JP2021142346A - Detector - Google Patents

Abstract

To improve an S/N ratio of a signal outputted from a detector.SOLUTION: A detector (100a) comprises a board (10), a light emitting part (20) arranged on the board to emit light, a light receiving part (31) arranged on the board to receive scattered light from an object out of the emitted light, and a sealing part (40) arranged on the board so as to cover the light emitting part and the light receiving part. The light receiving part also receives internally reflected light reflected by a boundary surface of the sealing part out of the light emitted from the light emitting part. A reflecting film (41) is arranged on at least a portion of a surface of the sealing part.SELECTED DRAWING: Figure 5

Description

The present invention relates to the technical field of a detector mounted on an optical measuring device that performs measurement using, for example, a laser beam.

As this type of measuring device, for example, a sensor unit in which a semiconductor laser and a light receiving element are arranged on the same plane is provided, and blood flow, blood volume, and blood flow in the living tissue are used by utilizing scattered light from the living tissue. A device for measuring speed, pulse, etc. has been proposed (see Patent Document 1).

Patent No. 4718324

However, the technique described in Patent Document 1 has a technical problem that there is room for improvement in, for example, the S / N ratio (Signal to Noise Ratio).

The present invention has been made in view of the above problems, for example, and an object of the present invention is to provide a detector capable of improving the S / N ratio.

The detector according to claim 1 has a substrate, a light emitting unit arranged on the substrate and emitting light, and an object of the emitted light arranged on the substrate in order to solve the above problems. A light receiving portion that receives scattered light from an object and a sealing portion that is arranged on the substrate so as to cover the light emitting portion and the light receiving portion are provided, and the light receiving portion is of the emitted light. The internally reflected light reflected at the interface of the sealing portion is further received, and the reflective film is arranged on at least a part of the surface of the sealing portion.

The actions and other gains of the present invention will be apparent from the embodiments described below.

It is a schematic block diagram which shows the structure of the detector which concerns on Example. It is a perspective view of the photodetector which concerns on Example. It is a block diagram which shows the structure of the light detection apparatus which concerns on Example. It is a conceptual diagram which shows the light incident on a light receiving element. It is a schematic block diagram which shows the structure of the detector which concerns on the 1st modification of an Example. It is a schematic block diagram which shows the structure of the detector which concerns on the 2nd modification of an Example. It is a schematic block diagram which shows the structure of the detector which concerns on the 3rd modification of an Example. It is a block diagram which shows the structure of the photodetector which concerns on the 3rd modification of an Example. It is a schematic block diagram which shows the structure of the detector which concerns on 4th modification of an Example. It is a block diagram which shows the structure of the photodetector which concerns on the 4th modification of an Example. It is a schematic block diagram which shows the structure of the detector which concerns on 5th modification of an Example. It is a block diagram which shows the structure of the light detection apparatus which concerns on 5th modification of an Example.

An embodiment according to the detector of the present invention will be described.

The detector according to the embodiment is, for example, a substrate that is a submount, a light emitting unit that is arranged on the substrate and emits light, and scattered light from an object of light that is arranged on the substrate and emitted. It includes a light receiving portion that receives light, and a sealing portion that is arranged on a substrate so as to cover the light emitting portion and the light receiving portion.

A light source such as a surface emitting laser can be applied to the light emitting unit. Here, when the object to be measured is a living body, a light source that emits light contained in a wavelength range of 700 nm (nanometers) to 1300 nm, which is relatively low in absorption by the living body, is desirable.

When a light source that emits light contained in the wavelength range of 700 nm to 1300 nm is used as the light emitting portion, the sealing portion has a transmittance of 10% or less for light having a wavelength of 650 nm or less (that is, visible light). Moreover, it is desirable to apply a resin having a transmittance of 90% or more with respect to light having a wavelength of 700 nm to 1300 nm. With such a configuration, it is possible to suppress the incident of visible light, which may be ambient light, on the light receiving portion, which is very advantageous in practical use.

When the object to be measured is a living body, the scattered light received by the light receiving portion such as a photodiode includes the light scattered by the stationary tissue of the living body (for example, skin) and the moving object of the living body (for example). Includes light scattered by (e.g., etc.) light. Then, the light scattered by the moving object of the living body undergoes a Doppler shift proportional to the velocity of the moving object. Therefore, interference light between the light scattered by the stationary tissue of the living body and the light scattered by the moving object of the living body is incident on the light receiving portion.

