Dispersive Fourier Transformation Research Articles

Real-time spectral transient dynamics measurement of mode-locked semiconductor disk lasers with DFT

The real-time measurement of transient dynamics of a semiconductor disk laser (SDL) was demonstrated using the dispersive Fourier transform (DFT) technology. Operating in a stable mode-locking state with a repetition rate of 425 MHz and a pulse width of 2.18 ps, the SDL exhibits significant changes in both spectral shape and pulse profile in the process of the establishment and extinction of mode locking. The pulse-resolved spectral evolution was captured, which includes relaxation oscillation, Q-switched oscillation and mode-locking states. Notably, we observed a progressive shift in the central wavelength—from 983.8 nm during initial mode-locking to 982.5 nm in the stabilization phase, and finally to 980 nm at extinction. The shift of mode locked wavelength can be attributed to thermal effect. To the best of our knowledge, this is the first time to observe the mode-locked dynamics in SDLs using a DFT technology.

Wavelength Stabilization of Entangled Biphotons Using Dynamic Temperature Compensation for Quantum Interference Applications

AbstractIn this paper, a dynamic temperature compensation method is presented to stabilize the wavelength of the entangled biphoton source, which is generated on spontaneous parametric down‐conversion from a magnesium oxide doped periodically poled lithium niobate waveguide. Utilizing the dispersive Fourier transformation technique, the photon wavelength variation is monitored in case of conventional static temperature control, revealing a long‐term wavelength drift up to 556.8 pm over a 14‐h measurement period. A Hong‐Ou‐Mandel (HOM) interferometer is constructed to assess the impact on quantum applications, showing a decrease in visibility from 95.5% to 69.4%. To address this issue, a digital proportional‐integral‐differential algorithm is implemented to dynamically compensate the working temperature variation of the waveguide, thereby instantly stabilizing the wavelength to a peak‐to‐peak fluctuation of +138.05 pm/‐127.61 pm with the standard deviation being 30.49 pm. The wavelength stability shows more than a hundredfold enhancement in terms of Allan deviation, reaching at an averaging time of 10000 s. With the dynamic control in operation, the HOM interference visibility turns to stable at 96.1% ± 0.6%. The method provides a simple and accessible solution for precisely controlling and stabilizing the wavelength of entangled biphotons, thus improving performance in various quantum information processing applications.

Dynamics of pulsating solitons with chaotic behaviors from a 1.7 μm ultrafast fiber laser

We demonstrate observation and dynamics of unique soliton pulsation regime in an ultrafast fiber laser at 1.7 μm. It is found that with either single-soliton pulse or multiple-soliton pulses in cavity the laser emission could exhibit periodic intensity and shot-to-shot spectra variations as measured based on the dispersive Fourier transformation (DFT) technique. Further, detailed studies turned out that the soliton pulsation can comprise numerous small pulses with random intensities, exhibiting chaotic characteristics. Besides, all the pulses within the multiple solitons possess identical pulsation period. In addition, despite of the fact that the temporal intervals between the multiple solitons are on the order of tens of nanoseconds among them, their pulsations demonstrate excellent synchronicity. The experimental observations are further revealed by numerical simulations. These results can provide insights into ways to optimize designs of laser sources and open up new potential for generation of pulsating solitons in ultrafast fiber lasers at different wavelengths.

Transient behaviors in a spectrum-tailored all-PM NALM mode-locked fiber laser

We demonstrate an all-polarization-maintaining (PM) dispersion-managed mode-locked ytterbium-doped fiber oscillator based on a nonlinear amplifying loop mirror (NALM). Experimentally, three mode-locking regimes with distinct tailored spectra are achieved with carefully designed cavity setup and adjusted pump power. Using the dispersive Fourier transformation (DFT) technique, the real-time transition dynamics among these regimes are observed as the pump power decreases. It is revealed that the intracavity gain does not decrease continuously during the relaxation period of the gain fiber. Instead, it decreases first and then increases, ultimately leading to the overdriving of NALM. This is attributed to the increase in the population inversion rate of gain fiber under the remaining pump. The dynamic evolution of intracavity gain and non-monotonic transmission properties of NALM collectively induce chaotic pulsation during the transformation. This work not only provides a new perspective for the design and development of novel spectrum-tailored laser sources, but also deepens the understanding of the transient dynamics of ultrafast fiber lasers.

