Light scanning device and confocal optical device using the same

A light scanning type confocal optical device comprises a light source section, a light transmitting section, a light scanning section, and a processing section. The scanning section includes a movable mirror, a fixed mirror and a converging lens. The movable mirror has an opening at the center, and is supported to be swingable about at least one axis. The fixed mirror is fixedly supported by an optically transparent plate. Reflection surfaces of the movable and fixed mirrors are located opposed to each other. The transmitting section includes an optical fiber having a core, whose end face substantially functions as a confocal pinhole. The light from the end face of the core is, upon passing through the opening, reflected by the fixed mirror toward the movable mirror. The light from the fixed mirror is then reflected by the movable mirror, and is converged by the converging lens onto an object surface.

BACKGROUND OF THE INVENTION
 The present invention relates to a light scanning type confocal optical
 device, which scans light emitted from a light source over the surface of
 an object, and detects light reflected from the surface or fluorescence,
 and also relates to a light scanning device applied to the optical device.
 In recent years, the light scanning type confocal optical microscope has
 been known as means for minutely observing living tissue or the surface or
 the inside of cells. The confocal optical microscope has a resolving power
 exceeding that of an ordinary optical system and, in addition, can obtain
 a three-dimensional image. However, an ordinary confocal optical
 microscope has a large optical system, and can not practicably be inserted
 into the living body. Thus, in general, living tissue is removed from the
 body in order for the tissue to be observed with the ordinary confocal
 optical microscope.
 In order to overcome this disadvantage, a smaller optical system of a light
 scanning type micro-confocal microscope is disclosed in the literature
 "Micromachined scanning confocal optical microscope" (OPTIC LETTERS, Vol.
 21, No 10, May, 1996) or U.S. Pat. No. 5,742,419.
 The literature suggests the possibility with which a three-dimensional
 image could be obtained in real time. To be more specific, the above light
 scanning type micro-confocal microscope, as shown in FIG. 8, comprises a
 light source 1, a light transmitting section 2, a light detecting section
 3, a light scanning section 4, and a processing section 5. The light
 transmitting section 2 has a single mode fiber. The light scanning section
 4 is inserted into the living body through an endoscope. By virtue of
 this, a three-dimensional image of the inside of the living body could be
 obtained in real time.
 FIG. 9 shows the structure of the light scanning section 4. In the light
 scanning section 4, a laser light is emitted from the light source 1, and
 transmitted through the single mode fiber 10. Then, it is reflected by a
 reflection surface 11, and deflected in an X direction by an electrostatic
 mirror 12 for scanning light in the X direction. Thereafter, it is totally
 reflected by a reflection portion 14, deflected in a Y direction by an
 electrostatic mirror 13 for scanning light in the Y direction, and then
 converged onto an object surface 16 by a diffraction lens 15.
 An end face of the single mode fiber 10 has a conjugate relationship with
 the object surface 16. Accordingly, the light reflected from the object
 surface 16 turns back on the above optical path, and converges on the end
 face of the single mode fiber 10. To be more specific, the light reflected
 from the object surface 16 is incident on the diffraction lens 15, and
 thereafter reflected successively by the electrostatic mirror 13, the
 reflection portion 14, the electrostatic mirror 12, and the reflection
 surface 11 in that order. Then, it is converged on the end face of the
 single mode fiber 10 by a converging function of the diffraction lens 15.
 The converged light is transmitted through the single mode fiber 10 of the
 light transmitting section 2, and detected by the light detecting section
 3.
 The above optical system composes a confocal optical system, since the end
 face of the core of the single mode fiber 10 functions as a pinhole. Thus,
 scattered light from that portion of the object surface 16 which excludes
 a convergence point is sufficiently weak in intensity at the end face of
 the fiber 10, and hardly detected by the light detecting section 3.
 Therefore, the above optical system has high resolution in a horizontal
 direction (XY direction) of the object surface 16 and a depth direction (Z
 direction) of the object surface 16, as compared with the ordinary optical
 system. In other words, it has higher longitudinal and transverse
 resolving powers than the ordinary optical system.
