Nonlinear Amplifying Loop Mirror Research Articles

All-polarization-maintaining Nd-doped ultrafast fiber laser oscillator at 929 nm mode-locked via a 3x3 nonlinear amplifying loop mirror

All-polarization-maintaining Nd-doped ultrafast fiber laser oscillator at 929 nm mode-locked via a 3x3 nonlinear amplifying loop mirror

All-PM Yb-doped mode-locked fiber laser with high single pulse energy and high repetition frequency

We demonstrate an all-polarization-maintaining (PM) ytterbium (Yb)-doped fiber laser with a figure-of-9 structure to generate mode-locked pulses with high single pulse energy and high repetition frequency. By exploiting the nonlinear amplifying loop mirror, a stably self-started mode-locking is achieved with a spectrum bandwidth of 13 nm and a pulse duration of 4.53 ps. The fundamental frequency is 97.966 MHz at the maximum output power of 143 mW in single pulse mode-locked operation, corresponding to the single pulse energy is 1.46 nJ. The output pulses maintain both high repetition frequency and high single-pulse energy. This laser oscillator can be an ideal seed source for applications such as high-energy amplifiers.

Peak-power and width tunable noise-like pulses from a figure-9 cavity with two separate gain segments

A novel feature of noise-like pulses (NLPs) from a dual pump module based figure-9 cavity has been presented in this manuscript. The laser is mode-locked by taking advantage of a non-linear amplifying loop mirror (NALM) and the cavity contains a LOOP and an ARM, each section comprises an Yb-doped fiber pumped by an independently controllable pump module. In stable conditions, the laser delivers nanosecond rectangular pulses at a fundamental repetition rate of 1.96 MHz. The NLPs are recognized from their double-scaled auto-correlation trace. Akin to typical NLPs, the pulse duration increases with the pump power of the pump modules placed at the LOOP, whereas, it is noticed that the pulse width tends to reduce with the power of the pump module placed outside the LOOP, which is an unconventional behavior for NLPs. Alongside the pulse duration, the peak power also behaves oppositely with the pump power of individual modules. In the best operating condition, the maximum average power is 766 mW corresponding to 136 W peak power and pulse energy of 390 nJ. This study offers a possible direction to explore the dynamics of NLPs in laser cavities with two independent pump modules.

Characterization of sub-20-attosecond timing jitter in erbium-doped fiber laser system

The significance of timing jitter stems from its pivotal role in enhancing the precision of applications like spectroscopy and frequency metrology. In this study, we introduce a comprehensive procedure for achieving low timing jitter values in mode-locked fiber laser systems, highlighting dispersion, intracavity pulse energy, pulse length, and spectral bandwidth as key parameters. Notably, we unveil the influence of fiber amplifier pump power on jitter, a factor neglected in established theories and recent experiments. Applying this procedure to a 200-MHz all-polarization-maintaining (PM) erbium-doped (Er:) nonlinear amplifying loop mirror (NALM) fiber laser system, we demonstrate an exceptionally low timing jitter of 14.25 attoseconds, measured using the balanced optical cross-correlation (BOC) technique and integrated from 10 kHz to 4 MHz. The implementation of our novel method offers the opportunity to improve jitter results in various fiber laser systems and increase the accuracy of fiber laser applications.

Spectrally tunable phase-biased NALM mode-locked Yb:fiber laser with nJ-level pulse energy

Applications of mode-locked fiber lasers benefit from robust and self-starting mode-locking, spectral tuning, high pulse energy and high average power. All-polarization-maintaining (PM) fiber lasers mode-locked with a phase-biased nonlinear amplifying loop mirror (NALM) have been shown to be very robust and reliably self-starting, and provide either spectral tuning or high pulse energy, but not both. We report on a simple method for concurrent spectral tuning and nanojoule-level pulse energy scaling of an all-PM phase-biased NALM mode-locked Yb:fiber laser, which we demonstrate over a 54 nm tuning range, reaching up to 1.67 nJ pulse energy and 126 mW average power. Unlike other laser configurations, our results show that net normal dispersion is not necessary or optimal for scaling the pulse energy of this type of mode-locked fiber laser.

Watt-level all polarization-maintaining femtosecond fiber laser source at 1100 nm.

