Showing papers on "Beam splitter published in 2008"

Optical design of reflectionless complex media by finite embedded coordinate transformations.

Abstract: Transformation optics offers an unconventional approach to the control of electromagnetic fields. The transformation optical structures proposed to date, such as electromagnetic "invisibility" cloaks and concentrators, are inherently reflectionless and leave the transmitted wave undisturbed. Here, we expand the class of transformation optical structures by introducing finite, embedded coordinate transformations, which allow the electromagnetic waves to be steered or focused. We apply the method to the design of several devices, including a parallel beam shifter and a beam splitter, both of which are reflectionless and exhibit unusual electromagnetic behavior as confirmed by 2D full-wave simulations.

Achromatic diffraction from polarization gratings with high efficiency.

Abstract: We demonstrate a broadband, thin-film, polarizing beam splitter based on an anisotropic diffraction grating composed of reactive mesogens (polymerizable liquid crystals). This achromatic polarization grating (PG) manifests high diffraction efficiency (~100%) and high extinction ratio (⩾1000:1) in both theory and experiment. We show an operational bandwidth Δλ/λ0~56% (roughly spanning visible wavelength range) that represents more than a fourfold increase of bandwidth over conventional PGs (and significantly larger than any other grating). The diffraction angle and operational region (visible, near-infrared, midwave infrared, and ultraviolet wavelengths) may be easily tailored during fabrication. The essence of the achromatic design is a stack of two chiral PGs with an opposite twist sense and employs the principle of retardation compensation. We fully characterize its optical properties and derive the theoretical diffraction behavior.

Transformation-optical design of adaptive beam bends and beam expanders

Abstract: We describe the design of adaptive beam bends and beam splitters with arbitrary bend and split angles by use of finite embedded coordinate transformations. The devices do not exhibit reflection at the entrance or exit surfaces. It is shown that moderate and practically achievable values of the relative permittivity and permeability can be obtained for beam bends and splitters with both small and large bend radius. The devices are also discussed in the context of reconfigurable metamaterials, in which the bend and split angles can be dynamically tuned. The performance of adaptive beam bends and splitters is demonstrated in full wave simulations based on a finite-element method. Furthermore, the design of an adaptively adjustable transformation-optical beam expander/compressor is presented. It is observed that a pure transformation-optical design cannot result in a reflectionless beam expander/compressor.

Atom Interferometry with up to 24-Photon-Momentum-Transfer Beam Splitters

Abstract: We present up to 24-photon Bragg diffraction as a beam splitter in light-pulse atom interferometers to achieve the largest splitting in momentum space so far. Relative to the 2-photon processes used in the most sensitive present interferometers, these large momentum transfer beam splitters increase the phase shift 12-fold for Mach-Zehnder (MZ) and 144-fold for Ramsey-Borde (RB) geometries. We achieve a high visibility of the interference fringes (up to 52% for MZ or 36% for RB) and long pulse separation times that are possible only in atomic fountain setups. As the atom's internal state is not changed, important systematic effects can cancel.

Fully valley-polarized electron beams in graphene.

Abstract: We propose a device to break the valley degeneracy in graphene and produce fully valley-polarized currents that can be either split or collimated to a high degree in a experimentally controllable way. The proposal combines two recent seminal ideas: negative refraction and the concept of valleytronics in graphene. The key new ingredient lies in the use of the specular shape of the Fermi surface of the two valleys when a high electronic density is induced by a gate voltage (trigonal warping). By changing the gate voltage in a n-p-n junction of a graphene transistor, the device can be used as a valley beam splitter, where each of the beams belong to a different valley, or as a collimator. The result is demonstrated through an optical analogy with two-dimensional photonic crystals.

