JPS6211400B2 - - Google Patents

Abstract

PURPOSE:To precisely measure the fluctuations of an article with the use of a simple construction by alternately emitting lights having different frequencies with the same frequency in response to the optical signals from a light source thereby to complementarily operate an optical differential device. CONSTITUTION:The intensities of the output lights from optical emitters 33 and 34 are denoted at P1 and P2; the switching frequency of an alternate drive circuit at fn; the distribution coefficients of the optical fibers 4 and 6 of an optical branch 36 at b1 : b2; the transmission efficiencies of the optical fibers 4 and 6 for transmission and reception at a1 and a2; the optical transmissivities of filters 11 and 12 at T1 and T2; the sensitivities of optical receivers 41 and 42 at s1 and s2; and the output currents at Is and Im. Then, the output voltage e1 of a logarithmic amplifier 43 is expressed by e1 = Glog (b1 a1 a2 S1 T1 / b2 S2), e = Glog (b1a1S1T2/b2S2) for the signals having wavelengthes lambda1 and lambda2 from the relationship of log Is/Im. As a result, if that output is synchronously detected by a frequency fn, the difference signal between the output signals e1 and e2 is extracted to generate the output signal of E0 = AGlog T1/T2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical measurement system, and more particularly, to an optical measurement system that converts physical fluctuations of an object to be measured into fluctuations in the amount of transmitted light, and measures the fluctuations in the amount of light at a position and location distant from the object to be measured. This relates to the measurement system. With the progress in the development of optical transmission lines such as optical fibers and optical elements such as semiconductor lasers and LEDs, optical telemetry systems and devices are replacing conventional electrical telemetry systems and devices as one of their applications. Various methods have been proposed.

However, in conventional optical telemetering systems, in order to eliminate the effects of fluctuations (offset, etc.) in optical elements such as the light source, receiver, or optical transmission line, a reference light that is not affected by the object to be measured is used. In order to do this, an optical separation circuit, a so-called bypass, is installed near the measurement unit, or a period in which no light is transmitted is periodically provided in the transmitted optical signal, and the signal during the period in which no light is transmitted is detected during reception signal processing. Utilizing this, methods have been taken to detect fluctuations in the transmission path or optical elements and compensate for unnecessary fluctuations. Therefore, a modulator to separate the optical paths or an optical circuit to create a special signal is required. Furthermore, when a long optical transmission line is used, variations in the characteristics of the transmission line become a problem, and there is a problem in that the offset of the entire optical transmission system cannot be completely compensated for.

Therefore, an object of the present invention is to realize an optical measurement system that can accurately measure fluctuations in an object to be measured with a generally simple configuration.

Another object of the present invention is to realize an optical measurement system that completely eliminates the offset of the optical measurement system, that is, the drift caused by disturbance, without providing an optical bypass circuit in the measurement section.

In order to achieve the above object, the present invention is characterized in that an optical measurement system is configured as described below.

A transmitting section including a light source, a measuring section located far from the transmitting section, a signal processing section that converts the optical signal sent from the measuring section into an electrical signal and processes the signal, and an optical transmission line that connects each of the above sections. In an optical measurement system consisting of A differential device is configured, and the signal processing section is configured to detect fluctuations in the object to be measured as a function of the ratio of the components having different wavelengths from the optical signal sent from the optical differential device. It is characterized by:

The above-mentioned regular optical signal will be described in detail below, but
This means that light components with different wavelengths are generated at regular intervals. Further, an optical differential device is a device that increases and decreases the amount of light in opposite directions with respect to the above-mentioned different wavelengths of light. Although the rates of increase and decrease are generally complementary, they do not necessarily need to be complementary depending on the application of the system of the present invention.

According to the optical measurement system according to the present invention, since the output optical signal of the optical differential device has different wavelengths in time series and increases and decreases regularly under the influence of the object to be measured, the reference light can be determined from only this information. Physical changes in the object to be measured can be accurately detected without using (reference light). Further, by giving a special time-series pattern period to the waveform of the light source, it is possible to perform various signal processing.

