JP2004003969A - Ultrasonic wave receiving apparatus and ultrasonic wave receiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic receiving apparatus which can reduce changes in detecting the sensitivity of a ultrasonic wave caused by changes in temperature or the like, and the variation of the detecting sensitivity due to a position of an ultrasonic wave detecting element. <P>SOLUTION: The apparatus comprises a light source 11 which generates a broad-band light, an ultrasonic wave detecting element 20 which includes an ultrasonic wave sensitive unit, which expands and contracts according to a received ultrasonic wave and modulates the intensity of the light generated by the light source due to a change in a reflection ratio of the light corresponding to the expansion and contraction, a spectrographic unit 15 which ejects the lights modulated by the ultrasonic wave detecting element to a different direction according to the frequency of the light, and a light detecting device 16 which has a plurality of photoelectric conversion elements for detecting the lights modulated by the ultrasonic wave detecting element by frequencies. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic receiving apparatus and an ultrasonic receiving method used for obtaining an ultrasonic image by receiving ultrasonic waves.
[0002]
[Prior art]
Conventionally, in an ultrasonic imaging apparatus, a piezoelectric ceramic represented by PZT (lead zirconate titanate), a PVDF (polyvinylidene fluoride), or the like as an element (vibrator) for transmitting and receiving ultrasonic waves One-dimensional sensor arrays using piezoelectric elements including polymer piezoelectric elements are common. While moving such a one-dimensional sensor array mechanically, a two-dimensional image at a plurality of cross-sections of a subject is acquired, and a three-dimensional image is obtained by combining the two-dimensional images.
[0003]
However, according to this method, since there is a time lag in the moving direction of the one-dimensional sensor array, cross-sectional images at different times are synthesized, so that the synthesized image becomes blurred. Therefore, it is not suitable for a subject that is intended for a living body as in the case where ultrasonic echo observation or the like is performed using an ultrasonic imaging apparatus.
[0004]
In order to acquire a high-quality three-dimensional image using ultrasonic waves, a two-dimensional sensor that can acquire a two-dimensional image without moving the sensor array is necessary.
However, when producing a two-dimensional sensor array using the above-mentioned PZT or PVDF, fine processing of elements and wiring to a large number of fine elements are necessary, and miniaturization and element integration beyond the current level are difficult. . Even if they are solved, there is a problem that crosstalk between elements increases, an SN ratio is deteriorated due to an increase in electrical impedance due to fine wiring, and an electrode portion of the fine element is easily broken. Therefore, it is difficult to realize a two-dimensional sensor array using PZT or PVDF.
[0005]
On the other hand, there is also known a sensor that detects a received ultrasonic signal by converting it into an optical signal. As such an optical detection type ultrasonic sensor, 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). Have been reported). When a two-dimensional sensor array is manufactured using such an ultrasonic sensor, there is an advantage that electrical wiring to a large number of fine elements is unnecessary and good sensitivity can be obtained.
[0006]
An optical detection type ultrasonic sensor having a two-dimensional detection surface is also known. For example, Non-Patent Document 3 describes that a polymer film having a Fabry-Perot structure is used for ultrasonic detection. Such a film-like ultrasonic sensor does not require processing on a large number of microelements, and thus can reduce costs. A photodetection type ultrasonic sensor uses an ultrasonic detection element that changes the reflection characteristics of light when receiving an ultrasonic wave.
[0007]
However, such an ultrasonic detection element has a large variation in detection sensitivity because the light reflection characteristics change due to changes in temperature and humidity. In addition, in an ultrasonic detection element having a two-dimensional detection surface, the light reflection characteristics differ depending on the position of the detection surface, resulting in variations in detection sensitivity. As described above, in an ultrasonic receiving apparatus using a light detection method, it is a big practical problem to control a change in detection sensitivity due to environmental factors such as temperature and structural factors. For this purpose, for example, the wavelength of the light emitted from the light source may be adjusted to a point where the sensitivity of the ultrasonic detection element is increased. However, the wavelength of the light source light is adjusted to a very steep reflection characteristic. It is difficult to install. On the other hand, a method of making broadband light incident on an ultrasonic detection element having different reflection characteristics depending on the position and filtering the reflected light may be considered, but in this case, the configuration of the ultrasonic detection element becomes complicated. There is a problem that the cost becomes high. Furthermore, a method of changing the reflection characteristics for each detection region of the ultrasonic detection element is also conceivable, but in this case also, the configuration of the ultrasonic detection element becomes complicated and the cost is increased.
