The geometry of a spherical surface, for example that of a precision optic, is completely determined by the radius –of-curvature at one point and the deviation from the perfect spherical form at all other points of the sphere. Full-field Optical Coherence Tomography (FF-OCT) is a parallel detection OCT technique that utilizes a 2D detector array. This technique avoids mechanical scanning in imaging optics, thereby speeding up the imaging process and enhancing the quality of images. The current paper presents an FF-OCT instrument that is designed to be used in sphere measurement with the principle of multiple delays (MD) OCT to evaluate the curvature and radius of curved objects in single-shot imaging. The optimum combination of the MD principle with the FF-OCT method was evaluated, and the radius of a metal ball was measured with this method. The generated 2n-1 contour lines were obtained by using an MDE with n delays in a single en-face OCT image. This method of measurement, it engaged in the measurement accuracy of spherical and enriches the means of measurement, to make a spherical scan techniques flexible application.
In this report we demonstrate results of measuring wavefront aberrations from different depths in a fabricated phantom using a coherence-gated Shack-Hartman wavefront sensing technique (CG-SH/WFS). The SH/WFS is equipped with a Mach-Zehnder interferometer and the coherence gate operates on principles of swept source (SS) interferometry. The CG-SH/WFS is able to differentiate wavefront signals from different depths separated by a depth resolution of 7.1 micron. The CG-SH/WFS delivers a similar SH spot pattern as that provided by a conventional SH/WFS. Due to the coherence gate, the sensor is capable of eliminating stray reflections. Hereby we present the results of measuring depth-resolved wavefront aberrations. The method is robust and all depth-resolved aberrations are recorded simultaneously without any mechanical movement. This technique has the potential of providing depth resolved correction in adaptive optics assisted ophthalmology imaging and in nonlinear microscopy.
This paper investigates the effects of fiber bundle on the performance of Full-field swept source OCT (FFSS-OCT) in
terms of depth range, depth resolution and transversal resolution. A superfast CMOS camera with full sensor resolution
1024 x 1024 pixels and 60 kHz in maximum frame rate is employed in the testing system. A fiber bundle which contains
18000 single fibers is used to transmit images from interference beam to the camera. Depth range and resolution are
assessed by varying optical path difference (OPD) between object arm and reference arm. The operation is repeated
under a set of frame rates from 1 kHz to 3 kHz. In addition, an USAF plate is used as a planar object to test transversal
resolution. For comparison, above parameters are tested as well with a bulk-optic setup which is built under the same
system configuration but without bundle. The results show that the difference between performances of bundle and Bulkoptic
setups is not remarkable. As a practical example, 3D profile of a coin is measured using two setups. In sum, this
investigation shows that the performance of bundle setup can compete with that of bulk-optic setup in implementing
FFSS-OCT. The quantitative results are helpful for researchers to incorporate bundles to FFSS-OCT systems in future.
In this report, we demonstrate characteristics and parameters of a coherence-gated Shack-Hartmann wavefront sensor
(CG/SH-WFS) that is capable of measuring depth-resolved wavefront aberrations. A technique of dynamic centroiding is
applied to CG/SH-WFS images and its precision is evaluated. The performance of the CG/SH-WFS system is compared
with a commercial SH-WFS measuring a reflective surface. Real-time wavefront measurements from a scattering sample
are also presented. The experiments demonstrate that the performance of CG/SH-WFS can replace conventional SHWFS
and also provide its unique advantages.
We demonstrate a direct Shack-Hartmann wavefront sensing method that allows depth-resolved
measurements. A coherence-gate Shack-Hartmann wavefront sensor (CG/SH-WFS) is implemented
by adding low coherence reflectometry gating to a SH-WFS. The depth resolution is determined by
the coherence gate, much narrower than the depth range of the SH-WFS. Distinctive wavefronts are
measured from five layers in a multiple-layer target. This paves the way towards depth-resolved
closed-loop adaptive optics assisted microscopy and imaging of the retina.
