Nonlinear Mirror Research Articles

Dissipative Soliton Resonances in a Mode-Locked Holmium-Doped Fiber Laser

We demonstrate what is believed to be the first dissipative-soliton-resonance mode-locking of a holmium-doped fiber (HDF) laser. A telecommunication band fiber source was used to pump a piece of thulium-doped fiber, resulting in 1.9-μm band lasing, which was subsequently used to intra-cavity-pump another piece of HDF, resulting in lasing beyond 2 μm. A nonlinear optical-loop mirror incorporating two pieces of high nonlinear fiber (HNLF) was employed as an artificial saturable absorber, and, meanwhile, to enhance the cavity nonlinearity. By varying the pump power from ~2.1 to ~4 W, the produced pulse could be tuned from ~4.85 to ~20.8 ns in duration while maintaining a nearly constant peak power, i.e., peak power clamping (PPC) effect. By further incorporating different lengths of HNLF, it was found that the longer the HNLF, the larger the pulse duration and the lower the pulse peak power, due to the expected stronger PPC effect. Meanwhile, spectral blue-shifting effect has occurred due to the increased fiber attenuation loss. Based on our preliminary experiments using the HDF laser as a test bed, a higher pulse energy at a longer wavelength could be expected with further enhanced pumping and gain-tailoring designs.

Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation

AbstractThe Magnetospheric Multiscale mission has observed electron whistler waves at the center and at the edges of magnetic holes in the dayside magnetosheath. The magnetic holes are nonlinear mirror structures since their magnitude is anticorrelated with particle density. In this article, we examine the growth mechanisms of these whistler waves and their interaction with the host magnetic hole. In the observations, as magnetic holes develop and get deeper, an electron population gets trapped and develops a temperature anisotropy favorable for whistler waves to be generated. In addition, the decrease in magnetic field magnitude and the increase in density reduce the electron resonance energy, which promotes the electron cyclotron resonance. To investigate this process, we used expanding box particle‐in‐cell simulations to produce the mirror instability, which then evolve into magnetic holes. The simulation shows that whistler waves can be generated at the center and edges of magnetic holes, which reproduces the primary features of the MMS observations. The simulation shows that the electron temperature anisotropy develops in the center of the magnetic hole once the mirror instability reaches its nonlinear stage of evolution. The plasma is then unstable to whistler waves at the minimum of the magnetic field structures. In the saturation regime of mirror instability, when magnetic holes are developed, the electron temperature anisotropy appears at the edges of the holes and electron distributions become more isotropic at the magnetic field minimum. At the edges, the expansion of magnetic holes decelerates the electrons, which leads to temperature anisotropies.

All-fibre optical gating system for measuring a complex-shaped periodic broadband signal with picosecond resolution in a nanosecond time window

We have developed an optical gating system for continuously monitoring a complex-shaped periodic optical signal with picosecond resolution in a nanosecond time window using an all-fibre optical gate in the form of a nonlinear loop mirror and a passively mode-locked femtosecond laser. The distinctive features of the system are the possibility of characterizing signals with a very large spectral bandwidth, the possibility of using a gating pulse source with a wavelength falling in the band of the signal under study and its all-fibre design with the use of standard fibres and telecom components.

Ultra-high current efficiency single-stage class-AB OTA with completely symmetric slew rate

An ultra-high current efficiency single-stage class-AB OTA with completely symmetric slew rate is presented. Based on adaptive biasing and nonlinear current mirror techniques employed in a proposed symmetric current recycling structure, the proposed OTA not only achieves the maximum output current proportional to Vin8, but also has the symmetric positive and negative slew rates. Also, the proposed self-biasing output stage makes the slew rate unconstrained. Simulation results demonstrate that the slew rate of the proposed OTA is enhanced by 1500% over that of the conventional folded cascode counterpart with a little increased power, which is suitable for large capacitive load applications.

Diverse mode of operation of an all-normal-dispersion mode-locked fiber laser employing two nonlinear loop mirrors.

In this paper, we propose an all-normal-dispersion ytterbium-fiber laser with a novel ring cavity architecture having two nonlinear amplifying loop mirrors (NALM) as saturable absorbers, capable of delivering distinctly different pulses with adjustable features. By optimizing the loop lengths of the individual NALMs, the cavity can be operated to deliver Q-switched mode-locked (Q-ML) pulse bunches with adjustable repetition rates, mode-locked pulses in dissipative soliton resonance (DSR) regime or noise-like pulse (NLP) regime with tunable pulse width. The DSR pulses exhibit characteristic narrowband spectrum, while the NLPs exhibit large broadband spectrum. The operation regime of the laser can be controlled by adjusting the amplifier pump powers and the polarization controllers. To the best of the authors' knowledge, this is the first demonstration of a single mode-locked cavity where narrowband DSR pulses and broadband NLPs alongside Q-ML pulse bunches can be selectively generated by employing two NALMs.