Diffraction grating based interferometric systems and methods

Abstract: Diffraction grating based fiber optic interferometric systems for use in optical coherence tomography, wherein sample and reference light beams are formed by a first beam splitter and the sample light beam received from a sample and a reference light beam are combined on a second beam splitter. In one embodiment, the first beam splitter is an approximately 50/50 beam splitter, and the second beam splitter is a non 50/50 beam splitter. More than half of the energy of the sample light beam is directed into the combined beam and less than half of the energy of the reference light beam are directed into the combined beam by the second beam splitter. In another embodiment, the first beam splitter is a non 50/50 beam splitter and the second beam splitter is an approximately 50/50 beam splitter. An optical circulator is provided to enable the sample light beam to bypass the first beam splitter after interaction with a sample. Two combined beams are formed by the second beam splitter for detection by two respective detectors. More than half of the energy of the light source provided to the first beam splitter is directed into the sample light beam and less than half of the energy is directed into the reference light beam. The energy distribution between the sample and reference light beams can be controlled by selection of the characteristics of the beam splitters.

Delayed-choice test of quantum complementarity with interfering single photons.

Abstract: We report an experimental test of quantum complementarity with single-photon pulses sent into a Mach-Zehnder interferometer with an output beam splitter of adjustable reflection coefficient R. In addition, the experiment is realized in Wheeler's delayed-choice regime. Each randomly set value of R allows us to observe interference with visibility V and to obtain incomplete which-path information characterized by the distinguishability parameter D. Measured values of V and D are found to fulfill the complementarity relation V2+D2 < or =1.

Tunable lateral displacement and spin beam splitter for ballistic electrons in two-dimensional magnetic-electric nanostructures

Abstract: We investigate the lateral displacements for ballistic electron beams in a two-dimensional electron gas modulated by metallic ferromagnetic (FM) stripes with parallel and antiparallel (AP) magnetization configurations. It is shown that the displacements are negative as well as positive, which can be controlled by adjusting the electric potential induced by the applied voltage and the magnetic field strength of FM stripes. Based on these phenomena, we propose an efficient way to realize a spin beam splitter, which can completely separate spin-up and spin-down electron beams in the AP configuration by their corresponding spatial positions.

Projector using independent multiple wavelength light sources

Abstract: A digital image projector (10) for increasing brightness includes a first light source (44, 44a); a second light source (44, 44b) that is spectrally adjacent to the first light source; a dichroic beamsplitter (46, 62) disposed to direct light of both the first and second light source; a spatial light modulator (60) that receives light from both the first and second light sources; and projection optics (70) for delivering imaging light from the spatial light modulator.

Cascade wide-angle Y-junction 1 x 16 optical power splitter based on silicon wire waveguides on silicon-on-insulator.

Abstract: A 1 x 16 optical power splitter with wide splitting angle, uniform outputs, and low excess loss is demonstrated. The 1 x 16 splitter comprising cascaded 1 x 2 splitters with arc-shaped branching waveguides is fabricated on the silicon-on-insulator (SOI) substrate. The gap between the branching waveguides is widened in a short propagation length such that influences of etch residues and air voids in the gap on the optical power uniformity are reduced significantly. The measured power uniformity of the 1 x 16 splitter is better than 0.3 dB at wavelength of 1550 nm.

Three-port beam splitter of a binary fused-silica grating

Abstract: A deep-etched polarization-independent binary fused-silica phase grating as a three-port beam splitter is designed and manufactured. The grating profile is optimized by use of the rigorous coupled-wave analysis around the 785 nm wavelength. The physical explanation of the grating is illustrated by the modal method. Simple analytical expressions of the diffraction efficiencies and modal guidelines for the three-port beam splitter grating design are given. Holographic recording technology and inductively coupled plasma etching are used to manufacture the fused-silica grating. Experimental results are in good agreement with the theoretical values.

Inherently phase-stable coherent two-dimensional spectroscopy using only conventional optics

Abstract: We introduce an inherently phase-stable setup for coherent two-dimensional femtosecond spectroscopy in noncollinear box geometry using only conventional beam splitters, mirrors, and delay stages. Avoiding diffractive optics, pulse shapers, and active phase-locking loops, our spectroscopy setup is simple, robust, and works for ultrabroad bandwidths in all spectral regimes (infrared, visible, and ultraviolet).

Two-optical-cycle pulses in the mid-infrared from an optical parametric amplifier

Abstract: Ultrabroadband mid IR pulses with energy as high as 2 μJ and tunability from 2 to 5 μm are generated as the idler beam of an 800 nm pumped optical parametric amplifier in periodically poled stoichiometric lithium tantalate. After bulk compression in a Ge plate and frequency-resolved-opticle-gating characterization, a pulse duration as low as 25 fs was measured, corresponding to two optical cycles of the 3.6 μm carrier wavelength.

