JP2001169394A - Optical microphone element and optical microphone system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized optical microphone element with high positioning precision of light receiving elements and light emitting elements and excellent yield and to provide an optical microphone system. SOLUTION: In the optical microphone element where light emitting elements and light receiving elements are placed on one substrate, the light emitting elements emit light to a diaphragm placed at a position opposite to the substrate and a reflected light from the diaphragm is received by the light receiving elements to detect a displacement of the diaphragm, vertical surface light emission type light emitting elements whose luminous intensity distribution is nearly concentrically uniform are placed in the center of the substrate and the light receiving elements are placed onto the substrate so as to surround the light emitting elements.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical microphone device and an optical microphone device using the optical microphone device.

[0002]

2. Description of the Related Art FIG.
It is a figure which shows schematic structure of. A diaphragm 2 is stretched near the entrance of the container 1. Then, the light emitting diode 3 and the phototransistor or the photodiode 5 are installed in the container 1, and the incident light L1 from the light emitting diode 3 is reflected by the inner side surface 2b of the diaphragm 2, and the reflected light L2 is converted to the phototransistor or the phototransistor. Light is received by a light receiving element 5 such as a diode. The sound wave 7 incident on the optical microphone element 10 is incident from the outer surface 2a of the diaphragm 2, and vibrates the diaphragm 2. When the diaphragm 2 vibrates, the reflected light L2
Is changed, and the light enters the different light receiving surface 5a of the light receiving element 5. By detecting the change in the light receiving surface 5a, the displacement of the diaphragm 2 can be detected. A lens 4 is used to position the incident light L1 and the reflected light L2.
Alternatively, 6 may be used. As described above, in the conventional optical microphone element, the incident light L1 is emitted from the light emitting element 3 to the diaphragm 2 at a certain angle, the reflected light L2 is received at the reflection angle corresponding to the incident angle, and the reflected light L2 is received. The sound wave is reproduced by detecting the displacement of the diaphragm 2 according to the change in the reflection angle of the sound wave.

[0003]

In such a conventional structure of the optical microphone element, the alignment between the light emitting element 3 such as a light emitting diode and the light receiving element 5 such as a phototransistor or a photodiode is as high as several tens of microns or less. Accuracy is required. For this reason, when the light emitting element 3, the light receiving element 5, the vibration plate 2, and the like are composed of individual components, it is difficult to perform high-accuracy alignment in manufacturing a product, which causes a problem of deteriorating the yield. there were. There is also a limit in reducing the size of the optical microphone element. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an optical microphone element that can easily align a light-receiving / emitting element and a diaphragm with high accuracy, and an optical microphone using the same. It is an object to provide a microphone device.

[0004]

According to the optical microphone element of the present invention, a light emitting element and a light receiving element are arranged on the same substrate, and light from the light emitting element is applied to a diaphragm installed at a position facing the substrate. In the optical microphone element which emits and receives the reflected light from the diaphragm with the light receiving element to detect the displacement of the diaphragm, the light emitting element has a vertical surface emission type light emitting element whose emission intensity distribution is substantially uniform in a concentric circle. An element is arranged at the center of the substrate, and the light receiving element is arranged concentrically so as to surround the light emitting element.

[0005] In the optical microphone element, the light receiving element can be composed of a plurality of elements. Further, in the optical microphone element, a plurality of the concentric circles can be formed. Further, in the optical microphone element, the light emitting element and the light receiving element can be simultaneously formed on the substrate. Further, in the optical microphone device of the present invention, the substrate may be a gallium arsenide wafer. Further, in the optical microphone element, the diaphragm can be installed substantially parallel to and close to the substrate.

