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JP2004003969

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DESCRIPTION JP2004003969
The present invention provides an ultrasonic receiving apparatus capable of reducing changes in
ultrasonic detection sensitivity due to environmental changes such as temperature, and
variations in detection sensitivity depending on the position of an ultrasonic detecting element.
SOLUTION: A light source 11 for generating broadband light, and expansion and contraction
according to received ultrasonic waves, and variation in light reflectance according to the
expansion and contraction, so that an ultrasonic sense of intensity modulation of light generated
by the light source The ultrasonic detecting element 20 including the unit, the spectral unit 15
emitting light modulated in intensity by the ultrasonic detecting element in different directions
according to the wavelength, and the light spectrally separated by the spectral unit are detected
for each of a plurality of wavelength components And a photodetector 16 having a plurality of
photoelectric conversion elements. [Selected figure] Figure 1
Ultrasonic receiving apparatus and ultrasonic receiving method
[0001] The present invention relates to an ultrasonic receiving apparatus and an ultrasonic
receiving method used to obtain an ultrasonic image by receiving ultrasonic waves.
Conventionally, in an ultrasonic imaging apparatus, a piezoelectric ceramic typified by PZT (lead
zirconate titanate) or PVDF (poly-fluorinated) as an element (vibrator) for transmitting and
receiving ultrasonic waves is used. A one-dimensional sensor array using a piezoelectric element
including a polymeric piezoelectric element such as vinylidene fluoride has been common. While
mechanically moving such a one-dimensional sensor array, three-dimensional images are
obtained by acquiring two-dimensional images of a plurality of cross sections of the subject and
synthesizing these two-dimensional images. However, according to this method, since there is a
time lag in the moving direction of the one-dimensional sensor array, the cross-sectional images
at different times are synthesized, so the synthesized image becomes blurred. Therefore, it is not
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suitable for a subject that targets a living body as in the case of performing ultrasound echo
observation and the like using an ultrasound imaging apparatus. [0004] In order to obtain highquality three-dimensional images using ultrasonic waves, two-dimensional sensors capable of
obtaining two-dimensional images without moving the sensor array are required. However, when
fabricating a two-dimensional sensor array using the above-described PZT or PVDF,
microfabrication of elements and wiring to a large number of microelements are necessary, and it
is difficult to achieve miniaturization and element integration beyond the current state . In
addition, even if they are solved, there is a problem that crosstalk between elements increases,
the SN ratio is deteriorated due to an increase in electrical impedance due to fine wiring, and
electrode parts of the fine elements are easily broken. Therefore, realization of a two-dimensional
sensor array using PZT or PVDF is difficult. On the other hand, a sensor of a method of
converting a received ultrasonic signal into an optical signal and detecting the signal is also
known. As an ultrasonic sensor of such a light detection method, one using a fiber Bragg grating
(abbreviated as FBG) (see non-patent document 1) or one using a Fabry-Perot resonator
(abbreviated as FPR) structure (non-patent document 2) Reference) is reported. When a twodimensional sensor array is manufactured using such an ultrasonic sensor, there is an advantage
that electrical wiring to a large number of microelements is not necessary, and good sensitivity
can be obtained. There is also known a light detection type ultrasonic sensor having a twodimensional detection surface.
For example, Non-Patent Document 3 describes that a polymer film having a Fabry-Perot
structure is used for detection of ultrasonic waves. Such a film-like ultrasonic sensor can
suppress costs because it is not necessary to process many fine elements. The ultrasonic sensor
of the light detection method utilizes an ultrasonic detection element that receives ultrasonic
waves and changes the reflection characteristic of light. However, such an ultrasonic detecting
element has a large variation in detection sensitivity because the light reflection characteristic
changes with changes in temperature and humidity. In addition, in the ultrasonic detection
element having a two-dimensional detection surface, the reflection characteristic of light differs
depending on the position of the detection surface, which causes variation in detection
sensitivity. As described above, in the ultrasonic wave receiving apparatus using the light
detection method, controlling a change in detection sensitivity due to environmental factors such
as temperature or structural factors is a serious problem in practice. For this purpose, for
example, it is conceivable to adjust the wavelength of light emitted from the light source to a
point at which the sensitivity of the ultrasonic detecting element becomes high. However, the
wavelength of the light source light is adjusted to very steep reflection characteristics. It is
difficult to get involved. On the other hand, although it is conceivable to use a method in which
broadband light is incident on an ultrasonic detection element having different reflection
characteristics depending on the position and the reflected light is separated by filtering, in this
case, the configuration of the ultrasonic detection element becomes complicated. There is a
problem that the cost is high. Furthermore, although it is conceivable to change the reflection
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characteristic for each detection area of the ultrasonic detection element, the configuration of the
ultrasonic detection element is also complicated in this case, and the cost also increases. [NonPatent Document 1] Takahashi (TAKAHASHI), two others, "Underwater Acoustic Sensor with
Fiber Bragg Grating Using Fiber Bragg Grating", Optical Review (OPTICAL REVIEW), Vol. 4, no. 6
(1997), P.J. 691-694 [Non-Patent Document 2] UNO (UNO), et al., "Fabrication and performance
of a fiber optic microprobe for measuring a megahertz ultrasonic range (Fabrication and
Performance of a Fiber Optic Micro-Probe for Megahertz Ultrasonic Field) Measurement), T. IEE
Japan, Vol.
