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In this article, a symmetrical nonlinear optical loop mirror (NOLM) exhibiting a polarization-dependent transmission is evaluated to generate optical pulse emission in a figure-eight fiber laser in the soliton and noise-like pulse (NLP) regimes. The NOLM structure relies on a 50:50 fiber coupler, a loop with highly twisted single-mode optical fiber and a quarter-wave retarder (QWR) to break the polarization asymmetry. The pulse operation regime is determined by properly adjusting the NOLM low-power transmission, which is easily realized by the rotation of the QWR angle. Soliton pulses of 1.48 ps pulse duration and peak power of 18 W were observed with a peak to peak separation of 1.25 µs, corresponding to a fundamental cavity repetition rate of 0.8 MHz. Moreover, by incrementing the NOLM low-power transmission, NLP emission is generated exhibiting a wide and smooth spectrum of 8.5 nm bandwidth.

In this work we browse an overview of the complex dynamics that arise in the non-stationary modes of operation of partly mode-locked fiber lasers under strict polarization control. Both ring and figure-eight cavities implementing saturable absorber mechanisms that rely on nonlinear polarization rotation were considered. The use of twisted fiber ensures robust operation, whereas precise polarization adjustments allow tailoring the nonlinear switching characteristic in a clear and repeatable manner. The enhanced flexibility of these sources allowed identifying and studying a broad spectrum of peculiar dynamics, in particular by implementing the temporal and spectral mapping techniques. These include the emergence, fusion, splitting, complex evolution and eventual decay of chaotic bunches of radiation, which are also subject to large spectral shifts, ample quasi-periodic instabilities, extreme-intensity events or the creation of solitons, among others, as well as the complex evolution of massively multiple soliton states. Finally, with the help of numerical simulation, several aspects of the physics underlying these puzzling behaviors could be elucidated.

This work presents a numerical approach to understand the self-regeneration mechanism of the fundamental soliton propagation driven by the nonlinear Schr \" odinger equation in the nonlinear fiber formalism. This approach shows that the interplay between dispersion and nonlinearity results in a compensation effect in the phase and the instantaneous frequency representation of the pulse envelope. For a better understanding of this compensation process, 3D mapping propagation graphs are presented.

A 3X3 plastic optical fiber (POF) twisted coupler has been fabricated as a compact sensor of multiple variables. The POFs are twisted into a combined body and the clad was removed by chemical method. Three LEDs of red, green, and blue colors can be used to shape a broad spectrum. Each led was connected at a different input port of the coupler. Since the twisted coupler makes the coupling of light from the input ports, we have a wide spectrum at each one output port. We develop a different sensor at each one output coupler: mass concentration (At the output-1), and curvature (At the output-2). The multi-sensing proposed in this work can increase the number of sensors as increase the number of output ports, and the bandwidth increase as increase the colors of light sources. On the other hand, we can use a wide spectrum lamp in a single input port and in the same way make multiple sensors in the output ports. The variation is evident in all wavelengths of the spectrum for measurements of sugar concentrations and fiber curvature. However, we can directly associate the sugar concentration variations with the spectrum in a range from 570 to 600 nm; and across the full spectrum for curvature measurements.

We study numerically supercontinuum generation (SCG) in four different 10-cm-long photonic crystal fibers (PCFs) at 800 nm and ~1060 nm, whose parameters are found in the literature, comparing the performance of noise-like pulses (NLPs) and ultrashort pulses (USPs) as the pump. Averaging hundreds of spectra produced by NLPs from two passively mode-locked fiber lasers (thulium and ytterbium), smooth and uniform curves similar to experimental ones were achieved, requiring low or moderate input peak powers. In contrast, spectra exhibiting poor flatness with strong fluctuations up to 24 dB were obtained when using USPs as the pump.

In this paper, we propose a novel approach for implementing spiking neurons through an optical system. Spiking neurons are a new approach to emulate the neural processes that occur in the brain, known as the third generation of artificial neural networks. They have been successfully used to build a new technology called neuromorphic engineering, which looks for a better performance than traditional computing in tasks usually performed by AI-based systems. Our optical system consists of a low-cost laser source, based on a microcontroller and a continuous-wave laser diode, the microcontroller allows producing synchronous or asynchronous pulses with complex time profiles. Here, through said system we have successfully reproduced most of the neural dynamics observed in biological neurons. These dynamics have been reproduced using a very simple optical array with a great potential for the development of neuromorphic systems. The optical system has been experimentally validated.

