JP2020018494A - Light source unit and photoacoustic device with the same - Google Patents

Abstract

To provide a light source unit that suppresses damages to a single fiber and can increase a spread angle of emitted light by increasing numerical apertures (NA) for light incident on the fiber.SOLUTION: A light source unit includes: a light radiation part for radiating a laser beam; a condensing lens system for condensing the laser beam that is radiated by the light radiation part; and a diffusion part for diffusing light.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a light source unit and a photoacoustic device having the same.

  2. Description of the Related Art Technologies for imaging a living body with minimal invasiveness using visible light or near-infrared light have been widely researched and developed in recent years. 2. Description of the Related Art As a living body imaging apparatus, there is a photoacoustic imaging apparatus that irradiates light from outside a living body and detects acoustic waves (ultrasonic waves) generated due to volume expansion of molecules in the living body that have absorbed light energy outside the living body. This is a technique that makes use of the advantages of both optical imaging and ultrasonic imaging, and is known as a technique that enables non-invasive imaging of a deeper part of a living body.

  Patent Document 1 discloses a photoacoustic apparatus in which light emitted from a light source is irradiated on a subject via a bundle fiber (Patent Document 1). The bundle fiber is a bundle of a plurality of single fibers, and has a plurality of light entrances, so that a large amount of light can be incident. On the other hand, since manufacturing is troublesome, it is preferable to use a single fiber from the viewpoint of reducing costs.

  Patent Literature 2 discloses a light source unit in which light emitted from a light source is transmitted and emitted by a single fiber via an optical system.

JP 2013-198657 A JP 2014-46072 A

  However, since the light source unit disclosed in Patent Document 2 has a configuration in which light condensed by the condenser lens system is incident on the single fiber, the end face of the single fiber may be damaged when using light of high intensity. Further, even if the light amount is suppressed to such an extent that the end face is not damaged, the numerical aperture (NA) of the light incident on the fiber becomes insufficient, and the divergence angle of the light emitted from the light source unit may be reduced.

  Therefore, an object of the present invention is to provide a light source unit that transmits light by a single fiber, thereby suppressing damage to a fiber end face and increasing a spread angle of emitted light.

  The light source unit according to the present invention includes a light irradiation unit that irradiates a laser beam, a condenser lens system that collects the laser light emitted from the light irradiation unit, and the laser that is condensed by the condenser lens system. It is characterized by having a diffusion part for diffusing light, and a single fiber for transmitting the laser light diffused by the diffusion part.

  A light source unit according to another aspect of the present invention includes a light irradiation unit that irradiates a laser beam, a condenser lens system that collects the laser light emitted from the light irradiation unit, and a condenser lens system that collects the laser light. A single fiber for transmitting the laser light, and a diffusion unit for diffusing the laser light transmitted by the single fiber.

  According to the light source unit of the present invention, since the laser beam is diffused by the diffusing unit and made incident on the single fiber after being condensed by the condenser lens system, damage to the fiber end face can be suppressed. Further, by adjusting the divergence angle of the diffuser, the NA of the light incident on the fiber can be increased, and the divergence angle of the light emitted from the light source unit can be increased.

1 is an overall configuration diagram of a photoacoustic device according to a first embodiment of the present invention. FIG. 2 is an enlarged view from a light irradiation unit to a single fiber according to the first embodiment of the present invention. In the first embodiment of the present invention, (a) a diffusion part (diffusion plate) having a diffusion angle of 10 degrees, (b) a diffusion part (diffusion plate) having a diffusion angle of 20 degrees, and (c) a diffusion part (diffusion) having a diffusion angle of 30 degrees. FIG. FIG. 6 is an overall configuration diagram of a photoacoustic device according to a second embodiment of the present invention. FIG. 5 is an enlarged view from a light irradiation unit to a single fiber according to a second embodiment of the present invention. FIG. 9 is an enlarged view from a single fiber of an optical transmission unit to a biological contact membrane in a second embodiment of the present invention.

  An embodiment of the present invention will be described, but the present invention is not limited to this.