118-E, no. 11 (1998), P.I. 487-492 [Non-patent document 3] Beard, 2 others, "Processing
mechanism of Fabry-Perot polymer film sensing concept for broadband ultrasonic detection
(Transduction Mechanisms of the Fabry-Perot Polymer Film Sensing Concept for Wideband)
"Ultrasound Detection" "IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND
FREQUENCY CONTROL", VOL. 46, NO. 6 (NOVEMBER 1999), P.J. SUMMARY OF THE INVENTION
In view of the above-described problems, the present invention is directed to an ultrasonic
receiving apparatus and an ultrasonic receiving method using a light detection method, which
are caused by environmental changes such as temperature. An object of the present invention is
to reduce the cost of the apparatus by simplifying the configuration of the apparatus while
reducing the change in the ultrasonic detection sensitivity and the variation in the detection
sensitivity due to the position of the ultrasonic detection element. SUMMARY OF THE
INVENTION In order to solve the above-mentioned problems, in the ultrasonic receiving
apparatus according to the present invention, a light source for generating broadband light, and
an expansion and contraction according to an ultrasonic wave to be received Accordingly, an
ultrasonic detection element including an ultrasonic sensing unit that modulates the intensity of
the light generated by the light source by fluctuating the light reflectance, and a spectral unit
that disperses the light intensity-modulated by the ultrasonic detection element. And light
detection means having a plurality of photoelectric conversion elements for detecting the light
split by the light splitting means for each of a plurality of wavelength components. Further, in the
ultrasonic wave receiving method according to the present invention, an ultrasonic wave is
sensed that is expanded and contracted according to the received ultrasonic wave, and the light
reflectance is fluctuated according to the expansion and contraction, thereby intensitymodulating incident light. Light is incident on an ultrasonic detection element including the unit,
the light modulated in intensity by the ultrasonic detection element is split, and the split light is
divided into a plurality of wavelength components using a photodetection means having a
plurality of photoelectric conversion elements Of the light detecting means based on the relation
obtained in step (a) of obtaining the relation between the wavelength of light and the reflection
intensity in the plurality of detection areas of the ultrasonic detection element by detecting Step
(b) of selecting a set of photoelectric conversion elements to be used for detecting ultrasonic
waves from a plurality of photoelectric conversion elements, and when receiving ultrasonic
waves, light is incident on the ultrasonic detection elements to Ultrasonic wave is received by the
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sound wave detection element Emitting the light whose intensity has been modulated in a
different direction depending on the wavelength by the spectral means, and detecting each of a
plurality of wavelength components using the set of photoelectric conversion elements selected
in step (b) And (c) obtaining information on ultrasonic waves received in the plurality of
detection areas of the ultrasonic detection element.
According to the present invention, the light reflected by the ultrasonic detection means is split
and incident on different photoelectric conversion elements, whereby the wavelength and the
reflection intensity of the light in a plurality of detection areas of the ultrasonic detection element
are obtained. You can ask for a relationship. Further, based on the relationship, by selecting in
advance the photoelectric conversion element to be used when receiving the ultrasonic wave, the
detection signal can be obtained based on the light having the optimum wavelength. BEST MODE
FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be
described in detail with reference to the drawings. The same reference numerals are given to the
same components, and the description will be omitted. FIG. 1 is a view showing an ultrasound
receiving apparatus according to a first embodiment of the present invention. This ultrasonic
wave receiving apparatus includes a light source 11, a demultiplexer 12, an optical transmission
path 13, a collimating unit 14, an ultrasonic detecting element 20, a spectral element 15, a
photodetector 16, a collimating lens 17, And 18 are included. Hereinafter, the relationship
between the wavelength of light at the ultrasonic detection element 20 and the reflection
intensity will be referred to as a reflection characteristic. As the light source 11, it is desirable to
use a light source having a bandwidth that can cover the range of the tilt band or more in the
reflection characteristic of the ultrasonic detection element 20. As such a light source, for
example, a light source such as an LED (light emitting diode), an SLD (super luminescent diode),
an ASE (Amplified Spontaneous Emission) light source, or an LD (laser diode) having a relatively
large line width is used. . The splitter 12 includes a half mirror, an optical circulator, or a
polarization beam splitter, and transmits incident light from a first direction in a second direction
and returns it from the second direction. The incoming light is reflected in a third direction
different from the first direction. In the present embodiment, a half mirror is used as the splitter
12. The half mirror transmits incident light in a direction opposite to the incident direction, and
reflects light returning from the direction opposite to the incident direction in a direction that
makes approximately 90 ° with the incident direction. The light transmission path 13 guides the
light having passed through the splitter 12 to the ultrasonic detection element 20. As the light
transmission path 13, a bundle fiber obtained by bundling a large number of (for example, 1024)
optical fibers is used. FIG. 1 shows optical fibers OF1 to OFM arranged on one line. As shown in
FIG. 1, a large number of optical fibers are bundled according to the shape (for example, circular)
of the receiving surface on the ultrasonic detection element side (left side in the figure), and the
splitter 12 side (right side in the figure) ) Are arranged on one line.
