Er-doped Fiber Laser Research Articles

Q-switched and vector soliton pulses from an Er-doped fiber laser with high stability based on a γ-graphyne saturable absorber.

As a Dirac material, an allotrope of graphene, namely γ-graphyne (γ-GY), is proved to have excellent nonlinear optical properties. Unfortunately, the saturable absorption properties and ultrafast photonics applications of γ-GY at the 1.5 μm band, which play vital roles in optical communication, have not been reported so far. Herein, γ-GY nanosheets (NSs) are prepared by an improved mechanochemical method, and a saturable absorber (SA) is fabricated by a laser-induced deposition method. The modulation depth (MD) and saturable fluence at 1.5 μm are found to be 5.40% and 23.46 μJ cm-2, respectively. Consequently, by inserting the as-prepared SA into an Er3+-doped fiber laser (EDFL), Q-switching and mode-locking operation with high stability are realized. Also, the mode-locking pulses are verified to be polarization-locked vector solitons (PLVSs) based on further study. With increasing pump power, the phase difference between the two orthogonal components increases, leading to the evolution of state of polarization (SOP). Additionally, the degrees of polarization (DOPs) are measured and all reach more than 97%, meaning high polarization stability. Therefore, this work not only broadens the application scope of γ-GY in ultrafast photonics, but also provides an important foundation for the study of soliton dynamics.

Generation of Q-switched pulses based on GaSb saturable absorber in an Er-doped fiber laser

In this study, we report the use of GaSb as a saturable absorber (SA) material in an Er-doped fiber (EDF) laser. The GaSb-based SA is prepared through the magnetron sputtering deposition technology, wherein a thin GaSb film is deposited on a microfiber. The modulation depth, saturable intensity, and non-saturable loss of the SA are determined to be 5.45 %, 37.3 MW/cm2, and 29.12 %, respectively. Under the Q-switching working state, the repetition frequeny is tuned from 73.15 to 93.7 kHz, and the pulse duration is changed from 5.17 to 2.33 μs at a pumping power of 310 to 500 mW. The highest average output power is 21.8 mW, which corresponds to a single pulse energy of 233.67 nJ. The generated laser pulses are in a stable state with a signal to noise ratio (SNR) of 65 dB. These results confirm the potential of GaSb as a successful saturable absorber candiatiate for building pulsed fiber lasers and in ultrafast optics applications.

Tunable compact asynchronous optical sampling system using Er-doped fiber laser

Abstract We report a compact, tunable, self-starting, all-fiber laser-based asynchronous optical sampling (ASOPS) system. Two Er-doped fiber oscillators were used as the pulsed-laser source, whose repetition rate could be set at 100 MHz with a tuning range of 1.25 MHz through a fiber delay line. By employing phase-locked and temperature control loops, the repetition rate offset of the two lasers was stabilized with 7.13 × 10−11 fractional instability at an average time of 1 s. Its capabilities in the terahertz regime were demonstrated by terahertz time-domain spectroscopy, achieving a spectral bandwidth of 3 THz with a dynamic range of 30 dB. The large range of repetition rate adjustment in our ASOPS system has the potential to be a powerful tool in the terahertz regime.

Investigations of the nonlinear optical properties of ZrGeTe4 nanosheets and their application in ultrafast photonics

We prepared ZrGeTe4 nanosheets and investigated their nonlinear optical properties. ZrGeTe4 nanosheets as a saturable absorber were applied in an Er-doped fiber laser for conventional soliton and harmonic mode-locking pulses generation.

1 570 nm and 1 548 nm Dual-wavelength Single-frequency Er-doped Fiber Laser

1 570 nm and 1 548 nm Dual-wavelength Single-frequency Er-doped Fiber Laser

Wavelength-Tunable and Asynchronous Dual-Wavelength Mode-Locked Er-Doped Fiber Laser

Wavelength-Tunable and Asynchronous Dual-Wavelength Mode-Locked Er-Doped Fiber Laser