全保偏非线性偏振环形镜锁模掺铒光纤激光器

The mode-locking mechanism of an all-polarization-maintaining fiber laser based on a nonlinear polarization loop mirror was demonstrated. Instead of a fiber coupler in the traditional nonlinear amplifying loop mirror based mode-locked fiber laser, a polarization beam splitter (PBS) was implied in the nonlinear polarization loop mirror. The combination of the PBS, non-reciprocal components and a piece of gain fiber acted as the core elements in nonlinear polarization loop mirror to achieve stable mode-locking in an all-polarization-maintaining fiber laser. A passively mode-locked erbium-doped fiber laser based on this mode-locking mechanism was also presented. The laser directly emited an optical pulse train of 141 fs duration (75 MHz) with 30 mW total output power. The laser had bidirectional outputs, and the power from two outputs was adjustable by adjusting the waveplate in the cavity. Moreover, the environment stability of the free-running laser was characterized, yielding an average output power fluctuation of 0.05% in 1 h and the relative repetition rate stability of 2.010-8 in 1 s. The configuration enables self-start mode-locking, generating optical pulse trains with high environmental stability, high repetition rate and short pulse duration and fully meets the requirements of ultra-short pulse laser sources in femtosecond based ranging, laser machining, spectroscopy and other applications in spaceflight technologies.

Experimental investigation of polarization-imbalanced nonlinear loop mirror with double-sense twisted fiber as a filter to clean up solitons

In the present work, we report the implementation of a novel polarization-imbalanced NOLM for soliton cleaning. The NOLM consists of a nearly symmetrical coupler with a 51/49 coupling ratio, and the fiber loop which, in contrast to previously reported results, consists of two 100 m pieces of fibers twisted in opposite directions. The use of the symmetrical coupler and two fiber spans twisted in opposite direction allowed a transmission of low-power radiation of 0.5 × 10−3 in the wavelength range of 1520–1560 nm. The maximum transmission at high power was 45% providing 30 dB contrast between high and low power transmission. We show more than 20 dB suppression of Kelley’s side bands of 0.6 ps pulses from the output of the fiber mode-locked laser. The experimental results are supported by the numerical simulation and show that cleanup of solitons is possible using a NOLM as intensity filter without dependence of wavelength.

Investigation of hybrid modulator based on nonlinear optical loop mirror and single-walled carbone nanotubes for mode-locking in Yb-doped ultrafast fiber laser

Algorithm for the mathematical modelling of a fiber oscillator with a hybrid modulator based on a nonlinear fiber mirror and single-walled carbon nanotubes is suggested. It is based on a numerical solution of the nonlinear Schrödinger equation. Using numerical simulation, optimum NOLM coupler ratio, laser spot diameter on the sample preventing sample degradation and high modulator effect are determined.It is shown that hybrid modulator accelerates the self-starting process and decreases the output pulse duration up to 10%.

Optical properties of mesoporous photonic crystals, filled with dielectrics, ferroelectrics and piezoelectrics

At present, it is very important to create new types of mirrors, nonlinear light frequency transformers and optical filters with controlled optical properties. In this connection, it is of great interest to study photonic crystals. Their dielectric permittivity varies periodically in space with a period permitting Bragg diffraction of light. In this paper, we have investigated the optical properties of mesoporous three-dimensional (3D) opal-type and one-dimensional (1D) anodic alumina photonic crystals, filled with different dielectrics, ferroelectrics and piezoelectrics. We have compared the optical properties of initial mesoporous photonic crystals and filled with different substances. The possibility of mesoporous photonic crystals using selective narrow-band light filters in Raman scattering experiments and nonlinear mirrors has been analyzed. The electromagnetic field enhancing in the case of exciting light frequency close to the stop band edges has been established. The optical harmonics and subharmonics generation in mesoporous crystals, filled with ferroelectrics and piezoelectrics was proposed.

Mode‐locked femtosecond 910 nm Nd:fibre laser with phase biased non‐linear loop mirror

The authors demonstrate a mode-locked Nd:fibre laser working at 910 nm incorporating a phase biased non-linear loop mirror. The broadest spectral width of the pulse is 11.9 nm and the output power is 20 mW with 450 mW pump power. The dechirped pulse width is 206 fs. To the best of authors' knowledge, this is the first demonstration of a 900 nm femtosecond neodymium fibre laser based on a non-linear loop mirror.

