Browsing by Author "Chen, J"

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210-km Bidirectional transmission system with a novel four-port interleaver to facilitate unidirectional amplification
(2006-01-01)
Huang, MF
;
Chen, J
;
Feng, KM
;
Wei, CC
;
Lai, CY
A novel bidirectional transmission system is proposed and experimentally demonstrated using a four-port interleaver to enable unidirectional amplification. Following bidirectional transmission through 210 km of standard single-mode fibers, sensitivity variations of less than 0.2 dB, with a bit-error rate level of 10(-9) at 10 Gb/s, were observed between bidirectional and unidirectional transmissions.
A diode-pumped high power Q-switched and self-mode-locked Nd : YVO4 laser with a LiF : F-2(-) saturable absorber
(2001-08-01)
Chen, YF
;
Tsai, SW
;
Wang, SC
;
Chen, J
;
電子物理學系
Simultaneous mode-locking and Q-switching has been accomplished in a diode-pumped Nd:YVO4/LiF:F-2(-) laser. At an absorbed pump power of 23.6 W, the average output power was 6.0W and the repetition rate of the Q-switched pulse was 260 kHz. A depth of mode-locking of 100% was obtained and there was no satellite pulse between mode-locked pulse trains. The mode-locked pulse inside the Q-switched pulse had a repetition rate of approximately 148 MHz and its average duration was estimated to be around 75 ps.
A sliding mode current control scheme for PWM brushless DC motor drives
(1999-05-01)
Chen, J
;
Tang, PC
;
交大名義發表
;
National Chiao Tung University
This paper proposes a sliding mode current control scheme for pulsewidth modulation (PWM) brushless de motor drives. An improved "equivalent control" method is used in this scheme. A simple algorithm is proposed that differs from the original equivalent control method, which requires extensive calculation to estimate the load parameters. This algorithm can be implemented using logic circuits. Moreover, using autotuning, the proposed algorithm can be applied without load information. An operating principle for the power stage switching devices called single-side firing is also proposed. Single-side firing solves the dead-time problem, allowing the PWM frequency to be increased and the sampling rate to be raised. This paper explains the current control algorithm, single-side firing principle, and implementation of the proposed scheme in detail. Simulations and experimental results are given to show the validity of this scheme.
Anomalous spin polarization and dualistic electronic nature of CrO(2)
(2003-06-01)
Huang, DJ
;
Tjeng, LH
;
Chen, J
;
Chang, CF
;
Wu, WP
Spin-resolved O 1s x-ray absorption measurements on CrO(2) reveal that the spin polarization of the states at the Fermi level approaches 100%, providing direct evidence of the half-metallic nature of CrO(2). The measurements also show the existence of an atomiclike Cr 3d state not far away from the Fermi level with a spin polarization of only 50%, establishing its Mott-Hubbard character. We conclude that CrO(2) has a dualistic electronic nature, in which the states at the Fermi level are bandlike, while those at higher energies are strongly localized of completely different origin and symmetry. The finding of an exceptionally large number of O 2p holes suggests their important role in preventing the strongly correlated CrO(2) from being an insulator.
Anomalous spin polarization and dualistic electronic nature of CrO2
(2003-06-01)
Huang, DJ
;
Tjeng, LH
;
Chen, J
;
Chang, CF
;
Wu, WP
Spin-resolved O 1s x-ray absorption measurements on CrO2 reveal that the spin polarization of the states at the Fermi level approaches 100%, providing direct evidence of the half-metallic nature of CrO2. The measurements also show the existence of an atomiclike Cr 3d state not far away from the Fermi level with a spin polarization of only 50%, establishing its Mott-Hubbard character. We conclude that CrO2 has a dualistic electronic nature, in which the states at the Fermi level are bandlike, while those at higher energies are strongly localized of completely different origin and symmetry. The finding of an exceptionally large number of O 2p holes suggests their important role in preventing the strongly correlated CrO2 from being an insulator.
Characteristics of MOCVD- and MBE-grown InGa(N)As VCSELs
(2005-08-01)
Yang, HPD
;
Lu, C
;
Hsiao, R
;
Chiou, C
;
Lee, C
We report our results on InGaNAs/GaAs vertical-cavity surface-emitting lasers (VCSELs) in the 1.3 mu m range. The epitaxial structures were grown on (10 0) GaAs substrates by metalorganic chemical vapour deposition (MOCVD) or molecular beam epitaxy (MBE). The nitrogen composition of the InGa(N)As/GaAs quantum-well (QW) active region is 0-0.02. The long-wavelength (up to 1.3 mu m) room-temperature continuous-wave (RT CW) lasing operation was achieved for MBE- and MOCVD-grown VCSELs. For MOCVD-grown devices with n- and p-doped distributed Bragg reflectors (DBRs), a maximum optical output power of 0.74 mW was measured for In(0.36)Ga(0.64)N(0.006)AS(0.994)/GaAs VCSELs. A very low J(th) of 2.55 kA cm(-2) was obtained for the InGaNAs/GaAs VCSELs. The MBE-grown devices were made with an intracavity structure. Top-emitting multi-mode 1.3 mu m In0.35Ga0.65N0.02As0.98/GaAs VCSELs with 1 mW output power have been achieved under RT CW operation. A J(th) of 1.52 kA cm-2 has been obtained for the MBE-grown In0.35Ga0.65N0.02As0.98/GaAs VCSELs, which is the lowest threshold current density reported. The emission characteristics of the InGaNAs/GaAs VCSELs were measured and analysed.
