JPS61272677A - Measuring instrument for length of optical path - Google Patents

Abstract

PURPOSE:To compensate variation in the optical path length of an optical fiber and variation in the phase characteristics of a light emitting and a photodetecting part and to measure the length of an optical path with high precision by performing control arithmetic processing on the basis of a delay time in an atmosphere to be measured and measuring the length of the optical path in the atmosphere. CONSTITUTION:A light emitting means 21 and photodetecting means are connected to one terminal of a directional coupler 31 through the optical fiber and a mirror 33 and a light projecting and photodetecting means 34 are connected to the other terminal; and a light emitting means 22 and a photodetecting means 23 are connected to one terminal of the directional coupler 32 and a mirror 35 and the means 34 are connected to the other terminal. Then, the means 21 is driven to measure the phase difference between a light wave reaching the means 24 and a light wave reaching the means 23 and the means 22 is also driven to measure the phase difference between the light wave reaching the means 23 and the light wave reaching the means 24 by a phase difference measuring means 25 respectively. An optical path length arithmetic processing means 26 calculates the length of the optical path in the atmosphere to be measured on the basis of both phase differences. Consequently, variation in the optical path length of the optical fiber which couples a main measuring instrument body and a projecting and photodetection optical system and variation in phase between the light emitting part and photodetection part are compensated to measure the optical path length precisely.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention transmits and receives light waves to and from an atmosphere to be measured via an optical fiber, and determines the optical path length of the atmosphere to be measured through which the light waves propagate based on the phase delay of this light wave. The present invention relates to an optical path length measuring device for measuring optical path length, and more particularly to improvements in means for compensating for errors in optical path length measurements caused by the optical fiber and the like.

[Technical disadvantages of the invention and its problems] FIG. 3 is a system diagram showing the configuration of a conventional optical path length measuring device. Modulation signal m1
A light wave 3 emitted from a light emitting source 2 according to a modulation signal S1 of
The light passes through the light projecting lens 4 and propagates in the atmosphere A to be measured, is reflected at the corner duplex 5, passes through the light receiving lens 6, and reaches the light receiving section 7. The light receiving section 7 converts the signal into an electrical signal S2, and then sends it to the phase difference detection section 8. In this phase difference detection section 8, the modulation signal source 1
The phase difference between the modulated signal S1 given by the modulation signal S1 and the electric signal S2 is detected, and based on this phase difference, the propagation time from when the light wave 3 is emitted to when it is received is determined. As a result, the optical path length of the atmosphere A to be measured is determined by the optical path length converting section 9 based on the propagation time of this light wave, and is displayed on the display section 11 provided inside or outside the optical path length measuring device main body 10. It becomes.

However, with the optical path length measuring means as described above, the optical path length of the atmosphere A to be measured is measured while including delay elements caused by the LED used as the light emitting source 2, the light receiving element of the light receiving section 7, or the amplifier. Values include errors.

Therefore, in general, the light wave 3 emitted from the light emission m2 is divided into a measurement light wave 3a and an internal reference light wave 3b in a time-division manner by the chopper beam splitter 12, and the error caused by the delay element is calculated based on the phase difference between the two light waves. After compensation, the optical path length of the atmosphere A to be measured is measured.

On the other hand, if the atmosphere A to be measured is an atmosphere A' in which electrical energy is unfavorable, such as an explosive gas atmosphere, the measuring device main body 10 cannot be installed in the atmosphere A'. Further, the chopper beam splitter 1
2 also requires electrical energy, so the same is true. Therefore, in such a case, as shown in Figure 4,
The measuring instrument main body 10 including the chopper beam splitter 12 is installed in a place away from the atmosphere A' to be measured, and this main body 1
Light emitting/receiving optical system 14 equipped with a light transmitting/receiving lens 13 from 0
are connected by an optical fiber 15 to transmit and receive light waves, thereby measuring the optical path length in the atmosphere to be measured A'.

