Wavelength-interval switchable Brillouin–Raman random fiber laser through Brillouin pump manipulation

A wavelength-interval switchable Brillouin–Raman random fiber laser(BRRFL) based on Brillouin pump(BP) manipulation is proposed in this paper. The proposed wavelength-interval switchable BRRFL has a full-open cavity configuration, featuring multiwavelength output with wavelength interval of double Brillouin frequency shifts. Through simultaneously injecting the BP light and its first-order stimulated Brillouin-scattered light into the cavity, the laser output exhibits a wavelength interval of single Brillouin frequency shift. The wavelength-interval switching effect can be manipulated by controlling the power of the first-order stimulated Brillouin scattering light. The experimental results show the multiwavelength output can be switched between double Brillouin frequency shift multiwavelength emission with a broad bandwidth of approximately 60 nm and single Brillouin frequency shift multiwavelength emission of 44 nm. The flexible optically controlled random fiber laser with switchable wavelength interval makes it useful for a wide range of applications and holds significant potential in the field of wavelength-division multiplexing optical communication.

2kW random fiber laser based on hybrid Yb-Raman gain [Invited]

High-power operation is one of the most important research topics surrounding random fiber lasers(RDFLs).Here we optimized the cavity structure and proposed a new scheme based on hybrid gain to address the issue of high-power backward light in traditional kilowatt-level RDFLs.Consequently,a record power of 1972 W was achieved while the maximum backward leaked power only reached 0.12 W.The conversion efficiency relative to the laser diode pump power was 68.4%,and the highest spectral purity of the random lasing reached 98.1%.This work may provide a reference for high-power RDFLs,Raman fiber lasers,and long-wavelength Yb-doped fiber lasers.

Generation of 1.3/1.4μm random fiber laser by bismuth-doped phosphosilicate fiber

We have successfully generated a 1.3/1.4μm random fiber laser(RFL)using bismuth(Bi)-doped phosphosilicate fiber.The Bi-doped RFL has shown excellent long-term operational stability with a standard deviation of approximately 0.34%over 1 h at a maximum output power of 549.30 mW,with a slope efficiency of approximately 29.21%.The Bi-doped phosphosilicate fiber offers an emission spectrum ranging from 1.28 to 1.57μm,indicating that it can be tuned within this band.Here,we demonstrated a wavelength-tuning fiber laser with a wavelength of 1.3/1.4μm,achieved through the using of a fiber Bragg grating or a tunable filter.Compared to traditional laser sources,the RFL reduces the speckle contrast of images by 11.16%.Due to its high stability,compact size,and high efficiency,this RFL is highly promising for use in biomedical imaging,communication,and sensor applications.

Kilowatt-level supercontinuum generation in a single-stage random fiber laser with a half-open cavity

The random distributed-feedback fiber laser(RFL) is a new approach to obtain a high-power stable supercontinuum(SC) source.To consider both structure simplification and high-power SC output,an innovative structure achieving a kilowatt-level SC output in a single-stage RFL with a half-open cavity is demonstrated in this paper.It consists of a fiber oscillator,a piece of long passive fiber and a broadband coupler,among which the broadband coupler acting as a feedback device is crucial in SC generation.When the system has no feedback,the backward output power is up to298 W under the pump power of 1185 W.When the feedback is introduced before the pump laser,the backward power loss can be reduced and the pump can be fully utilized,which could promote forward output power and conversion efficiency significantly.Under the maximum pump power of 1847 W,a 1300 W SC with spectrum ranging from 887 to1920 nm and SC conversion efficiency of 66% is obtained.To the best of our knowledge,it is the simplest structure used for high-power SC generation,and both the generated SC output power and the conversion efficiency are highest in the scheme of the half-opened RFL output SC.

Near-diffraction-limited linearly polarized narrow-linewidth random fiber laser with record kilowatt output

In this paper, we propose and experimentally investigate a linearly polarized narrow-linewidth random fiber laser(RFL) operating at 1080 nm and boost the output power to kilowatt level with near-diffraction-limited beam quality using a master oscillation power amplifier. The RFL based on a half-opened cavity, which is composed of a linearly polarized narrow-linewidth fiber Bragg grating and a 500 m piece of polarization-maintained Ge-doped fiber, generates a 0.71 W seed laser with an 88 pm full width at half-maximum(FWHM) linewidth and a 22.5 dB polarization extinction ratio(PER) for power scaling. A two-stage fiber amplifier enhances the seed laser to the maximal 1.01 k W with a PER value of 17 dB and a beam quality of M_x^2=1.15 and M_y^2=1.13. No stimulated Brillouin scattering effect is observed at the ultimate power level, and the FWHM linewidth of the amplified random laser broadens linearly as a function of the output power with a coefficient of about 0.1237 pm∕W.To the best of our knowledge, this is the first demonstration of a linearly polarized narrow-linewidth RFL with even kilowatt-level near-diffraction-limited output, and further performance scaling is ongoing.

