Q-switched mode-locking of an erbium-doped fiber laser using cavity modulation frequency detuning

We present the results of an investigation regarding a Q-switched mode-locked fiber laser scheme based on a cavity modulation frequency detuning technique. The approach is based on undamped laser relaxation oscillations occurring due to frequency detuning in the fundamental cavity resonance frequency. Through a range of experiments with an erbium-doped, fiber-based, ring-cavity laser, this approach has been shown to be capable of generating high-quality Q-switched mode-locked pulses from an optical fiber-based laser. The maximum frequency detuning range for a stable Q-switched mode-locking operation has been observed to vary depending on the pump power used. We found that the highest pulse peak power was obtained at the frequency detuning threshold at which the operation changed from the mode-locking to the Q-switched mode-locking regime.     

Mode-hop-free single-longitudinal-mode erbium-doped fiber laser frequency scanned with a fiber ring resonator

We describe the experimental construction of a single-longitudinal-mode erbium-doped fiber ring laser equipped with a ring resonator filter. The system is designed to avoid mode hopping and can be frequency scanned for spectroscopic sensor applications. We modified a conventional ring resonator filter to have the capability to reduce transmittance of unwanted modes, which is essential for frequency scanning without mode hopping.     

光学倍频影响激光外差干涉测量精度的机理

为了同时提高激光外差干涉测量的分辨力和精度,必须深入分析光学倍频对激光外差干涉测量精度的影响机理。在此基础上,建立了光学倍频相位测量模型,从理论上证明,光学倍频能够实现对激光外差干涉信号的细分,提高测量分辨力。光学倍频改变非线性误差的相位而使非线性误差减小,但同时改变了激光干涉多普勒频移的v/c平方项,使得残余累计误差增大。仿真结果表明,光学N倍频使非线性误差减小到原来的1/N,但使残余累计误差增大N2倍。因此,光学倍频仅适用于低速测量的场合。     

Effect of birefringence on the bandwidth of noise-like pulse in an erbium-doped fiber laser

We report on the generation of superbroad spectrum bunched noise-like pulses from a passively mode-locked erbium-doped fiber laser, in which the cavity is made of purely anomalous dispersion fibers. The maximum 3 dB spectral bandwidth of the pulse is about 98 nm. We show numerically that the superbroad spectrum of the pulse is caused by the fiber birefringence.     

Dual wavelength erbium-doped fiber laser using a tapered fiber

A tapered fiber is fabricated by heating and stretching a piece of optical fiber after the polymer protective cladding has been removed. An equidistant comb-like transmission spectrum, with a spacing of 1.6?nm and an extinction ratio of more than 5?dB, was obtained by the tapered fiber due to the multibeam interferences of the cladding modes. The tapered fiber was applied in a ring erbium-doped fiber laser (EDFL) to generate dual-wavelength lasing oscillations. The EDFL operates at wavelengths of 1557.0?nm and 1558.6?nm with a stable peak power and a signal-to-noise ratio of more than 40?dB.     

Tunable graphene-based Q-switched erbium-doped fiber laser using fiber Bragg grating

A graphene-based Q-switched erbium-doped fiber laser (EDFL) with a tunable fiber Bragg grating (TFBG) acting as a wavelength tuning mechanism is proposed and demonstrated. The proposed setup utilizes a newly-developed ‘ferrule-to-ferrule transfer’ technique to obtain a single graphene layer that allows for Q-switch operation in the EDFL using a highly doped-gain medium. A TFBG is used as a wavelength tuning mechanism with a tuning range of 10 nm, covering the wavelength range from 1547.66 nm to 1557.66 nm. The system has a wide repetition rate range of over 206.613 kHz from 1.387 kHz to 208.000 kHz with pulse durations of between 94.80 μs to 0.412 μs. The laser output is dependent on the pump power, with energy per pulse of 4.56 nJ to 16.26 nJ. The system is stable, with power and wavelength variations of less than 0.47 dBm and 0.067 nm. The output pulse train is free from self-mode locking and pulse jitters.     

Multifrequency erbium-doped fiber laser operating at room temperature

A method to realize room-temperature operation of a multifrequency Er-doped fiber laser with low-frequency shift feedback placed within a linear laser cavity is theoretically proposed and experimentally demonstrated. Simultaneous multiwavelength lasing with 0.5 nm wavelength spacing is experimentally demonstrated by applying a sinusoidal signal of 10 kHz to a fiber phase modulator inserted within the linear cavity to prevent single wavelength steady-state oscillation. In the linear cavity, an all-polarization-maintaining fiber Sagnac loop is used as a periodic filter, and a single-mode fiber loop with a polarization controller is used as a partial reflector and also as an output port.     

