JP5171241B2 - Physical quantity measurement system - Google Patents

Description

  The present invention relates to a physical quantity measurement system that measures physical quantities such as strain applied from each measurement object at each measurement object separated from each other using an FBG (Fiber Bragg Grating) sensor. .

In general, as shown in FIG. 14, the FBG sensor is centered on a reference wavelength λ _S set in advance for the FBG sensor 1 when light 2 having a broadband wavelength is incident from one end (incident end) of the FBG sensor. The reflected light 3 having a mountain-shaped wavelength characteristic as a wavelength is output from one end (incident end). Further, transmitted light 4 having a wavelength characteristic with the reference wavelength λ _S as the center wavelength is output from the other end (outgoing end) to the FBG sensor 1.

When distortion (physical quantity) is applied to the FBG sensor 1, the center wavelength λ _C of the reflected light 3 deviates from the reference wavelength λ _S. Since the wavelength shift Δλ (= λ _C −λ _S ) is proportional to the strain amount (physical quantity) ε, the strain amount (physical quantity) ε applied to the FBG sensor 1 can be measured by measuring the wavelength shift Δλ. It is. Note that the center wavelength λ _C of the transmitted light 4 performs the same operation as the center wavelength λ _C of the reflected light 3. Hereinafter, a physical quantity measurement technique using the FBG sensor 1 at the current time point will be described.

  (A) In FIG. 15, a plurality of FBG sensors 1 having such characteristics are attached to a measurement object, and each FBG sensor 1 is connected in series with an optical fiber 5, and one end (incident end) 5a of the optical fiber 5 is connected to This is an FBG sensor system that applies wide wavelength band pulsed light from a wide wavelength band pulsed light source 6 (see Patent Document 1).

Reflected light 3 from each FBG sensor 1 disposed at each of the distance positions L ₁ , L ₂ , L ₃ ... Of the optical fiber 5 is branched from the optical fiber 5 by the coupler 7 and sent to the wavelength shift amount detection unit 8. Are incident with a time difference corresponding to each of the distance positions L ₁ , L ₂ , L ₃ ..., So that the wavelength shift amount detector 8 has the center wavelength λ _C of the reflected light 3 from each FBG sensor 1. Wavelength shifts Δλ ₁ , Δλ ₂ , Δλ ₃ ,... From the reference wavelength λ _S can be detected individually. Therefore, the amount of distortion (physical quantity) applied to each FBG sensor 1 can be detected individually.

(B) Instead of the wide wavelength band pulse light source 6, it is also possible to use a wide wavelength band continuous light source (see Patent Document 2). In this case, the reference wavelength λ _S of each FBG sensor 1 needs to be set to different values λ _S1 , λ _S2 , λ _S3,. The wavelength shift amount detection unit 8 determines the known reference wavelengths λ _S1 , λ _S2 , λ _S3 ,..., The center wavelengths λ _C1 , λ _C2 , λ _C3,. Wavelength deviations Δλ ₁ , Δλ ₂ , Δλ ₃ ,... From the reference wavelengths λ _S1 , λ _S2 , λ _S3 ,.

(C) As shown in FIG. 16, a plurality of FBG sensors 1 having the same reference wavelength λ _S are connected in parallel via a coupler 7 with one optical fiber 5, and one end (incident end) of the optical fiber 5 is connected. ) Is applied from the narrow-band pulse light source 10 with narrow-band pulse measuring light 14 having a wavelength λ shifted by a minute wavelength Δλ with respect to the reference wavelength λ _S of each FBG sensor 1, and reflected light from each FBG sensor 1. A technique for measuring distortion from a level change amount of 3 has been proposed. That is, the reflected light 3 from each FBG sensor 1 disposed at each distance position L ₁ , L ₂ , L ₃ ... Of the optical fiber 5 is branched by the circulator 11 and converted into an electrical signal by the light receiver 12. Then, the amount of strain (physical quantity) applied to each FBG sensor 1 is obtained by the calculation unit 13 (see Patent Document 3).

As shown in FIG. 17, distortion is applied to the center wavelength λ _C of the wavelength characteristic of the reflected light from each FBG sensor 1 arranged at each distance position L ₁ , L ₂ , L ₃ . Then, for example, the wavelength characteristic itself moves to the right side because it moves to the right side in the figure. As a result, the level of the reflected light of the pulsed measuring light 14 itself when the pulsed measuring light 14 of a narrow band is applied, changes from the level L _S to the level L _L. This level change amount (L _L −L _S ) corresponds to the wavelength shift Δλ from the reference wavelength λ _S.
US Pat. No. 5,680,489 US Pat. No. 5,361,130 JP 2004-309218 A

  However, the strain measurement system using each of the FBG sensors (a) to (c) described above still has the following problems to be improved.

In the method of applying wide wavelength band pulsed light of (a) described in Patent Document 1, since pulse light in a wide wavelength band is used, wavelength components other than the vicinity of the reference wavelength λ _S are not used. The efficiency is poor and the S / N ratio decreases.

