Thin Optical Fiber Research Articles

低侵襲外科手術用光駆動ＳＭＡ能動かん子

In this paper, we propose a new method to drive SMA (shape memory alloy) -pipe active forceps for minimally invasive surgery. Two actuation methods of SMA pipe have previously been introduced, namely, hot/cold water circulation, and electric heating. The former suffers from rather slow response. Although the latter shows better response, it is unsuitable for surgery of current-sensitive areas. In this paper, optical heating and gas cooling are newly proposed for heat transfer of the shape memory alloy pipe. The use of optical heating and gas cooling allows to actuate forceps in dry conditions, which simplifies sterilization and eases manufacturing process. It also opens the way to applying this forceps to surgery of current-sensitive areas, such as cardiac and cerebral surgery. The prototype active forceps is fablicated using KTP/YAG laser as light source, thin optical fiber (core diameter: 0.3 [mm] ) as light guide, and CO2 freezing gas as coolant. Mathematical analysis provides fundamental heating/cooling performance. The prototype experimentally shows approximately 3 [sec] of heating/cooling speed.

眼底網膜手術用ファイバスコープ付きマイクロ能動かん子の開発

A new concept of eye microsurgical system is proposed. The final goal of our research project is not only improving surgical instruments but also establishing a total surgical system applicable to today's most difficult microsurgery at the bottom of an eyeball. The new prototype of micro forceps, which has a joint to enlarge the surgical area and also has a built-in thin optical fiberscope to increase the dexterity of retinal microsurgery, was designed as the first step of a long range research plan. Since this micro active forceps is equipped with thin optical fiber inside the stem to obtain a lateral view of the retina, drastic improvement of fine operations can be achieved. And the design of active joint and end-effector were optimized theoretically.

Measurement of 14.1 MeV neutrons with a Th-scintillator optical fibre detector

The flux of 14.1 MeV neutrons was measured with high spatial resolution in the vicinity of the target of a D–T neutron generator. The measurements were made by a thin optical fibre detector with a ZnS(Ag) scintillation tip mixed with a 232 Th neutron converter. The detector concept was originally developed at Nagoya University. The flux of 14.1 MeV neutrons could be measured with a spatial resolution of about 1 mm. The position of the impact area of the deuterium beam on the target surface was determined by the method as an application. A simple model for the calculation of the space dependence of the flux was developed, and it was shown to agree very well with the measurements. With the help of the model, both the vertical and horizontal position of the beam impact area centre can be determined from one single measurement through parameter fitting.

INTERVENTIONAL RADIOLOGY WITH LASER IN BONE AND JOINT

Laser energy is able to ablate, coagulate, and vaporize tissues. Its transmissibility in thin optical fibers makes it an ideal tool for use in percutaneous procedures. This article describes two applications in interventional musculoskeletal radiology. In percutaneous laser disc decompression the laser source is used to vaporize a small portion of the nucleus pulposus. In interstitial laser photocoagulation of osteoid osteoma the laser energy is used to coagulate and destroy the tumor by direct heating.

Thermal transport due to material and gas flow in a furnace for drawing an optical fiber

The transport processes involved in the neck-down region for optical fiber drawing are numerically investigated. In this manufacturing process, a moving glass rod is heated in a furnace containing an inert gas environment and drawn into a thin optical fiber. The conjugate problem is solved considering both radiation and convection, with focus on the latter. Two different flow configurations, involving inert gas flow in the same as well as in the opposite direction as the moving preform/fiber, are considered in this study. A coordinate transformation is used to change the complicated computational domains in the gas and the fiber to cylindrical ones. The transport in the fiber is coupled with that in the gas through the boundary conditions. The radiative thermal transport is calculated using an enclosure model developed in an earlier study. The numerical results on convective flow and transport are validated by comparing with results available in the literaturefor simpler configurations. The effects of several important parameters such as fiber draw speed, inert gas velocity, furnace dimensions, and gas properties on the flow and temperature distributions are investigated. For the aiding flow case, in which the inert gases flow in the same direction as the fiber, heat transfer to the fiber increases as the gas velocity increases. For opposing flow, a recirculating region appears in the gas, close to the moving fiber surface, causing reduction in heat transfer as compared to the aiding case. The thickness of this recirculating zone decreases with increasing inert gas velocity. Radiation is found to be the dominant mode of heat transfer in the overall heating of the preform/fiber, with nitrogen as the inert gas. However, near the edges of the furnace, radiation heat transfer is relatively small and convection becomes very important. Also, the convective transfer rate is relatively large near the flow entrance because of the large temperature difference between the gas and the fiber. However, away from the entrance, the gas heats up and the temperature difference relative to the fiber decreases, resulting in a smaller convective heat transfer rate. The relevance of the results to various aspects of the fiber-drawing process is discussed.

