JP2000266853A - Optical waveguide type doppler speedometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide type Doppler speedometer which simultaneously achieves miniaturization and low costs. SOLUTION: The speedometer is constituted including in a light waveguide substrate 11 a first Y branch circuit 8 to which a light signal of a laser diode 1 enters via an optical isolator 2, a second Y branch circuit 9 which projects the light signal to a collimator lens 5 and at the same time, receives a reflecting light from a moving object, and a third Y branch circuit 10 which mixes the reflecting light having undergone a Doppler shift and a direct light from the laser diode 1 without a Doppler shift and couples the light to a photodiode 7 for detecting a difference frequency. A piezoelectric element substrate light waveguide using lithium niobate single crystals or lithium tantalate single crystals, a plastic light waveguide using a polyimide fluoride resin or silicon resin, or the like can be used as the light waveguide. The three Y branch circuits can be formed in the light waveguide substrate of approximately 5×20 mm and therefore, the Doppler speedometer which is considerably compact as compared with the prior art can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide type Doppler velocimeter, and more particularly to an optical waveguide type Doppler velocimeter comprising an optical waveguide in which a directional coupler is integrated in one substrate.

[0002]

2. Description of the Related Art FIG. 2 shows a basic configuration example of a conventional optical fiber type Doppler velocimeter. As shown in FIG. 1, as a conventional Doppler speed meter using an optical fiber, a configuration using three 1-input / 2-output optical fiber fusion couplers is known. That is, the laser diode 1, the optical isolator 2, the optical fiber fusion type couplers 3, 4,
6, a collimating lens 5, and a photodiode 7. The Doppler speedometer configured in this way is
An optical signal having an oscillation frequency ν [Hz] is applied to a laser diode 1
And the optical signal enters the optical fiber fused coupler 3 via the optical isolator 2. The optical signal incident on the optical fiber fusion coupler 3 is branched into two outputs, and one of the branched lights is collimated by the collimator lens 5 via the optical fiber fusion coupler 4 and moves at v [m / sec]. The moving object is irradiated. The reflected light from the moving object undergoes a Doppler shift of Δf [Hz] according to the moving speed of the moving object, and the frequency becomes ν + Δf [Hz], and is coupled to the optical fiber fusion coupler 4 via the collimating lens 5,
The optical fiber fused coupler 4 branches again into two, and one of the branched lights enters the optical fiber fused coupler 6. The other branch light branched by the optical fiber fused coupler 4 enters the coupler 3 and returns to the laser diode 1 side, but is cut off by the optical isolator 2 and does not affect the laser diode 1. It is configured as follows. Two signals from the optical fiber fused couplers 3 and 4 enter the optical fiber fused coupler 6 and have a frequency ν [H
z] and ν + Δf [Hz] are combined. Accordingly, assuming that the intensities of the optical signals of the frequency ν are equal, the output of the optical fiber fused coupler 6 is 2ν + Δf [H
A signal having a frequency of [z] is generated and an optical signal having a difference frequency of [Delta] f [Hz] is generated. Can be. That is, since the value of Δf is proportional to the speed v of the moving object, v can be calculated if Δf is known.

[0003]

However, the conventional optical fiber type Doppler velocimeter as described above requires three optical fiber fusion type couplers each having a length of several centimeters. There is a disadvantage that it is difficult not only to reduce the cost but also to reduce the cost. The present invention has been made in view of the above, and an object of the present invention is to provide an optical waveguide type Doppler velocimeter that achieves both miniaturization and cost reduction by using an optical waveguide substrate having three Y branch circuits. And

[0004]

