Journals >Chinese Journal of Lasers
Contents
2007
Volume: 34 Issue 5
24 Article(s)
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Research Article
90° Conical Reflector Resonator for High Power Transverse Flow CO2Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Considering the structural characteristics of 5 kW transverse flow continuous wave CO2 laser electrically excited with pin-to-flat discharge, the 90° conical reflector designed as the resonator cavity of totally reflective mirror is investigated. Based on the Fresnel-Kirchhoff theory, the diffraction integrals equConsidering the structural characteristics of 5 kW transverse flow continuous wave CO2 laser electrically excited with pin-to-flat discharge, the 90° conical reflector designed as the resonator cavity of totally reflective mirror is investigated. Based on the Fresnel-Kirchhoff theory, the diffraction integrals equation of conical resonator is deduced by using Collins formula and taking gain influence into account. The results indicate that the resonator composed of conical reflector and plane output mirror is stable and low-step output modes are acquired for high power transverse flow CO2 laser. Limited by the processing accuracy, there is a processing residual blind-hole in the center, which brings considerable loss for TEMmn (m=0, n≠0) modes, so its output is difficult. However, the low-order modes of weak center field distribution for less loss have prior output..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 628 (2007)
Low Power Laser Diode-Pumped Solid-State Yb:YAG Laser at Room Temperature
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A low power laser diode (LD) end-pumped Yb:YAG laser has been demonstrated. At room temperature, the Yb:YAG laser has a quasi-three-level structure; and the lasing threshold is high because of serious re-absorption at the laser wavelength. In order to improve pump intensity, double LD polarization coupling system was eA low power laser diode (LD) end-pumped Yb:YAG laser has been demonstrated. At room temperature, the Yb:YAG laser has a quasi-three-level structure; and the lasing threshold is high because of serious re-absorption at the laser wavelength. In order to improve pump intensity, double LD polarization coupling system was employed in the experiment. The stable operation at 1030 nm was realized in a linear cavity by reducing doping concentration and efficient cooling with thermal electric cooler (TEC). The crystal is 0.7 mm in thickness and 11mm in diameter. The doping concentration (atomic percent) is 8%. The end face of crystal is coated for high reflection at 940 nm, which leads to a second pass of the pump light. The maximum output power of 192.8 mW at 1030 nm is obtained when the incident power is 2 W. The optical-optical conversion efficiency is 9.6%. The power instability is better than ±3.5% in 2 hours..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 633 (2007)
Beam Quality of 980 nm High Power Vertical-Cavity Surface-Emitting Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A simple method to measure the beam quality factor (M2) of high-power vertical-cavity surface-emitting laser (VCSEL) was designed by employing the charge coupled device (CCD) technology. When the injection currents were 900 mA, 1500 mA, 3000 mA and 6000 mA, respectively, the waists of a 980 nm bottom-emitting VCSEL witA simple method to measure the beam quality factor (M2) of high-power vertical-cavity surface-emitting laser (VCSEL) was designed by employing the charge coupled device (CCD) technology. When the injection currents were 900 mA, 1500 mA, 3000 mA and 6000 mA, respectively, the waists of a 980 nm bottom-emitting VCSEL with a 300 μm aperture were measured and the values of M2 were 66, 58, 44 and 53, respectively, which were calculated by Gauss fitting. In addition, far-field pattern was analyzed as the injection currents were 900 mA and 3000 mA. At the same time, far-field angles were measured and the values of them were in good agreement with the calculated value exactly..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 641 (2007)
Laser Diode Pumped Nd:NYW/LBO Green Laser
[in Chinese], [in Chinese], and [in Chinese]
A laser diode (LD) pumped Nd3+:NaY(WO4)2 (Nd:NYW) green laser is reported. LBO (LiB3O5) crystal intracavity with type-I critical phase matching was used for frequency doubling. The threshold pump power is 410 mW. The laser performance at 530 nm was carried out. The maximum output power of 87 mW was obtained with an incA laser diode (LD) pumped Nd3+:NaY(WO4)2 (Nd:NYW) green laser is reported. LBO (LiB3O5) crystal intracavity with type-I critical phase matching was used for frequency doubling. The threshold pump power is 410 mW. The laser performance at 530 nm was carried out. The maximum output power of 87 mW was obtained with an incident pump power of 1.5 W. The slope efficiency has been determined to be 7.98% and the optical-to-optical efficiency is more than 25%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 646 (2007)
