Er-doped Fiber Laser Research Articles

Synthesis of black arsenic-phosphorus and its application for Er-doped fiber ultrashort laser generation

A black arsenic-phosphorus saturable absorber (SA) was fabricated and experimentally applied for a passively Q-switched Er-doped fiber laser for the first time to the best of our knowledge. The high-quality black arsenic-phosphorus crystals were synthesized by the mineralizer-assisted chemical vapor transport (CVT) method, and the fewer-layer black arsenic-phosphorus thin film nanosheet SA was performed by a unique electrochemical delamination exfoliation procedure. Meanwhile, a stable passively Q-switched pulse was proposed based on the SA modified Er-doped ring fiber cavity, which had the repetition rate of 38.47 kHz, corresponding to a minimum pulse width of 5.26 µs, and a corresponding output power as high as 3.68 mW was obtained. The results suggest that black arsenic-phosphorus is a good choice to make practical two-dimensional saturable absorbers for potential ultrafast photonic applications due to its designable bandgap value and excellent optical characteristics.

Generation of stretched pulses from an all-polarization-maintaining Er-doped mode-locked fiber laser using nonlinear polarization evolution

We demonstrate the generation of stretched pulses from an all-polarization-maintaining (all-PM) Er-doped fiber laser by means of a nonlinear polarization evolution (NPE) method. A theoretical model is built to analyze the relationship between the nonlinear transmissivity and the angles of the fiber segments. By managing the dispersion of the oscillator to support stretched-pulse formation and exploiting an NPE section based on three PM fiber segments, a self-starting laser with a 90.5-MHz repetition rate and 90-fs pulse duration is achieved. Numerous laser systems can benefit from this approach, including frequency combs, outdoor ranging and mid-IR systems.

Stable and low-threshold random fiber laser via Anderson localization.

We report a stable and low-threshold Er-doped random fiber laser (RFL) based on a femtosecond-laser-inscribed random-distributed-grating array (RDGA) as the random feedback. The RDGA had a reflectivity of 93.5%, and its properties were numerically analyzed based on the transfer matrix method. The threshold of the laser was significantly reduced to 5.7 mW, and the linewidth was ~0.4 pm near the threshold as the Anderson localization effect existing in the RDGA significantly improved the laser quality factor (4 × 106). In addition, we propose a method to select RFL lasing modes by stretching a fiber grating filter used in the cavity with different axial strains. The center wavelength hardly drifted and the maximum jitter value of the peak power was less than 0.12 dB over 1 hour for the selected three lasing modes, which indicated that our laser operation was quite stable.

Black Phosphorus-Film with Drop-Casting Method for High-Energy Pulse Generation From Q-Switched Er-Doped Fiber Laser

We have reported high-energy pulse generation from a Q-switched Er-doped fiber laser based on black phosphorus (BP) with a drop-casting method. Poly dimethyl diallyl ammonium (PDDA) is employed to protect BP. A passive Q-switching operation is achieved by using the BP/polyvinyl alcohol (PVA) film as the saturable absorbers (SAs). When the pump power increases from 130.4 mW to 378 mW, the repetition rate increases from 13.33 kHz to 26.6 kHz, and the pulse duration decreases from 10.67 μs to 7.11 μs. The maximum pulse energy is 468.03 nJ, to the best of our knowledge, which is the highest pulse energy produced from Q-switched fiber laser based on BP-SA at 1.5 μm. The obtained high-energy pulse demonstrates that BP/PVA film fabricated by such a drop-casting method can provide an ideal SA for high pulse energy generation from fiber lasers, and it has a potential application of remote sensing.

Observation of Soliton Molecules in NPR Mode-Locked Er-Fiber Laser via Birefringence Management

We have experimentally demonstrated that soliton molecules can be achieved from an Er-doped fiber laser oscillator via polarization dispersion management in the anomalous dispersion regime. In the laser oscillator, selective high-birefringence (HIBI) fibers were cross-spliced twice to counteract the linear polarization dispersion, which could highlight the role of the accumulated nonlinear phase shift and thus ensure the stable generation of mode-locking pulses by means of nonlinear polarization rotation (NPR). Depending on the length of the HIBI fibers, the angle of waveplates, and the pumping power, different types of soliton, such as single-pulse soliton and soliton molecules in tightly and loosely bound state, are observed.