We propose to use the fast Fourier transformation (FFT) to analyze the spectral data of passively mode-locked fiber lasers, with the purpose of characterizing and classifying the different pulsed regimes arising in these lasers. The results show temporal information at the sub-ps scale. Specially, in the Fourier domain, the spectra of bound solitons depict several solitons with relative phases of π/2 and close to 0, distributed into a window that extends beyond the limited span of the autocorrelator. Besides, the FFT amplitude traces can help to classify the multi-pulse regimes generated by the laser; in particular, the exponential decay of intensity in such amplitude traces can be a fingerprint of noise-like pulses. Furthermore, the amplitude traces show some modulation that we attribute to Kelly’s sidebands. The proposed technique allows examining spectra from a mode-locked fiber laser independently of the active medium or laser cavity configuration without the need to use ultrafast photo- detectors.

Supercontinuum generated directly from an Erbium/Ytterbium fiber amplifier and their dependence on pump power has been experimentally reported. Waveforms of pulses remain unchanged in contrast with respective spectra from 0.1 to 12 W pump power.

In the present work we demonstrate a novel single-soliton ultra-low pulse repetition frequency passively mode-locked erbium-doped fiber laser. We mitigate the residual linear birefringence of fiber by fiber twist to achieve a strict control of polarization. For mode-locking the nonlinear polarization rotation (NPR) was used. Special technique was applied to reduce the overdriving of NPR that allows the generation of single soliton in ultra-long cavity. The strict control of polarization yields a stable relation between the polarization state of the pulses propagating in the cavity and the regimes of generation. A 192.12-kHz train of soliton pulses was obtained with pulse duration of 4.7 ps at 1560.1 nm, the average power was 29 μW and the estimated peak power was 30.8 W with an energy of 150.9 pJ.

Some complex dissipative dynamics associated with the noise-like pulse (NLP) regime of a passively mode-locked erbium-doped fiber laser are studied numerically. By means of a convenient 3D mapping of the spatio-temporal pulse evolution, for properly chosen dispersion parameters, several puzzling dissipative dynamics of NLPs are identified, including the expelling of sub-packets that move away from the main bunch, the sudden extinction of isolated sub-pulses, the collision between different internal fragments travelling at different speeds, the rising of sub-pulses, the formation of complex trajectories by substructures that first move away and then return to the main bunch, and so on. In addition, the emergence of optical rogue waves (ORWs) within NLPs is also demonstrated numerically; to help understand these behaviors evidenced in the time domain, spectral analyzes were also performed that show, among other things, that the spectrum of a NLP is notoriously distorted when it hosts an ORW phenomenon. These numerical results are consistent with previously published experimental results.

We study numerically complex noise-like pulse dynamics in a passively mode-locked erbium-doped fiber laser. Wavelength-dependent gain dynamics is modeled as a combination of a three-level and a four-level system, which approximate the gain behavior in the 1530-nm and 1560-nm regions, respectively. The typical deformation of the erbium gain spectrum as it saturates is properly reproduced by this approach. Several puzzling noise-like pulse dynamics that were recently observed experimentally are qualitatively reproduced numerically, in particular slow quasi-periodic energy variations and the emergence and walkoff of wavelength-shifted radiation components. These results clearly reveal that gain dynamics is deeply involved in the onset of such complex temporal and spectral instabilities in these sources.

The present work is a review of the chronological development of the laser invention, starting from the theoretical proposal of stimulatedemission to the invention of the first laser device. We present the most relevant research papers and discuss the difficulties that had to be faced, including the disputes that occurred at the time of registering the laser patent. Besides, the theoretical principles that make possible the emission of the laser are studied, describing the population inversion in a system of three levels of energy from a mathematical model and the architecture that must have a laser linear cavity.

