非线性放大复合环形镜及被动锁模掺铒光纤激光器的研究

提出采用两个光纤耦合器构成具有复合环的非线性放大环形镜。分析表明，改变构成非线性放大复合环形镜的光纤耦合器的耦合系数可以改变非线性复合光纤环形镜的非线性传输特性，调节非线性光反射和透射率。采用非线性放大复合环形镜与半导体饱和吸收体组成复合腔掺铒光纤激光器，获得了十分稳定的被动锁模脉冲输出，得到了重复频率为２４８ＭＨｚ的谐频锁模脉冲序列。实验表明，采用非线性放大复合环形镜构成复合腔光纤激光器，有可能获得高重复频率的锁模脉冲。     

NOLM-NALM fiber ring laser

We study the bidirectional lightwave propagations in an erbium-doped fiber ring laser and an inverted-S fiber ring laser, and observe their optical bistability behaviors. We develop a model for the inverted-S fiber ring laser using nonlinear optical loop mirror and nonlinear amplifying loop mirror (NOLM-NALM) principle, which operates in the nonlinear region. Good agreements between the laser experimental performance and the developed model are achieved. The laser shows good switching and pulse compression capabilities. In addition, the laser model illustrates the route to chaotic operation via period doubling bifurcation, when the input power increases. We also obtain quasi-periodic operation when the laser is amplitude modulated experimentally.     

利用NALM结构的被动锁模掺铒光纤激光器的研究

为了研究光纤中的非线性效应对锁模脉冲的影响,采用非线性放大环镜来实现被动锁模,在分析非线性放大环镜传输特性理论的基础上,对被动锁模掺铒光纤激光器进行了相关的实验研究。实验中观察到了重复频率为280.2MHz、中心波长是1556.235nm、线宽是0.4nm的稳定的锁模脉冲现象。研究结果对更深入地了解被动锁模产生现象、进一步开展后续研究具有极其重要的意义。     

All-optical modulation and demultiplexing systems with significanttiming jitter tolerance through incorporation of pulse-shaping fiberBragg gratings

In this letter, we demonstrate the use of a superstructured fiber Bragg grating to preshape optical pulses to obtain optimal operation of nonlinear all-optical switches. Specifically, we demonstrate the conversion of 2.5-ps soliton pulses into 20-ps rectangular pulses at the input to both fiber and semiconductor optical amplifier-based switches, and show that rectangular switching windows can be achieved thereby providing a 5-10-fold reduction in timing jitter sensitivity. Error free penalty free optical time-division-multiplexing switching was readily achieved over a ±7-ps timing mismatch range for the square pulse driven fiber nonlinear optical loop mirror switch versus a ±1-ps range for the switch driven directly with 2.5-ps laser pulses     

Simultaneous amplification and compression of ultrashort solitons in an erbium-doped nonlinear amplifying fiber loop mirror

A simple technique for simultaneous amplification and compression of ultrashort fundamental solitons is proposed. It is based on an erbium-doped nonlinear amplifying fiber loop mirror. Numerical simulations show that, unlike conventional erbium-doped fiber amplifiers in which nonlinear effects lead to serious degradation of pulse quality, the proposed device performs efficient high-quality amplification and compression of ultrashort solitons while nearly preserving the soliton nature of the input pulses. We have also studied the effects of loop characteristics, nonsoliton input pulses, and higher order fiber effects on the device performance and show that the proposed scheme is fairly insensitive to small variations in both the loop and input pulse parameters.     

