Showing papers on "Polarization rotator published in 1994"

Change of polarization of light beams on propagation in free space

Abstract: It is shown by use of a simple model that in general the state of polarization of a light beam generated by a partially coherent source changes as the beam propagates in free space.

Polarization properties of stimulated Brillouin scattering in single-mode fibers

Abstract: The polarization properties of stimulated brillouin scattering (SBS) in low birefringent optical fibers were evaluated using Stokes calculus. It was found that the Brillouin gain for orthogonally polarized pump and probe wave is half (in dB) of the gain for identical polarization, and not equal as often mentioned in literature. Therefore the polarization factor is K=1/sub 1/2/ for complete polarization scrambling, and not K=2. The spontaneous SBS has the same state of polarization as the pump, and its degree of polarization is 33.3% for low pump powers and near 100% for high pump powers. The experimental results agree very well with the calculations. >

Control of vertical-cavity laser polarization with anisotropic transverse cavity geometries

Abstract: We show the two-fold polarization degeneracy of etched air-post vertical-cavity surface emitting laser diodes can be lifted and a dominant polarization state selected through use of anisotropic transverse laser cavity geometries. For lasers with rhombus-shaped cavities, fundamental mode lasing emission linearly polarized along one specified crystal axis is obtained up to twice the threshold current. For dumbbell-shaped lasers, fundamental mode lasing emission linearly polarized along one specified crystal axis is maintained over the entire operating range of the device producing a maximum orthogonal polarization suppression ratio of 14 dB. >

Analysis of a reset-free polarization controller for fast automatic polarization stabilization in fiber-optic transmission systems

Abstract: We analyze the operation of a reset-free polarization controller comprising three endlessly rotatable wave plates: a first quarter-wave plate followed by a half-wave plate and a second quarter-wave plate, which is rotated synchronously with the first quarter-wave plate We show that for any arbitrary angular offset between the two quarter-wave plates; the controller allows continuous, reset-free transformations from any varying general input state of polarization into any general output state An integrated-optic realization of this scheme on z-propagation LiNbO/sub 3/ offers control speeds that well exceed the speed of natural polarization fluctuations in standard single-mode fibers, thus allowing fast automatic polarization stabilization in fiber-optic transmission systems >

Polarization dependent gain in erbium doped-fiber amplifiers

Abstract: Measurement of polarization hole burning is reported for an erbium doped fiber amplifier. This effect produces a dependence of gain, measured with a weak probe, on the polarization of the saturating signal; the maximum gain occurs for probe polarizations orthogonal to the signal. The pump also contributes to the gain dependence on polarization. Reduction of the degree of polarization of both pump and signal below 10% reduces the polarization dependent gain substantially. >

Polarimetric fiber laser sensors

Abstract: Apparatus for measuring a physical quantity such as pressure, temperature, strain etc., by using a beat frequency of a longitudinal mode, a transverse mode or two polarization modes of the optical fiber laser. In the rare-earth optical fiber laser as a resonator, there are two different polarization modes normal to each other. Since the optical path lengths of the optical fiber laser for the two polarization modes are different, longitudinal mode frequencies of each polarization mode are different depending on the birefringence of resonator which is varied as an external physical quantity such as pressure, temperature, strain etc. Due to the variation in the birefringence of the resonator, the longitudinal mode frequency difference between two polarization modes becomes varied. This variation is linearly proportional to the physical quantity externally applied. The difference in longitudinal mode frequency between polarization modes can be measured from a beat signal of the polarization modes. Accordingly, it is possible to measure the physical quantity by measuring the variation in polarization mode beat frequency.

Polarization aberrations. 1. Rotationally symmetric optical systems

Abstract: The polarization in isotropic radially symmetric lens and mirror systems in the paraxial approximation is examined. Polarized aberrations are variations in the phase, amplitude, and polarization state of the electromagnetic field across the exit pupil. Some are dependent on the incident polarization state and some are not. Expressions through fourth order for phase, amplitude, linear diattenuation, and linear retardance aberrations are derived in terms of the chief and marginal ray angles of incidence and the Taylor series expansion coefficients of the Fresnel equations for reflection and transmission at uncoated and thin-film-coated interfaces. Applications to polarization ray tracing are discussed.