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Alternatively, optical fibers arranged in one line may be stacked in multiple stages. The distal end
portion of the light transmission path 13 is connected to the ultrasonic detection element 20 via
the collimator unit 14 with the optical axis aligned. The collimating unit 14 includes, for example,
a collimating lens array in which collimating lenses are arrayed. The configurations of the light
transmission path 13 and the collimating unit 14 will be described in detail later. The ultrasonic
detection element 20 has a two-dimensional receiving surface 20a that causes distortion by the
propagating ultrasonic waves, and an ultrasonic sensing unit that expands and contracts
according to the ultrasonic waves received at the receiving surface 20a. There is. Since the light
reflectance of the ultrasonic sensing unit fluctuates according to the expansion and contraction,
light incident on the ultrasonic detection element 20 through the light transmission path 13 and
the collimator unit 14 is intensity-modulated and reflected. The spectral element 15 is formed of,
for example, a diffraction grating, a prism or the like, and emits incident light in different
directions depending on the wavelength. The spectral element 15 splits the light beams L1 to LM
emitted in parallel from the optical fibers OF1 to OFM, and guides a plurality of split light beams
to the light detector 16. Alternatively, an AWG (array waveguide grating) spectral element may
be used as the spectral element 15. FIG. 2 shows the configuration of the AWG spectral element.
It is common to use an arrayed waveguide grating included in a planar lightwave circuit (PLC) as
the AWG spectral element. As shown in FIG. 2, in the arrayed waveguide grating, an input-side
slab waveguide 52 to which one input waveguide 51 is connected and an output-side slab to
which a plurality of output waveguides 53a, 53b,. A plurality of arrayed waveguides 55a, 55b,...
Having a constant waveguide length difference are connected to the waveguide 54. The input
side slab waveguide 52 has a fan shape with the end of the input waveguide 51 as the center of
curvature. The output side slab waveguide 54 has a fan shape with the ends of the plurality of
output waveguides 53a, 53b,... As the center of curvature. The plurality of arrayed waveguides
55a, 55b,... Are radially arranged such that the respective optical axes pass through the centers
of curvature of both the input side slab waveguide 52 and the output side slab waveguide 54.
Thereby, the input side slab waveguide 52 and the output side slab waveguide 54 implement |
achieve the function equivalent to a lens. Incident light having different wavelengths λ1 to λN
enters the input waveguide 51, and is guided to the plurality of arrayed waveguides 55a, 55b,...
By the lens action of the input-side slab waveguide 52.
The plurality of wavelength components included in the incident light are excited in the arrayed
waveguides 55a, 55b,... And guided to the plurality of output waveguides 53a, 53b,. Referring
back to FIG. 1, the light detector 16 detects a plurality of wavelength components separated by
the light separating element 15. As the light detector 16, a two-dimensional photoelectric
converter is used, in which a plurality of photoelectric conversion elements are twodimensionally arranged, and incident light can be divided for each position and detected. As such
a two-dimensional photoelectric converter, for example, a PDA (photodiode array), a MOS sensor
or the like can be used. Alternatively, a programmable two-dimensional sensor such as a CCD
(charge coupled device) may be used. In the light transmission path 13, the dispersive element
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15, and the light detector 16, components having a predetermined wavelength included in a light
beam reflected from a predetermined minute region of the ultrasonic detection element are the
light detector 16. It is arrange | positioned so that it may inject into the predetermined
photoelectric conversion element of this. In the present embodiment, the light beams L1, L2,...
Emitted from the optical fibers OF1, OF2,... Connected to different regions of the ultrasonic
detection element are the first row of photoelectric conversion elements arranged in two
dimensions. Each corresponds to the second column,. Further, the wavelengths λ 1, λ 2,... Of
the separated components correspond to the first row, the second row,. By arranging the optical
system so that such correspondence can be obtained, the signal output from the photoelectric
conversion element located in the n-th row and the m-th column of the photodetector 16
becomes a light beam Lm emitted from the optical fiber OFm. It is identified as a component
having the wavelength λ n included. The collimating lens 17 collimates the light emitted from
the light source 11 and makes the light enter the splitter 12. Further, the collimating lens 18
collimates the light emitted from the optical fibers OF1, OF2,. Next, the structure of the ultrasonic
detection element 20 and the detection principle of ultrasonic waves will be described in detail
with reference to FIG. The ultrasonic detection element 20 is a multilayer film sensor including a
substrate 21 and a multilayer film 22 stacked on the substrate. The multilayer film 22 constitutes
a Bragg grating structure and works as an ultrasonic sensing unit. The substrate 21 is a film-like
substrate which is distorted by receiving ultrasonic waves, and has, for example, a circle having a
diameter of about 2 cm or more.
