JPH02154189A - Waveguide type speed sensor - Google Patents

Abstract

PURPOSE:To simplify constitution by making reference light travel reciprocally in a 2nd optical waveguide and providing an acoustooptic effect type frequency shifter in the 2nd optical waveguide. CONSTITUTION:Incident light 76 of frequency fo is branched in a (y) shape through an optical waveguide 54 and the light 76 which is guided to the side of an optical waveguide 56 is more-converted by the frequency shifter 64, frequency-shifted by the frequency fr of a surface acoustic wave 75, reflected by an end surface reflecting mirror 66, and further shifted by a frequency fr through the shifter 64 again, so that the frequency of reference light 77 returning to the optical waveguide 56 is fo+2fr. Further, the light 76 which is guided to the side of an optical waveguide 58, on the other hand, is passed through an optical waveguide 62 and a collimator lens 68 and reflected by a reflecting mirror 70 to return to the optical waveguides 62 and 58, so that the frequency of the signal light 78 is fo+fS. Then, the signal light 78 and reference light 77 beat at the Y branch part and projection light 79 of frequency 2fr-fS is projected from the optical waveguide 54. The frequency of the projection light 79 is detected to obtain the moving speed of the mirror 70.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a waveguide speed sensor.

(Prior Art) FIG. 3 is a plan view showing a schematic configuration of a conventional waveguide type speed sensor. In FIG. 3, reference numeral 2 indicates the entire conventional waveguide type speed sensor.

In this waveguide type speed sensor 2, 4 is a substrate, 6 to 26
is an optical waveguide formed on the substrate 4, 28 is light incident on the optical waveguide 6, 30 is light emitted from the optical waveguide 6, 32 is a mode splitter provided on the optical waveguide 10, and 34 is a mode splitter provided on the optical waveguide 12. 36 is the optical waveguide 2
an electro-optic effect type frequency shifter provided in 4;
8 is an optical waveguide! Mirror 40 is an optical fiber provided at the end surface of the optical waveguide 20, and 42 is a mirror whose moving speed is to be detected.

The operation of the waveguide type speed sensor 2 having the above configuration will be explained.

First, when the incident light 28 of frequency fO is incident on the optical waveguide 6, the incident light is Y-branched from the optical waveguide 6 into optical waveguides 8 and 12. The light branched to the optical waveguide 8 side is guided to the optical waveguide 10, and is then guided to the optical waveguide 20 via the mode splitter 32. The light guided into the optical waveguide 20 is reflected by the reflecting mirror 42, which is the target object whose moving speed is to be detected, through the optical fiber 40, and then returns to the optical waveguide 20 through the optical fiber 40. The wave is guided by the Here, 43 is the incident light on the reflecting mirror 42, and 45 is the reflected light from the reflecting mirror 42.

This reflected light 45 becomes signal light. The frequency of the light at this time is the frequency corresponding to the moving speed of the mirror 42 ("
0→-fs). The light is then guided from the optical waveguide 20 to the optical waveguide 18 and further to the optical waveguide I6.

On the other hand, the incident light 28 branched from the optical waveguide 6 to the optical waveguide 12 side is mode-converted by the mode converter 34 and reflected by the reflection mirror 38 via the optical waveguide 14, and then guided to the optical waveguide 26. and is guided to the optical waveguide 24.

At this time, the frequency shifter 36 provided in the optical waveguide 24
As a result, the light has a frequency of (fO+fr). The light whose frequency has been shifted by the frequency shifter 36 is guided to the optical waveguide 16 via the optical waveguide 22 as a reference light 46.

Then, the optical waveguides 18 and 22 are connected to the optical waveguides 18 and 22, respectively.
Signal light 4 with a frequency of (fo + "s") guided to 6
5 and the reference light 46 having a frequency of (fO+fr) receives a beat effect at the branching point, and as a result, the optical waveguide 16
The frequency of the light guided to is (fs-fr). In this case, the frequency component fr is the reference frequency determined by the frequency filter 36, and the frequency component S is the comparison frequency corresponding to the moving speed of the mirror 42, so the optical waveguide 16
The moving speed of the reflecting mirror 42 can be detected from the frequency difference between rr and fs using a spectrum analyzer (not shown) provided on the side.

(Problem to be Solved by the Invention) Conventional waveguide speed sensor 2 having the above configuration
In this case, since the frequency shifter 36 is of a type that utilizes an electro-optic effect, if the light is sent back and forth to the frequency shifter 36 twice, the frequency of the light will not be shifted. , it is necessary to configure the frequency filter 36 so that the light is guided only once.

However, if the structure is such that the light is guided only once to the frequency shifter 36, there is a problem in that the structure of the optical waveguide becomes very complicated as shown in FIG. In addition, as the configuration of the optical waveguide becomes more complex, the loss of light increases accordingly, so in order to suppress this loss,
There is a problem in that large elements such as the mode splitter 32 and the mode converter 34 are required, which not only makes the configuration even more complicated, but also increases the overall size.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a waveguide speed sensor that has a simple optical waveguide configuration and can be made smaller in overall size.

(Means for Solving the Problems) In order to achieve such an object, the waveguide speed sensor of the present invention transmits signal light whose frequency is shifted by Doppler shifting according to the moving speed of the target object. A first optical waveguide that guides a wave and a second optical waveguide that guides a reference light of a predetermined frequency, wherein the reference light 11q is configured to reciprocate in the second optical waveguide. In addition, it is characterized in that an acousto-optic effect type frequency shifter is arranged in the second optical waveguide.

(Operation) The signal light in the first optical waveguide is frequency-shifted by being Doppler-shifted according to the moving speed of the target object. The reference destination in the second optical waveguide is reciprocated within the second optical waveguide. During the round-trip process, the reference destination is converted into the original mode by an acousto-optic effect type frequency shifter in the second optical waveguide.