In addition, when the wide wavelength band continuous light source (b) described in Patent Document 2 is used, there is a problem that FBG sensors of the same standard (same reference wavelength λ _S ) cannot be used.

In the case where the wavelength of described in Patent Document 3 (c) lambda uses narrowband pulsed measuring light 14 which is offset by a small wavelength Δλ with respect to the reference wavelength lambda _S of the FBG sensor 1, the reference wavelength lambda _S The wavelength shift amount Δλ is obtained from the difference in detection level (L _L −L _S ) of the light receiver. This level (L _L −L _S ) difference is applied to the FBG sensor 1 and the pulse measurement light. Therefore, it is difficult to distinguish whether it is caused by the level fluctuation of 14 itself, and the measurement accuracy is lowered. Further, since the coupler 7 needs the same quantity as the FBG sensor 1, there is a problem that the manufacturing cost of the distortion measuring system increases.

The present invention has been made in view of such circumstances, and even when a plurality of FBG sensors having the same wavelength characteristics including a reference wavelength are connected in series with an optical fiber, the wavelength characteristics of reflected light when a physical quantity is applied. It can be detected in a short time and high precision, moreover, an object of the invention to provide a physical quantity measuring system that can measure in a short time and high accuracy the physical quantity to be applied to the FBG sensor.

In order to solve the above problems, the physical quantity measurement system of the present invention is
A plurality of FBG sensors that are provided in a plurality of measurement objects spaced apart from each other, and in which the center wavelength of reflected light with respect to incident light changes according to a physical quantity applied from the measurement object;
An optical fiber connecting the FGB sensors in series;
A wavelength-swept pulse light source that generates a plurality of pulse lights whose wavelengths are sequentially changed, and sequentially enters the incident end of the optical fiber as an incident pulse light;
A circulator that branches each reflected pulsed light that is sequentially incident on the optical fiber and is reflected by each FBG sensor and propagates toward the incident end;
A light receiver for receiving each reflected pulse light branched by this circulator;
A measurement value storage means for storing and holding the received light level of the reflected pulse light from each FBG sensor with respect to each incident pulse light, corresponding to the wavelength of the incident pulse light;
Wavelength characteristic calculating means for calculating the wavelength characteristic of the reflected light of each FBG sensor from the received light level of each reflected pulse light stored in the measured value storage means;
A physical quantity calculating means for obtaining a physical quantity applied to each FBG sensor from the calculated center wavelength of the wavelength characteristic;
With
The wavelength characteristic calculation means (35) is configured to select a group of received light levels of each reflected pulse light for each wavelength of the incident pulse light stored in the measurement value storage means (30), and the reflected pulse light having a different wavelength for each FBG sensor. The wavelength for calculating the wavelength characteristics of the reflected light of each of the FBG sensors using the data editing unit (32) recombined into the group (33) and the received light level of the reflected pulsed light having a different wavelength for each edited FBG sensor A characteristic calculation unit (35),
The center wavelengths of the FBG sensors in a state where the physical quantity is not applied are set to be equal to each other,
The transmission interval (T) of each pulsed light of each incident pulsed light that the wavelength swept pulse light source sequentially enters the incident end of the optical fiber is set to be equal to each other, and the pulsed light reciprocates through the optical fiber. It is set longer than the time required (2 nL / C) .

In the physical quantity measurement system configured as described above, the wavelength-swept pulse light source makes incident pulsed light composed of a plurality of pulsed light whose wavelengths change sequentially enter the optical fiber. That is, in an optical fiber in which pulsed light whose wavelength λ sequentially changes propagates, for example, no distortion (physical quantity) is applied to each FBG sensor, and the wavelength λ of the first pulsed light of incident pulsed light is In the case of the reference wavelength λ _S , the elapsed time from the output time of the incident pulse light at the light receiving time in the light receiver of the reflected light from each FBG sensor located at each distance position L ₁ , L ₂ , L ₃ ,. The time is times t ₁ , t ₂ , t ₃ ,... Corresponding to the distance positions L ₁ , L ₂ , L ₃ ,. When a physical quantity is applied to each FBG sensor, the wavelength characteristic of the reflected light shifts in the direction of the wavelength axis, so that the times t ₁ , t ₂ , t corresponding to the distance positions L ₁ , L ₂ , L ₃ ,. The levels FB ₁₁ , FB ₂₁ , FB ₃₁ ,... at t ₃ ,.

Then, when pulse light having a wavelength (λ _S + Δλ _A ) having a wavelength λ shifted by Δλ _A after the period T in the incident pulse light has been input to the optical fiber, predetermined time t ₁ , t ₂ , t ₃ ,. Levels FB ₁₂ , FB ₂₂ , FB ₃₂ ,... Corresponding to physical quantities are obtained at times t ₁ + T, t ₂ + T, t ₃ + T,. Further, when pulse light having a wavelength (λ _S + 2Δλ _A ) having a wavelength λ shifted by Δλ _A after a predetermined period T has elapsed is input to the optical fiber, the predetermined period T × at times t ₁ , t ₂ , t ₃ ,. Levels FB ₁₃ , FB ₂₃ , FB ₃₃ ,... Corresponding to physical quantities are obtained at times t ₁ + 2T, t ₂ + 2T, t ₃ + 2T,.

