Optical probe and optical tomography system

An optical probe includes a tubular outer envelope and a optical fiber which extends in the longitudinal direction of the outer envelope inside the outer envelope. By fixing a light deflecting element to the optical fiber and rotating the optical fiber by a driver, the light deflecting element is rotated. A protective member which has a higher resistance to wear than the outer peripheral surface of the optical fiber is fixed to a part of the outer peripheral surface of the optical fiber in a position near the front end of the optical fiber and is borne for rotation by a bearing portion on the probe outer envelope.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical probe, and more particularly to an optical probe having a tubular outer envelope and having a function of deflecting light emitted from the peripheral surface thereof in the direction of circumference or the axis of the outer envelope. The present invention also relates to an optical tomography system where such an optical probe is employed.

2. Description of the Related Art

As a conventional method for obtaining tomographic images of measurement targets, such as living tissue, a method that obtains optical tomographic images by OCT (Optical Coherence Tomography) measurement has been proposed (refer to Japanese Unexamined Patent Publication Nos. 6(1994)-165784 and 2003-139688). The OCT measurement is a type of light interference measurement method that utilizes the fact that light interference is detected only when the optical path lengths of divided light beams, that is, a measurement light beam and a reference light beam, match within a range of coherence length of a light source. That is, in this method, a low coherent light beam emitted from a light source is divided into a measuring light beam and a reference light beam, the measuring light beam is irradiated onto a measurement target, and the measurement light beam reflected by the measurement target is led to a multiplexing means. Whereas the reference light beam is led to the multiplexing means after its optical path length is adjusted so that its optical path length equalizes to that of the reflected light from an arbitrary position in the object. Then the measuring light and the reference light is multiplexed by the multiplexing means, and the intensities thereof are detected by the light detector.

In order to obtain a one-dimensional tomographic image, an interference strength waveform according to the reflectance distribution along the same axis as the direction of travel of the measuring light by scanning the optical path length of the measuring light according to the measuring area. That is, a reflected light intensity distribution according to the structure in the direction of depth of the object to be measured can be obtained. Further, when the projecting position of the measuring light applied to the object is one-dimensionally scanned in a direction perpendicular to the optical axis by the use of a deflecting means or a physical means, a two dimensional tomography representing a reflected light intensity distribution can be obtained. Further, when the projecting position of the measuring light is two-dimensionally scanned in directions perpendicular to the optical axis, a three dimensional tomography representing a reflected light intensity distribution can be obtained.

In the above OCT system, a tomographic image is obtained by changing the optical path length of the reference light, thereby changing the measuring position (the depth of measurement) in the object. This technique is generally referred to as “TD-OCT (time domain OCT)”. More specifically, in the optical path length changing mechanism for the reference light disclosed in Japanese Unexamined Patent Publication No. 6 (1994)-165784, an optical system which collects the reference light emitted from the optical fiber on a mirror is provided and the optical path length is adjusted by moving only the mirror in the direction of the optical axis of the reference light. Further, in the optical path length changing mechanism for the reference light disclosed in Japanese Unexamined Patent Publication No. 2003-139688, the reference light emitted from the optical fiber is turned to parallel light by a lens, the reference light in the form of parallel light is collected and caused to enter the optical fiber again by an optical path length adjusting lens, and the optical path length adjusting lens is moved back and forth in the direction of the beam axis of the reference light.

Whereas, as a system for rapidly obtaining a tomographic image without changing the optical path length of the reference light, there has been proposed an optical tomography system for obtaining an optical tomographic image by measurement of SD-OCT (spectral domain OCT). In the SD-OCT system, a tomographic image which is one-dimensional in the optical axis is formed without physically scanning the optical path length, by dividing broad band, low coherent light into measuring light and reference light by the use of an interferometer as in the above-described TD-OCT system, substantially equalizing the measuring light and the reference light to cause them to interfere with each other, decomposing the interference light into the optical frequency components, measuring the intensity of the interference light by the optical frequency components by an array type detector and carrying out a Fourier analysis on the obtained spectral interference waveforms by a computer. As in above-described TD-OCT system, a two-dimensional or a three-dimensional tomographic image can be obtained by scanning the projecting position of the measuring light in directions perpendicular to the optical axis.

