JPH04116416A - Optical-intensity modulation sensor - Google Patents

Abstract

PURPOSE:To make it possible to detect the measured value of an object to be measured precisely based on the modulation of a light signal without the effects from the outside by selectively branching a correcting light signal transmitted through optical fibers so as to bypass an optical modulator. CONSTITUTION:A measuring light signal and a correcting light signal having the different wavelength to each other from a light source X undergo time division, and the signals are outputted. The measuring light signal is inputted into a photodetector Y through an optical modulator 11 which modifies the signal based on the changing amount of an object to be measured with optical fibers 5 and 5' as transmitting paths. The signal is converted into the electric signal. Thus, the measured value of the object to be measured is obtained. The correcting light signal passes through the optical fibers 5 and 5' which also transmit the measuring light signal. The correcting light signal is selectively branched with a wave splitting part so as to bypass the optical modulator 11 and inputted into the photodetector Y. The signal is converted into the electric signal. The loss in the light signal caused by the optical fibers 5 and 5' themselves which are the transmitting paths due to the changing amount at the outside is electrically detected as the correcting value. The correcting value is fed back to the measured value obtained by the measuring light signal. Thus the measured value is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light intensity modulation sensor using a light modulation method.

[Conventional technology]

An optical intensity modulation sensor using an optical modulation method includes a light source, an optical fiber that transmits an optical signal, an optical modulator that changes the intensity two phases or the traveling direction of the light depending on the amount of change in the object to be measured, and an optical fiber that transmits the optical signal electrically. It consists of a photodetector that converts it into a signal.

FIG. 6 is a conceptual diagram showing the configuration of a conventional light modulation type light intensity modulation sensor.

In FIG. 6, 22 is a power source, 23 is a light emitting element, 24 is a condensing lens, 25 is an optical fiber, 26 is a collimating lens, 27 is an optical modulator, 28 is a fiber optic lens, 2
9 is a light receiving element, 30 is a photoelectric conversion circuit (0/E conversion circuit)
shows.

In the conventional optical intensity modulation sensor configured as described above, the light emitted from the light emitting element 23 is focused by the condensing lens 24 and enters the optical fiber 25 . optical fiber 2
The light incident on 5 (hereinafter referred to as "optical signal") is input to optical modulator 27 via collimating lens 26 . The optical signal input to the optical modulator 27 is modulated by the amount of change in the measurement target, and then transmitted to the light receiving element 29 via the fiber input lens 28 and the optical fiber 25, and converted into an electrical signal by the photoelectric conversion circuit 30. converted.

The optical modulator 27 modulates the optical signal based on external pressure changes, temperature changes, magnetic field changes due to the Faraday effect, electric field changes due to the Pockels effect, and the like.

Therefore, by converting the optical signal modulated by the optical modulator 27 into an electrical signal by the photoelectric conversion circuit 30, it is possible to obtain a measured value of the measurement target.

An example in which this conventional light modulation type light intensity modulation sensor is used as a pressure gauge will be described with reference to FIG.

FIG. 7 is a conceptual diagram showing the configuration of a pressure gauge using a conventional light modulation type light intensity modulation sensor.

In FIG. 7, 31 is a light source, 25 is an optical fiber, 3
2 is a fiber collimator, 33 is a connector, 34 is a diaphragm (pressure sensitive element), 35 is a screen, 29 is a light receiving element,
3G is an output terminal.

As shown in FIG. 7, a pressure gauge using a conventional light modulation type light intensity modulation sensor has a light source 31 and a fiber collimator 32.
An optical fiber 25 serving as a transmission path for optical signals is arranged between the fiber collimator 32 and the light receiving element 29, and a diaphragm corresponding to the optical modulator 27 shown in FIG. 6 is arranged between the two fiber collimators 32. 34 and 35 are arranged.

A pressure gauge using a light intensity modulation sensor using a conventional light modulation method configured as described above receives light from the light source 31 by moving up and down the screen 35 on the diaphragm 34 arranged between the fiber collimators 32 according to changes in the pressure of the object to be measured. The pressure of the object to be measured is electrically detected by changing the amount of light of the optical signal transmitted to the element 29 and electrically detecting the change in the amount of light by the light receiving element 29.

