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Register a new user1 Low power continuous-wave nonlinear optics in silica glass integrated waveguide structures
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Photonic integrated circuits (PICs) are a key component [1] for future telecommunication networks, where demands for greater bandwidth, network flexibility, low energy consumption and cost must all be met. The quest for all optical components has naturally targeted materials with extremely large nonlinearity, including chalcogenide glasses (ChG) [2] and semiconductors, such as silicon [3] and AlGaAs [4]. Yet issues such as immature fabrication technologies for ChG, and high linear and nonlinear losses for semiconductors, motivate the search for other materials. Here we present the first demonstration of nonlinear optics in integrated silica based glass waveguides using continuous wave (CW) light. We demonstrate four wave mixing (FWM), with low (7mW) CW pump power at a wavelength of 1550nm, in high index doped silica glass ring resonators capable of performing in photonic telecommunications networks as linear filters [5]. The high reliability, design flexibility, and manufacturability of our device raises the possibility of a new platform for future low cost nonlinear all optical PICs.
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Second-order nonlinear optical processes are used to convert light from one wavelength to another and to generate quantum entanglement. Creating chip-scale devices to more efficiently realize and control these interactions greatly increases the reach of photonics. Optical crystals and guided wave devices made from lithium niobate and potassium titanyl phosphate are typically used to realize second-order processes but face significant drawbacks in scalability, power, and tailorability when compared to emerging integrated photonic systems. Silicon or silicon nitride integrated photonic circuits enhance and control the third-order optical nonlinearity by confining light in dispersion-engineered waveguides and resonators. An analogous platform for second-order nonlinear optics remains an outstanding challenge in photonics. It would enable stronger interactions at lower power and reduce the number of competing nonlinear processes that emerge. Here we demonstrate efficient frequency doubling and parametric oscillation in a thin-film lithium niobate photonic circuit. Our device combines recent progress on periodically poled thin-film lithium niobate waveguidesand low-loss microresonators. Here we realize efficient >10% second-harmonic generation and parametric oscillation with microwatts of optical power using a periodically-poled thin-film lithium niobate microresonator. The operating regimes of this system are controlled using the relative detuning of the intracavity resonances. During nondegenerate oscillation, the emission wavelength is tuned over terahertz by varying the pump frequency by 100s of megahertz. We observe highly-enhanced effective third-order nonlinearities caused by cascaded second-order processes resulting in parametric oscillation. These resonant second-order nonlinear circuits will form a crucial part of the emerging nonlinear and quantum photonics platforms.
Semiconductor nanowires (NWs) are promising for realizing various on-chip nonlinear optical devices, due to their nanoscale lateral confinement and strong light-matter interaction. However, high-intensity pulsed pump lasers are typically needed to exploit their optical nonlinearity because light couples poorly with nanometric-size wires. Here, we demonstrate microwatts continuous-wave light pumped second harmonic generation (SHG) in AlGaAs NWs by integrating them with silicon planar photonic crystal cavities. Light-NW coupling is enhanced effectively by the extremely localized cavity mode at the subwavelength scale. Strong SHG is obtained even with a continuous-wave laser excitation with a pump power down to ~3 uW, and the cavity-enhancement factor is estimated around 150. Additionally, in the integrated device, the NWs SHG is more than two-order of magnitude stronger than third harmonic generations in the silicon slab, though the NW only couple s with less than 1% of the cavity mode. This significantly reduced power-requirement of NWs nonlinear frequency conversion would promote NW-based building blocks for nonlinear optics, specially in chip-integrated coherent light sources, entangled photon-pairs and signal processing devices.
We report an all-optical radio-frequency (RF) spectrum analyzer with a bandwidth greater than 5 terahertz (THz), based on a 50-cm long spiral waveguide in a CMOS-compatible high-index doped silica platform. By carefully mapping out the dispersion profile of the waveguides for different thicknesses, we identify the optimal design to achieve near zero dispersion in the C-band. To demonstrate the capability of the RF spectrum analyzer, we measure the optical output of a femtosecond fiber laser with an ultrafast optical RF spectrum in the terahertz regime.
Laser cooling of a solid is achieved when a coherent laser illuminates the material in the red tail of its absorption spectrum, and the heat is carried out by anti-Stokes fluorescence of the blue-shifted photons. Solid-state laser cooling has been successfully demonstrated in several materials, including rare-earth-doped crystals and glasses. Silica glass, being the most widely used optical material, has so far evaded all laser cooling attempts. In addition to its fundamental importance, many potential applications can be conceived for anti-Stokes fluorescence cooling of silica. These potential applications range from the substrate cooling of optical circuits for quantum information processing and cryogenic cooling of mirrors in high-sensitivity interferometers for gravitational wave detection to the heating reduction in high-power fiber lasers and amplifiers. Here we report the net cooling of high-purity Yb-doped silica glass samples that are primarily developed for high-power fiber laser applications, where special care has been taken in the fabrication process to reduce their impurities and lower their parasitic background loss. The non-radiative decay rate of the excited state in Yb ions is very small in these glasses due to the low level of impurities, resulting in near-unity quantum efficiency. We report the measurement of the cooling efficiency as a function of the laser wavelength, from which the quantum efficiency of the silica glass is calculated.
The demand for high-performance chip-scale lasers has driven rapid growth in integrated photonics. The creation of such low-noise laser sources is critical for emerging on-chip applications, ranging from coherent optical communications, photonic microwave oscillators remote sensing and optical rotational sensors. While Brillouin lasers are a promising solution to these challenges, new strategies are needed to create robust, compact, low power and low cost Brillouin laser technologies through wafer-scale integration. To date, chip-scale Brillouin lasers have remained elusive due to the difficulties in realization of these lasers on a commercial integration platform. In this paper, we demonstrate, for the first time, monolithically integrated Brillouin lasers using a wafer-scale process based on an ultra-low loss Si3N4/SiO2 waveguide platform. Cascading of stimulated Brillouin lasing to 10 Stokes orders was observed in an integrated bus-coupled resonator with a loaded Q factor exceeding 28 million. We experimentally quantify the laser performance, including threshold, slope efficiency and cascading dynamics, and compare the results with theory. The large mode volume integrated resonator and gain medium supports a TE-only resonance and unique 2.72 GHz free spectral range, essential for high performance integrated Brillouin lasing. The laser is based on a non-acoustic guiding design that supplies a broad Brillouin gain bandwidth. Characteristics for high performance lasing are demonstrated due to large intra-cavity optical power and low lasing threshold power. Consistent laser performance is reported for multiple chips across multiple wafers. This design lends itself to wafer-scale integration of practical high-yield, highly coherent Brillouin lasers on a chip.
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