Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-02-23
2003-11-25
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S043010, C372S046012, C257S080000, C257S084000, C257S432000, C362S234000, C362S259000, C362S235000, C362S232000, C359S387000, C359S613000, C359S656000, C359S019000, C359S020000
Reexamination Certificate
active
06654399
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor light projection apparatus which comprises an optical system for projecting lights emitted from a plurality of semiconductor light emitting devices onto a light projected area, and a distance measurement apparatus which comprises the semiconductor light projection apparatus and receives reflected light from an object to detect a distance from the object.
2. Description of the Related Art
A distance measurement apparatus has been developed, which projects light to a detected area from a semiconductor light projection apparatus built therein, constituted by semiconductor light emitting devices such as a semiconductor laser device and a light emitting diode, and receives the reflected light to measure a distance from a measured object in the detected area based on a delay time.
The distance measurement apparatus is used for a system which measures a distance between a certain automobile loading this apparatus and another automobile and gives an alarm when the distance between the automobiles becomes smaller than a predetermined value, and for a system which measures a distance from the certain automobile to another automobile or an obstacle during parking and gives the alarm when the distance therebetween is smaller than a predetermined value. The distance measurement apparatus is used also for a system which gives the alarm when light is intercepted at a range within a predetermined distance in a light projected area.
Furthermore, a system is devised, which controls a running of the automobile and facilitates the safe and proper running of the automobile by utilizing these systems.
In this case, considering also running conditions on a superhighway, the inter-automobile distance measurement system is required to be capable of measuring the distance between the automobile and another automobile running in front, which ranges from about 10 m to about 100 m or more, for example, about 120 m. To cope with this requirement, the semiconductor laser devices must be driven so as to perform laser oscillation at pulses of several tens to several hundreds nsec and emit light exhibiting power of about 20 W to about 80 W in total. In general, one semiconductor laser device can emit light exhibiting power of about 10 W to about 20 W when a peak current is set to about 20A. Accordingly, in order to meet above described requirement, it is conceived that one semiconductor laser device is driven with a large current or alternatively a plurality of semiconductor laser devices are simultaneously driven and light outputs from them are synthesized.
Since a life time of the semiconductor laser device lowers in reverse proportion to a magnitude of current, to drive one semiconductor laser device with a large current is not said to be a good condition for the device. Accordingly, a method which allow a plurality of semiconductor laser devices to perform laser oscillations and collect lights emitted from them to achieve a large amount of lights will be available.
As this method, a method which allows the semiconductor laser devices to emit lights by driving the semiconductor laser devices individually, each being coupled in parallel to a light source, and collects these lights is conceived. However, when this method is adopted, driving currents of the number equal to that of the semiconductor laser devices coupled in parallel to the light source must be made to flow therethrough, so that a quantity of power consumption becomes large and sharpness of waveforms of pulses is lost. Accordingly, this method is not very desirable in terms of driving conditions.
On the other hand, to solve such drawbacks, there have been methods, which are disclosed in Japanese Patent Applications Laid-Open Nos. 5-41561, 6-282807 and 7-307520. In these methods, a plurality of semiconductor laser devices are laminated so as to be integrated with each other and they are driven in the state where they are in series coupled to each other, and a plurality of light emission points as a light source are arranged at intervals of about 100 &mgr;m. The lights from the light emission points are collected by a collection lens and converted to a parallel light, and the parallel light is projected onto a projected area.
In this case, even when the interval between the light emission points in the light source is 100 &mgr;m, intervals between spots of laser beams from the semiconductor laser devices spread in proportion to a projection distance. As shown in
FIG. 25
, for example, a semiconductor laser apparatus
1
constituted by stacking three semiconductor laser devices
1
a
to
1
c
is disposed at a focal position of a collection lens
2
as an optical system, and the semiconductor laser apparatus
1
is allowed to emit light. Laser beams emitted from light emitting points La to Lc of the corresponding laser devices
1
a
to
1
c
are collected after passing through the collection lens
2
, and converted to parallel lights Sa to Sc.
At this time, when a diameter of each spot of the parallel lights Sa to Sc is D, a shift equal to that the interval of the arrangement of the laser devices
1
a
to
1
c
is created at a position distant from the devices
1
a
to
1
c
by a focal length f. Since a spot diameter becomes large to some degree practically, such shift is not a problem, and a state that the lights are collected is kept. When such parallel lights Sa to Sc travel by a distance to be objected, for example, by about several ten meters, the above described shift is widened to a degree that cannot be neglected. Thus, effects that the detection distance is lengthened is entirely lost by collecting the lights.
This state is illustrated in FIG.
26
. Specifically, if it is intended to lengthen the detection distance X, lights are projected so as to overlap spots when the detection distance is about X
1
. When the detection distance is lengthened to about X
2
larger than X
1
, not only a reduction of a quantity of light is brought about, but also formation of a dark area B where light is not projected is created by enlarging a distance between the spots. In this case, a measured object positioned in the dark area B accidentally in measuring the distance is not measured, so that the measured object is recognized as that no object exists. A disadvantage that a precise measurement can not be performed is brought about.
A degree of the spread of the interval between the spots is in proportion to a distance from the collection lens
2
, and as the distance from the collection lens
2
becomes larger, the spread of the interval between the spots becomes larger simply. Thus, a reduction of a quantity of light and occurrence of the dark area becomes remarkable, and this is a disadvantageous condition when it is intended to receive much reflection light from the object.
The reduction of a quantity of the reflection light is estimated in the following manner. When the distance between the light emission points La to Lc is assumed to be 100 &mgr;m, a spread angle &thgr; of the light source with respect to the focal length f of the collection lens
2
is expressed by the following formula.
&thgr;=arctan (0.1
/f
)
If the focal length f is 22 mm, the spread angle &thgr; becomes 0.26°. In a position apart from the position of the collection lens
2
by 22 mm that is 1000 times as long as the focal length f, a distance between centers of the spots is about 10 cm. Since the position of the center of the spot is sure to be shifted even when the spot diameter D is considered, a quantity of light per unit area reduces owing to the spread of light in the projected area. Accordingly, a quantity of light is surely reduced.
Therefore, when it is intended to set a distance of 100 m or more as a range of a measured distance, a quantity of light significantly and also a dark area occurs. It is necessary to take a countermeasure to increase the quantity of light by driving the semiconductor laser with large current. In this case, lowering of a life time of th
Abe Katsunori
Atsumi Kinya
Kimura Yuji
Denso Corporation
Flores-Ruiz Delma R.
Ip Paul
Posz & Bethards, PLC
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