JPH05142348A - Laser Doppler speedometer - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a laser Doppler velocimeter that does not require alignment adjustment of each optical component and is excellent in vibration resistance. [Structure] Laser diode 2, photodiode 3,
Each of the optical waveguides 4 and 5 and the 3 dB coupler 7 is integrated and integrally formed on the same semiconductor substrate 1. The laser diode 2 is arranged at one end of the optical waveguide 4 and emits a laser beam 10 to the moving object 9 and a laser beam 11 to the optical waveguide 4. The photodiode 3 is an optical waveguide 5
The reflected return light 1 which is arranged at one end of the
The combined light of 2 and the laser light 11 incident on the optical waveguide 5 from the optical waveguide 4 via the 3 dB coupler 7 is received.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser Doppler velocimeter for irradiating a moving object with laser light and measuring the Doppler shift of the reflected light by using an interferometer.

[0002]

2. Description of the Related Art Conventionally, a laser Doppler speedometer (hereinafter referred to as a speedometer) utilizing interference of light has been known as a device for measuring the moving speed of an object. The measurement principle of this speedometer is that when a moving object is irradiated with laser light, the frequency of the reflected light undergoes the Doppler effect and shifts from the original frequency f _O to the frequency f _O + f _D , so an interferometer is used. Then, the frequency f _D is measured, and the moving speed V of the moving object is obtained from this value.

As an example of this, FIG. 2 shows an outline of a device configuration of a speedometer. In FIG. 2, the laser light emitted from the laser 21 reaches the beam splitter 22, where the reference light (frequency f _O ) having no frequency change and the moving object 2 are emitted.
It is branched to the emitted light (frequency f _O ) emitted toward 0. The branched reference light is totally reflected in order by the total reflection mirrors 23 and 24, passes through the beam splitter 25, and enters the light receiver 26. On the other hand, the emitted light that has passed through the beam splitters 22 and 25 and is emitted toward the moving object 20 is reflected by the moving object 20 and undergoes the Doppler effect, and this reflected return light (frequency f _O + f _D ) is again generated. It reaches the beam splitter 25, changes its direction, and then enters the light receiver 26. In this way, the combined light of the reference light and the reflected return light is
The frequency of the output signal which is incident on the photodetector 26 and is optically heterodyne detected is equal to the beat frequency of the reference light and the reflected return light, that is, the Doppler frequency f _D ,
The Doppler frequency f _D is measured by the measuring device 27.
The moving speed V of the moving object 20 is obtained from this numerical value.

Although a Mach-Zehnder interferometer is shown in FIG. 2, various configurations such as a Michelson-Morley interferometer are proposed in addition to this.

[0005]

As described above, the conventional speedometer has the beam splitters 22 and 25 and the total reflection mirror 2.
Optical components such as 3, 24, etc., which are separately formed, are used, and in actual measurement, it is premised that these optical components are positioned extremely precisely.

However, the alignment adjustment of each optical component, which is performed as a preparation for this measurement, requires extremely high accuracy and is a very laborious task. Further, even if one of the optical components is displaced or angularly displaced by an external factor such as vibration, the reference light and the reflected return light do not interfere with each other, which makes measurement impossible. was there.

The present invention has been made to solve the above-mentioned problems, and does not require alignment adjustment of each optical component.
Moreover, it is an object of the present invention to provide a laser Doppler velocimeter having excellent vibration resistance.

[0008]

A laser Doppler velocimeter according to the present invention includes a semiconductor substrate, first and second optical waveguides formed on the semiconductor substrate, and an optical coupling with the first optical waveguide. A semiconductor laser, a light receiving element optically coupled to the second optical waveguide, and an optical coupling means for making light propagating through the first optical waveguide and formed on the semiconductor substrate into the second optical waveguide. Equipped with.

The semiconductor laser is formed by laminating a predetermined semiconductor material on a semiconductor substrate at one end of the first optical waveguide and is formed integrally with the semiconductor substrate. Laser light is emitted from the semiconductor laser toward a moving object. And the laser light is emitted to the first optical waveguide.

Further, the light receiving element is formed by laminating a predetermined semiconductor material on a semiconductor substrate at one end of the second optical waveguide and is integrally formed with the semiconductor substrate. The combined light of the laser light that enters the second optical waveguide from the waveguide through the optical coupling means and the reflected return light from the moving object that propagates through the second optical waveguide is received.

[0011]

Operation One of the laser beams emitted from the semiconductor laser is emitted toward the moving object, and the other is emitted directly into the first optical waveguide. The laser light emitted toward the moving object is reflected by the moving object, and the reflected return light enters the second optical waveguide. On the other hand, the laser light emitted directly into the first optical waveguide propagates through the first optical waveguide and enters the second optical waveguide through the optical coupling means as reference light having no frequency change. In the second optical waveguide, the reference light and the reflected return light described above are combined, and the combined light is received by the light receiving element.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

The structure of the speedometer according to this embodiment is shown in FIG. The speedometer includes a laser diode (hereinafter, referred to as LD) 2 as a semiconductor laser, a photodiode (hereinafter, P).
D) 3 and optical waveguides 4, 5 and the like are integrally formed on the semiconductor substrate 1, and a measuring device 6 for measuring an output signal optically heterodyne-detected by the PD 3 is provided.

