Showing papers on "Extinction ratio published in 1981"

Low-loss single-polarisation fibres

Abstract: Low-loss single-mode fibres that maintain polarisation well have been fabricated by the standard MCVD method. An extinction ratio of less than −30 dB at 1 km and a loss of 0.8 dB/km at 1.5 μm were achieved by the concentric circular germanosilicate core-clad fibres with the borosilicate elliptical jacket.

Distributed coupling on polished single-mode optical fibers.

Abstract: The core of a single-mode fiber can be reached by an optically controlled polishing technique which does not alter the fiber's mechanical strength. A directional coupler using two such fibers was designed showing a power extinction ratio from zero to more than 35 dB over a wide range of structure parameters with easy alignment operations and insertion loss lower than 1 dB.

Photon probe fault locator for single-mode optical fiber using an acoustooptical light deflector

Abstract: A new backscattering technique for diagnosing the attenuation characteristics, spatial imperfections with length (fault location), and splice loss in a single-mode optical fiber has been developed by using a TeO 2 acoustooptical light deflector operating at 120 MHz. Due to the small insertion loss and high extinction ratio of the deflector, the dynamic range of the backscattered signal has been increased by at least 10 dB, which corresponds to the extension of 5 km in measurable length for fiber loss of 1 dB/km, compared with the conventional back-scattering technique in which the beam splitter and polarizer-analyzer combination are utilized. Another advantage of this technique is in that the saturation of the amplifier is avoided by arbitrarily cutting off a large power in the early stage of the Rayleigh scattering signal. A single-mode fiber of 19.2 km in length has been examined, and the distance for fault location up to 18.4 km was obtained.

High-speed modulation of an electrooptic directional coupler

Abstract: A LiNbO 3 :Ti directional coupler driven by an RF signal has been tested at 1.06 μm over a large modulation bandwidth. An analytical model has been developed leading to simple usable expressions to describe the theoretical dependence of the frequency spectrum of sinusoidally modulated light. The frequency response has been measured with a scanning Fabry-Perot and also with a high-speed photodiode. Both methods provided results which are in good agreement. The 9 mm long switch exhibited a 2.5 GHz bandwidth; a 16 dB extinction ratio has been achieved with a driving power of approximately 50μW/MHz. The confirmation of practical modulation response expressions shows the advantage of the optical spectrum observation, which is a very simple measurement method without any bandwidth limitation. In addition, this method has the advantage of remaining quite accurate even for large modulation signals.

Erratum: Bistable optical switch using a yittrium‐iron‐garnet crystal with phase matching films

Abstract: A magneto‐optical switch using a yttrium‐iron‐garnet crystal plate with phase matching films requiring a drive voltage of only 5V is demonstrated at 1.3 μm wavelength. Using a semihard magnetic material, we developed a bistable magneto‐optical switch which drives with a switching speed of 20 μs. An extinction ratio of 24 dB was obtained.

Design considerations and test results of an evanescent switch-attenuator.

Abstract: An implementation technique of an evanescent switch using a cylindrical piezoelectric driver material is discussed. The driver has provisions for fine alignment of the prisms. The selection criteria for the choice of the prism material are evaluated in detail. The measured insertion loss was 10% ± 2%, and these are a 4000: 1 extinction ratio at 10.6 μm between the ON and OFF positions of the switch. The curve showing attenuation vs voltage applied across the piezoelectric driver indicates a large dynamic range for the device as a variable attenuator.

Integration of a Laser Diode and a Twin FET

Abstract: Monolithic integration of a double heterostructure laser diode and field effect transistors, all of GaAs/GaAlAs, involving only planar type fabrication processes is demonstrated. The ICs are fabricated using liquid phase epitaxy, and lift-off. The functions of normally-on type Schottky gate FETs and a Fabry-Perot type infra-red laser diode are successfully matched, to realize high speed modulation with high extinction ratio and no pattern effect. Moreover, activation of the laser by positively pulsed electric signals on gates is demonstrated utilizing an auto-bias of the ICs. The rise time of the pulsed response is about 0.4 ns, suggestive of GHz operation.

Extinction ratio of germanium wedge-plate infrared polarizers.

Abstract: Transmitting-type polarizers and analyzers for the far IR region of the optical spectrum can be constructed from plates mounted at the Brewster angle rather than Glan, Rochon, or Wollaston configurations. This constraint is caused mainly by the fact that at long wavelengths the required angle between the crystal optical axis and the crystal cut exceeds the critical angle of total internal reflection. The degree of polarization P of the transmitted light when the incident light impinges on a pile of plates mounted at the Brewster angle is given by

Extinction ratio of stripe-geometry DH AlGaAs lasers with "soft" turn-on

Abstract: The effect of high spontaneous emission on the extinction ratio of modulated laser-diode signals is discussed. A calculation based on the spectra taken from oxide-defined narrow-stripe lasers at "on" and "off" levels shows that high spontaneous emission at the "on" level can degrade the apparent extinction ratio of the source, due to material dispersion in optical fibers, and affect transmission bandwidth and useful device lifetime.

Optical waveguide polarizer

Abstract: PURPOSE:To obtain a polarizer which is a thin film and has the flat wavelength characteristics, by providing a minute conductive grating, which has a pitch shorter than the used wavelength, on the end face of an optical fiber or an optical waveguide. CONSTITUTION:A conductive grating 4 is provided across a core 2 and a clad 3. The width and the pitch of the grating are set to values sufficiently shorter than the used wavelength. A gold grating pattern which is produced by the electron beam lithography and has 0.4mum pitch, 0.15mum width, and 1,500Angstrom thickness has about 1/10 extinction ratio from the wavelength of visible rays to 1.3mum, and a grating pattern where the similar grating pattern is produced on this grating pattern after forming an insulating film consisting of SiO2 or the like has 1/100 extinction ratio. Conductive gratings 4 are formed in incidence ends 8 and 9 so that directions of gratings are orthogonal to each other, and light sources are provided in incidence ends 8 and 9 independently of each other, and their outputs are changed, thereby controlling the direction of polarization of the light emitted from an exit end 7.

Improvements in or relating to electronic telephone exchanges and optical fibre links for use therein

Abstract: An electronic telephone exchange of the type employing time-space-time switching, has an optical fibre data link connecting the space (3) and time switches (2,4). In order to meet the design requirements for use in a telephone exchange, the fibre optic link has to have fairly well defined performance parameters. In particular the overall diameters of the optical fibres (16) employed in the optical fibre link lies between 180 and 250 microns, preferably 200 microns, and the core diameter of the optical fibres (16) lies in the range 0.6 to 0.95 of the cladding diameter. Preferably the core diameter lies in the range 160 to 180 microns. The optical fibre link is characterised by the numerical aperture of the fibre, insertion loss of the fibre, sensitivity and dynamic range of the receiver (19) and the power output and extinction ratio of the transmitter (13).