  The light source unit according to the present embodiment includes a light irradiation unit that irradiates laser light, a condenser lens system that collects laser light emitted from the light irradiation unit, and a laser light that is collected by the condenser lens system. It has a diffusion part for diffusing. Further, it has a single fiber for transmitting the laser light diffused by the diffusion unit.

  Further, in the light source unit according to the present embodiment, the diffusion unit may be provided at a later stage than the single fiber. That is, a configuration having a single fiber for transmitting the laser light condensed by the condensing lens system and a diffusion unit for diffusing the laser light transmitted by the single fiber may be adopted.

  As described above, according to the light source unit according to the present embodiment, since the laser light is diffused by the light diffusing unit and made incident on the single fiber after being condensed by the condenser lens system, damage to the fiber end face can be suppressed. . Further, by adjusting the divergence angle of the diffuser, the NA of the light incident on the fiber can be increased, and the divergence angle of the light emitted from the light source unit can be increased.

(Condensing lens system)
The condensing lens system in the present embodiment preferably includes at least one of a convex lens, a telescope optical system, and a Fresnel lens.

(Single fiber)
The single fiber in the present embodiment transmits light, and a multi-fiber mode or a single mode fiber can be used.

(Diffusion section)
Although there is no particular limitation on the diffusion unit in the present embodiment, a lens diffusion plate in which minute lenses are arranged on one side of the substrate, a holographic diffusion plate, or the like can be used.

  Further, the diffusing portion may be integrally formed on the light incident end face of the single fiber.

The divergence angle θ_in of the laser light diffused by the diffusion unit is defined as n_in, the refractive index of a substance (air, liquid, or solid) in contact with the light incident end face of the single fiber, and NA, the numerical aperture of the single fiber. Is preferably represented by the following formula (I). Note that NA is an abbreviation for Numerical Aperture.
θ_in ≦ 2arcsin (NA / n_in) (I)
Further, it is particularly preferable that the compound is represented by the following formula (II).
θ_in ≦ 3arcsin (NA / n_in) (II)

(Light irradiation part)
The light irradiation unit in the present embodiment may have a light source unit that generates laser light. The light source unit includes a solid-state laser or a light-emitting element such as a semiconductor laser or a light-emitting diode.

(Photoacoustic device)
As an apparatus using the light source unit according to the present embodiment, a photoacoustic apparatus may be mentioned.

  The photoacoustic apparatus according to the present embodiment includes, in addition to the light source unit, a receiving unit that receives an ultrasonic wave generated from the subject and outputs a reception signal by irradiating the subject with the laser light.

(Receiver)
The receiving unit is not particularly limited, and a piezoelectric transducer or a capacitance transducer can be used.

(Information acquisition unit)
The photoacoustic apparatus according to the present embodiment may further include an information acquisition unit that acquires information on the subject using a reception signal of the reception unit.

  Hereinafter, details will be described by taking a photoacoustic apparatus (photoacoustic imaging apparatus) using the light source unit according to the present embodiment as an example.

[Embodiment 1]
FIG. 1 schematically shows a photoacoustic imaging apparatus (photoacoustic apparatus). Note that this example shows an apparatus configuration in a case where the light irradiation unit 101 includes a light source.

  First, a light beam 102 emitted from a light source (light irradiation unit) 101 enters a lens (condensing lens system) 103. Although the convex shape of the lens 103 is preferable in order to prevent light collection due to unexpected reflection into the light source, it is also possible to prevent the light collection in the light source by rotating the lens of another shape around an axis perpendicular to the paper surface. . The rotation angle is, for example, within 10 degrees. FIG. 2 shows an enlarged view from the light source 101 to the single fiber (optical transmission unit) 105. Hereinafter, the single fiber 105 is simply referred to as a fiber.