Since the levels FB ₁₁ , FB ₂₁ , FB ₃₁ , FB 41,... At the respective wavelengths λ _S , λ _S + Δλ _A , λ _S + 2Δλ _A , λ _S + 3Δλ _A ,... In the wavelength characteristics of the reflected light of the first FBG sensor are obtained. The wavelength characteristics of the reflected light can be obtained by obtaining the envelope of these levels.

As a result, the center wavelength λ _C in the wavelength characteristic of the reflected light is obtained, and the wavelength shift amount from the reference wavelength λ _S is obtained. Therefore, the amount of strain (physical quantity) applied to the FBG sensor can be measured. In this case, the level of the wavelength characteristics of the reflected light of each FBG sensor appears at a predetermined time position, so that the wavelength characteristics of the reflected light of each FBG sensor can be overlapped.

In such a configuration , according to the group of reflected pulsed light having different wavelengths for each FBG sensor, the wavelength characteristics of the reflected light for each FBG sensor can be easily obtained.

In another invention , the physical quantity calculation means includes a reference wavelength storage unit that stores a reference wavelength of the FBG sensor, and a shift that calculates a shift wavelength of the calculated center wavelength of the reflected light of each FBG sensor from the reference wavelength. and wavelength calculator, and a physical quantity calculation unit that calculates a physical quantity applied to the FBG sensor from the shift wavelengths this was calculated.

  In yet another invention, the wavelength-swept pulse light source includes a semiconductor laser in which one light emitting end face is AR coated, a collimating lens for collimating light emitted from the AR coated end face of the semiconductor laser, and a collimating Consists of a diffraction grating that receives collimated light emitted from the lens and diffracts it at an angle according to the wavelength, a reflector, and a reflector drive unit, and the wavelength continuously changes from the other emission end face of the semiconductor laser. A micro electro mechanical systems (MEMS) scanner that controls a reflector driving unit to emit light to be emitted, and a pulse that applies a pulse signal having a predetermined period and a predetermined duty ratio for driving the semiconductor laser as a drive signal to the semiconductor laser It consists of a generator.

  In yet another invention, the wavelength-swept pulse light source includes a wavelength-variable light source that emits light having a continuously variable wavelength and a constant level, and a pulse generator that emits a pulse signal having a predetermined period and a predetermined duty ratio. And an optical switch that receives the pulse signal and controls on / off of the light emitted from the wavelength variable light source to generate a plurality of pulse lights.

  In yet another invention, the wavelength-swept pulse light source includes a wavelength-variable light source that emits light having a continuously variable wavelength and a constant level, and a pulse generator that emits a pulse signal having a predetermined period and a predetermined duty ratio. And an optical amplifier that receives the pulse signal and controls the light emitted from the wavelength tunable light source to be turned on / off to generate the plurality of pulse lights.

  In yet another invention, the wavelength tunable light source includes a semiconductor laser in which one light emitting end face is AR-coated, a collimating lens for collimating light emitted from the AR-coated end face of the semiconductor laser, A diffraction grating that receives collimated light emitted from a collimating lens and diffracts it at an angle according to the wavelength, a reflector and a reflector driving unit, and is formed from the other AR-coated emission end face of the semiconductor laser. It is comprised with the MEMS scanner which controls a reflector drive part so that the light from which a wavelength changes continuously may be emitted.

  In the physical quantity measurement system configured in this way, even when a plurality of FBG sensors having the same wavelength characteristics including the reference wavelength are connected in series with an optical fiber, the wavelength characteristics of the reflected light when applying the physical quantity can be reduced in a short time. It can be detected with high accuracy, and the physical quantity applied to the FBG sensor can be measured in a short time and with high accuracy.

In the physical quantity measurement system configured in this way, even when a plurality of FBG sensors having the same wavelength characteristics including the reference wavelength are connected in series with an optical fiber, the wavelength characteristics of the reflected light when applying the physical quantity can be reduced in a short time. It can be detected with high accuracy, and the physical quantity applied to the FBG sensor can be measured with high accuracy in a short time.

(First embodiment)
FIG. 1 is a schematic configuration diagram of a physical quantity measurement system according to a first embodiment of the present invention. The same parts as those in the conventional strain measurement system shown in FIGS. 14, 15, and 16 are denoted by the same reference numerals, and detailed description of the overlapping parts is omitted.

Swept pulse light source 20 is composed of a wavelength-tunable light source 21 and the pulse generator 22. The wavelength tunable light source 21 generates the sweep light a having a constant level, with the wavelength λ shown in FIG. 4 continuously changing from λ ₁ to λ _m around the reference wavelength λ _S of the FBG sensor 1.

