Search

In this paper, an analytical model is represented to analyze and improve the performance of radio over fiber (RoF) links against nonlinear distortion. RoF transmission link comprised of a phase modulator, polarizer and optical filter is considered. By controlling angles of polarization, the signals are fed to the modulator. Polarizer helps to suppress intermodulation distortion along the considered link. Performance is found in terms of spurious-free dynamic range (SFDR). Results show an improvement of 7.5-dB in SFDR for a polarized link in comparison with the conventional link.

In this study, we propose and experimentally demonstrate a design of silicon metasurface that integrates the functions of a grating, a polarizer, and a band-pass filter in the near infrared regime. This metagrating device features double periodicity in one direction, which enables the near-field Moire effect to generate diffraction in the far field. Based on a high contrast two-dimensional grating, the metasurface utilizes the guided-mode resonance to enhance the coupling of evanescent waves. Our results demonstrate that strong diffraction only occurs in a certain wavelength range and is polarization-sensitive. Since the metagrating device is capable of multiple functionalities with a single component of subwavelength thickness, practical applications of flat optics can be expected in miniaturizing polarization-controlled optical systems, such as polarimetric imaging systems.

We experimentally demonstrate a simple approach to generate optical vortex (OV) beams using optical fibers. The main structure is realized by asymmetrically splicing a standard simple-mode fiber (SMF) with a two-mode fiber (TMF). The asymmetrical fusion joint can partly convert input fundamental mode to higher-order fiber modes. While the unconverted fundamental mode component can be eventually filtered out through adjusting the states of two polarization controllers (PCs) applied on the SMF and TMF, and one polarizer located behind output end of the TMF. By adjusting the two PCs, one can also selectively generate LP modes or OV modes with l = ±1. The relationship between offsets and conversion efficiency is measured and analyzed, which accords well with simulations. Performance of mode purity and working bandwidth are also measured in the experiment.

This report forms a part of the systematic investigation on the imaging behaviour of an optical system consisting of a lens made of a uniaxial birefringent crystal sandwiched between two linear polarizers into which primary spherical aberration is introduced. The optic axis of the birefringent crystal is perpendicular to the lens axis. The proposed system is illuminated with a polychromatic beam of light, the spectral profile of which is considered to be uniform for all wavelengths. The axial irradiance distribution function and the intensity point spread function are used as the image assessment parameters. Some specific cases are computed and illustrated graphically. The study reveals that if the variation of the birefringent parameters of the device with wavelength is less, a larger bandwidth may be used without considerably deviating from the imaging characteristics under strictly monochromatic illumination suffering from similar primary spherical aberration.

In this paper, a three-layer chiral structure is proposed to achieve the conversion of its performance between broadband circular polarization asymmetric transmission and broadband circular dichroism by rotating the upper layer of the structure. For circular polarization asymmetric transmission, its asymmetric transmission parameters can reach a maximum of 0.89 and over 0.5 from 134 to 225 THz. For circular dichroism, the co-polarized transmission coefficient of right-handed circularly polarized wave is above 0.8 and the co-polarized transmission coefficient of left-handed circularly polarized wave is lower than 0.25 from 137 to 214 THz. The above results have not been reported in previous papers. This structure provides potential applications for circular polarization converters and circular polarizers.

Two-wavelength common-path off-axis digital holography is proposed with a tri-window in a single shot. It is established using a standard 4f optical image system with a 2D Ronchi grating placed outside the Fourier plane. The input plane consists of three windows: one for the object and the other two for reference. Aided by a spatial filter together with two orthogonal linear polarizers in the Fourier plane, the two-wavelength information is encoded into a multiplexed hologram with two orthogonal spatial frequencies that enable full separation of spectral information in the digital Fourier space without resolution loss. Theoretical analysis and experimental results illustrate that our approach can simultaneously perform quantitative phase imaging at two wavelengths.

In this paper, we perform numerical and experimental studies of the optical response of an original configuration that consists of enhanced transmission guided mode-based metamaterials. The proposed structure is inspired by an annular aperture array where the cylindrical symmetry is broken in order to acquire polarization-sensitive metasurfaces. The experimental results, which are in good agreement with numerical simulations, demonstrate that the structure acts as a polarizer exhibiting an extinction ratio of (15:1) with a maximum transmission coefficient up to 85%, which is more efficient than what is expected with a typical plasmonic resonance.

