This PDF file contains the front matter associated with SPIE Proceedings Volume 7894, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

In this paper, we propose and demonstrate a new method to monitor heart rate using fiber optic microbending based sensor for in-bed non-intrusive monitoring. The sensing system consists of transmitter, receiver, sensor mat, National Instrument (NI) data acquisition (DAQ) card and a computer for signal processing. The sensor mat is embedded inside a commercial pillow. The heart rate measurement system shows an accuracy of +/-2 beats, which has been successfully demonstrated in a field trial. The key technological advantage of our system is its ability to measure heart rate with no preparation and minimal compliance by the patient.

The numerous potential applications of UV-induced fiber Bragg gratings (FBGs) in fiber optic sensing and telecommunication have generated a significant interest in this field in recent years. However, two major factors-the photosensitivity of the fiber in which the grating is written and the thermal stability of the grating-are of prime importance in terms of choosing the most appropriate fiber to use and of the long-term functionality of the grating over a wide range of temperatures. Based on the plasma chemical vapor deposition (PCVD) process, the high Ge (Germanium) and Ge/B (Germanium/Boron) co-doped photosensitive fiber were developed. It is mature technique that to precise control the dopant quantity by PCVD process. The photosensitive fibers with different doping composition and doping concentration have been studied. Based on the experimental results obtained from studies of several kinds of photosensitive fiber on both the photosensitivity and the temperature sustainability of the FBGs written into them, the experimental results exhibit that the Boron dopant brings deleterious influence on the FBG's high-temperature sustainability. The FBG sustainable temperature will become lower than 500°C when the Boron concentration reaches 14% in germanium highly doped photosensitive fiber.

The paper presents the concept of the modalmetric fiber optic sensor system for human psychophysical activity detection. A fiber optic sensor that utilizes intensity of propagated light to monitor a patient's vital signs such as respiration cardiac activity, blood pressure and body's physical movements. The sensor, which is non-invasive, comprises an multimode fiber proximately situated to the patient so that time varying acusto-mechanical signals from the patient are coupled by the singlemode optical fiber to detector. The system can be implemented in embodiments ranging form a low cost in-home to a high end product for in hospital use. We present the laboratory test of comparing their results with the known methods like EKG. addition, the article describes the work on integrated system to human psychophysiology activity monitoring. That system including a EMFIT, microwave, fiber optic and capacitive sensors.

A special type of Cyclic Olephin Polymer silver coated (COP/Ag) hollow waveguide was used for delivery of 4.45 μm laser radiation. This mid-infrared radiation having major signification in special lidar or spectroscopy applications was generated by new bulk Fe:ZnSe laser working at the room temperature in gain switched regime. The coherent pumping of Fe:ZnSe laser was performed by electro-optically Q-switched Er:YAG laser which wavelength (2.94 μm) corresponds to the maximum of Fe:ZnSe absorption peak. The Er:YAG laser energy and pulse-length used was 11 mJ and ~ 300 ns, respectively. The generated Fe:ZnSe laser output energy was reached 1.1 mJ with the pulse-length 240 ns. The aim of the presented project was to investigate the transmission possibility of 4.45 μm mid-infrared Fe:ZnSe radiation by the COP/Ag hollow glass waveguide. The inner waveguide diameter was 700 μm and length 103 cm. Midinfrared laser radiation was focused into the guidance protector by the CaF2 lens with the focal length 55 mm. After the coupling Fe:ZnSe radiation optimization, the maximum transmission of radiation through the waveguide reached 64%. The time evolution of the pulse was not changed by the delivery but the space structure is changing essentially. It follows from the radiation transport principle of the hollow waveguide. The bent waveguide transmission was also investigated and 60% was obtained. For the case of contact application the fused silica cap was performed. As conclude the compact delivery system for 4.45 μm mid-infrared radiation with the short 240 ns pulse length and transmitted power density 0.57 MW/cm2 was successfully investigated and it can be used for the applications.

There is a pressing need for a passive optical fiber dosimeter probe for use in real-time monitoring of radiation dose delivered to clinical radiation therapy patients. An optical fiber probe using radiochromic material has been designed and fabricated based on a thin film of the radiochromic material on a dielectric mirror. Measurements of the net optical density vs. time before, during, and after irradiation at a rate of 500cGy/minute to a total dose of 5 Gy were performed. Net optical densities increased from 0.2 to 2.0 for radiochromic thin film thicknesses of 2 to 20 μm, respectively.

