A fiber optic sensor for the measurement of the respiratory depth has been developed. The sensor is composed of a bent optic fiber which is connected to an elastic section of a chest belt so that its radius of curvature changes during respiration due to respiratory chest circumference changes (RCCC). The measurement of light transmission through the bent fiber provides information on its changes in curvature since a higher fraction of light escapes through the core-cladding surface of a fiber bent to a lower radius of curvature. The sensor can quantitatively measure the RCCC, although in relative terms, and it is sensitive enough to detect changes of the chest circumference due to the heart beat. Measurements of the RCCC were simultaneously performed with photoplethysmography (PPG)-the measurement by light absorption of the cardiac induced blood volume changes in the tissue-and a significant correlation was found between the RCCC and some parameters of the PPG signal. The fiber optic respiratory depth sensor enables a quantitative assessment of the respiratory induced changes in the cardiovascular parameters. © 1999 Society of Photo-Optical Instrumentation Engineers.

https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-4/issue-02/0000/Fiber-optic-sensor-for-the-measurement-of-the-respiratory-chest/10.1117/1.429909.pdf

Fiber optic sensor for the measurement of respiratory chest circumference changes.

We present results of an experimental investigation of the optical losses produced by bending large
core optical fibres, typical of those used in power beam delivery systems. Experiments have been
conducted over a range of core diameters for both plastic clad silica and all silica fibres, as a
function of bend radius. A theoretical model has been developed for predicting the magnitude of
the bend loss, and agreement was obtained with the experimental results. The study thus yields
design information for fibre beam delivery systems.

Bend loss in large core multimode optical fiber beam-delivery systems

A composite optical bend loss sensor for measuring 3-D forces has been developed. The sensor is composed of two optic fiber meshes which are embedded into a polydimethylsiloxane (PDMS) slab. The sensor consists of an array of optical fibers lying in perpendicular rows and columns sandwiched inside an elastomeric pad. A map of normal and shear stress is constructed based on observed macrobending through the intensity attenuation from physical deformation of two adjacent perpendicular fibers. Due to the new addition of the composite design and acrylic holder, the stability of the present sensor is found to be significantly better than our previously reported microfabricated optical bend loss sensor. In this paper, we will report the results of an optical bend loss simulation using the beam propagation method based on a series of images captured by a CCD camera on the fiber's bending curvatures. The result from the simulation will be compared with the results obtained from the experiment. Other results include vertical force and shear measurements at a single pressure point of the sensor. A force image algorithm is used to map the force distribution detected by the sensor. Here, we will present the results of six different shape patterns and two force magnitudes on each shape using a neural network system. We will also present a radio frequency sensor module, which we developed for the composite optical bend loss sensor for remote sensing.

Composite Optical Bend Loss Sensor for Pressure and Shear Measurement

A composite optical bend loss sensor for the measurement of pressure and shear has been developed. The sensor is 
composed of two layers of fiberoptic mesh sensors that are molded into a thin polydimethylsiloxane (PDMS) substrate. 
A 3-D displacement map is generated based on bent-induced intensity attenuations in the fibers when the sensor is 
pressed. The new design overcame some of the coupling and instability problems in our previously reported 
microfabricated optical bend loss sensor. Here we will report our preliminary study on the sensor including results from 
the normal and shear load measurement. The paper will also discuss a RF based wireless data acquisition system that we 
have developed and demonstrate its operation with the composite sensor.

A wireless composite optical bend loss sensor for pressure and shear measurement

Various technologies based on different light—tissue interaction phenomena have been developed for medical applications. Now the progress in the area of laser medical technologies depends more and more from the design of a special fiber—optical tools1'2 . Thus the flexible fabrication technique for such fiber tools manufacturing is needed . These tools should serve for a laser beam forming ( local spot or volume irradiation, inclination of irradiation direction, spot size and the intensity distribution variation, etc.), for the most effective use of laser power in a distinct medical operations. Traditional optical elements ( i.e. lenses, prisms, mirrors ) could not be used as for laser treatment in local difficult—to-reach places of the body in the most of otolaringological,proctological, neurosurgery and eye microsurgery operations as for endo—, laparo- and torocoscopical laser operations as well. The creation of a number of fiber-end optical components FEOC ), such as lens—ended fibers, scatterers,side—fiber components, etc. gives a broad way for laser medicine applications independently from the localisation of an object of treatment (internal or external tissues of pacient). These fiber tools could be based on the fiber tip forming , its orientation relatively the fiber axis or/and on partial changing the total internal reflection conditions upon the determined length of fiber. These irradiation—forming FEOCs having about the fiber diameter size it is possible to include in endoscopic laser complexes for the solving of different tasks of modern medicine and diagnostics.

