Fiber Laser Configuration Research Articles

2 × 4 kW near-single-mode laser output assisted by an optimized bidirectional oscillating-amplifying integrated fiber laser configuration

Bidirectional output oscillating-amplifying integrated fiber laser (B-OAIFL) can achieve the two-ports laser amplification based on a single cavity, showcasing a promising prospect. In order to improve both the laser power and beam quality, we first simulate and optimize the stimulated Raman scattering (SRS) effect in the B-OAIFL. The simulation results show the SRS effect can be suppressed by optimizing the diameter as well as the length of the active fiber at different locations. With the guidance of theoretical and experimental analysis for the combined suppression of SRS and transverse mode instability (TMI), a near-single-mode B-OAIFL with 2 × 4 kW was demonstrated. Based on this foundation, we further devoted ourselves to the pursuit of the optimization of the structure and performance. The necessity of the configuration of side pump, which was initially introduced for its exceptional performance in stabilizing temporal chaos, was reevaluated in detail. With its negative impacts on efficiency improvement and SRS suppression were analyzed and verified, we removed this configuration and finally demonstrated a more simplified design with superior performance. A total bidirectional output of 8105 W was achieved, with an O-O efficiency of 79.6% and a near-single-mode beam quality of M A 2∼1.36,M B 2∼1.63. No signs of TMI were observed, and the signal-to-SRS suppression ratio was over 38 dB. The results still demonstrate a promising potential for power scaling based on this configuration and parameters.

Linear Fiber Laser Configurations for Optical Concentration Sensing in Liquid Solutions

In this study, different configurations based on linear fiber lasers were proposed and experimentally demonstrated to measure the concentration of liquid solutions. Samples of paracetamol liquid solutions with different concentrations, in the range from 52.61 to 201.33 g/kg, were used as a case-study. The optical gain was provided by a commercial bidirectional Erbium-Doped Fiber Amplifier (EDFA) and the linear cavity was obtained using two commercial Fiber Bragg Gratings (FBGs). The main difference of each configuration was the coupling ratio of the optical coupler used to extract the system signal. The sensing head corresponded to a Single-Mode Fiber (SMF) tip that worked as an intensity sensor. The results reveal that, despite the optical coupler used (50:50, 60:40, 70:30 or 80:20), all the configurations reached the laser condition, however, the concentration sensing was only possible using a laser drive current near to the threshold value. The configurations using a 70:30 and an 80:20 optical coupler allowed paracetamol concentration measurements with a higher sensitivity of (−3.00 ± 0.24) pW/(g/kg) to be performed. In terms of resolution, the highest value obtained was 1.75 g/kg, when it was extracted at 20% of the output power to the linear cavity fiber laser configuration.

Multi-wavelength fiber laser via evanescent field confinement with Al2O3 nanolaminate-coated thinned fiber

We present the fabrication and analysis of an Erbium-doped optical fiber laser emitting at multiple wavelengths. This is accomplished via a filter constructed from a fiber taper coated with alumina (Al2O3). The taper is created using the flame brushing induction technique with a combination of Butane (25 %) and Oxygen (75 %). The diameter is reduced to a 20 µm waist and 2 mm burner displacement. The thin film of Al2O3 was deposited via atomic layer deposition (ALD), resulting in a 15 nm layer. The coated fiber taper was then inserted into a ring fiber laser cavity functioning as a selector filter. This fiber laser produced an output comprising six simultaneous wavelengths: 1531.14, 1531.79, 1532.45, 1541.85, 1544.45, and 1562.22 nm. Laser signal stability tests were performed for one hour at 25 °C at the six emission wavelengths, resulting in a maximum optical power fluctuation of 0.15 to 0.33 dB, a wavelength shift variation of 0.02 nm, and a signal-to-noise ratio of 31.79 dB in average. The laser lines emitted have an average spectral width of 0.06 nm. Our results show that the typical performance of the fiber laser configuration based on an optical fiber taper was improved by the addition of the Al2O3 layer and can be further improved. Our findings demonstrate that the standard operation of the fiber laser setup, which utilizes an optical fiber taper, was enhanced through the incorporation of an Al2O3 layer and has the potential for further development.

Study on Dual-Wavelength Wide-Spectrum Erbium-Doped Fiber Ring Laser for Optical Fiber Interferometric Sensing System

In this paper, a novel dual-wavelength wide-spectrum erbium-doped fiber ring laser (EDFRL) for optical fiber sensing system is proposed and experimentally demonstrated. The output of EDFRL is theoretically simulated and classified depending on the theoretical analysis of laser threshold condition into “excited state” and “nonexcited state”. The influence of pump wavelength, fiber laser configuration, EDF length and output coupling ratio of EDFRL is discussed. The EDFRL pumped at 1480 nm wavelength and backward-pumped mode could achieve the stable maximum wide-spectrum output power. The output power fluctuation is lower than 0.06 dB and the center wavelengths shift is less than 0.01 nm. The practicability of EDFRL in a hybrid M-Z and Sagnac interferometer optical fiber sensing system is demonstrated through the comparison of SLD and EDFRL. Consequently, the EDFRL proposed in this study is expected to replace the traditional SLD in the optical fiber interferometric sensing system at a lower cost.