[0008]
[Non-Patent Document 1]
Takahashi (TAKAHASHI) and two others, “Underwater Acoustic Sensor with Fiber Bragg Grating”, OPTICAL REVIEW, Vol. 4, no. 6 (1997), p. 691-694
[Non-Patent Document 2]
Uno, one other, "Fabrication and Performance of a Fiber-Optic Micro-Probe for Megafield Ultrasonic Field of Electricity" IEEE Japan), Vol. 118-E, no. 11 (1998), p. 487-492
[Non-Patent Document 3]
Beard, et al., "Transaction Mechanisms of the Fabric-Perot Polymer Sensing Concept for Wide Band Ultrasonic Detection"・ E-newsletter (IEEE TRANSACTIONS ONULTRASONICS, FERROELECTRICS, AND FREQEQUENCE CONTROL), VOL. 46, NO. 6 (NOVEMBER 1999), p. 1575-1582
[0009]
[Problems to be solved by the invention]
Therefore, in view of the above points, the present invention relates to a change in ultrasonic detection sensitivity due to an environmental change such as temperature or the position of an ultrasonic detection element in an ultrasonic reception device and an ultrasonic reception method using a light detection method. An object of the present invention is to reduce the variation in detection sensitivity and to simplify the configuration of the apparatus and reduce the cost.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problem, an ultrasonic receiving apparatus according to the present invention expands and contracts according to a light source that generates broadband light and received ultrasonic waves, and the light reflectance varies according to the expansion and contraction. An ultrasonic detection element including an ultrasonic sensitive unit that modulates the intensity of light generated by the light source, a spectral unit that splits the light whose intensity is modulated by the ultrasonic detection element, and a plurality of lights dispersed by the spectral unit And a light detecting means having a plurality of photoelectric conversion elements for detecting each wavelength component.
[0011]
In addition, the ultrasonic reception method according to the present invention includes an ultrasonic sensitive unit that modulates the intensity of incident light by expanding and contracting according to the received ultrasonic wave and changing the light reflectance according to the expansion and contraction. Light is incident on the ultrasonic detection element, the light whose intensity is modulated in the ultrasonic detection element is dispersed, and the dispersed light is detected for each of a plurality of wavelength components using a light detection means having a plurality of photoelectric conversion elements. Thus, the step (a) for determining the relationship between the wavelength of light and the reflection intensity in the plurality of detection areas of the ultrasonic detection element, and the plurality of photoelectric detectors of the light detection means based on the relationship determined in step (a). A step (b) of selecting a set of photoelectric conversion elements to be used for detecting ultrasonic waves from the conversion elements; and when receiving the ultrasonic waves, light is incident on the ultrasonic detection elements, and the ultrasonic detection elements When ultrasonic waves are received The intensity-modulated light is emitted in different directions according to the wavelength by the spectroscopic means, and detected for each of a plurality of wavelength components using a set of photoelectric conversion elements selected in step (b), (C) obtaining information relating to ultrasonic waves received in a plurality of detection areas of the ultrasonic detection element.
[0012]
According to the present invention, the relationship between the light wavelength and the reflection intensity in the plurality of detection regions of the ultrasonic detection element is obtained by dispersing the light reflected by the ultrasonic detection means and making it incident on different photoelectric conversion elements. be able to. In addition, a detection signal can be obtained based on light having an optimum wavelength by selecting in advance a photoelectric conversion element to be used when receiving ultrasonic waves based on the relationship.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a diagram showing an ultrasonic receiving apparatus according to the first embodiment of the present invention. This ultrasonic receiver includes a light source 11, a duplexer 12, an optical transmission path 13, a collimator 14, an ultrasonic detector 20, a spectroscopic element 15, a photodetector 16, a collimator lens 17, 18 and so on.
Hereinafter, the relationship between the wavelength of light and the reflection intensity in the ultrasonic detection element 20 is referred to as reflection characteristics.
[0014]
As the light source 11, it is desirable to use a light source having a bandwidth that can cover a range equal to or greater than the inclined band in the reflection characteristics 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. .
[0015]
The duplexer 12 is configured by a half mirror, an optical circulator, a polarization beam splitter, or the like, and allows incident light incident from the first direction to pass in the second direction and return from the second direction. Is reflected in a third direction different from the first direction. In the present embodiment, a half mirror is used as the duplexer 12. The half mirror transmits incident light in a direction opposite to the incident direction, and reflects light returning from the opposite direction of the incident direction in a direction that is approximately 90 ° with respect to the incident direction.
