Showing papers on "Extinction ratio published in 1982"

Fabrication of single-polarisation single-mode-fibre couplers

Abstract: Fused biconical taper fibre couplers have been fabricated from single-polarisation single-mode fibres. A CVD technique is applied to permit maintenance of parallel alignment of the fibres in the coupler fabrication process. The couplers can hold linear polarisation along the principal axis of the fibre branches, showing an extinction ratio of about −15dB.

Analysis of integrated-optics near 3 dB coupler and Mach-Zehnder interferometric modulator using four-port scattering matrix

Abstract: The scattering matrix formalism for a lossless four-port device is used to describe the interferometric performance of the integrated-optics near 3 dB coupler and, consequently, the Mach-Zehnder interferometric modulator as a function of coupler and/or power imbalance. For the case of a coupler consisting of three single-mode dielectric guides forming a Y junction, a fourth port is incorporated which takes all the power radiated out of the guided-wave system in the vicinity of the junction. The interferometric properties of the coupler are shown to be relatively insensitive to fabrication and/or design errors of a magnitude which would make the use of this junction in the reverse direction as a 3 dB divider very marginal. A coupler with an extinction ratio as an interferometer better than -26 dB corresponds to a power divider which couples 22 percent more power into one arm than the other. It is also shown that the near 3 dB coupler used as the output of an interferometric modulator is similarly insensitive to the inequality of the powers in the two arms.

Single-mode fiber-type polarizer

Abstract: The simple and novel fabrication technique of the fiber-type polarizer has been demonstrated and the polarization characteristics of the polarizer have been investigated. The polarizer structure consists of the eccentric core and the metal coat on the thin buffer layer whose thickness is controlled by chemical etching. The maximum extinction ratio of 41 dB (polarizer length L = 40.8 mm) was obtained at \lambda = 1.15 \mu m when the buffer layer thickness was about 0.3 μm. Although the insertion loss increases with decreasing the buffer layer thickness, the insertion loss of 0.66 dB was obtained with the extinction ratio of 22 dB (polarizer length L = 21.4 mm). An aluminum coat was superior to a gold coat for low propagation loss and a high extinction ratio.

Particle size evaluations using multiwavelength extinction measurements

Abstract: As the first phase of a program to develop a lidar method for remote evaluation of mean particle size of stationary source emissions, a data base was experimentally collected consisting of multiple-wavelength extinction coefficients and mean particle sizes of generated aerosols. Extinction data were collected using multi-wavelength (14) transmissometers and a 10-m long aerosol tunnel facility. Generated aerosols consisted of five size fractions of fly ash, three size fractions of silica, and single-size fractions of six other types of particulate material. Particle size evaluations were made by multistage impactor and by air permeability (Fisher) analysis of packed powder. The data base indicates that mean particle size smaller than l-microm diam could be estimated usefully from aerosol extinction measurements using a single-laser lidar system operating at 1.06- and 0.53-microm wavelengths. For larger mean particle sizes the extinction ratio is near unity, and longer wavelength systems are required. The data indicate that a two-laser lidar operating at 10.6 and 0.53 microm could provide estimates of mean particle size to diameters of at least 6 microm.

Electrooptic polarization modulation in multielectrode Al x Ga 1-x As rib waveguides

Abstract: A single mode rib waveguide (RWG) polarization modulator is described with a measured extinction ratio ≳27 dB, a power conversion ≈0.99, and a switching voltage of 12.5 V at \lambda = 1.064 \mu m. The modulator is based on a modified step \Delta\beta -reversal configuration. Contact with CdO and an Au overlay ensures low optical losses ( \lsim1 cm-1) for both polarizations.

Analysis of Integrated-Optics Near 3 dB Coupler and Mach-Zehnder Interferometric Modulator Using Four-Port Scattering Matrix

Abstract: The scattering matrix formalism for a lossless four-port device is used to describe the interferometric performance of the integrated optics near 3dB coupler and, consequently, the Mach-Zehnder interferometric modulator as a function of coupler and/or power imbalance. For the case of a coupler consisting of three single-mode dielectric guides forming a Y junction, a fourth port is incorporated which takes W the power radiated out of the guided-wave system in the vicinity of the junction. The interferometric properties of the coupler are shown to be relatively insensitive to fabrication and/or design errors of a magnitude which would make the use of this junction in the reverse direction as a 3 dB divider very marginal. A coupler with an extinction ratio as an interferometer better than -26 dB corresponds to a power divider which couples 22 percent more power into one arm than the other. It is also shown that the near 3 dB coupler used as the output of an interferometric modulator is similarly insensitive to the inequality of the powers in the two arms.

