Irina Trifanov

Combined Neodymium–Ytterbium-Doped ASE Fiber-Optic Source for Optical Coherence Tomography Applications

Optical coherence tomography (OCT) imaging at the 1060-nm region proved to be a successful alternative in ophthalmology not only for resolving intraretinal layers, but also for enabling sufficient penetration to monitor the subretinal vasculature in the choroid when compared to most commonly used OCT imaging systems at the 800-nm region. To encourage further clinical research at this particular wavelength, we have developed a compact fiber-optic source based on amplified spontaneous emission (ASE) centered at 1060 nm with 70-nm spectral bandwidth at full-width at half-maximum and output power 20 mW. Our approach is based on a combination of slightly shifted ASE emission spectra from a combination of Neodymium- and Ytterbium-doped fibers. Spectral shaping and power optimization have been achieved using in-fiber filtering schemes. We have tested the performance of the source in an OCT system optimized for this wavelength.

Algorithm for Excitation Optimization of Fabry–Pérot Filters Used in Swept Sources

We investigate the improvement in the nonlinearity of a conventional wavelength swept laser source on the basis of a fiber Fabry-Pérot tunable filter using a well-established optimization method, simulated annealing (SA). The signal driving the filter is constructed from many short ramps of different slopes that are interconnected. The values of the slopes are optimized through the SA algorithm to achieve maximum amplitude for the Fourier transformed peaks of the photodetected interferometric signal.

Experimental Method to Find the Optimum Excitation Waveform to Quench Mechanical Resonances of Fabry–Pérot Tunable Filters Used in Swept Sources

We report experimental evidence of improving the nonlinearity of conventional wavelength swept laser sources based on a fiber Fabry-Perot tunable filter as a wavelength-selective element. Our solution is based on applying a nonsinusoidal, synthesized waveform to the tunable filter that can be identified experimentally. A significant improvement in the optical coherence tomography image quality has been obtained without any software recalibration method.

Characterization of a fibre optic swept laser source at 1 μm for optical coherence tomography imaging systems

We report the development of a swept wavelength laser at 1 micron based on a linear cavity fibre configuration with an intra-cavity half symmetrical confocal Fabry-Perot tunable filter and a semiconductor optical amplifier as a gain medium. The performances of the source in terms of parameters like: sweep repetition rate (1-20 kHz), center wavelength (1065 nm), wavelength scanning range (max. 50nm), instantaneous line-width (<0.1nm) and a boosted output power of around 40 mW are demonstrated. The new source tested on an OCT system is exhibiting sufficient linearity in wave-number (k-space) at 1 kHz repetition rate; therefore no k-trigger, or wavelength rescaling process was needed.

Quasi-simultaneous optical coherence tomography and confocal imaging

A new approach of acquiring quasi-simultaneous optical coherence tomography (OCT) and confocal images is presented. The two images are generated using different principles, OCT and confocal microscopy. When the system is used to image the retina, the two images have depth resolutions, at present, of <20 microm and approximately 1 mm, respectively. The acquisition and display of en face OCT and confocal images are quasi-simultaneous, without the need of a beamsplitter. By using a chopper to periodically obstruct the reference beam in the OCT interferometer, synchronized with the XY-transversal scanner, much higher acquisition speed is obtained than in a previous report where we flipped an opaque screen in the reference arm of the interferometer. Successful operation of the novel configuration was achieved by: (1) stable synchronization of the choppers movement with the horizontal line scanner and (2) fast self-adjusting of the gain value of avalanche photodiodes, depending on the optical power. Images from coin, leaves, and retina in vivo have been collected to demonstrate the functionality of the system.

20-mW 70-nm bandwidth ASE fibre optic source at 1060-nm wavelength region for optical coherence tomography

Optical coherence tomography (OCT) imaging at 1060 nm region proved to be a successful alternative in ophthalmology not only for resolving intraretinal layers, but also for enabling sufficient penetration to monitor the sub-retinal vasculature in the choroids when compared to most commonly used OCT imaging systems at 800 nm region. To encourage further clinical research at this particular wavelength, we have developed a compact fiber optic source based on amplified spontaneous emission (ASE) centered at ~1060 nm with ~70 nm spectral bandwidth at full-width half maximum (FWHM) and output power >20 mW. Our approach is based on a combination of slightly shifted ASE emission spectra from a combination of two rare-earth doped fibers (Ytterbium and Neodymium). Spectral shaping and power optimization have been achieved using in-fiber filtering solutions. We have tested the performances of the source in an OCT system optimized for this wavelength.

Investigations of OCT imaging performance using a unique source providing several spectral wavebands

The authors report investigations into the suitability of a broadband supercontinuum fiber laser (SCFL) for use in Optical Coherence Tomography (OCT). The supercontinuum of light extending from 400 nm to 1800 nm can be used selectively in several spectral wavebands from 600 nm to 1700 nm in order to characterize the performance of single mode (SM) fiber OCT systems through spectral and auto-correlation measurements, dispersion measurements and image acquisition. Spectral selection and tailoring is made possible through a combination of bandpass optical filters. In addition, for the first time, given the optical bandwidth available, we perform evaluation of effective noise bandwidths which take into consideration the spectral behavior of the optical splitter in the balanced detection receiver.

Quasi-simultaneous OCT/confocal imaging

A new approach of acquiring quasi-simultaneous OCT and confocal images is presented. The two images are generated using different principles, optical coherence tomography (OCT) and confocal microscopy (CM). When the system is used to image the retina, the two images have depth resolutions, at present, of less than 20 μm and approximately 1 mm respectively. The acquisition and display of en-face OCT and confocal images are quasi-simultaneous, without the need of a beam splitter. By using a chopper to periodically obstruct the reference beam in the OCT interferometer, synchronized with the XY-transversal scanner, much higher acquisition speed is obtained than in a previous report where we flipped an opaque screen in the reference arm of the interferometer. Successful operation of the novel configuration was achieved by: (1) stable synchronization of the choppers movement with the horizontal line scanner and (2) fast self-adjusting of the gain value of avalanche photodiodes depending on the optical power. Images from coin, leafs and retina in vivo have been collected to demonstrate the functionality of the system.

Dual excitation waveform Fabry-Pérot tunable filters used in swept sources

We report experimental evidence of a novel method to quench the resonances of a Fabry-Perot tunable filter typically used as a wavelength selective element in swept source OCT systems. The method is based on applying a non-sinusoidal, synthesized waveform to the tunable filter, waveform that can be found experimentally in a few iteration steps. A significant improvement in the OCT image quality has been obtained without any software recalibration method.

Quasi-Simultaneous OCT/SLO Imaging

Quasi-simultaneous OCT and SLO images are produced without the need to split the signal from the retina. A chopper synchronized with the transverse scanner periodically blocks-off the reference beam in the OCT.