As another system for rapidly obtaining a tomographic image without changing the optical path length of the reference light, there has been proposed an optical tomography system for obtaining an optical tomographic image by measurement of SS-OCT (swept source OCT). The SS-OCT system employs a light frequency tunable laser as a light source, The high coherence laser beam is divided into measuring light and reference light. The measuring light is projected onto the object and the reflected light from the object is led to the multiplexing means. The reference light is led to the multiplexing means after it is made substantially equal to the measuring light in the optical path length to cause the measuring light and the reference light to interfere with each other, and the measuring light and the reference light are multiplexed by the multiplexing means. The intensity of the multiplexed light is detected by an optical detector. The intensity of the interference light is measured by the frequency component by sweeping the frequency of the light frequency tunable laser and a one-dimensional tomography in the optical axis is formed without physically scanning the optical path length by Fourier-transforming the spectral interference waveform thus obtained with a computer. As in above-described TD-OCT system, a two-dimensional or a three-dimensional tomographic image can be obtained by scanning the projecting position of the measuring light in directions perpendicular to the optical axis.

In the optical tomography system of each of the systems described above, a tomographic image along a certain surface of the object is generally obtained and for this purpose, it is necessary to at least one-dimensionally scan the measuring light beam in the object in perpendicular to the optical axis. As a means for effecting such a light scanning, there has been known, as disclosed in Japanese Patent No. 3104984, an optical probe having a tubular outer envelope and having a function of deflecting light emitted from the peripheral surface thereof in the direction of circumference of the outer envelope. More specifically, the optical probe comprises an inserting portion (outer envelope) which is inserted into the sample, a rotatable hollow shaft which is inserted inside the outer envelope, an optical fiber which is passed through the shaft, and a light deflecting element which is connected to the front end portion of the shaft to be rotated together therewith and deflects light radiated from the front endportion of the optical fiber in a direction of circumference of the outer envelope.

Observing an optical tomographic image has been expected to be developed from the digestive organ which has been reported in the past to a finer region such as a bronchus, a ureter, and a blood vessel. From such a viewpoint, it has been required to make thinner the optical probe. However, in the optical probe disclosed in Japanese Patent No. 3104984, it is necessary to have a certain wall thickness to ensure the strength of the shaft and to ensure a space between the shaft and the optical fiber inside thereof, which makes difficult to make thinner the optical probe.

There is a further demand that a deeper region of the object is to be observed. However, to realize this, it is necessary to make a probe as long as several meters, and it is very difficult to pass an optical fiber through the inside of a shaft which is cylindrical and elongated. Further, the optical fiber can be damaged when it is passed through the inside of such a shaft and accordingly, use of such a probe deteriorates the productivity. Further, since such a cylindrical shaft is high in its manufacturing cost, the optical probe is high in cost. when the optical fiber is rigid, it is conceivable not to pass the optical fiber through the shaft described above and to rotate together with a light deflecting element fixed to the tip of the optical fiber. However, in this case, it is necessary to set a space between the optical fiber and the inner peripheral surface of the outer envelope of the probe in order to smoothly rotate the optical fiber and in such a structure, it is not avoidable the front end the end of the optical fiber wobbling. When so, the orbit of the deflected light emitted from the optical probe is disturbed and it is impossible to construct an accurate tomographic image in the sample.

SUMMARY OF THE INVENTION

In view of the foregoing observations and description, the primary object of the present invention is to provide an optical probe which is easy to make thin, can be produced at low cost and at the same time the light emitted from the outer peripheral surface of the outer probe of the optical probe is orderly deflected to generate an orbit in a plane.

Another object of the present invention is to provide an optical tomography system which can be miniaturized and can be manufactured at low cost by the use of such an optical probe.

In accordance with the present invention, the above objects are accomplished by avoiding a complicated structure of passing a hollow shaft through the outer envelope of the optical probe and passing an optical fiber through the shaft, employing a structure where the optical fiber is rotated in the probe outer envelope and then causing a bearing portion provided outside the probe outer envelope to bear the optical fiber for rotation.

More specifically, in accordance with the present invention, there is provided an optical probe comprising

a tubular outer envelope,

a optical fiber which extends in the longitudinal direction of the outer envelope inside the outer envelope,

a drive means which rotates the optical fiber in the circumferential direction of the outer envelope,

a light deflecting element which is integrally held to rotate together with the optical fiber and deflects light emitted from a front end of the optical fiber,

a light collecting means which collects light emitted from the front end of the optical fiber and converges it on a body-to-be-scanned disposed externally of the circumference of the outer envelope,

a protective member which has a higher resistance to wear than the outer peripheral surface of the optical fiber, and is fixed to a part of the outer peripheral surface of the optical fiber in a position near the front end of the optical fiber, and

a bearing portion which is fixed to the inner peripheral surface of the probe outer envelope to bear for rotation the optical fiber by way of the protective member

The outer side of the clad of the optical fiber is generally provided with a coating formed of resin such as ultraviolet setting resin. In such a case, the outer peripheral surface of the optical fiber is formed by the resin. In this case, the protective member which has a higher resistance to wear than the outer peripheral surface of the optical fiber is formed of metal such as stainless steel.

