been found that the temperature of crystal does not affect the linearity of light polarization at the exit of crystal, but leads only to rotation of the polarization plane. It has been ascertained that in the range between 11 to 170 °C, the temperature dependence of the linear expansion coefficient and the difference between the refractive indices of unusual and ordinary beams can be neglected.

We demonstrated experimentally an opportunity to form space grating patterns in Ag3AsS3 semiconductor crystals under an influence of coherent femtosecond (195 fs) laser beams. The observation of the laser stimulated gratings has been performed using a cw He–Ne laser with power about 15 mW at 1150 nm wavelength. The photoinducing femtosecond laser with pulse duration about 190 fs and frequency 65 MHz bandpass has been used in the two-beam coherent regime at wavelength 1045 nm. The set of dichroic mirrors, polarizers, and lenses have been applied to form two space-separated beams, which interact with the studied Ag3AsS3 trigonal single crystals. The treatment has been performed during additionally applied dc-electrical strength equal to about 8 kV/cm with a frequency about 20 kHz directed perpendicularly to the optical axis. The monitoring of the photo-thermal effects and photo-destruction have been done using the optical fiber spectrometer Ocean Optics with spectral resolution 1 nm.