OPTICAL INSPECTION DEVICE, ELECTROMAGNETIC WAVE DETECTION METHOD, ELECTROMAGNETIC WAVE DETECTION DEVICE, ORGANISM OBSERVATION METHOD, MICROSCOPE, ENDOSCOPE, AND OPTICAL TOMOGRAPHIC IMAGE GENERATION DEVICE

An optical inspection device 1, comprising a light generation means 2, a light irradiation means 3 irradiating an object to be inspected 4 with light generated from the light generation means 2 and a photodetection means 6 photoelectrically converting signal light obtained from the object to be inspected 4 through irradiation of light by the light irradiation means 3, and inspecting the object to be inspected 4 based on output from the photodetection means 6, wherein a light amplification means 5 amplifying signal light obtained from the object to be inspected 4 is provided. There is thus provided an optical inspection device capable of photoelectically converting signal light from the object to be inspected with high sensitivity and promptly with its inexpensive configuration without increasing the intensity of light with which the object to be inspected is irradiated and without using an expensive low-noise and high-sensitivity photodetector.

REFERENCE SYMBOLS

BEST MODE FOR CARRYING OUT THE INVENTION

First, before explaining embodiments of the invention, the fundamental configuration of the optical inspection device of the invention will be described.

FIG. 1is a functional block diagram illustrating a fundamental configuration of the optical inspection device of the invention. The optical inspection device1has a light generation means2, a light irradiation means3, a light amplification means5and a photodetection means6. The light generation means2generates light for obtaining signal light from an object to be inspected, and generates light having a given wavelength or light having a given wavelength region according to a type of inspection. The light irradiation means3irradiates an object to be inspected4with the light generated by the light generation means2, thereby signal light is generated from the object to be inspected4. Here, the signal light generated from the object to be inspected4through light irradiation therefor is transmitted light or reflected light of irradiated light, fluorescence or phosphorescence generated through excitation by irradiated light, or light generated by nonlinear optical effects, for example, according to a type of inspection.

The light amplification means5inputs signal light according to a type of inspection obtained from the object to be inspected4, amplifies the input signal light and outputs it to the photodetection means6. The photodetection means6receives the signal light amplified by the light amplification means5and photoelectrically converts it. The electrical signals photoelectrically converted by the photodetection means6are processed according to a type of inspection at a signal processing circuit which is not shown, thereby the object to be inspected is inspected.

As above, signal light obtained from the object to be inspected4is amplified by the light amplification means5and then photoelectrically converted by the photodetection means6, which makes it possible to photoelectrically convert signal light with high sensitivity and promptly without increasing the intensity of light with which the object to be inspected4is irradiated and without using an expensive low-noise high-sensitivity photodetector even when signal light obtained from the object to be inspected4is weak.

Next, embodiments of the invention will be described with reference to the accompanying drawings.

First Embodiment

FIG. 2is a functional block diagram illustrating a configuration of the optical inspection device according to the first embodiment of the invention. The optical inspection device is a device for visualizing a route condition of a blood vessel12buried in fat11when a rigid endoscope is inserted to the inside of a body to approach organs like a stomach covered by fat. The device enables the scope-assisted surgery with avoiding bleeding due to wrong cutting of the blood vessel12.

For this reason, the optical inspection device shown inFIG. 2is provided, at a distal insertion portion of a rigid endoscope which is not shown, with a movable table15which can be moved in two-dimensional direction in a plane perpendicular to an insertion direction, and the movable table15is provided with a projector lens16for irradiating the object to be inspected with light and a collective lens17for collecting signal light from the object to be inspected at intervals of about 10 mm, for example. The computer21drives the movable table15in two-dimensional direction through a movable table control device22so that the movable table15scans with light with which the object to be inspected is irradiated.

Therefore, in the embodiment, the movable table15, the computer21and the movable table control device22constitute the light scan means.

The projector lens16is connected to a laser diode (LD)26as the light generation means via a single-mode optical fiber25. As the laser diode26, there is used one generating light having output of 50 mW, a spectral width of 1 nm and a central wavelength of 980 nm, for example. It is noted that light having a wavelength of 980 nm is low in optical absorptance at fat11of an organism and high in optical absorptance at hemoglobin in erythrocytes. An LD driver28drives the laser diode26based on sinusoidal modulation signals having a frequency of fm from a function generator27. Thus, the laser diode26generates light intensity-modulated at a frequency of fm, and the intensity-modulated light is guided to the projector lens16via the single-mode optical fiber25to be rendered to a parallel beam by the projector lens16, with which an organism is irradiated. In the optical inspection device, therefore, the single-mode optical fiber25and the projector lens16constitute the light irradiation means.

The light with which an organism is irradiated through the projector lens16is transmitted, reflected or scattered in fat11, and when the blood vessel12runs in the fat11, the light is absorbed by erythrocytes flowing therein and amplitude-modulated. As above, an organism is irradiated with light from the laser diode26, thereby signal light obtained from the organism is collected by the collective lens17and the collected signal light is amplified by a light amplification means32via a multimode optical fiber31. In the embodiment, the light amplification means32uses a waveguide-type optical amplifier such as a semiconductor optical amplifier, an optical fiber amplifier or the like, and is configured so as to have an amplification band of 3 nm and a gain of about 13 dB in a band having a wavelength of 980 nm, thereby the optical power of the received signal light is amplified to of about 20 times and the light is output.

The signal light amplified by the light amplification means32is received by a photodetection means (PD)34via a band-pass filter33and photoelectrically converted. As the band-pass filter33, there is used of dielectric-multilayer-type having a central wavelength of 980 nm and a passband width of about 1 nm, for example. As a photodetection means34, InGaAs/PIN photodiode is used, for example.

Outputs photoelectrically converted by the photodetection means34are converted to electric voltage by a transimpedance amplifier35and input in a lock-in amplifier36. With sinusoidal modulation signals having a frequency of fm from the function generator27as reference signals, the lock-in amplifier36extracts voltage signals synthesized with the reference signals from input voltage signals from the transimpedance amplifier35, The analog output signals extracted by the lock-in amplifier36are converted to digital signals by an analog-digital (A/D) converter37and provided to the computer21.

The computer21processes digital signals of each point of an organism obtained from the A/D converter37through optical scanning by two-dimensional driving of the movable table15, and displays an image on a monitor38.

According to the embodiment, signal light from an organism collected by the collective lens17is amplified by the light amplification means32via the multimode optical fiber31and then photoelectrically converted by the photodetection means34, which makes it possible to photoelectrically convert signal light with high sensitivity and promptly with constituting the photodetection means34by an inexpensive photodetector without increasing outputs of the laser diode26even when signal light obtained from an organism is weak. Then, there are obtained, from the lock-in amplifier36, output voltage lower at scanned points where blood vessels run than at scanned points where blood vessels do not run within scanned area of the fat11. Thus, it is possible to visualize the route of a blood vessel having a diameter of about 3 mm buried under fat having a thickness of 4 mm, for example. Therefore, an image displayed on the monitor38is observed, which enables the scope-assisted surgery with avoiding blood vessels, that is, with preventing bleeding due to cutting of blood vessels.

FIG. 3is a diagram illustrating two examples of an optical fiber amplifier which can be used as the light amplification means32shown inFIG. 2.FIG. 3(a) illustrates a configuration of a rare-earth-doped optical fiber amplifier, and FIG.3(b) illustrates a configuration of an optical Raman amplifier.

The rare-earth-doped optical fiber amplifier shown inFIG. 3(a) has an excitation light source41, a multiplex device42such as a dichroic mirror or the like, a rare-earth-doped optical fiber43and an excitation light removal device44, furthermore, it has optical isolators45and46at the input end and the output end respectively in order to prevent laser oscillation thereof. As the rare-earth-doped optical fiber43, there is used one in which an optical fiber is doped with a rare earth such as Nd, Yb, Er, Tm, Pr or the like.

InFIG. 3(a), signal light having a wave length of Xs input through the optical isolator45is multiplexed with excitation light having a wavelength of λp emitted from the excitation light source41at the multiplex device42, and input into the rare-earth-doped optical fiber43. Thus, the signal light is amplified using stimulated emission in the rare-earth-doped optical fiber43excited by excitation light. The output light from the rare-earth-doped optical fiber43is rendered to be incident on the excitation light removal device44, in which residual excitation light is removed so that only signal light is transmitted. Thereafter, signal light having transmitted through the excitation light removal device44is output via the optical isolator46.

When signal light having a wavelength of 980 nm is amplified by the rare-earth-doped optical fiber amplifier, as shown inFIG. 2, there is used, as each component, one having the following properties, for example. That is, as the excitation light source41, there is used one having a wavelength of 915 nm, optical output of 50 mW and a spectral width of 1 nm. As the multiplex device42, an optical fiber wavelength multiplex coupler is used. As the rare-earth-doped optical fiber43, there is used a single clad multimode Yb-doped optical fiber or a single clad single-mode Yb-doped optical fiber having a length of 1 m and a low level of Yb added. The excitation light removal device44removes excitation light having a wavelength of 915 nm and uses a dielectric multilayer filter allowing signal light having a wavelength of 980 nm to pass therethrough. As the isolators45and46, there are used ones having an operation wavelength of 980 nm, an isolation band of about 30 nm and return loss of 30 dB. Thus, it is possible to achieve a Yb-doped optical fiber amplifier for a wavelength band of 980 nm with low noise and high sensitivity.

With respect to the optical Raman amplifier shown inFIG. 3(b), in the configuration of the rare-earth-doped optical fiber amplifier shown inFIG. 3(a), a Silica optical fiber47is used instead of the rare-earth-doped optical fiber43and the Silica optical fiber47is excited by excitation light, thereby signal light is amplified using stimulated Raman scattering effects. The other configurations and operation are the same as in the rare-earth-doped optical fiber amplifier. Therefore, the same components are represented with the same reference symbols, and the description thereof will be omitted.