As shown in FIG. 4, the pulse generator 22 applies a pulse signal b having a very narrow pulse width of about 20 ns, that is, having a small duty ratio and a period T to the wavelength variable light source 21 as a drive signal. The wavelength tunable light source 21 makes incident pulsed light c whose pulse signal b in the swept light a has a specified level only during a high level period from the wavelength swept pulse light source 20 to one end (incident end) 5a of the optical fiber 5. Therefore, as shown in FIG. 4, the incident pulsed light c is composed of a plurality of pulsed light whose wavelength λ increases sequentially from λ ₁ to λ _m by Δλ _A around the reference wavelength λ _S of the FBG sensor 1. Has been.

N FBG sensors in which the reference wavelength λ _S and the wavelength characteristics of the reflected light 3 are equal to each of the distance positions L ₁ , L ₂ , L ₃ , L ₄ ,... L _n from one end (incident end) 5a of the optical fiber 5. 1 is inserted. The length of the optical fiber 5 L (= L m) required time one pulse light incident pulse light c reciprocates, using the refractive index of the optical fiber 5 n, the light speed C, (2nL / C) Therefore, the period of the pulse signal b, that is, the interval T of the Palace light of the incident pulse light c is

Based on the measurement start instruction of the measurement control unit 28, the incident pulse light c output from the wavelength sweep pulse light source 20 enters one end (incident end) 5a of the optical fiber 5, passes through the circulator 12, and passes through the circulator 12. length position _{L 1, L 2, L 3} , L 4, ... through the FBG sensor 1 provided in L _n reaches the far end of the optical fiber 5. Then, the reflected pulse light d with respect to the incident pulse light c of each FBG sensor 1 provided at each of the distance positions L ₁ , L ₂ , L ₃ , L ₄ ,... L _n is branched by the circulator 12 and electrically received by the light receiver 23. The signal is converted into a signal, converted into a digital reflected pulse signal by the A / D converter 24, and input to the data writing unit 25.

The output detection unit 26 activates the timing control unit 27 when the first pulsed light of the incident pulsed light c is incident on one end (incident end) 5a of the optical fiber 5. In the timing memory 29, each wavelength λ ₁ , λ ₂ , λ ₃ , λ of the incident pulsed light c is determined from the time when the first pulsed light of the incident pulsed light c is incident on one end (incident end) 5a of the optical fiber 5. _4, each of the pulse light ... lambda _m is up and is received by the distance position _{L 1, L 2, L 3} , L 4, ... L each provided _n FBG sensor 1 light receiver 23 is reflected by the The elapsed time is stored.

For example, as shown in FIG. 7, the elapsed time t ₁₁ of the reflected pulse signal of the first FBG sensor 1 from the emission time t ₀ of the first pulse light of the wavelength λ ₁ in the incident pulse light c, the second FBG sensor The elapsed time t ₂₁ of the reflected pulse signal No. 1 and the elapsed time t ₃₁ of the reflected pulse signal of the third FBG sensor 1 are stored.

Further, the elapsed time t ₁₂ of the reflected pulse signal of the first FBG sensor 1 from the time t _{0 with} respect to the second pulsed light of the wavelength λ ₂ in the incident pulsed light c, the elapsed time of the reflected pulse signal of the second FBG sensor 1 elapsed time t ₃₂ the time t _22, 3 number of the reflected pulse signals of the FBG sensor 1, ... are stored.

  The timing control unit 27 sets the set of the wavelength λ and the number of the FBG sensor 1 every time the elapsed time stored in the timing memory 29 reaches from the incident time from the output detection unit 26. To send. The data writing unit 25 obtains the signal value (FB) of the reflected pulse signal output from the A / D converter 24, the wavelength λ in the measurement value table 30 for each incident palace light shown in FIG. Write to the area 31 specified by.

  When the measurement of the acquisition of [all wavelengths × all FBG sensors] data for one incident pulsed light c is completed and the writing to the measured value table 30 for each incident palace light is completed, the data editing unit 32 is activated. Then, the data (group) of each measurement value for each incident pulse light stored in the measurement value table 30 for each incident pulse light is edited into the data (group) for each measurement value for each FBG sensor, and is shown in FIG. It writes in each area 34 of each measured value table 33 for each FBG shown.

Next, the wavelength characteristic calculator 35 measures the measured values (λ ₁ , λ ₂ , λ ₃ , λ ₄ ,... Λ _m) of one FBG sensor 1 in one vertical column in each measured value table 33 for each FBG ( Data) Using FB ₁₁ , FB ₂₁ , FB ₃₁ ,..., FB _m1 , a wavelength characteristic 36 having the horizontal axis of the wavelength λ of the reflected light of the FBG sensor 1 shown in FIG. Specifically, the wavelength _{λ 1, λ 2, λ 3} , λ 4, the measured value of ... lambda _{m (data) FB 11, FB 21, FB} 31, ..., obtaining an envelope in FB _m1.

