Steps on vicinal Si(001) are either one or two atomic layers high. When the tilt of the surface about [11̄0] is 2°, alternating type-A and type-B single steps dominate. When the tilt angle is increased to 4°, the steps combine to form straight, evenly spaced type-B double steps. Type-A double steps do not occur. At kinks the double steps split into single steps. Tunneling images of the double steps reveal the rebonded atoms described by the Chadi model.
A woofer–tweeter adaptive optical structured illumination microscope (AOSIM) is presented. By combining a low-spatial-frequency large-stroke deformable mirror (woofer) with a high-spatial-frequency low-stroke deformable mirror (tweeter), we are able to remove both large-amplitude and high-order aberrations. In addition, using the structured illumination method, as compared to widefield microscopy, the AOSIM can accomplish high-resolution imaging and possesses better sectioning capability. The AOSIM was tested by correcting a large aberration from a trial lens in the conjugate plane of the microscope objective aperture. The experimental results show that the AOSIM has a point spread function with an FWHM that is 140 nm wide (using a water immersion objective lens with NA=1.1) after correcting a large aberration (5.9 μm peak-to-valley wavefront error with 2.05 μm RMS aberration). After structured light illumination is applied, the results show that we are able to resolve two beads that are separated by 145 nm, 1.62× below the diffraction limit of 235 nm. Furthermore, we demonstrate the application of the AOSIM in the field of bioimaging. The sample under investigation was a green-fluorescent-protein-labeled Drosophila embryo. The aberrations from the refractive index mismatch between the microscope objective, the immersion fluid, the cover slip, and the sample itself are well corrected. Using AOSIM we were able to increase the SNR for our Drosophila embryo sample by 5×.
Focal plane array (FPA) technology is mature and is widely used for imaging applications. However, FPAs have broadband responses which limit their ability to provide high performance in hyperspectral applications such as detection of buried explosives, and identifying the presence of explosive chemicals and their concentrations. EPIR is currently developing Micro-Opto-Electro-Mechanical System (MOEMS) Fabry-Perot interferometer filter (FPF) devices for FPAs. In this paper, we present our approach to MOEMS FPF design and fabrication that will meet the size requirements for large format FPA hyperspectral imaging. We also report the performance of our FPF resonance cavity, capable of up to 3 μm change gap in tens of nanometer increments.
We demonstrate a fast, direct wavefront-sensing method for dynamic in vivo adaptive optical two-photon microscopy. By using a Shack-Hartmann wavefront sensor and open-loop control, the system provides high-speed wavefront measurement and correction. To measure the wavefront in the middle of a Drosophila embryo at early stages, autofluorescence from endogenous fluorophores in the yolk were used as reference guide stars. The method was tested through live imaging of a Drosophila embryo. The aberration in the middle of the embryo was measured directly for the first time. After correction, the contrast and signal intensity of the structure in the middle of the embryo was improved.
The Mid-wave infrared (MWIR) spectrum has applications to many fields, from night vision to chemical and biological sensors. Existing broadband detector technology based on HgCdTe allows for high sensitivity and wide range, but lacks the spectral decomposition necessary for many applications. Combining this detector technology with a tunable optical filter has been sought after, but few commercial realizations have been developed. MEMS-based optical filters have been identified as promising for their small size, light-weight, scalability and robustness of operation. In particular, Fabry-Perot interferometers with dielectric Bragg stacks used as reflective surfaces have been investigated. The integration of a detector and a filter in a device that would be compact, light-weight, inexpensive to produce and scaled for the entire range of applications could provide spectrally resolved detection in the MWIR for multiple instruments. We present a fabrication method for the optical components of such a filter. The emphasis was placed on wafer-scale fabrication with IC-compatible methods. Single, double and triple Bragg stacks composed of germanium and silicon oxide quarter-wavelength layers were designed for MWIR devices centered around 4 microns and have been fabricated on Silicon-On-Insulator (SOI) wafers, with and without anti-reflective half-wavelength silicon nitride layers. Optical testing in the MWIR and comparison of these measurements to theory and simulations are presented. The effect of film stress induced by deposition of these dielectric layers on the mechanical performance of the device is investigated. An optimal SOI substrate for the mechanical performance is determined. The fabrication flow for the optical MEMS component is also determined. Part of this work investigates device geometry and fabrication methods for scalable integration with HgCdTe detector and IC circuitry.
