All-fiber Raman Laser Research Articles

High Energy Singular Beams Generation From a Dissipative Soliton Resonance Raman Fiber Laser

We demonstrated the high energy 1.65 μm singular beam generation from a dissipative soliton resonance (DSR) all-fiber Raman laser experimentally. By utilizing advantages of the high nonlinearity and home-made mode-selective coupler (MSC), different DSR pulsed singular beams, including cylindrical vector beam (CVB) and vortex beams (VB), have been generated experimentally. The maximum pulse energy can be enhanced up to 698.19 nJ with high signal to noise ratio of 80 dB by optimizing the intra-cavity nonlinearity. Our research may provide a new method to generate high energy pulsed singular beams with a flexible operation wavelength.

Noise-like pulse generation in an Nd-doped single-mode all-fiber mode-locked Raman laser operating at 0.93 µm.

Based on the Nd-doped single-mode fiber (SMF) as the gain medium and SMF as the Raman medium, an all-fiber mode-locked Raman laser operating at 0.93 µm waveband was demonstrated for the first time. A mandrel with a diameter of 10 mm was employed to introduce bending losses to suppress the dominant emission of Nd-doped fiber at 1.06 µm. A noise-like pulse with a pulse width of 194.70 fs, a repetition rate of 1.73 MHz and a single pulse energy of 2.03 nJ was obtained in the mode-locked Raman laser with a Stokes wavelength of 932.59 nm. Such an ultrafast all-fiber Raman laser operating at 0.93 µm has the advantages of low cost, simple structure and compactness, and can be used as an ideal light source for the two-photon microscopy.

Mode-resolved analysis of pump and Stokes beams in LD-pumped GRIN fiber Raman lasers.

All-fiber Raman lasers have demonstrated their potential for efficient conversion of highly multimode pump beams into high-quality Stokes beams. However, the modal content of these beams has not yet been investigated. In this work, based on a mode decomposition technique, we are able to reveal the details of intermodal interactions in the different operation regimes of continuous wave multimode graded-index fiber Raman lasers. We observed that, above the laser threshold, the residual pump beam is strongly depleted in its transverse modes with principal quantum number below 10. However, the generated Stokes signal beam mainly consists of the fundamental mode, but higher-order modes are also present, albeit with exponentially decreasing population.

All-Fiber Gas Raman Laser by D2-Filled Hollow-Core Photonic Crystal Fibers

We report here an all-fiber structure tunable gas Raman laser based on deuterium-filled hollow-core photonic crystal fibers (HC-PCFs). An all-fiber gas cavity is fabricated by fusion splicing a 49 m high-pressure deuterium-filled HC-PCF with two solid-core single-mode fibers at both ends. When pumped with a pulsed fiber amplifier seeded by a tunable laser diode at 1.5 μm, Raman lasers ranging from 1643 nm to 1656 nm are generated. The maximum output power is ~1.2 W with a Raman conversion efficiency of ~45.6% inside the cavity. This work offers an alternative choice for all-fiber lasers operating at 1.6–1.7 μm band.

Mid-infrared cascaded stimulated Raman scattering and flat supercontinuum generation in an As-S optical fiber pump at 2 µm.

We demonstrate broadband mid-infrared cascaded stimulated Raman scattering (SRS) and flat supercontinuum (SC) generation in a chalcogenide optical fiber made from As2S5 glass. By using a 2 µm nanosecond laser as the pump source, mid-infrared cascaded SRS up to six orders ranging from 2149 to 3425 nm was experimentally observed, and this all-fiber Raman laser operating at 3.43 µm was realized for the first time to our knowledge. By introducing a 2 µm femtosecond laser as the excited source, the broadband flat mid-infrared SC with the spectral range of ∼10dB (from ∼1030 to 3441 nm) was observed. Our results verify that the As2S5 optical fibers possess promising applications for tunable mid-infrared Raman fiber lasers and SC light sources pumped by 2 µm pulsed lasers.

Multimode LD-pumped all-fiber Raman laser with excellent quality of 2nd-order Stokes output beam at 1019 nm.

A multimode all-fiber Raman laser enabling cascaded generation of high-quality 1019-nm output beam at direct pumping by highly-multimode (M2>30) 940-nm laser diodes has been demonstrated. The laser is made of a 100/140 graded-index fiber with special in-fiber Bragg gratings which secure sequential generation of the 1st (976 nm) and 2nd (1019 nm) Stokes orders. Comparing different 1019-nm cavity structures shows that the half-open cavity with one FBG and distributed feedback via random Rayleigh backscattering provides excellent quality (M2∼1.3) with higher slope efficiency of pump-to-2nd Stokes conversion than in the conventional 2-FBG cavity. The maximum achieved slope efficiency amounts to about 40% at output powers of up to 12 W limited by the 3rd Stokes generation.