For simplicity, the screen 35 has been used in the explanation, or there is also a method that uses two deflection plates and changes in the rotation angle.

[Invention or problem to be solved]

However, in such a conventional light modulation type light intensity modulation sensor, the connector 33 is affected by external temperature characteristics, and the optical fiber 25 itself, which is the optical signal transmission path, is exposed to external influences such as temperature change, pressure change, etc. Due to the application of vibrations, etc., the loss of optical signals occurring in the optical fiber 25 and connector 33 that are the transmission system is no longer constant, and as a result, only the optical signal modulation by the optical modulator 27 is precisely modulated by the photoelectric conversion circuit 30. The problem was that it could only be detected.

For example, as shown in FIG. 7, there is a pressure gauge to which a conventional light modulation type light intensity modulation sensor is applied.

A voltage is detected at the output terminal 36 by converting an optical signal whose light intensity is changed by the diaphragm 34 and the screen 35 into an electric signal due to a change in the pressure of the object to be measured. However, if the loss of the optical signal generated in the optical fiber 25 and connector 33, which are the transmission system, changes due to changes in measurement conditions (for example, temperature, etc.), the voltage detected at the output terminal 36 will be affected by this, and as shown in FIG. As shown in the figure, when the temperature To, which is the measurement condition, changes to the temperature T°, the loss of the optical signal in the transmission system changes, and the output voltage for the pressure PO of the measurement object changes from ■to to ■t°. It will change.

In this way, with conventional optical modulation type optical fibers, is it possible to relatively detect changes in the pressure of the object to be measured?As the optical signal loss in the transmission system changes due to changes in measurement conditions, it is difficult to detect the pressure of the object to be measured. No changes could be absolutely detected.

SUMMARY OF THE INVENTION In view of the above problems, the object of the present invention is to provide a precision optical fiber that is not affected by external changes such as temperature changes or mechanical pressure changes. Another object of the present invention is to provide a light intensity modulation sensor that can detect a measured value of a measurement target by modulating an optical signal in an optical modulator.

[Means to solve the problem]

The light intensity modulation sensor of the present invention includes: a light source that time-divisionally outputs a measurement optical signal and a correction optical signal having different wavelengths; an optical fiber that transmits the measurement optical signal and the correction optical signal; an optical modulator that modulates the measurement optical signal transmitted by the optical fiber according to the amount of change in the measurement target;
A branching unit that selectively branches the correction optical signal transmitted by the optical fiber so as to bypass the optical modulator, and converts the correction optical signal and the measurement optical signal modulated by the optical modulator into electrical signals. It is equipped with a photodetector that

[Effect]

According to the configuration of the present invention, the light source outputs the measurement optical signal and the correction optical signal having different wavelengths in a time-division manner. Using an optical fiber as a transmission path, the measurement optical signal is input to a photodetector via an optical modulator that modulates the amount of change in the measurement object, and is converted into an electrical signal, thereby obtaining a measurement value of the measurement object. In addition, using an optical fiber common to the measurement optical signal as a transmission path, the correction optical signal is selectively branched by a demultiplexer so as to bypass the optical modulator, and is input to a photodetector and converted into an electrical signal. Therefore, the loss caused to the optical signal by the amount of change in the optical fiber itself or the outside, which serves as the transmission path, is electrically detected as a correction value, and this correction value is fitted back to the measurement value of the measurement optical signal, thereby improving the measurement value. Make corrections.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS. 1 to 5.

FIG. 1 is a conceptual diagram showing the configuration of a light intensity modulation sensor according to a first embodiment of the present invention.

In FIG. 1, a light source The correction optical signal is time-divided and output.

4 is a condensing lens for condensing the optical signal output from the two-wavelength light emitting element 3; 5 and 5' are optical fibers for transmitting the measurement optical signal and the correction optical signal; and 6 is a collimating lens. 7 is a beam splitter, 8 is a filter that selects a measurement optical signal with wavelength λ1, 9 is a filter that selects a correction optical signal with wavelength λC, 10 is a reflector, and 11 is a filter that selects a measurement optical signal with wavelength λ1. It is an optical modulator that modulates signals.

