On the possibility of producing true real-time retinal cross-sectional images using a graphics processing unit enhanced master-slave optical coherence tomography system

In a previous report, we demonstrated master-slave optical coherence tomography (MS-OCT), an OCT method that does not need resampling of data and can be used to deliver en face images from several depths simultaneously. In a separate report, we have also demonstrated MS-OCT's capability of producing cross-sectional images of a quality similar to those provided by the traditional Fourier domain (FD) OCT technique, but at a much slower rate. Here, we demonstrate that by taking advantage of the parallel processing capabilities offered by the MS-OCT method, cross-sectional OCT images of the human retina can be produced in real time. We analyze the conditions that ensure a true real-time B-scan imaging operation and demonstrate in vivo real-time images from human fovea and the optic nerve, with resolution and sensitivity comparable to those produced using the traditional FD-based method, however, without the need of data resampling. © 2015 The Authors

Two spectral shaping methods of a broadband fibre source for biomedical OCT imaging

The authors report two investigation methods into the spectral shaping of an optical broadband source (BBS) to be used in Optical Coherence Tomography (OCT). The BBS spectrum extends from 450 nm to 1750 nm and is selectively used in multiple spectral wavebands. Spectral shaping is performed with: (i) an optical filter unit (a combination of dichroic and bandpass filters at different incident angles) and (ii) a double-pass prism sequence (a cube beam splitter, two equilateral prisms and a metallic mirror) which allow the freedom to select the characteristics of the spectrum (central wavelength, spectral bandwidth). BBS can allow imaging with a depth resolution of 2 μm or better. Such a high depth resolution makes BBS suitable for OCT imaging in embryology, cells culture and eye imaging, investigations which will complement the more traditional fluorescence labelling and confocal imaging

From talbot bands to no mirror terms in fourier domain OCT, a quest on the fundamental origin of the sensitivity decay with depth

We show that the decay of sensitivity with depth in Fourier Domain (FD)-OCT can be explained based on the superposition of wavetrain lengths after dispersion (diffraction). The more coherent the dispersed waves are, the slower the decay of sensitivity. An asymmetry in the decay curve with the optical path difference (OPD) can be introduced via an "intrinsic" delay which has the effect of shifting axially the two wavetrains relative to each other, originating from the object and reference beam of an interferometer. In this way, an equivalent Talbot Bands set-up is implemented, characterized by no mirror terms for the "extrinsic" delay introduced in the interferometer. Such configurations require that the two interfering beams use different parts of the diffraction grating in the interrogating spectrometer. Theory of Talbot Bands is presented and then how this knowledge can be transferred to the field of FD-OCT to achieve A-scans mirror terms free in one step. A theoretical rigorous model and a heuristic model are presented to quantify the Talbot bands. © 2009 SPIE

Dispositif bistable magnéto-optique

L'article présente un dispositif mixte bistable magnéto-optique, réalisé à l'aide d'une cavité laser active à laquelle est appliqué un champ magnétique axial, le champ étant contrôlé par une boucle de contre-réaction dans le dispositif

Dispositif bistable magnéto-optique

In this paper we present a mixed magneto-optical bistable device, realized to the active cavity of a laser by applying an axial magnetic field, the field being driven electronically by means of a feedback loop.L'article présente un dispositif mixte bistable magnéto-optique, réalisé à l'aide d'une cavité laser active à laquelle est appliqué un champ magnétique axial, le champ étant contrôlé par une boucle de contre-réaction dans le dispositif

Evaluation of effective noise bandwidth for broadband optical coherence tomography operation

Key noise parameters in optical coherence tomography (OCT) systems employing splitters with a nonflat spectral response are evaluated using a supercontinuum fiber laser source with a spectrum of 450 nm-1700 nm and a time domain OCT architecture based on 1300 nm fiber splitters. The spectral behavior of the splitter leading to balanced detection is measured over a range of 300 nm. Because of spectrally different signals at the balanced detector input a residual excess photon noise term results. A rigorous treatment of this noise term [Appl. Opt. 43, 4802 (2004)] introduced two new quantities that take into account the spectral properties of the coupler. In this report, we have evaluated these two noise bandwidth quantities and comparatively assessed the noise behavior predicted by the classical theory with the theory based on the two new noise bandwidths. We show that under certain operating parameters, the additional excess photon noise is twice that predicted for a coupler with a flat spectral response. © 2009 Optical Society of America

Fast algorithm for blind optimisation of optical systems; Statistics and methodology

Adaptive Optics (AO) improves the efficiency of the optical devices in confocal imaging systems by reducing wavefront aberrations. Aberration is caused by imperfections within the system and reduces the optical signal to noise ratio of the resultant images besides deteriorating the quality of the images. An AO system, comprises a wavefront sensor and a deformable mirror (DM), is a straightforward solution to compensate for this distortion. In confocal microscopy, the wavefront sensor can be supplanted with an optimisation algorithm. We have previously implemented the general simulated annealing (SA) algorithm for optimising confocal microscopes. In this paper the modified version of the SA algorithm, fast simulated annealing (FSA) is investigated which takes less than one hundredth of the optimisation time required by the general version. © 2013 © 2013 Taylor & Francis

Channeled spectrum display using a CCD array for student laboratory demonstrations

The channelled spectrum of an optical beam generated by a laser diode operated below threshold after traversing microscope glass plates is spectrally analysed using a grating and a CCD linear array. The experiment has the following goals: to display the resulting channelled spectrum, to familiarize students with an important topic in metrology and to illustrate some interesting topics from spectroscopy using a CCD array as a spectrometer

Noninvasive quantitative evaluation of the dentin layer during dental procedures using optical coherence tomography

A routine cavity preparation of a tooth may lead to opening the pulp chamber. The present study evaluates quantitatively, in real time, for the first time to the best of our knowledge, the drilled cavities during dental procedures. An established noninvasive imaging technique, Optical Coherence Tomography (OCT), is used. The main scope is to prevent accidental openings of the dental pulp chamber. Six teeth with dental cavities have been used in this ex vivo study. The real time assessment of the distances between the bottom of the drilled cavities and the top of the pulp chamber was performed using an own assembled OCT system. The evaluation of the remaining dentin thickness (RDT) allowed for the positioning of the drilling tools in the cavities in relation to the pulp horns. Estimations of the safe and of the critical RDT were made; for the latter, the opening of the pulp chamber becomes unavoidable. Also, by following the fractures that can occur when the extent of the decay is too large, the dentist can decide upon the right therapy to follow, endodontic or conventional filling. The study demonstrates the usefulness of OCT imaging in guiding such evaluations during dental procedures