However, the optical path length of the optical fiber 15 itself changes due to environmental changes such as temperature changes. For example, if the total length of the optical fiber 15 is 100 m or more, several tens of
When the temperature changes by 1°, the optical path length of the fiber itself is
It changes by about 0#.

Therefore, the optical path length of the atmosphere to be measured A' is
Even if the calculation is performed by an arithmetic processing means within 0, this calculated value may have an error, and there is a problem in terms of accuracy.

[Purpose of the invention]

The present invention was made based on these circumstances,
The purpose of this is to be able to ignore changes in the optical path length of the optical fiber that connects the main body of the optical path length measuring instrument and the light emitting/receiving optical system, even if the measurement atmosphere is unfavorable with electrical energy. Another object of the present invention is to provide an optical path length measuring device that can accurately measure optical path length.

[Summary of the invention]

In order to achieve the above object, the present invention connects a first light emitting means and a second light receiving means to one end of a first directional coupler via an optical fiber, and connects a first directional coupler to the other end. The mirror and the light emitting/receiving means are connected via an optical fiber, and the second light emitting means and the first light receiving means are connected to one end of the second directional coupler via the optical fiber. ．． At the other end, a second mirror and the light emitting/receiving means are connected via an optical fiber, and by driving the first light emitting means, the first mirror is connected through the first directional coupler. A light wave is reflected by the light beam and reaches the second light receiving means, and the light beam is emitted through the first directional coupler and is emitted to the atmosphere to be measured by the light receiving means, and the light wave is received by the second light receiving means through the second directional coupler. While measuring the phase difference with the light wave reaching the means, by driving the second light emitting means, the light is reflected by a second mirror via the second directional coupler and reaches the first light receiving means. Measure the phase difference between the light wave and the light wave that is emitted into the atmosphere to be measured by the light emitting/receiving means via the second directional coupler and reaches the second light receiving means via the first directional coupler. The optical path length of the atmosphere to be measured is calculated based on the measured side phase difference.

[Embodiments of the invention]

FIG. 1 is a system diagram showing the configuration of an embodiment in which the present invention is applied to optical path length measurement in a measurement atmosphere A' where electrical energy is unfavorable. In addition, Fig. 3.

Components that are the same as those in FIG. 4 are given the same reference numerals, and detailed explanations will be omitted. In FIG. 1, reference numeral 20 denotes the main body of the optical path length measuring instrument; The second light emitting section 21.22 and the first light emitting section 21.22. Second light receiving sections 23 and 24 are provided, each including light emitting elements 21a and 22a and light receiving elements 23a and 24a. The optical path length measuring device main body 20 is installed in a place away from the atmosphere to be measured A', and
The light emitting/receiving optical system 30 provided inside is an optical fiber 41.
．． The connections are made as follows via 42, 43, and 44.

That is, the first light emitting section 21 is connected to the light emitting and receiving optical system 3.
The first 2 points x 2 ports directional coupler (hereinafter referred to as
The second light emitting section 22 is connected to one port at one end of the first coupler (abbreviated as a first coupler) 31 by the optical fiber 41, and the second light emitting section 22 is connected to the second two points in the light emitting/receiving optical system 30. It is connected to one port at one end of a boat directional coupler (hereinafter abbreviated as second coupler) 32 via the optical fiber 42 . In addition, the first light receiving section 2
3 is connected to the other port at one end of the second coupler 32 by the optical fiber 43, and the second light receiving section 24 is connected to the other port at one end of the first coupler 31 by the optical fiber 43. connected via.

On the other hand, one port at the other end of the first coupler 31 is connected to the first internal reference beam mirror 33 via an optical fiber 45, and the other port is connected via an optical fiber 46 to the light emitting/receiving port. It is connected to mirror 34. Further, one port at the other end of the second coupler 32 is connected to the second internal reference light mirror 35 via an optical fiber 47, and the other ports 1 to 1 are connected to the light emitting light via an optical fiber 48. It is connected to the light receiving mirror 34.

