Cascaded continuous-wave singly resonant optical parametric oscillator pumped by a single-frequency fiber laser

We present a cascaded continuous-wave singly resonant optical parametric oscillator (SRO) delivering idler output in mid-IR and terahertz frequency range. The SRO was pumped by an ytterbium-doped fiber laser with 27 W linear polarization pump powers, and based on periodically poled MgO:LiNbO₃ crystal (PPMgLN) in two-mirror linear cavity. The PPMgLN is 50 mm long with 29.5 μm period. The idler power output at 3811 nm was obtained 2.6 W. The additional spectral components that have been attributed to cascaded optical parametric processes are described at increasing pump levels. Besides the initial signal component at about 1476.8 nm, further generated wavelengths with frequency shifts about 47 cm^?1, 94 cm^?1 and 104 cm^?1 were observed. It was speculated that the idler waves lie in the terahertz (THz) domain from the observed results.     

Femtosecond mode-locked holmium fiber laser pumped by semiconductor disk laser

We report on a 2085 nm holmium-doped silica fiber laser passively mode-locked by semiconductor saturable absorber mirror and carbon nanotube absorber. The laser, pumped by a 1.16 μm semiconductor disk laser, produces 890 femtosecond pulses with the average power of 46 mW and the repetition rate of 15.7 MHz.     

Miniaturized fiber inline Fabry-Perot interferometer fabricated with a femtosecond laser

We report a miniaturized inline Fabry-Perot interferometer directly fabricated on a single-mode optical fiber with a femtosecond laser. The device had a loss of 16 dB and an interference visibility exceeding 14 dB. The device was tested and survived in high temperatures up to 1100 degrees C. With an accessible cavity and all-glass structure, the new device is attractive for sensing applications in high-temperature harsh environments.     

Raman fiber laser pumped by a semiconductor disk laser and mode locked by a semiconductor saturable absorber mirror

A 1.6μm mode-locked Raman fiber laser pumped by a 1480nm semiconductor disk laser is demonstrated. Watt-level core pumping of the single-mode fiber Raman lasers with low-noise disk lasers together with semiconductor saturable absorber mirror mode locking represents a highly practical solution for short-pulse operation.     

Wavelength-tunable erbium fiber ring laser in single-frequency operation utilizing Fabry-Perot laser with Sagnac cavity

We propose and demonstrate experimentally a stabilized and wavelength-selective erbium-doped fiber ring laser in single-longitudinal-mode operation with Fabry-Perot laser diode (FP-LD) and using a tunable bandpass filter (TBF) inside and outside a Sagnac ring cavity. The side-mode suppression ratios of 21 dB and 36.5 dB and the output power of -3.6 dB m and -8.7 dB m in the wavelengths of 1524.45-1562.35 nm and 1531.07-1562.35 nm with the tuning step of 1.4 nm can be achieved when the TBF outside and inside Sagnac loop, respectively. The output wavelength variation of zero and the output power fluctuation of <0.1 dB are also obtained. Moreover, the transmission efficiency of the ring laser has also been performed experimentally under a 1.25, 2.5 and 10 Gb/s external modulation, respectively.     

Stable wavelength-tuning laser in single-frequency by optical-injected Fabry-Perot laser diode and RSOA for long fiber distance propagation

In this demonstration, we propose and experimentally investigate a stable wavelength-tuning laser configuration by using self-seeded Fabry-Perot laser diode (FP-LD) and external-injected reflective semi-conductor optical amplifier (RSOA). Here, this proposed laser can be tuned in the wavelength range of 1534.05 to 1553.00 nm with a 1.1 nm tuning-step. And the output powers and side-mode suppression ratios (SMSRs) are measured at −5.3 to 4.6 dBm and 31.2 to 50.1 dB/0.05 nm, respectively. And, the proposed laser also can be directly modulated at 2.5 Gb/s on-off keying (OOK) modulation format and propagates 75 km single-mode fiber (SMF) with no optical amplifier and dispersion compensation.     

Hysteresis and nonlinear thermooptic waves in a semiconductor Fabry-Perot interferometer

We propose and demonstrate the existence of temperature hysteresis phenomena in a Fabry-Perot interferometer, resulting from a change in the refractive index of the interferometer material when heated by laser radiation. We also demonstrated theoretically that temperature multistability in the distributed interferometric system may cause the emergence of nonlinear thermooptic switching waves and found an approximate expression for the propagation velocity of such waves. We present the results of experimental observations of temperature multistability and thermooptic switching waves in a germanium Fabry-Perot interferometer illuminated by CO₂-laser radiation.     