Optical communication frequency standard using a fiber laser to excite cold rubidium two-photon transition

We propose to utilize an Er-doped fiber laser locked to a cooled Rb two-photon transition (TPT) resonance as a frequency standard for fiber-based optical communication. We show experimentally that a continuous wave laser beam can enhance the strength of cooled Rb TPT as much as 2.5 times. The cooled Rb TPT resonance excited by the fiber frequency combs has a measured linewidth of about 900 kHz. After locking the repetition rate of the fiber laser to the cooled Rb TPT resonance, the stability reaches 1.5×10−13 with 100 s averaging time. The results demonstrate that the proposed method in this paper is promising to provide the radio frequency standard for fiber-based optical communication.

A dual-wavelength Q-switched fiber laser based on reduced graphene oxides

This report demonstrates a dual-wavelength stable Q-switched Er-doped fiber (EDF) laser with a reduced graphene oxide (rGO)-based saturable absorber. The rGO is prepared by depositing the graphene oxide on fluorine mica (FM) using a thermal reduction method. The modulation depth and saturable intensity of rGO/FM are measured to be 5.8% and 73.6 MW cm−2. By employing the rGO/FM film in the EDF laser cavity, stable dual-wavelength Q-switching operation is achieved. The two wavelength peaks locate at 1531.84 nm and 1558.14 nm. The shortest pulse duration is 1.83 µs. The maximum output power is measured to be 14.65 mW, corresponding to the maximum single pulse energy of 154.34 nJ. The experimental results evidently show that the rGO is a promising type of nonlinear material.

Wavelength locking of Er-doped random fiber laser

This paper demonstrates the wavelength locking of a coherent random lasing system, i.e. an Erbium-doped random fiber laser with a disordered array of fiber Bragg gratings. To lock lasing modes of the disordered system, an external seed light from a tunable laser was introduced into the cavity. It was found that different emission wavelengths/modes can be selected to emit separately through injection locking. The wavelength fluctuation of the output is less than 0.01%, and the power fluctuation is less than 4%. The proposed method is also applicable to general disordered systems, providing an efficient way to control or select light emission in these systems.

Mode-Locked All-Fiber Laser Emitting Two-Color High-Order Transverse Mode

We demonstrate that the mode-locked all-fiber laser can simultaneously emit two-color broadband LP11 transverse mode in the near-infrared region by sharing a common mode-selective coupler (MSC). The MSC mode converter is designed to achieve simultaneous dual-channel mode conversion corresponding to the wavelength regions at 1.0 and $1.5~\mu \text{m}$ , in which each channel possesses broadband mode conversion from LP01 to LP11 mode with high mode purity. As a proof of concept, we implement an all-fiber ytterbium (Yb)- and erbium (Er)-doped fiber lasers with a mode-locked two-color LP11 modal output. The laser consists of two ring cavities combined with a common MSC mode converter. The generated LP11 modal pulses have a full width at half maximum of 11 and 8.1 nm for Yb- and Er-doped fiber laser, respectively. The presented fiber laser would represent a promising light source in the field of structured light and ultrafast optics.

Mode-locking in Er-doped fiber laser with reduced graphene oxide on a side-polished fiber as saturable absorber

In this work, the generation of highly stable mode-locked pulses from a side-polished fiber (SPF) embedded with graphene oxide (rGO) nanoparticles (NPs) is proposed and demonstrated. The rGO NPs are obtained from a graphene oxide solution prepared using Hummer's technique, before being reduced by a hydrothermal route. The rGO NPs, suspended in the form of a solution, are then drop-casted onto the SPF. The SPF is fabricated by polishing away the cladding layer of a single-mode fiber section, leaving the core exposed and allowing the evanescent field of the signal propagating through the fiber to interact directly with the NPs. The SPF is integrated into an erbium doped fiber laser (EDFL) cavity, and the strong nonlinear optical response and spectral filtering by the rGO NPs as well as total anomalous dispersion of the laser cavity generates highly stable soliton mode-locked pulses with visible Kelly's sidebands at 1544.02 nm. The output pulses have a pulse repetition rate of 16.79 MHz and pulse duration of 1.17 ps throughout the mode-locking operation range of 64.44�280.5 mW. The rGO NP coated SPF in this work demonstrates the viability and performance of the SPF for mode-locked pulse generation via evanescent field interactions. © 2019

Low-repetition-rate, high pulse energy all-polarization-maintaining Er-doped fiber laser mode-locked with a nonlinear amplifying loop mirror

We demonstrate a low repetition rate mode-locked Er-doped fiber laser using an all-polarization-maintaining (PM) nonlinear amplifying loop mirror. Stable single pulse generation had a pulse energy of 4 nJ and a repetition rate as low as 1.96 MHz. A section of standard single mode PM fiber was used to compress the output pulses from 2.5 ps down to 660 fs, being nearly transform-limited. The robust mode-locking design and all-PM cavity make this fiber laser stable and compact. The output average power fluctuation is within 0.17% over 10 h. Therefore, this source is ideally suitable for high pulse energy applications, such as micro-machining and nonlinear microscopy through further amplification.

