Journals >Chinese Journal of Lasers
Contents
2004
Volume: 31 Issue 10
27 Article(s)
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Research Article
Experimental Investigations of External Cavity Using Photorefractive Phase Conjugator for CW Ti∶Sapphire Laser
[in Chinese], [in Chinese], and [in Chinese]
With self-pumped phase conjugator (SPPC) of Ce∶BaTiO3, the performance of CW Ti∶sapphire laser has been improved. The output threshold decreases from 4.7 W (without phase conjugator cavity) to 3.6 W (with phase conjugator cavity) and the slope efficiency increases from 26% to 30%. Theoretic analyses with external-cavitWith self-pumped phase conjugator (SPPC) of Ce∶BaTiO3, the performance of CW Ti∶sapphire laser has been improved. The output threshold decreases from 4.7 W (without phase conjugator cavity) to 3.6 W (with phase conjugator cavity) and the slope efficiency increases from 26% to 30%. Theoretic analyses with external-cavity laser theory are in accordance with the above experimental results. In addition, the frequency of the laser appears a blue shift of 142 MHz at 3rd minute after SPPC feedback and a red shift of 243 MHz at 6th minute after SPPC feedback, which are due to phase-conjugate self-scanning effect. Moreover, the dark storage characteristic of the SPPC grating is obtained by measuring the dark decay of SPPC reflectivities. In dark, the SPPC reflectivity declines from 80.5% to 75% in the initial 1.5 hours, subsequently decays slowly, and remains almost at the former value for about 15 hours..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1165 (2004)
Study of Beam Quality and Focus of Frequency Doubling in a KTP Crystal on Nd∶YAG Laser by the Resonant External Ring Cavity
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In order to solve the problem of fine focus in laser assisted microprocessing, a method of Nd∶YAG frequency doubling is adopted to acquire short wave laser. The frequency doubling in a KTP crystal on Nd∶YAG laser is carried out by the resonant external ring cavity. The maximum average power of Nd∶YAG is 50 W with Q-swiIn order to solve the problem of fine focus in laser assisted microprocessing, a method of Nd∶YAG frequency doubling is adopted to acquire short wave laser. The frequency doubling in a KTP crystal on Nd∶YAG laser is carried out by the resonant external ring cavity. The maximum average power of Nd∶YAG is 50 W with Q-switch and its frequency is 1005 Hz. A 0.532 μm green light output with 31.4% light conversion efficiency is obtained when the average input power of 1.064 μm laser is 35 W. The proportion of TEM00 model in the green light is 95%. This method is proved to be effective to solve the problem of mini-focus, especially useful in the application of laser rapid prototyping. The experimental results for the characteristics of ring cavity frequency doubling are analyzed and compared with those of 1.064 μm laser on the beam quality..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1169 (2004)
Parallel Driving to Plasma Electrode Pockels Cells
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Plasma-electrode Pockels cells (PEPC) are used in large high-power laser driver for inertial confinement fusion (ICF) to restrain the self-oscillation produced by the multipass amplifier and isolate the back beams. With parallel driving technology, the miniaturization and low cost of Pockels cells driver can be realizePlasma-electrode Pockels cells (PEPC) are used in large high-power laser driver for inertial confinement fusion (ICF) to restrain the self-oscillation produced by the multipass amplifier and isolate the back beams. With parallel driving technology, the miniaturization and low cost of Pockels cells driver can be realized. In this paper, the approaches and issues of parallel drive for PEPC electro-optical switches are described. The parallel drive electro-optical switches include the parallel driving of plasma discharge and switching crystal charge. With the isolate resistance and decouple diode, the pre-ionization of two Pockels cells are parallel driven successfully. Moreover the plasma electrodes of two Pockels cells are accuracy synchronously taken place. By adjusting the forming line of switch pulses and transmission cable length, the parallel charge of Pockels cells can also be achieved. And the experimental results are given in the end..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1173 (2004)
Equivalence of Talbot Effect of the Grating Illuminated by the Pulsed Laser and Continuous Polychromatic Light