The demultiplexer Z is composed of a beam splitter 7, a filter 9, and a reflecting mirror 1.0, and selectively branches the correction optical signal transmitted through the optical fiber 5 so as to bypass the optical modulator II.

Y is a photodetector that converts the correction optical signal and the measurement optical signal modulated by the optical modulator 11 into electrical signals, and is composed of a light receiving element 12 and a photoelectric conversion circuit 13. Also 14
is a fiber optic lens.

A light intensity modulation sensor configured in this way usually uses a light source
Using the power source 1 as a power source, the two-wavelength light emitting element 3 outputs a measuring optical signal of wavelength λ1.

Then, by switching the power source of the light source X to the power source 2 once every several milliseconds to several seconds, the two-wavelength light emitting element 3 outputs a correction optical signal of wavelength λC.

Normally, a light source X outputs a measurement optical signal with a wavelength λ1 from a two-wavelength light emitting element 3, the light is focused by a condenser lens 4, and input into an optical fiber 5. The measuring optical signal input to the optical fiber 5 is transmitted through the optical fiber 5 and input to the beam splitter via the collimating lens 6. The measurement optical signal input to this beam splitter 7 is filtered to a filter 8.
However, since the measurement optical signal has a wavelength λ1, it is input to the optical modulator 11 by passing only through the filter 8 (in the direction of arrow A). The measurement optical signal input to the optical modulator 11 is modulated by the amount of change in the object to be measured.

Thereafter, the measurement optical signal modulated by the optical modulator 11 is inputted to the light receiving element 12 of the photodetector Y and the photoelectric conversion circuit 13 via the beam splitter 7, the fiber optic lens 14, and the optical fiber 5'. By converting it into a signal, a measured value of the measurement object is obtained.

Also, once every few milliseconds to several seconds, light source
Outputting a correction optical signal of wavelength λC from the wavelength light emitting element 3;
The light is focused by a focusing lens 4 and input into an optical fiber 5.

The correction optical signal incident on the optical fiber \5 is transmitted through the optical fiber 5 and input to the beam splitter 7 via the collimating lens 6. The correction optical signal input to the beam splitter 7 is split into two parts, one on the filter 8 side and one on the filter 9 side, but since the wavelength of the correction optical signal is λC, it is transmitted only through the filter 9 (in the direction of arrow B). , reflector 1
0 and is input to the photodetector Y via the beam splitter 7° fiber optic lens 14 and the optical fiber 5. That is, the correction optical signal is branched so as to bypass the optical modulator 11. The correction optical signal inputted to the photodetector Y is then converted into an electrical signal, which is the value when not modulated by the optical modulator 11, that is, the optical fiber 55' itself, which is a transmission path for the measurement optical signal and the correction optical signal. The loss caused to the optical signal by the amount of change given to is detected as a correction value. Then, the detected correction value is fed back to the measurement value of the measurement object obtained by the measurement optical signal by a correction circuit (not shown), thereby correcting the measurement value.

At this time, it is desirable that the transmission system does not have nonlinear wavelength characteristics with respect to the loss that becomes the correction value. That is, for example, the wavelength λ
If the loss due to the transmission system for the measurement optical signal of wavelength λC is 10 dB, the loss due to the transmission system for the correction optical signal of wavelength λC is 10×K (K is a constant) dB, and so on. It is desirable that the loss caused by the transmission system and the correction optical signal have a linear relationship.