Axial distribution of emission and rate of deposition of diamond-like film in r.f. discharges in CH 4

Spatial distribution of the deposition rate of diamond-like thin films inside a r.f. discharge was studied experimentally. A thin optical fiber was inserted along the axis of the discharge which made negligible perturbation on the discharge itself. Deposited film thickness along the fiber was determined by using a scanning electron microscope and uniform and stable films up to 24 μm thick were made over periods of up to 19 h. The spatial distribution of deposition resembled the diffusion profile and from the comparison of its second derivative and the spatial distribution of emission it was found that the deposition precursor does not react with the ground-state molecules. From the analysis of available chemical kinetics and transport data for methane discharges it was found that the deposition precursor is CH 3 radical. Spatial distribution of emission was obtained using a CCD camera with interference filters.

Correlated reflection and conductivity measurements on (2,5-dimethyl-dicyanoquinonediimine)2Cu crystals and films

We present correlated temperature dependent reflection and conductivity measurements on crystals and films of the undeuterated (h8) and the partly deuterated (d6) (2,5-dimethyl- dicyanoquinonediimine)2Cu radical anion salt. Using thin optical fibers, it was possible to study individual needle like crystals of a diameter of only a few μm. The temperature dependence of the reflectivity of single (d6) needles in the visible and the near-infrared region shows a ‘‘dip’’, which coincides with the phase transition in the conductivity. To interpret our data, we extended the commonly used models for the conductivity from Drude and Epstein, so that we are able to deal with reflection and conductivity in terms of one consistent model. For the (d6) films, a metal–insulator phase transition has been proved by reflection and conductivity. With the assumption of a broad distribution of different phase transition temperatures for the crystallites of the films, the observed spectra of films can also be treated with the model used for the crystals.

Diode lasers: Experimental and clinical review

Diode lasers are now capable of delivering up to 60 W of power down thin optical fibres, and their medical applications have increased considerably over the past 5 years. Most of the recent experimental and clinical work has been performed using the 805 nm diode laser wavelength, which is more heavily absorbed and is less penetrating than the 1064 nm Nd-YAG wavelength in most tissues. In contact and non-contact mode, the overall tissue effects from the diode laser are similar to the Nd-YAG laser, but with interstitial therapy the 805 nm wavelength produces significantly greater necrosis than the 1064 nm wavelength. Experimental work has established the effectiveness of the diode laser and clinical work has confirmed its suitability for a wide variety of procedures. Diode lasers have the major advantages of being small, compact, portable, efficient, easy to use and virtually maintenance free; they are likely to replace more cumbersome lasers for many medical applications.

Effects of a modified Q-switched Nd-YAG laser on human vascular tissue: An ex vivo study

Relatively disappointing results with continuous-wave lasers stimulated us to evaluate pulsed lasers for interventional radiology. In this article, we describe our efforts to assess the effects of this technology ex vivo. We modified a Q-switched yttrium aluminum garnet (Nd-YAG) laser to emit pulses of 300 mJ maximum with a 20-Hz repetition rate, at 1064 nm, and with a duration that ranged from 300 ns to 2.3 microseconds. The lengthening of the pulse duration by a factor of 100 (compared with the conventional nanosecond Q-switched Nd-YAG laser) and the ability to define it exactly were obtained by controlling the opening and closing of the Pockels cell electronically. Lengthening the pulse duration made it possible to reduce peak power while conserving the same total energy. In this way, high energy was transmitted through thin optical fibers. One hundred fifty millijoules with 2-microsecond pulses, 140 mJ with 1-microsecond pulses, and 100 mJ with 500-ns pulses were transmitted through a 300-micron silica-polymer fiber. The transmission coefficient was identical for the three pulse durations. Ex vivo irradiation experiments were performed on human atheromatous arteries in saline solution using a 300-micron diameter optical fiber. Craters were easily obtained. Their depth and width were related to maximum energy transmission and irradiation time. No carbonization occurred and no destruction of the optical fiber was observed. A modified Q-switched Nd-YAG laser can transmit high-energy pulses through thin optical fibers without damaging them and can destroy human atheroma in an ex vivo setting.

