Showing papers on "Beam splitter published in 2000"

A fast and compact quantum random number generator

Abstract: We present the realization of a physical quantum random number generator based on the process of splitting a beam of photons on a beam splitter, a quantum mechanical source of true randomness. By utilizing either a beam splitter or a polarizing beam splitter, single photon detectors and high speed electronics the presented devices are capable of generating a binary random signal with an autocorrelation time of 11.8 ns and a continuous stream of random numbers at a rate of 1 Mbit/s. The randomness of the generated signals and numbers is shown by running a series of tests upon data samples. The devices described in this paper are built into compact housings and are simple to operate.

Optical Quantum Random Number Generator

Abstract: A physical random number generator based on the intrinsic randomness of quantum mechanics is described. The random events are realized by the choice of single photons between the two outputs of a beam splitter. We present a simple device, which minimizes the impact of the photon counters' noise, dead-time and after pulses.

Guiding Neutral Atoms on a Chip

Abstract: We demonstrate the guiding of neutral atoms by the magnetic fields due to microfabricated current-carrying wires on a chip. Atoms are guided along a magnetic field minimum parallel to and above the current-carrying wires. Two guide configurations are demonstrated: one using two wires with an external magnetic field, and a second using four wires without an external field. These guide geometries can be extended to integrated atom optics circuits, including beam splitters.

Beam splitter for guided atoms

Abstract: We have designed and experimentally studied a simple beam splitter for guided atoms realized with a current carrying Y-shaped wire nanofabricated on a surface (atom chip). Such a Y-configuration beam splitter has many advantages compared to conventional designs based on tunneling, especially that it will enable robust beam splitting. This and other similar designs can be integrated into more sophisticated surface-mounted atom optical devices at the mesoscopic scale.

Photonic-crystal-based beam splitters

Abstract: We proposed and demonstrated two different methods to split electromagnetic waves in three-dimensional photonic crystals. By measuring transmission spectra, it was shown that the guided mode in a coupled-cavity waveguide can be splitted into the coupled-cavity or planar waveguide channels without radiation losses. The flow of electromagnetic waves through output waveguide ports can also be controlled by introducing extra defects into the crystals. Our results may have an important role in the design of efficient power splitters in a photonic circuit.

Image projection system with a polarizing beam splitter

Abstract: An image projection system having a wire grid polarizing beam splitter (4) which functions as both the polarizer and the analyzer in the system. A light source (20) produces a light beam directed at the beam splitter (14) which reflects one polarization and transmits the other. A liquid crystal array (26) is disposed in either the reflected or transmitted beam. The array modulates the polarization of the beam, encoding image information thereon, and directs the modulated beam back to the beam splitter. The beam splitter again reflects one polarization and transmits the other so that the encoded image is either reflected or transmitted to a screen (25). The wire grid polarizing beam splitter is capable of being oriented at various angles with respect to the source light beam and modulated beam, and accepts relatively divergent light.

Imaging system using polarization effects to enhance image quality

Abstract: The quality of images produced by confocal microscopy, and especially scanning laser confocal microscopy, is enhanced especially for images obtained in turbid mediums such as many biological tissue specimens, by reducing speckle from scatterers that exist outside (above and below) the focal plane region which is being imaged by utilizing sheared beams, both of which are focused to spots in the focal or image plane (region of interest) and polarizing the beams to have opposite senses of circular polarization (right and left handed circular polarization). The return light from the image plane of certain polarization is detected after passing through the confocal aperture of the confocal microscope. Light from scatterers outside the region of interest, which are illuminated by both of the sheared beams, interfere thereby reducing speckle due to such scatterers, and particularly scatters which are adjacent to the image plane. Sheared beams having orthogonal linear polarization, as may be obtained from a Wollaston or Nomarski prism are converted into circularly polarized beams of opposite polarization sense by a quarter wave plate. The optical signals representing reflections from the focal plane are derived by polarizing optics which may either, be a polarizing beamsplitter in the incident beam path or with a retarder and analyzer. The retarder may be selected to provide different polarization phase shift of the return light, and with the analyzer, detects the degree of elliptical polarization representing the optical activity and circular dichroism producing the optical signal representing the image.