An Ultra-Low-Voltage Bulk-Driven Analog Voltage Buffer with Rail-to-Rail Input/Output Range

This paper presents a low-voltage high driving capability rail-to-rail Class-AB CMOS bulk-driven (BD) operational transconductance amplifier (OTA) for analog voltage buffer with minimal current consumption. The proposed OTA design consists of adaptively biased Class-AB differential input stage to improve the effective transconductance and adaptive load relying on nonlinear current mirrors, configured in partial positive feedback mode to enhance the overall gain. In addition, because of adaptive bias and load configuration, the load-driving capability of OTA increases for a large change in differential input. The circuit is designed using UMC 65-nm CMOS process node and is operated at supply voltage of 0.5 V with a standby current consumption of 4.25 $$\upmu $$μA. Simulation results show that the buffer based on the proposed BD-OTA achieves an average slew rate of 93.2 mV/$$\upmu $$μs for a capacitive load of 100 pF, which is nearly 29 times that of conventional OTA with 13$$\%$$% increment in quiescent power dissipation.

Modelocking of a thin-disk laser with the frequency-doubling nonlinear-mirror technique

We demonstrate a frequency-doubling nonlinear-mirror (NLM) modelocked thin-disk laser. This modelocking technique, composed of an intracavity second harmonic crystal in combination with a dichroic output coupler, offers robust operation decoupled from cavity stability (as in semiconductor saturable absorber mirror (SESAM) modelocking) combined with an ultrafast saturable loss and high modulation depth (as in Kerr-lens modelocking (KLM)). With our NLM diode-pumped Yb:YAG thin-disk laser we achieve 21 W of average power at 323-fs pulse duration, which is an order of magnitude shorter than the previously obtained duration with the same technique in bulk lasers. Using these first results, we present a theoretical model for the NLM technique, which accurately predicts its loss modulation properties and the shortest achievable pulse duration without relying on any fitting parameters. Based on this simulation, we expect that the NLM technique will enable thin-disk lasers with average power of more than 100 W, with potentially sub-200 fs pulses. This could potentially solve the pulse duration limitations with SESAM modelocked Yb:YAG thin-disk lasers without imposing strong cavity stability constraints such as in KLM.

Plasma sheath: An equivalent nonlinear mirror between electron density and transmitted electromagnetic signal

An experiment on the propagation of electromagnetic (EM) signals in continuous time-varying plasma is designed to establish the nonlinear mirror between electron density and transmission coefficient. The nonlinearity is confirmed from the theoretical and experimental results. The amplitude and phase can be considered nonlinear functions of electron density when the complex interaction between plasma and EM waves is ignored. Results show that amplitude and phase distributions are asymmetrical when electron density follows symmetric distribution. The skewness of amplitude is positive, whereas the skewness of phase is negative. The nonlinear degree is closely related to the ratio of plasma frequency to the incident wave frequency and the range of electron density. The conclusions are crucial to the modeling of plasma sheath channels and understanding the blackout problem.

Atomically thin semiconductors as nonlinear mirrors

We show that a transition-metal dichalcogenide monolayer with a radiatively broadened exciton resonance would exhibit perfect extinction of the transmitted field. This result holds for $s$- or $p$-polarized weak resonant light fields at any incidence angle, due to the conservation of the in-plane momentum of excitons and photons in a flat defect-free two-dimensional crystal. In contrast to extinction experiments with single quantum emitters, exciton-exciton interactions lead to an enhancement of reflection with increasing power for incident fields that are blue detuned with respect to the exciton resonance. By taking into account quantum fluctuations, we show that the extinction of such a nonlinear mirror is limited; for light intensities leading to maximal reflection, the transmitted field is in a multimode squeezed state.

Wavevector-Selective Nonlinear Plasmonic Metasurfaces.

Electromagnetic metasurfaces with strong nonlinear responses and angular selectivity could offer many new avenues for designing ultrathin optics components. We investigated the optical second harmonic generation from plasmonic metasurfaces composed of aligned gold nanopillars with a pronounced out-of-plane tilt using a flexible nonlinear Fourier microscope. The experimental and computational results demonstrate that these samples function as wavevector-selective nonlinear metasurfaces, that is, the coherent second harmonic signal does not only depend on the polarization and wavelength of the excitation beam, but also of its direction of incidence, in spite of the subwavelength thickness of the active layer. Specifically, we observe that the nonlinear response can vary by almost two orders-of-magnitude when the incidence angle is changed from positive to negative values compared to the surface normal. Further, it is demonstrated that these metasurfaces act as a directional nonlinear mirrors, paving the way for new design of directional meta-mirrors in the nonlinear regime.

