Ultrafast Temporal SU(1,1) Interferometer.

Interferometers are highly sensitive to phase differences and are utilized in numerous schemes. Of special interest is the quantum SU(1,1) interferometer which is able to improve the sensitivity of classical interferometers. We theoretically develop and experimentally demonstrate a temporal SU(1,1) interferometer based on two time lenses in a 4f configuration. This temporal SU(1,1) interferometer has a high temporal resolution, imposes interference on both time and spectral domains, and is sensitive to the phase derivative which is important for detecting ultrafast phase changes. Therefore, this interferometer can be utilized for temporal mode encoding, imaging, and studying the ultrafast temporal structure of quantum light.

Single-shot analysis of amplified correlated light.

Correlated beams are important in classical and quantum communication as well as other technologies. However, classical amplifiers, which are essential for long transmission of correlated beams, degrade the correlation due to noise and due to the amplifier spectral response. We measure, with a novel high resolution single-shot measurement system, the impact of amplifiers on correlated beams. We develop a new method for analyzing the correlation between the signal and idler beams by choosing peaks in the pulses according to their power levels. We demonstrate how to tailor the correlation after the amplifier to obtain either higher or lower correlation. Our research may influence the future use of amplifiers in non-classical communication systems as well as the transmission of quantum information over long distances.

Polarization dynamics of ultrafast solitons.

We study the polarization dynamics of ultrafast solitons in mode-locked fiber lasers. We find that when a stable soliton is generated, its state of polarization shifts toward a stable state, and when the soliton is generated with excess power levels it experiences relaxation oscillations in its intensity and timing. On the other hand, when a soliton is generated in an unstable state of polarization, it either decays in intensity until it disappears, or its temporal width decreases until it explodes into several solitons, and then it disappears. We also found that when two solitons are simultaneously generated close to each other, they attract each other until they collide and merge into a single soliton. Although these two solitons are generated with different states-of-polarization, they shift their state of polarization closer to each other until the polarization coincides when they collide. We support our findings by numerical calculations of a non-Lagrangian approach by simulating the Ginzburg-Landau equation governing the dynamics of solitons in a laser cavity. Our model also predicts the relaxation oscillations of stable solitons and the two types of unstable solitons observed in the experimental measurements.

Cross-phase modulation aberrations in time lenses.

We study the aberrations of four-wave mixing based time lenses resulting from the cross-phase modulations of the pump wave. These temporal aberrations have no spatial equivalent and are important when imaging weak signals with strong pump waves. We show that as the pump power increases, the cross-phase modulations of the pump are responsible for shifting, defocusing, and imposing temporal coma aberrations on the image. We present experimental results of these aberrations with high agreement to analytical and numerical calculations.

Phase retrieval by an array of overlapping time-lenses.

Temporal imaging of both the intensity and the phase is important for investigating ultra-short events such as rogue waves or mode-locked laser dynamics in a record high resolution. We developed a temporal phase retrieval scheme based on several overlapping time-lenses, where all the time-lenses use the same fibers and detectors leading to high stability and low noise levels. We show that our phase retrieval technique converges faster than techniques that resort to a single time-lens, together with the Fourier transform of the signal.

Full-Stokes temporal imaging.

We developed a full-Stokes temporal imaging system which measures the Stokes vector of ultrafast signals as a function of time. The system is based on a time-lens array where each time-lens in the array projects the signal on a different state of polarization.

Bidirectional Soliton Rain Dynamics Induced by Casimir-Like Interactions in a Graphene Mode-Locked Fiber Laser.

We study experimentally and theoretically the interactions among ultrashort optical pulses in the soliton rain multiple-pulse dynamics of a fiber laser. The laser is mode locked by a graphene saturable absorber fabricated using the mechanical transfer technique. Dissipative optical solitons aggregate into pulse bunches that exhibit complex behavior, which includes acceleration and bidirectional motion in the moving reference frame. The drift speed and direction depend on the bunch size and relative location in the cavity, punctuated by abrupt changes under bunch collisions. We model the main effects using the recently proposed noise-mediated pulse interaction mechanism, and obtain a good agreement with experiments. This highlights the major role of long-range Casimir-like interactions over dynamical pattern formations within ultrafast lasers.

Demonstration of temporal cloaking.

Recent research has uncovered a remarkable ability to manipulate and control electromagnetic fields to produce effects such as perfect imaging and spatial cloaking. To achieve spatial cloaking, the index of refraction is manipulated to flow light from a probe around an object in such a way that a 'hole' in space is created, and the object remains hidden. Alternatively, it may be desirable to cloak the occurrence of an event over a finite time period, and the idea of temporal cloaking has been proposed in which the dispersion of the material is manipulated in time, producing a 'time hole' in the probe beam to hide the occurrence of the event from the observer. This approach is based on accelerating the front part of a probe light beam and slowing down its rear part to create a well controlled temporal gap--inside which an event occurs--such that the probe beam is not modified in any way by the event. The probe beam is then restored to its original form by the reverse manipulation of the dispersion. Here we present an experimental demonstration of temporal cloaking in an optical fibre-based system by applying concepts from the space-time duality between diffraction and dispersive broadening. We characterize the performance of our temporal cloak by detecting the spectral modification of a probe beam due to an optical interaction and show that the amplitude of the event (at the picosecond timescale) is reduced by more than an order of magnitude when the cloak is turned on. These results are a significant step towards the development of full spatio-temporal cloaking.

Complex Fiber Micro-Knots.

