高次谐波锁模飞秒掺镱光纤激光器的噪声情况

高重复频率的飞秒激光在高速激光测距和三维成像等领域有着非常重要的作用。其中基于飞秒光纤激光器的高次谐波锁模是获得GHz量级以上高重复频率脉冲的重要手段之一。基于含腔内光栅对色散补偿的非线性偏振旋转（NPR）锁模的掺镱（Yb）光纤激光器,在180 mW泵浦光时获得了稳定的143 MHz基频锁模脉冲序列,当泵浦光功率升至1 W时获得了最高20次谐波（2.86 GHz）锁模脉冲序列输出。系统地对比研究了基频锁模与高次谐锁模状态下,脉冲重复频率精密锁定后的艾伦偏差和相位噪声,7次谐波锁模状态下重复频率锁定精度能够保持在10?13 Hz@1 s的稳定度,为高次谐波锁模飞秒激光脉冲序列用于精密测量提供了实验依据。     

有理数谐波锁模掺铒光纤环形激光器

在主动谐波锁模光纤环形激光器实验中获得数倍于调制频率ｆｍ的高重复率脉冲序列,其中ｆｐ＝２ｆｍ的输出脉冲序列极为稳定,所得的最高锁模脉冲重复频率ｆｐ＝４ｆｍ≈６ＧＨｚ。实验证实了一种被称之为有理数谐波锁模（ＲＨＭＬ—ＲａｔｉｏｎａｌＨａｒｍｏｎｉｃＭｏｄｅ－ｌｏｃｋｉｎｇ）新技术在较低的调制频率和极简单的腔构条件下也同样成立。实验观察到ＲＨＭＬ激光器允许失谐范围不小于±２ｋＨｚ,失谐比大于１０－６。     

Mode-locking at very high repetition rates more than terahertz inpassively mode-locked distributed-Bragg-reflector laser diodes

We propose a technique for achieving mode-locking at very high repetition rates more than terahertz with high output power using a distributed-Bragg-reflector (DBR) laser, including an intracavity saturable absorber. This method is based on harmonic passive mode-locking at high gain levels and the selectivity of harmonic numbers related to the spectrum-filtering property of the intracavity Bragg reflector. Transform-limited pulses at repetition rates from 500 GHz to 1.54 THz were generated with an output power exceeding 15 mW. We studied stability of harmonic pulses by using conventional self-consistent mode-locking equations. We also discuss the effect of the spectrum-filtering properties of the intracavity Bragg reflector to the characteristics of mode-locked pulses     

High-repetition-rate optical pulse generation using a rationalharmonic mode-locked fiber laser

Rational harmonic mode locking takes place in an actively mode-locked fiber laser when the modulation frequency f_m=(n+1/p)f_c, where n and p are both integers and f_c is the inverse of the cavity round-trip time, the 22nd order of rational harmonic mode locking has been observed when f_m ≈1 GHz. An optical pulse train with a repetition rate of 40 GHz has been obtained using a modulation frequency f_m=10 GHz. The theory of rational harmonic mode locking has also been developed. The stability of the mode-locked pulses is improved considerably when a semiconductor optical amplifier is incorporated into the fiber laser cavity. The supermode noise in the RF spectrum of a mode-locked laser is removed for a certain range of current in the semiconductor optical amplifier     

Mode-locked erbium-doped fiber ring laser using intracavity polarization-maintaining loop mirror

Erbium-doped fiber lasers at repetition rate of 40 and 80 GHz are demonstrated in an injection-locked and rational harmonic mode-locked ring cavity. The cavity has a polarization-maintaining loop mirror. The injection-locking pulse is generated at repetition rates of 20 and 40 GHz from another rational harmonic mode-locked fiber laser. When these pulses are injected into the second fiber laser, pulses at twice the repetition rates viz. 40 and 80 GHz are produced.     

石墨烯锁模的全保偏光纤激光器

报道了一种基于反射式石墨烯可饱和吸收镜锁模的全保偏掺铒光纤激光器。分别使用单层和十层石墨烯作为可饱和吸收器件,通过全保偏结构,避免了外界环境对腔内偏振态的影响,获得了高稳定性、高偏振度、易自启动的锁模脉冲输出,脉冲宽度分别为697 fs和502 fs。实验表明,十层石墨烯相比于单层石墨烯能够获得更窄的脉冲宽度,更高的峰值功率,具有好的锁模效果。研究同时发现,经十层石墨烯锁模,进一步提高泵浦功率,可在全保偏光纤腔中获得重复频率62.94 MHz的二阶谐波锁模脉冲输出。并通过非线性薛定谔方程对谐波锁模产生的机理进行了分析。这种基于反射式可饱和吸收镜的全保偏锁模光纤激光器有望成为实现基频锁模与谐波锁模可切换的单偏振激光源。     

5-GHz pulsed fiber Fabry-Pe/spl acute/rot laser mode-locked using carbon nanotubes

We demonstrate passive mode-locking of a short-cavity (/spl sim/2 cm) fiber Fabry-Pe/spl acute/rot laser by incorporating a carbon-nanotube-based saturable absorber. Stable pulses are generated with a pulsewidth as short as 0.68 ps at a repetition rate as high as 5.18 GHz. This is the smallest femtosecond fiber pulsed laser ever demonstrated to date.     

