Browsing by Author "Lai, Y"

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A novel phase-noise-suppressed and delay-time-tunable mode-locked erbium-doped fiber laser
(2002-10-15)
Lin, GR
;
Lai, Y
;
光電工程學系
;
Department of Photonics
A phase-noise-suppressed and delay-time-tunable actively mode-locked erbium-doped fiber ring laser is demonstrated by using voltage-controlled and frequency-discriminated phase shifter as an inherent timing module. By changing the voltage from -3.35 to 3.6 V, the maximum tuning range of phase and delay-time of 500 MHz optical pulse-train from the laser can be up to 340degrees (similar to1.9pi) and 1.9 ns (nearly 1 period), respectively. Optimized responsivity and tuning deviation are 0.27 ps/mV and less than or equal to 4%. The single-sided-band phase the laser operated at feedback controlled mode is significantly reduced to -100 dBc/Hz (measured at frequency of 10 kHz offset from center), which is at least 10 dB smaller than that of the laser operated at free-running mode. (C) 2002 Published by Elsevier Science B.V.
Amplitude-squeezed fiber-Bragg-grating solitons
(2004-02-01)
Lee, RK
;
Lai, Y
;
光電工程研究所
;
Institute of EO Enginerring
Quantum fluctuations of optical fiber-Bragg-grating solitons are investigated numerically by the back-propagation method. It is found that the band-gap effects of the grating act as a nonlinear filter and cause the soliton to be amplitude squeezed. The squeezing ratio saturates after a certain grating length and the optimal squeezing ratio occurs when the pulse energy is slightly above the fundamental soliton energy.
Crucial effects of the anisotropy on optical field induced pattern formation in nematic liquid crystal films
(2004-04-05)
Hsu, HK
;
Chen, SH
;
Lai, Y
;
光電工程學系
;
Department of Photonics
We present here the crucial effects of material anisotropy on optical field induced pattern formation in the one-feedback-mirror arrangement which utilizes the nematic liquid crystal film as the nonlinear medium. By using the quasi-static electric-field-biased planar-aligned homogeneous nematic liquid crystal (NLC) films, we observe both the hexagon and the roll patterns which can be switched optically due to the intrinsic anisotropic distribution of the threshold intensity. The anisotropy comes from the anisotropic nonlinear response of the NLC film and is the crucial factor for such a one-feedback-mirror system to form both the roll and hexagon patterns. The observed phenomena can be explained from the linear stability analysis of the governing diffusion-like equation. The experimental results indicate that the stable roll patterns are formed at low input light power and the stable hexagon patterns formed at high input power. (C) 2004 Optical Society of America.
Direct generation of 10GHz 816fs pulse train from an asynchronous modelocked Er-fiber laser
(2005)
Lin, CY
;
Hsiang, WW
;
Tien, MF
;
Lai, Y
;
光電工程學系
By employing the technique of asynchronous modelocking (ASM), we have Successfully demonstrated the direct generation of stable 10GHz 816fs Pulse trains with Super-Mode-Suppression-Ratio > 70dB from a hybrid modelocked Er-fiber laser. (c) 2005 Optical Society of America.
Evolutionary programming synthesis of optimal long-period fiber grating filters for EDFA gain flattening
(2002-11-01)
Lee, CL
;
Lai, Y
;
光電工程學系
;
Department of Photonics
An innovative long-period fiber grating (LPG) synthesis method based on the stochastic evolutionary programming (EP) algorithms is demonstrated to be effective for designing optimal LPG filters. Synthesis of a single-stage LPG filter for the entire C-band erbium-doped fiber amplifier (EDFA) gain flattening is used as an example to show the feasibility and the effectiveness of the proposed algorithm. To the best of our knowledge, this is the first demonstration that good EDFA gain flattening for the entire band can be achieved with a single-stage LPG filter that is properly designed.
Far-field emission narrowing effect of microdisk lasers
(1998-05-04)
Lee, TD
;
Cheng, PH
;
Pan, JS
;
Tsai, RS
;
Lai, Y
Far-field intensity distribution of semiconductor microdisk lasers is experimentally measured and the emission angle is found to be much smaller than that of a planar source with the same near-held width. In fact the emission angle is determined mainly by the disk radius instead of the disk thickness. A scalar diffraction theory in the cylindrical coordinate is developed to explain such an emission-angle-narrowing phenomenon and numerical calculation based on a vectorial diffraction theory is carried out to explain the measured polarization state. (C) 1998 American Institute of Physics.