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Using of the cross mutual spectral density of the partially coherent theory, the self-imaging of grating under illumination with arbitrary degree of partial coherence is developed. Both the temporal and the averaged distributions of diffracted intensities at the self-imaging distances are formulated, which can be appliUsing of the cross mutual spectral density of the partially coherent theory, the self-imaging of grating under illumination with arbitrary degree of partial coherence is developed. Both the temporal and the averaged distributions of diffracted intensities at the self-imaging distances are formulated, which can be applied to either continuous or pulsed illuminations with any kind of spectra. The theoretical result shows that the ultra-short laser pulse and the continuous polychromatic illuminations, whose spectrum distributions are the same, have the similar averaged self-image distribution. So, the Talbot effect may help to study the temporal and spectral characteristics of ultra-short laser pulses. An experiment using a light-emitting diode (LED) as the source of illumination is performed, and the experimental results confirm with the theoretical ones..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1177 (2004)
Investigation on Diffractive Optical Elements for Converting Gaussian Beam into Square Uniform Focused Spot
[in Chinese], [in Chinese], and [in Chinese]
A diffractive optical element (DOE) with 8 levels is designed to implement the wavefront transformation with two-dimensional weighed serial iterative algorithm. The DOE converts a circular-Gaussian laser beam into a 10 μm×10 μm flat-top square focused spot, which realizes the transformation of beam-shape and the uA diffractive optical element (DOE) with 8 levels is designed to implement the wavefront transformation with two-dimensional weighed serial iterative algorithm. The DOE converts a circular-Gaussian laser beam into a 10 μm×10 μm flat-top square focused spot, which realizes the transformation of beam-shape and the uniform distribution of the amplitude at the same time. The DOE is applied to high-density holographic storage, and it meets the needs of the uniform distribution of the incident focused spot. The simulated results show that the energy transformation efficiency is up to 91.2%, the uniformity error is 4.6%, and the error is below 0.023%, which nearly satisfy the need. The tolerance of the incident beam and the focus is analyzed too. Three sets of masks on 8 levels phase DOEs have been processed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1183 (2004)
Finite Difference Analysis of Dispersion Properties of Photonic Crystal Fibers
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A finite difference scheme based on semi-vectorial wave equations is used to study the dispersion properties of photonic crystal fibers (PCF). Using a central difference scheme, the semi-vectorial wave equations are cast into algebraic eigenvalue problems, from which modal fields and propagation constants are obtained.A finite difference scheme based on semi-vectorial wave equations is used to study the dispersion properties of photonic crystal fibers (PCF). Using a central difference scheme, the semi-vectorial wave equations are cast into algebraic eigenvalue problems, from which modal fields and propagation constants are obtained. The results obtained by the semi-vectorial finite difference method are coincided well with those by the full-vectorial finite difference method and the finite element method as well as experimental results, and are more accurate than those by the scalar effective index model. It can be shown that the semi-vectorial finite difference method is an effective numerical tool for the design of photonic crystal fibers with desirable dispersion..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1257 (2004)
Theories and Applications on Output Energy Distribution of Hollow Fiber
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The electromagnetic distribution in hollow fiber always is one of key research points of hollow waveguide. Under certain hypotheses, the energy distribution of output laser passed through hollow waveguide seems to reflect the electromagnetic distribution in hollow fiber, but the conventional measurement approaches are The electromagnetic distribution in hollow fiber always is one of key research points of hollow waveguide. Under certain hypotheses, the energy distribution of output laser passed through hollow waveguide seems to reflect the electromagnetic distribution in hollow fiber, but the conventional measurement approaches are much complex and the device is too expensive. A simple and effective method for measuring the energy distribution and its applications on mode purity analysis and coupling status detection of hollow waveguide are introduced in this paper. Finally, the output beam waist problem for a beam passing through a hollow fiber is discussed and the output beam focus of different hollow fibers is measured..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1261 (2004)
Study on Experiment of Fiber Bragg Grating Pressure Sensitivity
