Nonlinear Loop Mirror Research Articles

Dissipative soliton resonance in a normal dispersion all-polarization-maintaining thulium-doped fiber laser

We report a first demonstration of dissipative soliton resonance (DSR) in a normal dispersion thulium-doped fiber laser (TDFL) constructed entirely of polarization-maintaining fibers. A nonlinear fiber loop mirror with a combination of normal and anomalous dispersion fibers inside the loop ensures a self-starting mode-locking operation in the DSR regime. The oscillator generated linearly polarized optical pulses with a fundamental repetition frequency of 5.735 MHz and a nearly constant peak power clamped at ∼ 4.35 W. The pulse duration extends from 217 ps to 6 ns, when the pump power increases from 417 mW to 1.86 W. The maximum average output power of the DSR pulses was 151 mW, corresponding to the single pulse energy of 26 nJ.

Background-reduced spectral peak generation using a nonlinear loop mirror with a gas cell.

Spectral peaking in an optical fiber is a useful phenomenon for comb mode filtering and wavelength standards. However, for highly sensitive spectroscopic applications, it is important to suppress the pedestal components. Here we propose and demonstrate pedestal-suppressed spectral peak generation using a nonlinear fiber loop mirror with a molecular gas cell. The physical mechanism and fundamental properties were investigated numerically, and the output characteristics were examined experimentally. Almost background-free spectral peaks were generated successfully in the 1.65-µm wavelength range using a CH4 gas cell. The maximum signal-to-background ratio was more than 30 dB. Stable operation without any feedback control was achieved. It is expected that the proposed method is useful for highly sensitive spectroscopic applications.

Pulse convergence analysis and pulse information calculation of NOLM fiber mode-locked lasers based on machine learning method

Nowadays, mode-locked fiber laser has been extensively applied in various fields such as communication, biomedical, nuclear physics and material processing. By controlling the parameters of cavity elements, people can realize the output of ultrafast pulse with different states. Utilizing the traditional numerical method, the influence of different cavity parameters on the pulses can be computed accurately, which provides the simulation basis for the fabrication of mode-locked fiber lasers. However, with the development of the practical application demand, the performance requirements of the mode-locked pulse are also increasing. The traditional numerical methods have shown some defects in the calculation speed and analysis ability at this time. To improve the shortcomings of the existing numerical methods, in this work, we propose using the machine learning method to analyze the mode-locked pulse convergence of the nonlinear loop mirror (NOLM) fiber mode-locked laser and calculated its pulse information. Firstly, the mapping between cavity parameters and convergence region is established by the support vector machine (SVM) model, and utilizing it, the influence of different cavity parameters on mode-locking is investigated. Then, we train two artificial neural networks (ANN) for calculating the pulse shape and spectral shape in the mode-locked state and find out the cavity parameters under which.the spectral shape approximates to a parabola based on genetic algorithm and the ability of ANN in rapid computing. Finally, we construct the laser cavity according to the numerical result and obtain the mode-locked pulse with a parabolic shape spectrum. The authors believe that the model presented in this work will show widely application prospects in the numerical calculation of fiber lasers.

Supercontinuum generation in NALM fiber laser with pulse type switchable

We report a supercontinuum (SC) generation based on pulse type switchable nonlinear amplification loop mirror (NALM) mode-locked fiber laser. In the experiment, we obtained a dissipative soliton (DS) mode-locked pulse with a spectral width of 20.04 nm and a pulse duration of 1.68 ps, which is used as a SC generation. The spectrum width of SC generated by DS is up to 940 nm (1460–2400 nm), and the unflatness of SC in 1580.2–2177.6 nm is less than 0.9 dB. By adjusting the polarization controller (PC) and pump power, the switching between DS and bound state soliton (BSS) is realized. The spectral width of SC generated by BSS is up to 962 nm (1438–2400 nm), and the 10 dB bandwidth is 689.2 nm. In addition, we carried out temperature sensing experiments and proved that our SC system has good smoothness and fineness. Our results demonstrate the SC generation with two switchable pulse type, which provides the possibility for different application requirements.