A multilayer film 22 having a Bragg grating structure is formed on the substrate 21 by
alternately laminating two types of material layers having different refractive indexes. In FIG. 3, a
material layer A having a refractive index n1 and a material layer B having a refractive index n2
are shown. Assuming that the pitch (spacing) of the periodic structure of the multilayer film 22 is
d and the wavelength of the incident light is λ, the Bragg's reflection condition is expressed by
the following equation. However, m is any integer. 2d · sin θ = mλ (1) Here, θ is an incident
angle measured from the incident surface, and when θ = π / 2, the following equation is
obtained. 2d = mλ (2) The Bragg grating selectively reflects light of a specific wavelength that
satisfies the Bragg's reflection condition and transmits light of other wavelengths. When
ultrasonic waves are propagated to the ultrasonic detection element 20, the ultrasonic detection
element 20 is distorted as the ultrasonic waves propagate, and the pitch d of the periodic
structure changes at each position of the multilayer film 22. Along with this, the wavelength λ of
the selectively reflected light changes. In the reflection characteristics of the Bragg grating, there
is an inclined band in which the light reflectance changes before and after the central wavelength
having the highest light reflectance (low transmittance). When ultrasonic waves are applied while
light having a central wavelength in the range of this inclined band is incident on the multilayer
film 22, intensity change of reflected light (or transmitted light) according to the intensity of
ultrasonic waves at each position on the receiving surface is obtained. It can be observed. By
converting the intensity change of the light into the intensity of the ultrasonic wave, it is possible
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to acquire two-dimensional intensity distribution information of the ultrasonic wave. As a
material of the substrate 21, optical glass such as quartz glass (SiO 2) or BK 7 (product of Schott)
is used. Moreover, as a substance used for material layers A and B, the combination of the
substance from which a refractive index mutually differs 10% or more is desirable. Examples
thereof include a combination of SiO 2 and titanium oxide (Ti 2 O 3), a combination of SiO 2 and
tantalum oxide (Ta 2 O 5), and the like. The material layers A and B are formed on the substrate
21 by a method such as vacuum evaporation or sputtering. Incidentally, in order to suppress
multiple reflection of ultrasonic waves, it is effective to increase the distance through which the
ultrasonic waves propagate. The ultrasonic wave attenuates considerably during propagation,
and the longer the propagation distance, the greater the amount of attenuation. Therefore, if a
sufficient propagation distance is taken, ultrasonic waves can be sufficiently attenuated while the
ultrasonic waves propagated to one end are reflected back at the other end.
For this reason, in the present embodiment, an optical fiber is used as the optical transmission
path, and the received ultrasonic wave is propagated to the optical fiber. That is, the light
transmission path has the function of passing light and the function of backing as attenuating
ultrasonic waves. FIG. 4 is a cross-sectional view showing a part of the light transmission path
13, the collimator part 14 and the ultrasonic detecting element 20 shown in FIG. 1 in an enlarged
manner. As shown in FIG. 4, the optical fibers OF 1, OF 2,... Included in the optical transmission
path (bundle fiber) 13 have their optical axes aligned with the plurality of collimating lenses 14 a
included in the collimating part (collimating lens array) 14. And the two-dimensional
arrangement and connection to the ultrasonic detection element 20. The optical fibers OF1,
OF2,... Are bundled using an adhesive 25. The optical fibers OF1, OF2,... Are, for example, single
mode or multimode fibers having a length of about 2 m, and are covered with a low-viscosity
member (covering material 23) containing a resin-based material. In order to attenuate the
ultrasonic wave while propagating through the optical fiber, a length of 2 m is effective, but by
covering the optical fiber with the above-mentioned members, the propagation energy loss of the
ultrasonic wave is further increased Ultrasonic attenuation can be accelerated. Here, the light
transmitted through the optical fibers OF 1, OF 2,... Is diffracted when it is emitted from the
optical fiber. Therefore, when the optical fibers OF1, OF2,... Are directly connected to the
ultrasonic detection element 20, light is diffused, and sufficient interference does not occur in the
ultrasonic detection element. For this reason, the detection sensitivity is significantly
deteriorated. In order to avoid this phenomenon, a plurality of collimate lenses 14a are
connected to one end of the optical fibers OF1, OF2,... In order to prevent the diffusion of the
outgoing light. The plurality of collimating lenses 14 a collimate the light guided by the
respective optical fibers OF 1, OF 2,... With respect to a plurality of positions on the ultrasonic
receiving surface of the ultrasonic detecting element 20. As the collimating lens 14a, a gradient
index lens (hereinafter, abbreviated as a GRIN lens) is used. The GRIN lens is known, for example,
under the product name Selfoc (registered trademark of Nippon Sheet Glass Co., Ltd.) lens. The
GRIN lens is a gradient index lens having a refractive index that varies depending on the position,
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and changing its length changes the optical characteristics.