[0016]
The optical transmission path 13 guides the light that has passed through the duplexer 12 to the ultrasonic detection element 20. As the optical transmission line 13, a bundle fiber in which a large number (for example, 1024) of optical fibers are bundled is used. FIG. 1 shows optical fibers OF _{1 to} OF _M arranged on one line. As shown in FIG. 1, a large number of optical fibers are bundled in accordance with the shape of the receiving surface (for example, a circle) on the ultrasonic detection element side (left side in the figure), and the duplexer 12 side (right side in the figure). ) Are arranged on one line. Alternatively, optical fibers arranged on one line may be stacked in a plurality of stages.
[0017]
The tip of the optical transmission line 13 is connected to the ultrasonic detection element 20 through the collimator 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 optical transmission line 13 and the collimator unit 14 will be described in detail later.
[0018]
The ultrasonic detection element 20 includes a two-dimensional reception surface 20a that is distorted by propagating ultrasonic waves, and an ultrasonic sensitive part that expands and contracts in accordance with the ultrasonic waves received on the reception surface 20a. Since the light reflectance of the ultrasonic sensitive part varies according to the expansion and contraction, the light incident on the ultrasonic detection element 20 through the optical transmission path 13 and the collimating part 14 is reflected after being subjected to intensity modulation.
[0019]
The spectroscopic element 15 is configured by, for example, a diffraction grating, a prism, or the like, and emits incident light in different directions depending on the wavelength. The spectroscopic element 15 splits the light beams L _{1 to} L _M emitted in parallel from the optical fibers OF _{1 to} OF _M and guides the plurality of split light beams to the photodetector 16.
[0020]
Alternatively, an AWG (arrayed waveguide grating) spectroscopic element may be used as the spectroscopic element 15. FIG. 2 shows the configuration of the AWG spectroscopic element.
As the AWG spectroscopic element, an arrayed waveguide grating included in a planar lightwave circuit (PLC) is generally used. As shown in FIG. 2, the arrayed waveguide grating includes 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,. It is configured by connecting the waveguide 54 with a plurality of arrayed waveguides 55a, 55b,... Having a certain waveguide length difference.
[0021]
The input side slab waveguide 52 has a sector shape with the end portion of the input waveguide 51 as the center of curvature. The output-side slab waveguide 54 has a sector shape with the ends of the plurality of output waveguides 53a, 53b,. The plurality of arrayed waveguides 55a, 55b,... Are arranged radially so that their 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 realize a function equivalent to that of the lens.
[0022]
Incident light having a plurality of different wavelengths λ _{1 to} λ _N enters the input waveguide 51 and is guided to the plurality of arrayed waveguides 55 a, 55 b,... By the lens action of the input-side slab waveguide 52. A plurality of wavelength components included in the incident light are excited in the arrayed waveguides 55a, 55b,... And guided to a plurality of output waveguides 53a, 53b,... Having a waveguide length corresponding to each wavelength.
[0023]
Referring again to FIG. 1, the photodetector 16 detects a plurality of wavelength components separated by the spectroscopic element 15. As the photodetector 16, a two-dimensional photoelectric converter is used in which a plurality of photoelectric conversion elements are two-dimensionally arranged and incident light can be divided and detected for each position. 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.
[0024]
The optical transmission path 13, the spectroscopic element 15, and the photodetector 16 are configured such that a component having a predetermined wavelength included in a light beam reflected from a predetermined minute region of the ultrasonic detection element is a predetermined wavelength of the photodetector 16. It arrange | positions so that it may inject into a photoelectric conversion element. In the present embodiment, the light beams L ₁ , L ₂ ,... Emitted from the optical fibers OF ₁ , OF ₂ ,... Connected to different regions of the ultrasonic detection elements are the photoelectric conversion elements arranged in two dimensions. This corresponds to the first column, the second column,. Further, the wavelengths λ ₁ , λ ₂ ,... Of the dispersed components correspond to the first row, the second row,. By arranging the optical system so as to obtain such correspondence, the signal output from the photoelectric conversion element located in the n-th row and m-th column of the photodetector 16 is converted into the light beam L emitted from the optical fiber OF _m. It is specified as a component having a wavelength λ _n included in _m .
The collimating lens 17 makes the light emitted from the light source 11 collimated and enters the splitter 12. In addition, the collimating lens 18 makes the light emitted from the optical fibers OF ₁ , OF ₂ ,...
[0025]
Next, the structure of the ultrasonic detection element 20 and the principle of ultrasonic detection 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 laminated on the substrate. This multilayer film 22 constitutes a Bragg grating structure and functions as an ultrasonic sensitive part.
