JPH067063B2 - Measuring device using interferometric optical fiber sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a physical quantity measuring device using an interference type optical fiber sensor, and more particularly to a device for measuring a physical quantity such as temperature and pressure with high sensitivity. Is.

[Conventional technology]

Since the measurement using the interferometric optical fiber sensor can perform highly sensitive measurement, various applications are expected. That is, focusing on the fact that the light flux emitted from the coherent light source is divided into two light fluxes and propagated through the optical fiber, and the phase difference between these two light fluxes changes according to the physical quantity to be measured applied to the optical fiber, The physical quantity to be measured is measured from the interference state of two light fluxes. The homodyne method and the heterodyne method are considered for the detection of the interference optical signal.The homodyne method does not require large-scale peripheral devices compared to the heterodyne method, and is simple with only basic optical components such as a lens and a polarizer. In addition, it has an advantage that a measurement system can be configured.

FIG. 6 (a) is a basic configuration diagram showing a conventional interference-type optical fiber sensor measuring device by the homodyne method, including a coherent light source unit 1, a two-beam separation unit 2, an interference-type optical fiber sensor 3,
The homodyne photodetector 4 is provided. FIG. 2B shows a specific example in which a Mach-Zehnder type sensor is used as the interference type optical fiber sensor 3 in such a measurement system. The coherent light source unit 1 is a laser 5 and the two beam separation unit 2 is a half beam. A photodiode 6 is used as the mirror 6 and the homodyne type photodetector 4. When the measured physical quantity given to the measurement optical fiber 7 changes, the phase difference between the light beam propagating in the measurement optical fiber 7 and the light beam propagating in the reference optical fiber 8 changes, and the light interfered by the half mirror 9 is changed. Is detected by the photodiode 6. Same figure (c)
Shows a specific example in which a polarization interference type sensor is used as the interference type optical fiber sensor 3, and linearly polarized light emitted from the polarizer 10 is separated into two light beams orthogonal to each other in the optical fiber 11, The phase difference between the two light fluxes changes according to the given physical quantity to be measured. The analyzer 12 takes out the interference light and detects the light intensity by the photodiode 6.

[Problems to be solved by the invention]

However, in the homodyne method, the sensor output I detected through the homodyne photodetector, that is, the optical-electrical converter, is the cosine function I = 1 + cosφ (1) of the phase difference φ of the two light fluxes, so It is a multi-valued function of the phase difference φ corresponding to the physical quantity S. Therefore, conversely, the physical quantity S to be measured can be uniquely determined only when the phase difference φ is within the range of 0 ≦ φ ≦ π.

On the other hand, the phase sensitivity per unit length of the optical fiber when the change in the measured physical quantity is ΔS and the phase change proportional to the measured physical quantity is Δφ can be expressed by Δφ / (ΔS · l). Therefore,
Under the limitation of 0 ≦ φ ≦ π, an attempt to increase the phase sensitivity narrows the measurement range of the physical quantity to be measured, and conversely, a wide measurement range of the physical quantity to be measured decreases the sensitivity. There was a problem.

[Means for solving problems]

The measuring device using the interferometric optical fiber sensor of the present invention is made in view of the above problems, the coherent light source unit (1) in which the wavelength of the laser light generated according to the control input changes.
A two-beam splitting part (2) for splitting the laser beam from the coherent light source part into two beams, and each laser beam from the two-beam splitting part is transmitted through two optical fibers, one of which is an optical fiber. An interferometric optical fiber sensor (3) that synthesizes and outputs both lights after the physical quantity to be measured is applied to, and a photodetector that detects the intensity of light from this interferometric optical fiber sensor and outputs an electrical signal ( 4) and an electric signal from this photodetector, and an adjusting unit (21) that outputs a control signal for controlling the wavelength of the laser light so that the value of the input signal becomes a predetermined constant value.
And a wavelength control section (22) for outputting a control input to the coherent light source section in response to a control signal from this adjusting section.