When signal light having a wavelength of 980 nm is amplified by the optical Raman amplifier, as shown inFIG. 2, there is used, as the excitation light source41, one having a wavelength of 940 nm, optical output of 300 mW and a spectral width of 6 nm, for example. As the Silica optical fiber47, there is used a multimode optical fiber or a single-mode optical fiber having a core diameter of 6 μm and a length of 2 km. The excitation light removal device44removes excitation light having a wavelength of 940 nm and uses a dielectric multilayer filter allowing signal light having a wavelength of 980 nm to pass therethrough. As the other components, there are used ones having properties described for the rare-earth-doped optical fiber amplifier shown inFIG. 3(a). Thus, it is possible to achieve an optical Raman amplifier for a wavelength of 980 nm with low noise and high sensitivity.

It is noted that, although the configurations shown inFIGS. 3(a) and3(b) are of forward excitation so that excitation light is transmitted in the rare-earth-doped optical fiber43and the Silica optical fiber47in the same direction as signal light, they can be of backward excitation so that excitation light is transmitted in the opposite direction of signal light, or bidirectional excitation.

Second Embodiment

FIG. 4is a functional block diagram illustrating a configuration of the optical inspection device according to the second embodiment of the invention. In the embodiment, a laser scanning confocal fluorescence microscope51is constituted, and a He—Ne laser52continuously oscillating at a wavelength of543nm is provided as the light generation means. With respect to laser light emitted from the He—Ne laser42, its light intensity is adjusted by a light intensity adjustment device53such as an acousto-optic modulator (AOM) or the like, for example. Then, the light passes through a dichroic mirror54, an X-Y galvano scanner mirror55, a pupil lens56, a tube lens57and an objective lens58, and is collected so that a living cell sample60to be inspected is irradiated therewith. Thus, in the laser scanning confocal fluorescence microscope51, the light intensity adjustment device53, the dichroic mirror54, the X-Y galvano scanner mirror55, the pupil lens56, the tube lens57and the objective lens58constitute the light irradiation means. Moreover, the X-Y galvano scanner mirror55constitutes the light scan means.

It is noted that there is used, as the living cell sample60, an object to be inspected dyed with fluorescent dye or an object to be inspected in which fluorescent protein is expressed. Here, an object to be inspected in which fluorescent protein DsRed is expressed, is used. Thus, when the living cell sample60is irradiated with laser light from the He—Ne laser52, DsRed is excited and thus fluorescence having a wavelength of about 570 nm to 650 nm is generated.

The fluorescence generated from the living cell sample60passes through the objective lens58, the tube lens57, the pupil lens56and the X-Y galvano scanner mirror55to the dichroic mirror54. The dichroic mirror54is configured so as to allow light having a wavelength of 543 nm to pass therethrough and so as to reflect light having a wavelength longer than 570 nm. Thereby, the fluorescence having a wavelength of about 570 nm to 650 nm generated in the living cell sample60is reflected by the dichroic mirror54.

The fluorescence reflected by the dichroic mirror54passes through an optical isolator61and is collected by a collective lens62, thereafter it is amplified by a light amplification means63having a semiconductor optical amplifier or an optical fiber amplifier. Then, the amplified fluorescence is received by a photomultiplier tube (PMT)64as the photodetection means and photoelectrically converted. The light amplification means63is configured so as to have a gain band having a gain of about 10 dB and a wavelength of 620 nm to 650 nm, for example.

The whole of laser scanning confocal fluorescence microscope51is controlled by a computer65. Thus, laser light from the He—Ne laser52is deflected by the X-Y galvano scanner mirror55, and the living cell sample60is two-dimensionally scanned in a plane perpendicular to a light axis from the objective lens58. Then, the photoelectrically-converted output obtained from the photomultiplier tube64is processed at each scanned point to display a fluorescence image on a monitor66.

According to the embodiment, fluorescence generated from the living cell sample60through irradiation with laser light from the He—Ne laser52is amplified by the light amplification means63and then photoelectrically converted by the photomultiplier tube64, which makes it possible to photoelectrically convert fluorescence with high sensitivity and promptly with using the inexpensive photomultiplier tube64without increasing the intensity of laser light with which the living cell sample60is irradiated even when fluorescence as signal light obtained from the living cell sample60is weak.

In addition, the optical isolator61is disposed at the input side of the light amplification means63, which can prevent back reflection to the living cell sample60. Thereby, it is possible to prevent damages to the living cell sample60due to excessive light irradiation therefor and variation given to signal light. The reason will be described below. Generally, when light is amplified using an optical amplifier, it is unavoidable to add amplified spontaneous emission (ASE) noises. Thus, in the configuration ofFIG. 4, it could be possible that one part of ASE generated at the light amplification means63is returned to the side of the living cell sample60and the excessive light irradiation damages the living cell sample60or varies signal light emitted from the living cell sample60. In the embodiment, however, the optical isolator61is disposed at the incidence side of the light amplification means63, which can prevent back reflection with ASE to the living cell sample60and thus prevent damages to the living cell sample60and variation of signal light therefrom.

Third Embodiment

FIG. 5is a functional block diagram illustrating a configuration of the optical inspection device according to the third embodiment of the invention. In the embodiment, a laser scanning multiphoton fluorescence microscope71is constituted, and this embodiment is different, as compared with the configuration of the laser scanning confocal fluorescence microscope51shown inFIG. 4, mainly in aspects that a Titanium-sapphire laser72is used as the light generation means; the gain of the light amplification means63is controlled by the computer65through a gain control means73; and the dichroic mirror54is disposed between the tube lens57and the objective lens58and its optical properties are rendered to be applied for the wavelength of emitted light from the Titanium-sapphire laser72.

In the embodiment, ultrashort optical pulses having a repetition rate of 80 MHz, a pulse width of 150 fs and an oscillation wavelength of 1000 nm are generated from the Titanium-sapphire laser72. With respect to the ultrashort optical pulses from the Titanium-sapphire laser72, its optical average power is adjusted to 500 mW by the light intensity adjustment device53. Then, the pulses pass through the X-Y galvano scanner minor55, the pupil lens56, the tube lens57, the dichroic mirror54and the objective lens58, and are collected to irradiate the living cell sample60to be inspected therewith. Thereby, DsRed, for example, in the living cell sample60is multiphoton-excited (two-photon-excited, for example) to generate fluorescence.

The fluorescence generated from the living cell sample60passes through the objective lens58to the dichroic mirror54. The dichroic mirror54is configured so as to allow light having a wavelength of 1000 nm from the Titanium-sapphire laser72to pass therethrough and so as to reflect light having a short wavelength of 700 nm or shorter. Thereby, fluorescence having a wavelength of about 570 nm to 650 nm generated in the living cell sample60is reflected by the dichroic minor54.

The fluorescence reflected by the dichroic mirror54passes through the optical isolator61, is collected by the collective lens62and amplified by the light amplification means63, thereafter the amplified fluorescence is received by the photomultiplier tube64and photoelectrically converted.

Here, the fluorescence generated from the living cell sample60through two-photon excitation, for example, by excitation optical pulses from the Titanium-sapphire laser72lasts for about some nanoseconds. That is, the fluorescence generated from the living cell sample60becomes pulse light synchronized with excitation optical pulses from the Titanium-sapphire laser72. Thus, in the embodiment, the computer65controls through the gain control means73so that, in synchronization with the timing at which this pulse form of fluorescence is incident on the light amplification means63, the gain of the light amplification means63is increased at the timing of incidence of fluorescence.

The gain of the light amplification means63is controlled in a way that when a semiconductor optical amplifier is used, its driving current is increased or decreased or turned on or off, or in a way that when an optical fiber amplifier is used, the intensity of excitation light from an excitation light source is increased or decreased or the excitation light is turned on or off.

According to the embodiment, fluorescence generated from the living cell sample60through multiphoton excitation by excitation optical pulses from the Titanium-sapphire laser72is amplified by the light amplification means63and then photoelectrically converted by the photomultiplier tube64, which makes it possible to photoelectrically convert fluorescence resulted by two-photon excitation with high sensitivity and promptly with using the inexpensive photomultiplier tube64without increasing the intensity of laser light with which the living cell sample60is irradiated even when fluorescence as signal light obtained from the living cell sample60is weak.

In addition, the gain of the light amplification means63is controlled in synchronization with the timing of incidence of fluorescence on the light amplification means63, which can reduce the mixture of ASE noises during time in which fluorescence is not incident and thus improve the S/N.

Fourth Embodiment

FIG. 6is a functional block diagram illustrating a configuration of the optical inspection device according to the fourth embodiment of the invention. In the embodiment, a laser scanning CARS microscope81is constituted, and a two-wavelength optical pulse source82is provided as the light generation means. The two-wavelength optical pulse source82is configured so as to generate light having a wave length of 1064 nm and 816 nm, for example, at a pulse width of about 5 ps and a repetition rate of 80 MHz, respectively. With respect to two-wavelength pulse light from the two-wavelength optical pulse source82, its optical average power is adjusted to some tens of mW respectively by the light intensity adjustment device53. Then, the light passes through the X-Y galvano scanner mirror55, the pupil lens56, the tube lens57and the objective lens58and is collected to irradiate a non-dyed living cell sample83to be inspected therewith. Thereby, CARS light is generated from the living cell sample83.

The transmitted light including CARS light from the living cell sample83is collected by the collective lens62and amplified by the light amplification means63, thereafter the output light is rendered to be incident on a band-pass filter84to extract CARS light having desired wavelength components. Then, the CARS light having passed through the band-pass filter84is received by the photomultiplier tube64and photoelectrically converted.

