JPH0225757A - Light applied measuring instrument - Google Patents

Abstract

PURPOSE:To prevent an error caused by the wavelength dependency generated by a variation of an ambient temperature of an optical transmitter and to exactly execute the measurement by inserting an optical filter consisting of a narrow band filter between a photosensor part and an optical receiver. CONSTITUTION:An optical transmitter 1 is connected to a photosensor part consisting of a lens 3, a polarizer 4, a Faraday element 5, an analyzer 6 and a lens 7 through an optical fiber 2, and transmits a light beam. It is amplified by an amplifier 10 through an optical fiber 8, a narrow-band filter 15 and an optical receiver 9, and thereafter, one is connected to an integrator 11 and the other is connected to an amplifier 13 through a coupling capacitor 12, and outputs of both of them are outputted to a divider 14. In such a way, even if optical wavelength of its wave is varied by a variation of an ambient temperature of the optical transmitter 1, a light beam transmits through only some band by the optical filter 15, therefore, an error caused by the wavelength dependency is prevented, and the measurement can be executed exactly.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention is an optical method for optically measuring a coating measurement quantity by changing the optical characteristics and light intensity depending on the quantity to be measured, such as an electric field or a magnetic field. The present invention relates to an optical measurement device that detects

(Prior Art) FIG. 2 is a block diagram of a conventional optical application measuring device, and shows, as an example, a magnetic field measuring device using the Faraday effect. In the figure, 1 is an optical transmitter.

2 is an optical fiber, 3 is a lens, 4 is a polarizer, 5 is a Faraday element, 6 is an analyzer, 7 is a lens, 8 is an optical fiber,
9 is an optical receiver, 10 is an amplifier, 11 is an integrator, 12 is a coupling capacitor, 13 is an amplifier, and 14 is a divider.

Next, the operation will be explained. The light emitted from the optical transmitter (D passes through the optical fiber 2, becomes a parallel beam at the lens 3, and enters the polarizer 4.The light then becomes linearly polarized light at the polarizer 4, and enters the Faraday element 5, but parallel to the traveling direction of the light. When there is a magnetic field in the direction, this magnetic field rotates the plane of polarization of the linearly polarized light due to the Faraday effect 6 Therefore, if the analyzer 6 is set to transmit light with a plane of polarization at a certain angle (- is the polarizer 4 and analyzer 6 so that the linearity is the best.
The light is intensity-modulated by the magnetic field (which is arranged so that its plane of polarization forms an angle of 45°).

Then, this light is focused by a lens 7, photoelectrically converted by an optical receiver 9 via an optical fiber 8, and then amplified by an amplifier 10 to the required voltage. In order to amplify only the modulation component, the other one passes only the alternating current component through a coupling capacitor 12 and is amplified by an amplifier 13. Then, by dividing these two outputs by the divider 14, errors due to loss changes and optical power changes in the optical transmission line (for example, the optical fiber itself or the coupling part with the lens) and the optical transmitter 1 are divided. is compensated for. That is, since the degree of optical intensity modulation by the magnetic field in the optical sensor section (consisting of lens 3, polarizer 4, Faraday element 5, analyzer 8, and lens 7) remains unchanged, the optical power of optical transmitter 1 Even if the loss in the optical transmission path becomes small or the loss in the optical transmission path becomes large, the average received light power (the amount by which the modulation component is removed, i.e.,
(corresponding to the output of the integrator 11) also becomes smaller, and as a result of division, a constant output is always obtained.

(Problem to be Solved by the Invention) The conventional optical measurement device is configured as described above, but the optical transmitter 1 changes its emission wavelength due to changes in ambient temperature, and the optical sensor section exhibits wavelength dependence. There was a problem where an error would occur if there was.

The present invention has been made to solve the above-mentioned problems and provides an optical measuring device that can perform accurate measurements even when the ambient temperature changes.

[Structure of the invention]

(Means and Effects for Solving the Problems) The optical measurement device according to the present invention has an optical filter inserted between the optical sensor section and the optical receiver.

In this way, the optical application measuring device according to the present invention is
Even if the wavelength of the light wave changes due to changes in the ambient temperature of the optical transmitter, only a certain wavelength band is transmitted through the optical filter, so errors due to wavelength dependence do not occur and accurate measurements can be made.

(Example).

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figures, the same symbols as in Figure 2 indicate the same things, 1
Reference numeral 5 denotes a narrow band filter, and the light that passes through the Faraday element 5, is analyzed by the analyzer 6, and is received by the optical fiber 8 passes through this narrow band filter 15 and enters the optical receiver 9. ing. Others are the same as before.

Next, the operation will be explained. Since the light incident on the optical receiver 9 passes through the narrow band filter 15, only the amount of light corresponding to the band decrement of the narrow band filter 15 is received. Therefore, even if the polarization wavelength of the optical transmitter 1 changes depending on the ambient temperature, the wavelength of the light received by the optical receiver 9 will maintain a constant band. In this case, if the bandpass filter 15 is selected so that only a narrow band within the emission spectrum of the optical transmitter 1 is transmitted, the band can be kept constant over a wide temperature range. The light entering the optical fiber 2 operates in the same manner as in the conventional case, so a description of the lever will be omitted.