[0026]
The board | substrate 21 is a film | membrane-like board | substrate which produces distortion by receiving an ultrasonic wave, for example, has a circle | round | yen about 2 cm in diameter, or more. A multilayer film 22 having a Bragg grating structure is formed on the substrate 21 by alternately laminating two kinds of material layers having different refractive indexes. FIG. 3 shows a material layer A having a refractive index n ₁ and a material layer B having a refractive index n ₂ .
[0027]
When the pitch (interval) of the periodic structure of the multilayer film 22 is d and the wavelength of incident light is λ, the Bragg reflection condition is expressed by the following equation. However, m is an arbitrary 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 reflection condition and transmits light of other wavelengths.
[0028]
When the ultrasonic wave is propagated to the ultrasonic wave detection element 20, the ultrasonic wave detection element 20 is distorted as the ultrasonic wave propagates, and the pitch d of the periodic structure changes at each position of the multilayer film 22. As a result, the wavelength λ of the selectively reflected light changes. In the reflection characteristic of the Bragg grating, there is an inclined band in which the light reflectance changes before and after the center wavelength having the highest light reflectance (low transmittance). When an ultrasonic wave is applied while light having a central wavelength in the range of the inclined band is incident on the multilayer film 22, the intensity change of the reflected light (or transmitted light) according to the intensity of the ultrasonic wave at each position on the receiving surface is changed. Observable. By converting the change in the intensity of the light into the intensity of the ultrasonic wave, the two-dimensional intensity distribution information of the ultrasonic wave can be acquired.
[0029]
As the material of the substrate 21, optical glass such as quartz glass (SiO ₂ ) and BK7 (product of Schott) is used. Moreover, as a substance used for the material layers A and B, a combination of substances whose refractive indexes are different from each other by 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 deposition or sputtering.
[0030]
By the way, in order to suppress the multiple reflection of the ultrasonic wave, it is effective to increase the distance that the ultrasonic wave propagates. Ultrasound is attenuated to some extent during propagation, and the amount of attenuation increases as the propagation distance increases. Therefore, if a sufficient propagation distance is provided, the ultrasonic wave can be sufficiently attenuated while the ultrasonic wave propagated to one end is reflected and returned 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. In other words, the optical transmission path is provided with a function as a backing part for attenuating ultrasonic waves as well as a function for transmitting light.
[0031]
FIG. 4 is an enlarged cross-sectional view showing a part of the optical transmission path 13, the collimating unit 14, and the ultrasonic detection element 20 shown in FIG. As shown in FIG. 4, the optical fibers OF ₁ , OF ₂ ,... Included in the optical transmission path (bundle fiber) 13 are respectively connected to the plurality of collimating lenses 14 a included in the collimating portion (collimating lens array) 14. Are further connected to the ultrasonic detection element 20 in a two-dimensional manner. The optical fibers OF ₁ , OF ₂ ,... Are bundled using an adhesive 25.
[0032]
The optical fibers OF ₁ , OF ₂ ,... 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. However, by covering the optical fiber with the above member, the propagation energy loss of the ultrasonic wave can be further increased. Ultrasonic attenuation can be accelerated.
[0033]
Here, the light transmitted through the optical fibers OF ₁ , OF ₂ ,... Is diffracted when emitted from the optical fibers. For this reason, if the optical fibers OF ₁ , OF ₂ ,... Are directly connected to the ultrasonic detection element 20, the light diffuses and sufficient interference does not occur in the ultrasonic detection element. For this reason, detection sensitivity will deteriorate remarkably. In order to avoid this phenomenon, a plurality of collimator lenses 14a are connected to one end of each of the optical fibers OF ₁ , OF ₂ ,... To prevent the emitted light from diffusing. 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 detection element 20.
[0034]
As the collimating lens 14a, a gradient index lens (hereinafter abbreviated as GRIN lens) is used. The GRIN lens is known, for example, under the product name of Selfoc (registered trademark of Nippon Sheet Glass Co., Ltd.) lens. The GRIN lens is a gradient index lens having a different refractive index depending on its position, and its optical characteristics change by changing its length. For example, when the GRIN lens has a length that is ¼ of the distance between the object image planes (the pitch at which the light erects), the incident light is emitted as parallel light.
[0035]
In this embodiment, a Selfoc lens array NA0.46 (product of Nippon Sheet Glass Co., Ltd.) in which a number of Selfoc lenses are arranged is used with a length of 0.25 L (L is the distance between object image planes). Each Selfoc lens is connected to an optical fiber as a collimating lens 14a.
