Self-rolled-up microtubes have been developed over the past decade as optical ring resonators, which exhibit unique merits such as directional emission, perfect emitter-field overlap, controlled transferability and flexible structural design, and find various applications in coherent light sources, micro-sensing, nanomechanics and topological devices. Nevertheless, the reported rolled-up microtube resonators so far are based on either passive material or active media with relatively small exciton binding energy and oscillator strength, making it less favorable for strong light-matter interaction at room temperature. Although wide bandgap materials, such as GaN, ZnO and organics, exhibit large exciton binding energy and oscillator strength, it is very challenging to make such materials into 3D rolled-up structures. In this work, we overcome the technical difficulties and fabricat GaN-based self-rolled-up microtubes from coherently strained AlGaN/GaN bilayer around 50nm thick with an embedded InGaN quantum well grown by MOCVD. Such ultrathin-walled microtubes can then be easily shifted onto an etched trench to become freestanding, with a typical Q-factor measured to be over 800. Both the on-substrate and freestanding microtubes exhibit lasing at room temperature, which have not been observed on ultrathin-walled microtubes based on other materials, highlighting the outstanding optical properties of the active media. Based on the same method, we also fabricated self-bent-up microdisks which support 3-dimensional WGM with a Q-factor of ~1300 and single mode lasing at room temperature, which is not achieved by conventional microdisks with the same size and material. Such rolled-up devices provide the degree of freedom of the WGM photons in the vertical dimension and is promising for applications in multifunction on-chip devices.
Three dimensional (3-D) modeling is important in applications ranging from manufacturing to entertainment. Multiview registration is one of the crucial steps in 3-D model construction. The automatic establishment of correspondences between overlapping views, without any known initial information, is the main challenge in point clouds registration. An automatic registration algorithm is proposed to solve the registration problem of rigid, unordered, scattered point clouds. This approach is especially suitable for registering datasets that are lacking in features or texture. In general, the existing techniques exhibit significant limitations in the registration of these types of point cloud data. The presented method automatically determines the best coarse registration results by exploiting the statistical technique principal component analysis and outputs translation matrices as the initial estimation for fine registration. Then, the translation matrices obtained from coarse registration algorithms are used to update the original point cloud and the optimal translation matrices are solved using an iterative algorithm. Experimental results show that the proposed algorithm is time efficient and accurate, even if the point clouds are partially overlapped and containing large missing regions.
We report on the fabrication, characterization and integration of semiconductor microtube lasers on silicon. These
microtubes are fabricating using standard photolithography techniques on epitaxially grown strained bilayer films, and
show remarkable spectral properties attributable to whispering-gallery-mode type optical resonances. We have
demonstrated coherent emission coupled to the optical microcavity modes in both GaAs/InGaAs and InGaAsP
microtubes with embedded quantum dots. Furthermore, the GaAs/InGaAs microtubes have shown room temperature,
continuous wave lasing. The microtubes can be transferred to any foreign substrate without affecting their optical
properties. Work is in progress to couple the tubes with integrated silicon-on-insulator waveguides.
We have studied the design, fabrication and characterization of free-standing rolled-up InGaAs/GaAs quantum
dot microtube ring resonators, formed by the controlled release of coherently strained InGaAs/GaAs quantum dot
heterostructures from the host substrate. The dependence of the 3-dimenionally confined optical modes on the tube wall
thickness and surface geometry is investigated both theoretically and experimentally. We have further demonstrated
optically pumped rolled-up microtube lasers at room temperature, which exhibit emission wavelengths in the range of
1.1 - 1.3 μm and a low threshold of ~ 4 μW. The design and fabrication of electrically injected rolled-up InGaAs/GaAs
quantum dot microtube devices is also described.
We have investigated the fabrication and emission characteristics of InGaAs/GaAs quantum dot microtubebased
coherent light sources on GaAs and Si, which are formed by self-rolling of pseudomorphically strained
semiconductor bilayers through controlled release from the substrate. Tailoring of the optical modes is achieved by
engineering the shape of the microtube ring resonators. Using substrate-to-substrate transfer method, we have also
achieved, for the first time, three-dimensionally confined quantum dot microtube optical ring resonators on Si, that are
relatively free of dislocations. Sharp polarized and regularly spaced optical modes, with an intrinsic Q-factor of ~ 3,000,
were measured at 77 K.
This paper presents a thorough description of the high-frequency noise characterization and modeling of CMOS transistors for radio frequency (RF) integrated circuit (IC) design. It covers two main topics: high-frequency noise characterization and physics-based noise models. In the first section, two de-embedding procedures are presented for noise and scattering parameter de-embedding to get rid of the parasitic effects from the probe pads and interconnections in the device-under-test (DUT). With the intrinsic noise parameters, two extraction methods to obtain the channel noise, induced gate noise and their correlation in MOSFETs are discussed and experimental results are presented. Based on the noise information obtained in the first section, the second part of the paper presents physics-based noise models for the noise sources of interest in deep submicron MOSFETs. It discusses the model derivation, channel noise enhancement in deep submicron MOSFETs and impact of channel length modulation (CLM) effect. Finally a simple and accurate analytical model for channel noise calculation will be presented.