Here, we report
A novel characterization method is proposed to extract the optical frequency field-effect mobility (
- Publication Date:
- NSF-PAR ID:
- Journal Name:
- Photonics Research
- Page Range or eLocation-ID:
- Article No. 615
- Optical Society of America
- Sponsoring Org:
- National Science Foundation
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Here, we report
-based optical parametric oscillation (OPO) with widely separated signal–idler frequencies from crystalline aluminum nitride microrings pumped at . By tailoring the width of the microring, OPO reaching toward the telecom and mid-infrared bands with a frequency separation of 64.2 THz is achieved. While dispersion engineering through changing the microring width is capable of shifting the OPO sideband by , the OPO frequency can also be agilely tuned in the ranges of 1 and 0.1 THz, respectively, by shifting the pump wavelength and controlling the chip’s temperature. At high pump powers, the OPO sidebands further evolve into localized frequency comb lines. Such large-frequency-shift OPO with flexible wavelength tunability will lead to enhanced chip-scale light sources.
Materials with strong second-order (
) optical nonlinearity, especially lithium niobate, play a critical role in building optical parametric oscillators (OPOs). However, chip-scale integration of low-loss materials remains challenging and limits the threshold power of on-chip OPO. Here we report an on-chip lithium niobate optical parametric oscillator at the telecom wavelengths using a quasi-phase-matched, high-quality microring resonator, whose threshold power ( ) is 400 times lower than that in previous integrated photonics platforms. An on-chip power conversion efficiency of 11% is obtained from pump to signal and idler fields at a pump power of 93 µW. The OPO wavelength tuning is achieved by varying the pump frequency and chip temperature. With the lowest power threshold among all on-chip OPOs demonstrated so far, as well as advantages including high conversion efficiency, flexibility in quasi-phase-matching, and device scalability, the thin-film lithium niobate OPO opens new opportunities for chip-based tunable classical and quantum light sources and provides a potential platform for realizing photonic neural networks.
The mid-IR spectroscopic properties of
doped low-phonon and crystals grown by the Bridgman technique have been investigated. Using optical excitations at and , both crystals exhibited IR emissions at , , , and at room temperature. The mid-IR emission at 4.5 µm, originating from the transition, showed a long emission lifetime of for doped , whereas doped exhibited a shorter lifetime of . The measured emission lifetimes of the state were nearly independent of the temperature, indicating a negligibly small nonradiative decay rate through multiphonon relaxation, as predicted by the energy-gap law for low-maximum-phonon energy hosts. The room temperature stimulatedmore »
Variability of relationship between the volume scattering function at 180° and the backscattering coefficient for aquatic particles
Properly interpreting lidar (light detection and ranging) signal for characterizing particle distribution relies on a key parameter,
, which relates the particulate volume scattering function (VSF) at 180° ( ) that a lidar measures to the particulate backscattering coefficient ( ). However, has been seldom studied due to challenges in accurately measuring and concurrently in the field. In this study, , as well as its spectral dependence, was re-examined using the VSFs measured in situat high angular resolution in a wide range of waters. , while not measured directly, was inferred using a physically sound, well-validated VSF-inversion method. The effects of particle shape and internal structure on the inversion were tested using three inversion kernels consisting of phase functions computed for particles that are assumed as homogenous sphere, homogenous asymmetric hexahedra, or coated sphere. The reconstructed VSFs using any of the three kernels agreed well with the measured VSFs with a mean percentage difference at scattering angles . At angles immediately near or equal to 180°, the reconstructed depends strongly on the inversion kernel. derived with the sphere kernels was smaller than those derived with the hexahedra kernel but consistent with estimated directly from high-spectral-resolution lidar and in situbackscattering sensor. The possible explanation was that the sphere kernels are able to capture the backscattering enhancement feature near 180° that has been observed for marine particles. derived using the coated sphere kernel was generally lower than those derived with the homogenous sphere kernel. Our result suggests that is sensitive to the shape and internal structure of particles and significant error could be induced if a fixed value of is to be used to interpret lidar signal collected in different waters. On the other hand, showed little spectral dependence.
The use of multispectral geostationary satellites to study aquatic ecosystems improves the temporal frequency of observations and mitigates cloud obstruction, but no operational capability presently exists for the coastal and inland waters of the United States. The Advanced Baseline Imager (ABI) on the current iteration of the Geostationary Operational Environmental Satellites, termed the
Series (GOES-R), however, provides sub-hourly imagery and the opportunity to overcome this deficit and to leverage a large repository of existing GOES-R aquatic observations. The fulfillment of this opportunity is assessed herein using a spectrally simplified, two-channel aquatic algorithm consistent with ABI wave bands to estimate the diffuse attenuation coefficient for photosynthetically available radiation, . First, an in situABI dataset was synthesized using a globally representative dataset of above- and in-water radiometric data products. Values of were estimated by fitting the ratio of the shortest and longest visible wave bands from the in situABI dataset to coincident, in situ data products. The algorithm was evaluated based on an iterative cross-validation analysis in which 80% of the dataset was randomly partitioned for fitting and the remaining 20%more »