Objective: To demonstrate optical coherence tomography for high-resolution, noninvasive imaging of the human retina. Optical coherence tomography is a new imaging technique analogous to ultrasound B scan that can provide cross-sectional images of the retina with micrometer-scale resolution. Design: Survey optical coherence tomographic examination of the retina, including the macula and optic nerve head in normal human subjects. Settings Research laboratory. Participants: Convenience sample of normal human subjects. Main Outcome Measures: Correlation of optical coherence retinal tomographs with known normal retinal anatomy. Results: Optical coherence tomographs can discriminate the cross-sectional morphologic features of the fovea and optic disc, the layered structure of the retina, and normal anatomic variations in retinal and retinal nerve fiber layer thicknesses with 10- μm depth resolution. Conclusion: Optical coherence tomography is a potentially useful technique for high depth resolution, cross-sectional examination of the fundus.

Optical Coherence Tomography of the Human Retina

In this paper, we present two novel algorithms to realize a finite dimensional, linear time-invariant state-space model from input-output data. The algorithms have a number of common features. They are classified as one of the subspace model identification schemes, in that a major part of the identification problem consists of calculating specially structured subspaces of spaces defined by the input-output data. This structure is then exploited in the calculation of a realization. Another common feature is their algorithmic organization: an RQ factorization followed by a singular value decomposition and the solution of an overdetermined set (or sets) of equations. The schemes assume that the underlying system has an output-error structure and that a measurable input sequence is available. The latter characteristic indicates that both schemes are versions of the MIMO Output-Error State Space model identification (MOESP) approach. The first algorithm is denoted in particular as the (elementary MOESP scheme)...

Subspace model identification-Part 1. The output-error state-space model identification class of algorithms

Introduction Part I: Preliminaries Linear Algebra and Preliminaries Disctrete-time Linear Systems Stochastic Processes Kalman Filter Part II: Realization Theory Realization of Deterministic Problems Stochastic Realization Theory I Stochastic Realization Theory II Part III: Subspace Identification Subspace Identification I: ORT Subspace Identification II: CCA Identification of Closed-loop System Appendices Least-squares Method Input Signals for System Identification Overlapping Parametrization Matlab(R) Programs Solutions to Problems

Subspace methods for system identification

OBJECTIVE\nTo analyze glaucomatous eyes with known focal defects of the nerve fiber layer (NFL), relating optical coherence tomography (OCT) findings to clinical examination, NFL and stereoscopic optic nerve head (ONH) photography, and Humphrey 24-2 visual fields.\n\n\nDESIGN\nCross-sectional prevalence study.\n\n\nPARTICIPANTS\nThe authors followed 19 patients in the study group and 14 patients in the control group.\n\n\nINTERVENTION\nImaging with OCT was performed circumferentially around the ONH with a circle diameter of 3.4 mm using an internal fixation technique. One hundred OCT scan points taken within 2.5 seconds were analyzed.\n\n\nMAIN OUTCOME MEASURES\nMeasurements of NFL thickness using OCT were performed.\n\n\nRESULTS\nIn most eyes with focal NFL defects, OCTs showed significant thinning of the NFL in areas closely corresponding to focal defects visible on clinical examination, to red-free photographs, and to defects on the Humphrey visual fields. Optical coherence tomography enabled the detection of focal defects in the NFL with a sensitivity of 65% and a specificity of 81%.\n\n\nCONCLUSION\nAnalysis of NFL thickness in eyes with focal defects showed good structural and functional correlation with clinical parameters. Optical coherence tomography contributes to the identification of focal defects in the NFL that occur in early stages of glaucoma.

Evaluation of focal defects in the nerve fiber layer using optical coherence tomography

This paper exploits the concept of a predictor space in the minimal realization problem for systems generating an analytic impulse response matrix. The predictor space constructed, by stochastic input and output processes forms the state space for the stochastic system representation, where a system is represented by the basis of the predictor space and the innovation process of input. The minimal realization problem is then solved for a given analytic impulse response matrix by defining a stochastic system driven by white noise whose input-output covariance equals the given impulse response matrix. It is shown that the coefficient matrices of the stochastic system representation constitute a solution to the minimal realization problem for the deterministic system with given impulse response matrix. The paper provides a unifying overview to many aspects of the realization problem and its algorithms.