In this state, the light wave emitted from the first light emitting section 21 is transmitted to the first coupler 31 via the optical fiber 41, and is further transmitted to the first internal reference light beam via the optical fibers 45 and 46. The light is transmitted to the mirror 33 and the light emitting/receiving mirror 34. Then, the first internal reference beam mirror 3
The light wave reflected by the optical fiber 45, the first coupler 31 . The signal is transmitted to the second light receiving section 24 via the optical fiber 44, where it is converted into an electrical signal S3. On the other hand, the light wave projected by the light emitting and receiving mirror 34 is transmitted to the light emitting and receiving lens 3 as an external measurement light wave.
After being transformed in a predetermined direction by 6, the corner mirror 5
The light is reflected by the corner mirror 5, returns to the light emitting/receiving mirror 34, and is transmitted to the optical fiber 48. The signal is transmitted to the first light receiving unit 23 via the second coupler 32° optical fiber 43, where it is converted into an electrical signal S4.

Further, the light wave emitted from the second light emitting section 22 is transmitted to the second coupler 32 via the optical fiber 42, and further transmitted to the second internal reference light mirror 35 via the optical fibers 47 and 48. and is transmitted to the light emitting/receiving mirror 34. Then, the light wave reflected by the second internal reference light mirror 34 is transferred to the optical fiber 47 second coupler 32 as an internal reference light wave. The signal is transmitted to the first light receiving section 23 via the optical fiber 43, where it is converted into an electrical signal S5. On the other hand, the light wave projected by the light emitting/receiving mirror 34 is converted into a predetermined direction by the light emitting/receiving lens 36 as an external measurement light wave, and then reaches the corner mirror 5, where it is reflected by the above-mentioned Returning to the light emitting/receiving mirror 34,
Optical fiber 46. First coupler 31. The electrical signal S is transmitted to the second light receiving unit 24 via the optical fiber 44, and
6.

Each of the electric signals 83 to S6 is sent to a phase difference detection section 25, where a phase difference Δφ1 between the electric signals S3 and 84 is detected, and a phase difference Δφ2 between the electric signals S5 and 86 is detected. These phase differences Δφ1. Δφ2 is given to the control/arithmetic processing section 26. This control/arithmetic processing section 26 has a function of controlling a changeover switch 27 for driving the first and second light emitting sections 21 and 22 in a time-divisional manner, and also has the function of controlling the changeover switch 27 for driving the first and second light emitting sections 21 and 22 in a time-divisional manner, and also has the function of controlling the changeover switch 27 that drives the first and second light emitting sections 21 and 22 in a time-divisional manner, and also has the function of controlling the changeover switch 27 that drives the first and second light emitting sections 21 and 22 in a time-divisional manner. It has a function of determining the optical path length of the atmosphere to be measured A' by performing predetermined arithmetic processing and correction on Δφ2, converting it into a distance signal S7, and outputting it to the display section 11.

Next, the operation of this embodiment will be explained. First, when the changeover switch 27 is connected to the terminal 27a side by time-divisional control of the control/arithmetic processing section 26, the first light emitting section 21
A modulation signal S1 is supplied from the modulation signal source 1 to the first light emitting section 21, and the first light emitting section 21 is driven. Then, the external measurement light wave is projected into the measurement atmosphere A' by the light projecting/receiving mirror 34, reflected by the corner mirror 5, and then received by the first light receiving section 23 via a predetermined path, and converted into an electrical signal S4. converted. At the same time, the internal reference light wave is reflected by the first internal reference light mirror 33, is received by the second light receiving section 24 via a predetermined path, and is converted into an electrical signal S3. Then, the phase difference Δφ1 between the electric signals 83 and 84 is detected by the phase difference detection section 25 and stored in the control/arithmetic processing section 26.

