Showing papers on "Beam splitter published in 1998"

Eye fixation monitor and tracker

Abstract: Apparatus and method are provided for assessing direction of fixation of an eye by detecting polarization related changes in light retro-reflected from the fundus of the eye. By assessment of polarization related changes in retro-reflected light from multiple retinal areas either sequentially or simultaneously, characteristic bi-refringence signatures of portions of the retina can be identified which are used to assess the direction of fixation of the eye. Interference from corneal bi-refringence is reduced using incident light having a polarization state that is substantially independent of meridional direction. Light source (55) provides a diverging beam of polarized light on faceted prism (56). Mask (57) containing seven round apertures is placed adjacent to faceted prism (56) to isolate seven round beams of light. Light retro-reflected from eye (58) is partially reflected by beam splitter (59) which is imaged by lens (60) onto the detection system including polarizing beam splitter (61), and six element detectors (62, 63).

Quantum optics of lossy beam splitters

Abstract: The familiar input-output relations for an optical beam splitter are generalized to allow for linear absorption by the medium forming the mirror. Beam-splitter losses generally affect the noise levels detectable in experiments involving nonclassical Light. When employed to investigate two-photon interference effects, a lossy beam splitter can lead to apparent nonlinear absorption, which, in the most extreme case, leads to either both or neither of the photons being absorbed. The degree of second-order coherence of antibunched light can be maintained on transmission through the beam splitter but any amplitude squeezing in the incident light is degraded.

Automated 'plug & play' quantum key distribution

Abstract: An improved « plug & play » interferometric system for quantum key distribution is presented. Self-alignment and compensation of birefringence remain, while limitations due to reflections are overcome. Original electronics implementing the BB84 protocol makes adjustment simple. Key creation with 0.1 photon per pulse at a rate of 325 Hz with a 2.9% QBER – corresponding to a net rate of 210Hz - over a 23 Km installed cable was performed. Quantum key distribution allows two remote parties, Alice and Bob, to generate a secret key, with privacy guaranteed by quantum mechanics. It has been demonstrated in optical fibers by several groups [1,2,3]. However continuous active adjustment, either of polarization or path length in the setups was necessary. Our group introduced in 1997 an interferomete r with Faraday mirrors featuring self-alignment. A key creation rate of the order of 1Hz with the B92 two states protocol was achieved [5]. In this letter, we present a modification of this set-up, allowing a higher key creation rate, with implementation of the BB84 four states protocol. Moreover, this system uses InGaAs/InP avalanche photodiodes cooled to only 173K as photon counters, and electronics allowing automatic timing. We then discuss results of experiments in the laboratory over a 4.9km optical fiber spool and in the field, over 23km of installed fibers. The 97 system was operated at a frequency of 1 kHz. At this low repetition rate, there is never more than one pulse in the optical fiber. When increasing the frequency, the quantum bit error rate QBER rises because of false counts arising from reflected photons and from afterpulses. To get round this difficulty, we developed the system depicted in Fig. 1. Bob sends a light pulse through a circulator. This pulse splits at the coupler C1. The first half travels through the short arm. A polarization controller is set so that this pulse is completely transmitted at the polarizing beam splitter PBS. It then propagates to Alice, where it splits again at coupler C2 to provide a timing signal. It then travels through Alice's equipment and is reflected back to Bob. Thanks to the Faraday mirror, the birefringence of the optical link is compensated, and the pulse comes back orthogonally polarized. It is then reflected by the PBS and takes the long arm, where Bob applies a phase shift φB with its modulator PMB. The second pulse propagates through both arms in reverse order. Alice applies to it a phase shift φA. Since both pulses travel exactly the same optical path, they reach the coupler C1 simultaneously with identical polarization, giving rise to interference. Thanks to this improved interferometer, reflections directly into the detectors are suppressed. According to the phase applied by Alice and Bob, the pulse