All-fiber dual-frequency Raman laser for terahertz telecommunication systems

The two-wave (2λ) fiber laser based on the stimulated Raman scattering is proposed in order to improve terahertz technologies realization and to increase the efficiency of radiation sources for telecommunication systems in the terahertz range. As a result of the analysis of the available experimental data in our work it was found that the Raman gain profile in single-mode fibers makes it possible to realize a 2λ laser in the fully fiber configuration. The main advantage of the proposed terahertz source is a significant reduction of the phase noises as it should be expected due to the both lasers will be pumped using a common source. The main parameters of the fiber Bragg gratings for 2λ laser cavity are determined and it is shown its possibility to meet the modern requirements for the monolithic integration in fully fiber device design. The possibility of reducing the threshold pump power by at least 400 times has been proved by simulating for different typesof fibers, and it will significantly lowered the weight and size characteristics of such a laser.

976 nm all-fiber Raman laser with high beam quality at multimode laser diode pumping

A 976 nm all-fiber Raman laser enabling high beam quality at direct multimode laser diode pumping with low beam quality (M2 > 30) is demonstrated. The laser is performed in a 100/140 multimode graded-index fiber with special in-fiber Bragg gratings that secure generation of the Stokes beam with relatively good quality (M2 ⩽ 2) and high slope efficiency of the pump-to-Stokes conversion (70%) at output powers of up to ~50 W.

High-brightness all-fiber Raman lasers directly pumped by multimode laser diodes

High-brightness fiber laser sources usually utilize active rare-earth-doped fibers cladding-pumped by multimode laser diodes (LDs), but they operate in limited wavelength ranges. Singlemode-passive-fiber based Raman lasers are able to operate at almost any wavelength being pumped by high-power fiber lasers. One of the interesting possibilities is to directly pump graded-index (GRIN) multimode passive fibers by available high-power multimode LDs at 915–940 nm, thus achieving high-power Raman lasing in the wavelength range of 950–1000 nm, which is problematic for rare-earth-doped fiber lasers. Here we review the latest results on the development of all-fiber high-brightness LD-pumped sources based on GRIN fiber with in-fiber Bragg gratings (FBGs). The mode-selection properties of FBGs inscribed by fs pulses supported by the Raman clean-up effect result in efficient conversion of multimode pump into a high-quality output beam at 9xx nm. GRIN fibers with core diameters 62.5, 85 and $100~\unicode[STIX]{x03BC}\text{m}$ are compared. Further scaling capabilities and potential applications of such sources are discussed.

High-efficiency LD-pumped all-fiber Raman laser based on a 100 µm core graded-index fiber

We demonstrate a high-power, high-efficiency Raman laser based on a 100 µm core graded-index (GRIN) fiber directly pumped by 915 nm multimode laser diode modules in all-fiber configuration. Optimization of GRIN fiber length and pumping scheme was performed. As a result, 62 W of CW power has been obtained at a wavelength of 954 nm with a slope efficiency of 85%. The joint action of Raman clean-up effect and mode-selection properties of special fiber Bragg gratings inscribed in the central part of the GRIN fiber core results in significant beam quality enhancement for the generated Stokes beam ( < 3) in comparison with that of the pump radiation ( > 30). In addition, the exact value of the operating wavelength near the Raman gain maximum was varied. To the best of our knowledge, this is the first study of the impact of a Raman gain spectral profile on the power, spectrum and beam quality parameter M2 of multimode Raman laser. It appears that they very much dependent on the spectral region of Raman gain at which we work, when the wavelength is selected by a fiber Bragg grating inscribed in a multimode GRIN fiber.

Generating high-quality beam in a multimode LD-pumped all-fiber Raman laser.

We report on the first demonstration of an all-fiber CW Raman laser based on a multimode graded-index fiber directly pumped by multimode fiber-coupled laser diodes. A joint action of Raman clean-up effect and mode-selection properties of special fiber Bragg gratings inscribed in the central part of the graded-index fiber core, results in high-efficiency conversion of a multimode (M2~26) pump at 915 nm into a high-quality (M2~2.6) output beam at 954 nm. About 50 W output power has been obtained with slope efficiency of 67%. The proposed development and integration of key multimode fiber technologies opens the door to new type of LD-pumped high-power high-beam-quality fiber lasers that may operate at almost any wavelength defined by available LDs.