In order to achieve the above object, an optical waveguide type Doppler velocimeter according to the present invention has a first and a second circuit in which one ends of respective branch circuits are connected. And an optical waveguide substrate having a third Y-branch circuit connected to the first and second Y-branch circuits, and an optical signal of a laser diode is input to the optical waveguide substrate via an optical isolator. Outputting output light from the optical waveguide substrate to a moving object via a collimating lens, and inputting reflected light from the moving object to the optical waveguide substrate via the collimating lens; The output light from the substrate is received by the photodiode. The invention according to claim 2 of the optical waveguide Doppler velocimeter according to the present invention includes a light source that outputs light having a desired frequency ν, an optical waveguide substrate that inputs an optical signal from the light source, and an optical waveguide substrate. A collimating lens that emits an optical signal to the moving object and couples reflected light from the moving object to the optical waveguide substrate; and a photodiode that detects an optical signal from the optical waveguide substrate, the optical waveguide comprising: The substrate is composed of three symmetric Y branch circuits, one branch of the first Y branch is coupled to one branch of the second Y branch, and the other branch of the first Y branch is a second branch. A third branch of the third Y branch is coupled to one branch of the third Y branch, and the other branch of the second Y branch is coupled to the other branch of the third Y branch, and the frequency ν [H
z] is output to the moving object via the first Y branch circuit, the second Y branch circuit and the collimating lens, and is supplied from the first Y branch circuit to the third Y branch circuit. The reflected light of the frequency ν + Δf [Hz] is incident on the third Y-branch circuit via the collimator lens and the second Y-branch circuit, where the optical signal of the frequency ν and the optical signal of the frequency ν + Δf are output. Are combined to extract the difference frequency signal Δf, and the difference frequency signal Δf
f was detected by the photodiode.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the accompanying drawings. FIG. 1 is a basic configuration diagram showing an embodiment of an optical waveguide type Doppler velocimeter according to the present invention. The optical waveguide type Doppler velocimeter includes a laser diode 1, an optical isolator 2, and Y branch circuits 8, 9,. An optical waveguide substrate 11 including the optical waveguide 10, a collimator lens 5, and a photodiode 7 are provided. The Y-branch circuit of the optical waveguide substrate 11 will be described in a little. 5, a second Y-branch circuit 9 for receiving the reflected light from the moving object, which is the output of the collimator lens 5, and the reflected light from the moving object subjected to the Doppler shift and the Doppler shift from the laser diode 1. And a third Y-branch circuit 10 for mixing the direct light that has not received the light and coupling the mixed light to the photodiode 7. The optical waveguide Doppler velocimeter configured as described above emits an optical signal having an oscillation frequency ν [Hz] from the laser diode 1, and the optical signal is transmitted via the optical isolator 2 to the first Y branch circuit of the optical waveguide substrate 11. It is incident on 8 and is branched into 2 outputs. One of the branch outputs enters the second Y branch circuit 9,
The other enters the third Y branch circuit 10. The optical signal that has entered the second Y-branch circuit 9 is collimated by the collimating lens 5 and applied to a moving object that moves at v [m / sec]. The reflected light from the moving object undergoes a Doppler shift of Δf [Hz] according to the moving speed of the moving object, and has a frequency of ν +
Δf [Hz] is coupled to the second Y-branch circuit 9 of the optical waveguide substrate 11 via the collimating lens 5, and is branched into two by the second Y-branch circuit 9, one output of which is the first Y-branch circuit 8
The other output is output to the third Y branch circuit 10. The reflected light from the moving object incident on the first Y branch circuit 8 from the second Y branch circuit 9 returns to the laser diode 1 side via the first Y branch circuit 8, but is cut off by the optical isolator 2 and It is configured not to affect the diode 1. On the other hand, the light having the frequency ν + Δf [Hz] emitted from the second Y branch circuit 9 to the third Y branch circuit 10 is transmitted to the first Y branch circuit 8 by the third Y branch circuit 10.
And an optical signal having a frequency ν [Hz] incident from the light source.
Therefore, assuming that the intensities of the optical signals of the frequency ν are equal, the output of the third Y branch circuit 10 is 2ν + Δf [Hz].
An optical signal of Δf [Hz], which is a difference frequency from a signal of a given frequency, is generated, and the optical signal of Δf [Hz] is converted into an electric signal in the photodiode 7, whereby the speed of the moving object can be grasped. . That is, since the value of Δf is proportional to the speed v of the moving body, v can be calculated if Δf is known.

As an optical waveguide, a piezoelectric element substrate optical waveguide using lithium niobate single crystal or lithium tantalate single crystal, a plastic optical waveguide using fluorinated polyimide resin or silicon resin, or a silicon single crystal or A quartz optical waveguide formed by forming a silicon dioxide film on quartz glass can be used. Three Y branch circuits are 5mm ×
Since it can be formed in an optical waveguide substrate of about 20 mm, an extremely small Doppler velocimeter can be realized as compared with the related art.

[0007]

As described above, the optical waveguide type Doppler velocimeter according to the present invention employs an optical waveguide substrate having three Y-branch circuits for processing an optical signal. There is a great advantage that a speedometer can be realized.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram showing one embodiment of an optical waveguide type Doppler velocimeter according to the present invention.

FIG. 2 is a diagram showing a basic configuration example of a conventional optical fiber type Doppler velocimeter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser diode 2 Optical isolator 5 Collimating lens 7 Photodiode 8 First Y branch circuit 9 Second Y branch circuit 10 Third Y branch circuit 11 Optical waveguide board

Claims (2)

[Claims] 1. An optical waveguide having first and second Y branch circuits connected to one ends of respective branch circuit sections and a third Y branch circuit connected to the first and second Y branch circuits. A substrate, and input an optical signal of a laser diode to an optical waveguide substrate via an optical isolator, and output light from the optical waveguide substrate to a moving object via a collimating lens, and output light from the moving object. An optical waveguide type Doppler velocimeter, wherein reflected light is input to the optical waveguide substrate via the collimating lens, and output light from the optical waveguide substrate is received by a photodiode. 2. A light source for outputting light of a desired frequency ν, an optical waveguide substrate for inputting an optical signal from the light source, an optical signal from the optical waveguide substrate for emitting to a moving object, and A collimating lens that couples the reflected light from the optical waveguide substrate to the optical waveguide substrate, and a photodiode that detects an optical signal from the optical waveguide substrate. The optical waveguide substrate includes three symmetric Y branch circuits,
One branch of the first Y branch is coupled to one branch of the second Y branch, and the other branch of the first Y branch is coupled to one branch of the third Y branch. Further, the other branch of the second Y branch is coupled to the other branch of the third Y branch, and an optical signal having a frequency ν [Hz] emitted from the light source is output from the first Y branch. The reflected light of the frequency ν + Δf [Hz] which is emitted from the first Y-branch circuit to the third Y-branch circuit and reflected from the moving object while being emitted to the moving object via the second Y-branch circuit and the collimating lens. And enters the third Y-branch circuit via the second Y-branch circuit, where the optical signal having the frequency ν and the frequency ν +
An optical waveguide type Doppler velocimeter, wherein a difference frequency signal Δf is extracted by combining with an optical signal of Δf, and the difference frequency signal Δf is detected by the photodiode.