Nonlinear Amplifying Loop Mirror Research Articles

Delay-differential-equation model for mode-locked lasers based on nonlinear optical and amplifying loop mirrors

Delay differential equation model of a nonlinear optical--nonlinear amplifying loop mirror mode-locked laser is developed that takes into account the finite relaxation rate of the gain medium and asymmetric beam splitting at the entrance of the nonlinear mirror loop. Asymptotic linear stability analysis of the continuous wave solutions performed in the limit of large delay indicates that in a class-B laser flip instability is preceded by the modulational instability and therefore cannot give rise to stable square wave patterns. Numerically it is shown that the model can demonstrate large windows of regular fundamental and harmonic mode-locked regimes with single and multiple pulses per cavity round trip time separated by domains of irregular pulsing.

Tunable all-normal-dispersion femtosecond Yb:fiber laser with biased nonlinear amplifying loop mirror

We demonstrate a self-starting tunable all-normal-dispersion (ANDi) ytterbium (Yb):fiber laser based on the biased nonlinear amplifying loop mirror (NALM), which generates a stable femtosecond dissipative soliton with an average output power of 154 mW at a pump power of 816 mW. It has a dechirped pulse duration of 178 fs, a repetition rate of 88.6 MHz. Taking advantage of the intracavity-birefringence induced spectral filtering effect, its center wavelength tunes from 1029 to 1039 nm with a spectral bandwidth of 12 nm. The proposed ANDi femtosecond fiber laser provides a high-energy short-pulse laser source with strong stability.

All Few-mode Fiber Spatiotemporal Mode-Locked Figure-eight Laser

Spatiotemporal mode-locked (STML) fiber lasers attract great interest owing to their distinctive spatiotemporal characteristics and potential to generate high-energy pulse. Herein, we report an all few-mode fiber figure-eight laser STML by a nonlinear amplifying loop mirror at 1.0 μm. The laser can generate single and multiple pulses at different central wavelengths. In particular, various types of bound-state solitons, such as conventional bound-state solitons and double bound-state solitons, are also achieved and further confirmed by the numerical simulations. The obtained results contribute to further understanding the nonlinear characteristics of STML fiber lasers and such a laser has potential applications in optical communications, especially in information coding.

Nd-Doped Polarization Maintaining All-Fiber Laser With Dissipative Soliton Resonance Mode-Locking at 905 nm

Moving the fiber laser emission to the region below one micron may provide a cheaper, more compact and robust alternatives to the existing solid state lasers. Here, for the first time we report a neodymium mode-locked fiber laser emitting at 905 nm in the all-fiber polarization maintaining configuration. We obtain a self-starting pulse generation in nonlinear amplifying loop mirror (NALM) cavity configuration. To suppress a dominant emission at 1064 nm corresponding to a 4-level laser scheme, we use an active fiber - 920/1064 division multiplexer - active fiber sandwich-like sequence in the NALM loop. A rectangular shape dissipative soliton had nJ energy, 30 pm spectral width and 80 - 430 ps width linearly depending on the pump power. Excellent agreement with numerical simulation allowed us to recover pulse shape and width for the pulses out of autocorrelation window.

Noise-like pulses with 2.15 MHz repetition rate in an all-polarization-maintaining mode-locked fiber laser at the center wavelength of 1550 nm

We demonstrate a 2.15 MHz repetition-rate mode-locked figure-of-9 erbium-doped fiber laser at a center wavelength of 1550 nm by using an all-polarization-maintaining nonlinear amplifying loop mirror configuration. This laser can be self-started mode-locked and generate Gaussian-shape noise-like pulses (NLPs). The single pulse energy is approximately 11.68 nJ at a repetition rate of 2.15 MHz. Dispersion compensation fibers are added into the cavity to make the laser operate in a net normal dispersion regime and generate NLPs at the center wavelength of 1550 nm. These characteristics give it a great application potential, such as low spectral coherence interference, optical sensing and micromachining. In addition, we have investigated the evolution of these characteristics, contributing to further understanding the Gaussian-shape NLP.

848 kHz repetition-rate narrowband dissipative soliton ps-pulsed Figure-9 fiber laser.

