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Nonlinear absorption can limit the efficiency of nonlinear optical devices. However, it can also be exploited for optical limiting or switching applications. Thus, characterization of nonlinear absorption in photonic devices is imperative for designing useful devices. This work uses the nonlinear transmittance technique to measure the two-photon absorption coefficients ( α 2 ) of AlGaAs waveguides in strip-loaded, nanowire, and half-core geometries in the wavelength range from 1480 to 1560 nm. The highest α 2 values of 2.4, 2.3, and 1.1 c m / G W were measured at 1480 nm for 0.8-µm-wide half-core, 0.6-µm-wide nanowire, and 0.9-µm-wide strip-loaded waveguides, respectively, with α 2 decreasing with increasing wavelength. The free-carrier absorption cross section was also estimated from the nonlinear transmittance data to be around 2.2 × 10 − 16 c m 2 for all three geometries. Our results contribute to a better understanding of the nonlinear absorption in heterostructure waveguides of different cross-sectional geometries. We discuss how the electric field distribution in the different layers of a heterostructure can lead to geometry-dependent effective two-photon absorption coefficients. More specifically, we pinpoint the third-order nonlinear confinement factor as a design parameter to estimate the strength of the effective nonlinear absorption, in addition to tailoring the bandgap energy by varying the material composition.

The goal of SiEPICfab is to conduct research in the fabrication of silicon photonic devices and photonic integrated circuits, and to make leading-edge silicon photonic manufacturing accessible to Canadian and international academics and industry. SiEPICfab builds on the success of the Silicon Electronic Photonic Integrated Circuits (SiEPIC) program, which has been offering research training workshops since 2008, by adding a fabrication facility “fab”. We have developed a rapid prototyping facility to support a complete ecosystem of companies involved in silicon photonics product development, including modelling, design, library development, fabrication, test, and packaging of silicon photonics. SiEPICfab allows designers to rapidly complete design-fabricate-test cycles, with technologies such as sub-wavelength sensors, PN junction ring modulators, silicon defect-based detectors, single photon detectors, single photon sources, and photonic wire bond integration of lasers and optical fibres.

Hyperpolarizability is a measure of the nonlinear optical characteristics of natural or meta-atoms describing how the atoms become nonlinearly polarized by the induced local-field. However, determining hyperpolarizability in the case of structured plasmonic meta-atoms is not straightforward due to their relatively larger sizes, unique shapes, and the index of refraction of the surrounding dielectric medium. Also, the order-of-magnitude of hyperpolarizability may vary with the frequency of light especially when inter-band transitions in metals become dominant. Here, we experimentally and theoretically estimated the order-of-magnitude of the 1st-order hyperpolarizability of gold meta-atoms that can be used in designing nonlinear metasurfaces.

Commercial silicon photonic (SiP) biosensor architectures rely on expensive swept-tunable lasers that limit their use for widespread, point-of-care applications. An alternative is the use of fixed wavelength lasers integrated directly on a silicon photonic platform. This study investigates the design considerations of such architectures.

A broadband and sensitive time-resolved terahertz (THz) configuration relying on noncollinear optical interactions is presented. This noncollinear scheme enables a higher THz generation and detection efficiency in nonlinear crystals. The concept relies on a pair of thick (2 mm) GaP crystals with a phase grating etched on their surface to achieve phase matching between a diffracted near-infrared pulse and a THz wave propagating at normal incidence. This system is compared to a standard collinear scheme based on thin (0.2 mm) crystals and, while both systems provide access to a spectral bandwidth extending up to 6.5 THz, it is found that the noncollinear configuration improves the THz signal by more than a factor of 400 and the dynamic range of the system by 30 dB at a frequency of 3 THz.

We demonstrate a time-resolved terahertz (THz) system taking advantage of noncollinear frequency mixing in thick generation and detection crystals to perform broadband and high-sensitivity spectroscopy. A phase grating etched at the surface of a 2 mm-thick GaP crystal is used to control phase-matching conditions by diffracting near-infrared pulses. Our dual grating configuration allows long nonlinear interaction lengths that maximize THz generation and detection efficiencies while maintaining an accessible spectral window up to 7 THz.