[Action]

The phase difference between the two light fluxes that changes due to the change in the physical quantity to be measured becomes constant by changing the wavelength of the laser light, and the change amount of the wavelength of the laser light, that is, the control signal from the adjusting unit changes the physical quantity to be measured. You can know the quantity.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 1 is a block diagram showing an embodiment of the present invention. In this embodiment, an interference type optical fiber sensor measuring device 20 based on the conventional homodyne method is provided with an adjusting section 21 and a wavelength controlling section 2.
A feedback control system consisting of 2 is added, and the wavelength of light emitted from the light source is used as a parameter for performing feedback control. FIG. 2 is a block diagram showing a more specific configuration of the coherent light source section 1 and the wavelength control section 22. The coherent light source unit 1 has a semiconductor laser 30 and a current control unit 31, and a constant current is always supplied to the semiconductor laser 30. The wavelength controller 22 includes a temperature control mount 33 on which the semiconductor laser 30 is mounted, an electronic cooler 34 that cools the temperature control mount 33, a temperature sensor 35 that measures the temperature of the temperature control mount 33, and a temperature sensor 35.
A current driver 36 for driving the electronic cooler 34 is provided so that the temperature detected by the control unit 21 becomes the temperature commanded by the adjusting unit 21. In the figure, the solid arrow indicates that signal transmission is performed by electrical coupling, the double dashed arrow indicates thermal coupling, and the double solid arrow indicates optical coupling. Is shown. The adjusting unit 21 is an electronic PI
The D adjuster inputs the interference light intensity output of the homodyne type photodetector 4 and outputs a corresponding temperature command signal so as to change the wavelength of the semiconductor laser 30 so that the value becomes constant.

FIG. 3 is a characteristic diagram for explaining the feedback control operation in this embodiment, and is a three-dimensional coordinate of the measured physical quantity S, the wavelength λ, and the interference light intensity I. A point P1 indicates the intensity of the interference light when the measured physical quantity is S ₁ and the wavelength of the light source is λ ₀ , and its value is I ₁ . Now, the measured physical quantity S applied to the interferometric optical fiber sensor 3 is from S ₁ to S ₂
The phase difference φ changes and the interference light intensity I changes to I ₁
To I ₂ . This change corresponds to the change from the state of point P1 to the state of point P2 along the characteristic A in FIG. Here, when the physical quantity to be measured S is fixed to S ₂ , the interference light intensity I and the wavelength λ have a characteristic B relationship. Therefore, in the adjusting unit 21, the point P
In order to bring the state of _No. 2 into the state of point P3 along the characteristic B, that is, in order to set the interference light intensity I to I ₁ , the temperature designation signal is output so that the wavelength of the semiconductor laser 30 becomes λ _1. To do.

Next, this feedback control will be described using an equation. The interference light intensity I when the wavelength λ ₁ (corresponding to λ ₀ in FIG. 3) and the measured physical quantity S ₁ is It is represented by. Further, the interference light intensity I when the wavelength λ ₂ (corresponding to λ ₁ in FIG. 3) and the measured physical quantity S ₂ is It is represented by. Since the two interference light intensities are equal, Therefore, if the measured physical quantity S ₁ is taken as the reference point, the measured physical quantity S can be known from the change in λ.

In this embodiment, since the wavelength λ is configured to be determined by the temperature t of the semiconductor laser 30, the measured physical quantity S can be detected from the temperature t.

FIG. 4 is a coherent light source unit 1 and a wavelength control unit 2 of FIG.
Instead of 2, the wavelength is controlled by the injection current. Here, the temperature of the semiconductor laser 30 of the coherent light source unit 1 is controlled by the temperature control unit 40 and the temperature control mount 3.
3, the injection current from the injection current driver 41 of the wavelength control unit 22 is controlled while being kept constant by the electronic cooler 34 and the temperature sensor 35. Therefore, in this case, the adjusting unit 21
A current command signal is given to the wavelength control unit 22 from, and the measured physical quantity S can be known from the change in the current value indicated by the current command signal.