Further, the protective member may be provided with an abutment portion which abuts against a part of the bearing portion to suppress the movement of the protective member in the direction of axis of the optical fiber.

The tomography system of the present invention is characterized in that the optical probe of the present invention is employed in each of the above described various systems of the optical tomography systems. That is, in accordance with the present invention, there is provided an optical tomography system for obtaining a tomographic image of an object to be measured comprising

a light source which emits light,

a light dividing means which divides light emitted from the light source into measuring light and reference light,

a projecting optical system which projects the measuring light onto the object,

a multiplexing means which multiplexes the reflected light from the object when the measuring light is projected onto the object and the reference light,

an interference light detecting means which detects interference light of the reflected light and the reference light which have been multiplexed by the multiplexing means, and

a tomographic image obtaining means which detects intensities of the interference light in positions in the direction of depth of the object on the basis of the frequency and intensity of the detected interference light and obtains a tomographic image of the object on the basis of the intensity of the reflected light in each position of the depth,

wherein the improvement comprises that the projecting optical system includes an optical probe of the present invention.

The optical probe in accordance with the present invention, since an optical fiber disposed in the outer envelope of the probe holds the light deflecting element and the optical fiber is rotated to rotate the light deflecting element, can be very simpler in structure as compared with the conventional optical probe where a hollow shaft is passed through the outer envelope of the probe and an optical fiber is passed through the shaft. Accordingly, the optical probe of the present invention is easy to make thin and can be manufactured at low cost.

Further, since in the optical probe in accordance with the present invention, an optical fiber is disposed in the outer envelope of the probe, the optical fiber cannot be very difficult to dispose even if the optical probe is substantially long unlike the case where the hollow shaft intervenes therebetween. Accordingly, the manufacturing cost can be low,

Even if the optical fiber is directly disposed in the outer envelope as disclosed above, the optical fiber cannot be rotated with its front end wobbling, since the optical fiber is supported for rotation by the bearing portion on the probe outer envelope. Thus in accordance with the optical probe, the light emitted from the outer peripheral surface of the outer probe of the optical probe is orderly deflected to generate an orbit in a plane.

Further, since the optical fiber is borne by way of the protective member which has a higher resistance to wear than the outer peripheral surface of the optical fiber, the outer peripheral surface of the rotating optical fiber is prevented from being worn out by friction with the inner peripheral surface of the probe outer envelope.

When the protective member is provided with an abutment portion which abuts against a part of the bearing portion to suppress the movement of the protective member in the direction of axis of the optical fiber, the protective member is prevented from being separated from the bearing portion, whereby the optical fiber can be prevented from being rotated with the protective member being separated from the bearing portion so that the outer peripheral surface of the optical fiber and/or the light deflecting element is rubbed against the inner peripheral surface of the probe outer envelope to be damaged or to be worn out.

Further, since the optical probe of the present invention is applied, the optical tomography system of the present invention can be miniaturized and can be manufactured at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1is a side cross-sectional view showing an optical probe in accordance with a first embodiment of the present invention,

FIG. 2is a front cross-sectional view of the optical probe ofFIG. 1,

FIG. 3is a perspective view of an optical tomographic system to which the optical probe ofFIG. 1is applied,

FIG. 4is a side cross-sectional view showing an optical probe in accordance with a second embodiment of the present invention,

FIG. 5is a schematic view showing an example of the optical tomography system by the SD-OCT measurement to which the optical probe of the present invention is applied,

FIG. 6is a schematic view showing an example of the optical tomography system by the SS-OCT measurement to which the optical probe of the present invention is applied, and

FIG. 7is a schematic view showing an example of the optical tomography system by the TD-OCT measurement to which the optical probe of the present invention is applied.

DESCRIPTION OF THE PREFERRED EMBODIMNTS

Embodiments of the present invention will be described in detail with reference to the drawings, hereinbelow.FIG. 1shows a side cross-sectional shape of an optical probe10in accordance with a first embodiment of the present invention andFIG. 2is a front cross-sectional view of the optical probe10taken along line A-A inFIG. 1. For example, the optical probe10forms a front end portion of an endoscope which forms a part of an optical tomography system.FIG. 3shows an entire shape of the optical tomography system.