Laser frequency stabilization based on a universal sub-Doppler NICE-OHMS instrumentation for the potential application in atmospheric lidar

Abstract. Lidar is an effective tool for high-altitude atmospheric measurement in which a weak absorption line for the target gas is selected to ensure a large optical depth. The laser frequency stabilization to the line center is required, and a sub-Doppler (sD) spectroscopy of the target line is preferred as a frequency reference. In this paper, a novel universal sD noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) instrumentation based on a fiber-coupled optical single-sideband electro-optic modulator (f-SSM) for the potential application in atmospheric lidar for different target gases with different types of lasers is reported. The f-SSM can replace all frequency actuators in the system, so as to eliminate the individual design of feedback servos that often are tailored for each laser. The universality of the instrumentation was demonstrated by the alternative use of either an Er-doped fiber laser or a whispering-gallery-mode laser. Then the instruments based on both lasers were used to produce the sD signals of acetylene, which worked as a frequency reference to stabilize the laser. By performing the lockings, relative frequency stabilizations of 8.3×10-13 and 7.5×10-13 at an integration time of 240 s were demonstrated.

Intracavity cylindrical vector beam generation from all-PM Er-doped mode-locked fiber laser.

We demonstrate a practical method that is used to generate on-demand first- and higher-order cylindrical vector beams, in the 1550 nm band, directly from an all polarization maintaining mode-locked Er-fiber laser. On demand typical 1st order CVBs, including the radially and azimuthally polarized beams, can be easily achieved by properly adjusting the angle of a half-wave plate with respect to the fast axis of the vortex wave plate. The spatial beam mode can be flexibly switched with no disturbance on the time domain mode-locking output. The laser outputs the desired vector beams at 1571 nm with a spectral bandwidth at full-width at half-maximum of 32 nm. The mode-locked laser pulses have a repetition rate of 74.9 MHz. Moreover, the proposed method can be easily extended to create higher-order CVBs. Our research provides a convenient way to generate ultrafast pulses in highly flexible-controlled structured modes, which is essential for optical fabrication and light trapping applications.

Influence of optical absorption of polysiloxane polymers on active fiber heating under lasing conditions

Optical properties of conventional polysiloxane polymers used in fiber optics were analyzed. Transmission spectra and absorption coefficients of polymers in the operating wavelength range of Yb and Er doped fiber lasers were measured. Heating of Yb-doped active fiber inside the industrial laser unit poured with a silicone polymer protective layer was investigated. A part of the pump power converted into heat during laser generation was evaluated using experimental data obtained by substituting the active fiber with an electrically heated copper wire. Mathematical model of fiber laser unit heating was developed.

Passively mode-locked dual-wavelength Er-doped fiber laser based on antimony tin oxide as saturable absorber

As a typical transparent conductive oxide, antimony tin oxide (ATO) is widely applied in many optical fields. However, investigations of the nonlinear absorption properties of ATO have not been reported so far. In this study, ATO was employed as a saturable absorber (SA) for producing an Er-doped pulsed fiber laser. To our knowledge, this is the first time that ATO has been used to fabricate an SA. Its appearance and nonlinear saturable absorption characteristics were investigated in our experiment. The saturation intensity and modulation depth of the ATO-SA were 7.51 MW cm−2 and 2.30%, respectively. By adjusting the polarization controllers and the pump power, dual-wavelength pulses were generated within an Er-doped fiber laser. The dual-wavelength pulses were centered at wavelengths of 1558.3 nm and 1558.7 nm with a repetition rate of 1.04 MHz. The pulse width was 4.42 ns. Our results fully prove that ATO with its excellent nonlinear absorption properties will have wide potential ultrafast photonic applications.

Optical Nonlinearity of ZrS₂ and Applications in Fiber Laser.