In this paper, we study the limitations of decreasing the repetition rate for the narrowband dissipative soliton picosecond (ps) pulsed Figure-9 fiber laser with periodically saturable absorber (SA), and demonstrate how to decrease the repetition rate of this kind of fiber laser. By asymmetrically increasing the passive fiber length of nonlinear amplifying loop mirror (NALM) to lower SA saturation power, Q-switching instability can be avoided, thus effectively reducing the repetition rate of ps pulses. To combat noise-like pulse caused by excessive reduction of SA saturation power, we invoke the non-reciprocal output characteristics of periodic SA, and combined with increasing the intracavity fiber length outside the SA, we further reduce the laser repetition rate. Repetition rates for ∼10 and ∼20 ps pulses are reduced to 1.7 MHz and 848 kHz, respectively, which are, to the best of our knowledge, the lowest repetition rates of Figure-9 lasers reported thus far.

140 kHz, 1.2 ps pulses from an all-PM Yb-doped fiber master oscillator-power amplifier

We report on an environmentally stable mode-locked all polarization maintaining fiber laser with a nonlinear amplifying loop mirror (NALM) at a ultralow repetition rate. Experimentally, using different cavity lengths we have achieved stable mode-locking at different repetition rates. By carefully adjusting the length of the total fiber of NALM, we achieve stable broadband pulse trains with a repetition rate as low as 140 kHz. The pulses can be further amplified up to 27 μJ and compressed down to 1.16 ps. The laser system has potential application for industrial application.

High-precision passive stabilization of repetition rate for a mode-locked fiber laser based on optical pulse injection

We have proposed and implemented a novel scheme to obtain high-precision repetition rate stabilization for a polarization-maintaining mode-locked fiber laser. The essential technique lies in the periodic injection of electronically modulated optical pulses into a nonlinear amplifying loop mirror within the laser resonator. Thanks to the nonlinear cross-phase modulation effect, the injected pulses referenced to an external clock serves as a stable and precise timing trigger for an effective intensity modulator. Consequently, synchronous mode-locking can be initiated to output ultrafast pulses with a passively stabilized repetition rate. The capture range of the locking system reaches to a record of 1 mm, which enables a long-term stable operation over 15 hours without the need of temperature stabilization and vibration isolation. Meanwhile, the achieved standard deviation is as low as 100 μHz with a 1-s sample time, corresponding to a fluctuation instability of 5.0×10-12. Additionally, the repetition rate stabilization performance based on the passive synchronization has been systematically investigated by varying the average power, central wavelength and pulse duration of the optical injection.

Comparison of two low-noise CEO frequency stabilization methods for an all-PM Yb:fiber NALM oscillator

We present a comparison of two low-noise carrier-envelope offset (CEO) frequency stabilization methods studied using an ytterbium (Yb) fiber laser oscillator based on a nonlinear amplifying loop mirror. We first investigate the phase locking performance achieved with cross-gain modulation (XGM) via injection of an auxiliary low-power continuous-wave (CW) laser into the fiber gain medium. Amplification of the injected CW laser light cross-modulates the gain of the oscillator, resulting in an intra-cavity power modulation, thus providing control of the CEO frequency. The XGM method is then compared with the conventional pump-current modulation scheme. Both stabilization methods provide similar locking performances with sub-200-mrad of integrated residual carrier-envelope-phase (CEP) noise (10 Hz to 1 MHz), suitable for high-resolution comb spectroscopy applications.

Dynamic behaviors of multiple-soliton pulsation in an L-band passively mode-locked fiber laser with anomalous dispersion.

As a universal phenomenon in nonlinear optical systems, the soliton pulsating behavior is useful to achieve high pulse energy and can further enrich the complex soliton dynamics. To the best of our knowledge, herein we have demonstrated the observation of multiple-soliton pulsations in an L-band mode-locked fiber laser based on a nonlinear amplifying loop mirror with anomalous dispersion for the first time. Based on the dispersive Fourier transform method, we find that the pulsations in the multi-soliton regime are accompanied with the pulse width breathing and spectrum oscillation. In addition, the corresponding number of pulsating solitons increases linearly from 8 to 16 with the pump power. Our findings can facilitate a better understanding of the complex mechanism of soliton pulsations.