输出大啁啾脉冲的展宽脉冲锁模光纤激光器

报道了一种大啁啾脉冲输出的全光纤展宽脉冲锁模激光器,以非线性偏振旋转(NPR)实现自启动锁模。激光器其余部分为全单模光纤(SMF)结构,提供很大的正色散,光栅对提供色散补偿,输出展宽脉冲。实验中得到了重复频率36.96MHz,单脉冲能量1.81nJ的稳定锁模脉冲序列,使用频谱分析仪观测得到脉冲序列一次谐波信噪比(SNR)达到80dB。直接输出脉冲有很大的正啁啾,脉宽为2.17ps,经过腔外压缩可获得70fs的脉冲。这种能压缩到百飞秒量级的大啁啾脉冲非常适用于光纤啁啾脉冲放大(CPA)系统。     

"Rational harmonic mode-locking" in a phase-modulated fiber laser

The repetition rate multiplication was observed in a phase-modulated mode-locking fiber laser when the modulation frequency was detuned by a fraction of the fundamental frequency. This phenomenon is quite similar to the rational harmonic mode-locking in amplitude modulated lasers, which almost everybody believed could not exist when applying phase modulation. The harmonics of the amplified driving signal is the reason behind this phenomenon. Because most RF amplifiers cannot avoid generating high-order harmonics of the amplifying signal, the "rational harmonic mode-locking" can be obtained in most phase-modulation fiber lasers when the driving signal is amplified, even in some cases when using linear amplifiers.     

Gigabit optical pulse generation with FM mode-locked LiNdP4O12lasers

FM mode locking of an LiNdP4O12(LNP) laser with an intracavity modulator is reported. Mode-locked optical pulses with a pulse width of 49 ps at a repetition rate of 960 MHz, corresponding toc/2L(c:light velocity,L:cavity length), have been obtained. A pulse repetition rate as high as 2.88 GHz has been achieved with a multiple mode-locking technique.     

2.5 GHz and 5 GHz harmonic mode-locking of a diode-pumped bulkerbium-ytterbium glass laser at 1.5 microns

Third-order harmonic mode locking of a diode-laser pumped bulk Er:Yb:glass laser by frequency modulation with a lithium niobate modulator is reported. Stable pulses at a repetition rate of 2.5 and 5 GHz with a pulse duration down to 9.6 ps are obtained. The average output power is 3 mW, the pulse peak power is 120 mW at 2.5 GHz repetition rate, and the pulses are approximately 1.4 times transform limited. The pulse duration can be increased up to 30 ps by decreasing the mode-locker drive power     

Repetition-rate-multiplication in actively mode-locking fiber laser by using phase modulated fiber loop mirror

We demonstrate a simple scheme to multiply the repetition rate in an actively mode-locking fiber laser by using a phase modulated optical fiber loop mirror (PMOLM). The PMOLM can convert phase modulation to amplitude modulation at double the modulation frequency. In principle, it is easy to double the repetition rate. However, the PMOLM also induces residual chirp which can disable this method in some cases. Numerical simulation shows that the best results can be obtained when the intracavity dispersion is negative and the modulation frequency is an odd harmonic of half of the cavity fundamental frequency. This agrees with the experimental results, in which an 80-GHz 1.74-ps transform limited pulse was obtained. By using rational harmonic modulation which requires detuning the modulation frequency and adjusting the modulation index, the repetition rate can be increased by three or four times.     

Fourier-limited 1.6-ps pulses with variable repetition rate from 1to 26 GHz by passive mode-locking of a semiconductor laser in anexternal cavity

By passive mode-locking of a semiconductor laser (λ=1.3 μm) in an external cavity, 1.6 ps sech²-shaped pulses are generated with variable repetition rates from 1 to 26 GHz, presently limited only by the geometry of the set-up. The time-bandwidth product is between 0% and 40% over the theoretical limit. Wavelength tuning up to 50 nm is possible     