Powerful Narrow Linewidth Random Fiber Laser

In this paper, we demonstrate a narrow linewidth random fiber laser, which employs a tunable pump laser to select the operating wavelength for efficiency optimization, a narrow-band fiber Bragg grating （FBG） and a section of single mode fiber to construct a half-open cavity, and a circulator to separate pump light input and random lasing output. Spectral linewidth down to 42.31 GHz is achieved through filtering by the FBG. When 8.97 W pump light centered at the optimized wavelength 1036.5nm is launched into the half-open cavity, 1081.4 nm random lasing with the maximum output power of 2.15 W is achieved, which is more powerful than the previous reported results.

Passively spatiotemporal gain-modulation-induced stable pulsing operation of a random fiber laser

Unlike a traditional fiber laser with a defined resonant cavity, a random fiber laser(RFL), whose operation is based on distributed feedback and gain via Rayleigh scattering(RS) and stimulated Raman scattering in a long passive fiber, has fundamental scientific challenges in pulsing operation for its remarkable cavity-free feature. For the time being, stable pulsed RFL utilizing a passive method has not been reported. Here, we propose and experimentally realize the passive spatiotemporal gain-modulation-induced stable pulsing operation of counterpumped RFL. Thanks to the good temporal stability of an employed pumping amplified spontaneous emission source and the superiority of this pulse generation scheme, a stable and regular pulse train can be obtained.Furthermore, the pump hysteresis and bistability phenomena with the generation of high-order Stokes light is presented, and the dynamics of pulsing operation is discussed after the theoretical investigation of the counterpumped RFL. This work extends our comprehension of temporal property of RFL and paves an effective novel avenue for the exploration of pulsed RFL with structural simplicity, low cost, and stable output.

Dental Imaging With Near-Infrared Transillumination Using Random Fiber Laser

Contrary to the conventional detection method like radiography,the near infrared light source has been demonstrated to be suitable for dental imaging due to different reflectivity among enamel,dentin,and caries lesion.In this paper,three light sources with different bandwidths based on a transillumination method are compared.The contrast among enamel,dentin,and caries lesion is calculated in different situations.The experimental results show that the random fiber laser has the best comprehensive quality in dental imaging due to its high spectral density,low coherence,and deep penetration.This work provides a guidance for light source selection in dental imaging.

Temperature-controlled mode selection of Er-doped random fiber laser with disordered Bragg gratings

In this paper, we proposed a way to realize an Er-doped random fiber laser(RFL) with a disordered fiber Bragg grating(FBG) array, as well as to control the lasing mode of the RFL by heating specific locations of the disordered FBG array. The disordered FBG array performs as both the gain medium and random distributed reflectors, which together with a tunable point reflector form the RFL. Coherent multi-mode random lasing is obtained with a threshold of between 7.5 and 10 mW and a power efficiency between 23% and 27% when the reflectivity of the point reflector changes from 4% to 50%. To control the lasing mode of random emission, a specific point of the disordered FBG array is heated so as to shift the wavelength of the FBG(s) at this point away from the other FBGs.Thus, different resonance cavities are formed, and the lasing mode can be controlled by changing the location of the heating point.

Random Bragg-grating-based wavelength-tunable random fiber laser with a full-open cavity

A full-open-cavity wavelength-tunable random fiber laser(WT-RFL) with compact structure and hundreds of picometers tuning range is proposed and demonstrated. A π fiber Bragg grating(FBG) is used in the WT-RFL as a filter to select lasing wavelengths. The two random Bragg grating arrays(RBGAs) and a section of high gain erbium-doped fiber result in a low lasing threshold and high stability. A numerical model to analyze the tunable characteristics is developed. The results show that the laser threshold is 22 m W, and the maximum peak-power fluctuation is 0.55 d B. To the best of our knowledge, it is the first time that a compact and full-open-cavity WT-RFL with two RBGAs and a π-FBG is proposed.

Hundred-watt-level linearly polarized tunable Raman random fiber laser

A high power linearly polarized tunable Raman random fiber laser（RFL） was studied theoretically and experimentally. The parameters required for the system design were obtained through numerical simulation, based on which a hundred-watt-level linearly polarized tunable RFL was successfully demonstrated. The central wavelength can be continuously tuned from 1113.76 to 1137.44 nm, and the output power exceeds 100 W for all of the lasing wavelengths with the polarization extinction ratio（PER） exceeding 20 d B at the maximum output power.Besides, the linewidth, spectral evolution, and temporal dynamics of a specified wavelength（1124.72 nm） were investigated in detail. Moreover, the theoretical results and the experimental results fit well. To the best of our knowledge, this is the first time for a hundred-watt-level linearly polarized tunable RFL ever reported.