Stochastic theory of minimal realization

Objective: To evaluate the retinal nerve fiber layer (RNFL) thickness in patients with unilateral pseudoexfoliation syndrome (PXS) without glaucoma by using optical coherence tomogr

Analysis of Retinal Nerve Fiber Layer Thickness in Patients with Pseudoexfoliation Syndrome Using Optical Coherence Tomography

Cell library is the keystone component that enables adoption of advanced electronic design automation (EDA) tools, such as logic synthesis and automatic place-and-route. The EDA tools are essential for scaling circuit complexity by orders of magnitude. We have designed a dual RSFQ/ERSFQ cell library for the MIT-LL SFQ5ee process, that can be used with the superconductor EDA tools suite that is being developed. In addition to satisfying the margins criterion, the performance of each cell has been optimized for Monte-Carlo statistical variations across multiple process corners including minimizing the spread of timing distributions. To enable a digital design flow using HDL simulations with timing back-annotation Liberty files have been developed for multiple process corners, using the load-dependent timing char-acterization. The cells have been designed for a standard height of 40 μm with a grid size of 20 μm. The library provides dedicated tracks for signal and power routing. Multiple independent biases are supported for RSFQ designs. The cells can be interconnected either by abutting or using passive transmission lines. Dedicated moat slots have been provided which are uniformly distributed across the cell. All cells are re-optimized post-layout. The library currently contains 22 unique types of cells. Initial validation of the cell library was performed by designing RSFQ and ERSFQ shift registers for the MIT-LL SFQ5ee fabrication process, which yielded wide operating margins. In addition, we present measurement results for a chip designed and fabricated to characterize several library cells using a multiplexing scheme.

Superconductor Standard Cell Library for Advanced EDA Design

As superconducting circuits grow in complexity, full transient simulation and verification at the Josephson junction level using analog circuit simulators become increasingly computationally expensive. To enable faster functional and timing verification using timing back annotation and static timing analysis, logic models of rapid single flux quantum library cells are developed using hardware description languages like Verilog together with the required timing characteristics. These include propagation delays and minimum pin-to-pin pulse arrival time separation at various process and operating corners. These timing parameters must satisfy required margins and yield using Monte Carlo simulations with statistical variations. For each library cell, these timing parameters depend not only on the adjacent cells but also on their internal states. These delay variations are driven by bias current redistribution, load inductance, and load junction critical currents. We present our methodology for extracting these timing parameters to enable timing back annotation and static timing analysis. We demonstrate our methodology with a parallel counter as a reference circuit and show that timing back annotated simulation can closely match results from full circuit simulation.

Timing Characterization for RSFQ Cell Library

Rapid single flux quantum technology is one of the most promising developments for future high-speed microprocessors, network routers, and analog-to-digital converters. This technology is based on well-timed signals and fast signal transmission. However, as the complexity of the circuits or the operating frequency of these signals increase, it becomes harder to achieve a successful timing scheme. Another case that prevents successful timing is thermal noise, which becomes more significant with the increase of the number of cells. Earlier studies on noise analysis show that the timing variations of the delay on a cascaded path vary up to 10% compared with the delay of the same type of single cell. On the other hand, circuit parameters may change during the fabrication process, and as a result, timing of the cell differs from the design value. For these reasons, we define a statistical model for the wiring cells, such as Josephson transmission lines, splitters, and mergers that can be used to calculate the timing delay and jitter instead of time-consuming simulations. We also discuss a possible method to identify the sensitive paths to the delay fluctuations among different alternatives. In this study, we analyze the delay and the jitter of cascaded combinations of the most common wiring cells to determine the correlation effect on delay and jitter between the consecutive gates. Then, we propose a statistical method to analyze these timings faster and easier. Finally, we discussed how to estimate the output probability of the clocked gates without performing an actual simulation.

A Statistical Approach to Delay, Jitter and Timing of Signals of RSFQ Wiring Cells and Clocked Gates

We designed and tested the digital readout circuitry for superconducting nanowire single-photon detectors (SNSPDs). The designed time-to-digital converter (TDC) comprises a decision-making block, a clock controller, and a counter with parallel-to-serial (P2S) interface. We also designed an on-chip pattern generator to imitate a digitized SNSPD response that allowed us to screen the circuitry without bonding actual SNSPDs. Both rapid single-flux quantum (RSFQ) and its energy-efficient rapid single-flux quantum (ERSFQ) versions were designed for comparison and debugging purposes. To optimize the design of the feeding Josephson transmission line (FJTL) required by the ERSFQ variant, we compared different power grid structures and types of FJTLs. Using an 8-bit counter with P2S interface as a device under test, we also investigated the effect of FJTL's size on the bias margins. FJTL with a 75% junction overhead is sufficient for the ERSFQ circuit to match the margins of its RSFQ counterpart. All chips have been fabricated at MIT-LL using the SFQ5ee process node. Experimental results and future research directions are presented.

Mustafa Eren Celik

Papers

Analysis of Retinal Nerve Fiber Layer Thickness in Patients with Pseudoexfoliation Syndrome Using Optical Coherence Tomography

Superconductor Standard Cell Library for Advanced EDA Design

Timing Characterization for RSFQ Cell Library

A Statistical Approach to Delay, Jitter and Timing of Signals of RSFQ Wiring Cells and Clocked Gates

Low-Power Digital Readout Circuit for Superconductor Nanowire Single-Photon Detectors