Pulsating dynamics of noise-like pulses in a fiber laser with nonlinear optical loop mirror

We experimentally investigate the nature of pulsating noise-like pulses (NLPs) in a fiber laser based on the nonlinear optical loop mirror. By adjusting the intra-cavity polarization, three types of pulsating NLPs can be obtained in the cavity. By utilizing the dispersive Fourier transformation technique, the real-time evolution dynamics of NLP pulsation have been investigated in detail. Different from the conventional pulsating behavior, the NLPs undergo remarkable and periodical variations in their width with slight changes in pulse peak powers during pulsation process. We speculate that the wavelength-dependent gain saturation is involved in the pulsating NLP evolution. Quasi-periodic energy oscillations are associated with cyclic generation and subsequent walkoff of wavelength-shifted components, resulting in the different pulsating dynamics of NLP. Moreover, during pulsation process, the NLP splitting could happen with the increasing of energy. All these findings will help to complement our understanding of NLP pulsation in a fiber laser.

Compressive time-stretch spectroscopy with pulse-by-pulse intensity modulation.

The photonic time-stretch technique is a single-pulse broadband spectroscopy method enabled by dispersive Fourier transformation. This technique enables an extremely high spectrum acquisition rate, determined by the repetition rates of femtosecond mode-locked lasers, which are typically in the range of tens of MHz. However, achieving this high spectrum acquisition rate necessitates a compromise in either the spectral resolution or the spectral bandwidth to prevent overlaps between adjacent stretched pulses. In this study, we introduce a method that overcomes this limitation by incorporating compressive sensing with pulse-by-pulse amplitude modulation, enabling the decomposition of excessively stretched, overlapping pulses. Through numerical evaluations of optofluidic microparticle flow analysis and high-speed gas-phase molecular spectroscopy, we demonstrate the efficacy of our noise-resilient algorithm, showcasing a severalfold increase in the spectrum acquisition rate without compromising resolution and bandwidth.

Dispersive Fourier transform based dual-comb ranging

Laser-based light detection and ranging (LIDAR) offers a powerful tool to real-timely map spatial information with exceptional accuracy and owns various applications ranging from industrial manufacturing, and remote sensing, to airborne and in-vehicle missions. Over the past two decades, the rapid advancements of optical frequency combs have ushered in a new era for LIDAR, promoting measurement precision to quantum noise limited level. For comb LIDAR systems, to further improve the comprehensive performances and reconcile inherent conflicts between speed, accuracy, and ambiguity range, innovative demodulation strategies become crucial. Here we report a dispersive Fourier transform (DFT) based LIDAR method utilizing phase-locked Vernier dual soliton laser combs. We demonstrate that after in-line pulse stretching, the delay of the flying pulses can be identified via the DFT-based spectral interferometry instead of temporal interferometry or pulse reconstruction. This enables absolute distance measurements with precision starting from 262 nm in single shot, to 2.8 nm after averaging 1.5 ms, in a non-ambiguity range over 1.7 km. Furthermore, our DFT-based LIDAR method distinctly demonstrates an ability to completely eliminate dead zones. Such an integration of frequency-resolved ultrafast analysis and dual-comb ranging technology may pave a way for the design of future LIDAR systems.

Bio-ultrasonic synthesis of tin oxide quantum dots: effect of bio-carbon and their UV photocatalytic activity

An ecofriendly synthesis is realized to elaborate tin oxide quantum dots (SnO2 -QDs) using the plant aqueous extract of Aloe Barbadensis Miller (Aloe Vera) and SnCl4.5H2O at room temperature as a biological solvent and a precursor respectively. The effect of Aloe Vera extract concentration on the properties of SnO2-QDs has been studied. Morphological and structural properties of the as synthesized nanoparticles have been characterized using field effect-scanning electron microscopy (FE-SEM) and x-ray diffraction (XRD). The chemical composition of the nanoparticles was studied by Raman, energy dispersive x-ray (EDX) and Fourier transformation infra-red (FTIR) spectroscopy. The optical properties were investigated by UV–Vis spectrophotometer. The x-ray diffraction analysis showed that all samples have a tetragonal rutile structure, with an estimated crystal size closed to the exciton Bohr radius, indicating a strong confinement of the carriers in the material. The crystallite size of SnO2-QDs nanoparticles decreases as Aloe Vera plant extract concentration increases. The formation of SnO2-QDs and the presence of graphitic carbon in samples were confirmed by Raman spectroscopy, EDX analysis and Fourier transformation infra-red (FTIR) spectroscopy. The blue shift in absorption is the most likely due to the quantum confinement effect. An Ostwald-repining growth model based on the concept of surface energy has been proposed to explain the kinetic growth of SnO2 QDs. The photocatalytic activities of the as-prepared powders were confirmed by the fast and efficient degradation of methylene blue (MB).

Dynamics of h-shape narrow bandwidth dissipative soliton in Yb-doped fiber laser

We demonstrate a narrow bandwidth mode-locked ytterbium-doped fiber laser based on the carboxyl-functionalized graphene oxide (GO-COOH). In the combination of GO-COOH and intracavity filtering effects, the narrow bandwidth spectrum exhibits an h-shape at 1060.76 nm central wavelength with a 3-dB bandwidth of 0.47 nm. Furthermore, the 3-dB bandwidth can be compressed to 0.049 nm by adjusting the polarization controller. The formation of h-shape dissipative soliton has been investigated by applying the dispersive Fourier transformation and numerical simulation. The h-shape narrow bandwidth dissipative soliton we demonstrated provides a new insight for investigating the evolution dynamics of solitons with special shapes.