Further, in the optical microphone device of the present invention, a vertical surface emitting type light emitting element having a light emission intensity distribution substantially concentrically arranged at the center of the substrate, and concentrically surrounding the light emitting element. A light receiving element is arranged, and light is emitted from the light emitting element to a diaphragm installed at a position facing the substrate, and an optical microphone element that receives reflected light from the diaphragm with the light receiving element, in a different concentric circle. A differential detector for detecting a differential signal of a signal detected by the light receiving element belonging to the light receiving element, and detecting a displacement of the diaphragm from an output of the differential detector. In the optical microphone device, the diaphragm can be installed substantially parallel to and close to the substrate.

[0007]

FIG. 1 is a diagram showing a basic structure of an optical microphone device according to the present invention. FIG. 1A shows a cross-sectional shape, and an electronic circuit board 12 is provided on the bottom surface 8 of the container 1.
Is mounted, and a substrate 9 on which a light emitting element and a light receiving element are arranged is mounted on the substrate 12. The attachment can also be performed by electrically connecting the substrate 9 and the substrate 12 by, for example, flip chip bonding. If the bottom surface 8 is formed of a semiconductor substrate such as silicon, an electronic circuit can be formed thereon, and the electronic circuit substrate 12 can be omitted. In the embodiment shown in FIG. 1, a surface emitting laser diode LD is used as a light emitting element, and a photodiode PD is used as a light receiving element. A circular surface emitting laser diode LD is arranged at the center of the substrate 9, and the light receiving elements PD are arranged concentrically around the surface emitting laser diode LD.

FIG. 1B is an enlarged plan view showing a light emitting / receiving section of a substrate 9 on which the light emitting / receiving elements shown by dotted lines in FIG. 1A are mounted. As shown in the figure, a circular light emitting element LD is arranged at the center, and light receiving elements PD1, PD2,... PDn are arranged concentrically around the light emitting element LD. Note that a vertical surface emitting laser can be used as the light emitting element LD used here. This light emitting element L
D and the light receiving element PD can be simultaneously manufactured on a gallium arsenide wafer by a semiconductor manufacturing process. Therefore, since the alignment accuracy between the light emitting element LD and the light receiving element PD is determined by the accuracy of the mask used in the semiconductor manufacturing process, the alignment accuracy can be 1 μm or less,
This can be realized with a high accuracy of 1/100 or less as compared with the positioning accuracy of the light receiving / emitting element of the conventional optical microphone element.

In general, a vertical surface emitting type light emitting element has a characteristic in which a light emission intensity distribution is substantially uniform concentrically. Therefore, the radiated light emitted from the light emitting element LD installed at the center toward the diaphragm 2 at a predetermined angle is concentrically reflected with the same intensity, and the diaphragm 2 is vibrated by receiving the sound wave 7. As a result, the reflection angle changes and the light reaches the light receiving element PD concentrically. Therefore, the vibration displacement of the diaphragm 2 can be detected by detecting a change in the amount of received light of the light receiving elements PD1 to PDn arranged concentrically. As a result, the strength of the incident sound wave 7 can be detected, so that it can be used as an optical microphone element. An electrode 11 is formed for driving the light emitting element LD and the light receiving element PD or detecting the amount of incident light.

Next, a vertical surface emitting laser (hereinafter referred to as VCSEL) which is a light emitting element used in the present invention will be described. FIG. 2 shows the emission intensity distribution of the VCSEL. As shown in the figure, the emission intensity distribution is given as a Gaussian distribution with respect to the inside of the nucleus. The emission intensity distribution P0 (θ) is represented by the equation (1).

(Equation 1)

When the calculation of the light emission distribution coefficient α is performed for a one-dimensional case, it is represented by the following equation (2).

(Equation 2) Then, when this is used to calculate the emission intensity distribution for the designated azimuth, the distribution as shown in FIG. 2 is obtained.

FIG. 3 is a diagram showing a case where the emission intensity distribution is calculated and illustrated in two dimensions. In this case, the two-dimensional emission intensity distribution P0 (θ) is given by equation (3).

