Lyot filter based multiwavelength fiber ring laser actively mode-locked at 10 GHz using an electroabsorption modulator

A multiwavelength fiber ring laser comprising of a Lyot filter and hybrid gain medium is presented. A wavelength channel spacing of 100 GHz is achieved by appropriate tuning of the Lyot filter length. Four wavelength channels are simultaneously mode-locked at 10 GHz using an electroabsorption modulator. We highlight how the intra-cavity modulator can affect the stability of the mode-locked laser spectrum when used in conjunction with a Lyot filter. We show that, due its reduced polarization sensitivity, an electroabsorption modulator significantly improves the stability of the mode-locked laser spectrum when compared to using a Mach-Zehnder modulator.     

Wideband multiwavelength erbium-doped fiber ring laser with frequency shifted feedback

Wideband multiwavelength erbium-doped fiber ring lasers with frequency shifted feedback are described. The use of an intra-cavity gain flattening filter (GFF) was proposed in order to increase the lasing spectral bandwidth, leading to a demonstration of 34 lasing wavelengths in 28 nm bandwidth in C-band. The GFF induced spectral output power fluctuation is discussed. Multiwavelength operation was also demonstrated for the first time in L-band, where wideband laser operation was obtained without a GFF. Optical bistability and Kerr effect induced pulsation were determined to be limiting factors to stable operation range in this kind of multiwavelength lasers.     

掺Yb3+光纤F-P腔被动锁模激光器的实验研究

 掺镱(Yb³⁺光纤被动锁模激光器谐振腔采用线性腔结构，腔内插入二分之一波片和偏振分束器引入偏振旋转，结合半导体可饱和吸收镜的自起动，实现稳定的被动锁模运转。腔内插入光栅对，提供负的群速度色散，以补偿光纤所带来的正色散，达到压缩脉宽的目的。当泵浦功率为300 mW、光栅对的距离为10 cm时，获得稳定的锁模运转，锁模输出功率28 mW，脉冲重复频率20 MHz，输出光谱宽度达15 nm，按脉冲变换极限公式，其脉冲时间宽度与频带宽度的乘积为0.315计算，脉宽可达100 fs以下。     

Periodic intensity variations on the pulse-train of a passively mode-locked fiber ring laser

We investigate the evolvement of the periodic intensity variations of the pulse-train in a fiber ring laser mode-locked by the nonlinear polarization rotation technique. It is found that the phenomenon of such intensity fluctuations is related to the orientation of the polarization controllers when the pump power is fixed. The numerical results show that the mechanism of the periodic intensity variations is caused by the interaction of the nonlinear polarization rotation and the passive polarizer in the cavity.     

Passively mode-locked ytterbium fiber laser utilizing chirped-fiber-Bragg-gratings for dispersion control

A robust, self-starting picosecond pulse source based on ytterbium (Yb³⁺) doped fiber laser is described. Utilizing a chirped-fiber-Bragg-grating (C-FBG) for dispersion control, solitary mode-locking is obtained without bulk dispersion compensation elements. A semiconductor saturable absorber (SESAM) is used for stable self-starting. 3.6 ps pulses are produced, with 45 MHz basic repetition-rate and mW scale average output power at 1060 nm. Detailed numerical simulations based on the modified nonlinear Schrödinger equation agree well with the experimental results and are used as a design tool for the solitary mode-locked picosecond laser. The presented design can be simply employed in an all-fiber environmentally-stable system.     

Multiwavelength actively mode-locked fiber ring laser with a dispersion compensated cavity

A multiwavelength actively mode-locked fiber ring laser that utilises a single semiconductor optical amplifier as both a gain and mode-locking element is presented. It is verified experimentally that the number of mode-locked wavelengths may be maximised by compensating for the anomalous intra-cavity dispersion. This is achieved through the inclusion of an appropriate length of normal dispersion fiber in the laser cavity. Using this technique, the number of wavelengths simultaneously mode-locked at 10 GHz was increased from 2 to 5.     

Tunable 12×10 GHz mode-locked semiconductor fiber laser incorporating a Mach-Zehnder interferometer filter

A stable multiwavelength mode-locked semiconductor fiber ring laser incorporating a fiber Mach-Zehnder interferometer (MZI) filter was proposed and experimentally demonstrated. A semiconductor optical amplifier (SOA) serves as an optically controlled mode-locking element due to gain exhaustion caused by external injected optical pulses. Another SOA severs as a constant-gain medium. A fiber MZI filter with a temperature control is incorporated into the fiber ring cavity to acquire a stable and tunable multiwavelength oscillation. Twelve wavelengths are synchronously mode-locked at 10 GHz, pulse width of mode-locked pulse are about 30 ps. Proposed multiwavelength mode-locked semiconductor fiber ring laser has some distinct advantages, such as simple and compact structure, easy integration, convenient tuning, good stability, potential high repetition rate operating, which has potential application in the future WDM communication system.     