Next, the center wavelength calculator 37 calculates the center wavelengths λ _C1 , λ _C2 , λ _C3 , λ _C4 ,... Λ _Cn of the wavelength characteristics 36 of the reflected light in the calculated 1st to nth FBG sensors 1. It is obtained and sent to the shifted wavelength calculation unit 39 of the physical quantity calculation means 38.

Shift the wavelength calculating unit 39, as shown in FIG. 6, the center wavelength lambda _C1 of each FBG sensor _{1, λ C2, λ C3,} λ C4, ... λ Cn of the FBG sensor 1 stored in the reference wavelength memory 40 Wavelength shifts Δλ ₁ , Δλ ₂ , Δλ ₃ , Δλ ₄ ,... Δλ _m from the reference wavelength λ _S are calculated.

The physical quantity calculation unit 41 multiplies each wavelength shift Δλ ₁ , Δλ ₂ , Δλ ₃ , Δλ ₄ ,... Δλ _m by a constant K, and applies distortion (physical quantity) applied to each of the FBG sensors 1 from No. 1 to n. ) Ε ₁ , ε ₂ , ε ₃ , ε ₄ ,... Ε _n are calculated and displayed on the display 42.

In the physical quantity measurement system of the first embodiment configured as described above, even when a plurality of FBG sensors 1 having the same wavelength characteristics including the reference wavelength λ _S are connected in series by the optical fiber 5, the physical quantity is applied. The wavelength characteristic 36 of the reflected light can be detected with high accuracy in a short time.

  Further, incident pulsed light composed of a plurality of pulsed light whose wavelengths λ sequentially change as measurement light incident on one end (incident end) 5a of an optical fiber 5 in which a plurality of FBG sensors 1 of the same standard are connected in series. c, and the time interval T of each pulsed light is set to be equal to each other and longer than the time required for the pulsed light to reciprocate the optical fiber 5 (2 nL / C).

Therefore, as shown in FIG. 7, the previous wavelength is within a period T from the output time of the pulse light of one wavelength λ constituting the incident pulse light c to the output time of the pulse light of the next wavelength (λ + Δλ _A ). All the reflected pulses from the FBG sensors 1 from No. 1 to No. n with respect to the pulsed light of λ are received with a time shift. Therefore, the wavelength characteristics 36 of the reflected light of each FBG sensor 1 can be overlapped as shown by the reflected pulsed light d in FIG. 4, and the emission period of the incident pulsed light c can be shortened.

(Second Embodiment)
FIG. 8 is a schematic configuration diagram of a wavelength sweep pulse light source 20a incorporated in the physical quantity measurement system of the second embodiment of the present invention. That is, the physical quantity measurement system of the second embodiment is a system in which the wavelength sweep pulse light source 20 in the physical quantity measurement system of the first embodiment shown in FIG. 1 is replaced with the wavelength sweep pulse light source 20a shown in FIG. Therefore, description other than this wavelength sweep pulse light source 20a is abbreviate | omitted.

  The wavelength swept pulse light source 20 a is composed of a wavelength variable light source 21 and a pulse generator 22. In FIG. 8, in the wavelength tunable light source 21, the light emitted from the end surface of the semiconductor laser (LD) 51 that is AR-coated is converted into collimated light by the collimating lens 52 and incident on the diffraction grating 53. The diffracted light emitted from the diffraction grating 53 is incident on the MEMS scanner 54.

  The MEMS scanner 54 includes a reflector 55 and reflector drive means 56, and the diffracted light with respect to the collimated light incident from the diffraction grating 53 is reflected by the reflection surface of the reflector 55 to the diffraction grating 53, and again the diffraction grating. When the diffracted light diffracted by 53 and incident on the LD 51 is incident on the LD 51 via the collimator lens 52, the diffracted light incident on the LD 51 becomes light having a desired wavelength and the desired wavelength. Is reciprocally changed (reciprocatingly rotated) at a predetermined period by the reflector driving means 56 such that the reciprocating sweep is performed including a predetermined wavelength range. With such a configuration, the wavelength-swept swept light a is oscillated and output from the end surface of the LD 51 that is not AR-coated.

  As described above, the pulse generator 22 applies a pulse signal b having a period T, which is as narrow as about 20 ns, to the LD 51 as a drive signal. Therefore, the oscillation time of the sweep light a is controlled by the pulse signal b having a period T. As a result, the above-described incident pulsed light c composed of a plurality of pulsed light whose wavelengths λ sequentially change is emitted from the LD 51 and is incident on one end (incident end) 5 a of the optical fiber 5.

  9 includes a wavelength tunable light source 21, a pulse generator 22, and an optical switch 69. That is, in this wavelength swept pulse light source 20a, instead of directly controlling on / off of the semiconductor laser 51 with the pulse signal b, light emitted from the end surface of the LD 51 that is not AR-coated is transmitted between the LD 51 and the circulator 12. On / off control is performed by an optical switch 69 provided in a plurality of pulse lights whose wavelengths are sequentially changed.

