Showing papers on "Polarization rotator published in 1997"

Polarization properties of vertical-cavity surface-emitting lasers

Abstract: Polarization-state selection, polarization-state dynamics, and polarization switching of a quantum-well vertical-cavity surface-emitting laser (VCSEL) for the lowest order transverse spatial mode of the laser is explored using a recently developed model that incorporates material birefringence, the saturable dispersion characteristic of semiconductor physics, and the sensitivity of the transitions in the material to the vector character of the electric field amplitude. Three features contribute to the observed linearly polarized states of emission: linear birefringence, linear gain or loss anisotropies, and an intermediate relaxation rate for imbalances in the populations of the magnetic sublevels. In the absence of either birefringence or saturable dispersion, the gain or loss anisotropies dictate stability for the linearly polarized mode with higher net gain; hence, switching is only possible if the relative strength of the net gain for the two modes is reversed. When birefringence and saturable dispersion are both present, there are possibilities of bistability, monostability, and dynamical instability, including switching by destabilization of the mode with the higher gain to loss ratio in favor of the weaker mode. We compare our analytical and numerical results with recent experimental results on bistability and switchings caused by changes in the injection current and changes in the intensity of an injected optical signal.

Polarization of Light

Abstract: Polarized Optical Waves Light Propagation in an Anisotropic Dielectric Medium Propagation of the States of Polarization in Optical Devices Stress--Induced or Stress--Modified Anisotropy Components and Devices Used in the Context of Optical Anisotropy Polarization Phenomena in the Fied of Guided Waves Appendices Bibliography Index

Fault-tolerant optical routing switch

Abstract: An electromagnetically controlled optical switch (100) having a plurality of optical inputs (101). An optical signal at each input (101) is spatially decomposed into two coparallel, orthogonally polarized beams by a birefringent element (130). An array (140) of field-controlled polarization rotators are positioned in the paths of the decomposed light beams so that the polarization of the emergent beam pairs are set to be at one of the orthogonal states (i.e., both beams are either vertical or horizontally polarized). A following birefringent element (150) spatially routes the light beam pairs based upon their polarization. A second array (160) of polarization rotators follows the second birefringent element (150) and is set to be in the opposite state from the first array (140), such that the emergent beams are orthogonal to their input states before they entered the first polarization rotator (140). The beams are combined by a firefringent element (170) to form a plurality of combined beams that are coupled to output ports (102, 103).

Polarization properties of corner-cube retroreflectors: theory and experiment

Abstract: Polarization properties of the corner-cube retroreflector are discussed theoretically by use of ray tracing and analytical geometry. The Jones matrices and eigenpolarizations of the six propagation trips of the corner-cube retroreflector are derived. An experiment is also set up for the determination of the linear eigenpolarizations and the output states of polarization for incident linearly polarized light. The experimental results are consistent with theoretical expectations.

Optical attenuator using polarization modulation and a feedback controller

Abstract: An optical power regulator employs a variable optical attenuator having a first birefringent element that spatially separates the input optical beam into two orthogonally-polarized beams. Both beams pass through a polarization modulator (e.g., a liquid crystal material) that rotates their polarizations to an extent determined by the control voltage applied across the polarization modulator. A final birefringent element spatially separates both beams exiting the polarization modulator into two pairs of orthogonally-polarized beams (i.e., two horizontally-polarized and two vertically-polarized components). The thicknesses and optical properties of the birefringent elements are selected so that two of the four beams are combined by the final birefringent element to exit at the output port of the regulator, while the remaining two beams are blocked. As a result, the degree of attenuation is determined by the degree of polarization rotation by the polarization modulator, which in turn is a function of the control voltage applied to the polarization modulator. Preferably, the liquid crystal material used in the polarization modulator has a high optical birefringence and a low dielectric anisotropy, which results in a relatively shallow attenuation curve as a function of applied voltage. The intensity of the optical signal is measured by a photodetector and used by a controller to output the control voltage applied to the liquid crystal material to maintain a desired optical power level at the output port of the regulator.

Polarization Evolution and Polarization Instability of Solitons in a Birefringent Optical Fiber

Abstract: Ultrashort optical solitons with different states of polarization are used to map the polarization evolution in a fixed section of a weakly birefringent fiber. Soliton polarization evolution was compared to linear propagation. A significant change in the polarization behavior between the solitons and linear regime is observed. Although solitons contain a continuum of instantaneous intensities, they transform their polarization as a unit, demonstrating the particlelike nature of solitons.