(Equation 3)

The distribution calculation coefficients α and β for the θ and ψ directions
It is calculated in the same manner as in. The light emission distribution coefficient α is given by Expression (4), and the light emission distribution coefficient β is given by Expression (5).

(Equation 4)

(Equation 5)

As is clear from the two-dimensional emission intensity distribution obtained in this manner, the intensity distribution of the light emitting element is almost concentrically uniform in the vertical surface emitting laser.
Accordingly, in order to efficiently receive the laser light emission as the displacement (displacement) of the diaphragm 2, it is optimal to arrange the light receiving elements concentrically. Then, the differential signal of the signal detected by the light receiving elements belonging to different concentric circles arranged concentrically becomes a signal giving a change in sound pressure. Here, it is possible to limit or select the dynamic range of the received signal by providing two or more light receiving elements concentrically.

In the optical microphone device shown in FIG. 1, since the diaphragm 2 is fixed at the end of the container 1, the diaphragm 2 is large at the center due to sound pressure and does not vibrate at the end.
In other words, it is considered that the lens vibrates like a lens. However, in the case of such a lens-shaped vibration, a considerable sound pressure is required, and when the size of the diaphragm 2 is large, and in the case of a diaphragm having a diameter of about 3 mm, such a lens-shaped vibration is required. It is not necessary to consider in practice, and it may be considered that the diaphragm 2 is vibrating in parallel with the substrate 9 at the center thereof.

FIG. 4 is a diagram for explaining the principle of modulation of the amount of received light by the optical microphone element of the present invention. Radiation light emitted from the light emitting element LD at a predetermined angle is reflected by the diaphragm 2 so as to have a maximum sensitivity equivalent to a half-half full angle, and is incident on the light receiving element PD. It is assumed that the diaphragm 2 is initially at the position 2c, and vibrates by the amount of deviation δ due to the vibration and moves to the position 2d. Further, the distance between the light receiving / emitting elements LD, PD and the diaphragm 2 is L, and the half angle at half angle from the light emitting element LD is θ. Let A be the diameter between the light receiving portions of the reflected light when the diaphragm 2 is at rest, and B be the diameter of the reach of the reflected light when the diaphragm 2 moves by the amount of deviation δ.

Here, θ, L, δ, A, and B are respectively changed, and the moving width r of the reflected light is calculated by equation (6). The results are shown in Table 1.

(Equation 6)

[0018]

[Table 1]

As described above, the moving width on the circumferential light receiving element is determined by the radiation angle of the light emitting element. An appropriate PD width (greater than 3 microns) is secured by the target sound pressure and the amount of deviation δ of the diaphragm 2. In this case, if A and B are too large, the area occupied by the light-emitting element and the light-receiving element on the gallium arsenide wafer increases, and the number of light-emitting and light-emitting elements that can be taken out from one wafer decreases. In addition, as shown in FIG. 1B, the area of the electrode 11 from the light emitting / receiving element and the pad for the wire bond connected to the electrode 11 are required. It is sufficient that the area of the pad for wire bonding is 100 μm square or less. In the case of flip chip bonding, the pad area may be 50 μm square or less.

The light-receiving elements formed concentrically can be formed as a single concentric light-receiving element, but can also be formed by dividing the light-receiving elements into a plurality of light-receiving elements. Further, as will be described later, at least two concentric circles are required to extract a differential signal from two different concentric light receiving elements, but the number is not limited to two and a plurality of concentric circles can be formed. . Generally, a laser diode used as a vertical surface emitting type light emitting element has a large temperature dependency, and its light emission output changes with time. A change in the amount of light also occurs due to a change in the drive current of the laser diode, or the like. Therefore, if a light emission signal is directly or indirectly input to the light receiving element without taking any measures, the output taken out of the light receiving element changes as it is in accordance with the light quantity change of the laser diode. In such a state, an error occurs due to a temperature dependency and a change in drive current in the output signal from the light receiving element.

