Showing papers in "Optical Review in 2003"
TL;DR: A new illumination method for a medical endoscope: narrow band imaging (NBI), in which the spectral bandwidth of the filtered light is narrowed, which has been shown that NBI can enhance the capillary pattern and the crypt pattern on the mucosa.
Abstract: We propose a new illumination method for a medical endoscope: narrow band imaging (NBI), in which the spectral bandwidth of the filtered light is narrowed. To confirm how the spectral specifications of the filtered light influence a reproduced image, an experiment was conducted observing the endoscopic images of the back mucosa of a human tongue. In addition, the effect of NBI on endoscopic images was investigated through preliminary clinical tests in colonoscopy and upper gastrointestinal endoscopy. It has been shown that NBI can enhance the capillary pattern and the crypt pattern on the mucosa. These patterns are useful features for diagnosing an early cancer.
287 citations
TL;DR: In this article, a number of optical elements with subwavelength structured surfaces have been developed, where the structures are equivalent to refractive index materials with form birefringence, and many new optical elements are realized using the artificial refractive indices of these sub-wavelength structures.
Abstract: Various optical elements with subwavelength structured surfaces have been developed. The periods of the subwavelength structures are too short to generate diffracted light waves. But the structures are equivalent to refractive index materials with form birefringence. Many new optical elements are realized using the artificial refractive indices of these subwavelength structures. Some typical elements are described here in the passive element regime, and fabrication methods of the elements are explained.
186 citations
TL;DR: A color holographic reconstruction system by time division multiplexing method with reference lights of laser that can reconstruct acolor holographic image by switching reference Lights of red, green and blue colors at certain intervals is reported.
Abstract: 3D-TV systems by holography technique have been studied in the world. In this paper, we report a color holographic reconstruction system by time division multiplexing method with reference lights of laser. The method can reconstruct a color holographic image by switching reference lights of red, green and blue colors at certain intervals. We can observe a color holographic image using red and green lasers as the reference lights, a high minute liquid crystal display (LCD) panel as a spatial light modulator (SLM) and electro-shutters as the shuttering device of the laser lights in the optical system. This approach has some advantages. Namely, the structure of the optical system can be simple and the number of LCD panels in the optical system can be decreased.
73 citations
TL;DR: In this article, the authors investigated the spread area of light waves in the waveguide layer and the accumulation of field energy by numerical simulation using the finite differential time domain (FDTD) method and showed that, in the case of a doubly periodic GMRG filter with a Q factor of 600, the field energy is spread over an area 5 um in width, which corresponds to the expected value from the angular tolerance.
Abstract: It is known that a doubly periodic guided-mode resonant grating (GMRG) filter has a broad angular selectivity with a narrow spectral bandwidth. This means that the doubly periodic GMRG filter operates for small beam diameter and grating area. This report describes the wave localization in the doubly periodic GMRG filter. We investigated the spread area of light waves in the waveguide layer and the accumulation of field energy by numerical simulation using the finite differential time domain (FDTD) method. Simulation results showed that, in the case of a doubly periodic GMRG filter with a Q factor of 600, the field energy is spread over an area 5 um in width, which corresponds to the expected value from the angular tolerance. And the magnitude of the field energy in the waveguide layer was Q factor times greater than the incident energy. On the other hand, a singly periodic GMRG filter with the same Q factor spread the field energy over an area 72 urn in width. This filter does not work for a small size structure or a small diameter light beam.
53 citations
TL;DR: In this paper, the Brillouin scattering method was used to analyze the acoustic fluxes constituting an acoustic domain in a piezoelectric semiconducting n-CdS.
Abstract: Acoustic fluxes constituting an acoustic domain in a piezoelectric semiconducting n-CdS were analyzed by Brillouin scattering method. Obtained results were as follows: 0.8 GHz and 2.0 GHz acoustic fluxes were faster than the sound velocity 1.75 × 105 cm/s. The observed profile of the 2.0 GHz flux agreed fairly well with the simulated one performed numerically by KdV equation. The faster positions of the acoustic domain were formed by lower frequency acoustic fluxes and the slower positions understood by acoustic fluxes around maximum gain frequency generated first in a small signal regime.