We demonstrate a compact watt-level all polarization-maintaining (PM) femtosecond fiber laser source at 1100 nm. The fiber laser source is seeded by an all PM fiber mode-locked laser employing a nonlinear amplifying loop mirror. The seed laser can generate stable pulses at a fundamental repetition rate of 40.71 MHz with a signal-to-noise rate of >100 dB and an integrated relative intensity noise of only ∼0.061%. After two-stage external amplification and pulse compression, an output power of ∼1.47 W (corresponding to a pulse energy of ∼36.1 nJ) and a pulse duration of ∼251 fs are obtained. The 1100 nm femtosecond fiber laser is then employed as the excitation light source for multicolor multi-photon fluorescence microscopy of Chinese hamster ovary (CHO) cells stably expressing red fluorescent proteins.

Recent Advances, Applications, and Perspectives in Erbium-Doped Fiber Combs

Optical frequency combs have emerged as a new generation of metrological tools, driving advancements in various fields such as free-space two-way time–frequency transfer, low-noise microwave source generation, and gas molecule detection. Among them, fiber combs based on erbium-doped fiber mode-locked lasers have garnered significant attention due to their numerous advantages, including low noise, high system integration, and cost-effectiveness. In this review, we discuss recent developments in erbium-doped fiber combs and analyze the advantages and disadvantages of constructing fiber combs utilizing different erbium-doped mode-locked fiber lasers. First, we provide a brief introduction to the basic principles of optical frequency combs. Then, we explore erbium-doped fiber combs implemented utilizing various mode-locking techniques, such as nonlinear polarization rotation (NPR), real saturable absorber (SA), and nonlinear amplifying loop mirror (NALM). Finally, we present an outlook on the future perspectives of erbium-doped fiber combs.

Ultra-flat and high-efficient mid-infrared supercontinuum generation in indium fluoride fiber

We demonstrate ultra-flat and high-efficient mid-infrared supercontinuum (MIR SC) generation in indium fluoride (InF3) fiber with output average power of 9.9 W, power conversion efficiency of 67.8 % and 3 dB-spectrum width of >1570 nm. It is pumped by amplified 2 μm noise-like pulses and generated in a piece of 10 m InF3 fiber with core diameters of 9.5 μm. The 2 μm noise-like pulses is realized by nonlinear amplifying loop mirror mode-locking technique and amplified by two-stage amplifiers with pulse repetition rate of 1.513 MHz and 3-dB pulse envelope width of 2.2 ns. To further increase efficiency, the InF3 fiber is spliced directly to the pigtail of main amplifier with 92.47 % coupling efficiency, which is in good agreement with 92 % theoretical result of fundamental-mode coupling efficiency. To the best of the authors’ knowledge, this work achieves the flattest (3 dB spectral coverage of 2120–3690 nm) and corresponding highest efficiency (67.8 %) in MIR SC seeded by 2 μm pulses.

C- and L-Bands Wavelength-Tunable Mode-Locked Fiber Laser

We report a single-wavelength tunable mode-locked fiber laser. The single wavelength can be tuned from 1537.49 nm to 1608.06 nm by introducing a Sagnac loop filter. As far as we know, this is the widest single-wavelength tuning range achieved in an erbium-doped mode-locked all-fiber laser based on nonlinear amplifying loop mirror (NALM). The laser’s pulse width changes from 549 fs to 808 fs throughout the tuning process, the maximum average output power is 5.72 mW, and the single-pulse energy is 0.34 nJ at a central wavelength of 1556.53 nm. This laser source can serve as an efficient tool for applications that require a broad tunability range. The combination of femtosecond pulses and extensive wavelength tuning capabilities makes this laser system highly valuable in fields such as fiber optic communications, spectroscopy, sensing, and other applications that benefit from ultrafast and tunable laser sources.

All-multimode fiber spatiotemporal mode-locked figure-eight laser based on multimode gain fiber.

In this paper, we report for the first time on an all-multimode fiber spatiotemporal mode-locked figure-eight laser operating at 1.0µm. This laser utilizes a multimode gain fiber and a nonlinear amplifying loop mirror mechanism. It can generate mode-locked noise-like pulses at different central wavelengths. Additionally, we observed the presence of a multi-soliton state within the cavity by reducing intracavity gain. This study contributes to a broader investigation of various pulse phenomena in spatiotemporal mode-locked lasers and provides valuable insights into further exploring the evolution of spatiotemporal dynamics in such systems.

