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Switchable multi-wavelength and tunable wavelength spacing erbium-doped fiber laser based on a phase-shifted fiber Bragg grating combined with a Mach-Zehnder interferometer
摘要： A switchable multi-wavelength fiber laser with tunable wavelength spacing is proposed. It is based on a structure filter composed of a phase-shifted fiber Bragg grating (PSFBG) and a Mach-Zehnder interferometer (MZI), and the MZI is fabricated by splicing a section of polarization-maintaining fiber with two segments of multi-mode fibers. By adjusting the variable optical attenuator in the cavity and slightly changing the temperature, stable single-, dual-, triple- and quadruple-wavelength emissions can be obtained. The minimum wavelength spacing of adjacent peaks is 0.176 nm, and the maximum is 17.86 nm. The laser line emissions can be switched from 1527.684 nm to 1550.224 nm with optical signal to noise ratio of more than 50 dB. The maximum wavelength fluctuation of the fiber laser is less than 0.025 nm over 50 min. When the strain applied to the filter is changed, the tunable wavelength spacing can be achieved. The wavelength spacing of dual-wavelength laser can be continuously tuned from 21.82 nm to 22.69 nm by applying strain of 0–258 με to the filter.
关键词： Tunable,Switchable multi-wavelength,Phase-shifted fiber Bragg grating,Fiber laser
更新于2025-11-28 14:24:03
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - All-Fiber 2.07 μm Distributed Feedback Laser Based on π-Phase-Shifted FBG Inscribed in Heavily Doped Holmium Fiber by Femtosecond Laser Pulses
摘要： Distributed-feedback (DFB) fiber laser is a versatile source of low-noise single-frequency radiation that finds applications in spectroscopy, optical communications and sensing devices. Depending on the active medium, different lasing wavelengths can be obtained: 1.03–1.12 μm for Yb, 1.53–1.62 μm for Er, and 1.73–1.93 μm for Tm-doped fibers. Special fiber Bragg grating (FBG) with a length of 20–70 mm and phase shift in the structure, directly written in an active medium, serves as distributed feedback cavity of this type of laser. Commonly, special UV photosensitive fibers and phase masks inscription technique are used for an FBG fabrication. Alternative femtosecond (fs) point-by-point technique [1] has a number of advantages as compared to UV-based ones: 1) wide variety of active fibers can serve as a host material for an FBG, thanks to the nonlinear mechanism of fs pulses absorption, 2) FBG period can be easily tuned by controlling fs pulses frequency and velocity of fiber translation during the inscription process, 3) each fiber grating “pitch” can be written independently, which means that phase shift with an exact value and position along FBG can be introduced. Despite the number of publications dealing with holmium fiber lasers [2], there no publications devoted to DFB ones. At the same time, such type of laser sources has a great potential as a master oscillator in all-fiber coherent beam combination systems [3]. We report on the creation of holmium-doped DFB fiber laser with a wavelength of 2.07 μm operating in single-frequency regime (Fig. 1a). The laser is based on custom-made single-mode holmium-doped fiber having absorption coefficient about 43 dB/m at 1.125 μm, which is the wavelength of pump Yb fiber laser. 42-mm π-phase-shifted FBG was directly inscribed in the active fiber by femtosecond IR laser pulses and served as distributed feedback cavity of the laser. Lasing threshold was reached at 350 mW pump power, and output power exceeded 36 mW at pump power of 4.8 W (Fig. 1b). Single-polarization mode operation was observed with linewidth of ~10 kHz. Additionally to the room-temperature operation regime we will present and discuss the laser operation regimes at cryogenic temperature (77 K), as well as high-temperature (>400 K). To the best of our knowledge, it is the first realization of all-fiber DFB laser based on holmium active medium.
关键词： femtosecond laser pulses,holmium-doped fiber,single-frequency radiation,Distributed-feedback fiber laser,π-phase-shifted FBG
更新于2025-09-23 15:19:57
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Performance Analysis of Single-Stage LED Buck Driver Topologies for Low-Voltage DC Distribution Systems
摘要： The demand for lean protein is the main reason for raising domesticated birds in poultry farms for the purpose of farming meat or eggs for food. In these poultry farms, artificial lighting system is an essential factor for the success of the commercial production of egg layers and broilers. Lighting loads connected to the existing AC system requires DC power. Nearly 25% of the total power consumed in India is by lighting loads. Therefore, low-voltage DC distribution system is the new requirement of electrical network to improve energy conservation. In this paper, an energy efficient single-stage LED driver topology is proposed as a better alternative to fluorescent lights used in poultry farms. The proposed topology is a phase-shifted buck converter with reduced size of passive components. The converter is mathematically modelled and designed for a power of 24 W LED lights. An experimental prototype is developed for the proposed converter and the results are validated in terms of cost, energy savings, and energy efficiency with various other LED driver topologies like conventional buck converter and interleaved buck converter. Further to justify the outcome of the proposed LED driver, a case study is also done for poultry farms.