For example, when the GRIN lens has a length of 1⁄4 of the object image plane distance (the pitch
at which light forms an erect image), incident light is emitted as parallel light. In the present
embodiment, a SELFOC lens array NA 0.46 (product of Nippon Sheet Glass Co., Ltd.) in which a
large number of SELFOC lenses are arranged is 0.25 L in length (L is the distance between the
object image plane) , And each SELFOC lens is connected to the optical fiber as a collimating lens
14a. As shown in FIG. 4, the collimating lens 14 a may be covered by a covering material 23. As
in the case of the optical fibers OF1, OF2,. The optical fiber and the collimating lens, or the
collimating lens and the ultrasonic detecting element are connected using a fusion or an
adhesive. In the case of using an adhesive, it is desirable to use a resin-based adhesive containing
an epoxy type. In such an adhesive, the acoustic impedance is similar to the members of the
optical fiber and the collimating lens and the substrate of the ultrasonic detecting element, so
that the ultrasonic waves are prevented from being reflected at the boundaries of the members
when propagating It is because it can. Also, as the adhesive 25 for bundling a plurality of optical
fibers, it is desirable to use a resin-based adhesive containing an epoxy-based resin. This is
because ultrasonic waves can be attenuated, crosstalk of ultrasonic waves between adjacent
optical fibers can be prevented, and flexibility as a cable can be maintained. In the present
embodiment, STYCAST (a product of Emerson & Cuming) is used as such an adhesive. Next, the
operation of the ultrasonic receiving apparatus according to the present embodiment will be
described with reference to FIG. 1, FIG. 5, and FIG. FIG. 5 is a flowchart showing the operation of
the ultrasound receiving apparatus according to the present embodiment. First, calibration is
performed before receiving ultrasonic waves. Here, calibration refers to an operation of
measuring the reflection characteristics of the ultrasonic detection element at that time and
determining the wavelength component to be adopted as a detection signal. That is, the
ultrasonic detection element is very sensitive to the surrounding environment such as
temperature and humidity, and the reflection characteristic is likely to change. For example, the
central wavelength of the reflected light of an ultrasonic detecting element using a Bragg grating
changes at a rate of 0.01 nm / ° C. In addition, in the ultrasonic detection element having a twodimensional detection surface, there is structural variation for each minute region of the
detection surface.
In order to reduce the change in sensitivity due to such environmental or structural factors,
calibration is performed in advance. Note that this calibration may be performed as needed after
the reception of ultrasonic waves is started. In step S1, the ultrasonic wave receiver is driven.
From this, for example, broadband light having a spectral characteristic as shown in (a) of FIG.
The light emitted from the light source passes through the collimator lens 17, the splitter 12, and
the collimator lens 18, and enters the optical fibers OF1 to OFM arranged in one line. The light
transmitted through each optical fiber is incident on each minute area of the ultrasonic detecting
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element 20, and the light reflected corresponding to the light reflectance of each minute area is
emitted from the optical fiber. The light beams L1 to LM emitted from the optical fibers OF1 to
OFM again pass through the collimator lens 18, are reflected by the splitter 12, and enter the
light separating element 15. The light beams L <b> 1 to LM are separated by the light separating
element 15, and the respective wavelength components enter the plurality of photoelectric
conversion elements included in the respective columns of the light detectors 16 according to the
wavelengths. Thus, in step S2, detection signals of the photoelectric conversion elements
corresponding to the wavelengths λ1 to λN are obtained from the respective columns of the
light detectors 16 corresponding to the light beams L1 to LM. FIG. 6 (b) is a graph obtained
based on the detection signal of the photoelectric conversion element included in the m-th
column of the photodetector 16, which passes through the optical fiber OFm and corresponds to
the ultrasonic detection element The spectral distribution of the light ray Lm reflected from the
minute area is shown. As shown in (b) of FIG. 6, the light ray Lm has the highest intensity at the
wavelength λX which is selectively reflected by the Bragg reflection condition. FIG. 6C shows
the reflection characteristics of the Bragg grating in a minute region of the ultrasonic detecting
element corresponding to the light beam Lm. As described above, in the reflection characteristics
of the Bragg grating, there is an inclined band Δλ where the light reflectance changes sharply
before and after the central wavelength λX having the highest light reflectance (low
transmittance). When applying ultrasonic waves to observe a change in the structure of the
Bragg grating, a large intensity change is observed in the spectral region of this inclined band
Δλ. This is represented by λ n in FIGS. 6 (b) and (c). Therefore, in the minute region of the
ultrasonic detecting element corresponding to the light beam Lm, the light in the spectral region
centered at the wavelength λ n exhibits the largest intensity change.