In this article, we study the operation and basic elements in a passively mode-locked fiber ring laser (PML-FRL), emphasizing the saturable absorber (SA) effect seen as a nonlinear filter in transmission, which is produced by the non-linear polarization rotation (NPR) and a linear polarizer. Besides, we employ a technique of 3D mapping measurements for characterizing ultra-short pulse dynamics.

A polymer optical Sagnac interferometer is proposed as a compact and low-cost refractive index sensor for the first time to our best knowledge. The Sagnac interferometer is fabricated by only one piece of fiber to facilitate its fabrication and to avoid losses due to misalignment or fusion. The coupler was developed based on chemical and twisting techniques of ∼ 5 c m of fiber. We modified the coupling ratio by varying the refractive index of media surrounding the coupler and consequently modified the transmission. For several values of mass percent concentration of sugar solutions surrounding the coupler, we found that transmittance decreases as the mass concentration increases. However, the decay is faster for the low concentration, while the decay is slower for higher concentrations. Two sets of experiments were carried out, at high ( ≥ 1 gm/100 ml) and low ( < 1 g m / 100 m l ) mass concentration of sugar solutions. The calibration of the sensor was done at 733 nm, where the response of the interferometer displays larger transmission variations for different solutions. The refractive index estimation was possible by correlation of the transmittance function (calculated by fitting the experimental data) with a linear refractive index model. The estimated resolution of the system is 0.057 weight percent of sugar solution, determined by the noise of the system.

In this paper, the performance of a switchable multi-wavelength Er–Yb-doped fibre ring laser incorporating a comb filter is described. The comb filter was developed by using the double-pass Mach–Zehnder interferometer with a Sagnac interferometer (DMZI–SI) arranged in series, a 10-m-long PANDA-type polarisation-maintaining optical fibre, and polarisation controllers (PCs). The laser output can be switched from 1536 to 1548 nm (C-band) via careful adjustment of the PCs. A side-mode separation ratio, greater than 28 dB, was obtained to facilitate stable single-, double-, quadruple-, and quintuple-wavelength emissions, with spectral power and wavelength fluctuations of 0.47–1.06 dB and 0.01–0.06 nm, respectively. The measurements were performed for 60 min at 25 °C. The proposed comb-filter configuration facilitates the double-clad fibre ring laser to realise switchable multi-wavelength emission. Experimental results reveal that the proposed laser demonstrates high stability and significantly improved performance compared to the existing DMZI–SI filter-based systems. This indicates their potential for use in applications involving optical sensing, communication systems, and microwave generation.

An all-fiber acousto-optic tunable bandpass filter based on a 1.185-mm long coreless core mode blocker is reported. Experimental results demonstrate a minimal insertion loss of 1.2 dB at the optical resonant wavelength of 1527.7 nm with 3-dB optical bandwidth of 0.83 nm. The optimization of the device takes into account the attenuation of the acoustic wave and leads to an asymmetric configuration in which the coupling section is shorter than the recoupling part. Under the effect of a standing flexural wave the device can be operated as a bandpass modulator. The device exhibits a maximum modulation depth of 28%, 4 dB of insertion loss and 0.97 nm of optical bandwidth at 4.774 MHz.

In this paper, we report an experimental study of the supercontinuum (SC) generated by molecules of solitons (MS) and noise-like pulses (NLP) in two different types of optical fibers: 500m of standard fiber (SMF-28, Corning) and 100m of High-Nonlinearity Fiber with a zero dispersion-slope (HNLF-ZS, Furukawa). We extracted information on the inner structure of SC by using a nonlinear optical loop mirror (NOLM) as an intensity filter. The NOLM suppresses pulses with low peak power, which is especially pronounced for wavelengths longer than ~1750 nm for both fibers, and particularly in the region between 1450 nm and 1640 nm for the High-Nonlinearity fiber. It is worth mentioning that depending on the application, the required properties of SC light can vary considerably. Therefore, it is the main importance to know the properties of the different SC sources.

