JPS6152800A - Optical fiber measuring apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber measuring device that uses optical fibers for transmitting optical signals in a device that measures physical quantities by applying polarization of light.

[Conventional technology]

- FIG. 3 is a block diagram showing a conventional device, showing an example in which a pressure sensor is constructed using a photoelastic element. In the figure, (1
) is a light source, (2) is an optical fiber, (31 is a microlens, (41 is a polarizer, (5) is a photoelastic element, (6) is an A wavelength plate, (7) is an analyzer, 181 and +91 are respectively Microlens, +101, old) is an optical fiber, eta, (131 is a pre-receiver, respectively)
C119 is an adder, 9th is a subtracter, and ←Q is a divider.

The light emitted from the light source il+ is transmitted through an optical fiber (21), collimated by a microlens (31), converted into linear polarization by a polarizer (41), and input to a photoelastic element (51). - The pressure to be measured is applied to the surface, and the applied pressure causes a birefringence phenomenon.If the photoelastic element (5) 1 is an isotropic medium, then the pressure direction The refractive index of , and the refractive index of the two directions perpendicular to it are different (that is, the speed of light is different).Therefore, light with an electric field component in the pressure direction and light with an electric field component perpendicular to it are photoelastic elements. (
5), a phase difference will occur at the output end of the hermitage. For example, if the linearly polarized light output from a polarizer (41) is
at an angle of 45° with respect to their axes (i.e., the axis indicating the direction in which pressure is applied to the photoelastic element (51) and @I in the plane perpendicular to the traveling direction of the seven lights perpendicular to this When the light is incident on the photoelastic element (5) in the polarization direction, the output light of the photoelastic element (51 becomes an elliptical polarized light according to the pressure. This fully circularly polarized light has wavelength A. Another 90 on board (6)
A phase difference of ' is given and a leading bias is applied.
The analyzer (71 splits the light into two polarized components perpendicular to each other, and each component light is focused by a microlens t8i (91), transmitted through optical fibers no+ and i'u, and sent to optical receivers aa and O, respectively. By calculating the sum of the outputs of these optical receivers α2 and α3) with a difference adder α4 and a subtractor αυ, and calculating the ratio of the two with a divider αQ, the fluctuation of the optical power of the coming light is calculated. In addition, an output proportional to the pressure applied to the photoelastic element (5) can be obtained without being affected by the change in loss in the light source '@II optical fiber (21).

Although the above description has been made regarding the case where pressure is measured using a photoelastic element as a sensing element, the same applies to the case where a magnetic field or an electric field is measured using a Faraday element or a Pockels element as a sensing element.

[Problems that the invention attempts to solve]

Since the conventional device n was constructed as described above, there was a problem that if the optical transmission losses in the optical fibers tlOi +, :'(tυ were not the same, this would cause measurement errors.

The present invention was made to solve these problems, and an object of the present invention is to provide an optical fiber measuring device in which fluctuations in the light source and the light transmission system do not cause measurement errors.

[Means for solving problems]

In this invention, an optical signal serving as a reference and an optical signal representing a physical quantity to be measured are transmitted through the same optical fiber to prevent fluctuations in the optical transmission system from causing measurement errors.

Furthermore, in another invention according to this application, the number of parts of the device is completely reduced by using a single optical fiber transmission device for both forward and backward transmission of light.

[Effect]

In other words, if linearly polarized light is passed through a ventilation optical effect element before being input to an optical modulation element such as a photoelastic element, and a modulation signal with a constant amplitude and constant frequency is provided to the ventilation optical effect element, this modulation An optical signal carrying a signal and a modulated signal by the optical modulation element at the same time is transmitted by the same optical fiber transmission device. After converting this transmitted optical signal into a total electrical signal,
By fully extracting only No. 5 and expressing the modulated signal by the optical modulation element based on the amplitude of this constant frequency signal,
This prevents fluctuations in the light source and light transmission system from causing measurement errors.

In another invention, a polarizing beam splitter is inserted between the optical beam and the electro-optical element, and a reflective film is provided at the end of an optical modulation element such as a photoelastic element to reflect the light. A single source fiber transmission device can be used for optical outbound and inbound transmission.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention, in which the same reference numerals as in FIG.
b), (3c), and (3d) are microlenses, respectively;
The fin is an AC voltage source with a constant voltage and constant frequency, (181 is a ventilation optical effect element % (1!J, +21J) are polarization preserving optical fibers, (21) is an analyzer, (
22) is a photoelectric converter, (23) is a filter, (24) is a rectifier, and (25) is an amplifier.