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Fiber Bragg gratings (FBG) using as pressure, temperature, and strain sensors are triumphantly applied in optical sensing fields in recent years. However, the sensitivity of a bare FBG is insensitive to the ambient environment. So it is necessary to package FBG to enhance its sensitivity. Two polymers are mixed togetheFiber Bragg gratings (FBG) using as pressure, temperature, and strain sensors are triumphantly applied in optical sensing fields in recent years. However, the sensitivity of a bare FBG is insensitive to the ambient environment. So it is necessary to package FBG to enhance its sensitivity. Two polymers are mixed together to package fiber grating. Pressure experiments are studied at 23℃. It can be seen that fiber grating packaged with polymers is high sensitivity for pressure in the range from 0 MPa to 10 MPa. The measured pressure sensitivity is -1.22×10-4/MPa, more than 62 times than that of a bare fiber grating..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1266 (2004)
Beam Transmission
Influence of Laser Non-Uniformity and Thermal Effects in an Inner Optical System on the Far-Field Behavior
[in Chinese], [in Chinese], and [in Chinese]
Although for a real high-power and high-energy laser the propagation distance of lasers in the beam control system (or called the inner optical system) is much shorter than that in the long-distance atmosphere, the thermal effect of a high-power-density laser beam passing through the inner optical system remarkably affAlthough for a real high-power and high-energy laser the propagation distance of lasers in the beam control system (or called the inner optical system) is much shorter than that in the long-distance atmosphere, the thermal effect of a high-power-density laser beam passing through the inner optical system remarkably affects the far-field beam quality. By using a four-dimensional simulation code, detailed numerical calculations are performed for the high-power laser propagation in the inner optical system, where an annular profile with linear non-uniformity in the x direction is used to model the high-power laser. The astigmatic parameter, power in the bucket (PIB) and position of the peak intensity are chosen as the parameters for characterizing beam quality in the far-field. It is found that the thermal effect in the inner optical system reduces the peak intensity and beam focusability, thus degrades the far-field beam quality. In addition, the non-uniformity of the initial beam affects the focusability and gives rise to the astigmatism. It is worth noting that the thermal blooming is a nonlinear effect, which affects the intensity distribution and results in a shift of the position of peak intensity in the far-field. The physical interpretation is given and confirmed by numerical results..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1193 (2004)
Holography and Information Processing
Recording and Reconstruction of Synthetic Aperture Digital Holography
[in Chinese], [in Chinese], and [in Chinese]
This paper introduces the fundamental principle of the recording and numerical reconstruction of the synthetic aperture digital holography, and proposes two numerical reconstructed methods: one is the numerical reconstructed complex amplitude superposition or intensity superposition from the single reference beam sub hThis paper introduces the fundamental principle of the recording and numerical reconstruction of the synthetic aperture digital holography, and proposes two numerical reconstructed methods: one is the numerical reconstructed complex amplitude superposition or intensity superposition from the single reference beam sub hologram, the other one is the numerical reconstructed complex amplitude superposition or intensity superposition of the multi reference beams sub hologram. The experimental research results show: Synthetic aperture technique can improve the resolution of digital holography evidently. Comparing with the conventional numerical reconstructed method of direct combined sub-hologram, the proposed two kinds of numerical reconstructed methods are the same in improving the resolution of reconstructing image of digital holography, but the difficulty of recording and reconstruction of synthetic aperture digital holography by the intensity superposition method is decreased..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1207 (2004)
Efficient Grating Transferring System for Recombining Optically Variable Device