Molybdenum gallium carbide as saturable absorbers in 1.5-μm passive mode-locked fibre laser

A saturable absorber (SA) is one of the important components in a passive mode-locked fibre laser configuration to attain picosecond- to femtosecond-competent ultrashort pulses for fulfilling the imperatives of industries, particularly engineering and life sciences. The substantiation of a newfound SA in the generation of mode-locked pulses utilising molybdenum gallium carbide (Mo2Ga2C)—a MAX phase nanomaterial—was authenticated in this work. A Mo2Ga2C SA thin film was fabricated via a simple solution with polyvinyl alcohol (PVA) as the hosting medium. Linear absorption, modulation depth, non-saturable absorption, and saturation intensity of the 17.141-μm Mo2Ga2C SA were found to be 8.29%, 19.82%, 9.21% and 2.85 kW/cm2, respectively. The fabricated Mo2Ga2C SA was then implemented into an erbium-doped fibre laser (EDFL) system to realise the eminently stable mode-locked fibre laser at a centre wavelength of 1559.2 nm and rudimentary signal-to-noise ratio (SNR) of 54.8 dB. The pulse repetition rate and pulse width were measured to be 968.72 kHz and 2.028 ps successively. The maximum pulse energy and peak power are 10.219 nJ and 24.12 mW. In corroboration with previous reports, the implementation of Mo2Ga2C as a mode-locker is propitious in validating the impressively stable and ultrafast nonlinear fibre laser system for further multidisciplinary applications, for instance, medical instrumentation, sensing and range finding, communication, and military due to its excellent optical, physical, thermal, and mechanical properties.

Noise-like pulse generation in 1.95 µm region using bulk α-alumina saturable absorber

This work presents a tapered fiber decorated with bulk α-alumina with 4.08% modulation depth and 21.67 MW/cm2 saturation intensity which was responsible to induce noise-like pulse (NLP) in an “eye-safe” wavelength region. The light-matter interaction within evanescent field of ultrathin tapered fiber established NLP in a ring configuration of thulium-doped fiber laser with a broad spectral bandwidth of 45 nm centered at 1948 nm wavelength. The NLP was emitted at 11.36 MHz repetition rate in a net anomalous laser cavity. The generated pulse had a maximum pulse energy of 2.46 nJ at 1587 mW pumping power. The robustness of the NLP performance was validated with 3 h stability test, which opens new possibilities for future research of this material in the wavelength of exceeding 1.9 μm.

Paracetamol concentration-sensing scheme based on a linear cavity fiber laser configuration

A paracetamol concentration-sensing scheme based on a linear cavity fiber laser configuration is demonstrated experimentally. The laser cavity has a fiber sensor at one end, that allows refractive index measurements. The refractometer consists of a cleaved fiber tip combined with an FBG functioning as a reflecting mirror. The combination of a fiber loop mirror at the other end allows to reflect all the light from the FBG and refractometer, forming a linear cavity. By measuring the intensity variation of the Fresnel reflection at the fiber-to-liquid interface, the measured concentration is linear and have a concentration sensitivity of -8.74±0.34×10-5µW/(g/kg), over a range of 52.61 to 219.25 g/kg, and with a resolution of 2.77 g/kg.The results obtained present high stability and prove the potential of the fiber laser system to performed real-time measurements of concentration, in a non-invasive way.

Photon-to-photon modulation in fiber laser system using emerging materials

Graphene was the first two dimension (2D) material demonstrated as temporal modulator in fiber laser system more than a decade ago. Following its success, other types of 2D materials with comparable and superior performance were discovered. In this review, we outlined the types of optical modulation into wavelength, amplitude, polarization, phase and temporal modulation. We also discussed each modulation working principles along with its fiber laser configuration. Additionally, we compiled each modulator’s performance based on a wide range of 2D materials that were published recently. Some novel and emerging materials such as quantum dot (QD), one dimension (1D), three dimension (3D), composite and organic materials were highlighted.

