Multiwavelength Raman Fiber Laser Research Articles

High-order tunable multi-wavelength random Raman fiber laser based on few-mode fiber filter

In recent years, multi-wavelength fiber lasers have become one of the research hotspots and have been extensively applied in optical fiber communication systems. However, the presented multi-wavelength fiber lasers mainly operate in the 1.5 μm band. In this paper, a few-mode fiber filter-based cascaded high-order tunable multi-wavelength random Raman fiber laser (MWRRFL) is demonstrated, for the first time, in which a tuning range covers the 1.1–1.5 μm band. In the half-open MWRRFL, a few-mode fiber-based intermodal interferometer filter is inserted in the point reflector as a wavelength selector. The synergetic effect including high Raman gain and Rayleigh backscattering intensity in the hybrid of dispersion-shifted fiber and standard single-mode fiber is employed. It presents the capability for flat multi-wavelength random lasing stimulation. As a result, the wavelength channel number of the 6th-order random lasing is 6, with a maximum power variation of 4.66 dB and good temporal stability. The proposed cascaded tunable MWRRFL could provide a versatile source for optical fiber communication, optical fiber sensing, spectrum analysis, etc.

Spectral characteristic of multi-wavelength random fiber laser using a microfiber knot resonator

We demonstrate a U-band multi-wavelength random Raman fiber laser (RRFL) based on a microfiber knot resonator (MKR). The RRFL has a forward-pump half-open cavity, wherein a 10-km single mode fiber provides both Rayleigh backscattering feedback and Raman gain. A MKR with a 0.18 nm free spectral range is used as the broadband comb filter. Up to 40 and 38 wavelength channels within 3 dB bandwidth were achieved from the intracavity and the end of the RRFL, respectively. The laser showed a good stability with maximum 0.38 and 0.1 dB peak power fluctuation within an hour at the two outputs, respectively. The spectral evolution with two envelopes was observed, and the impact of the MKR was discussed. The MKR is a small-size all-fiber and wavelength-insensitive broadband filter, which suits well with the broadband operation of the RRFL. The proposed RRFL has a simple structure and good potential tunability and provides guidance for flexible multi-wavelength lasers in the U-band and other wavebands, which have great potential in applications.

Broadband pumping enabled flat-amplitude multi-wavelength random Raman fiber laser.

A flat-amplitude multi-wavelength random Raman fiber laser with broad spectral coverage and a high optical signal-to-noise ratio (OSNR) is challenging and of great interest. In this Letter, we theoretically and experimentally proved that broadband pumping can help realize a broader, flat-amplitude multi-wavelength random Raman fiber laser. The influence of pump bandwidth, tunability of the spectral envelope, and channel spacing are investigated. As a result, with a 40 nm pump bandwidth, a spectral coverage of 1116-1125 nm with 19 laser lines and 31 dB OSNR is achieved, and the standard deviation in the peak intensities of the central nine lines is ${\sim}{1}.{1}\;{\rm dBm}$∼1.1dBm. This technique can also be applied to the multi-wavelength Raman (or random Raman) fiber lasers at other wavelengths and provide a reference for multi-wavelength applications in sensing, communication, and optical component testing.

基于ASE泵浦的1.7 μm波段可调谐多波长拉曼光纤激光器实验研究

基于ASE泵浦的1.7 μm波段可调谐多波长拉曼光纤激光器实验研究

Erbium-Doped Fiber Amplification Assisted Multi-Wavelength Brillouin-Raman Fiber Laser

Multi-wavelength fiber laser based on Brillouin scattering in optical fiber has the potential of application in dense wavelength division multiplexing (DWDM) system. To enhance the performance of the fiber lasers, researchers proposed usages of erbium, or Raman amplification techniques. In an earlier work, it was reported that extracting residual Raman pump out of the laser cavity improves the performance of a multi-wavelength Raman fiber laser. In this paper, we proposed a setup utilizing the residual Raman pump to pump an erbium-doped fiber in multi-wavelength Brillouin-Raman fiber laser. Results show that the additional erbium-doped fiber is capable of amplifying the propagating Brillouin Stokes by more than 15-dB. This in turn helps in achieving lower stimulated Brillouin threshold and subsequently allow for higher number of Brillouin Stokes lines to be generated.