A cube beam splitter (CBS), which is more often used in two beam interferometers to generate orthogonally directed light beams, can interestingly be used to construct a two beam interferometer by aligning its beam splitting surface parallel to the direction of propagation of light. It is shown that in such a configuration, an optical sample placed so as to intercept one half of the expanded incident beam may be tested for phase or surface distortions. The proposed set-up can be used as well to construct a phase shifting interferometer by properly incorporating a quarter-wave plate and a polarizer for phase shifting, which can then be used to analyze phase or surface irregularities in optical samples. The monolithic design of the proposed interferometer makes it relatively immune to ambient vibrations.

It is shown that a cube beam splitter can serve as a single-element birefringence-sensitive interferometer. The polarization-masked beam splitter is oriented as in Gate’s Interferometer i.e., the beam splitting interface is parallel to the incident plane beam. The output consists of a pair of collinearly propagating orthogonally polarized beams which intercepts the birefringent sample placed before a linear polarizer. It is interesting to note that in the proposed method, measurement of birefringence remains unaffected by any phase non-uniformity that might be present in the sample.

In this communication we propose an analytical model of phase sensitive transverse interaction between two orthogonally polarized Gaussian pusles. To realize it we consider a Gaussian pulse propagating through an electro optic modulator. Using polarizer we first decompose it into two linearly orthogonal polarized waves. Then the orthogonal components of the pulses move through the optical fiber. By controlling the applied voltage across the modulator and controlling the ratio of length to width of the modulator we can change the phase relation between the pulses. With the method a switching at a very long distance can be organized in the optical fiber.

Black phosphorus exhibits extreme anisotropic properties due to its special lattice structure. In this paper, we numerically show that strong anisotropic perfect absorption can be realized in a nanostructured monolayer black phosphorus with the excitation of plasmonic resonances. Under normal incidences, the structure shows a 99.56% absorption for one polarization at the resonance wavelength while only 9.48% absorption for the other polarization at the same wavelength. The anisotropic responses are purely attributed to the intrinsic material anisotropy of black phosphorus which is different from conventional metallic or graphene plasmonic absorbers. The wavelength of peak absorption is tunable by changing the electron concentration in black phosphorus. As an example of application, we proposed a new design of tunable reflective polarizer based on black phosphorus and a polarization extinction ratio around 23 dB can be achieved.

A polarization control method using crystal birefringence is suggested to manipulate polychromatic light. This scheme can be used with narrower bandwidth to produce various spectral effects, such as a notch filter, a flat top, and triangle-type, nipple-type, and central-frequency-dominant distributions. A modulated spectrum with greater bandwidth can be used as an optical frequency ruler, and phenomena called complementary spectra are also proposed, where the two spectral distributions, produced by rotating the polarizer, complement each other in the sense that the peaks and valleys in one spectrum are the reverse in the other. These results benefit the controlling of the spectral shape and the measurement of an unknown optical frequency.

This report forms a part of the systematic investigation on the imaging behaviour of a birefringent lens sandwiched between two linear polarizers. Since an appreciable amount of light energy is absorbed in the polarizers, an analytical formula for the light throughput of the proposed system has been developed. A comparative study of the performance of the said system with an isotropic lens of reduced size which give equal light levels at the output side has been performed.

The imaging characteristics of an optical system consisting of a lens made of a birefringent material sandwiched between two polarizers are studied analytically. The birefringent lens has some pre-specified primary coma present in it. Expressions are obtained for the effective pupil function and the intensity point spread function of this system. Some specific cases are computed and illustrated graphically. The performance of the proposed system has been compared with that of an identical clear aperture lens.

We report a scheme for polarization sensitive near field imaging of nanostructured samples by making use of broadband polarized near field illumination and detection of polarization states of scattered light by a spectrally encoded analyzer. The analyzer comprising a combination of polarizer, a multi-order waveplate and a broadband quarter waveplate allows analysis of the spectrally encoded polarization states of scattered light for characterization of the polarization properties of nano structures from a single image scan. The scheme was validated by measuring the near field polarization parameters of silver nanowires. The approach allows simultaneous measurement of polarization characteristics as well as spectral features of the nano materials.

Topological aspect of the geometric phase (GP) due to pure polarization projection is studied using the 2D Fourier transform (2D-FT) method. Projection of orthogonal polarization state results in a phase singularity in the 2D parameter space of ellipticity and orientation of polarization ellipse. Projection of its surrounding states results in an accumulation of GP in different amount that form a spiral structure. A half wave plate–quarter wave plate combination is used to generate different polarization states which are projected using a polarizer. The accumulated phase for each orientation of the wave plate is extracted from 2D-FT of the interferogram, obtained by interfering it with a reference beam in a Mach–Zehnder like interferometer.