Generation of photon-number-entangled soliton pairs through interactions
(2005-01-01)
Lee, RK
;
Lai, Y
;
Malomed, BA
;
光電工程學系
;
光電工程研究所
Two simple schemes for generating macroscopic (many-photon) continuous-variable entangled states by means of continuous interactions (rather than collisions) between solitons in optical fibers are proposed. First, quantum fluctuations around two time-separated single-component temporal solitons are considered. Almost perfect correlation between the photon-number fluctuations can be achieved after passing a certain distance, with a suitable initial separation between the solitons. The photon-number correlation can also be achieved in a pair of vectorial solitons with two polarization components. In the latter case, the photon-number-entangled pulses can be easily separated by a polarization beam splitter. These results offer possibilities to produce entangled sources for quantum communication and computation.
Improving the spectral sharpness of an apodized fibre grating
(2000-09-01)
Yang, C
;
Lai, Y
;
光電工程學系
;
Department of Photonics
We fabricate a steep skirt fibre Bragg grating (FBG) by employing an apodized phase mask. Gaussian UV beams with different FWHM are used on the mask to derive better spectral responses. The ratio of the FBG reflection bandwidth at -0.5 to -20 dB is improved from 0.35-0.55.
Learning evolution design of multiband-transmission fiber Bragg grating filters
(2003-10-01)
Shu, SF
;
Lai, Y
;
Pan, CL
;
光電工程學系
;
Department of Photonics
A composite fiber Bragg grating (FBG) structure with several apodized sections is utilized for designing dense wavelength division multiplexing (DWDM) multiband transmission filters. A learning genetic algorithm (LGA) is also developed to determine the optimum design parameters of these filters. By taking advantage of a knowledge base (KB) that stores the FBG parameter sets and the corresponding transmission profile feature sets, our LGA can generate a suitable initial population and perform evolutionary optimization starting from it. This has made the LGA evolve more quickly to more accurate results than the methods without using the KB. The LGA can also store new results into the KB according to its decision procedure and improve its precision of initial prediction as it works through more and more examples. (C) 2003 Society of Photo-Optical Instrumentation Engineers.
Mode emission characteristics of semiconductor microdisc and microring lasers
(1996-10-01)
Lee, TD
;
Cheng, PH
;
Pan, JS
;
Tai, K
;
Lai, Y
We fabricate both microdisc and microring InGaAsP-InGaAs quantum well semiconductor lasers using an etching-and-bonding technique. Their emission properties are studied by optical pumping at 77 K. Single mode lasing is achieved for discs with a diameter of 5 mu m. Multimode emission is observed for rings with larger diameters. Both fundamental and higher order lasing modes are observed and are found to exhibit interesting emission characteristics.
Mode emission properties of semiconductor micro-disk and micro-ring lasers
(1999)
Lee, TD
;
Cheng, PH
;
Pan, JS
;
Tai, K
;
Lai, Y
We have successfully fabricated optically pumped semiconductor micro-disk and micro-ring lasers under the InGaAsP/InGaAs system at the 1.5 mu m wavelength and under the InGaP/InGaAlP system at the 0.66 mu m wavelength. The spontaneous emission factor beta of these micro-lasers is estimated directly from their output-pump curves and its dependence on the cavity volume is verified. Interesting phenomena regarding the far-field emission pattern and lasing linewidth of these micro-cavity lasers are experimentally observed and theoretically studied.
Optical birefringence and polarization dependent loss of square- and rectangular-lattice holey fibers with elliptical air holes: numerical analysis
(2005-01-10)
Liu, YC
;
Lai, Y
;
光電工程學系
;
Department of Photonics
Polarization dependent leakage loss as well as optical birefringence for the fundamental mode in square- and rectangular-lattice holey fibers with elliptical air holes are studied numerically based on the full-vector finite element method for the first time. It is shown that high birefringence in the order of 10(-2) and large polarization dependent loss required for single-polarization single-mode transmission are both achievable by using the proposed structure. (C) 2005 Optical Society of America.
Optimal narrowband dispersionless fiber Bragg grating filters with short grating length and smooth dispersion profile
(2004-05-01)
Lee, CL
;
Lai, Y
;
光電工程學系
;
Department of Photonics
An effective optimization approach to the inverse design problems of complex fiber Bragg grating filters is developed in the present paper. Based on a multi-objective evolutionary programming (MOEP) algorithm, the proposed method can efficiently search for optimal solutions and simultaneously take into account various requirements of the designed filter. To improve the efficiency of the MOEP based algorithm, an adaptive mutation process is proposed and verified. One of the advantages of the proposed optimization method is the capability to impose additional constrains on the desired coupling coefficient, which ensures the convenience and possibility for actually fabricating the designed devices with the commercially available photosensitive fibers. To verify the effectiveness of the proposed method, an optimal narrowband dispersionless fiber Bragg grating filter for DWDM optical fiber communication systems is designed. We successfully demonstrate that complicated dispersionless FBG filters with short grating lengths and smooth dispersion profiles can be obtained by using the proposed algorithm. (C) 2004 Elsevier B.V. All rights reserved.