Optical polarization of the Seyfert galaxies IC 4329A and MRK 376

Abstract: Measurements of the optical polarizations of the two highly polarized Seyfert 1 galaxies IC 4329A and Mrk 376 are presented. Continuum and line polarization of the two objects were observed with the Steward Observatory 2.25-m telescope using a two-channel photoelectric Pockels cell polarimeter, a single-channel scanner, and a digicon attached to a flint prism spectrograph. Results indicate that, for both galaxies, the emission line polarization and underlying continuum polarization are identical, rising toward short wavelengths, and therefore must be explained by a common mechanism. Such a mechanism is suggested to involve polarization produced by aligned grains in the galactic disk. A model for polarization in IC 4329A by this mechanism predicts a grain size three times smaller than Galactic polarizing grains, as well as a visual extinction of about 2 magnitudes, a gas to dust mass ratio close to 100 and a polarization to extinction ratio comparable to the Galactic ratio.

Single-Mode Fiber-Type Polarizer

Abstract: The simple and novel fabrication technique of the fiber-type polarizer has been demonstrated and the polarization characteristics of the polarizer have been investigated. The polarizer structure consists of the eccentric core and the metal coat on the thin buffer layer whose thickness is controlled by chemical etching. The maximum extinction ratio of 41 dB (polarizer length L = 40.8 mm) was obtained at Lambda = 1.15 µm when the buffer layer thickness was about 0.3 µm. Although the insertion loss increases with decreasing the buffer layer thickness, the insertion loss of 0.66 dB was obtained with the extinction ratio of 22 dB (polarizer length L = 21.4 mm). An aluminum coat was superior to a gold coat for low propagation loss and a high extinction ratio.

Electro-optic cells

Abstract: A Pockels cell (10) comprises an electro-optic crystal having front (12) and rear optical faces cut at the Brewster angle to the longitudinal axis of the cell. The cell is surrounded by dielectric material (13) and a pair of longitudinally spaced apart and longitudinally extending electrodes (15, 16) are formed on the dielectric material. Each electrode extends to the edge of its respective optical face. When used for Q-switching in a laser system, the orientation of the faces minimise Fresnel reflection losses while the electrode configuration ensures that a high extinction ratio may be obtained.

Electrooptic Polarization Modulation in Multielectrode Al/sub x/Ga/sub 1- x/As Rib Waveguides

Abstract: A single mode rib waveguide (RWG) polarization modulator is described with a measured extinction ratio /spl gsim/27 dB, a power conversion /spl ap/0.99, and a switching voltage of 12.5 V at /spl lambda/ = 1.064 µm. The modulator is based on a modified step delta beta-reversal configuration. Contact with CdO and an Au overlay ensures low optical losses (/spl lsim/1 cm/sup -1/) for both polarizations.

Signal-to-Noise Ratio in Polarization Modulation Method for Magneto-Optical Measurement

Abstract: The signal-to-shot-noise ratio (SNR) in the polarization modulation method using a photomultiplier for measuring a magneto-optic rotation angle \varPsi is calculated as a function or the modulation amplitude a0, taking the magneto-optic ellipticity angle χ, the extinction ratio of the polarizer, and the partial polarization of the light source into account. The SNR increases to a saturation value of (S/N)0 as a0 increases, in accordance with the formula S/N=(S/N)0 [1+(2\varPsi2+4\varGamma')/a02]-1/2. Here, \varGamma' is the `practical extinction ratio' of the polarizer, in which the influence of the ellipticity χ as well as the influence of the partial polarization of the light source are included. The SNR measurement was performed at λ=0.63 µm, using a monochromator and polarizers of the Glan-Thompson or dichroic-sheet type. The reult agrees with our calculation.

Fresnel Light Modulator with an Array of Channel Waveguides

Abstract: One-dimensional focusing and optical modulation have been achieved using a Fresnel light modulator (FLM) based on a Fresnel lens consisting of Ti-diffused channel waveguides on LiNbO 3 . By this device, the height of diffraction pattern near the focal point is modulated with an applied voltage while the focusing effect is almost kept. The experimental results obtained from the FLM with 13 zones at 633 nm are as follows: the focal length is 12.4 cm, the full width of beam at half power 47 μm, the half-wave voltage 28 V, the extinction ratio 10.9 dB and the insertion loss 11.6 dB.

Thin film fresnel light modulators

Abstract: Thin film Fresnel modulators were analyzed and studied experimentally. These devices, which can electrically control the phase of the diffracted light from a one-dimensional Fresnel lens, have the following advantages: (1) they can perform simultaneous focusing and optical modulation; (2) the light output is unaffected by temperature variation; (3) no analyzer is required; (4) a high optical input power can be used. The light modulator may be of the amplitude type, using a channel waveguide, or the phaseshift type, using a slab waveguide. The former has a better light extinction ratio and consumes less power, while the latter has a high light output and is easy to fabricate. A LiNbO3 crystal was cut in the Y direction and thermally diffused with Ti,producing one-dimensional lens 2 mm wide with a total length of 5 mm, having 13 zones. Electrodes were placed on the even-numbered zones by photolithography. In the amplitudetype, the diameter of the focal spot used 56 μm, the extinction ratio was 18.1 dB, the half-wave voltage was 28 V and an efficiency of -10.1 dB was obtained. In the phase-shift type, the spot diameter was 53 μm, the extinction ratio was 11.7 dB, the half-wave voltage was 39 V and an efficiency of -10.6 dB was obtained. The focal length of both types was 12.4 cm.