This article presents a theoretical study on an optical module (OM) that can be inserted between an object under investigation and a Fourier-domain optical coherence tomography system, transforming the latter into a polarisation-sensitive optical coherence tomography optical coherence tomography (OCT) system. The module consists of two electro-optic modulators, a Faraday rotator, a linear polariser and a quarter-wave plate. A detailed description on how the module can be used to extract both the net retardance and the fast axis orientation of a linear birefringent sample is presented. This is achieved by taking two sequential measurements for different values of retardance produced by the electro-optic modulator. The module keeps measurements free from undesired polarimetric effects due to birefringence in the single-mode optical fibre and diattenuation in fibre-based couplers within OCT systems. Simulations have been carried out in order to evaluate the effects of chromatic behaviour of the components within the OM.

For a full-Stokes polarimeter (FSP), generally there are two types of noise, signal-dependent Poisson shot noise and signal-independent additive Gaussian noise, which will degrade the signal-to-noise ratio on the measured Stokes parameters. The relation between the immunity to Gaussian noise and the condition of the measurement matrix has been widely studied in the recent literature. In this paper, we present a new merit function and use it to achieve optimal configurations with immunity to both types of noise. The numerical results show that, for the FSP consisting of variable retarders followed by a fixed polarizer, the four measurement channels immune to these two types of noise can be optimally composed by a 102.2° retardance with a pair of azimuths ±71.9° and a 142.1° retardance with a pair of azimuths ±34.95°, or by two quarter-wave plates with four pairs of azimuths (±70.15°, ±87.84°) and (±42.82°, ±19.14°). The tolerances of the retardances or azimuths in the optimized configurations are evaluated for practical manufacturing, assembling and alignment.

We analyzed the effect of resonant coupling between core and cladding modes in a helical core fiber with large core offset using the fully vectorial method based on the transformation optics formalism. Our study revealed that the resonant couplings to lower order cladding modes predicted by perturbative methods and observed experimentally in fibers with small core offsets are in fact prohibited for larger core offsets. This effect is related to the lack of phase matching caused by elongation of the optical path of the fundamental modes in the helical core. Moreover, strong couplings to the cladding modes of the azimuthal modal number much higher than predicted by perturbative methods may be observed for large core offsets, as the core offset introduces higher order angular harmonics in the field distribution of the fundamental modes. Finally, in contrast to previous studies, we demonstrate the existence of spectrally broad polarization sensitive couplings to the cladding modes suggesting that helical core fibers with large core offsets may be used as broadband circular polarizers.

From the fact that interference fringe visibility is not always proportional to the modulus of the coherence degree, we derive the possibility of a perfect visibility of fringes without a perfect coherence everywhere in the interference field. A similar situation was known to exist for spatial coherence, but it is impossible for temporal coherence. Here we consider it in the case of polarisation coherence; we express a necessary and sufficient condition for perfect polarisation coherence with the intention to depart from it. Since crystal optic interferences are described in a situation where polarisation coherence is not perfect, we describe examples with no polariser or analyser and yet with perfect fringe visibility.

For a given crystal optics device with polarization properties there are two kinds of trajectories that can be drawn on the Poincare sphere, namely the isolated and real trajectories. Using Stokes vectors and Mueller matrices, the parametric equations that represent the evolution of the state of polarization due to the passage of light through polarizers and optical components exhibiting linear or circular birefringence are given. The geometrical trajectories given by these equations, are useful for analyzing or designing optical birefringent networks and they are easy to obtain with today's computer software. An example of their application in the analysis of a Solc filter is given.

The tunable Solc filter can be realized with a single mode fiber coil between two orthogonal polarizers and a uniform magnetic field. The filter the authors built has a band pass centered at 492 nm and a band width equal to 13 nm. The spectral transmittance of this filter is tunable through the intensity of the magnetic field.

Thin and flexible bi-layer terahertz chiral metamaterials are experimentally demonstrated in both handednesses at terahertz frequencies. The structures are made of conjugated C8 metallic resonators fabricated on a flexible polyimide substrate. These structures exhibit chirality and can distinguish circularly polarized waves at the frequency range from 0.5 to 0.9 THz, equivalent to 57.15% bandwidth. The structures can be used as circular polarizers for terahertz waves.