Polarization diversity detection of optical signals transmitted through a polarization-mode dispersive medium

Abstract: An apparatus and method which utilize polarization diversity detection to compensate for polarization-mode dispersion (PMD) introduced in an optical signal propagating over a medium such as optical fiber. A received optical signal is separated into first and second polarization components by a polarization beam splitter (PBS). A control signal corresponding to a phase difference between the polarization components is used to drive at least one polarization controller located in the optical signal path before the PBS, such that the two polarization components are aligned with the PSPs of the received optical signal. The control signal may also be used to adjust a variable delay element such that phases of the two polarization components are aligned before the components are combined to provide a PMD-compensated output signal. Other aspects of the invention are directed to polarization control using a rotator element with low numerical aperture input and output signal coupling, and to the use of feedback control to compensate for variations in loss through a polarization controller.

Polarization decorrelation in optical fibers with randomly varying birefringence

Abstract: Polarization decorrelation in single-mode fibers with randomly varying birefringence is studied. We find that decorrelation length is minimized for a given beat length if the average autocorrelation length of the birefringence is close to the average beat length. The differential time delay between the polarization modes is found to depend on the autocorrelation length of the birefringence rather than on the decorrelation length of the polarization modes.

Quantum Cryptography with Polarized Photons in Optical Fibres: Experiment and Practical Limits

Abstract: An all-fibre quantum cryptography set-up based on the polarization of single photon pulses is described. The feasibility of establishing a key over more than 1 km has been experimentally demonstrated. The limits due to the topological effects, the birefringence, and the polarization mode dispersion of fibres are discussed. A set-up using only two non-orthogonal polarization states and polarizers instead of analysers is proposed.

Oscillation polarization mode selective semiconductor laser, light source apparatus and optical communication system using the laser

Abstract: A distributed feedback semiconductor laser selectively performs one of two oscillations in different polarization modes having different polarization planes. The laser includes a substrate, a light waveguide formed on the substrate, which at least partially includes an active layer, a diffraction grating formed around the waveguide, and an injecting unit for injecting a modulation current into a portion of the waveguide. The waveguide and the grating are constructed such that oscillation wavelengths of the polarization modes are different from each other and minimum values of threshold gain in the polarization modes near the Bragg wavelength are approximately equal to each other. The semiconductor laser can be driven by a minute modulation current and prevents degradation of response characteristics due to dynamic wavelength fluctuation in a high-frequency range when used in optical communication systems in which the switching of polarization mode is performed.

Polarization multistability and instability in a nonlinear dispersive ring cavity

Abstract: We study the role of polarization in modulational instabilities in a synchronously pumped ring resonator that is filled with an isotropic nonlinear dispersive medium. To describe nonlinear propagation of the polarized field through the ring, we introduce two coupled driven and damped nonlinear Schrodinger equations. These equations, which result from averaging propagation and boundary conditions over each circulation through the ring, permit a simple stability analysis. This analysis predicts polarization multistability in the steady state as well as the emergence of stable pulse trains whose polarization state is either parallel or orthogonal to a linearly polarized synchronous pump beam. The analytical predictions are confirmed and extended by numerical simulations of polarized wave propagation in the cavity.

High spin polarization at the HERA electron storage ring

Abstract: This paper describes the progress made in 1992 towards increasing the vertical electron beam polarization at HERA. Utilizing harmonic spin-orbit corrections and beam tuning, the vertical polarization has been increased from 15% to nearly 60% at a beam energy of 26.7 GeV. The long-term reproducibility of the polarization is excellent. Measurements of the build-up time and the energy dependence of the polarization are also described.

Apparatus and method employing fast polarization modulation to reduce effects of polarization hole burning and polarization dependent loss

Abstract: The effects of polarization dependent hole burning and/or polarization dependent loss are reduced by modulating the state of polarization (SOP) of an optical signal being launched into the transmission path periodically between first and second states of polarization of at least one pair of orthogonal states of polarization. Ideally, the launched modulated signal should spend equal time intervals in both states of the orthogonal pair. In one exemplary embodiment, the SOP is modulated such that it moves along a great circle on the Poincare' sphere. In another exemplary embodiment, the SOP is modulated such that it traces a complete great circle on the Poincare' sphere. In a preferred embodiment, a complete great circle is traced at a uniform speed on the Poincare' sphere.

