Showing papers on "Waveplate published in 1984"

Optical frequency shifter for heterodyne interferometry using counterrotating wave plates.

Abstract: A method of optical frequency shifting for heterodyne interferometry based on counterrotating wave plates is described. It is possible with this technique to obtain a higher-frequency shift with fewer components.

Single mode optical fiber polarimetric stress sensor having optical common mode rejection

Abstract: An instrument for measuring stress is arranged to be insensitive to stresses caused by conditions other than that of the phenomenon to be measured. The instrument employs two equal lengths of optical fibers of the kind exhibiting birefringence when stressed. Polarized light is directed into one of the optical fibers along its longitudinal axis. The two optical fibers are arranged in series with respect to the longitudinal transmission of the polarized light through those fibers. A polarization rotator is situated in the light path between the two optical fibers. The polarized light transmitted through the polarization rotator is rotated by an amount causing stresses imposed equally on the two optical fibers to have equal and opposite effects of the transmitted polarized light. The invention may be embodied to permit the measurement of acceleration, pressure, fluid flow rate, magnetic field gradient, magnetic field strength, electric field strength, electric field gradient, or any other phenomena that can be made to produce stress on an optical fiber. The invention is especially useful in differential measurement because the device measures the difference in stress imposed on the two optical fibers.

Guided wave optical frequency shifter

Abstract: This invention is a frequency shifter for receiving an optical carrier signal input and producing an output including a sideband that is shifted in frequency from the carrier. The frequency shifter includes an optical waveguide formed in a substrate of an electro-optically active material such as lithium niobate. A plurality of electrodes formed on the substrate cooperate with a signal generator to apply two perpendicular electric fields to the optical waveguide. The resultant of the two fields is a rotating electric field which produces a rotating birefringence in the optical waveguide. The rotating birefringence acts as a rotating wave plate, which shifts the frequency of optical signals input to the optical waveguide. The wave plate is preferably a half wave plate, which converts all of the input optical energy into the sideband.

Development in laser interferometry for position sensing

Abstract: Interferometric developments which improve the performance of the laser interferometer as a position sensing device are described. The double pass attachment is an optical accessory which doubles the resolution of the Hewlett-Packard linear and plane mirror interferometers. Unlike previous attempts to extend resolution optically, this device does not fold just one of the two interfering beams and hence does not introduce error due to its own motion. Simple addition of a quarter wave plate to the attachment gives a differential version of the plane mirror interferometer. Various configurations of this differential interferometer, and their application to machine tools and to integrated circuit lithographic and inspection equipment, are discussed. A new ‘wavelength tracking’ device, based on differential interferometry, directly and precisely monitors changes in laser wavelength inside a highly stable mechanical cavity. Easily incorporated as an additional interferometer axis, the device improves compensation for changes in laser wavelength.

Photo-electromagnetic reproducing device

Abstract: PURPOSE:To reduce the extinction ratio and realize the high S/N reproduction by arranging a 1/2 wave plate between the polarizing beam splitter and stop- down lens. CONSTITUTION:A 1/2 wave plate 4 is arranged between a beam splitter 3 and a stop-down lens 5. The optical beam emitted from a semiconductor laser 1 is made into parallel lights by a collimater lens 2, passes through the beam splitter 3, and irradiated after being stopped-down by the lens 5. Its reflecting light is detected by an optical detector 11 through a lens 10. At that time, since the 1/2 wave plate is being arranged, the direct polarized light surface can be coincided with optical anisotropic axis of the lens 5. Therefore, extinction ratio, which is the ratio against light quantity leaked from the analyzer 9 can be reduced and high S/N reproduction can be made.

Optical polarization restoration apparatus

Abstract: An active system for restoring the polarization state of light emerging from a single-mode optical fiber. The system changes the slowly varying elliptical polarization resulting from environmental effects on the long fiber to a linear polarization state of fixed orientation. The elliptically polarized light is converted into two orthogonal linearly polarized beams. One of the beams is used in a feedback circuit to null its intensity thereby restoring all the input light to the other linear polarization state.

Apparatus for controlling the rotation of the plane of linear polarization of linearly polarized radiant energy traversing an element of chromium chalcogenide spinel magnetic semiconductor with elliptically polarized radiant energy

Abstract: Apparatus employing a light beam to affect another light beam. A primary beam of linearly polarized monochromatic light is directed on an element of chromium chalcogenide spinel magnetic semiconductor, specifically single crystal CdCr 2 Se 4 . A control beam of monochromatic light is selectively elliptically polarized and directed at the element. As the light beams traverse the same path through the element the circularly polarized control beam interacts with the element thereby changing the effect of the element on the linearly polarized primary beam to rotate the plane of linear polarization of the primary beam. A linear polarization analyzer receives the primary beam from the element and passes, blocks, or diverts light depending upon the plane of linear polarization of the incident light.