The transmittance of simple one-dimensional gratings and two-dimensional pillar arrays is usually broadband with poor selectivity in the infrared region. In this paper, it is demonstrated that covering graphene on top of a Ag grating will improve both the magnitude and coherence of the transmitted infrared radiation. The underlying mechanism of this anomalous blocking-assisted transmission is attributed to the excitation of localized magnetic resonances. Quantitative predictions of the resonance wavelength for different geometric parameters and graphene chemical potentials are provided based on the equivalent-circuit model. The enhancement is alignment-free and actively tunable. Such graphene-covered gratings may help improve the performance and robustness of optical devices, such as polarizers, color filters, lab-on-chip sensors, and transparent conductors.

The interference between optical beams of different polarizations plays a fundamental role in reproducing the optical analog of the electron spin weak measurement. The extraordinary point in optical weak measurements is represented by the possibility to estimate with great accuracy the Goos-Haenchen (GH) shift by measuring the distance between the peak of the outgoing beams for two opposite rotation angles of the polarizers located before and after the dielectric block. Starting from the numerical calculation of the GH shift, which clearly shows a frequency crossover for incidence near to the critical angle, we present a detailed study of the interference between s and p polarized waves in the critical region. This allows to determine in which conditions it is possible to avoid axial deformations and reproduce the GH curves. In view of a possible experimental implementation, we give the expected weak measurement curves for Gaussian lasers of different beam waist sizes propagating through borosilicate (BK7) and fused silica dielectric blocks., Comment: 16 pages, 7 figures

We present the design, analysis, and measurement of a triple-band linear and circular reflective polarizer based on an E-shaped metamaterial. Measured results show that the proposed reflective polarizer can convert a linearly polarized wave to its cross-polarized wave at the three resonant frequencies, which can also convert the linearly polarized wave to a circularly polarized wave at three other resonant frequencies. Furthermore, the reflective wave can maintain the same rational direction at the three resonant frequencies when the incident is a circularly polarized wave. The simulated and measured results are in agreement in the entire frequency range, and the polarization conversion ratio (PCR) is over 90% for both linear and circular polarizations. The mechanism of polarization conversion is interpreted by using surface current distributions.

Measured reflection spectra from elytra of Chrysina aurigans scarabs are reported. They show a broad reflection band for wavelengths from 0.525 to 1.0 μm with a sequence of maxima and minima reflection values superimposed on a mean value of around 40% for the high reflection band. Different mechanisms contributing to the reflection spectra have been considered, with the dominant effect, reflection of left handed circularly polarized light, being produced by a laminated left handed twisted structure whose pitch changes with depth through the procuticle in a more complex way than that characterizing broad band circular polarizers based on cholesteric liquid crystals.

We study the interaction of electromagnetic (EM) radiation with single-layer graphene and a stack of parallel graphene sheets at arbitrary angles of incidence. It is found that the behavior is qualitatively different for transverse magnetic (or p-polarized) and transverse electric (or s-polarized) waves. In particular, the absorbance of single-layer graphene attains a minimum (maximum) for the p (s)-polarization at the angle of total internal reflection when the light comes from a medium with a higher dielectric constant. In the case of equal dielectric constants of the media above and beneath graphene, for grazing incidence graphene is almost 100% transparent to p-polarized waves and acts as a tunable mirror for the s-polarization. These effects are enhanced for a stack of graphene sheets, so the system can work as a broad band polarizer. It is shown further that a periodic stack of graphene layers has the properties of a one-dimensional photonic crystal, with gaps (or stop bands) at certain frequencies. When an incident EM wave is reflected from this photonic crystal, the tunability of the graphene conductivity renders the possibility of controlling the gaps, and the structure can operate as a tunable spectral-selective mirror., This work was partially supported by FEDER through the COMPTETE Program and by the Portuguese Foundation for Science and Technology (FCT) through Strategic Project PEst-C/FIS/UI0607/2011., EC under Graphene Flagship

The frequency modulation to amplitude modulation (FM-to-AM) effect is one of the few remaining scientific issues in a large-scale laser facility which could prevent fusion ignition. A fiber-based polarization?rotation filter which consists of a fiber polarizer, a section of polarization-maintaining fiber, a half-wave plate and a polarization beam splitter is proposed to suppress the FM-to-AM effect. Theoretical analysis and experimental demonstration in the preamplifier module of the SG-III laser facility prove the effectiveness of this filter.