Apparatus for rapid phase imaging interferometry and method therefor

Abstract: The apparatus performs phase imaging interferometry on a test medium with spatially varying optical length. The apparatus uses a polarization based phase shift element in either the probe or reference arm of the interferometer to simultaneously generate both the conventional in-phase spatial interferogram of the test medium, and a quadrature interferogram which is ninety degrees out of phase with the conventional interferogram at all image positions, allowing a reconstruction of the test medium's interferometric phase image over 0 to 2π radians. In contrast to the prior art, the present invention accomplishes the phase shifting operation in a single interferometer stage, using a polarizing beam splitter which accomplishes polarized seggregation of the interferometer output beam. The apparatus has high resistance to vibrations, instability and misalignment errors.

High efficiency field-sequential color projector using two SLMs

Abstract: A display is disclosed operating in a field-sequential color mode having first and second light valves which are simultaneously illuminated with different color beams having different polarizations provided from a color wheel The light valves provide an image forming light to a projection lens for projecting the image forming light onto a screen The wheel has front and back surfaces which are displaced from each other and have segments of different colors for separating a polarized white light into the simultaneous different color beams A retardation film for converting the polarization of colors reflected from the back surface from a first polarization to a second polarization The wheel is rotated for sequentially illuminating the light valves with different colors of different polarizations simultaneously The display further includes a polarizing beam splitter assembly for directing the different color light beams from the wheel to the light valves and directing the image forming light to the projection lens The polarizing beam splitter assembly includes a plurality of polarizing beam splitter sub-assemblies A clean-up polarizer for absorbing the first or second polarizations is located between two halves of the polarizing beam splitter assembly

Wave-plate polarizing beam splitter based on a form-birefringent multilayer grating.

Abstract: We have fabricated a novel device that acts as a quarter-wave plate at normal incidence and as a polarizing beam splitter at an angle of incidence of ?40 deg. The device is made from a multilayer SiO2/Si3N4 surface-relief zeroth-order one-dimensional grating with a period of 0.3 µm. The device is designed for an operating wavelength of 632.8??nm. We designed the device by using rigorous coupled-wave analysis and fabricated it by direct-write electron-beam lithography and reactive ion etching. Measurements confirmed the performance of the device as a wave plate and as a polarizing beam splitter.

Broadband Division-of-Amplitude Polarimeter Based on Uncoated Prisms

Abstract: A broadband division-of-amplitude polarimeter (DOAP) is presented. It can provide the real-time measurement of any state of polarization of light, described by its Stokes vector, in large spectral windows. The light is split first into two beams by a prism and then into four beams by means of any polarizer device that will separate the two linear orthogonal states of polarization. Finally, the Stokes vector is directly deduced from the four measured intensities. To avoid interference effects, the splitting of light into four beams is induced only by refractive-index contrast effects between semi-infinite media that are weakly dependent on the wavelength. An experimental setup working from 0.4 to 2 mum is described. It provides similar sensitivities for all the states of polarization, and its characteristics are constant, on a scale of a few percent, within the spectral window. Calibrations performed at 458 and 633 nm display good agreement between theoretical and experimental values. The accuracy of the prism DOAP, evaluated by measurement of the Stokes vector produced by a rotating Glan polarizer, is better than 1%. An infrared extension of this polarimeter is also presented.

All-reflective Michelson, Sagnac, and Fabry-Perot interferometers based on grating beam splitters.

Abstract: All-reflective Michelson, Sagnac, and Fabry–Perot interferometers based on grating beam splitters are experi-mentally demonstrated at a wavelength of 1064??nm. A 1200-groove/mm grating diffracting 0 and -1 orders with an efficiency of 48.2% for each order was used as a near-50/50 beam splitter. The all-reflective Sagnac and Michelson interferometers were formed by reintroducing both of the diffracted beams back to the grating. The Fabry–Perot interferometer was formed in a Littrow configuration by using a 1700-groove/mm grating with a blazing efficiency of 91% as a cavity coupler. These interferometers encompass all the fundamental configurations of all-reflective laser interferometric gravitational-wave detectors, promising improved wave-front quality by avoiding volume thermal effects in transmissive optics under high-power laser illumination.

