JPH0653615A - Light sensing device and semiconductor laser for light sensing device - Google Patents

Abstract

PURPOSE:To obtain a light sensing device which is compact and safe for eyes by using semiconductor laser as a light source and by making the wavelength longer than a specified value. CONSTITUTION:Semiconductor laser 13 driven by a laser driver 12 repeats the specified light emitting. Then, the light coming from a light source is discharged forward in the air through an optical transmission system 14. The laser is irradiated to an object. The dispersed or reflected light from hear is caught by an optical reception system 15. In a light detector 16, such light is converted into an electric signal, and the information signal is transmitted to a signal processing circuit 17. The signal processing circuit 17 provides the measured results of the time during transmission and reception of laser, or the spectrum of the object measured. A data processing section 18 converts actual data transmitted from the signal processing circuit 17 into measured results of distribution by considering the correlation with statistical processing or measured time. The wavelength of a semiconductor laser 13 is specified more than 1.4mum, thereby two conditions of safety security for laser beams and excellent optical transmissivity in the air become compatible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sensing device for irradiating a target with light and obtaining information on the target from the reflected or scattered light, and a semiconductor laser for a light source thereof.

[0002]

2. Description of the Related Art Conventionally, as this type of optical sensing device, a light wave distance measuring device for measuring a distance to a target has been known. It is also known as a laser radar in the field of environmental measurement such as meteorology and space, which measures suspended matter in the atmosphere. These are described in detail in Chapter 27 of the Laser Handbook (Laser Society, edited by Ohmsha), so please refer to them. However, since such an optical sensing device is large and its use is limited to surveying and meteorology,
It was still far from our daily life. However, due to the recent seriousness of environmental problems, it has gradually become known as a meteorological observation network and for installing satellites. Further, for such a purpose, a compact and portable device is strongly desired. Furthermore, recently, an inter-vehicle distance sensor of an automobile as an optical sensing device based on the same principle has been put into practical use for the purpose of preventing accidents.

In the development of such applications, Japanese Patent Application Laid-Open No. 56-56
-76074 has been filed for application as an on-vehicle obstacle detection device using a light emitting element having a wavelength of 1.38 μm. The reason for this is that there is sunlight that reaches the ground as a noise source of the measurement light, and in order to prevent this from entering the measurement system, wavelengths with low solar energy density as described in line 5 on page 6 of the specification are used. It is what you select and use.

[0004]

However, at the same time, as described in JP-A-56-76074, page 6, line 12, the transmittance in the atmosphere is poor and the wavelength is low in the propagation efficiency. Therefore, this wavelength is disadvantageous when the transmitted light is pulsed or in order to improve the detection capability with a weak output, and it can be used only for a sensor having a short reach.

Further, in the above-mentioned sensing device, since a laser is used as a light source, it is necessary to secure safety for a human body as the portability increases. In particular, in a vehicle-mounted device that projects the light parallel to the ground, the safety for the human body must be taken into consideration until it is sufficient. In the above-mentioned conventional example, such consideration is not made at all. Furthermore, in order to widely disseminate such a sensing device, it is necessary to reduce the size of the device itself and increase portability, and to realize a sensing device that is large enough to be mounted on a vehicle and has no design problem.

The present invention has been made for the purpose of improving the safety and reducing the size of the apparatus.

[0007]

A light sensing device according to the present invention emits light to the front, and captures reflected or scattered light from an object in front of the light by a light receiving element, whereby the light is absorbed between the object and the light receiving element. Of the distance, or
An optical sensing device for measuring a reflected or scattered object, characterized in that a semiconductor laser having a light source wavelength of 1.4 μm or more is used. Also, the light source is 1.4μ
Another feature is that the semiconductor laser is an InGaAsP-based semiconductor laser of m to 1.7 μm. Further, the light source is a quantum well type semiconductor laser having an oscillation region width of 200 μm or more.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration of an optical sensing device according to the present invention. First, the semiconductor laser 3 driven by the laser driver 2 repeats predetermined light emission. Next, the light emitted from the light source is emitted to the front air through the transmission optical system 4. The laser hits an object to be measured (not shown), and scattered or reflected light from the object is captured by the receiving optical system 5. The photodetector 6 converts this into an electric signal,
The received information signal is passed to the signal processing circuit 7. The signal processing circuit 7 measures the time from the laser emission to the laser reception, or outputs the result of spectroscopic measurement of the measured object. The data processing unit 8 statistically processes the raw data from the signal processing circuit 7 or correlates the measurement time with the raw data, converts the raw data into a distribution measurement result, and collects and discharges the raw data in a form that is easy for an observer to handle. As its name implies, the system control of No. 1 manages, controls, and issues orders for the entire flow.