We analyze polarization singularities of optical beams that propagate through crystals possessing structural dislocations. We show that screw dislocations of crystalline structure can lead to the appearance of purely screw-type dislocations of light wavefronts. This can happen only in crystals that belong to trigonal and cubic systems. These polarization singularities will give rise to optical vortices with the topological charge equal to ?1, whenever a crystal sample is placed between crossed circular polarizers. We have also found that edge dislocations present in the cubic and trigonal crystals, with the Burgers vector perpendicular to the three-fold symmetry axes, can impose mixed screw-edge dislocations in the wavefronts of optical beams and generate singly charged optical vortices. The results of our analysis can be applied for detecting and identifying dislocations of different types available in crystals.

Mueller matrix measurements are most commonly performed using a set of polarization state generating (PSG) optics and an independent set of polarization state analyzing (PSA) optics. However, for polarized confocal microscopy and polarization sensitive optical coherence tomography it would be advantageous if the same set of polarization optics could be used for both PSG as well as PSA. This has not been possible because, in this configuration, a complete set of incident and analyzer states cannot be generated using polarizers and waveplates alone. In an earlier attempt to address this issue it was shown that by using two Faraday rotators, with independently variable circular retardance, in the polarization optics, complete Mueller matrix measurement can be performed. However, a practical implementation of this approach has proved to be difficult due to the requirement to vary the circular retardance. In this paper we show that by incorporating only one Faraday rotator in the polarization optics, one can generate the complete set of incident and analyzer states required for Mueller matrix measurements without the need to vary the circular retardance of the Faraday rotator.

In this paper we propose a cavity design for a fibre ring laser with two linear polarizers that allows precise control of the multisoliton generation process while keeping a constant laser pump power. This design also has other potential beneficial features as a consequence of the control of nonlinear evolution of polarization in the laser cavity.

We report the development of a near real time single mode fiber-optic based polarization sensitive optical coherence tomography (PSOCT) setup utilizing a swept source. The setup has a polarization modulator (PM) and polarizer in a sample arm to serve as a polarization state generator and analyzer. Since only intensity information is used to retrieve the polarization parameters of the sample, the problem of phase jitters present in the swept source is avoided. Further, the use of polarization elements after the sample arm fiber makes the approach insensitive to the random birefringence of fibers. The swept source based PSOCT (SS-PSOCT) setup was calibrated by carrying out measurements on a quarter-wave plate whose fast axis orientation was rotated from 0° to 360° in steps of 10°. The setup has been used for imaging birefringence of mice tail tendon, thigh muscle ex vivo and human nail fold in vivo.

Modulation of polarization is commonly employed in optical interferometry through the use of polarizers and quarter-wave retarders. Phase shifts between interfering beams can be easily controlled with such techniques. This communication describes some details of modulation of polarization which are useful in phase shifting interferometry applied to the study of phase objects. As an application, the case of a two-beam phase grating interferometer is discussed on the grounds of polarization analysis as an example. The configuration presented does not require micro-polarizer arrays or additional software to eliminate noise caused by vibration. This system does not use a double window, and generates two beams, the separation of which can be varied according to the characteristics of the grid used. Experimental results are also given.

We propose a broadband circular polarizer in the terahertz region using helical metamaterials. The finite difference time domain method was used to design the structure and perform the simulation. By properly selecting the parameters of helical metamaterials, including the radius of wires, number of helix-periods, spacing of grids, length of helix-period, and radius of helix, we obtained a broadband helical circular polarizer in the terahertz region that can achieve an extinction ratio above 20:1 in the wavelength range from 66 to 105 µm.

We propose a robust interferometric method to measure the Jones matrix of polarization components, especially liquid crystal displays. Phase values are measured by a simple common path interferometer containing a birefringent crystal as beam splitter and a polarizer as beam combiner. This solution eliminates the sensitivity of traditional interferometric techniques to vibration, temperature variation or wavefront distortion. The proposed phase measurement method is applicable to the measurement of both spatially homogeneous and binary modulated states, thus the modulation transfer function and inter-pixel interference can also be studied. We demonstrate this technique by the measurement of a liquid crystal on silicon display. The resulting Jones matrix, as a function of displayed gray level, can be efficiently embedded in any numeric model of an optical system containing the analyzed spatial light modulator.

