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Beam splitters, especially those with tunable split ratios, play significant role in interferometers, spectrometers, and communication systems. To this end, we proposed a polarization-controllable beam splitter based on dielectric metasurface composed of an array of dielectric pillars. The dielectric metasurface presents phase gradients along two orthogonal directions, say, x- and y- axis, with each phase gradient applicable to one of two orthogonal linear polarizations. Due to the orthogonality of the dual phase gradients in both position and polarization, an elliptically polarized incident beam can be diffracted into two refracted beams, one lies within xoz plane and the other in yoz plane. More importantly, the split ratio of the two refracted beams is continuously tunable by changing the ellipticity of incident beam. Under extreme case, x- or y- polarized incident beam is refracted into one beam, but in different planes for different kind of linear polarization. Besides, the refracted angle of each refracted beam in respective refracted plane can be easily set by adjusting the phase difference of adjacent rows or columns of metasurface. With same method, a polarization-controllable dual-wavelength beam splitter is also achieved on the basis of phase-gradient metasurface. Such a noncoplanar beam splitter with tunable split ratios may play significant role in novel miniature optical devices and systems.

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.

Subwavelength gratings (SWG) are periodic structures which behave as controllable homogeneous metamaterials. SWGs are extremely interesting when they are used in platforms with a limited choice of material refractive indices, enabling the design of a myriad of high-performance devices. Here we present a novel technique to gain control over the intrinsic anisotropy of the synthesized metamaterial. We show that tilting the silicon segments in a SWG structure mainly affects the in-plane (TE) modes, with little impact on the out-of-plane (TM) modes. Moreover, we present a methodology to quickly but accurately calculate the modes of a tilted periodic structure modeling the structure as a rotated uniaxial crystal which can be solved with an anisotropic mode solver. Measurements on a set of fabricated tilted SWG waveguides validate our simulation results. By using the presented technique, we design a polarization beam splitter based on a 2x2 multimode interferometer. The design is based on the optimization of the tilting angle to tone the beat length of the TE modes to be a half of the beat length of the TM modes., Integrated Optics: Design, Devices, Systems and Applications, April 1-4, 2019, Prague, Czech Republic, Series: Proceedings of SPIE

pA stable multimodal system is developed by combining two common-path digital holographic microscopes (DHMs): coherent and incoherent, for simultaneous recording and retrieval of three-dimensional (3-D) phase and 3-D fluorescence imaging (FI), respectively, of a biological specimen. The 3-D FI is realized by a single-shot common-path off-axis fluorescent DHM developed recently by our group. In addition, we accomplish, the phase imaging by another single-shot, highly stable common-path off-axis DHM based on a beam splitter. In this DHM configuration, a beam splitter is used to divide the incoming object beam into two beams. One beam serves as the object beam carrying the useful information of the object under study, whereas another beam is spatially filtered at its Fourier plane by using a pinhole and it serves as a reference beam. This DHM setup, owing to a common-path geometry, is less vibration-sensitive and compact, having a similar field of view but with high temporal phase stability in comparison to a two-beam Mach-Zehnder-type DHM. The performance of the proposed common-path DHM and the multimodal system is verified by conducting various experiments on fluorescent microspheres and fluorescent protein-labeled living cells of the mossitalicPhyscomitrella patens/italic. Moreover, the potential capability of the proposed multimodal system for 3-D live fluorescence and phase imaging of the fluorescent beads is also demonstrated. The obtained experimental results corroborate the feasibility of the proposed multimodal system and indicate its potential applications for the analysis of functional and structural behaviors of a biological specimen and enhancement of the understanding of physiological mechanisms and various biological diseases./p.

