Passively mode-locked fiber ring laser using semiconductor saturable absorber mirror

We experimentally demonstrate a fiber laser passively mode-locked by a semiconductor saturable absorber mirror (SESAM) in a ring cavity. A pulse series with a temporal width of 1 ns is generated at a repetition rate of 12.3 MHz. With careful polarization adjustment, the pulse width decreases, the peak power increases and the spectral sidebands are formed in the optical spectrum. The reason of the phenomenon above has been analyzed. In addition, the characteristic of the pulse with different length of the Er³⁺ Doped Fiber (EDF) is studied and the results show that it is reabsorption that causes the laser to shift to longer wavelength direction when the EDF length increases.     

Mode-locked fiber laser based on an attenuation-imbalanced nonlinear optical loop mirror

We propose a mode-locked figure-eight fiber laser by utilizing an attenuation-imbalanced nonlinear optical loop mirror (AI-NOLM) for the first time. Stable self-starting passively mode-locked pulses as short as 296 fs are obtained. We have also confirmed that the pulse width of the laser can be varied by changing the amount of attenuation in the AI-NOLM.     

Passively mode-locked Nd:GGG laser with a semiconductor saturable absorber mirror

The mode-locking operation of the Nd:GGG crystal with a semiconductor saturable absorber mirror (SESAM) was demonstrated. Continuous wave (CW) mode-locking was obtained with the pulse duration of 11 ps and the pulse repetition rate of 40.38 MHz. At 7 W of pump power, the maximum average output power of 1.1 W was obtained with the slope efficiency of 18.1%.     

A novel actively and passively mode-locked semiconductor optical amplifier fiber ring laser

A novel actively and passively mode-locked semiconductor optical amplifier fiber ring laser was presented, where semiconductor optical amplifier provided cavity gain and introduced nonlinear polarization rotation, whereas, intensity modulator not only acted as modulator but also polarizer. The pulses with duration below 3 ps (FWHM) and peak power about 16 mW at a repetition rate of 10 GHz can be obtained in our system and the system stability may be enhanced. To investigate system parameters effects on mode-locked pulses, a theoretical model was developed.     

Chaotic dynamics of erbium-doped fiber laser with nonlinear optical loop mirror

We experimentally and numerically demonstrate the chaotic dynamics of the erbium-doped fiber laser with a nonlinear optical loop mirror. When the polarization controllers are fixed at an appropriate orientation, we observe that the fiber laser exhibits a period-doubling route to chaos with increasing the pump power in the experiment and simulation. The numerical simulation shows a good agreement with the experimental results. The results show experimentally and numerically that the chaotic dynamics of the erbium-doped fiber laser is related to the polarization state and the pump power of light in the cavity.     

Numerical study of a harmonic mode-locked semiconductor optical amplifier fiber ring laser

An improved harmonic mode-locked Semiconductor optical amplifier (SOA) fiber ring lasers has been presented and numerically investigated based on the self-reproduction theory. The numerical result shows that a narrower optical pulse train with a more symmetrical-temporal shape can be obtained, when the modulation SOA is DC biased on high current, whereas the gain SOA is DC biased on the low current functions as a gain compensator in the experimental setup. Also, the system parameters effects on the characteristic of the harmonic mode-locked pulse have been investigated.     

High-energy femtosecond stretched-pulse fiber laser with a nonlinear optical loop mirror

A stretched-pulse fiber laser with a nonlinear optical loop mirror (NOLM) that produces 100-fs pulses with 1-nJ energy is demonstrated. These results constitute a 30-fold increase in pulse energy over previously reported femtosecond fiber lasers with a NOLM. Compared with previous stretched-pulse lasers, this laser offers a cleaner spectrum and improved stability, with comparable pulse duration and energy. Implications for the construction of truly environmentally stable lasers are discussed.     

Multiwavelength erbium-doped fiber laser employing a nonlinear optical loop mirror

A stable and broad bandwidth multiwavelength erbium-doped fiber laser is proposed and demonstrated successfully. A nonlinear optical loop mirror which induces wavelength-dependent cavity loss and behaves as an amplitude equalizer is employed to ensure stable room-temperature multiwavelength operation. Up to 50 wavelengths lasing oscillations with wavelength spacing of 0.8 nm within a 3-dB spectral range of 1562-1605 nm has been achieved. The measured power fluctuation of each wavelength is about 0.1 dB within a 2-h period.     