CMOS sensors used in high-quality imaging systems of human eye require subtraction of the fixed pattern noise (FPN) to increase the signal to noise ratio (SNR). In this paper, we evaluated the efficiency of the FPN subtraction as a function of temperature (in the range from +70°C to -50°C) and integration time (from 12.5 to 287.5 ms) for a low-cost commercial CMOS sensor. We also compared the quality of the photos taken at different sensor temperatures on a phantom and on voluntary subjects. The experimental set-up includes a modified fundus camera for retinal examination (Centervue SpA, Italy) equipped with a 5Mpixel CMOS sensor and a temperature regulation system. The problem of water condensation on the sensor surface at low temperatures was overcome by using an original sensor sealing method.

A motion compensated fiber optic confocal microscope system is demonstrated using a combination of a Fourier domain common-path optical coherence tomography (CP-OCT) distance sensor and a high-speed linear motor. The confocal microscope is based on 460 micron diameter fiber bundle terminated with a gradient index (GRIN) lens. Using the peak detection of a 1-D A-scan data of CP-OCT, the distance deviation from the focal plane could be monitored in real-time. When the distance deviation surpasses a certain threshold, the linear motor drives the confocal microscope probe at a speed related to the change in the deviation to maintain the deviation within a predetermined limit. The motion compensation was achieved for a confocal microscope imaging rate of 1Hz with an average distance error of 4 microns.

Interstitial fiber-optic based strategies for therapy monitoring and assessment rely on detecting treatment-induced changes in the light distribution in biological tissues. We present an optical technique to identify spectrally and spatially specific tissue chromophores in highly scattering turbid media. Typical optical sensors measure non-directional light intensity (i.e. fluence) and require fiber translation (i.e. 3-5 positions), which is difficult to implement clinically. Point radiance spectroscopy is based on directional light collection (i.e. radiance) at a single point with a side-firing fiber that can be rotated up to 360°. A side firing fiber accepts light within a well-defined solid angle thus potentially providing an improved spatial resolution. Experimental measurements were performed using an 800-μm diameter isotropic spherical diffuser coupled to a halogen light source and a 600 μm, ~43° cleaved fiber (i.e. radiance detector). The background liquid-based scattering phantom was fabricated using 1% Intralipid (i.e. scattering medium). Light was collected at 1-5° increments through 360°-segment. Gold nanoparticles, placed into a 3.5 mm diameter capillary tube were used as localized scatterers and absorbers introduced into the liquid phantom both on- and off-axis between source and detector. The localized optical inhomogeneity was detectable as an angular-resolved variation in the radiance polar plots. This technique is being investigated as a non-invasive optical modality for prostate cancer monitoring.

Extremely flexible hollow fibers with 100-μm-bore size or less were developed for infrared laser delivery. Fabrication process and transmission properties of the ultra-thin hollow fiber were discussed. The silver layer was inner-plated by using the conventional silver mirror-plating technique. Concerning the fabrication parameters used up to now for 320-μm bore-sized fibers, the target flowing rate for plating solutions was 10 ml/min. Parallel bundles of silica capillary were used to increase the cross-sectional area. To achieve the target, bundles with 560 pieces, 1200 pieces, and 9600 pieces were used for the capillary with inner diameters of 100-μm, 75-μm, and 50-μm, respectively. The loss for the 50-μm bore size, 10-cm length silver hollow fiber was 10 dB at the wavelength of 1 μm.

A new silica-based fiber design has been developed which exhibits improved transmission properties over a very wide spectral range. In the near infrared wavelength region, the attenuation of the new fiber is similar to standard near infrared fibers having a low -OH silica core and F-doped cladding. Simultaneously, the fiber has excellent UV transmission down to 200nm comparable to standard high -OH fibers. Additionally, the UV-defect concentrations in this low -OH fiber have been reduced significantly, such that the solarization degradation properties are close to UV optimized high -OH fibers with high radiation resistance. First results of spectral performance testing are given using different light sources, including Deuterium lamp and Tungsten-halogen lamp. In addition, the test results evaluating UV solarization are reviewed. Finally, potential applications in the medical and industrial fiber sensing field will be discussed.