We report the generation of cylindrical vector beams using a concentric metallic grating fabricated on optical fibers with a period smaller than the wavelength of the incident light. Similar to the wiregrid linear polarizer, such a subwavelength metallic annular structure strongly reflects azimuthal polarization and allows radial polarization to transmit through. Due to the polarization selectivity of the concentric metallic grating, a cylindrical vector beam is obtained when a circularly polarized light is launched into the fiber. Such a device is suitable for the end mirror coupler in an all-fiber laser design to produce radially polarized modes.

Periodic structures with artificial anisotropic dielectrics are studied. The artificial anisotropic dielectric material in this work is made of two alternating isotropic dielectric layers. By a proper choice of the dielectric constant of the layers, we can realize a uniaxial anisotropic medium with controllable anisotropy. The artificial anisotropic dielectric is then used in periodic structures. For these structures, the optical axis of the artificial dielectric is assumed to be parallel or perpendicular to the period of the structure. Diffraction of plane waves by these structures is analyzed by a fully vectorial rigorous matrix method based on a generalized transmission line?(TL) formulation. The propagation constants and field distributions are computed and diffraction properties of such structures are studied to show that, by a proper choice of structural parameters, these periodic structures with artificial anisotropic dielectrics can be used as polarizers or polarizing mirrors.

An infrared polarization switch was fabricated by sandwiching liquid crystal between two silicon prisms. The liquid crystal was so aligned as to exhibit the ordinary index no for p polarization and the extraordinary index ne for s polarization. Consequently, a p polarized beam was reflected at the boundary, while an s polarized beam passed through the liquid crystal layer. When an electric voltage (15 V) was applied between the prisms, the liquid crystal was reoriented in the direction perpendicular to the prism surface. Accordingly, an s polarized beam was reflected and a p polarized beam passed through the liquid crystal layer.

Theoretical attenuation characteristics of a metal clad four-layer thin film optical waveguide with a high index buffer are presented. Metal clad optical waveguides with a high index buffer layer possess a unique property which arises from the effect of periodic coupling between the lossless modes of a dielectric waveguide and the lossy modes supported by the high index buffer clad with metal. It is observed that both transverse electric (TE) and transverse magnetic (TM) pass polarizers can be produced using this structure. High extinction ratio polarizers for a high index dielectric buffer layer and a metallic overlayer for ion exchanged planar optical waveguides for λ = 0.6328 μm have been designed; this corresponds to the most commonly used He‐Ne laser. Results are presented for As2S3 as a buffer layer and Al, Au and Ag as metal claddings. We have shown that a waveguide polarizer extinction coefficient as high as 800 dB can be obtained for both polarizations. An oscillatory behavior similar to that of semiconductor clad waveguides is observed for both TE and TM mode losses. The effect of the buffer thickness and index on the guided modes is also presented.

A real-time gray level intensity pseudocolor encoding method utilizing a liquid crystal television (LCTV) is presented. The LCTV is used under two different polarizer/analyser combinations to generate a positive image and a negative image of an object. The images are also encoded with two different primary colors by positioning the color filters at the two optical paths respectively. The superposition of these images produces a gray level pseudocolor encoded image. Discussions on the properties of the LCTV is provided. Preliminary experimental results are also demonstrated.

The authors study the practical possibilities of filters constructed with linear polarizers with their polarizing axis in different orientations. A filter of such characteristics placed on the Fourier plane of an optical imaging system and the introduction of an analyzer in that system permit the assignment of levels of grey to the different orientations of the spatial frequencies present in the object. Thus, directional information of the object is extracted. Moreover, the method is dynamic: different grey-codings can be obtained by a simple turning of the analyzer without changing the fibers. This flexibility permits the saving of time in the directional analysis of an image.

The polarization state of light transmitted by cholesteric liquid crystals when the incident vibration direction makes any angle with the director, and when p>> lambda is studied. Theoretical investigations show that figures observed between polarizer and analyser on samples of variable thickness are quite complex except when the incident vibration is parallel to the director or makes an angle equal to pi /4 with it. Experimental verifications are given for those two cases.

The birefringent filter presented shows a field-of-view extended in one dimension. This device is composed of a series of polariscopes placed between parallel polarizers. Each polariscope gives straight line fringes in the far field. By proper choice of the thickness of the birefringent elements, the spectrum of the light transmitted by the filter consists of a small number of lines, or a single line. In the last case the filter gives an extended straight monochromatic fringe in the far field. This device acts as a preselector filter only.