High power high signal-to-noise ratio multiwavelength Raman fiber laser based on random distributed feedback

A multiwavelength Raman fiber laser based on random distributed feedback and a Sagnac fiber loop filter (SFLF) that can deliver 2.33 W output power is demonstrated. The effect of polarization state on the signal-to-noise ratio (SNR) of multiwavelength emission is investigated by the insertion and removal of a polarization beam splitter (PBS) in the cavity. With the help of a PBS and a polarization controller (PC), stable six-wavelength emission with SNR > 21 dB is achieved. To the best of our knowledge, this is the highest output power in a multiwavelength Raman fiber laser ever reported.

Multiwavelength Raman fiber laser based on polarization maintaining fiber loop mirror and random distributed feedback

We experimentally demonstrate a configuration to realize multiwavelength generation in a Raman fiber laser structure. The system includes a fiber loop mirror (FLM) containing a piece of polarization maintaining (PM) single mode fiber, and a 1 km-long passive fiber which is core pumped by a 1120 nm pump laser providing Raman amplification and random distributed feedback via Rayleigh scattering. Up to 1 W multiwavelength laser output is realized due to interference between modes supported by the FLM. As a consequence, a 35 nm bandwidth multiwavelength spectrum from 1155 to 1190 nm with ~0.75 nm spacing (OSNR ~10 dB) is obtained.

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 1064nm 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 1320nm has been observed with a spacing of 0.40nm and an extinction ratio >30dB. 12 lasing lines around 1601nm have also been achieved with a spacing of 0.58nm. The multiwavelength output powers as high as 108 and 138mW 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.

Tunable Multi-Wavelength Fiber Laser Based on Random Rayleigh Back-Scattering

A novel all-fiber tunable multi-wavelength Raman fiber laser is achieved in a 50 km single-mode fiber connected to a multi-channel wavelength tunable component (MCWTC), i.e., a F–P cavity combined with a long-period fiber gratings based Mach–Zehnder interferometer, that is obtained by micro-processing. Raman amplified Rayleigh scattering feedback provides the mechanism for random lasing that is split to equidistance wavelengths and tuned continuously from 1553.9 to 1565.4 nm by the MCWTC.

Discrimination of bending and temperature by using a multiwavelength raman fiber laser incorporating a sampled fiber Bragg grating

A simple and practical scheme for simultaneous measurement of bending and temperature based on a multiwavelength Raman fiber laser incorporating a single sampled fiber Bragg grating (FBG) is investigated. By using a sampled FBG and a Raman gain medium, we generated a multiwavelength Raman fiber laser and then applied it to discriminate between bending and temperature. Because the bending-induced tension strain gradient changes the chirp ratio of the sampled FBG, the wavelength spacing of the multiwavelength Raman fiber laser is changed as the bending curvature increases. The wavelength spacing, however, is not changed by the applied temperature change, but only multiple lasing wavelengths are shifted to longer wavelengths because of the positive thermal properties of the sampled FBG. Because the proposed sensing configuration combines a signal source with a sensing probe, no additional light sources for sensing signals are required. Accordingly, the proposed sensing technique allows for distinguishing between the bending and the temperature sensitivities.