Influence of carrier transport on performance of SLALOM with apolarization-independent MQW SLA

The switching performance of the semiconductor laser amplifier in a loop mirror (SLALOM) with a polarization-independent multiquantum-well SLA influenced by the carrier transport is discussed. It is shown that the switching window is polarization-dependent in the case of ultra-short pulses used as switching pulses because of the carrier transport effect between quantum wells. The influence of polarization can be suppressed by modifying the polarization state of local switching pulses     

Sampling pulses with semiconductor optical amplifiers

We demonstrate three techniques to measure the instantaneous frequency and intensity of optical pulses using semiconductor optical amplifiers (SOAs). Four-wave mixing, gain-saturation, and interferometric switching through a nonlinear optical loop mirror are three mechanisms by which sampling is done. We have experimentally measured the intensity and chirp profiles of pulses with energies as low as 10 fJ. Since the nonlinearity in the SOA is relatively slow, these measurement techniques are most appropriate for picosecond pulses often found in telecommunication applications. The temporal resolution of these methods are limited by timing jitter, which was ≈0.5 ps for the mode-locked laser diodes we used in our experiments, and by the width of the switching window     

Synchronization of passively mode-locked erbium-doped fiber lasersand its application to optical communication networks

We synchronized two passively mode-locked erbium-doped fiber lasers using a phase lock loop with a large dynamic range and bandwidth, which is realized by using a novel acoustooptic-modulator-grating scheme. Cross-correlation of the two lasers shows the interlaser jitter is under 2 ps (same as the laser pulse width) for period as long as hours. To prove the quality of phase locking, we apply synchronized lasers in two all-optical network applications, one of which requires the lasers to have the same wavelength and the second requires the lasers to be at different wavelengths. In the single wavelength application, the synchronized lasers drive a cascade of two low-birefringence, polarization maintaining, optical logic gates with switching timing window of 4 and 5 ps, respectively. We obtain nonlinear transmission of ~50% at a switching energy of 8 pJ and contrast ratio of 16 dB, which are comparable performance as that obtained using a single laser. In the different wavelength application, we use 0.8 ps pulses to switch 2 ps pulses in a two-wavelength nonlinear optical loop mirror demultiplexer with timing window of 5.5 ps. Stable switching is reached at a efficiency as high as 90% at switching energy of 0.8 pJ, and a contrast ratio of 20 dB. Excellent agreement is found between the experimental data and the simulated results, which exclude the timing jitter     

Picosecond square pulse generation using nonlinear fibre loop mirror

Square pulses with controllable picosecond durations have been generated from a CW input signal in the region of 1.5 mu m by using switching in a nonlinear loop mirror. The square pulses are generated in synchronism with a pulsed driver which can be a noise burst. Shaped pulses have also been derived using this technique.<>     

全保偏非线性偏振环形镜锁模掺铒光纤激光器

研究了基于非线性偏振环形镜锁模的全保偏光纤激光器锁模机制。在非线性偏振环形镜中,用偏振分束器取代传统的非线性放大环形镜锁模激光器中的光纤耦合器,并辅以非互易性元件和增益光纤,作为全保偏光纤激光器中实现稳定锁模的核心器件。构建了一台基于非线性偏振环形镜的掺铒光纤锁模激光振荡器,实现了重复频率75 MHz,时域脉冲宽度141 fs,总输出功率约30 mW的稳定锁模脉冲序列输出。该激光器具有双向输出,且通过调节腔内波片可调节输出功率。此外,对激光器输出功率和重复频率的稳定性进行了评价,在自由运转情况下,1 h内输出脉冲序列的平均功率波动小于0.05%,重复频率的1 s相对稳定度为2.010-8。该结构的全保偏光纤激光器可开机自启动锁模,且环境稳定性高、重复频率较高、脉冲宽度窄,能满足激光测距、激光加工、激光光谱成像、航天等应用对超短脉冲光源的需求。     

基于光纤环形镜的光纤激光器的优化设计

对基于光纤环形镜和光纤光栅的线形腔光纤激光器进行了优化设计.以光纤光栅作为激光器的输出端镜,分别将光纤环形镜和非线性放大环形镜与其构成激光器的谐振腔;在光纤光栅与光纤环形镜构成的谐振腔中引入偏振控制器,并以加入偏振控制器的环形镜作为激光输出端镜,对上述三种实验装置的激光输出特性进行了分析比较.     

