Narrow-linewidth Fiber Laser Research Articles

Tunable and Switchable Dual-Wavelength SLM Narrow-Linewidth Fiber Laser with a PMFBG-FP Filter Cascaded by Multi-Ring Cavity

A single longitudinal mode (SLM) dual-wavelength switchable erbium-doped fiber laser (DW-EDFL) based on polarization-maintaining fiber Bragg grating Fabry–Perot cavity (PMFBG-FP) cascaded multiple sub-ring cavities (MSCs) is proposed. A PMFBG-FP with a narrow-band transmission peak and MSCs was implemented as an optical filter to achieve stable dual-wavelength laser output and guaranteed SLM status. By stretching the PMFBG, a highly stable dual-wavelength tunable output could be achieved with a maximum tuning interval of 0.17 nm. The optical signal-to-noise-ratio (OSNR) at dual-wavelength lasing was higher than 57 dB, and the optimal wavelength and power fluctuations within 0.5 h were 0.01 nm and 0.79 dB, respectively. Meanwhile, the measured linewidths of each wavelength were 1.55 kHz and 1.65 kHz, respectively. The measured polarization states of the two laser wavelengths were linear and orthogonal, with a degree of polarization (DOP) of nearly 100%.

4 kW narrow-linewidth fiber laser based on a simple one-stage MOPA structure

One-stage master oscillator power amplification (MOPA) structure is a simple and robust way to acquire high-power narrow-linewidth fiber lasers (NLFLs), which have wide applications in spectral/coherent beam combination. In this work, an NLFL system was established based on a home-made fiber oscillator seed. By using this one-stage MOPA system, a 4 kW output power was achieved with 3 dB linewidth of about 0.53 nm and optical-to-optical conversion efficiency of 76.9%. The signal to Raman ratio was ∼22 dB. The measured beam quality (M2 factor) was about 1.6 at the output power of 3780 W then degraded to 2.8 at the maximum power of 4 kW. To the best of our knowledge, the 4 kW is the highest output power for such narrow linewidth one-stage MOPA fiber lasers.

Temporal characteristics of the light output from optical fibers with PRBS-modulated laser injection.

Pseudo-random binary sequence (PRBS) phase modulation is an effective method to promote the stimulated Brillouin scattering (SBS) threshold of high-power narrow linewidth fiber lasers. Most studies focus on the subjects of PRBS pattern selection, filter parameter optimization, threshold promotion, etc. In this paper, the temporal characteristics of the light output from optical fibers with PRBS modulated laser injection are investigated theoretically. We found that serious temporal fluctuations, i.e., high intensity pulses, existed in the output laser and backward Stokes light, even though the time-averaged backward Stokes power is only 1% of the input laser power. Based on the transient three wave coupling equations, through exploring the influence of clock rate and PRBS pattern, we demonstrate that this phenomenon arises from the long dwell times in PRBS patterns. Finally, modified PRBS patterns are proposed to significantly eliminate the intense pulses without decreasing the original SBS threshold.

Real-Time Definite Sequence Modulation Based Spectral Broadening Scheme for High-Power Narrow-Linewidth Fiber Laser

High-power narrow-linewidth continuous fiber lasers have wide applications in the fields of power synthesis, nonlinear frequency conversion, and industrial processing. The output power of kW or even MW can be achieved by adopting spectral synthesis. However, in the power amplification process, the nonlinear effect represented by the stimulated Brillouin scattering (SBS) effect limits the further increase of the laser power. And the accompanying self-pulsing effect poses a threat to the safety of the laser system. A high-order phase modulation scheme using a definite time sequence has been proposed to realize the controllable spectral broadening of the seed source, so as to suppress the SBS effect and improve the output power in the amplification stage. In this paper, we demonstrate a real-time definite time sequence generation scheme by using an integrated field-programmable gate array (FPGA) and digital-to-analog converter (DAC). Combined with a single-stage phase modulator, the broadened bandwidth up to 30 GHz and controllable spectral shape can be achieved by adjusting the output waveform of the DAC directly. The generation principles and waveform control methods of real-time sequence are introduced in detail. Proven by a master oscillator power amplifier (MOPA) structure, the laser output power has increased by 30% under the extended bandwidth of 10 GHz compared to the cascaded white noise modulation case. This scheme provides a compact real-time control module for spectral broadening, which lays the foundation for implementing low-cost, compact, and standardized high-power narrow-linewidth fiber lasers.