That is, for the optical fiber OFm, the highest detection sensitivity can be obtained by using the
signal output from the photoelectric conversion element (n, m) to which the wavelength λ n is
incident in the m-th column of the photodetector as the detection signal of the ultrasonic wave.
You can get it. Similarly, for each row in which the light beams L1, L2,... Emitted from the optical
fibers OF1, OF2,... Are incident, the signal output from any photoelectric conversion element is
used as a detection signal of ultrasonic waves. If it is selected, the highest detection sensitivity
can be obtained for each minute area of the ultrasonic detection element 20. Referring again to
FIG. 5, in step S3, the photoelectric conversion element to be used is selected for each row of the
light detection elements 16 based on the result of the prior detection. Next, ultrasonic waves are
received. In step S4, the ultrasonic wave receiver is driven. As a result, the broadband light
emitted from the light source is incident on a minute area of the ultrasonic detection element 20
through the optical fibers OF1 to OFM. The light beams L <b> 1 to LM reflected from the
respective minute regions are separated by the light separating element 15 and enter the light
detector 16. In this state, an ultrasonic wave is applied to the ultrasonic detection element 20
(step S5). As a result, the pitch of the periodic structure changes in each minute region of the
ultrasonic detection element 20, and the detection signal output from the photoelectric
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conversion element selected in step S3 exhibits a large intensity change. Next, in step S6, a
detection signal output from the photoelectric conversion element selected in step S3 is acquired.
Furthermore, these detection signals are processed to convert the change in intensity of the
reflected light into the intensity of the ultrasonic wave. Thereby, it is possible to twodimensionally measure the intensity of the ultrasonic wave received in each minute area of the
ultrasonic detection element. A modified example of the present embodiment will be described
with reference to FIG. In this example, an ultrasonic detection element (etalon sensor) 30 shown
in FIG. 7 is used in place of the ultrasonic detection element 20 in FIG. The other configuration is
the same as that described with reference to FIGS. 1 and 4. As shown in FIG. 7, the substrate 31
is a film-like substrate that is deformed by ultrasonic waves. A substrate 32 is disposed opposite
to the substrate 31 and they form a similar structure to the etalon. Assuming that the light
reflectance of the substrates 31 and 32 is R, the distance between the substrates is d, and the
wavelength of the incident light is λ, the transmittance of the etalon is expressed as follows.
However, n is any integer. T = {1 + 4R / (1-R) <2> · sin <2> (φ / 2)} <− 1> (3) φ = 2π / λ · 2nd
cos θ (4) where θ is It is an emission angle measured from the perpendicular of the emission
surface, and when θ = 0, the following equation is obtained. φ = 4πnd / λ (5) The etalon
transmits light of wavelength λ with a transmittance T, and reflects it with a light reflectance R =
(1-T). When ultrasonic waves are propagated to the ultrasonic detecting element 30, the
substrate 31 is distorted, and the distance d between the substrates 31 and 32 changes at each
position on the receiving surface, so that the reflectance for light of wavelength λ changes.
Therefore, in the same manner as described with reference to FIG. 5, the pre-detection is
performed, and in the light detector, the photoelectric conversion element on which the light
having the central wavelength is incident in the region where the change in light reflectance is
large is selected. Ultrasonic waves are applied to the substrate 31 while light is incident. Thereby,
the intensity change of the reflected light according to the intensity of the ultrasonic wave at
each position of the receiving surface can be observed. The intensity of the ultrasonic wave can
be two-dimensionally measured by converting the change in the intensity of the reflected light
into the intensity of the ultrasonic wave. Next, an ultrasonic receiving apparatus according to a
second embodiment of the present invention will be described with reference to FIG. In the
present embodiment, a bundle fiber having an ultrasonic sensing unit as shown in FIG. 8A in
place of the ultrasonic detection element 20, the light transmission path 13 and the collimator
unit 14 shown in FIG. 40 is used. The other configuration is the same as that in the first
embodiment. FIG. 8B shows the configuration of the fiber 40 a included in the bundle fiber 40.
The fiber 40 a includes an optical fiber 41 and a collimating lens 42. In the present embodiment,
as in the first embodiment, a selfoc lens having a length of 0.25 L is used as the collimating lens
42. Moreover, both are connected by the resin adhesive containing fusion | melting or an epoxy
type. A multilayer film 43 in which two types of material layers are alternately stacked is formed
at one end of the collimator lens 42. The multilayer film 43 constitutes a Bragg grating structure
and works as an ultrasonic sensing unit. As a material of the multilayer film 43, for example, a
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combination of SiO 2 and titanium oxide (Ti 2 O 3), a combination of SiO 2 and tantalum oxide
(Ta 2 O 5), or the like is used.