Quadratic phase mismatch in multisoliton interferograms based on time-stretched dispersive Fourier transformation

Quadratic phase mismatch in multisoliton interferograms based on time-stretched dispersive Fourier transformation

Real-time characterizations of soliton explosions and pulsations in a Tm-doped fiber laser

Over the years, 2 μm mode-locked fiber laser has been widely developed as an important light source for various significant applications. Worth to note that, with the help of real-time spectroscopy technique, i.e., time-stretched dispersive Fourier transformation (TS-DFT), various complex nonlinear soliton dynamics have been revealed, such as soliton molecules, soliton explosions and soliton pulsations, enhancing our understanding of the ultrafast physics. However, due to the lack of appropriate dispersive components at 2 μm band with low optical transmission loss for TS-DFT measurement, the investigation of ultrafast soliton dynamical phenomena in the 2 μm mode-locked fiber lasers is still limited. In this work, we demonstrate the direct real-time observation of soliton explosion and pulsation phenomena at 2 μm band mode-locked fiber laser, for the first time as far as we know, by using specially designed linearly chirped fiber Bragg gratings as dispersive component for TS-DFT measurement. For explosions, we observe slight explosion and drastic explosion, respectively. Particularly, the soliton pulsating explosions are also characterized in real time where the explosions occur in the process of soliton pulsation. In addition, dual-wavelength soliton rains are also observed by carefully adjusting the cavity parameters. Our work provides supplements to the current investigation of 2 μm band ultrafast science, and might enrich our understanding of soliton dynamics.

Generation and observation of noise-like pulses in an ultrafast fiber laser at 1.7 μm

In this manuscript, we demonstrate the generation and real-time dynamics of noise-like pulses (NLPs) in a 1.7 μm ultrafast thulium-doped fiber laser with all-fiber structure. NLPs with a central wavelength of ∼ 1742.5 nm and a 3-dB spectral width of ∼ 10.95 nm could be observed with pulse energy up to 4.19 nJ. The dynamic characteristics of NLPs were explored by using time-stretch dispersive Fourier transformation technology, which shows that the NLPs actually consist of many chaotic small pulse envelopes with random and changeable energies. These experimental results indicate that NLPs are the intrinsic features of fiber lasers and hold significant importance for further academic research, which can contribute to the development and application of 1.7 μm fiber laser in fields such as biomedicine and short-range remote sensing.

Transient breathing dynamics during extinction of dissipative solitons in mode-locked fiber lasers

The utilization of the dispersive Fourier transformation approach has enabled comprehensive observation of the birth process of dissipative solitons in fiber lasers. However, there is still a dearth of deep understanding regarding the extinction process of dissipative solitons. In this study, we have utilized a combination of experimental and numerical techniques to thoroughly examine the breathing dynamics of dissipative solitons during the extinction process in an Er-doped mode-locked fiber laser. The results demonstrate that the transient breathing dynamics have a substantial impact on the extinction stage of both steady-state and breathing-state dissipative solitons. The duration of transient breathing exhibits a high degree of sensitivity to variations in pump power. Numerical simulations are utilized to produce analogous breathing dynamics within the framework of a model that integrates equations characterizing the population inversion in a mode-locked laser. These results corroborate the role of Q-switching instability in the onset of breathing oscillations. Furthermore, these findings offer new possibilities for the advancement of various operational frameworks for ultrafast lasers.Graphical abstract

Generation and Dynamics of Multiple Pulses in an Ultrafast Fiber Laser with a Single-Mode Fiber–Graded-Index Multimode Fiber–Single-Mode Fiber-Based Saturable Absorber

In this study, we have investigated the evolution process and dynamic characteristics of a multi-pulse regime in an erbium-doped fiber ring laser based on a single-mode fiber–graded-index multimode fiber–single-mode fiber (SMF-GIMF-SMF) structure as an optical modulator. By utilizing the excellent nonlinear optical absorption of the SMF-GIMF-SMF (SMS) device with a modulation depth of ~8.68%, stable single-pulse mode locking at the frequency of 9.84 MHz can be readily observed at low pump power. In addition, the single-pulse operation can evolve into a multiple-pulse regime on account of the peak-power-clamping effect via suitably raising the pump power and carefully regulating the polarization state. Further, the single-shot temporal evolution of multiple pulses is monitored, indicating that this state shows unique and interesting temporal characteristics with variable pulse separations and inconsistent pulse intensities, which, as far as we know, is the first such observation in ultrafast fiber lasers. Additionally, this study, based on the time-stretch dispersive Fourier transformation method, suggests that these multiple pulses consist of chaotic wave envelopes with erratic intensities and changeable pulse energy. We believe that these findings have profound implications for revealing fascinating nonlinear pulse dynamics in ultrafast fiber optics.