Polarization behavior of birefringent multitransverse mode vertical-cavity surface-emitting lasers

Abstract: An analysis has been undertaken of the effect of birefringence on the selection of polarization states of a weakly index guided vertical-cavity surface-emitting laser (VCSEL) supporting both a fundamental and a first-order transverse mode. It is shown that for small index steps polarization switching due to spatial-hole burning effects can occur. For larger index steps it is found that higher order modes can emerge which are orthogonally polarized to the dominant polarization of the fundamental mode.

Experimental investigation of linear polarization in high-birefringence single-mode fibers

Abstract: We report on measurements of linear polarization ratio in high-birefringence fibers as a function of wavelength. Comparison with standard step-index and with dispersion-shifted fibers reconfirms that the modes of polarization-maintaining fibers are not linearly polarized.

Polarization modulation dynamics of vertical-cavity surface-emitting lasers with an extended cavity

Abstract: Vertical-cavity surface-emitting lasers (VCSELs) are known to exhibit a small birefringence and dichroism whose axes are directed along the crystal axes of the quantum wells and which fix the polarization of the oscillating light. In this paper, we consider the dynamics of the polarization of light in such a laser, extended by means of a quarter-wavelength plate in an external cavity. Periodic variations are experimentally observed. A theoretical analysis and numerical results are proposed, using a recent model which includes the carriers' spin interaction. A good match is found between experimental and numerical results.

A short polarization splitter without metal overlays on InGaAsP-InP

Abstract: A new and very short polarization splitter on InGaAsP-InP is designed and realized for the first time. The component contains a ridge waveguide directional coupler of 0.4 mm length and an output section of 0.7 mm. It uses the large waveguide birefringence of the first-order TE and TM modes to obtain polarization selective directional coupling. In this way, additional metal layers on the waveguides to create birefringence are avoided and fabrication becomes very simple. Components are realized, which show splitting ratios close to -20 dB. Excess losses are below 1 dB. The polarization splitting is investigated in the wavelength region of 1525-1560 nm and found to be better than -9 dB.

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

Abstract: An oscillation polarization mode selective semiconductor laser for selectively performing one of oscillations in different polarization modes, is provided. The semiconductor laser includes a substrate, a laser structure formed on the substrate, and a phase shift region formed in the laser structure. The laser structure includes an active region in which population inversion is established by a current injection thereinto. At least a portion of the phase shift region has a strained quantum well structure in which degrees of a change in refractive index for internal light in different polarization modes due to a current injection thereinto are different from each other. The polarization mode of a light output from the laser can be changed by a small amount of current injected into the phase shift region, and fluctuation in the output intensity can be suppressed during a transition operation in polarization mode.

Wavelength conversion apparatus with improved efficiency, easy adjustability, and polarization insensitivity

Abstract: A wavelength conversion apparatus has an optical amplifier, a wavelength converter, and an optical coupler coupled to form an optical ring resonator. The optical amplifier supplies pump light. The wavelength converter generates converted light, either from the pump light alone or by interaction between the pump light and signal light supplied from a signal source. The optical coupler extracts the converted light. The optical ring resonator preferably includes a tunable optical bandpass filter that defines the wavelength of the pump light. The optical coupler may also couple the signal light into the optical ring resonator, preferably through a polarization beam splitter and at least one polarization rotator, making the apparatus insensitive to the polarization of the signal light.

Polarization and transverse-mode dynamics of gain-guided vertical-cavity surface-emitting lasers.

Abstract: Transverse-mode competition and polarization selection in gain-guided vertical-cavity surface-emitting lasers are studied by use of a transverse continuous model that incorporates basic physical mechanisms of polarization dynamics. Polarization stability and polarization switching within the fundamental Gaussian mode are described. The first-order transverse mode always starts lasing orthogonally polarized to the fundamental one. At larger currents polarization coexists with several active transverse modes. These results are shown to be sensitive to the carrier spin-flip relaxation rate.

Integrated optical time delay unit

Abstract: A True Time Delay system for creating variable time delays of an optical signal suitable for use with a phased array antenna system in order to avoid beam-squint in broadband applications. The TTD is adapted to be integrated on a planar silica waveguide in order to substantially reduce the package size of the device. In one embodiment of the invention, the TTD is formed from a polarization beam splitter, a polarization rotator and a spiral waveguide. In an alternate embodiment of the invention, the TTD includes a polarization sensitive Mach Zehnder interferometer, a quarter wave polarization rotator and a spiral waveguide. In both embodiments of the invention Bragg reflective gratings are written into the spiral waveguide at different spacings to reflect optical signals of different wavelengths to create various time delays.