The optical tomography system will be first described in brief with reference toFIG. 3. The system comprises an endoscope50including the optical probe10; a light source unit51, a video processor52, and an optical tomographic processing system53to which the endoscope50is connected; and a monitor54connected to the video processor52. The endoscope50comprises an outer envelope11which is flexible and elongated, a control portion56connected to the rear end of the endoscope outer envelope11and a universal code57which extends outward from a side portion of the control portion56.

A light guide (not shown) which transmits illuminating light from the light source unit51is passed through the universal code57, and a light source connector58which is removably connected to the light source unit51is provided on the end of the universal code57. A signal cable59extends from the light source connector58and a signal connector60which is removably connected to the video processor52is provided on the end of the signal cable59. The light source unit51is for projecting the illuminating light onto a part of a sample70a tomographic image of which is to be obtained as described later.

A bight control knob61for controlling a bight portion provided in the probe outer envelope11and a light guide drive portion62are provided on the control portion56, and the light guide drive portion62and the optical tomographic processing system53are connected to each other by way of a light guide63. The probe outer envelope11is inserted into the sample70such as a human organ.

The optical probe10will be described with reference toFIGS. 1 and 2, hereinbelow. The optical probe10comprises: a cylindrical probe outer envelope11having a closed front end; an annular bearing portion12fixed to a part of the inner peripheral surface of the outer envelope11; a single optical fiber13, which is provided inside the outer envelope11to extend in the direction of the axis of the outer envelope11; and a gear14afixed to a part of the outer peripheral surface of the optical fiber13, a gear14bin mesh with the gear14aand a motor15which rotates the gear14b.

A cylindrical protective member16is fixed to a part of the probe outer envelope11near the front end thereof and the protective member16is borne for rotation by the bearing portion12. Accordingly, when the motor15is driven, the optical fiber13is rotated about its longitudinal axis in the circumferential direction of the probe outer envelope11by way of the gears14aand14b. In this embodiment, the gears14aand14band the motor15form a drive means for rotating the optical fiber13.

The protective member16is made of material which is higher in resistance to wear than the outer peripheral surface of the optical fiber13. When the optical fiber13has a core13aand a clad13b, and a coating13cformed of resin such as ultraviolet setting resin is provided on the outer peripheral surface of the clad13bas shown inFIG. 2, the outer peripheral surface of the optical fiber13is formed by resin. In this case, the protective member is made of metal such as stainless steel higher in resistance to wear than resin or resin such as Teflon® having a high resistance to wear. Though not shown, the optical fiber13is provided with a similar protective member fixed in a position near to the gear14aand the protective member is borne for rotation by a bearing portion similar to the bearing portion12.

The optical probe10is further provided with a rod lens18fixed to the front end of the optical fiber13and a prism mirror17fixed to the rod lens18, The prism mirror17is rotate together with the optical13to deflect by900light L emitted from the front end of the optical fiber13in the circumferential direction of the probe outer envelope11, and a rod lens18which collects light L emitted from the front end of the optical fiber13to converge on the sample70as the object to be scanned which is disposed externally of the circumference of the outer envelope11. In this particular embodiment, the rod lens18and the prism mirror17double as a light-guide means which leads the light L reflected by the sample70to the front end of the optical fiber13to enter the optical fiber13from the front end as will be described later.

An incident optical system20is disposed inside the endoscope50to be opposed to the base end of the optical fiber13as shown inFIG. 3. Light L propagating the light guide63and emitted from the light guide63is collected by the incident optical system20and enters the optical fiber13from the base end thereof.

Operation of the optical probe10will be described, hereinbelow. A light source such as a laser (not shown) is disposed in the optical tomographic processing system53shownFIG. 3, and the light L such as a laser beam emitted therefrom enters the light guide63and propagates therethrough. The light L entering the optical fiber13by way of the incident optical system20after emitted from the light guide63propagates through the optical fiber13, is emitted from the front end thereof, is reflected by 90° by the prism mirror17after collected by the rod lens18and is emitted outside the probe10through the outer envelope11which is light-transmittable. Then when the motor15is driven, the optical fiber13rotates as described above and the prism mirror17and the rod lens18fixed thereto are rotated together with the optical fiber13.

