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Microring resonators in Ta2O5 platform are demonstrated at 780 nm with quality factors > 1.4 million. Devices are engineered with tunable on-chip reflections to create effective cavity lengths of ~ 300 mm, suitable for compact, narrow-linewidth lasers.

In this work, we investigated the edge doping effect to graphene plasmon resonances in graphene nanoribbons (GNRs), which is known to affect the electronic doping of GNRs but has not been systematically studied. We found the Fermi levels, which reflect that the sheet charge carrier densities, extracted from the graphene plasmon resonance frequencies, vary across GNRs of different widths on the same sample. Using Raman spectroscopy, we confirmed that the variation of the sheet charge carrier density is caused by edge doping, which has a stronger effect on narrower GNRs. To further understand the edge doping effect, electron beam irradiation (EBI) is applied to modify the charge state of the edge. Using EBI, we successfully demonstrated the tuning of the graphene plasmon resonances due to the change of the edge doping states. These findings demonstrated the importance of the edge doping effect in determination of the surface plasmon frequency in GNRs.

Nonlinear frequency conversion plays a crucial role in advancing the functionality of next-generation optical systems. Portable metrology references and quantum networks will demand highly efficient second-order nonlinear devices, and the intense nonlinear interactions of nanophotonic waveguides can be leveraged to meet these requirements. Here we demonstrate second harmonic generation (SHG) in GaAs-on-insulator waveguides with unprecedented efficiency of 40 W$^{-1}$ for a single-pass device. This result is achieved by minimizing the propagation loss and optimizing phase-matching. We investigate surface-state absorption and design the waveguide geometry for modal phase-matching with tolerance to fabrication variation. A 2.0 $\mu$m pump is converted to a 1.0 $\mu$m signal in a length of 2.9 mm with a wide signal bandwidth of 148 GHz. Tunable and efficient operation is demonstrated over a temperature range of 45 $^{\circ}$C with a slope of 0.24 nm/$^{\circ}$C. Wafer-bonding between GaAs and SiO$_2$ is optimized to minimize waveguide loss, and the devices are fabricated on 76 mm wafers with high uniformity. We expect this device to enable fully integrated self-referenced frequency combs and high-rate entangled photon pair generation., Comment: 7 pages, 7 figures

The mid-infrared atmospheric window of $3--5.5\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ holds valuable information regarding molecular composition and function for fundamental and applied spectroscopy. Using a robust, mode-locked fiber-laser source of $l11\text{ }\mathrm{fs}$ pulses in the near infrared, we explore quadratic (${\ensuremath{\chi}}^{(2)}$) nonlinear optical processes leading to frequency comb generation across this entire mid-infrared atmospheric window. With experiments and modeling, we demonstrate intrapulse difference frequency generation that yields few-cycle mid-infrared pulses in a single pass through periodically poled lithium niobate. Harmonic and cascaded ${\ensuremath{\chi}}^{(2)}$ nonlinearities further provide direct access to the carrier-envelope offset frequency of the near infrared driving pulse train. The high frequency stability of the mid-infrared frequency comb is exploited for spectroscopy of acetone and carbonyl sulfide with simultaneous bandwidths exceeding 11 THz and with spectral resolution as high as $0.003\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$. The combination of low noise and broad spectral coverage enables detection of trace gases with concentrations in the part-per-billion range.

Palladium germanide thin films were investigated for infrared plasmonic applications. Palladium thin films were deposited onto amorphous germanium thin films and subsequently annealed at a range of temperatures. X-ray diffraction was used to identify stoichiometry, and Scanning Electron Micrographs, along with Energy Dispersive Spectroscopy (EDS) was used to characterize composition and film quality. Resistivity was also measured for analysis. Complex permittivity spectra were measured from 0.3 to 15 µm using IR ellipsometry. From this, surface plasmon polariton (SPP) characteristics such as propagation length and mode confinement were calculated and used to determine appropriate spectral windows for plasmonic applications with respect to film characteristics. Films were evaluated for use with on-chip plasmonic components.

The mid-infrared atmospheric window of 3-5.5 μm holds valuable information regarding molecular composition and function for fundamental and applied spectroscopy. Using a robust, mode-locked fiber-laser source of11 fs pulses in the near infrared, we explore quadratic (χ^{(2)}) nonlinear optical processes leading to frequency comb generation across this entire mid-infrared atmospheric window. With experiments and modeling, we demonstrate intrapulse difference frequency generation that yields few-cycle mid-infrared pulses in a single pass through periodically poled lithium niobate. Harmonic and cascaded χ^{(2)} nonlinearities further provide direct access to the carrier-envelope offset frequency of the near infrared driving pulse train. The high frequency stability of the mid-infrared frequency comb is exploited for spectroscopy of acetone and carbonyl sulfide with simultaneous bandwidths exceeding 11 THz and with spectral resolution as high as 0.003 cm^{-1}. The combination of low noise and broad spectral coverage enables detection of trace gases with concentrations in the part-per-billion range.

