| Applications |
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| Art Conservation |
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| Retina Imaging |
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| Drug Coating |
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| Polarization Sensitive OCT |
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| AO enhanced OCT |
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| Cochlear Implantation |
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| Doppler OCT |
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| Mouse Lung |
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| Endoscopic Imaging |
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| Functional Imaging |
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| Developmental Biology |
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| 3D Imaging |
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| Nature Photonics |
| Peer Reviewed Papers |
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Retina Imaging
Swept source OCT is becoming an attractive technique for in-vivo human retina imaging, due to the long coherence length of the source which enables a large depth measurement range and the balanced detection scheme which allows high collection efficiency of sample signals. Figure 1 presents results from in vivo retinal imaging of a human subject, these images allow the identification of major intra-retinal layers as well as en-face imaging of the macular and optic nerve head.
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| Figure 1. High-definition macular image acquired using Thorlabs 850 nm swept laser source. NFL – nerve fiber layer, IPL – inner plexiform layer, INL – inner nuclear layer, OPL – outer plexiform layer, ONL – outer nuclear layer, IS / OS – photoreceptor inner segment / outer segment junction, PR OS – photoreceptor outer segments, RPE – retinal pigment epithelium, CH – choroid, ONH – optic nerve head. |
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The images were taken with a new swept source OCT system based on an external cavity tunable semiconductor laser at 850 nm. This OCT imaging system, jointly developed with researchers at MIT, provides high-speed data collection (16 - 24 kHz A-scan rate) and excellent axial resolution (~7 μm). The core of this new swept source OCT system is a rapidly tunable laser that utilizes a short free-space cavity (15 cm singlepass cavity length) with a center wavelength of 850 nm. The cavity, with the schematic shown in Figure 2, contains a semiconductor optical amplifier, collimating lens, half-wave plate, and resonant tunable filter. The laser architecture and imaging system is described in Optics Letters (V. J. Srinivasan, et. al, Optics Letters, 32 (4), 361, 2007). A dispersion balanced Mach-Zehnder interferometer is used to calibrate the OCT data point from time to optical frequency space.
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| Figure 2. Schematic of Thorlabs 850 nm frequency-swept laser |
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Human retinal imaging was performed with a pair of galvanometer scanning mirrors and an average power of 400 µW at the cornea. An 80 MHz balanced receiver was used to detect the signals. Fast Fourier transformation yields the axial reflectance profile with a measured sensitivity of >93 dB. The data acquisition and processing is performed in real-time on the Thorlabs OCT system at 32 frames per second (512 axial scans per frame).
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| Figure 3. The en-face imaging of the optic nerve head, with the imaging plan sectioning in the depth direction in the 3D volume of the sample. |
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Image & Movie Courtesy: 2007 Optical Society of America, and Prof. James G. Fujimoto of Department of Electrical Engineering and Computer Science of Massachusetts Institute of Technology.
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