We propose a strategy to improve sensing performance of sub-wavelength-grating (SWG) waveguide-based sensors by introducing a substrate-overetch (SOE) geometry. The proposed SOE-SWG waveguide shows enhanced analyte interaction and a reduced group index, which improves the sensitivity of resonator-based sensors. The SiO2 overetch process was realized in Ar/C4F8/O2 plasma for 40 sec with a SiO2/Si selectivity of 10:1, obtaining a 285-nm anisotropic overetch in the SiO2 layer. Sensor performance of the SOE-SWG architecture is characterized by using isopropyl alcohol solutions, indicating an enhanced bulk sensitivity up to 575 nm/RIU (479 nm/RIU before the SOE), and a maximum waveguide mode sensitivity larger than one.

This study focuses on design of Gallium Nitride waveguides on two different substrate platforms for correlated photon pair generation

Plasmonic metasurfaces are promising as enablers of nanoscale nonlinear optics and flat nonlinear optical components. Nonlinear optical responses of such metasurfaces are determined by the nonlinear optical properties of individual nanostructured plasmonic meta-atoms, which are the building blocks of the metasurfaces. Unfortunately, no simple methods exist to determine the nonlinear coefficients (hyperpolarizabilities) of the meta-atoms hindering designing of nonlinear metasurfaces. Here, we develop the equivalent RLC circuit model of such meta-atoms to estimate their second-order nonlinear optical parameter i.e. the first-order hyperpolarizability in the optical spectral range. In parallel, we extract from second-harmonic generation experiments the spectrum of the 1st-order hyperpolarizabilities of individual meta-atoms consisting of asymmetrically shaped (elongated) plasmonic nanoprisms. Moreover, we verify our results using nonlinear hydrodynamic-FDTD and with calculations based on nonlinear scattering theory. All three approaches: analytical, experimental, and computational, yield results that agree very well. Our empirical RLC model can thus be used as a simple tool to enable efficient design of nonlinear plasmonic metasurfaces.

We experimentally measure the microscopic 2nd-order nonlinear optical response of plasmonic meta-atoms known as the 1st-order hyperpolarizability. This result is crucial to design nonlinear metasurfaces consisting of plasmonic meta-atoms.

Photonic crystal cavities on silicon-on-insulator wafers with quality factors at 70,000 level were demonstrated using a Bosch etch process, with near-vertical sidewalls.

We derive an empirical expression, based on the Wemple-DiDomenico refractive index model, useful to calculate the refractive index of III-V semiconductors as a function of the band-gap and photon energies.

Here, we experimentally determine the order-of-magnitude value of the 1st-order hyperpolarizability of plasmonic meta-atoms in metasurfaces. This result will prove useful in designing nonlinear metasurfaces for a variety of applications.

A collection of N emitters can exhibit an N-fold broadening of the radiative linewidth resulting from the development of a macroscopic dipole moment. Such a broadening of the radiative linewidth has previously been observed in systems of several nanoparticles and has often been described in terms of superradiant behavior. However, the understanding of the physics behind the observed dependence of radiative linewidth on the number of irradiated nanoparticles is far from complete. In this paper, we present theoretical and experimental results that elucidate this broadening mechanism in plasmonic systems and draw a connection with the phenomenon of Dicke superradiance. We demonstrate that, in the limit where radiative broadening dominates, the extinction linewidth of a planar array of plasmonic nanoantennas scales linearly with the number of nanoantennas contained within a circle of radius equal to the resonant optical wavelength. We explain this classical phenomenon as a weak superradiance effect, which corresponds to the case in the Dicke model where only the ground state and the first collective excited state contribute to the enhanced radiation. Publisher PDF

Efficient, broadband terahertz detection through electro-optic sampling is an enabling technology for numerous applications, including time-resolved spectroscopy of condensed matter systems and fundamental investigations of the quantum vacuum. The technique is inherently sensitive, but ultimately limited by the intrinsic optical properties of the known nonlinear crystals. In this study the authors imprint a phase grating on the surface of a nonlinear crystal, to define a noncollinear detection geometry inside the crystal. This surface grating allows improved phase-matching conditions, which lead to a doubling of detection bandwidth and efficiency.