The above and other objects and features of the present invention will become more apparent from the detailed description in conjunction with the following drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of an optical measuring device according to the present invention. In the same figure,
1 is a transmitting section, 2 is a received signal processing section, 3 is a measuring section that changes the amount of transmitted light according to the displacement of the object to be measured,
4 and 5 are optical fibers that connect the transmitting section and the measuring section, and the measuring section and the signal processing section, respectively.

The transmitter includes first and second light emitters 33 and 34
(The respective wavelengths are λ ₁ and λ ₂ , and the output level is
P ₁ and P ₂ ), an alternating drive circuit 32 that alternately opens and closes the optical output from the light emitters (the frequency is _o ), and an alternating drive circuit 32 that adds the optical power of the two light emitters to the same optical path. A part of the output light from the wave unit 35 and the multiplexer 35 is coupled to the transmission optical fiber 4, and the other part is coupled to the signal processing unit 2 (the distribution ratio is
b ₁ to b ₂ ).

The measurement unit 3 includes a lens 13 that converts the light transmitted by the optical fiber 4 into parallel light, and a filter 11 that transmits at least the light of wavelength λ ₁ and blocks the wavelength λ ₂ (transmittance is T ₁ (t)). ) and a filter 12 (transmittance is T ₂ (t)) that transmits the wavelength λ ₂ and blocks the wavelength λ ₁ , and a displacement plate movable in a direction perpendicular to the parallel light; A lens 14 that focuses parallel light whose intensity is varied by a plate and couples it to the optical fiber 5, the displacement plate support 15, and pressure guiding holes that apply pressures P _r1 and P _r2 to each of the diaphragms 21 and 22. 23 and 2
4. It consists of connecting rods 18 and 19 that apply the fluctuations of the diafrags 21 and 23 to the displacement plate, and optical fiber holding parts 16 and 17. The support part 15 is composed of a leaf spring, and the connecting rods 18, 19
When the displacement plate is displaced by
is displaced by the plate spring 15 while holding the parallelogram, so no angular deflection occurs with respect to the optical axis.

The received signal processing unit 2 is a branching unit 3 of the transmitting unit 1.
A first light receiver 42 sends a part of the light branched from the optical fiber 6 through the optical fiber 6 and converts the sent light into an electrical signal I _R , and the light sent from the measurement section through the return fiber 5. a second photoreceiver 41 that converts the signal Is into an electric signal _Is ; a logarithmic amplifier 43 that obtains a signal _logIs / _Ir from the outputs of the first and second photoreceivers 41 and 42; It consists of a synchronous detector 44 that obtains an output Eo corresponding to the amount of movement (assumed to be x).

The operation of this embodiment will be explained below using waveform diagrams.

FIG. 2 shows waveforms at various parts of the above embodiment.

Let the intensities of the output lights of the light emitters 33 and 34 be P ₁ and P ₂ , respectively, and the switching frequency of the alternating drive circuit.
If _o , the output of the multiplexing section will be as shown in figure a. Here, the sizes of P ₁ and P ₂ do not necessarily have to be the same. Frequency _o is 2 of the fluctuation frequency of the measured object
It is sufficient if it is twice or more, and it can usually be set in the range of several Hz to several tens of MHz. The distribution ratio of the optical fibers 4 and 6 of the optical branch 36 is b ₁ :b ₂ (b ₁ + b ₂ = 1), the transmission efficiency of the transmission and return optical fibers 4 and 5 is α ₁ and α ₂ , the filter 11 and 12
T ₁ and T ₂ , the light transmittance of the receivers 41 and 4
2, the output current I _S of _the photo receiver ₄₁ is I _S1 = P _{1 b 1 α 1 α 2 S 1} T ₁ and I _S2 =
P ₂ b ₁ α ₁ α ₂ S ₁ T ₁ , and the output current I _n of the photoreceiver 42 is I _n1 =P ₁ b ₂ S ₂ and I _n2 =P ₂ b ₂ S ₂ respectively.
(Figures b and c). In reality, the output P(a
The waveform of the output current I _n (FIG. b) is slightly deformed and there is a slight time lag as compared to FIG.