A 100 km Fiber Bragg Grating Sensor System Based on Swept Laser and Optical Amplification
[in Chinese], [in Chinese], and [in Chinese]
A novel method of Er-doped optical fiber (EDF) dual-wavelength Raman hybrid amplification for fiber Bragg grating (FBG) sensor system based on swept laser is proposed for achieving ultra-long distance quasi-distributed measurement. Such a method employs a high power swept laser as the light source. Dual-wavelength RamaA novel method of Er-doped optical fiber (EDF) dual-wavelength Raman hybrid amplification for fiber Bragg grating (FBG) sensor system based on swept laser is proposed for achieving ultra-long distance quasi-distributed measurement. Such a method employs a high power swept laser as the light source. Dual-wavelength Raman fiber amplification is adopted to achieve low-noise bidirectional amplification of FBG signals, and two sections of EDFs arranged along the fiber link remotely are used for generation of amplified spontaneous emission (ASE) light to illuminate remotely-located FBG sensors and also amplification of sensor signals with the residual Raman pump power, making the whole sensor system capable of obtaining reasonably good signal-noise-ratio (SNR) for an ultra-long distance. The experimental results show that an optical SNR of ～7 dB has been achieved for a 100 km transmission distance with a swept laser, a low Raman pump power of ～170 mW at wavelength of 1455 nm and a Raman pump power of ～2 W at wavelength of 1480 nm, which leads to realization of FBG-based sensing along ultra-long distance..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 680 (2007)
Design of Single-Polarization Single-Mode Micro-Structured Polymer Optical Fiber
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The single-polarization single-mode (SPSM) micro-structured polymer optical fiber (MPOF) was designed based on polymethyl methacrylate (PMMA). A full vector plane wave expansion method together with perfectly matched boundary conditions is adopted to study the SPSM properties. The dependence of SPSM bandwidth and operaThe single-polarization single-mode (SPSM) micro-structured polymer optical fiber (MPOF) was designed based on polymethyl methacrylate (PMMA). A full vector plane wave expansion method together with perfectly matched boundary conditions is adopted to study the SPSM properties. The dependence of SPSM bandwidth and operation wavelength on fiber parameters was investigated numerically. It indicates that only one polarization state of the fundamental mode can be transmitted within the visible light region from 0.57 μm to 0.71 μm according to the different cutoff wavelength for two orthogonal polarization modes. Moreover, the confinement loss of guiding mode is investigated using the beam propagation method. For MPOF with only 7 rings of holes, the confinement loss less than 1.24 dB/m is obtained at the 0.65 μm. This low loss SPSM-MPOF can greatly eliminate the polarization crosstalk and polarization mode dispersion..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 684 (2007)
Reconstruction of Parameters of Fiber Gratings from Time-Delay Characteristics Using the Genetic Algorithm
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A new method of parameter reconstruction for fiber gratings from desired time-delay characteristics is presented by genetic algorithm (GA) in conjunction with the transfer matrix method in this paper. The objective function in this method is time-delay of fiber gratings, and the individuals of population are the parameA new method of parameter reconstruction for fiber gratings from desired time-delay characteristics is presented by genetic algorithm (GA) in conjunction with the transfer matrix method in this paper. The objective function in this method is time-delay of fiber gratings, and the individuals of population are the parameters of fiber gratings, including the grating length, refractive index modulation, grating period and grating chirp. The optimal solution is obtained through many generations calculation. The real-coded genetic algorithm is used for parameter reconstruction of uniform, chirped and apodized fiber gratings. Numerical simulating results show that the method is very effective for parameter reconstruction of fiber gratings according to desired time-delay characteristics. An apodized chirped fiber grating is reconstructed from an ideally linear time-delay characteristics whose slope is 100 ps/nm, maximum time-delay is 300 ps and center wavelength is 1555.2 nm. The method proposed can effectively obtain the parameters of fiber gratings from time-delay figures, and can be applied in the design of optically controlled phased-array antennas based on the time-delay characteristics of fiber gratings..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 688 (2007)
