JPH0862332A - Lightwave ranging device - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the distance measurement accuracy of a lightwave distance measuring device. The lightwave distance measuring apparatus 1 includes a light emitting section 2 for emitting modulated light, a light transmitting optical fiber 3 for guiding the emitted light from the light emitting section 2 toward a reflector 7, and a reflected light from the reflector 7. It is composed of a light receiving optical fiber 6 for receiving light, and a measuring section 5 for measuring the phase difference between the reflected light from the reflector 7 and the emitted light to obtain the distance to the reflector 7. Then, the length L of the optical fiber 3 for light transmission is determined so that the phase difference between the reflected lights from both end surfaces thereof is 180 °. The reflected lights from the both end surfaces cancel each other out, and the phase of the received light received by the distance measuring unit 51 hardly deviates from the phase of the reflected light from the reflector 7 to be originally received.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wave distance measuring device used in a surveying instrument.

[0002]

2. Description of the Related Art In a light wave distance measuring device, a modulated signal is given to a light emitting element such as a light emitting diode, and the emitted modulated light is sent to an external reflector via an optical fiber for light transmission, and reflection modulation from the reflector is performed. The light is received by the light receiving element through the light receiving optical fiber, and the distance is measured by detecting the phase difference between the emission modulated light and the reflection modulated light at that time.

In this case, a part of the emitted modulated light is reflected at the incident end and the outgoing end of the light transmitting optical fiber, and the light receiving element not only reflects the light reflected from the reflector but also the light transmitting optical fiber. It also receives the reflected light from the entrance end and the exit end. In addition, the reflected light from the entrance end and the exit end of the light-receiving optical fiber is also received, although it is very small. The phase of each reflected light will be described with reference to FIG.

FIG. 3 is a diagram showing the phase of reflected light received by a conventional lightwave distance measuring apparatus. In this figure, the phase of the reflected light 60 from the reflector, which is originally the reflected light to be detected by the optical distance measuring device, is θ60, and the reflected lights 61 and 62 (multiplexed) from the incident end and the outgoing end of the optical fiber for light transmission are multiplexed. The phases of the reflected light are θ61 and θ62. In addition, the reflected light 61, 62
Let θ 63 be the phase of the reflected combined light 63 obtained by combining.

The light receiving element is used to reflect the respective reflected lights 60, 6 as described above.
When 1 and 62 are received, the received light 64 at that time is obtained by combining the reflected light 60 from the reflector and the reflected combined light 63, and the phase thereof is θ64.

[0006]

By the way, as shown in FIG. 3, the phase θ64 of the received light 64 is largely deviated from the phase θ60 of the reflected light 60 which should be the object of measurement. When the distance measuring device measures the distance to the reflector 7 based on the phase θ64 of the received light 64, there is a problem that the distance measuring accuracy is lowered.

The present invention has been made in view of such circumstances, and an object thereof is to provide an optical wave distance measuring device capable of improving distance measuring accuracy.

[0008]

In order to solve the above-mentioned problems, a light-wave distance measuring apparatus according to the invention of claim 1 emits intensity-modulated modulated light, and emits modulated light from the light-emitting means. An optical fiber for transmitting light that guides the emitted modulated light to the outside so as to direct the object to be measured, and an optical fiber for receiving light,
Measuring means for receiving reflected modulated light from the measuring object through the light receiving optical fiber, and measuring a phase difference between the emitted modulated light and the reflected modulated light to obtain a distance to the measuring object. In the lightwave distance measuring device comprising, the length of at least one of the light-transmitting optical fiber and the light-receiving optical fiber is from the modulated light reflected from one end face of the fiber and the other end face. The phase difference from the reflected modulated light is set to 180 °.

Further, in the optical distance measuring apparatus according to the present invention, the modulation frequency of the modulated light is f, the refractive index of the core portion of the fiber is N, the light velocity is C, and the coefficient is α (where α is Odd number), the length l of at least one of the optical fiber for light transmission and the optical fiber for light reception is l
= Α · C / (4fN).

