Polarization Hole Research Articles

Vector soliton rain

Soliton rain is a bunch of small soliton pulses accompanying the main pulse with the period of a round trip. It was found previously that soliton-soliton interaction through the overlapping of their tails or soliton-dispersive wave interaction can result in spikes with an anomalous amplitude satisfying the rogue waves (RW) criteria. Here, we report for the first time on the experimental observation of the polarization dynamics of soliton rain in an erbium–doped fiber laser mode-locked by single wall carbon nanotubes. Unlike the previous study, we have found that the soliton rain dynamics can be driven by polarization hole burning in the orientation distribution of inversion. Completion between holes, filled by the pump wave and rotation of the state of polarization of lasing pulse, is controlled by the pump power and in the cavity polarization controller, which results in repulsion or attraction of the soliton rain pulses and the main pulse. As a result, the different soliton rain patterns including RW can be observed.

Distortion of Magnetic Fields in a Starless Core. V. Near-infrared and Submillimeter Polarization in FeSt 1-457

The relationship between submillimeter (submm) dust emission polarization and near-infrared (NIR) $H$-band polarization produced by dust dichroic extinction was studied for the cold starless dense core FeSt 1-457. The distribution of polarization angles ($90^{\circ}$-rotated for submm) and degrees were found to be very different between at submm and NIR wavelengths. The mean polarization angles for FeSt 1-457 at submm and NIR wavelengths are $132.1^{\circ} \pm 22.0^{\circ}$ and $2.7^{\circ} \pm 16.2^{\circ}$, respectively. The correlation between $P_H$ and $A_V$ was found to be linear from outermost regions to relatively dense line of sight of $A_V \approx 25$ mag, indicating that NIR polarization reflects overall polarization (magnetic field) structure of the core at least in this density range. The flat $P_H/A_V$ versus $A_V$ correlations were confirmed, and the polarization efficiency was found to be comparable to the observational upper limit (Jones 1989). On the other hand, as reported by Alves et al., submm polarization degrees show clear linearly decreasing trend against $A_V$ from $A_V \approx 20$ mag to the densest center ($A_V \approx 41$ mag), appearing as "polarization hole" structure. The power law index for the $P_{\rm submm}$ versus $A_V$ relationship was obtained to be $\approx -1$, indicating that the alignment for the submm sensitive dust is lost. These very different polarization distributions at submm and NIR wavelengths suggest that (1) there is different radiation environment at these wavelengths or (2) submm-sensitive dust is localized or the combination of them.

Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic β−Ga2O3

We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ yielding a comprehensive analysis of generalized ellipsometry data obtained from 0.75--9 eV. The eigenpolarization model permits complete description of the dielectric response. We obtain, for single-electron and excitonic band-to-band transitions, anisotropic critical point model parameters including their polarization vectors within the monoclinic lattice. We compare our experimental analysis with results from density functional theory calculations performed using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional. We present and discuss the order of the fundamental direct band-to-band transitions and their polarization selection rules, the electron and hole effective mass parameters for the three lowest band-to-band transitions, and their excitonic contributions. We find that the effective masses for holes are highly anisotropic and correlate with the selection rules for the fundamental band-to-band transitions. The observed transitions are polarized close to the direction of the lowest hole effective mass for the valence band participating in the transition.

High Power Switchable Dual-Wavelength Linear Polarized Yb-Dozped Fiber Laser around 1120 nm

A single-and dual-wavelength switchable polarized Yb-doped double-clad fiber laser around 1120 nm based on a pair of fiber Bragg gratings (FBGs) is demonstrated. The polarization-maintaining (PM) linear cavity is composed of a double clad PM Yb-doped fiber (YDF) and a pair of PM FBGs. The laser can operate in stable dual-wavelength or wavelength-switching modes due to the polarization hole burning (PHB) and the spatial hole burning (SHB) enhanced by the PM linear cavity. In dual-wavelength operation, the two orthogonally polarized wavelengths are centered at 1118.912 nm and 1119.152 nm, with an interval of 0.24 nm and a signal to noise ratio (SNR) of 35 dB. The maximum output power is 14.67 W when the launched LD pump is 24 W corresponding to an optical efficiency of 61.1%. The lasing lines switchover may be realized by adjusting the polarization controller (PC) fitted in the cavity. The two single-wavelengths are 1118.912 nm and 1119.152 nm. When the injected LD pump is 24 W, the highest output powers are 7.68 W and 8.64 W corresponding to optical efficiencies of 32% and 36% respectively. The spectral linewidth of the lasing lines are 0.075 nm and 0.07 nm, and the average numerical values of PER aredB and 19.9 dB, respectively.