  The light beam 102 condensed by the lens 103 enters the diffusion plate 104. The diffusion plate (diffusion unit) 104 is placed near the beam waist position of the light beam 102 in the condensed state. The diffusing plate 104 has a fine structure on its surface that diffuses a light beam at an angle corresponding to an angle converted from the NA (Numerical Aperture) of the fiber 105. As an example, a light beam 102 emitted from the light source 101 is Gaussian, and a multimode fiber having an NA of 0.22 is used as the fiber 105. The required angle of incidence (full angle) on the fiber is 25.4 degrees, and by using a diffuser having a diffusion angle (full width at half maximum) of 10 degrees, as shown in the graph of FIG. A coupling efficiency of 7% can be achieved. 3A to 3C, the horizontal axis indicates the plus or minus angle from the optical axis, the vertical axis indicates the normalized light amount, the dotted line indicates the incident beam shape, and the solid line indicates the output beam shape. . In FIG. 3B, the coupling efficiency of about 86.5% is obtained by using a diffusion plate having a diffusion angle of 20 degrees, and in FIG. 3C, the coupling efficiency is obtained by using a diffusion plate having a diffusion angle of 30 degrees. It shows that a coupling efficiency of 69.4% can be achieved. When a diffusion plate having a diffusion angle of 10 degrees is used, the shape of the beam emitted from the fiber 105 is close to Gaussian. On the other hand, when a diffuser having a diffusion angle of 20 degrees is used, the shape of the output beam from the fiber 105 is such that both end angles of the diffused incident beam exceed the fiber NA, so that both ends of the incident beam shape propagate in the fiber. Not done. Therefore, the shape becomes closer to a flat top than the Gaussian shape. As described above, the diffusion angle of the diffusion plate 104 is determined according to the coupling efficiency to the fiber 105 and the desired output beam shape.

  When using a diffusion plate with a diffusion angle of 10 degrees or a diffusion angle of 20 degrees for the fiber of NA 0.22,

を満足する。上記ＮＡ０．２２のファイバに対して拡散角３０度の拡散板を使用する場合は、

To be satisfied. When using a diffusion plate with a diffusion angle of 30 degrees for the fiber of NA 0.22,

を満足する。

To be satisfied.

  For example, assuming that the light amount distribution of the light beam 102 emitted from the light source 101 is Gaussian, and assuming that the diameter of the light beam 102 is D, the wavelength is λ, and the focal length of the lens 103 is f, the radius w0 of the beam waist is

と計算できる。λを０．５３２μｍ、ｆを１００ｍｍ、Ｄを１ｍｍとすると、ｗ０は３４μｍとなる。このビームウエスト近傍に拡散角が２０度の拡散板１０４を配置すると仮定する。拡散板１０４とファイバ１０５までの距離Ｌは、下記式で表される。

Can be calculated. Assuming that λ is 0.532 μm, f is 100 mm, and D is 1 mm, w0 is 34 μm. It is assumed that a diffusion plate 104 having a diffusion angle of 20 degrees is arranged near the beam waist. The distance L between the diffusion plate 104 and the fiber 105 is represented by the following equation.

Here, D _core is the diameter of the core 201 of the fiber 105, NA is the NA of the fiber 105, and n is the refractive index of a substance between the diffusion plate 104 and the fiber 105. If Dcore is 105 μm, NA is 0.22, and n is 1, L is 82 μm. By arranging the diffusion plate 104 at this distance, particularly the surface to be diffused, the above-mentioned coupling efficiency of about 86.5% can be obtained. If the distance L between the diffusion plate 104 and the fiber 105 is mechanically fixed by using glass or the like, the optical system is stabilized, so that it is better. Further, the difference plate 104 may be rotated around an axis perpendicular to the plane of the paper to prevent unexpected reflection into the light source.

  On the other hand, by increasing the focal length of the lens 103, the accuracy required for the distance between the lens 103 and the diffusion plate 104 can be made relatively low. This will be described below.

  The beam radius w (z) with respect to the displacement amount z of the diffusion plate 104 is represented by the following equation.

  Now, w0 is 34 μm, λ is 0.532 μm, and if z is 2 mm, w (z) is 35 μm. That is, even if the diffuser plate 104 is shifted by 2 mm in the optical axis direction, the beam diameter increases only by 2 μm. That is, the distance between the diffusion plate 104 and the fiber 105 is more sensitive than the distance between the lens 103 and the diffusion plate 104, and only the distance between the diffusion plate 104 and the fiber 105 needs to be managed accurately.