One KHz Order Narrow Linewidth Fiber Laser Using Rayleigh Backscattering Mechanism in an Additional Piece Optical Fiber

A simple, low-cost, single-longitudinal mode, C-band narrow-linewidth optical fiber laser is presented based on the methodology of the Rayleigh backscattering (RBS). In this paper, a 1551 nm fiber ring laser is developed, and single-mode fiber (SMF) is added to compress the line width. When the SMF length of the RBS cavity is 120 m, the laser has better performance than that in other SMF lengths with a laser line width of 1.46 KHz with housing shield. The optical signal-to-noise ratio (OSNR) is 59.86 dB, and its maximum output power is 9.4 mW. It can quickly achieve the single longitude-mode operation by controlling the variable optical attenuator (VOA). The bit error rate at 10 Gb/s PRBS NRZ modulation is measured to be 10−9 when the optical receiving power is −16.2 dBm.

High Power Narrow-Linewidth Fiber Laser Based on Double-Tapered Fiber

A homemade double-tapered Yb-doped fiber is employed in a high-power narrow-linewidth fiber amplifier to improve the thresholds of nonlinear effects and transverse mode instability (TMI) effect. A bidirectional pumping configuration is employed, and a phase-modulated single-frequency fiber laser serves as the seed laser. As a result, an output power of 3630 W with 0.21 nm linewidth (stimulate Brillouin scattering limited) and an output power of 4180 W with 0.59 nm linewidth (TMI limited) are realized, corresponding to the slope efficiency of ∼77%. The beam quality at the maximum output power is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm M}_{\rm x}^{2}= 1.57, {\rm M}_{\rm y}^{\rm 2} = 1.39$</tex-math></inline-formula> . The results could provide a well reference for the power scaling of narrow-linewidth Yb-doped fiber amplifier.

3.3 kW narrow linewidth FBG-based MOPA configuration fiber laser with near-diffraction-limited beam quality

This paper demonstrates a narrow-linewidth fiber laser with near-diffraction-limited beam quality and high Raman suppression ratio by utilizing Master Oscillator Power-Amplifier structure based on narrow-bandwidth fiber Bragg gratings. The output power reaches 3.31 kW with a slope efficiency of 85.0 %. At the maximum output power, the 3 dB, 10 dB, and 20 dB linewidths are 0.40 nm, 1.20 nm, and 3.09 nm, respectively. The beam quality M2 factor is 1.32 and the Raman suppression ratio reaches 26.3 dB. A pair of narrow-bandwidth fiber gratings were used in the oscillator to compress the linewidth of the seed laser. We used backward-pumping configuration and plum-coiled gain fiber in the amplification stage to suppress the Raman effect and select transverse mode by fiber-bending. Finally, a compact all-fiber laser was obtained with narrow-linewidth, high beam quality, and effective suppression of the Raman effect. To the best of our knowledge, this is the highest output power for a sub-nanometer-linewidth laser using narrow-bandwidth fiber gratings and none-wavelength-locked laser diodes, which achieves near-diffraction-limit beam quality. This provides a solution for high-power narrow-linewidth laser sources with high beam quality.

3.96 kW All-Fiberized Linearly Polarized and Narrow Linewidth Fiber Laser with Near-Diffraction-Limited Beam Quality.

In this paper, we realize a 3.96 kW all-fiberized and polarization-maintained (PM) amplifier with narrow linewidth and near-diffraction-limited beam quality. Based on a master oscillator power amplifier (MOPA) configuration seeded with phase-modulated single-frequency laser, a 3.96 kW signal laser is achieved with a 3 dB linewidth of 0.62 nm at the pump power of 5.02 kW. At the maximum output power, the polarization extinction ratio (PER) is ~13.9 dB, and the beam quality (M2 factor) is M2x = 1.31, M2y = 1.41. As far as we know, this is the maximum output power of PM narrow linewidth fiber laser with near-diffraction-limited beam quality and all-fiber format.

Bidirectional tandem-pumped high-brightness 6 kW level narrow-linewidth confined-doped fiber amplifier exploiting the side-coupled technique.

In this work, a bidirectional tandem-pumped high-power narrow-linewidth confined-doped ytterbium fiber amplifier is demonstrated based on side-coupled combiners. Benefiting from the large-mode-area design of the confined-doped fiber, the nonlinear effects, including stimulated Raman (SRS) and stimulated Brillouin scattering (SBS), are effectively suppressed. While the transverse mode instability (TMI) effect is also mitigated through the combination of confined-doped fiber design and the bidirectional tandem pumping scheme. As a result, narrow-linewidth fiber laser with 5.96 kW output power is obtained, the slope efficiency and the 3-dB linewidth of which are ∼81.7% and 0.42 nm, respectively. The beam quality is well maintained during the power scaling process, being around M2 = 1.6 before the TMI occurs, and is well kept (M2 = 2.0 at 5.96 kW) even after the onset of TMI. No SRS or SBS is observed at the maximum output power, and the signal-to-noise ratio reaches as high as ∼61.4 dB. To the best of our knowledge, this is the record power ever reported in narrow-linewidth fiber lasers. This work could provide a good reference for realizing high-power high-brightness narrow-linewidth fiber lasers.