That is, in the embodiment, the transmitted light including CARS light from the living cell sample83is amplified by the light amplification means63having a gain band wider than the wavelength region of the CARS light, thereafter the band-pass filter84extracts CARS light having desired wavelength components and the photomultiplier tube64receives it. For example, when the wavelength of CARS light generated from the living cell sample83is about 660 nm, the light amplification means63is configured so as to have a gain band of wavelength from 650 nm to 670 nm and amplify transmitted light in such a gain band by 10 dB, for example, and the band-pass filter84is constituted by a dielectric multilayer filter having a central wavelength of 660 nm and a transmitted band width of about 10 nm Moreover, CARS light generated from the living cell sample83is generated with the same repetition rate as of the excitation optical pulse train from the two-wavelength optical pulse source82and with duration of about some picoseconds. Thus, the computer65controls through the gain control means73so that, in synchronization with the timing at which CARS light is generated, the gain of the light amplification means63is increased at the timing of incidence of CARS light, in the same way as in the third embodiment.

The whole of laser scanning CARS microscope81is controlled by the computer65, in the same way as in the third embodiment. Thereby, excitation pulses from the two-wavelength optical pulse source82are deflected by the X-Y galvano scanner mirror55, and the living cell sample60is two-dimensionally scanned in a plane perpendicular to a light axis from the objective lens58. Then, photoelectrically-converted output obtained from the photomultiplier tube64at each scanned point is processed so that a fluorescence image is displayed on the monitor66.

According to the embodiment, CARS light generated from the non-dyed living cell sample83is amplified by the light amplification means63and then photoelectrically converted by the photomultiplier tube64, which makes it possible to photoelectrically convert CARS light with high sensitivity and promptly with using the inexpensive photomultiplier tube64without increasing the intensity of laser light with which the living cell sample83is irradiated even when CARS light as signal light obtained from the living cell sample83is weak.

In addition, the band-pass filter84extracts CARS light having desired wavelength components from output light of the light amplification means63, and the gain of the light amplification means63is controlled in synchronization with the timing of incidence of CARS light generated from the living cell sample83, which makes it possible to remove undesired ASE noises which are within the gain band but out of desired wavelength region of the light amplification means63and thus improve the S/N.

Fifth Embodiment

FIG. 7is a block diagram illustrating a schematic configuration of the electromagnetic wave detection device according to the fifth embodiment of the invention. The electromagnetic wave detection device amplifies electromagnetic waves to be detected emitted from a sample to be observed and provides them as electrical signals to a signal processing system. In the embodiment, since used for observing electromagnetic waves which are spontaneously emitted such as fluorescence and the like through bioluminescence, chemiluminescence and bioluminescence energy transfer, unlike the first to the fourth embodiments, the light generation means and the light irradiation means are not essential components.

The electromagnetic wave detection device according to the embodiment is provided with a mode adjustment means110adjusting the mode state of detected incident multimode electromagnetic waves, an amplification means120amplifying the electromagnetic waves whose mode state has been adjusted by the mode adjustment means110and a conversion means130converting the electromagnetic waves amplified by the amplification means120to electrical signals and outputting them to the signal processing system. The amplification means120has amplification properties excellent in the SNR for a specific amplification spatial mode, and the mode adjustment means110adjusts incident multimode electromagnetic waves to of a mode substantially equal to the amplification spatial mode by the amplification means120by converting the energy mode distribution.

FIG. 8is a diagram explaining mode adjustment by the mode adjustment means110. The mode adjustment means110is configured so that incidence of multimode electromagnetic waves is allowed at the incidence side and, at the output side, adjustment is made to have the energy mode distribution substantially equal to of the amplification spatial mode of the subsequent amplification means120, that is, the energy mode distribution with high consistency.FIG. 8(a) is an example of energy mode distribution of incident electromagnetic waves at the incidence side of the mode adjustment means. In this example, energy is distributed to a fundamental mode represented by the mode No. 1 and high-order modes represented by mode No. 2 to No. 7FIGS. 8(b) and8(c) are diagrams illustrating energy mode distribution of electromagnetic waves at the output side of the mode adjustment means110in different cases, respectively. InFIG. 8(b), the allowed mode is only two modes represented by mode No. 1 and No. 2, and energy in each mode at the incidence side of the mode adjustment means110is converted to these two modes with low loss. Moreover,FIG. 8(c) shows an example in which each of modes No. 1 to No. 7, which is the same for the incidence side, is allowed as energy mode distribution at the output side of the mode adjustment means but the distribution of two modes with mode No. 1 and No. 2 is significantly high because of the variation of energy mode distribution. That is, the number of spatial modes is artificially reduced inFIG. 8(c). The mode adjust means110may be either of one reducing the number of modes itself as inFIG. 8(b) or one varying the energy distribution as inFIG. 8(c).

With the schematic configuration ofFIG. 7, electromagnetic waves to be detected which are scattered waves or waves with distorted wavefront are incident on the mode adjustment means110according to a mode allowed at the incidence side of the mode adjustment means110. At that time, as a larger number of high-order modes are allowed, the coupling efficiency between detected electromagnetic waves and the mode adjustment means110becomes higher. Thereafter, the detected light is subjected to mode adjustment by the mode adjustment means110and emitted to the amplification means120. Then, the mode distribution of energy of detected electromagnetic waves emitted from the mode adjust means110is substantially equal to the amplification spatial mode of the amplification means120, which reduces energy loss due to inconsistency of the mode. Furthermore, the detected electromagnetic waves are amplified by the amplification means120, emitted to the conversion means130, and converted to electrical signals by the conversion means130. The electrical signals output from the conversion means130are converted to desired data by the subsequent signal processing system.

According to the embodiment, as explained above, there is disposed the mode adjustment means110adjusting, by converting the energy mode distribution, incident multimode electromagnetic waves to of a mode substantially equal to the amplification spatial mode of the amplification means120before the amplification means and the conversion means, which makes it possible to collect detected electromagnetic waves with high efficiency even when they are scattered electromagnetic waves or electromagnetic waves with distorted wavefront, thus enabling high-speed high-sensitivity photodetection.

Sixth Embodiment

FIG. 9is a diagram illustrating a schematic configuration of the rigid endoscope blood vessel imaging device according to the sixth embodiment of the invention. The device detects signal light to be detected obtained by irradiation with laser light and visualizes the position of blood vessels existent under fat.

The rigid endoscope blood vessel imaging device is configured so that an organism sample200is irradiated with laser light for lighting while being scanned, and light reflected or scattered in the surface and the inside of the organism sample200is detected by the electromagnetic wave detection device having the configuration shown inFIG. 7and converted to electrical signals, thereafter the electrical signals are processed by the signal processing system to display an image.

The rigid endoscope blood vessel imaging device is provided, as the lightning optical system, with a single-mode fiber (SMF) outputting Er-doped fluoride fiber laser161having a wavelength of 543 nm and output of 2 mW, an isolator162, a single-mode fiber (SMF)163and a collimator164, and is configured so that the desired observation position of the organism sample200is irradiated with laser light emitted from the Er-doped fluoride fiber laser161as a substantially-parallel beam through the collimator164via the isolator162and the SMF163.

Furthermore, a laser driver166driving the Er-doped fluoride fiber laser161is provided, and the Er-doped fluoride fiber laser161is configured so that its output condition is controlled through the laser driver166, by the computer169to be described controlling the whole of rigid endoscope blood vessel imaging device.

Moreover, in order to detect signal light from the organism sample200, the rigid endoscope blood vessel imaging device shown inFIG. 9is provided, as components corresponding respectively to the mode adjustment means110, the amplification means120and the conversion means130in the electromagnetic wave detection device shown inFIG. 7, with a tapered fiber111, an Er-doped fluoride optical fiber amplifier121and a silicon PIN-PD (PIN photo diode)131. Furthermore, there are provided, after PIN-PD131, an electric amplifier167amplifying electrical signals output from the PIN-PD131and an analog-to-digital (AD) converter168converting analog electrical signals amplified by the electric amplifier167to digital signals.

The tapered fiber is an optical fiber having a configuration in which the diameter of core portion where light is wave-guided is varied from the input side to the output side. The incidence surface of the tapered fiber111is disposed at a position front onto the organism sample200and adjacent to the collimator164and fixed, together with the collimator164, on a scan mount165. AsFIG. 10shows a schematic shape of a longitudinal section of the core portion, the tapered fiber111is of tapered form with a core diameter at the input side being larger than that at the output side. In the embodiment, there is used one with a core diameter at the input side and the output side being 50 μm and 4 μm respectively and a length being 1.0 m.

The isolators173aand173bare disposed at the input side and the output side of the Er-doped fluoride optical fiber amplifier121to block back reflection. The LD177is excitation light source of the Er-doped fluoride fiber175, and a laser diode having a wavelength of 975 nm and output of 100 mW is used. Moreover, a driver172connected to the LD177and driving it is provided. The WDM coupler174is configured so as to multiplex excitation light from the LD177and signal light emitted from the isolator173aat the incidence side and output it to the Er-doped fluoride fiber175. The Er-doped fluoride fiber175is a single-mode Er-doped fluoride fiber having a core diameter of 4 μm, and it amplifies signal light by excitation light and outputs residual excitation light and ASE. The optical amplifier176is provided at the output side of the Er-doped fluoride fiber175, and it removes residual excitation light and ASE to emit only signal light. The signal light is emitted from the Er-doped fluoride optical fiber amplifier121through the isolator173b.The Er-doped fluoride optical fiber amplifier121can amplify output of the tapered fiber111by about 15 dB.

Moreover, the rigid endoscope blood vessel imaging device of the embodiment has a computer169controlling each unit of the device and processing digital signals output from an AD converter168, as shown inFIG. 9. The computer169is connected to the laser driver166, the driver171and the driver172to control the Er-doped fluoride fiber laser161, the Er-doped fluoride optical fiber amplifier121and the scan mount165respectively, and is configured to perform signal processing with associating output signals of the AD converter168with each information of output of the Er-doped fluoride fiber laser161, the gain of the Er-doped fluoride optical fiber amplifier121and the position of the scan mount165and display the result on a display monitor170.

With the above configuration, when the rigid endoscope blood vessel imaging device of the embodiment is used in observing an organism sample, the computer169causes the scan mount165to scan through the driver171, and drives the Er-doped fluoride fiber laser161through the laser driver166so that the organism sample200is irradiated with laser light from the collimator164. The laser light is reflected or scattered in the surface and the inside of the organism sample200and incident on the tapered fiber111as signal light having a wavelength of 543 nm.