 The above light scanning type micro-confocal optical microscope has a lower
 resolving power than the ordinary confocal optical microscope; however,
 its resolving power is sufficient for diagnosis involving observation of
 an internal organ or the like. In addition, the micro-confocal optical
 microscope has a considerably compact structure.
 In insertion of such a micro-confocal optical microscope into the living
 body through the endoscope to observe the inside of the body, its view
 direction obliquely crosses its insertion direction. Accordingly, it is
 difficult to accurately move the object surface 16 in the Z direction
 only. In other words, the above micro-confocal microscope has bad
 observational operability.
 Furthermore, the conventional micro-confocal microscope uses two reflection
 surfaces 11 and 14 and two one-dimensional scanning mirrors 12 and 13, in
 order to achieve two-dimensional scanning. However, use of such a large
 number of reflection surfaces causes attenuation of light due to
 reflection performed between the large number of surfaces, thus lowering
 the detection sensitivity.
 BRIEF SUMMARY OF THE INVENTION
 The present invention has been made to overcome the above disadvantages. An
 object of the invention is to provide a light scanning type compact
 confocal optical device, which has the view direction coincident with the
 insertion direction, thus improving the operability.
 Another object of the invention is to provide a light scanning device,
 which allows realization of such a compact confocal optical system.
 Still another object of the present invention is to provide a light
 scanning type confocal optical device or light scanning device, which has
 a small number of reflection surfaces, such that detection sensitivity is
 improved.
 Additional objects and advantages of the invention will be set forth in the
 specification which follows, and in part will be obvious from the
 description, or may be learned by practice of the invention. The objects
 and advantages of the invention may be realized by means of the
 instrumentalities and combinations particularly pointed out hereinafter.

DETAILED DESCRIPTION OF THE INVENTION
 FIG. 1 shows a light scanning type confocal optical device having a light
 scanning device, according to the first embodiment of the present
 invention. Referring to FIG. 1, the optical device comprises a light
 source section 112, a light transmitting section 114, a light scanning
 section 116, a light detecting section 118, and a processing section 120.
 The light source section 112 is constituted by, e.g., a laser oscillator.
 The light transmitting section 114 comprises, e.g., a four-terminal
 coupler 212 for sorting incident light and detected light, and four
 optical fibers 214, 216, 218 and 220 connected to the four-terminal
 coupler 212. The light scanning section 116 has a movable mirror 122, a
 fixed mirror 126 and a converging lens 130. The processing section 120
 processes data on the basis of scanned information and data from the light
 detecting section 118.
 The light source section 112 and the four-terminal coupler 212 are
 optically connected to each other by the optical fiber 214. The light
 scanning section 116 and the four-terminal coupler 212 are optically
 connected to each other by the optical fiber 216. The light detecting
 section 118 and the four-terminal coupler 212 are optically connected to
 each other by the optical fiber 218. The optical fiber 220 connected to
 the four-terminal coupler 212 has a free end, and is subjected to
 non-reflection processing.
 The movable mirror 122 has a light transmission region, e.g., an opening
 124 at its center, and is supported to be swingable about at least one
 axis. The fixed mirror 126 is fixedly supported by an optically
 transparent plate 128, such as a glass plate. A reflection surface of the
 movable mirror 122 is located opposite to a reflection surface of the
 fixed mirror 126. Accordingly, the fixed mirror 126 reflects the light
 passing through the opening 124 toward the reflection surface of the
 movable mirror 122, and then the movable mirror 122 reflects the light
 reflected from the fixed mirror 126 toward the converging lens 130. The
 conversing lens 130 converges the light transmitted from the movable
 mirror 122 through the plate 128 onto an object surface 132.
 The optical fiber 216 is a step index type optical fiber having a core and
 a clad, more preferably, a single mode fiber having a small core diameter.
 The core of an end face of the optical fiber 216 is substantially regarded
 as a point light source. Furthermore, a confocal optical system is
 provided such that the core of the end face has a conjugate relationship
 with a focal point of the converging lens 130. The core of the end face
 substantially functions as a confocal pinhole in the confocal optical
 system.