Quantum correlations in bound-soliton pairs and trains in fiber lasers
(2004-12-01)
Lee, RK
;
Lai, Y
;
Malomed, BA
;
光電工程學系
;
光電工程研究所
Quantum correlations in pairs and arrays (trains) of bound solitons modeled by the complex Ginzburg-Landau equation (CGLE) are calculated numerically, on the basis of linearized equations for quantum fluctuations. We find strong correlations between the bound solitons, even though the system is dissipative. Some degree of the correlation between the photon-number fluctuations of stable bound soliton pairs and trains is attained and saturates after passing a certain distance. The saturation of the photon-number correlations is explained by the action of nonconservative terms in the CGLE. Photon-number-correlated bound soliton trains offer possibilities to produce multipartite entangled sources for quantum communication and computation.
Quantum-noise properties of matter-wave gap solitons
(2005-09-01)
Lee, RK
;
Ostrovskaya, EA
;
Kivshar, YS
;
Lai, Y
;
光電工程學系
We study quantum-noise squeezing and quantum correlations of gap solitons in a Bose-Einstein condensate loaded into a one-dimensional optical lattice. By employing a linearized quantum theory we find that quantum-noise squeezing of gap solitons, produced during their evolution, is enhanced compared with the atomic solitons in a lattice-free case due to intrasoliton structure of quantum correlations induced by the Bragg scattering in the periodic potential. We also show that nonlinear interaction of gap solitons in dynamically stable bound states can produce strong atom-number correlation between the soliton pairs.
Quasistatic electric-field-modulated optical pattern transition in a thin nematic liquid-crystal film with a single feedback mirror
(2004-10-04)
Hsu, HK
;
Lai, Y
;
Chen, SH
;
光電工程學系
;
Department of Photonics
We present here the pattern formation in the transverse profile of a continuous-wave laser beam passing through a parallel planar-aligned nematic liquid crystal (NLC) film biased by a quasistatic electric field and then reflected back to the sample cell by a single planar mirror. The effect of the biasing voltage is studied through the ability to change the nonlinearity by modulating the orientation of the NLC molecules electrically. By suitably modulating the quasistatic electric field the optical pattern transition from the hexagon to the roll is achieved. The pattern transition can be explained by the linear stability analysis for the nonlinear liquid crystal film with optical feedback. (C) 2004 American Institute of Physics.
Resonance fluorescence spectrum near photonic bandgap
(2003)
Lee, RK
;
Lai, Y
;
光電工程學系
;
Department of Photonics
We theoretically calculate the resonance fluorescence spectrum from a two-level atom which is embedded in a photonic bandgap crystal and is resonantly driven by a classical pump light. Non-Markovian noises caused by the non-uniform distribution of photon density states near the photonic bandgap, are taken into account by a new approach which linearizes the optical Bloch equations by using the Liouville operator expansion. These linearized equations can be solved directly in the Fourier domain to obtain the correlation functions of the atomic operators and then the fluorescence spectrum from the atom. We find that if the atomic energy level is far from the bandgap, fluorescence spectra with Mollow triplets are observed. When the atomic energy level is near the bandgrap, the relative magnitude and the number of the fluorescence peaks are found to be varied accordinu to the wavelength offset.
Spontaneous emission factor versus cavity volume in low dimensional photonic micro-cavities
(1997-10-15)
Cheng, PH
;
Lee, TD
;
Pan, JS
;
Lai, Y
;
Tai, K
Micro-ring and micro-disk lasers an formed at the same time by transferring the epitaxial layers of 1.55 mu m wavelength InGaAs/ZnGaAsP quantum wells on a glass substrate. The spontaneous emission factor beta in such micro-rings of 5 mu m diameter and 0.2 x 0.5 mu m(2) cross-section is 0.16, which is four times that in micro-disk lasers of the same diameter. The result confirms for the first time that the micro-ring being a lower dimensional photonic system has a larger beta. Study of beta versus the cavity size indicates that the observed spontaneous emission factor is approximately the reciprocal of the normalized cavity volume, when normalization is done to the cubic of the wavelength in the medium. (C) 1997 Elsevier Science B.V.
Spontaneous emission factor versus cavity volume in low dimensional photonic micro-cavities
(1997-10-15)
Cheng, PH
;
Lee, TD
;
Pan, JS
;
Lai, Y
;
Tai, K
Micro-ring and micro-disk lasers an formed at the same time by transferring the epitaxial layers of 1.55 mu m wavelength InGaAs/ZnGaAsP quantum wells on a glass substrate. The spontaneous emission factor beta in such micro-rings of 5 mu m diameter and 0.2 x 0.5 mu m(2) cross-section is 0.16, which is four times that in micro-disk lasers of the same diameter. The result confirms for the first time that the micro-ring being a lower dimensional photonic system has a larger beta. Study of beta versus the cavity size indicates that the observed spontaneous emission factor is approximately the reciprocal of the normalized cavity volume, when normalization is done to the cubic of the wavelength in the medium. (C) 1997 Elsevier Science B.V.