Here, since the core diameter at the incidence side of the tapered fiber111is 50 μm, as compared with a fiber having a core diameter of 4 μm, the area of incidence surface is larger and a spatially wider range of signals can be collected, and a large number of other high-order modes in addition to the fundamental mode can be incident. At the output side of the tapered fiber, on the other hand, the core diameter is as small as 4 μm, and thus the energy distribution among modes is adjusted and concentrated to the fundamental mode.

The signal light whose mode has been adjusted is incident on the Er-doped fluoride optical fiber amplifier121and then on the single-mode Er-doped fluoride fiber175, shown inFIG. 11, having a fundamental mode as the amplification spatial mode and a core diameter of 4 μm. Since the mode distribution at the output side of the tapered fiber is substantially equal to the amplification spatial mode of the Er-doped fluoride fiber175, the coupling efficiency at the combining portion thereof is higher. Thus, energy loss of signal light incident on the tapered fiber111can be minimized and amplification can be performed in a substantially-single mode at the Er-doped fluoride optical fiber amplifier121, which makes it possible to suppress generation of ASE and thus obtain signal light having the high SNR.

Furthermore, signal light emitted from the Er-doped fluoride optical fiber amplifier121is converted to electrical signals by the PIN-PD131, amplified by the electric amplifier167, converted to digital signals by the AD converter168and transmitted to the computer169, as shown inFIG. 9. The computer169performs signal processing with associating the electrical signals with information of scanned position and the like obtained from the driver171to generate a blood vessel image, and displays it on the monitor170. Thus, it becomes possible to image the position of blood vessels existent under fat at high speed.

According to the embodiment, as explained above, the tapered fiber111is disposed before the Er-doped fluoride optical fiber amplifier121, which can expand a light receiving surface and, further, since the number of spatial modes allowed at the incidence side is large, lots of signal light to be detected can be incident even if it is scattered light or light with distorted wavefront. Moreover, the tapered fiber111converts energy mode distribution to of a mode substantially equal to the amplification spatial mode of the Er-doped fluoride optical fiber amplifier121having a small number of amplification spatial modes, which can reduce ASE, thus enabling optical amplification with high SNR. Furthermore, the use of the tapered fiber111enables mode adjustment with small energy losses. Therefore, the optical amplification in which the light intensity of signals is high but the light intensity of noises is low is enabled even when detected signal light is scattered light or light with distorted wavefront. Therefore, the optical amplifier is disposed before the PIN-PD131, which enables photodetection at high speed and with high sensitivity.

Moreover, the tapered fiber111, which is one kind of optical fibers, is used as the mode adjustment means110, which stably achieves a long spatial-mode-adjustment waveguide. When the waveguide is longer, it becomes possible to adjust spatial mode adiabatically, thus enabling the spatial mode adjustment with smaller loss. Moreover, the use of the optical fiber makes fine adjustment of spatial optical system unnecessary, thus improving the degree of freedom in use. Furthermore, with respect to the tapered fiber111, the degree of freedom for its design is significantly high, which enables the mode adjustment means suitable for the condition of light to be detected. Moreover, the tapered fiber111can be produced relatively easily, which makes it possible to provide a low-cost photodetection device.

Moreover, there is used, as the amplification means120, the Er-doped fluoride optical fiber amplifier121, which enables amplification having the high amplification efficiency with high gain and low noise. Furthermore, the optical amplification is enabled in wavelength regions where no operation is possible with the Silica optical fiber amplifier and, in particular, the efficient optical amplification in visible bands becomes possible.

Seventh Embodiment

FIG. 12is a block diagram illustrating a schematic configuration of the electromagnetic wave detection device according to the seventh embodiment of the invention. With respect to the electromagnetic wave detection device, in the configuration of the electromagnetic wave detection device shown inFIG. 7, a plurality of mode adjustment means110is provided and a multiplex means140is provided between the mode adjustment means110and the amplification means120.

With the configuration, electromagnetic waves to be detected are input to the plurality of mode adjustment means110so that the spatial mode is adjusted in each of the mode adjustment means110. Thereafter, the electromagnetic waves output from the plurality of mode adjustment means110are input to the multiplex means140to be multiplexed. The detected electromagnetic signal waves output from the multiplex means140are amplified by the amplification means120and also converted to electrical signals by the conversion means130. The electrical signals output from the conversion means130are converted to desired data by the subsequent signal processing system.

According to the embodiment, there is disposed, before the amplification means120and the conversion means130, the plurality of mode adjustment means110adjusting the mode of incident multimode electromagnetic waves which are incident in parallel, which makes it possible to collect signal waves with high efficiency even when the electromagnetic waves to be detected are scattered electromagnetic waves or electromagnetic waves with distorted wavefront, thus enabling electromagnetic wave detection at high speed and with high sensitivity, in addition to the effects exerted by the first embodiment. Furthermore, there is provided the multiplex means140multiplexing a plurality of electromagnetic waves output from the plurality of mode adjustment means110, which can further improve the operation stability of the whole device by multiplexing incident electromagnetic waves with the number of modes reduced.

Eighth Embodiment

FIG. 13is a diagram illustrating a schematic configuration of the rigid endoscope blood vessel imaging device according to the eighth embodiment of the invention using the electromagnetic wave detection device shown inFIG. 12. With respect to the rigid endoscope blood vessel imaging device, in the rigid endoscope blood vessel imaging device shown inFIG. 9, a lens for lighting164bis used instead of a collimator164a,and a plurality of tapered fibers111is provided in parallel and at the output side thereof a fiber coupler141is provided as the multiplex means140. Moreover, the lens for lighting164band the plurality of tapered fibers111are fixed to the scan mount165so that their incidence surfaces are front onto the organism sample200.

Unlike the collimator164ashown inFIG. 9, the lens for lighting164bdiffuses laser light having transmitted through the SMF163to irradiate the area of organism sample200front onto the incidence surface of the tapered fiber111. The laser light is reflected or scattered in the surface and the inside of the organism sample200and incident on the plurality of tapered fibers111as multimode light. With respect to the signal light incident on each of tapered fibers111, its energy distribution among modes is adjusted, thereafter the light is incident, as light with the small number of modes including the fundamental mode, on the fiber coupler141to be multiplexed. Then, the signal light multiplexed by the fiber coupler141is incident on the Er-doped fluoride optical fiber amplifier121. Since other configurations and operation are the same as in the sixth embodiment, the same components are represented with the same reference symbols, and the description thereof will be omitted.

According to the embodiment, as explained above, the plurality of tapered fibers111is provided, and more light can be collected. Moreover, a device having a smaller number of spatial modes generally achieves more stable operation, so that the operation stability of the whole device can be further improved when multiplexing signal light by the multiplex means with the number of spatial modes reduced.

Ninth Embodiment

FIG. 14is a block diagram illustrating a schematic configuration of the electromagnetic wave detection device according to the ninth embodiment of the invention. The electromagnetic wave detection device is configured so that one mode adjustment means110and one amplification means120are paired and a plurality thereof is provided in parallel in the configuration of the electromagnetic wave detection device shown inFIG. 7and the output from each of the amplification means120is input to the conversion means130capable of processing the output in parallel.

In the above configuration, electromagnetic waves to be detected are input to the plurality of mode adjustment means110so that the spatial mode is adjusted in each of the mode adjustment means110. Thereafter, electromagnetic waves output from the plurality of mode adjustment means110are input to the corresponding amplification means120to be amplified, and also converted to electrical signals in parallel by the conversion means130. The electrical signals output from the conversion means130are converted to desired data by the subsequent signal processing system.

According to the embodiment, there are disposed a plurality of mode adjustment means110adjusting, by converting the energy mode distribution, incident multimode electromagnetic waves which are incident in parallel to of a mode substantially equal to the amplification spatial mode of the amplification means120before the corresponding amplification means120and the conversion means130respectively, which makes it possible to collect detected electromagnetic waves with high efficiency even when they are scattered electromagnetic waves or electromagnetic waves with distorted wavefront, thus enabling photodetection at high speed and with high sensitivity. Furthermore, a plurality of mode adjustment means110and a plurality of amplification means120corresponding thereto are provided, and electromagnetic waves output from each of amplification means120are converted to electrical signals in parallel, which makes it possible to simultaneously obtain information of a plurality of points such as image information and the like.

Tenth Embodiment

FIG. 15is a diagram illustrating a schematic configuration of the high sensitivity endoscope according to the tenth embodiment of the invention using the electromagnetic wave detection device shown inFIG. 14. The high sensitivity endoscope is configured so that it irradiates the organism sample200with laser light for lighting and the light reflected or scattered in the surface and the inside of the organism sample200is detected by the electromagnetic wave detection device shown inFIG. 14and converted to electrical signals, thereafter the electrical signals are processed by signal processing system to display an image.

As the optical system irradiating the organism sample200with laser light for lighting, the high sensitivity endoscope is provided with an LD180having a wavelength of 635 nm and output of 20 mW, an isolator181, a multi-mode fiber (MMF)182aand a lens for lighting183, and is configured so that the output from the LD180as the light source is output, via the isolator181and the MMF182a,to the air from the lens for lighting183, with which the organism sample200is irradiated.

Moreover, a laser driver179driving the LD180is provided, and the LD180is configured so that its output is controlled through the laser driver179by the computer169controlling the whole of the high sensitivity endoscope.

Furthermore, The electromagnetic wave detection device detecting light to be detected from the organism sample200uses 128×128 tapered fibers111as the mode adjustment means110, 128×128 semiconductor optical amplifiers (SOA)122corresponding to each of the tapered fibers111as the amplification means120and a CCD camera132having 128×128 pixels as the conversion means130, respectively. Moreover, an isolator184ais provided between each of tapered fibers111and the corresponding SOA122respectively, and an isolator184band a band-pass filter (BPF)185for removing ASE are provided between each of the SOA122and the CCD camera132. The analog-to-digital (AD) converter168converting analog electrical signals to digital signals is provided after the CCD camera132.

