Showing papers in "Optics Express in 1998"
TL;DR: The hardware and theory of operation of an OCT elastography system that measures internal displacements as small as a few micrometers by using 2D cross-correlation speckle tracking is described.
Abstract: Optical coherence tomography (OCT) has been applied to the study of the microscopic deformation of biological tissue under compressive stress. We describe the hardware and theory of operation of an OCT elastography system that measures internal displacements as small as a few micrometers by using 2D cross-correlation speckle tracking. Results obtained from gelatin scattering models, pork meat, and intact skin suggest possible medical applications of the technique.
659 citations
TL;DR: An optical coherence tomography system is described which can image up to video rate and features a high speed scanning delay line in the reference arm based on Fourier-transform pulse shaping technology.
Abstract: An optical coherence tomography system is described which can image up to video rate. The system utilizes a high power broadband source and real time image acquisition hardware and features a high speed scanning delay line in the reference arm based on Fourier-transform pulse shaping technology. The theory of low coherence interferometry with a dispersive delay line, and the operation of the delay line are detailed and the design equations of the system are presented. Real time imaging is demonstrated in vivo in tissues relevant to early human disease diagnosis (skin, eye) and in an important model in developmental biology (Xenopus laevis).
624 citations
TL;DR: An analysis of channel drop filter structures composed of two waveguides and an optical resonator system shows that 100% transfer can occur by creating resonant states of different symmetry, and by forcing an accidental degeneracy between them.
Abstract: We present a general analysis of channel drop filter structures composed of two waveguides and an optical resonator system. We show that 100% transfer between the two waveguides can occur by creating resonant states of different symmetry, and by forcing an accidental degeneracy between them. The degeneracy must exist in both the real and imaginary parts of the frequency. Based on the analysis we present novel photonic crystal channel drop filters. Numerical simulations demonstrate that these filters exhibit ideal transfer characteristics.
513 citations
TL;DR: These investigations demonstrate the utility of OCT as a diagnostic imaging modality in clinical and research dentistry and provide guidance in dental restorative procedures.
Abstract: We use optical coherence tomography (OCT) to perform a comprehensive program of in vivo and in vitro structural imaging of hard and soft tissues within the oral cavity. We have imaged the different types of healthy oral mucosa as well as normal and abnormal tooth structure. OCT is able to differentiate between the various types of keratinized and non-keratinized mucosa with high resolution. OCT is also able to provide detailed structural information on clinical abnormalities (caries and non-caries lesions) in teeth and provide guidance in dental restorative procedures. Our investigations demonstrate the utility of OCT as a diagnostic imaging modality in clinical and research dentistry.
404 citations
TL;DR: Using simple back projection algorithms it is now possible to image sensorimotor and cognitive activation of adult and pre- and full-term neonate human brain function in times < 30 sec and with two dimensional resolutions of < 1 cm in two dimensional displays.
Abstract: Imaging of the human body by any non-invasive technique has been an appropriate goal of physics and medicine, and great success has been obtained with both Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) in brain imaging. Non-imaging responses to functional activation using near infrared spectroscopy of brain (fNIR) obtained in 1993 (Chance, et al. [1]) and in 1994 (Tamura, et al. [2]) are now complemented with images of pre-frontal and parietal stimulation in adults and pre-term neonates in this communication (see also [3]). Prior studies used continuous [4], pulsed [3] or modulated [5] light. The amplitude and phase cancellation of optical patterns as demonstrated for single source detector pairs affords remarkable sensitivity of small object detection in model systems [6]. The methods have now been elaborated with multiple source detector combinations (nine sources, four detectors). Using simple back projection algorithms it is now possible to image sensorimotor and cognitive activation of adult and pre- and full-term neonate human brain function in times < 30 sec and with two dimensional resolutions of < 1 cm in two dimensional displays. The method can be used in evaluation of adult and neonatal cerebral dysfunction in a simple, portable and affordable method that does not require immobilization, as contrasted to MRI and PET.
354 citations
TL;DR: Polarization Sensitive Optical Coherence Tomography (PS- OCT) was used to image the reduction of birefringence in biological tissue due to thermal damage and demonstrates the potential of PS-OCT for burn depth assessment.