As shown in FIG. 4, the collimating lens 14 a may be covered with a covering material 23. This is because the ultrasonic waves are attenuated quickly in the same manner as in the optical fibers OF ₁ , OF ₂ ,.
[0036]
The optical fiber and the collimating lens, or the collimating lens and the ultrasonic detection element are connected using fusion or an adhesive. When using an adhesive, it is desirable to use a resin adhesive including an epoxy resin. In such adhesives, the acoustic impedance is similar to that of optical fiber and collimating lens members and the substrate of the ultrasonic detection element, so that reflection of ultrasonic waves at the boundary of each member is suppressed when propagating. Because it can. In addition, it is desirable to use a resin adhesive including an epoxy as the adhesive 25 for bundling a plurality of optical fibers. This is because the ultrasonic wave is attenuated to prevent ultrasonic crosstalk between adjacent optical fibers and to maintain flexibility as a cable. In this embodiment, STYCAST (product of Emerson & Cuming) is used as such an adhesive.
[0037]
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 ultrasonic receiving apparatus according to this embodiment.
First, calibration is performed before receiving ultrasonic waves. Here, the calibration refers to an operation of measuring the reflection characteristics of the ultrasonic detection element and determining a wavelength component to be used as a detection signal. That is, the ultrasonic detection element is very sensitive to the surrounding environment such as temperature and humidity, and its reflection characteristics are likely to change. For example, the center wavelength of reflected light of an ultrasonic detection element using a Bragg grating changes at a rate of 0.01 nm / ° C. Further, in an ultrasonic detection element having a two-dimensional detection surface, there is a 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.
This calibration may be performed at any time after the reception of ultrasonic waves is started.
[0038]
In step S1, the ultrasonic receiver is driven. Thereby, for example, broadband light having a spectral characteristic as shown in FIG. Light emitted from the light source passes through a collimating lens 17, a demultiplexer 12, a collimator lens 18, and enters the optical fiber _OF 1 _{~OF M} which are arranged on one line. The light transmitted through each optical fiber is incident on each minute region of the ultrasonic detection element 20, and the reflected light corresponding to the light reflectance of each minute region is emitted from the optical fiber. The light beams L _{1 to} L _M emitted from the optical fibers OF _{1 to} OF _M pass through the collimator lens 18 again, are reflected by the branching filter 12, and enter the spectroscopic element 15. Light L ₁ ~L _M is spectrally in the spectral element 15, the respective wavelength components, the plurality of photoelectric conversion elements included in each column of the photodetectors 16, is incident depending on the wavelength.
[0039]
Thus, in step S2, from the respective columns of the photodetector 16 corresponding to light L ₁ ~L _M, the detection signal of the photoelectric conversion element corresponding to the wavelength lambda ₁ to [lambda] _N are obtained.
FIG. 6B is a graph obtained based on the detection signal in the photoelectric conversion element included in the m-th column of the photodetector 16, and passes through the optical fiber OF _m , and the corresponding ultrasonic detection element shows the spectral distribution of the reflected light beam L _m from a minute region. As shown in FIG. 6B, the light beam L _m has the highest intensity at the wavelength λ _X that is selectively reflected by Bragg reflection conditions.
[0040]
FIG. 6 (c) shows the reflection characteristics of the Bragg grating in the micro region of the ultrasonic detecting element corresponding to the light beam L _m. As described above, in the reflection characteristic of the Bragg grating, there is an inclined band Δλ where the light reflectance changes sharply before and after the center wavelength λ _X having the highest light reflectance (low transmittance). When observing a change in the structure of the Bragg grating by applying an ultrasonic wave, a large intensity change is observed in the spectral region of the inclined band Δλ. This is represented by λ _n in FIGS. 6B and 6C.
[0041]
Therefore, for the minute region of the ultrasonic detection element corresponding to the light beam L _m , the light in the spectral region having the wavelength λ _n as the central wavelength shows the greatest intensity change. That is, for the optical fiber OF _m , the highest detection is achieved by using the signal output from the photoelectric conversion element (n, m) on which the wavelength λ _n is incident as the ultrasonic detection signal in the m-th column of the photodetector. Sensitivity can be obtained.
[0042]
Similarly, a signal output from any photoelectric conversion element is detected as an ultrasonic detection signal for each column on which light beams L ₁ , L ₂ ,... Emitted from the optical fibers OF ₁ , OF ₂ ,. Is selected, the highest detection sensitivity can be obtained for each minute region of the ultrasonic detection element 20.