Multiphoton scanning laser microscope based on femtosecond fiber laser

We present a multiphoton scanning laser microscope based on a femtosecond frequency-doubled erbium-doped fiber laser. The laser used in the epi-illumination microscope setup generated 95 fs pulses at the wavelength of 780 nm with 44.3 mW average power at 100 MHz pulse repetition rate. The imaging process was controlled by custom software developed in the NI LabVIEW environment. Detection of two-photon fluorescence was proven by acquiring a series of images from various biological samples. Full Text: PDF ReferencesJ.W. Lichtman, J.A. Conchello, "Fluorescence microscopy", Nature methods 2(12), 910 (2005). CrossRef W. Zipfel, R. Williams, W. Webb, "Nonlinear magic: multiphoton microscopy in the biosciences", Nat. Biotechnol. 21, 1369 (2003). CrossRef Coherent, Chameleon Ultra Datasheet (2019). DirectLink J. Boguslawski et al., "In vivo imaging of the human eye using a 2-photon-excited fluorescence scanning laser ophthalmoscope", J. Clin. Invest. 132(2), e154218 (2022). CrossRef M.J. Marzejon et al., "Two-photon microperimetry with picosecond pulses", Biomed. Opt. Expr. 12, 462 (2021). CrossRef A. Fast et al., "Institutional Drivers Influence on CSR Engagement: A Comparison of Developed & Developing Economies", Sci. Rep. 10, 18093 (2020). CrossRef D. Stachowiak et al., "Femtosecond Er-doped fiber laser source tunable from 872 to 1075 nm for two-photon vision studies in humans", Biomed. Opt. Expr. 13, 1899 (2022). CrossRef MenloSystems, T-light Femtosecond Fiber Laser 1560 nm (2013). DirectLink J. Yao, L.V. Wang, "Photoacoustic microscopy", Laser and Photonics Rev. 7, 758 (2013). CrossRef D. Stachowiak et al., "Frequency-doubled femtosecond Er-doped fiber laser for two-photon excited fluorescence imaging", Biomed. Opt. Expr. 11, 4431 (2020). CrossRef B.R. Masters et al., "Mitigating thermal mechanical damage potential during two-photon dermal imaging", J. Biomed. Opt. 9, 1265 (2004). CrossRef

Spotlighting the Simultaneous Formation of Coherent and Incoherent Dissipative Solitons in an Er-Doped Bidirectional Ultrafast Fiber Laser

The emergence of localized structures originating from instabilities is of particular interest to scientists interested in exploring the rich nonlinear dynamics associated with complex dynamical systems. In the context of ultrafast lasers, the localized structures can be broadly divided into two categories: coherent structures of the dissipative soliton (DS) and incoherent structures such as the noiselike pulse (NLP). These two different types of structures have unique properties and applications and their physical origins are markedly different. Having both in a single fiber laser is an intriguing but challenging problem. Here we demonstrate the formation of the DS and NLP in a bidirectional ultrafast fiber laser and study their buildup dynamics from $Q$-switched instabilities. The clockwise light is a DS while the counterclockwise light is a NLP. The synchronized buildup dynamics of a DS or NLP from $Q$-switched instabilities provides vital evidence of the $Q$-switched instabilities as a universal indicator for the generation of localized structures in ultrafast lasers. The evenly spaced $Q$-switched spikes before the onset of a DS (NLP) exhibit intensity fluctuations, which is strikingly different than in the mode-locking regime in unidirectional oscillators, hence providing decisive evidence of the interaction between the counterpropagating light fields in the bidirectional lasers. The spectra cross-correlation and the histogram of the spectral intensity confirm the concurrent formation of a DS and NLP. Numerical simulations confirmed experimental observations. These findings help deepen understanding of the behavior of bidirectional ultrafast lasers and also demonstrate their potential as multifunctional ultrafast laser sources.

Investigation of stable pulse mode-locking regimes in a NALM figure-9 Er-doped fiber laser.

We demonstrate three typical mode-locking processes of a nonlinear amplifying loop mirror (NALM) fiber laser via a general nonlinear Schrödinger equation-based (GNLSE) simulation model. First, the pulse evolutions in the NALM cavity were separately simulated under asymmetric and weakly asymmetric conditions. We found that the splitting ratio and positions of the gain fiber can result in a suitable phase bias between clockwise and counter-clockwise beams, enabling the realization of a self-starting low-threshold operating condition. To assess the roles of the splitting ratio and gain in the mode-locking process, we simulated three pulse formation processes: in the soliton, stretched-pulse, and dissipative soliton mode-locking regimes. The simulation results show that the splitting ratio, gain, and dispersion directly influence the mode-locking condition and pulse characteristics, thereby providing effective quantified guidance for high-quality pulse generation. Finally, an experimental NALM oscillation operating under stretched pulse conditions was established to investigate the impact of the splitting ratio and pump power on the pulse characteristics. The experimental results prove that the splitting ratio, gain, and dispersion can be used to manipulate the mode-locking threshold, self-starting threshold, nonlinear effects, and pulse characteristics.