HARMONI is a visible and near-infrared integral field spectrograph equipped with two complementary adaptive optics systems, fully integrated within the instrument. A Single Conjugate AO (SCAO) system offers high performance for a limited sky coverage and a Laser Tomographic AO (LTAO) system provides AO correction with a very high sky-coverage. While the deformable mirror performing real-time correction of the atmospheric disturbances is located within the telescope itself, the instrument contains a suite of state-of-the-art and innovative wavefront sensor systems. Laser guide star sensors (LGSS) are located at the entrance of the instrument and fed by a dichroic beam splitter, while the various natural guide star sensors for LTAO and SCAO are located close to the science focal plane. We present opto-mechanical architecture and design at PDR level for these wavefront sensor systems., Comment: 11 pages, 13 figures, conference

Highly-compact devices capable of beam splitting are intriguing for a broad range of photonic applications. In this work, we report on the fabrication of optical waveguide splitters with rectangular cladding geometry in a Ti:Sapphire crystal by femtosecond laser inscription. Y-splitters are fabricated with 30 μm × 15 μm and 50 μm × 25 μm input ends, corresponding to two 15 μm × 15 μm and 25 μm × 25 μm output ends, respectively. The full branching angle θ between the two output arms are changing from 0.5° to 2°. The performances of the splitters are characterized at 632.8 nm and 1064 nm, showing very good properties including symmetrical output ends, single-mode guidance, equalized splitting ratios, all-angle-polarization light transmission and intact luminescence features in the waveguide cores. The realization of these waveguide splitters with good performances demonstrates the potential of such promising devices in complex monolithic photonic circuits and active optical devices such as miniature tunable lasers., This work is supported by the National Natural Science Foundation of China (No. 11404194). Authors acknowledge support from Junta de Castilla y León (Project SA046U16) and MINECO (FIS2015-71933-REDT). Authors would like to thank Prof. Xiaotao Hao from Shandong University for the help on micro-photoluminescence measurement.

International audience; This paper proposes digital holographic microscopy applied to the study of the production of lipids in Chlorella vulgaris microalgae. We propose to use several wavelengths to establish a chromatic phase contrast being the signature of the presence, or absence, of lipids in a set of microalga culture. In order to achieve this goal, the 3-color microscope has to be perfectly calibrated so that a point-to-point chromatic contrast can be evaluated without any distortion due to aberrations. The analysis of chromatic phase contrasts leads to measure the experimental probability density functions of the chromatic phase contrast distribution. Statistical analysis of the phase distribution in stressed cells and for not stressed cells reveals a difference in the probability densities. These experimental curves are fitted with two different theoretical modeling, one for the stressed algae (production of lipids), and one other for not-stressed algae. Fitting to experimental data demonstrates that the proposed approach opens the way for an in-situ and non-destructive experimental method to evaluate the production rate of lipids from Chlorella vulgaris algae.

International audience; The stabilization of a relatively simple optoelectronic oscillator tunable across the X-band based on a laser subjected to optical feedback is achieved. Specifically, a resonance effect based on locking the two inherent frequencies of the system, as well as, self-modulation were utilized to achieve a sub-ps phase jitter.

Mach-Zehnder interferometer is a common device in quantum phase estimation and the photon losses in it are an important issue for achieving a high phase accuracy. Here we thoroughly discuss the precision limit of the phase in the Mach-Zehnder interferometer with a coherent state and a superposition of coherent states as input states. By providing a general analytical expression of quantum Fisher information, the phase-matching condition and optimal initial parity are given. Especially, in the photon loss scenario, the sensitivity behaviors are analyzed and specific strategies are provided to restore the phase accuracies for symmetric and asymmetric losses., Comment: 10 pages, 3 figures

International audience; This paper proposes a quality assessment of focusing criteria for imaging in digital off-axis holography. In literature, several refocus criteria have been proposed in the past to get the best refocus distance in digital holography. As a general rule, the best focusing plane is determined by the reconstruction distance for which the criterion function presents a maximum or a minimum. To evaluate the robustness of these criteria, a set of thirteen criteria is compared with application on both amplitude and phase images from off-axis holographic data. Experimental results lead to define general rule and to exhibit the most robust criteria for accurate and rapid refocusing in digital holography.