Biomedical Photonics and Laser Medicine
Fiber Laser Cutting Technology on Coronary Artery Stent
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Coronary artery stent is an important mechanical device designed to open arteries that have been occluded. In this paper, the processing techniques including output power, frequency, cutting speed, pulse width and assistant air pressure, which influence the quality of the coronary artery stent, have been studied with tCoronary artery stent is an important mechanical device designed to open arteries that have been occluded. In this paper, the processing techniques including output power, frequency, cutting speed, pulse width and assistant air pressure, which influence the quality of the coronary artery stent, have been studied with the fiber laser precision cutting system. The best processing techniques have been gained with the analysis and experiments. The high quality coronary artery stents have been cut with the output power of 7 W, pulse length of 0.15 ms, repeat frequency of 1500 Hz, scanning speed of 8 mm/s and oxygen gas pressure of 0.3 MPa..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 733 (2007)
Laser Manufacturing
Microripple Structures Induced by Femtosecond Laser Pulses
[in Chinese], [in Chinese], and [in Chinese]
Periodic microripple structures were formed on the sample surface after micromachining on Cr-coated glass and fused silica by trains of femtosecond laser pulses from the oscillator. The heights of these microripple structures varied from 10 nm to 300 nm by increasing the laser power and saturated at a higher laser powePeriodic microripple structures were formed on the sample surface after micromachining on Cr-coated glass and fused silica by trains of femtosecond laser pulses from the oscillator. The heights of these microripple structures varied from 10 nm to 300 nm by increasing the laser power and saturated at a higher laser power. The morphology, sizes and heights of theses microstructures are depended on the irradiation fluences and parameters of the femtosecond laser pulses. Chemical methods proved that the microripple structures are composed of not chromium material but the substrate material of glass or fused silica. Furthmore, two kinds of grating with different periods and linewidths were fabricated by selecting the laser power and micromachining speed properly, which indicated the good micromachining performances of the femtosecond laser oscillator..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 715 (2007)
Identification of Terahertz Absorption Spectra of Illicit Drugs Using Back Propagation Neural Networks
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
On the base of absorption spectra in the range from 0.2 to 2.6 THz of nine illicit drugs using terahertz time-domain spectroscopy (THz-TDS) technique, the THz absorption spectra of the nine different illicit drugs were identified successfully by back propagation (BP) neural networks. Firstly, absorption spectra of the On the base of absorption spectra in the range from 0.2 to 2.6 THz of nine illicit drugs using terahertz time-domain spectroscopy (THz-TDS) technique, the THz absorption spectra of the nine different illicit drugs were identified successfully by back propagation (BP) neural networks. Firstly, absorption spectra of the nine illicit drugs, which were pretreated by second derivation, were used to train the BP neural network. Secondly, absorption spectra of the nine illicit drugs which were measured in different time, pretreated by second derivative too, were identified by BP neural network and the identification rate of 89% was achieved. The model of BP neural network was processed in Matlab. The results indicated that it is feasible to apply BP neural network model on the identification of illicit drugs, and providing an effective method in the secure inspection and identification for illicit drugs using THz-TDS technique..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 719 (2007)
Damage Threshold Improvement of Fused Silica Chip by CO2Laser Pretreatment