  Further, the wavelength swept pulse light source 20 a shown in FIG. 10 includes a wavelength variable light source 21, a pulse generator 22, and an optical amplifier 70. That is, in this wavelength sweep pulse light source 20a, light emitted from the end surface of the LD 51 that is not AR-coated is controlled on / off by the optical amplifier 70 instead of the optical switch 69.

  The MEMS (Micro Electro Mechanical Systems) scanner 54 means a scanner formed by a micro electro mechanical structure (a structure that operates mechanically under the control of an electrical signal).

  Here, wavelength sweeping by the MEMS scanner 54 will be described. When the MEMS scanner 54 is reciprocally swept at a predetermined sweep period by applying the drive signals Da and Db shown in FIG. 12 (the reflector 55 is reciprocally rotated), as shown in FIG. The reciprocating rotation angle of 54 changes almost sinusoidally. As a result, the swept wavelength λ also changes in a sine wave shape.

  Therefore, the reciprocal sweep of the MEMS scanner 54 is performed so that the predetermined wavelength range (measurement wavelength range) of the swept light a is close to the straight line of the waveform changing in a sine wave shape as shown in FIG. Is set (range of reciprocating rotation angle). That is, it is set by adjusting the amplitude of the drive signals Da and Db. One of the drive signals Da and Db described above is output to the measurement control unit 28a as a trigger signal Tr.

  In FIG. 8, the 0th-order light of the diffraction grating 53 is incident on an optical resonator 57 such as an etalon, and only light of a predetermined wavelength is transmitted. Then, the transmitted light is converted into an electrical signal by the light receiver (PD) 58 and output to the measurement control unit 28a. That is, transmitted light is generated at a predetermined wavelength interval, for example, a frequency of 500 GHz corresponding to the wavelength sweep of the output light (the original sweep light a of the incident pulse light c), and is converted into an electric signal by the light receiver 58. . The wavelength (frequency) of this transmitted light is known. Therefore, the oscillation wavelength of the wavelength-swept pulse light source 20a (the wavelength λ of each pulse light of the wavelength-swept incident pulsed light c) can be obtained using an electrical signal obtained by photoelectrically converting the transmitted light.

  Next, the configuration and operation of the reflector 55 and the reflector driving means 56 of the MEMS scanner 54 will be described with reference to FIG.

  The reflector 55 is a pair of fixed substrates 59, 60 arranged in parallel with each other in a horizontally long rectangle, and a direction orthogonal to the fixed substrates 59, 60 from the center of the long side edge of the pair of fixed substrates 59, 60. A pair of shaft portions 61, 62 extending in a predetermined width and length and capable of being twisted and deformed along the length direction of the shaft portion 61 at the center of one of the long side edges of the horizontally long rectangle. The reflector 63 is connected to the tip and connected to the tip of the shaft 62 at the center of the other long side edge.

Since the reflection plate 63 is supported at its central portion by the shaft portions 61 and 62 that can be twisted and deformed, it can rotate with respect to the fixed substrates 59 and 60 about the line connecting the shaft portions 61 and 62 as the central axis. it can. Further, the natural frequency f ₀ of the portion composed of the shaft portions 61 and 62 and the reflecting plate 63 is determined by the shape and mass of the reflecting plate 63 itself and the spring constant of the shaft portions 61 and 62. A reflective surface 64 for reflecting light is formed on one surface side of the reflective plate 63.

  The support substrate 65 is made of an insulating material, and support bases 65a and 65b projecting forward are formed on the upper and lower portions on one side, and the fixed substrates 59 and 60 of the reflector 55 are formed on the upper and lower sides. Are fixed in contact with the support bases 65a and 65b. In addition, electrode plates 66 and 67 that are opposed to both ends of the reflection plate 63 of the reflector 55 are formed in patterns at both ends of the central portion on the one surface side of the support substrate 65.

  The electrode plates 66 and 67 constitute a reflector driving means 56 (see FIG. 8) together with the drive signal generator 68, and an electrostatic force is applied alternately and periodically to both ends of the reflector 63. The reflecting plate 63 is reciprocally rotated around a line connecting the shaft portions 61 and 62. Note that the rotation axis of the reflecting plate 63 is set to be parallel to the diffraction grooves of the diffraction grating 53.

  The reflector 55 configured as described above receives the diffracted light from the diffraction grating 53 by the reflection surface 64 of the reflection plate 63, causes the reflected light to enter the diffraction grating 53, and diffracts it again.