Non-linear photonic loop mirror based co-site interference canceller

Full duplex-in band (FDIB) is a well-established solution for increasing the data rate and spreading the link range for future communication systems. FDIB systems need no additional bandwidth requirement. However, they are confronted with a major interference challenge on the same site, called co-site interference (CSI). Long-established co-site interference cancellation (CSIC) methods achieve a cancellation depth upto 35 dB, conversely it has space containments, manufacturing imperfections, induces noise penalties and limits isolation bandwidth. To overcome these problems, RF photonic CSIC methods have been developed, which have produced 30 dB wide-band interference suppression. They also increase bandwidth, have a flexible structure, minimize losses and prevent periodic power fading. But these systems have a problem of inherent DC drift, low maintenance of coherence, and low isolation at low transmission power. Thus, there is a high need for photonic CSIC designs of FDIB systems that operate over wider bandwidths and at higher transmission powers. Here, a newfangled CSIC system based on a non-linear photonic loop and frequency down-conversion is proposed. It shows excellent CSIC suppression of greater than 61 dB, for a single frequency signal of interest (SOI) with maximum RF power of 13 dBm. Without frequency down-conversion, the system maintains an average cancellation depth of 62.541 dB for single frequency SOI. After frequency down conversion, the system maintains an average cancellation depth of 61.208 dB for narrow band SOI. The system attains 18% error vector magnitude at −20 dB RF output power, which confirms the comprehensive quality of the system.

Switchable multi-wavelength thulium-doped fiber laser using a two-taper fiber filter

An individually switchable and tunable multiwavelength thulium-doped fiber laser (TDFL) is proposed and experimentally demonstrated. The key component of the laser is a comb filter composed of two fiber tapers separated by a short middle section. A nonlinear loop mirror (NOLM) is inserted into the laser cavity to suppress the intense gain competition. By properly adjusting the polarization controllers (PCs) in the cavity, the laser can operate in at most sextuple wavelength state. In addition to these laser output characteristics, the experiment result also shows that single wavelength tuning can be achieved, and the tuning range is 1952.06 nm to 1975.62 nm. This multi-wavelength TDFL may be useful in optical fiber sensing or other fields desiring flexible optical source.

Bound-State Soliton and Noise-like Pulse Generation in a Thulium-Doped Fiber Laser Based on a Nonlinear Optical Loop Mirror

We demonstrate a thulium-doped, mode-locked, all-fiber laser capable of operating in two generation regimes: dispersion-managed soliton and noise-like pulse (NLP). Employing a nonlinear optical loop mirror as an artificial saturable absorber, the oscillator generated optical pulses with a fundamental pulse repetition frequency of ~15.795 MHz. The total net dispersion of the laser cavity had a slightly anomalous group delay dispersion value of −0.016 ps2. After appropriate adjustment of a polarization controller, bound states of a dispersion-managed soliton composed of three pulses with fixed soliton separations were also observed. NLP generation, tunable over 35 nm from 1943.5 to 1978 nm, was also presented in the same laser setup. To our knowledge, this is the first report of the generation of tunable NLPs in a mode-locked thulium-doped fiber laser based on a nonlinear loop mirror saturable absorber.

All-Polarization Maintaining Noise-Like Pulse From Mode-Locked Thulium-Doped Fiber Laser Based on Nonlinear Loop Mirror

In this paper, we present a figure-eight all-polarization maintaining thulium-doped mode-locked fiber laser based on a nonlinear optical loop mirror operating at noise-like pulse regimes. The total cavity length is 34.5 m, and the calculated net group delay dispersion is estimated to be ∼−2.616 ps <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . At the maximum pump power, stable noise-like pulse centered at 1943 nm with a spectral full width at half maximum of 32 nm, a pulse energy of 13.51 nJ, and a coherence spike width of 236 fs is generated at a repetition rate of 5.96 MHz with the signal-to-noise ratio ∼64 dB. The polarization extinction ratio is > 15 dB at any mode-locking operation. The slope efficiency and the output power fluctuation of the laser are 5.16% and 0.039%, respectively. The laser does not require polarization state controllers, and it holds very high stability, which is insensitive to temperature changes or mechanical vibrations. Through further amplification, it will be a good laser source for real-time interrogation of fiber Bragg gratings and supercontinuum generation.