Polarizing beam splitter of deep-etched triangular-groove fused-silica gratings.

Abstract: We investigated the use of a deep-etched fused-silica grating with triangular-shaped grooves as a highly efficient polarizing beam splitter (PBS). A triangular-groove PBS grating is designed at a wavelength of 1550 nm to be used in optical communication. When it is illuminated in Littrow mounting, the transmitted TE- and TM-polarized waves are mainly diffracted in the minus-first and zeroth orders, respectively. The design condition is based on the average differences of the grating mode indices, which is verified by using rigorous coupled-wave analysis. The designed PBS grating is highly efficient over the C+L band range for both TE and TM polarizations (>97.68%). It is shown that such a triangular-groove PBS grating can exhibit a higher diffraction efficiency, a larger extinction ratio, and less reflection loss than the binary-phase fused-silica PBS grating.

Polarized head-mounted projection display

Abstract: An image display system and associated method for image displaying The system includes an image source configured to generate image light, projection optics configured to project the image light, and a polarizing beam splitter optically coupled to the projection optics and configured to propagate into a first optical path first polarized light having a first polarization and to propagate into a second optical path second polarized light having a second polarization The system includes a quarter wave converter disposed in the first optical path and configured to rotate the first polarization by a quarter phase as the first polarized light first passes through the quarter wave converter, and includes a reflective screen disposed in the first optical path and configured to reflect rotated first polarized light from the quarter wave converter back through the quarter wave converter for further quarter phase rotation.

Postselective two-photon interference from a continuous nonclassical stream of photons emitted by a quantum dot

Abstract: We report an electrically driven semiconductor single-photon source capable of emitting photons with a coherence time of up to 400 ps under fixed bias. It is shown that increasing the injection current causes the coherence time to reduce, and this effect is well explained by the fast modulation of a fluctuating environment. Hong-Ou-Mandel-type two-photon interference using a Mach-Zehnder interferometer is demonstrated using this source to test the indistinguishability of individual photons by postselecting events where two photons collide at a beam splitter. Finally, we consider how improvements in our detection system can be used to achieve a higher interference visibility.

Laser beam machining apparatus

Abstract: A laser beam machining apparatus including a laser beam irradiation unit, the laser beam irradiation unit including: a laser beam oscillator for oscillating a laser beam; a beam splitter by which the laser beam oscillated by the laser beam oscillator is split into a first laser beam and a second laser beam; a rotary half-wave plate disposed between the laser beam oscillator and the beam splitter; a condenser lens disposed in a first optical path for guiding the first laser beam split by the beam splitter; a first reflecting mirror disposed in a second optical path for guiding the second laser beam split by the beam splitter; a first quarter-wave plate disposed between the beam splitter and the first reflecting mirror; a second reflecting mirror disposed in a third optical path for splitting thereinto the second laser beam returned to the beam splitter through the second optical path; a second quarter-wave plate disposed between the beam splitter and the second reflecting mirror; and a cylindrical lens disposed between the beam splitter and the second quarter-wave plate.

Single-frame measurement of the complete spatiotemporal intensity and phase of ultrashort laser pulses using wavelength-multiplexed digital holography

Abstract: We show that a simple (few-element) arrangement for wavelength-multiplexed digital holography allows the measurement of the electric field E(x,y,t) of a femtosecond laser pulse on a single shot. A slightly rotated two-dimensional diffractive optical element and a variable-wavelength filter together generate multiple spectrally resolved digital holograms that are simultaneously captured in a single frame by a digital camera. An additional simultaneous measurement of the spectral phase for a spatially filtered replica of the pulse with frequency-resolved optical gating completes this three-dimensional measurement. An experimental implementation of the technique is presented and its current limitations are discussed.