In this structure, a normal laser is 100 ns.
Transmitted as the following pulses and remotely measuring various information such as distant objects, states, distances, directions, sizes, shapes, velocities, densities, compositions, etc. by the powerful output and directivity of the laser light. Is. In the present invention, the wavelength of the semiconductor laser 3 is set to 1.4 μm or more, which is a major feature, because the safety of the laser light is ensured and the atmospheric light transmittance is good.

FIG. 2 is a drawing 13 of JIS C6802-1991, "A of Class 1 Visible and Near Infrared Laser Products".
It is a reprint of "EL (exposure emission limit)", but it can be seen that near infrared light, which has a longer wavelength than visible light, is safer. For example, visible ns from 400 nm to 700 nm
At the order of emission duration, the emission energy is 2 ×
The upper limit is 10 ^-7 J, but the wavelength is from 1400 nm to 10 ⁵
In nm, it is 8 × 10 ⁻⁵ J, which is allowed up to 400 times.
Similarly, when this is obtained with the 830 nm laser which is the most easily available and has an output, the upper limit of the emission energy is 3.6 × 10 ^−7.
If it is changed to 0 nm or more, the output can be increased 200 times or more. That is, when the wavelength of the semiconductor laser is set to 1400 nm or more, even in the class 1 laser device which is said to be absolutely safe for the human body, the detection ability can be greatly improved.

FIG. 3 shows the wavelength of light and the transmittance of the eyeball and the absorption rate of the fundus of the eye. Visible light and near-infrared light pass through the eyeball well, and when the wavelength is 1.4 μm or more, almost no light enters the eye. However, it can be seen that energy is absorbed in the corneal surface layer. Further, it is said that the visible light which passes through the eyeball and focuses on the retina has a light intensity per unit area of 10,000 times on the cornea. This is the reason why a large difference in safety with respect to the wavelength of the laser appears.

On the other hand, FIG. 4 shows the transmittance of the atmosphere with respect to the wavelength at a distance of 1.6 km (Laser Handbook, FIG. 27.2 is reproduced). The transmittance is improved from the wavelength of 1.4 μm to 1.8 μm. It can be seen that the peak reaches up to 80%. In addition, Japanese Patent Laid-Open No. 56-760
Similarly, the transmittance of light in the atmosphere with respect to the propagation distance of 300 m in FIG. 3B of 74 is also good at wavelengths of 1.4 μm to 1.8 μm. Therefore, it is easily understood that if the wavelength of the semiconductor laser is set within the range of 1.4 to 1.8 μm, it is possible to realize a remote sensing device with high eye safety and long reach. Needless to say, for objects that can be used with a finite reach, even more safety can be ensured if the light emission peak is adjusted to this distance and output is suppressed. It should be noted that water and carbon dioxide are absorbed in places where the atmospheric transmittance is poor.
Next, a light source for achieving this object of the present invention will be described.

FIG. 5 shows an example of a gain waveguide type stripe structure of an InGaAsP laser having a wavelength of 1 μm band. Since it is basically the same as the case of the AlGaAs laser which has been most practically used, please refer to that manual as well. The basic structure is such that an InGaAsP active layer 53 is sandwiched between p-type and n-type InP clad layers 55 and 52 on an InP substrate 51, and a p-InGaAsP cap for facilitating the formation of an ohmic electrode is stacked thereon. Layer 56
Pile up. As an ohmic electrode, Au is provided on the p-side 58.
Au-Ge-Ni is often used for the -Zn and n-side 59. In addition, SiO ₂ 5
7 is used. In the InGaAsP laser having a wavelength of 1.4 μm or more, when the third InP clad layer is grown by liquid phase,
Since the active layer is melted back and the interface becomes uneven, in order to avoid this, an InGaAsP anti-meltback 54 is attached, or the third layer is formed at a low temperature and under a high degree of supercooling.
The layer p-InP is grown. In addition, when the vapor phase growth method (MO-CVD etc.) other than the liquid layer growth or MBE is used,
Since there is no meltback phenomenon, the AM layer is unnecessary. The active layer thickness may be about 0.1 μm to 0.2 μm, and the stripe width may be about 10 μm. Regarding the wavelength, In _1-x Ga _x A
s _y P _1-y activity composition ratio of the layer x, by changing the y, 1.
11 μm to 1.67 μm are obtained. The optimum wavelength for the present invention is around 1.55 μm from the two points of manufacturing the laser and practically using the sensing device.

