Optical coherence tomography (OCT) is an emerging imaging technique for a wide range of biological, medical, and material investigations [1,2]. Advances in the use of OCT for microscopy applications have provided researchers with a novel means by which biological specimens and non-biological samples are visualized. OCT was initially developed for imaging biological tissue because it permits the imaging of tissue microstructure in situ, yielding micron-scale image resolution without the need for excision of a specimen for tissue processing. OCT is analogous to ultrasound B-mode imaging except that it uses low-coherence light rather than high-frequency sound and performs imaging by measuring the backscattered intensity of light from structures in tissue. OCT can image tissue or specimens in cross-section, as is commonly done in ultrasound, or in en face sections, as in con-focal and multi-photon microscopy. The OCT image is a gray-scale or false-color multi-dimensional representation of backscattered light intensity that represents the differential backscattering contrast between different tissue types on a micron scale. Because OCT performs imaging using light, it has a one to two order-of-magnitude higher spatial resolution than ultrasound and does not require contact with the specimen or sample. The use of light also enables the spectroscopic characterization of tissue and cellular structures.

Optical Coherence Tomography

Power scaling of ytterbium-doped fiber superfluorescent sources based on single-stage and two-stage cladding-pumped fiber configurations is reported. For the single-stage configuration, a novel fiber-end termination scheme was employed to suppress laser oscillation in combination with a simple all-fiber scheme for achieving a predominantly single-ended output. The fiber was cladding-pumped by a diode stack at 976 nm and yielded ~62 W of single-ended amplified spontaneous emission output for 119 W of launched pump power, limited by the onset of parasitic lasing. At pump powers in excess of 40 W, the slope efficiency with respect to the launched pump power was 67%. The emission spectrum spanned the wavelength range from 1030 to 1100 nm and the bandwidth (FWHM) was 12 nm. Scaling to higher power levels was demonstrated using a two-stage cladding-pumped fiber configuration comprising of a low-power fiber superfluorescent seed source and a high-power amplifier. The two-stage source yielded 122 W of amplified spontaneous emission output (limited by available pump power) in a beam with M2 ap 2.1. The slope efficiency for the amplifier with respect to the launched pump power was 77%. The prospects for further improvement in performance and output power are considered.

Power Scaling of Ytterbium-doped Fiber Superfluorescent Sources

Optical coherence tomography (OCT) is an attractive imaging technique for developmental biology because it permits the imaging of tissue microstructure in situ, yielding micron-scale image resolution without the need for excision of a specimen and tissue processing. OCT enables repeated imaging studies to be performed on the same specimen in order to track developmental changes. OCT is analogous to ultrasound B mode imaging except that it uses low-coherence light rather than sound and performs cross-sectional imaging by measuring the backscattered intensity of light from structures in tissue (1). The principles of OCTimaging are shown schematically in Fig. I. The OCT image is a gray-scale or false-color two-dimensional (2-D) representation of backscattered light intensity in a cross-sectional plane. The OCT image represents the differential backscattering contrast between different tissue types on a micron scale. Because OCT performs imaging using light, it has a oneto two-order-of-magnitude higher spatial resolution than ultrasound and does not require specimen contact. OCT was originally developed an9 demonstrated in ophthalmology for high-resolution tomographic imaging of the retina and anterior eye (2-4). Because the eye is transparent and is easily optically accessible, it is well suited for diagnostic OCT imaging. OCT is promising for the diagnosis of retinal disease because it can provide images of retinal pathology with 10-~ resolution, almost one order of magnitude higher than previously possible using ultrasound. Clinical studies have been performed to assess the application of OCT for a number of macular diseases (3,4). OCT is especially promising for the diagnosis and monitoring of glaucoma and macular edema associated with diabetic retinopathy because it permits the quantitative measurement of changes in the retinal or retinal-nerve fiber layer thickness. Because morphological changes often occur before the onset of physical symptoms, OCT can provide a powerful approach for the early detection of these diseases. Recently, OCT has been applied for imaging in a wide range of nontransparent tissues (5-9). In tissues other than the eye, the imaging depth is limited by optical attenuation resulting from scattering and absorption. Ophthalmic imaging is typically performed at 800-nm wavelengths. However, because optical scattering decreases with

Optical coherence tomography imaging in developmental biology.

Full-field optical coherence tomography OCT using a complementary metal-oxide semiconductor CMOS camera with an in- tegrated a digital signal processor DSP is demonstrated. The CMOS- DSP camera employed is typically used in machine vision applications and is based on an array of 10241024 direct readout pixels that are randomly addressable in space and time. These characteristics enable the camera to be used as a fast full-field detector in carrier-based optical metrology systems. The integrated DSP facilitates basic signal process- ing including real-time filtering and undersampling. The optical setup used to implement this OCT method is composed of a free-space Mich- elson interferometer and a superluminescent diode SLD light source, with an electromechanical shaker for depth scanning. Unlike classical OCT approaches, however, the setup does not require any electrome- chanical device for lateral scanning. A 6430 pixel region of interest was imaged at 235 frames/s and sampled in depth, corresponding to a volumetric measurement of 875410150 m. Measurements carried out on a simple calibration specimen indicated lateral and axial resolu- tions of 14 and 22 m, respectively. The presented approach offers an inexpensive and versatile alternative to traditional OCT systems and pro- vides the basis for a functional machine vision system suitable for indus- trial applications.

https://ulir.ul.ie/bitstream/handle/10344/1090/Connelly_full_field_optical.pdf?sequence=2

Full-field optical coherence tomography with a complimentary metal-oxide semiconductor digital signal processor camera

Highly efficient operation of a double-clad ytterbium-doped helical-core fiber in a superfluorescent (nonlasing) configuration has been demonstrated. The fiber was cladding-pumped by a diode-stack at 976 nm and yielded 107 W of amplified spontaneous emission from the two ends of the fiber for 168 W of absorbed pump power in an output beam with a beam propagation factor (M2) of 2.8. At pump powers over 40 W, the slope efficiency with respect to the absorbed pump power was 76%. The emission spectrum spanned the wavelength range from 1030 to 1160 nm and the bandwidth (full-width at half-maximum) was 37 nm

High-Power Broadband Ytterbium-Doped Helical-Core Fiber Superfluorescent Source

Summary form only given. Optical coherence tomography (OCT) has proven over the past few years to be a powerful new optical imaging modality. OCT uses interferometric detection and a short-coherence-length light source to achieve high sensitivity, high-dynamic range, and high resolution (1-10 /spl mu/m). Biomedical applications include ophthalmology, microscopy, endoscopy, laproscopy, dermatology, developmental biology, dentistry etc. One of the key components in OCT systems is the optical source. This paper presents preliminary results on the use of spectrally flattened rare-earth-doped fiber ASE source in OCT systems. Rare-earth-doped fibers are a very promising candidate for future OCT systems. The authors expect spectrally shaped rare earth-doped fiber ASE sources to play an important role in future OCT systems. In the near future, source powers in excess of 100 mW and coherence lengths under 10 cm should be available at a variety of wavelengths. The authors review some of the design details on this Nd source, quantify its optical parameters power, bandwidth, blindness, etc.), and present its application in tomographic biomedical imaging (e.g. skin and bone structure). The authors also compare its performance with other types of sources such as: semiconductor sources (light-emitting diodes, edge-emitting diodes, superluminescent diodes), model-lock lasers, and supercontinuum sources.

Spectrally shaped rare-earth-doped fiber ASE sources for use in optical coherence tomography

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Spectrally shaped rare-earth-doped fiber ASE sources for use in optical coherence tomography