Electrically gain-switched vertical-cavity surface-emitting lasers

The authors report electrical gain-switching of a packaged vertical-cavity surface-emitting laser (VCSEL). Pulse durations as short as 24 ps at repetition rates up to 2 GHz were obtained from a four-quantum-well GaAs/AlGaAs VCSEL, which emits 0.8 mW continuous wave power in a single mode at room temperature and has a current threshold of 5 mA. Simultaneous measurement of the optical spectrum showed an almost transform limited linewidth indicating ultralow chirp. Optical pumping with subpicosecond pulses of the same packaged devices, held at a constant electrical bias, yielded 22 ps pulses, in good agreement with the electrical pumping. Simple calculations show that the pulse duration obtained by gain-switching is limited by the design constraints necessary to operate the VCSEL continuous wave at room temperature with low-threshold current, high-quantum efficiency, and reasonable output power     

Tunable GHz Repetitive ps Pulse InGaN Laser

Using sinusoidal waveform, an InGaN laser unit which incorporated a 50-Omega impedance-matching unit was used to generate <70-ps pulses with a repetition frequency ranging from 800MHz to 3.0 GHz. At 1.0 GHz, the pulses with a pulsewidth of 31ps and a peak power of >450 mW were obtained using +27dBm of RF power. Tuning characteristics of this gain-switching laser were studied     

20 GHz active mode-locking of a 1.55 ?m InGaAsP laser

Active mode-locking of a 1.55 ?m wavelength InGaAsP laser at repetition rates up to 20 GHz is reported. The pulsewidth is 5 ps at 20 GHz, with a peak pulse power of 18 mW coupled into a single-mode output fibre.     

Theory and experiments of a mode-beating noise-suppressed and mutually injection-locked Fabry-Perot laser diode and erbium-doped fiber amplifier link

By using Fabry-Perot laser diode (FPLD) as a resonant ultranarrow bandpass filter in an Erbium-doped fiber amplifier or laser (EDFA or EDFL), the theory and experiment for side-mode suppression and linewidth reduction of mutually injection-locked EDFL-FPLD and EDFA-FPLD links are demonstrated. Based on the amplified feedback injection loop, the 3-dB linewidth of 3.4 MHz for the EDFA-FPLD link is determined by using self-heterodyne interferometric spectral analysis. The EDFA-FPLD link exhibits a nearly mode-beating noise-free performance as compared to the EDFL-FPLD link. This is due to the release of the resonant cavity configuration in the EDFL-FPLD link at a cost of slightly lower side-mode suppression ratio (/spl sim/42 dB). The maximum output power of the EFDA-FPLD link is 20 mW under an FPLD input power of 0.1 mW.     

Alternate multiwavelength modelocked fiber laser

We demonstrate alternate mode-locking of three 30-ps pulse trains at three different wavelengths, each at a repetition rate of 3.8 GHz. The successive multiwavelength pulsed operation is reached in an actively mode-locked erbium-doped fiber laser in which an unbalanced Mach-Zehnder interferometer has been introduced. This component plays both the role of intensity modulator and tunable filter.     

基于半导体光放大器交叉增益调制效应的主动锁模光纤激光器

提出一种腔内损耗小的基于半导体光放大器(SOA)交叉增益调制效应(XGM)的主动锁模光纤激光器结构。使用光环行器成功减小了激光器的腔内损耗,提高了激光器的输出功率。从理论上对有理数谐波锁模过程中腔内脉冲复合的物理机制进行了详细分析。利用有理数谐波锁模技术,在调制频率为10 GHz下,得到了重复频率为30 GHz的皮秒级光脉冲序列输出,其峰值功率约0.5 mW。由于半导体光放大器的宽增益谱与滤波器的较大可调谐范围,使得激光器输出可以在较大的波长可调谐范围内保持较大功率输出。成功实现了调制频率为20 GHz的谐波锁模短光脉冲输出,可调谐范围达40 nm,峰值功率大于0.65 mW。半导体光放大器和激光器的短腔长保证了激光器的长期稳定性。     

Harmonic Signal Generation and Frequency Up-Conversion Using a Hybrid Mode-Locked Multisection DFB Laser

Harmonic signal generation and frequency up-conversion are demonstrated using a hybrid mode-locked multisection distributed-feedback (MS-DFB) laser. Hybrid mode-locking is realized by direct injection of electrical local oscillator (LO) signals into the laser gain control section. The harmonic signals are generated when multiple optical modes produced by the hybrid mode-locked MS-DFB laser are detected in a photodiode (PD). In addition, if data signals at f_IF are applied to the device along with LO signals at fLO, optical sidebands separated from the optical modes by f_IF are generated and harmonic up-converted signals are obtained by mode-beating in PD. Using this method, we demonstrate generation of the third-harmonic millimeter-waves at 30.79 GHz with f_LO at 10.263 GHz, and up-conversion of 12.5-Mb/s 32 quadrature amplitude modulation data at 300-MHz f_IF into 30-GHz band