Further, generally, both the wavelength and the laser output light intensity change due to the change of the injection current, so the measured physical quantity S can be known as a combined effect of these. That is, ΔI ₁ (see FIG. 5 (a)) is generated as a change amount of the light intensity I due to the change of the injection current i, and at the same time, the change of the wavelength λ due to the change of the injection current i and thus the phase difference φ (= ΔI ₂ (see FIGS. 5 (b) to 5 (d)) is generated as the change amount of the light intensity I due to the change of (n · 2π / λ · l). At this time, if ΔI ₂ is as shown in FIG.
They act additively with respect to ₁ , and in the case as shown in FIG. The former case corresponds to the case where the feedback gain is large in the wavelength controller 22 in FIG. 1, and the latter case corresponds to the case where the feedback gain is small.
Thus, the present invention also includes a method of knowing the physical quantity S to be measured from a change in current value through a plurality of actions.

〔The invention's effect〕

As described above, according to the measuring apparatus using the interference type optical fiber sensor of the present invention, the wavelength of the laser light is changed so that the interference light intensity is constant, and this change amount is changed by the control signal from the adjusting unit. Since it is possible to take out and know the amount of change in the physical quantity to be measured, while maintaining high phase sensitivity,
The measurement range of the physical quantity to be measured can be expanded.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a partial detailed block diagram thereof, FIG. 3 is a characteristic diagram for explaining the operation of the present embodiment, and FIG. Another detailed block diagram of other parts, FIG. 5 is a characteristic diagram for explaining an example of the operation when the configuration shown in FIG. 4 is used, and FIG. 6 is a configuration showing a conventional interferometric optical fiber sensor measuring device. It is a figure. DESCRIPTION OF SYMBOLS 1 ... Coherent light source part, 2 ... Two-beam separation part, 3 ... Interference type optical fiber sensor, 4 ... Homodyne type photodetection part, 20 ... Interference type optical fiber sensor measuring device, 21 ... Adjustment part, 22 ... Wavelength control part .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Ishihara 1-4-1 Sakuramura Umezono, Shinji-gun, Ibaraki Electronic Technology Research Institute, Industrial Technology Institute (72) Masafumi Tagawa 4-7 Harigaya, Urawa City, Saitama Prefecture No. 25 In stock company Sumita Optical Glass Works Urawa factory (72) Inventor Hiroshi Yamazaki 4-28-1, Nishirokugo, Ota-ku, Tokyo Yamatake Honeywell Co., Ltd. Kamata factory Tokio Goto (56) References Special Kai 59-32815 (JP, A) JP 57-192821 (JP, A) JP 60-170723 (JP, A)

Claims (1)

[Claims] 1. A coherent light source section in which the wavelength of a laser beam generated according to a control drive signal changes, a two-beam splitting section for splitting a laser beam emitted from the coherent light source section into two beams, and a measuring unit. It has an optical fiber and a reference optical fiber, and transmits each laser beam from the two-beam separation unit to each of these two optical fibers, and applies the measured physical quantity to the measurement optical fiber, and then synthesizes both laser beams. Optical fiber sensor that outputs the electric signal, a photodetector that detects the intensity of light from the interferometric optical fiber sensor, and outputs an electric signal, and an electric signal from the photodetector that is input to this electric signal. A control unit that outputs a corresponding control command signal, and a wavelength control unit that outputs the control drive signal to the coherent light source unit in response to the control command signal from the control unit, wherein the control command signal is , Wavelength system The coherent light source unit is set to a value such that the coherent light source unit emits a laser beam having a predetermined constant wavelength by a control drive signal output from the unit, and the measured physical quantity is measured from the change amount of the control command signal. A measuring device using an interferometric optical fiber sensor.