Referring again to FIG. 5, in step S <b> 3, a photoelectric conversion element to be used is selected for each column of the light detection elements 16 based on the result of prior detection.
[0043]
Next, ultrasonic waves are received.
In step S4, the ultrasonic receiver is driven. Thereby, the broadband light emitted from the light source is incident on the minute region of the ultrasonic detection element 20 via the optical fibers OF _{1 to} OF _M. Light L ₁ ~L _M reflected from each of the small regions are spectrally in the spectral element 15, enters the light detector 16.
[0044]
In this state, an ultrasonic wave is applied to the ultrasonic detection element 20 (step S5). Thereby, 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 conversion element selected in step S3 shows a large intensity change.
[0045]
Next, in step S6, a detection signal output from the photoelectric conversion element selected in step S3 is acquired. Further, these detection signals are processed to convert the intensity change of the reflected light into the intensity of the ultrasonic wave. Thereby, the intensity | strength of the ultrasonic wave received in each micro area | region of an ultrasonic detection element can be measured two-dimensionally.
[0046]
A modification of this embodiment will be described with reference to FIG. In this example, an ultrasonic detection element (etalon sensor) 30 shown in FIG. 7 is used instead of the ultrasonic detection element 20 in FIG. Other configurations are the same as those 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. Opposite the substrate 31, a substrate 32 is disposed, and these form a structure similar to that of an etalon.
[0047]
When the light reflectance of the substrates 31 and 32 is R, the distance between these substrates is d, and the wavelength of the incident light is λ, the transmittance of the etalon is expressed as follows. However, n is an arbitrary integer.
T = {1 + 4R / (1-R) ² · sin ² (φ / 2)} ⁻¹ (3)
φ = 2π / λ · 2nd · cos θ (4)
Here, θ is an emission angle measured from the normal 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 transmittance T and reflects it with light reflectance R = (1-T).
[0048]
When an ultrasonic wave is propagated to the ultrasonic detection 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 with respect to light of wavelength λ changes. Therefore, in the same manner as described with reference to FIG. 5, prior detection is performed, and in the photodetector, a photoelectric conversion element in which light having a central wavelength is incident on a region having a large change in light reflectance is selected, and broadband is selected. An ultrasonic wave is 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 on the receiving surface can be observed. By converting the intensity change of the reflected light into the intensity of the ultrasonic wave, the intensity of the ultrasonic wave can be measured two-dimensionally.
[0049]
Next, an ultrasonic receiving apparatus according to the second embodiment of the present invention will be described with reference to FIG. In the present embodiment, instead of the ultrasonic detection element 20, the optical transmission line 13, and the collimator 14 shown in FIG. 1, a bundle fiber having an ultrasonic sensitive part as shown in FIG. 40 is used. Other configurations are the same as those in the first embodiment.
[0050]
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 this 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-type adhesive agent containing melt | fusion or an epoxy type.
[0051]
At one end of the collimating lens 42, a multilayer film 43 in which two types of material layers are alternately laminated is formed. The multilayer film 43 constitutes a Bragg grating structure and functions as an ultrasonic sensitive part. As a material of the multilayer film 43, for example, a 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 deposition or sputtering.
[0052]
The fiber 40a is covered with a low-viscosity member (covering material 44) so that the ultrasonic wave propagated to one end of the fiber 40a is attenuated before the other end is reflected. Further, as shown in FIG. 8B, the covering material 44 may cover the collimating lens 42. Thereby, since the energy loss of the ultrasonic wave propagated to the fiber 40a can be increased, the ultrasonic wave can be attenuated quickly and the effect as a backing portion can be improved.
A bundle fiber 40 having an ultrasonic sensitive part is produced by bundling a plurality of such a plurality of fibers 40a using a resin adhesive containing an epoxy resin.
[0053]
In the first and second embodiments described above, the ultrasonic detection performance can be improved by adding an optical amplifier. This modification will be described with reference to FIG.
The ultrasonic receiving apparatus shown in FIG. 9 is obtained by adding at least one of an optical amplifier 91 and an optical amplifier 92 to the ultrasonic receiving apparatus shown in FIG. The optical amplifier 91 is disposed between the collimating lens 17 and the duplexer 12, amplifies the parallel light incident from the collimating lens 17, and outputs the amplified parallel light to the duplexer 12. On the other hand, the optical amplifier 92 is disposed between the duplexer 12 and the spectroscopic element 15, amplifies the light incident from the demultiplexer 12, and outputs the amplified light to the spectroscopic element 15.