Optical coherence microscopy for the in-depth study of biological structures: system based on a parallel detection scheme

Abstract: We present a new microscopy system based on the OCT principle, that uses a multiplexed lock-in detection scheme to generate a 2D head-on image in parallel without lateral scanning. Our 'full-field optical coherence microscopy' comprises a Michelson interferometer built with a polarizing beam splitter, and uses a photoelastic birefringence modulator to modulate the optical path difference between the two orthogonal polarizations. A novel signal processing method is used to achieve a demodulation in parallel on every pixel of a 256 X 256 CCD camera. A 840 nm electroluminescent diode with 20 micrometers coherence length is used to illuminate the field of view through the microscope objective lens. In-depth exploration of the sample is realized by changing the plane of focus. The lateral resolution of the images is limited by the camera pixel size and is 2 micrometers . The axial sectioning ability is approximately 8 micrometers . Having validated our setup on model samples, we now evaluate its performance on biological structures. As an example, images of onion cells from 50-400 micrometers below the surface are obtained in 1 s with 100 dB sensitivity.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Quantum state engineering using conditional measurement on a beam splitter

Abstract: State preparation via conditional output measurement on a beam splitter is studied, assuming the signal mode is mixed with a mode prepared in a Fock state and photon numbers are measured in one of the output channels. It is shown that the mode in the other output channel is prepared in either a photon-subtracted or a photon-added Jacobi polynomial state, depending upon the difference between the number of photons in the input Fock state and the number of photons in the output Fock state onto which it is projected. The properties of the conditional output states are studied for coherent and squeezed input states, and the probabilities of generating the states are calculated. Relations to other states, such as near-photon-number states and squeezed-state-excitations, are given and proposals are made for generating them by combining the scheme with others. Finally, effects of realistic photocounting and Fock-state preparation are discussed.

Scanning computed confocal imager

Abstract: There is provided a confocal imager comprising a light source emitting light (11), with light modulating apparatus (32) in optical communication with the light source for varying the spatial and temporal pattern of the light. Beam splitting system (22) receives the scanned light and directs the scanned light onto a target (15) and passes light reflected from the target to video capturing system (34) for receiving the reflected light and transferring a digital image of the reflected light to a computer (36) for creating a virtual aperture and outputting the digital image. In a transmissive mode of operation the invention omits the beam splitting system and captures light passed through the target.

Detector having a transmission grating beam splitter for multi-wavelength sample analysis

Abstract: A detector for DNA sample identification is provided with a transmission grating beam splitter (TGBS). The TGBS split fluoresced light from a tagged DNA sample into 0th order and a 1st order components, both of which are detected on a two-dimensional detector array of a CCD camera. The 0th and 1st order components are detected along a column of pixels in the detector array, and are spaced apart from one another. The DNA samples are tagged with four fluorescent dyes, one dye specific for each nucleotide, and all four dyes responding in slightly different manner to the same monochromatic excitation signal. The TGBS splits fluoresced incoming light into 0th and 1st order components, which are then spread out among a number of pixels in the detector array. The 1st component of this light is received by pixels whose position relative to the 0th order component depends on the frequency of fluorescence. Thus, the position at which signal energy is detected on the array is indicative of the particular dye, and therefore, the corresponding nucleotide tagged by that dye. Monitoring signal energy at the 0th order pixel and selected 1st order pixels, provides a set of data from which one may then identify the particular nucleotide.

Modified white-light Mach-Zehnder interferometer for direct group-delay measurements.

Abstract: A modified white-light Mach–Zehnder interferometer based on a single beam splitter is described for direct group-delay measurements. The arms of the interferometer are folded in such a manner that a single beam splitter can be used to split the incoming beam and combine the outgoing beams. This method offers a twofold advantage: The measuring range of the interferometer is twice as large as that of the Michelson interferometer, and the systematic error that is associated with the beam splitter is minimized because of the configuration. We report the results of measurements on various optical components performed in the 555–630-nm spectral region and propose a scheme for the processing of the experimental data. We present a comparison of the data analyzed by the proposed processing scheme along with the theoretical calculations.