Ultra-high speed random bit generation based on Rayleigh feedback assisted ytterbium-doped random fiber laser

In this paper, we propose an ultra-high speed random bit generator without the time-delay signature based on an ytterbium-doped random fiber laser(YRFL) with Rayleigh scattering feedback. The spectrum of the YRFL has a relatively broad bandwidth(0.35 nm) and the lasing temporal intensity shows random fluctuations without cavity induced time-delay signatures(TDS),which are essential for ultra-high speed random bit generation. The chaotic signal and its time-delayed signal sampling at40 Giga samples per second(GS/s) are converted to digital 8-bit signals. By selecting 5 least significant bits from each 8-bit digital signal and using bitwise exclusive-OR operation, we experimentally achieve 200 Gbps physical random bit generation based on ytterbium-doped random fiber laser with the verified randomness. The combination of broadband emission and free of TDS makes random fiber lasers new promising sources for high performance random bit generation in a simple and compact configuration, which has a great potential in cryptography and secure communication applications.

LD-Pumped Random Fiber Laser Based on Erbium-Ytterbium Co-Doped Fiber

In this paper,a cladding-pumped erbium-ytterbium co-doped random fiber laser(EYRFL)operating at 1550 nm with high power laser diode(LD)is proposed and experimentally demonstrated for the first time.The laser cavity includes a 5-m-long erbium-ytterbium co-doped fiber that serves as the gain medium,as well as a 2-km-long single-mode fiber(SMF)to provide random distributed feedback.As a result,stable 2.14 W of 1550 nm random lasing at 9.80 W of 976 nm LD pump power and a linear output with the slope efficiency as 22.7%are generated.This simple and novel random fiber laser could provide a promising way to develop high power 1.5μm light sources.

小型化全光纤激光器壳体结构设计与分析

为了进一步优化小型化激光器的性能,在一般性原则的基础上设计了一款输出功率大于10 W、1030 nm高稳定性的小型化全光纤激光器壳体结构。壳体体积为220 mm×270 mm×75 mm,质量小于7 kg;壳体结构采用柔性支撑的减振设计,并可使激光器在温度-55℃~45℃的小型化平台下保持正常运行。利用有限元分析软件对激光器壳体进行了热分析与随机振动分析,按照设计图纸对小型化全光纤激光器样机进行了加工,并进行了实验验证。结果表明,激光器壳体在45℃下,激光器最热面温度为49.5℃,温升约为4.5℃,散热性能良好;在随机振动功率谱密度总均方根10.77 g的实验条件下,激光器最大3σ应力为171 MPa,随机振动响应均方根值仅为24.5 g,壳体结构力学性能良好;激光器壳体结构的散热性能以及力学性能完全满足设计要求,实验结果与仿真结果吻合度较高。该研究为小型化光纤激光器项目的具体实施提供了一定参考。

Hundred-watt level high-order mode all-fiberized random distributed feedback Raman fiber laser with high mode purity

An all-fiberized random distributed feedback Raman fiber laser(RRFL)with LP_(11) mode output at 1134 nm has been demonstrated experimentally,where an intracavity acoustically induced fiber grating is employed for modal switching.The maximum output power of LP_(11) mode is 93.8 W with the modal purity of 82%,calculated by numerical mode decomposition technology based on stochastic parallel-gradient descent algorithm.To our best knowledge,this is the highest output power with high purity of LP_(11) mode generated from the RRFL.This work may pave a path towards advanced fiber lasers with special temporal and spatial characteristics for applications.

Cascaded Random Raman Fiber Laser With Low RIN and Wide Wavelength Tunability

Cascaded random Raman fiber lasers(CRRFLs)have been used as a new platform for designing high power and wavelength-agile laser sources.Recently,CRRFL pumped by ytterbium-doped random fiber laser(YRFL)has shown both high power output and low relative intensity noise(RIN).Here,by using a wavelength-and bandwidth-tunable point reflector in YRFL,we experimentally investigate the impacts of YRFL on the spectral and RIN properties of the CRRFL.We verify that the bandwidth of the point reflector in YRFL determines the bandwidth and temporal stability of YRFL.It is found that with an increase in the bandwidth of the point reflector in YRFL from 0.2 nm to 1.4 nm,CRRFL with higher spectral purity and lower RIN can be achieved due to better temporal stability of YRFL pump.By broadening the point reflector’s bandwidth to 1.4 nm,the lasing power,spectral purity,and RIN of the 4th-order random lasing at 1349 nm can reach 3.03 W,96.34%,and–115.19 dB/Hz,respectively.For comparison,the spectral purity and RIN of the 4th-order random lasing with the point reflector’s bandwidth of 0.2 nm are only 91.20%and–107.99 dB/Hz,respectively.Also,we realize a wavelength widely tunable CRRFL pumped by a wavelength-tunable YRFL.This work provides a new platform for the development of ideal distributed Raman amplification pump sources based on CRRFLs with both good temporal stability and wide wavelength tunability,which is of great importance in applications of optical fiber communication and distributed sensing.

