Optics: measuring and testing – By light interference – Using fiber or waveguide interferometer
Reexamination Certificate
2000-12-01
2003-08-19
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
Using fiber or waveguide interferometer
Reexamination Certificate
active
06608684
ABSTRACT:
TECHNICAL FIELD
The present invention relates to physical engineering, in particular, to the study of internal structure of objects by optical means, and can be applied for medical diagnostics of individual organs and systems of human body in vivo, as well as for industrial diagnostics, for example, control of technological processes.
BACKGROUND ART
In recent years, there has been much research interest in the optical coherence tomography of scattering media, in particular, biological tissues. Optical coherence tomography apparatus are fairly well known and comprise a low coherent light source and an optical interferometer, commonly designed as either a Michelson optical fiber interferometer or a Mach-Zender optical fiber interferometer.
For instance, an optical coherence tomography apparatus known from the paper by X.Clivaz et al., “High resolution reflectometry in biological tissues”, OPTICS LETTERS, Vol. 17, No. 1, Jan. 1, 1992, includes a low coherent light source and a Michelson optical fiber interferometer comprising a beam-splitter optically coupled with optical fiber sampling and reference arms. The sampling arm incorporates an optical fiber piezoelectric phase modulator and has an optical probe at its end, whereas the reference arm is provided with a reference mirror installed at its end and connected with a mechanical in-depth scanner which performs step-by-step alteration of the optical length of this arm within a fairly wide range (at least several tens of operating wavelengths of the low coherent light source), which, in turn, provides information on microstructure of objects at different depths. Incorporating a piezoelectric phase modulator in the interferometer arm allows for lock-in detection of the information-carrying signal, thus providing a fairly high sensitivity of measurements.
The apparatus for optical coherence tomography reported in the paper by J. A.Izatt, J. G. Fujimoto et al., Micron-resolution biomedical imaging with optical coherence tomography, Optics & Photonics News, October 1993, Vol. 4, No. 10, p. 14-19 comprises a low coherent light source and an optical fiber interferometer designed as a Michelson interferometer. The interferometer includes a beam-splitter, a sampling arm with a measuring probe at its end, and a reference arm, whose end is provided with a reference mirror, movable at constant speed and connected with an in-depth scanner. This device allows for scanning the difference in the optical lengths of the sampling and reference arms. The information-carrying signal is received in this case using a Doppler frequency shift induced in the reference arm by a constant speed movement of the reference mirror.
Another optical coherence tomography apparatus comprising a low coherent light source and an optical fiber interferometer having a beam-splitter optically coupled to a sampling and reference arms is known from RU Pat. No. 2,100,787, 1997. At least one of the arms includes an optical fiber piezoelectric in-depth scanner, allowing changing of the optical length of said interferometer arm by at least several tens of operating wavelengths of the light source, thus providing information on microstructure of media at different depths. Since □ piezoelectric in-depth scanner is a low-inertia element, this device can be used to study media whose □ harachteristic time for changing of optical characteristics or position relative to the optical probe is very short (the order of a second).
Major disadvantage inherent in all of the above-described apparatus as well as in other known apparatus of this type is that studies of samples in the direction approximately perpendicular to the direction of propagation of optical radiation are performed either by respective moving of the samples under study or by scanning a light beam by means of bulky lateral scanners incorporated into galvanometric probes. This does not allow these devices to be applied for medical diagnostics of human cavities and internal organs in vivo, as well as for industrial diagnostics of hard-to-access cavities. (Further throughout the text, a device performing scans in the direction approximately perpendicular to the direction of propagation of optical radiation is referred to as a “lateral scanner” in contrast to a device that allows for scanning the difference in the optical lengths of interferometer arms referred to as a “in-depth scanner”).
Apparatus for optical coherence tomography known from U.S. Pat. No. 5,383,467, 1995 comprises a low coherent light source and an optical interferometer designed as a Michelson interferometer. This interferometer includes a beam-splitter, a sampling arm with an optical fiber sampling probe installed at its end, and a reference arm whose end is provided with a reference mirror connected with an in-depth scanner, which ensures movement of the reference mirror at a constant speed. The optical fiber sampling probe is a catheter, which comprises a single-mode optical fiber placed into a hollow metal tube having a lens system and an output window of the probe at its distal end. The optical tomography apparatus includes also a lateral scanner, which is placed outside the optical fiber probe and performs angular and/or linear scanning of the optical radiation beam in the output window of the optical fiber probe. However, although such geometry allows for introducing the probe into various internal cavities of human body and industrial objects, the presence of an external relative to the optical fiber probe lateral scanner and scanning the difference in the optical lengths of the sampling and reference arms by means of mechanical movement of the reference mirror significantly limit the possibility of using this device for performing diagnostics of surfaces of human cavities and internal organs in vivo, as well as for industrial diagnostics of hard-to-access cavities.
Apparatus for optical coherence tomography known from U.S. Pat. No. 5,582,171, 1996 comprises a low coherent light source and an optical fiber interferometer designed as a Mach-Zender interferometer having optical fiber sampling and reference arms and two beam-splitters. The reference arm includes a unit for changing the optical length of this arm. This unit is designed as a reference mirror with a spiral reflective surface arranged with a capability of rotating and is connected with a driving mechanism that sets the reference mirror in motion. The sampling arm is provided with an optical fiber probe having an elongated metal cylindrical body with a throughhole extending therethrough, and an optical fiber extending through the throughhole. A lateral scanner is placed at the distal end of the probe, which lateral scanner comprises a lens system, a rotatable mirror, and a micromotor for rotating the mirror, whereas an output window of the probe is located in the side wall of the cylindrical body. This device allows imaging of walls of thin vessels, but is unsuitable as a diagnostic means to image surfaces of cavities and internal organs inside a human body, as well as for industrial diagnostics of hard-to-access large-space cavities.
Another optical coherence tomography apparatus is known from U.S. Pat. No. 5,321,501, 1994 and comprises a low coherent light source optically coupled with an optical fiber Michelson interferometer, which includes a beam-splitter and optical fiber sampling and reference arms. The reference arm has a reference mirror mounted at its end and connected with an in-depth scanner. The latter performs movement of the reference mirror at a constant speed, thereby changing the optical length of this arm by at least several tens of operating wavelengths of the light source. The interferometer also comprises a photodetector whose output is connected with a data processing and displaying unit, and a source of control voltage connected with the in-depth scanner. The sampling arm incorporates an optical fiber probe having an elongated body with a throughhole extending therethrough, wherein a sheath with an optical fiber embedded in it extends through the throu
Feldchtein Felix I.
Gelikonov Grigory V.
Gelikonov Valentin M.
Gladkova Natalia D.
Sergeev Alexander M.
Imalux Corporation
Lyons Michael A.
Pearne & Gordon LLP
Turner Samuel A.
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