Second-harmonic generation is demonstrated with 38 W-1 conversion efficiency in a single-pass waveguide. A highly uniform wafer-scale process is used to fabricate these devices, which are suitable for frequency-comb stabilization.

We demonstrate a polarization rotator integrated at the output of a GaAs waveguide producing type I second harmonic generation (SHG). Form-birefringent phase matching between the pump fundamental transverse electric (TE) mode near 2.0 $\mu$m wavelength and the signal fundamental transverse magnetic (TM) mode efficiently generates light at 1.0 $\mu$m wavelength. A SiN waveguide layer is integrated with the SHG device to form a multi-functional photonic integrated circuit. The polarization rotator couples light between the two layers and rotates the polarization from TM to TE or from TE to TM. With a TE-polarized 2.0 $\mu$m pump, type I SHG is demonstrated with the signal rotated to TE polarization. Passive transmission near 1.0 $\mu$m wavelength shows ~80 % polarization rotation across a broad bandwidth of ~100 nm. By rotating the signal polarization to match that of the pump, this SHG device demonstrates a critical component of an integrated self-referenced octave-spanning frequency comb. This device is expected to provide crucial functionality as part of a fully integrated optical frequency synthesizer with resolution of less than one part in 10$^{14}$., Comment: 7 pages, 7 figures

International audience; We describe molecular beam epitaxy (MBE) growth conditions for self-assembled indium nanostructures, or islands, which allow for the tuning of the density and size of the indium nanostructures. How the plasmonic resonance of indium nanostructures is affected by the island density, size, distribution in sizes, and indium purity of the nanostructures is explored. These self-assembled nanostructures provide a platform for integration of resonant and non-resonant plasmonic structures within a few nm of quantum wells (QWs) or quantum dots (QDs) in a single process. A 4× increase in peak photoluminescence intensity is demonstrated for near-surface QDs resonantly coupled to indium nanostructures

A nonlinear platform using gallium arsenide (GaAs) waveguides cladded with SiO 2 has been demonstrated on silicon substrates. It is suitable for efficient nonlinear applications. Second harmonic generation (SHG) with record-high efficiency of 38, 000% W−1 cm−2 has been achieved.

We demonstrate wide-band frequency down-conversion to the mid-infrared (MIR) using four-wave mixing (FWM) of near-infrared (NIR) femtosecond-duration pulses from an Er:fiber laser, corresponding to 100 THz spectral translation. Photonic-chip-based silicon nitride waveguides provide the FWM medium. Engineered dispersion in the nanophotonic geometry and the wide transparency range of silicon nitride enable large-detuning FWM phase-matching and results in tunable MIR from 2.6 to 3.6 μm on a single chip with 100-pJ-scale pump-pulse energies. Additionally, we observe up to 25 dB broadband parametric gain for NIR pulses when the FWM process is operated in a frequency up-conversion configuration. Our results demonstrate how integrated photonic circuits pumped with fiber lasers could realize multiple nonlinear optical phenomena on the same chip and lead to engineered synthesis of broadband, tunable, and coherent light across the NIR and MIR wavelength bands.

We demonstrate plasma-deposited (temperature < 300°C), deuterated silicon nitride waveguides with 0.22 dB/cm propagation loss at λ = 1552 nm. Pumping at λ = 1560 nm, we obtain a 550 nm-bandwidth Kerr-microcomb and octave-spanning supercontinuum.

We present a scheme for generating super-octave, long-wave infrared combs in the molecular fingerprint region using intra-pulse difference frequency generation in an orientation patterned GaP crystal. We demonstrate high resolution dual-comb spectroscopy in methanol vapor.

Suspended-silicon waveguides are used for broadband mid-IR supercontinuum with low input power. Pumped with 100 fs, 3 pm pulses, these devices extend the mid-IR comb coverage across 126 THz from 1.74 pm to 6 pm.

Using all-silicon fusion-bonded membrane waveguides, we demonstrate efficient input/output couplers with 1.8 dB loss at λ = 3.06 μm 1×2 power splitters (Y- and MMI-type), 25 μm bends, and 0.35 dB transitions to fusion-sealed micro-channels.

Using an amplified single-branch Er:fiber laser (100 MHz), we generate infrared (3– 12 µm) frequency combs in a combination of lithium niobate and orientation-patterned gallium phosphide. Dual-comb spectroscopy of trace gases and alcohol vapors is demonstrated.

We demonstrate nanophotonic waveguides for mid-infrared supercontinuum generation and high-harmonic generation. The waveguide geometry enables phase-matching of harmonic generation to higher-order modes. Simulations reveal how periodic poling enables high-harmonic generation through a cascaded mechanism.