It is noted that there is used, as the tapered fiber111, one having a core diameter at the input side and the output side of 50 μm and 9 μm respectively and a length of 1.0 mm, and it is configured so that the incident surface thereof is front onto the organism sample200and signal light from respectively different positions of the organism sample200is incident by irradiation with laser light from the lens for lighting183, and it is fixed, together with the lens for lighting183, to a housing178. Moreover, the SOA122is configured to be controlled by the computer169through the driver186.

Thus, signal light having a wavelength of 635 nm reflected or scattered in the surface or the inside of the organism sample200is input on each of the tapered fibers111and its mode is adjusted. Output from each of the tapered fiber111is input to the corresponding SOA122through the isolator184and amplified by about 18 dB. Output from each SOA122is incident on the corresponding BPF185via the corresponding isolator184, and ASE is removed. Output from each BPF185is input so as to correspond to each pixel of the CCD camera132having 128×128 pixels, and converted to electrical signals. Furthermore, signal output converted to electrical signals by the CCD camera132is converted to digital signals by the AD converter168.

Moreover, the high sensitivity endoscope of the embodiment has a computer169controlling each unit of the device and processing digital signals output from the AD converter168. The computer169is connected to the laser driver179and the driver186respectively to control the LD180and the SOA122, and performs signal processing with associating output signals from the AD converter168with output of the LD180and the gain of the SOA122so as to display the result on the display monitor170as an endoscope image, for example.

According to the embodiment, as explained above, it is possible to achieve the same effects as in the sixth embodiment and obtain an endoscope image at higher speed and with higher sensitivity as compared with the conventional technique. In the embodiment, moreover, a plurality of tapered fibers111and a plurality of SOA122corresponding thereto are provided, and it is possible to simultaneously obtain information of a plurality of points of the organism sample200by converting optical output from each SOA122to electrical signals in parallel. Therefore, the embodiment is effective particularly when generating two-dimensional images.

Furthermore, the SOA122is used as the amplification means122, which makes it possible to constitute a compact and low-cost photodetection system and to integrate with a plurality of semiconductor optical amplifiers or other semiconductor devices such as photodiode (PD) or the like. Moreover, the embodiment also has an advantage that provided power may be small. Furthermore, the SOA can operate in a wider wavelength region as compared with the optical fiber amplifier, and thus it can be applied for a variety of detected light.

Eleventh Embodiment

FIG. 16is a block diagram illustrating a schematic configuration of the electromagnetic wave detection device according to the eleventh embodiment of the invention. With respect to the electromagnetic wave detection device, in the configuration of the electromagnetic wave detection device shown inFIG. 7, a collecting means150collecting electromagnetic waves to be detected is provided before the mode adjustment means110. Thus, it is possible to further increase the amount of signal electromagnetic waves which can be detected, in addition to the effects exerted by the invention of claim16.

Twelfth Embodiment

FIG. 17is a diagram illustrating a schematic configuration of the rigid endoscope blood vessel imaging device according to the twelfth embodiment of the invention using the electromagnetic wave detection device shown inFIG. 16. With respect to the rigid endoscope blood vessel imaging device, a collective lens151is provided before the incidence surface of the tapered fiber111in the rigid endoscope blood vessel imaging device shown inFIG. 9. The collective lens151is provided before the tapered fiber111, which makes it possible to take a larger portion of light reflected or scattered in the surface and the inside of the organism sample200into the tapered fiber111. Moreover, there is an advantage that even substances to be detected existent in a deep portion of an object to be detected or far portion therefrom can be also detected with high sensitivity and high SNR.

Thirteenth Embodiment

FIG. 18is a diagram illustrating a schematic configuration of a laser scanning multiphoton microscope according to the thirteenth embodiment of the invention. In the embodiment, the electromagnetic wave detection device shown inFIG. 16is used in the laser scanning multiphoton microscope so as to detect signal light from the living cell sample.

As shown inFIG. 18, the laser scanning multiphoton microscope of the embodiment is constituted including a Titanium-sapphire laser187, a light intensity adjustment device188, an X-Y galvano scanner mirror189, a pupil lens190, a tube lens191, a dichroic mirror192, and an objective lens193constituting the objective optical system, an isolator202, a collective lens152, a tapered waveguide112, an SOA123, a PIN-PD133, an electric amplifier167, an AD converter168and a gain control means203.

The Titanium-sapphire laser187is a light source generating ultrashort optical pulses having a repetition rate of 80 MHz, a pulse width of 150 fs and an oscillation wavelength of 1060 nm With respect to the ultrashort optical pulses from the Titanium-sapphire laser187, their optical average power is adjusted to100mW by the light intensity adjustment device188, and the pulses pass through the X-Y galvano scanner mirror189, the pupil lens190, the tube lens191, the dichroic mirror192and the objective lens193and are collected so that the living cell sample201to be inspected is irradiated therewith. At that time, the X-Y galvano scanner mirror189is driven to scan the position on the sample irradiated with laser light. Thus, it is possible to generate fluorescence in a desired area in the living cell sample201through multiphoton excitation (two-photon excitation, for example) of red fluorescent protein (DsRed), for example.

Moreover, the objective lens193guides fluorescence generated from the living cell sample201to the dichroic mirror192. The dichroic mirror192is configured so as to allow light having a wavelength of 1060 nm from the Titanium-sapphire laser187to pass therethrough and so as to reflect light having a short wavelength of 700 nm or shorter. Thus, fluorescence having a wavelength of about 570 nm to 650 nm generated in the living cell sample201is reflected by the dichroic mirror192.

The collective lens152, the tapered waveguide112, the SOA123and the PIN-PD133correspond respectively to the collecting means150, the mode adjustment means110, the amplification means120and the conversion means130of the electromagnetic wave detection device shown inFIG. 16. The fluorescence reflected by the dichroic mirror192is collected by the collective lens152via the isolator202and input to the tapered waveguide112. The tapered waveguide112has 8 spatial modes at the incidence side, and is configured so that the number of modes is decreased to 2 at the output side by mode adjustment. The fluorescence output from the tapered waveguide112is incident on the SOA123controlled by the external computer169through the gain control means203and amplified, thereafter the silicon PIN-PD133converts it to electrical signals. Since the number of modes of incident signal light is decreased, the SOA123can suppress the occurrence of ASE and perform amplification with high SNR.

Furthermore, electrical signals output from the PIN-PD133are amplified by the electric amplifier167, converted to digital signals by the AD converter168and transmitted to the external computer169. The computer169performs signal processing with associating signals received from the AD converter168with information of scanned positions and the like obtained from the X-Y galvano scanner mirror189and displays the result on the monitor170as a microscope image.

It is noted that, in the laser scanning multiphoton fluorescence microscope, the fluorescence generated from the living cell sample201through two-photon excitation, for example, by excitation optical pulses from the Titanium-sapphire laser187lasts for about some nanoseconds. That is, the fluorescence generated from the living cell sample201becomes pulse light synchronized with excitation optical pulses from the Titanium-sapphire laser187. Thus, in the embodiment, the computer169controls so that, in synchronization with the timing at which the pulse form of fluorescence is incident on the SOA123, the gain of the SOA123is increased at the timing of incidence of fluorescence.

According to the embodiment, fluorescence generated from the living cell sample201through multiphoton excitation by excitation optical pulses from the Titanium-sapphire laser187is subjected to mode adjustment so that the number of spatial modes is decreased using the tapered waveguide112, amplified by the SOA, and then photoelectrically converted by the silicon PIN-PD133. Thus, it is possible to photoelectrically convert fluorescence resulted by two-photon excitation with high sensitivity and at high speed without excessively increasing the intensity of laser light with which the living cell sample201is irradiated even when fluorescence as signal light obtained from the living cell sample201is weak.

In addition, the gain of the SOA123is controlled in synchronization with the timing of incidence of fluorescence on the SOA123, which can reduce the mixture of ASE generated by providing power to the optical amplifier during time in which fluorescence is not incident, thus improving the S/N. Furthermore, it is possible to easily adjust the level of signals to be detected by varying the gain of the SOA123.

Fourteenth Embodiment

FIG. 19is a block diagram illustrating a schematic configuration of the electromagnetic wave detection device according to the fourteenth embodiment of the invention. With respect to the electromagnetic wave detection device, in the configuration of the electromagnetic wave detection device shown inFIG. 7, a plurality of collecting means150and the multiplex means140multiplexing detected electromagnetic waves from the plurality of collecting means150are provided before the mode adjustment means110.

In the above configuration, electromagnetic waves to be detected are collected by the plurality of collecting means150and input to the multiplex means140. The multiplex means140multiplexes the input plurality of detected light, and outputs it to the mode adjustment means110. The other operation is the same as in the electromagnetic wave detection device inFIG. 7.

According to the embodiment, a plurality of collecting means150is provided, which makes it possible to collectively obtain signal electromagnetic waves from a plurality of parts and, further, multiple means140collects the signal electromagnetic waves from a plurality of parts, which increases the energy of the signal electromagnetic waves input to the amplification means120and further improves the SNR.

Fifteenth Embodiment

FIG. 20is a diagram illustrating a schematic configuration of rigid endoscope blood vessel imaging device according to the fifteenth embodiment of the invention shown inFIG. 19. With respect to the rigid endoscope blood vessel imaging device, in the rigid endoscope blood vessel imaging device shown in FIG.9, the lens for lighting164bis used instead of the collimator164aand there are provided, before the tapered fiber111, a plurality of collective lenses151, a plurality of multi-mode fiber (MMF)182bconnected to the collective lenses151and the multimode fiber coupler142multiplexing signal light from each MMF182b.It is noted that the collective lens151and the multimode fiber coupler142correspond respectively to the collecting means150and the multiplex means140inFIG. 19.