LCD projection system with polarization doubler

Abstract: A projector system includes a lamp, a reflector collector optic, a light pipe, a Polarizing Beam Splitter (PBS), and an LCD (Liquid Crystal Display) panel. The light pipe has a square or octagonal entrance pupil, reflecting internal walls coated with a cold mirror coating, is tapered in shape, and has a rectangular exit pupil. The PBS converts an unpolarized beam from the exit pupil of the light pipe into a uni-polarized beam which it directs to the LCD panel.

Fermion and boson beam-splitter statistics

Abstract: Input-output relations are derived for a lossless beam splitter with two input arms and two output arms. The inputs are two-particle states, either fermions or bosons, with both particles in the same arm or one in each of the input arms. The output states are derived for the four distinct two-particle input states. The statistics of the outputs for fermion and boson inputs are compared with each other and with the statistics for classical particles. For input particles in the same arm, the output statistics are the same for all three varieties of particle. For input particles in different arms, the output particle-number variances are reduced for fermions but increased for bosons, while the interarm correlation is increased for fermions but reduced for bosons in comparison to classical particles.

Dual liquid-crystal wavelength-selective optical switch

Abstract: A liquid-crystal switching element relying upon a segmented liquid-crystal polarization modulator, at least one frequency-dispersive grating and one or more polarization-dispersive elements, such as Wollaston prisms, to switch separate wavelength-divided signals among four optical paths. The switching is done complementally between the fibers of each pair, and the same switching is done for the two pairs. According to the invention, all four beams can be processed by a single set of serial optics. The invention is particularly useful as an optical interconnect between two optical fiber communications wings in which each wing includes two counter-rotating fibers. The invention advantageously uses a dielectric thin-film beam splitter for one of the polarization-dispersive elements and a Wollaston prism for the other. The reflective embodiment in which a mirror replaces all the components on the output side can be improved by using two semitransparent electrode layers on the input side separated by a quarter-wavelength of dielectric.

A simple technique for observing periodic nonlinearities in Michelson interferometers

Abstract: We describe a simple, convenient method for measuring nonlinearities in displacement-measuring Michelson interferometers. Nonlinearities with a spatial periodicity of one optical fringe are a well-known source of error in precision interferometry. Our experimental technique for observing these errors is most immediately applicable to commercial interferometer systems for which the cube-corner retroreflectors can be attached directly to the faces of a beamsplitter cube, creating a monolithic interferometer optic with excellent noise immunity. The optical path difference in this bolted-together interferometer can be changed slightly by rotating the interferometer relative to an external laser. It should be noted that the basic principle described here—generating small path differences through a rotation of the optics relative to the laser—may itself be a source of significant errors in certain length measurements. The validity of our method has been demonstrated by measuring optical mixing errors of calculable magnitude. We describe a matrix method suitable for modeling optical mixing errors in both single-pass and double-pass (plane mirror) interferometers. Also, we report experimental measurements of periodic nonlinearities for two representative interferometers and conclude that, in the majority of engineering metrology applications, these errors are of only minor importance.

Compatible optical pick-up apparatus for recording and reproducing information from recording media having different formats

Abstract: An optical pick-up apparatus for recording and reproducing information from recording media using a first, second, and third light source to emit light beams having various wavelengths corresponding to a first, second and third recording media, respectively. A dichroic beam splitter has a first, second, and third input surface for receiving the light beams emitted from the first, second and third light sources, respectively, and an output surface through which the light beams received through the input surfaces is transmitted toward the first, second, and third recording media. A converging device converges the light beams transmitted through the output surface of the dichroic beam splitter toward the first, second, and third recording media, and a photodetector receives light beams reflected from the first, second, and third recording media that has been transmitted through the dichroic beam splitter.