Next, the operation of the apparatus shown in FIG. 1 will be explained.

The light from the light source (1) is linearly polarized by a polarizer (41) and input to the ventilation optical effect element (181. In this case, the direction of the linearly polarized light by the polarizer (4) is set relative to the electric field direction of the electro-optic element. and set it at an angle of 45°.

'''L optical effect: ti+u111Kl';
An alternating current voltage with a width and a constant frequency is applied, and the passing light has different phase differences depending on the polarization component in the direction of the electric field due to this voltage and the polarization component in the direction perpendicular to it. Since the direction of the linearly polarized light by the polarizer (41) is at an angle of 45° with respect to the electric field direction of the ventilation optical effect element (18), the two components of the polarized light are as follows.Here, (IJQ is The angular frequency of light, Ei, is the amplitude of the electric field of the output light from the polarizer (41).

Applied voltage t' Vrsin of ventilation optical effect element (181)
(ωt), then e after passing through the electro-optical element decoy
The phase of z acid component ey acid component is expressed based on the phase of ex acid component, and Vπ is ez (!: In order to set the phase difference of ey to π, the voltage (half wavelength voltage).

When the light represented by equation (2) passes through the entire magnetic wave plate (6), the light after passing through the magnetic wave plate (6) becomes. This light is collected by a microlens (3a), transmitted through a polarization preserving optical fiber (1!J k ;nl), and collimated by a microlens (3b).
i rnate ) and enters the photoelastic element (5).

Optical fiber mackerel and microlens (3a), (3b)
The term "optical fiber transmission device" includes f, and its transmission efficiency (expressed as an optical power ratio) is defined as fcβ1.

β1 changes due to mechanical deformation of the optical fiber (i value). In the photoelastic element (51), a phase difference a relative to the applied pressure P is generated.

Here, the value of the pressure that causes the P7rFi phase difference π is called the half-wavelength pressure.

Photoelastic element +51k The emitted light is a microlens (3c)
The light is condensed and transmitted through a polarization-maintaining optical fiber, collimated by a microlens (3d), and incident on an analyzer (21). (3c), (20), (3
Let the total transmission efficiency of the optical fiber transmission device be β2, which is +1·T in d).

Polarization preserving optical fiber (Ll, +201 is for polarization component.

Since each of ey' and 1 is transmitted independently, an analyzer (
At the incident point of 21), the phase of the ex acid component is set as the entire reference. When the polarization plane of the analyzer (21) is installed at the same angle as the polarization plane of the gold polarizer (4), the optical power 10 that has completely passed through the analyzer (21) becomes a total constant. However, 1. =aE1.

In the region of θ x π, 5 ina x θ, so Equation (7)
By substituting all the expressions +31 and +51 into this, we obtain.

The optical power expressed by equation (9) is input to the photoelectric converter (22) and converted into an electrical signal.
In 22), it is assumed that a voltage proportional to the input power is output, and the ratio is measured '&1. kη and 'rL, output voltage V. is the voltage V. Inside is the component V of angular frequency ω. l and other components V. 2, so filter this (23)
Separated by . When vo1' is peak detected by the rectifier (24), the output Vo 1p is as follows.

If you perform all the divisions of V.2//Vo1p using a divider (IQ), you can calculate P from that v3.

The amplifier (25) inputs V3k from the divider αQ and uses the formula α
The calculation of → is performed by the analog calculation circuit and the value of P is output.

As explained above, according to the present invention, fluctuations in the transmission efficiency β□ and β2 of optical fibers do not appear in the output.
Pressure Pk pressure can be measured well.

FIG. 2 is a block diagram showing another embodiment of the invention of this application. The same reference numerals as those in FIG. . (
26) is a polarizing beam splitter 1 (27) is a three-wavelength plate, and (50) is a photoelastic element corresponding to the photoelastic element (5) in Fig. 1, but a reflective film (51) is provided on the end surface. The light is reflected here and sent back to the photoelastic element (
50) and an optical fiber transmission device consisting of (3b), (19), and (3a), as well as a polarizing beam splitter (27) and an electro-optical element (18i).
26), so the Kanki Optical Effect (18) 1, ) 8
The wave plate (27) and the photoelastic element (50) rotate the plane of polarization during the reciprocating path, and the end wave plate (27) is the first
The same function as the wavelength plate (6) shown in the figure is used.