This paper proposes a modified polarization converter for generating radially and azimuthally polarized beams. Based on a Mach–Zehnder-like interferometric structure, the device consists of a pair of lateral displacement beamsplitters (LDBs) and two half-wave plates that manipulate the states of polarization of incident linearly polarized light. Through the coherent superposition of two orthogonal Hermite–Gaussian modes in the far field, radially and azimuthally polarized beams can be obtained simultaneously. A prototype was assembled to demonstrate the feasibility of the design. The proposed design has the advantage of having a simple, symmetric, compact, and robust structure. In addition, the introduction of LDBs substantially reduces the cost of this device. Moreover, the design can be applied to a broadband pulsed laser with considerable potential in high-power applications.

Controllable power combination and distribution of multiple sources into multiple transmission lines may increase efficiency and flexibility of ECRH systems. A new quasi-optical version of diplexer based on a resonating system, coupling two transmission lines, is under development at IFP-CNR. Two dielectric beam splitters work as input/output ports for the diplexer, which can be thought as a Fabry Perot resonator. A third beam splitter can be inserted in the middle of the resonator. In this case the diplexer looks like a pair of mirrored resonators coupled by through the central splitter. Each beam splitter is made of a water-free silica layer, three quarter of wavelength thick at 140 GHz. The simulated performances were tested as a function of the frequency on the two splitters simpler model. Preliminary results confirm qualitatively theoretical predictions as well as the good channel separation obtainable with the three splitters version. Present work describes the system realization together with the low power tests performed. (C) 2011 EURATOM ENEA-CNR-Association/Instituto di Fisica del Plasma. Published by Elsevier B.V. All rights reserved.

We present wideband nonpolarizing beam splitters (NPBSs) for the telecommunication C-band. We show that silicon-on-insulator subwavelength periodic elements operating near leaky-mode resonance provide useful spectral expressions enabling effective beam division. Particle swarm optimization is the design method of choice. Periodic single-layer and multilevel NPBSs are provided exhibiting ~50/50 beam ratio under oblique and normal incidence. We compare the spectral performance of the beam splitters with that of their thin-film effective-medium counterparts, thereby verifying the resonance-mediated origin of the spectra sought. The beam splitters are found to be reasonably tolerant to deviations in angle of incidence and structural parameters.

We report on Y-branch superficial depressed-cladding waveguides fabricated by femtosecond laser writing of MgO∶LiTaO3 crystal. The cladding waveguides with a rectangular cross-section are single mode for both transverse electric and transverse magnetic polarization, and show good transmission properties at a telecommunication wavelength of 1.55 μm. Divergence angles as large as 2.6 deg are successfully achieved in the splitters with nearly equalized splitting ratios (1:1). The fabricated shallow structures are excellent photonic elements for optoelectronic applications., This work was supported by the National Natural Science Foundation of China (Grant No. U1332121) and Ministerio de Economía y Competitividad under Project FIS2013-44174-P, Spain.

We report on the fabrication of three-dimensional waveguide beam splitters in a dielectric Bi4Ge3O12 (BGO) crystal by direct femtosecond laser writing. In the laser written tracks of BGO crystal, positive refractive index is induced, resulting in so-called Type I configuration waveguiding cores. The “multiscan” technique is utilized to shape cores with designed cross-sectional geometry in order to achieve guidance at mid-infrared wavelength of 4 μm. The fundamental mode guidance along both TE and TM polarizations has been obtained in the waveguide structures. With this feature, we implement beam splitters from 2D to 3D geometries, and realize 1 × 2, 1 × 3, and 1 × 4 power splitting at 4μm., This work was supported by the National Natural Science Foundation of China (No. 11274203), Junta de Castilla y León under project (SA086A12-2), and Ministerio de Economía y Competitividad under project (FIS2013-44174-P), Spain.