Passively Mode-locked Erbium-doped Fiber Laser Based on Nonlinear Fiber Loop Mirror

Passively Mode-locked Erbium-doped Fiber Laser Based on Nonlinear Fiber Loop Mirror

Femtosecond all-polarization-maintaining Nd fiber laser at 920 nm mode locked by a biased NALM.

We demonstrate a femtosecond all-polarization-maintaining Nd fiber laser working at 920 nm mode locked by a biased non-linear loop mirror. The broadest spectral width of the pulse is 25.2 nm and the output power is 8 mW with 320 mW pump power. The measured pulse width is 109 fs with extra-cavity compression. The laser configuration of all-polarization-maintaining fiber can directly enhance the environmental stability of generated pulses. The seed pulses of the oscillator were amplified over 400 mW, which served as the light source for a two-photon microscope. To the best of our knowledge, this is the first demonstration of a 920 nm femtosecond Nd polarization-maintaining fiber laser based on a non-linear loop mirror.

Dispersion managed thulium-doped fiber laser mode-locked by the nonlinear loop mirror

Intracavity dispersion management in a passively mode-locked thulium-doped all-fiber laser, based on a nonlinear optical loop mirror (NOLM) saturable absorber is reported. Fundamental soliton and stretched pulse soliton generation are demonstrated, when the oscillator operates with anomalous net dispersion. Gaussian pulses with a duration of 253 fs and 26.4 nm spectral bandwidth centered at wavelength of 1967 nm were generated with a fundamental pulse repetition frequency of ~15.8 MHz. In soliton mode-locking regime the oscillator delivering optical solitons with a 3 dB spectral width of 7.96 nm and duration of 675 fs. To the best of our knowledge, this is the shortest fundamental soliton generated from thulium-doped fiber laser with all anomalous dispersion based on a nonlinear fiber loop mirror saturable absorber reported till date.

Dispersion management of a nonlinear amplifying loop mirror-based erbium-doped fiber laser.

We report an investigation of dispersion management of an all-polarization-maintaining Er-fiber oscillator mode-locked via a nonlinear amplification loop mirror in a figure-nine cavity configuration with two output ports. The performance of the laser was investigated within the net cavity dispersion ranging from -0.034 ps2 to +0.006 ps2. We show that the spectral and temporal phase of the pulses at both figure-nine outputs have clearly different characteristics. One of the laser outputs provides pulses with significantly better quality; nonetheless, the rejection output also offers ultrashort pulses with broad spectra. Pulses as short as 79 fs with an energy of 83 pJ were generated directly from the laser in the near-zero dispersion regime.

Interval-Adjustable Multi-Wavelength Erbium-Doped Fiber Laser With the assistance of NOLM or NALM

A novel interval-adjustable multi-wavelength erbium-doped fiber laser (EDFL) is experimentally demonstrated in this paper. The proposed EDFL is based on the cascaded structure of two-segment Sagnac filter and nonlinear optical loop mirror (NOLM). By properly adjusting the polarization controllers (PCs), the wavelength interval and number of output wavelengths can be changed. When the wavelength interval is 2nm and 0.5nm, the number of wavelengths is 1-3 and 5-8, respectively. At the same time, when the number of output wavelengths is 6~8, the wavelengths can be tuned within a certain range. In order to compare the effects of two similar nonlinear loop mirrors on the outputs, a nonlinear amplifying loop mirror (NALM) is used to replace the NOLM in the laser cavity. The number of output wavelengths is increased to 10 when using NALM. The structure and principle of NOLM and NALM are analyzed. The influences of the two structures on the stability and output power of the laser are also discussed.

All Polarization Maintaining Fiber-Based Optical Comb System with Nonlinear Loop Mirror Mode-Locking

All Polarization Maintaining Fiber-Based Optical Comb System with Nonlinear Loop Mirror Mode-Locking

Stable multiwavelength semiconductor amplifier fiber laser based on nonlinear fiber loop mirror

A stable multiwavelength semiconductor amplifier (SOA) fiber laser using a nonlinear fiber loop mirror (NOLM) and a Lyot–Sagnac loop mirror is presented and experimentally demonstrated. The Lyot–Sagnac loop mirror serves as a wavelength selection device, and the wavelength spacing is controlled by the length of polarization-maintained fiber (PMF). The NOLM serves as a power equalizer to achieve power equalization and improve stability. Moreover, the NOLM can also suppress the mode competition effect within homogenous broadening linewidth of SOA. Multiwavelength output with power equality has been achieved at room temperature, with no obvious power fluctuation. The number of lasing lines is 31 within the 10-dB bandwidth, and the wavelength spacing is 0.63 nm. In addition, the average optical signal-to-noise ratio is up to 25.15 dB. Finally, narrower wavelength spacing is obtained by increasing the length of the PMF.

