Hybrid Fourier domain modelocked laser utilizing a fiber optical parametric amplifier and an erbium doped fiber amplifier

To our knowledge, we report the first Fourier domain modelocked laser (FDML) constructed using optical parameter amplifier (OPA) in conjunction with an erbium-doped fiber amplifier (EDFA), centered at ~1556nm. We utilized a onepump OPA and a C-band EDFA in a series configuration with a polygon-grating wavelength filter to generate a hybrid FDML spectrum. Results demonstrate a substantially higher output power, better spectral shape and significantly more stable bandwidth than individual configurations. We believe this technique has the potential to enable several amplifiers to complement individual deficiencies resulting in improved spectral shapes and power generation for imaging applications such as optical coherence tomography (OCT). © 2010 Copyright SPIE - The International Society for Optical Engineering.published_or_final_versionThe Fiber Lasers VII: Technology, Systems, and Applications, San Francisco, CA., 25 January 2010. In Proceedings of SPIE, 2010, v. 7580, p. 1-7, article no. 75802

Wavelet domain compounding for speckle reduction in optical coherence tomography

Visibility of optical coherence tomography (OCT) images can be severely degraded by speckle noise. A computationally efficient despeckling approach that strongly reduces the speckle noise is reported. It is based on discrete wavelet transform (DWT), but eliminates the conventional process of threshold estimation. By decomposing an image into different levels, a set of sub-band images are generated, where speckle noise is additive. These sub-band images can be compounded to suppress the additive speckle noise, as DWT coefficients resulting from speckle noise tend to be approximately decorrelated. The final despeckled image is reconstructed by taking the inverse wavelet transform of the new compounded sub-band images. The performance of speckle reduction and edge preservation is controlled by a single parameter: the level of wavelet decomposition. The proposed technique is applied to intravascular OCT imaging of porcine carotid arterial wall and ophthalmic OCT images. Results demonstrate the effectiveness of this technique for speckle noise reduction and simultaneous edge preservation. The presented method is fast and easy to implement and to improve the quality of OCT images.published_or_final_versio

Wavelength-swept spectral and pulse shaping utilizing hybrid Fourier domain modelocking by fiber optical parametric and erbium-doped fiber amplifiers

We report the first Fourier domain modelocked (FDML) laser constructed using optical parametric amplifier (OPA) in conjunction with an erbium-doped fiber amplifier (EDFA), centered at ∼1555nm, to the best of our knowledge. We utilize a one-pump OPA and a C-band EDFA in serial configuration with a tunable Fabry-Perot interferometer to generate a hybrid FDML spectrum. Results demonstrate a substantially better spectral shape, output power and stability than individual configurations, with decreased sensitivity to polarization changes. We believe this technique has the potential to enable several amplifiers to complement individual deficiencies resulting in improved spectral shapes and power generation for imaging applications such as optical coherence tomography (OCT). © 2010 Optical Society of America.link_to_subscribed_fulltex

Improved phase-resolved optical Doppler tomography using the Kasai velocity estimator and histogram segmentation

Significant improvements are reported in the measurable velocity range and tissue motion artefact rejection of a phase-resolved optical coherence tomography and optical Doppler tomography system. Phase information derived from an in-phase and quadrature demodulator is used to estimate the mean blood flow velocity by the Kasai autocorrelation algorithm. Ahistogram-based velocity segmentation algorithm is used to determine block tissue movement and remove tissue motion artefacts that can be faster or slower in velocity than that of the microcirculation. The minimum detectable Doppler frequency is about 100 Hz, corresponding to a flow velocity resolution of 30 lm/s with an axial-line scanning frequency of 8.05 kHz and a mean phase change measured over eight sequential scans; the maximum detectable Doppler frequency is ±4 kHz (for bi-directional flow) before phase wrap-around. © 2002 Elsevier Science B.V. All rights reserved

Blood-vessel closure using photosensitizers engineered for two-photon excitation

The spatial control of optical absorption provided by two-photon excitation has led to tremendous advances in microscopy and microfabrication. Medical applications of two-photon excitation in photodynamic therapy have been widely suggested, but thus far have been rendered impractical by the low two-photon cross-sections of photosensitizer drugs (which are compounds taken up by living tissues that become toxic on absorption of light). The invention of efficient two-photon activated drugs will allow precise three-dimensional manipulation of treatment volumes, providing a level of targeting unattainable with current therapeutic techniques. Here we present a new family of photodynamic therapy drugs designed for efficient two-photon excitation and use one of them to demonstrate selective closure of blood vessels through two-photon excitation photodynamic therapy in vivo. These conjugated porphyrin dimers have two-photon cross-sections that are more than two orders of magnitude greater than those of standard clinical photosensitizers. This is the first demonstration of in vivo photodynamic therapy using a photosensitizer engineered for efficient two-photon excitation. © 2008 Macmillan Publishers Limited. All rights reserved