Interstitial laser photocoagulation for the treatment of prostatic cancer

Interstitial laser photocoagulation (ILP) is a new percutaneous technique for local ablation of deep-seated tumours. We have applied this to treat a focal abnormality in a patient with prostatic carcinoma, under local anaesthesia and sedation. Transrectal ultrasound and computed tomography (CT) were used to guide three 18G needles, inserted transperineally, into the abnormal area. A thin (0.8 mm outer diameter) optical fibre was passed down each needle, so that the tip of the fibre lay within the tumour. The other end of the fibre was connected to a portable diode laser, which was activated at 2 W for 500 s. Real-time monitoring with ultrasound showed a gradually enlarging echogenic zone around the fibre-tip and a marked increase in colour Doppler signal; the echogenicity and Doppler signal decreased within a few minutes of completing treatment. Dynamic CT treatment 10 days later showed the treated area as a non-enhancing, avascular zone. Biopsies from this region confirmed the presence of necrosis. There were no complications. ILP appears to be a safe and effective way of ablating areas of focal abnormality in the prostate.

ISOTROPIC LIQUID CRYSTALLINE FILM AND FIBER STRUCTURES FOR OPTICAL LIMITING APPLICATION

The principal optical nonlinearities of isotropic liquid crystals are reviewed, and their potentials for all-optical limiting and switching applications are assessed. Our dynamic grating studies of a class of isotropic liquid crystals show that, in the nanosecond and longer time scales, the principal mechanisms for nonlinearities are laser induced ordering (molecular orientations), thermal and density fluctuations. We report optical limiting results obtained with bulk thin film and optical fiber fabricated from these isotropic crystals.

Local treatment of colorectal liver metastases: A comparison of Interstitial Laser Photocoagulation (ILP) and Percutaneous Alcohol Injection (PAI)

The purpose of this study was to evaluate the relative merits of two physical methods of locally destroying colorectal liver metastases-interstitial laser photocoagulation (ILP) which causes thermal necrosis, and percutaneous alcohol injection (PAI) which causes cellular dehydration and coagulative necrosis. Seventy-six liver metastases in 22 patients were treated by ILP or PAI. Both techniques were performed using local anaesthesia and intravenous sedation/analgesia. Ultrasound was used to localize the tumours and guide the needles percutaneously. ILP: Up to eight 19 G needles were inserted into the tumour, and down each needle was passed a thin optical fibre; the tumour was heated using low power laser light (2 W) for 500 s from a Nd:YAG or diode laser. PAI: 0.5-1 ml of sterile 95% absolute alcohol was injected into multiple sites of the tumour using a single 19-22 G needle. Dynamic CT scan was used to evaluate the extent of treatment-induced necrosis. Ultrasound showed echogenic changes around the needles/fibre-tips during ILP and PAI; this gave a reasonable guide to the extent of thermal damage for smaller tumours during ILP, but not during PAI. ILP: 54 tumours were treated (median size 2.7 cm). Laser-induced necrosis was clearly seen 24 h after treatment as a well-defined area of non-enhancement on the dynamic CT scan; greater than 50% necrosis of tumour volume was achieved in 87% of tumours (complete necrosis was found in 52% of tumours). PAI: 22 tumours were treated (median size 1.5 cm). Dynamic CT showed patchy areas of non-enhancement in five tumours, decreased density in seven tumours, and no change in 10 tumours; complete tumour necrosis was never achieved. There were no major complications after ILP or PAI, but pain during treatment was more common and more severe with PAI. ILP is a simple, safe and effective treatment for colorectal liver metastases; PAI is relatively ineffective for these tumours (although it has been shown to be much more effective for small hepatocellular carcinomas).