Random distributed feedback fiber laser pumped by an ytterbium doped fiber laser

A random distributed feedback fiber laser operating at 1115 nm has been demonstrated experimentally in standard communication optical fibers by using a LD-pumped Yb-doped fiber laser as the pump source. We have studied the effect of different fiber spans on this new type of random fiber laser output power. It is shown that the generation power is the highest up to 198 mW in a 50 km fiber span. The slope efficiency is more than 28.7%. Stable, high-power continuous-wave (CW) lasing can be generated when the pump power is 3.6 W. The threshold power has also been calculated which well proves a random fiber laser operating via Rayleigh scattering, amplified through the Raman scattering.     

Generation of millimeter-wave sub-carrier optical pulse by using a Fabry-Perot interferometer

A novel scheme is proposed to transform a Gaussian optical pulse to a millimeter-wave (mm-wave) frequency modulation pulse by using a Fabry-Perot interferometer (FPI) for radio-over-fiber (ROF) system.It is shown that modulation frequency of mm-wave is determined by the optical path of the Fabry-Perot (F-P) cavity, and amplitude decay time and energy transfer efficiency are related to the reflectivity of the F-P cavity mirror. The effect of pulse train extension on inter-symbol interference is also discussed.     

Transformation of the spectrum of the longitudinal modes of a semiconductor laser on introduction of its radiation into fiber light guides

We investigated the influence exerted by the radius of the bend of fiber light guides with light-transmitting cores of different diameters on the transformation of the spectrum of longitudinal modes of the semiconductor laser radiation introduced into them. It is shown that the bended segment of the light guide acts as a spectrum selector, and the spectral composition of the radiation at the output of a light guide is different in different spots of the speckle structure. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 260–263, March–April, 2000.     

Mutual injection locking of an erbium-doped fiber laser and a fiber-pigtailed Fabry-Perot laser diode

Mutual injection locking of a fiber-pigtailed Fabry-Perot laser diode (FPLD) and a closed-loop erbium-doped fiber-amplifier-based laser (EDFL) system are studied. A single FPLD longitudinal mode can be lasing in the EDFL-FPLD link, with a reduced linewidth of <0.017 nm and an improved sidemode-suppressing ratio of 50 dB. The FPLD's optimized current range is below threshold within 10%, and its required feedback-injecting power is 12.4 microW (corresponding to 0.03% of the EDFL output power). The maximum detuning ranges of the current and temperature of the FPLD that preserve the narrow linewidth and the highest sidemode-suppressing ratio of the EDFL-FPLD link are 2.4 mA and 2.2 degrees C, respectively. The power dissipated by the EDFL-FPLD link is 20% more than that of the free-running EDFL.     

用于单频光纤激光器的光纤光栅双腔Fabry-Perot结构传输谱特性理论研究

分析了基于光纤光栅的全光纤型双腔Fabry-Perot(F-P)结构传输谱特性. 理论推出了两腔F-P结构传输率具体计算公式,给出在光栅中心波长处产生单谐振传输峰时,腔长与组成光栅反射率各需满足的条件. 基于理论分析结果,分两部分数值模拟了对称及非对称两腔F-P结构传输谱,讨论了计算结果并给出定性的解释,总结了腔长及光栅长度、折射率调制深度的设计原则. 结论表明,当单腔F-P结构腔长增大到阻带内出现多个谐振峰时,通过合理选取两腔结构的腔长及光栅参数,双腔F-P结构能够在整体长度不变条件下,抑制中心波长两侧的次谐振峰,而中心波长处的主谐振峰不受影响. 关键词： 光纤光栅 Fabry-Perot结构 光纤激光器     

Calculation of laser modes in an active Perot-Fabry-Interferometer

The mode structure and the diffraction losses of a Perot-Fabry-Interferometer filled with an active material are calculated analytically with aGreen's function method. The active material is described by a complex susceptibility. The mode pattern and the diffraction losses derived here are in good agreement with the results of Fox andLi, who obtained the mode pattern and the diffraction losses of the decaying modes of a Perot-Fabry-Interferometer by a machine calculation. Furthermore the case of different dielectric constants between the active material and the outer space and the example of a Perot-Fabry-Interferometer with infinite mirrors are discussed. Throughout the paper only a single mode is treated and it is assumed that the inversion in the active material is constant.     