When the reflected light signal is taken out by the light receiving element in the optical microphone element according to the present invention, there is a possibility that the light quantity changes due to the temperature dependency of the emitted laser signal, a change in the driving current, and the like. In order to solve this problem, in the present invention, a plurality of light receiving elements are arranged and a difference between signals received by the light receiving elements is extracted. Further, in the present invention, since the plurality of light receiving elements are manufactured in the same manufacturing process, their mutual variations are extremely small, and by taking the difference between them, the canceling error which is a problem can be minimized.

FIG. 5 shows an example of a circuit diagram of an optical microphone device using the optical microphone element of the present invention. Here, VCSEL represents a surface emitting laser diode, and PD1 and PD2 represent light receiving elements such as photodiodes arranged around the VCSEL so as to surround it. These VCSEL and light receiving element PD
1 and PD2 are connected in series between the power supply 20 and the ground 30 via the resistors R3, R1 and R2, respectively, and are configured such that a predetermined drive current flows. The connection point between the resistor R1 and the light receiving element PD1 is connected to the inverting input terminal of the differential amplifier IC1. The connection point between the resistor R2 and the light receiving element PD2 is connected to a non-inverting input terminal. Differential amplifier I
The output of C1 is taken out by a buffer differential amplifier IC2 to obtain an output 40. The power supply 20 and the ground 30
Is connected to a bypass capacitor C11 for canceling a noise signal.

The incident light emitted from the VCSEL is concentrically reflected by the diaphragm 2 and is input to the light receiving elements PD1 and PD2, respectively. Note that the diaphragm 2 is disposed substantially parallel to the substrate 9 and is disposed very close to the substrate 9. In addition, since the amount of displacement (movement) of the diaphragm 2 is about 1 micron, it can be considered that the diaphragm 2 almost moves in parallel with the substrate 9. In the example shown in FIG. 5, the light receiving element PD1 arranged concentrically inside is connected to the inverting input terminal, and the light receiving element PD2 arranged outside is connected to the non-inverting input terminal. There is no need to connect to the optimum terminal depending on the actual circuit design situation.

The output current iout of the differential amplifier IC1
And iout = i1- between the differential input currents i1 and i2.
There is a relationship of i2. Here, when there is a change in δi1 and δi2 independently of the differential inputs i1 and i2, iout =
((I1 + δi1)-(i2 + δi2)). Here, when the photodiodes PD1 and PD2 change at the same time, the change amounts δi1 and δi2 are δi1 = δi2 and iout = i1-i2. Therefore, temporarily, VCSE
When a change in light emission occurs due to a temperature change or a drive current change in L, the change is simultaneously transmitted to the light receiving elements PD1 and PD2, and is canceled, so that the differential output iout
Does not show a change in the VCSEL. When the currents are independent changes and the magnitudes of the currents are different, iout = [(i1
−i2) + (δi1−δi2)], and the difference appears as a change in output. This means that the reflected optical signal changes due to a change, for example, vibration or displacement of the diaphragm, and consequently, the reflected light received concentrically changes, and there is a separate input change in each light receiving element.

FIG. 6 is a circuit diagram showing the configuration of another optical microphone device according to the present invention. In this embodiment, the input currents i1 and i2 are added to the adder circuit IC via the resistor R, respectively.
3 and the subtraction circuit IC4. Then, the output current i1 + i2 of the addition circuit IC3 and the output current i1-i2 of the subtraction circuit IC4 are input to the circuit 50. An output that is inversely proportional to the output current i1 + i2 is obtained from the output of the circuit 50. The output of the circuit 50 is taken out as (i1−i2) / (i1 + i2) to the output 40 via the arithmetic unit IC5.
Thus, the division circuit is constituted by the circuit 50 and the arithmetic unit IC5. If such a circuit configuration is adopted, a more stable output can be obtained as compared with the circuit configuration of FIG. 5 when both the input currents i1 and i2 increase or decrease.