Simultaneous Measurements of Void Fraction and Temperature above a Horizontal Surface in Nucleate Poll Boiling.

In the present report, simultaneous measurements of void fraction and temperature above a horiozontal surface in nucleate pool boiling were investigated using a thin optical fiber void sensor and a micro thermocouple sensor. As a result, the relationship of the bubble population density and heat flux with two kinds of surface roughness was obtained. It is shown that there is a cold spot around the center of the nucleation site in the superheated layer formed above the heating surface, and that there is an isolated hot spot about 0.3 mm in height apart from the nucleation site.

Raising the accuracy of the diffraction method of measuring the diameter of thin homogeneous optical fibers

Raising the accuracy of the diffraction method of measuring the diameter of thin homogeneous optical fibers

Thermal Modeling of the Optical Fiber Drawing Process

AbstractA new general method for determining the local dimensionless heat convection coefficient (Nusselt number) and the temperature distribution in thin and thick optical fibers during the drawing process was developed. The axial heat transfer by conduction was included in the analysis as an addition to previously developed models. The developed model can serve as a general thermal solver for thin (<200μm in dia.) and thick (>200μm in dia.) fibers. The general method was compared with existing methods and it was found to be in agreement in the case of thin fiber analysis but not in the case of thick fiber analysis, where axial conduction effects are significant. Results of a parametric study to examine the effects of diameter of fiber and drawing speed on the temperature distribution are presented.

Laser angioplasty of arterial stenoses.

To establish the optimal conditions for recanalization of obstructed arteries without damage to vessel walls, an Nd-YAG laser coupled to a 0.2-mm-diameter optical fiber was used on obstructed human cadaver coronary and peripheral arteries and on popliteal arteries in amputated limbs. Vaporization of atheromatous plaques was consistently obtained with energy of 360-600 J and a diluted blood perfusate (3 g/100 ml hemoglobin) at a rate of 30 ml/min. The arterial wall was protected from thermal injury by inserting the optical fiber into an inflated balloon catheter and by cooling the system with the perfusate. Since recanalization of occluded arteries was consistently obtained without damage to the arterial wall or debris and thin and flexible optical fibers were easy to guide in the arteries, percutaneous transluminal Nd-YAG laser angioplasty was used in obstructed femoral and popliteal arteries in 12 patients. The first trials in man with Nd-YAG laser showed the method to be feasible, effective, and at low risk, although further studies are required to improve penetration of the obstruction and increase the diameter tunnel.

Locally Detailed Electroluminescence for Thin Optical Fiber Coupling to LEDs

AbstractLocally detailed electroluminescence properties of a single heterojunction (SH) light emitting diode (LED) are reported. The knowledge and consideration of such properties is of major interest when thin optical fibers are to be attached to a side face of a Fabry‐Perot structure. The virgin electroluminescence spectrum inside the active region was calculated and is taken as reference for the local emission spectrum at near‐field points at a side face. Considerable peak shifts, up to 120 meV. and intensity reductions occur for the transmitted spectrum, when proceeding from the n‐side of the junction to the p‐side.

Scattering patterns from thin optical fibres

The light scattering property of a thin optical fibre is studied theoretically. Plane polarized electromagnetic waves with their E-vector and H-vector parallel to the fibre axis are considered to fall perpendicularly on the fibre. Selected maxima and minima in the scattered light patterns are found to be very sensitive to the fibre parameters. The results may be used as a sensitive quality control of the fibre radius or refractive index while the fibre is being drawn.

Endoscopy: developments in optical instrumentation.

Optical fibers transmit high-intensity illumination for viewing internal organs and tissue. Remote viewing is obtained by relays of lenses or graded-index-of-refraction rods in rigid endoscopes and by precisely aligned fiber-optic bundles in flexible fiberscopes. Endoscopy is considered for routine examinations, such as in colonoscopy. Lasers are used as surgical tools through endoscopes for cutting and coagulation. They may also be used to provide illumination for the efficient transmission of light through thin optical fibers.