In response to rotation of the prism mirror17, the light L emitted therefrom is deflected in the circumferential direction of the probe outer envelope11, thereby scanning the sample70in the direction of arrow R inFIG. 3. The light L is reflected by the sample70while scattering and a part of the reflected light impinges upon the prism mirror17and is reflected toward the rod lens18. The part of the reflected light is collected by the rod lens18and enters the optical fiber13from the front end thereof.

The reflected light thus propagating through the optical fiber13is emitted from the base end of the optical fiber13, enters the light guide63by way of the incident optical system20shown inFIG. 3, and propagates through the light guide63to be transmitted to the optical tomographic processing system53. In the optical tomographic processing system53, the above described reflected light is branched from the optical path of the light L to the optical probe10, and is detected by an optical detector (not shown). A tomographic image of the sample70is formed on the basis of the output of the optical detector and the tomographic image is displayed on the monitor54shown inFIG. 3.

As can be understood from the description above, the optical probe10of this embodiment, where the optical fiber13is disposed in the probe outer envelope11and the optical fiber13is rotated to rotate the prism mirror17as the light deflecting element, can be very simpler in structure as compared with the conventional optical probe where a hollow shaft is passed through the outer envelope of the probe and an optical fiber is passed through the shaft. Accordingly, the optical probe10is easy to make thin and can be manufactured at low cost.

Further, since in the optical probe10of this embodiment, an optical fiber13is directly disposed in the outer envelope11of the probe10, the optical fiber13cannot be very difficult to dispose even if the optical probe10is substantially long unlike the case where the hollow shaft intervenes therebetween. Accordingly, the manufacturing cost can be low.

Even if the optical fiber13is directly disposed in the outer envelope11as disclosed above, the-optical fiber13cannot be rotated with its front end wobbling, since the optical fiber13is supported for rotation by the bearing portion12on the probe outer envelope11. Thus in accordance with the optical probe10, the light emitted L from the outer peripheral surface of the outer probe11of the optical probe10can be orderly deflected to generate an orbit in a plane.

Further, since the optical fiber13is borne by way of the protective member16which has a higher resistance to wear than the outer peripheral surface of the optical fiber13, the outer peripheral surface of the rotating optical fiber13is prevented from being worn out by friction with the inner peripheral surface of the probe outer envelope11.

A second embodiment of the present invention will be described, hereinbelow.FIG. 4is a side view partly cut away of an optical probe100in accordance with the second embodiment of the present invention. InFIG. 4, the elements analogous to those inFIGS. 1 to 3are given the same reference numerals and will not be described unless necessary. (the same in the following drawings) The optical probe100of the second embodiment differs from that10of the first embodiment in that a protective member16′ having a pair of abutment portions16ais used in place of the protective member16.

The protective member16′ is disposed so that the pair of abutment portions16aon the respective sides of the bearing portion12. The abutment portions16ahave an outer diameter between the inner diameter and the outer diameter of the bearing portion12. When the protective member16′, that is, the optical fiber13tends to move in the axial direction of the optical fiber13, one of the abutment portions16aabuts against the corresponding end surface of the bearing portion12and inhibits the movement of the optical fiber, whereby the optical fiber13can be prevented from being rotated with the protective member16′ being separated from the bearing portion12so that the outer peripheral surface of the optical fiber13and/or the prism mirror17is rubbed against the inner peripheral surface of the probe outer envelope11to be damaged or to be worn out.

The bearing12may be in plurals without being limited to a single as described above. Further, it is possible to dispose a plurality of optical fibers13to rotate them together. Grease may be provided between the bearing portion12and the protective layer16or16′ to rotate the optical fiber13more smoothly. Further, the inner space of the probe outer envelope11may be filled with a high viscosity fluid such as oil.

In the embodiment described above, the prism mirror17which is the light deflecting element and the rod lens18which is the light collecting means are disposed in close contact with each other. However, this is not essential but the prism mirror17and the rod lens18may be spaced from each other. Positions of the light deflecting element and the light collecting means along the optical axis in the above embodiments may be reversed and the light deflecting element may be positioned on the side nearer to the light source.

Examples of the optical tomography system to which the optical probes of the present invention are to be applied will be described, hereinbelow. The optical tomography system1shown inFIG. 5is for obtaining a tomographic image of an object of measurement such as a living tissue or a cell in a body cavity by measuring the SD-OCT. The optical tomography system1comprises: a light source unit210which emits light La; a light dividing means3which divides the light La emitted from the light source unit210into measuring light L1and reference light L2; an optical path length adjusting means220which adjusts the optical path length of the reference light L2divided by the light dividing means3; an optical probe10which guides to the object Sb to be measured the measuring light beam L1divided by the light dividing means3; a multiplexing means4for multiplexing a reflected light beam L3from the object Sb when the measuring light beam L1is irradiated onto the object Sb from the probe10, and the reference light beam L2; and an interference light detecting means240for detecting interference light beam L4of the reflected light beam L3and the reference light beam L2which have been multiplexed by the multiplexing means4.

