Photonic generation of frequency-switchable microwave signals exploiting polarization-induced spectrum splitting in fiber grating-based Fabry-Perot filters

Frequency-switchable microwave signals are optically generated using a dual-wavelength single-longitudinal-mode erbium-doped fiber ring laser. The splitting of the resonance peak is observed in fiber grating-based Fabry-Perot (F-P) filters depending on the injected light polarization states. Choosing two different resonance peaks of the grating-based F-P filter and using a variable saturable absorber formed by a section of incompletely transparent erbium-doped fiber, wavelength-switchable dual-wavelength single longitudinal-mode operation is achieved in the fiber ring laser. Microwave frequency switched among 8.75, 21.25 and 25.4 GHz is implemented by feeding the output laser to a high-speed photodetector.     

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.     

Stable single-longitudinal-mode fiber laser using PM FBG F-P etalon and PM fiber saturable absorber

we present a stable and high efficiency single-longitudinal-mode (SLM) fiber ring laser by using polarization-maintaining fiber Bragg grating Fabry-Perot (PM FBG F-P) etalon combining PM fiber saturable absorber. The PM FBG F-P etalon, which is directly fabricated in hydrogen-loaded PM fiber, is used as reflector and mode-selecting component to reduce the longitudinal-mode density greatly. Meanwhile, a segment un-pumped PM Er³⁺-doped fiber (EDF) serves as saturable absorber to suppress mode hopping and ensure the stable SLM operation. Stable SLM laser output at 1550.4 nm with linewidth of 2.0 kHz is observed. Laser output power is 43.7 mW for a pump power of 148 mW, optical-optical efficiency is 29.5% and signal-to-noise ratio (SNR) is larger than 55 dB.     

超低频率全正色散半导体可饱和吸收镜被动锁模光纤激光器

 通过延长激光器环形腔腔长,利用高浓度掺杂的单模掺镱光纤,搭建了超低重复频率、全正色散结构的半导体可饱和吸收镜被动锁模光纤激光器。激光器的中心波长、重复频率、平均功率及单脉冲能量分别为1 064 nm,281.5 kHz,11 mW和39 nJ。为了稳定中心波长,实现自启动,激光器腔体内接入了一个带通滤波器。该激光器运行稳定,无调Q不稳定现象,极大减小了半导体可饱和吸收镜被损坏的机会。     

Single-walled carbon nanotubes on side polished fiber as a universal saturable absorber for various laser output states

We demonstrated four different laser operational states in the same passive fiber ring laser cavity by controlling solely the polarization state in a saturable absorber. The demonstrated laser operational states were continuous wave, mode-locking, Q-switching, and Q-switched mode-locking. The saturable absorber was fabricated by spin-coating a single-walled carbon nanotubes (SWCNT)/polymer composite on a side polished fiber providing enhanced nonlinear interaction with the SWCNT. The wide tuning range of the saturable absorber allows the simple means to generate different forms of laser output from a single laser cavity.     

Mode-locked ytterbium fiber laser tunable in the 980-1070-nm spectral range

Spectral tuning of a mode-locked Yb-doped fiber laser over a 90-nm range is reported. Using semiconductor saturable absorber mirrors in a fiber laser cavity incorporating a grating-pair dispersive delay line, we obtain reliable self-starting mode locking over the whole tuning range. The wide tuning range is achieved by optimization of reflection characteristics and bandgap energy of the multiple-quantum-well semiconductor saturable absorber and by proper engineering of the laser cavity.     

Low-repetition-rate,all-polarization-maintaining Yb-doped fiber laser mode-locked by a semiconductor saturable absorber

A low-repetition-rate, all-polarization-maintaining(PM)-fiber sub-nanosecond oscillator is presented, which is simple and low-cost, composed of standard components. The ring cavity is elongated by 114-m-long standard PM fiber, and passively mode-locked by a fiber pigtailed semiconductor saturable absorber. Linearly polarized pulses with 1.66 MHz repetition rate and 22 dB polarization extinction ratio are generated at a wavelength of 1030 nm, which is determined by an intracavity filter. In addition, to demonstrate that the oscillator is a good seed for high energy pulse generation, an all-fiber master oscillator power amplifier is built and amplified pulses with energy about 2 μJ are obtained.     