[0054]
As the optical amplifier, for example, an optical fiber amplifier EDFA (Er-Doped Optical Fiber Amplifier) doped with erbium (Er) is used. This EDFA can increase the light intensity by about 1 to 2 digits.
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. Further, when the optical amplifier is disposed between the ultrasonic detection element 20 and the photodetector 16, the intensity of incident light incident on the ultrasonic detection element 20 does not change, but the reflection incident on the photodetector 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.
[0055]
In any case, since the amount of reflected light incident on the photodetector 16 is increased by amplifying the intensity in the state of light, the influence of electrical noise in the photodetector 16 is reduced, and the ultrasonic receiving apparatus The SN ratio can be improved. Furthermore, when both are used together, it is possible to further improve the S / N ratio.
[0056]
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.
An ultrasonic detection unit 60 shown in FIG. 10 includes the ultrasonic detection element in the first or second embodiment, and is connected to the lens 18 and the duplexer 12 through a collimator unit and an optical transmission path. .
[0057]
Further, the ultrasonic imaging apparatus includes an ultrasonic transmission unit 70 and a drive signal generation circuit 71. The ultrasonic transmission unit 70 transmits ultrasonic waves based on the drive signal generated from the drive signal generation circuit 71. The ultrasonic transmission unit 70 is configured by a vibrator in which an electrode is formed on a piezoelectric element, for example. The piezoelectric element includes a piezoelectric ceramic typified by PZT (lead zirconate titanate), a piezoelectric material typified by a polymer piezoelectric element such as PVDF (polyvinylidene fluoride), and the like. When a voltage is applied to the electrodes of the vibrator by sending a pulsed electric signal or a continuous wave electric signal from the drive signal generating circuit 71, the piezoelectric element expands and contracts due to the piezoelectric effect. Thereby, an ultrasonic pulse or a continuous wave ultrasonic wave is generated from the vibrator.
[0058]
The ultrasonic waves transmitted from the ultrasonic transmitter 70 are reflected by the subject and received by the ultrasonic detector 60. At this time, the ultrasonic sensitive part of the ultrasonic detection unit 60 expands and contracts according to the ultrasonic wave received on the receiving surface, and the light reflectance of the ultrasonic sensitive part varies according to the expansion and contraction. On the other hand, light generated from the light source and passed through the duplexer 12 is incident on the ultrasonic detection unit 60. This light is intensity-modulated and reflected by fluctuations in light reflectance in the ultrasonic detector 60. The reflected light is incident on the spectroscopic element 15 via the collimator lens 18 and the demultiplexer 12, and is separated and incident on the photodetector 16.
[0059]
The ultrasonic imaging apparatus 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, an image display unit 85, and a secondary unit. And a 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, and detection in a signal processing unit 81, and further converted into a digital signal in an A / D converter 82. Is done.
[0060]
The primary storage unit 83 stores a plurality of pieces of surface 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, and gradation processing. The image display unit 85 is a display device such as a CRT or LCD, for example, and displays an image based on the image data subjected to these processes. Further, the secondary storage unit 86 stores data processed by the image processing unit 84.
[0061]
The system control unit 80 controls the drive signal generation circuit 71 so as to generate a drive signal at a predetermined timing, and captures a detection signal output from the photodetector 16 after a predetermined time has elapsed from the transmission time. The processing unit 81 is controlled. In this way, by limiting the reading time period by controlling the drive signal and the detection signal, it is possible to detect ultrasonic waves reflected from a specific depth of the subject. In addition, the system control unit 80 obtains reflection characteristics in a plurality of detection regions of the ultrasonic detection unit 60 based on the detection result of the photodetector 16 at the time of calibration, and based on the reflection characteristics, the photodetector A signal output from the selected set of photoelectric conversion elements when a set of photoelectric conversion elements used for ultrasonic detection is selected from the plurality of 16 photoelectric conversion elements and ultrasonic waves are received. The signal processing unit 81 is controlled so as to be used as a detection signal.
Here, the ultrasonic detector 60 and the ultrasonic transmitter 70 may be provided separately, or the ultrasonic probe 1 is formed by combining the ultrasonic transmitter 70 and the ultrasonic detector. You may do it.