Combined optical sensor and communication antenna system

Abstract: The invention provides a combined optical sensor and communications antenna system (10). The system includes a primary reflector (12) for reflecting radiation. The primary reflector includes a centrally located core (14), which is adapted to transmit the radiation therethrough. An axis (18) centrally extending through the core forms an optical axis of the system. The system further includes a secondary reflector (16) positioned along the optical axis of the system for rereflecting and focusing the radiation reflected from the primary reflector toward the core of the primary reflector. The system still further includes a beam splitter (20) positioned adjacent the primary reflector on the opposite side from the secondary reflector, for separating and redirecting the radiation rereflected from the secondary reflector into an optical radiation component and a radiofrequency radiation component. Finally, the system includes a focal plane assembly (22) located adjacent the beam splitter to receive the optical radiation from the beam splitter, and a radiofrequency feed assembly (24) located adjacent the beam splitter to receive the radiofrequency radiation from the beam splitter.

Common path interferometer for spectral image generation

Abstract: Optical instruments having, inter alia, optics to process wavelengths of electromagnetic radiation to produce an interferogram. The instruments include at least one optical path and optical elements positioned along this path for splitting the electromagnetic radiation and spectrally dispersing the wavelengths to produce first and second sets of spectrally dispersed beams which interfere with each other to produce a plurality of different fringes of different wavelengths. The optics for dispersing the wavelengths includes a matched pair of gratings. The gratings may be reflective or they may be transmissive. The optics also includes a beam splitter and first and second mirrors. The gratings may be positioned in a variety of locations along the optical path. The instruments can also include a detector for detecting the interferogram and means for processing the detected interferogram to produce spectral information.

Polarization luminaire and projection display

Abstract: A polarization luminaire is disclosed having a light source, a system of the optical integrator, a polarized light splitting device for splitting a light emitted from the light source into two kinds of polarized lights whose polarization directions are perpendicular to each other and whose traveling directions are apart from each other by an angle of less than 90 degrees, and a polarization conversion device for causing the two kinds of polarized lights to have the same polarization direction. The polarized light splitting device is placed on one of the entrance side and the outputting side of the first lens plate of the system of the optical integrator or is placed within the second lens plate. A prism beam splitter having a polarized light splitting film constituted by a thermally stable dielectric multi-layer film is suitable for the polarized light splitting device. Most of the polarized lights can be utilized by causing the polarized lights to have the same polarization direction. Further, the polarized lights, which have uniform brightness, can be emitted. Consequently, the polarization luminaire is suited to be a luminaire for use in a projection display that has liquid crystal light valves.

High efficiency volume diffractive elements in photo-thermo-refractive glass

Abstract: Novel volume holographic elements were made from Bragg diffractive gratings in photo-thermo-refractive (PTR) glass with absolute diffraction efficiency ranging from greater than approximately 50% up to greater than approximately 93% and total losses below 5%. Both transmitting and reflecting volume diffractive elements were done from PTR glasses because of high spatial resolution enabling recording spatial frequencies up to 10000 mm−1. The use of such diffractive elements as angular selector, spatial filter, attenuator, switcher, modulator, beam splitter, beam sampler, beam deflectors controlled by positioning of grating matrix, by a small-angle master deflector or by spectral scanning, selector of particular wavelengths (notch filter, add/drop element, spectral shape former (gain equalizer), spectral sensor (wavelength meter/wavelocker), angular sensor (pointing locker), Bragg spectrometer (spectral analyzer), transversal and longitudinal mode selector in laser resonator were described. Combinations of those elements in the same volume are available too.

High-performance thin-film polarizing beam splitter operating at angles greater than the critical angle

Abstract: A new type of thin-film polarizing beam splitter (PBS) is proposed that is based on the effects of light interference and frustrated total internal reflection. This PBS has a significantly better performance than conventional thin-film PBS’s. It is nonabsorbing, broadband, and wide angle and has high extinction ratios in both the transmitted and the reflected beams. The principles and theory of this PBS are described in detail. Several PBS’s designed for the visible and the infrared spectral regions are described. The measured results for a prototype visible PBS of this type are presented as well.

Dense plasma diagnostics with an amplitude-division soft-x-ray laser interferometer based on diffraction gratings.