Here, the electric field intensity of the light scattered by the stationary tissue of the living body is expressed by the following equation (1), and the electric field intensity of the light scattered by the moving object of the living body is expressed by the following equation (2). The strength of can be expressed by the following equation (3).

“A ₀ ” and “A ₁ ” are the amplitudes of light, “f ₀ ” is the frequency of light, and “Δf” is the frequency that fluctuates due to the Doppler shift. “I” is an i vector and “j” is a j vector. The i vector and the j vector are unit vectors representing the traveling direction of light.

The first term of the above equation (3) is a constant light component, and the second term is a beat component. As can be seen from the above equation (3), the closer the i-vector direction and the j-vector direction are, the stronger the beat component becomes.

By the way, the light emitted from the light emitting unit is scattered in various directions depending on the object to be measured. In addition, the light scattered by the moving object of the living body is weaker than the light scattered by the stationary tissue of the living body. Therefore, it is difficult to sufficiently strengthen the beat component of the above equation (3) only with scattered light.

However, in the present embodiment, since the light emitting portion is covered with the sealing portion, a part of the light emitted from the light emitting portion passes through the sealing portion and reaches the object to be measured, and the other portion. Is reflected at the interface of the sealing portion. Therefore, the scattered light from the object to be measured and the internally reflected light reflected at the interface of the sealing portion are incident on the light receiving portion.

The internally reflected light is incident on the light receiving portion at an incident angle close to 90 degrees, and can be treated in the same manner as the light scattered by the stationary tissue of the living body. In addition, although the ratio of the internally reflected light to the light emitted from the light emitting portion is small, the ratio of the internally reflected light reflected at the interface and incident on the light receiving portion is higher than the ratio of the scattered light scattered by the measurement object and incident on the light receiving portion. Is high enough.

That is, in the present embodiment, the beat component of the above equation (3) can be sufficiently strengthened by using the internally reflected light. In addition, among the light scattered by the moving object of the living body due to the internally reflected light, the beat component related to the light incident on the light receiving portion at an incident angle close to 90 degrees is strongly measured.

As a result, according to the detector according to the present embodiment, the S / N ratio can be improved. In addition, the spatial resolution of the detector can be improved. Further, in the detector, since the light emitting portion and the light receiving portion are integrally molded, for example, the manufacturing process can be shortened, which is very advantageous in practical use.

In one aspect of the detector according to the present embodiment, the light receiving unit includes a first photoelectric conversion element and a second photoelectric conversion element, and the anode of the first photoelectric conversion element and the anode of the second photoelectric conversion element are mutually exclusive. It is electrically connected, or the cathode of the first photoelectric conversion element and the cathode of the second photoelectric conversion element are electrically connected to each other.

According to this aspect, the DC component of the current output by the first photoelectric conversion element and the DC component of the current output by the second photoelectric conversion element can be offset, and the S in the signal output from the detector can be offset. The / N ratio can be improved.

In another aspect of the detector according to this embodiment, a reflective film is arranged on at least a part of the surface of the sealing portion.

According to this aspect, the amount of internally reflected light can be increased, which is very advantageous in practical use. As the reflective film, a thin film such as aluminum can be applied.

In another aspect of the detector according to the present embodiment, the sealing portion is formed by the thickness of the sealing portion (that is, between the substrate surface and the upper surface of the sealing portion) from the light receiving portion side toward the light emitting portion side. It has a first inclined surface in which the thickness of the sealing portion becomes thinner from the light emitting portion side to the light receiving portion side, and has a first inclined surface and a second inclined surface in which the thickness of the sealing portion becomes thinner. The inclined surfaces are formed so that the angles formed by each other approach 90 degrees.

According to this aspect, the magnitude of the emission angle of the light emitted from the light emitting portion and the magnitude of the incident angle of the internally reflected light to the light receiving portion can be made substantially the same. Here, since the emission angle is approximately 90 degrees, the incident angle is also approximately 90 degrees, which makes it relatively easy to strengthen the beat component of the above equation (3).

In this aspect, the sealing portion has an upper surface that is a surface along the substrate surface of the substrate, one side of the upper surface is shared with the first inclined surface, and the other side of the upper surface faces the one side. May be shared with the second slope.

