Conference Agenda

Semiconductor lasers are very sensitive to optical feedback. Here we study experimentally the effect of optical feedback on the spatial coherence of a diode laser using the speckle technique. Speckle is a noisy structure arising from the interference of coherent waves as they propagate through a diffusive medium. Using a multimode fibre as the diffusive medium, we observe that, during the laser turn-on, without feedback, the speckle contrast increases gradually (revealing a gradual increase in spatial coherence), but, with sufficiently strong feedback, the speckle contrast increases sharply (revealing an abrupt increase in spatial coherence). For pump currents above the threshold, high-contrast regions alternate with low-contrast regions. We also observe that, under appropriate current modulation, high-contrast regions are suppressed. Our findings may find application in laser-based illumination systems, because optical feedback can be used in combination with current modulation to reduce speckles over a wide range of pump currents.

We study the relaxation behavior of an optical cavity with

memory in its nonlinear response. We show that the relaxation time of

the optical cavity with memory is mostly dominated by the timescale

of the thermal relaxation of the nonlinearity. However, when crossing

a bifurcation into the bistable regime, we observe slowing down of the

optical response by several orders of magnitude compared to the ther-

mal relaxation time. Experimentally, this slowing down was verified

using an oil-filled cavity.

The ability to detect near infrared light has important applications in telecoms, medical diagnostics and remote sensing. Traditional free-space up-conversion systems based on bulk crystals are not suitable for integration purposes, due to their large footprint. Here, we employ a nonlocal dielectric metasurface as an ultra-thin up-converter, by exploiting quasi-bound states in the continuum to increase the conversion efficiency of the nonlinear process.

We demonstrate a quantum interface that simultaneously converts the wavelength, bandwidth, and duration of single-photon-level pulses, enabling compatibility between disparate quantum systems. Using difference frequency generation in a lithium niobate waveguide driven by a highly chirped pump, we transform pulses from 798 nm, 5 GHz, 150 ps (quantum dot-like) to 1300 nm, 35 GHz, < 25 ps (telecom standard). This nonlinear optical time lens achieves over 80% internal conversion efficiency and compresses output pulses below detector resolution. The device offers a compact solution for integrating quantum emitters, memories, and telecom networks, with potential for further pulse shape control.

We present experimental and theoretical representation of quantum-like Schrödinger's cat states, by exploiting orbital angular momentum of the light. We investigated complex superposition as 3-Cat, 6-Cat and Fock-Cat states.