关键词： energy savings,Phase-Shifted Buck Converter (PSBC),dimming control,digital controller,LED driver
更新于2025-09-19 17:13:59
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Tuneable Q-Factor of MEMS Cantilevers with Integrated Piezoelectric Thin Films
摘要： In atomic force microscopes (AFM) a resonantly excited, micro-machined cantilever with a tip is used for sensing surface-related properties. When targeting the integration of AFMs into vacuum environments (e.g., for enhancing the performance of scanning electron microscopes), a tuneable Q-factor of the resonating AFM cantilever is a key feature to enable high speed measurements with high local resolution. To achieve this goal, in this study an additional mechanical stimulus is applied to the cantilever with respect to the stimulus provided by the macroscopic piezoelectric actuator. This additional stimulus is generated by an aluminum nitride piezoelectric thin film actuator integrated on the cantilever, which is driven by a phase shifted excitation. The Q-factor is determined electrically by the piezoelectric layer in a Wheatstone bridge configuration and optically verified in parallel with a laser Doppler vibrometer. Depending on the measurement technique, the Q-factor is reduced by a factor of about 1.9 (electrically) and 1.6 (optically), thus enabling the damping of MEMS structures with a straight-forward and cheap electronic approach.
关键词： phase shifted excitation,vacuum,electronically tuneable Q-factor,AFM,MEMS cantilever,AlN,piezoelectric,peak shaping
更新于2025-09-09 09:28:46
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Design and Analysis of a Novel Phase-Shifted Bragg Grating for Bloch Surface Waves
摘要： A novel phase-shifted Bragg grating (PSBG) for Bloch surface waves (BSWs) propagating along the interface between a semiconductor thin layer and a multilayer stack is proposed. This structure is composed of a set of a special ridge fabricated on a multilayer stack supporting a Bloch surface wave. The multilayer stack is periodic, with the unit cell composed of two layers with different materials and thicknesses. The light con?nement capability and transmission properties of the proposed structure are investigated in the wavelength range of 1450–1650 nm by using the ?nite-element method and ?nite-difference time-domain method. Compared to existing PSBG structures based on surface plasmon polaritons waves, the proposed con?guration does not include any metal and the absorption losses upon propagation of the surface wave are negligibly small. Simulation results also indicate that the proposed structure exhibits outstanding transmission properties. The proposed PSBG for BSWs could be applied in narrow bandpass ?ltering, all optical computing, and enable on-chip integration photonic circuits.
关键词： resonance domain.,guided waves,Bloch surface waves,Phase-shifted Bragg grating
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Atlanta, GA, USA (2018.10.31-2018.11.2)] 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Self-powered Gate Driver Design for a Gallium Nitride Based Phase Shifted Full Bridge DC-DC Converter for Space Applications
摘要： Radiation hardened Gallium Nitride (GaN) Field Effect Transistors (FETs) for space DC-DC converter applications have been released to the market recently. However; space qualified digital isolators with small propagation delays, fast rise and fall times, and high common mode transient immunity necessary for isolated GaN gate drivers are not currently available. In this work, a self-powered isolated GaN gate drive circuit for a Phase Shifted Full Bridge DC-DC converter for space applications is designed and tested. Signal isolation and energy transfer to bias GaN gate driver chips are achieved using pulse transformers. Operation is successfully verified in a converter using 200 V radiation hardened GaN FETs and delivering 400 W from a 100 V DC bus. Experimental results show the effects that the voltage rate of change of the switch nodes have on dead time accuracy for the top switches in the proposed implementation, and a description of how better dead time accuracy was obtained is included.
关键词： rad-hard,radiation,hardened,phase-shifted,Gallium,self-powered,pulse transformer,space,gate driver,DC-DC,GaN
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Atlanta, GA, USA (2018.10.31-2018.11.2)] 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Design Considerations for a Gallium Nitride Based Phase Shifted Full Bridge DC-DC Converter for Space Applications
摘要： The main design considerations for the practical implementation of a Phase Shifted Full Bridge DC-DC converter with synchronous rectification using recently released radiation hardened Gallium Nitride (GaN) Field Effect Transistors (FETs) for space applications are presented in this paper. A brief survey comparing the benefits of GaN FETs for space power applications against current Silicon power transistor technology is conducted. Also, the main drivers for topology selection, and design considerations to implement the selected topology for space applications resulting from the limited radiation hardened components available today are described in detail. In addition, power loss breakdown from analysis and final design choices are presented. A converter was designed to validate design based on the considerations outlined. The implemented converter operates from a 100 V DC bus and delivers 400 W from a fixed 20 V output at more than 95% efficiency.
关键词： rad-hard,converter,space,radiation hardened,full bridge,phase shifted,DC-DC,GaN
更新于2025-09-04 15:30:14