With such a configuration, the height of the detector can be suppressed, which is very advantageous in practical use.

Examples of the detector of the present invention will be described with reference to the drawings.

The detector according to the embodiment will be described with reference to FIG. FIG. 1 is a schematic configuration diagram showing a configuration of a detector according to an embodiment. 1 (a) is a top view, FIG. 1 (b) is a bottom view, and FIG. 1 (c) is a side view.

In FIG. 1, the detector 100 includes a substrate 10, a surface emitting laser 20 arranged on the substrate 10, a light receiving element 31 arranged on the substrate 10, the surface emitting laser 20, and the light receiving element 31. It is configured to include a sealing portion 40 arranged on the substrate 10 so as to cover the substrate 10.

The surface emitting laser 20 as an example of the "light emitting unit" according to the present invention emits light having a wavelength of, for example, 850 nm. The wavelength of the light emitted from the surface emitting laser 20 may be included in the range of 700 nm to 1300 nm, and is not limited to 850 nm.

The sealing portion 40 is made of a resin such as an epoxy resin. The resin constituting the sealing portion 40 has a transmittance of 10% or less for light having a wavelength of 650 nm or less and a transmittance of 90% or more for light having a wavelength of 700 nm to 1300 nm. Dye is mixed.

The anode and cathode of the surface emitting laser 20 are electrically connected to an electrode (not shown) on the upper surface of the substrate 10 by wire bonding or the like. The electrodes on the upper surface of the substrate 10 penetrate the lower surface of the substrate 10.

As shown in FIG. 1B, on the lower surface of the substrate 10, a terminal 20a electrically connected to the anode of the surface emitting laser 20 and a terminal 20c electrically connected to the cathode of the surface emitting laser 20 As an example of the "light receiving unit" according to the present invention, the terminal 31a electrically connected to the anode of the light receiving element 31 and the terminal 31c electrically connected to the cathode of the light receiving element 31 are exposed. doing.

The size of the detector 100 is, for example, 3 mm × 3 mm. The distance from the upper surface of the surface emitting laser 20 to the upper surface of the sealing portion 40 and the distance from the upper surface of the light receiving element 31 to the upper surface of the sealing portion 40 are, for example, 0.5 mm. The distance between the light emitting point of the surface emitting laser 20 (see FIG. 1A) and the center of the light receiving surface of the light receiving element 31 (see FIG. 1A) is, for example, 0.6 mm.

When the detector 100 is mounted on a photodetector, as shown in FIG. 2, it is mounted on a circuit board housed in a case 300 made of, for example, aluminum or the like. The case 300 is provided with a window 301 so as not to interfere with the light emitted from the surface emitting laser 20 and the light incident on the light receiving element 31.

The size of the case 300 is, for example, 10 mm × 15 mm × 3 mm. The size of the window 301 is, for example, 3 mm × 3 mm.

Next, the photodetector will be described with reference to FIG. FIG. 3 is a block diagram showing a configuration of a photodetector according to an embodiment. In this embodiment, a laser Doppler blood flow meter is given as an example of a photodetector.

In FIG. 3, the photodetector includes a detector 100 (that is, a photocurrent converter) and a current-voltage converter 200. The input light (incident light) to the detector 100 is light emitted from the surface emitting laser 20 and reflected or scattered by an object (for example, a human finger).

The light receiving element 31 is a photodiode such as a PIN diode. The detector 100 outputs the current Idt output by the light receiving element 31 as the detection current Idt from the terminal 31a. Further, the detector 100 outputs a current (−Idt) in which the polarity of the detection current Idt output from the terminal 31a is reversed from the terminal 31c.

The current-voltage conversion unit 200 includes input terminals In1 and In2, a fully differential amplifier 230, feedback resistors Rf1 and Rf2, an amplifier 240, and an output terminal Out. The current-voltage conversion unit 200 converts the detection current Idt input from the detector 100 to the input terminals In1 and In2 into a voltage signal and outputs it as an optical detection signal from the output terminal Out.

The fully differential amplifier 230 has an input terminal In + electrically connected to the input terminal In1, an input terminal In− electrically connected to the input terminal In2, an output terminal Out-, an output terminal Out +, and a reference. It has a potential terminal Vref. The reference potential is input via the reference potential terminal Vref. The output terminals Out- and Out + are electrically connected to the input terminals In- and In + of the amplifier 240, which will be described later, respectively.