Cross-reference maximum likelihood reconstruction for positron emission tomography with empiric studies
(2001-08-01)
Chen, J
;
Tu, K
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Chen, T
;
Lu, H
;
Liu, R
Encoding ASK labeled CSRZ-DPSK payload by using only one dual-drive Mach-Zehnder modulator with enhanced label performance
(2005-10-01)
Peng, WR
;
Lu, YC
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Chen, J
;
Chi, S
;
光電工程學系
This theoretical study presents a novel modulation scheme which simultaneously encodes the amplitude shift keying label on the carrier-suppressed return-to-zero differential phase shift keying payload using only one dual-drive Mach-Zehnder modulator. Compared with the previous scheme, in which three optical modulators are required, we offer a simple, compact, and cost-effective method. We theoretically evaluate and simulate the performance differences between the two schemes. It is found that the sensitivity of the label is 2 dB better than the previous scheme and the payload, with optimized extinction ratio in the electroabsorption eraser, has almost the same performance after 120-km standard single-mode fiber transmission.
Enhancing the frequency response of cross-polarization wavelength conversion
(2005-08-01)
Wei, CC
;
Huang, MF
;
Chen, J
;
光電工程學系
;
Department of Photonics
This work presents a novel wavelength conversion scheme, differential cross-polarization modulation (DXPoM), using an extra birefringence delay to enhance the performance of the conventional cross-polarization modulation. Simulation and experimental results confirm that the predicted performance is enhanced. Using the proposed scheme improves rise time by over 300 %, reduces timing jitter by 50 %, and increases extinction ratio by 9 %.
Improved SPM tolerance and cost-effective phase-modulation duobinary transmission over 230-km standard single-mode fiber using a single Mach-Zehnder modulator
(2005-12-01)
Lu, YC
;
Chen, J
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Feng, KM
;
Yeh, PC
;
Huang, TY
This letter proposes and experimentally demonstrates a cost-effective phase-modulation duobinary modulation scheme for improving self-phase modulation tolerance using a single modulator. Successful transmission over 230 km of standard single-mode fiber was achieved.
Interleaver technology: Comparisons and applications requirements
(2004-01-01)
Cao, S
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Chen, J
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Damask, JN
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Doerr, CR
;
Guiziou, L
An overview of interleaver technologies is presented, based on the workshop held at the Optical Fiber Communications Conference, March 23, 2003. The requirements for and several realizations of interleaver filters are detailed.
Magnetic circular dichroism in Fe 2p resonant photoemission of magnetite
(2004-02-01)
Chen, J
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Huang, DJ
;
Tanaka, A
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Chang, CF
;
Chung, SC
Measurements of magnetic circular dichroism in Fe 2p resonant photoemission and calculations based on a full-multiplet cluster model reveal the parameters of the electronic structure of Fe3O4. We obtained on-site Coulomb energy U-dd of 3d electrons, charge-transfer energy Delta which is defined as the energy required to transfer an electron from O 2p to Fe 3d, and the hybridization strength between Fe 3d and O 2p at different Fe ion sites of Fe3O4 by analyzing the data of magnetic circular dichroism. The charge-transfer energy of Fe3+ ions was found to be significantly smaller than that of Fe2+ ions. We determined the energy positions of the low-lying multiplets of each Fe ion site. These energy positions for Fe3+ ion sites are 1.5-2.5 eV higher than those obtained from band-structure calculations. Our calculations also show that the photoemission spectral weight in binding energy bigger than 10 eV is substantial, in contrast to the results of band-structure calculations. Our findings conclude that Fe3O4 is a system with strong electron-electron interactions.
Metro add-drop network applications of cascaded dispersion-compensated interleaver pairs using a recirculating loop
(2005-06-01)
Feng, KM
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Huang, MF
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Wei, CC
;
Lai, CY
;
Lin, TY
A 50-GHz channel spaced dispersion-compensated interleaver pair for a metro add-drop network application was demonstrated using a recirculating loop. After five cascaded nodes (ten interleavers), a 2.5-dB sensitivity differential at bit-error-rate level around 10(-9) was observed between the compensated and uncompensated pairs within a +/- 10-GHz detuning frequency window.