Theoretical and Experimental Optimization of O-Band Multiwavelength Mixed-Cascaded Phosphosilicate Raman Fiber Lasers

We theoretically analyze and experimentally optimize an O-band mixed-cascaded multiwavelength phosphosilicate Raman fiber laser (MRFL). The theoretical analyses show that the output power is insensitive to the variation of Raman fiber length when it exceeds the optimal length. However, the pump threshold, slope conversion efficiency, and output power of the mixed-cascaded MRFL strongly depend on the output coupling ratio of the output optical coupler. When a 1064-nm Yb3+-doped double-clad fiber laser is used to pump a section of phosphosilicate fiber (PSF) in a mixed-cascaded Raman cavity, both the Raman gains of P2O5 and SiO2 in the fiber are utilized, and multiwavelength lasing around 1320 nm with a wavelength spacing of 0.8 nm has been obtained. The different coupling output ratios and Raman fiber lengths are used to optimize the output performances of the O-band mixed-cascaded MRFL. The maximum output power of the O-band MRFL is 1.3 W with the coupling output ratio of 80% and the PSF length of 1 km. The experimental results are in good agreement with the theoretical ones.

Double random mirror Hi–Bi photonic crystal fiber Sagnac based multiwavelength fiber laser

In the present work, a multiwavelength Raman fiber laser based in a Sagnac configuration is presented. The Sagnac configuration is composed of a Hi–Bi photonic crystal fiber in the middle of two dispersion compensation fibers. The pump power induces two random mirrors to work in opposite directions in the Sagnac, leading to the amplified signal and the multiple scattering signals from the random mirror traveling through the Hi–Bi photonic crystal fiber in a counter-propagating way interfering in the output port.

A Long-Distance Remote Sensing Technique Using a Multiwavelength Raman Fiber Laser Based on Fiber Bragg Gratings Embedded in a Quartz Tube

A long-distance remote sensing technique using a multiwavelength Raman fiber laser with fiber Bragg gratings (FBGs) embedded in a quartz tube is proposed. A Raman linear cavity for multiwavelength generation was configured by using a long length of single mode fiber and FBGs. To discriminate concurrent sensitivities, such as temperature and strain sensitivities, FBG2 was etched to reduce the cladding diameter. Then, two FBGs with different cladding diameters put in a quartz capillary tube and FBG1 with a large diameter (125 μm) was firmly attached in a quartz capillary tube with UV curable epoxy. Since the two FBGs have identical material composition, the multiwavelength Raman fiber laser outputs have the same temperature sensitivities. However, since the FBG1 with a diameter of 125 μm was substantially fixed in a quartz capillary tube, the strain-induced wavelength shift was effectively suppressed. Since the FBG2 with a small cladding diameter of 60 μm only responds to the external strain change, the multiwavelength Raman fiber laser outputs have different strain sensitivities. Therefore, it is possible to simultaneously measure temperature and strain over a long distance of more than 75 km by using the proposed multiwavelength Raman fiber laser without additional input sources.

Multiwavelength Raman Fiber Lasers Using Hi-Bi Photonic Crystal Fiber Loop Mirrors Combined With Random Cavities

Different multiwavelength Raman fiber lasers based on a hybrid cavity setup are proposed. The lasing schemes are based in highly birefringent photonic crystal fiber loop mirrors combined with random cavities. The Hi-Bi PCF loop mirrors are characterized by an interferometric output; whereas the random mirrors are created by cooperative Rayleigh scattering due to Raman gain. This configuration allows suppression of Rayleigh associated noise growth, while taking advantage of it as an active part of the laser cavity, enhancing the achievable gain. The proposed fiber lasers present stable operation at room temperature although different output maxima and shapes depending on the fiber loop mirror/random mirror combination.

Thermally Tunable Multiwavelength Raman Fiber Laser Based on a Novel In-line Interferometer

A thermally tunable multiwavelength Raman fiber laser based on a simple in-line interferometer is investigated. A novel in-line interferometer is realized by using a single long-period fiber grating incorporating a core misalignment method. Cladding modes from the guided core mode are excited in the splicing point between two optical fibers when two core regions are misaligned. By removing an external buffer coating layer in the fiber, the cladding modes can be propagated and recoupled to the core mode at a long-period fiber grating. Since the long-period fiber grating couples the core mode to the cladding modes, the interaction between the core mode and the cladding modes induces an interference pattern, which realizes a multichannel filter. Since the transmission characteristics of the long-period fiber grating are effectively controlled by changing the applied temperature, a thermally tunable multichannel filter based on the proposed in-line interferometer can be obtained. When the proposed multichannel filter is inserted within the ring cavity of a Raman fiber laser, a multiwavelength Raman fiber laser is realized. A high extinction ratio of more than 40 dB is achieved. The output power is stable, and the power fluctuation is measured to be less than 0.7 dB, and the proposed multiwavelength Raman laser has a high thermal tunablity of -0.48 nm/◦C.