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In order to improve the damage threshold of fused silica chip, the bare fused silica chip with small aperture etched by hydrofluoic acid is scanned by 10.6 μm CO2 laser with a raster scaning form, and the laser power increases periodically. Results show the surface micro-topography of the pretreated chip is greatly impIn order to improve the damage threshold of fused silica chip, the bare fused silica chip with small aperture etched by hydrofluoic acid is scanned by 10.6 μm CO2 laser with a raster scaning form, and the laser power increases periodically. Results show the surface micro-topography of the pretreated chip is greatly improved. The means of S:1 method is used to measure its damage threshold. Under the conditions of moderate laser polishing, the zero probability damage threshold of the fused silica chip is increased by 30%, and no negative effect on transmission wavefront is introduced. The validity of CO2 laser pretreatment enhancing the bare fused silica chip damage resistant is proved..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 723 (2007)
Visual Numerical Study on Surface Micro-Topography of Sheet Metal by Laser Peening
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Visual numerical simulations and experiments of laser peen forming on stainless SUS304 sheet metal are done. Based on the finite element analysis software ABAQUS/CAE, the conversion model during laser peen forming of laser shock wave loading is founded, by which the pulsed laser energy is converted to shock wave pressuVisual numerical simulations and experiments of laser peen forming on stainless SUS304 sheet metal are done. Based on the finite element analysis software ABAQUS/CAE, the conversion model during laser peen forming of laser shock wave loading is founded, by which the pulsed laser energy is converted to shock wave pressure. The tracks controlling of sheet metal deforming by pulsed laser continuous peening is solved with user subprogram. The dynamic deforming process of sheet metal by laser peening is visualized. With the above model, the micro plastic fluid process of the sheet metal after pulsed laser peening is analyzed, and the variation of surface micro-topography is studied..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 728 (2007)
Laser Physics
Influence on Resonant Tunneling Spectral Character of Two-Dimensional Magnetic Optical Quantum Wells
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The non-magnetic material closed optical quantum well structures and magnetic material optical quantum well structures are designed based on the non-magnetic material open optical quantum well structures. The transmission spectra and field distributions of these three kinds of wells are calculated by finite-difference The non-magnetic material closed optical quantum well structures and magnetic material optical quantum well structures are designed based on the non-magnetic material open optical quantum well structures. The transmission spectra and field distributions of these three kinds of wells are calculated by finite-difference time-domain method (FDTD), the quantized energy states are researched, and the feasibility of enhancing spectral intensity greatly by self-structure is disclosed. It is found that the optical transmittance of the magnetic quantum well is close to 1, and energy loss is less. Compared with the closed photonic quantum well structures, the device′s volume can be reduced, the degree of free regulation of energy band project can be increased, and more photon bound states can be obtained. The results show that the open optical quantum well is traveling wave well, and its capability of capturing photons is weak. But the closed quantum well and the magnetic material optical quantum well are standing wave well, the capabilities for them to capture photons are strong, while the light field gradient of the magnetic material optical quantum well is bigger..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 649 (2007)
Study on the Improved High-Power Femtosecond Pulse Generation System
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Theoretical analysis on the femtosecond pulse generation system is presented. The finite gain bandwidth of the ytterbium-doped fiber amplifier limits the performance of pulse compression by distorting both the chirp and pulse shape. To generate additional bandwidth whilst retaining the desired linearly-chirped similariTheoretical analysis on the femtosecond pulse generation system is presented. The finite gain bandwidth of the ytterbium-doped fiber amplifier limits the performance of pulse compression by distorting both the chirp and pulse shape. To generate additional bandwidth whilst retaining the desired linearly-chirped similariton characteristics, the amplified parabolic pulses are injected into highly-nonlinear fiber (HNLF). The compression efficiency and pulse duration of compressed pulse are investigated for different parameters of HNLF. The quantitative analysis shows that lower group-velocity dispersion (GVD) is preferable; higher nonlinearity parameter can lead to more short minimum pulse duration of compressed pulse, however, the compression efficiency decays more rapidly with increasing HNLF length. The shorter compressed pulse can be obtained through increasing the length of HNLF in a certain range, meanwhile, the compression efficiency must be taken into account..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 655 (2007)