Self-starting mode-locking in an all-PM Yb-doped fiber laser oscillator enabled by a 3x3 nonlinear optical lossy loop mirror

Ultrafast fiber oscillators based on loop mirror saturable absorbers often suffer from a problematic self-starting mode-locking operation. It is usually necessary to provide an additional phase shift in the loop, guaranteeing repeatable initiation of the pulsed regime. 3x3 even splitting ratio fiber couplers have recently introduced a required phase shift in an all-fiber loop mirror architecture. Until now, mode-locking induced by a 3x3 fiber coupler has been associated only with nonlinear amplifying loop mirrors. Here, we present a self-starting ultrafast dispersion-managed all-polarization-maintaining Yb-doped oscillator that utilizes a nonlinear optical lossy loop mirror instead. We show three ways of inserting asymmetric losses in a loop via a variable optical attenuator, a fiber coupler, and a very simple lossy splice. Complete characterization of all output ports of the oscillator proves significant spectral and temporal breathing of the pulse when circulating through the net normal dispersion cavity, which can deliver nJ-level pulse energy. The system guarantees excellent stability, low noise and performance comparable to nonlinear amplifying loop mirrors while being simpler, cheaper, and providing more usable output ports with different pulse characteristics.

On the design of low phase noise and flat spectrum optical parametric frequency comb

Optical frequency combs (OFCs) have become increasingly pervasive in recent years, with their advantageous frequency coherence properties enabling significant developments in numerous fields, such as optical communications, spectroscopy, and microwave signal processing. Recent interest in OFC development emphasizes minimizing and mitigating phase noise of individual comb lines for high-quality signal generation, processing, and detection. Cavity-less electro-optic combs and parametric combs are attractive sources for these applications in that they permit flat spectra, tunable tone spacing, and robustness to temperature variations. Although previous research has demonstrated broadband parametric OFC generation, the scaling of the phase noise has not been systematically investigated. Here, we demonstrate a 25 GHz-spacing cavity-less parametric OFC generator and investigate the interaction between electronic and optical noise sources that affect its phase noise and linewidth. In addition, we study the optimal design of a nonlinear amplified loop mirror based pulse shaper with a focus on the impact of pump power on the signal-to-pedestal power ratio, which ultimately influences the spectral flatness and the optical signal-to-noise ratio (OSNR) after the parametric expansion. Notably, we design the OFC using all polarization-maintaining (PM) components, demonstrating the performance of PM highly nonlinear fibers in parametric comb generation. This results in a PM cavity-less comb with <9 dB power variation over 110 nm, >0 dBm power per tone, <10 kHz linewidth, and >23 dB OSNR. These characteristics make it highly desirable for application in communication and signal processing.

All-normal dispersion widely tunable dual-wavelength mode-locked fiber laser based on NALM.

We experimentally and numerically demonstrate the all-normal dispersion (ANDi) ytterbium (Yb)-doped fiber laser based on nonlinear amplifying loop mirror (NALM) mode-locked, which allows tunable single-wavelength and dual-wavelength outputs. The pulses tuning ranges of the dual-wavelength are from 1032.24 nm to 1053.13 nm and from 1047.94 nm to 1069.05 nm, and the repetition frequency difference varies from 1766Hz to 1834Hz. To our knowledge, this is the widest dual-wavelength tuning range of Yb-doped fiber lasers based on NALM mode-locked. We test for 90 minutes and have high stability in both single-wavelength and dual-wavelength. In addition, the pulsed collision dynamics between two solitons at different wavelengths are numerically studied. Numerical results show that during the pulse collision, the two solitons pass through each other and maintain their properties, which also confirms the particle nature of the isolated wave. Our research contributes to the dynamics of dual-wavelength solitons collision in NALM mode-locked fiber laser and provides what we believe to be is a new idea for tunable Yb-doped dual-comb sources.

Amplitude noise suppression in Yb:doped NALM oscillators utilizing saturable absorber settings.