Effect of Rayleigh-scattering distributed feedback on multiwavelength Raman fiber laser generation

We experimentally demonstrate a Raman fiber laser based on multiple point-action fiber Bragg grating reflectors and distributed feedback via Rayleigh scattering in an ~22-km-long optical fiber. Twenty-two lasing lines with spacing of ~100 GHz (close to International Telecommunication Union grid) in the C band are generated at the watt level. In contrast to the normal cavity with competition between laser lines, the random distributed feedback cavity exhibits highly stable multiwavelength generation with a power-equalized uniform distribution, which is almost independent on power.

Comparative study of Raman fiber laser in symmetrical and asymmetrical cavities

We propose and demonstrate a novel technique to generate a stable multiwavelength Raman fiber laser (RFL) based on an asymmetrical all-fiber Raman laser cavity by using a wideband chirped fiber Bragg grating (CFBG). The wideband CFBG as an input reflector has a high reflectivity covering the spectral range from 1402 to 1463 nm. Output couplers are composed of three discrete fiber Bragg gratings (FBGs), which generate a multiwavelength laser with center wavelengths of 1415, 1430, and 1445 nm. The output power variations from detuning the center wavelengths of the in-out reflectors are compared experimentally and theoretically in symmetrical and asymmetrical cavities. It is shown that the RFL output with an asymmetric cavity is more stable than that of a symmetric cavity.

Numerical analysis of multi-wavelength cascaded Raman fiber lasers based on genetic algorithm

A novel numerical method is presented for the calculations of the coupled propagation equations in multi-wavelength Raman fiber lasers. By taking the advantages of genetic algorithm and shooting method, only a few of the best individuals at each generation are chosen to implement several shootings in order to accelerate theirs converging. The output characteristics of an all-fiber three-wavelength Raman fiber laser have been analyzed based on the proposed algorithm. Results show that the total output power linearly depends on the pump power with a slope efficiency of ∼51%. For the three output Stokes, the slope efficiencies of the longer wavelengths are larger than that of the shorter ones because the optical energy at the Stokes with shorter wavelengths allows for a transfer of optical power to the longer Stokes via stimulated Raman scattering. We also find that the total output power degrades by less than 10% by adjusting the output-coupler reflectivity and is insensitive to the variation of the Raman fiber length over a large range.

多波长级联拉曼光纤激光器的设计

多波长级联拉曼光纤激光器的设计

Stable and spacing-adjustable multiwavelength Raman fiber laser based on mixed- cascaded phosphosilicate fiber Raman linear cavity

A novel multiwavelength Raman fiber laser based on the mixed-cascaded Stokes effects of phosphosilicate fiber is proposed and demonstrated experimentally. By using stimulated Raman scattering of both P(2)O(5) and SiO(2) along 1 km phosphosilicate fiber pumped with a 1064 nm double-clad fiber laser, the mixed-cascaded Raman linear cavity is formed by a pair of fiber Bragg gratings at 1239 nm, a polarization-maintaining fiber (PMF) Sagnac loop filter, and a conventional optical loop mirror. Up to 15-wavelength stable oscillations around 1320 nm are obtained with a wavelength spacing of 0.44 nm and power nonuniformity of less than 4 dB. By changing the length of the PMF in the Sagnac loop filter from 10 to 5.5 m, the wavelength spacing is adjustable from 0.44 to 0.8 nm. The extinction ratio of the laser is more than 30 dB. Excellent stability is also observed with a peak power fluctuation of less than 0.8 dB in 1 h.