[0010]

In the optical distance measuring apparatus according to the present invention, the phase difference between the modulated light reflected from one end face and the modulated light reflected from the other end face is 18 in the length of the fiber.
Since the setting is made to be 0 °, the reflected modulated lights from the respective end faces are almost equal in quantity, so that the reflected modulated lights from the respective end faces cancel each other out, and the reflected modulated lights actually received are equal to each other. The phase hardly shifts with respect to the phase of the reflection-modulated light from the measurement object that should be received originally.

[0011]

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

FIG. 1 is a diagram showing the overall construction of a lightwave distance measuring apparatus according to an embodiment of the present invention. The lightwave distance measuring device 1 includes a light emitting section (light emitting means) 2 which emits intensity-modulated modulated light.
And a light-transmitting optical fiber 3 that guides the light emitted from the light emitting unit 2 (emission modulated light) through the objective lens 4 toward a reflector (for example, a corner cube or a ref sheet) 7 that is a measurement object, and An optical fiber 6 for receiving the reflected light (reflected modulated light) from the reflector 7 via the objective lens 4, and a reflected light from the reflector 7 via the optical fiber 6 for receiving the reflected light and the emitted light. A measuring unit (measuring means) 5 for measuring the phase difference from light and obtaining the distance to the reflector 7. The light emitting unit 2 includes a light emitting element 22 such as a light emitting diode,
It is composed of a modulator 21 that modulates the light emitted from the light emitting element 22. The measuring unit 5 includes a light receiving element 52 that receives the reflected light, and a distance measuring device 51 that measures the distance to the reflector 7 by obtaining the phase difference between the reflected light and the emitted light.
In addition, it is assumed that the phase information and the modulation frequency information of the emitted light are sent from the modulator 21 to the distance measuring device 51 via a signal line (not shown).

In the light-wave distance measuring device 1 having the above-described structure, in this embodiment, the length l of the light-transmitting optical fiber 3 is calculated by the following equation (1).
Set to the length determined by.

L = α · C / (4fN) (1) where α: coefficient (where α is an odd number) C: speed of light f: modulation frequency N: core of optical fiber for light transmission Partial refractive index Length l of the optical fiber 3 for light transmission determined by the above formula (1)
In this case, the phase difference between the respective reflected lights at the incident end face and the outgoing end face of the light transmitting optical fiber 3 is 180 °. Next, the phase of each reflected light received by the measurement unit 5 when the length L of the light transmitting optical fiber 3 is set to the above equation (1) will be described with reference to FIG.

FIG. 2 is a diagram showing the phase of the reflected light received by the optical distance measuring apparatus of this embodiment. In this figure, the phase of the reflected light 10 from the reflector 7 which is originally the reflected light to be detected by the optical distance measuring apparatus 1 is θ10, the reflected light 11 from the incident end face and the outgoing end face of the optical fiber 3 for light transmission, 12
Let the phases of θ11 and θ12 be. Also, the reflected light 11, 1
The phase of the reflected combined light 13 obtained by combining 2 is set to θ13.

The light receiving element 52 is arranged to
When 11 and 12 are received, the received light 14 at that time is obtained by synthesizing the reflected light 10 from the reflector 7 and the multiple reflected light 13, and the phase thereof is θ14.

By the way, in this embodiment, as described above, the phase difference between the reflected light 11 and the reflected light 12 from the incident end face and the outgoing end face of the light transmitting optical fiber 3 is 180 °, and the reflected light 11, Since the respective light quantities of 12 are almost equal, the reflected lights 11 and 12 cancel each other out, and the received light 1 received by the distance measuring unit 51 is
The phase θ14 of 4 does not substantially deviate from the phase θ10 of the reflected light 10 from the reflector 7 which should be received.