[0026]

As described above in detail, according to the present invention, since the light emitting element and the light receiving element can be formed simultaneously on the same substrate, the mutual positional accuracy can be reduced to 1 micron or less. There is a feature that extremely high accuracy of 1/100 or less can be achieved as compared with the positional accuracy of the light receiving / emitting element. In addition, a vertical surface-emitting light-emitting element whose emission intensity distribution is almost concentrically arranged and a light-receiving element arranged concentrically around it are adopted, so that outputs from multiple light-receiving elements are used as differential signals. The difference can be detected and output. Therefore, as compared with a case where an output signal is formed using a single light receiving element, the influence of a change in temperature, a change in drive current, or the like of the light emitting element can be reduced, and a stable signal output can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a basic principle of an optical microphone element of the present invention.

FIG. 2 is a diagram showing an emission intensity distribution of a vertical surface emitting laser used in the present invention.

FIG. 3 is a diagram showing a two-dimensional emission intensity distribution of a light-emitting element used in the present invention.

FIG. 4 is a diagram for explaining the principle of modulating the amount of received light of the optical microphone element according to the present invention.

FIG. 5 is a diagram showing a circuit configuration of an optical microphone device using the optical microphone element of the present invention.

FIG. 6 is a diagram showing another circuit configuration of an optical microphone device using the optical microphone element of the present invention.

FIG. 7 is a diagram showing a basic structure of a conventional optical microphone element.

[Explanation of symbols]

 LD light emitting element PD light receiving element 2 diaphragm 9 substrate 11 electrode VCSEL vertical surface emitting laser IC1, IC2 differential amplifier IC3 addition circuit IC4 subtraction circuit 50, IC5 division circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Hattori 1-14-6 Dogenzaka, Shibuya-ku, Tokyo Inside Kenwood Corporation (72) Inventor Hiroshi Miyazawa 1-16-16 Dogenzaka, Shibuya-ku, Tokyo Kenwood Corporation (72) Inventor Democracy Takeda 1-14-6 Dogenzaka, Shibuya-ku, Tokyo F-term (reference) in Kenwood Corporation 5D021 DD04

Claims (8)

[Claims] 1. A light-emitting element and a light-receiving element are arranged on the same substrate, light is emitted from the light-emitting element to a diaphragm installed at a position facing the substrate, and reflected light from the diaphragm is reflected by the diaphragm. In an optical microphone element that detects a displacement of the diaphragm by receiving light with a light receiving element, a vertical surface emission type light emitting element in which a light emission intensity distribution is substantially uniform concentrically is disposed at the center of the substrate as the light emitting element, An optical microphone element, wherein the light receiving element is arranged concentrically so as to surround the light emitting element. 2. The optical microphone element according to claim 1, wherein said light receiving element is composed of a plurality of elements. 3. The optical microphone element according to claim 1, wherein a plurality of said concentric circles are formed. 4. The optical microphone element according to claim 1, wherein the light emitting element and the light receiving element are formed on the substrate at the same time. 5. The optical microphone device according to claim 1, wherein the substrate is a gallium arsenide wafer. 6. The optical microphone element according to claim 1, wherein the diaphragm is disposed substantially in parallel with and close to the substrate. 7. A vertical surface-emitting light emitting element having a light emission intensity distribution substantially concentrically arranged at the center of a substrate, and a light receiving element arranged concentrically so as to surround the light emitting element.
An optical microphone element that radiates light from the light emitting element to a diaphragm installed at a position facing the substrate and receives reflected light from the diaphragm with the light receiving element, and a light receiving element belonging to a different concentric circle is detected. An optical microphone device, comprising: a differential detector that detects a differential signal of a signal; and detecting a displacement of the diaphragm from an output of the differential detector. 8. The optical microphone device according to claim 7, wherein the diaphragm is installed substantially in parallel with and close to the substrate.