An innovative undergraduate level Nanofabrication course with a focus on photonics is proposed. This course challenges the definition of what constitutes an undergraduate class in a research-intensive university. Namely, instructor and teaching assistants (TAs) propose a moderately challenging graduate-level research project that has not been previously published; challenge the Team, consisting of the students, with the TAs and instructor, to research during the class, as a Team; have the Team collaborate on writing a research paper with the goal of submitting it to an archival journal. Through this process, students learn the course content and experience how research is conducted.

Universal quantum computing holds the promise to fundamentally change today’s information-based society, yet a hardware platform that will provide a clear path to fault-tolerant quantum computing remains elusive. One recently proposed platform involves the use of circuit-bound photons to build cluster states and perform one-way measurement-based quantum computations on arrays of long-coherence-time solid-state spin qubits. Herein, we discuss the challenges that are faced during any practical implementation of this architecture by itemizing the key physical building blocks and the constraints imposed on the spin qubits and the photonic circuit components by the requirements of fault-tolerant performance. These considerations point to silicon as a leading candidate to host such a platform, and a roadmap for developing a silicon photonic circuit-based platform for measurement-based, fault-tolerant universal quantum computing is offered.

The AlGaAs material platform has been intensively used to develop nonlinear photonic devices on-a-chip, thanks to its superior nonlinear optical properties. We propose a new AlGaAs waveguide geometry, called half-core etched, which represents a compromise between two previously studied geometries, namely the nanowire and strip-loaded waveguides, combining their best qualities. We performed tunable four-wave mixing (FWM) experiments in all three of these geometries in the telecommunications C-band (wavelengths around 1550 nm ), with a pulsed pump beam and a continuous-wave (CW) signal beam. The maximum FWM peak efficiencies achieved in the nanowire, strip-loaded and half-core geometries were about − 5 dB , − 8 dB and − 9 dB , respectively. These values are among the highest reported in AlGaAs waveguides. The signal-to-idler conversion ranges were also remarkable: 161 nm for the strip-loaded and half-core waveguides and 152 nm for the nanowire. Based on our findings, we conclude that the half-core geometry is an alternative approach to the nanowire geometry, which has been earlier deemed the most efficient geometry, to perform wavelength conversion in the spectral region above the half-bandgap. Moreover, we show that the half-core geometry exhibits fewer issues associated with multiphoton absorption than the nanowire geometry.

We report on the study of the third-order nonlinear optical interactions in InxGa1-xAsyP1-y/InP strip-loaded waveguides. The material composition and waveguide structures were optimized for enhanced nonlinear optical interactions. We performed self-phase modulation, four-wave mixing and nonlinear absorption measurements at the pump wavelength 1568 nm in our waveguides. The nonlinear phase shift of up to 2.5 π has been observed in self-phase modulation experiments. The measured value of the two-photon absorption coefficient α 2 was 19 cm/GW. The four-wave mixing conversion range, representing the wavelength difference between maximally separated signal and idler spectral components, was observed to be 45 nm. Our results indicate that InGaAsP has a high potential as a material platform for nonlinear photonic devices, provided that the operation wavelength range outside the two-photon absorption window is selected.

Gallium Nitride (GaN), being a direct bandgap semiconductor with a wide bandgap and high thermal stability, is attractive for optoelectronic and electronic applications. Furthermore, due to its high optical nonlinearity — the characteristic of all 111-V semiconductors — GaN is also expected to be a suitable candidate for integrated nonlinear photonic circuits for a plethora of apphcations, ranging from on-chip wavelength conversion to quantum computing. Although GaN devices are in commercial production, it still suffers from lack of a suitable substrate material to reduce structural defects like high densities of threading dislocations (TDs), stacking faults, and grain boundaries. These defects significandy deteriorate the optical quality of the epi-grown GaN layer, since they act as non-radiative recombination centers. Recent studies have shown that GaN grown on (−201) β-Gallium Oxide (Ga 2 O 3 ) has superior optical quality due to a better lattice matching as compared to GaN grown on Sapphire (Al 2 O 3 ) [1-3]. In this work, we report on the fabrication of GaN waveguides on GaiOj substrate and their optical characterization to assess their feasibihty for efficient four-wave mixing (FWM).

