A compact Ti:sapphire femtosecond pulse amplifier without stretcher at high repetition rate

We report a simple approach to amplify Ti:sapphire femtosecond pulses to moderate energy levels by achirped regenerative amplifier. The seed pulses are broaden naturally because of the material dispersionof system components in regenerative cavity. The off-focusing Ti:sapphire crystal avoids effectively theoptical damage. It sustains amplification over a wavelength range from 775 nm to more than 810 nmwith a birefringent filter and an oscillation bandwidth of 7.7 nm, and produces 2.1 ps chirped outputpulse energy of 100μJ at 1.1-mJ pumping energy. This system shows good performances in stability andefficiency with the benefits of two thin-film polarizers and TEM00 mode pumping laser.     

Period doubling of a femtosecond Ti:sapphire laser by total mode locking

Period doubling of an 84-MHz repetition-rate Kerr-lens mode-locked Ti:sapphire laser operated at 830 nm and producing ~300mW of average power has been observed and explained in terms of total mode locking of TEM(00) and TEM(01) modes in an effective confocal cavity. This configuration leads to a spatial sweeping action of a single-peaked pulse at 42 MHz. Period tripling and quadrupling is observed for certain cavity configurations.     

LD泵浦Nd:YVO4双波长运转腔内和频491 nm激光器

分析了Nd:YVO4激光器实现双波长运转及腔内和频的条件,利用一种LD泵浦Nd:YVO4晶体产生1 064 nm和914 nm双波长激光束,采用一个线性平凹腔结构,利用腔内Ⅰ类临界相位匹配LBO和频,获得了连续波输出的全固态激光器。实验采用端面结构,在5.0 W的808 nm泵浦功率下,获得了最高功率为2.5 mW连续波TEM00的激光输出,光-光转换效率为0.05%。     

Spatial and temporal filtering of a 10-W Nd:YAG laser with a Fabry--Perot ring-cavity premode cleaner

We report on the use of a fixed-spacer Fabry-Perot ring cavity to filter spatially and temporally a 10-W laser-diode-pumped Nd:YAG master-oscillator power amplifier. The spatial filtering leads to a 7.6-W TEM (00) beam with 0.1% higher-order transverse mode content. The temporal filtering reduces the relative power fluctuations at 10 MHz to 2.8x10(-9)/ radicalHz, which is 1 dB above the shot-noise limit for 50 mA of detected photocurrent.     

Ti:sapphire laser intracavity difference-frequency generation of 30 mW cw radiation around 4.5 μm

A cw mid-IR coherent source based on difference-frequency generation is designed and characterized. For mid-IR generation, a periodically poled MgO:LiNbO(3) crystal is placed inside a compact Ti:sapphire laser cavity. This provides high-power pump radiation for the nonlinear process. Optical injection by an external-cavity diode laser ensures single-frequency operation of the Ti:sapphire laser, while signal radiation is provided by a fiber-amplified Nd:YAG laser. Mid-IR radiation can be generated with 3850-4540 nm tuning range, narrow linewidth, Cs-standard traceability, and TEM(00) spatial mode. 30 mW power is obtained at 4510 nm.     

级联光栅结合Sagnac环的可调谐光纤激光器

提出并验证了一种单-双波长可调谐掺铒光纤激光器。利用级联光纤布拉格光栅(Cascaded Fiber Bragg gratings,Cascaded FBGs)结合Sagnac环结构所产生的复合滤波效应,实现较高精细度滤波,并通过调节环内偏振控制器(Polarization Controller,PC),引入双折射效应,得到波长可调谐的光纤激光器。基于耦合模理论并使用传输矩阵法对该结构的传输特性进行了分析,在此基础上搭建实验系统,验证了理论分析的正确性。实验结果表明:通过调节PC,激光器输出激光的波长范围约为1 555.644～1 556.112 nm,双波长间隔的可调范围约为0.108～0.452 nm,单-双波长的边模抑制比(SMSR)均高于40 dB;在稳定性测试中,输出单-双波长激光的波长最大漂移量小于0.008 nm。该方法具有结构简单、调谐方便、易于实现且精细度较高的优点,可应用于密集波分复用及全光通信系统等领域。     

Photonic generation of microwave signals using dual-wavelength single-longitudinal-mode fiber lasers

Photonic generation of microwave signals is demonstrated with a dual-wavelength single-longitudinal-mode erbium-doped fiber ring laser. Microwave signal with a frequency of 21.07 GHz is obtained by aligning the reflection band of a uniform fiber Bragg grating to the two transmission peaks within a fiber Bragg grating-based Fabry-Perot filter. Stable dual-wavelength single-longitudinal-mode operation is guaranteed by means of the combined filtering effect of a saturable absorber and the Fabry-Perot filter. This approach provides an effective solution to the photonic generation of high-frequency microwave signals.     