Polarization of light: Fourth-order effects and polarization-squeezed states

Abstract: The polarization properties of a monochromatic beam of light are ordinarily determined by three numbers, for example, the Stokes parameters. However, three numbers are no longer sufficient when intensity fluctuations in the polarized modes (or the correlation between them) are recorded. It is shown that in this case nine parameters, which can be arranged into 3×3 matrices, must be prescribed. The transformation properties of these matrices under polarization converters and the invariants of the matrices are analyzed. Specifically, the fourth-order polarization P4 is introduced. Several examples are examined of light with “hidden” polarization—light which is not polarized in the ordinary sense (P2=0) but is polarized in fourth order (P4≠0)—as well as “polarization-squeezed” light in which the quantum fluctuations of the Stokes parameters are suppressed.

Polarization and transverse-mode selection in quantum-well vertical-cavity surface-emitting lasers: index- and gain-guided devices

Abstract: We study polarization switching and transverse-mode competition in vertical-cavity surface-emitting lasers (VCSELs) in the absence of temperature effects. We use a model that incorporates the vector nature of the laser field, saturable dispersion, different carrier populations associated with different magnetic sublevels of the conduction and heavy hole valence bands in quantum-well media, spin-flip relaxation processes and cavity birefringence and dichroism. We consider both index- and gain-guided VCSELs and we find that spin-flip dynamics and the linewidth enhancement factor are crucial for the selection of the polarization state corresponding to a given injection current. For index-guided VCSELs the effect of spatial hole burning on the polarization behaviour within the fundamental mode regime is discussed. For gain-guided VCSELs, transverse-mode and polarization selection are studied within a Maxwell - Bloch approximation which includes field diffraction and carrier diffusion. Polarization switching is found in the fundamental mode regime. The first-order transverse mode starts lasing orthogonally polarized to the fundamental mode. At larger currents polarization coexistence with several active transverse modes occurs.

Wavelength insensitive passive polarization converter employing electro-optic polymer waveguides

Abstract: The present invention relates to a wavelength insensitive passive polarization converter which can rotate the direction of optic axis of waveguide by employing poled electro-optic polymer waveguides and a method for controlling the optic axis direction of the poled polymer waveguides. A passive polarization converter of present invention is equipped with poling electrodes at top and bottom of a planar waveguide consisting of three layers of electro-optic polymer, and it comprises: a polarizer in which poling-induced optic axis aligned horizontally; a polarization rotator in which the azimuth angle of the optic axis is slowly changed along the propagation direction from horizontal to vertical direction; and, an analyzer in which poling-induced optic axis aligned vertically. The polarization converter of the invention which contains no periodic structures, is much less sensitive to wavelength, channel dimensions and polarizing structures in principle and may be more easily fabricated by the design of the poling electrode structure, as compared with prior art devices containing such structures.

Polarization independent demultiplexing in a polarization diversity nonlinear optical loop mirror

Abstract: We present a novel technique to achieve polarization insensitive all-optical demultiplexing using standard dispersion shifted fibers in a nonlinear optical loop mirror. A polarization dependence of /spl plusmn/0.2 dB is reported with no power penalty due to change in polarization.

Polarization reversal in crystals

Abstract: Characteristics of spontaneous polarization reversal have been studied in detail for the first time in crystals subjected to a pulsed electric field in the range 15 - 70 kV . The switching process has been observed by recording a transient switching current and subsequent piezoelectric probe mapping and optical and secondary electron microscopy methods. The measured value of spontaneous polarization is . The ionic potassium DC current was observed to have a strong effect on the polarization switching. The developed experimental set-up has made it possible to fabricate a periodic domain structure and to generate an optical second harmonic power.

Polarization quadrature measurement of subwavelength diffracting structures

Abstract: The amplitude and the phase of the diffracted far field depends on polarization when the diffracting structure is comparable to or less than the wavelength. When the far-field amplitude and the phase of one polarization with respect to the orthogonal polarization is measured, small changes in the structure can be measured. To make the far-field polarization measurements, we design a detector that measures the relative polarization amplitude and the phase in quadrature. We predict numerically and verify experimentally the polarization amplitude and the phase for an optical disc and a set of gratings with varying depth. Our results show that this measurement technique is sensitive to small variations in the diffracting structure and that it can be useful in applications such as critical dimension and overlay metrology in microelectronics fabrication.