A light intensity modulation sensor configured as described above normally transmits a measuring optical signal of wavelength λ1 from the two-wavelength light emitting element 3 to the optical fiber 5.
Collimation rinse6. Beam splitter 7, filter 8
and further input the measuring optical signal modulated by the amount of change in the measurement target in the optical modulator 11 to the photodetector Y via the beam splitter 7 and the optical fiber 5''. Then, by switching the power source of the light source Fiber 5. Collimating lens 6, beam splitter 7 serving as a splitting section Z,
Through the filter 91 and the reflecting mirror 10, the optical fiber 5'
By inputting the signal to the photodetector Y via the optical fiber 5,5" that serves as the transmission path, the loss caused to the optical signal due to the amount of change in itself or externally is detected as a correction value. Then, this correction value is used by the correction circuit. The measured value is corrected by feeding back the measured value of the measurement target using the measurement optical signal.

Next, FIG. 2 shows an example in which the demultiplexer Z is composed of a wavelength selection mirror and a mirror.

FIG. 2 is a conceptual diagram showing the configuration of a light intensity modulation sensor according to a second embodiment of the present invention.

In FIG. 2, 15.15' is a wavelength selection mirror that transmits the measuring optical signal of wavelength λ1 and reflects the correction optical signal of wavelength λC. 16.16 is a mirror and constitutes the demultiplexing section Z. Also, the same reference numerals as in the first embodiment are the same.

As shown in FIG. 2, a wavelength selection mirror 15 is arranged at a position opposite to the collimating lens 6, a mirror 16 is arranged at a position opposite to this wavelength selection mirror 15, and a mirror 16 is arranged at a position opposite to this mirror 16. ', and a wavelength selection mirror 15' is located opposite to this mirror 16'.
A branching section Z is constructed by arranging .

In the light intensity modulation sensor configured in this way, the measuring optical signal of wavelength λ1 from the light source The light is inputted to the fiber human light lens 14 through the arrow (in the direction indicated by the arrow). Further, the correction optical signal of wavelength λC from the light source X is transmitted through the collimating lens 6,
After being reflected to the mirror 16 side by the 45° reflection wavelength selection mirror 15, the wavelength selection mirror 15 is reflected by the mirror 16' and the wavelength selection mirror 15.
′ is input to the fiber input lens 14 via
direction of arrow B). As the wavelength selection mirror 1515', for example, a dichroic mirror or a cold mirror is used.

Next, FIG. 3 shows an example in which the demultiplexing section Z is composed of a spectroscopic prism and a mirror.

FIG. 3 is a conceptual diagram showing the configuration of a light intensity modulation sensor according to a third embodiment of the present invention.

In FIG. 3, X is a light source consisting of power supplies 1, 2 and a two-wavelength light emitting element 3, which time-divisionally outputs a measurement optical signal and a correction optical signal having different wavelengths. 4 is a condenser lens, 7 is a beam splitter, 6 is a collimating lens,
11 is an optical modulator, and Y is a photodetector consisting of a light receiving element 12 and a photoelectric conversion circuit 13, which are similar to those in the first embodiment. Further, 18 is a spectroscopic prism, and 19 is a reflecting mirror, which constitutes a branching section Z that selectively branches the correction optical signal so as to bypass the optical modulator 11. Also 19
is a reflecting mirror, and 17 is an optical fiber.

A light intensity modulation sensor configured in this way usually uses a light source
Using the power source 1 as a power source, the two-wavelength light emitting element 3 outputs a measuring optical signal of wavelength λ1.

Then, by switching the power source of the light source X to the power source 2 once every several milliseconds to several seconds, the two-wavelength light emitting element 3 outputs a correction optical signal of wavelength λC.

Normally, a measurement optical signal of wavelength λ1 is output from the two-wavelength light emitting element 3 of the light source The measurement optical signal input to the optical fiber 17 is transmitted to the beam splitter 7 and the collimating lens 6.
The measurement optical signal of wavelength λ1 is input to the optical modulator 11 by transmitting it to the spectroscopic prism 18 through the spectroscopic prism 18 and separating it into spectra using the spectroscopic prism 18. The measurement optical signal input to the optical modulator 11 is modulated by the amount of change in the measurement target, and then reflected by the reflector 19 and sent back to the optical modulator 1.
12 Spectral prism 18. The light is input to a photodetector Y via a collimating lens 6 and a beam splitter 7. Then, by converting the measuring optical signal into an electrical signal by the light receiving element 12 and the photoelectric conversion circuit 13 of the photodetector Y,
Obtain the measured value of the measurement target.