Statistical properties of Er/Yb co-doped random Rayleigh feedback fiber laser

In this Letter, we experimentally investigate fast temporal intensity dynamics and statistical properties of the claddingpumped Er/Yb co-doped random Rayleigh feedback fiber laser(EYRFL) for the first time, to the best of our knowledge. By using the optical spectral filtering method, strong and fast intensity fluctuations with the generation of extreme events are revealed at the output of EYRFL. The statistics of the intensity fluctuations strongly depends on the wavelength of the filtered radiation, and the intensity probability density function(PDF) with a heavy tail is observed in the far wings of the spectrum. We also find that the PDF of the intensity in the central part of the spectrum deviates from the exponential distribution and has the dependence on the laser operating regimes, which indicates some correlations among different frequency components exist in the EYRFL radiation and may play an important role in the random lasing spectrum stabilization process.

基于M-Z滤波的波长可调谐掺铒光纤随机激光器

提出了一种基于M-Z结构的可调谐掺铒光纤随机激光器,并对随机激光输出过程、随机激光的波长可调谐输出以及随机激光的稳定性进行了实验研究。通过采用光纤熔接手段将两个2×2光纤耦合器进行熔接,构成全光纤M-Z滤波结构。实验结果表明,激光器的阈值功率为120 mW,调整可调谐衰减器改变增益损耗,实现波长可调谐输出,其中单波长输出分别为1 554.4,1 555.2和1 556.3 nm,信噪比达到31.65 dB;双波长输出分别为1 525.9,1 556.2和1 531.6,1 556.2 nm,信噪比优于21.92 dB;三波长输出分别为1 527.4,1 546.9,1 551.6和1 526.9,1 530.0,1 549.8 nm,信噪比优于20.10 dB;四波长输出为1 525.9,1 530.1,1 547.9和1 552.3 nm,信噪比优于18.95 dB;其中单波长和双波长的功率波动分别优于1.65和1.99 dB;激光器斜率效率为0.627%。

Tandem pumping architecture enabled high power random fiberlaser with near-diffraction-limited beam quality

In this contribution, we present the tandem pumping avenue leveraged performance scaling of random fiber laser to record 3 kW level with inherent temporal stability and near-diffraction-limited beam quality. The high power system employs a four-stage master oscillator power amplifier chain. The master oscillator is a half-opened cavity structured random distributed feedback fiber laser centered at 1080 nm and pumped by incoherent amplified spontaneous emission source. Narrowband random laser seed is selected by employing a spectral filtering module with a maximum output power of 1.08 W, full width at half maximum linewidth of 0.47 nm and spectral optical-signal-to-noise ratio of about 42 dB. As to the main amplification stage, for given 104 W pre-amplified random laser seed and 3.61 kW pump laser, an ultimate output power of 3.03 kW can be obtained,corresponding to an optical-to-optical conversion efficiency of 81.05%. Nearly single-transverse-mode amplified random laser can be achieved even at full power level for inherent high thermal modal instability threshold enabled by tandem pumping and inducing bending loss for high-order transverse-mode. Further performance scaling of this high power random laser system, such as power boosting, operation wavelength tuning and linewidth alteration, is the next goal.

长距离分布式光纤传感技术研究进展

分布式光纤传感技术是光纤传感领域的重要组成部分,具有以下突出优势:无需在光纤上制作传感器,传感光纤集传感与传输于一体,可实现远距离、大范围的传感与组网;可连续感知光纤传输路径上每一点的温度、应变、振动等物理参量的空间分布和变化信息,单根光纤上能获得多达数万点的传感信息.由于在长距离连续传感方面具有不可替代的优势,分布式光纤传感技术在周界安防、石油电力、大型结构等领域的安全监控方面具有非常广阔的应用前景.本文主要介绍电子科技大学光纤传感与器件研究团队在长距离分布式光纤静(布里渊光时域分析仪)、动(相位敏感型光时域反射仪)态参量传感技术取得的研究进展,包括基础与应用研究两个方面.