JPS62144023A - Optical measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain the titled apparatus excellent in measuring accuracy by compensating transmission loss causing a measuring error, by standardizing the amplitude value of an AC component on the basis of the value based on a DC component and obtaining a measured value on the basis of said value. CONSTITUTION:When the temp. of a sensor part 17 is low, because loss difference in both polarizing directions in the sensor part 17 is large, the amplitude value A of an AC component is large. When the temp. of the sensor part 17 becomes high, the loss difference in both polarizing directions in the sensor part 17 becomes small and, therefore, the amplitude value A of the AC component becomes small. The signal of the sensor part 17 is subjected to A/D conversion in a signal processing circuit 21 to detect a max. value and a min. value and, from these values, the level B of the DC component of the signal is calculated and the amplitude value A is standardized by the operation of A/B. As mentioned above, not only the loss variation of a transmission path and a connection part but also the variation of a photoelectric converter 19 can be compensated and the extremely accurate measurement of temp. is enabled.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides an optical measurement device that can accurately determine physical quantities to be measured without depending on optical transmission path loss, coupling loss, fluctuation, etc. Regarding.

[Technical background of the invention and its problems]

2. Description of the Related Art Conventionally, various optical measuring devices have been known that optically measure physical quantities by utilizing a phenomenon in which physical quantities such as temperature, pressure, magnetic field, electric field, etc. cause changes in the intensity and phase of light waves. One of them is to transmit a constant light output through an optical tube, and use the sensor section to measure the light output.
There is a 111 device called the Motoji Fishhook, which calculates a physical quantity based on the change in the amount of light. In such Ill,
As a sensor, a magnetic sensor or the like is used, which is a combination of a polarization-maintaining fiber magneto-optical element and a polarizer, in which the radiation loss of two principal axes changes depending on the temperature, for example.

However, when using changes in optical loss, changes in loss in the optical transmission line, coupling loss in optical elements, etc. directly appear as measurement errors.

Therefore, for example, in a temperature sensor that utilizes the temperature dependence of the basic absorption characteristics of a semiconductor element, as shown in Figure 4,
By simultaneously transmitting the reference light of wavelength λ2, which is longer than the basic absorption wavelength, that is not subject to loss fluctuation due to temperature, along with the light of wavelength λ for temperature measurement, and taking the difference in received light ψ between the two, the transmission line and optical Compensate for loss fluctuations in the target joint @
It has also been proposed to do so.

However, such devices have limited application fields and require multiplexers, demultiplexers, etc., making the configuration difficult. ! It had the disadvantage of being sloppy.

[Purpose of the invention]

The present invention was made based on the above problem, and its purpose is to provide an optical measuring device in which the amount of loss varies depending on the physical quantity to be measured, without complicating the structure. It is an object of the present invention to provide an optical measurement device that enables compensation for loss fluctuations in transmission lines and coupling parts and can be applied to a wide range of fields.

(Summary of the invention) The present invention is characterized by the following configuration.

That is, by guiding a light wave from a light source that emits light waves while sweeping the wavelength to a polarization-maintaining fiber via an optical isolator and a non-polarizing beam splitter, the output end 1 of the polarization-maintaining fiber 1 antifAIl! J, and returns the light wave whose polarization shape h periodically changes to the input end via this antitAIII, and the loss difference of the return waves in mutually orthogonal polarization directions is It changes depending on the situation. Then, the feedback wave from this sensor section is received by a photoelectric conversion element via the polarization maintaining fiber and the non-polarization beam splitter, and the amplitude value of the AC component of the output of this photoelectric conversion element is calculated based on the DC component. It is characterized in that the measurement value of the physical quantity to be measured is standardized by the value.

〔Effect of the invention〕

■If the loss of fast waves occurring in the sensor section differs depending on the polarization direction, when a light wave whose polarization state changes periodically is incident on this sensor section, the intensity of the feedback wave will change depending on the period of the polarization state of the incident light wave. changes periodically based on changes in Therefore, the output of the photoelectric conversion element also becomes a signal containing an alternating current component.

The width of this alternating current component, that is, the loss difference in the leakage direction of the feedback wave changes depending on the physical quantity to be measured, so the physical quantity to be measured can be obtained from this loss difference. 'By the way, the output of the photoelectric conversion element fluctuates not only due to loss in each of the 11 feedback wave directions, but also due to optical transmission line loss, coupling loss, photoelectric conversion loss, etc. Although the losses in the rear end lead to measurement errors, they exert D3W at a rate equal to the DC level and width of the AC component of the output of the photoelectric conversion element.

In the present invention, the amplitude value of the AC component is normalized by the value based on the DC component, and the measurement end is cooled based on this value, so transmission line loss etc. that lead to measurement errors are compensated for.
We can provide equipment with high measurement accuracy. Moreover, this invention can be applied to all optical measurement devices that utilize the fact that the amount of loss changes depending on the physics being measured.
It has a wide range of application, and since it is not necessary to use a plurality of light waves with different wavelengths, it does not require a multiplexer or a demultiplexer, and has the advantage of having a simple structure.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an example of a temperature sensor using a polarization maintaining fiber in the sensor section.