Build-up dynamics of a self-mode-locked Thulium-doped fiber laser explored by dispersive Fourier transformation

Build-up dynamics of a self-mode-locked Thulium-doped fiber laser explored by dispersive Fourier transformation

Intrinsic Discrepancy of Multi-Soliton Interferogram in Dispersive Fourier Transform Measurements Due to Impulsive Response of Fast Electronics

Intrinsic Discrepancy of Multi-Soliton Interferogram in Dispersive Fourier Transform Measurements Due to Impulsive Response of Fast Electronics

Spectrally resolved ultrafast transient dynamics of a femtosecond fiber-feedback optical parametric oscillator.

We report on spectrotemporal transient dynamics in a femtosecond fiber-feedback optical parametric oscillator (FFOPO) system. Burst modulation of the pump beam in combination with dispersive Fourier transformation sampling allows to record single-pulse signal spectra at 41 MHz sampling rate. Therefore, each individual pulse of the signal transients can be spectrally resolved. We characterize the signal output behavior for anomalous as well as for normal intra-cavity dispersion. Amongst steady state output we observed period-doubling cycles and other attractors, which occured at higher intra-cavity nonlinearity levels. The experimental findings are supported by numerical simulations, in order to identify the linear and nonlinear effects, which govern the wavelength tuning behavior of this FFOPO system. We find that steady state operation is preferred and that the wavelength tuning stability of the FFOPO dramatically increases when using a normal dispersion feedback fiber.

"Invisible" pulsation and period-doubling bifurcation of harmonic mode locking in a bidirectional fiber laser.

The harmonic mode-locking (HML) "invisible" pulsation (IP) is reported, here, in a bidirectional passively mode-locked fiber laser (BPMLFL). With the help of dispersive Fourier transform (DFT) technology, it is found that due to the alike nonlinear effects experienced by two pulse trains in HML, their evolution is consistent during the IP. Further, as the increase of pump power, period-doubling bifurcations (PDBs) can be observed based on the IP phenomenon in the HML regime, the PDB path experienced by the HML from steady to chaotic is statistically obtained. Finally, the IP and PDB in the bidirectional laser are reproduced and studied through numerical simulations. The effect of IP on the coherence of solitons is further analyzed. We believe our research results will provide new insights into the study of soliton dynamics in fiber lasers.

Single-shot dynamics of dual-comb generation in a polarization-multiplexing fiber laser

Dual optical frequency combs have been a recurrent case of study over the last decade due to their wide use in a variety of metrology applications. Utilizing a single cavity laser to generate a dual comb reduces system complexity and facilitates suppression of common noise. However, a dual-comb regime in single cavity lasers tends to be more unstable and difficult to achieve. Therefore, having a better understanding about the way they are generated could improve and automate their generation and control. In this paper, we investigate the build-up dynamics and collision of dual comb in a polarization-multiplexing ring-cavity fiber laser using DFT (Dispersive Fourier Transform) method. We observe a bunch of meta-stable short-lived mode-locking states before the laser entered the dual-comb mode-locking state. The energy level of this short-lived initial pulses determines its evolution. If it decreases too much, the pulse will eventually collapse while if it stays above certain level, it will be successfully generated. The results presented in this paper increase the understanding of dual-comb generation inside a single cavity laser and may contribute in future attempts to increase the stabilization of this regime.

Revealing the pulse dynamics in a Mamyshev oscillator: from seed signal to oscillator pulse.

The Mamyshev oscillator (MO) is a promising platform to generate high-peak-power pulse with environmentally stable operation. However, rare efforts have been dedicated to unveil the dynamics from seed signal to oscillator pulse, particularly for the multi-pulse operation. Herein, we investigate the buildup dynamics of the oscillator pulse from the seed signal in a fiber MO. It is revealed that the gain competition among the successively injected seed pulses leads to higher pump power that is required to ignite the MO, hence resulting in the higher optical gain that supports buildup of multiple oscillator pulses. The multiple oscillator pulses are identified to be evolved from the multiple seed pulses. Moreover, the dispersive Fourier transform (DFT) technique is used to reveals the real-time spectral dynamics during the starting process. As a proof-of-concept demonstration, a highly intensity-modulated pulse bunch was employed as the seed signal to reduce the gain competition effect and avoid the multi-pulse starting operation. The experimental results are verified by numerical simulations. These findings would give new insights into the pulse dynamics in MO, which will be meaningful to the communities interested in ultrafast laser technologies and nonlinear optics.