Research on the Method to Stabilize Second Harmonic Generation by Injecting 2ω Signal
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
After analyzing the type I phased matched coupling equations for second harmonic generation (SHG) course, it is found that when the input 2ω signal intensity and the preliminary phase difference θ(0)=2(0)-21(0) change, the output 2ω intensity varies along with the length of SHG in different way. When the input 2ω sigAfter analyzing the type I phased matched coupling equations for second harmonic generation (SHG) course, it is found that when the input 2ω signal intensity and the preliminary phase difference θ(0)=2(0)-21(0) change, the output 2ω intensity varies along with the length of SHG in different way. When the input 2ω signal intensity is not zero and θ(0)=2(0)-21(0)≠±π/2, part of the energy oscillates between 1ω and 2ω. It is proposed that this kind of phenomenon can be used to improve the stability of the output 2ω intensity. Simulation proves that the method of injecting 2ω signal can greatly improve the stability of SHG course. Further simulation shows that length of SHG crystal changes as the input 2ω intensity and phase difference between 1ω and 2ω changing..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 661 (2007)
Materials and Thin Films
Properties of Sol-Gel and Polymer Host for Solid-State Dye Lasers
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In this paper, solid-state dye lasers of sol-gel host and polymethyl metacrylate (PMMA) host were both prepared, pyrromethene-567 (PM567) was used as laser gain media, and the second harmonic generation (SHG) of Q-switched Nd:YAG laser (532 nm, 20 ns) was used as a pumping source. In sol-gel host, peak wavelength of ouIn this paper, solid-state dye lasers of sol-gel host and polymethyl metacrylate (PMMA) host were both prepared, pyrromethene-567 (PM567) was used as laser gain media, and the second harmonic generation (SHG) of Q-switched Nd:YAG laser (532 nm, 20 ns) was used as a pumping source. In sol-gel host, peak wavelength of output laser spectrum was 560 nm, and full width at half maximum (FWHM) of the bandwidth was 9 nm. In polymer host, peak wavelength of output laser spectrum was 561 nm, and the FWHM was 8 nm. The relation of output energy versus input energy was also studied. For the sol-gel and the PMMA host solid-state PM567 lasers, respectively, the slope efficiencies were 43% and 26.3%, and the highest energy outputs in the experiment were 13 mJ and 99 mJ..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 707 (2007)
Blue Up-Conversion in Yb3+and Tm3+-Codoped KY(WO4)2
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Thulium and ytterbium codoped KY(WO4)2 crystals were prepared by using top seeded solution growth (TSSG) method. Its absorption spectra were recorded in the region of 290～1200 nm at room temperature. The energy transfer mechanism from Yb3+ to Tm3+ ions was analyzed by using up-conversion model and the transitions of enThulium and ytterbium codoped KY(WO4)2 crystals were prepared by using top seeded solution growth (TSSG) method. Its absorption spectra were recorded in the region of 290～1200 nm at room temperature. The energy transfer mechanism from Yb3+ to Tm3+ ions was analyzed by using up-conversion model and the transitions of energy levels were assigned. The rate equation of Yb3+ ions to Tm3+ ions energy transition was set up. The efficiency of Yb3+ ions to Tm3+ ions energy transition is close to 1. The up-conversion blue fluorescences at 476 nm were measured when the sample was pumped by 974 nm diode laser. The value of emission cross section for 1G4 to 3H6 transition is estimated with Fadenbrug-luechtbauer method and the peak value is about 1.51×10-20 cm2..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 711 (2007)
Measurement and Metrology
Influence of Acceleration on the Error of Laser Dual-Frequency Interferometer