Square-Wave Pulse Passively Mode-Locked Thulium-Doped Fiber Laser With Adjustable Pulse Duration and Amplitude

A passively mode-locked thulium-doped fiber laser with square-wave pulse generation has been demonstrated using a figure-of-eight configuration with two gain mediums respectively located in the left and right loops. In this laser, mode-locking is achieved based on equivalent saturation absorption of a nonlinear amplifying loop mirror (NALM). The pulse amplitude and width of the square-wave pulse can be continuously extended through controlling pump power of gain mediums in the left and right loops. Moreover, the pulse dynamics and autocorrelation trace reveal the obtained square-wave pulse is a new kind of noise-like pulse, i.e., noise-like square-wave pulse, with capability of supporting higher pulse energy. This find enriches laser pulse dynamics and has important potential applications in laser detection, sensing and other fields.

10GHz regeneratively mode-locked erbium-doped fiber laser combined with nonlinear amplifying loop mirror

Mode-locked fiber lasers can generate short pulses with a high repetition rate. It can be used in nonlinear optical imaging, photo-communication and other fields. Obtaining narrow pulses with high repetition frequency has become a hot research topic. In this article, we demonstrate a hybrid mode-locked fiber laser, which is a regeneratively mode-locked erbium fiber laser operating at 10 GHz, incorporating a nonlinear amplifying loop mirror to generate a 1.9 ps pulse sequence. This all-fiber laser with a high-repetition-rate and short pulses has the advantages of high stability and self-starting, which has a wide range of applications.

Dissipative solitons in a compact Er-doped all-fiber figure-of-9 laser

We designed and demonstrated a compact all-fiber dissipative soliton (DS) fiber laser. The proposed Erbium doped fiber laser is mode-locked by nonlinear amplified loop mirror (NALM), which has a typical figure-of-9 structure and operates in normal net-cavity dispersion regime. The NALM-based fiber laser is constructed by only three polarization maintaining fiber components, which can generate long-term stable, self-started pulses with 0.29 nJ pulse energy and 354 fs pulse width under 55.6 MHz repetition rate. It is proved both numerically and experimentally that the essential dissipative mechanism for the DS generation is provided by spectral filtering effect of the NALM loop. Our results clearly show that the DS's spectral bandwidth can be modulated by changing length of the fiber in the NALM loop.

Noise-like pulses under different intra-cavity nonlinearity

We report on the influence of the average nonlinear coefficient on noise-like pulse (NLP) in a figure-of-eight erbium-doped fiber laser. Since the nonlinear switching point of nonlinear amplifying loop mirror (NALM) shifts with distinct laser configurations, through changing the length of highly nonlinear fiber (HNLF) in NALM, properties of output pulse have been compared and analyzed. The spectral evolutions occur and the peak power of NLP presents a decline when the HNLF is lengthened in NALM. Also, the tuning range of the duration of NLP shows a difference based on the average nonlinear coefficient selected.

Compact, All-PM Fiber Integrated and Alignment-Free Ultrafast Yb:Fiber NALM Laser With Sub-Femtosecond Timing Jitter

We report a simple and compact design of a dispersion compensated mode-locked Yb:fiber oscillator based on a nonlinear amplifying loop mirror (NALM). The fully polarization maintaining (PM) fiber integrated laser features a chirped fiber Bragg grating (CFBG) for dispersion compensation and a fiber integrated compact non-reciprocal phase bias device, which is alignment-free. The main design parameters were determined by numerically simulating the pulse evolution in the oscillator and by analyzing their impact on the laser performance. Experimentally, we achieved an 88 fs compressed pulse duration with sub-fs timing jitter at 54 MHz repetition rate and 51 mW of output power with 5.5 * 10-5 [20 Hz, 1 MHz] integrated relative intensity noise (RIN). Furthermore, we demonstrate tight phase-locking of the laser's carrier-envelope offset frequency (fceo) to a stable radio frequency (RF) reference and of one frequency comb tooth to a stable optical reference at 291 THz.

Intrinsic amplitude-noise suppression in fiber lasers mode-locked with nonlinear amplifying loop mirrors.