FIG. 6 shows a typical structure of a refractive index guided stripe laser having a wavelength band of 1 μm. In the refractive index guided type, a waveguide having a refractive index distribution is formed in a localized gain region, which serves as a waveguide region and determines a horizontal transverse mode. The waveguide width W is about 2 μm. From the relationship with the current injection stripe width S, the rib waveguide type of S> W and S = W
BH (embedded) type can be roughly divided into two. The figure shows the former type. Generally, in the refractive index guided stripe structure, the horizontal and transverse modes are stable, and the longitudinal modes are easily unified. In addition, it is also characterized in that optical damage is unlikely to occur and operation at high light output density is possible.

The InGaAsP-based laser is popular mainly for optical communication, and a laser having a CW output of several 10 mW and a pulse of several 100 mW is obtained.

FIG. 7 shows a new type laser having an active layer having a multiple quantum well structure. The structure has many points in common with the above-mentioned gain waveguide type. That is, n on the n-InP substrate 71
A type InP clad layer 72 is grown, and an active layer 73In _1-x Ga _x As _y P _1-y having a quantum well structure is stacked on the clad layer 72, and is sandwiched by a p-InP clad layer 74 to form a sandwich structure. At this time, MOCVD or MBE method is used for forming the quantum wells and the like, and the composition x is 0.76.
Alternatively, fix it at 0.65. For the y composition, y
The upper limit of is taken from 0.4 to 0.9, and the bottom of y is shaken to be 0.1. Further, at this time, the well width is set to 100 angstroms or less and the barrier width is set to about 70 angstroms. After forming the active layer in this way, a cap layer 75p-In for obtaining ohmic contact is formed.
After growing GaAsP and insulating unnecessary portions with SiO ₂ 76, the stripe width of the p-electrode 77 is broadened to 200 μm or more. The resonator length is 400 to 500 μm.
With this, the oscillation wavelength is 1.4 μm to 1.6 μm.
m, a giant pulse semiconductor laser with an output of 10 W and a pulse width of 100 ns or less can be obtained by increasing the area of the laser oscillation region. This is a one-digit to two-digit increase in output, so it is extremely effective in improving the remote sensing capability of measuring the returned light by scattering the light. Further, as mentioned above, the wavelength range has no effect on the eyes, so that the safety is extremely high. The quantum well structure laser has several features. First
Is that low threshold currents are possible. This is convenient for lowering the power of the device and making it battery-operated. The second feature is that the oscillation wavelength can be changed only by changing the width of the quantum well. This means that the parameter for controlling the wavelength can be changed by changing the material composition as well as by changing the width of the well, so that the degree of freedom is extremely high. The third feature is that the temperature dependence of the threshold current is smaller than that of the double hetero laser. This is very convenient in practice, and a device having little temperature dependence can be realized. The fourth characteristic is that the high speed modulation characteristic is superior to that of the double hetero laser. This is also an important factor for an optical sensing device that transmits light in pulses. By making it possible to use the quantum well laser in this manner, a number of good results are obtained for practical machines.

Other than the above-mentioned InGaAsP system, there is a possibility of realizing a semiconductor laser having a wavelength of 1.4 μm or more, InGaA near 2 μm and in the range of 3 to 4 μm.
sSb system, InAsPSb system in the 1-6 μm band, 4-8
PbSSe system in the μm band, PbSn in the 6 to 28 μm band
There are Te type and PbSnSe type. However, in general, when the oscillation wavelength becomes long, an alloy having a small band-to-band energy is used, so that electrons and holes are easily excited by thermal energy and a pn junction is not formed. Further, the higher the temperature, the shorter the life of these charges. Therefore, a cooler is required to prevent this. Therefore, the miniaturization of the device, which is another object of the present invention, may be conflicting. Caution must be taken.