Precision glass molding is a more cost efficient process for the large volume manufacturing of highly complex optical surfaces than direct manufacturing. Glassy carbon (GC) molds are used for precision glass molding, because they can be operated at temperatures up to 2000 degrees C. Used today mainly for manufacturing aspheric lenses, we consider here material technology for diffractive optical element (DOE). For diffractive optics the surface structuring is in the micrometer range and a surface roughness Ra lower than 20 nm is required. We introduce a reactive ion etching process with a titanium hard mask. Fused silica (FS) molds with identical optical functionality were fabricated for comparison. All molds were used for precision glass molding of a low T-g glass L-BAL42. We will compare GC and FS as mold materials in terms of quality and robustness. Optical performance measurements of the molded glass DOEs are shown and are in good agreement with the theoretical predictions. The results confirm that precision glass molding based on GC molds is a very promising technology to economically fabricate small structures in glass for DOEs.

Στην παρούσα εργασία μελετάμε τη λειτουργία των διαχωριστών δέσμης, καθώς και τη στατιστική κατανομή ενός και δύο σωματιδίων σε απλό και διπλό πηγάδι δυναμικού. Εξετάζουμε υπό ποιες συνθήκες τα δύο αυτά συστήματα μας δίνουν σύμπλεκτες καταστάσεις. Για τους διαχωριστές δέσμης καταλήγουμε στο συμπέρασμα ότι η καταλληλότερη διάταξή τους για να έχουμε μέγιστη απόδοση σύμπλεκτων καταστάσεων, είναι αυτοί να βρίσκονται σε διαδοχική σειρά μεταξύ τους. Από την άλλη μεριά, η μελέτη πηγαδιών δυναμικού, που έγινε γραφικά και αριθμητικά, μας έδειξε ότι τα γεωμετρικά χαρακτηριστικά τού κάθε πηγαδιού, δηλαδή το πάχος και το ύψος του, καθορίζουν τις ιδιοενέργειες τού συστήματος, τις πυκνότητες πιθανότητας των κυματοπακέτων και τελικά την πιθανότητα δημιουργίας σύμπλεκτων καταστάσεων. Γνωρίζοντας τη στατιστική κατανομή των σωματιδίων, ελέγχουμε τη συμπεριφορά τους άρα και την πληροφορία που αυτά μεταφέρουν. Τα παραπάνω βρίσκουν εφαρμογή στα qubits και τους κβαντικούς υπολογιστές. In the current project we study the function of the beam splitters as well as the statistical behavior of one and two particles in a single and a double quantum well. We examine the conditions under which these two systems provide us with entangled states. For the beam splitters we come to the conclusion that the most appropriate array for having entangled states, is to put them in successive line. On the other hand, the graphical and numerical study of the quantum wells showed that the geometrical characteristics of a quantum well, that is to say thickness and height, define the energy of the system, the density probability of the wave packets and finally the probability for having entangled states. Having knowledge of the statistical behavior of the particles, we may then control the informations that they carry. All the above have many applications in qubits and quantum computers.

A method was described previously that permits the systematic design of optical multilayer coatings with arbitrary spectral characteristics defined for two widely separated spectral regions. It is shown here that this method, based on the use of buffer layers, can be adapted to permit the specification of performance in more than two wavelength ranges. Examples are given of coatings designed for three and four spectral regions. The limitations of the method are discussed.

A miniaturized sensor head for the optical measurement of velocities of fluids based on laser Doppler velocimetry is demonstrated. Holographic optical elements mounted on a glass substrate are used for beam splitting and deflection. Volume holograms in dichromated gelatin exhibit good optical efficiency (75% transmission of a cascade of two holographic optical elements). With diffractive devices one can achieve achromatic behavior that makes the sensor insensitive to wavelength drifts or mode hopping of a semiconductor laser. Not applicable

International audience; Sol-gel derived inorganic-organic hybrid materials (HYBRIMERs) have shown a great potential for planar and channel waveguides due to their high photosensitivity, low-cost processing and good suitability for doping. These materials have been synthesized with a high content of titanium (40%) and with three different chelating agents: acetylacetone, methacrylic acid and trifluoroacetic acid. The degree of photopolymerization of the methacrylate part changes with the nature of the chelating agent. Trifluoroacetic acid and methacrylic acid are the chelating agents showing the highest photopolymerization conversion. All coatings were crack free (thickness $1 mm), transparent in the visible spectra range with refractive indexes from 1.54 to 1.58. Simple confined structures based on trifluoroacetic acid with well-defined shapes, smooth surfaces (RMS ¼ 0.28 nm) and good optical properties were synthesized. Straight and bent channel waveguides and beam splitters were patterned by UV exposure and wet etching, and light confinement effects into the different channel waveguides were shown.