Switchable dual-wavelength single-longitudinal-mode erbium-doped fiber laser using an inverse-Gaussian apodized fiber Bragg grating filter and a low-gain semiconductor optical amplifier

We present a stable and switchable dual-wavelength erbium-doped fiber laser. In the ring cavity, an inverse-Gaussian apodized fiber Bragg grating serves as an ultranarrow dual-wavelength passband filter, a semiconductor optical amplifier biased in the low-gain regime reduces the gain competition of the two wavelengths, and a feedback fiber loop acts as a mode filter to guarantee a stable single-longitudinal-mode operation. Two lasing lines with a wavelength separation of approximately 0.1 nm are obtained experimentally. A microwave signal at 12.51 GHz is demonstrated by beating the dual wavelengths at a photodetector.     

Power scaling and frequency stabilization of an injection-locked Nd:YAG rod laser

The power scaling and frequency stabilization of a high-power, injection-locked, arc-lamp-pumped Nd:YAG laser at 1064 nm are discussed theoretically and experimentally. Thermal lensing and induced birefringence at high pump powers are modeled, and the effectiveness of the model for compensating thermal lensing is demonstrated with four different laser heads. Two distinct active frequency-stabilization schemes for injection-locked lasers are also compared theoretically and experimentally. These efforts yield a 24-W, linearly polarized, continuous-wave, TEM(00) output with a spectral linewidth of 1.5 Hz measured by heterodyne detection.     

宽带铋基掺铒光纤放大器增益及噪声特性研究

利用Er3 离子四能级结构速率方程组和光功率传输方程组,数值模拟了铋基掺铒光纤放大器(EDFA)的增益及噪声特性,模拟结果与实验报道结果取得了很好的一致。同时,详尽地分析了增益及噪声特性与光纤长度、泵浦功率和输入信号功率的关系,优化了放大器的性能,从理论上得出一个20dB增益带宽达76nm、噪声系数接近4dB的铋基EDFA。研究表明了铋基掺铒光纤放大器适合用作于现代DWDM系统中C L波段的光纤放大器。     

High-power 980-nm pump laser modules for erbium-doped fiber amplifiers

High-power fiber-coupled pump modules with an emission wavelength of 980 nm and output powers in excess of 200 mW, as measured at the fiber end, have been fabricated. Laser-to-fiber coupling efficiencies in excess of 77% are observed to be in excellent agreement with a mathematical model. Also, the output power stability of these modules has been monitored during severe temperature cycling, and the relative power variation was less than 4% for all the tested modules.     

70-femtosecond Gaussian pulse generation in a dispersion-managed erbium-doped fibre laser

We experimentally demonstrated the generation of transform-limit Gaussian ultrashort pulses as short as 70 fs from a dispersion-managed mode-locked erbium-doped fibre (EDF) laser. The output spectrum is close to the Gaussian profile with a full-width half-maximum (FWHM) output of 49?nm, and the measured autocorrelation trace exhibits the Gaussian profile. The shortest pulse duration of 70 fs was observed after external recompression. The time-band product is 0.44, showing the best transform limit pulse.     

Single-frequency 1559-nm erbium-doped fiber laser pumped by a 650-nm semiconductor laser

A single-frequency laser with a 2-cm-length erbium-doped fiber and fiber-grating coupler mirrors was operated successfully with a 650-nm semiconductor pump laser. Laser pump threshold was 0.91-mW and 34- ?W output power at 1559 nm was obtained for 6-mW pump power.     

All-optical synchronization of self-pulsating laser diodes with frequency multiplication and division

Abstract

We investigate optical synchronization with frequency multiplication and division of self-pulsating laser diodes. Using a simple rate equation model to describe self-pulsation we show that synchronization with frequency multiplication can be accompanied by large variations in the period of the emitted laser pulses over the injected pulse cycle. These variations are not obvious in the frequency domain treatment of synchronization. By applying a frequency division synchronizing signal to our model, we also show that the sensitivity of the phase difference between the injected signal and laser emission to power increases with increasing frequency division ratio and leads to the presence of power synchronization ranges.     

Tunable graphene Q-switched erbium-doped fiber laser with suppressed self-mode locking effect

Self-mode locking effect in a wideband tunable graphene-based passively Q-switched erbium-doped fiber laser has been observed experimentally. Q-switching is achieved by using graphene as a saturable absorber, while a tunable bandpass filter with a narrow bandwidth is used to obtain wideband tunability. We propose to suppress the modulation on each pulse from self-mode locking by introducing three subring resonators constructed with three 3 dB couplers into the laser ring cavity. Moreover, the laser output characteristics with respect to pump power are studied in detail. A stable Q-switched erbium-doped fiber laser with a tunable range from 1522 nm to 1568 nm is demonstrated experimentally.     