Switchable quadruple-wavelength Erbium-doped fiber laser based on a chirped fiber grating and polarization-maintaining fiber

A switchable quadruple-wavelength Erbium-doped fiber laser based on two Sagnac loops with a chirped fiber grating and polarization-maintaining fiber is proposed and demonstrated experimentally at room temperature. The two loops act as comb filters to excite multi-wavelength output. On the basis of the polarization hole burning effect, the laser can switch flexibly to output ten different modes from single-wavelength to quadruple-wavelength. All of the lasing lines with narrow linewidth have the optical signal-to-noise ratio of more than 35dB. The laser with good power uniformity shows better stability with respect to the wavelength and peak power.

Population gratings in saturable optical fibers with randomly oriented rare-earth ions

Formation of the dynamic population gratings in optical fibers with randomly oriented rare-earth ions is analyzed with a special interest to the grating component for readout with the orthogonal light polarization. It is shown that as compared with a simple model case of the collinearly oriented dipole-like centers their random orientation leads to approximately 2-times growth of the effective saturation power Psat when it is estimated from the incident power dependence of the fiber absorption or from that of the fluorescence intensity. An optimal incident power, for which the maximum of the dynamic population grating amplitude for collinear light polarization is observed, also follows this change in Psat, while formation of the grating for orthogonal polarization needs essentially higher light power. The reduced anisotropy of the active centers, which is in charge of the experimentally observed weakening of the polarization hole burning (PHB) and of the fluorescence polarization, compensates in some way the effect of random ion orientation. The ratio between the maximum conventional (i.e. for the interacting waves collinear polarizations) two-wave mixing (TWM) amplitude and the initial not saturable fiber optical density proves to be, however, nearly the same as in the model case of collinearly oriented dipoles. The ratio between the PHB effect and the amplitude of the anisotropic grating, which is responsible for TWM of the orthogonally polarized waves, is also not influenced significantly by the reduced anisotropy of ions.

Single- and dual-wavelength switchable linear polarized Yb(3+)-doped double-clad fiber laser.

A single- and dual-wavelength switchable linear polarized Yb-doped double-clad fiber laser is proposed, in which the resonance cavity was composed of a fiber Bragg grating fabricated in a polarization-maintaining fiber and a dichromatic mirror with high reflectivity. The polarization hole burning is enhanced through selective polarization feedback by the polarization-maintaining fiber Bragg grating. The switchover of single and dual wavelengths is realized by tuning the rotation angle of a cubic polarization beam splitter that is inserted between the dichromatic mirror and the collimator in the cavity. The laser features wavelengths of 1070.08 and 1070.39 nm, output power of 1.0 W, signal to noise ratio of 45 dB, and slope efficiency of 34%, as well as a very narrow linewidth of 0.022 nm. The polarization characteristics are analyzed by measuring the laser power transmitted through a Glan-Thomson polarizer during rotation.

On the radiation driven alignment of dust grains: Detection of the polarization hole in a starless core(Corrigendum)

1 Max-Planck-Institut fur extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany e-mail: falves@mpe.mpg.de 2 Instituto de Ciencia de Materiales de Madrid (CSIC), Sor Juana Ines de la Cruz 3, 28049 Madrid, Spain 3 Observatorio Astronomico Nacional, Alfonso XII 3, 28014 Madrid, Spain 4 Institut de Ciencies de l’Espai (CSIC-IEEC), Campus UAB, Facultat de Ciencies, C5 par 2a, 08193 Bellaterra, Catalunya, Spain 5 Departamento de Fisica – ICEx – UFMG, Caixa Postal 702, 30.123-970 Belo Horizonte, Brazil 6 Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA 7 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany

On the radiation driven alignment of dust grains: Detection of the polarization hole in a starless core

We aim to investigate the polarization properties of a starless core in a very early evolutionary stage. Linear polarization data reveal the properties of the dust grains in the distinct phases of the interstellar medium. Our goal is to investigate how the polarization degree and angle correlate with the cloud and core gas. We use optical, near infrared and submillimeter polarization observations toward the starless object Pipe-109 in the Pipe nebula. Our data cover a physical scale range of 0.08 to 0.4 pc, comprising the dense gas, envelope and the surrounding cloud. The cloud polarization is well traced by the optical data. The near infrared polarization is produced by a mixed population of grains from the core border and the cloud gas. The optical and near infrared polarization toward the cloud reach the maximum possible value and saturate with respect to the visual extinction. The core polarization is predominantly traced by the submillimeter data and have a steep decrease with respect to the visual extinction. Modeling of the submillimeter polarization indicates a magnetic field main direction projected onto the plane-of-sky and loss of grain alignment for densities higher than $6\times10^4$ cm$^{-3}$ (or $A_V > 30$ mag). Pipe-109 is immersed in a magnetized medium, with a very ordered magnetic field. The absence of internal source of radiation significantly affects the polarization efficiencies in the core, creating a polarization hole at the center of the starless core. This result supports the theory of dust grain alignment via radiative torques.