Fiber micro-knots are a promising and a cheap solution for advanced fiber-based sensors. We investigated complex fiber micro-knots in theory and experiment. We compared the measured spectral response and present an analytical study of simple micro-knots with double twists, twin micro-knots, figure-eight micro-knots, and tangled micro-knots. This research brings the simple fabrication process and robustness of fiber micro-knots into the world of complex resonators which may lead to novel optical devices based on fiber micro-knots.

Fused Microknot Optical Resonators in Folded Photonic Tapers for in-Liquid Durable Sensing.

Optical microknot fibers (OMFs) serve as localized devices, where photonic resonances (PRs) enable self-interfering elements sensitive to their environment. However, typical fragility and drifting of the knot severely limit the performance and durability of microknots as sensors in aqueous settings. Herein we present the fabrication, electrical fusing, preparation, and persistent detection of volatile liquids in multiple wetting⁻dewetting cycles of volatile compounds and quantify the persistent phase shifts with a simple model relating to the ambient liquid, enabling durable in-liquid sensing employing OMF PRs.

Polarization dependence of asymmetric off-resonance long period fiber gratings: erratum.

Correction of Fig. 3 which was taken with different conditions than stated in the text. The figure presented here is the correct version with improved resolution.

Long period fiber gratings with off-resonance spectral response based on mechanical oscillations.

We present long period fiber gratings with off-resonance spectral response. Our long period fiber gratings are created by the periodic structure of large perturbations in the fiber diameter. These perturbations result in unique spectral response, even in off-resonance frequencies. Writing these long period fiber gratings is based on utilizing the mechanical vibrations of tapered fibers during the tapering process. This writing method is simple and robust; it has high efficiency, high reproducibility, and low polarization dependency; and it enables real-time tunability of the periodicity, efficiency, and length of the grating. We also demonstrate a complex grating by writing multiple gratings one on top of the other. Finally, we utilize the formation of the gratings in different fiber diameters to investigate the Young's modulus of tapered fibers.

Temporal superresolution based on a localization microscopy algorithm.

We investigate the resolution limits of time lenses based on a four-wave mixing process and present a superresolution technique in the time domain based on a localization microscopy algorithm. Our temporal superresolution technique retrieves features shorter by a factor of 2 than the resolution limit of the system. We present both measured and calculated results of the superresolution scheme and present calculated superresolution of input signals with higher complexity.

Dynamical range and stability enhancement in electrically fused microknot optical resonators.

Microknot resonators (MKRs), locally fused using a two-probe technique, have exhibited significantly improved optical performance and mechanical stability. They have been operated with low losses both in situ and as transferred devices. We found consistently more than threefold dynamical range enhancement, which remained stable in time, in electrically fused MKRs. These devices can be harbored in next-generation optical sensors, actuators, and optomechanical applications incorporating MKR-assisted microstructures taking advantage of this simple and robust fusing technique.

High-Order Modes Micro-Knot Excited by a Long-Period Fiber Grating.

We suggest a fiber micro-knot fabricated on a long-period fiber grating. The long-period fiber grating excites high-order modes into the micro-knot and transfers the output back to the Gaussian mode. We show theoretically and experimentally that these micro-knots have an improved Q-factor, higher stability, and have an increased evanescence wave coupling to the environment than single mode fiber micro-knots. These high-order fiber micro-knots can be beneficial for various fiber detectors and optical data processing systems.

Polarization dependence of asymmetric off-resonance long period fiber gratings.

We present the polarization dependence of strong asymmetric long period fiber gratings written on tapered fibers. We found that for off-resonance conditions the spectral response and the output mode strongly depend on the input state of polarization. We utilize this dependence to obtain a mode selective device and demonstrate radially polarized and azimuthally polarized fiber lasers based on these asymmetric long period fiber gratings.

Fused fiber micro-knots.

We present fusing of a fiber micro-knot by a CO2 laser beam. We demonstrate tuning of the coupling strength and tuning of the spectral resonance of the micro-knot by the fusing process. The experimental results reveal that fusing the fiber micro-knots increases the coupling efficiency and improves the robustness and the stability of the micro-knots.

How synchronized human networks escape local minima.

Finding the global minimum in complex networks while avoiding local minima is challenging in many types of networks. In human networks and communities, adapting and finding new stable states amid changing conditions due to conflicts, climate changes, or disasters, is crucial. We studied the dynamics of complex networks of violin players and observed that such human networks have different methods to avoid local minima than other non-human networks. Humans can change the coupling strength between them or change their tempo. This leads to different dynamics than other networks and makes human networks more robust and better resilient against perturbations. We observed high-order vortex states, oscillation death, and amplitude death, due to the unique dynamics of the network. This research may have implications in politics, economics, pandemic control, decision-making, and predicting the dynamics of networks with artificial intelligence.

Controlling synchronization in large laser networks.

Synchronization in large laser networks with both homogeneous and heterogeneous coupling delay times is examined. The number of synchronized clusters of lasers is established to equal the greatest common divisor of network loops. We experimentally demonstrate up to 16 multicluster phase synchronization scenarios within unidirectional coupled laser networks, whereby synchronization in heterogeneous networks is deduced by mapping to an equivalent homogeneous network. The synchronization in large laser networks is controlled by means of tunable coupling and self-coupling.

All-optical control of an individual resonance in a silicon microresonator.

We experimentally demonstrate selective control of the Q and transmission of an individual resonance of an optical microcavity by optically controlling its intracavity loss via inverse Raman scattering. A strongly overcoupled resonance is brought into critical coupling with continuous tuning of the on-resonance transmission by >9 dB and reduction of the intrinsic Q factor by more than a factor of five. Adjacent resonances experience minimal disturbance and can be selectively controlled by tuning the control beam to the appropriate control resonance. These dynamics are analogous to Zeno effects observed in decoherence-driven atomic ensembles and two-level systems.