Mid-infrared supercontinuum generation in silicon-germanium all-normal dispersion waveguides.

We demonstrate coherent supercontinuum generation spanning over an octave from a silicon germanium-on-silicon waveguide using ∼200 pulses at a wavelength of 4 µm. The waveguide is engineered to provide low all-normal dispersion in the TM polarization. We validate the coherence of the generated supercontinuum via simulations, with a high degree of coherence across the entire spectrum.

Nonlinear light generation in topological nanostructures.

Topological photonics has emerged as a route to robust optical circuitry protected against disorder and now includes demonstrations such as topologically protected lasing and single-photon transport. Recently, nonlinear optical topological structures have attracted special theoretical interest, as they enable tuning of topological properties by a change in the light intensity and can break optical reciprocity to realize full topological protection. However, so far, non-reciprocal topological states have only been realized using magneto-optical materials and macroscopic set-ups with external magnets, which is not feasible for nanoscale integration.

Nonlinear Wavefront Control with All-Dielectric Metasurfaces.

Metasurfaces, two-dimensional lattices of nanoscale resonators, offer unique opportunities for functional flat optics and allow the control of the transmission, reflection, and polarization of a wavefront of light. Recently, all-dielectric metasurfaces reached remarkable efficiencies, often matching or out-performing conventional optical elements. The exploitation of the nonlinear optical response of metasurfaces offers a paradigm shift in nonlinear optics, and dielectric nonlinear metasurfaces are expected to enrich subwavelength photonics by enhancing substantially nonlinear response of natural materials combined with the efficient control of the phase of nonlinear waves.

High-resolution chalcogenide fiber bundles for longwave infrared imaging.

A flexible chalcogenide fiber bundle (FB) with a resolution as high as ~31 lp/mm has been fabricated for delivering thermal images of objects at room temperature. The FB is composed of ~200,000 single fibers with a Ge-As-Te-Se glass core 15 μm in diameter and a polyetherimide (PEI) cladding 16.8 μm in diameter.

CMOS compatible fabrication of micro, nano convex silicon lens arrays by conformal chemical vapor deposition.

We present a novel CMOS-compatible fabrication technique for convex micro-nano lens arrays (MNLAs) with high packing density on the wafer scale. By means of conformal chemical vapor deposition (CVD) of hydrogenated amorphous silicon (a-Si:H) following patterning of silicon pillars via electron beam lithography (EBL) and plasma etching, large areas of a close packed silicon lens array with the diameter from a few micrometers down to a few hundred nanometers was fabricated. The resulting structure shows excellent surface roughness and high uniformity.

Experimental demonstration of linearly polarized 2-10 μm supercontinuum generation in a chalcogenide rib waveguide.

This Letter reports the production of a supercontinuum extending from ≈2  μm to >10  μm generated using a chalcogenide buried rib waveguide pumped with 330 femtosecond pulses at 4.184 μm. This is, to the best of our knowledge, the broadest mid-infrared supercontinuum generated in any planar waveguide platform.

Atomically thin optical lenses and gratings.

Two-dimensional (2D) materials have emerged as promising candidates for miniaturized optoelectronic devices due to their strong inelastic interactions with light. On the other hand, a miniaturized optical system also requires strong elastic light-matter interactions to control the flow of light. Here we report that a single-layer molybdenum disulfide (MoS) has a giant optical path length (OPL), around one order of magnitude larger than that from a single-layer of graphene.

Tailoring of the Brillouin gain for on-chip widely tunable and reconfigurable broadband microwave photonic filters.

An unprecedented Brillouin gain of 44 dB in a photonic chip enables the realization of broadly tunable and reconfigurable integrated microwave photonic filters. More than a decade bandwidth reconfigurability from 30 up to 440 MHz, with a passband ripple <1.9  dB is achieved by tailoring the Brillouin pump.

Producing air-stable monolayers of phosphorene and their defect engineering.

It has been a long-standing challenge to produce air-stable few- or monolayer samples of phosphorene because thin phosphorene films degrade rapidly in ambient conditions. Here we demonstrate a new highly controllable method for fabricating high quality, air-stable phosphorene films with a designated number of layers ranging from a few down to monolayer. Our approach involves the use of oxygen plasma dry etching to thin down thick-exfoliated phosphorene flakes, layer by layer with atomic precision.

Mid-infrared nonlinear optical response of Si-Ge waveguides with ultra-short optical pulses.

We characterize the nonlinear optical response of low loss Si(0.6)Ge(0.4) / Si waveguides in the mid-infrared between 3.

High-resolution chalcogenide fiber bundles for infrared imaging.

An ordered chalcogenide fiber bundle with a high resolution for infrared imaging was fabricated using a stack-and-draw approach. The fiber bundle consisted of about 810,000 single fibers with an As2S3 glass core of 9 μm in diameter and a polyetherimide (PEI) polymer cladding of 10 μm in diameter. The As2S3/PEI fibers showed good transparency in the 1.

High Q factor chalcogenide ring resonators for cavity-enhanced MIR spectroscopic sensing.

We report the characteristics of high Q factor chalcogenide ring resonators designed for sensing in the mid-infrared (MIR). The resonators consisted of an exposed Ge11.5As24Se64.