In this report we investigate the possibility of narrowing the depth range of a physical Shack-Hartmann wavefront sensor
(SH-WFS) using coherence gating technique in spectral domain. A time-domain low coherence interferometry (LCI) setup
 has already been demonstrated capable of generating similar Shack-Hartmann spots pattern to that delivered by a
conventional SH-WFS. Stray reflections are eliminated in the images due to a narrow coherence gating introduced by the
interferometric technique. Hereby we present another approach by employing a wavelength tuneable light source to
obtain Shack-Hartmann spot patterns with coherence gating in a 3D volume without axial scanning. Signal strength is
enhanced in contrast with a conventional SH-WFS and signal to noise ratio is improved compared to the previous time-domain
setup. This novel technique has the potential of providing depth resolved wavefront aberration information,
which can guide better wavefront correction in adaptive optics assisted ophthalmology imaging and confocal microscopy
In the present paper we investigate the possibility of narrowing the depth range of a physical Shack - Hartmann
wavefront sensor (SH-WFS) by using coherence gating. We have already demonstrated a low coherence interferometry
(LCI) set-up, capable of generating similar spots patterns as a conventional SH-WFS and also capable of eliminating
stray reflections. Here, we evaluate the accuracy of wavefront measurements using a coherence-gated (CG)/SH-WFS.
This is based on a Mach-Zehnder interferometer combined with a SH-WFS, that implements time-domain (TD)-LCI
acquisition. The wavefront measurement errors introduced by the non-uniform distribution of the reference power over
the photo-detector array were investigated. The effect on the centroid nodes accuracy due to different numbers of phaseshifting
interferometry (PSI) steps applied was also evaluated. This novel technique has the potential of providing depth
resolved aberration information, which can guide better correction in adaptive optics assisted OCT and confocal imaging
A Line-field Spectral Domain Optical Coherence Tomography method is proposed to enable fast B-Scan imaging. This
system was constructed from a combination of a conventional Spectral Domain OCT and a line field imaging system,
which directs a line-shaped focus onto a specimen. An array of depth-information-encoded-spectra was collected by a
two-dimensinal CCD camera. Numeric frequency resampling was applied to rows collected from the camera, followed
by Fourier transformation on each individual spectrum obtained. This lead to B-Scan images generated from a single
shot event. The performances of the imaging system are discussed. Images from skin of human fingers in-vivo and
osseous tissue of human teeth are presented.
Comparative evaluation of signal-to-noise ratio (SNR) is presented using a Full-field (FF)-OCT configuration, which is
adapted to work in either Swept-Source (SS)-Full-field OCT or Time Domain (TD)-Full-field OCT regime. We
implement the two regimes in the same set-up, using the same CCD camera and the same samples. We describe the
experimental set-up and the procedure implemented to verify the theory which says that Spectral Domain (SD)-OCT is
superior to TD-OCT. A simple theoretical analysis of the signal-to-noise ratio is presented to evaluate the improvement
from TD-OCT to SD-OCT in FF configuration. Experimental results demonstrate that the SNR is indeed better in the
SS-OCT regime, however not to the level predicted by theory. More work is required to understand why the experimental set-up does not achieve the improvement predicted by theory. We also show how to perform the measurements and imaging in the two regimes of operation. The system can deliver B-Scan OCT images in the SS-OCT regime and C-scan OCT images in the TD-OCT regime.
Full-field Optical Coherence Tomography (FF-OCT) is a parallel detection OCT technique using a 2D detector array.
This technique avoids mechanical scanning in imaging optics. Therefore, it can speed up the imaging process and
enhance the imaging quality. We present a FF-OCT instrument to be used in conjunction with the principle of multiple
delays (MD) OCT to evaluate the topography of curved objects in a single-shot imaging. We evaluate the optimum
combination of the MD principle with the FF-OCT method and measure the radius of a metal ball with this method. We
managed to obtain 2n-1 contour lines using an MDE with n delays in a single en-face OCT image to evaluate the
curvature of the object surface.