39 citations
TL;DR: In this paper, the characteristics of reflected near infrared light, which is incident on the skin surface, scattered in the skin tissue and detected, in the wavelength range from 1000 nm to 1900 nm, were calculated.
Abstract: We have calculated the characteristics of reflected near infrared light, which is incident on the skin surface, scattered in the skin tissue and detected, in the wavelength range from 1000 nm to 1900 nm. We have used a Monte Carlo method to calculate the propagation path, the average photon visit depth, the average photon path length, etc. for the cases of short source-detector distances, to which the isotropic scattering approximation cannot be applied. An experiment to validate the simulation results was also conducted using a liquid phantom.
29 citations
TL;DR: The axial resolution of optical coherence tomography (OCT) is determined by the coherence length of the light source as discussed by the authors, which is the length of a light source.
Abstract: The axial resolution of optical coherence tomography (OCT) is determined by the coherence length of the light source We demonstrate for the first time high-resolution OCT of biological tissue using a halogen lamp as the light source for a low coherence interferometer High-resolution OCT imaging with 35 μm resolution was performed successfully for onion and porcine skin, although the coherence light power for illumination of a sample is as small as 100 nW
27 citations
TL;DR: In this paper, a temperature-insensitive partial least squares analysis for glucose measurement is presented based on Near Infrared spectroscopy in the wavelength range from 1,250 to 1,800nm.
Abstract: Temperature-insensitive partial least squares analysis for glucose measurement is presented based on Near Infrared spectroscopy in the wavelength range from 1,250 to 1,800nm. Experiments are performed using aqueous glucose solutions. To create a temperature-insensitive prediction model, the glucose concentration and water temperature are varied independently. The results of the predicted glucose concentration agree well with the actual glucose concentration with an error of 4.4%.
26 citations
TL;DR: In this article, the applicability of the diffusion approximation over the radiative transfer theory for describing ultrafast laser transport in biological tissues is numerically studied and investigated over different kinds of tissue conditions and geometries.
Abstract: The diffusion model that is an approximation of the equation of radiation transfer is typically used to describe photon migration in scattering-dominant media. In general biological tissue is highly scattering and very weakly absorbing against near-infrared light, yet it is heterogeneous and may contain relatively highly absorbing or low-scattering regions. Here applicability of the diffusion approximation over the radiative transfer theory for describing ultrafast laser transport in biological tissues is numerically studied and investigated over different kinds of tissue conditions and geometries. Tissues having tumors of different sizes, locations and nature as well as dual-tumor and low-scattering conditions are considered. Radiation transfer analysis is taken as a comparison objective and it is initially proved to be accurate in benchmark comparisons with Monte Carlo simulation. The results predict systematically about the compatible conditions where and when we can use the diffusion approximation and the conditions in which the diffusion approximation may provide misleading results.
25 citations
TL;DR: In this paper, the authors used the iterative Monte Carlo technique for estimating the hemoglobin concentration and oxygenation of a local blood layer in a human skin tissue model on the basis of visible and near infrared reflectance spectra.
Abstract: A new method is studied for estimating the hemoglobin concentration and oxygenation of a local blood layer in a human skin tissue model on the basis of visible and near infrared reflectance spectra. This method uses the iterative Monte Carlo technique for a multi-layered skin tissue model. The numerical simulation was performed to investigate the effects of estimation errors for epidermis and dermis layers on the results for the local blood layer. Experiments with skin tissue phantoms were performed to verify the possibility of this method.
24 citations
TL;DR: In this paper, the performance characteristics of power build-up cavity (PBC) as the light source of a Raman spectroscopy-based gas sensor were studied and the key parameter to optimize stable and high intra-cavity power operation was beam diameter of the back reflected beam from external cavity to diode laser.