Nonlinear diffraction in orientation-patterned semiconductors.

This work represents experimental demonstration of nonlinear diffraction in an orientation-patterned semiconducting material. By employing a new transverse geometry of interaction, three types of second-order nonlinear diffraction have been identified according to different configurations of quasi-phase matching conditions. Specifically, nonlinear Čerenkov diffraction is defined by the longitudinal quasi-phase matching condition, nonlinear Raman-Nath diffraction satisfies only the transverse quasi-phase matching condition, and nonlinear Bragg diffraction fulfils the full vectorial quasi-phase matching conditions.

Positive and negative phototunability of chalcogenide (AMTIR-1) microdisk resonator.

We demonstrate externally photo-induced partially-reversible tuning of the resonance of a microdisk made of AMTIR-1 (Ge(33)As(12)Se(55)). We have achieved for the first time, to the best of our knowledge, both positive and negative shift in a microresonator with external tuning. A positive resonance shift of 1 nm and a negative resonance shift of 0.

Nonlinear optical response of low loss silicon germanium waveguides in the mid-infrared.

We have investigated the nonlinear optical response of low loss Si(0.6)Ge(0.4) / Si waveguides in the mid-infrared wavelength range from 3.

Multi-milliwatt mid-infrared supercontinuum generation in a suspended core chalcogenide fiber.

A low-loss suspended core As(38)Se(62) fiber with core diameter of 4.5 μm and a zero-dispersion wavelength of 3.5 μm was used for mid-infrared supercontinuum generation.

1.8-10 μm mid-infrared supercontinuum generated in a step-index chalcogenide fiber using low peak pump power.

By pumping an 11-cm-long step-index chalcogenide fiber with ∼330  fs pulses at 4.0 μm from an optical parametric amplifier, mid-infrared supercontinuum generation spanning from ∼1.8 to ∼10  μm within a dynamic range of ±15  dB has been demonstrated at a relatively low power threshold of ∼3000  W.

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.

Tunable wideband microwave photonic phase shifter using on-chip stimulated Brillouin scattering.

We present the first microwave photonic phase shifter using stimulated Brillouin scattering (SBS) on-chip. The unique ability of SBS to generate both narrowband gain and loss resonances allows us to achieve low ±1.5 dB amplitude fluctuations, which is a record for integrated devices, along with 240° continuously tunable phase shift.

Negligible nonlinear absorption in hydrogenated amorphous silicon at 1.55 μm for ultra-fast nonlinear signal processing.

Three-photon absorption (3PA) has been observed as the dominant mechanism for nonlinear absorption in wide-bandgap hydrogenated amorphous silicon (a-Si:H-W) at 1.55 μm. The nonlinear index n2 and 3PA coefficient were measured to be 22 × 10(-17)m(2)/W and 5.

Adaptive optics enhanced direct laser writing of high refractive index gyroid photonic crystals in chalcogenide glass.

Chiral gyroid photonic crystals are fabricated in the high refractive index chalcogenide glass arsenic trisulfide with an adaptive optics enhanced direct laser writing system. The severe spherical aberration imparted when focusing into the arsenic trisulfide is mitigated with a defocus decoupled aberration compensation technique that reduces the level of aberration that must be compensated by over an order of magnitude. The fabricated gyroids are shown to have excellent uniformity after our adaptive optics method is employed, and the transmission spectra of the gyroids are shown to have good agreement with numerical simulations that are based on a uniform and diffraction limited fabrication resolution.

Low-loss chalcogenide waveguides for chemical sensing in the mid-infrared.

We report the characteristics of low-loss chalcogenide waveguides for sensing in the mid-infrared (MIR). The waveguides consisted of a Ge₁₁.₅As₂₄Se₆₄.

Relative contribution of stoichiometry and mean coordination to the fragility of Ge-As-Se glass forming liquids.

The structural relaxation properties of 34 compositions of Ge-As-Se glass forming liquids are investigated by differential scanning calorimetry (DSC). The fragility index (m) and activation energies for enthalpy relaxation (Ea) exhibit universal trends with respect to stoichiometry and mean coordination (⟨r⟩), respectively. The liquid fragility which defines the full temperature dependence of the relaxation processes shows no well defined trend with respect to ⟨r⟩ but instead is found to be closely determined by the excess or deficiency in selenium with respect to stoichiometry.

Self-reconstructing all-optical poling in polymer fibers.

Self-sustained all-optical poling second-harmonic generation (SHG) experiments are conducted in single-core and multicore dye-doped poly(methyl methacrylate) optical fibers. By tuning the polarization of the fundamental beam, the SHG signal is degraded and is reconstructed spontaneously up to its initial level. We found a new situation in which the photo-induced self-organization of azo polymers creates a well-ordered periodic structure.

Narrow linewidth Brillouin laser based on chalcogenide photonic chip.

We present, to the best of our knowledge, the first demonstration of a narrow linewidth, waveguide-based Brillouin laser that is enabled by large Brillouin gain of a chalcogenide chip. The waveguides are equipped with vertical tapers for low-loss coupling. Due to optical feedback for the Stokes wave, the lasing threshold is reduced to 360 mW, which is five times lower than the calculated single-pass Brillouin threshold for the same waveguide.