Quadruple-wavelength actively mode-locked fiber laser with polarization-controlled wavelength switching

An actively mode-locked fiber laser with two overlapping cavities is proposed and successfully demonstrated to generate switchable quadruple-wavelength picosecond pulses. The wavelengths are specified by two Bragg gratings in polarization-maintaining and absorption-reducing fiber. By simple adjustment of two polarization controllers, the proposed laser can be made to operate at quadruple wavelength or to switch between wavelengths at room temperature. For wavelength switching, four single-wavelength, six dual-wavelength, and four triple-wavelength operations were performed without changing the repetition rate of the output pulses.     

Suppression of continuous lasing in a carbon nanotube polyimide film mode-locked erbium-doped fiber laser

We demonstrated an erbium-doped mode-locked fiber laser using a single-walled carbon nanotube-dispersed polyimide (SWNT-PI) film. Different mode-locking operations were compared and analyzed utilizing SWNT-PI films with different concentrations (2, 1, and 0.25 wt.%, respectively). It was found that the continuous single-pulse mode-locking operation was often accompanied by a continuous wave oscillation part for the 1 and 0.25 wt.% SWNT-PI films, whereas the 2 wt.% SWNT-PI film presented the most excellent mode-locking performance, thanks to sufficient modulation depth. Using the 2 wt.% SWNT-PI film, a stable pulse train with a pulse width of 840 fs and a repetition rate of 15.3 MHz was achieved. The average output power was 0.33 mW at the pump power of 155 mW under an output coupling ratio of 10%. Operational performance of the laser cavity when employing the 2 wt.% SWNT-PI film was also demonstrated.     

Passively mode-locked fiber laser sensor for acoustic pressure sensing

The development is reported of a multi-longitudinal mode fiber laser sensor based on passive mode locking employing carbon nanotubes in the laser cavity. A polymer membrane is employed beneath the pre-strained erbium-doped fiber (EDF) to convert the sound pressure disturbance into axial strain, alter the cavity length, and induce a shift of the longitudinal modes beat. Hence, acoustic pressure measurement can be carried out by detecting the shift of the beat frequency. Experimental results show comparable strain and sound pressure sensitivity of ~0.5 kHz/με and 147.2 Hz/Pa, respectively. The proposed sensor is an alternative for the measurement of acoustic pressure and possesses the advantages of good stability and ease of interrogation.     

错位熔接长周期光纤光栅横向压力传感器

阐述并实验证明了基于长周期光纤光栅和错位熔接结构的横向压力传感器,当施加于错位熔接点的横向压力改变时,干涉谱的相位保持不变,而纤芯模能量减少,包层模能量增加,导致消光比减小,以此通过消光比的变化实现对横向压力的测量.当横向压力从0⁰.98N增加时,传感器对压力的反应是单调且接近线性的.结果证明,该传感器具有消光比灵敏度高,成本低,结构简单的优点,在工业领域具有应用前景.     

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.     

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.     

Generation of soliton and bound soliton pulses in mode-locked erbium-doped fiber laser using graphene film as saturable absorber

We report an observation of soliton and bound-state soliton in passive mode-locked fibre laser employing graphene film as a passive saturable absorber (SA). The SA was fabricated from the graphene flakes, which were obtained from electrochemical exfoliation process. The graphene flakes was mixed with polyethylene oxide solution to form a polymer composite, which was then dried at room temperature to produce a film. The film was then integrated in a laser cavity by attaching it to the end of a fibre ferrule with the aid of index matching gel. The fibre laser generated soliton pulses with a 20.7 MHz repetition rate, 0.88 ps pulse width, 0.0158 mW average output power, 0.175 pJ pulse energy and 18.72 W peak power at the wavelength of 1564 nm. A bound soliton with pulse duration of ~1.04 ps was also obtained at the pump power of 110.85 mW by carefully adjusting the polarization of the oscillating laser. The formation of bound soliton is due to the direct pulse to pulse interaction. The results show that the proposed graphene-based SA offers a simple and cost efficient approach of generating soliton and bound soliton in mode-locked EDFL set-up.     

Switchable dual-wavelength fiber laser mode-locked by monolayer graphene on D-shaped fiber

A switchable mode-locking fiber laser is demonstrated by means of a monolayer graphene saturable absorber (SA) based on a D-shaped fiber. The monolayer graphene, which is grown by chemical vapor deposition, is transferred onto the D-shaped fiber and then the light–graphene interaction via the evanescent field of the fiber is enhanced greatly. Using such a graphene-based SA, the single-wavelength mode locking can be switched from 1531.5 to 1559.1 nm by appropriately adjusting the polarization controller (PC). In addition, the stable dual-wavelength mode-locking operation is also observed at the proper state of PC.     