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The technology to make a large area master with the grating of optically variable device (OVD) is role in holographic image embossing. A computerized recombining system is designed for transferring the grating of the optically variable device onto the surface of the pressure-sensitive materials with high efficiency. ThThe technology to make a large area master with the grating of optically variable device (OVD) is role in holographic image embossing. A computerized recombining system is designed for transferring the grating of the optically variable device onto the surface of the pressure-sensitive materials with high efficiency. The induced heating device is used to heat the nickel shim quickly so that the temperature on the surface of the shim can be adjusted precisely. The system can produce a large area OVD plate transferred it with the method of array. The properties of the OVD′s on the nickel plates before and after transferring process are measured and analyzed. The principle of the recombining system is explained. Some aspects to affect the quality of transferring are given. The results show that the diffraction efficiency of transferred OVD can be higher than that of original shim. The size of recombining OVD plate can be achieved up to 1000 mm×1600 mm..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1212 (2004)
Influence of the Tilting of the Photorefractive Hologram Grating on Wavelength Demultiplexer
[in Chinese], [in Chinese], and [in Chinese]
The influence of the tilting of the photorefractive hologram grating on wavelength demultiplexer is studied. An effective method, which can predict the influence of the grating tiling on the demultiplexing performance, is presented in order to avoid the unnecessary experimental spending. The phase error caused by the tThe influence of the tilting of the photorefractive hologram grating on wavelength demultiplexer is studied. An effective method, which can predict the influence of the grating tiling on the demultiplexing performance, is presented in order to avoid the unnecessary experimental spending. The phase error caused by the tilting of the Bragg grating is corrected with a Fourier analysis. The spectral response of the demultiplexer is calculated by using a rigorous coupled wave analysis method. The influence of the tilting of the Bragg grating on the spectral response is analyzed. It is shown that the phase difference due to the tilting of the grating can result in a large insertion loss and a large crosstalk. It is pointed out that the hologram tilting must be avoided as much as possible since it deteriorates the final performance seriously when a photorefractive hologram Bragg grating is used for wavelength demultiplexing. The experimental method of the grating image processing is also introduced in the paper. The experimental results accorded with theoretical computation commendably by testing the spectral responses of two demultiplexers with the tilting gratings..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1217 (2004)
Laser Manufacturing
Nozzle Path Planning of Edge-Shared Nested Workpiece in Laser Cutting
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Nesting software optimizes material yield, but if the parts cannot be cut efficiently, ensuring part quality and increased the throughput, the savings gained in material efficiency are lost. Based on graph theory, the mathematical model of nozzle path planning problem for the laser cutting of the edge-shared nested regNesting software optimizes material yield, but if the parts cannot be cut efficiently, ensuring part quality and increased the throughput, the savings gained in material efficiency are lost. Based on graph theory, the mathematical model of nozzle path planning problem for the laser cutting of the edge-shared nested regular or irregular parts is established in this paper. The optimization objective of the problem is defined as minimum pierce points and shortest vacant path of nozzle in edge-shared cutting, which includes machining quality, efficiency and manufacturing cost. Three algorithms to solve the problem are presented that can meet the laser cutting technics. The first algorithm is a new Eulerian trail algorithm to solve the problem under ideal circumstances, The second algorithm uses the algorithm based on the minimum weight and maximum matching algorithms of complete graph with the vertices of odd degree to solve the problem under general circumstances, The third algorithm uses the scrap areas to investigate further reduction in the number of pierce points. Every sort of application instance of the three algorithms mentioned is presented and their validity is testified..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1269 (2004)
Numerical Simulation of Pulsed Laser Induced Ultrasound in Monolayer and Double Layer Materials