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In order to reduce the dual-frequency interferometer measuring error induced by acceleration of measured object, a theoretical model of the interferometry measuring error was put forward by considering second-order Doppler frequency shift. The simulated results show that when muzzle velocity is zero the cumulative erroIn order to reduce the dual-frequency interferometer measuring error induced by acceleration of measured object, a theoretical model of the interferometry measuring error was put forward by considering second-order Doppler frequency shift. The simulated results show that when muzzle velocity is zero the cumulative error induced by acceleration of 0.6g can be up to 2.5 nm in 0.4 s, which is not negligible in nanometer measurement. Moreover, when muzzle velocity is not zero, the acceleration motion may result in more error and deceleration motion may result in less error. At last, experiments were done to validate the model..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 694 (2007)
Retrieving Optical Concealment Depth of Underwater Target by Remote Sensing
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Because of the huge difference of optical characteristic between underwater target and Scchi-Disk, it was unscientific and inaccurate to estimate the optical concealment depth (OCD) of underwater target using Scchi-Disk depth (SD). A method to determine the optical concealment depth of underwater target by satellite reBecause of the huge difference of optical characteristic between underwater target and Scchi-Disk, it was unscientific and inaccurate to estimate the optical concealment depth (OCD) of underwater target using Scchi-Disk depth (SD). A method to determine the optical concealment depth of underwater target by satellite remote sensing of ocean color is proposed. The influence of underwater target on light transmission in the water was analyzed on the foundation of the concept of underwater target optical concealment depth, and the semi-analysis transform model of the Scchi-Disk depth and underwater target optical concealment depth was obtained based on the transfer equation of contrast. Then the model of retrieving the optical concealment depth of underwater target by remote sensing of ocean color was setup. Finally, an in-situ experiment was implemented, and the results of experiment showed that the black model error of theoretical and experimental data was less than 30%, while for the white mode the error was less than 20%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 699 (2007)
Laser Doppler Vibrometer for Acousto-Optic Communication
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
This paper introduces the application background for developing an laser Doppler vibrometer (LDV) for underwater acoustic communication and expounds the principle of laser Doppler vibrometer and two coherent detection methods. Using the way of homodyne coherent detection, a fiber laser Doppler vibrometer is designed anThis paper introduces the application background for developing an laser Doppler vibrometer (LDV) for underwater acoustic communication and expounds the principle of laser Doppler vibrometer and two coherent detection methods. Using the way of homodyne coherent detection, a fiber laser Doppler vibrometer is designed and completed. To prove the system can be used in underwater acousto-optic communications, with this system, the acoustic frequency and intensity of underwater sound source are detected. Through the analysis of experimental data, two conclusions are gotten: first, the system is able to detect the acoustic frequency of underwater sound source, the standard deviation of measuring ten acoustic frequencies near the frequency of 7 kHz is less than 8 Hz; second, the signal intensity of system detection is an exponential function of acoustic press level of underwater sound source. For the acoustic band of 3.5 kHz and 7 kHz used in underwater communications, the smallest sound press level of detection reached 146.2 dB and 150.8 dB respectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 703 (2007)
Optical Communication
A New Family of Two-Dimensional Optical Orthogonal Codes and Its Performance Analysis
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A new two-dimensional (2D) optical orthogonal code (OOC) constructed using OOC for time spreading and one-coincidence sequence (OCS) for wavelength hopping named OOC/OCS is presented. Compared with other 2D OOC, the number of wavelengths for OOC/OCS is not limited to a prime number or its power. OOC/OCS can be construcA new two-dimensional (2D) optical orthogonal code (OOC) constructed using OOC for time spreading and one-coincidence sequence (OCS) for wavelength hopping named OOC/OCS is presented. Compared with other 2D OOC, the number of wavelengths for OOC/OCS is not limited to a prime number or its power. OOC/OCS can be constructed flexibly, and also can use available wavelengths adequately. Auto-correlation and cross-correlation performances of OOC/OCS are analyzed, and the mean value of cross-correlation is also deduced. In the end, the performance of OOC/OCS with different parameters is analyzed and discussed, according to different parameters of multi-wavelength optical code division multiple access (MW OCDMA) system. Given OCS and code weight w, bit error ratio (BER) of OCDMA system is decreased when code length L is increased. Given OOC and code length N, BER of OCDMA system is decreased when the number of wavelengths is increased..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 667 (2007)