Waveband-switchable multiwavelength mixed-cascaded phosphosilicate raman fiber lasers

In this paper, the mixed-cascaded Raman scattering has been developed to investigate multiwavelength phosphosilicate Raman fiber lasers (MRFLs). With a tunable Yb³⁺-doped double-clad fiber laser (YDCFL) as the Raman pump source, we propose a compact and waveband-switchable (from the O- to U-band) MRFL using two- or three-mixed-cascaded Raman scattering of both SiO₂/GeO₂ and P₂O₅ in a P-doped fiber. We also confirm experimentally the feasibility of the proposed mixed-cascaded MRFL. When a 1064 nm YDCFL was used to pump a spool of 1-km P-doped fiber, the compact linear-cavity MRFLs in the O- and L-band operation were obtained, respectively, based on the two- and three-mixed cascaded Raman scattering. Up to 16-wavelength stable oscillation around 1320 nm has been observed with a spacing of 0.40 nm and an extinction ratio >30 dB. 12 lasing lines around 1601 nm have also been achieved with a spacing of 0.58 nm. The multiwavelength output powers as high as 108 and 138 mW were obtained in the O- and L-band operations, respectively. The wavelength spacing of the MRFLs is flexibly adjustable, and the peak wavelength of each lasing line is continuously tunable over the wavelength spacing. In addition, the important characteristics of the mixed-cascaded MRFLs, including the linewidth broadening, the signal-to-noise ratio and the conversion efficiency, are discussed.     

超短脉冲超强激光与固体靶相互作用中高能离子的产生

用2D3V PIC粒子模拟方法得到了超短脉冲超强激光与固体靶相互作用中高能离子产生的图像，并对其机理进行了研究。在靶前后表面都观察到了高能离子的产生，并诊断了离子能谱。模拟结果表明，在靶前表面所产生的高能离子，角分布较大，在向靶内输运过程中会损失能量；在靶后表面产生的高能离子，定向性很好，能获得很高的能量。模拟得到的离子能量和实验观测结果在量级上相符。     

Stable multiwavelength fiber ring laser with equalized power spectrum based on a semiconductor optical amplifier

We experimentally demonstrated a new structure of a multiwavelength semiconductor optical amplifier (SOA) ring laser based on a fiber Sagnac loop filter that can generate up to 25 stable output lasing wavelengths at room temperature. By varying the length of a polarization-maintaining (PM) fiber within the Sagnac loop filter, the wavelength spacing between the output lasing wavelengths can be changed to a desired value. By tuning a polarization controller (PC) within the Sagnac loop filter, stable multiwavelength 1550-nm operation with up to 17 lasing lines within 3 dB power level variation and with a wavelength spacing of ∼0.8 nm was achieved. The optical signal-to-noise ratios (OSNRs) of all the lasing wavelengths are greater than 40 dB.     

Simple tunable multiwavelength Brillouin/Erbium fiber laser utilizing short-length photonic crystal fiber

We have demonstrated a simple ring cavity tunable multiwavelength Brillouin/Erbium fiber laser (MWBEFL), in which 70 m highly nonlinear photonic crystal fiber (HNL-PCF) is used as the Brillouin gain medium. The fiber laser utilizes recycling mechanism to enhance stimulated Brillouin scattering (SBS). The configuration that consists of only 3 optical components is easy to be integrated and improves the practicality. At the maximum 1480 nm pump power of 110 mW and the Brillouin pump power of 3 dBm, 10 stable output channels with more than 10 dB optical signal to noise ratio (OSNR) and 0.078 nm channel spacing could achieve 10 nm tuning ranges.     

Full L-band coverage of multiwavelength erbium-doped fiber laser

We propose and experimentally demonstrate a dual-pass unbalanced in-line Sagnac interferometer as a novel comb filter for implements in erbium-doped fiber lasers to obtain wide wavebands of multiwavelength radiations with enhancements of signal-to-noise ratios (SNRs). The hybrid combinations of the comb filter with the two schemes of nonlinear polarization rotation and intensity dependent loss have successfully not only enlarged the lasing bandwidth up to 47 nm but also enhanced the SNR up to 40 dB. The simultaneous lasing-wavelengths of 117 channels are also obtained. The multiwavelength lasing spectra with free spectral range of 0.4 nm covering the full L-band are useful for the applications of DWDM and WDM-PON systems.     