A long-cavity passively mode-locked thulium-doped all-fiber laser is reported incorporating a tapered acousto-optic tunable bandpass filter (AOTBF). The operation of the AOTBF relies on the intermodal coupling between core and cladding modes when a flexural acoustic wave propagates along an 80-microm tapered fiber. The filter works in transmission and exhibits a 3-dB bandwidth of 9.02 nm with an insertion loss of 3.4 dB. The laser supports ultrashort pulse generation at a low repetition rate of 784.93 kHz. Optical pulses with 2.43 nm of optical bandwidth and 2.1 ps pulse duration were obtained in a broad tuning range from 1824.77 to 1905.16 nm.

We present the suitability of two optimized split-step methods for validating the femtosecond pulse propagation problem in the nonlinear fiber optics formalism that is governed by an extended nonlinear Schrödinger equation. In particular, the embedded split-step Fourier method (embedded-SSFM) and the embedded symmetrized split-step Fourier method (embedded-SymSSFM), which are optimized by the implementation of a step size control algorithm, are tested in terms of the femtosecond soliton fission phenomenology to analyze the numerical stability. As a result, it is possible to validate that these numerical methods introduce the appropriate resolution as function of the accuracy order that is needed at different stages of the soliton fission dynamics, which involves very large spectral shifts driven by the interaction between the nonlinear response and the high-order dispersion contribution of the optical fiber. Thus, the presented numerical methods can be used to validate accurately complex processes such as the development of supercontinuum spectra in the current formalism.

We present a simple and efficient experimental approach to synchronized dual-wavelength pulsed operation in an all-fiber laser. Four different dual-wavelength emissions of synchronized picosecond pulses are generated through simple adjustments of a wave retarder. Autocorrelation traces exhibit modulation profiles corresponding to dual-wavelength emissions with wavelength separations ranging over one order of magnitude, from 0.96 to 9 nm. In all cases, it is observed stable dual-wavelength operation and perfect synchronization between both pulsed components, without requiring of intra-cavity dispersion management. For the first time, to the best of our knowledge, synchronous tunable dual-wavelength pulse emission in a single-cavity Er/Yb double clad ring fiber laser is experimentally demonstrated.

In this paper, we experimentally demonstrate generation of diverse structures of robust optical pulses obtained with a ring cavity passively mode-locked fiber laser based on a double-clad erbium-ytterbium doped fiber, and operating at net-anomalous cavity dispersion. A half-wave and a quarter-wave retarder plates allow adjustable saturable absorbing action by the nonlinear polarization rotation technique. Pulsed laser operation in quasi- continuous wave, molecules of solitons, and single-wavelength noise-like pulses (NLPs) regimes is obtained by properly adjusting the wave retarders. In the soliton and NLPs operating regimes, the central laser wavelength lies in the 1540 nm region. The obtained NLPs exhibit narrow peak coherence of ∼231 fs.

This work explains in detail the role of the dispersion contribution provided by a single-mode optical fibre (SMF) in the pulse propagation problem modelled by the nonlinear Schrödinger equation. Firstly, the basics of chromatic dispersion in fibre are presented, including a modified Sellmeier equation for representing the dispersion contribution of the fibre core material (in an illustrative case of fused silica doped with germanium dioxide) that is modified by the waveguide dispersion contribution. At the same time, the contribution of the second-, third- and fourth-order dispersion parameters are illustrated for a SMF. Finally, a numerical analysis of the propagation problem is presented in order to understand the dispersion effects for a sech2 pulse profile, as well as the interplay of its contribution with the nonlinear Kerr effect, which is also involved in the pulse propagation. For a better understanding of the numerical methods applied to develop the propagation problem, we include a guide detailing the stages to follow in the numerical approach, considering how to select the initial parameters as well as the iterative steps of the numerical method.

Supercontinuum (SC) generation directly from noise-like pulse (NLP) emission is demonstrated in a mode-locked thulium-doped all-fiber laser with nonlinear polarization rotation. The laser supports NLP emission at a repetition rate of 812.79 kHz, producing optical pulses of 2 ns pulse duration and 400 nm of optical bandwidth, which expands from 1800 nm to 2200 nm at floor level and covers the entire thulium band. The SC source presents a high dynamic range, higher than 50 dB, a high degree of spectral flatness, without significant spectral variations or pump remnants, and an output average power of 20.25 mW. Moreover, our proposal avoids the inclusion of external components and devices, thus preserving the robustness and simplicity in a single all-fiber system.