Environment-stable sub-100 fs Er: fiber laser with a 3 dB bandwidth of 78 nm.

A robust all polarization-maintaining (PM) passively mode-locked Er-doped fiber laser is demonstrated based on the biased nonlinear amplifier loop mirror (NALM). With a π/2 nonreciprocal free-space phase shifter, stable single pulse mode locking can be obtained at the central wavelength of 1565.7 nm with a 3 dB spectral bandwidth of 24.6 nm in the soliton regime. The repetition rate of the pulse train is 98.13 MHz. The direct output pulse duration is 109 fs, which is nearly transform-limited. After the intracavity dispersion management, the robust self-started mode-locking in the stretched-pulse regime is realized at 1564 nm, and the 3 dB spectral bandwidth reaches up to 78 nm. The repetition rate of the pulse train is 199.6 MHz. In particular, the direct output pulse width is only 77 fs with a low integrated relative intensity noise (RIN) of only 0.0044% (integrated from 1 Hz to 1 MHz). To the best of our knowledge, this is the shortest pulse width directly from the all-PM NALM laser oscillator.

GaSb Film is a Saturable Absorber for Dissipative Soliton Generation in a Fiber Laser

Nanotechnology is at the forefront of scientific research and offers great prospects for the development of technology. As a type of III-V semiconductor, GaSb materials exhibit numerous outstanding optical and electrical characteristics that are very promising for nonlinear optical device applications. In this study, the electronic band structures of GaSb are theoretically calculated, and its application in dissipative soliton fiber lasers is validated. A GaSb thin film is deposited on a microfiber using magnetron sputtering deposition, and the morphology, chemical composition, structure, and nonlinear optical characteristics of the proposed microfiber-GaSb device are investigated. After incorporating it into an Er-doped fiber laser, dissipative soliton laser pulses are readily obtained with a fundamental frequency of 43.5 MHz. With increasing pump power, the fiber laser could work in the fundamental frequency mode-locking state. At a pump power of 570 mW, the pulse width and the output power are measured to be 917 fs and 49.75 mW, separately. These results reveal that GaSb can be used as an efficient saturable absorber, which will have potential applications in ultrafast optics.

Single crystalline BiOCl nanosheets with oxygen vacancies for ultrafast mode-locking operation

In this work, we synthesized the single-crystalline square BiOCl nanosheets with oxygen vacancies via the facile solvothermal route. The prepared BiOCl nanosheets were deposited on a tapered microfiber as a saturable absorber. Via the evanescent filed interaction with the BiOCl saturable absorber, a soliton mode-locked Er-doped fiber laser was demonstrated for the first time, producing a pulse duration of 990 fs at a central wavelength of 1563 nm with a FWHM bandwidth of 3.2 nm. The signal-to-noise ratio was 36 dB at the fundamental repetition rate of 7.9 MHz. Our results confirmed that the BiOCl nanosheets with abundant oxygen vacancies could be applied for the ultrafast photonics.

Bi2O2Te Nanosheets Saturable Absorber‐Based Passive Mode‐Locked Fiber Laser: From Soliton Molecules to Harmonic Soliton