Parametric coupling between macroscopic quantum resonators

Abstract: Time-dependent linear coupling between macroscopic quantum resonator modes generates both a parametric amplification also known as a 'squeezing operation' and a beam splitter operation, analogous to quantum optical systems. These operations, when applied properly, can robustly generate entanglement and squeezing for the quantum resonator modes. Here, we present such coupling schemes between a nanomechanical resonator and a superconducting electrical resonator using applied microwave voltages as well as between two superconducting lumped-element electrical resonators using a rf SQUID-mediated tunable coupler. By calculating the logarithmic negativity of the partially transposed density matrix, we quantitatively study the entanglement generated at finite temperatures. We also show that characterization of the nanomechanical resonator state after the quantum operations can be achieved by detecting the electrical resonator only. Thus, one of the electrical resonator modes can act as a probe to measure the entanglement of the coupled systems and the degree of squeezing for the other resonator mode.

Broadband directional couplers fabricated in bulk glass with high repetition rate femtosecond laser pulses.

Abstract: A femtosecond fiber laser was applied to fabricate broadband directional couplers inside bulk glass for general power splitting application in the 1250 to 1650-nm wavelength telecom spectrum. The broadband response was optimized over the 400-nm bandwidth by tailoring the coupling strength and the waveguide interaction length to balance the differing wavelength dependence of the straight interaction and bent transition regions. High spatial finesse of the femtosecond-laser writing technique enabled close placement (~6 μm) of adjacent waveguides that underpinned the wavelength-flattened broadband response at any coupling ratio in the 0% to 100% range. The spectral responses were well-represented by coupled mode theory, permitting simple design and implementation of broadband couplers for bulk 3D optical circuit integration.

Analytic treatment of controlled reversible inhomogeneous broadening quantum memories for light using two-level atoms

Abstract: It has recently been discovered that the optical analog of a gradient echo, in an optically thick material, could form the basis of an optical memory that is both completely efficient and noise-free Here we present analytical calculations showing that this is the case There is close analogy between the operation of the memory and an optical system with two beam splitters We can use this analogy to calculate efficiencies as a function of optical depth for a number of quantum memory schemes based on controlled inhomogeneous broadening In particular, we show that multiple switching leads to a net 100% retrieval efficiency for the optical gradient echo even in the optically thin case

Beam splitting of low-contrast binary gratings under second Bragg angle incidence

Abstract: Beam splitting of low-contrast rectangular gratings under second Bragg angle incidence is studied. The grating period is between lambda and 2 lambda. The diffraction behaviors of the three transmitted propagating orders are illustrated by analyzing the first three propagating grating modes. From a simplified modal approach, the design conditions of gratings as a high-efficiency element with most of its energy concentrated in the -2nd transmitted order (similar to 90%) and of gratings as a 1 x 2 beam splitter with a total efficiency over 90% are derived. The grating parameters for achieving exactly the splitting pattern by use of rigorous coupled-wave analysis verified the design method. A 1 x 3 beam splitter is also demonstrated. Moreover, the polarization-dependent diffraction behaviors are investigated, which suggest the possibility of designing polarization-selective elements under such a configuration. The proposed concept of using the second Bragg angle should be helpful for developing new grating-based devices. (C) 2008 Optical Society of America.

Self-standing parallel plate beam splitter, method for manufacturing the same, and laser diode package structure using the same

Abstract: Disclosed herein are a self-standing parallel plate beam splitter, a method for manufacturing the same, and a laser diode package structure using the same. The self-standing parallel plate beam splitter according to the present invention is easy to manufacture and is applicable to various laser diode packages, thereby enabling easy implementation of a laser diode package that is capable of performing bidirectional communication, a laser diode package having a triplexer function, a laser diode package having a wavelength locking function, and a laser diode package having a front side monitoring function to monitor the operation state of a laser diode chip using some of laser light emitted from the front side of the laser diode chip.

Slow Light Beam Splitter

Abstract: We demonstrate a slow light beam splitter using rapid coherence transport in a wall-coated atomic vapor cell. We show that particles undergoing random and undirected classical motion can mediate coherent interactions between two or more optical modes. Coherence, written into atoms via electromagnetically induced transparency using an input optical signal at one transverse position, spreads out via ballistic atomic motion, is preserved by an antirelaxation wall coating, and is then retrieved in outgoing slow light signals in both the input channel and a spatially-separated second channel. The splitting ratio between the two output channels can be tuned by adjusting the laser power. The slow light beam splitter may improve quantum repeater performance and be useful as an all-optical dynamically reconfigurable router.