We present an experimental analysis of the pulse profile variability within the mode-locked regions of an erbium-doped figure-eight fiber laser (EDFEFL). The tuning of the mode-locked regions was carried out by varying and recording the values of the angle of the polarization controllers in the ring section and in the nonlinear optical loop mirror (NOLM). Within the mode-locked regions, we obtained a large variability of the temporal profile, specifically amplitude and width of the noise-like pulses (NLPs). Subsequently, we recorded and studied the changes in the spectral domain. We identified the mode-locked regions where the temporal profile of the pulse remains constant (stationary state), and where it expels sub-packets (non-stationary state). Finally, a theoretical analysis of the power transmission through the polarizing in the ring section and in the NOLM switching characteristic as a function of wave plate angles is also performed, which allows an understanding of the existence of the multiple mode-locked regions and pulse profile adjustability. We analyze NLPs with a carrier wavelength of 1560 nm with duration of the order of nanoseconds and a repetition rate of 0.9 MHz.

We introduce a photochemical alternative procedure for uric-acid crystals degradation by controlled exposure of pulsed near infrared radiation from a ring fiber laser. The laser provides a wide spectrum from 1050 nm to 1120 nm, this spectrum exhibits a burst pulsed response with a pulse packet frequency rate of 210 kHz and an internal pulse frequency of 29 MHz. To demonstrate the technique, uric acid crystals were prepared synthetically and exposed under different radiation conditions, then by using an effective digital image processing the samples are before and after compared. Results confirm it is possible to exponentially reduce the number of crystals by an adequate combination of energy and number of pulses. The technique offers the possibility to reduce up to 50 % of the initial uric acid in a long period of safety wavelength radiation.

In this work we study statistically the internal structure of noiselike pulses generated by a passively mode-locked fiber laser. For this purpose, we use a technique that allows estimating the distribution of the amplitudes of the sub-pulses in the bunch. The technique takes advantage of the fast response of the optical Kerr effect in a fiber nonlinear optical loop mirror (NOLM). It requires the measurement of the energy transfer characteristic of the pulses through the NOLM, and the numerical resolution of a system of nonlinear algebraic equations. The results yield a strongly asymmetric distribution, with a high-amplitude tail that is compatible with the existence of extreme-intensity sub-pulses in the bunch. Following the recent discovery of pulse-energy rogue waves and spectral rogue waves in the noiselike pulse regime, we propose a new way to look for extreme events in this particular mode of operation of mode-locked fiber lasers, and confirm that rogue wave generation is a key ingredient in the complex dynamics of these unconventional pulses.

This paper presents the experimental results obtained in the development of novel optical fiber lasers architectures operating in continuous-wave and pulsed regimes. The first laser shown is an actively Q-switched operating at 1565 nm with a double-clad fiber doped with Er 3+ /Yb 3+ , pulse widths in the order of hundreds of ns, repetition rate from 200 kHz to 310 kHz, and average power up to 2.5 W. The second architecture is a passive mode-locked laser with higher harmonics generation. Output characteristics are; center wavelengths 1563 nm, noise-like pulses with durations around 80 ns, harmonics evolution up to the order 1270, and repetition rates to 259 MHz. The results presented seek to provide a comparison between two types of optical fiber lasers of great technological interest.

We propose and study analytically and numerically a nonlinear amplifying loop mirror scheme for multilevel amplitude regeneration, whose operation relies on the manipulation of light polarization. Polarization control increases the number of degrees of freedom of the setup, making it easier to meet the demanding requirements for regenerating complex modulation formats. By adjusting one of those additional parameters, namely, the ellipticity of input polarization, if all the other ones are properly set and fixed, the transfer characteristic is shaped for optimal two-level amplitude regeneration for two different state power ratios. The cascadability of the proposed scheme is demonstrated for the optical star-8 quadrature amplitude modulation format as an example.