OCDMA light source using directly modulated Fabry-Perot laser diode in an external injection scheme
(2006-05-01)
Peng, PC
;
Peng, WR
;
Feng, KM
;
Chiou, HY
;
Chen, J
This investigation proposes and experimentally demonstrates an optical code-division multiple-access (OCDMA) light source using a directly modulated Fabry-Perot laser diode in an external injection scheme. This light source has an optical sidemode suppression ratio of over 27.5 dB and a pulsewidth of around 55 ps. Such a narrow pulsewidth has great potential for a two-dimensional OCDMA system. Additionally, the bit-error-rate performance with a 2(31) - 1 pseudorandom bit sequence indicates the feasibility of this light source in a 2.488-Gb/s system application.
Orbital magnetic moments of oxygen and chromium in CrO2
(2002-11-01)
Huang, DJ
;
Jeng, HT
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Chang, CF
;
Guo, GY
;
Chen, J
With measurements of the magnetic circular dichroism and band-structure calculations in the local spin density approximation (LSDA+U) approach, we revealed that the orbital moment of O in CrO2 is ferromagnetically coupled to that of Cr, whereas the spin moment of O is antiferromagnetically coupled to that of Cr. Spin and orbital magnetic moments of Cr and O are enhanced as Coulomb interaction energy U increases. Comparing the magnetic circular diachromism data with the LSDA+U calculations, we conclude that it is essential to include the on-site Coulomb energy for adequately describing the orbital magnetic moments of CrO2.
Orbital moments of CrO2 and Fe3O4 studied by MCD in soft X-ray absorption
(2004-07-01)
Huang, DJ
;
Chang, CF
;
Chen, J
;
Lin, HJ
;
Chung, SC
We present studies of orbital magnetic moments of CrO2 and Fe3O4 by measuring magnetic circular dichroism (MCD) in soft X-ray absorption. The results show that Fe3O4 exhibits large orbital moments, as a consequence of the strong Coulomb interactions of Fe 3d electrons. In contrast, orbital moments of Cr in CrO2 are nearly quenched, revealing that Cr 3d electrons are strongly hybridized with O 2p electrons and more delocalized as compared with those of Fe in Fe3O4. Comparing the MCD data with the band structure calculations based on local spin density approximation with on-site Coulomb energy U taken into account, we conclude that to include the on-site Coulomb interactions of 3d electrons is essential for adequately describing the electronic structure of CrO2 and Fe3O4. (C) 2004 Elsevier B.V. All rights reserved.
Performance comparisons between direct NRZ and gain-switched RZ modulation on Fabry-Perot lasers
(2005)
Peng, WR
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Peng, PC
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Chen, J
;
Tsai, SY
;
Chi, S
We firstly study the performance comparisons between direct non-return to zero and gain-switched return to zero data formats on a Fabry-Perot laser. With high speed electrical AND gate, we also investigate the relation between the pulse width of electrical drive signal and the quality of optical eye diagrams. It is found that shorter pulse width of electrical signal can completely eliminate the pattern effect and the sensitivity of RZ format is 3.8-dB better than NRZ format at data rate = 2.488-Gbps.
Performance of a Mott detector for undulator-based spin-resolved spectroscopy
(2002-11-01)
Huang, DJ
;
Wu, WP
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Chen, J
;
Chang, CF
;
Chung, SC
To measure spin-polarized core-level electron spectra, a spectrometer equipped with a highly efficient retarding-potential Mott spin polarimeter using undulator-based soft-x-ray beamlines has been set up. With a thin film of Au as a target this polarimeter has an efficiency estimated to be similar to2x10(-4). The performance of this system for spin-polarized spectroscopy has been tested using core-level spin-polarized photoemission of magnetic and nonmagnetic thin films excited with linearly and circularly polarized light, respectively. Measurements using a new spin-resolved absorption technique are also discussed. (C) 2002 American Institute of Physics.
Simultaneous mode locking in a diode-pumped passively Q-switched Nd : YVO4 laser with a GaAs saturable absorber
(2001-11-20)
Chen, YF
;
Huang, KF
;
Tsai, SW
;
Lan, YP
;
Wang, SC
Simultaneous mode locking and Q switching is accomplished in a diode-pumped Nd:YVO4/GaAs laser. The average output power is similar to2.0 W at 10.6-W absorbed pump power, and the repetition rate of the Q-switched pulse is similar to 120 kHz. The mode-lo eked pulse inside the Q-switched pulse has a repetition rate of similar to 148 MHz, and its average duration is estimated to be similar to 100 ps. (C) 2001 Optical Society of America.
Study of differential cross-polarization modulation in a semiconductor optical amplifier
(2005-10-17)
Wei, CC
;
Chen, J
;
光電工程學系
;
Department of Photonics
Differential cross-polarization modulation (DXPoM) wavelength conversion using a semiconductor optical amplifier has been proposed to outperform substantially traditional cross-polarization modulation (XPoM). This work presents analytical small-signal models of XPoM and DXPoM. The transfer function of DXPoM is used to elucidate the significant improvement in bandwidth and the relationships among the modulation bandwidth, the delay, the operating points and other device parameters of a semiconductor optical amplifier (SOA). (c) 2005 Optical Society of America.