Multi-wavelength fiber laser based on nonlinear polarization rotation in semiconductor optical amplifier and photonic crystal fiber

A nonlinear polarisation rotation (NPR) based multi-wavelength laser source is demonstrated using a semiconductor optical amplifier (SOA) and photonic crystal fiber (PCF). The SOA acts as not only the gain medium but also the phase retarder for multi-wavelength oscillation in conjunction with an isolator. The incorporation of PCF improves the NPR effect and thus assists in the multiwavelength generation. The wavelength spacing reduces from 4.82 to 2.76 nm as the PCF length increases from 50 to 100 m. With a 100 m long PCF, the proposed laser produces at least 42 lasing wavelengths with optical signal to noise ratio of more than 10 dB.     

Supermode-noise-free eighth-order femtosecond soliton from a backward dark-optical-comb-injection mode-locked semiconductor optical amplifier fiber laser

A backward dark-optical-comb-injection mode-locked semiconductor optical amplifier fiber laser (SOAFL) with a femtosecond pulse width and an ultrahigh supermode-noise suppressing ratio (SMSR) is primarily demonstrated. The mode-locked SOAFL pulse with a spectral linewidth of 0.45 nm is shortened from 15 to 8.6 ps under chirp compensation in a 420 m long dispersion-compensated fiber, corresponding to a time-bandwidth product of 0.48. The eighth-order soliton is obtained by the nonlinearly soliton's compression of the chirp-compensated SOAFL pulse in a 112 m long single-mode fiber at an input peak power of 51 W, providing the pulse width, the linewidth, and the nearly transform-limited time-bandwidth product are <200 fs, 13.8 nm, and 0.34, respectively. The phase noise and integrated timing jitter at an offset frequency below 1 MHz are -105 dBc/Hz and 0.8 ps, respectively. An ultrahigh pulse-compression ratio of 43 and a SMSR of 87 dB for the eighth-order SOAFL soliton are reported.     

Passively harmonic mode-locked erbium-doped fiber soliton laser with a nonlinear polarization rotation

Based on the nonlinear polarization rotation technique, we report on a stable passive 23rd harmonic mode-locked erbium-doped fiber soliton laser for the first time to the best of our knowledge. In this laser, 23 solitons are uniformly distributed in the cavity simultaneously, and all solitons have the same energy and duration. The increase of the coupler output enhances the dispersive radiation, and the longer cavity strengthens the interaction between solitons and dispersive waves. The two above factors play the key function to generate the 23rd harmonic mode-locked operation.     

The suppression of optical regenerator employing semiconductor laser amplifier loop mirror on the additive noise

In this paper, transmission properties of the regenerator employing a semiconductor laser amplifier loop mirror (SLALOM) are discussed. The ability of the regenerator to suppress the additive noise in the input data train is calculated. It’s shown that the regenerator can greatly suppress noise in communication system and improve their communication capacity by choosing suitable semiconductor laser amplifier(SLA) and the power of injected continuous wave.     

10 GHz regeneratively mode-locked semiconductor optical amplifier fiber ring laser and its linewidth characteristics

A 10 GHz regeneratively mode-locked semiconductor optical amplifier fiber ring laser with a picosecond pulse duration was newly constructed, and the linewidth change of a longitudinal mode was measured for various laser cavity lengths using a delayed self-heterodyne detection method. The detected line shape was approximately Gaussian for cavity lengths of 3.4-171 m. This result indicates that the laser linewidth depends strongly on thermal or acoustic cavity length fluctuations. The linewidth was proportional to the inverse square root of the cavity length, and a linewidth of 1.7 kHz was obtained for a cavity length of 171 m.     

Polarization-insensitive nonlinear optical loop mirror demultiplexer with twisted fiber

We experimentally demonstrate reduction of the polarization sensitivity of a nonlinear optical loop mirror (NOLM) from 5 to 0.5 dB by use of 550 m of twisted dispersion-shifted fiber with a twist rate of 8 turns/m (24 turns/beat length). The twisting of the fiber induces circular birefringence and equates the parallel-and the orthogonal-polarization nonlinear phase-shift terms. Experimental results show that the polarization sensitivity monotonically decreases from 5 dB for nontwisted fiber to 0.5 dB for fiber that is twisted at a rate of 8 turns/m, and the twist rate should be more than 4 turns/m (>10 turns/beat length) for emulation of circularly polarized fiber. The minimum polarization sensitivity occurs when the control-pulse polarization is aligned with one of the eigenmodes of the twisted fiber. With the fiber twisted at a rate of 8 turns/m in the NOLM, the nonlinear transmission is 23% at a switching energy of 4 pJ/pulse. Simulations confirm the observed behavior and show that the remaining polarization sensitivity results from energy transfer between orthogonal modes of the signal pulse.     