Such a material layer is formed on the collimating lens 42 by a method such as vacuum
evaporation or sputtering. The fiber 40a is covered with a low viscosity member (covering
material 44) so that the ultrasonic wave is attenuated before the ultrasonic wave propagated to
one end of the fiber 40a is reflected at the other end. Furthermore, as shown in (b) of FIG. 8, the
covering material 44 may cover up to the collimating lens 42. Thereby, the energy loss of the
ultrasonic wave propagated to the fiber 40a can be increased, so that the ultrasonic wave can be
quickly attenuated to enhance the effect as the backing portion. By bundling a plurality of such
fibers 40a with a resin-based adhesive containing an epoxy-based resin, a bundle fiber 40 having
an ultrasonic sensing part is produced. In the first and second embodiments described above,
ultrasonic detection performance can be improved by adding an optical amplifier. This
modification will be described with reference to FIG. The ultrasonic receiver shown in FIG. 9 is
obtained by adding at least one of the optical amplifier 91 and the optical amplifier 92 to the
ultrasonic receiver shown in FIG. The optical amplifier 91 is disposed between the collimating
lens 17 and the splitter 12, amplifies the parallel light incident from the collimating lens 17, and
emits the amplified parallel light to the splitter 12. On the other hand, the optical amplifier 92 is
disposed between the splitter 12 and the dispersive element 15, amplifies the light incident from
the splitter 12 and emits the light to the dispersive element 15. As the optical amplifier, for
example, an erbium (Er) -doped optical fiber amplifier EDFA (Er-doped optical fiber amplifier) is
used. The EDFA can increase the light intensity by about one to two orders of magnitude. When
such an optical amplifier is disposed between the light source 11 and the ultrasonic detection
element 20, the intensity of incident light incident on the ultrasonic detection element 20 is
amplified. When the optical amplifier is disposed between the ultrasonic detection element 20
and the light detector 16, the intensity of incident light incident on the ultrasonic detection
element 20 does not change, but the reflection incident on the light detector 16 The light
intensity is amplified. In this case, the intensity change of the reflected light modulated by the
received ultrasonic wave is also amplified. In any case, by amplifying the intensity in the light
state, the light amount of the reflected light incident on the light detector 16 is increased, so the
influence of electrical noise in the light detector 16 is reduced, The SN ratio of the acoustic wave
receiver can be improved.
Furthermore, in the case of using both of them, further improvement of the SN ratio can be
realized. An ultrasonic imaging apparatus to which the ultrasonic receiving apparatus according
to the first or second embodiment of the present invention is applied will be described with
reference to FIG. The ultrasonic wave detection unit 60 shown in FIG. 10 includes the ultrasonic
wave detection element in the first or second embodiment, and is connected to the lens 18 or the
duplexer 12 via the collimator unit or the light transmission path. . The ultrasonic imaging
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apparatus further includes an ultrasonic wave transmission unit 70 and a drive signal generation
circuit 71. The ultrasonic wave transmission unit 70 transmits an ultrasonic wave based on the
drive signal generated from the drive signal generation circuit 71. The ultrasonic wave
transmission unit 70 is configured of, for example, a vibrator in which an electrode is formed on
a piezoelectric element. The piezoelectric element includes a piezoelectric ceramic typified by
PZT (lead zirconate titanate), a material having piezoelectricity typified by a polymeric
piezoelectric element such as PVDF (polyvinylidene fluoride), and the like. When a pulse-like
electric signal or a continuous wave electric signal is sent from the drive signal generation circuit
71 to the electrodes of the vibrator and a voltage is applied, the piezoelectric element expands
and contracts due to the piezoelectric effect. Thereby, an ultrasonic pulse or continuous wave
ultrasonic wave is generated from the vibrator. The ultrasonic waves transmitted from the
ultrasonic wave transmission unit 70 are reflected by the subject and received by the ultrasonic
wave detection unit 60. At this time, the ultrasonic sensing unit of the ultrasonic detection unit
60 expands and contracts according to the ultrasonic wave received on the reception surface,
and the light reflectance of the ultrasonic sensitive unit fluctuates according to the expansion and
contraction. On the other hand, light generated from the light source and transmitted through
the demultiplexer 12 is incident on the ultrasonic detection unit 60. This light is intensitymodulated and reflected by the fluctuation of the light reflectance in the ultrasonic detection unit
60. The reflected light is incident on the dispersive element 15 through the collimator lens 18
and the splitter 12, and is split and incident on the light detector 16. The ultrasonic imaging
apparatus further includes a system control unit 80, a signal processing unit 81, an A / D
converter 82, a primary storage unit 83, an image processing unit 84, and an image display unit
85. , And a secondary storage unit 86. A detection signal output from a predetermined
photoelectric conversion element of the photodetector 16 is subjected to processing such as
phase adjustment, logarithmic amplification, detection and the like in the signal processing unit
81, and further converted into a digital signal in the A / D converter 82. Be done. The primary
storage unit 83 stores a plurality of plane data based on the converted data.