On the other hand, the drive signal generator 68 that constitutes a part of the reflector driving means 56 (see FIG. 8), for example, is an electrode based on the potential of the reflector 55 as shown in FIGS. Driving signals Da and Db having a frequency corresponding to the natural frequency f ₀ and having a phase shifted by 180 ° are applied to the plates 66 and 67, and between the electrode plate 66 and one end side of the reflecting plate 63. In addition, an electrostatic force (attractive force) is applied alternately and periodically between the electrode plate 67 and the other end side of the reflecting plate 63, and the reflecting plate 63 has a predetermined angular range at the natural frequency f ₀ or a frequency in the vicinity thereof. Is reciprocated.

In the MEMS scanner 54 constituted by the reflector 55 and the reflector driving means 56, the reflector 55 is extended from the pair of fixed substrates 59 and 60 and a predetermined length from the edge thereof with a predetermined width. The shafts 61 and 62 that can be twisted and deformed along the length direction are connected to the ends of the shafts 61 and 62 at their edges, and are formed in a symmetrical shape with respect to the shafts 61 and 62. And a reflection plate 63 having a frequency corresponding to the natural frequency f ₀ of the portion composed of the shaft portions 61 and 62 of the reflector 55 and the reflection plate 63. A force is applied to 63 to rotate the reflecting plate 63 back and forth at a natural frequency f ₀ .

For this reason, the reflecting plate 63 can be reciprocally rotated at a high speed with a small amount of electrical energy, and the center of rotation is inside the reflecting plate 63 (in this case, the central portion). The amount of change in the reflection angle of the incident light on can be increased. The spring constants of the shaft portions 61 and 62 are determined by the length, width, thickness, and material of the shaft portions 61 and 62, and the natural frequency f ₀ depends on the spring constant and the shape, thickness, material, and the like of the reflector 63. By selecting these parameters, the natural frequency f ₀ can be set within a range of several hundreds of Hz to several tens of kHz.

  Therefore, since the wavelength sweep pulse light source 20a of the physical quantity measurement system of the second embodiment is configured as the MEMS scanner 54 using the reflector 55 and the reflector driving means 56 as described above, the sweep speed is high. (Up to several 10 kHz).

  8, 9, and 19, the external resonator type tunable light source 21 that sweeps the wavelength by the reciprocating motion of the MEMS scanner 54 has been described. However, the embodiment is limited to the light source having such a configuration. Any light source capable of continuously sweeping the wavelength may be used.

1 is a schematic configuration diagram of a physical quantity measurement system according to a first embodiment of the present invention. The figure which shows the memory content of the measurement value table classified by incident pulse light formed in the physical quantity measurement system of the embodiment The figure which shows the memory content of the measurement value table classified by FBG formed in the same physical quantity measurement system Time chart showing the operation of the physical quantity measurement system The figure which shows the wavelength characteristic of the reflected light of each FBG sensor calculated with the same physical quantity measurement system The figure which shows the relationship between the wavelength characteristic of the reflected light at the time of no load in the FBG sensor, and the wavelength characteristic of the reflected light at the time of load The figure which shows the relationship between the transmission time of the incident pulse light in the same physical quantity measurement system, and the reception time of the reflected light from each FBG sensor The schematic block diagram of the wavelength sweep pulse light source integrated in the physical quantity measurement system concerning 2nd Embodiment of this invention The schematic block diagram which shows the modification of the wavelength sweep pulse light source in the physical-quantity measurement system of the 2nd Embodiment Schematic configuration diagram showing another modification of the same wavelength swept pulse light source An exploded perspective view of the MEMS scanner incorporated in the same wavelength sweep pulse light source The figure which shows the drive signal of the MEMS scanner Illustration of wavelength sweep by the MEMS scanner The figure which shows the wavelength characteristic of the reflected light and transmitted light of a FBG sensor Diagram showing a conventional strain measurement system The figure which shows other conventional distortion measurement systems Diagram showing the measurement principle of the conventional strain measurement system

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... FBG sensor, 5 ... Optical fiber, 12 ... Circulator, 20, 20a ... Wavelength sweep pulse light source, 21 ... Wavelength variable light source, 22 ... Pulse generator, 23, 58 ... Light receiver, 24 ... A / D converter, 25 ... Data writing unit, 26 ... Output detection unit, 27 ... Timing control unit, 28, 28a ... Measurement control unit, 29 ... Timing memory, 30 ... Measurement value table for each incident pulse, 31, 34 ... Area, 32 ... Data Editing unit, 33 ... Measurement value table for each FBG, 35 ... Wavelength characteristic calculation unit, 36 ... Wavelength characteristic, 37 ... Center wavelength calculation unit, 38 ... Physical quantity calculation means, 39 ... Deviation wavelength calculation unit, 40 ... Reference wavelength memory, 41 DESCRIPTION OF SYMBOLS ... Physical quantity calculation part, 42 ... Display, 51 ... Semiconductor laser (LD), 52 ... Collimating lens, 53 ... Diffraction grating, 54 ... MEMS scanner, 55 ... Reflector, 56 ... Reflector drive Step 57: Optical resonator 59, 60 Fixed substrate 61, 62 Shaft 63 63 Reflecting plate 64 Reflecting surface 65 Support substrate 65a 65b Support plate 66 67 67 Electrode plate , 68 ... Driving signal generator, 69 ... Optical switch, 70 ... Optical amplifier