The light source unit210comprises a light source111which emits low coherence light La such as an SLD (super luminescent diode), ASE (amplified spontaneous emission) or a super continuim where an ultra short pulse laser beam is projected onto a nonlinear medium to obtain broad band light and an optical system112which enters the light emitted from the light source111into an optical fiber FB1.

The light dividing means3comprises, for instance, a 2×2 fiber optic coupler and divides the light beam La led thereto by way of the optical fiber FB1from the light source unit210into the measuring light beam L1and the reference light beam L2. The light dividing means3is optically connected to two optical fibers FB2and FB3, and the measuring light beam L1is propagated through the optical fiber FB2while the reference light beam L2is propagated through the optical fiber FB3. In this embodiment, the light dividing means3also functions as the multiplexing means4.

The optical probe10previously shown inFIG. 1is optically connected to the optical fiber FB2and the measuring light beam L1is guided to the probe10from the optical fiber FB2. The probe10is inserted into a body cavity, for instance, through a forceps port by way of a forceps channel and is removably mounted on the optical fiber FB2by an optical connector31.

The optical path length adjusting means220is disposed on the side of the optical fiber FB3radiating the reference light beam L2. The optical path length adjusting means220changes the optical path length of the reference light beam L2in order to adjust an initiating position of a range over which a tomographic image is to be obtained and comprises a reflecting mirror22which reflects the reference light beam L2radiated from the optical fiber FB3, a first lens21adisposed between the reflecting mirror22and the optical fiber FB3, and a second lens21bdisposed between the first lens21aand the reflecting mirror22.

The first lens21amakes parallel the reference light beam L2radiated from the core of the optical fiber FB3and at the same time, collects the reference light beam L2reflected by the reflecting mirror2on the core of the optical fiber FB3. The second lens21bcollects the reference light beam L2made parallel by the first lens21aon the reflecting mirror22and at the same time, makes parallel the reference light beam L2reflected by the reflecting mirror22. That is, the first and second lenses21aand21bform a confocal optical system.

Accordingly, the reference light beam L2radiated from the optical fiber FB3is turned to a parallel light by the first lens21aand is collected on the reflecting mirror22by the second lens21b. Subsequently, the reference light beam L2reflected by the reflecting mirror22is turned to a parallel light by the second lens21band is collected on the core of the optical fiber FB3by the first lens21a.

The optical path length adjusting means220is further provided with a base portion23to which the second lens21band the reflecting mirror22are fixed and a mirror movement means24which moves the base portion23in the direction of the optical axis of the first lens21a. In response to movement of the base portion23in the direction of arrow A, the optical path length of the reference light beam L2can be changed.

The multiplexing means4comprises a 2×2 fiber optic coupler as described above, and multiplexes the reference light beam L2which has been shifted in its frequency and has been changed in its optical path length by the optical path length adjusting means220and the reflected light beam L3from the object Sb to emit the multiplexed light beam toward the interference light detecting means240by way of an optical fiber FB4.

The interference light detecting means240detects interference light L4of the reflected light beam L3and the reference light beam L2which have been multiplexed by the multiplexing means, and comprises a collimator lens141which makes parallel the interference light beam L4radiated from the optical fiber FB4, a spectral means142which divides the interference light beam L4having a plurality of wavelength bands by the wavelength bands and a light detecting means144which detects each wavelength band of the interference light beam L4divided by the spectral means142.

The spectral means142comprises, for instance, a diffraction grating element, and spectrally divides the interference light beam L4entering it to output the divided interference light beam L4to the light detecting means144. The light detecting means144is formed by, for instance, a CCD element which comprises a plurality of, for instance, one-dimensionally or two-dimensionally arranged photosensors and each of the photosensors detects each wavelength band of the interference light beam L4spectrally divided as described above.

The light detecting means144is connected to an image obtaining means250comprising, for instance, a computer system such as a personal computer. The image obtaining means250is connected to a display system260formed, for instance, by a CRT or a liquid crystal display system.