Nonlinear mirror mode-locked Pr:YAlO3 laser

Mode-locking of a praseodymium based solid-state laser by a nonlinear mirror is reported, for the first time to the best of our knowledge. Pr:YAlO3 crystal having 0.6 at.% of Pr3+ ions was used as an active medium. For mode-locking, a nonlinear BBO crystal together with a properly designed dichroic mirror were employed to form an output coupler with intensity dependent reflection. A continuous-wave mode-locked laser operation with a mean output power of 100 mW was achieved under 3.5 W InGaN laser diode pumping. The laser emitted 250 ps pulses with a repetition rate of 105 MHz at a center oscillation wavelength of 747 nm.

L‐band dissipative soliton resonance fiber laser based on nonlinear amplification loop mirror

ABSTRACTA kind of L‐band dissipative soliton resonance ring erbium‐doped fiber laser based on nonlinear amplifying loop mirror is proposed. In the experiment, a 10 m long erbium‐doped fiber is pumped by a 980 nm semiconductor laser. The stable dissipative soliton resonance square wave pulses are observed at room temperature by adjusting the fiber polarization controller. With the increasing of the pump power, pulse width is gradually broadened. Pumping power increased from 100 to 700 mW, corresponding pulse width obtained from 700 ps to 3.7 ns. The single pulse energy is increased from 5.2 to 27.4 nJ, which shows the fiber laser has a good stability. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1194–1197, 2017

Picosecond Optical Pulse Generation by Nonlinear Mirror Mode-Locking: A Review

Background/Objectives: This article provides comprehensive review on nonlinear mirror mode-locked laser which is compact, efficient, simplest and stable source of picosecond optical pulse and is of immense research interest. Methods/ Analysis: Starting with the basics of nonlinear mirror mode-locking technique, a chronological development of the subject is presented. Issues with the efficiency and stability of the nonlinear mode-locking are addressed in both theoretical and experimental perspective. Different schemes of nonlinear mirror mode-locking, reported till date, are illustrated and compared in reference to the obtained pulse durations, power scaling, self starting and self sustained efficient modelocking. Findings: Nonlinear mirror, comprising a second harmonic generating crystal and a dichroic output coupler, can mode-lock a laser due to its behaviour analogous to fast saturable absorber. Efficiency of the laser is increased with the diode pumping; however nonlinear mirror is observed prone to passive Q-switching instability. Simultaneously Q-switched and mode-locked operation gives a simple way of increasing the peak power but is of no use because of rapid fluctuations of pulse amplitude and repetition rate. Incorporation of an accousto-optic Q-switch in the laser cavity helps run the laser in actively Q-switched and passively mode-locked regime which provides enormous stability of the Q-switched and modelocked pulse envelops and the enhanced peak power becomes useful. Pure contentious wave mode-locking is obtained by incorporation of additional intensity dependent loss mechanism by way of introducing third harmonic generation in the laser cavity and it gives an inverse saturable nonlinear loss modulation. Inverse saturable nonlinear mirror produces efficient, self sustained and stable contentious wave mode-locked picosecond optical pulse train. Application /Improvement: Nonlinear mirror mode-locked lasers have wide application in micromachining, optical frequency conversion, pumping optical parametric oscillators etc. Propositions are made for getting improved nonlinear mirror mode-locking to get bandwidth limited pulse width.

Picosecond bismuth fibre laser mode-locked by a nonlinear loop mirror

The influence of the concentration of bismuth active centres (BACs) in phosphosilicate fibres on their optical parameters, including gain coefficient and non-saturable losses, has been studied. A range of BAC concentrations optimal for designing ultrashort-pulse (USP) lasers was chosen based on the obtained results. The optimised fibre was used to fabricate an all-fibre USP laser mode-locked by a nonlinear loop mirror, which emits pulses with an energy of and a repetition rate of . A bismuth fibre amplifier made it possible to increase the pulse energy to . After compression in a diffraction grating compressor, the pulse duration decreased to .

Stabilisation of a radiation wavelength of a nanosecond fibre laser by a passive nonlinear loop mirror

A method for stabilising the radiation wavelength of a mode-locked fibre nanosecond laser is proposed and realised. Generation of nanosecond laser pulses with a spectral bandwidth of , which corresponds to a transform-limited pulse, is demonstrated.