In this Letter, we investigate steady states of fiber lasers mode-locked with a nonlinear amplifying loop mirror that have an inherent amplitude-noise-suppression mechanism. Due to the interaction of the sinusoidal transmission function with the fluctuating intracavity pulse amplitude, we show that under specific preconditions, this mechanism may lead to a detectable difference in relative intensity noise at the reflected and transmitted output port of the laser. We present systematic intensity noise measurements with a nonlinear fiber-based system that replicates a single roundtrip in the laser cavity. The experimental results and simulations clearly show a reduction of the intracavity amplitude fluctuations up to 4 dB for certain steady states.

Reduction of excess intensity noise of picosecond Yb soliton fiber lasers in a >10-mW power regime

We demonstrate that excess intensity noise of soliton fiber lasers in the average power regime exceeding 10 mW can be reduced by increasing the intracavity dispersion and reducing the pump power. Based on this strategy, we present a polarization-maintaining picosecond Yb fiber laser mode-locked by a nonlinear amplifying loop mirror whose excess noise is equal to the shot noise at an optical power of >10 mW.

Self-Started Dual-Wavelength Mode-Locking With Well-Controlled Repetition Rate Difference

Dual-wavelength mode-locked fiber lasers are considered as ideal solutions for fast, precise, and sensitive dual-comb spectroscopy. In this study, we present a self-started dual-wavelength fiber laser by combining a nonlinear amplifying loop mirror and a Lyot filter. Nonlinear phase accumulation, dual-wavelength competition, and crosstalk between the mode-locking mechanism and filtering effect are well addressed to realize the self-started dual-wavelength mode-locking. Furthermore, by temperature controlling the specific polarization-maintaining fiber, our dual-wavelength laser can be continuously tuned in a wavelength range of ~6 nm, corresponding to a well-controlled repetition rates change of 80 Hz and their difference change of 30 Hz. Mutual coherence of the dual-wavelength pulses is demonstrated by detecting the multi-heterodyne beat notes and measuring the fluctuation of the repetition rate difference. Within 10 hours of measurement, the dual-wavelength repetition rates difference remains stable at 1180 Hz with an Allan deviation of ~9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> Hz @ 1s. By virtue of the all polarization-maintaining structure, our dual-wavelength laser shows improved long-term stability and repeatability, which will facilitate the turn-key, robust, and reproducible dual-comb spectroscopy for high-power or field applications.

1.3\xa0\xb5m dissipative soliton resonance generation in Bismuth doped fiber laser

In this work, a Figure-9 (F9) bismuth-doped fiber laser (BiDFL) operating in the dissipative soliton resonance (DSR) regime is presented. The 1338 nm laser used a BiDF as the active gain medium, while a nonlinear amplifying loop mirror (NALM) in an F9 configuration was employed to obtain high energy mode-locked pulses. The wave breaking-free rectangular pulse widened significantly in the time domain with the increase of the pump power while maintaining an almost constant peak power of 0.6 W. At the maximum pump power, the mode-locked laser delivered a rectangular-shaped pulse with a duration of 48 ns, repetition rate of 362 kHz and a radio-frequency signal-to-noise ratio of more than 60 dB. The maximum output power was recorded at around 11 mW with a corresponding pulse energy of 30 nJ. This is, to the best of the author’s knowledge, the highest mode-locked pulse energy obtained at 1.3 μm as well as the demonstration of an NALM BiDFL in a F9 configuration.

10 µJ noise-like pulse generated from all fiberized Tm-doped fiber oscillator and amplifier.

Herein, we presented a high energy noise-like (NL) pulse Tm-doped fiber laser (TDFL) system. Relying on the nonlinear amplifying loop mirror (NALM), stable noise-like pulses with coherence spike width of ∼317 fs and envelope width of ∼4.2 ns were obtained from an all polarization-maintaining fiberized oscillator at central wavelength of ∼1946.4 nm with 3 dB bandwidth of ∼24.9 nm. After the amplification in an all-fiberized TDF amplifier system, the maximum average output power of ∼32.8 W and pulse energy of ∼10.1 µJ were obtained, which represents the highest pulse energy of NL pulse at ∼2 µm, to the best of our knowledge. We believe that the high energy NL pulse source has the potential application in mid-infrared supercontinuum generation.