TADPOL: A 1.3 mm SURVEY OF DUST POLARIZATION IN STAR-FORMING CORES AND REGIONS

We present {\lambda}1.3 mm CARMA observations of dust polarization toward 30 star-forming cores and 8 star-forming regions from the TADPOL survey. We show maps of all sources, and compare the ~2.5" resolution TADPOL maps with ~20" resolution polarization maps from single-dish submillimeter telescopes. Here we do not attempt to interpret the detailed B-field morphology of each object. Rather, we use average B-field orientations to derive conclusions in a statistical sense from the ensemble of sources, bearing in mind that these average orientations can be quite uncertain. We discuss three main findings: (1) A subset of the sources have consistent magnetic field (B-field) orientations between large (~20") and small (~2.5") scales. Those same sources also tend to have higher fractional polarizations than the sources with inconsistent large-to-small-scale fields. We interpret this to mean that in at least some cases B-fields play a role in regulating the infall of material all the way down to the ~1000 AU scales of protostellar envelopes. (2) Outflows appear to be randomly aligned with B-fields; although, in sources with low polarization fractions there is a hint that outflows are preferentially perpendicular to small-scale B-fields, which suggests that in these sources the fields have been wrapped up by envelope rotation. (3) Finally, even at ~2.5" resolution we see the so-called "polarization hole" effect, where the fractional polarization drops significantly near the total intensity peak. All data are publicly available in the electronic edition of this article.

Polarization attractors in harmonic mode-locked fiber laser.

We report on a polarimetry of harmonic mode-locked erbium-doped fiber laser with carbon nanotubes saturable absorber. We find new types of vector solitons with locked, switching and precessing states of polarization. The underlying physics presents interplay between birefringence of a laser cavity created by polarization controller along with light induced anisotropy caused by polarization hole burning.

Short monolithic dual-wavelength single-longitudinal-mode DBR phosphate fiber laser.

We propose and demonstrate a 5-cm-long monolithic dual-wavelength single-longitudinal mode distributed Bragg reflector (DBR) all-phosphate fiber laser. Strong UV-induced fiber Bragg gratings are directly written in highly Er/Yb codoped phosphate fiber. The separation between gratings is selected as 1cm to only excite two longitudinal modes in the DBR cavity. By exploiting the spatial hole burning effect and the polarization hole burning effect, stable narrow-linewidth dual-wavelength lasing emission with 38pm wavelength spacing and a total emitted power of 2.8mW is obtained from this DBR fiber laser. A microwave signal at 4.58GHz is generated by the heterodyne detection of the dual-wavelength laser.

A 100 mW-level single-mode switchable dual-wavelength erbium-doped fiber laser

A switchable dual-wavelength CW erbium-doped fiber laser with two cascaded fiber Bragg gratings has been proposed and demonstrated experimentally at room temperature. The laser uses a linear resonant cavity configuration incorporating a Sagnac loop with a polarization controller (PC) and can switch flexibly to output a single wavelength or dual wavelengths based on the polarization hole burning (PHB) effect. The slope efficiency and maximum output power can reach 23% and 96 mW, respectively. The two lasing peaks of the laser, with a narrow linewidth output and an optical signal-to-noise ratio of more than 50 dB, are located in the C and L bands of the optical communication window, respectively. The laser shows good stability with respect to the wavelength and output power.

Polarization of the fluorescence excited in erbium-doped fibers in 1490–1570 nm spectral range

We present data on the polarization degree of the fluorescence, excited in erbium-doped fibers (EDF) by linearly polarized light at three essentially different wavelengths in the spectral range of the fundamental absorption of Er3+ (1492, 1526, and 1568nm). Experiments were performed in otherwise similar single-mode fibers with a broad range of erbium concentration (≈640–5600wtppm). The polarization degree of the fluorescence demonstrated expected decay with the incident light power and proved to be significantly weaker for the central excitation wavelength of 1526nm. The maximum value of the experimentally observed effect (≤0.3%) is significantly lower than it is predicted by model of the randomly oriented non-interacting dipoles. This discrepancy is explained by the reduced anisotropy (to the value 0.7–0.8) of the erbium ions absorption/emission, the effect which was utilized to explain the experimentally observed weak polarization hole burning in EDF earlier. Additional reduction in the fluorescence polarization degree and accelerated depolarization relaxation which were experimentally observed in fibers with high erbium concentration are attributed to the spatial migration of the excited state.