Also, once every few milliseconds to several seconds, light source
Outputting a correction optical signal of wavelength λC from the wavelength light emitting element 3;
The light is focused by a focusing lens 4 and input into an optical fiber 17 . The correction optical signal input to the optical fiber 17 is transmitted to the spectroscopic prism 18 via the beam splitter 7, the optical fiber 17, and the collimating lens 6. Then, the optical signal for correction is split by the spectroscopic prism 18 and output in the direction of the reflecting mirror 19'', so as to bypass the optical modulator 11.Then, by being reflected by the reflecting mirror 19', the signal is split again. Spectroscopic prism 18. Inputs to the photodetector Y via the collimating lens 6 and beam splitter 7. By converting the correction optical signal input to the photodetector Y into an electrical signal, the light is not modulated in the optical modulator 11. In other words, the loss caused to the correction optical signal by the amount of external change applied to the optical fiber 17 itself, which is the transmission path for the measurement optical signal and the correction optical signal, is detected as a correction value. The correction circuit (
(not shown), the measured value is corrected by feeding back to the measured value of the measurement object obtained by the measuring optical signal (wavelength λ1).

A light intensity modulation sensor configured as described above normally transmits a measuring optical signal of wavelength λ1 from a two-wavelength light emitting element to a condensing lens 4.
Optical fiber 17. The light is input to the spectroscopic prism 18 via the beam splitter 7 and the collimating lens 6, and is outputted to the optical modulator 11 by being split into spectra. The modulated measurement optical signal is reflected by the reflecting mirror 19 and inputted to the photodetector Y via the spectroscopic prism 18° collimating lens 6 and beam splitter 7 again, thereby obtaining a measurement value of the measurement target.

Then, by switching the power source of the light source X to the power source 2 once every several milliseconds to several seconds, the two-wavelength light emitting element 3 outputs a correction optical signal of wavelength λC, and the condenser lens 4. Optical fiber 17. The beam is inputted to the spectroscopic prism 18 via the beam splitter 7 and the collimating lens 6, and is split into spectra, thereby selectively branching to the reflecting mirror 19' side so as to bypass the optical modulator 11, and being reflected by the reflecting mirror 19'.
Spectroscopic prism 18. By inputting the correction optical signal to the photodetector Y via the collimating lens 6 and the beam splitter 7, the loss caused to the correction optical signal by the amount of external change in the optical fiber 17 itself, which serves as the transmission path, can be corrected. Detect as a value. Then, the correction circuit feeds back this correction value to the measurement value of the measurement object based on the measurement optical signal, thereby correcting the measurement value.

Next, FIG. 4 shows an example in which the demultiplexer Z is composed of a wavelength selection mirror.

In FIG. 4, Z is a demultiplexer, which is composed of a wavelength selection mirror that transmits a measurement optical signal of wavelength λ1 and rejects a correction optical signal of wavelength λC. Also, the same reference numerals as in the second embodiment are the same. Further, 20 is a mirror.

As shown in FIG. 4, a wavelength selection mirror for O0 reflection, which is a demultiplexer Z, is placed at a position facing the collimating lens 6, and a mirror 20 is placed at a position facing the wavelength selection mirror via an optical modulator 11. Place. In the optical intensity modulation sensor configured in this way, a measuring optical signal with a wavelength λ1 is transmitted through a wavelength selection mirror, modulated by the optical modulator 11, reflected by the mirror 20, and then transferred again to the wavelength selection mirror and the collimating lens. 6 and beam splitter 7 to the photodetector Y (in the direction of arrow C). In addition, the correction optical signal of wavelength λC is approximately l 0 due to the wavelength selection mirror with 0° reflection.
096 is reflected and input to the photodetector Y via the collimating lens 6 and beam splitter 7.

Above is the first part. Second. FIG. 5(a) shows an example showing the relationship between the light emission level and the light reception level of the measurement optical signal and the correction optical signal by the light intensity modulation sensors of the third and fourth embodiments.
Shown in (b).