Mode-locked fiber laser using an SU8/SWCNT saturable absorber

We report the fabrication of a saturable absorber based on SU8 single wall carbon nanotube (SWCNT) composite material. Thin films with a controllable thickness can be fabricated using a simple and reliable process. These films can be inserted between two FC/APC connectors in order to have an inline saturable absorber. A passive mode-locked laser was built by interleaving the fiberized saturable absorber in an erbium-doped fiber (L-band) ring cavity laser. The laser produces 871 fs pulses with a repetition rate of 21.27 MHz and a maximum average power of 1 mW.     

147 fs碳纳米管倏逝场锁模全光纤掺铒光纤激光器

利用化学腐蚀法在光纤包层表面成功制备了调制深度为3.9%的单壁碳纳米管饱和吸收体.组建了环形腔结构的全光纤掺铒光纤激光器,以制备的单壁碳纳米管薄膜为锁模元件,利用倏逝场锁模实现了锁模输出.锁模脉冲的中心波长为1556 nm,3 dB光谱带宽为24 nm,脉冲宽度为147 fs,重复频率为150 MHz.在520mW抽运功率下,平均输出功率为21 mW,相应的单脉冲能量为0.14 nJ.     

High-energy pulses from a figure 8 fiber laser with normal net dispersion

In this paper we show numerically that high-energy pulses can be obtained with a figure-eight Erbium-doped fiber laser with large normal net dispersion, and in which an anomalous-dispersion Nonlinear Optical Loop Mirror (NOLM) is used as the effective saturable absorber. One advantage of this configuration over the ring cavity is the possibility to adjust the length of the NOLM loop to avoid overdriving the saturable absorber. The ring section of the laser includes a bandpass filter to balance the combined effects of Kerr nonlinearity and normal dispersion. Strict polarization control is performed in the NOLM as well as in the ring section of the laser. The NOLM is a power-symmetric scheme whose switching relies on nonlinear polarization rotation. This architecture allows a precise control of the low-power NOLM transmission through the orientation of a quarter-wave retarder, whose adjustment is shown to be critical for stable pulsed operation. Pulse formation appears to depend critically on the filter width. If it is wide enough, ps pulses with a large positive linear chirp are produced. After dechirping outside the laser, nearly transform-limited pulses with durations down to 240 fs, energies up to 10 nJ and peak powers beyond 40 kW are predicted.     

Photonic generation of microwave signals using dual-wavelength single-longitudinal-mode fiber lasers

Photonic generation of microwave signals is demonstrated with a dual-wavelength single-longitudinal-mode erbium-doped fiber ring laser. Microwave signal with a frequency of 21.07 GHz is obtained by aligning the reflection band of a uniform fiber Bragg grating to the two transmission peaks within a fiber Bragg grating-based Fabry-Perot filter. Stable dual-wavelength single-longitudinal-mode operation is guaranteed by means of the combined filtering effect of a saturable absorber and the Fabry-Perot filter. This approach provides an effective solution to the photonic generation of high-frequency microwave signals.     

High-energy saturable absorber mode-locked fiber laser system

We demonstrate a mode-locked erbium-doped fiber laser with a 1-microm InGaAs saturable absorber that produces 84-ps, 1-nJ transform-limited pulses. Measurements of the InGaAs multiple quantum well revealed a slow saturable absorber that is useful for passive mode locking. Optical fiber was added to extend the cavity and vary the repetition rate from 51 kHz to 5.4 MHz. The narrow spectral width of the laser output (<0.04 nm) permits amplification to 0.2 microJ/pulse with minimal pulse broadening. Pulse energies as large as 1.7 microJ can be achieved with pulse widths of <330 ps. Average powers of 0.5 W at megahertz repetition rates are demonstrated.     

Stable single longitudinal mode fiber ring laser based on polarization maintaining erbium doped fiber

A stable single longitudinal mode (SLM) fiber ring laser that incorporates polarization maintaining erbium doped fiber (PM EDF) acting as gain medium and saturable absorber is proposed and demonstrated. Both theoretical deviation and experimental result prove that optical intensity is time invariant when the laser operates in single longitudinal mode, the SLM operation can be approximately verified by optical intensity analysis, which is practical to analyze longitudinal mode in the application of engineering. The linewidth of the fiber ring laser is measured by the delayed self-heterodyne interferometery, and an acousto-optic frequency shifter is employed to shift the lasing frequency and eliminate zero frequency interfere. The SLM operation is verified by the scanning Fabry–Perot interferometer, whereas the lasing frequency drift slowly during a period of 2 h, PM EDF is proved to be effective on suppressing mode hopping and selecting longitudinal mode.     