In the figure, the wavelength swept light source 11 is, for example, a distributed feedback semiconductor laser (DFB) that can change the oscillation wavelength of several people in the A-mode.
(laser). For sweeping the oscillation wavelength, for example, a thermal wavelength sweeping method using a microheater submount, which was previously proposed by the present inventors, can be used. That is, according to the thermal wavelength m method, the oscillation output can be kept constant by APC (automatic power control), and stable wavelength sweeping becomes possible. The waveform of the sweep can be changed arbitrarily, but in this embodiment, the wavelength is swept in proportion to time. Therefore, a sawtooth wave-like wavelength sweep signal is provided from the sawtooth wave generator 12 to the wavelength sweep light source 11 . Further, the wavelength swept light source 11 is made to emit light at a constant level by the DC bias 7'Rm 13.

The light from the wavelength swept light source 11 passes through the optical isolator 14
After passing through a non-polarizing beam splitter 15, the beam enters a polarization maintaining fiber 16. At this time, if light is incident such that the angle between the polarization direction of the wavelength swept light source 11 and the main axis direction of the polarization maintaining fiber 16 is 45 degrees, the polarization state at the output end of the polarization maintaining fiber 16 will be , according to the wavelength sweep, changes periodically from linearly polarized light to circularly polarized light, and further to linearly polarized light orthogonal to the linearly polarized light. This light wave is incident on the sensor section 17.

The sensor section 17 is covered with a polarization-maintaining fiber whose cutoff wavelength is at least 0.2 mm shorter than the wavelength of the light source, and whose principal axis is aligned with the polarization-maintaining fiber for optical transmission. The loss due to immersion is different between the first main axis and the second main axis, and the difference in loss between the two becomes smaller as the temperature applied to the sensor section 17 becomes higher.

That is, in general, polarization maintaining fibers have a refractive index change in the principal axis direction due to residual stress in the core due to cooling during manufacturing. Therefore, if the temperature of the fiber is increased, 2
Since the difference in stress in the directions of the two principal axes becomes smaller, the difference in refractive index in the directions of both principal axes also becomes smaller, and the difference in radiation loss also becomes smaller.

A light wave whose polarization state changes periodically as described above is introduced into the sensor section 17 . A reflective hood 18 is formed at the output end of the sensor section 17 .

Since the shoulder wave preservation fiber 16 and the sensor section 17 are arranged so that their main axes form an angle of 45 degrees, the sensor section]7
Orthogonal a-polarized light is alternately incident on the first principal axis and second principal axis. Since the radiation loss in both principal axis directions is different, the anti-cutting film 18
The feedback wave reflected by the polarization maintaining fiber 16 and fed back to the input end of the polarization maintaining fiber 16 for optical transmission becomes an optical signal with periodic intensity changes.

The amplitude becomes smaller as the temperature applied to the sensor section 17 becomes higher.

The feedback wave is reflected by IJ to a non-polarizing beam splitter 15 whose branching ratio changes by 1% or more even if the polarization state at the input end of the polarization-maintaining fiber 16 changes.
The output of the -4° photoelectric converter 19, which is photoelectrically converted by the photoelectric converter 19, is amplified by the amplifier 20 and sent to the signal processing circuit 2.
) will be introduced.

FIG. 2 is a diagram showing signal waveforms input to the signal processing circuit 2). When the temperature applied to the sensor section 17 is low, the loss difference in both width wave directions in the sensor section is large, so
As shown in Figure (a), the amplitude of the AC component is 1! A is big. As the temperature applied to the sensor section 17 becomes higher, the loss difference in both width wave directions in the sensor section 17 becomes smaller, so the amplitude value A of the AC component becomes smaller. The signal processing circuit 2) A/D converts this signal, detects the maximum value and minimum value, determines the level B of the DC component of the signal from these values, and converts the signal to A/D.
The amplitude value A is normalized by the following calculation.

As described above, according to this embodiment, not only can loss fluctuations in the transmission line and coupling portion be compensated for, but also fluctuations in a single photoelectric converter can be compensated for, making extremely accurate temperature measurement possible.

FIG. 3 is a diagram showing an example in which the present invention is applied to a magnetic sensor using a Faraday element in the sensor section.

This embodiment differs from the previous embodiment in that the sensor section 3
It is 1.