Abstract: We report the demonstration of an amplitude-division soft-x-ray interferometer that can be used to generate high-contrast interferograms at the wavelength of any of the saturated soft-x-ray lasers (5.6-46.9 nm) that are available at present. The interferometer, which utilizes grazing-incidence diffraction gratings as beam splitters in a modified Mach-Zehnder configuration, was used in combination with a tabletop 46.9-nm laser to probe a large-scale (~2.7-mm-long) laser-created plasma.

Interferometric sensor for detection of surface-bound bioreactions

Abstract: An integrated optical interferometer for direct detection of affinity reactions is presented. A modern version of a Young’s interferometer is built with a waveguide structure as beam splitter and as sensing element. Resistive waveguides were produced by plasma-enhanced chemical vapor deposition of silicon oxinitride. At the output of this device a fringe pattern is detected by a CCD line camera. The adsorption of molecules on top of the waveguides is observed with a detection limit of 750 fg/mm2. The resolvable variation of effective refractive index is 9 × 10-8.

How does a Mach-Zehnder interferometer work?

Abstract: The Mach-Zehnder interferometer is a particularly simple device for demonstrating interference by division of amplitude. A light beam is first split into two parts by a beamsplitter and then recombined by a second beamsplitter. Depending on the relative phase acquired by the beam along the two paths the second beamsplitter will reflect the beam with efficiency between 0 and 100%. The operation of a Mach-Zehnder interferometer is often used as an example in quantum mechanics because it shows a clear path-choice problem. However, it is not at all obvious at first glance that it works as claimed, until reflection phase shifts are considered in detail.

Apparatus and method for autofocus

Abstract: A laser generates a collimated laser beam which passes through a lens off-axis. The beam is focused at a focal plane on a substrate surface. A first position sensitive detector receives the laser beam reflected from the substrate surface through the lens to generate a first signal proportional to lateral beam offset. A beam splitter may be provided to direct a portion of the laser beam before passing through the lens toward a second position sensitive detector to generate a second signal proportional to laser beam pointing instability. Apparatus computes the difference between the first and second signals, the difference being a defocused error signal. It is preferred that the first position sensitive detector be located at a distance from the lens that is at least twice the lens focal length.

Optical polarization beam combiner/splitter

Abstract: An optical polarization beam splitter comprises a first optical fiber having an end defining a first optical axis, a second optical fiber having an end defining a second optical axis, and a third optical fiber having an end defining a third optical axis parallel to and spaced apart from the second optical axis. A collimating lens is disposed along the first optical axis positioned to form a collimated optical beam from the first optical fiber. A focussing lens is disposed along a path of the collimated optical beam. A birefringent walk-off crystal has a first face adjacent to the focussing lens and a second face located at a focal plane of the focussing lens and in contact with the ends of the second and third optical fibers. The birefringent crystal is oriented such that and has a thickness between its first and second faces selected such that a first component of the optical beam having a first polarization exits the crystal at its second face and enters the end of the second optical fiber along the second optical axis and a second component of the optical beam having a second polarization orthogonal to the polarization of the first polarization exits the crystal at its second face and enters the end of the third optical fiber along the third optical axis.

Waveguide atom beam splitter for laser-cooled neutral atoms

Abstract: A laser-cooled neutral-atom beam from a low-velocity intense source is split into two beams while it is guided by a magnetic-field potential. We generate our multimode beam-splitter potential with two current-carrying wires upon a glass substrate combined with an external transverse bias field. The atoms are guided around curves and a beam-splitter region within a 10-cm guide length. We achieve a maximum integrated flux of 1.5×105 atoms/s with a current density of 5×104 amp/cm2 in the 100‐µm-diameter wires. The initial beam can be split into two beams with a 50/50 splitting ratio.

Hybrid shearing and phase-shifting point diffraction interferometer

Abstract: A new interferometry configuration combines the strengths of two existing interferometry methods, improving the quality and extending the dynamic range of both. On the same patterned mask, placed near the image-plane of an optical system under test, patterns for phase-shifting point diffraction interferometry and lateral shearing interferometry coexist. The former giving verifiable high accuracy for the measurement of nearly diffraction-limited optical systems. The latter enabling the measurement of optical systems with more than one wave of aberration in the system wavefront. The interferometry configuration is a hybrid shearing and point diffraction interferometer system for testing an optical element that is positioned along an optical path including: a source of electromagnetic energy in the optical path; a first beam splitter that is secured to a device that includes means for maneuvering the first beam splitter in a first position wherein the first beam splitter is in the optical path dividing light from the source into a reference beam and a test beam and in a second position wherein the first beam splitter is outside the optical path: a hybrid mask which includes a first section that defines a test window and at least one reference pinhole and a second section that defines a second beam splitter wherein the hybrid mask is secured to a device that includes means for maneuvering either the first section or the second section into the optical path positioned in an image plane that is created by the optical element, with the proviso that the first section of the hybrid mask is positioned in the optical path when first beam splitter is positioned in the optical path; and a detector positioned after the hybrid mask along the optical path.

