221 research outputs found

    OPTICAL QPSK SIGNAL QUALITY DEGRADATION DUE TO PHASE ERROR OF PUMP LIGHT

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    The influence of pump phase error on phase-sensitive optical amplifier (PSA) repeaters and the waveform degradation due to chromatic dispersion and fiber nonlinearities in the optical multi-relay transmission of quadrature phase-shift keying phase-conjugated twin waves are considered theoretically. First, the influence of noise from the pump phase error, optical local oscillator, receiver, and the amplified spontaneous-emission (ASE) in PSA repeaters is investigated with the assumption that transmission fibers are linear lossy channels. The bit-error rate (BER) is estimated as a function of the signal-to-noise ratio, and the relationship between the number of transmission relays and the fiber launch power is clarified. Waveform degradation due to chromatic dispersion and the optical fiber nonlinearities in transmission fibers are investigated with the noiseless condition, and the maximum repeatable number as a function of the fiber launch power is calculated. Finally, we show the relationship among the maximum repeatable number, standard deviation of pump phase error in PSA repeaters, and the fiber launch power to clarify the optimum transmission condition with consideration of the noise and the waveform degradation

    位相感応型光増幅のための励起光位相同期回路における和周波光発生型キャリア抽出の偏波依存性

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    This study aimed to build a numerical model of carrier extraction from dual-polarization phase-conjugated twin waves (DP-PCTWs) to investigate polarization dependence on the carrier extraction in a pump phase-locked loop for phase-sensitive optical amplifier repeaters. First, the numerical model was developed, and extracted carrier power of 40-Gbit/s DP-PCTWs with quadrature phase-shift keying format was calculated. Numerical results show the extracted carrier disappears when the PCTWs are circular polarization, and polarization dependence exists on the carrier extraction. Then, carrier extraction of a 10-Gbit/s DP-PCTW with binary phase-shift keying format was experimentally demonstrated. The extracted carrier power was found to be relatively low when the DP-PCTWs are circular polarization, and this trend agrees closely with the numerical results. These results show the reasonability of the numerical model and existence of polarization dependence on the carrier extraction from DP-PCTWs

    Large-scale Filamentary Structure around the Protocluster at Redshift z=3.1

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    We report the discovery of a large-scale coherent filamentary structure of Lyman alpha emitters in a redshift space at z=3.1. We carried out spectroscopic observations to map the three dimensional structure of the belt-like feature of the Lyman alpha emitters discovered by our previous narrow-band imaging observations centered on the protocluster at z=3.1. The feature was found to consist of at least three physical filaments connecting with each other. The result is in qualitative agreement with the prediction of the 'biased' galaxy-formation theories that galaxies preferentially formed in large-scale filamentary or sheet-like mass overdensities in the early Universe. We also found that the two known giant Lyman alpha emission-line nebulae showing high star-formation activities are located near the intersection of these filaments, which presumably evolves into a massive cluster of galaxies in the local Universe. This may suggest that massive galaxy formation occurs at the characteristic place in the surrounding large-scale structure at high redshift.Comment: 11 pages, 3 figures, accepted for publication in ApJ Letter

    The Halpha Luminosity Function of the Galaxy Cluster Abell 521 at z = 0.25

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    We present an optical multicolor-imaging study of the galaxy cluster Abell 521 at z=0.25z = 0.25, using Suprime-Cam on the Subaru Telescope, covering an area of 32×2032 \times 20 arcmin2^2 (9.4×5.8h5029.4 \times 5.8 h_{50}^{-2} Mpc2^2 at z=0.25z = 0.25). Our imaging data taken with both a narrow-band filter, NB816NB816 (λ0=8150\lambda_0 = 8150\AA and Δλ=120\Delta \lambda = 120\AA), and broad-band filters, B,V,RC,iB,V,R_{\rm C}, i^\prime, and zz^\prime allow us to find 165 Hα\alpha emitters. We obtain the Hα\alpha luminosity function (LF) for the cluster galaxies within 2 Mpc; the Schechter parameters are α=0.75±0.23\alpha = -0.75 \pm 0.23, ϕ=100.25±0.20\phi^\star = 10^{-0.25 \pm 0.20} Mpc3^{-3}, and L=1042.03±0.17L^\star = 10^{42.03 \pm 0.17} erg s1^{-1}. Although the faint end slope, α\alpha, is consistent with that of the local cluster Hα\alpha LFs, the characteristic luminosity, LL^\star, is about 6 times (or 2\approx 2 mag) brighter. This strong evolution implies that Abell 521 contains more active star-forming galaxies than the local clusters, being consistent with the observed Butcher-Oemler effect. However, the bright LL^\star of Abell 521 may be, at least in part, due to the dynamical condition of this cluster.Comment: 21 pages, 7 figures, ApJ, Part 1, in pres