Abstract: Performance characteristics of power build-up cavity (PBC) as the light source of a Raman spectroscopy based gas sensor were studied. The key parameter to optimize stable and high intra-cavity power operation was beam diameter of the back reflected beam from external cavity to diode laser. The optimum diameter determined by an appropriate distance between the cavity and diode laser was found to be comparable with the waveguide cross section of diode laser for the effective spatial filtering, where inevitable cavity coupling loss caused by slight spatial mode mismatching existed. A PBC with a finesse of ∼10300 achieved a stable TEM00 mode in excess of intra-cavity power of 80 watts pumped by a 10 milliwatts diode laser. Simultaneously, the PBC wavelength is found to be passively locked effectively at 670 +/− 0.15 nm where the center of the gain region exists. A Raman spectrum of nitrogen measurement was demonstrated.
TL;DR: In this paper, a new version of the laser speckle flowgraphy was developed to study the dependence of the blood flow of the skin tissue under the sacrum and the supporting pressure against the body.
Abstract: A new version of the Laser Speckle Flowgraphy was developed to study the dependence of the blood flow of the skin tissue under the sacrum and the supporting pressure against the sacrum. The measuring unit consists of the laser diode, imaging system, line sensor, scanning mirror, and one-board microcomputer. The speckle signal is analyzed and sent to a personal computer, where the blood flow in a tissue area of 19 cm × 25 cm is evaluated and displayed on a 2-D color map. It was found that the blood flow in the skin tissue sharply decreased under the sacrum when it was supported by a hard surface, while the decrease became negligible when the surface was replaced by a soft airbag.
TL;DR: Simulation results with a simulation program with integrated circuit emphasis showed that the network was able to detect the approaching velocity and direction, and also recognized simple shapes such as a circle, square, triangle and rectangle.
Abstract: We proposed an analog network for motion detection of an approaching object with simple-shape recognition based on the visual systems of lower animals. Locusts can detect an approaching object by performing a simple process in a descending contralateral motion detector (DCMD) existing in their brain, which senses the increase in size and expansion velocity of the image projected on a retina just before collision. The responses correspond to the approaching velocity and direction. Frogs can recognize a simple shape by performing a simple process in a tectum and thalamus existing in their brain based on retinal information; this is called the Ewert von Seelen model. The proposed network was constructed with simple analog metal-oxide-semiconductor (MOS) circuits. Simulation results with a simulation program with integrated circuit emphasis (SPICE) showed that the network was able to detect the approaching velocity and direction, and also recognized simple shapes such as a circle, square, triangle and rectangle.
TL;DR: In this paper, the beam quality factors depend significantly on the transverse-mode confining structures of the waveguide structure and the transversal mode confining structure of the semiconductor laser.
Abstract: Output beam characteristics have been analyzed by numerical simulation for semiconductor lasers with various waveguide structures. It was found that the beam quality factors depend significantly on the transverse-mode confining structures.
TL;DR: In this paper, the spectral properties of two different types of conjugated polymers (polythiophene PT10 and polysilane PDHS) with nanoscale TiO2 particles forming a Maxwell Garnett or a Bruggeman composite are studied.
Abstract: Nonlinear spectral properties of two different types of conjugated polymers (polythiophene PT10 and polysilane PDHS) with nanoscale TiO2 particles forming a Maxwell Garnett or a Bruggeman composite are studied. According to the present simulations, it is possible both to enhance and to tailor the magnitude and the spectral properties, respectively, of the effective degenerate third-order nonlinear susceptibility of the composite. This is done simply by tuning the volume fraction of TiO2 inclusions and by changing the topology of the composite.
TL;DR: An imaging colorimeter is presented where the non imaging optical photodetector of the instrument is replaced with a charge-coupled device (CCD) sensor of a color video camera, enabling the independent capture of color information for any spatial point within its field of view.
Abstract: There has been a considerable effort made in several medical fields in the objective color analysis and characterization of biological tissues. Conventional colorimeters have proved inadequate for this purpose, since they do not provide spatial color information and because the measuring procedure randomly affects the color of the tissue. In this paper an imaging colorimeter is presented where the non imaging optical photodetector of the instrument is replaced with a charge-coupled device (CCD) sensor of a color video camera, enabling the independent capture of color information for any spatial point within its field of view. Combining imaging and colorimetry, the acquired image is calibrated and corrected under several ambient light conditions, providing non contact reproducible color measurements free of the errors and limitations present in conventional colorimeters. The technique has been used in hospital clinics for a wide variety of patients. These features highlight the potential of the imaging colorimeters as clinical and research tools for the standardization of clinical diagnosis and the objective evaluation of treatment efficacy.