Group VIB transition metal dichalcogenides (TMDs) have been successfully demonstrated as saturable absorbers (SAs) for pulsed fiber lasers. For the group comprising IVB TMDs, applications in this field remain unexplored. In this work, ZrS2-based SA is prepared by depositing a ZrS2 nanostructured film onto the side surface of a D-shaped fiber. The nonlinear optical properties of the prepared SA are investigated, which had a modulation depth of 3.3% and a saturable intensity of 13.26 MW/cm2. In a pump power range of 144–479 mW, the Er-doped fiber (EDF) laser with ZrS2 can operate in the dual-wavelength Q-switching state. The pulse duration declined from 10.0 μs down to 2.3 μs. The single pulse energy reached 53.0 nJ. The usage of ZrS2 as a SA for pulse generation in fiber lasers is presented for the first time. Compared to the experimental results of dual-wavelength Q-switched fiber lasers with two-dimensional (2D) materials, our laser performance was better. Our work indicates that the group comprising IVB TMD ZrS2 has bright prospects for nonlinear optical applications.

Compact low-noise passively mode-locked Er-doped femtosecond all-fiber laser with 2.68 GHz fundamental repetition rate.

A passively mode-locked Er-doped fiber laser with a fundamental repetition rate of 2.68GHz is reported. The oscillator operating at a central wavelength of 1558.35nm has a compact, robust structure and low-noise performance. The timing jitter integrated from 30MHz down to 300Hz is 82.5fs, and the timing jitter performance is analyzed based on the theory model. The amplification and compression of the high repetition rate optical pulses are also investigated. After a three-stage amplifier, the average power is boosted to 430mW. Meanwhile, based on the nonlinear self-phase modulation effect, the spectral bandwidth is broadened from 7.56 to 19.2nm, and the corresponding pulse width is compressed to 244fs.

Passively Q-switched fiber lasers based on pure water as the saturable absorber.

We propose and demonstrate a passively Q-switched Er-doped fiber laser based on pure water as the saturable absorber (SA). The SA is made of two optical ferrules matched with a cannula, and the gap between the end-facets is filled with pure water. The nonlinear response of this SA has been characterized, and stable Q-switching operation at 1558.03nm has been achieved. The maximum output power is 21.1mW with 65.0kHz repetition rate. The duration is 1.44μs, and the pulse energy reaches 324.8nJ. To the best of our knowledge, this is the first demonstration of the passively Q-switched laser with pure water as the SA. It provides further evidence of the possibility of liquid as an effective SA for pulsed lasers.

Bulk-structured PtSe2 for femtosecond fiber laser mode-locking.

The interest in pulsed fiber laser technology surrounds lots of critical optoelectronic applications ranging from optical communications, remote sensing to industrial material processing. Here, a femtosecond Er-doped fiber laser at 1560 nm have been demonstrated by using bulk-structured transition metal dichalcogenides (TMDs) - PtSe2 as the pulse modulator. The PtSe2 modulator was fabricated by using mechanically exfoliated methods from its single crystal and the exfoliated PtSe2 was directly transferred to the polished surface of the D-shaped fiber. Due to the strong interaction between PtSe2 and evanescent field, a self-starting Q-switched operation can be obtained. Furthermore, the mode-locking operation can be achieved easily by controlling the intra-cavity polarization states. Stable mode-locked operation can be maintained with pulse duration of 861 fs and signal to noise ratio (SNR) of 61.1 dB. These experimental results can validate the excellent nonlinear optical performance of PtSe2, and may make inroads for the ultrafast applications of the bulk and low-dimensional TMDs.

Femtosecond 78-nm Tunable Er:Fibre Laser Based on Drop-Shaped Resonator Topology

We report for the first time on study of a passively mode-locked Er-doped fibre laser with ultra-wide tuning (from 1524 to 1602 nm) of the central wavelength of its femtosecond output (503–940 fs). The recently proposed drop-shaped cavity topology for fibre lasers enabled a compact widely tuneable femtosecond laser with a single discrete element, a reflective diffraction grating used for wavelength tuning of the output radiation. The key features of the proposed laser are: spectral tuning does not require adjustment of any other cavity elements; stable generation with a single pulse per round trip is provided over the entire wavelength tuning range; and the output pulses are close to transform limited and feature relatively high (>58 dB) signal-to-noise ratio of laser inter-mode beats indicating high quality of mode locking across the entire wavelength tuning range. The proposed laser configuration relying on the new drop-shaped cavity topology simultaneously delivers stability and reliability of mode locking, possibility of broad-range wavelength tunability, and adjustability of the output pulse repetition rate of the laser (which is important in various metrological and other applications).