An LD 2 is formed at one end of one of the optical waveguides 4 so as to be located on the same optical axis as the optical waveguide 4. The LD 2 is moved from the emitting portion 2a on one end face to the moving object 9a. At the same time as emitting the laser beam 10 toward the laser beam 1, the laser beam 1 is directly introduced into the optical waveguide 4 from the emitting portion 2b of the end face on the opposite side.
1 is emitted. Further, the other end of the optical waveguide 4 is provided with an AR coat 8 for preventing the reflection of light on this surface. Further, the substantially central portion of the optical waveguide 4 is curved so as to be close to the optical waveguide 5, and a 3 dB coupler 7 as an optical coupling means is provided.
Is formed.

Further, one end of the other optical waveguide 5 is provided with a light receiving surface 5a for guiding the reflected return light 12 from the moving object 9 to the inside, and the other end is provided with this optical waveguide 3. The PD 3 is formed so as to be located on the same optical axis line.

The LD 2, PD 3, optical waveguides 4, 5 and 3 dB coupler 7 are formed by a conventional semiconductor process.
Although it is formed integrally on the semiconductor substrate 1, the LD
In order to optically couple the active layer of PD2 and the light receiving layer of PD3 with the corresponding optical waveguides 4, 5, the active layer of LD2, PD3
It is preferable that the light receiving layer and the optical waveguides 4 and 5 are simultaneously formed to have the same height.

Next, the measuring mechanism of the speedometer having the above structure will be described.

[0018] First, the emission part 2a of LD2, and at the same time to the mobile object 9 moves at a moving speed V laser beam 10 (frequency f _O) is emitted, the light guide 4 from the emitting portion 2b on the opposite side laser beam 11 (frequency f _O) is emitted within.

Laser light 1 emitted toward a moving object 9
0 is reflected by the moving object 9 and is returned to the semiconductor substrate 1 side in a state where the frequency is shifted due to the Doppler effect at this time. A part of the reflected return light (frequency f _O + f _D ) 12 enters the optical waveguide 5 from the light receiving surface 5 a formed on the end surface of the semiconductor substrate 1.

On the other hand, the laser light 11 emitted directly into the optical waveguide 4 is the reference light (frequency f _O ) which is not changed in frequency.
Propagates through the optical waveguide 4 as a part of the 3 dB coupler 7
It is incident on the optical waveguide 5 via. The laser light 11 that has entered the optical waveguide 5 interferes with the above-described reflected return light 12 that propagates through the optical waveguide 5, and this combined light enters the PD 3. PD
The output from 3 is a beat output equal to the frequency difference f _D between the laser light 11 as the reference light and the reflected return light 12 that has undergone the Doppler effect, and this output is measured by the measuring instrument 6.

The material of the semiconductor substrate 1 shown in this embodiment is
The material is not particularly limited as long as it is a material that has a good matching with the semiconductor material forming the semiconductor laser, the photodiode, the optical waveguide, etc. in addition to InP or GaAs.
In addition, the emitting portion 2a of the LD 2 and the light receiving surface 5a of the optical waveguide 5
May be provided with a guide member such as an optical fiber for guiding the laser light 10 and the reflected return light 12, respectively.

[0022]

As described above, in the laser Doppler velocimeter according to the present invention, the semiconductor laser, the light receiving element, the first and second optical waveguides, and the optical coupling portion are integrated on the same semiconductor substrate. Formed integrally, from the semiconductor laser,
The laser light is emitted to the moving object and is emitted to the first optical waveguide, and in the light receiving element, the reflected return light from the moving object propagating in the second optical waveguide and the second light are transmitted through the optical coupling means. Since the combined light with the laser light incident on the optical waveguide is received, it is possible to configure an integrated laser Doppler velocimeter as a whole. Therefore, it is not necessary to adjust the alignment of each optical component such as a semiconductor laser and a beam splitter as in the conventional case, and since it is an integrated type, it is also excellent in vibration resistance, and it is also possible to measure the speed of a moving object in a vibrating environment. Become.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the structure of a laser Doppler velocimeter according to the present invention.

FIG. 2 is a schematic configuration diagram showing a configuration of a conventional laser Doppler speedometer.

[Explanation of symbols]

1 ... Semiconductor substrate, 2 ... Laser diode (semiconductor laser), 3 ... Photodiode (light receiving element), 4 ... Optical waveguide (first optical waveguide), 5 ... Optical waveguide (second optical waveguide), 7 ... 3 dB Coupler (optical coupling means), 9 ... Moving object, 10, 11 ... Laser light, 12 ... Reflected return light.

Claims (3)

[Claims] 1. A semiconductor substrate, first and second optical waveguides formed on the semiconductor substrate, a semiconductor laser optically coupled to the first optical waveguide, and a second optical waveguide and an optical waveguide. A combined light receiving element and formed on the semiconductor substrate,
And a light coupling means for causing light propagating through the first optical waveguide to enter the second optical waveguide, wherein the semiconductor laser is provided on the semiconductor substrate at one end of the first optical waveguide. A predetermined semiconductor material is laminated to be integrally formed with the semiconductor substrate, laser light is emitted from the semiconductor laser toward a moving object, and laser light is emitted to the first optical waveguide. A predetermined semiconductor material is laminated on the semiconductor substrate at one end portion of the second optical waveguide, and is integrally formed with the semiconductor substrate, and the second optical waveguide is formed by the light receiving element via the optical coupling means. A laser Doppler velocimeter, which receives a combined light of a laser light incident on a waveguide and a reflected return light from the moving object propagating through the second optical waveguide. 2. The semiconductor laser includes a first emitting portion for emitting laser light toward the moving object, and a second emitting portion for emitting laser light into the first optical waveguide.
The laser Doppler velocimeter according to claim 1, further comprising: 3. The laser Doppler velocimeter according to claim 1, wherein the optical coupling means forms the first optical waveguide and the second optical waveguide in close proximity to each other.