Next, when the changeover switch 27 is switched to the terminal 27b side by the time-divisional control of the control/arithmetic processing section 26, the modulation signal S1 is transmitted from the modulation signal source 1 to the second light emitting section 22.
is supplied, and the second light emitting section 22 is driven. Then, the external measurement light wave is projected into the measurement atmosphere A' by the light projecting/receiving mirror 34, reflected by the corner mirror 5, and then received by the second light receiving section 24 via a predetermined path, and converted into an electrical signal S6. converted. At the same time, the internal reference light wave is reflected by the second internal reference light mirror 35, is received by the first light receiving section 23 via a predetermined path, and is converted into an electric signal @S5. Then, the phase difference Δφ2 between both electrical signals 85°S6 is detected by the phase difference detection section 25 and stored in the control/arithmetic processing section 26. Thereafter, the control/arithmetic processing section 26 determines the phase difference Δφ1. After Δφ2 is subjected to predetermined calculations and corrections and converted into a distance signal S7, it is displayed on the display unit 1 as the optical path length of the atmosphere to be measured A'.
1 is displayed.

In this way, the first light emitting section 21 and the second light emitting section 22 are driven in a time-division manner, and the phase differences between the electric signals S3 and S4 and S5 and S6 are determined according to the respective internal reference light waves and external measurement light waves. Δφ1. When Δφ2 is detected and predetermined calculations are performed on these, delays due to the light emitting section 21.22, the light receiving section 23.24, and the optical fibers 41 to 48 can be ignored, and an example of the electrical signals 83 to S6 used in the atmosphere to be measured is FIG.

In the figure, t1 to t4 are the first. Second light emitting section 21.2
2 and 1st. The delay time of the signal by the second light receiving unit 23° 24, T1 to T4 are the delay times of the light wave by the optical fibers 41 to 44, and TX is the light wave by the atmosphere A' to be measured from the light emitting/receiving lens 36 to the corner mirror 5. shows the one-way delay time. Note that the delay time caused by the optical fibers 45 to 48 is sufficiently short compared to the optical fibers 41 to 44, and the drift of the optical path length is small and can be ignored, so it can be taken as a constant from the final result. Just correct it.

As is clear from FIG. 2, the output (electrical signal) 8 at the first light receiving section 23 when the first light emitting section 21 is driven
The total delay time U11 of 4 is U11=t1+TI+T3+t
3+2TX...(1). Further, the total delay time U12 of the output (electrical signal) S3 in the second light receiving section 24 at this time is U12=t1+T1+T4+t4
...(2) becomes. Therefore, the delay time difference ΔU1 between the two is ΔU1=U11-U12=73+t 3-1-2 T x-T 4- t
4-8L+2TX...(3)
becomes. However, it is assumed that ΔL=T3+t3-T4-t4.

Similarly, the total delay time U2 of the output (electrical signal) S5 at the first light receiving section 23 when the second light emitting section 22 is driven.
1 is U21=t 2+T2+T3+t3...
(4) becomes. Further, the total delay time U22 of the output (electrical signal) 86 in the second light receiving section 24 at this time is U22
=t2+72+T4+t4+2Tx (5). Therefore, the delay time difference ΔU2 between the two is ΔU 2
= U 21- U 22 = T 3 + t 3- T 4. -t4. -2
T x-8L-2TX...(
6).

Here, ΔU1 calculated using the above equations (3) and (6)
゜△U2 is the output of the phase difference detector 25 shown in FIG. Tx
=-(7). Therefore, the result processed by the control/arithmetic processing section 26 is only the delay time Tx of the light wave due to the atmosphere to be measured A', and the delay due to the light emitting section 21, 22, the light receiving section 23, 24, and the optical fibers 41 to 44. Not affected by changes in time.

According to this embodiment, the optical path length of the atmosphere to be measured A' is measured in the control/arithmetic processing section 26 based only on the delay time Tx due to the atmosphere to be measured, so that, for example, the temperature Even if the optical path lengths of the optical fibers 41 to 44 change due to the change, this will not be affected in any way, and there is no possibility that an error will occur in the measured value. Therefore, even in an atmosphere where electrical energy is unfavorable, such as an explosive gas atmosphere, optical path length measurement can be performed with high accuracy.