Polarization noise reducing element

Abstract: PURPOSE: To reduce polarization noise while holding the merit of a polarized wave separation type optical directional coupler and to measure backscattered light or Fresnel reflected light from an optical fiber highly accurately by using the characteristics of double-refractive media. CONSTITUTION: N (N≥2) double-refractive media are arranged in series and the angle θ formed by the main axes of at least one group or more of adjacent double-refractive media is set up to an angle approximately satisfied with tan 2 (2θ)=2. An optical pulse projected from a light source 1 is passed through a polarized wave separation type optical direction coupler 3, made incident upon a polarization holding optical fiber 4, and then made incident upon a testing SMF5. The light scattered backward or reflected in the testing SMF5 is passed through the fiber 4 again and only the polarized component rectangular to a polarizing direction of the incident optical pulse is guided to a photodetector 6 by the coupler 3 and detected. The fiber 4 concerned has double refractive property larger than that of a normal SMF, and when the polarization direction coincides with the main axis, the optical fiber propagates the incident light while holding the polarization direction of the incident light. COPYRIGHT: (C)1986,JPO&Japio

Tension adjusted inline optical fiber attenuator

Abstract: An single-mode fiber attenuator is disclosed which may be formed by a tandem combination of a birefringent polarization-preserving fiber and a single polarization fiber. The birefringent fiber functions as a variable wave plate and the single polarization fiber functions as a fiber polarizer. By continuously changing the local birefringence of the birefringent fiber with, For example, tension, pressure, or temperature, the phase difference between the two polarization components of light traveling through the birefringent fiber is continuously modified. The difference in phase causes suppression of one of the polarization components as it enters the fiber polarizer and, therefore, the output of the fiber polarizer, the sum of the two polarizations, is attenuated. The attenuator may be tuned by changing the local birefringence of the birefringent fiber. An inline optical fiber bandpass filter may be formed by cascading a plurality of appropriately arranged inline fiber attenuators formed in accordance with the present invention. In addition the device is adaptable for use as an inline attenuator or a gauge.

Optical fiber type polarization plane control device

Abstract: PURPOSE: To simplify an optical system and to reduce the insertion loss of transmitted light down to approximate zero by using optical fibers as the whole control of the polarization plane of light. CONSTITUTION: Elliptical polarized light incident upon an optical fiber coil 4 is converted into straight polarized light by the coil 4 and made incident upon a magneto- optical polarizing device 6. The polarizing device 6 applies a magnetic field in parallel with an optical fiber 2 and rotates the polarization plane of the passing straight polarized light by θ 2 ° so that the polarized light coincides with a direction corresponding to a setting direction (x axis direction). An optical demultiplexer 7 divides the incident light into two polarized components in the (x) and (y) axis directions which are intersected with each other at right angles and photodetectors 8, 9 detect respective polarized components. Namely, the photodetector 9 detects the main component turning its polarization plane to the (x) axis direction and the photodetector 8 detects the unnecessary wave component of the (y) axis direction intersected with the (x) axis at right angles. The output of the photodetector 8 is sent to a current control device 13 and fed back to current sources 11, 12 so that the unnecessary wave component of the (y) axis direction is minimized. Thus, the rotational frequency of the polarization planes of the magneto-optical polarizers 3, 6 can be corrected. COPYRIGHT: (C)1986,JPO&Japio

Critical Slowing Down and Magnetically-Induced Self-Pulsing in a Sodium-Filled Fabry-Perot Resonator

Abstract: The level degeneracy of the ground state of atoms acting as a nonlinear medium in optical bistability experiments has attracted much attention recently. The well-known process of transverse optical pumping between Zeeman levels has been discussed as a mechanism yielding considerable nonlinearity even at low power densities1, and the corresponding experiment has been performed on a resonator filled with sodium atoms2. The process of longitudinal optical pumping has also been studied3. While in Refs. 2 and 3 only a single mode of the radiation field interacts with the atoms, the case of two orthogonally polarized degenerate modes has been dicussed, too. It has been predicted4 and experimentally established5 that optical tristability may arise, and it is quite obvious that in the two-mode case the system is capable of displaying a rich variety of behaviour6–9. In this paper we report on an expansion of the experiment of Ref. 2 to the study of transients in the one- and two-mode case.