A mode-locked random laser generating transform-limited optical pulses.

Ever since the mid-1960's, locking the phases of modes enabled the generation of laser pulses of duration limited only by the uncertainty principle, opening the field of ultrafast science. In contrast to conventional lasers, mode spacing in random lasers is ill-defined because optical feedback comes from scattering centres at random positions, making it hard to use mode locking in transform limited pulse generation. Here the generation of sub-nanosecond transform-limited pulses from a mode-locked random fibre laser is reported.

A random optical parametric oscillator.

Synchronously pumped optical parametric oscillators (OPOs) provide ultra-fast light pulses at tuneable wavelengths. Their primary drawback is the need for precise cavity control (temperature and length), with flexibility issues such as fixed repetition rates and marginally tuneable pulse widths. Targeting a simpler and versatile OPO, we explore the inherent disorder of the refractive index in single-mode fibres realising the first random OPO - the parametric analogous of random lasers.

Distributed birefringence sensing at 10 accuracy over ultra-long PMF by optical frequency comb and distributed Brillouin amplifier.

Brillouin dynamic gratings (BDG) can measure the distributed birefringence of polarization-maintaining fibers (PMF), however, its sensing range is limited by both stimulated Brillouin scattering depletion and fiber losses in PMF, which are significantly higher than those in standard single-mode fibers. In this work, we theoretically and experimentally verify that BDG can be sustained over ultra-long distances when assisted by distributed Brillouin amplification, significantly extending the distributed birefringence measurement distance. Using an optical frequency comb pumped by a narrow linewidth laser to both generate and interrogate the amplified BDG, a birefringence measurement accuracy of 7.

Generation of high performance optical chirped pulse for distributed strain sensing application with high strain accuracy and larger measurement range.

A photonic approach for generating low frequency drifting noise, arbitrary and large frequency chirping rate (FCR) optical pulses based on the Kerr effect in the nonlinear optical fiber is theoretically analyzed and experimentally demonstrated. Due to the Kerr effect-induced sinusoidal phase modulation in the nonlinear fiber, high order Kerr pulse with a large chirping rate is generated. In the concept-proof experiments, the FCR of the m Kerr pulse has been significantly improved by a factor of 2m+1.

Broadband ultrasound sensing based on fused dual-core chalcogenide-PMMA microfibers.

High-frequency ultrasound sensors are essential for high-resolution medical ultrasonic imaging and industrial ultrasonic non-destructive monitoring. In this paper, we propose highly sensitive broadband ultrasound sensors based on fused dual-core chalcogenide-polymethyl methacrylate (AsSe-PMMA) microfibers. We demonstrate that ultrasound response is determined by the differential slope of transmission spectra in the dual-core microfiber, which is verified by detecting the acoustic response in various microfibers of different tapering parameters.

Mode conversion of SH guided waves with symmetry inversion in plates.

When shear horizontal ultrasonic guided waves interact with thickness discontinuities in plates, the reflected and transmitted wavefields can be composed of several modes due to mode conversion. It is known that in a plate with a symmetric discontinuity, with respect to the plate's mid-plane, mode conversion is restricted to modes that share the same symmetry as the incident mode. In this paper, we use an analytical model based on the reciprocity principle and finite element analysis to investigate mode conversion due to the interaction with different types of discontinuity, namely, non-symmetric, symmetric and geometrically symmetric but with opposite boundary conditions, that is one side of the discontinuity free and the other rigidly fixed.

Longitudinal mode dynamics in SOA-based random feedback fiber lasers.

We experimentally demonstrate that single-mode operation of an SOA-based random fiber laser is only possible in pulsed regime at driving currents close to the threshold, whereas multimode regime dominates under higher SOA currents. Theoretical simulations support random frequency spacing of the laser modes to be due to residual stress on the optical fiber. Pulsed regime is shown to be due to randomly driven Q-switching induced by a scintillation effect in the Rayleigh backscattered light, which effectively translates as a time-varying cavity loss.

Characterization of the wide band chirp of laser diodes with time-resolved spectroscopy.

This paper reports a high-resolution amplified optical sampling time-resolved spectroscopy technique for characterization of the chirp of laser diodes with no limitations on measuring chirp ranges. The chirp induced by slowly (25 Hz) and rapidly (>100  MHz) varying current waveforms was measured. Although the slowly varying case used a triangular current waveform to modulate a distributed feedback laser diode, a non-linear chirp was measured, and a chirp excursion of 71 GHz was found.

Alignment-free characterization of polarizing beamsplitters.

Traditional methods for measurement of polarizing beamsplitter (PBS) parameters, especially the extinction ratio, require highly polarized light sources, alignment procedures, and/or experimental parameters that change over time, such as polarization rotations. In this work, a new method is presented that employs unpolarized light and a Faraday mirror. It is shown that precise extinction ratio and insertion loss values can be achieved in three single-sweep measurements without any alignment requirements or time-varying signals of any kind.

A method of treatment for nonunion after fractures using mesenchymal stromal cells loaded on collagen microspheres and incorporated into platelet-rich plasma clots.

Purpose: There is evidence showing that mesenchymal stromal cells (MSC) may constitute a potential therapeutic strategy to induce bone regeneration. In this work, we investigate the capacity of autologous bone marrow (BM) MSC loaded on collagen microspheres (CM) and included into autologous platelet-rich plasma (PRP) clots (MSC/CM/PRP) to induce bone formation in patients with nonunion lesions.

Methods: MSC were isolated from BM cells of patients with nonunion lesions.