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Taking account of the temperature-dependence of the thermal physical parameters, the thermoelastic generated ultrasound and transient temperature fields by pulsed laser in mono-layer and double-layer materials are numerical simulated by finite element method. In the mono-layer plate, whose thickness is less than the ceTaking account of the temperature-dependence of the thermal physical parameters, the thermoelastic generated ultrasound and transient temperature fields by pulsed laser in mono-layer and double-layer materials are numerical simulated by finite element method. In the mono-layer plate, whose thickness is less than the central wavelength of the generated ultrasound, Lamb wave, mainly with a non-dispersion symmetric mode and a dispersion anti-symmetric mode, is obtained by numerical simulation. When the sample thickness increases so that the higher modes can propagate in the plate, a skimming surface longitudinal wave and a Rayleigh wave are formed at the sample surface. Furthermore, the normal displacement on the surface of two kinds of two-layer system, one is Ni/Al systems and the other is Al/Cu system, is calculated. Because the high frequency surface acoustic wave due to less penetration depth is more influenced by the properties of the surface layer during propagating and the low frequency surface wave is more influenced by the substrate, normal dispersion is observed in Ni/Al system and anomalous dispersion is observed in Al/Cu system, respectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1275 (2004)
Laser Physics
Laser-Diode Pumped Passively Q-Switched Nd∶GdVO4 Laser
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Passively Q-switched Nd∶GdVO4 laser performance was investigated by using laser-diode as pump source, and Cr4+∶YAG (Cr4+∶Y3Al5O12), GaAs and dye as saturable absorber, respectively. The laser crystal sample of 4 mm×4 mm×6 mm with 1% Nd concentration was used. For Cr∶YAG with small signal transmission 91% and Passively Q-switched Nd∶GdVO4 laser performance was investigated by using laser-diode as pump source, and Cr4+∶YAG (Cr4+∶Y3Al5O12), GaAs and dye as saturable absorber, respectively. The laser crystal sample of 4 mm×4 mm×6 mm with 1% Nd concentration was used. For Cr∶YAG with small signal transmission 91% and 95%, the thresholds were 0.63 W and 0.57 W, respectively. At the pump power of 3.69 W, stable laser pulses with 64 ns and 80 ns pulse duration, 3.66 μJ and 3.41 μJ pulse energy, 325 kHz and 378 kHz pulse repetition rate were generated with the two Cr∶YAG saturable absorbers, respectively. The threshold for a 580 μm GaAs wafer was 0.39 W. At the pump power of 3.69 W, stable laser pulses with 7.8 ns pulse duration, 2.15 μJ energy and 366 kHz pulse repetition rate were produced with GaAs saturable absorber. The narrowest Q-switched laser pulse could be obtained with a dye wafer with 70% initial transmission. But because of its high insert loss, the threshold was high and the output was not stable..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1153 (2004)
Yb3+-Doped Fiber Laser Based on Synchronously Pumped Mode-Locking
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Synchronously pumped mode-locking can be obtained when the frequency for gain switching of the pump-laser is equal to (or an integer multiple of) the cavity mode spacing, corresponding to the harmonic mode-locked status. A synchronously pumped mode-locked yetterbium-doped fiber laser (YDFL) is obtained when the pump seSynchronously pumped mode-locking can be obtained when the frequency for gain switching of the pump-laser is equal to (or an integer multiple of) the cavity mode spacing, corresponding to the harmonic mode-locked status. A synchronously pumped mode-locked yetterbium-doped fiber laser (YDFL) is obtained when the pump semiconductor laser current is modulated sinusoidally at the appropriate frequency. By modulating frequency of the pump laser narrower output pulses are obtained on the second harmonic and rational harmonic mode-locked status and the 4th-order rational harmonic mode-locking status. At the repetition rate of 625 kHz,the pulse width of second harmonic mode-locked pulse train is less than 20 ns, approximately 1/40 of the pump-pulse-width. The average output power is about 2.34 mW and the energy convert efficiency is about 5%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1157 (2004)
All-Fiber Type Short Cavity Er/Yb Co-Doped Fiber Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A short cavity Er/Yb co-doped fiber laser of high output power and high slope efficiency is demonstrated. Its resonant cavity is composed of a section of single mode Er/Yb co-doped fiber and two fiber Bragg gratings with the same reflection wavelength. A fiber grating is used for output of resonant cavity with 60% reflA short cavity Er/Yb co-doped fiber laser of high output power and high slope efficiency is demonstrated. Its resonant cavity is composed of a section of single mode Er/Yb co-doped fiber and two fiber Bragg gratings with the same reflection wavelength. A fiber grating is used for output of resonant cavity with 60% reflectivity. Its 3 dB-bandwidth is measured as 0.16 nm. The other fiber grating is used for high broadband reflector and input of pump light with 99% reflectivity. Its 3 dB-bandwidth is measured as 1.02 nm. This fiber laser is pumped by a 980 nm semiconductor laser. Meanwhile, the Er/Yb co-doped fiber with different lengths is measured by different pump power, and the optimized length of the fiber is only 13 cm. A short cavity fiber grating laser is done by using 13 cm Er/Yb co-doped fiber as gain medium. Its maximum output power is 11 mW and its power stability is better than ±0.01 dB. The laser has a threshold of 35 mW and a slope efficiency of 15.3%. Its 1552.2 nm output spectral 25 dB-bandwidth is measured as 0.3 nm. Edge-mode suppression ratio >60 dB has been achieved and its wavelength stability is 0.05 nm. This fiber laser is able to be used for dense-wavelength-division-multiplex (DWDM) system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1161 (2004)