Manipulating terahertz wave by a magnetically tunable liquid crystal phase grating.

Abstract: This investigation demonstrates the feasibility of a magnetically tunable liquid crystal phase grating for the terahertz wave. The phase grating can be used as a beam splitter. The ratio of the zeroth and first-order diffracted THz-beams (0.3 THz) polarized in a direction perpendicular to that of the grooves of the grating can be tuned from 4:1 to 1:2. When the THz wave is polarized in any other direction, this device can be operated as a polarizing beam splitter.

Catadioptric system, apparatus, and method for producing images on a universal, head-up display

Abstract: A present novel and non-trivial system, apparatus, and method for employing a catadioptric optical system in a Head-Up Display (“HUD”) system are disclosed. A catadioptric optical module is configured to produce a large image size within a small space envelope by folding the optical path back through module and separating the paths by use of a beam splitter. Such module comprised of a beam splitter, collimating mirror, and correcting lens produces collimated beams of light from an image source providing either polarized or non-polarized beams of light. If polarized beams are provided, the module includes a quarter-wave retarder, and the configuration of the module permits the image source to provide either s-polarized or p-polarized beams. A combiner arm assembly comprising of at least one combiner receives the collimated beams, where the employment of a plurality of combiners extends the relatively small instantaneous field of view.

Mobile telephonehaving internal inkjet printhead arrangement and an optical sensing arrangement

Abstract: A mobile telephone includes an optical sensing arrangement enabling the telephone to decode tags of coded data printed on media fed through the telephone via internal and external media pathway defined by a body of the telephone; a beam splitter deflecting incoming light onto an image sensor of the telephone; a first infrared LED directing light onto media present in the external pathway; a filter and lens arrangement receiving and directing light reflected from the external media onto the beam splitter; a second infrared LED directing light onto media present in the internal pathway; and a mirror arrangement directing light reflected from the internal media into the beam splitter. The coded data contains printing instructions for the printhead, and the filter and lens arrangement includes an infrared filter for removing non-infrared ambient light, whereby a signal to noise ratio of the reflected light is improved.

Wideband two-port beam splitter of a binary fused-silica phase grating

Abstract: The usual beam splitter of multilayer-coated film with a wideband spectrum is not easy to achieve. We describe the realization of a wideband transmission two-port beam splitter based on a binary fused-silica phase grating. To achieve high efficiency and equality in the diffracted 0th and -1st orders, the grating profile parameters are optimized using rigorous coupled-wave analysis at a wavelength of 1550 nm. Holographic recording and the inductively coupled plasma dry etching technique are used to fabricate the fused-silica beam splitter grating. The measured efficiency of (45% x 2) = 90% diffracted into the both orders can be obtained with the fabricated grating under Littrow mounting. The physical mechanism of such a wideband two-port beam splitter grating can be well explained by the modal method based on two-beam interference of the modes excited by the incident wave. With the high damage threshold, low coefficient of thermal expansion, and wideband high efficiency, the presented beam splitter etched in fused silica should be a useful optical element for a variety of practical applications.

Indistinguishable photons from a diode

Abstract: We generate indistinguishable photons from a semiconductor diode containing an InGaAs/GaAs quantum dot. By using an all-electrical technique to populate and control a single-photon emitting state, we filter out dephasing by Stark shifting the emission energy on time scales below the dephasing time of the state. By mixing consecutive photons on a beam splitter, we observe two-photon interference with a visibility of 64%.

Independent polarisation control of multiple optical traps.

Abstract: We present a system which uses a single spatial light modulator to control the spin angular momentum of multiple optical traps. These traps may be independently controlled both in terms of spatial location and in terms of their spin angular momentum content. The system relies on a spatial light modulator used in a "split-screen" configuration to generate beams of orthogonal polarisation states which are subsequently combined at a polarising beam splitter. Defining the phase difference between the beams with the spatial light modulator enables control of the polarisation state of the light. We demonstrate the functionality of the system by controlling the rotation and orientation of birefringent vaterite crystals within holographic optical tweezers.