 The movable mirror 122 is supported in a manner varying in accordance with
 the scanning method required for measurement. For example, when scanning
 is one-dimensionally performed, the movable mirror 122 is supported to be
 swingable about one axis. In other words, it is swung about the axis to
 achieve one-dimensional scanning. When scanning is two-dimensionally
 performed, the movable mirror 122 is supported to be swingable about two
 perpendicular axes. In other words, it is swung about the axes to achieve
 two-dimensional scanning. Needless to say, it may be supported to be
 swingable about two axes, and swung about one of the axes to achieve
 one-dimensional scanning.
 The light from the light source section 112 reaches the four-terminal
 coupler 212, and then the coupler 212 transmits half of the light to the
 light scanning section 116 through the optical fiber 216. The light from
 the optical fiber 216 passes through the opening 124, and is reflected by
 the fixed mirror 126 toward the reflection surface of the movable mirror
 122. The light from the reflection surface of the movable mirror 122 is
 incident on the converging lens 130, and is then converged onto the object
 surface 132 due to a refracting function of the converging lens 130.
 The light incident on the object surface 132 is reflected irregularly
 therefrom in accordance with the shape and reflectance, etc. of the
 object. Of the irregularly reflected light, the light incident onto the
 converging lens 130 is transmitted to the movable mirror 122, and
 reflected therefrom to the fixed mirror 126. Then, the light reflected
 from the fixed mirror 126 reaches the end face of the optical fiber 216.
 In other words, part of the light reflected from the object surface 132
 strikes on and passes through the converging lens 130, and the light
 passed through the lens travels to the end face of the optical fiber 216,
 after being reflected by the movable mirror 122 and then by the fixed
 mirror 216 and passing through the opening 214, while being converged by a
 refracting function of the converging lens 130.
 The light returned from the light scanning section 116 is transmitted from
 the end face of the optical fiber 216 to the core thereof, and then
 reaches the four-coupler 212 through the optical fiber 216. The coupler
 212 transmits half of the light to the light detecting section 118 through
 the optical fiber 218. The light detecting section 118 detects the
 waveform and intensity, etc. of the light as information of the light, and
 sends the information to the processing section 120. The processing
 section 120 processes the information along with driving data of the
 movable mirror 122, to thereby obtain data such as the intensity of
 detected light at respective positions of the object surface 132.
 Needless to say, the structure of the confocal optical device according to
 the first embodiment may be modified variously. For example, in the
 above-mentioned structure, optical scanning is achieved due to swinging of
 the mirror 122. However, such a structure may be modified as follows: the
 mirror 122 is fixed, and the mirror 126 is swung in order to perform
 optical scanning. Alternatively, both the mirrors 122 and 126 may be
 swingably supported, and swung about perpendicular axes to achieve
 two-dimensional scanning.
 According to the first embodiment, when the confocal optical device is
 inserted into the living body through the endoscope, the insertion
 direction of the device accords with the view direction of the confocal
 optical system, in which the inside of the living body is viewed with the
 system. Therefore, the light scanning section 116 can be easily and
 accurately moved in a direction perpendicular to the object surface 132.
 Furthermore, in the first embodiment, the number of reflection surfaces is
 only two. In other words, only the movable mirror 122 and fixed mirror 126
 have reflection surfaces. Accordingly, the degree of the attenuation of
 light which occurs due to reflection is small, and thus lowering of the
 detection sensitivity can be greatly restricted.
 Next, a driving mirror, which may be applied for the above mentioned
 confocal optical device, will be explained. It is a specific structural
 unit, and includes the movable mirror 122. To be more specific, in this
 specification, the driving mirror means a functional unit or a device
 including a movable mirror capable of being swung and driving means for
 swinging the movable mirror.
 FIG. 2 shows an electrostatically driving type driving mirror for scanning
 light two-dimensionally, which is applied to the confocal optical device
 according to the first embodiment.
 In the driving mirror, a reflection surface-holding portion 142 is
 supported by a pair of torsion bars 144 connected to an inner frame 146,
 and the inner frame 146 is supported by a pair of torsion bars 148
 connected to an outer frame 150. The pair of torsion bars 144 and the pair
 of torsion bar 148 can be elastically twisted about their perpendicular
 axes. Due to this structure, the reflection surface holding portion 142
 can be swung about the axis of the pair of torsion bars 144 relative to
 the inner frame 146, and also swung about the axis of the pair of torsion
 bars 148 relative to the outer frame 150.