Trapping Cold Atoms in a Quasi-Two Dimension Magnetic-Optical-Trap
[in Chinese], and [in Chinese]
The setup and the experiment of a quasi-two dimension magnetic-optical-trap (MOT) are introduced in the paper. Four rectangular coils combining four elliptical spot beams and two orbicular spot beams are used to obtain a MOT and trap cold atoms. The characteristic of the trap is a pole shape and a bulk trap capacity, sThe setup and the experiment of a quasi-two dimension magnetic-optical-trap (MOT) are introduced in the paper. Four rectangular coils combining four elliptical spot beams and two orbicular spot beams are used to obtain a MOT and trap cold atoms. The characteristic of the trap is a pole shape and a bulk trap capacity, so the trap can capture more atoms, atomic cloud. The data of experiment are as following.
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1188 (2004)
Materials and Thin Films
Spectra Properties and Upconversion Mechanisms of Er3+-Doped Heavy Metal Oxyfluoride Germanate Glass
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The absorption and upconversion spectra of Er3+-doped heavy metal oxyfluoride germanate glass were investigated, and upconversion mechanisms of Er3+ in the glass were analyzed. The Judd-Ofelt intensity parameters Ωt (t=2, 4, 6), spontaneous transition probability, fluorescence branching ratio and radiative lifetime τraThe absorption and upconversion spectra of Er3+-doped heavy metal oxyfluoride germanate glass were investigated, and upconversion mechanisms of Er3+ in the glass were analyzed. The Judd-Ofelt intensity parameters Ωt (t=2, 4, 6), spontaneous transition probability, fluorescence branching ratio and radiative lifetime τrad of each energy levels for Er3+ were calculated by Judd-Ofelt theory. The results showed that the intense green and weak red emissions were observed, a two-photon upconversion process was assigned to the green and red emissions, and the possible upconversion mechanisms were involved in excited state absorption and energy transfer between excited Er3+ ions. Raman spectrum indicated the fluoride ions in the glass network had important influence on upconvesion fluorescence..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1198 (2004)
Preparation of Metallic Coating on Surface of Diamond Particles by Pulsed Laser Deposition
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A new technique is introduced to prepare Ti or Ni coatings on diamond particle surfaces as metallic protection layers by the pulsed excimer laser deposition. Compressive strength and the surface form and structure of the uncoated and coated diamond particles are measured and analyzed by a compressive strength meter andA new technique is introduced to prepare Ti or Ni coatings on diamond particle surfaces as metallic protection layers by the pulsed excimer laser deposition. Compressive strength and the surface form and structure of the uncoated and coated diamond particles are measured and analyzed by a compressive strength meter and a metallograph, respectively. Specific ingredients of the coated metallic films on the diamond particles are determined by X-ray diffractometer (XRD) as well. The test results show the compressive strength of the Ti-coated diamond particles increases greatly. Furthermore, because the energy of the plasma produced by using the pulsed excimer laser to ablate a metallic target is much higher, TiC film can be formed on the diamond particle even if the ambient temperature is not very high, which can enhance the interface bond strength between the diamond particles and the Ti films. The formation of this type of TiC film is very helpful to prolong the lifetime of diamond saws..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1203 (2004)
Optical Communication
Modeling the Noise Accumulation of Optical Paths in WDM Optical Transport Networks
