Enhancing and inhibiting stimulated Brillouin scattering in photonic integrated circuits.

On-chip nonlinear optics is a thriving research field, which creates transformative opportunities for manipulating classical or quantum signals in small-footprint integrated devices. Since the length scales are short, nonlinear interactions need to be enhanced by exploiting materials with large nonlinearity in combination with high-Q resonators or slow-light structures. This, however, often results in simultaneous enhancement of competing nonlinear processes, which limit the efficiency and can cause signal distortion. Here, we exploit the frequency dependence of the optical density-of-states near the edge of a photonic bandgap to selectively enhance or inhibit nonlinear interactions on a chip. We demonstrate this concept for one of the strongest nonlinear effects, stimulated Brillouin scattering using a narrow-band one-dimensional photonic bandgap structure: a Bragg grating. The stimulated Brillouin scattering enhancement enables the generation of a 15-line Brillouin frequency comb. In the inhibition case, we achieve stimulated Brillouin scattering free operation at a power level twice the threshold.

Low-threshold Brillouin laser at 2 µm based on suspended-core chalcogenide fiber.

We present, to the best of our knowledge, the first demonstration of a 2 µm Brillouin laser based on a thulium-doped fiber pump and a chalcogenide fiber. A short 1.5 m piece of suspended-core chalcogenide As38Se62 fiber is employed as a gain medium, taking advantage of its small effective mode area and high Brillouin gain coefficient. A record-low lasing threshold of 52 mW is achieved, which is about 10 times lower than previously demonstrated in silica fiber cavities.

Phase-locking and pulse generation in multi-frequency brillouin oscillator via four wave mixing.

There is an increasing demand for pulsed all-fibre lasers with gigahertz repetition rates for applications in telecommunications and metrology. The repetition rate of conventional passively mode-locked fibre lasers is fundamentally linked to the laser cavity length and is therefore typically ~10-100 MHz, which is orders of magnitude lower than required. Cascading stimulated Brillouin scattering (SBS) in nonlinear resonators, however, enables the formation of Brillouin frequency combs (BFCs) with GHz line spacing, which is determined by the acoustic properties of the medium and is independent of the resonator length. Phase-locking of such combs therefore holds a promise to achieve gigahertz repetition rate lasers. The interplay of SBS and Kerr-nonlinear four-wave mixing (FWM) in nonlinear resonators has been previously investigated, yet the phase relationship of the waves has not been considered. Here, we present for the first time experimental and numerical results that demonstrate phase-locking of BFCs generated in a nonlinear waveguide cavity. Using real-time measurements we demonstrate stable 40 ps pulse trains with 8 GHz repetition rate based on a chalcogenide fibre cavity, without the aid of any additional phase-locking element. Detailed numerical modelling, which is in agreement with the experimental results, highlight the essential role of FWM in phase-locking of the BFC.

Multi-wavelength gratings formed via cascaded stimulated Brillouin scattering.

We present the experimental observation of multi-wavelength fiber Bragg gratings in As2Se3 fiber. The gratings are internally written via two-photon absorption of 1550 nm pump light and its first and second order Stokes waves generated by cascaded stimulated Brillouin scattering (SBS). We demonstrate a parameter regime that allows for 4 dB grating enhancement by suppression of SBS.

Multicore, tapered optical fiber for nonlinear pulse reshaping and saturable absorption.

We present a new method to create a coupled waveguide array via tapering a seven-core telecommunications fiber. The fiber based waveguide array is demonstrated to exhibit the novel physics associated with coupled waveguide arrays, such as discrete diffraction and discrete self-focusing. The saturable absorber characteristics of the device are characterized and an autocorrelation measurement reveals significant single-pass pulse reshaping.