By keeping the band constant in this way, the optical power changes with temperature changes (if the spectral distribution is not constant in the range where the emission spectrum of optical transmitter 1 shifts in wavelength due to temperature changes), this is due to the divider. By dividing by 14, it is repaired and accurate measurements can be made.

A method of installing the optical filter 15 between the optical transmitter 1 and the optical fiber 2 has been proposed in JP-A-61-193033. In order to input the light into the fiber 2, the end face of the optical fiber must be as close as possible to the light emitting surface of the LED, and installing the optical filter 15 in this area will cause coupling loss between the optical transmitter 1 and the optical fiber 2. . In contrast, in the present invention, an optical filter 15 is installed between the optical fiber 8 and the optical receiver 9. Photodiodes constituting the optical receiver 9 are commercially available with wide light-receiving areas, and even if the distance between the optical fiber 8 and the optical receiver 9 is increased somewhat, coupling loss may occur. There isn't. Therefore, by installing the optical filter 15 in this portion, a larger amount of light can be obtained, and alignment adjustment is also easier.

Further, in the present invention, since no optical filter is installed between the optical transmitter 1 and the optical sensor section composed of the polarizer 4, Faraday element 5, analyzer 6, etc., the amount of light passing through the optical sensor section is This makes it easier to observe the light spot on a monitor TV, etc., and makes it easier to adjust the optical axis.

Further, as shown in FIG. 3, the present invention transmits light from three light emitting diodes If, Ig, and
, 2b, 2c to the Faraday element 5,
The present invention can also be applied to a method in which three beams of light are passed through the Faraday element 5 separately, focused on one point, taken into one optical fiber 8, and sent to an optical receiver. At this time, the optical filter 15 focuses three beams of light. If it is installed between the optical sensor section and the optical receiver, not only one optical filter 15 is required, but also all three lights pass through the same optical filter 15, so the filter effect is exactly the same for all three lights. This is convenient for maintaining the balance of light. In this method, in order to keep the amount of received light constant, the received light waveform is monitored, and the current flowing through the light emitting diodes If, Ig, and lh is fed back to adjust the amount of light emitted so that the waveform always maintains the same level. There is. At this time, as shown in FIG. 4, the center wavelength λf of the optical filter 15 is
Center wavelength λ of the emission spectrum of the light source.

Choose something a little larger. In this way, the amount of change in the current flowing through the light emitting diodes If, Ig, and lh due to feedback in response to a constant change in the amount of light emission can be reduced. This principle will be explained below. Now consider a case where the amount of received light decreases. A feedback circuit increases the current flowing through the light emitting diode to increase the amount of light emitted, but as the current increases, heat generation in the light emitting diode increases, ambient temperature increases, and the emission spectrum shifts to the longer wavelength side. now.

λf〉λ. Since it is closed, λ. As the value increases, the amount of light that can pass through the optical filter 15 increases, and since the amount of received light increases, the current decreases somewhat due to feedback. Therefore, when the steady state is reached, the current change due to feedback is λ. = λf. In addition, when the amount of received light increases, the current flowing through the light emitting diode is reduced by the feedback circuit, reducing the amount of light emitted. At the same time, the heat generation of one light emitting diode decreases, and the emission spectrum shifts to the short wavelength side, and the optical filter 1
5 to reduce the amount of light passing through. Therefore, in this case also λ. =λf, the range of current change due to feedback can be made smaller. Therefore, more accurate feedback can be expected and the accuracy of the measuring instrument can be improved.

Note that the above embodiments are examples of magnetic field measurement using the Faraday effect, electric field and voltage measurement using the Pockels effect, acceleration measurement using the photoelastic effect, and light intensity modulation depending on the amount of ground cover measured. The same effect can be achieved with the application of objects.

〔Effect of the invention〕

As described above, according to the present invention, since the optical filter is inserted in the middle of the path from the optical transmitter to the optical sensor, even if the emission wavelength of the optical transmitter changes depending on the ambient temperature, the optical filter allows a certain wavelength band to be emitted. This allows for accurate measurements without wavelength-dependent errors.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical application measurement device according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a conventional optical application measurement device, and FIG. 3 is a configuration diagram showing another embodiment of the invention. FIG. 4 is a diagram showing the center wavelength and emission spectrum of the filter of the present invention. 1... Optical transmitter 2.8... Optical fiber 4.
...Polarizer 5...Faraday element 6...
Analyzer 9... Optical receiver 15... Optical filter 16... Conductor 41... Emission spectrum of light source 42... Bandwidth representative of optical filter Patent attorney Yudo Noriyuki Chika Kendai Daishimaru Fig. λ0 tf λf>10 Fig. Roasted skin

Claims (1)

[Claims] An optical sensor section whose optical characteristics change depending on the amount to be measured and changes the intensity of light; an optical transmitter that transmits light to this optical sensor section via an optical transmission section; and an optical transmission section that transmits the light from the optical sensor section. An optical application measurement device comprising an optical transmission section and an optical receiver that receive data through the optical sensor, characterized in that an optical filter consisting of a narrow band filter is inserted between the optical sensor section and the optical receiver. measuring device.