TL;DR: In this paper, the magnitude of spectral change in blood glucose measurements with diffuse reflectance spectroscopy is investigated by simulation of light propagation in skin tissue and measurements of absorbance spectra of aqueous glucose solution.
Abstract: The magnitude of spectral change in blood glucose measurements with diffuse reflectance spectroscopy is investigated. Spectral change is estimated by simulation of light propagation in skin tissue and measurements of absorbance spectra of aqueous glucose solution. Required sensitivity of spectrophotometers for monitoring change in the blood glucose concentration as small as 10 mg/dL has been obtained using the estimated change in the absorbance spectrum and mean pathlength of light in tissue.
TL;DR: In this article, an electroforming process was used to make the metallic micromold insert for micro-molding of microlens array and the wettability property of the fabricated mold insert was examined by measuring the contact angle of the polymer in the pliable state.
Abstract: In micromolding of microlens array, it is important to prepare a mold insert of superb quality, which contains the micro-cavity of lens shape, because the geometrical quality of the mold insert defines the final quality of the molded micro-optics. In the present study, the electroforming process was used to make the metallic micro-mold insert for micro-molding of microlens array. The wettability property of the fabricated mold isnert was examined by measuring the contact angle of the polymer in the pliable state on the mold insert. Microlenses were compression-molded with the fabricated mold insert. The effects of the molding temperature and wettability property on the replication quality of the molded lenses were analyzed experimentally.
TL;DR: In this paper, a simple batch process for fabrication of microlens and micro-array array at the end of an optical fiber or optical fiber bundle using self-photolithography and etching techniques is described.
Abstract: This paper describes a simple batch process for fabrication of microlens and microlens array at the end of an optical fiber or an optical fiber bundle using self-photolithography and etching techniques. A photoresist micro-cylinder was exactly formed at the core of the fiber end by exposing an UV light from the other end of the fiber and conventional development, rinse processes. A photoresist microlens was formed by thermal reflowing of the fiber at 170°C for 1 h. A measurement of transmissivity showed that the fabricated photoresist microlens is applicable for a wavelength that is longer than 450 nm. Alternatively, a glass microlens was fabricated at the core of the fiber by dry etching with an SF6 gas using the photoresist microlens as a mask. The focusing of the lensed fiber was confirmed and simulation work showed that the lensed fiber could focus the light with a beam spot of 2 μm, numerical aperture (NA) of 0.285 and a depth of focus of 16 μm.
TL;DR: In this article, a Fourier transform phase-modulation fluorometer was proposed to obtain a fluorescence decay waveform from a non-fluorescent material. But the proposed method requires the measurement of the fluorescence signal waveform and the corresponding amplitude and phase spectra.
Abstract: I propose a concept of a novel Fourier-transform phase-modulation fluorometer by which a fluorescence decay waveform can be obtained. In the fluorometer, the modulation frequency of the excitation light source is swept continuously from a start frequency fmin to an end frequency fmax with a time duration T. The resultant fluorescence signal waveform is Fourier-transformed to obtain amplitude and phase spectra. The ratio of the amplitude spectrum and the difference of the phase spectrum over those of the reference spectra that are obtained from a non-fluorescent material are calculated, respectively, and the pair of both spectral data is inverse-Fourier-transformed again to obtain the fluorescence decay waveform. To verify and demonstrate the effectiveness of the concept, I carried out (1) numerical simulations, (2) determination of a time constant of a passive resistor-capacitor (RC) differential circuit, and (3) measurement of a fluorescent decay waveform of YAG materials packed in Nichia’s white LED.
TL;DR: In this article, a GaP microlens for collecting laser light was developed in the tip of a near-field probe using the two-dimensional finite difference time domain (2-D FDTD) method.