One end of the feedback resistor Rf1 is electrically connected to the input terminal In + of the fully differential amplifier 230, and the other end is electrically connected to the output terminal Out- of the fully differential amplifier 230. Convert to voltage.

One end of the feedback resistor Rf2 is electrically connected to the input terminal In− of the fully differential amplifier 230, and the other end is electrically connected to the output terminal Out + of the fully differential amplifier 230. Convert to voltage.

The fully differential amplifier 230 converts the current Idt input to the input terminal In1 into a voltage signal −Rf1 · Idt and outputs it from the output terminal Out−. At the same time, the fully differential amplifier 230 converts the current −Idt input to the input terminal In2 into the voltage signals Rf2 · Idt and outputs the current −Idt from the output terminal Out +. That is, the fully differential amplifier 230 is configured as a transimpedance amplifier that independently converts the currents input to the input terminals In1 and In2 into currents and voltages and outputs them differentially.

The amplifier 240 amplifies and outputs the potential difference (2, Rf, Idt) between the voltage signal −Rf1 · Idt input from the input terminal In− and the voltage signal Rf2 · Idt input from the input terminal In + (note that). , Rf1 = Rf2 = Rf).

The photodetector signal output from the current-voltage converter 200 is input to a signal processing device (not shown) via one of the wires 302 (see FIG. 2). The signal processing device calculates biological information such as blood flow value, blood flow velocity, and pulse by processing a photodetection signal. Since various known modes can be applied to the method of obtaining the blood flow value or the like from the photodetection signal, the detailed description thereof will be omitted.

In the current-voltage conversion unit 200 described above, the potential difference between the input terminal In + of the fully differential amplifier 230 and the reference potential terminal Vref is almost zero due to the negative feedback provided by the feedback resistors Rf1 and Rf2. Similarly, the potential difference between the input terminal In− of the fully differential amplifier 230 and the reference potential terminal Vref is almost zero. As a result, the potential of the input terminal In + and the potential of the input terminal In− are almost the same.

Therefore, the current voltage is connected to the terminal 31a electrically connected to the input terminal In + of the fully differential amplifier 230 via the input terminal In1 of the current-voltage converter 200, and to the input terminal In− of the fully differential amplifier 230. The potential difference between the terminal 31c and the terminal 31c electrically connected via the input terminal In2 of the conversion unit 200 is also almost zero. That is, the light receiving element 31 can be operated in a zero bias state, that is, in a so-called power generation mode. Therefore, the dark current generated in the light receiving element 31 can be reduced or eliminated.

As a result, the noise current caused by the fluctuation of the dark current can be reduced, and the S / N ratio related to the photodetection signal output from the current-voltage converter 200 can be improved.

Next, the light incident on the light receiving element 31 of the detector 100 will be described with reference to FIG. FIG. 4 is a conceptual diagram showing light incident on the light receiving element.

Most of the laser light emitted from the surface emitting laser 20 (see “emission light” in FIG. 4) passes through the sealing portion 40 and is irradiated to the living body which is an object through the window 301 of the case 300. The laser beam irradiated to the living body is reflected and scattered by the living body, and a part of the laser light is transmitted through the sealing portion 40 and incident on the light receiving element 31. Further, a part of the laser light emitted from the surface emitting laser 20 is reflected at the interface of the sealing portion 40 and is incident on the light receiving element 31 (see “internally reflected light” in FIG. 4).

The light reflected / scattered by the living body is reflected / scattered by the stationary tissue of the living body (see “Return light from the stationary tissue” in FIG. 4) and the moving object of the living body such as erythrocytes. Light (see "Returning Light from Erythrium" in FIG. 4) and. Here, the light reflected and scattered by the moving object of the living body causes a Doppler shift proportional to the velocity of the moving object.

The light received by the light receiving element 31 is caused by the constant light component (that is, the component that does not fluctuate due to reflection / scattering by the living body) and the beat component (that is, the Doppler-shifted modulation component) due to the interference of the above lights with each other. Includes (see equation (3) above).