Tunable optical filter

Abstract: An tunable optical filter of the kind used, for example, in wavelength-division multiplexing (WDM) optical communication systems and tunable source applications, has an interference filter element which is pivotable to adjust the operating wavelength of the filter. In order to reduce polarization dependency as the angle of the interference filter element changes, the light beam to be filtered is passed through the filter element twice, the second time with its polarization state shifted, specifically orthogonal, relative to the polarization state during the first pass. As a result, polarization dependent effects are equalized. The optical filter comprises a pivotally mounted filter element, an input optical fiber for directing a light beam to be filtered through the filter element in a first direction with a first polarization state, optical elements for rotating the polarization state of the filtered light beam and returning the light beam through the filter element (10) a second time, and an output optical fiber for receiving the light beam following passage of the light beam though the filter element the second time. The optical elements may comprise a reflector for reflecting a light beam emerging from the optical filter element to return through the optical filter element in the opposite direction, and a polarization rotator, such as a quarter-wave plate or a Faraday rotator, for rotating the polarization state of the light beam through 90 degrees before passage in the opposite direction.

System and method for measuring polarization dependent loss

Abstract: Polarization dependent loss (PDL) of an optical component is computed in a deterministic method that requires only four measurements, each having a unique input state of polarization.

Optical-fibre passively mode locked laser generator with non-linear polarization switching

Abstract: A passively-mode-locked laser generator having an active optical fibre and fibre pumping means adapted to cause the generation of an emission signal in the fibre, a polarization control means, signal extraction means and at least one optical component with transmissiveness depending on polarization is disclosed. The components are inserted in an optical fibre path that, for a pumping energy lower than a predetermined value corresponding to a linear propagation condition of the signal, gives rise to a polarization rotation of the emission signal through an angle causing the extinction of the signal itself within the optical component with transmissiveness depending on polarization. For a pumping energy of a higher power than the predetermined value, the generator causes a polarization rotation of the emission signal through an angle corresponding to the transmission with low losses of only pulses of high peak power of the emission signal.

Polarization independent picosecond fiber laser

Abstract: A polarization insensitive fiber laser. A pair of 45 degree Faraday rotators are positioned on either end of the fiber gain source. The resulting laser is insensitive to external perturbations with respect to known entrance and exit polarization states of the laser light. Modelocking, both passive and active, is possible. Configuration wherein the fiber is a combination of polarization preserving and Erbium-doped, and a saturable absorber is included provide a self-starting, polarization insensitive modelocked laser.

Optical rotator and rotation-angle-variable half-waveplate rotator

Abstract: The device of the present invention for an optical rotator and a half-waveplate rotator comprises a retarder or polarization modulator interposed between two crossed or parallel quarter-wave plates, depending on being used as optical rotator or half-waveplate rotator, oriented such that the fast or slow axis of the retarder or modulator is at angle of 45° relative to fast or slow axes of the quarter-wave plates. The rotation angle of the optical rotator and half-waveplate rotator is equal to one-half the retardance of the retarder or modulator and electrically adjustable when using a polarization modulator.

A Novel Birefringent Distributed Bragg Reflector Using a Metal/Dielectric Polarizer for Polarization Control of Surface-Emitting Lasers

Abstract: We propose a novel polarization control structure in vertical cavity surface-emitting lasers using a birefringent metal/dielectric polarizer terminating a distributed Bragg reflector (DBR). Polarization-dependent reflectivity at the resonant wavelength is theoretically predicted by adjusting the phase condition in the DBR. An experimental result shows a reflectivity difference for two polarization states. The possibility of polarization control as well as polarization switching is suggested.

Thin-film magneto-optic polarization rotator

Abstract: In a polarization rotator device, a thin-film magneto-optic medium (2) is magnetized by a thin-film magnet (4). To serve as an optical isolator, the device may include polarizers (51, 52). In such an optical isolator, in which the magneto-optic medium (2) was formed as a Bi-YIG triple-layer structure, and the thin-film magnet (4) as a single-crystal iron-cobalt layer, an extinction ratio better than -20 dB was realized.

Polarization rotator with frequency shifting phase conjugate mirror and simplified interferometric output coupler

Abstract: An interferometer that is used with a frequency shifting phase conjugate mirror (PCM), to produce a 90° polarization rotation, employs only two adjustable elements: a specially shaped prism, and a beam deflector that is preferably a porro prism. The primary prism is shaped and oriented so that a linearally polarized input beam is divided into ordinary (o) and extraordinary (e) subbeams. One of the subbeams is refracted out of the prism along a controlled length path, and then returned back into the prism by the deflector. The second subbeam is retained within the prism by total internal reflection, and directed onto a exit path that coincides with the path of the first subbeam after its reentry into the prism. The recombined output beam is directed into the PCM, from which it is reflected back into the prism for a reverse pass. The difference in path lengths between the o and e subbeams is selected to produce a net 90° polarization rotation after both passes.