The image processing unit 84 reconstructs two-dimensional data or three-dimensional data
based on the data, and performs processing such as interpolation, response modulation
processing, gradation processing, and the like. The image display unit 85 is, for example, a
display device such as a CRT or an LCD, and displays an image based on the image data subjected
to the processing. Further, the secondary storage unit 86 stores the data processed by the image
processing unit 84. The system control unit 80 controls the drive signal generation circuit 71 so
as to generate a drive signal at a predetermined timing, and takes in a detection signal output
from the light detector 16 after a predetermined time has elapsed from the transmission time.
Control the signal processing unit 81. As described above, by limiting the time zone in which the
drive signal and the detection signal are controlled and read, it is possible to detect the ultrasonic
wave reflected from the specific depth of the subject. Further, the system control unit 80 obtains
reflection characteristics in a plurality of detection areas of the ultrasonic wave detection unit 60
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based on the detection result of the light detector 16 at the time of calibration, and based on
those reflection characteristics, the light detector A set of photoelectric conversion elements to
be used for detection of ultrasonic waves is selected from a plurality of 16 photoelectric
conversion elements, and when ultrasonic waves are received, signals output from the selected
set of photoelectric conversion elements The signal processing unit 81 is controlled so as to use
as a detection signal. Here, the ultrasonic wave detection unit 60 and the ultrasonic wave
transmission unit 70 may be provided separately, or the ultrasonic wave transmission unit 70
and the ultrasonic wave detection element are combined to form the ultrasonic wave probe 1.
You may. As described above, according to the present invention, the reflection characteristic of
the ultrasonic detecting element is determined by calibration, and the photoelectric conversion
element used for detecting the ultrasonic wave is selected based on the reflection characteristic.
Therefore, even if the reflection characteristics change due to the environment such as
temperature and humidity, it is possible to maintain high detection sensitivity. In addition,
similarly, it is also possible to suppress variations in sensitivity among detection areas of the
ultrasonic detection element. Furthermore, since broadband light is used to select the wavelength
to be used for ultrasonic wave detection from the spectral light, there is no need to control the
wavelength of light according to the environment or detection area, and reflection characteristics
for each detection area There is no need to change the As a result, the configuration of the
ultrasound receiving apparatus can be simplified and miniaturized. Therefore, the manufacturing
of the ultrasonic wave receiving apparatus is facilitated, and the cost can be reduced. BRIEF
DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a configuration of an
ultrasound receiving apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram showing the configuration of an AWG spectral element. FIG. 3 is a view for
explaining the ultrasonic detection principle of the ultrasonic detection element shown in FIG. 1;
FIG. 4 is an enlarged cross-sectional view showing a connection portion of the ultrasonic
detection element, the collimator unit, and the optical transmission path shown in FIG. 1; FIG. 5 is
a flowchart showing the operation of the ultrasonic receiving apparatus according to the first
embodiment of the present invention. FIG. 6 is a diagram for explaining the operation of the
ultrasonic receiving apparatus according to the first embodiment of the present invention. FIG. 7
is a view showing a modified example of the ultrasonic receiving apparatus according to the first
embodiment of the present invention. FIG. 8 is a schematic view showing a part of an ultrasonic
wave receiving apparatus according to a second embodiment of the present invention. FIG. 9 is a
view showing a modification of the ultrasonic receiving apparatus according to the first and
second embodiments of the present invention. FIG. 10 is a block diagram showing an ultrasonic
imaging apparatus to which the ultrasonic receiving apparatus according to the present
invention is applied. [Description of the code] 1 ultrasonic probe 11 light source 13 light
transmission path 14 collimating part 14a, 17, 18 collimating lens 15 spectral element 16
photodetector 20, 30 ultrasonic detecting element 20a receiving surface 21, 31, 32 Substrates
22, 43 Multilayer film 23 Coating material 25 Adhesive 40 Bundled fiber 40a having an
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ultrasonic sensing part Fiber 41, OF1 to OFM optical fiber 42 Collimator lens 44 Coating material
51 Input waveguide 51 52 Input side slab waveguide 53a, 53b, ... Output waveguide 54 Output
side slab waveguide 55a, 5 5b, ... Array waveguide 60 Ultrasonic wave detection unit 70
Ultrasonic wave transmission unit 71 Drive signal generation circuit 80 Timing control unit 81
Signal processing unit 82 A / D converter 83 Primary storage unit 84 Image processing unit 85
Image display unit 86 2 Secondary storage unit 91, 92 Optical amplifier
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