基于非线性光纤环形镜的少模脉冲幅度调制再生器

随着网络带宽需求的快速增加,波分复用系统的容量已接近非线性香农极限.为了适应未来网络的发展,空分复用技术引起了越来越多的关注.本文首次提出基于少模非线性光纤环形镜(FM-NOLM)的脉冲幅度调制(PAM)全光再生器,描述了其工作原理和具体设计过程.采用COMSOL软件对组成FM-NOLM的硫化物高非线性光纤进行了模式特性仿真.以LP01,LP11,LP21三个光纤模式为例,确定了再生器的参数,计算出每个模式的功率转移函数曲线.仿真分析了该少模PAM-4全光再生器的噪声抑制(NRR)性能,并与单模情形进行了比较.研究表明,1)对于每个空间模式的PAM信号,所有再生电平具有一致的功率转移性能;2)当输入信噪比(SNR)约大于20 dB时,三种模式的噪声抑制比均可超过3 dB,并随着输入信噪比线性增加,其斜率约为1.2;3)在相同输入SNR条件下,三种模式的噪声抑制比相差不大,不超过1.1 dB.为了说明再生器的再生性能,当输入SNR为25 dB时,我们还给出了再生前后PAM-4信号的功率分布直方图.与现有的再生方案相比,本文方案的均匀多电平再生转移性能,使其更适合高频谱效率的长距空分复用系统和任意电平数的PAM信号再生.此外,该方案也能够扩展到波长域,有效提高光通信系统的传输容量.     

Passively Q-switched Er-doped fiber laser using a semiconductor saturable absorber mirror

A passively Q-switched Er-doped fiber laser using a semiconductor saturable absorber mirror (SESAM) is demonstrated. Q-switching is observed with the output power produced at a slope efficiency of 29.4% with respect to the absorbed pump power. The maximum average output power of 8.37 mW is achieved. The pulse repetition frequency obtained can be turned from 1.72 to 7.95 kHz. The pulse energy of 17.2 nJ has been obtained at the pump power of 46.75 mW, and the pulse width is 30 μs.     

NRZ to Manchester code conversion based on nonlinear optical fiber loop mirror

An approach to convert NRZ signal to Manchester code at 20 Gbit/s based on nonlinear optical fiber loop mirror (NOLM) is demonstrated. Using 20 Gbit/s NRZ data and optical clock as external pumps of the NOLM, the conversion of NRZ to Manchester code is successfully realized. The eye diagrams, waveforms and optical spectra are presented. We investigated the extinction ratio (ER) penalty (5 dB) to evaluate the system performance and analyzed the method to improve it. The proposed scheme is potential for applications in future networks.     

980-nm all-fiber mode-locked Yb-doped phosphate fiber oscillator based on semiconductor saturable absorber mirror and its amplifier

A 980-nm semiconductor saturable absorber mirror(SESAM) mode-locked Yb-doped phosphate fiber laser is demonstrated by using an all-fiber linear cavity configuration. Two different kinds of cavity lengths are introduced into the oscillator to obtain a robust and stable mode-locked seed source. When the cavity length is chosen to be 6 m, the oscillator generates an average output power of 3.5 m W and a pulse width of 76.27 ps with a repetition rate of 17.08 MHz. As the cavity length is optimized to short, 4.4-m W maximum output power and 61.15-ps pulse width are produced at a repetition rate of 20.96 MHz. The output spectrum is centered at 980 nm with a narrow spectral bandwidth of 0.13 nm. In the experiment, no undesired amplified spontaneous emission(ASE) nor harmful oscillation around 1030 nm is observed. Moreover,through a two-stage all-fiber-integrated amplifier, an output power of 740 m W is generated with a pulse width of 200 ps.     

Multiwavelength fiber laser using S-band erbium-doped fiber amplifier and semiconductor optical amplifier

A multiwavelength fiber ring laser that is based on an S-band erbium-doped fiber amplifier (EDFA) and a semiconductor optical amplifier (SOA) is developed. An optical switch is used to switch the multiwavelength fiber laser between S-band and L-band. This fiber laser can stably lase seven wavelengths in the S-band or 28 wavelengths in the L-band. Additionally, the lasing wavelengths with a signal-to-noise ratio of over 33 dB and a wavelength spacing of 100 GHz are demonstrated experimentally. The average powers of the lasing wavelength in the S-band and the L-band are −7.53 and −12.15 dBm, respectively.