Moreover, the lens for lighting164band each collective lens151are fixed to the scan mount165so that they are front onto the sample200. Furthermore, unlike the collimator164ashown inFIG. 9, the lens for lighting164bdiffuses laser light having transmitted through the SMF163to irradiate the area of the organism sample200front onto the incidence surface of each collective lens151.

Thus, laser light emitted from the lens for lighting164bis reflected or scattered in the surface and the inside of the organism sample200, collected by the plurality of collective lens151and multiplexed by the multimode fiber coupler142through the MMF182b,thereafter it is incident on the tapered fiber11as multimode light. Since other configurations and operation are the same as in the sixth embodiment, the same components are represented with the same reference symbols, and the description thereof will be omitted.

According to the embodiment, as explained above, the plurality of collective lenses151is provided, which make it possible to collectively obtain signal light from a plurality of parts and thus to further increase the amount of signal light which can be detected. Moreover, signal light from a plurality of parts is collected by the multimode fiber coupler142and thus the number of the subsequent tapered fiber111, Er-doped fluoride optical fiber amplifier121and PIN-PD131can be reduced to one. In addition, signal light from a plurality of parts is collected, which can increase signal light energy input to the Er-doped fluoride optical fiber amplifier121. Therefore, it becomes possible to obtain an endoscope image at higher speed and with higher sensitivity.

Sixteenth Embodiment

FIG. 21is a block diagram illustrating a schematic configuration of the electromagnetic wave detection device according to the sixteenth embodiment of the invention. With respect to the electromagnetic wave detection device, the collecting means150is provided before each mode adjustment means110in the configuration of the electromagnetic wave detection device shown inFIG. 14. Thus, it becomes possible to guide a larger amount of detected electromagnetic wave to the mode adjustment means110, in addition to the effects exerted by the electromagnetic wave detection device according to the ninth embodiment.

Seventeenth Embodiment

FIG. 22is a diagram illustrating a schematic configuration of the rigid endoscope blood vessel imaging device according to the seventeenth embodiment of the invention using the electromagnetic wave detection device shown inFIG. 21. With respect to the rigid endoscope blood vessel imaging device, the collective lens152is provided before the plurality of tapered fibers111in the rigid endoscope blood vessel imaging device according to the tenth embodiment shown inFIG. 15. The collective lens152is provided before the tapered fiber111, which makes it possible to take a larger portion of light reflected or scattered in the surface and the inside of the organism sample200into each tapered fiber111. Since other configurations and operation are the same as in the tenth embodiment, the same components are represented with the same reference symbols, and the description thereof will be omitted.

According to the embodiment, as explained above, the collective lens152is provided before the tapered fiber111, which make it possible to further increase the amount of signal light which can be detected. Therefore, it becomes possible to obtain an endoscope image at higher speed and with higher sensitivity.

It is noted that the invention is not limited to the above embodiments, and many variations and modifications can be implemented. For example, the laser scanning confocal fluorescence microscope51shown in the second embodiment and the laser scanning multiphoton fluorescence microscope71shown in the third embodiment are not limited to of reflection type, and can be configured as of transmission type. Similarly, the laser scanning CARS microscope81shown in the fourth embodiment is not limited to of transmission type and can be configured as of reflection type, respectively.

Moreover, although the tapered fiber111or the tapered waveguide112is used as the mode adjustment means, the means is not limited thereto, and a tapered photonic crystal waveguide, a long-period fiber bragg grating, a refractive-index modulation flat waveguide or the like can be used.

For example, in the thirteenth embodiment, there can be used, instead of the tapered waveguide112, a refractive-index distribution type waveguide having nonuniform refractive-index distribution in a longitudinal direction of the waveguide or a waveguide having nonuniform stress distribution or nonuniform temperature distribution in a longitudinal direction of the waveguide. In this case, the variation of refractive-index, stress or temperature in the optical waveguide causes energy transfer among spatial modes. Such variation of refractive-index, stress or temperature is intentionally given into the optical waveguide, which can induce the variation of energy ratio among spatial modes.

Moreover, although the Er-doped fluoride optical fiber amplifier or the SOA is used as the amplification means120in the fifth to seventeenth embodiments, the means is not limited thereto. For example, instead of these amplifiers, there can be used an optical fiber amplifier using stimulated Raman scattering effects. The wavelength region where the rare-earth-doped optical fiber amplifier operates is very discrete, and thus there is wavelength region in which optical amplifying effects cannot be obtained. However, since the optical fiber amplifier using stimulated Raman scattering effects do not specify the wavelength region where it operates, the use thereof enables optical amplification in any wavelength region. Moreover, other optical fiber amplifiers like a fiber Brillouin optical amplifier, a fiber parametric optical amplifier and the like can be also used. Furthermore, a dye amplifier can be also used. Since the dye has a wider range of amplification band as compared with the fiber amplifier or the semiconductor optical amplifier, the use thereof enables amplification of a wider band range of signals. In addition, the optical amplification at a variety of wavelengths becomes possible, depending on design of the dye.

Moreover, although the PIN-PD or the CCD camera is used as the conversion means130, the means is not limited thereto, and APD, PMT, CMOS, EM-CCD or EB-CCD can be used, for example.

Although the fiber coupler or the multimode fiber coupler is used as the multiplex means140, the means is not limited thereto, and a flat waveguide optical coupler, a spatial beam combiner, a polarized wave synthesis coupler, a wavelength synthesis coupler and the like, for example, can be also used.

Although the collective lens is used as the collecting means, the means is not limited thereto, and a Gradient Index (GRIN) lens, a lensed fiber or the like can be used, for example.

Moreover, the invention can be effectively applied not only to the imaging device, the endoscope and the like shown in the above embodiments but also to the case in which the above optical measurement method such as flow site meter, FCS, SPR, LPIA, HA or the like is performed.

It is noted that, as explained in the above fifth to seventeenth embodiments, the inventions according to the sixteenth to the thirty-eighth aspects of the application have the following effects.

Moreover, according to the invention of the sixteenth aspect of the application, there is disposed the mode adjustment means adjusting, by converting the energy mode distribution, incident multimode electromagnetic waves to of a mode substantially equal to the amplification spatial mode of the amplification means before the amplification means and the conversion means, which makes it possible to collect electromagnetic waves to be detected with high efficiency even when they are scattered electromagnetic waves or electromagnetic waves with distorted wavefront, thus enabling electromagnetic wave detection at high speed and with high sensitivity.

Furthermore, according to the invention of the seventeenth aspect of the application, the mode adjust means reduces the number of spatial modes of incident electromagnetic waves, which makes it possible to reduce the number of spatial modes with small loss, thus enabling electromagnetic amplification with high SNR by the amplification means, in addition to the effects exerted by the invention in claim16.

Moreover, according to the invention of the eighteenth aspect of the application, the energy ratio among spatial modes of incident electromagnetic waves is varied, which can vary the energy ratio among spatial modes, in addition to the effects exerted by the invention in claim16. Thus, a large amount of energy is concentrated to a part of spatial modes, and the artificial reduction of the number of spatial modes can be achieved.

Furthermore, according to the invention of the nineteenth aspect of the application, the waveguide is used as the mode adjust means, which can achieve variation of spatial modes with high stability, in addition to the effects exerted by the invention in claim16.

Moreover, according to the invention of the twentieth aspect of the application, the optical fiber is used as the waveguide, which can stably achieve a long spatial-mode-adjustment waveguide, in addition to the effects exerted by the invention in claim19. When the waveguide is longer, it becomes possible to adjust the spatial mode adiabatically, thus enabling the spatial mode adjustment with smaller loss. Moreover, the use of optical fiber makes fine adjustment of the spatial optical system unnecessary, thus improving the degree of freedom in use.

Furthermore, according to the invention of the twenty-first aspect of the application, there is used, as the mode adjustment means, the tapered optical fiber with a degree of freedom in design being significantly high among optical fibers, which achieves the mode adjustment means suitable for the condition of light to be detected, in addition to the effects exerted by the invention in claim20. Moreover, the tapered fiber can be produced relatively easily, which makes it possible to provide a low-cost photodetection device.

Moreover, according to the invention of the twenty-second aspect of the application, the variation of refractive-index, stress or temperature is intentionally given into the optical waveguide, which can induce the variation of energy ratio among spatial modes, in addition to the effects exerted by the invention in claim19.

Furthermore, according to the invention of the twenty-third aspect of the application, the optical fiber amplifier is used as the amplification means, which enables optical amplification with high gain and low noise, in addition to the effects exerted by the invention in claim16.

Moreover, according to the invention of the twenty-fourth aspect of the application, the rare-earth-doped optical fiber amplifier is used as the optical fiber amplifier, which enables optical amplification with high gain, low noise and high efficiency, in addition to the effects exerted by the invention in claim23.

Furthermore, according to the invention of the twenty-fifth aspect of the application, the rare-earth-doped fluoride optical fiber amplifier is used as the rare-earth-doped optical fiber amplifier, which enables optical amplification in wavelength regions where no operation is possible with the Silica optical fiber amplifier, in addition to the effects exerted by the invention in claim24. Particularly, the efficient optical amplification in visible bands becomes possible.

Moreover, according to the invention of the twenty-sixth aspect of the application, there is used, as the fiber amplifier, the optical fiber amplifier using stimulated Raman effects, which enables optical amplification in any wavelength regions, in addition to the effects exerted by the invention in claim23.

Furthermore, according to the invention of the twenty-seventh aspect of the application, the semiconductor optical amplifier is used as the amplification means, which makes it possible to constitute a compact and low-cost photodetection system, in addition to the effects exerted by the invention in claim16.

Moreover, according to the invention of the twenty-eighth aspect of the application, the optical amplifier including dye is used as the amplification means, which makes it possible to amplify a wider band range of signals, in addition to the effects exerted by the invention in claim16. Furthermore, the optical amplification at a variety of wavelengths becomes possible, depending on design of the dye.