Operation of the optical tomography system1having a structure described above will be described, hereinbelow. When a tomographic image is to be obtained, the optical path length is first adjusted by moving the base23in the direction of the arrow A so that the object Sb is positioned in the measurable area. The light beam La is emitted from the light source unit210and the light beam La is divided into the measuring light beam L1and the reference light beam L2by the light dividing means3. The measuring light beam L1is radiated from the optical probe10toward a body cavity and is projected onto the object Sb. At this time, the measuring light beam L1radiated from the optical probe10is caused to one-dimensionally scan the object Sb by the optical probe10operating as described above. Then the reflected light beam L3from the object Sb and the reference light beam L2reflected by the reflecting mirror22are multiplexed, and the interference light beam L4of the reflected light beam L3and the reference light beam L2is detected by the interference light detecting means240. Information on the intensity distribution of the reflected light in the direction of depth of the object Sb is obtained by carrying out frequency analysis on the detected interference light beam L4in the image obtaining means50after carrying out a suitable waveform compensation and noise removal.

By causing the measuring light beam L1to scan the object Sb by the optical probe10as described above, information on the direction of depth of the object Sb along the direction of scan is obtained and accordingly tomographic images on the cross-section including the direction of scan can be obtained. The tomographic images thus obtained are displayed by the display system260. Further, for instance, by moving the optical probe10right and left inFIG. 5so that the measuring light L1scans the object Sb in a second direction perpendicular to said direction of scan, tomographic images on the cross-section including the second direction can be further obtained.

Another example of the optical tomography system to which the optical probes of the present invention are to be applied will be described, hereinbelow. The optical tomography system300shown inFIG. 6is for obtaining a tomographic image of the object of measurement by measuring the SS-OCT and specifically differs from the optical tomography system1shown inFIG. 5in that structure of the light source unit and the interference light detecting means.

The light source unit310of this system emits a laser beam La while sweeping its wavelength at a predetermined period. Specifically, the light source unit310comprises a semiconductor optical amplifier (a semiconductor gain medium)311and an optical fiber FB10connected to the semiconductor optical amplifier311at opposite ends thereof. The semiconductor optical amplifier311emits weak light to one end of the optical fiber FB10in response to injection of a drive current and amplifies light input from the other end of the optical fiber FB10. When a drive current is supplied to the semiconductor optical amplifier311, a pulse-like laser beam La is emitted to the optical fiber FB1by a resonator formed by the semiconductor optical amplifier311and the optical fiber FB10.

Further, an optical divider312is connected to the optical fiber FB10and a part of the light beam propagated through the optical fiber FB10is emitted from the optical divider312toward the optical fiber FB11. Light emitted from the optical fiber FB11travels through the collimator lens313, the diffraction grating314and the optical system315and is reflected by the rotating polygon mirror316. The reflected light is returned to the optical fiber FB11by way of the optical system315, the diffraction grating314and the collimator lens313.

The rotating polygon mirror316rotates in the direction indicated by arrow RH, to vary the angle of each reflective surface thereof with respect to the optical axis of the optical system315. Thereby, only a light beam having a specific frequency, from among the light spectrally split by the diffraction grating314, is returned to the optical fiber FB11. The frequency of the light beam that reenters the optical fiber FB11is determined by the angle formed by the optical axis of the optical system315and the reflective surface of the rotating polygon mirror316. Then the light beam of a specific frequency band impinging upon the optical fiber FB5L enters the optical fiber FB10, and as a result, only a laser beam La of the specific frequency band is emitted toward the optical fiber FB1.

Accordingly, when the rotating polygon mirror316rotates in the direction indicated by arrow R1at a constant speed, the wavelength A of the light beam which reenters the optical fiber FB11changes at a period with time. As a result, a laser beam La which is swept in its wavelength is emitted from the light source unit310toward the optical fiber FB1.

The interference light detecting means240detects interference light beam L4of the reflected light beam L3and the reference light beam L2which have been multiplexed by the multiplexing means4and the image obtaining means250detects the intensities of the reflected light beam L3in positions in the direction of depth of the object Sb by carrying out frequency analysis on the interference light beam L4detected by the interference light detecting means240and obtains a tomographic image of the object Sb. The tomographic images thus obtained are displayed by the display system260. In this embodiment, a mechanism where the interference light L4is divided into a pair of lights which are guided to optical detectors40aand40band a balanced detection is carried out in a calculating means241is formed. As can be understood, in this embodiment, the interference light detecting means240is formed by the optical detectors40aand40band the calculating means241.