Method and apparatus for performing scanning optical coherence confocal microscopy through a scattering medium

Abstract: An apparatus and method for performing optical coherence domain reflectometry. The apparatus preferably includes a single output light source to illuminate a sample with a probe beam and to provide a reference beam. The reference beam is routed into a long arm of an interferometer by a polarizing beamsplitter. A reflected beam is collected from the sample. A 90° double pass polarization rotation element located between the light source and the sample renders the polarizations of the probe beam and reflected beam orthogonal. The polarizing beamsplitter routes the reflected beam into a short arm of the interferometer. The interferometer combines the reference beam and the reflected beam such that coherent interference occurs between the beams. The apparatus ensures that all of the reflected beam contributes to the interference, resulting in a high signal to noise ratio.

Spectroscopic remote sensing exhaust emission monitoring system

Abstract: A spectroscopic IR and UV-vis absorption remote exhaust emission monitoring system and sensing instrument for non-invasive, multicomponent analysis of the exhaust plume emitted by in-use vehicles. The concentration of CO, CO2, HC, NO, N2O, C2H2, NH3, SO2, Aromatic hydrocarbons, aldehydes, HONO, NO2, and dust, among others and in any combination there-of, in such a mixture can be determined in real-time, or via post-processing of stored spectral data. The sensor employs an IR and a UV-vis sources, and the physically offset, collimated beams traverse the probed air column, typically a roadway, a plurality of times, before returning to the instrument. Although the IR and UV-vis beams converge at the optics opposite the instrument, they are not coaxial and, thus, do not require an optical device (i.e., dichroic beam splitter) to separate them. The separate IR and UV-vis beams are focused on the slits of rapid spectrometers, where they are analyzed to yield wavelength-resolved spectra (i.e., graphs of digital signal intensity versus radiation wavelength). These spectrometers can either be rapid scanning dispersive devices, dispersive devices employing linear or two-dimensional detector arrays, or Fourier transform spectrometers. The graphs are converted into absorbance spectra and are subsequently processed with pattern recognition algorithms and a spectral reference database to afford analyte concentration.

Interference and the lossless lossy beam splitter

Abstract: By directing the input into a particular mode it is possible to obtain as output all of the input light for a beam splitter which is 50% absorbing. This effect is also responsible for nonlinear quantum interference when two photons are incident on the beam splitter.

Methods of fabricating grating assisted coupler devices

Abstract: Advantageous methodologies are disclosed for embedding periodic patterns in optical waveguide elements such as optical fibers. Polarization independence in an elongated waist region of a coupler can be established by measuring polarization characteristics during fusion and elongation, and controlling the heating and stretching to impart a cross-sectional shape, such as a hybrid dumbbell-ellipsoid produces a polarization insensitive drop wavelength. Alternatively, or additionally, polarization dependence can be minimized by angular deformation of the elements along its light transmissive axis. In addition, an element of relatively low photosensitivity is held in an hydrogen or deuterium environment pressurized to about 1000 to 5000 psi. While the environment is pressurized, a scanning UV beam is transmitted through a photomask and impinges on the coupler waist. In writing the grating, the in-diffused gas is constantly replenished, enabling the grating to grow. Prior to writing the periodic pattern dimensional variations in the element which can affect spectral bandwidth are sensed by writing a test pattern in the element and then locally measuring the spectral properties of the test pattern progressively along the element and adjusting the local level of background index of refraction so that the modal index of refraction is substantially constant, minimizing imperfections in the precision of the wavelength pattern. The scanning writing beam, which can be of substantially larger cross-sectional dimensions than the waveguide element (which may be in the 4-10 micron range) is caused to track on the element despite positional imprecision and temporal shifting by using fluorescence induced in the elements to provide an error signal for positive correction. To apodize the grating in accordance with a selected function, a constant power beam is directed through a rotating half-wave plate and into a polarizing beam splitter, where it is divided into two beams having oppositely varying d.c. amplitude characteristics. One beam is varied by a periodic pattern, and the other beam is free of a periodic pattern. Alternately, a scanner toggles the constant intensity beam between the two beam paths in rapid succession, varying the duty cycle of toggling as the beams scan along the coupler waist to produce the desired apodization profile of the grating.