In addition, since the polarizing beam splitter (26) acts as 't'i (III) photons on the light from the light source (1), it corresponds to the polarizer (4) in FIG.
) acts as an analyzer for the return light that is reflected by the polarization preserving optical fiber F191, and the phase difference that has occurred up to that point changes the intensity of the light that is reflected as input light to the photoelectric converter (22). 1. is converted, so the same 1. as explained in FIG. ;p, , the pressure P shown by the equation (1→) can be totally calculated.

Compared to the device shown in FIG. 1, the device shown in FIG. 2 uses the same fiber for all the reciprocating paths, so it has fewer parts.
In addition, since the photoelastic element and the vented optical effect element are passed through twice, there is an advantage that the Hi-tonic ratio becomes large. The plane of polarization is rotated at an AC% pressure of
It has the advantage of being able to accurately measure the physical Nk of the measurement target and requiring only one optical receiver.Furthermore, according to the second invention of this application, the total number of parts can be further reduced and the equipment can be simplified. It can be configured in a small size.

Although the embodiment of the present invention has been described in which the physical quantity to be measured is pressure, it is also applicable to voltage measurement making full use of the Pockels effect and magnetic field measurement making full use of the Faraday effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing the entire structure of another invention of this application, and FIG. 3 is a block diagram showing a conventional device. In the figure, 111 is a light sister, (41 is a polarizer, i51
, (50) are photoelastic elements, (6) is an A wavelength plate, tle is a divider, (17) is an AC voltage source, (1& is a ventilation optical effect element, (1!J), y(2ol is Each is a polarization preserving optical fiber, (21) is an analyzer, (22) is a photoelectric converter, (23) is a filter, and (2) is a polarization preserving optical fiber.
4) is a rectifier, (25) is an amplifier, (26) is 1 flat 0
The beam splitter (27) is a four-wavelength plate, and (51) is a reflective film. Note that the same reference numerals in each figure indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A light source that generates light, a polarizer that converts the light from this light source into linearly polarized light, an electro-optic effect element that modulates the phase of the output light of this polarizer, and a constant amplitude constant as a modulation signal to this electro-optic effect element. A means for applying an alternating current voltage at a certain frequency, a quarter-wave plate for applying an optical bias to the output light from the electro-optic effect element, and a polarization-maintaining optical fiber for transmitting the output light from the quarter-wave plate. An optical fiber transmission device, into which the light transmitted by the optical fiber transmission device is incident, an optical modulation element that modulates the phase of the incident light by a change in birefringence according to the physical quantity to be measured, and a An optical fiber transmission device that has a polarization preserving optical fiber that transmits light, an analyzer into which the light transmitted by this optical fiber transmission device is incident, and converts the light that has passed through this analyzer into an electrical signal proportional to the intensity of the light. a photoelectric converter for converting, a filter for separating the electrical signal output from the photoelectric converter into a signal component having the constant frequency, which is the frequency of the modulation signal of the ventilation optical effect element, and other signal components; and an output of the filter. An optical fiber measuring device comprising a processing circuit that calculates a ratio of the magnitude of the other signal components to the magnitude of the signal component of the constant frequency. (2) A light source that generates light, a polarizing beam splitter that transmits the light from this light source as linearly polarized light and reflects the linearly polarized light incident from the direction opposite to the direction of the light from this light source, and this polarized beam An electro-optic effect element that phase-modulates the light transmitted through the splitter, means for applying an alternating current voltage of constant amplitude and constant frequency as a modulation signal to the electro-optic effect element, and applying an optical bias to the output light from the electro-optic effect element. A 1/8 wavelength plate, an optical fiber transmission device having a polarization preserving optical fiber that transmits the output light from this 1/8 wavelength plate, the light transmitted by this optical fiber transmission device is incident, and the light transmitted by this optical fiber transmission device is , an optical modulation element that provides phase modulation by birefringence change according to a physical quantity to be measured; the optical fiber transmission device that reflects light that has passed through the optical modulation element and passes it through the optical modulation element in reverse; an 8-wavelength plate, a means for passing through the electro-optic effect element in reverse and entering the polarizing beam splitter for reflection, and a means for receiving reflected light from the polarizing beam splitter and converting it into an electrical signal proportional to the intensity of the incident light. a photoelectric converter for converting, a filter for separating the electrical signal output from the photoelectric converter into a signal component having the constant frequency, which is the frequency of the modulation signal of the electro-optic effect element, and other signal components; and an output of the filter. An optical fiber measuring device comprising a processing circuit that calculates a ratio of the magnitude of the other signal components to the magnitude of the signal component of the constant frequency.