Abstract: Polarization Sensitive Optical Coherence Tomography (PS-OCT) was used to image the reduction of birefringence in biological tissue due to thermal damage. Through simultaneous detection of the amplitude of signal fringes in orthogonal polarization states formed by interference of light backscattered from turbid media and a mirror in the reference arm of a Michelson interferometer, changes in the polarization due to the optical phase delay between light propagating along the fast and slow axes of birefringent media were measured. Inasmuch as fibrous structures in many biological tissues influence the polarization state of light backscattered, PS-OCT is a potentially useful technique to image the structural properties of turbid biological materials. Birefringence of collagen, a constituent of many biological tissues, is reduced by denaturation that takes place at a temperature between 56-65 °C, thus providing an “optical marker” for thermal damage. Images showing reduction of birefringence due to thermal damage in porcine tendon and skin are presented and demonstrate the potential of PS-OCT for burn depth assessment.
353 citations
TL;DR: Third harmonic generation microscopy is used to make dynamical images of living systems for the first time, showing dynamic plant activity, and non-fading image characteristics even with continuous viewing, indicating prolonged viability under these THG-imaging conditions.
Abstract: Third harmonic generation microscopy is used to make dynamical images of living systems for the first time. A 100 fs excitation pulse at 1.2 μm results in a 400 nm signal which is generated directly within the specimen. Chara plant rhizoids have been imaged, showing dynamic plant activity, and non-fading image characteristics even with continuous viewing, indicating prolonged viability under these THG-imaging conditions.
315 citations
TL;DR: It is demonstrated that EOCT can serve for several clinical purposes such as performing directed biopsy, monitoring functional states of human body, guiding surgical and other treatments and monitoring post-operative recovery processes.
Abstract: We report results of application of our endoscopic optical coherence tomography (EOCT) system in clinical experiments to image human internal organs. Based on the experience of studying more than 100 patients, we make first general conclusions on the place and capabilities of this method in diagnosing human mucous membranes. It is demonstrated that EOCT can serve for several clinical purposes such as performing directed biopsy, monitoring functional states of human body, guiding surgical and other treatments and monitoring post-operative recovery processes. We show that applications of OCT are more informative in the case of internal organs covered by epithelium separated from underlying stroma by a smooth basal membrane and therefore concentrate on the results of the EOCT study of three internal organs, namely of larynx, bladder, and uterine cervix. Finally, we report first examination of internal organs in abdomen with the use of laparoscopic OCT.
229 citations
TL;DR: A simple means to obtain the gradient of the objective function directly is demonstrated, leading to straightforward application of gradient-based optimisation methods.
Abstract: Optical tomography schemes using non-linear optimisation are usually based on a Newton-like method involving the construction and inversion of a large Jacobian matrix. Although such matrices can be efficiently constructed using a reciprocity principle, their inversion is still computationally difficult. In this paper we demonstrate a simple means to obtain the gradient of the objective function directly, leading to straightforward application of gradient-based optimisation methods.
227 citations
TL;DR: It is shown that this multiresolution watermarking method is more robust to proposed methods to some common image distortions, such as the wavelet transform based image compression, image rescaling/stretching and image halftoning.
Abstract: In this paper, we introduce a new multiresolution watermarking method for digital images. The method is based on the discrete wavelet transform (DWT). Pseudo-random codes are added to the large coefficients at the high and middle frequency bands of the DWT of an image. It is shown that this method is more robust to proposed methods to some common image distortions, such as the wavelet transform based image compression, image rescaling/stretching and image halftoning. Moreover, the method is hierarchical.
213 citations
TL;DR: By means of high resolution two-photon microscopy, skin and subcutaneous tissue structures can be imaged utilizing their endogenous fluorescence and 3D resolve both the living and cornified keratinocytes in the epidermis, the collagen/elastin fibers in the dermal layer and the cartilage in the sub cutaneous layer is demonstrated.
Abstract: The non-invasive determination of deep tissue three dimensional structure and biochemistry is the ultimate goal of optical biopsy. Two-photon microscopy has been shown to be a particularly promising approach. The use of infrared radiation in two-photon microscopy is critical for deep tissue imaging since tissue absorption and scattering coefficients for infrared light are much lower than for shorter wavelengths. Equally important, tissue photodamage is localized to the focal region where fluorescence excitation occurs. This report demonstrates that, by means of high resolution two-photon microscopy, skin and subcutaneous tissue structures can be imaged utilizing their endogenous fluorescence. From a freshly prepared tissue punch of a mouse ear, we were able to resolve in 3D both the living and cornified keratinocytes in the epidermis, the collagen/elastin fibers in the dermal layer and the cartilage in the subcutaneous layer. The ability to non-invasively acquire 3D structures of these tissue components may find application in areas such as non-invasive diagnosis of skin cancer and the study of wound healing processes.