Pulse oximeters measure a patient's heart rate and blood oxygenation by illuminating the skin and measuring the intensity of the light that has propagated through it. The measured intensities, called photoplethysmograms (PPGs), are highly susceptible to motion, which can distort the PPG derived data. Part of the motion artifacts are considered to result from sensor deformation, leading to a change in emitter-detector distance. It is hypothesized that these motion artifacts correlate to movement of the emitter with respect to the skin. This has been investigated in a laboratory setup in which motion artifacts can be reproducibly generated by translating the emitter with respect to a flowcell that models skin perfusion. The top of the flowcell is a diffuse scattering Delrin skin phantom under which a cardiac induced blood pulse is modeled by a changing milk volume. By illuminating the flowcell, a PPG can be measured. The emitter's translation has been accurately measured using self-mixing interferometry (SMI). The motion artifacts in the PPG as a result of emitter motion are shown to correlate with the emitter's displacement. Moreover, it is shown that these artifacts are significantly reduced by a least-mean-square algorithm that uses the emitter's displacement measured via SMI as artifact reference.

Microsurgery requires constant attention to the involuntary motion due to physiological tremors. In this work, we demonstrated a simple and compact hand-held microsurgical tool capable of surface tracking and motion compensation based on common-path optical coherence tomography (CP-OCT) distance-sensor to improve the accuracy and safety of microsurgery. This tool is miniaturized into a 15mm-diameter plastic syringe and capable of surface tracking at less than 5 micrometer resolution. A phantom made with Intralipid layers is used to simulate a real tissue surface and a single-fiber integrated micro-dissector works as a surgical tip to perform tracking and accurate incision on the phantom surface. The micro-incision depth is evaluated after each operation through a fast 3D scanning by the Fourier domain OCT system. The results using the surface tracking and motion compensation tool show significant improvement compared to the results by free-hand.

Scanning light sources in biophotonic devices are considered as either extended or pulsed sources when their potential optical hazard is evaluated. While the existing evaluation criteria are directly applicable to scanning light sources in most cases, different dwell-time and overlap between the beams need to be taken into account to obtain maximum irradiation. The effect of dwell-time and overlap of scanning light source on the irradiation of lights to skin was theoretically and experimentally analyzed in this report.

The feasibility of a biosensor for DNA label-free detection, based on long period fiber gratings, has been investigated. The surface of the grating has been functionalized with Peptide Nucleic Acid (PNA) probes. DNA strands, matched with the PNA probes, have been immobilized on the surface itself. The possibility of a resonant wavelength shift in the transmission spectrum due to the DNA capture will be discussed. The problem of reusing the sensor for multiple measurements will also be addressed.

Early detection of high-risk coronary atherosclerosis remains an unmet clinical challenge. We have previously demonstrated a near-infrared fluorescence catheter system for two-dimensional intravascular detection of fluorescence molecular probes [1]. In this work we improve the system performance by introducing a novel high resolution sensor. The main challenge of the intravascular sensor is to provide a highly focused spot at an application relevant distance on one hand and a highly efficient collection of emitted light on the other. We suggest employing a double cladding optical fiber (DCF) in combination with focusing optics to provide a sensor with both highly focused excitation light and highly efficient fluorescent light collection. The excitation laser is coupled into the single mode core of DCF and guided through a focusing element and a right angle prism. The resulting side-fired beam exhibits a small spot diameter (50 μm) throughout a distance of up to 2 mm from the sensor. This is the distance of interest for intravascular coronary imaging application, determined by an average human coronary artery diameter. At the blood vessel wall, an activatable fluorescence molecular probe is excited in the diseased lesions. Next light of slightly shifted wavelength emits only in the places of the inflammations, associated with dangerous plaques [2]. The emitted light is collected by the cladding of the DCF, with a large collection angle (NA=0.4). The doublecladding acts as multimodal fiber and guides the collected light to the photo detection elements. The sensor automatically rotates and pulled-back, while each scanned point is mapped according to the amount of detected fluorescent emission. The resulting map of fluorescence activity helps to associate the atherosclerotic plaques with the inflammation process. The presented detection system is a valuable tool in the intravascular plaque detection and can help to differentiate the atherosclerotic plaques based on their biological activity, identify the ones that prone to rupture and therefore require more medical attention.