We present the generation of 41 noise-like pulse (NLP) envelopes with complex shapes using a passively mode-locked, erbium-doped figure-eight fiber laser (EDFEFL). The tuning of each of the complex forms was carried out by varying the polarization state within the laser cavity, using a quarter-wave retarder (QWR2) inside a nonlinear optical loop mirror (NOLM), which is part of the EDFEFL. The position of the retarder plate was identified and recorded for each of the complex shapes. The temporal and spectral characterization was done using the position of the WQR2 wave plate as an independent variable. We present a single-shot analysis of the dynamics for the temporal amplitude, the full width at half-maximum (FWHM), and the root-mean-square (RMS) width for each of the 360 cycles measured for the 41 complex envelopes. We also perform an analysis for the case in which the pulse is completely divided into subpackets. We analyze the corresponding spectral profile for each of the complex forms generated. Finally, we evaluate the performance of the NOLM theoretical model with our experimental results. The wavelength of the NLPs is 1560 nm; the period of the cavity fiber laser is 1.1 ms; and the temporal FWHM is within the range of nanoseconds.

In this paper, we proposed a system to integrate optical and electronic instrumentation devices to predict a mode-locking fiber laser response, using a remote data acquisition with processing through an artificial neural network (ANN). The system is made up of an optical spectrum analyzer (OSA), oscilloscope (OSC), polarimeter (PAX), and the data acquisition automation through transmission control protocol/internet protocol (TCP/IP). A graphic user interface (GUI) was developed for automated data acquisition with the purpose to study the operational characteristics and stability at the passively mode-locked fiber laser (figure-eight laser, F8L) output. Moreover, the evolution of the polarization state and the behavior of the pulses are analyzed when polarization is changed by proper control plate adjustments. The data is processed using deep learning techniques, which provide the characteristics of the pulse at the output. Therefore, the parameter classification-identification is in accordance with the input polarization tilt used for the laser optimization.

In this paper, we carry out a numerical study on nonlinear and chaotic effects produced by the propagation of hyperbolic secant optical pulse in standard fibre. We use the fourth-order Runge–Kutta in the interaction picture (RK4IP) method to analyse the pulse interaction in the fibre medium, this method was employed due to its potential to reduce the numerical error while simultaneously allow increasing the step size. During the study, the input peak power was varied up hundreds of kW trough 1 km of standard single-mode fibre (SMF-28); as a consequence, it was possible to observe the generation of nonlinear and chaotic effects on the final spectrum. These numerical results show the spectral and temporal evolution of energy in a 3D rendering, here, it was possible to demonstrated break frequencies and fragmentation of packets of energy by changing the pump power. Finally, we show that this analysis can be used in subsequent studies employing complex dynamic pulses (noise-like pulses, NLPs). Keywords: Fibre optics, Nonlinear fibre optics, Optical solitons, Generalized nonlinear Schrödinger equation

In the present work, we investigated the polarization-imbalanced non-linear optical loop mirror (NOLM) for compressing the soliton spectrum as well as removing the sidebands. In the passive mode-locked soliton fiber laser, the spectra of solitons are usually accompanied with dispersive waves that can form spectral sidebands. The sidebands are the result of a constructive interference between the soliton and dispersive waves that take place at frequencies in which the phase difference is 2π. These sidebands may contain a significant part of the energy of the output spectrum, it is important first clean the spectrum by removing the sidebands and then compress the spectrum to have an optimal soliton profile. Our NOLM consists of a nearly symmetrical coupler with a 51/49 coupling ratio, and a fiber loop which consists of two 50-m pieces of SMF-28 fibers twisted in opposite directions. The maximum transmission of the NOLM at high power was 34%. At the NOLM output we reached a spectral compression of more than 50% for different values of input power. Although the sidebands around 1555 nm and 1570 nm were totally cleaned, nearly 5% of the sidebands were remaining around 1560 nm and 1567 nm. In order to get stronger spectral compression, the signal at the NOLM output was first amplified then sent into 1 km of SMF-28. For minimum input power the full width at half maximum (FWHM) bandwidth of the spectrum decreased from 5.5 nm to 0.67 nm. For higher input power the FWHM decreased from 4.23 nm to 0.59 nm.