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A mathematic model is presented for the noise accumulation within optical paths in optical transport networks according to the hypothetical reference model (HRM) defined in ITU-T recommendation G.873. The optical paths may pass through multiple optical nodes and fiber links with optical amplifiers. Analytic calculationA mathematic model is presented for the noise accumulation within optical paths in optical transport networks according to the hypothetical reference model (HRM) defined in ITU-T recommendation G.873. The optical paths may pass through multiple optical nodes and fiber links with optical amplifiers. Analytic calculation formulae are derived and simplified according to the node isolation principle. An engineering equivalent model is given, as well as the corresponding calculation formulae. The impact of the gain (attenuation) distribution within an optical node on the noise power is analyzed. Optimum design principles are proposed for optical nodes to reduce noise power in optical paths. The noise models for optical path can be used as a reference for designing optical nodes and fiber transmission spans in optical networks..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1222 (2004)
Design of a Tunable Dense-Wavelength-Division-Multiplexing Filter Based on Analog Birefringent Structure
[in Chinese], [in Chinese], and [in Chinese]
A new structure of tunable polarization interference dense wavelength division multiplexing (DWDM) filter based on the analog birefringent module is presented. It is composed of several cascaded analog birefringent modules with the same structure located between two polarizing devices. Each analog birefringent module cA new structure of tunable polarization interference dense wavelength division multiplexing (DWDM) filter based on the analog birefringent module is presented. It is composed of several cascaded analog birefringent modules with the same structure located between two polarizing devices. Each analog birefringent module consists of a pair of birefringent plates for splitting and combination, respectively, and in between a set of two medium plates of different indices of refraction and one half-wave plate. The center-frequency tunability characteristic of the filter is investigated as well. Results show that as a definite flattening requirement is satisfied, the passband and stopband with wide flatness width and high isolation can be obtained and the center frequency tunability can be accomplished simultaneously when slightly rotating the analog birefringent module unit. The feasibility of the analog birefringent structure is verified through an experiment..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1227 (2004)
Effects of Degree of Polarization of the Output Pulse on Polarization Mode Dispersion in Optical Fiber Transmission Systems
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The polarization mode dispersion (PMD) of the optical fiber transmission system has been the main factor to limit the transmission capacity and distance of the system. The degree of polarization (DOP) of optical signals is related to the PMD of the system. The expression of the output pulse Stokes vector is derived basThe polarization mode dispersion (PMD) of the optical fiber transmission system has been the main factor to limit the transmission capacity and distance of the system. The degree of polarization (DOP) of optical signals is related to the PMD of the system. The expression of the output pulse Stokes vector is derived based on Jones matrix model proposed by A. Orlandini. The basic properties of degree of polarization of optical pulse have been investigated. It is shown that the degree of polarization of optical signals changes with polarization state of the input, and reaches its maximum at the position of the principal state of polarization; it decreases with the increase of the PMD magnitude; And it decreases also with the increase of absolute value of the initial pulse chirp coefficient, but has no relation with the sign of chirping coefficient..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1231 (2004)
Impact of Bi-Directional Pump Power Scheme on Gain of Raman Fiber Amplifier
[in Chinese], and [in Chinese]
On-off gain characteristics of bi-directionally pumped Raman fiber amplifier are numerically simulated through shooting method. The results show that the on-off gain is approximatively independent of forward pump power percentage under constant total pump power. The results are coincided with the analytical solution unOn-off gain characteristics of bi-directionally pumped Raman fiber amplifier are numerically simulated through shooting method. The results show that the on-off gain is approximatively independent of forward pump power percentage under constant total pump power. The results are coincided with the analytical solution under small signal power. When the signal power increases till the pump power depletion causing by signal can not be ignored, its on-off gain slightly increases with enhancement of forward pump power percentage under constant total pump power. In addition, the distributions of the signal power, forward pump power, backward pump power and total power along fiber under various input signal power and various forward/back pump power are given through diagram..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1235 (2004)