The Radial Angular Filter Array (RAFA) is a novel silicon micro-machined optical filter for real-time high resolution measurement of the angular distribution of scattered photons. It includes a radially-distributed series of micro-channels facing a focal point that is several millimeters away from the edge of the device. In this work, three RAFA designs were devised to enhance the angular resolution, while lessening the complexity of the output coupling. These new RAFA designs solved issues associated with a previous prototype device, including the signal loss in high angle channels and light leakage beyond the acceptance angle. Typically, channels in the RAFA are 60 μm deep with a minimum length of 10 mm. To characterize the RAFA designs, we used an incoherent broadband source, collimation optics, turbid samples, and a spectrometer. The tests identified which design features resulted in improved performance, including the preferred output coupling structure, the recommended near specular direction blocking range, the choice of constant aspect ratio or solid angle, and other geometrical parameters.

The highly sensitive Raman cell based on the hollow optical fiber that is suitable for the real-time breath analysis is reported. Hollow optical fiber with inner coating of silver is used as a gas cell and a Stokes light collector. A very small cell whose volume is only 0.4 ml or less enables fast response and real-time measurement of trace gases. To increase the sensitivity the cell is arranged in a cavity which includes of a long-pass filter and a high reflective mirror. The sensitivity of the cavity cell is more than two times higher than that of the cell without cavity.

This paper presents a design procedure for a fibre interferometer, the optical system and its associated electronic control. Analog and digital circuits were optimized to achieve a low cost compact system. The lock-in amplifier required for phase control was designed using a FPGA. The errors in an interferometric measurement were studied in detail and its results were used to estimate the capabilities of the interferometer. These matched our observed resolution of 40 nm. A stabilization technique of controlling the path length difference between the arms of interferometer nullifies any phase errors. The design and testing of the control circuit are described in detail. In addition, the FPGA was programmed to carry out phase stepping, as this technique is used to calculate the desired phase. The interferometer was used to measure samples with step heights in the hundreds of nanometers, with improvements in accuracy through averaging of data. We verified the successful working of the instrument by measuring a height of 423 nm for a 420 nm structure.

The integration of a fluorescence microscopy/spectroscopy module in cell-based lab-on-a-chip systems is of high interest for applications in cell-based diagnostics and substance evaluation in situ. We present an on-chip integrated lensless fluorescence imaging module applying the principle of contact/proximate optical lithography. The pixel resolution is comparable with a 4 x objective microscope. The module can be used for morphology and fluorescence imaging of mammalian cells (15 - 20 μm) as well as for testing the concentration of a fluorescent substance. The biological samples or solutions are sustained in disposable sterilized microfluidic chips with 1 μm thick silicon nitride (Si₃N₄) membranes. These chips are assembled on the surface of a 5 megapixel colored CMOS image sensor array with 1.75 μm pixel size, which is coated with an additional interference filter. Each culturing chip consists of a MEMS cavity chip and a PDMS microfluidic interface. The surface of the CMOS image sensor is smoothened using SU-8 photoresist spin-coating for a commercial grade interference filter (optical density ≥ 5) coating by Plasma-Ion Assisted Deposition thereafter. The function is demonstrated by primary imaging results of the non-/fluorescent mammalian cells/microspheres as well as by differentiating different concentrations of FITC solutions.

Fiber-optic Raman tweezers for molecular analysis of bio-particles in turbid media is proposed. The Raman tweezers consists of a single hollow optical fiber and a specially designed trapping lens mounted at the fiber tip. Raman spectra of polystyrene particles dispersed in NaCl aqueous solution are observed.

Presently, there is no truly flexible delivery system for light from Er:Yag medical lasers (λ = 2.94 μm) which allows surgeons to work unrestricted. Instead, either a relatively inflexible articulated arm or multi-mode fibre, limited to large bend radii, must be used. One proposed solution is the use of novel types of hollow core - band gap optical fibre rather than more traditional large area solid core fibres. In these silica based fibres, material absorption and damage limitations are overcome by using a photonic band gap structure. This confines radiation to lower order modes, that are guided in a small diameter air core. The overall fibre diameter is also smaller, which allows a smaller mechanical bend radius. Together with the guidance in air, this improves the laser power damage threshold. However, there are many practical hurdles that must be overcome to achieve a robust system for use in surgery. One of the main problems is that the fibre structure is hollow and ingress of dust, vapour, fluids and other contaminants need to be prevented to ensure safe in-vivo usage. Additionally, any infibre contamination will degrade the laser damage resistance of the fibre leading to potential catastrophic failure. The development of a robust and hermetically sealed end cap for the fibre, without adversely affecting beam quality or damage threshold is an essential prerequisite for the safe and efficient use of such fibres in surgery. In this paper we report on the progress on implementing end caps and describe novel methods of sealing off these hollow fibres in particular for surgical applications. This work will demonstrate that the use of these superior fibres with low loss guidance at 2.94 μm in surgery is feasible.