We present a new technique for light scanning by use of viscoelastic-based deformable phase diffraction gratings. Mechanical stretching of the grating permits control of its spatial period, and thus the orders of diffraction can be spatially deflected. In the experiments the viscoelastic gratings with triangular and rectangular profiles have been characterized at lambda = 633 nm. It is demonstrated that the reversible elongation can exceed 20% of the initial length. For the triangular profile grating, the diffraction angle of the first order changed from 6.6 degrees to 5.4 degrees while the diffraction efficiency remained almost constant at approximately 17%. Dynamic scanning of a laser beam at frequencies of approximately 1 kHz is demonstrated by use of electromechanically driven viscoelastic gratings.

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

This thesis is concerned with the guiding of cold atoms using optical forces, which is of great importance in the field of atom optics. Atomic beams can be used for precision sensor equipment, building nano-scale structures, construction of quantum computers and to further the understanding of the properties of atoms. Atoms are guided along light beams using the dipole force; there are two regimes under which this force works. Typically red-detuned guides are used (atoms are attracted towards the light) such guides, however, require large detuning and high powers. In this thesis we investigate the use of blue-detuned (atoms are repelled from the light) hollow light beams of moderate power (a few hundred mW) and confine atoms in the dark centre of the beams. Several magneto-optical traps (MOTs) have been constructed to exploit different guiding geometries. Hollow beams have been generated using a variety of methods; in particular the use of a computer controlled spatial light modulator (SLM) has provided great versatility and simplicity to the experimental arrangements. First, experiments were performed with a low-velocity intense source (LVIS) of atoms. A co-linear LG beam significantly enhances the observed flux, however, considerable difficulties are encountered loading atoms into oblique guides. Imaging a hole in the walls of the light tube was used to improve the loading efficiency. Second, guiding a free-falling atom cloud is performed using a non-diffracting Bessel beam. It is found that while the potential of the Bessel beam is steeper than equivalent LG beams the power distribution across the beam severely limits its usefulness. The next study investigated higher-order LG guide beams generated with an SLM. High order modes have a narrower profile so confine the atoms with less interaction with the guide beam, leading to a more natural guide (as opposed to a pushing force). Finally the SLM was used to create non-trivial beam shapes for beam splitters and interferometers.

Switchable beam steerers based on zenithal bistable liquid crystal (LC) gratings are designed and theoretically investigated. The nematic orientation profiles and the optical transmittance properties of the gratings are rigorously calculated, respectively, via a tensorial formulation of the Landau-de Gennes theory and the full-wave finite-element-method. By proper design of the grating geometry, beam steering with high diffraction efficiency is demonstrated between the two stable LC states. The tolerance of the device performance with respect to material parameters is assessed, evidencing spectral operation windows of more than 50 nm in the visible for a beam steering efficiency higher than 90%. (C) 2014 Optical Society of America

We use mixed-period dielectric grooves to surround a single metal slit to realize two-beam nonsymmetrical and symmetrical emitting for the transmitted light emerged from the subwavelength slit. This proposed slit-groove-based structure is formed by combining two typical slit-groove structures, both possessing unidirectional beaming but with different beaming angles. Here, the typical slit-groove structure refers to the single slit perforated in the metal film, and the slit is surrounded by periodic dielectric grooves on the exit surface of the metal film. By using the finite-difference time-domain method, the simulation results show that two-beam emitting can be produced with flexible splitting angles via such combined structure. In addition, the power ratio of two-beam emitting can be changed via using appropriate groove number to surround the slit of the combined structure.