Therefore, the output voltage e _l of the logarithmic amplifier is logI _S /I
From the relationship of _n , for signals with wavelengths λ ₁ and λ ₂ ,
e _l1 = Glogb ₁ α ₁ α ₂ S ₁ T ₁ /b ₂ S ₂ and e _l2 = Glogb ₁ α ₁ α ₂ S ₁ T ₂ /b ₂ S ₂ , respectively. Here, G is the amplification factor of the amplifier 43.
Amplifiers that operate in this manner are generally well known (e.g. Burr-Brown BB-4217KG).
Therefore, the details will be omitted.

If the output e _l of this logarithmic amplifier 43 is subjected to synchronous detection at the alternating drive frequency _o , the output signals e _l1 and e _l2
The difference signal Eo can be extracted, and its output Eo is Eo=AGlogb ₁ α ₁ α ₂ S ₁ T ₁ /b ₂ S ₂ -AGlogb ₁ α ₁ α 2 S ₁ T ₂ /b _{2 S 2 =} AGlogT
₁ / _T2 . Here, A is the conversion coefficient of the synchronous detector. As is clear from the above equation, according to the optical measuring device of the present invention, the output Eo is not affected by any characteristic fluctuations of the light source light multiplexer, the optical branch, the optical transmission fiber, and the optical receiver.

FIG. 3 shows a two-wavelength differential displacement-light converter used in the measurement section of the present invention, that is, a means for making complementary fluctuations in which lights of different wavelengths are increased and the other light is decreased. This shows the main part configuration of. Combining unit 36, light P ₁ that has passed through the transmission optical fiber
converts the light emitted from the optical fiber into a parallel light beam using the lens 13, and then passes the light through the optical filters 11 and 12.
The amount of transmitted light is modulated by a displacement plate that combines
The light is focused by the lens 14 and made incident on the return optical fiber 5, and the light receiver 41 obtains an output Eo proportional to the displacement amount x of the displacement plate. Note that parts given the same reference numerals as in FIG. 1 are parts having substantially the same functions as those in FIG. 1.

Let T ₁ and T ₂ be the transmittance of the filter for each wavelength λ ₁ and λ ₂ , respectively, then the output Eo of the phase detector is Eo = AlogT ₁ /T ₂ , and more specifically, T ₁ and T ₂ are respectively T ₁ = r ₁₁ + r ₂₁ /2 + r ₁₁ - r ₂₁ /π [sin ^-1 (x/r) + x/rcos {sin ^-1 (x/r)
}] T ₂ = r ₂₂ + r ₁₂ /2-r ₂₂ -r ₁₂ /π [sin ^-1 (x/r) + x/rcos {sin ^-1 (x/r)
}].

Here, r ₁₁ and r ₂₁ are the transmittances of filters 11 and 12 for light with wavelength λ ₁ , respectively, and r ₁₂ and r ₂₂
are the transmittances of filters 11 and 12 for wavelength λ ₂ , respectively, r is the radius of the parallel beam, and x is the displacement from the central axis. When the filter 11 transmits only the light with wavelength λ ₁ and the filter 12 transmits only the light with wavelength λ ₂ , that is, when r ₁₁ = r ₂₂ = 1, r ₂₁ = r ₁₂ = 0, Eo = A {8/π( x/r)+4/3π(32/ ^π2−
1) (x/r) ² }. Here, the beam radius r may change depending on the state of light transmission within the optical fiber. It is preferable to insert a radial radiator ′ in order to keep the diameter of the light beam hitting the displacement plate constant.

Figure 4 shows the relationship between the standard displacement amount (x/r), which is the displacement x normalized by the radius r of the light beam, and the output Eo. In the figure, A is r ₁₁ = r ₂₂ = 1, r ₂₁ = r ₁₂ =
0, B is r ₁₁ = r ₂₂ = 0.9, r ₂₁ = r ₁₂ = 0.1, C is r ₁₁ = r ₂₂ = 0.1, r ₂₁ =
0, r ₁₂ =0.2.