Switchable single-longitudinal-mode narrow linewidth fiber laser with cylindrical vector beam output

We experimentally demonstrated a switchable single-longitudinal-mode (SLM) narrow linewidth fiber laser with cylindrical vector beam (CVB) output. A mode selective filter is composed of a fiber Bragg grating and a mechanical long period fiber grating (LPFG), and it is used to realize the mode switch and wavelength switch. The compound ring cavity structure is composed of a main ring cavity and two passive subring cavities (SCs) so that the SLM operation is achieved. By controlling the polarization state of the light in the laser cavity and the pressure applied to the mechanical LPFG, both the radially and azimuthally polarized CVBs are obtained at 1543.35nm and 1544.38nm. Meanwhile, the signal-to-noise ratio is higher than 60dB. The 20dB linewidth of the proposed fiber laser for each wavelength is approximately 5.7kHz and 6.8kHz.

Stabilized Narrow-Linewidth Brillouin Random Fiber Laser With a Double-Coupler Fiber Ring Resonator

A stabilized coherent narrow-linewidth Brillouin random fiber laser with low lasing noise is proposed and investigated experimentally, which employs stimulated Brillouin scattering and Rayleigh scattering in optical fibers to provide the gain and the random distributed feedback, respectively. The stabilized lasing output with suppressed noise is realized utilizing a simple structure of a double-coupler fiber ring resonator, which is composed of a section of single-mode fiber and two optical couplers with different coupling ratios. Compared with the existing free-running Brillouin random fiber lasers, much more stabilized laser output can be obtained as the double-coupler fiber ring resonator effectively acts as a narrow-bandwidth mode filter through the Vernier effect that constrains the dense random longitudinal modes competition within a small frequency range. In the experiment, a stable ultra-narrow linewidth of approximately 586.4 Hz is obtained from the laser output. Statistical analysis of mode hopping in the proposed laser indicates a great improvement in multi-mode resonances and frequency jitters with the imbedding of the ring resonator. In addition, measurement results of relative intensity noise and frequency noise of the proposed laser showcase a great suppression in mode-competition-induced lasing instability and a significant improvement in the noise level compared to the free-running Brillouin random fiber lasers. The proposed all-fiber-based stabilization technique makes a step forward for developing practically robust and reliable Brillouin random fiber lasers. Such a stabilized highly coherent narrow-linewidth laser source with low cost and low power consumption will find promising applications in high-resolution spectrometers, microwave photonics, and optical sensing.

Tunable Narrow-Linewidth Fiber Laser Based on the Acoustically Controlled Polarization Conversion in Dispersion Compensation Fiber

Researches on high coherence light sources always pursue fast tuning speed, linear tunability and persistence of narrow linewidths at different tuning channels. Fortunately, acousto-optical interaction (AOI) can be employed in the fast management of the lasing wavelength. Herein, we propose a fast tunable narrow-linewidth fiber laser assisted by the acoustically-induced polarization selection in dispersion compensation fiber (DCF). The lasing wavelength is determined by the acoustically-induced band-pass grating in DCF. The large dispersion slope of the DCF suppresses the bandwidth of the TM₀₁ peak to be less than 1 nm. The acousto-optic-controlled polarization conversion effectively restrains the acousto-optic frequency shift. With side longitudinal mode suppressions induced by the combintion of the self-injection feedback and saturable absorption filtering, the output laser successfully achieves the narrow-linewdith operation and owns a low relative intensity noise floor of &#x2212;135 dB&#x002F;Hz. By controlling the acoustic-wave frequency, the laser can be linearly tuned with a large wavelength range (over 20 nm, linear fitting R² reaches 0.99781), and the laser linewidths remain about &#x223C;2 kHz in different tuning channels. The laser tuning dynamics under the acousto-optical controlling are experimentally revealed, and the lasing tuning response time is &#x223C;800 &#x03BC;s.

3.1 kW 1050 nm narrow linewidth pumping-sharing oscillator-amplifier with an optical signal-to-noise ratio of 45.5 dB.