Suppression of Q-switching instabilities in broadened-waveguide monolithic mode-locked laser diodes

It is predicted theoretically that broadening the optical confinement layer in monolithic mode-locked semiconductor lasers may suppress Q-switching instability, by increasing the carrier transport time, and lead to emission of shorter, more stable optical pulses.     

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.     

Single-longitudinal-mode dual-wavelength fiber ring laser by incorporating variable saturable absorbers and feedback fiber loops

A single-longitudinal-mode dual-wavelength fiber ring laser is proposed and demonstrated experimentally by introducing feedback fiber loops and a variable saturable absorber in a fiber ring cavity. A dynamic ultra-narrow bandpass filter is formed by the combined interactions of cascaded fiber Bragg gratings, feedback fiber loops and low-pumped erbium-doped fiber. Both ultra-narrow bandpass filter and accurate control for the cavity length are not required for the single-longitudinal-mode performance. The proposed scheme offers a possibility of generating terahertz waves by photomixing the lasing wavelengths in a high-speed photodetector.     

Switchable triple-wavelength erbium-doped fiber laser using a single fiber Bragg grating in polarization-maintaining fiber

A stable and narrow wavelength spacing multiwavelength erbium-doped fiber laser is proposed and demonstrated. The laser can produce simultaneous dual- and triple-wavelength lasing oscillations with a narrow wavelength spacing of less than 0.1 nm via using a single fiber Bragg gratings written in polarization-maintaining (PM) fiber. By adjusting polarization controller, the wavelength spacing of dual-wavelength lasing oscillations can be tuned to as small as 0.032 nm. The maximum amplitude variation for every lasing wavelength is less than 0.5 dB. The room-temperature operation principle is based on the polarization hole burning and deeply saturated effect in an ordinary erbium-doped fiber ring laser (EDFRL). The laser has the advantages of simple all-fiber configuration, low cost, high stability and operating at room temperature.     

Room temperature multiwavelength erbium-doped fiber ring laser using a highly nonlinear photonic crystal fiber

A multiwavelength laser source is demonstrated with a high power erbium-doped fiber amplifier as the gain medium. A highly nonlinear photonic crystal fiber (PCF) is inserted in the ring cavity to provide nonlinear gain by four-wave mixing. A Sagnac loop is incorporated in the ring cavity serving as a comb-like multichannel filter. The comparison between fiber ring laser without PCF and with PCF shows that the highly nonlinear PCF can generate a larger number of excited wavelengths and help stabilize the output power.     

Continuation of periodic solutions in the waveguide array mode-locked laser

We apply the adjoint continuation method to construct highly accurate, periodic solutions that are observed to play a critical role in the multi-pulsing transition of mode-locked laser cavities. The method allows for the construction of solution branches and the identification of their bifurcation structure. Supplementing the adjoint continuation method with a computation of the Floquet multipliers allows for explicit determination of the stability of each branch. This method reveals that, when gain is increased, the multi-pulsing transition starts with a Hopf bifurcation, followed by a period-doubling bifurcation, and a saddle-node bifurcation for limit cycles. Finally, the system exhibits chaotic dynamics and transitions to the double-pulse solutions. Although this method is applied specifically to the waveguide array mode-locking model, the multi-pulsing transition is conjectured to be ubiquitous and these results agree with experimental and computational results from other models.     

Simulation of the passively mode-locked laser with a SESAM

By solving the Haus master equation through split step Fourier transform method, several programs which can simulate the soliton mode-locked dynamic processes of the passively mode-locked solid laser with a semiconductor saturable absorber mirror (SESAM) are established, based on a MATLAB environment. The pulse evolution equations are solved numerically. Sample calculations for a diode-pumped Nd³⁺:YVO₄ (0.5% doped) laser with a SESAM are presented to demonstrate the use of the simulation programs and the related formulas. Several theoretical results such as the pulse width, the peak power and the average output power are obtained with a given cavity structure, which are in good agreement with the reported experimental results.     

A widely tunable hybrid brillouin-erbium fiber laser (BEFL) system

This paper presents a tunable hybrid brillouin-erbium fiber laser system with a maximum tuning range of more than 36.7 nm. The system was configured in a ring set-up with another fiber laser used as the brillouin pump at about 8 mW maximum launched power. Stable Stokes signals at an average of about 0.08 nm wavelength shift were observed across the tuning range. The dependency of the Stokes signal tuning range on the laser's spectral gain is also elaborated.