An acousto-optical waveguide device with compensation of polarization mode dispersion

Abstract: An acousto-optical waveguide device with compensation of polarization mode dispersion (PMD) comprises at least one first and one second optical path in optical waveguide and at least one compensation optical path (35; 36; 37; 38; 51; 52; 53; 54) connected to the first and second optical path; the compensation optical path (35; 36; 37; 38; 51; 52; 53; 54) has a prefixed PMD such that the passage time of a first polarization component of an optical signal in the first optical path and in the compensation optical path (35; 36; 37; 38; 51; 52; 53; 54) is substantially equal to the passage time of a second polarization component in the second optical path and in the compensation optical path (35; 36; 37; 38; 51; 52; 53; 54).

Polarization directions of noncollinear phase-matched optical parametric downconversion output

Abstract: An analysis of the output polarization of a noncollinear type I optical parametric downconversion source is presented. Such a source can be made by pumping a nonlinear crystal with an extraordinary-polarized beam to produce pairs of ordinary-polarized photons. A polarization map of the output light illustrates dramatic variation in the polarization direction at large scattering angles. The effect of this variation in polarization direction is seen on a map of the nonlinear conversion efficiency. The apparent ambiguity in the polarization for the particular case in which one of the outputs propagates along the crystal optic axis is also discussed. © 1997 Optical Society of America [S0740-3224(97)02005-5]

Polarization properties of fiber lasers with twist-induced circular birefringence

Abstract: We have experimentally observed and theoretically analyzed the polarization properties of fiber lasers with twist-induced birefringence. Twisting a fiber induces the circular birefringence of a fiber laser cavity, and this birefringence reduces the effects of intrinsic linear birefringence on the polarization properties of fiber lasers. The frequencies of their polarization eigenmodes coincide with each other gradually as the twist rate increases, and the directions of polarization eigenmodes deviate from the birefringence axis at a much larger twist rate than the magnitude of intrinsic linear birefringence. We describe the successful experimental results for Nd and Er fiber lasers.

Polarization threshold switches based on ordered GaInP

Abstract: We report on optoelectronic switching devices with high photoconductive gain which are sensitive to the polarization direction of the optical input. Due to the large polarization anisotropy of the absorption coefficient of ordered GaInP, an electrical output can be switched “on” and “off” by rotating the linear polarization of the input light. Depending on the external adjustment of the working point, the structure can operate as a polarization threshold switch or a polarization detector, respectively. First results exhibit a switching contrast of 25 dB and a contrast of the detector signal of 7 dB between two perpendicularly polarized incident light beams, respectively.

Measurement of polarization mode dispersion in systems having polarization dependent loss or gain

Abstract: The principal states of polarization and their propagation characteristics are analyzed for both unitary and nonunitary optical systems in terms of the complex plane representation of polarization. A new method for the estimation of the polarization mode dispersion of the system is proposed together with experimental and simulation results.

Long cavity laser system including frequency doubling long cavity fiber optic laser system

Abstract: A polarization controlled laser system receiving a pump laser beam includes a long laser cavity for precluding mode hopping. Preferably, the long laser cavity is defined by first and second dichroic reflectors, a rare earth doped optical fiber disposed between the first and second dichroic reflectors for amplifying the pump laser beam to thereby produce an amplified laser beam, a polarization controller for controlling polarization of the amplified laser beam, and a polarization selector for selecting the polarization of the amplified laser beam. The polarization selector can include a polarizing optical fiber while the polarization controller advantageously may include a polarization maintaining optical fiber. Alternatively, the rare-earth doped optical fiber, the polarization controller, and the polarization selector are all formed from a single polarizing rare-earth doped optical fiber. The polarization controlled laser system may be converted to a frequency doubled polarization controlled laser system by adding a doubling crystal to the long laser cavity. Methods for generating polarization controlled laser beams using a long laser cavity formed from a rare-earth doped optical fiber are also described.

Polarization mode dispersion measuring instrument and method

Abstract: A polarization mode dispersion measuring apparatus includes a variable wavelength light source for providing light of a variety of wavelengths; a light intensity modulator optically connected to the light source to provide light of modulated intensity; a polarization controller optically connected to the light intensity modulator to provide light of controlled polarization; a beam splitter optically connected to the polarization controller to provide beams of p and s polarization components; an O/E conversion unit optically connected to the beam splitter to provide electrical signals with respect to the beams of the p and s polarization components; and an analyzing unit for controlling the light intensity modulator to provide a sine wave of a predetermined frequency and a predetermined intensity, and the light source and the polarization controller to determine parameters of Jones matrix from the electrical signals and a polarization mode dispersion defined by the parameters, thereby measuring a polarization mode dispersion of an object placed between the polarization controller and the beam splitter.