In this paper, the amplified spontaneous emission (ASE) suppression in a 1050 nm fiber laser with a pump-sharing oscillator-amplifier (PSOA) structure is studied theoretically and experimentally. A theoretical model of a fiber laser with a PSOA structure is established. The characteristics of the ASE for the PSOA structure and the pump-independent oscillator-amplifier (PIOA) structure are compared and analyzed. The experimental results show that the ASE can be effectively suppressed by utilizing the PSOA structure, which agree with the simulation results. A 1050 nm high-power narrow-linewidth fiber laser with PSOA structure is demonstrated, in which the gain fiber lengths of the oscillator and amplifier are 1.6 m and 9 m, respectively, to ensure the interconnection of pump power between the oscillator and amplifier. Finally, the maximum output power of 3.1 kW has been achieved, the linewidth is 0.22 nm at 3 dB, the beam quality M2 ≈ 1.33, and the optical signal-to-noise ratio (OSNR) is 45.5 dB.

Narrow-Linewidth Er-Doped Fiber Lasers With Random Distributed Feedback Provided By Artificial Rayleigh Scattering

A compact random fiber laser based on a short artificial Rayleigh reflector and heavily-doped Er fibers (custom-made and commercial as a reference) has been proposed, characterized and optimized in terms of efficiency, linewidth and noise level. A 10-cm artificial Rayleigh reflector with mean scattering level of &#x002B;41.3 dB&#x002F;mm relative to the natural Rayleigh scattering of the host fiber and low insertion loss level (&#x223C;0.05 dB&#x002F;cm at 1535 nm) was fabricated using a femtosecond direct writing technique. Its implementation as a distributed output mirror in a half-open cavity of a 980-nm diode pumped Er-doped fiber laser results in random lasing at 1535 nm in single- and few-mode regimes with power up to 100 mW, slope efficiency up to 16.5&#x0025;, and signal-to-noise ratio up to 60 dB. A single-frequency regime with &#x223C;10 KHz linewidth was observed at output power up to 2.5 mW. Tunability potential of such random lasers is also demonstrated.

High-power narrow-linewidth fiber lasers using optical spectrum broadening based on high-order phase modulation of inversion probability-tuning sequence.

Continuous fiber laser with ultra-high power and narrow linewidth is one of the key devices in the field of high-precision industrial processing, beam combining, and nonlinear frequency conversion. Under the premise of ensuring the signal quality, continuously increasing the output power is the focus of high-power narrow-linewidth fiber lasers. Driven by the white noise or pseudo-random binary sequence (PRBS), using cascaded phase modulations to broaden the spectrum of the seed source to suppress the stimulated Brillouin scattering (SBS) effect in the master oscillator power amplifier (MOPA) structure is an effective solution to increase the output power. However, this type of optical spectrum needs to be optimized, and the randomness of the driving signal causes a self-pulsing effect, which limits the further increase of the output power. In this paper, the influence of the frequency interval and randomness of the driving signal on the SBS effect in the laser system is analyzed. The modulated spectral type can be simply adjusted through changing the bit rate and inversion probability. Combining with high-order phase modulation, an approximate rectangular spectral broadening of the seed source with a tunable bandwidth up to 30 GHz is achieved. Compared with the cascaded white noise case, the output power of this scheme is increased by 600 W under the extended bandwidth of 27 GHz. It is fully verified that the seed source spectrum with high in-band flatness and low randomness can effectively suppress the SBS effect in the fiber laser and increase the output power.

Multi-Wavelength and Narrow Linewidth Fiber Laser Based on Composite Resonator

Multi-Wavelength and Narrow Linewidth Fiber Laser Based on Composite Resonator

Research progress of narrow linewidth fiber laser oscillator (Invited)

Research progress of narrow linewidth fiber laser oscillator (Invited)

Brillouin Dual-wavelength Narrow-linewidth Fiber Laser and Its Application in Frequency-swept Microwave-signal Generation

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Research Progress on Ytterbium-Doped Silica Glass Fiber for High-Power Narrow-linewidth Fiber Lasers

Research Progress on Ytterbium-Doped Silica Glass Fiber for High-Power Narrow-linewidth Fiber Lasers

Six kilowatt record all-fiberized and narrow-linewidth fiber amplifier with near-diffraction-limited beam quality

Abstract In this work, an all-fiberized and narrow-linewidth fiber amplifier with record output power and near-diffraction-limited beam quality is presented. Up to 6.12 kW fiber laser with the conversion efficiency of approximately 78.8% is achieved through the fiber amplifier based on a conventional step-index active fiber. At the maximum output power, the 3 dB spectral linewidth is approximately 0.86 nm and the beam quality factor is M x 2 = 1.43, M y 2 = 1.36. We have also measured and compared the output properties of the fiber amplifier employing different pumping schemes. Notably, the practical power limit of the fiber amplifier could be estimated through the maximum output powers of the fiber amplifier employing unidirectional pumping schemes. Overall, this work could provide a good reference for the optimal design and potential exploration of high-power narrow-linewidth fiber laser systems.