 On the reflection surface holding portion 142, a +X electrode 152 and a -X
 electrode 154 are formed, functioning as an optical reflection surface.
 They are connected to electrodes 160 and 162 by wiring patterns 156 and
 158 extending on the inner frame 146, respectively. On the inner frame
 146, a +Y electrode 164 and a -Y electrode 166 are formed, and connected
 to electrodes 172 and 174 by wiring patterns 168 and 170, respectively.
 Furthermore, the above structural unit is provided with one ground
 electrode (not shown) which is located opposite to the +X electrode 152,
 the -X electrode 154, the +Y electrode 164 and the -Y electrode 166.
 When a voltage is applied between the +X electrode 152 and the ground
 electrode, an electrostatic force generates which has a value proportional
 to the absolute value of the applied voltage, and the +X electrode 152 is
 attracted toward the ground electrode. Similarly, when a voltage is
 applied between the -X electrode 154 and the ground electrode, the. -X
 electrode 152 is attracted toward the ground electrode by a generated
 electrostatic force having a value proportional to the absolute value of
 the applied voltage. Accordingly, when voltages having different values
 (different absolute values) are applied to the +X electrode 152 and the -X
 electrode 154, respectively, the reflection surface-holding portion 142 is
 twisted about the axis of the pair of torsion bars 144 (referred to as a Y
 axis in the first embodiment), and the reflection surface (the +X
 electrode 152 and -X electrode 154) is deflected about the Y axis.
 Therefore, the reflection surface (the +X electrode 152 and the -X
 electrode 154) is periodically swung about the Y axis, and the light
 reflected from the reflection surface is scanned in a reciprocating manner
 along the axis of the pair of torsion bars 148 (which is referred to as an
 X axis), when alternating voltages which have opposite phases with a
 minimum voltage of 0V are applied to the +X electrode 152 and the -X
 electrode 154, respectively. For example, the above is achieved, when an
 alternating voltage, which is represented by a solid line in FIG. 3, is
 applied to the +X electrode 152, and an alternating voltage, which is
 represented by a broken line in FIG. 3, is applied to the -X electrode
 154.
 Similarly, voltages having different values are applied to the +Y electrode
 164 and the -Y electrode, respectively, to thereby swing the reflection
 surface holding portion 142 about the X axis. As a result, the reflection
 surface (the +X electrode 152 and the -X electrode 154) is deflected about
 the X axis, and the light reflected from the reflection surface is scanned
 along the Y axis.
 Therefore, the light reflected from the reflection surface (the +X
 electrode 152 and the -X electrode 154) is two-dimensionally scanned
 (e.g., raster-scanned), by applying voltages having opposite phases and
 varying periodically as shown FIG. 3 to the +X electrode 152 and the -X
 electrode 154, and applying voltages, which have opposite phases and vary
 in a linear fashion over time, to the +Y electrode 164 and the -Y
 electrode 166.
 Next, an electrostatically driving type driving mirror for scanning light
 one-dimensionally will be explained with reference to FIG. 4, which may be
 applied to the confocal optical device according to the first embodiment,
 instead of the driving mirror of FIG. 2.
 The driving mirror shown in FIG. 4 is a structural unit having one swinging
 function, whereas the driving mirror in FIG. 2 has two swinging functions.
 In other words, it has a similar structure to that of FIG. 2, apart from
 that it does not include the inner frame 146 of the driving mirror of FIG.
 2.
 More specifically, the reflection holding portion 142 is supported by the
 pair of torsion bars 144 connected to the outer frame 150, which can be
 elastically twisted about the axis of the pair. Due to this structure, it
 can be swung about the axis of the pair relative to the outer frame 150.
 On the reflection surface holding portion 142, the +X electrode 152 and the
 -X electrode 154 are formed, functioning as a reflection surface, and
 connected to the electrodes 160 and 162 by the wiring patterns 156 and
 158. In addition, one ground electrode (not shown) is provided opposite to
 the +X electrode 152 and the -X electrode 154.