Optical frequency combs based on fiber lasers mode-locked (ML) with a nonlinear amplifying loop mirror (NALM) have become the backbone of many cutting-edge applications, ranging from precision spectroscopy to quantum physics. Being extremely precise measurement tools, understanding their passive stability and low-noise operation regimes is vital. While several influences on the laser noise have been studied, many parameters remain poorly understood. Here, we systematically analyze under which preconditions the artificial saturable absorber settings of the laser can be modified during operation without losing mode-locking and the effects on laser noise, the spectrum and the output power. Our results show that it is possible to decrease the amplitude noise (AM noise) of the laser by more than 50 % by simply rotating a wave plate within the laser cavity. Additionally, we discuss differences to a similar effect observed in a NALM-alike laser amplifier and of changing the output coupling. These findings deepen our understanding and capabilities of optimizing the noise performance of ML fiber lasers, enable us to investigate new parameter spaces, and can be used to further optimize the noise performance of the NALM laser design, making it an ideal light source for advanced setups both in research and industry.

Uni-and bidirectional soliton rains in a NALM mode-locked Tm-doped fiber laser

We report the generation of different drifting patterns of soliton rains in a Tm-doped fiber laser mode locked by the technique of nonlinear amplifying loop mirror. The directional control of drifting soliton rain has been achieved by varying pump power and polarization. At a stable pumping level, a kind of bidirectional soliton rain is observed from a unidirectional one for the first time. In the bidirectional case, the forward and backward solitons, leaving from the two sides of the condensed phase, appear in the spectrum as two typical soliton peaks on a wide pedestal, 2 nm in separation. The spectral result implies that the secondary drifting solitons are formed by developing one strong sideband of the primary soliton rain, induced by a shift of the transmission peak.

Noise-like pulses generation and its beam self-cleaning effect in an all-fiber multimode cavity with a figure-8 scheme

The beam profiles of multimode mode-locked fiber lasers are highly multimode, the speckled beam profiles limit their potential application. To improve the beam profiles of multimode mode-locked fiber lasers, we proposed an all-fiber figure-8 multimode cavity and experimentally demonstrated the generation of noise-like pulses (NLPs) and beam self-cleaning of NLPs in the cavity at 1.5 µm. The laser was mode locked by a nonlinear amplifying loop mirror, an Er/Yb co-doped fiber provided gain, and 50 m OM4 fiber introduced enough nonlinear phase shift difference. The scheme generated NLPs with 159 mW average power, 2.78 MHz repetition rate and 57.19 nJ pulse energy. The packet duration of the NLPs increased from 0.61 ns to 2.99 ns when the pump power was increased from 2 W to 9 W. Nonlinear beam self-cleaning with a near Gaussian beam profile output was achieved in the multimode fiber laser. The M2 was measured to be 2.41 at the pulse energy of 6.83 nJ. We also obtained spatiotemporal mode-locked pulses with 1.03 ps duration and speckled beam profiles. This is the first experimental demonstration of NLPs in multimode fiber lasers, and beam self-cleaning of NLPs was observed for the first time. The results enriched nonlinear dynamics in multimode fiber lasers.

978 Nm All-Polarization-Maintaining Mode-Locked Fiber Laser Based on Phase-Biased Nonlinear Amplifying Loop Mirror

Terahertz (THz) wave generation based on ultrafast laser are one of the most predominant and popular technologies. In particular, for THz generation by photoconductor antenna and optical rectification, higher optical to THz conversion efficiency usually requires ultrafast laser excitation into semiconductor or nonlinear crystal, therefore it is of great desire to develop ultrafast laser with high performance. CW Yb-doped lasers at 980 nm have been applied to generate THz wave range from 0.5 to 6 THz by DFG technique. To meet the demand of some THz wave generation (e.g. BNA crystal, gold nanoplasma), 980 nm ultrafast fiber laser are ideal pump sources and in desire to be developed. Here we demonstrate a 978 nm robust all-polarization-maintaining (PM) picosecond fiber laser mode- locked by phase-biased nonlinear amplifying loop mirror (PB- NALM). By introducing a nonreciprocal - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pi$</tex-math></inline-formula> /2 phase shifter into the fiber loop, a self-starting stable mode-locking is obtained with the center wavelength of 978.14 nm and a 3-dB bandwidth of 0.43 nm. The pulse duration is 8.1 ps corresponding to the time bandwidth product (TBP) of 1.09. The maximum average output power is 14.5 mW with a repetition rate of 45.438 MHz. After a master oscillator power amplification system, the 978 nm average output power reaches 2.12 W, which is then injected into a PPLN crystal for second harmonic generation and 52 mW 489 nm ultrashort lasers is obtained. This is, to the best of our knowledge, the first report of PB-NALM-based mode-locked fiber laser at 978 nm. The 978 nm ultrafast fiber laser and SHG to 489 nm have great potential in terahertz emission by shorter NIR and blue light.