Here, detection of the interference light beam L4in the interference light detecting means240and image generation in the image obtaining means250will be described briefly. Note that a detailed description of these two points can be found in “Optical Frequency Scanning Interference Microscopes”, M. Takeda, Optics Engineering Contact, Vol. 41, No. 7, pp. 426-432, 2003.

When the measuring light beam L1is projected onto the object Sb, the reflected light L3from each depth of the object Sb and the reference light L2interfere with each other with various optical path length difference1. When the light intensity of the interference fringe at this time versus each optical path length difference is assumed to be S(l), the light intensity I(k) detected in the interference light detecting means240is expressed by the following formula.

I⁡(k)=∫0∞⁢S⁡(l)⁡[l+cos⁡(kl)]⁢ⅆl
wherein k represents the wave number and l represents the optical path length difference. The above formula may be considered to be given as an interferogram of a light frequency range having a wave number of ω/c (k=ω/c) as a variable. Accordingly, a tomographic image is generated by obtaining in the image obtaining means250information on the distance of the object Sb from the measurement initiating position and information on the intensity of reflection by carrying out frequency analysis by Fourier-transform on the spectral interference fringes detected by the interference light detecting means240and determining the intensity S(l) of the interference light beam L4.

In the optical tomography system300, an optical probe10the same in arrangement as that employed in the system ofFIG. 5is employed and the operation is the same as that employed in the system ofFIG. 5.

Still another example of the optical tomography system to which the optical probes of the present invention are to be applied will be described, hereinbelow. The optical tomography system400shown inFIG. 7is for obtaining a tomographic image of the object of measurement by measuring the TD-OCT and comprises a light source unit210provided with a light source111which emits laser light La and a light collecting lens112, a light dividing means2which divides a laser light La emitted from the light source unit210and propagated through the optical fiber FB1, a light dividing means3which divides the laser light La passing therethrough into measuring light L1and reference light L2, an optical path length adjusting means220which adjusts the optical path length of the reference light L2divided by the light dividing means3and propagated through the optical fiber FB3, an optical probe10which projects onto the object Sb the measuring light L1divided by the light dividing means3and propagated through the optical fiber FB2, a multiplexing means4(the light dividing means3doubles) which multiplexes the reflected light L3from the object Sb when the measuring light L1divided by the light dividing means is projected onto the object Sb and the reference light L2, and an interference light detecting means240which detects interference light L4of the reflected light L3and the reference light L2which have been multiplexed by the multiplexing means4.

The optical path length adjusting means220comprises a collimator lens21which makes parallel the reference light beam L2radiated from the optical fiber FB3, a reflecting mirror23which is movable in the direction of arrow A to change the distance from the collimator lens21, and a mirror moving means24which moves the reflecting mirror23and changes the optical path length of the reference light L2in order to change the measuring position in the object Sb in the direction of depth. The reference light L2which has been changed in its optical path length by the optical path length adjusting means220is guided to the multiplexing means4.

The interference light detecting means240detects the intensity of the interference light L4propagating through the optical fiber FB2from the multiplexing means4. Specifically, only when the optical length difference between the sum of the total optical path length of the measuring light L1and the optical path length of the reflected light L3reflected or scattered rearward at a certain point on the object Sb and the reference light L2is smaller than the coherence length of the light source, an interference signal whose amplitude is proportional to the amount of the reflected light is detected. Further, as the optical path length is scanned by the optical path length adjusting means220, the position of the reflecting point (depth) in which the interference signal is obtained is changed, whereby the interference light detecting means240detects a reflectance signal in each measuring position of object Sb. Information on the measuring position is output from the optical path length adjusting means220to the image obtaining means. On the basis of the signals detected by the interference light detecting means240and information on the measuring-position in the mirror moving means24, information on the intensity distribution of the reflected light in the direction of depth of the object Sb is obtained by the image obtaining means250.

By causing the measuring light beam L1to scan the object Sb by the optical probe10as described above, information on the direction of depth of the object Sb is obtained and accordingly tomographic images on the cross-section including the direction of scan can be obtained. The tomographic images thus obtained are displayed by the display system260. Further, for instance, by moving the optical probe10right and left inFIG. 5so that the measuring light L1scans the object Sb in a second direction perpendicular to said direction of scan, tomographic images on the cross-section including the second direction can be obtained.

In the optical tomography system400, an optical-probe10the same in arrangement as that employed in the system ofFIG. 5is also employed and the operation is the same as that employed in the system ofFIG. 5.

Though the optical tomography systems1,300and400in which the optical probe10is employed, the optical probes100in accordance with previously described other embodiments of the present invention may be, of course, employed instead of the optical probe10.