Claims (6)

A plurality of FBG sensors (1) that are provided in a plurality of measurement objects spaced apart from each other, and in which the center wavelength of reflected light with respect to incident light varies according to a physical quantity applied from the measurement object;
An optical fiber (5) for serially connecting the FGB sensors;
A wavelength sweep pulse light source (20, 20a) that generates a plurality of pulsed light whose wavelengths are sequentially changed, and sequentially enters the incident end of the optical fiber as incident pulsed light (c);
A circulator (12) for branching each reflected pulse light that is sequentially incident on the optical fiber and is reflected by the FBG sensors and propagates toward the incident end;
A light receiver (23) for receiving each reflected pulse light branched by the circulator;
A measurement value storage means (30) for storing and holding the received light level of the reflected pulse light from each FBG sensor with respect to each incident pulse light according to the wavelength of the incident pulse light;
Wavelength characteristic calculating means (35) for calculating the wavelength characteristic of the reflected light of each FBG sensor from the received light level of each reflected pulse light stored in the measured value storage means;
A physical quantity calculating means (38) for obtaining a physical quantity applied to each FBG sensor from the calculated center wavelength of the wavelength characteristic ;
With
The wavelength characteristic calculation means (35) is configured to select a group of received light levels of each reflected pulse light for each wavelength of the incident pulse light stored in the measurement value storage means (30), and the reflected pulse light having a different wavelength for each FBG sensor. The wavelength for calculating the wavelength characteristics of the reflected light of each of the FBG sensors using the data editing unit (32) recombined into the group (33) and the received light level of the reflected pulsed light having a different wavelength for each edited FBG sensor A characteristic calculation unit (35),
The center wavelengths of the FBG sensors in a state where the physical quantity is not applied are set to be equal to each other,
The transmission interval (T) of each pulsed light of each incident pulsed light that the wavelength swept pulse light source sequentially enters the incident end of the optical fiber is set to be equal to each other, and the pulsed light reciprocates through the optical fiber. It is set longer than the time required (2nL / C).
A physical quantity measuring system characterized by that. The physical quantity calculation means (38) includes a reference wavelength storage unit (40) for storing a reference wavelength (λ _S ) of the FBG sensor;
A shift wavelength calculation unit (39) that calculates a shift wavelength of the calculated center wavelength (λ _C ) of the reflected light of each FBG sensor from the reference wavelength, and from each of the calculated shift wavelengths to each FBG sensor. A physical quantity calculation unit (41) for calculating the applied physical quantity ;
The physical quantity measuring system according to claim 1 . The wavelength swept pulse light source (20a)
A semiconductor laser (51) in which one light emitting end face is AR coated;
A collimating lens (52) for collimating light emitted from the AR-coated end face of the semiconductor laser;
A diffraction grating (53) that receives collimated light emitted from the collimating lens and diffracts the collimated light at an angle corresponding to the wavelength;
A MEMS that includes a reflector (55) and a reflector drive unit (56), and controls the reflector drive unit to emit light having a wavelength that continuously changes from the other emission end face of the semiconductor laser. A scanner (54);
3. A pulse generator (22) for applying a pulse signal having a predetermined period and a predetermined duty ratio for driving the semiconductor laser as a drive signal to the semiconductor laser. Physical quantity measurement system. The wavelength swept pulse light source (20a)
A wavelength tunable light source (21) that emits light having a continuously changing wavelength and a constant level;
A pulse generator (22) for generating a pulse signal having a predetermined period and a predetermined duty ratio;
An optical switch (69) for receiving the pulse signal and generating on-off control of light emitted from the wavelength tunable light source to generate the plurality of pulse lights ;
The physical quantity measurement system according to claim 1 or 2, characterized by comprising: The wavelength swept pulse light source (20a)
A wavelength tunable light source (21) that emits light having a continuously changing wavelength and a constant level;
A pulse generator (22) for generating a pulse signal having a predetermined period and a predetermined duty ratio;
In response to this pulse signal, according to claim 1 or claim characterized in that it comprises a light amplifier (70) for generating said plurality of pulse light emitted light on / off control to from the variable wavelength light source Item 3. The physical quantity measurement system according to Item 2 . The wavelength tunable light source (21)
A semiconductor laser (51) in which one light emitting end face is AR coated;
A collimating lens (52) for collimating light emitted from the AR-coated end face of the semiconductor laser;
A diffraction grating (53) that receives collimated light emitted from the collimating lens and diffracts the collimated light at an angle corresponding to the wavelength;
A reflector driving unit configured to include a reflector (55) and a reflector driving unit (56), and to emit light whose wavelength continuously changes from the other AR-coated emission end face of the semiconductor laser. A MEMS scanner (54) for controlling the unit ;
The physical quantity measurement system according to claim 4 or 5, characterized by comprising:

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