Watt-level 1.6 μm dissipative soliton ultrafast laser and external generation of ∼70 fs noise-like pulses for supercontinuum generation

Here, we propose a high power dissipative soliton (DS) laser with a central wavelength of ∼1612 nm. The whole laser system includes the mode-locking oscillator and the corresponding master oscillator power amplifier (MOPA). The mode-locking oscillator is a nonlinear amplifier loop mirror (NALM) cavity, which has a net normal dispersion enabling the generation of nJ-level DS pulses. To further enhance the output power of the 1.6 μm DS pulses, the specially-designed MOPA system consisting of multiple-stage single-pass amplifier is constructed, which can amplify the output power to watt level and meanwhile keeps a high suppression ratio to C-band amplified spontaneous emission (ASE). This high power 1.6 μm DS laser will have further applications in biomedical research and material processing. In the amplifier, we observe the automatic evolution of the DS pulses into the noise-like (NL) pulses under high pumping strength. At the maximum pump power, the MOPA system delivers the NL pulses with an output power of over 2 W. The narrowest spike duration is ∼70 fs (fs). This 1.6 μm fs-scale NL laser is a good pump source for generating the mid-infrared supercontinuum without short wavelength region loss. To demonstrate the superiority of this NL laser, a broad supercontinuum from ∼0.87 μm to ∼3.75 μm waveband is achieved with a piece of highly germanium-doped (Ge-doped) fiber.

Transient dynamics in mode-locked all-PM Er-doped fiber laser with NALM

In this study, we utilized the Time-Stretch Dispersive Fourier Transform (TS-DFT) method to explore rapid transient states in both time and frequency domains of an all-polarization-maintaining dispersion-managed figure-eight mode-locked laser with Nonlinear Amplifying Loop Mirror (NALM). We detail the different stages of build-up dynamics at varying pump powers, encompassing the Q-switching (QS) stage, transient single pulse formation, pulsation beating patterns, bound states, and the final transition to a single pulse state. Our findings reveal that the mode-locked bound state regime emerges from a single pulse stage following QS, different from previously reported directly resulting from QS pulses or relaxation oscillations. In a novel contribution to the field, we have experimentally demonstrated the transient single pulse stage of build-up dynamics and compared it with the fundamental mode-locked single pulse.

Study of transition dynamics from breathing single pulse to higher-order pulses and hysteresis in a figure-of-9 fiber laser

This study investigates the nonlinear dynamics and hysteresis phenomena in a figure-of-9 fiber laser. The laser cavity consists of an Erbium doped nonlinear amplifying loop mirror (NALM) containing a Dispersion Compensation Fiber (DCF) segment, coupled to a nonlinear optical loop mirror (NOLM). A lumped-element model is developed for the laser cavity accounting for bi-directional light propagation. The model is based on the modified nonlinear Schrödinger equation (NLSE) with coefficients directly related to the parameters of each cavity segment. Gain saturation is taken into consideration for stable laser operation. The numerical results show that self-starting passive mode-locking and self-structuration of soliton lattices occur in the cavity of the laser. The soliton structuring is based on the concept of dissipative solitons, which requires a balance between dispersion-nonlinearity and gain-loss. The gain-loss parameters influence both the temporal pulse interactions and the NALM’s transmission, leading to a large variety of single and multiple breathing dissipative soliton dynamics. In that context, riveting studies of the transition dynamics from breathing single pulses to high-order multiple breathing dissipative solitons and hysteresis with respect to unsaturated amplifier gain in a figure-of-9 all-fiber laser are explored.