TL;DR: A new method is developed for determining the quantum fourth- order correlations in spatially extended detection systems such as this one, which reveals the expected phase-matching-induced spa- tial correlations in a 2-f Fourier-transform system.
Abstract: A single-photon-sensitive intensified charge-coupled-device (ICCD) camera has been used to simultaneously detect, over a broad area, degenerate and nondegenerate photon pairs generated by the quantum-optical process of spontaneous parametric down-conversion. We have developed a new method for determining the quantum fourth-order correlations in spatially extended detection systems such as this one. Our technique reveals the expected phase-matching-induced spatial correlations in a 2-f Fourier-transform system.
TL;DR: A wavelet-based watermark casting scheme and a blind watermark retrieval technique that can detect the embedded watermark without the help from the original image are investigated.
Abstract: A wavelet-based watermark casting scheme and a blind watermark retrieval technique are investigated in this research An adaptive watermark casting method is developed to first determine significant wavelet subbands and then select a couple of significant wavelet coefficients in these subbands to embed watermarks A blind watermark retrieval technique that can detect the embedded watermark without the help from the original image is proposed Experimental results show that the embedded watermark is robust against various signal processing and compression attacks
TL;DR: High-resolution amplified pulse shaping using an acousto-optic modulator (AOM) at a center-wavelength of 795nm is demonstrated and a complex pulse shape with hyperbolic secant amplitude andhyperbolic tangent frequency sweep is created, which is useful for applications in adiabatic rapid passage experiments.
Abstract: We demonstrate high-resolution amplified pulse shaping using an acousto-optic modulator (AOM) at a center-wavelength of 795nm The output pulses have energy of 200μJ/pulse and a transform-limited pulsewidth of 150fs A spectral modulation of over 40 features is achieved in a single pulse We characterize the pulses using the STRUT (Spectrally and Temporally Resolved Upconversion Technique) Using predistortion techniques, we demonstrate that the pulses can be shaped in amplitude and phase We create a complex pulse shape with hyperbolic secant amplitude and hyperbolic tangent frequency sweep, which is useful for applications in adiabatic rapid passage experiments
TL;DR: A non-invasive method of imaging laser irradiated blood vessels has been achieved using Color Doppler Optical Coherence Tomography (CDOCT), which may increase understanding of the mechanisms behind treatment of vascular disorders.
Abstract: A non-invasive method of imaging laser irradiated blood vessels has been achieved using Color Doppler Optical Coherence Tomography (CDOCT). This method may increase understanding of the mechanisms behind treatment of vascular disorders. The CDOCT system used a 1280 nm center wavelength superluminescent diode. A 585 nm, 360 μs pulsed dye laser was used to irradiate hamster dorsal skin flap window preparations. Irradiation sites were imaged with CDOCT prior to, immediately after, and 24 hours after laser irradiation. The processed CDOCT signal provided an estimate of the blood flow velocity. An increase in the blood vessel backscattered signal was observed as blood or vessel walls were coagulated. A decrease in damaged blood vessel reflectivity occurred after twenty four hours.
TL;DR: The spatial positions of internal defects were determined from a commercial grade of lead zirconate titanate ceramic material, from a sample of single-crystal silicon carbide, and from a Teflon-coated wire.
Abstract: We have used optical coherence tomography to study the internal structure of a variety of non-biological materials. In particular, we have imaged internal regions from a commercial grade of lead zirconate titanate ceramic material, from a sample of single-crystal silicon carbide, and from a Teflon-coated wire. In each case the spatial positions of internal defects were determined.
TL;DR: A qualitative description of the hologram's properties and a comparison of sensitivities between the crystals will be presented.
Abstract: A set of twelve specially doped lithium niobate crystals were grown to test the effect of the dopant on holographic recording in the crystals via the photorefractive effect. The crystals were doped with Ce, Co, Cr, Cu, Fe, Mn, Ni, Rh, Tb, Fe:Ce, Fe:Cr, and Fe:Mn. The transmission spectra was measured for each crystal and holograms have been written in each of the crystals with wavelengths from 457 nm to 671 nm. The wavelength sensitivity, scattering, and stability of the holograms varied substantially among the crystals. A qualitative description of the hologram’s properties and a comparison of sensitivities between the crystals will be presented.