Intracavity sum frequency generation using a tunable laser containing an active mirror

Abstract: A means for intracavity sum frequency generation is described in which a er operates simultaneously, cw, at two wavelengths where the net gain at one wavelength is substantially lower than that at the other. The optical alignment of the resonator provides a region where both fundamental wavelengths are overlapped, and another region where both feedback paths are spatially distinct. An active feedback mirror is located in the path of the lower net gain laser transition to provide optical amplification at that wavelength. The laser resonator further contains a sum frequency generating crystal for intracavity sum frequency generation of the two fundamental wavelengths. The sum frequency generating crystal is placed near a laser resonator cavity mode waist in the region where both wavelengths are spatially superimposed, producing the sum frequency of the two wavelengths. An intracavity polarization rotator provides the appropriate orientation of the polarization of the two fundamental wavelengths in the laser gain element as well as in the non-linear sum frequency generating crystal. Line narrowing of the individual two fundamental wavelengths produces a line narrowed sum frequency generated output. Sum frequency generation at 459 nm is demonstrated in a non-critically phase matched Type II KTP crystal by operating a Ti:sapphire laser simultaneously at 808 nm and 1.064 μ.

Large polarization mode dispersion in fiber optic cables

Abstract: The recently observed difference in polarization mode dispersion (PMD) between spooled and cabled single-mode optical fibers is investigated experimentally. To discriminate between a large polarization mode-coupling length or a large birefringence as a cause of high PMD, both parameters are measured. The results show a factor of 50 difference between the mode-coupling lengths of spooled and cabled fibers, which accounts for the larger PMD's of cabled fibers. It is suggested that cables with a loose tube design especially suffer from large polarization mode-coupling lengths. Internal stress is shown to be the dominant source of birefringence in standard telecommunication fibers by observing the shift of the PMD spectrum over a wide wavelength interval as a function of temperature. >

Laser system with phase-conjugator-enhanced output

Abstract: A laser system includes a linear array of broad area lasers. Such a laser source produces a beam that has a polarization axis in the direction in which the array extends and a coherency axis orthogonal to that. The laser is injection locked by phase conjugating a portion of the array's light output. The phase conjugator has a conjugation axis. The coherency axis is aligned with this conjugation axis. External cavity optics include a polarization rotator to align the polarization axis with the coherency axis before the beam reaches the phase conjugator. Thus, the polarization, coherency, and conjugation axes are all aligned, optimizing the action of the phase conjugator. The approach works in both a single-beam and a dual-beam phase conjugation mode. The result is a laser system output of higher intensity, greater coherence, and a narrower frequency range.

An elliptically-polarizing undulator with phase adjustable energy and polarization

Abstract: We present a planar helical undulator designed to produce elliptically-polarized light. Helical magnetic fields may be produced by a variety of undulators with four parallel cassettes of magnets. In our design, all cassettes are mounted in two planes on slides so that they may be moved parallel to the electron beam. This allows us to produce X-rays of left- or right-handed elliptical or circular polarization as well as horizontal or vertical linear polarization. In model calculations, we have found that by sliding the top pair of rows with respect to the bottom pair, or the left pair with respect to the right pair, we retain the polarization setting but change the magnetic field strength, and hence the X-ray energy. This allows us to select both energy and polarization by independent phase adjustments alone, without changing the gap between the rows. Such a design may be simpler to construct than an adjustable-gap machine. We present calculations that model its operation and its effects on an electron beam.

Polarization properties of four-wave interaction in dynamic recording material based on bacteriorhodopsin

Abstract: The polarization properties of four-wave interaction on polymer films with bacteriorhodopsin that possess anisotropically saturating nonlinearity are studied both theoretically and experimentally. The amplitude and the polarization of the diffracted wave for recording material with anisotropically saturating nonlinearity are calculated. Low saturation intensity allows the operation of the polarization of low-intensity signals to be realized. It is shown that control of the diffractive wave polarization is possible only with the variation of the light recording intensity.

Feedback-induced polarization switching in a Nd-doped fiber laser.

Abstract: We demonstrate a switching effect between the two polarization eigenstates of a Nd-doped fiber laser when it is subjected to an optical feedback signal. Conditions for an optimization of this effect are recognized to depend on the relative orientation of the fiber eigenaxes and the polarization states of the pump and feedback beams.