Next, the light receiving element paired with the light emitting element will be briefly described. FIG. 8 shows a PIN photodiode having a wavelength of 1 μm band using InGaAs as an i-layer. Since the photosensitivity is sufficiently high up to around 1 to 1.65 μm, it can be used as a light receiving element in the entire wavelength range of 1 μm band. The light is back-illuminated and is introduced into the InGaAs layer through a transparent InP substrate with a wavelength of 0.92 μm or more. If the InGaAs layer is thick enough, light will not reach the InGaAs surface.
The surface recombination there does not affect the quantum efficiency. The thickness of the i layer is 2 to 3 μm, and the carrier concentration is 10 ¹⁴ to
It is 10 ¹⁶ cm ⁻³ , and the response speed has a frequency characteristic of CR time constant limitation. When the light receiving diameter is 100 μm, a rising and falling time of about 0.1 ns can be obtained. Dark current is G
2 digits smaller than e. The PIN photodiode using Ge is also in the 1 μm band, but the quantum efficiency sharply drops at 1.5 μm or more, so it is not suitable for the present sensing device. In addition, GaSb, AlGaAsSb,
PIN of many binary, ternary and quaternary crystals such as InGaSb
There is a photodiode. In the long wavelength band above 2 μm, HgCdTe may be suitable. Further, there is an avalanche diode which has a structure different from that of the PIN photodiode and which can multiply the photocurrent generated in the semiconductor.
This may be used when high sensitivity and high speed response are required.

[0019]

As described above, according to the present invention, since the semiconductor laser is used as the light source and the wavelength thereof is set to 1.4 μm or more, it is possible to provide a remote sensing device which is small and has high eye safety. . In the InGaAsP-based semiconductor laser having a quantum well structure incorporated in the active layer, the wavelength is about 1.5 μm, the duration is several tens of nanometers.
s, peak value: several tens of watts of pulsed laser could be realized, and a small device with high sensing ability could be realized. As a result, as a measuring device to which the present invention is applied, various highly portable portable weather laser radars, inter-vehicle distance sensors for vehicles useful for preventing accidents, obstacle sensors, remote gas for the purpose of monitoring leakage of dangerous gas Various applications such as sensors can be developed. Also, since it is highly eye-safe, it can be used safely even in urban areas.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical sensing device of the present invention.

Figure 2: Class 1 visible and near infrared laser products AEL
The standard diagram showing.

FIG. 3 is a measurement diagram showing a wavelength of light, eyeball transmittance, and fundus absorptivity.

FIG. 4 is an observation diagram showing transmittance in the atmosphere with respect to wavelength.

FIG. 5 is a schematic configuration diagram of a gain waveguide type stripe structure of an InGaAsP laser.

FIG. 6 is a configuration diagram of a refractive index guided stripe structure of an InGaAsP laser.

FIG. 7 is a schematic configuration diagram of an InGaAsP multiple quantum well laser according to the present invention.

FIG. 8 is a configuration diagram of an InGaAs PIN photodiode.

[Explanation of symbols]

 11 system control 12 laser driver 13 semiconductor laser 14 transmission optical system 15 reception optical system 16 photodetector 17 signal processing circuit 18 data processing unit 51 n-InP substrate 52 n-InP 53 InGaAsP active layer 54 InGaAsP AM layer 55 p-InP 56 p-InGaAsP 57 SiO2 58 p-electrode 59 n-electrode 71 n-InP substrate 72 n-InP 73 InGaAsP active layer 74 p-InP 75 p-InGaAsP 76 SiO2 77 p-electrode 78 n-electrode

Claims (3)

[Claims] 1. A light-emitting element emits light in the forward direction and captures reflected or scattered light from an object in front of it by a light-receiving element to calculate the distance between the object and the light-receiving element, or An optical sensing device for measurement, wherein a semiconductor laser having a light source wavelength of 1.4 μm or more is used. 2. The light source has a wavelength of 1.4 μm to 1.7 μm.
2. The optical sensing device according to claim 1, which is an InGaAsP-based semiconductor laser of m. 3. The semiconductor laser for a photo-sensing device according to claim 2, wherein the oscillation region width is 200 μm or more, and the active region has a quantum well structure.