Optical microscopy provides noninvasive imaging of biological tissues at subcellular level. The optical aberrations induced by the inhomogeneous refractive index of biological samples limits the resolution and can decrease the penetration depth. To compensate refractive aberrations, adaptive optics with Shack-Hartmann wavefront sensing has been used in microscopes. Wavefront measurement requires light from a guide-star inside of the sample. The scattering effect limits the intensity of the guide-star, hence reducing the signal to noise ratio of the wavefront measurement. In this paper, we demonstrate the use of interferometric focusing of excitation light onto a guide-star embedded deeply in tissue to increase its fluorescent intensity, thus overcoming the excitation signal loss caused by scattering. With interferometric focusing, we more than doubled the signal to noise ratio of the laser guide-star through scattering tissue as well as potentially extend the imaging depth through using AO microscopy.
ix Conference Committee xi Introduction SESSION 1 EPIC 6898 02 Photonic crystal slow light devices in silicon (Invited Paper) [6898-55] T. F. Krauss, Univ. of St. Andrews (United Kingdom) 6898 03 Optical modulation techniques for analog signal processing and CMOS compatible electro-optic modulation (Invited Paper) [6898-52] D. M. Gill, M. Rasras, K.-Y Tu, Y.-K. Chen, A. E. White, S. S. Patel, Alcatel-Lucent Bell Labs. (USA); D. Carothers, A. Pomerene, R. Kamocsai, J. Beattie, BAE Systems (USA); A. Kopa, A. Apsel, Cornell Univ. (USA); M. Beals, J. Mitchel, J. Liu, L. C. Kimerling, Massachusetts Institute of Technology (USA) 6898 04 Process flow innovations for photonic device integration in CMOS (Invited Paper) [6898-03] M. Beals, J. Michel, J. F. Liu, D. H. Ahn, D. Sparacin, R. Sun, C. Y. Hong, L. C. Kimerling, Massachusetts Institute of Technology (USA); A. Pomerene, D. Carothers, J. Beattie, BAE Systems (USA); A. Kopa, A. Apsel, Cornell Univ. (USA); M. S. Rasras, D. M. Gill, S. S. Patel, K. Y. Tu, Y. K. Chen, A. E. White, Lucent Technologies Bell Labs. (USA) 6898 05 40-Gbps monolithically integrated transceivers in CMOS photonics (Invited Paper) [6898-01] T. Pinguet, B. Analui, G. Masini, V. Sadagopan, S. Gloeckner, Luxtera (USA) 6898 06 Photonic analog-to-digital conversion with electronic-photonic integrated circuits (Invited Paper) [6898-02] F. X. Kartner, R. Amatya, M. Araghchini, J. Birge, H. Byun, J. Chen, M. Dahlem, N. A. DiLello, F. Gan, C. W. Holzwarth, J. L. Hoyt, E. P. Ippen, A. Khilo, J. Kim, M. Kim, A. Motamedi, J. S. Orcutt, M. Park, M. Perrott, M. A. Popovi þ , R. J. Ram, H. I. Smith, G. R. Zhou, Massachusetts Institute of Technology (USA); S. J. Spector, T. M. Lyszczarz, M. W. Geis, D. M. Lennon, J. U. Yoon, M. E. Grein, R. T. Schulein, Massachusetts Institute of Technology, Lincoln Lab. (USA) SESSION 2 INTEGRATION 6898 08 Ge photodetectors integrated in CMOS photonic circuits (Invited Paper) [6898-04] G. Masini, S. Sahni, Luxtera (USA); G. Capellini, Univ. Roma Tre (Italy); J. Witzens, J. White, D. Song, C. Gunn, Luxtera (USA) 6898 09 Toward silicon-based longwave integrated optoelectronics (LIO) (Invited Paper) [6898-05] R. Soref, Air Force Research Lab. (USA) 6898 0A Efficient silicon-photonic modulator with recessed electrodes [6898-06] D. W. Zheng, B. T. Smith, M. Asghari, Kotura, Inc. (USA)
We present an investigation of the structural properties, atomic structure, adsorbate mode of growth, and interface formation of the room-temperature K/Si(100)2\ifmmode\times\else\texttimes\fi{}1 system by a combination of core-level and valence-band photoemission spectroscopies using synchrotron-radiation and scanning-tunneling-microscopy experiments. The results indicate that, at saturation coverage, the potassium atoms appear to form one-dimensional chains parallel to the silicon dimer rows along the 〈110〉 direction 7.68 \AA{} apart with a single site of adsorption. These K chains pass over the surface step edges to be connected between themselves. The growth and occurrence of a second layer are clearly related to the presence of impurities which, even at very low levels, are shown to significantly increase the K sticking coefficient. It demonstrates the extreme sensitivity of this system and stresses the crucial importance of quality in surface preparation and alkali-metal deposition. At a lower coverage, the K atoms are adsorbed on various coexisting sites with no long-range order. An ordering transition leading to the formation of the one-dimensional linear K metallic chains occurs. The adsorbate-adsorbate interaction is the dominant driving force in this adsorbate-ordering transition. The valence-band results indicate that the K atoms are covalently bonded to the Si atoms through the dangling bond, which makes the cave the most favorable adsorption site for the K atoms. This investigation brings new insights into the understanding of the structural properties of (alkali metal)/Si(100)2\ifmmode\times\else\texttimes\fi{}1 systems.
Microelectromechanical systems (MEMS) fabrication developed out of the thin-film processes first used for semiconductor fabrication. To understand the unique features of the MEMS fabrication process it is helpful to consider the semiconductor fabrication process.