We experimentally demonstrate a simple configuration for mid-infrared (MIR) frequency comb generation in quasi-phase-matched lithium niobate waveguides using the cascaded-$\chi^{(2)}$ nonlinearity. With nanojoule-scale pulses from an Er:fiber laser, we observe octave-spanning supercontinuum in the near-infrared with dispersive-wave generation in the 2.5--3 $\text{\mu}$m region and intra-pulse difference-frequency generation in the 4--5 $\text{\mu}$m region. By engineering the quasi-phase-matched grating profiles, tunable, narrow-band MIR and broadband MIR spectra are both observed in this geometry. Finally, we perform numerical modeling using a nonlinear envelope equation, which shows good quantitative agreement with the experiment---and can be used to inform waveguide designs to tailor the MIR frequency combs. Our results identify a path to a simple single-branch approach to mid-infrared frequency comb generation in a compact platform using commercial Er:fiber technology.

We present a new class of photon pair sources on a silicon chip. The source is based on nanophotonic periodically poled lithium niobate waveguides and presents MHz rate pair generation.

We experimentally demonstrate broadband mid-infrared (3-5 μm) frequency combs in quasi-phase-matched lithium niobate waveguides leveraging cascaded-x(2) supercontinuum generation and difference-frequency generation pumped by an Er:fiber laser.

We spectrally resolve the second-order coherence of biphoton pairs using a time-of-flight fiber spectrometer. Spectrally resolved coincidence-to-accidental ratios of over 300 are measured using a thin-film lithium niobate waveguide source on a silicon chip.

Infrared spectroscopy is a powerful tool for basic and applied science. The molecular spectral fingerprints in the 3 um to 20 um region provide a means to uniquely identify molecular structure for fundamental spectroscopy, atmospheric chemistry, trace and hazardous gas detection, and biological microscopy. Driven by such applications, the development of low-noise, coherent laser sources with broad, tunable coverage is a topic of great interest. Laser frequency combs possess a unique combination of precisely defined spectral lines and broad bandwidth that can enable the above-mentioned applications. Here, we leverage robust fabrication and geometrical dispersion engineering of silicon nanophotonic waveguides for coherent frequency comb generation spanning 70 THz in the mid-infrared (2.5 um to 6.2 um). Precise waveguide fabrication provides significant spectral broadening and engineered spectra targeted at specific mid-infrared bands. We use this coherent light source for dual-comb spectroscopy at 5 um., 26 pages, 5 figures

We present an approach to fabrication and packaging of integrated photonic devices that utilizes waveguide and detector layers deposited at near-ambient temperature. All lithography is performed with a 365 nm i-line stepper, facilitating low cost and high scalability. We have shown low-loss SiN waveguides, high-$Q$ ring resonators, critically coupled ring resonators, 50/50 beam splitters, Mach-Zehnder interferometers (MZIs) and a process-agnostic fiber packaging scheme. We have further explored the utility of this process for applications in nonlinear optics and quantum photonics. We demonstrate spectral tailoring and octave-spanning supercontinuum generation as well as the integration of superconducting nanowire single photon detectors with MZIs and channel-dropping filters. The packaging approach is suitable for operation up to 160 \degree C as well as below 1 K. The process is well suited for augmentation of existing foundry capabilities or as a stand-alone process.

We utilize silicon-nitride waveguides to self-reference a telecom-wavelength fiber frequency comb through supercontinuum generation, using 11.3 mW of optical power incident on the chip. This is approximately ten times lower than conventional approaches using nonlinear fibers and is enabled by low-loss (

The microscale integration of mid- and long-wave-infrared photonics could enable the development of fieldable, robust chemical sensors, as well as highly efficient infrared frequency converters. However, such technology would be defined by the choice of material platform, which immediately determines the strength and types of optical nonlinearities available, the optical transparency window, modal confinement, and physical robustness. In this work, we demonstrate a new platform, suspended AlGaAs waveguides integrated on silicon, providing excellent performance in all of these metrics. We demonstrate low propagation losses within a span of nearly two octaves (1.26–4.6 μm) with exemplary performance of 0.45 dB/cm at λ=2.4 μm. We exploit the high nonlinearity of this platform to demonstrate 1560 nm-pumped second-harmonic generation and octave-spanning supercontinuum reaching out to 2.3 μm with 3.4 pJ pump pulse energy. With mid-IR pumping, we generate supercontinuum spanning from 2.3 to 6.5 μm. Finally, we demonstrate the versatility of the platform with mid-infrared passive devices such as low-loss 10 μm-radius bends, compact power splitters with 96±1% efficiency, and edge couplers with 3.0±0.1 dB loss. This platform has strong potential for multifunctional integrated photonic systems in the mid-infrared.

We demonstrate octave-spanning long-wave infrared light generation from 6—12 µm via intra-pulse difference-frequency-generation driven by a few-cycle pulse from an amplified Er:fiber frequency comb in orientation-patterned gallium phosphide.

We demonstrate the generation of broadband (6—12 μm) long-wave infrared frequency combs via intra-pulse difference-frequency generation in orientation-patterned gallium phosphide and use the source to perform dual-comb spectroscopy on methanol.

We demonstrate mid-infrared frequency comb generation via optical parametric amplification in lithium niobate and silicon-nitride waveguides, tunable from 3.5—5 µm and 2.5—3.5 µm, respectively.