Multiple wavelength image plane interferometry

Abstract: A system for interferometric inspection of an object (140) includes a number of improvements to reduce spurious reflections and provide precision measurement of large objects. A neutral density filter of absorptive glass is used as an attenuator (160) to reduce undesirable reflections which may otherwise result in detector saturation. A wedge-shaped beam splitter (146) having at least one anti-reflective surface is also utilized to reduce unwanted reflections. The system uses multiple wavelength interferometry to provide range information for an object. Additional improvements in precision may be provided by using a wavelength calibration device such as an etalon, a wavemeter, or a reference cell having relatively narrow transmission peaks, to improve the accuracy in determining the laser wavelengths. The wavelength information may be used to more precisely determine range values for the object. The various improvements in precision and accuracy facilitate use of differing optical path lengths for the reference beam and object beam so that overall system size and complexity is reduced.

Method of exposure and exposure equipment

Abstract: PROBLEM TO BE SOLVED: To expose plural patterns to a substrate to be exposed to produce a superposed pattern on a same shot by dividing a luminous flux emitted from an exposure light source into plural ones and making each divided luminous flux illuminate a mutually different area of an exposure field by adjusting desired illuminating conditions for each. SOLUTION: A linearly polarized beam emitted from a laser beam source 1 is converted into a circular polarized beam by a λ/2 plate, and is launched to a polarizing beam splitter 3. The polarizing beam splitter 3 reflects s- polarized beam and passes p-polarized beam, dividing the beam that has passed the λ/2 plate into two luminous fluxes. The p-polarized beam passing through the polarizing beam splitter 3 is reflected by a mirror 4, is reflected by a mirror 7 and by one of the reflecting planes of a roof prism 9 after the illuminating conditions are controlled by an illumination system 5, and illuminates area A on a reticle 11. On the other hand, the s-polarized beam is reflected by a mirror 8 and by the other reflecting plane of the roof prism 9 after the illuminating conditions are controlled by an illumination system 6, and illuminates area B on the reticle 11.

Optical system and method for high contrast projection display

Abstract: An optical system for a projection display includes one or more polarizing beam splitters, one or more reflective light valves disposed to receive light transmitted through the one or more splitters and one or more phase correcting members, each disposed between the one or more splitters and the one or more light valves, whereby contrast of the display is substantially improved.

Quantum state engineering using conditional measurement on a beam splitter

Abstract: State preparation via conditional output measurement on a beam splitter is studied, assuming the signal mode is mixed with a mode prepared in a Fock state and photon numbers are measured in one of the output channels. It is shown that the mode in the other output channel is prepared in either a photon-subtracted or a photon-added Jacobi polynomial state, depending upon the difference between the number of photons in the input Fock state and the number of photons in the output Fock state onto which it is projected. The properties of the conditional output states are studied for coherent and squeezed input states, and the probabilities of generating the states are calculated. Relations to other states, such as near-photon-number states and squeezed-state-excitations, are given and proposals are made for generating them by combining the scheme with others. Finally, effects of realistic photocounting and Fock-state preparation are discussed.

Line narrowing device with double duty grating

Abstract: A line narrowing system in which a polarizing beam splitter (22), a polarization rotator (24) and a reflecting optic (14) are configured to cause light in an expanded beam from a laser gain medium to illuminate a grating (16) at least twice in each pass through the line narrowing system before returning to the gain medium (3) for further amplification. In a preferred embodiment, the grating is an echelle grating arranged in a Littrow configuration.

Method and apparatus for measuring micro structures, anisotropy and birefringence in polymers using laser scattered light

Abstract: A method and apparatus for measuring microstructures, anistropy and birefringence in polymers using laser scattered light includes a laser which provides a beam that can be conditioned and is directed at a fiber or film which causes the beam to scatter. Backscatter light is received and processed with detectors and beam splitters to obtain data. The data is directed to a computer where it is processed to obtain information about the fiber or film, such as the birefringence and diameter. This information provides a basis for modifications to the production process to enhance the process.