An aluminum coated all-fiber mirror and a Mach–Zehnder interferometer for developing a switchable and tunable multi-wavelength laser

In this paper, a tunable and switchable multi-wavelength erbium doped linear fiber laser, based on an optical fiber loop mirror containing a Mach–Zehnder interferometer (MZI) and an aluminum coated optical fiber cleaved end is presented. The MZI, obtained by core-offset splicing a piece of photonic crystal fiber (PCF) between two segments of a single mode fiber (SMF), acts as a wavelength selective filter (WSF). The full reflecting mirror implemented is obtained by thermal evaporation of aluminum on a cleaved fiber end, technique which has not been deeply explored for compact fiber laser configurations. In this way, both optical loop mirror and the aluminum coated fiber work together to make a resonant cavity. By rotating the wave plates of a polarization controller, the polarization state of the cavity modes diversifies, and the laser setup can emit one, two, three or four laser wavelengths, which can be switched from 1526 to 1562 nm. In addition, this laser arrangement can be tuned within a 5 nm interval and has a side-mode suppression ratio of 42 dB for single-wavelength operation. Finally, the proposed laser configuration achieved a high stability for more than an hour at room temperature.

Molybdenum Aluminum Boride as the Q-Switcher and Mode-Locker in the Erbium-Doped Fiber Laser Configuration

Molybdenum Aluminum Boride as the Q-Switcher and Mode-Locker in the Erbium-Doped Fiber Laser Configuration

An actively Q-switched multi-wavelength ytterbium fiber laser with cascaded polarization-maintaining Bragg gratings

In this paper, we investigate the multi-wavelength lasing characteristics of an actively Q-switched ytterbium-doped fiber laser with two cascaded polarization maintaining fiber Bragg gratings (PM-FBGs). By properly adjusting the polarization states in the cavity, a total of 15 wavelength combinations, including single-, dual-, tri-, and quad-wavelength emission states, have been achieved. Stable Q-switched pulses with repetition rates ranging from 10 to 28 kHz are obtained. The influence of repetition rate and pump power upon the pulse width are also investigated. The high spectral stability in lasing operation indicates effectiveness of the proposed cascaded PM-FBGs in actively Q-switched multi-wavelength fiber laser configurations.

109 fs, 553 MHz pulses from a polarization-maintaining Yb-doped ring fiber laser with SESAM mode-locking

Femtosecond lasers with high repetition rate promote efficiency and accuracy greatly in the field of micro-processing by taking advantage of the so-called ablation cooling effect. In this letter, we demonstrate a novel high-repetition-rate Yb-doped fiber laser configuration with SESAM mode-locking, in which a short segment of commercially available polarization-maintaining gain fiber is implemented. The laser operates at a fundamental repetition rate of 553 MHz and has a maximum average output power of 242 mW. The shortest output pulse has a transform-limited duration of 109 fs. The repetition rate is expected to be boosted to GHz by reducing the spatial length and the proposed high-repetition-rate femtosecond fiber laser would have great potential in the field of micromachining.

High-resolution spectral analysis of long single-frequency pulses generated by a self-sweeping Yb-doped fiber laser

Continuous wave self-sweeping operation is demonstrated in a classical ring cavity configuration of Yb-doped fiber laser with a saturable absorber, which is usually used to obtain single-frequency lasing. Using heterodyne-based high-resolution spectral analysis we demonstrate that the laser generates a series of long (up to 1 ms) rectangular pulses consisting of single frequency radiation (the linewidth <0.7 MHz). At the same time, the lasing frequency changes between pulses regularly in a stepwise manner by one intermode beating frequency within a self-sweeping range of 100 pm. The effect of cavity configuration on pulse parameters (duration and chirp) is investigated. We also demonstrate that saturable absorbing mirrors design can be used to control the self-sweeping direction and value of the frequency jump.

Mid-Infrared Random Fiber Laser Assisted by the Passive Feedback

Random fiber lasers (RFLs), featuring a simple open cavity but with unique lasing characteristics, have captured considerable attention in the past several decades. Particularly, RFLs assisted by the passive feedback exhibit excellent robustness and compactness owing to the combination of active amplification and passive feedback from random distributed Rayleigh scattering. However, RFLs with the aid of the passive feedback reported previously are primarily operating in the near-infrared wavelength region of 1.1 μm or 1.5 μm based on the ytterbium or erbium doped active fibers. Here, we propose and demonstrate a random fiber laser configuration combining the passive feedback from a piece of single mode fiber with the active gain based on the thulium doped fiber, and extend the operation wavelength to the critically important mid-infrared wavelength band of ~2 μm. The spectral and temporal characteristics of the lasing output are evaluated and compared with those generated in a single pass amplification structure and a conventional resonant structure. Our results show that the passive feedback assisted RFL has a stabilized lasing wavelength and notably suppressed temporal dynamics. This work not only advances the development of RFLs, but also provides a promising strategy to achieve mid-infrared laser emission with a comparatively low relative intensity noise.

Saturable absorber based on the fiber coupler coated by CNTs

We report on a new method for fabrication of saturable absorbers for operation in ring fiber lasers as a mode-locking element taking advantages of the manufacturing technologies of fiber couplers and microfiber tapers coated with carbon nanotubes. It is demonstrated in the experiment that the transmittance of the fabricated saturable absorber increases with an increase of the input radiation power. Also, we have shown that the fabricated saturable absorber enables generation of picosecond soliton pulses in ring fiber laser configuration.