Compact non-cascaded all-fiber Raman laser operating at 1174 nm

We investigate a non-cascaded, all-fiber, single-mode Raman fiber laser (RFL) operating at 1174 nm with an optical slope efficiency of 68%. An ~1-km commercial single-mode fiber is used as the Raman gain medium. The RFL cavity is formed between a high reflectivity fiber Bragg grating (FBG) and a perpendicularly-cleaved fiber facet. The laser is pumped by using a homemade ytterbium-doped fiber laser (YDFL) and can be frequency doubled to generate yellow light. Under the optimum condition, A 6.9-W 1174-nm laser is obtained at maximum available power (24 W) of a laser diode pump. The optical conversion efficiency and the net slope efficiency of the RFL were respectively, 29% and 38%, with respect to launched diode laser power. We also demonstrate yellow-light generation by frequency doubling of the RFL.

An all-fiber Raman laser for cylindrical vector beam generation

We demonstrate a compact Raman all-fiber oscillator for cylindrical vector beam generation. The laser is based on a strongly guiding passive fiber with two fiber Bragg gratings inscribed in it, which separates the different transverse modes in wavelength. Additionally, the impact of core ellipticity in strongly guiding fibers for the generation of cylindrical vector beams is theoretically analyzed. In this work, the elliptical core is compensated by introducing stress. Thereby, an azimuthally polarized beam with an output power of 480 mW and a radially polarized beam with an output power of 400 mW are generated, limited only by the onset of nonlinear effects inside the Raman fiber oscillator. Switching between these two cylindrical vector beams is possible by rotating the polarization of the pump. The presented concept is well suited for all-fiber microscopic applications.

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.

High-Power and Widely Tunable All-Fiber Raman Laser

A high-power and widely tunable all-fiber Raman laser is demonstrated. The Raman fiber laser has been tuned over a range of 60 nm from 1075 to 1135 nm and delivers up to 5.0 W of Stokes output power for 6.5 W of launched pump power. Efficiencies ranging from 76.1 to 93.1% and laser thresholds from 0.78 to 2.59 W have been measured. The spectrum of the depolarized Raman gain coefficient of the germanosilicate fiber has also been inferred from our experimental measurements.

Influence of light polarization on dynamics of all-fiber Raman lasers: theoretical analysis

Using Stokes-vectors formalism, we present a simple model describing steady and dynamic characteristics of all-fiber Raman lasers. This model allows us to describe experimental behaviors that are not yet understood in Raman lasers. In lasers made with standard fibers we show theoretically that weak birefringence and the optical Kerr effect lead to the emergence of unstable regimes similar to those recently observed in experiments [Opt. Lett. 28, 2464 (2003)]. However, the model shows that lasers made with polarization-maintaining fibers are always stable, as evidenced in experiments.

Influence of spectral broadening on steady characteristics of Raman fiber lasers: from experiments to questions about validity of usual models

We investigate the limits of validity of models commonly used to describe all-fiber Raman lasers. To this end, we record the characteristics of an all-fiber Raman laser in which pump and Stokes waves remain linearly polarized. We show that they significantly deviate from the characteristics predicted by the usual model. The observed discrepancy arises from spectral broadening effects leading to a decrease of the mean reflectivity of the fiber Bragg grating mirrors with the incident pump power. Usual single-mode and multi-mode models are shown to be irrelevant to describe these effects. We also show that coupling among longitudinal modes must be taken into account for further modeling of spectral broadening.

High-Power CW Linearly Polarized All-Fiber Raman Laser

We demonstrate a high-power continuous-wave linearly polarized all-fiber Raman laser. The maximum Stokes output power of 4.7 W at 1120-nm wavelength with conversion slope efficiency of 87% was achieved. It is shown that Raman laser threshold greatly depends on pump polarization degree while Raman laser polarization depends on the design of Raman converter rather than on polarization of the pump laser. Slope efficiency was found to be independent on pump polarization degree.

Short-pulse, all-fiber, Raman laser with dispersion compensation in a holey fiber.

The use of Raman gain in conventional fiber followed by dispersion compensation in a holey fiber in a synchronously pumped laser configuration allowed compression by a factor of 8.5 of output pulses at a selected wavelength with respect to the pump pulses. We obtained 2-ps output pulses at 1.14 microm from a totally fiber-integrated laser pumped with 17-ps pulses at 1 microm. Higher pulse compression should be possible with nonlinear chirp compensation. Ultrashort-pulse, all-fiber Raman lasers at wavelengths shorter than 1.3 microm are feasible.

Realization of femtosecond soliton oscillation in all-fiber Raman laser with soliton self-frequency shift suppression

In order to obtain the true oscillation of femtosecond solitons in fiber Raman lasers where relatively long fibers are usually used, it is necessary to suppress the soliton self-frequency shift (SSFS) in fibers. The oscillation of femtosecond solitons in a synchronously pumped all-fiber Raman ring laser by suppressing the SSFS effect is described. It is shown that proper choices of both the Stokes oscillation wavelength and pump power level are required for SSFS suppression. Optical pulses as short as 400 fs with low-amplitude noise have been generated from the compact fiber Raman laser.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>