[0062]
【The invention's effect】
As described above, according to the present invention, the reflection characteristic of the ultrasonic detection element is obtained by calibration, and the photoelectric conversion element used for ultrasonic detection is selected based on the reflection characteristic. Even if the reflection characteristics change depending on the environment, it is possible to maintain high detection sensitivity. Similarly, it is possible to suppress variation in sensitivity for each detection region of the ultrasonic detection element. Furthermore, since the wavelength used for ultrasonic detection is selected from the spectral light using broadband light, there is no need to control the wavelength of light according to the environment and detection area, and the reflection characteristics for each detection area There is no need to change. Thus, the configuration of the ultrasonic receiving apparatus can be simplified and reduced in size. Accordingly, the ultrasonic receiving device can be easily manufactured, and the cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of an ultrasonic receiving apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of an AWG spectroscopic element.
FIG. 3 is a diagram for explaining the principle of ultrasonic detection of the ultrasonic detection element shown in FIG. 1;
4 is an enlarged cross-sectional view illustrating a connection portion of the ultrasonic detection element, the collimator unit, and the optical transmission path illustrated in FIG. 1;
FIG. 5 is a flowchart showing an 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 diagram showing a modification 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 receiving apparatus according to a second embodiment of the present invention.
FIG. 9 is a diagram 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.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ultrasonic probe 11 Light source 13 Optical transmission line 14 Collimating part 14a, 17, 18 Collimating lens 15 Spectroscopic element 16 Photodetector 20, 30 Ultrasonic detection element 20a Reception surface 21, 31, 32 Substrate 22,43 Multilayer Film 23 Coating material 25 Adhesive 40 Bundle fiber 40a having ultrasonic sensitive part Fiber 41, OF _{1 to} OF _M optical fiber 42 Collimating lens 44 Coating material 51 Input waveguide 51 52 Input side slab waveguides 53a, 53b,. Output waveguide 54 Output side slab waveguide 55a, 55b, ... Array waveguide 60 Ultrasonic detector 70 Ultrasonic transmitter 71 Drive signal generator 80 Timing controller 81 Signal processor 82 A / D converter 83 Primary storage Part 84 Image processing unit 85 image display unit 86 the secondary storage unit 91 and 92 an optical amplifier

Claims (5)

A light source that generates broadband light;
An ultrasonic detecting element including an ultrasonic sensitive part that modulates the intensity of light generated by the light source by expanding and contracting according to the received ultrasonic wave, and the light reflectance varies according to the expansion and contraction;
A spectroscopic means for spectrally splitting the light whose intensity is modulated by the ultrasonic detection element;
A light detecting means having a plurality of photoelectric conversion elements for detecting light separated by the spectroscopic means for each of a plurality of wavelength components;
An ultrasonic receiving apparatus comprising: The ultrasonic receiving apparatus according to claim 1, further comprising an optical transmission path for transmitting light between the ultrasonic detecting element and the spectroscopic means. It is possible to detect ultrasonic waves in a plurality of detection areas of the ultrasonic detection element,
The spectroscopic means simultaneously splits a plurality of light beams respectively guided from a plurality of detection areas of the ultrasonic detection element,
The ultrasonic receiver according to claim 1, wherein the light detecting unit detects a plurality of light beams separated by the spectroscopic unit for each wavelength component. Based on the detection result of the light detection means at the time of calibration, a relationship between the wavelength of light and the reflection intensity in the plurality of detection areas of the ultrasonic detection element is obtained, and based on those relationships, the light detection means Select a set of photoelectric conversion elements to be used for ultrasonic detection from a plurality of photoelectric conversion elements, and detect signals output from the selected set of photoelectric conversion elements when receiving ultrasonic waves. The ultrasonic receiving apparatus according to claim 3, further comprising control means used as a signal. The light is incident on the ultrasonic detection element including the ultrasonic sensitive part that modulates the intensity of the incident light by expanding and contracting according to the received ultrasonic wave and changing the light reflectance of the expansion and contraction part according to the expansion and contraction. The ultrasonic detection element is configured to split the intensity-modulated light in the ultrasonic detection element and detect the dispersed light for each of a plurality of wavelength components using a light detection unit having a plurality of photoelectric conversion elements. Obtaining a relationship between the light wavelength and the reflection intensity in a plurality of detection areas of (a),
A step (b) of selecting a set of photoelectric conversion elements to be used for ultrasonic detection from a plurality of photoelectric conversion elements of the light detection means based on the relationship obtained in step (a);
When receiving the ultrasonic wave, the light is incident on the ultrasonic detection element, and the ultrasonic wave is received by the ultrasonic detection element, and the intensity-modulated light is emitted in different directions depending on the wavelength, A step of obtaining information related to ultrasonic waves received in a plurality of detection areas of the ultrasonic detection element by detecting for each of a plurality of wavelength components using a set of photoelectric conversion elements selected in step (b) ( c) and
An ultrasonic receiving method comprising:

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