  The light beam 102 incident on the core 201 of the fiber 105 in FIG. 2 reaches the two-branch fiber coupler 106 in FIG. The light beam 102 that has passed through the fiber coupler 106 is split into two, and propagates in the irradiation fiber 107, respectively. The irradiation fiber 107 is connected to a probe 108, and irradiates the object to be measured 110 as two irradiation light beams 109 from opposite positions in the probe 108. Here, the emission end face of the irradiation fiber 107 and a part of the ultrasonic probe 111 are in contact with the acoustic impedance matching agent 112. Examples of the acoustic impedance matching agent 112 include water, oil, gel, and the like. The acoustic impedance matching agent 112 does not directly contact the measurement target 110 via the biological contact film 113. The emission end face of the irradiation fiber 107 is arranged or processed so that the principal ray of the emitted light coincides with the center of the acoustic wave axis of the ultrasonic probe near the surface of the measurement target 110. For example, when water is used as the acoustic impedance matching agent 112, if the end face of the irradiation fiber 107 is processed so as to be inclined by 30 degrees with respect to the optical axis of the irradiation fiber 107, the chief ray of the emitted light is determined by Snell's law. It is inclined about 34 degrees with respect to the optical axis. By processing the end face of the irradiation fiber 107 in this manner, the inclination angle of the irradiation fiber 107 can be reduced, and the probe 108 can be downsized.

  The light scattered in the measurement target 110 reaches in-vivo molecules (not shown) such as hemoglobin and melanin, and those molecules that have absorbed light energy generate acoustic waves (ultrasonic waves) due to volume expansion. An acoustic wave generated from each biomolecule propagates in a living body, a part of which propagates to the surface of the measurement target 110, and is converted into an electric signal by an ultrasonic probe 111 including an acoustic wave lens. The electric signal of the acoustic wave is transmitted to the digitizer 116 via the cable 114, the analog signal is converted into a digital signal, and the controller 118 performs signal processing.

  In the probe 108, only the ultrasonic probe 111 or both the ultrasonic probe 111 and the irradiation fiber 107 are scanned by using the stage 116 in an XY plane substantially parallel to the surface of the measurement target 110. Perform the operation. An encoder (not shown) is arranged near the stage 116, and the position information in the scanning operation is sent to the digitizer 116 using the cable 117, and sent to the controller 118 together with the acoustic wave information. The controller 118 controls the light source 101 and the stage 116, and has display means for displaying acoustic wave information, encoder information, or an acoustic imaging image obtained by processing the information, as necessary.

  In this embodiment, as described above, by arranging the diffusing plate 104 in front of the fiber 105, the incident NA to the fiber 105 can be controlled.

  When the fiber 105 is a multimode fiber, the transmission efficiency of the light amount can be increased by using the multimode fiber. The lens 103 is a single lens in this embodiment, but may be an optical system using a plurality of optical surfaces, such as a Kepler telescope or a galleo telescope. Alternatively, the lens 103 may be a Fresnel lens. Further, the diffusion plate 104 may be integrally formed on the end face of the core 201 of the fiber 105. The light source 101 is a laser in this embodiment, but may be a laser diode.

[Embodiment 2]
FIG. 4 schematically shows a photoacoustic imaging apparatus according to another embodiment. The description of the same parts as those in FIG. 1 is omitted, and only different parts from the first embodiment will be described. The light beam 102 emitted from the light source 101 enters the lens 103, and the light beam 102 condensed by the lens 103 enters the fiber 105. FIG. 5 shows an enlarged view from the light source 101 to the fiber 105. The end face of the fiber 105 is placed at a position near the beam waist of the light beam 102 in a condensed state, and the light beam 102 in a substantially parallel state enters the core 201 of the fiber 105.

  FIG. 6 is an enlarged view of the vicinity of the irradiation fiber 107 and the biological contact film 113. The spread angle of the light beam 801 emitted from the core 201 of the irradiation fiber 107 is a small spread angle because the incident light beams are substantially parallel. For example, even when a multi-mode fiber having an NA of 0.22 is used as the emission fiber 107, the emission NA is 0.22 or less, for example, 0.15 or less. The light beam 801 emitted from the core 201 is diffused by the diffusion plate 802 and is incident on the living body contact film 113, and is incident on the measurement target 110 (not shown). Assuming that the full spread angle of the fiber emitted light beam 801 emitted from the core 201 is θin, the full spread angle of the diffusion plate 802 in the probe is θd, and the full spread angle of the post-diffusion light beam 803 incident on the biological contact film 113 is θout, the following expression is obtained. . The spread full angle of the in-probe diffusion plate 802 is determined using this relational expression.