The Hanbury Brown and Twiss experiment with fermions

Abstract: We realized an equivalent Hanbury Brown and Twiss experiment for a beam of electrons in a two-dimensional electron gas in the quantum Hall regime. A metallic split gate serves as a tunable beam splitter which is used to partition the incident beam into transmitted and reflected partial beams. The current fluctuations in the reflected and transmitted beam are fully anticorrelated demonstrating that fermions tend to exclude each other (anti-bunching). If the occupation probability of the incident beam is lowered by an additional gate, the anticorrelation is reduced and disappears in the classical limit of a highly diluted beam.

Optical information storage device having phase compensating mechanism and polarization plane rotating mechanism

Abstract: An optical information storage device including a first photodetector for detecting a regenerative signal from reflected light from an optical recording medium, a second photodetector for detecting a tracking error signal and a focusing error signal from the reflected light, and a beam splitter for separating the reflected light into a first beam directed toward the first photodetector and a second beam directed toward the second photodetector. The optical information storage device further includes a phase compensating mechanism provided between the beam splitter and the first photodetector for compensating for a phase difference of the first beam, a Wollaston prism provided between the phase compensating mechanism and the first photodetector for separating the first beam into two beams having orthogonal polarization planes, and a polarization plane rotating mechanism for rotating the polarization plane of the first beam incident on the Wollaston prism.

High-intensity pulsed source of space-time and polarization double-entangled photon pairs

Abstract: Two spatially separated type-I nonlinear crystals are pumped by femtosecond laser pulses to create entangled photon pairs in the process of spontaneous parametric down-conversion. The two-photon entangled state exhibits high-visibility quantum interference for both polarization and space-time variables without the need of stringent spectral postselection by using narrow-band filters. The visibility is insensitive to the thickness of the crystals, unlike in the case of pulse pumped type-II parametric down-conversion; therefore the intensity can be easily increased by using thick nonlinear crystals. This method will be indispensable in experiments that require a pulsed source of entangled photon pairs, such as generation of multiphoton entangled states, quantum teleportation, and quantum communications. Femtosecond pulse pumped spontaneous parametric down-conversion ~SPDC! is very useful for the realization of certain types of experiments in quantum optics, such as generation of multiphoton entangled states, quantum teleportation, quantum communications, etc @1#. Since the 1990s type-II SPDC has been used extensively as a source of twophoton entangled states for space-time, polarization, and space-time2polarization double entanglement @2#. However, type-II SPDC has its limitation for femtosecond applications. The degree of entanglement of the two-photon state generated in type-II SPDC pumped by femtosecond pulses strongly depends on the thickness of the nonlinear crystal @3‐5#. To obtain high-visibility quantum interference in pulse pumped type-II SPDC, one can only do the following: ~i! use a thin BBO crystal (’100 mm) or ~ii! accomplish spectral postselection by using narrow-band filters @6,7#. Both methods severely limit the available entangled photon flux reaching the detectors. In this paper, we experimentally demonstrate two methods for generating a pulsed source of space-time and polarization double-entangled photon pairs that exhibit highvisibility quantum interference. The visibility is shown to be insensitive to the thickness of the crystals and the bandwidth of the filters. Therefore, high-intensity pulsed entangled photon pairs can be easily generated by simply using thicker nonlinear crystals, which has a great advantage over pulse pumped type-II SPDC. It has recently been shown by Kwiat et al. and by Burlakov et al. that SPDC created from two spatially separate type-I nonlinear crystals pumped by cw laser beams exhibit high-visibility quantum interference @8,9#. In both cases, temporal compensation was not an important issue. We shall demonstrate in this paper that pulse pumped type-I SPDC in the two-crystal scheme requires great attention to the overlapping of the two-photon amplitudes temporally, unlike cw pumped two-crystal cases. Consider the experimental setup shown in Fig. 1. A frequency doubled radiation of a mode-locked Ti:sapphire laser is used to pump two type-I BBO crystals. The pump has a pulse width of ’80 fsec and a central wavelength of 400 nm. The repetition rate of the pump pulse is 82 MHz. The pump is polarized at 45°. A BBO crystal is placed in each arm of a balanced Mach-Zehnder interferometer ~MZI!. The thickness of both BBO crystals is 3.4 mm. The pump beam is then blocked by mirrors M 3 and M 4 while transmitting 800-nm collinear degenerate SPDC. The optic axes of the two BBO crystals are orthogonal to each other: the optic axis of the BBO (BBO1) in the arm that contains M 3 is oriented in the horizontal ( () plane and the other BBO (BBO2) is oriented vertically ( l). Due to type-I phase matching in the BBO’s, the pair of SPDC photons created from BBO1 are vertically ~V! polarized and the SPDC from BBO2 is polarized horizontally ( H). At each output port of the nonpolarizing beam splitter ~NPBS!, a detector package consisting of a GlanThompson analyzer (A1 , A2), an interference filter (F1 , F2), and a single-photon detector ~EG&G SPCM-AQ-142! are placed. Interference filters are mainly used for alignment purposes and to suppress background noise from the pump. The simplified version of the quantum state after NPBS can be written as ~we only consider coincidence contributing terms!