That is, in the phase measurement by the distance measuring section 51, the phase measurement error due to the influence of the reflected combined light 13 can be greatly suppressed, and the accuracy of the distance measurement can be greatly improved accordingly. The effect will be specifically described below in comparison with the conventional example.

The modulation frequency f is 100 MHz, and the refractive index N of the core portion of the light transmitting optical fiber 3 is 1. 5, the speed of light C is 300,000 km / s, and the length 1 of the optical fiber 3 for light transmission is assumed to be 16
cm, the phase difference of the reflected light from both end surfaces of the light-transmitting optical fiber 3 is 57.6 °, the reflected lights cannot cancel each other, and the magnitude of the multiple reflected light is also reflected. It becomes 6.87% with respect to the reflected light from the container 7. Therefore, the phase of the received light also differs significantly from the phase of the reflected light from the reflector 7.

On the other hand, if the length 1 of the light transmitting optical fiber 3 is determined based on the above equation (1) and is set to 50 cm, the position of the reflected light from both end faces of the light transmitting optical fiber 3 is determined. The phase difference is 180 °, the reflected lights cancel each other out, and the size of the multiple reflected lights is also the reflector 7
It becomes 0.16% with respect to the reflected light from. Therefore,
The influence of the multiple reflected light can be greatly reduced, the phase of the received light becomes almost the same as the phase of the reflected light from the reflector 7, and the phase measurement error can be suppressed to about 2%.

In the above description, the length of the light transmitting optical fiber is set based on the equation (1), but the light receiving optical fiber is set based on the equation (1). Good. Further, the lengths of both the light transmitting optical fiber and the light receiving optical fiber may be set based on the equation (1).

Further, if the modulation frequency is further increased, the length of the optical fiber becomes shorter based on the equation (1), so that the storage space for the optical fiber can be made narrower.

[0023]

As described above, according to the optical distance measuring apparatus of the present invention as defined in claim 1 or 2, since the reflected modulated lights from the respective end faces of the fiber cancel each other out, the phase measurement error due to the multiple reflected lights is greatly reduced. Therefore, the accuracy of distance measurement can be significantly improved.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a lightwave distance measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a phase of reflected light received by the lightwave distance measuring apparatus of this embodiment.

FIG. 3 is a diagram showing a phase of reflected light received by a conventional lightwave distance measuring apparatus.

[Explanation of symbols]

 1 Light Wave Distance Measuring Device 2 Light Emitting Unit 3 Light Transmitting Optical Fiber 4 Objective Lens 5 Measuring Unit 6 Light Receiving Optical Fiber 10 Reflected Light from Reflector 11 Reflected Light from Emitting End Face of Light Transmitting Optical Fiber 12 Light Transmitting Light Reflected light from the incident end face of the fiber 13 Reflected combined light 14 Received light 21 Modulator 22 Light emitting element 51 Distance measuring device 52 Light receiving element

Claims (2)

[Claims] 1. A light emitting means for emitting intensity-modulated modulated light, a light-transmitting optical fiber for guiding the emitted modulated light to the outside so as to direct the emitted modulated light from the light emitting means toward an object to be measured, Optical fiber and the reflected modulated light from the measurement object is received via the light receiving optical fiber, and the distance to the measurement object by measuring the phase difference between the emitted modulated light and the reflected modulated light. In the lightwave distance measuring device, the length of at least one of the optical fiber for light transmission and the optical fiber for light reception is the modulated light reflected from one end face of the fiber. And the phase difference between the modulated light reflected from the other end face and the modulated light is set to 180 °. 2. When the modulation frequency of the modulated light is f, the refractive index of the core of the fiber is N, the light velocity is C, and the coefficient is α (where α is an odd number), the optical fiber for light transmission and The lightwave distance measuring apparatus according to claim 1, wherein the length l of at least one of the light receiving optical fibers is determined by l = α · C / (4fN).