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Ultrafast measurements of optical spectral coherence by single-shot time-stretch interferometry.

ABSTRACT: The palette of laser technology has significantly been enriched by the innovations in ultrafast optical pulse generation. Our knowledge of the complex pulse dynamics, which is often highly nonlinear and stochastic in nature, is however limited by the scarcity of technologies that can measure fast variation/fluctuation of the spectral phase (or coherence) and amplitude in real-time, continuously. To achieve this goal, we demonstrate ultrafast interferometry enabled by optical time-stretch for real- time spectral coherence characterization with microsecond-resolution. Accessing the single-shot interferograms continuously, it further reveals the degree of second-order coherence, defined by the cross-spectral density function, at high speed-a capability absent in any existing spectroscopic measurement tools. As the technique can simultaneously measure both the high-speed variations of spectrally resolved coherence and intensity, time-stretch interferometry could create a new arena for ultrafast pulse characterization, especially favorable for probing and understanding the non-repetitive or stochastic dynamics in real-time.

SUBMITTER: Xu Y

PROVIDER: S-EPMC4904794 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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Ultrafast measurements of optical spectral coherence by single-shot time-stretch interferometry.

Xu Yiqing Y Wei Xiaoming X Ren Zhibo Z Wong Kenneth K Y KK Tsia Kevin K KK

Scientific reports 20160613

The palette of laser technology has significantly been enriched by the innovations in ultrafast optical pulse generation. Our knowledge of the complex pulse dynamics, which is often highly nonlinear and stochastic in nature, is however limited by the scarcity of technologies that can measure fast variation/fluctuation of the spectral phase (or coherence) and amplitude in real-time, continuously. To achieve this goal, we demonstrate ultrafast interferometry enabled by optical time-stretch for rea ...[more]

PMID: 27295560

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Project description:PURPOSE:Central foveal thickness (CFT) measurements from optical coherence tomography (OCT) scans provide a precise measure of severity of pathologic changes in the fovea, progress of disease and response to treatment. Although these measures are additionally valuable to assess foveal development in infants, their reproducibility is not known. The goal of this retrospective study is to evaluate the variation and reproducibility of CFT measurements using handheld spectral-domain OCT (hh-SDOCT) in supine infants compared to conventional adult tabletop imaging. METHODS:Imaging sessions with multiple macular, volume scans in one eye were selected for analysis from two participant groups: Group 1, 25 imaging sessions from 21 preterm infants without macular edema imaged supine in the nursery using hh-SDOCT (Leica/Bioptigen Envisu C2300, RTP, NC); Group 2, 25 imaging sessions from 25 adults imaged using tabletop Bioptigen SDOCT. For each imaging session, three macular OCT volumes with acceptable image quality were selected for analysis. CFTs were measured using a customized script for automatic segmentation. An expert grader and a typical grader corrected the segmentation lines for the central foveal frame. Coefficient of variations (CV) and intraclass correlation coefficients (ICC) were calculated for graders and systems and compared to the previous literature on OCT reproducibility. RESULTS:CFT measurements were repeatable and reproducible for both handheld and tabletop SDOCT systems. For handheld, grader ICC (CI) and mean CV were 0.94 (0.90-0.97) and 3.8 (typical) and 0.98 (0.96-0.99) and 2.9 (expert), and for tabletop were 0.91(0.83-0.96) and 2.1 (typical) and 0.92 (0.86-0.96) and 1.9 (expert). Intergrader reproducibility of handheld and tabletop SDOCT systems were ICC(CI) 0.97 (0.95-0.98) and 0.93 (0.89-0.96) respectively, and both are comparable to previously reported reproducibility of tabletop systems. CONCLUSION:Handheld SDOCT is a reproducible instrument to measure foveal thicknesses in supine infants. It can be used in clinical research to evaluate foveal changes during retinal development and pathological conditions.

Project description:Understanding measurement variability and relationships between measurements obtained on different optical coherence tomography (OCT) machines is critical for clinical trials and clinical settings.To evaluate the reproducibility of retinal thickness measurements from OCT images obtained by time-domain (TD) (Stratus; Carl Zeiss Meditec) and spectral-domain (SD) (Cirrus; Carl Zeiss Meditec, and Spectralis; Heidelberg Engineering) instruments and formulate equations to convert retinal thickness measurements from SD-OCT to equivalent values on TD-OCT.A cross-sectional observational study was conducted in private and institutional practices. Persons with diabetes mellitus who had at least 1 eye with central-involved diabetic macular edema, defined as Stratus central subfield thickness (CST) of 250 ?m or greater, participated. An additional normative cohort (individuals with diabetes but without diabetic macular edema) was enrolled. Each study eye underwent 2 replicate Stratus scans followed by 2 replicate Cirrus or Spectralis scans (real-time image registration used) centered on the fovea.Optical coherence tomography CST and macular volume.The Bland-Altman coefficient of repeatability for relative change in CST (the degree of change that could be expected from measurement variability) was lower with Spectralis (7%) compared with Cirrus (14%) and Stratus (12% and 15% within Cirrus/Stratus and Spectralis/Stratus groups, respectively). For each cohort, the initial Stratus CST was within 10% of the replicate Stratus measurement nearly all of the time; the conversion equations predicted a Stratus CST within 10% of the observed thickness 86% and 89% of the time for Cirrus/Stratus and Spectralis/Stratus groups, respectively, which is similar to the agreement on Stratus test-retest. The Bland-Altman limits of agreement for relative change in CST between machines (the degree of change that could be expected from measurement variability [combining within and between instrument variability]) were 21% for Cirrus and 19% for Spectralis when comparing predicted vs actual Stratus measurement.Reproducibility appears to be better with Spectralis than with Cirrus and Stratus. Conversion equations to transform Cirrus or Spectralis measurements to Stratus-equivalent values, within 10% of the observed Stratus thickness values, appear feasible. Central subfield thickness changes beyond 10% when using the same machine or 20% when switching machines, after conversion to Stratus equivalents, are likely due to a change in retinal thickness rather than measurement error.

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Ultrafast measurements of optical spectral coherence by single-shot time-stretch interferometry.

Publications

Ultrafast measurements of optical spectral coherence by single-shot time-stretch interferometry.

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