From the above figure, the standard displacement amount |x/r|<0.3 has almost no It becomes a straight line.

Also, when the displacement x is 0, T ₁ and T ₂ are equal.
AlogT ₁ /T ₂ =Eo=0, and the zero point can be easily detected.

Therefore, even though the optical measurement system according to the invention uses a logarithmic amplifier, the displacement x
Since the output Eo changes linearly, there is no need to use an anti-logarithmic converter in the signal processing circuit.

If the characteristics of the optical parts such as optical multiplexing and optical branching of the transmitting section 1 and the optical fibers 4 and 5 have a non-negligible effect due to the difference in wavelength of light, the light emitted from the light source will not reach the optical receiver 41. During transmission, the transmission rate varies depending on the wavelength. In this case, if the ratio of the transmittance of light of two wavelengths λ ₁ and λ ₂ is k, then equation (1) is Eo=A{8/π(x/r)+〓(〓-1)(x/r)
³ }+Alogk (2) In this case, the zero point of the output and the zero point of the displacement may not match, and the range of linear variation centered on the zero point may also become narrow.

However, in this case, it is possible to correct the deviation by utilizing the focal position shift due to the chromatic aberration of the lenses 13 and 14. In FIG. 3, out of the light emitted from the optical fiber 4, the light with wavelength λ ₁ is focused at 10 as shown by solid line 8, while the light with wavelength λ ₂ is focused at 30 as shown by broken line 9. . Therefore, when the transmission ratio k is 1, it is sufficient to place the input end of the optical fiber at a position of 20 between 10 and 30. When the transmission ratio k is not 1, for example, the input end of the optical fiber may be placed at a position of 20 between 10 and ₃₀ . If the light transmission rate is high,
By moving the input end of the optical fiber 5 to the left, or vice versa, to the right, the transmission ratio of the entire system can be made 1, correcting the zero point and expanding the linear range from the zero point. be able to.

FIG. 5 shows the configuration of another embodiment of the optical system according to the present invention, which is particularly designed to eliminate the effects of background light and dark current of the light receiver.
In the configuration of the embodiment shown in FIG. 1, if there is a dark current ΔIs in the photoreceiver 41, the output of the photoreceiver 41 will be I _S1 =P ₁ b ₁ α ₁ α ₂ for optical signals of wavelengths λ ₁ and λ ₂ , respectively. S ₁ T ₁ + ΔIs, I _S2 = P ₂ b ₁ α ₁ α ₂ S ₁ T ₂ + ΔIs, so the output of the logarithmic amplifier 43 is e _l1 = Glogb ₁ α ₁ α ₂ S ₁ T ₁ /b ₂ S ₂ +ΔIs
/P ₁ b ₂ S ₂ and e _l2 = Glogb ₁ α ₁ α ₂ S ₁ T ₂ /b ₂ S ₂ +ΔIs
/P ₂ b ₂ S ₂ , so that even when the displacement x is zero, there may be a case where the output voltage Eo does not become zero, especially when the signal current is small. In order to eliminate these problems, in this embodiment, a kind of modulation circuit is provided between the alternating drive circuit 32 and the light emitters 33 and 34 _, that is, the light _emitter
A circuit 37 for intermittent light emission of 3 and 34 is provided,
A center frequency _c ,
Narrow band amplifiers 45 and 46 of 2 _o in the band and detectors 47 and 48 are connected in cascade, respectively. Components having the same reference numerals as those in FIG. 1 have the same functions.

Therefore, the output currents of the detectors 47 and 48 are expressed by the following equation when the light emitter 33 emits light.