Cold atom beam splitter realized with two crossing dipole guides.

Abstract: Cold rubidium atoms, coupled and guided in a vertical laser beam by the dipole force, have been split into two atomic beams, by using a second time-dependent laser beam crossing the vertical one at a 0.12 rad angle. Transfer efficiency as large as 40% has been obtained. At 10 mm below the cold atom source, the two atomic beams have a few hundred micron size and are more than one millimeter apart from each other.

Cryptographic key distribution using light pulses of three macroscopic quantum states

Abstract: At a sender site of a secure communication network, a first coherent light pulse sequence is phase modulated with a random bit sequence by a phase modulator, and a second coherent light pulse sequence synchronised to the first coherent light pulse sequence is transformed by an optical transducer to a superposition of coherent states. The outputs of the modulator and the transducer are multiplexed and transmitted over an optical communication link. At a receiver site, a homodyne detector receives the transmitted light pulse sequence and detects a random bit sequence and a superposition of quantum states. The homodyne detector may include a local light oscillator, phase control circuitry for controlling the local light source so that the local light oscillator produces first and second local light oscillations having a phase difference of 90 degrees therebetween, and a beamsplitter for receiving light from the optical communication link and mixing the first coherent light pulse sequence with the first local light oscillations and mixing the second coherent light pulse sequence with the second local light oscillation.

Optical signal interleaver

Abstract: An interleaver and a deinterleaver for filtering optical signals are described. The interleaver separates subsets of channels. The deinterleavers mix subsets of channels. Interleavers and deinterleavers can be used to increase the bandwidth of an optical network. The interleavers and deinterleavers can be used to interface components designed for a first channel spacing to components designed for a second channel spacing. An optical fiber (305) receives an optical signal, collimator (310) collimates the optical signal, a beam splitter splits the beam into a first and second sub-beam, the first sub-beam is reflected by cube interface (322) to etalon (360), which includes a reflecting surface (360), the second sub-beam is reflected off back surface (324), the two sub-beams are then reflected to a collimater (350), the combined signal, which can have either construcive or destructive light interference, is then carried by optical fiber (355).

Diffractive selectively polarizing beam splitter and beam routing prisms produced thereby

Abstract: A diffractive having a grating period that exhibits significant polarization selectivity is used as a polarizing beamsplitter for obliquely incident polarized light. The grating is preferably a subwavelength of the illuminating beam and is preferably designed to substantially transmit transverse magnetic mode (TM) polarized light and to substantially reflect transverse electric mode (TE) polarized light at certain wavelengths or angles of incidence. Due to ease of manufacture, the polarizing beamsplitter may be integrated along with other optical elements, such as a subwavelength retarder, to form a polarization beam router, a dichroic beam combiner, a beam splitter on a curved surface, or an optical pickup using an optical beam splitter and router.