Passively Q-Switched Pulses Generation from Erbium-Doped Fiber Laser Using Lutetium Oxide as Saturable Absorber

Abstract In this paper, a configuration of a passive Q-switched Erbium-doped fiber laser (EDFL) using a Lutetium Oxide (Lu2O3) thin film as a saturable absorber (SA) is experimentally implemented to generate high pulse energy with a high signal to noise ratio. A stable Q-switched pulse train is initiated at the input pump power of 30.442mW, and a maximum pulse energy of 16.11 nJ is obtained at an output power of 0.97 mW, which confirms the stability of the pulses. It was possible to increase the repetition rate of the Q-switched laser from 31.25 to 60.2 kHz as the pump power was raised from 30.442 mW to 71.652 mW. Moreover, the pulse width decreased from 11.4 µs to 4.27 µs and 66.4 dB of the received signal-to-noise ratio at the radio frequency spectrum was achieved.

Stable and narrow linewidth linear cavity CW-active Q-switched erbium-doped fiber laser

A stable and narrow-linewidth, continuous wave and active Q-switching erbium-doped fiber laser, incorporating a fiber Bragg grating and a fiber Fabry-Perot tunable filter, was designed and experimentally implemented. Here, we proposed combining three approaches to suppress the mode hopping and improve both the output power stability and narrow the linewidth: first, two narrow-band optical filters, fiber Bragg grating and Fabry-Perot tunable filter were utilized in the laser cavity; second, the cavity configuration was optimized as a function of the output coupling ratio; finally, a 1.5 m long segment of unpumped erbium-doped fiber was inserted in the cavity to act as an induced virtual long and weak fiber Bragg grating. Using a 90% output coupling ratio, and monitoring over 120 min at room temperature, the 3 dB linewidth and power fluctuation of the fiber laser emission at 1550 nm were 16 kHz and 0.0025 dB respectively. Also, an optical signal to noise ratio (OSNR) of 82 dB was obtained. Keeping the same fiber laser configuration, laser pulses were also obtained using the Q-switching technique, realized by using dynamic spectral overlapping between the Bragg grating and the tunable filter. A stable output peak power of 5.6 W was achieved with a pulse width of 450 ns at a repetition rate of 1 kHz.

Endless Single-Mode Photonics Crystal Fiber Metalens for Broadband and Efficient Focusing in Near-Infrared Range.

The advent of the ‘lab-on-fiber’ concept has boosted the prosperity of optical fiber-based platforms integrated with nanostructured metasurface technology which are capable of controlling the light at the nanoscale for multifunctional applications. Here, we propose an endless single-mode large-mode-area photonic crystal fiber (LMA-PCF) integrated metalens for broadband and efficient focusing from 800 to 1550 nm. In the present work, the optical properties of the substrate LMA-PCF were investigated, and the metalens, consisting of dielectric TiO2 nanorods with varying radii, was elaborately designed in the fiber core region with a diameter of 48 μm to cover the required phase profile for efficient focusing with a high transmission. The focusing characteristics of the designed metalens were also investigated in detail over a wide wavelength range. It is shown that the in-fiber metalens is capable of converging the incident beams into the bright, symmetric, and legible focal spots with a large focal length of 315–380 μm depending on the operating wavelength. A high and average focusing efficiency of 70% was also obtained with varying wavelengths. It is believed the proposed fiber metalens may show great potential in applications including fiber laser configuration, machining, and fiber communication.

Numerical analysis of ring erbium-doped fiber laser with Q-switching based on dynamic overlapping of narrowband filters

The investigated Q-switching technique is based on the spectral overlap between a Fabry–Perot (F–P) filter and a fiber Bragg grating. This Q-switching concept is implemented in a ring erbium (Er)-doped fiber laser configuration. We use a traveling-wave analytical model to study the peak power and the time duration of the output pulses with respect to the cavity parameters, such as the Er-doped fiber length, the pumping power, and the scanning frequency of the fiber F–P tunable filter. Experimental results are used to validate the proposed Q-switched fiber laser model.

151W monolithic diffraction-limited Yb-doped photonic bandgap fiber laser at ~978nm.

We demonstrate that the strong 4-level Yb emission in a fiber laser can be almost completely suppressed in an Yb all-solid double-clad photonic bandgap fiber, resulting in highly efficient high-power monolithic Yb fiber lasers operating at the 3-level system. We have achieved single-mode continuous wave laser output power of ~151W at ~978nm with an efficiency of 63% with respect to the launched pump power in a practical monolithic fiber laser configuration for the first time. The demonstrated power in this work are setting new records for diffraction-limited double-clad fiber lasers operating at ~978nm.