I _R1 = P ₁ b ₁ S ₁ G ₁ S ₁ ′ I _S1 = P ₁ b ₂ α ₁ α ₂ S ₂ T ₁ G ₂ S ₂ ′ When the light emitter 34 emits light, I _R2 = P ₂ b ₁ S ₁ G ₁ S ₁ ′ I _S2 = P ₂ b ₂ α ₁ α ₂ S ₂ T ₂ G ₂ S ₂ ′ where G ₁ and G ₂ are the gains of narrowband amplifiers 46 and 45, respectively, S ₁ ′ and S ₂ ' are the detection sensitivities of the detectors 48 and 47, respectively.

Therefore, the output Eo of the synchronous detector 44 which has passed through the logarithmic amplifier 43 is expressed by the following equation using the same operation as explained with reference to FIG.

Eo=AGlogT ₁ /T ₂ where A and G are the gains of the synchronous detector 44 and the logarithmic amplifier 43. According to this embodiment, it is possible to eliminate the influence of the background photocurrent and dark current of the photodetectors 41 and 42, and furthermore, it is possible to realize an optical measurement system in which variations in the characteristics of the narrowband amplifiers and detectors used for this purpose do not affect the output. .

In the above embodiment, the optical signal from the light source is such that lights of different wavelengths are generated alternately in the same period, and the operations of the optical differential device are completely complementary, that is, the amount of increase in one and the amount of attenuation in the other are Although the case where the values are equal has been described, the present invention is not limited to the above embodiment.

FIG. 6, FIG. 7, and FIG. 8 are diagrams showing waveforms of optical signals in other embodiments. both,
a, b are signals with wavelengths λ ₁ and λ ₂ , respectively, and c
is the combined transmission signal, and the dotted line shows the state changed by the optical differential means (when λ ₁ increases). Note that the amplitude of c is shown enlarged. In the case of FIG. 6, the repetition period of two wavelengths a and b is equal, the duty cycle is 50%, and the phases are shifted from each other by θ. Therefore, the combined signal is λ ₁ +λ ₂ during period T
It consists of a t ₁ period of components of , a t ₂ period of λ ₁ , a t ₃ period without λ ₁ , λ ₂ , and a t ₄ period of λ ₂ .

Figure 7 shows that the periods of the signals λ ₁ and λ ₂ are equal to T, and the duty cycles of λ ₁ and λ ₂ are respectively
50% and 15%.

In FIG. 8, a synchronization signal is inserted every fixed period T ₀ of the λ ₁ signal, the periods of λ ₁ and λ ₂ are equal to T, and the duty cycle is 25%.

If the output of the optical differential device of these signals is sampled at a predetermined period, λ ₁ , λ ₂ , λ ₁ +λ
₂ , λ ₁ and λ ₂ can be separated, processing of λ ₁ and λ ₂ is performed in the same way as in the previous embodiment, and the signal of λ ₁ + λ ₂ is used as a monitor of the total optical power. , λ ₁ and λ ₂ do not exist, a more effective signal processing circuit can be constructed by using the signal as a zero-drift compensation signal for a photoreceiver, dark current, or amplifier. In addition to the above examples, encoded optical signals can also be used.

In short, when the light source signal of the present invention is composed of two pulsed signals with different wavelengths, λ ₁ and λ ₂
It is sufficient that the states in which only the optical signals are transmitted are regularly arranged.

In addition, in the above embodiments, the case where the optical differential device mainly uses a transmission filter is described, but it can also be realized by an optical differential device that combines reflection plates with different reflection coefficients for λ ₁ and λ ₂ of different wavelengths. It is clear from the above description that this is the case.