Therefore, since the signal light whose frequency has been shifted in accordance with the moving speed of the target object and the reference light have the same mode, when they are combined, each frequency component is beat, and the target object is detected based on the beat frequency. It becomes possible to detect the moving speed of an object.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a plan view showing a schematic configuration of a waveguide type speed sensor according to an embodiment of the present invention. In FIG. 1, reference numeral 50
1 shows the entire waveguide type speed sensor of this embodiment. In this waveguide type speed sensor 50, 52 is a Z-cut ζ
Substrate made of lithium oxide (LiNbos), 5
4 to 62 are optical waveguides having a Y-branch configuration as a whole. 64 is an acousto-optic frequency shifter provided in the middle of the optical waveguide 60; 66 is an end face reflection mirror 68 provided at the end of the optical waveguide 60 at the end of the substrate 52; A collimating lens 70 disposed at a predetermined distance from the terminal end is a reflecting mirror whose moving speed is to be detected. In this embodiment, a collimating lens 68 is provided, or instead of the collimating lens 68, one end of a polarization preserving type optical fiber is provided facing the terminal end of the optical waveguide 62, and a rod lens is attached to the other end of the optical fiber. In addition to establishing
A reflecting mirror 70 may be placed opposite the other end of the optical fiber.

Here, the configuration of the frequency shifter 64 will be explained.
This frequency shifter 64 includes a pair of comb-shaped electrodes 72 and 72 provided in the middle of the optical waveguide 60, and
．． This comb-shaped electrode 72.7 is composed of surface acoustic wave absorbing layers 74.74 provided on both sides of the comb-shaped electrode 72.72, and a high-frequency voltage is applied to the comb-shaped electrode 72.72.
2, a surface acoustic wave 75 is propagated to the optical waveguide 60 as shown by a two-dot chain line.

Explain the action.

First, incident light 76 having a frequency of rO is input into the optical waveguide 54 . The light 76 incident on the optical waveguide 54 is Y-branched and guided to optical waveguides 56 and 58, respectively. The light 76 having the frequency fO guided to the optical waveguide 56 side is mode-converted by the frequency shifter 64, and accordingly, the frequency is shifted by the frequency fr of the surface acoustic wave 75. The frequency-shifted light is reflected by the end reflection mirror 66 and further frequency-shifted by the frequency fr by the frequency shifter 64. As a result, the light returns to the optical waveguide 52 (reference light 77).
) is finally (rO+2rr).

On the other hand, the light 76 guided to the optical waveguide 58 side is further guided to the optical waveguide 62, is emitted from the end of the optical waveguide 62, is reflected by the reflection mirror 70 via the collimating lens 68, and is reflected again by the reflection mirror 70. Optical waveguides 62 to 58
come back to. At this time, the frequency fO of the light 76 incident on the reflection mirror 70 is Doppler-shifted according to the moving speed of the reflection mirror 70, so that the frequency of the light (signal light 78) reflected by the reflection mirror 70 becomes (fo+rs). .

Then, the frequency is Doppler shifted (fO → GoS)
The signal light 78 that is guided through the optical waveguide 58 as
The frequency guided through the optical waveguide 56 is (ro+2 "r
) is subjected to a beat effect at the Y branch, and as a result, the frequency of the output light 79 output from the optical waveguide 54 is (
2fr-fs).

Therefore, by detecting the frequency of the emitted light 79, the moving speed of the reflecting mirror 70 can be detected.

FIG. 2 is a plan view showing a schematic configuration of a waveguide speed sensor according to another embodiment of the present invention, in which parts corresponding to those in FIG. The explanation for this will be omitted.

In the waveguide speed sensor 100 of the embodiment shown in FIG.
Each of the optical waveguides 80 to 94 is of an asymmetrical X-branch type, and the optical waveguide 86 has a frequency shifter 64, and the terminal end of the optical waveguide 94 has a polarization maintaining optical fiber 96 with a rod lens 98. It is characterized in that the incident light 76 and the outgoing light 79 are separated.

The rest of the configuration is the same as that in FIG. 1, so a description thereof will be omitted. Further, since its operation is similar to that of the embodiment shown in FIG. 1, its explanation will be omitted.

(Effects of the Invention) As is clear from the above explanation, according to the present invention,
In addition to using an acousto-optic effect type frequency filter,
Since light can be sent back and forth to the frequency shifter, the configuration of the optical waveguide is simplified. Furthermore, as the optical waveguide configuration is simplified, optical loss is also reduced, eliminating the need for elements such as mode splitters and mode converters that were required to deal with optical loss in the conventional example. In addition to being simpler, the overall size can also be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a schematic configuration of a waveguide type speed sensor according to an embodiment of the present invention, and FIG. 2 is a plan view showing a schematic configuration of a waveguide type speed sensor according to another embodiment of the present invention. It is. FIG. 3 is a plan view of a waveguide type speed sensor according to a conventional example. 50.100... Waveguide speed sensor, 52... Substrate, 54-62. 80-94... Optical waveguide, 64...
Frequency shifter, 66... End face reflection mirror 70...
Reflection mirror (target object), 77... Reference light, 78...
・Signal light.

Claims (1)

[Claims] (1) A first optical waveguide that guides a signal light whose frequency has been shifted by Doppler shifting according to the moving speed of the target object, and a second optical waveguide that guides a reference light of a predetermined frequency. In the waveguide speed sensor, the reference light is configured to reciprocate in the second optical waveguide, and an acousto-optic effect type frequency shifter is disposed in the second optical waveguide. Features of waveguide type speed sensor.