TL;DR: Diffuse optical reflection tomography is used to reconstruct absorption images from continuous-wave measurements of diffuse light re-emitted from a "semi-infinite" medium.
Abstract: Diffuse optical reflection tomography is used to reconstruct absorption images from continuous-wave measurements of diffuse light re-emitted from a “semi-infinite” medium. The imaging algorithm is simple and fast and permits psuedo-3D images to be reconstructed from measurements made with a single source of light. Truly quantitative three-dimensional images will require modifications to the algorithm, such as incorporating measurements from multiple sources.
TL;DR: A stable regime looking like a waveguide appears in certain conditions, in which the beam to propagate in a narrow tube, is reported here: a stable regime is simply modeled in terms of saturated reorientation of the nematic.
Abstract: We report on experiments dealing with the propagation of a collimated laser beam in a dye doped nematic confined in a capillary of optical fiber size. The nematic is aligned in a such a way that the source beam is self focused. The behavior of the beam - focusing, multifocus regime, filamentation and undulation - already observed in larger cylindrical geometry and pure nematic is shown here to be reproduced in the dye doped medium, at much lower powers. Another feature is reported here: a stable regime looking like a waveguide appears in certain conditions, in which the beam to propagate in a narrow tube. This regime is simply modeled in terms of saturated reorientation of the nematic.
TL;DR: A compact and effcient source of amplitude-squeezed light is described, which employs a semi-monolithic degenerate MgO:LiNbO(3) optical parametric amplifier pumped by a frequency-doubled Nd:YAG laser at 532 nm.
Abstract: A compact and effcient source of amplitude-squeezed light is described. It employs a semi-monolithic degenerate MgO:LiNbO(3) optical parametric amplifier pumped by a frequency-doubled Nd:YAG laser at 532 nm. Injection-seeding of the amplifier by a 1064 nm wave permits active stabilization of the cavity length and stable operation. At a pump power of 380 mW, a maximum noise reduction of 6.5 dB in the amplitude fluctuations of the 0.2 mW 1064 nm wave was detected. The average detected noise reduction in continuous operation over 14 minutes was 6.2 dB. Taking the detection effciency into account, this corresponds to a squeezing of 7.2 dB in the emitted wave.
TL;DR: An image processing system which is developed to align autofluorescence and high-magnification images taken with a laser scanning ophthalmoscope and the noise levels drop by a factor of n and the image quality is improved.
Abstract: We describe an image processing system which we have developed to align autofluorescence and high-magnification images taken with a laser scanning ophthalmoscope. The low signal to noise ratio of these images makes pattern recognition a non-trivial task. However, once n images are aligned and averaged, the noise levels drop by a factor of √n and the image quality is improved. We include examples of autofluorescence images and images of the cone photoreceptor mosaic obtained using this system.
TL;DR: The three-dimensional rendering presents a new technique to view the optic nerve that is clinically important since morphological changes of the lamina cribrosa of the optic nerves may be involved in glaucoma.
Abstract: A scanning laser confocal microscope was used to visualize the human fundus (the back portion of the eyeball, as seen by means of the ophthalmoscope) in vivo from near the retinal surface to deep within the optic nerve head. Thirty-two optical sections based on reflected light were acquired, digitized and aligned to compensate for small eye movements. The registered stack of optical sections was reconstructed with three-dimensional volume rendering software and presented as a movie. The three-dimensional rendering presents a new technique to view the optic nerve. This technique is clinically important since morphological changes of the lamina cribrosa of the optic nerve may be involved in glaucoma.
TL;DR: The problem of three-dimensional visualization of a human lens in vivo has been solved by a technique of volume rendering a transformed series of 60 rotated Scheimpflug (a dual slit reflected light microscope) digital images.
Abstract: The problem of three-dimensional visualization of a human lens in vivo has been solved by a technique of volume rendering a transformed series of 60 rotated Scheimpflug (a dual slit reflected light microscope) digital images. The data set was obtained by rotating the Scheimpflug camera about the optic axis of the lens in 3 degree increments. The transformed set of optical sections were first aligned to correct for small eye movements, and then rendered into a volume reconstruction with volume rendering computer graphics techniques. To help visualize the distribution of lens opacities (cataracts) in the living, human lens the intensity of light scattering was pseudocolor coded and the cataract opacities were displayed as a movie.