基于古斯-汉欣位移的双通道窄带滤波器

本文利用光束在对称金属包覆波导表面反射得到的异常大的古斯-汉欣(Goos-Hänchen)位移,通过实验实现了双通道窄带滤波.当入射激光波长为859.60 nm时,两通道滤波的峰值位置分别为859.604 nm和859.688 nm,峰值半宽(FWHM)为0.036 nm,而消光比达到15.3 dB.峰值波长可通过改变入射角或小孔位置实现调谐. 关键词： 古斯-汉欣(Goos-Hä nchen)位移 光波导 双通道 滤波器     

Ultrafast mode-locked dual-wavelength thulium-doped fiber laser using a Mach-Zehnder interferometric filter

A simple and robust method to generate a dual-wavelength mode-locked laser using a tunable Mach-Zehnder filter (TMZF) and a single-wall carbon nanotube (SWCNT) based saturable absorber (SA) is proposed and demonstrated. The proposed laser uses a thulium-doped fiber for lasing in the two-micron region and exploits the interferometric spectrum of the TMZF to produce dual peaks with nearly equal magnitude. SWCNT based SA enables mode-locking at a threshold value of 150.4?mW with distinct dual-wavelength peaks at 1919.2?nm and 1963.7?nm. The peaks have a calculated pulse width of 1.8?ps and 1.6?ps, respectively with a repetition rate of 9.1?MHz with a relatively high optical-signal-to-noise ratio value of 59.1?dB. The output is also observed to remain unchanged over time, indicating high stability. The proposed laser has a promising application, particularly in ultrafast gas molecular spectroscopy and sensing.     

A novel dual-wavelength fiber Bragg grating and its application in fiber ring laser

A novel method for fabricating dual-wavelength fiber Bragg gratings (FBGs) by using one phase mask is developed. The method is based on a double-exposure technique. Our technique lends itself to writing gratings with controllable reflectivity and separation of two Bragg wavelengths. A grating with two equal transmission peaks of 20.25 dB is obtained by this method and the separation of the two Bragg wavelengths is about 0.8 nm. With the grating, we demonstrate a dual-wavelength erbium-doped fiber ring laser whose interval of the two peaks is 0.8 nm. The laser's peak powers can get 3.1 mW above and have a good stability.     

Tunable microwave photonic notch filter using a dual-wavelength fiber laser with phase modulation

A novel tunable microwave photonic notch filter using a phase-modulated dual-wavelength fiber laser is presented. A stable dual-wavelength erbium-doped fiber laser with a linear cavity is formed by a polarization-maintaining uniform fiber Bragg grating (PM-FBG) and a polarization maintaining linearly chirped fiber Bragg grating (PM-LCFBG), both of which were fabricated on a high-birefringence (Hi-Bi) fiber. It is found that a stable room-temperature dual-wavelength operation can be achieved due to the presence of two reflection peaks arising from the orthogonal states of polarization (SOP) of the PM-FBG. Experimental results show stable dual-wavelength lasing operation with a wavelength separation of ∼0.36 nm and a large optical signal-to-noise ratio (OSNR) of over 40 dB under room temperature. The dual-wavelength fiber laser is combined with a phase modulator and a segment of single-mode fiber (SMF) as a dispersive device to form a tunable microwave photonic notch filter. By stretching the PM-FBG to tune the wavelength separation of the dual-wavelength fiber laser, a tunable microwave photonic notch filter with various free spectral ranges (FSRs) and a rejection ratio greater than 35 dB was developed.     

Channel waveguides in Ca4GdO(BO3)3 fabricated by He+ implantation for blue-light generation

Blue light at 405 nm is generated by frequency doubling of a Ti:sapphire tunable laser in He(+)-implanted channel waveguides in gadolinium calcium oxoborate crystal. A conversion efficiency of approximately 2% W(-1) cm(-2) is achieved between TM00 fundamental and TE01 harmonic modes.     

Switchable single-longitudinal-mode dual-wavelength erbium-doped fiber ring laser incorporating a semiconductor optical amplifier

We propose and demonstrate a novel single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber ring laser incorporating a semiconductor optical amplifier. The SOA biased in its low-gain regime greatly reduces the gain competition of the two wavelengths. The stable SLM operation is guaranteed by a passive triple-ring cavity and a fiber Fabry-Perot filter. The dual-wavelength output with a 40 GHz wavelength spacing is switchable in the range of 1533-1565.4 nm.     