AbstractAs a recent addition to the emerging 2D bismuth oxychalcogenides (Bi2O2X, where X = S, Se, and Te), atomically‐thin bismuth oxytellurium (Bi2O2Te) exhibits unique thermoelectric and photoelectric properties. In this study, high‐quality Bi2O2Te nanosheets (NSs)‐based saturable absorber (SA) with a modulation depth of 8.2% is developed using the liquid phase exfoliation (LPE) method and is successfully applied to a passively mode‐locked Er‐doped fiber laser (EDFL) for the first time (with reference to the available literature). Due to the excellent nonlinear saturable absorption property of Bi2O2Te NSs, various switchable and stable mode‐locking states can be realized in the same EDFL, including fundamental frequency conventional soliton (CS), soliton molecules, and harmonic mode‐locking (HML) states. Among them, the CS pulse at 7.48 MHz (fundamental frequency) with a high signal‐to‐noise ratio (SNR) of 67.25 dB is obtained. The 2nd, 3rd, and 4th‐order soliton molecules are observed with a soliton pulse separation of ≈6.2 ps. Moreover, for HML, a maximum repetition rate of 1.78 GHz (i.e., corresponding to the 238th‐order harmonic) is obtained. The results reveal that Bi2O2Te NSs demonstrate excellent nonlinear optical modulation properties and can serve as a fundamental basis for promotion of academic research and innovation of engineering applications involving ultrafast photonics.

The nonlinear optical property of germanium saturable absorber and its application in normal dispersion Er-doped fiber laser

Recently, germanium (Ge) has been considered as the two-dimensional (2D) material saturable absorber (SA) due to its excellent nonlinear saturable absorption properties. However, previous reports explored the nonlinear saturable absorption properties of Ge SA in anomalous dispersion Er-doped fiber (EDF) laser. To date, the mode-locked operation achieved by normal dispersion EDF laser based on Ge SA has not yet been reported until now. In this work, Ge SA with saturation intensity of 11.69 MW/cm2 and modulation depth of 6.17 % was used to demonstrate a normal dispersion EDF laser. Morphological and nonlinear saturable absorption properties of Ge were also investigated. To the best of our knowledge, the mode-locked pulse with repetition rate of 6.66 MHz were achieved in normal dispersion EDF laser based on Ge SA for the first time. Compared with previous work about Ge SA in anomalous dispersion regime, our result proves that Ge also has excellent optical performance in normal dispersion regime.

Uni- and Bi-directional Er3+-doped fiber soliton laser mode-locked by GIMF-based SA

In this paper, we have experimentally demonstrated an ultrafast Er-doped fiber laser mode-locked by the GIMF-based saturable absorber without an optical isolator for various soliton behaviors. The adjustment of the polarization controller results in different losses for the counter-propagating lasers. And thus, not only the bidirectional solitons, but also the quasi-unidirectional solitons are realized. For the bidirectional operation, the counterpropagating conventional solitons with the pulse energy of >1.12 nJ demonstrates different central wavelengths, repetition rates, and pulse widths. For the unidirectional operation, the laser operates in either the clockwise or the counter-clockwise directions with an emission strengths difference of larger than 31 dB. Interestingly, the bidirectional operations could show different soliton state of the forward conventional solitons and backward bound solitons. Our research would be beneficial for the further understanding of the formation and transformation of the bidirectional solitons and can find vital applications in gyroscopic and other dual-channel applications.

Time-resolved mode analysis in Er-doped self-sweeping ring fiber laser

We present here a detailed study of the mode composition of an Er-doped ring self-sweeping fiber laser. Time-resolved heterodyne measurements prove that the radiation consists of slightly overlapping rectangular mode packets, each of which corresponds to generation of individual longitudinal modes. Optical frequency of each following packet sequentially increases by two free spectral ranges of the laser cavity. The presence of parametric processes during sequential growth of the neighboring mode packets is experimentally demonstrated for the first time in a self-sweeping laser. Instantaneous linewidth of the laser radiation does not exceed 4 kHz during every step of single longitudinal mode generation, which is also accompanied by a small change of the optical frequency (chirp) of ∼40 kHz associated with an integral change of the laser cavity refractive index. The results are useful for calculations and modeling of laser systems based on dynamic gratings.