The ratio of the light reflected at the interface of the sealing portion 40 (hereinafter, appropriately referred to as “internally reflected light”) incident on the light receiving element 31 is that the light scattered by the object to be measured (here, the living body) is the light receiving element. It is sufficiently strong compared to the ratio of light incident on 31. Then, the internally reflected light is incident on the light receiving element 31 at an incident angle close to 90 degrees. Therefore, among the light reflected and scattered by the moving object of the living body, the light incident on the light receiving element 31 at an incident angle close to 90 degrees is selectively emphasized (the above-mentioned equation (3)). reference).

Specifically, for example, in the detector 100, the incident light is closer to 90 degrees with respect to the light receiving element 31 as compared with the case where the surface emitting laser is not covered with the sealing portion (that is, there is no internally reflected light). The signal intensity of the beat component of the light incident at the angle increases by 15 dB.

<First modification>
A first modification of the detector according to the embodiment will be described with reference to FIG. FIG. 5 is a schematic configuration diagram showing the configuration of the detector according to the first modification of the embodiment.

In FIG. 5, the detector 100a is arranged on the upper surface of the sealing portion 40 and includes a reflective film 41 made of, for example, aluminum or the like. The reflective film 41 may be arranged so as to cover the entire upper surface of the sealing portion 40, or may be arranged only above, for example, the surface emitting laser 20 and the light receiving element 31.

When the reflective film 41 is arranged so as to cover the entire upper surface of the sealing portion 40, the reflectance of the laser light related to the reflective film 41 is, for example, 20%, and the transmittance of the laser light is, for example, 80%. Etc., the reflectance and transmittance of the reflective film 41 may be set so that the light emitted from the surface emitting laser 20 is surely irradiated to the object.

As can be seen from the above equation (3), if any of the light reflected / scattered by the moving object of the living body and the light reflected / scattered by the stationary object of the living body or the internally reflected light is strong, the beat component. Becomes stronger. Therefore, by arranging the reflective film 41 on the upper surface of the sealing portion 40, the internally reflected light can be strengthened, so that the S / N ratio of the signal output from the light receiving element 31 can be further improved.

<Second modification>
A second modification of the detector according to the embodiment will be described with reference to FIG. FIG. 6 is a schematic configuration diagram showing the configuration of the detector according to the second modification of the embodiment.

In FIG. 6A, the sealing portion 40a of the detector 100b has a first inclined surface that descends from the side of the light receiving element 31 toward the side of the surface emitting laser 20, and the light receiving element from the side of the surface emitting laser 20. It has a second inclined surface that descends toward the side of 31. Here, in particular, the first inclined surface and the second inclined surface are formed so that the angle formed by each other approaches 90 degrees.

Since the angle formed by the first inclined surface and the second inclined surface is close to 90 degrees, the emission angle of the light emitted from the surface emitting laser 20 and the incident angle of the internally reflected light on the light receiving element 31 are substantially the same. Will be the same. Since the emission angle of the light emitted from the surface emitting laser 20 is close to 90 degrees, the angle of incidence of the internally reflected light on the light receiving element 31 is also close to 90 degrees. As a result, the amount of internally reflected light incident substantially perpendicular to the light receiving element 31 can be increased, so that the S / N ratio of the signal output from the light receiving element 31 can be further improved.

In FIG. 6B, the sealing portion 40b of the detector 100c shares one side with the first inclined surface and shares the other side facing the one side with the second inclined surface. Has an upper surface. With this configuration, the height of the detector 100c can be suppressed while increasing the amount of internally reflected light incident substantially perpendicular to the light receiving element 31, which is extremely advantageous in practical use.

<Third modification example>
A third modification of the detector according to the embodiment will be described with reference to FIGS. 7 and 8. FIG. 7 is a schematic configuration diagram showing the configuration of the detector according to the third modification of the embodiment. FIG. 8 is a block diagram showing a configuration of a photodetector according to a third modification of the embodiment.

In FIG. 7, the detector 100d is further provided with a light receiving element 32 arranged on the substrate 10. As shown in FIG. 7A, in the light receiving element 32, the distance between the light receiving element 32 and the light emitting point of the surface emitting laser 20 is substantially equal to the distance between the light receiving element 31 and the light emitting point of the surface emitting laser 20. It is arranged so as to be. As shown in FIG. 7B, on the lower surface of the substrate 10, a terminal 32a electrically connected to the anode of the light receiving element 32 and a terminal 32c electrically connected to the cathode of the light receiving element 32 are provided. It is exposed.