Tunable dual-wavelength fiber laser based on a polarization-maintaining fiber Bragg grating and a Hi-Bi fiber optical loop mirror

We demonstrate experimentally the operation of a linear cavity dual-wavelength fiber laser using a polarization maintaining fiber Bragg grating (PM-FBG) as an end mirror that defines two closely spaced laser emission lines. The PM-FBG is also used to tune the laser wavelengths. The total tuning range is ∼8 nm. The laser operates in a stable dual-wavelength mode for an appropriate adjustment of the cavity losses for the generated wavelengths. The high birefringence (Hi-Bi) fiber optical loop mirror (FOLM) is used as a tunable spectral filter to adjust the losses. The FOLM adjustment was performed by the temperature control of the Hi-Bi fiber.     

Self-starting Ti:sapphire holographic laser oscillator

We demonstrate, for the first time to our knowledge, operation of a holographic laser oscillator that uses laser-pumped Ti:sapphire (Ti(3+) : Al(2)O(3)) as the gain medium. The device is self-starting and self-adaptive by virtue of spontaneous gain-grating formation. We present experimental results of the system that include gain-switched pulses of 25-60-ns duration in a TEM(00) mode and as much as 11 mJ of output energy from a plane output coupler and 47 mJ from an intracavity polarizer port.     

High-power Er:YAG laser with quasi-top-hat output beam

A simple method for simultaneously exciting the fundamental (TEM00) transverse mode and first order Laguerre-Gaussian (LG01) donut mode in an end-pumped solid-state laser to yield a quasi-top-hat output beam is reported. This approach has been applied to an Er:YAG laser, in-band pumped by an Er,Yb fiber laser, yielding 9.6 W of continuous-wave output at 1645 nm in a top-hat-like beam with beam propagation factor (M2)<2.1 for 24 W of incident pump power at 1532 nm. The corresponding slope efficiency with respect to incident pump power was 49%. The prospects of further scaling of output power and improved overall efficiency are considered.     

Er-doped photonic crystal fiber amplifier with 70 W of output power

We report for the first time, to the best of our knowledge, on a large mode area Er-doped photonic crystal fiber laser system. The fiber core had a diameter of 40 μm and NA of <0.04 leading to a mode field diameter of about 31 μm around 1550 nm wavelength. More than 70 W of single-frequency output power at 1556 nm could be extracted using a master-oscillator power-amplifier scheme. Near diffraction limited output beam quality has been verified by measuring the TEM(00) content with a nonconfocal scanning ring cavity.     

利用倾斜光纤光栅的可开关双波长光纤激光器

报导了一种在四波混频作用下利用倾斜光纤布拉格光栅进行波长选择的可开关双波长掺铒光纤激光器。通过将倾斜光纤光栅与单模光纤进行横向错位焊接,使光栅的反向LP01和LP11两个模式具有相近的有效反射率,从而可以用来进行激光器的双波长选择。接入腔内的一段高非线性光子晶体光纤引入的四波混频效应克服了模式竞争,使得双波长激光在室温下稳定振荡。腔内起偏器和偏振控制器的联合作用可产生依赖于波长的损耗,以补偿光纤光栅两反射峰峰值的大小差异。基于以上原理,通过调节腔内的偏振态,该激光器实现了室温下稳定的双波长输出,也实现了在两波长之间的转换。两波长激光均有超过45 dB的信噪比,最大的功率波动为0.8 dB     

LD泵浦Nd:YVO_4双波长运转腔内和频491nm激光器

分析了Nd:YVO4激光器实现双波长运转及腔内和频的条件,利用一种LD泵浦Nd:YVO4晶体产生1 064 nm和914 nm双波长激光束,采用一个线性平凹腔结构,利用腔内Ⅰ类临界相位匹配LBO和频,获得了连续波输出的全固态激光器。实验采用端面结构,在5.0 W的808 nm泵浦功率下,获得了最高功率为2.5 mW连续波TEM00的激光输出,光-光转换效率为0.05%。     

Dual-wavelength S-band erbium-doped fiber double-ring laser

We propose and demonstrate an S-band CW dual-wavelength erbium-doped fiber (EDF) dual-ring laser using a compound-ring filter (CRF) with various coupling losses inside the gain cavity. Employing a ring filter combined within the cavity, the fiber laser can lase a dual wavelength without any filter inside the ring loop. The dual-wavelength output exhibits a good performance having optical side-mode suppression ratios (SMSRs) of 31.6 and 31.8 dB and output powers of ?9.6 and ?9.3 dBm at 1505.58 and 1506.43 nm, respectively, when the coupling loss is 30% inside the cavity. In addition, the output stabilities of the dual-wavelength laser have also been analyzed.