Note that the present invention is not limited to the above embodiments,
Of course, various modifications can be made without departing from the gist of the present invention.

〔Effect of the invention〕

As detailed above, the present invention connects the first light emitting means and the second light receiving means to one end of the first directional coupler via an optical fiber, and connects the first mirror to the other end. and the light emitting and receiving means are connected via an optical fiber, and the second light emitting means and the first light receiving means are connected to one end of the second directional coupler via the optical fiber, and the other end is connected to the second directional coupler. The second mirror and the light emitting/receiving means are connected via an optical fiber, and the first light emitting means is driven.
The second mirror is reflected by the first mirror through the directional coupler.
The light waves reaching the light receiving means are emitted into the atmosphere to be measured by the light emitting and receiving means via the first directional coupler, and are emitted into the atmosphere to be measured by the light receiving means.
By measuring the phase difference between the light wave and the light wave reaching the first light receiving means via the directional coupler, and driving the second light emitting means, the light wave reaches the first light receiving means via the second directional coupler. The light wave is reflected by the second mirror and reaches the first light receiving means, and the light wave is emitted to the atmosphere to be measured by the light emitting and receiving means through the second directional coupler, and is transmitted through the first directional coupler to the first light receiving means. The phase difference between the light waves reaching the second light receiving means is measured, and the optical path length of the atmosphere to be measured is calculated based on the measured phase differences.

Therefore, according to the present invention, it is possible to compensate for changes in the optical path length of the optical fiber that connects the main body of the optical path length measuring device and the light emitting/receiving optical system, as well as changes in the phase characteristics of the light emitting section and the light receiving section. It is possible to provide an optical path length measuring device that can accurately measure the optical path length even in an unfavorable measurement atmosphere.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a diagram for explaining the function and effect of the embodiment, and Figs. 3 and 4 are diagrams for explaining the conventional example. It is a diagram. 71... Modulation signal source, 5... Corner mirror, 11
... Display section, 20 ... Optical path length measuring instrument main body, 21.2
2... 1st. second light emitting section, 23.24...first.
Second light receiving unit, 25... Phase difference detector, 26... Control/arithmetic processing unit, 30... Light emitting/receiving optical system, 31.3
2... 1st. Second 2x2 directional genitalia <1st. Second
coupler〉, 33.35... 1st. Second internal reference beam mirror, 3
4...Mirror for light emission/reception, 36...Lens for light emission/reception, 41-48...Optical fiber.

Claims (1)

[Claims] first and second light emitting means and first and second light receiving means;
A first direction in which the first light emitting means and the second light receiving means are connected at one end via an optical fiber, and the first mirror and the light emitting/receiving means are connected at the other end via an optical fiber. The optical coupler, the second light emitting means and the first light receiving means are connected at one end via an optical fiber, and the second mirror and the light emitting/receiving means are connected at the other end via an optical fiber. A second directional coupler to be connected, and a light wave that is reflected by a first mirror via the first directional coupler and reaches the second light receiving means by driving the first light emitting means. measuring the phase difference between a light wave that is emitted into the atmosphere to be measured by the light emitting and receiving means via the first directional coupler and reaches the first light receiving means via the second directional coupler; By driving the second light emitting means, a light wave is transmitted through the second directional coupler, reflected by the second mirror, and reaching the first light receiving means, and the light wave is transmitted through the second directional coupler. a phase difference measuring means for measuring a phase difference between a light wave emitted by the light projecting light receiving means into the atmosphere to be measured and reaching the second light receiving means via the first directional coupler; and this phase difference measuring means. An optical path length measuring device comprising: an optical path length calculating means for calculating the optical path length of the atmosphere to be measured based on both phase differences measured by the method.