That is, the sensor section 31 is provided via the rod lens 32 at the output end of the polarization maintaining fiber 16 for optical transmission. In the figure, numeral 33 denotes a polarization separation prism, and its transmission axis is arranged at 45° with respect to the main axis of the polarization maintaining fiber 16. The light transmitted through the polarization separation prism 33 is guided to another polarization separation prism 1, . The transmission axis of this polarization separation prism 35 is arranged so as to coincide with the transmission axis of the polarization separation prism 33. Therefore, if no magnetic field is applied to the Faraday element 34, the light wave that has passed through the Faraday element 34 also passes through the polarization separation prism 35 and is reflected by the reflective film 36 provided at the base end of this prism 35. Again, polarization separation prism 35 ~ Faraday element 34 ~ polarization separation prism 33 ~ Otsudo lens 3
2 to the polarization maintaining fiber 16. Also,
When a magnetic field is applied to the Faraday rope 34,
Since the plane of polarization of the light wave propagating through the Faraday probe 34 is rotated, the propagating light undergoes loss due to reflection at the polarization separation prism 35°33. Therefore, the magnetic field can be measured based on the amount of loss of the feedback light.

On the other hand, the light wave reflected by the polarization separation prism 33 passes through a waveguide 37 for optical path adjustment, and is reflected by a reflection II! provided at the base end of this waveguide 37. 39, and is fed back again via the waveguide 37, the wave separating prism 33, the rod lens 32, and the polarization maintaining fiber 16. The feedback light that returns through this path is not affected by the magnetic field at all.

The light wave that enters the polarization separation prism 33 from the rod lens 32 is a light wave whose polarization state changes periodically in accordance with the wavelength sweep of the wavelength swept light source 11, as in the above-described embodiment. 33 exhibits a switching action that alternately repeats transmission and reflection of light. Therefore, as the wavelength sweeps, the optical path changes periodically, causing a change in loss, and it is possible to cause the feedback light incident on one photoelectric conversion element to have a periodic intensity change.

In this embodiment, the return light reflected from the reflective film 38 is the brightest and does not depend on the magnetic field, so it is used as a reference signal. Furthermore, the amount of feedback light reflected from the reflective film 36 decreases as the applied magnetic field increases. Therefore, the signal processing circuit 2) can compensate for the loss caused by the measurement error by normalizing the amplitude value of the AC component of the input signal by the maximum value (reference signal).

As described above, the present invention normalizes the amplitude value of the alternating current component of the output signal of the photoelectric conversion element by the maximum value, minimum value, or their average value, which is independent of the physical type. Limited to examples: not of the month. For example, the sensor section can be applied to a wide range of applications, such as electric field sensors such as LiNb0a and LiDingaOi, voltage sensors, and temperature sensors that utilize II absorption of semiconductors, in addition to those described above.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a flat 11 sensor according to an embodiment of the present invention, FIG. 2 is a main waveform diagram of the sensor, and FIG.
FIG. 4 is a block diagram showing the configuration of an i-electric field sensor according to an embodiment of the present invention, and FIG. 4 is a diagram for explaining a conventional optical measuring device. 11... wavelength swept light source, 14... optical isolator,
15... Non-polarizing beam splitter, 16... Polarization maintaining fiber, 17.31... Sensor section, 18.36
゜38... Reflective film, 19... Photoelectric converter, 20...
・Old width gauge, 32...Rod lens, 33.35...
Kuboken Prism, 34...Faraday element, 37.
...4 waves.

Claims (3)

[Claims] (1) A light source that emits light waves while sweeping the wavelength, an optical isolator that allows the light waves from this light source to pass in only one direction, and a non-polarized beam that splits the light waves that have passed through the optical isolator regardless of the polarization state. a polarization-maintaining fiber that guides the light wave introduced through the non-polarizing beam splitter to a measurement point and periodically changes the polarization state of the light wave at the output end by wavelength sweeping the light source; The light wave from this polarization-maintaining fiber is guided and returned to the input end via a reflective film provided at the end, and the loss difference of the return waves in mutually orthogonal polarization directions changes depending on the physical quantity to be measured. a photoelectric conversion element that receives a feedback wave from the sensor unit via the polarization-maintaining fiber and the non-polarization beam splitter and photoelectrically converts it, and an amplitude value of an alternating current component of the output of the photoelectric conversion element. an optical measuring device comprising: means for normalizing the physical quantity with a value based on a DC component to obtain a measured value of the physical quantity to be measured. (2) The sensor section includes a polarization-maintaining fiber whose loss difference in two principal axes changes depending on temperature and whose cutoff frequency is at least 0.2 μm shorter than the wavelength of the light source, and an end of the polarization-maintaining fiber. 2. The optical measuring device according to claim 1, further comprising a reflective film provided on the portion of the optical measuring device. (3) The sensor unit includes a polarization separation prism that alternately distributes the light waves from the polarization maintaining fiber according to periodic changes in the polarization state, and one polarization divided by the polarization separation prism. A magneto-optical element that rotates the plane of polarization of a light wave in one wave direction by an applied magnetic field, and a guide that propagates a light wave in the other polarization direction distributed by the polarization separation prism while maintaining the polarization direction. 2. The optical measuring device according to claim 1, comprising a waveguide and a reflective film provided at each end of the magneto-optical element and the waveguide.