TL;DR: Filtering out the long-wavelength components of strongly Raman-shifted, higher energy pulses squeezed the directly detected photocurrent fluctuations down to 3.8+/-0,2 dB (59%) below the shot noise level.
Abstract: We present new results on photon number squeezing of spectrally filtered solitons in fibers. The impact of frequency low-, high-, and bandpass filtering on noise reduction has been measured as a function of fiber length for 130-fs pulses close to the soliton energy. For short fibers our results agree qualitatively with theoretical predictions. For longer fibers, however, the measured squeezing increases to an unexpectedly large value. Spectral filtering of a strongly Raman-shifted, higher energy pulse squeezed the directly detected photocurrent fluctuations down to 3.8±0.2 dB (59%) below the shot noise level. The measured noise reductions are broadband from 5 to 90 MHz.
TL;DR: Experimental results obtained with laser-ultrasonics are processed using the Synthetic Aperture Focusing Technique (SAFT), yielding improved flaw detectability and spatial resolution, and practical interest of coupling SAFT to laser-ULTrasonic is discussed.
Abstract: Laser-ultrasonics is an emerging nondestructive technique using lasers for the generation and detection of ultrasound which presents numerous advantages for industrial inspection. In this paper, the problem of detection by laser-ultrasonics of small defects within a material is addressed. Experimental results obtained with laser-ultrasonics are processed using the Synthetic Aperture Focusing Technique (SAFT), yielding improved flaw detectability and spatial resolution. Experiments have been performed on an aluminum sample with a contoured back surface and two flat-bottom holes. Practical interest of coupling SAFT to laser-ultrasonics is also discussed.
TL;DR: An approach to improve the performance of a broad class of watermarking schemes through attack characterization, which uses the reference watermark to characterize any modifications of the resulting marked signal, so that the robust watermark can be more reliably extracted.
Abstract: In this paper, we propose an approach to improve the performance of a broad class of watermarking schemes through attack characterization. Robust and reference watermarks are both embedded into a signal. The reference watermark is used to characterize any modifications of the resulting marked signal, so that the robust watermark can be more reliably extracted. Analysis and simulations are provided to demonstrate the effectiveness of the approach.
TL;DR: An image watermarking algorithm based on constraints in the Discrete Cosine Transform (DCT) domain that defines circular detection regions according to the given parameters and is resistant to JPEG compression and filtering.
Abstract: In this paper we propose an image watermarking algorithm based on constraints in the Discrete Cosine Transform (DCT) domain. An image watermarking algorithm has two stages: signature casting (embedding) and signature detection. In the first stage it embeds an identifying label in the image. This is recognized in the second stage. The proposed algorithm has two processing steps. In the first step certain pixel blocks are selected using a set of parameters while in the second step a DCT coefficient constraint is embedded in the selected blocks. Two different constraint rules are suggested for the parametric modification of the DCT frequency coefficients. The first one embeds a linear constraint among certain selected DCT coefficients and the second defines circular detection regions according to the given parameters. The watermarks cast by the proposed algorithm are resistant to JPEG compression and filtering.
TL;DR: This work experimentally verified the interference resulting of the superposition of two Bessel beams propagating in free space and showed for first time the self imaging effect using nondiffracting beams.
Abstract: We experimentally verified the interference resulting of the superposition of two Bessel beams propagating in free space and showed for first time the self imaging effect using nondiffracting beams. Our results are supported by numerical simulations and possible applications are discussed.
TL;DR: This work has used a newly developed Yb-doped high-power fiber source in an optical coherence tomography (OCT) apparatus and analyzed various properties of interest for OCT measurements such as spectral shape, related gate width, central wavelength, bandwidth, and power output.
Abstract: We have used a newly developed Yb-doped high-power fiber source in an optical coherence tomography (OCT) apparatus. We have analyzed various properties of interest for OCT measurements such as spectral shape, related gate width, central wavelength, bandwidth, and power output.
TL;DR: Crystal structures of Calcium ions have been prepared in a linear Paul trap and their collective motion excited with resonant rf-fields and images of the fluorescing ions are obtained with a CCD camera and show high spatial resolution.
Abstract: Crystal structures of Calcium ions have been prepared in a linear Paul trap and their collective motion excited with resonant rf-fields. The trapped ions are laser-cooled and images of the fluorescing ions are obtained with a CCD camera and show high spatial resolution. Crystals with up to 15 ions arrange in a linear string and their eigenmodes can subsequently be selectively excited. The collective motion of the string can then be observed via the CCD images.