Figure 5 (aL (in bl), ■ is the emission level of the correction optical signal with wavelength λC, ■ is the emission level of the measurement optical signal with wavelength λ1, ■, ■ is the light reception level of the correction optical signal, ■, ■
indicates the light reception level of the measurement optical signal.

As shown in Fig. 5(a), when the loss caused to the optical signal by the optical fiber itself, which is the transmission path, is small, the reception level ■ and the emission level ■ of the correction optical signal are almost the same, and the measurement Compared to the light reception level (2) or the light emission level (2) of the optical signal, it is lowered by the amount (2) modulated by the optical modulator. On the other hand, as shown in FIG. 3(b), if the optical fiber itself, which is the transmission path, causes a lot of loss to the optical signal, the light reception level of the measurement optical signal ■ and the light reception level of the correction optical signal ■ In both cases, the luminescence levels are lower than those in (1) and (2). In this case, the loss in the transmission system is detected as a correction value by comparing the light reception level and the light emission level of the correction optical signal. For example, if the correction value based on the correction optical signal becomes significantly large, the light emission level of the two-wavelength light emitting element may be increased until the measured value based on the measurement optical signal reaches a certain value.

Note that the first thing. Second. In the third and fourth embodiments, the light source
As an optical signal with two different wavelengths λ1. An optical signal for measuring λC and an optical signal for correction may be used, or optical signals having three or more different wavelengths may be used. Further, the modulation method of light by the optical modulator 11 is not particularly limited.

〔Effect of the invention〕

According to the optical intensity modulation sensor of the present invention, the measurement optical signal via the optical modulator and the correction optical signal bypassing the optical modulator are time-shared using a common optical fiber serving as a transmission path from the light source. By converting the optical signal for correction and the optical signal for measurement into electrical signals, the loss caused to the optical signal by the amount of change in the optical fiber itself or the outside, which is the transmission path, can be electrically corrected. The measured value is corrected.

Therefore, even if changes such as temperature changes, mechanical pressure changes, etc. are applied to the optical fiber, which is the transmission path for optical signals, and the measurement conditions in the transmission system change, it can be accurately measured without being affected by the changes. It is possible to obtain a light intensity modulation sensor that can detect a measurement value of a measurement target by modulating an optical signal in an optical modulator, and can be constructed at a relatively low cost.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the configuration of a light intensity modulation sensor according to a first embodiment of the present invention, FIG. 2 is a conceptual diagram showing the configuration of a light intensity modulation sensor according to a second embodiment of the present invention, and FIG. FIG. 4 is a conceptual diagram showing the configuration of a light intensity modulation sensor according to a fourth embodiment of the present invention, FIG. 5 is a conceptual diagram showing the configuration of a light intensity modulation sensor according to a fourth embodiment of the invention, a, ) and (b) are waveform diagrams showing the light emission level and light reception level of a light signal by a light intensity modulation sensor according to an embodiment of the present invention, and FIG. 6 is a waveform diagram showing a light intensity modulation sensor using a conventional light modulation method. Fig. 7 is a conceptual diagram showing the structure of a pressure gauge using a light intensity modulation sensor using a conventional light modulation method. Fig. 8 shows a pressure gauge using a light intensity modulation sensor using a conventional light modulation method. FIG. 3 is a diagram showing the relationship with output voltage. X...Light source, 5.5', 17...Optical fiber, 11 Optical modulator, Y...Photodetector, Z...Demultiplexer diagram, pressure

Claims (1)

[Claims] A light source that time-divisionally outputs a measurement optical signal and a correction optical signal having different wavelengths, an optical fiber that transmits the measurement optical signal and the correction optical signal, and a measurement optical signal that is transmitted by this optical fiber. an optical modulator that modulates the optical signal according to the amount of change in the measurement target; a demultiplexer that selectively branches the correction optical signal transmitted by the optical fiber so as to bypass the optical modulator; A light intensity modulation sensor comprising an optical signal and a photodetector that converts the measurement optical signal modulated by the optical modulator into an electrical signal.