氧化石墨烯被动锁模掺镱光纤激光器多脉冲现象的实验研究

利用氧化石墨烯作为可饱和吸收体,在被动锁模全正常色散掺镱光纤激光器中研究了多脉冲的现象,在同一抽运功率不同偏振态下,实验获得了矩形脉冲谐波锁模、耗散孤子谐波锁模、准谐波锁模,脉冲峰值周期性调制,脉冲簇、脉冲束、混沌多重脉冲的多脉冲现象,插入激光腔内的2nm窄带滤波器具有限制增益带宽、对脉冲塑形、诱导多脉冲产生的作用,调节偏振控制器相当于改变腔内增益,是实现不同类型多脉冲现象的主要原因,本实验研究有利于加深对多脉冲动力学行为在正常色散区域氧化石墨烯锁模掺镱光纤激光器中的理解。     

氧化石墨烯被动调Q掺铒光纤激光器

报道了基于氧化石墨烯的被动调Q掺铒光纤激光器。激光器采用环形腔结构,调Q器件为自制的氧化石墨烯可饱和吸收镜。泵浦功率在81~505 mW范围内时,得到了重复频率68~124 kHz的稳定的调Q脉冲输出,脉宽为0.47~1.60 s。由于泵浦功率限制,激光器最大输出功率为10 mW, 相应单脉冲能量为80.6 nJ。此种基于氧化石墨烯可饱和吸收体的被动调Q光纤激光器体积小、成本低廉、结构简单、稳定性高、光束质量高,具有广阔的应用前景。     

Dual-wavelength narrow-linewidth fiber laser based on F-P fiber ring filter

A dual-wavelength fiber laser with a narrow-linewidth, based on a P-F fiber filter has been proposed. Polarization-maintaining fiber Bragg grating (PM-FBG) and a F-P fiber filter are introduced based on the traditional fiber laser. PM-FBG is used as the wavelength selection device. The fiber F-P filter consists of two optical couplers and a section of un-pumped erbium-doped fiber (EDF). Due to the delay of cavity and the loss generated by the EDF, the filter has comb spectral response. The incorporation of the fiber F-P filter leads to the suppression of undesirable modes. At the room temperature, under 980 nm LD pumped, the maximum output of the two wavelengths is respectively ?2.259 dBm and 0.568 dBm, with the 3-dB bandwidth separately 0.1 nm and 0.14 nm, realizing the narrow linewidth and dual-wavelength output.     

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。     

Switchable single-longitudinal-mode dual-wavelength erbium-doped fiber ring laser based on one polarization-maintaining fiber Bragg grating incorporating saturable absorber and feedback fiber loop

Switchable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber ring laser based on one polarization-maintaining fiber Bragg grating (PMFBG) is demonstrated. Due to the enhancement of the polarization hole burning (PHB) by the PMFBG, the laser can be designed to operate in stable dual-wavelength or wavelength-switching modes with a wavelength spacing of 0.336 nm at room temperature by adjusting a polarization controller (PC). The stable SLM operation is guaranteed by a compound-ring cavity and a saturable absorber (SA). The optical signal-to-noise ratio (OSNR) is over 45 dB. The amplitude variation in nearly one and half an hour is less than 0.2 dB.     

A Single Mode Fibre Laser by Applying Self-Injection Locking with a DFB Structure

We report a novel single-frequency fibre ring laser using self-injection locking with a distributed-feedback （DFB） fibre laser at 1550nm. The operating wavelength is controlled by a saturable absorber and a DFB fibre laser in the ring cavity, the saturable absorber acts as a narrow band-pass filter. In the primary experiment, the laser output exceeds 100mW with the linewidth less than 2kHz. The laser is stable, and no mode-hopping is observed within eight hours. Compared with other cavity designs using spatial hole-burning, our laser shows high controllability.     

Pulsed erbium fiber laser with an acetylene-filled photonic crystal fiber for saturable absorption

We investigate the dynamics of an erbium-doped fiber ring laser that is equipped with an intracavity hollow core photonic crystal fiber gas cell. The cell is filled with acetylene as a saturable absorber. We observe cw operation at low pressures, Q switching at intermediate pressure levels, and mode locking at high pressures applied. Moreover, we show that the transition from the cw to the pulsed mode may be exploited for sensitive gas detection.