Extreme pulses in gain-switched semiconductor lasers.

Semiconductor lasers subjected to strong current modulation produce gain-switched optical pulse trains. These lasers can also produce pulse trains at sub-harmonic repetition rates relative to the driving current modulation. We experimentally observe, and numerically model, that these pulse trains can be interrupted by single-cycle extreme pulses whose characteristics and statistics are similar to rogue waves. Modeling indicates that drops in the circulating optical power in the optical cavity precede the appearance of extreme pulses. At the single photon level, the stochastic source terms in the optical field equation dominate the circulating optical power.

Multiphoton Nanosculpting of Optical Resonant and Nonresonant Microsensors on Fiber Tips.

This work presents a multiphoton nanosculpting process that is employed to fabricate three-dimensional (3D) mechanically assisted optical resonant and nonresonant microsensors on fiber tips. The resonant microsensor consists of a complex 3D optical cavity design with submicron resolution and advanced micromechanical features including a hinged, multipositional mirror, a 3D spring body to displace this mirror without deforming it, and adhesive-retaining features for sealing the cavity. These features represent a breakthrough in the integration and fabrication capabilities of micro-optomechanical systems. The demonstrated dynamic optical surface enables directional thin-film deposition onto obscured areas. We leverage the rotation of the dynamically movable mirror to deposit a thin reflective coating onto the inner surfaces of a Fabry-Pérot cavity (FPC) with curved geometry. The reflective coating in conjunction with the dynamically rotatable mirror greatly improves the quality factor of the FPC and enables a new class of highly integrated multipurpose sensor systems. A unique spring body FPC on an optical fiber tip is used to demonstrate pressure sensing with a sensitivity of 38 ± 7 pm/kPa over a range of -80 to 345 kPa. The nonresonant microsensor consists of microblades that spin in response to an incident flow. Light exiting the core of the optical fiber is reflected back into the fiber core at a flow-dependent rate as the blades pass by. The fiber tip flow sensor operates successfully over a range of 9-25 LPM using nitrogen gas and achieves a linear response of 706 ± 43 reflections/LPM over a range of 10.9-12 LPM. The nanostructuring technology presented in this work offers a path forward for utilizing 3D design freedom in micromechanically enhanced optical and optofluidic systems to facilitate versatile processing and advantageous geometries beyond the current state-of-the-art.

Tunable, low-phase-noise microwave signals from an optically injected semiconductor laser with opto-electronic feedback.

We experimentally demonstrate the generation of microwave signals with linewidths below 3 Hz and a tuning range over 35 GHz from a semiconductor laser subject to optical injection and opto-electronic feedback. The feedback loop uses neither a microwave spectral filter nor an amplifier to achieve a reduction in the microwave linewidth of six orders of magnitude. Two microwave frequencies, 25.4 and 45.9 GHz, are chosen to highlight single-sideband phase measurements of -105 and -95 dBc/Hz at a 10-kHz offset, respectively. Finally, we demonstrate that longer-term stability can be further improved via asymmetric mutual injection.