Supercontinuum generation in standard single-mode fiber pumped by a nanosecond-pulse laser

We have experimentally investigated supercontinuum generation in a conventional single-mode fiber pumped with a nanosecond pulse source. The experimental results show that, when pump power increases, the spectral flatness is improved obviously and the spectral broadening only occurs in a red-shifted radiation rather than a blue-shifted radiation. A supercontinuum source is experimentally reported with a flatness of 4.7 dB over 180 nm (ranging from 1555 to >1735 nm) at pump power P _R = 5 W and is predicted to have the flatness of less than 1 dB at P _R > 8 W. The cascade of stimulated Raman scattering (SRS) together with soliton fission plays the key roles in supercontinuum generation.     

Generation of new longitudinal modes in an amplifying dye solution

A novel phenomenon is reported for the first time that the generation of the newlongitudinal modes in amplifying multi-longitudinal mode laser in a dye amplifier.The newmodes are located on the violet side within the gain band of the amplifing medium.The phe-nomenon is explained by the theory of third-order nonlinear polarization in the case of four-wave resonances.The intensity of the new modes created are comparable with or even higherthan that of the original modes.The effect can be expected to serve as a new method for ex-tention of spectral tuning ranges of laser.     

Supercontinuum generation in a standard fiber pumped by noise-like pulses from a figure-eight fiber laser

We report the experimental study of broadband spectrum generation in a piece of standard fiber (SMF-28) using as the pump a train of noise-like pulses, or sub-nanosecond packets of sub-ps pulses with randomly varying amplitudes. The pulses are generated by an erbium-doped figure-eight fiber laser, and present a wide (∼50 nm) optical spectrum, which represents a significant advantage to seed the generation of new frequencies. Another advantage of the pulses is their relatively large energy, as they are made up of a large number of ultrashort pulses. After amplification with an Erbium Doped Fiber Amplifier (EDFA), the pulses were injected in a 0.75 km length of SMF-28 fiber. We obtained experimentally at the end of the fiber an output signal spectrum extending from 1530 nm to at least 1750 nm (the upper limit of the spectrum analyzer) for pump pulses with an average power of 20.4 mW, corresponding to a few kilowatts peak power. The spectral broadening is due to Raman self-frequency shift (SFS). It is noteworthy that the spectrum of the newly created frequencies was extremely uniform over the range of measurement. Considering that the Raman shift is directly related to the pump pulse duration, spectral flatness is a direct consequence of the random distribution of amplitudes and durations of the pulses in the packet. Finally, the results show the capabilities of noise-like pulses from a fiber laser for applications in supercontinuum generation based on nonlinear phenomena such as Raman SFS.     

对光纤布拉格光栅法布里-珀罗腔纵模间隔问题的研究

对光纤布拉格光栅(FBG)法布里-珀罗(F-P)腔的透射特性进行了深入分析,指出了FBG F-P腔透射谱中纵模位置的影响因素,讨论了与普通F-P腔的联系和区别.应用光栅的有效镜面模型对FBG反射主瓣内反射系数的相位因子进行线性模拟,定义了FBG有效长度的概念并得出其表达式.提出将FBG的有效长度纳入到FBG F-P腔的等效腔长中,用等效腔长来计算FBG F-P腔中的纵模间隔.数值仿真和实验结果都表明,用等效腔长计算所得的纵模间隔与实际的FBG F-P腔中的纵模间隔符合很好,误差极小. 关键词： 光纤布拉格光栅 法布里-珀罗腔 纵模间隔 有效镜面模型     

Generation of twin beams from an optical parametric oscillator pumped by a frequency-doubled diode laser

Quantum-correlated twin beams were generated from a triply resonant optical parametric oscillator with an a-cut KTP crystal pumped by a frequency-doubled diode laser. A total output of 5.1 mW was obtained in the classical-nonclassical light-conversion system driven by a 50-mW diode laser at 1080 nm. A quantum-noise reduction of 4.3 dB (63%) in the intensity difference between the twin beams was successfully observed at the detection frequency of 3 MHz.