One million pulse circulations in a fiber ring using a SLALOM forpulse shaping and noise reduction

The distinctly nonlinear input-output characteristics of a nonlinear element consisting of a semiconductor laser amplifier (SLA) in a loop mirror configuration (SLALOM) that may be utilized for pulse shaping and noise reduction is described. As an example, it is shown that nearly unlimited circulations of optical pulses in a fiber ring are possible     

2R-Regeneration of an RZ-DPSK Signal Using a Nonlinear Amplifying Loop Mirror

The performance of a nonlinear amplifying loop mirror as a 2R-regenerator for return-to-zero differential-phase-shift-keyed signals has been investigated experimentally. The measured power characteristics and phase functions show that the signal amplitude is regenerated while the signal phase is preserved in the setup. A significant eye-opening improvement and a negative power penalty of about 1.5 dB were obtained     

Experimental investigation on evolution of a split multi-wavelength bright-dark pulse in a mode-locked thulium-doped fiber laser

We report the experimental observation of evolving phenomenon of a split multi-wavelength bright-dark pulse in the nonlinear amplifying loop mirror (NALM)-based mode-locked thulium-doped fiber laser (TDFL) with a figure-eight configuration. Bright-dark pulse with 10 wavelengths was successfully obtained at the pump power of 3 W. The time interval between the bright and dark pulses was discovered not only increasing linearly with the pump power but also approximately equaling to the reciprocal of modulation frequency of radio frequency (RF) spectrum. Moreover, we also observed that the spectrum of split multi-wavelength bright-dark pulse can further present up to 13 wavelengths.     

All-optical loop mirror switch employing an asymmetric amplifier/attenuator combination

For the first time a report is made on a loop mirror switch containing the nonreciprocal combination of a semiconductor laser amplifier and an optical attenuator. Self-routing of optical pulses has been demonstrated on 10 ns pulses with powers of <250 mu W, within a 17 m loop. The model predicts the form of the switching.<>     

Demonstration of the nonlinear fibre loop mirror as an ultrafast all-optical demultiplexer

The all fibre nonlinear optical loop mirror (NOLM) is used in the two wavelength version to show good contrast stable switching of selected pulses from a stream of short pulses. The polarisation properties of the device enable operation as a genuine four port demultiplexer.<>     

Multiwavelength L-Band Brillouin–Erbium Comb Fiber Laser Utilizing Nonlinear Amplifying Loop Mirror

In this paper, we demonstrate a novel multiwavelength L-band Brillouin-erbium fiber laser utilizing nonlinear amplifying loop mirror. The erbium-doped fiber section in the fiber loop mirror provides efficient amplification of Brillouin pump (BP) to generate the stimulated Brillouin scattering in the single-mode fiber coil. The laser structure can achieve symmetry breaking of the loop without requirements to an asymmetric coupler or polarization controller. The proposed fiber laser has a low threshold power of about 10 mW to create the first Brillouin-Stokes signal. The maximum number of 27 Stokes signals with a spacing of 0.089 nm is achieved by setting the BP wavelength at 1604 nm and its BP power is set at 2.2 mW.     

Experimental investigation of all-optical switching in fibre loop mirror device

Nonlinear optical switching has been experimentally demonstrated in a monomode fibre loop mirror (Sagnac) interferometer using both Q-switched and CW-mode locked pulses of a Nd:YAG laser at 1.32 mu m. The switching crossover for a 25 m loop occurs at 22 W. It has been shown that incomplete switching occurs due to pulse shape effects. The presence of Raman scattering results in a step-like, rather than periodic, response.<>     

Self-adjustments of positions of quantised modelocked pulses infigure-eight fibre laser

For the first time, self-adjustments of positions of quantised modelocked optical pulses are observed in a passively harmonic modelocked fibre laser by using a dispersion-imbalanced nonlinear optical loop mirror with lumped dispersive elements