All-fiber short-pulse vortex laser with adjustable pulse width

A laser with short pulse width and direct output of a vortex beam was reported herein. This laser was fabricated from a nonlinear loop mirror (NOLM) and a coupler composed of a single mode fiber and few-mode fiber fused together. The NOLM is responsible for generating pulses, and the coupler acts as a beam splitter and mode converter. Two stable vortex modes can be formed by adjusting the polarization controller, whose pulse widths are 1.098 ps and 542 fs, respectively.

All fiber multiwavelength Tm-doped double-clad fiber laser assisted by four-wave mixing in highly nonlinear fiber and Sagnac loop mirror

A four-wave mixing (FWM) based multi-wavelength laser based on a double-cladding thulium-doped fiber laser (DC-TDFL) is proposed and demonstrated. A highly nonlinear fiber (HNLF) in conjunction with a Sagnac loop mirror formed by polarization maintaining fibers (PMFs) is used to induce the FWM effect as well as to mitigate gain-competition in the DC-TDFL. This increases the number of lasing wavelengths that can be generated. Approximately 35, 55, and 68 stable lasing lines are achieved within 10 dB, 20 dB, and 28 dB bandwidths by adjusting the polarization controllers. A uniform channel spacing of 0.38 nm is obtained with minimal wavelength drifts and power fluctuations of 0.056 nm and 2.8 dB. This is, to the best of the author’s knowledge, the first demonstration of large numbers of lasing channels in the 1.97μm wavelength region from a DC-TDFL.

Research on Multi-wavelength Fiber Laser Based on Nonlinear Effect

A multi-wavelength erbium-doped fiber laser (MWEDFL) is introduced, which uses highly erbium-doped fiber (EDF) as the gain medium and uses the nonlinear effect of the single mode fiber to suppress the mode competition. In order to obtain higher side mode suppression ratio and flatness, a nonlinear fiber loop mirror is added to the structure. The results show that a stable multi-wavelength laser with 16 lasing wavelengths and a side mode suppression ratio (SMSR) higher than 30dB is obtained.

All-fiber thulium-doped mode-locked fiber laser and amplifier based on nonlinear fiber loop mirror

We report on a self-starting, anomalous dispersion mode-locked Tm-doped fiber laser based on all polarization maintaining (PM) fiber components. The oscillator, which is based on a nonlinear optical loop mirror, generates stable, linearly polarized sub-picosecond solitons at a repetition frequency of 11.78 MHz, centered at 1996.6 nm with a spectral width of 7.12 nm. Amplification of the pulses in a single-stage thulium-doped fiber amplifier resulted in an increase of the pulse energy to over 11 nJ at which soliton splitting process was demonstrated.

Machine Learning Methods for Control of Fibre Lasers with Double Gain Nonlinear Loop Mirror

Many types of modern lasers feature nonlinear properties, which makes controlling their operation a challenging engineering problem. In particular, fibre lasers present both high-performance devices that are already used for diverse industrial applications, but also interesting and not yet fully understood nonlinear systems. Fibre laser systems operating at high power often have multiple equilibrium states, and this produces complications with the reproducibility and management of such devices. Self-tuning and feedback-enabled machine learning approaches might define a new era in laser science and technology. The present study is the first to demonstrate experimentally the application of machine learning algorithms for control of the pulsed regimes in an all-normal dispersion, figure-eight fibre laser with two independent amplifying fibre loops. The ability to control the laser operation state by electronically varying two drive currents makes this scheme particularly attractive for implementing machine learning approaches. The self-tuning adjustment of two independent gain levels in the laser cavity enables generation-on-demand pulses with different duration, energy, spectral characteristics and time coherence. We introduce and evaluate the application of several objective functions related to selection of the pulse duration, energy and degree of temporal coherence of the radiation. Our results open up the possibility for new designs of pulsed fibre lasers with robust electronics-managed control.