FIGS. 9a, 9b, and 9c are diagrams each showing the main part configuration when the optical differential device is of a reflective type. In the figure, 4 and 5 are optical fibers for transmitting and receiving, respectively, and 49 is a cylindrical lens, which has a distributed refractive index and focuses the light from the fiber 4 into a parallel beam with a certain spread from the end surface A. This lens outputs light, focuses the input from end face A, and introduces it into the receiving fiber. Reference numeral 50 denotes a reflector whose reflectance varies depending on the wavelength. In the above figure, the reflected light from the reflection plate 50 becomes parallel light that is axially symmetrical with respect to the optical axis of the lens, and is reflected by the lens 4.
9 and has a focal point at the junction of the fiber 5 and the lens 49. Therefore, the relative positions of the two fibers 4 and 5 are axially symmetrical with respect to the optical axis of the lens 49, and the distance between them is determined by the distance between the surface A of the lens 49 and the reflective surface of the reflector plate 6. Especially b is lens 49
The surface of c is a surface diagonal to the optical axis, and the end face reflected light on the A surface is focused on a part other than the end surface of the fiber 5. In the case of c, the reflective surface of the reflector 6 is diagonal to the optical axis. By making it a surface, the signal light from the reflecting surface is focused on a portion other than the position axially symmetrical to the fiber 4 with respect to the optical axis.

[Brief explanation of the drawing]

1 and 5 are diagrams showing the configuration of an embodiment of the optical measurement system according to the present invention, FIG. 2 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 1, and FIG. 3 is a diagram showing the configuration of an embodiment of the optical measurement system according to the present invention. FIG. 4 is a diagram illustrating the relationship between the displacement of the object to be measured and the output in the embodiment shown in FIG. 6, 7 and 8 are other optical signal waveform diagrams, and FIG. 9 is a diagram showing the main part configuration of the reflective optical differential device. 1... Transmission section, 2... Signal processing circuit, 3... Measurement section, 4, 5, 6... Optical fiber, 11, 12...
... Filter, 13, 14 ... Lens, 15 ... Filter support, 16, 17 ... Optical fiber holding part, 18, 19 ... Connecting rod, 21, 22 ... Diaphragm, 23, 24 ... Pressure hole , 32... alternating drive circuit, 33, 34... semiconductor laser, 35...
...Multiplexer, 36... Branch, 37... Modulator, 4
1, 42... Light receiver, 43... Logarithmic amplifier, 44
... Synchronous detector, 45, 46 ... Narrowband amplifier,
47, 48...detector.

Claims (1)

[Claims] 1. Means for periodically generating first and second pulsed lights having different wavelengths, and converting physical fluctuations of the object to be measured into displacements, an optical differential device that differentially varies the amount of light transmitted; a light receiver that converts the output of the optical differential device into an electrical signal; and a physical change in the object to be measured based on the electrical signal output from the light receiver. What is claimed is: 1. An optical measurement system comprising: a signal processing circuit for detecting the light, an optical differential device with the light generating means, and an optical transmission path connecting the light receiver and the optical differential device. 2. The optical measurement system according to claim 1, wherein the means for regularly generating light of different wavelengths includes two light emitters having different emission wavelengths, and an alternating drive circuit that regularly and alternately switches the light emitters. and a combining section that combines the outputs of the two semiconductor lasers,
The signal processing section includes a first light receiver that converts a part of the output light of the multiplexing section into an electrical signal, a second light receiver that converts the light from the optical means into an electrical signal, and the first and An optical measurement system comprising a logarithmic amplifier that amplifies the logarithm of a ratio of 2 and a synchronous detector that synchronously detects the output of the logarithmic amplifier. 3. The optical measurement system according to claim 2, further comprising means for modulating the light of the light emitter at a frequency higher than the driving frequency,
and an optical measurement system in which a bandpass amplifier and a wave detector are connected in cascade to each of the output parts of the second optical receiver. 4. The optical measurement system according to claim 1, wherein the optical means is a two-wavelength differential displacement-light converter. 5. In the optical measurement system according to claim 4, the displacement-light converter includes a first optical lens that converts the light emitted from the optical fiber into parallel light, and a first optical lens that converts the light emitted from the optical fiber into parallel light; a second optical lens that focuses the light on the optical axis; and a displacement plate that is arranged at right angles between the two lenses and has two filters with different transmission wavelength ranges, the boundary of which is movable around the optical axis of the lens. Optical measurement system. 6. The optical measurement system according to claim 5, wherein the input end of the optical fiber is movable in the axial direction of the optical lens.