Numerical Research of Flat Supercontinuum Generated in Dispersion-Flattened/Decreasing Fiber
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Supercontinuum generated in dispersion-flattened/decreasing fiber is simulated and analyzed in detail. It is found that the peak power of pump pulse is very important to supercontinuum generation from the fiber and there is a threshold power. With the increasing of the peak power of pump pulse, the spectral width becomSupercontinuum generated in dispersion-flattened/decreasing fiber is simulated and analyzed in detail. It is found that the peak power of pump pulse is very important to supercontinuum generation from the fiber and there is a threshold power. With the increasing of the peak power of pump pulse, the spectral width becomes wider and the flatness of supercontinuum becomes better. But if the peak power of pump pulse is increased further, the flatness becomes bad. In the end, a optimal peak power for supercontinuum generation is found. It is also found that the fourth and fifth order group-velocity dispersions are crucial to flatly wideband supercontinuum generation from the fiber, dispersion of the third and the other higher than fifth order can be ignored. It is further found that the higher-order nonlinear effects such as stimulated Raman scattering and self-steepening are negligible in the case..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1239 (2004)
Study on Signal Extinction Ratio in WDM-OTDM Wavelength Conversion
[in Chinese], [in Chinese], and [in Chinese]
The extinction ratio performance of converted two-channel time division multiplexing output signals in all-optical WDM (wavelength division multiplexing)-OTDM (optical time division multiplexing) converter based on cross-gain modulation (XGM) in semiconductor optical amplifier (SOA) is analyzed .The effects on the extiThe extinction ratio performance of converted two-channel time division multiplexing output signals in all-optical WDM (wavelength division multiplexing)-OTDM (optical time division multiplexing) converter based on cross-gain modulation (XGM) in semiconductor optical amplifier (SOA) is analyzed .The effects on the extinction ratio of converted signal is studied regarding to various parameters such as the power and wavelength of two-channel WDM input pump and probe, the bit rate, the extinction ratio of the pump, the SOA bias current, cavity length, and confinement factor. Which can provide the theoretical basis for the optimization of wavelength converter and signal processing in WDM switching nodes. It is shown by numerical simulation that high pump input power and long pump wavelength enhance signal extinction ratio of corresponding channel but decrease the adjacent channel extinction ratio. High pump extinction ratio can do too, however, the increasing amplitudes of different channels are different. Meanwhile extinction ratio of converted signal can be improved with low probe power, short probe wavelength, long cavity length, high confinement factor, and large biased current. Especially extinction ratio equalization of each channel should be considered in all-optical WDM-OTDM wavelength conversion..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1245 (2004)
Characterization of Single Step Buried Waveguides on BK7 Glass by Copper Ion Exchange
[in Chinese], [in Chinese], [in Chinese], and G. C. Righini
Planar optical waveguides were fabricated by copper ion-exchange on BK7 glass substrate. The effective refractive index was measured by prism-coupling technique at the wavelength of 632.8 nm. Refractive index profile was determined by Inverse-WKB method. The results showed that the best fitting to the index profile wasPlanar optical waveguides were fabricated by copper ion-exchange on BK7 glass substrate. The effective refractive index was measured by prism-coupling technique at the wavelength of 632.8 nm. Refractive index profile was determined by Inverse-WKB method. The results showed that the best fitting to the index profile was improved Gauss function, and the index profile appeared to be a buried waveguide′s index profile. The diffused coefficient of copper ion-exchange at 570℃ was obtained as De≈1.2133×10-14 m2/s. At the same time, the BK7 ion-exchanged glass samples were determined by electron microscope scan (EMS) and secondary ion mass spectroscopy (SIMS) measurements, the copper ions concentration in the BK7 glass waveguides′ surface was gotten. It could be shown that the BK7 glass planar waveguides were buried waveguides. The fabricated BK7 buried glass was obtained by single step copper ion exechange..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 10, 1252 (2004)
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