Pure antimony film as saturable absorber for Q-switched erbium-doped fiber laser

This paper reports on the use of Antimony (Sb) polymer film to generate stable Q-switching pulses in Erbium-doped fiber laser (EDFL) cavity. The SA is fabricated by coating a thin layer of Sb on a polyvinyl alcohol (PVA) film through physical vapour deposition (PVD) process. A 1 × 1 mm area of the film SA is cut and integrated into between two fiber ferrules inside the laser cavity for intra-cavity loss modulation. Self-starting and stable Q-switched pulses are obtained within a pump power range from 60 to 142 mW. Within this range, the repetition rate increases from 70.82 to 98.04 kHz, while pulse width decreases from 7.42 to 5.36 μs. The fundamental frequency signal-to-noise ratio of the pulse signal is 74 dB, which indicates the excellent stability of the pulses. The maximum output power and pulse energy are 8.45 mW and 86.19 nJ, respectively. Our demonstration shows that Sb film SA capable of generating stable pulses train operating at 1.55-micron region.     

Switchable and tunable multiple-channel erbium-doped fiber laser using graphene-polymer nanocomposite and asymmetric two-stage fiber Sagnac loop filter

A high-performance multiple-channel erbium-doped fiber laser (EDFL) is proposed and experimentally demonstrated, using graphene-polymer nanocomposite as a multiwavelength equalizer and an asymmetric two-stage polarization-maintaining fiber (PMF) Sagnac loop as a flexible comb filter. At first, the filtering characteristics of the PMF Sagnac loop filter (SLF) are investigated. Both theoretical and experimental results show that it can provide a flexibly switchable and tunable comblike filtering. Then, the two-stage PMF SLF is inserted into a graphene-assisted EDFL cavity for generating multiwavelength oscillation. The extreme-high third-order optical nonlinearity of graphene is exploited to suppress the mode competition of the EDFL, and a stable multiple-channel lasing is observed. By carefully adjusting the polarization controllers in the two-stage PMF SLF, not only can the lasing-line number per channel be switchable between single and multiple wavelengths, but also the wavelength spacing in the triple-wavelength condition can be tunable. In the case of triple wavelengths per channel, up to 12 wavelengths with four channels stable oscillations can be achieved. The multiple-channel EDFL can keep a high extinction ratio of >40 dB and a narrow linewidth of <0.01 nm.     

Thermal characteristics of optical pulse transit time delay and fiber strain in a single-mode optical fiber cable

Thermal characteristics of optical pulse transit time delay and fiber strain in a single-mode optical fiber cable are investigated theoretically and experimentally. Measurements of the transit time delay shift are made by a spatial interference technique using a 1.5-in long fiber, six-fiber unit, and cable. Experimental results for a jacketed fiber whose fiber axis is well centered in nylon coating are in good agreement with those predicted from the theory. A jacketed fiber whose fiber axis is positioned eccentrically from the jacket center exhibits a small change in fiber strain at low temperature due to fiber buckling compared with that for the well-centered jacketed fiber. The loss increase for the off-centered jacketed fiber is explained by the buckling model. Furthermore, thermal characteristics of the unit-type cable examined here are found to coincide with those for the constituent six-fiber unit.     

Fiber-Bragg-grating force sensor based on a wavelength-switching actively mode-locked erbium-doped fiber laser

A fiber-Bragg-grating (FBG) transverse-force sensor based on a wavelength-switching actively mode-locked erbium-doped fiber laser is proposed, in which a FBG is used as both the sensing element and the wavelength-selection element of the laser. When a force is applied to the FBG, the induced birefringence in the FBG causes the laser to emit pulses at two close wavelengths, whose separation is proportional to the applied force. To suppress the interference between the two wavelengths, the laser is made to emit at the two wavelengths alternately by use of a polarization-switching technique. The wavelength separation is converted into a time difference by transmission of the laser pulses through a dispersive single-mode fiber, so the wavelength measurement is replaced by the less-expensive time measurement. The output of the sensor is insensitive to temperature and axial strain changes along the FBG. To interrogate similar FBG sensing elements connected in series it is necessary only to change the modulating frequency of an electro-optic modulator to select the corresponding laser cavity. The practicability of this approach was demonstrated experimentally with two multiplexed sensing elements.     

Suppression of self-pulsing behavior in erbium-doped fiber lasers with a semiconductor optical amplifier

We experimentally demonstrate that the stability of cw and mode-locked erbium-doped fiber ring lasers can be improved significantly with a semiconductor optical amplifier (SOA) inside the cavity. The fast saturable gain of the SOA suppresses significantly the self-pulsing that is due to ion pairs in the erbium-doped fiber, which acts as a saturable absorber. A linear stabilization analysis of the laser system agrees with our experimental results.