Abstract: A GaP microlens for collecting laser light was developed in the tip of a near-field probe. It is important to realize a near-field optical probe head with high throughput and a small spot size. The design and fabrication results of the GaP microlens array are described. The most suitable GaP microlens with a probe was calculated as having a 10 μm radius using the two-dimensional finite difference time domain (2-D FDTD) method. The full width half maximum (FWHM) spot size variation and optical power density tolerance were calculated as 157 nm ± 5 nm and 7%, respectively. A spherical GaP microlens was fabricated with a radius of 10 μm by controlling the Cl2/Ar gas mixture ratio. The difference between the theoretical spherical shape and the fabricated GaP microlens was evaluated as 40 nm at peak to valley. The FWHM spot size and optical throughput of the fabricated microlens were measured as 520 nm and 63%, respectively. The microlens was the same as a theoretical lens with a 10 μm radius. The micron-lens array fabrication process for a near-field optical head was demonstrated in this experiment.
TL;DR: In this article, the performance bound on multiple-pulse position modulation (MPPM) was derived from the error probability, cutoff rate, and inverse pulse width approximation expressions, and compared with the power and bandwidth efficiency of MPPM.
Abstract: In this paper we derive the performance bound on multiple-pulse position modulation (MPPM). We compare this bound with power and bandwidth efficiency of MPPM derived from the error probability, cutoff rate, and inverse pulse width approximation expressions.
TL;DR: The DPF values obtained in this study should contribute to a better understanding of noninvasive measurements by NIRS in neonates.
Abstract: Near-infrared spectroscopy (NIRS) has been used for measurement of changes in cerebral hemoglobin concentrations in neonates to study cerebral oxygenation and hemodynamics. In this study, measurements by time-resolved reflectance spectroscopy (TRS) were performed in a piglet model with various degrees of cerebral oxygenation to estimate the differential pathlength factor (DPF). A portable three-wavelength TRS system (TRS-10, Hamamatsu Photonics K.K.) with a probe attached to the head of a piglet was used. Eleven newborn piglets were anesthetized and respired by a ventilator to induce stepwise hypoxia loading. The DPF showed positive linear relationship with arterial hemoglobin (Hb) oxygen saturation and sagittal sinus venous Hb oxygen saturation at 761 and 795 nm. The DPF at 835 nm also showed very slight positive linear relationship with arterial hemoglobin oxygen saturation. The DPF values obtained in this study should contribute to a better understanding of noninvasive measurements by NIRS in neonates.
TL;DR: In this paper, the authors proposed a new structure containing multimode interference waveguides with partial nonlinear Kerr-like material whose function is like a phase shifter for all-optical logic gates.
Abstract: We propose a new structure containing multimode interference waveguides with partial nonlinear Kerr-like material whose function is like a phase shifter for all-optical logic gates. It has the advantages of compactness and insensitivity to relative phase difference between the incident beams. In this paper, we analyze the structure by finite difference time domain method and demonstrate such logic gates as AND, NOT and XOR logics.
TL;DR: A multi-spectral imaging system is evaluated for mapping melanin density, total-hemoglobin density, and oxygen saturation in human skin using three pre-computed “look-up” tables for color conversions.
Abstract: A multi-spectral imaging system is evaluated for mapping melanin density, total-hemoglobin density, and oxygen saturation in human skin. In this system, the distribution of pigments in human skin is estimated and displayed from digital video signals using three pre-computed “look-up” tables for color conversions. The accuracy of the system is analyzed based on computer simulation by changing the number of bands, quantization levels of the camera system, and dimensions of approximation for spectral reflectance. The optimal system is examined based on the results of computer simulation.
TL;DR: For the purpose of developing reflection pulse oximetry, the authors analyzed the light propagation in tissue to calculate the photon-visit depth for reflected light and to estimate the measured intensities of transmitted and reflected light using the analytical solutions of the photon diffusion equation.