This study aims to develop a photothermal imaging system through a coherent infrared bundle. This system will be used to determine the oxygenation level of various tissues, suspected malignant tissues in particular. The oxygenation estimation is preformed using a computerized algorithm. In order to evaluate the system, different bundle configurations were used for the determination of the optimal one. Bundle transmittance and the algorithm's estimation ability were measured, measurements were performed using agar phantoms consisting of varying ratios of Methylene Blue and ICG. A bundle consisting of 19 Teflon waveguides with a of 1.1mm was found to be the optimal configuration with an RMS of the error of 9.38%. At a second stage the system was validated on blood samples with varying oxygenation levels and there oxygenation levels were estimated. This stage had an RMS of the error of 10.16% for the oxygenation level estimation for samples with a 50% oxygenation level and higher. Once the basic system was validated successfully on agar phantoms and blood samples a portable system was designed and built in order to fit the system for portable use. The portable system consists of a white light illuminating source followed by filters transmitting certain wavelengths, a transmitting fiber, a thermal imaging bundle and a portable thermal camera. This portable system will be evaluated in order to have an adequate portable system for implementing the method out of the lab.

Over the years, technological achievements within the laser medical diagnostic, treatment, and therapy markets have led to ever increasing requirements for greater control of critical laser beam parameters. Increased laser power/energy stabilization, temporal and spatial beam shaping and flexible laser beam delivery systems with ergonomic focusing or imaging lens systems are sought by leading medical laser system producers. With medical procedures that utilize laser energy, there is a constant emphasis on reducing adverse effects that come about by the laser itself or its optical system, but even when these variables are well controlled the medical professional will still need to deal with the multivariate nature of the human body. Focusing on the variables that can be controlled, such as accurate placement of the laser beam where it will expose a surface being treated as well as laser beam shape and uniformity is critical to minimizing adverse conditions. This paper covers the use of fiber optic beam delivery as a means of defining the beam shape (intensity/power distribution uniformity) at the target plane as well as the use of fiber delivery as a means to allow more flexible articulation of the laser beam over the surface being treated. The paper will present a new concept of using a square core fiber beam delivery design utilizing a unique micro lens array (MLA) launch method that improves the overall stability of the system, by minimizing the impact of the laser instability. The resulting performance of the prototype is presented to demonstrate its stability in comparison to simple lens launch techniques, with an emphasis on homogenization and articulated fiber delivery.

For applications of fiber guided pulsed UV-laser radiation in biomedical optics, laser spectroscopy or laser micro processing which need good beam quality low mode or single mode optical fibers are required. We investigated the transmission properties at 355 nm wavelength with laser peak powers up to 5 GW/cm² or laser fluences up to 9.5 J/cm². In some cases fibers were damaged during prolonged irradiation at this intensity level. So these fluences or intensities can be used as estimation for the damage threshold. It turns out, that degradation or microstructural damage in the fiber core plays a minor role in long term transmission as long as the intensity stays below the damage threshold. Fiber lengths of many meters are possible. Single mode UV laser beam guiding is possible. UV beam guiding with high pulse repetition rate, moderate peak power will be compared with that of moderate repetition frequency, high peak power lasers

High-order skew modes will be excited in multimode step-index fibers using special excitation conditions. As a result, light with an angle of incidence larger than the maximum angle for meridional modes given by the numerical aperture of the fiber can be coupled into a fiber. Combining the selective mode-excitation with new powerful broadband light-sources, the spectral light-guidance of such skew modes in different optical fibers will be described in detail. Results of the proposed system in context of different light-sources will be discussed. A new evanescent sensor approach based on controlled coupling of skew modes will be introduced. Finally, first steps to construct such sensors for medical and analytical applications will be presented.