In this study, we propose several designs for integrated waveguides based on quaternary III-V semiconductor compounds InGaAsP (on InP substrate) and AlGaAsSb (on GaSb substrate), and report on their fabrication and optical characterization. III-V semiconductor compounds tend to exhibit strong nonlinearities; these typically come along with undesirable effects such as nonlinear absorption. In quaternary III-V compounds, one has a good control over this characteristic. For instance, by shifting the band-gap wavelength through adjusting the material composition, one can change the range of wavelengths that can experience two-photon absorption. Therefore, it would be possible to minimize the losses due to nonlinear absorption [1]. Based on the possible band-gap wavelength and refractive index ranges that can be achieved in these two compounds, one can expect that both InGaAsP and AlGaAsSb waveguides can be suitable for wide-range wavelength conversion. InGaAsP waveguides can, for example, be co-integrated with InGaAsP laser sources to extend their operation ranges to longer wavelengths (2 μm and beyond). The properties of AlGaAsSb, on the other hand, allow passive waveguide devices operating in the Telecom C-band.

Gallium Nitride (GaN), along with other III-Nitrides, is attractive for optoelectronic and electronic applications due to its wide direct energy bandgap, as well as high thermal stability. GaN is transparent over a wide wavelength range from infra-red to the visible band, which makes it suitable for lasers and LEDs. It is also expected to be a suitable candidate for integrated nonlinear photonic circuits for a wide range of applications from all-optical signal processing to quantum computing and on-chip wavelength conversion. Despite its abundant use in commercial devices, there is still need for suitable substrate materials to reduce high densities of threading dislocations (TDs) and other structural defects like stacking faults, and grain boundaries. All these defects degrade the optical quality of the epi-grown GaN layer as they act as non-radiative recombination centers.

We experimentally demonstrate that the spectral sensitivity of a Mach-Zehnder (MZ) interferometer can be enhanced through structural slow light. We observe a 20-fold resolution enhancement by placing a dispersion-engineered, slow-light, photonic-crystal waveguide in one arm of a fiber-based MZ interferometer. The spectral sensitivity of the interferometer increases roughly linearly with the group index, and we have quantified the resolution in terms of the spectral density of interference fringes. These results show promise for the use of slow-light methods for developing novel tools for optical metrology and, specifically, for compact high-resolution spectrometers.

We propose nonlinear integrated waveguide designs based on semiconductors not widely used for nonlinear photonics previously. The materials belong to the group III-V and are expected to demonstrate interesting nonlinear optical properties.

Explosive growth in internet traffic has prompted huge interest in the area of all-optical signal processing. It can provide much higher data rates at much lower heat dissipation as compared to electronics. Wavelength conversion is an important aspect of all-optical signal processing, since it enables adding, dropping, multiplexing and de-multiplexing of WDM channels. All-optical wavelength conversion can readily be achieved by employing the third-order optical nonlinearity that leads to four-wave mixing (FWM).

Silicon photonic crystal waveguides have enabled a range of technologies, yet their fabrication continues to present challenges. Here, we report on a post-processing method that allows us to tune the operational wavelength of slow-light photonic crystal waveguides in concert with optical characterization, offsetting the effects of hole-radii and slab thickness variations. Our method consist of wet chemical surface oxidation, followed by oxide stripping. Theoretical modelling shows that the changes in optical behavior were predictable, and hence controlled tuning can be achieved by changing the number of processing cycles, where each cycle removes approximately 0.25 nm from all exposed surfaces, producing a blueshift of 1.6±0.1 nm in operating wavelength.