A Variable Optical Attenuator Based on the Photonic Crystal Waveguide
[in Chinese], [in Chinese], and [in Chinese]
A novel variable optical attenuator (VOA) based on the photonic crystal (PC) waveguide infiltrated with liquid crystals is demonstrated. The PC waveguide decrement is controlled by adjusting rotation angle of the liquid cyrstals orientation vector. And the VOA properties are numerically investigated by using the finiteA novel variable optical attenuator (VOA) based on the photonic crystal (PC) waveguide infiltrated with liquid crystals is demonstrated. The PC waveguide decrement is controlled by adjusting rotation angle of the liquid cyrstals orientation vector. And the VOA properties are numerically investigated by using the finite difference time domain (FDTD) method. Numerical simulation shows that the attenuator in the PC waveguide can be changed based on the orientation of liquid crystals by adjusting the applied field. Furthermore, the attenuator lies in 0.5～25.4 dB with rotation angle of the liquid crystals varying from 0° to 90°, the insertion loss is less than 0.2 dB, and the size is in micron dimension..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 671 (2007)
10 GHz-Spaced over 1100 Channel Flat Supercontinuum Source Generated in a Microstructure Fiber
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The generation of a flat supercontinuum (SC) spectrum of over 100 nm in the 1.55 μm region by injecting 1.6 ps, 10-GHz repetition rate optical pulses into an 80-m-long dispersion-flattened highly nonlinear microstructure fiber (HNL-MF) is demonstrated. The experimental microstructure fiber with a nonlinearity of ～11 W-The generation of a flat supercontinuum (SC) spectrum of over 100 nm in the 1.55 μm region by injecting 1.6 ps, 10-GHz repetition rate optical pulses into an 80-m-long dispersion-flattened highly nonlinear microstructure fiber (HNL-MF) is demonstrated. The experimental microstructure fiber with a nonlinearity of ～11 W-1·km-1 has small normal dispersion and is characterized by flattened chromatic dispersion. The chromatic dispersion is about -0.58 ps·nm-1·km-1 at 1550 nm, and it varies less than 1.5 ps·nm-1·km-1 between 1500 and 1650 nm. The generated flat broadband supercontinuum ranging from 1503 to 1593 nm has the flatness of ±2.5 dB. This flat broadband supercontinuum can simultaneously supply more than 1100 multi-wavelength channels with 10-GHz spacing. The multi-wavelength pulse trains at 10 Gbit/s based on spectral slicing are also demonstrated. Such supercontinuum source has important applications, such as wavelength division multiplexing optical communication system and optical wavelength convertor..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 5, 675 (2007)
Reviews
Femtosecond Laser Micromachining: Frontier in Laser Precision Micromachining
[in Chinese], and [in Chinese]
Femtoseond laser micromachining enables fabrication of true three-dimensional (3D) microstructures with high precision and low heat effect and damage threshold, showing unique advantages over the traditional laser micromachining technology. We first review the histories of laser microprocessing and ultra-short pulse laFemtoseond laser micromachining enables fabrication of true three-dimensional (3D) microstructures with high precision and low heat effect and damage threshold, showing unique advantages over the traditional laser micromachining technology. We first review the histories of laser microprocessing and ultra-short pulse laser technology, and then outline the mechanisms of the interactions of ultra-short laser pulse with metals and transparent media. Next, we introduce several major technical approaches in the field of femtosecond laser micromachining such as femtosecond laser direct writing, multi-beam interference and projection patterning, as well as their applications in fabrication of 3D integrated optical devices, microfluidic chips, and chemical and biological sensors, etc. Lastly, we highlight the opportunities and challenges in the field, and suggest some directions for the future research..
Chinese Journal of Lasers
- Publication Date: Apr. 07, 2020
- Vol. 34, Issue 5, 595 (2007)
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