The integration of thermal and photodynamic therapy into a scanning fiber endoscope (SFE) for the purpose of pixel accurate laser therapy during an endoscopic procedure has been examined using two distinct methods: combining R- 635nm, G-532nm, B-440nm (RGB) laser light for imaging with high-power 405nm single-mode or multi-mode laser light for therapy. The single-mode system utilizes a SIFAM 405/635nm fused fiber device to combine single-mode 405nm and 635nm laser light into the core of a single output fiber. The multi-mode system uses a custom combiner (Lightel Technologies) to guide single-mode RGB light from one fiber into the core of a custom single-mode dual cladding fiber (DCF, Coherent) and places multi-mode 405nm light from a second input optical fiber into the inner cladding of the DCF. This multi-mode system has a higher output power measured at 300mW compared to the singlemode system measured at 30mW before the addition of combiners. A lens system from the SFE at the distal tip of each therapeutic system was used to focus the light without scanning. The resulting minimum spot diameters were 77microns for the single-mode system and 311microns for the multi-mode system, which equates to fluence rates of 644W/cm2 and 395W/cm2 respectively. Future studies will integrate a scanning fiber probe to the outputs of each system allowing the therapeutic light to be directed throughout an entire image as well as the ability to use wide-field fluorescence imaging with 405nm excitation.

Spectroscopy in the long-wave infrared (LWIR) wavelength region (8 to 12 μm) is useful for detecting trace chemical compounds, such as those indicative of weapons of mass destruction (WMD). To enable the development of field portable systems for anti-proliferation efforts, current spectroscopy systems need to be made more robust, convenient, and practical (e.g., miniaturized). Hollow glass waveguides have been used with a Quantum Cascade Laser source for the delivery of single-mode laser radiation from 9 to 10 μm. The lowest loss measured for a straight, 484 μm-bore guide was 0.44 dB/m at 10 μm. The smallest 300 μm-bore waveguide transmitted singlemode radiation even while bent to radii less than 30 cm.

Single-crystal (SC) fibers have the potential of delivering extremely high laser energies. Sapphire fibers have been the most commonly studied SC fiber and the losses for sapphire fibers have been as low as 0.4 dB/m for a 300- micron core-only fiber at 3 microns. In this study we report on the growth of SC yttrium aluminum garnet, Y₃Al₅O₁₂(YAG) fibers from undoped SC source rods using the Laser Heated Pedestal Growth (LHPG) technique. The advantage of YAG over sapphire is the slight improvement in IR transmission of YAG. The IR transmission of bulk YAG has been shown to extend to 5 μm where the absorption coefficient is 0.6 cm^-1. The garnet family of crystals is one of the most commonly used oxide crystal hosts for lasing ions in high power solid-state lasers, with the most commercially common laser host being YAG. Thus, it is reasonable to assume that YAG fibers will have high laser damage thresholds. The optical losses for 400-μm diameter YAG fibers have been measured to be about 3 dB/m at 2.94 μm. The longest length of YAG fiber grown has been about 60 cm.

We present a simple fiber-optic confocal method for high-precision thickness measurement of optically transparent and non-transparent objects that require noncontact measurement. The method is based on measurement of confocal backreflection responses from the opposite surfaces of objects, which imposes inessential limitations on the shape, thickness, and transparency of testing objects. A novel reference comparison method to eliminate additional errors existing commonly in confocal microscope designs is adapted. The measurement error highly depends on the axial response of confocal microscope, and was measured to be 5.0 μm using a single-mode optical fiber construction, 60× objective lenses, and a 658-nm-wavelength laser source. We demonstrate the method using lensed-fiber sensors, which reduces the size of the experimental setup so that the method can be utilized for smaller samples at in-vivo situation. We demonstrate the proof-of-concept measurement using biological samples.

For infrared thermal imaging of body temperature, a flexible and coherent bundle of hollow optical fibers was fabricated. Differences in the transmission efficiency among the fibers were numerically compensated to obtain high temperature resolution of 1°C for measuring body temperature. In a lens system with 10-fold magnification and hollow fibers of 320- μm inner diameter, the spatial resolution is around 3 mm. The hollow-fiber bundle enables observation of the surface temperature of inner organs and blood flow of the surfaces when the bundle is introduced into the human body with an endoscope.

We propose a new method for k-domain linearization using fiber Bragg gratings (FBGs) in a wavelength-swept source for optical coherence tomography (OCT). A wavelength-swept source with a scanning fiber Fabry-Perot tunable filter is constructed using a conventional ring laser cavity. Five FBGs are used to recalibrate the nonlinear response from the wavelength-swept source. We achieved good quality sample imaging using the k-domain linearization algorithm based on FBGs. The sensitivity at 2 mm is improved by more than 10 dB after k-domain linearization.