Gallium nitride (GaN), a wide-bandgap III–V semiconductor material with a bandgap wavelength λg = 366 nm (for Wurtzite GaN) and transparency window covering the visible spectrum, has a large number of applications for photonics and optoelectronics. However, the optical quality of this material suffers from growth imperfections due to the lack of a suitable substrate. Recent studies have shown that GaN grown on (−201) β – Ga2O3 (gallium oxide) has better lattice matching and hence superior optical quality as compared to GaN grown traditionally on Al2O3 (sapphire). In this work, we report on the fabrication of GaN waveguides on Ga2O3 substrate, followed by a wet-etch process aimed at the reduction of waveguide surface roughness and improvement of side-wall verticality in these waveguides. The propagation loss in the resulting waveguides has been experimentally determined to be 7.5 dB/cm.

We propose several designs of nonlinear optical waveguides based on quaternary III-V semiconductors AlGaAsSb and InGaAsP. These semiconductor materials have been widely used for laser sources. Their nonlinear optical properties, however, yet remain unexplored, while the materials definitely hold promise for nonlinear photonics on-a-chip. The latter argument is based on the fact that III-V compounds tend to exhibit high values of the nonlinear optical susceptibilities, while the nonlinear absorption in these materials can be minimized in the wavelength range of interest through a proper selection of the material composition. We present the modal analysis for the designed waveguide structures and show that the effective mode area much less than 1 μm2 can be achieved through a design optimization in each of the two compounds. We also present specific waveguide designs that demonstrate zero dispersion at the wavelengths of interest. The designed AlGaAsSb and InGaAsP waveguides are thus expected to demonstrate high values of the nonlinear coefficient and efficient nonlinear optical interactions.

We present a wet chemical method for tuning the slow light operating wavelength of silicon photonic crystal waveguides. This procedure compensates for the effects of slab thickness - and systematic hole radii - variations.

We have experimentally demonstrated broadband tuneable four-wave mixing in AlGaAs nanowires with the widths ranging between 400 and 650 nm and lengths from 0 to 2 mm. We performed a detailed experimental study of the parameters influencing the FWM performance in these devices (experimental conditions and nanowire dimensions). The maximum signal-to-idler conversion range was 100 nm, limited by the tuning range of the pump source. The maximum conversion efficiency, defined as the ratio of the output idler power to the output signal power, was -38 dB. In support of our explanation of the experimentally observed trends, we present modal analysis and group velocity dispersion numerical analysis. This study is what we believe to be a step forward towards realization of all-optical signal processing devices.

The authors report on the fabrication of GaAs nanopillars with different profiles/topologies using colloidal lithography and dry etching. GaAs nanopillars with different shapes and dimensions were successfully fabricated using inductively coupled plasma reactive ion etching. Two different etch chemistries CH4/H2/Cl2 and Ar/Cl2 were investigated. The fabricated nanopillar arrays had a typical period of ∼500 nm, and the depths could be varied from a few nanometers to 4 μm. The CH4/H2/Cl2 chemistry with optimized gas flows and plasma powers is shown to produce nanopillars with smooth sidewalls compared to those fabricated with the Ar/Cl2 chemistry. The GaAs nanopillar arrays have appreciably lower reflectivities in the measured wavelength range from 400 to 850 nm and are typically one order of magnitude lower compared to planar GaAs, which shows their potential for photovoltaic applications.

We report on fabrication and optical characterization of GaAs nanopillar (NP) arrays, obtained using a combination of low-cost mask generation by self-assembled silica particles (nanosphere lithography) and dry etching. Tapered structures (conical and frustum NP arrays) are fabricated by appropriate optimization of process parameters. Significant suppression of surface reflectance is observed for both geometries over a broad wavelength range. Simulations, based on finite difference time domain (FDTD) method, show good agreement with reflectivity measurements and serve as a guideline for design of NPs and understanding their interaction with light. A combination of wet chemical etching and sulfur–based passivation of GaAs NPs, results in more than one order of magnitude enhancement in PL intensity and recovery of PL line-width, which is very promising for photovoltaic applications.