  FIG. 6 shows a diagram in which light is emitted from the two irradiation fibers 107 that form a left and right pair. However, the number of irradiation fibers 107 may be one, or three or more. The end face of the irradiation fiber 107 and the diffuser plate 802 in the probe are in contact with the acoustic impedance matching agent 112, and the full angle of the diffuser plate 802 in the probe is determined by the refractive index between the acoustic impedance matching agent 112 and the diffuser plate 802 in the probe. You. In FIG. 6, the point where the principal rays of the left and right irradiation fibers 107 overlap is located on the biological contact film 113, but the point may be located above or below the biological contact film 113. In this embodiment, the irradiation fiber 107 is directly inclined with respect to the biological contact film 113, but the optical axis of the irradiation fiber may be inclined using a mirror or a prism.

  The fiber 105 and the irradiation fiber 107 may be single mode fibers or multimode fibers.

101 light source (light irradiation part)
102 luminous flux 103 lens (condensing lens system)
104 Diffusion plate (diffusion part)
105 Single fiber (optical transmission unit)
106 Fiber Coupler 107 Irradiation Fiber 108 Probe 109 Irradiation Beam 110 Measurement Target 111 Ultrasonic Probe 112 Acoustic Impedance Matching Agent 113 Biological Contact Film 114 Cable 115 Digitizer 116 Stage 117 Cable 118 Controller

Claims (16)

A light irradiator for irradiating laser light,
A condenser lens system for condensing the laser light emitted from the light irradiator,
A diffusing unit for diffusing the laser light condensed by the condensing lens system,
A single fiber for transmitting the laser light diffused by the diffusion unit,
A light source unit having: A light irradiating unit that irradiates laser light, and a condenser lens system that condenses the laser light irradiated from the light irradiating unit
A single fiber for transmitting the laser light focused by the focusing lens system,
A diffusing unit for diffusing the laser light transmitted by the single fiber,
A light source unit having: The condenser lens system includes a convex lens,
The light source unit according to claim 1. The condenser lens system includes a telescope optical system,
The light source unit according to claim 1. The condenser lens system includes a Fresnel lens,
The light source unit according to claim 1. The single fiber is a multi-fiber mode, or a single mode fiber,
The light source unit according to claim 1. The diffusion portion is integrally formed on the light incident end face of the single fiber,
The light source unit according to claim 1. The divergence angle θ_in of the laser light diffused by the diffusing unit is as follows, where n_in is the refractive index of a substance in contact with the light incident end face of the light transmitting unit, and NA is the numerical aperture of the light transmitting unit. The light source unit according to claim 1, wherein the light source unit is represented by Formula (I).
θ_in ≦ 2arcsin (NA / n_in) (I) The divergence angle θ_in of the laser light diffused by the diffusing unit is as follows, where n_in is the refractive index of a substance in contact with the light incident end face of the light transmitting unit, and NA is the numerical aperture of the light transmitting unit. The light source unit according to claim 1, wherein the light source unit is represented by Formula (II).
θ_in ≦ 3arcsin (NA / n_in) (II) The light irradiation unit has a light source unit that generates the laser light,
The light source unit according to claim 1. The light source unit includes a solid-state laser,
The light source unit according to claim 1. The light source unit includes a semiconductor laser or a light emitting diode,
The light source unit according to claim 1. A light source unit according to any one of claims 1 to 12,
A photoacoustic apparatus including a receiving unit configured to receive an ultrasonic wave generated from the subject by irradiating the subject with the laser light and output a reception signal.   14. The photoacoustic device according to claim 13, wherein the receiving unit includes a piezoelectric transducer.   The photoacoustic apparatus according to claim 13, wherein the receiving unit includes a capacitance type transducer.   The photoacoustic apparatus according to any one of claims 13 to 15, further comprising an information acquisition unit configured to acquire information on the subject using the reception signal.

Images