Optical disk apparatus compatible with different types of mediums

Abstract: A polarizing beam splitter for separating an upstream beam from a downstream beam according to the polarization of an incident beam is provided between first and second light sources emitting laser beams at respective wavelength and an objective lens. A phase plate for providing a phase difference to a beam incident on the polarizing beam splitter is provided between the polarizing beam splitter and the light sources. A portion of the laser beam incident on the polarizing beam splitter is reflected by the polarizing beam splitter and caused to be incident on a photo-detecting unit, so as to prevent an unnecessary portion of the laser beam is incident on the photo-detecting unit. According to the invention, the laser beam is used efficiently and the cost of fabricating an optical disk apparatus is reduced by eliminating a need for a gain controlling circuit in the photo-detecting unit.

Folded optical system having improved image isolation

Abstract: An optical collimating assembly for imaging light from a display. The optical assembly includes first and second linear polarization filters having polarization directions that are orthogonal to one another. A folded imaging assembly that includes a first beam splitter, a first ¼ wave plate, and a second beam splitter is located between the polarization filters. A second ¼ wave plate is also located between the polarization filters. The first ¼ wave plate has a birefringence axis that is orthogonal to the birefringence axis of the second ¼ wave plate. In the preferred embodiment of the present invention, the ¼ wave plates are constructed from the same birefringent material. One of the reflectors is preferably constructed from a material having a reflectivity that depends on the direction of linear polarization of light striking the beam splitter.

Interferometer system with two wavelengths, and lithographic apparatus provided with such a system

Abstract: In an interferometer system, variations of the refractive index in the medium traversed by the measuring beam (123) can be detected by using two measuring beams (123, 125) having wavelengths which differ by a factor of three. For this choice of the wavelength ratio, the interference filters of the polarization elements, such as the beam splitter (127), the λ/4 plates (130, 131) and the antireflection coatings can be manufactured relatively easily, and the detection accuracy is increased.

Numerical modeling of weakly fused fiber-optic polarization beamsplitters. Part II: the three-dimensional electromagnetic model

Abstract: For part I see ibid., p. 685, 1998. We establish a three-dimensional (3-D) electromagnetic model for simulating the power transfer characteristics of fused tapered fiber-optic couplers by combining a vectorial modal calculation for the optical waveguide with dumbbell-shaped cross section, as reported in Part I of this paper, and the step-like approximation method for the tapered structure. The model is used to study weakly fused couplers functioning as polarization beamsplitters. The simulation results are compared to the measured ones and it is shown that good agreement has been achieved not only for the coupling power variation during the drawing process, but also for the spectral response of the coupler. We also study the dependence of the coupling behavior of the extremely weakly fused couplers on different coupler structure parameters. The dependence on the aspect ratio of the cross-sectional shape and the heated length is found to be sensitive. The model is a useful tool in helping design couplers for proper operating conditions.

Polarized beam splitter and an illumination optical system and a projector provided with a polarized beam splitter

Abstract: A projector includes: imaging members producing primary color light images; an illumination optical system for illuminating the imaging members; an image combining optical system for combining the color light images; and a projection optical system for projecting a combined color light image onto a screen. The illumination optical system includes a beam splitter for splitting a visible light beam into two components having perpendicular polarization directions; a converter for making the polarization directions of the components coincide; and a color separator for separating light from the converter into rays of the plurality of primary colors. The beam splitter can have a first transparent base; a second transparent base; and a polarizing multilayered film placed between the first and second transparent bases. The polarizing multilayered film includes high refraction layers each having a refractive index nH and low refraction layers each having a refractive index nL lower than the refractive index nH, the high refraction layers and the low refraction layers being alternately laminated to one another. A maximum efficiency incident angle for the polarization splitting film is shifted from an incident angle of a main ray from the light source in order to make an illumination nonuniformity.