Compact and stable temporally magnified tomography using a phase-locked broadband source

Unveiling external motion dynamics of solitons in passively mode-locked fiber lasers

Real-time measurement of ultrafast pulses together with high temporal resolution and long recording length is an urgent requirement of all optical communication systems and nonlinear science. Here, external motion dynamics of soliton pairs in mode-locking ultrafast fiber lasers can be single-shot characterized with long recording length, by using an asynchronous four-wave-mixing (FWM)-based temporal magnifier (AFTM) system. Recording length of more than one thousand roundtrips can be achieved through the AFTM system. Temporal propagation dynamics of soliton pairs with tunable separations are observed, revealing that soliton pairs with narrower separation display vibration-like dynamics, while the two solitons with wider separation remain relatively unchanged. We believe our results will provide a promising solution for real-time measurement of ultrafast pulse and can offer novel insights for ultrafast transient dynamics in nonlinear optics.

Sensitivity-enhanced ultrafast optical tomography by parametric- and Raman-amplified temporal imaging

To overcome the speed limitation of conventional optical tomography, a temporal imaging technique has been integrated with optical time-domain reflectometry to realize ultrafast temporally magnified (TM) tomography. In this Letter, the sensitivity of TM tomography has been further enhanced using optical parametric amplification and distributed Raman amplification, and this technique is named temporally encoded amplified and magnified (TEAM) tomography. As a result, a 78-dB sensitivity has been realized, comparable to ultrafast optical coherence tomography systems. In addition, an 86.7-μm axial resolution can be realized across a 67.5-mm imaging range. To demonstrate the significance of sensitivity improvement, tomographic imaging of a centimeter-thick phantom is provided at an A-scan rate of 44 MHz.

Panoramic-reconstruction temporal imaging for seamless measurements of slowly-evolved femtosecond pulse dynamics

Single-shot real-time characterization of optical waveforms with sub-picosecond resolution is essential for investigating various ultrafast optical dynamics. However, the finite temporal recording length of current techniques hinders comprehensive understanding of many intriguing ultrafast optical phenomena that evolve over a timescale much longer than their fine temporal details. Inspired by the space-time duality and by stitching of multiple microscopic images to achieve a larger field of view in the spatial domain, here a panoramic-reconstruction temporal imaging (PARTI) system is devised to scale up the temporal recording length without sacrificing the resolution. As a proof-of-concept demonstration, the PARTI system is applied to study the dynamic waveforms of slowly evolved dissipative Kerr solitons in an ultrahigh-Q microresonator. Two 1.5-ns-long comprehensive evolution portraits are reconstructed with 740 fs resolution and dissipative Kerr soliton transition dynamics, in which a multiplet soliton state evolves into a stable singlet soliton state, are depicted.Real-time characterization of ultrafast dynamics comes with a tradeoff between temporal resolution and recording length. Here, Li et al. use a temporal reconstruction technique inspired by panoramic microscopy to image the dynamics of slowly evolved dissipative Kerr solitons in a microresonator.

Real-time observation of round-trip resolved spectral dynamics in a stabilized fs fiber laser

Fiber-stretcher based phase-lock loop (PLL) is a mature technique in fiber mode-locked lasers for repetition-rate stabilization. However, undesired side effects may be induced if not properly handled, which is easily overlooked owing to the lack of single-shot spectral analyzers. Thanks to the ultrafast spectral analyzing capability of optical time-stretch, an intriguing spectral dynamics is observed in a repetition-rate-stabilized nonlinear polarization rotation (NPR) mode-locked laser. Under the dynamic state, the optical spectra of pulses undergo dramatic evolution in every round trip while the pulse energy is relatively constant. Indicated by estimated cross-spectral densities, such spectral dynamics results in noticeable degradation in optical spectral coherence. The physical origin of the round-trip evolved spectral dynamics is attributed to the local birefringence induced by the fiber stretcher. Therefore, the results are helpful for a proper use of fiber-stretcher based PLL in fiber lasers, particularly when a good spectral coherence is desired. Furthermore, our study has also provided a potentially useful optical source for applications where fast spectral modulation is desired.

High-speed OCT light sources and systems [Invited]

Imaging speed is one of the most important parameters that define the performance of optical coherence tomography (OCT) systems. During the last two decades, OCT speed has increased by over three orders of magnitude. New developments in wavelength-swept lasers have repeatedly been crucial for this development. In this review, we discuss the historical evolution and current state of the art of high-speed OCT systems, with focus on wavelength swept light sources and swept source OCT systems.