C. Husko

Temporal solitons and pulse compression in photonic crystal waveguides

We demonstrate soliton-effect pulse compression in mm-long photonic crystal waveguides resulting from strong anomalous dispersion and self-phase modulation. Compression from 3ps to 580fs, at low pulse energies(~10pJ), is measured via autocorrelation.

Stable aqueous dispersions of optically and electronically active phosphorene.

Significance Few-layered phosphorene, which is isolated through exfoliation from black phosphorus, has attracted great interest due to its unique electronic and optical properties. Although solution-based exfoliation methods have been developed for black phosphorus, these techniques have thus far used anhydrous organic solvents. This approach minimizes exposure to known oxidizing species, but at the cost of limited exfoliation yield and relatively thick flakes. Here, we overcome these limitations by using stabilizing surfactants in deoxygenated water, which results in phosphorene down to the monolayer limit. The resulting aqueous phosphorene dispersions show layer-dependent photoluminescence and enable high-performance field-effect transistors. Overall, this approach holds promise for the solution-phase production of few-layered phosphorene in emerging large-volume applications including electronics and optoelectronics. Understanding and exploiting the remarkable optical and electronic properties of phosphorene require mass production methods that avoid chemical degradation. Although solution-based strategies have been developed for scalable exfoliation of black phosphorus, these techniques have thus far used anhydrous organic solvents in an effort to minimize exposure to known oxidants, but at the cost of limited exfoliation yield and flake size distribution. Here, we present an alternative phosphorene production method based on surfactant-assisted exfoliation and postprocessing of black phosphorus in deoxygenated water. From comprehensive microscopic and spectroscopic analysis, this approach is shown to yield phosphorene dispersions that are stable, highly concentrated, and comparable to micromechanically exfoliated phosphorene in structure and chemistry. Due to the high exfoliation efficiency of this process, the resulting phosphorene flakes are thinner than anhydrous organic solvent dispersions, thus allowing the observation of layer-dependent photoluminescence down to the monolayer limit. Furthermore, to demonstrate preservation of electronic properties following solution processing, the aqueous-exfoliated phosphorene flakes are used in field-effect transistors with high drive currents and current modulation ratios. Overall, this method enables the isolation and mass production of few-layer phosphorene, which will accelerate ongoing efforts to realize a diverse range of phosphorene-based applications.

Soliton dynamics in semiconductor photonic crystals

Semiconductor optical waveguides have been the subject of intense study as both fundamental objects of study, as well as a path to photonic integration. In this talk I will focus on the nonlinear evolution of optical solitons in photonic crystal waveguides made of semiconductor materials. The ability to independently tune the dispersion and the nonlinearity in photonic crystal waveguides enables the examination of completely different nonlinear regimes in the same platform. I will describe experimental efforts utilizing time-resolved measurements to reveal a number of physical phenomena unique to solitons in a free carrier medium. The experiments are supported by analytic and numerical models providing a deeper insight into the physical scaling of these processes.

Silicon-Phosphorene Nanocavity-Enhanced Optical Emission at Telecommunications Wavelengths

Generating and amplifying light in silicon (Si) continues to attract significant attention due to the possibility of integrating optical and electronic components in a single material platform. Unfortunately, silicon is an indirect band gap material and therefore an inefficient emitter of light. With the rise of integrated photonics, the search for silicon-based light sources has evolved from a scientific quest to a major technological bottleneck for scalable, CMOS-compatible, light sources. Recently, emerging two-dimensional materials have opened the prospect of tailoring material properties based on atomic layers. Few-layer phosphorene, which is isolated through exfoliation from black phosphorus (BP), is a great candidate to partner with silicon due to its layer-tunable direct band gap in the near-infrared where silicon is transparent. Here we demonstrate a hybrid silicon optical emitter composed of few-layer phosphorene nanomaterial flakes coupled to silicon photonic crystal resonators. We show single-mode emission in the telecommunications band of 1.55 μm ( Eg = 0.8 eV) under continuous wave optical excitation at room temperature. The solution-processed few-layer BP flakes enable tunable emission across a broad range of wavelengths and the simultaneous creation of multiple devices. Our work highlights the versatility of the Si-BP material platform for creating optically active devices in integrated silicon chips.

High-energy ultra-short pulses from pure-quartic solitons

Conventional optical solitons are remarkably stable pulses that arise from the balance of the nonlinearity and the anomalous quadratic dispersion in the medium in which they propagate, such as optical fibres [1] or silicon chips [2], Due to their self-reinforced stability, they are ideal candidates to generate transform-limited pulses from simple laser architectures [3], However, generating ultrashort high-energy pulses from soliton lasers is difficult, due to the spectral sideband generation of periodically perturbed solitons [4], which limits the shortest width, and the soliton energy scaling, which limits the energy at a given width. Consequently, laser architectures had to become more complex, with additional recompressing stages [5], Here, by means of experimental measurements, nonlinear Schrödinger equation (NLSE) simulations, and analytical developments, we show that the recently discovered pure-quartic solitons (PQS) [6] have the potential to outperform conventional solitons in yielding high-energy ultrashort pulses and bring soliton lasers back to the forefront of ultrafast laser research.

Phase sensitive amplification in integrated waveguides (Conference Presentation)

Phase sensitive amplification (PSA) is an attractive technology for integrated all-optical signal processing, due to its potential for noiseless amplification, phase regeneration and generation of squeezed light. In this talk I will review our results on implementing four-wave-mixing based PSA inside integrated photonic devices. In particular I will discuss PSA in chalcogenide ridge waveguides and silicon slow-light photonic crystals. We achieve PSA in both pump- and signal-degenerate schemes with maximum extinction ratios of 11 (silicon) and 18 (chalcogenide) dB. I will further discuss the influence of two-photon absorption and free carrier effects on the performance of silicon-based PSAs.

A hybrid silicon-phosphorene nanolaser

We show evidence of lasing from a hybrid nanostructure composed of a silicon optical resonator and a two-dimensional phosphorene film. The ~1555 nm emission wavelength opens possibilities for optically-active devices for integrated silicon photonics.

Pulse compression and slow-light enhanced three-photon absorption in GaInP photonic crystal waveguides

We demonstrate first observations of slow-light enhanced three-photon absorption(ThPA) in photonic crystal waveguides.The injected pulses demonstrate self-phase modulation(SPM) with scalings deviating from n<inf>g</inf> ²(SPM) and n<inf>g</inf> ³(ThPA).A thorough analysis suggests pulse compression leading to increased peak powers.

Ultrafast all-optical modulation in GaAs photonic crystal cavities

We demonstrate all-optical modulation via ultrafast optical carrier injection in a GaAs photonic crystal cavity using a degenerate pump-probe technique. The low switching(absorption) energy∼120fJ(10fJ), and fast response(∼15ps), limited only by carrier lifetime, suggest practical all-optical switching applications.

Impact of Nonlinearity and Disorder on Slow Modes in Membrane Photonic Crystals

Disorder induced scattering is crucial for understanding slow light in Photonic Crystal. We investigate dispersion and scattering losses on PhC structures with tailored dispersion and discuss their potential for delay control and all-optical switching.