Innovative laser technologies for fiber tools fabrication

The paper deals with a problem of light focusing on the tissue for laser surgery, diagnostic and therapeutics with assistance by tapered tips. Optimization of the shape and geometrical dimensions of laser scalpels sought to minimize tissue damage by means of exception of light leaking through the tapered surface and decrease of distal end inner reflection. These results can be achieved by simultaneous attaching,spherical shape to the front surface of tapered tip also optimization of fiber-tip distance and tip dimensions. Analytical and ray-tracing calculations have been performed for sapphire (n equals 1.75) and silica (n equals 1.45) tip materials and air or saline (n equals 1.33) mediums. The diameter of aperture diaphragm and reflection number of incident beam in the tip have been varied from 1 to 5 fiber core diameter and from 1 to 10, respectively. Several numerical methods for evaluation of tip efficiency for optimized and conventional tips were discussed. Some versions of commercially available tip modernization have been presented. Modification of front surface of the tapered tip increased the angular aperture from 4 degrees to 12 degrees (in air) and from 8 degrees to 15 degrees (in saline) with obviating light leaking in commercial tip by Hans Sttetler SA, Switzerland. Replacement of the contact flat laser scalpel (surgical laser technologies, Malvern, PA) to an optimized one allowed us to increase the taper angle from 1.9 degrees to 10 degrees and produced, therefore, shorter and stronger tip without reducing its optical properties.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Shape-dimension optimization of contact medical laser delivery systems

Bent multimode optical fibers were studied using a 3D ray tracing program. Effect of fiber bending increased with smaller input aperture beams. Transmission of fibers decreased for the longer proximal straight part of the fiber. Significant focusing effect and output light redistribution were detected if a proximal straight part of the fiber was less than 1 fiber diameter. Transmission of hollow waveguides considerably depended on the inner surface quality. Calculated data were in accordance with experimental measurements of fiber transmission and output light distribution. Ray tracing is a useful approach to simulate different delivery systems using optical fibers and hollow waveguides.

Transmission of straight and curved multimode optical fibers

Biomedical science and practical medicine need special techniques for reliable real-time remote detection and determination information from human tissue. Most applications of these techniques in interior organs are based on optical fibers which should not only be able to deliver excitation light with minimal loss but provide effective light gathering from tissue being under the test. As emitted from tissue optical signal is often weak especially if autofluorescence spectroscopy is chosen for diagnostics, an efficient collection by fiber optics probe became essential. The main part of the proposed fiber optics probes is a specially designed tapered tip with one flat surface and another spherical one. This tip operates as a collector, transmitter and coupler to deliver light to the tissue and backward to the detector simultaneously. To find geometrical dimensions of tips optimized for these purposes calculating formulas have been adduced. These optimized tips could collect fluorescence signal from biological sites in wide angular aperture region and could transport light without leakage on tapered surface. When delivery fibers are placed at the focal plane of tip spherical surface an efficient optical coupling with them is achieved. Ray tracing of the tapered tips has been performed on sapphire and quartz tip materials in air and in saline to determine the best sensor design.

Tapered fiber optic sensors for laser medicine

During the clinical endoscopic LIF-diagnostics of human digestion organs is needed to register fluorescence spectra in situ. Taking into account intensive bloodstream and therefore strong hemoglobin absorption of laser light the registered fluorescence signal is strongly dependent on distal probe geometry. The contact optics sensor is specially designed to enhance acquisition of auto- and exogenous fluorescence spectra from tissues. The fiber optics sensor consists of cylindrical sapphire or silica body with flat proximal and spherical distal end and tapered tip. The latter one has been made of optical material. This tip has been arranged abutting against the proximal end of the cylindrical body. Such sensor design offers to collect autofluorescent light in wide angle region effectively. Moreover that offers to use sensor simultaneously as an efficient both laser radiation collector and fiber coupler to transport exciting light at the testing site and backward. The produced distal probe has been used through the biopsy channel to endoscope. Original beam splitter throws 80% of fluorescent signal toward detector and simultaneously transmits up to 85% of He-Cd laser radiation to the tissue.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Contact fiber optic sensor for endoscopic laser-induced fluorescence analysis

Light attenuation in a sample of human brain has been measured using a small (0.5 mm in diameter) fiber isotropic detector and similar to that an isotropic irradiator. Two lasers, He-Ne (633 nm) and GaAs (890 nm), were used. In vivo measurements were performed with rabbit brain. Penetration depth of 633 nm light was 1.3 mm and 2.4 mm respectively for human and rabbit brain. Propagation of 890 nm light was significantly higher, penetration depth was 2.8 mm for human tissue and 5.3 for rabbit.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Igor Kravchenko

Papers

Shape-dimension optimization of contact medical laser delivery systems

Transmission of straight and curved multimode optical fibers

Tapered fiber optic sensors for laser medicine

Contact fiber optic sensor for endoscopic laser-induced fluorescence analysis

Light penetration in human and rabbit brains: measurements using an isotropic detector