    The HI content of star-forming galaxies at z = 0.24

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    We use observations from the Giant Metrewave Radio Telescope (GMRT) to measure the atomic hydrogen gas content of star-forming galaxies at z = 0.24 (i.e. a look-backtime of ~3 Gyr). The sample of galaxies studied were selected from Halpha-emitting field galaxies detected in a narrow-band imaging survey with the Subaru Telescope. The Anglo-Australian Telescope was used to obtain precise optical redshifts for these galaxies. We then coadded the HI 21 cm emission signal for all the galaxies within the GMRT spectral line data cube. From the coadded signal of 121 galaxies, we measure an average atomic hydrogen gas mass of (2.26 +- 0.90)*10^9 solar masses. We translate this HI signal into a cosmic density of neutral gas at z = 0.24 of Omega_gas = (0.91 +- 0.42)*10^-3. This is the current highest redshift at which Omega_gas has been constrained from 21 cm emission and our value is consistent with that estimated from damped Lyman-alpha systems around this redshift. We also find that the correlations between the Halpha luminosity and the radio continuum luminosity and between the star formation rate and the HI gas content in star-forming galaxies at z = 0.24 are consistent with the correlations found at z = 0. These two results suggest that the star formation mechanisms in field galaxies ~3 Gyr ago were not substantially different from the present, even though the star formation rate is 3 times higher.Comment: 11 pages, contains 9 figures and 1 table. Accepted for publishing in MNRAS 2007 January 22. Received 2007 January 22; in original form 2006 November 3

    SDSSp J104433.04-012502.2 at z=5.74z=5.74 is Gravitationally Magnified by an Intervening Galaxy

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    During the course of our optical deep survey program on Lα\alpha emitters at z5.7z \approx 5.7 in the sky area surrounding the quasar SDSSp J104433.04-012502.2 at z=5.74z=5.74, we found that a faint galaxy with mBm_B(AB) 25\approx 25 is located at \timeform{1".9} southwest of the quasar. Its broad-band color properties from BB to zz^\prime suggest that the galaxy is located at a redshift of z1.5z \sim 1.5 -- 2.5. This is consistent with no strong emission line in our optical spectroscopy. Since the counter image of the quasar cannot be seen in our deep optical images, the magnification factor seems not to be very high. Our modest estimate is that this quasar is gravitationally magnified by a factor of 2.Comment: 11 pages, 5 figures, PASJ, in pres

    The Discovery of a Very Narrow-Line Star Forming Obat a Redshift of 5.66ject

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    We report on the discovery of a very narrow-line star forming object beyond redshift of 5. Using the prime-focus camera, Suprime-Cam, on the 8.2 m Subaru telescope together with a narrow-passband filter centered at λc\lambda_{\rm c} = 8150 \AA with passband of Δλ\Delta\lambda = 120 \AA, we have obtained a very deep image of the field surrounding the quasar SDSSp J104433.04-012502.2 at a redshift of 5.74. Comparing this image with optical broad-band images, we have found an object with a very strong emission line. Our follow-up optical spectroscopy has revealed that this source is at a redshift of z=5.655±0.002z=5.655\pm0.002, forming stars at a rate 13 h0.72 M\sim 13 ~ h_{0.7}^{-2} ~ M_\odot yr1^{-1}. Remarkably, the velocity dispersion of Lyα\alpha-emitting gas is only 22 km s1^{-1}. Since a blue half of the Lyα\alpha emission could be absorbed by neutral hydrogen gas, perhaps in the system, a modest estimate of the velocity dispersion may be \gtrsim 44 km s1^{-1}. Together with a linear size of 7.7 h0.71h_{0.7}^{-1} kpc, we estimate a lower limit of the dynamical mass of this object to be 2×109M\sim 2 \times 10^9 M_\odot. It is thus suggested that LAE J1044-0123 is a star-forming dwarf galaxy (i.e., a subgalactic object or a building block) beyond redshift 5 although we cannot exclude a possibility that most Lyα\alpha emission is absorbed by the red damping wing of neutral intergalactic matter.Comment: 6 pages, 2 figures. ApJ Letters, in pres

    Complete set of polarization transfer observables for the 16O(p,n)16F{}^{16}{\rm O}(\vec{p},\vec{n}){}^{16}{\rm F} reaction at 296 MeV and 0 degrees

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    We report measurements of the cross section and a complete set of polarization transfer observables for the 16O(p,n)16F{}^{16}{\rm O}(\vec{p},\vec{n}){}^{16}{\rm F} reaction at a bombarding energy of TpT_p = 296 MeV and a reaction angle of θlab\theta_{\rm lab} = 00^{\circ}. The data are compared with distorted-wave impulse approximation calculations employing the large configuration-space shell-model (SM) wave functions. The well-known Gamow-Teller and spin-dipole (SD) states at excitation energies of ExE_x \lesssim 8 MeV have been reasonably reproduced by the calculations except for the spin--parity JπJ^{\pi} = 22^- state at ExE_x = 5.86 MeV. The SD resonance at ExE_x \simeq 9.5 MeV appears to have more JπJ^{\pi} = 22^- strength than JπJ^{\pi} = 11^- strength, consistent with the calculations. The data show significant strength in the spin-longitudinal polarized cross section IDL(0)ID_L(0^{\circ}) at ExE_x \simeq 15 MeV, which indicates existence of the JπJ^{\pi} = 00^- SD resonance as predicted in the SM calculations.Comment: 6 figures, submitted to Physical Review

    Terahertz wireless communication at 560-GHz band using Kerr micro-resonator soliton comb

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    Terahertz (THz) waves have attracted attention as carrier waves for next-generation wireless communications (6G). Electronic THz emitters are widely used in current mobile communications; however, they may face technical limitations in 6G with upper-frequency limits. We demonstrate wireless communication in a 560-GHz band by using a photonic THz emitter based on photomixing of a 560-GHz-spacing soliton microcomb in a uni-travelling carrier photodiode together with a THz receiver of Schottky barrier diode. The on-off keying data transfer with 2-Gbit/s achieves a Q-factor of 3.4, thus, satisfying the limit of forward error correction.Comment: 17 pages, 4 figur
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