Abstract: For the purpose of developing reflection pulse oximetry, we have analyzed the light propagation in tissue to calculate the photon-visit depth for reflected light and to estimate the measured intensities of transmitted and reflected light using the analytical solutions of the photon diffusion equation. The effects of the reflectance of the probe surface have been studied, and a low reflecting surface has been found to provide deeper photon-visit depth than a high reflecting surface for reflection pulse oximetry. Based on analytical estimation, we made reflection type probes, and conducted preliminary experiments to confirm the feasibility of this type of pulse oximetry.
TL;DR: The configuration of the four-wavelength optical imager system and test measurements for foot disease were presented, and arteriosclerosis obliterate patients and healthy volunteers were clearly distinguishable.
Abstract: A new four-wavelength optical imager has been developed for the evaluation of various vascular diseases. Four-wavelength optical intensity images are transformed to an oxygenation mapping, which further provide maps of rapid changes in hemoglobin distribution in human skin related with peripheral blood flow. This paper presents the configuration of the system and test measurements for foot disease. Forty-nine volunteers took part in our measurements with an occlusion test of their legs. Some differences were observed in oxygenation change between healthy volunteers and patients, and arteriosclerosis obliterate (ASO) patients and healthy volunteers were clearly distinguishable.
TL;DR: In this paper, a new optical storage media using minute spheres arranged on a surface relief grating (SRG) was fabricated using a confocal optical system as a record and readout system.
Abstract: We have fabricated a new optical storage media using minute spheres arranged on a surface relief grating (SRG). Using minute spheres as recording bits, we can limit recordable regions by sphere size, and can realize high resolution reproduction in the plane direction. Surface relief structures were made on a polymer thin film on which we performed diffusion arrangement and adsorptive fixation of minute spheres. The stability of the arranged spheres was confirmed for heating and washing. Furthermore, we used a dipping method for a more simple arrangement of minute spheres on a large area of the substrate and made a monolayer sample of the spheres. We were able to realize a highly sensitive reconstruction of the medium using a confocal optical system as a record and readout system.
TL;DR: In this paper, a novel all-fiber optical delay line for an advanced optical coherence tomography (OCT) system is proposed using the distributed reflectance characteristic of a chirped fiber Bragg grating (CFBG), which can be obtained without leaving the fiber that forms the system.
Abstract: A novel all-fiber optical delay line for an advanced optical coherence tomography (OCT) system is proposed. Using the distributed reflectance characteristic of a chirped fiber Bragg grating (CFBG), the optical delay can be obtained without leaving the fiber that forms the system. The proposed delay line consists of a pair of identical CFBGs. The gratings are cascaded in reverse order to cancel the inherent wavelength dependency of CFBGs. Tunable optical delay is obtained by applying small strain on one of the CFBGs through an attached piezo actuator. The small displacement induced by the piezo actuator is amplified by a factor of up to 100 due to the distributed reflectance characteristic of the CFBGs. This principle and characteristics of the proposed optical delay line are analyzed in detail.
TL;DR: It is shown in this paper that the walls surrounding this space are the most important IVI for the construction of the RVSI.
Abstract: The apparent color of an object depends on how we recognize the space where it is placed in terms of illumination. We call this the recognized visual space of illumination (RVSI). What we see in the space first, namely, the initial visual information (IVI) determines properties of the RVSI, and we will show in this paper that the walls surrounding this space are the most important IVI for the construction of the RVSI. A normal room was illuminated by a ceiling light at 60 lx and its central area was also lit by a hidden illumination of 400 lx. Two halves of a miniature room with walls on three sides and a floor were inserted from left and right sides into the hidden illumination to gradually create one miniature room, and the apparent lightness of a test patch was judged as a function of the amount of the inserted portions to measure construction of RVSI for the hidden illumination. The apparent lightness was around 55 in L∗ when no IVI was in the hidden illumination, it gradually went down with more IVI to around 40 L∗ to return toward its nominal lightness of 24 L∗ in the case of test patch N2. The drop was large with the present condition of IVI where, in the end, the space of the hidden illumination was surrounded by walls, compared to the previous results where the space was filled only by objects; this indicated the importance and efficiency of walls for constructing RVSI.