一种主动冷却的高温光纤式叶尖定时传感器

针对现有高温光纤式叶尖定时传感器最高耐温只到650℃,无法满足更高温度条件下燃气轮机叶片振动监测需求的问题,研究并设计一种采用主动冷却方式的高温光纤式叶尖定时传感器。为提高传感器的耐温性能,采用中空式的结构设计以及主动冷却的降温方式提高传感器探头的耐温性能。应用Ansys有限元分析软件进行热-流-固耦合分析,对传感器设计的可靠性进行理论论证。在此基础上,对设计的高温光纤式叶尖定时传感器进行高温试验验证。结果表明:试验结果与仿真结果具有良好的一致性,该传感器工作温度最高可达1 300℃,满足大多数高温环境下燃气轮机叶片振动参数监测的要求。     

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.     

Analysis of polarization properties of a mode-locked fiber laser gyroscope

We investigated the polarization characteristics of a mode-locked fiber laser gyroscope (MLPLG) formed with a Nd-doped fiber as an optical gain medium and a Sagnac loop mirror. The output pulse patterns and the polarization states were found to be determined by fiber birefringence in the different sections of the MLPLG. We describe the conditions for the MLPLG to operate with automatic reciprocity leading to the possibility of phase-error-free operation.     

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.     

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 fiber laser mode-locked by carbon nanotubes

We have proposed a switchable mode-locked fiber laser by means of carbon nanotube saturable absorber and fiber Bragg gratings (FBGs). The single-wavelength mode-locking operation can be switched between 1549.5 and 1559.5 nm, respectively, which correspond to the central wavelengths of two FBGs. With the appropriate setting of polarization controller, the stable dual-wavelength operation can be achieved due to the high stability of saturable absorber based on carbon nanotubes. Our method provides a simple, stable, low-cost, dual-wavelength ultrafast-pulsed source.     

Ultrafast stretched-pulse fiber laser mode-locked by carbon nanotubes

Ultrafast fiber sources having short pulses, broad bandwidth, high energy, and low amplitude fluctuations have widespread applications. Stretched-pulse fiber lasers, incorporating segments of normal and anomalous dispersion fibers, are a preferred means to generate such pulses. We realize a stretched-pulse fiber laser based on a nanotube saturable absorber, with 113 fs pulses, 33.5 nm spectral width and ?0.07% amplitude fluctuation, outperforming current nanotube-based designs.     

Wavelength switching in an actively mode-locked Fabry-Perot laser diode with a highly dispersive external cavity

We demonstrate a simple and reliable scheme for wavelength switching in an actively harmonic mode-locked Fabry-Perot laser diode (FPLD) that is coupled to a highly dispersive external fiber cavity. Wavelength switching between FPLD modes is achieved by detuning of the modulation frequency applied to the FPLD. A side-mode suppression ratio of as much as 40 dB is maintained, and the supermode noise suppression ratio is more than 50 dB for the whole wavelength switching operation range of 4.7 nm when the pulse repetition rate is ~2 GHz. The wavelength-switching mechanism of our laser is based on the wavelength-dependent cavity resonance frequency shift that is due to chromatic dispersion, and we verify that our experimental results closely coincide with analytical results.     

Transportable optical frequency comb based on a mode-locked fibre laser

A new transportable frequency comb has been developed at the National Physical Laboratory. The transportable frequency comb is based around a MenloSystems FC1500 optical frequency synthesizer, which is capable of measuring any frequency between 500 and 2100 nm. Measurements made by the comb while off-sites are referenced to the SI second via a global positioning system (GPS)-disciplined Rapco 2804AR rubidium oscillator. All components of the system (except for the GPS antenna) have been integrated into a single mobile unit. Measurements of high-stability narrow-band optical sources using this system, with either the GPS-disciplined oscillator or a hydrogen maser as a reference, are described. Some of these measurements were made simultaneously with a hydrogen-maser-referenced Ti:sapphire-based comb. It was found that the GPS-referenced transportable comb has a fractional inaccuracy of better than 4 10^-12 (averaged over several hours) when compared with the maser-referenced Ti:sapphire comb, and a fractional frequency instability of 1times10^-12 for an averaging time of 10 s. It was also demonstrated that continuous frequency measurements are possible with this system over a period of 60 h or more.     

Passive mode-locked laser based on quantum dot superlattice

Passive mode-locking is achieved in two sectional lasers with an active layer based on superlattice formed by ten layers of quantum dots. Tunnel coupling of ten layers changes the structural polarization properties: the ratio between the TE and TM polarization absorption coefficients is less by a factor of 1.8 in the entire electroluminescence spectrum range for the superlattice.     

Bound-state solitons in a linear-cavity fiber laser mode-locked by single-walled carbon nanotubes

The bound-state solitons generated from a nanotube-mode-locked linear-cavity fiber laser are experimentally observed and numerically simulated for the first time to author’s best knowledge. Two chirped fiber Bragg gratings are exploited as the mirrors for the proposed laser. The pulse duration of solitons is about 6.3?ps and the pulse-to-pulse separation is about 23?ps in the experimental observations. Numerical simulations confirm the experimental results and agree well with the experimental observations. Both experimental and numerical results show that the bound-state solitons are strongly stable.     

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.