Abundant dynamics of group velocity locked vector solitons from Er-doped fiber laser based on GO/PVA film

Abstract With the insertion a segment of polarization-maintaining fiber (PMF) inside the cavity, abundant dynamics of group velocity locked vector solitons (GVLVSs) in Er-doped fiber laser have been investigated by using graphene oxide/polyvinyl alcohol (GO/PVA) film as a saturable absorber (SA). The generated Kelly sidebands in emission spectra reveal peak-valley or valley-peak alternation and slightly shift in two orthogonal components, which are the characteristics of GVLVSs. Through proper adjustment of polarization controllers (PCs) inside the EDFLs cavity, versatile vector soliton dynamics such as polarization locked GVLVSs (PL-GVLVSs), polarization rotation GVLVSs (PR-GVLVSs), dual wavelength GVLVSs, bound state GVLVSs, bunch GVLVSs and harmonic mode-locking GVLVSs (HML-GVLVSs) have been observed. The separation between two emission peaks from the dual wavelength GVLVSs was controlled by the Lyot filter and related to the insertion length of PMF inside the cavity. Unlike PL-GVLVSs, the period-doubling phenomenon has been found in two orthogonal components of the PR-GVLVSs. Besides, the bound state GVLVSs were generated showing strongly modulated interference fringes in emission spectrum. For the bunch and HML GVLVSs, the number of solitons inside the cavity increased with the pump power, and it showed the quintuple solitons and the 7th HML-GVLVSs at the highest pump power.

Soliton phenomena in normal and anomalous dispersion regions in Er-doped mode-locked fiber lasers based on Cr2Si2Te6 saturable absorbers.

Investigations of optical solitons have always been a hot topic due to their important scientific research value. In recent years, ultrafast lasers based on two-dimensional materials such as saturable absorbers (SAs) have become the focus of optical soliton research. In this work, various soliton operations are demonstrated in Er-doped fiber lasers (EDFLs) based on ${{\rm Cr}_2}{{\rm Si}_2}{{\rm Te}_6}$ SAs. First, a low-threshold passively mode-locked EDFL with traditional soliton output is constructed, and the pump threshold is as low as 10.1mW. Second, by adjusting the net dispersion of the cavity, stable dissipative soliton operation can also be obtained. Traditional soliton mode-locked operation with controllable Kelly sidebands from first order to fourth order is realized by adjusting the pump power in a double-ended pumped structure, and the SNR is as high as 55dB. All results prove that ${{\rm Cr}_2}{{\rm Si}_2}{{\rm Te}_6}$ used as SA material has great potential and wide application prospects in investigating optical soliton operations in mode-locked fiber lasers with both normal and anomalous dispersion.

The generation and observation of pulses with switchable single/dual wavelengths and tunable bandwidth from a SWNT mode-locked Er-doped fiber laser

Mode-locked pulse outputs with switchable single/dual wavelengths and widely tunable spectral bandwidth are demonstrated by fully exploiting multiple soliton formation mechanisms combining single-wall carbon nanotube, intracavity loss tuning and nonlinear polarization rotation. An isolator with single-polarization fiber pigtails is additionally inserted in a ring fiber laser cavity to introduce polarization-dependent loss modulation for gain profile tuning and nonlinear polarization rotation. Mode-locked by a home-made single-wall carbon nanotube saturable absorber, switchable single/dual-wavelength pulses centered in the 1530- or/and 1550-nm gain regions of erbium-doped fiber are experimentally observed by tuning the intracavity loss to tilt the gain profile. Moreover, the spectral bandwidths of single-wavelength pulses centered in the 1530- and 1550 nm regions could be continuously tuned from 2.4 to 4.0 nm, and 2.7 to 9.0 nm, respectively. Such widely tunable spectral bandwidths are attributed to hybrid mode-locked mechanisms combining the nonlinear polarization rotation and single-wall carbon nanotube. Our results give a deep insight into the well-controlled gain profile tuning and provide a relatively simple setup and method to obtain bandwidth-tunable, wavelength-switchable pulse outputs, showing the potential to meet various requirements of ultrafast laser applications.

Switchable property of dissipative soliton and dispersion-management soliton in fiber laser

We numerically and experimentally demonstrated that the central wavelength of the output pulses in an Er-doped mode-locked fiber laser can be switched from ∼1561 to ∼1531 nm, while these two pulses exhibit dispersion-management soliton and dissipative soliton, respectively. The switch capability of our fiber laser with different pulse waveforms can be attributed to combining the double-hump gain spectrum of Er-doped fiber and third-order dispersion (TOD) effect. By considering the TOD effect, the two wavelengths can be operated in different dispersion regime. The transient switch dynamics of these different type of solitons are also observed by time stretched technique. These findings provide a good foundation for comprehensively studying pulse formation dynamics in laser cavities, and benefit for design dual-wavelength fiber lasers.