The "light receiving element 31" and the "light receiving element 32" according to the present modification are examples of the "first photoelectric conversion element" and the "second photoelectric conversion element" according to the present invention, respectively.

In this modification, in particular, as shown in FIG. 8, the terminal 31a electrically connected to the anode of the light receiving element 31 and the terminal 32a electrically connected to the anode of the light receiving element 32 are formed on the circuit board 200. They are electrically connected to each other. The cathode of the light receiving element 31 is electrically connected to the terminal 31c. The cathode of the light receiving element 32 is electrically connected to the terminal 32c.

Since the light receiving elements 31 and 32 are connected in series, the detector 100d uses the difference current (Idt2-Idt1) between the current Idt1 output by the light receiving element 31 and the current Idt2 output by the light receiving element 32 as the detection current Idt. Output from terminal 31c. Further, the detector 100d outputs a current (−Idt) in which the polarity of the detection current Idt output from the terminal 31c is reversed from the terminal 32c.

With this configuration, the DC component of the current Idt1 output by the light receiving element 31 and the DC component of the current Idt2 output by the light receiving element 32 can be offset, which corresponds to the signal light component included in the input light. The detection current Idt mainly containing the AC component can be output. As a result, the S / N ratio in the photodetection signal output by the current-voltage conversion unit 200 can be improved.

<Fourth modification>
A fourth modification of the detector according to the embodiment will be described with reference to FIGS. 9 and 10. FIG. 9 is a schematic configuration diagram showing the configuration of the detector according to the fourth modification of the embodiment. FIG. 10 is a block diagram showing a configuration of a photodetector according to a fourth modification of the embodiment.

In this modification, in particular, as shown in FIG. 10, the anode of the light receiving element 31 and the anode of the light receiving element 32 are electrically connected to each other inside the detector 100e. With such a configuration, it is not necessary to provide the circuit board 200 with wiring for electrically connecting the anode of the light receiving element 31 and the anode of the light receiving element 32, which is very advantageous in practical use.

As shown in FIG. 9, on the lower surface of the detector 100e, a terminal 31c electrically connected to the cathode of the light receiving element 31 and a terminal 32c electrically connected to the cathode of the light receiving element 32 are provided. Be exposed.

<Fifth modification>
A fifth modification of the detector according to the embodiment will be described with reference to FIGS. 11 and 12. FIG. 11 is a schematic configuration diagram showing the configuration of the detector according to the fifth modification of the embodiment. FIG. 12 is a block diagram showing a configuration of a photodetector according to a fifth modification of the embodiment.

In this modification, in particular, as shown in FIG. 12, the cathode of the light receiving element 31 and the cathode of the light receiving element 32 are electrically connected to each other inside the detector 100f. With such a configuration, it is not necessary to provide the circuit board 200 with wiring for electrically connecting the cathode of the light receiving element 31 and the cathode of the light receiving element 32, which is very advantageous in practical use. In addition, in this modification as well, the DC component of the detection current caused by the steady component of the incident light on the light receiving element can be suppressed as in the third modification described above. As a result, the S / N ratio in the photodetection signal output by the current-voltage conversion unit 200 can be improved.

The present invention is not limited to the above-described embodiment, and can be appropriately modified within the scope of claims and within the scope not contrary to the gist or idea of the invention that can be read from the entire specification. It is also included in the technical scope of the present invention.

10 ... Substrate, 20 ... Surface emitting laser, 31, 32 ... Light receiving element, 40, 40a, 40b ... Sealing part, 41 ... Reflective film, 100, 100a, 100b, 100c, 100d, 100e, 100f ... Detector, 200 ... current-voltage converter, 230 ... fully differential amplifier, 240 ... amplifier, 300 ... case, 301 ... window

Claims (1)

With the board
A light emitting unit that is arranged on the substrate and emits light,
A light receiving unit arranged on the substrate and receiving scattered light from the object of the emitted light, and a light receiving unit.
A sealing portion arranged on the substrate so as to cover the light emitting portion and the light receiving portion.
With
The light receiving portion further receives the internally reflected light reflected at the interface of the sealing portion of the emitted light.
A detector characterized in that a reflective film is arranged on at least a part of the surface of the sealing portion.

Images