 The reflection surface (the +X electrode 152 and the -X electrode 154) is
 periodically swung about the Y axis, and the light reflected from the
 reflection surface is scanned along the X axis in a reciprocating manner.
 A galvano-mirror, which is well known as a driving mirror for scanning
 light one-dimensionally, will be explained with reference to FIG. 5 and
 may be applied to the confocal optical device according to the first
 embodiment.
 A galvano-mirror 190 has a reflecting member 192 which has an opening 124
 formed in its center, and which is fixed to a shaft of a galvano-motor
 194. The galvano-mirror 190 is the same as a well known general
 galvano-mirror, with the exception of the following feature: the opening
 124 is formed in the center of the reflecting member 192. Accordingly, the
 reflecting member 192 is swung around the shaft 196 by the galvano-motor
 194 as in the general galvano-mirror, whereby reflected light is scanned
 in a reciprocating manner in an imaginary plane perpendicular to the shaft
 196.
 FIG. 6 shows a light scanning type confocal optical device having a light
 scanning device, according to the second embodiment.
 In FIG. 6, identical structural elements to those in FIG. 1 are denoted by
 the same reference numerals, and their explanations will be omitted. The
 scanning section 116 of the second embodiment differs in structure from
 the optical scanning section 116 of the first embodiment. The other
 structural elements are completely the same as those of the first
 embodiment. Accordingly, their operations are also the same.
 The optical scanning section 116 has a movable mirror 122, a fixed mirror
 126 and a converging lens 130. The converging lens 130 is a plano-convex
 lens, and the fixed mirror 126 is provided on a flat surface of the
 converging lens 130. The fixed mirror 126 is formed of a metal film. To be
 more specific, a metal film is selectively formed on the flat surface of
 the converging lens 130 by, e.g., deposition, thereby forming the fixed
 mirror 126.
 The reflection surface of the movable mirror 122 is located opposite to
 that of the fixed mirror 126. The fixed mirror 126 reflects the light
 passing through the opening 124 toward the reflection surface of the
 movable mirror 122, and the movable mirror 122 reflects the light from the
 fixed mirror 126 toward the converging lens 130. The converging lens 130
 converges the light from the movable mirror 122 onto the object surface
 132.
 The confocal optical device of the second embodiment has a smaller number
 of structural elements than the confocal optical device of the first
 embodiment. In this regard, it is advantageous.
 FIG. 7 shows a light scanning type confocal optical device having a light
 scanning device, according to the third embodiment.
 In FIG. 7, identical structural elements to those in FIG. 1 are denoted by
 identical reference numerals, and their explanation will be omitted. The
 confocal optical device of the third embodiment are completely the same as
 the confocal optical device of the second embodiment, except for the
 position of the core of the end face of the optical fiber 216, which
 functions as a confocal pinhole. Therefore, its operation is also the
 same.
 More specifically, according to the third embodiment, the optical fiber 216
 extends through the opening 124 of the movable mirror 122, and the core of
 the end face of the optical fiber 216, which as mentioned above, serves as
 the confocal pinhole, is located between the movable mirror 122 and the
 fixed mirror 126.
 The reflection surface of the movable mirror 122 is opposite to that of the
 fixed mirror 126. The fixed mirror 126 reflects the light emitted from the
 optical fiber 216 toward the reflection surface of the movable mirror 122,
 and the movable mirror 122 reflects the light from the fixed mirror 126
 toward the converging lens 130. The converging lens 130 converges the
 light from the movable mirror 122 onto the object surface 132.
 By virtue of the above structure, in the optical device of the third
 embodiment, there is no possibility that the light emitted from the
 optical fiber 216 may be incident on and returned by some portion of the
 opening 124. In this regard, the optical device of the third embodiment is
 advantageous.
 Additional advantages and modifications will readily occur to those skilled
 in the art. Therefore, the invention in its broader aspects is not limited
 to the specific details and representative embodiments shown and described
 herein. Accordingly, various modifications may be made without departing
 from the sprit or scope of the general inventive concept as defined by the
 appended claims and their equivalents.