194 μm switchable dual-wavelength Tm3+ fiber laser employing high-birefringence fiber Bragg grating

A 1.94 μm switchable dual-wavelength Tm(3+) fiber laser employing two high-birefringence fiber Bragg gratings (HB-FBGs) is demonstrated. The polarization hole burning effect enhanced by the HB-FBG is first observed and adopted to guarantee stable dual-wavelength operation in the spectral region near 2 μm at room temperature. The wavelength spacing between the dual lasing wavelengths is 0.81 nm. The polarization states of the dual-output lasers are orthogonal. By adjusting a polarization controller, a single-wavelength mode operating at one of the dual wavelengths can be selected. The side-mode-suppression ratio of each laser can be greater than 60 dB. The power fluctuation measurement at both operating wavelengths shows that this Tm(3+) fiber laser has good stability.

A dual-reflected-structure switchable multi-wavelength erbium-doped fiber laser using the multi-mode fiber as the wavelength selector

A simple and effective dual-reflected-structure switchable multi-wavelength polarization-maintaining erbium-doped fiber laser is proposed and demonstrated. Using the structure of single-mode fiber (SMF)-multi-mode fiber (MMF)-SMF as the wavelength selective filter and reflector simultaneously the polarization-maintaining erbium-doped fiber as the gain medium and an optical circulator as the all-reflecting mirror, the laser realizes stable single-wavelength, dual-wavelength and triple-wavelength oscillations based on polarization hole burning of a multi-mode fiber by means of adjusting the polarization controller. The 3 dB bandwidth is about 0.01 nm. The side-mode suppression ratios (SMSRs) are over 50 dB. The power fluctuation and wavelength shifts are measured to be less than 1.5 dB and 0.01 nm over an hour at room temperature.

Photonic generation of microwave signal by beating a dual-wavelength single longitudinal mode erbium-doped fiber ring laser based on the polarization maintaining fiber bragg grating

A single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber (EDF) ring laser based on one polarization maintaining fiber Bragg grating (PMFBG) is demonstrated.Due to the polarization hole burning enhanced by the PMFBG, the laser can be designed to operate in stable dual-wavelength oscillation with a wavelength spacing of 0.182 nm at room temperature by adjusting a polarization controller. A section of unpumped EDF acting as a saturable absorber and a feedback fiber loop is used to ensure SLM operation in each of the two lasing lines. A microwave signal at 22.807 GHz is obtained by beating the dual-wavelength fiber laser at a photodetector. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:347–351, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27280

A Switchable Multi-wavelength Erbium-Doped Photonic Crystal Fiber Laser with Linear Cavity Configuration

A switchable multi-wavelength erbium-doped photonic crystal fiber laser with a linear cavity configuration based on a Sagnac loop mirror is proposed and demonstrated experimentally. The laser is based on saturated spectral hole burning and the polarization hole burning effects can be switched among single-wavelength, dual-wavelength, triple-wavelength and quadruple-wavelength outputs at room temperature. The wavelength period of the output spectrum is easily varied by using polarization maintaining fibers of different lengths. The proposed fiber laser has a signal-to-noise ratio of higher than 30 dB and achieves a low threshold power of 37mW. The power fluctuations of the lasing lines are less than 0.54 dB, 1.7 dB and 2.9 dB when the laser operates at single-wavelength, dual-wavelength and triple-wavelength for one hour.

A switchable multiwavelength fibre laser with polarization-maintaining erbium fibre

A multiwavelength fibre laser with wavelength-switchable operation has been demonstrated, utilizing the combined effects of polarization hole burning and intensity-dependent transmission. Polarization-maintaining erbium fibre (PM-EDF) with an anisotropic gain is used as the gain medium to suppress the mode competition. Simultaneously, the PM-EDF and the polarizer in the cavity form an equivalent periodic filter. Four lasing wavelengths simultaneously oscillating are obtained, which are stable over an hour at room temperatures. Furthermore, by adjusting the polarization controllers the laser can also produce triple-, dual- and single-wavelength lasing oscillations, which can be switched among the four simultaneously oscillating wavelengths.

A new mechanism to suppress the homogeneous gain broadening for stable multi-wavelength erbium-doped fiber laser

A suppressant effect of wavelength competition for multi-wavelength lasing oscillations is experimentally demonstrated in an ordinary erbium-doped fiber laser (EDFL). The polarization hole burning is exploited by a segment of erbium-doped fiber (EDF) coiled round the plates of the three-loop polarization controller. The mechanism to suppress the wavelength competition is discussed in detail. Results show that the mechanism is helpful to obtain stable multi-wavelength lasing oscillations at room temperature in the EDFL. By properly adjusting the comb filter, three-wavelength and tunable dual-wavelength lasing oscillations have been achieved. The power fluctuation is measured to be less than 0.75dB over 30min for all the multi-wavelength lasing oscillations obtained in the experiment. The 3dB bandwidth of each lasing oscillation is 0.01nm and the 30dB bandwidth is 0.10nm. The side mode suppression ratio (SMSR) of the three-wavelength lasing oscillation is more than 45dB and that of the dual-wavelength lasing oscillations is more than 50dB.