Furthermore, according to the invention of the twenty-ninth aspect of the application, the amplification means varies the gain depending on the timing of incidence of incident electromagnetic waves, which can prevent, in detecting intermittent signal light, mixture of excessive noises by turning the optical amplifier on or off in synchronization with the signal light, in addition to the effects exerted by the invention in claim16.

Moreover, according to the invention of the thirtieth aspect of the application, the collecting means is used before the mode adjust means, which can further increase the amount of incident electromagnetic waves which can be detected, in addition to the effects exerted by the invention in claim16.

Furthermore, according to the invention of the thirty-first aspect of the application, a plurality of collecting means is provided, which makes it possible to collectively obtain incident electromagnetic waves from a plurality of parts and thus further increase the amount of incident electromagnetic waves which can be detected, in addition to the effects exerted by the invention in claim16.

Moreover, according to the invention of the thirty-second aspect of the application, the multiplex means collects incident electromagnetic waves from a plurality of parts, which can reduce the number of the subsequent mode adjustment means, amplification means and conversion means, in addition to the effects exerted by the invention in claim31. Besides, incident electromagnetic waves from a plurality of parts are collected, which can increase the energy of incident electromagnetic waves input to the amplification means.

Furthermore, according to the invention of the thirty-third aspect of the application, there is disposed a plurality of mode adjustment means adjusting, by converting the energy mode distribution, incident multimode electromagnetic waves which are incident in parallel to of a mode substantially equal to the amplification spatial mode of the amplification means before the amplification means and the conversion means, which makes it possible to collect signal waves with high efficiency even when incident electromagnetic waves are scattered electromagnetic waves or electromagnetic waves with distorted wavefront, thus enabling photodetection at high speed and with high sensitivity. In addition, there is provided the multiplex means multiplexing a plurality of electromagnetic waves output from a plurality of mode adjustment means, which can further improve the operation stability of the whole device when multiplexing electromagnetic waves with the number of modes reduced.

Moreover, according to the invention of the thirty-fourth aspect of the application, there is disposed a plurality of mode adjustment means adjusting, by converting the energy mode distribution, incident multimode electromagnetic waves which are incident in parallel to of a mode substantially equal to the amplification spatial mode of the amplification means before each corresponding amplification means and conversion means, which makes it possible to collect signal waves with high efficiency even when incident electromagnetic waves are scattered electromagnetic waves or electromagnetic waves with distorted wavefront, thus enabling photodetection at high speed and with high sensitivity. In addition, a plurality of mode adjustment means and a plurality of amplification means corresponding thereto are provided, and electromagnetic waves output from each of amplification means are converted to electrical signals in parallel, which makes it possible to simultaneously obtain information of a plurality of points such as image information and the like.

Furthermore, according to the invention of the thirty-fifth aspect of the application, incident multimode electromagnetic waves are adjusted to of a mode substantially equal to the amplification spatial mode at the amplification step by converting the energy mode distribution, which makes it possible to collect the incident electromagnetic waves with high efficiency even when they are scattered electromagnetic waves or electromagnetic waves with distorted wavefront, thus enabling photodetection at high speed and with high sensitivity.

Moreover, according to the invention of the thirty-sixth aspect of the application, electromagnetic waves to be detected obtained from an organism are detected by the electromagnetic wave detection device described in any one of claims16to35, which makes it possible to collect electromagnetic waves to be detected with high efficiency even when they are scattered electromagnetic waves or electromagnetic waves with distorted wavefront, thus enabling observation of the organism through electromagnetic wave detection at high speed and with high sensitivity.

Furthermore, according to the invention of the thirty-seventh aspect of the application, there is provided the electromagnetic wave detection device described in any one of claims16to35, which makes it possible to collect electromagnetic waves to be detected with high efficiency even when they are scattered electromagnetic waves or electromagnetic waves with distorted wavefront, thus enabling microscope observation through electromagnetic wave detection at high speed and with high sensitivity.

Moreover, according to the invention of the thirty-eighth aspect of the application, there is used the electromagnetic wave detection device described in any one of claims16to35, which makes it possible to collect electromagnetic waves to be detected with high efficiency even when they are scattered electromagnetic waves or electromagnetic waves with distorted wavefront, thus enabling generation of endoscope image through electromagnetic wave detection at high speed and with high sensitivity.

There will be described an example in which the optical detection device according to the first aspect of the application is applied in the optical tomographic image generation device. Before explaining the optical tomographic image generation device according to the invention of the application, there will be described a reference example of the optical tomographic image generation device which has been developed together with the invention of the application.

First Reference Example

FIG. 23is a functional block diagram illustrating a fundamental configuration of the optical tomographic image generation device according to the first reference example of the application. The optical tomographic image generation device has a wavelength-variable light source unit301which can control the wavelength of light to be emitted. The wavelength-variable light source unit301is controlled by an image process unit302having a personal computer through a wavelength control unit303, so that the wavelength-variable light source unit301emits light having a smooth variation of light intensity and a wavelength varying with time, as shown inFIG. 23.

The wavelength-variable light source unit301is connected to one end of an optical multiplex-demultiplex unit305. The optical multiplex-demultiplex unit305demultiplexes light from the wavelength-variable light source unit301to two, and causes one to be incident, as reference light, on a reference-side optical transmission unit306and the other to be incident, as inspection light, on a inspection-side optical transmission unit307. The reference light incident on the reference-side optical transmission unit306is emitted from the reference-side optical transmission unit306, passes through a lens308and is reflected by a light reflection unit309, thereafter the reflected reference light passes through the lens308again, is transmitted through the reference-side optical transmission unit306and incident on the optical multiplex-demultiplex unit305.

On the other hand, the inspection light demultiplexed by the optical multiplex-demultiplex unit305and incident on the inspection-side optical transmission unit307is emitted from the inspection-side optical transmission unit307and passes through a lens310, thereafter an object to be inspected311such as an organism or the like is irradiated with the light. The inspection light with which the object to be inspected311has been irradiated is reflected and scattered in the surface and the inside of the object. With respect to the reflected and scattered inspection light, one part thereof is rendered to pass through the lens310and is incident on the inspection-side optical transmission unit307again, thereafter it is transmitted through the inspection-side optical transmission unit307and incident on the optical multiplex-demultiplex unit305again.

The optical multiplex-demultiplex unit305multiplexes reflected reference light and reflected inspection light incident respectively from the reference-side optical transmission unit306and the inspection-side optical transmission unit307to generate interference light such as one shown inFIG. 23. The interference light generated by the optical multiplex-demultiplex unit305is received by a photoelectric conversion unit312and photoelectrically converted.

The photoelectric conversion signals output from the photoelectric conversion unit312are provided to an analog signal process unit313, and the analog signal process unit313attenuates low-frequency components of the photoelectric conversion signals relative to high-frequency components thereof. That is, in the analog signal process unit313, a High-Pass Filter (HPF) or a Band-Pass Filter (BPF) removes low-frequency components of the photoelectric conversion signals, and a high-frequency amplifier amplifies only high-frequency components or high-frequency components are amplified while reducing low-frequency components, for example. The analog output signals from the analog signal process unit313are converted to digital signals by an analog-digital (A/D) conversion unit314and provided to the image process unit302.

The image process unit302performs Fourier transformation for digital output signals from the A/D conversion unit314and converts the frequency to spatial distance. Therefore, the information corresponds to optical signals reflected and scattered in each depth position at which the inspection-side optical transmission unit307irradiates the object to be inspected311with inspection light. The image process unit302obtains information from each depth position, as described above, every time a position of the object to be inspected311which the inspection-side optical transmission unit307irradiates with inspection light is varied, and generates a tomographic image of the object to be inspected311based on such information to display it on a display unit315.

As above, before the A/D conversion unit314converts photoelectric conversion signals of interference light of reflected reference light and reflected inspection light obtained from the photoelectric conversion device312to digital signals, the analog signal process unit313attenuates low-frequency components relative to high-frequency components, which can emphasize information from deep portion of the object to be inspected311. Therefore, when analog output signals from the analog signal process unit313are converted to digital signals by the A/D conversion unit314later, it is possible to convert information from the deep portion of the object to be inspected311to digital signals with high accuracy without burying the information in quantization noises, thus improving the penetration depth of a tomographic image.

Next, a concrete embodiment of the first reference example will be described with reference to the accompanying drawings.

FIG. 24is a functional block diagram illustrating a configuration of the optical tomographic image generation device according to the first reference example of the invention. In the embodiment, a Fourier domain mode locked laser (FDML)321is used as the wavelength-variable light source unit. The FDML321is constituted by a semiconductor optical amplifier (SOA), a fiber Fabry-Perot wavelength tunable filter (FFPTF), an optical isolator, a single-mode fiber (SMF) and an optical fiber coupler for output, as disclosed in US 2006/0,187,537, for example. A plurality kinds of SMF is used and the total length thereof is 4.3 km, and wavelength distribution of the whole of a laser resonator is arranged to be nearly zero.

In the embodiment, an image process unit322having a personal computer controls FFPTF of an FDML321through a filter control unit323so as to output, from the FDML321, light having a swept wavelength range of 1010 nm to 1090 nm, a repetition rate of 50 kHz and optical average power of about 5 mW.

The output end of the FDML321is connected to a first port24aof an optical circulator324having the first port24ato the third port24c.The optical circulator324outputs light input from the first port24ato the second port24b,and outputs light input from the second port24bfrom the third port24c.

The second port324bof the optical circulator324is connected to a first port325aof a 3 dB coupler325as the optical multiplex-demultiplex unit having a first port325ato the fourth port325d,and the 3 dB coupler325demultiplexes light input to the first port325ato the third port325cand the fourth port325dwith an intensity ratio of 50:50 respectively.

The third port325cof the 3 dB coupler325is connected to a single-mode fiber (SMF)326as the reference-side optical transmission unit, and light demultiplexed by the 3 dB coupler325is input to the SMF326as reference light. The SMF326is provided with a polarization controller327along the path thereof to adjust a polarization state of reference light. The reference light having transmitted through the SMF326is converted to a parallel beam by a lens328and emitted into the air, thereafter the emitted reference light is attenuated by an optical attenuator329to have a desired light intensity and then reflected by a reflective mirror330. The reference light reflected by the reflective mirror330is rendered to be incident on the SMF326through the optical attenuator329and the lens328, and input to the third port325cof the 3 dB coupler325.

On the other hand, the fourth port325dof the 3 dB coupler325is connected to an SMF331as the inspection-side optical transmission unit, and light demultiplexed by the 3 dB coupler325is input to the SMF331as inspection light. The inspection light having transmitted through the SMF331is converted to a parallel beam by a lens332and emitted into the air, thereafter transmitted direction of the emitted inspection light is two-dimensionally scanned by a galvano scanner mirror333and collected by the lens334on the object to be inspected335such as an organism and the like. The galvano scanner mirror333is controlled by the image process unit322through a scanner driver336. The inspection light reflected and scattered in the surface or the inside of the object to be inspected335is rendered to be transmitted, as reflected inspection light, through the lens334, the galvano scanner mirror333, the lens332and the SMF331again and input to the fourth port325dof the 3 dB coupler325.

The reflected reference light input to the third port325cof the 3 dB coupler325and the reflected inspection light input to the fourth port325dthereof are rendered to interfere with each other at the 3 dB coupler325, and output as interference light from the first port325aand the second port325b.Here, the interference light output from the first port325aand the interference light output from the second port325bhave a phase opposite from each other.

The interference light output from the first port325aof the 3 dB coupler325passes through the second port324band the third port324cof the optical circulator324and is input to the first port337aof a Dual-balanced receiver337as the photoelectric conversion unit. Moreover, the interference light output from the second port325bof the 3 dB coupler325is input to the second port337bof the dual-balanced receiver337. Thus, the dual-balanced receiver337photoelectrically converts interference light input respectively to the first port337aand the second port337bto obtain analog signals in which direct-current components have been cancelled and only interference components (alternating-current components) are existent. As the dual-balanced receiver337, there is used one having an electric response band of 80 MHz, for example. It is noted that the polarization controller327provided in the reference-side optical transmission unit adjusts a polarization state of the reference light so that analog signals obtained from the dual-balanced receiver337are increased, that is, so that the reflected reference light and the reflected inspection light appropriately interfere with each other.

The analog signals output from the dual-balanced receiver337are input to a highpass filter (HPF)338as the analog signal process unit so that low-frequency components thereof are removed. The analog output signals from the HPF338are amplified by an amplifier339by about 10 dB, and then input to the A/D conversion unit340to be converted to digital signals. It is noted that there is used, as the A/D conversion unit340, one with 14 bits and 100 MS/s, for example.

The digital output signals from the A/D conversion unit340are input to the image process unit322. The image process unit322performs Fourier transformation for digital output signals from the A/D conversion unit340to calculate a power spectrum. The frequency is converted from a wavelength swept rate of the FDML321to the spatial distance in a depth direction of the object to be inspected335, and the power is converted to the reflected and scattered light intensity in each depth position in the object to be inspected335. As above, the image process unit322calculates and obtains the distribution between the spatial distance and the reflected and scattered light intensity in a depth direction, and generates a tomographic image of the object to be inspected335based on such data to display it on a monitor341.

Thus, in the embodiment, the photoelectric conversion signals of interference light of the reflected reference light and the reflected inspection light obtained from the dual-balanced receiver337are input to the HPF338so that low-frequency components thereof are removed, and analog output signals from which the low-frequency components have been removed are amplified by the amplifier339and converted to digital signals by the A/D conversion unit340, which makes it possible to convert information from the deep portion of the object to be inspected335to digital signals with emphasizing the information without burying it in quantization noise, thus improving the penetration depth of a tomographic image.

Eighteenth Embodiment

FIG. 25is a functional block diagram illustrating a configuration of the optical tomographic image generation device according to the eighteenth embodiment of the invention. With respect to the embodiment, in the first reference example, the reflected inspection light obtained from the object to be inspected335is amplified and then rendered to interfere with the reflected reference light. For this reason, with respect to the embodiment, optical multiplex-demultiplex unit is constituted by a 3 dB coupler345for optical demultiplex wave and a 3 dB coupler346for optical multiplex wave in the configuration shown in

FIG. 24. In the following description, the components having a function same as of the component shown inFIG. 24are represented with the same reference symbols, and the description thereof will be omitted.

InFIG. 25, the output end of the FDML321is connected to the first port345aof the 3 dB coupler345for optical demultiplex wave, and the 3 dB coupler345demultiplexes light from the FDML321input to the first port345ato the third port345cand the fourth port345dwith an intensity ratio of 50:50 respectively.

The third port345cof the 3 dB coupler345is connected to the first port347aof an optical circulator347, and reference light from the 3 dB coupler345is output from the second port347bof the optical circulator347. Moreover, the fourth port345dof the 3 dB coupler345is connected to the first port348aof the optical circulator348, and inspection light from the 3 dB coupler345is output from the second port348bof the optical circulator348. It is noted that the second port345bof the 3 dB coupler345is free.

The second port347bof the reference-side optical circulator347is connected to the SMF326, and the polarization state of reference light output from the second port347bis adjusted by the polarization controller327, in the same way as in the first reference example, thereafter the light passes through the lens328and the optical attenuator329and is reflected by the reflective mirror330. The reflected reference light reflected by the reflective mirror330is rendered to be incident on the SMF326again through the optical attenuator329and the lens328, input to the second port347bof the optical circulator347and output from the third port347cthereof.

On the other hand, the second port348bof the inspection-side optical circulator348is connected to the SMF331, and the inspection light output from the second port348bthrough the SMF331passes through the lens332, the galvano scanner mirror333and the lens334and is collected on the object to be inspected335, in the same way as in the first reference example. With respect to the inspection light reflected and scattered by the object to be inspected335through irradiation for the object to be inspected335with inspection light, one part thereof passes through, as reflected inspection light, the lens334, the galvano scanner mirror333, the lens332and the SMF331again and is input to the second port348bof the optical circulator348and output from the third port348cthereof.

In the embodiment, the reflected inspection light from the object to be inspected335output from the third port348cof the optical circulator348is amplified by an optical amplifier351by 10 dB, for example. As the optical amplifier351, there is used a rare-earth-doped optical fiber amplifier using rare-earth-doped optical fibers, an optical fiber amplifier using Silica optical fibers such as the optical Raman amplifier or a semiconductor optical amplifier.

The third port347cof the reference-side optical circulator347is connected to the first port346aof the 3 dB coupler346for optical multiple wave. Moreover, the third port348cof the inspection-side optical circulator348is connected to the second port346bof the 3 dB coupler346for optical multiple wave.

Thus, in the 3 dB coupler346for optical multiple wave, reflected reference light input to the first port346aand the reflected inspection light input to the second port346bare rendered to interfere with each other, and output from the third port346cand the fourth port346d.

The third port346cand the fourth port346dof the 3 dB coupler346are connected to the first port337aand the second port337bof the dual-balanced receiver337respectively to obtain analog signals in which direct-current components have been cancelled by the dual-balanced receiver337and only interference components (alternating-current components) are existent. The other configurations and operations are the same as in the first reference example.

According to the embodiment, the reflected inspection light obtained from the object to be inspected335is amplified by the optical amplifier351and then rendered to interfere with the reflected reference light, which makes it possible to extract information from the deep portion of the object to be inspected335and thus further improve the penetration depth of a tomographic image.

Nineteenth Embodiment

FIG. 26is a functional block diagram illustrating a configuration of the optical tomographic image generation device according to the nineteenth embodiment of the invention. With respect to the embodiment, an optical band-pass filter (BPF)352is disposed between the optical amplifier351and the second port346bof the 3 dB coupler346for optical multiplex wave in the configuration of the eighteenth embodiment shown inFIG. 25. The optical BPF352has a dielectric multilayer having a transmitted wavelength bandwidth of 1 nm, for example, and is configured so that the transmitted central wavelength is variable by changing an angle of the dielectric multilayer relative to the incident light axis. With respect to the optical BPF352, the image process unit322controls the angle of the dielectric multilayer relative to the incident light axis through the filter control unit353, and varies the transmitted central wavelength in synchronization with variation with time of swept wavelength output from the FDML321. That is, the transmitted central wavelength of the optical BPF352is controlled to have the same wavelength as one swept and output from the FDML321. Since other configurations and operation are the same as in the eighteenth embodiment, the same components having a function same as of the components shown inFIG. 25are represented with the same reference symbols, and the description thereof will be omitted.

Thus, in the embodiment, the reflected inspection light obtained from the object to be inspected335is amplified by the optical amplifier351, thereafter the optical BPF352in which the transmitted wavelength is variable allows only reflected inspection light having a wavelength to be swept to pass therethrough, which enables lower noise of the reflected inspection light to be multiplexed with the reflected reference light. Therefore, information from the deep portion of the object to be inspected335can be extracted with higher accuracy.

It is noted that, for the inventions of the application disclosed in the eighteenth and nineteenth embodiments, many variations and modifications can be implemented. For example, the amplifier339can be disposed between the dual-balanced receiver337and the HPF338. Moreover, the analog signal process unit is not limited to the HPF338and can be constituted using the BPF. Furthermore, in the first to third embodiments, there can be used, instead of the HPF338and the amplifier339, the high-frequency amplifier having a low gain in a low-frequency band and a high gain in a high-frequency band.

Moreover, according to the thirty-ninth aspect of the application, as described in the above eighteenth and nineteenth embodiments, the photoelectric conversion signals of interference light of the reflected inspection light and the reflected reference light though SSOCT are provided to the analog signal process unit so that low-frequency components of the photoelectric conversion signals are attenuated relative to high-frequency components, and then the analog-digital conversion unit converts them to digital signals so that a tomographic image is generated, which makes it possible to convert information from the deep portion of the object to be inspected such as an organism or the like to digital signals with high accuracy without burying the information in quantization noises, thus improving the penetration depth of the tomographic image.