JPS59500584A - Sensor using fiber optic interferometer - 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] Sensors using fiber optics and interferometers Related applications This application is a United States patent application series filed on April 14, 1982. This corresponds to the continuation-in-part application of number box No. 368.422.

Background of the invention The invention generally relates to a closed loop or "sagnac" fiber optical interferometer. related to fiber-optic waveguides in fiber-optic interferometers. It relates to sensors for environmental quantities that can have an influence.

An interferometer places a change in phase between two coherent signals that interfere with each other. It functions based on this principle. A closed loop interferometer uses one fiber loop The change in phase that occurs between two optical signals propagating in opposite directions in It works as a principle. Closed-loop interferometers fully account for this relative phase change. i.e., they are measured on a “physical” scale, i.e., they are the overall relative phase between two optical signals propagating in opposite directions in a loop It measures change.

This optical fiber loop of the interferometer can detect temperature, acoustic pressure, vibration, motion and electromagnetic It is sensitive to many environmental effects such as field. Such external phenomena are caused by the optical The optical transmission characteristics can be changed. This is due to, for example, the birefringence of fibers The geometric path length or speed of an optical signal propagating through a fiber changes the amplitude, phase, or polarization state of light propagating through it caused by Thus, sensitivity to environmental effects means that the desired As long as the sensing port can be separated from other environmental quantities to which this fiber is sensitive, means that the fiber interferometer loop can act as a sensor element .

Here, ``bilateral environmental effects (i.e., waves propagating in opposite directions) (effect that does not cause a phase shift between In other words, the effect of causing a phase shift between waves propagating in opposite directions) , it is necessary to consider them separately. In addition, the interactive and non-interactive effects are as follows: It can be considered on any of the following scales: That is, one of them is ``Overall scale,'' which refers to the effect of an environmental phenomenon as a whole loop. It is something that can be obtained. The other one is the ``differential scale'', which This phenomenon is considered to occur only in a local, small segment of the fiber. It is like Certain environmental effects, such as rotation and Faraday effects, This is a non-bidirectional effect on the differential scale, which is The relative relationship between light signals propagating in opposite directions through the same small portion of Causes a change in phase. Such non-interactive and differential effects are cumulative , and the resulting overall scale effect is also non-interactive. It is true. Other environmental effects, such as pressure, can also be bidirectional on a differential scale. light signals propagating in opposite directions through the same small section of fiber. There is no net change in relative phase between the signals. overall scale odor As such, these bidirectional and differential effects typically also have a cumulative effect that is bidirectional. It is directional. Therefore, both directions on such a differential scale effects, even if they are bidirectional on a differential scale. There is some kind of effect that makes such an effect non-interactive on the overall scale. Impossible to be detected by a closed loop interferometer unless a method is devised It is Noh.

In the prior art, this closed-loop interferometer typically Detecting non-interactive and differential effects. 4-c. 7. − 7° interferometer, which traces the optical paths of light propagating in opposite directions to polarization modes. When used with a polarizer that limits the motion to one of the Relatively insensitive to environmental effects other than directional and differential effects. like this Polarizer is a U.S. patent application filed September 30, 1981, serial no. No. 307.095, a continuation-in-part, filed November 9, 1981. Disclosed in co-pending United States Patent Application Serial No. 3T9.311 has been done. This United States Patent Application Serial No. 307°095 also , United States Patent Application Serial No. 249, filed March 31, 1981. , No. 714, which is a partial continuation application. In this type of interferometer, temperature and Any bidirectional and differential environmental phenomenon, such as pressure, has opposite effects on each other. The optical transmission characteristics of both fiber optics for optical signals propagating in the direction are substantially equal. have a great influence. Therefore, there is a difference between these signals propagating in opposite directions. No or only a small change in relative phase occurs. With this invention transforms differential and bidirectional effects such as acoustic pressure into global scale and non-bidirectional effects. This type of effect can be detected by making it a directional effect. This paper attempts to teach the structure of a similar loop interferometer.

Disclosure summary This invention uses a closed-loop optical interferometer to Environmental phenomena that have bidirectional effects on length can be It attempts to detect by producing an effect.

Briefly, the detected phenomenon is spatially asymmetric and This is achieved by being non-uniform. The three disclosed here The basic principles utilized in the basic implementation of are as follows.

In other words, if the quantity Q to be detected is changed over time and around the loop, to the closed-loop interferometer as given at a point away from the center of the path of Is Rukoto. This also forces the rapidly changing Qs in opposite directions from each other. By the time one of the propagating light signals reaches the detector, it has to pass more than the other signal. equivalent to being given to a point on a path such that it must be propagated a distance of do. As used herein, "waves propagating in opposite directions" or "waves propagating in opposite directions" The term ``optical signal propagating in the opposite direction in the interferometer loop'' refers to This is a term used to collectively refer to both types of optical signals. Also, “waves propagating in the opposite direction” (or optical signal) refers to the direction in which acoustic waves propagate within a loop. Only light waves propagating in opposite directions shall be meant.

The quantity to be detected is expressed as the effect on two oppositely propagating light signals. Certain aspects of the basic principle for spatially asymmetric and non-uniform This is disclosed in the first and second embodiments. That is, this basic principle is This is because it is considered easier to understand with these two examples. be. These two embodiments are sensors for acoustic waves. The effect is non-uniform for two oppositely propagating waves of light. It utilizes a coil of fiber optic waveguide that is wound in a special way.

That is, this loop has a winding arrangement in relation to the wave to be detected. has been done. In other words, the wave of interest is the result of all optical signals propagating with it. In other words, it has a uniform effect on optical signals propagating in the same direction as the wave. However, on the other hand, it has a non-uniform effect on optical signals propagating in the opposite direction. It has been done so that In the first embodiment, this is due to the lengthwise direction of the coil. The axial velocity of light waves propagating in the same direction along the longitudinal axis is This is achieved by winding the coil to match the speed of propagation of the acoustic waves.

In a second embodiment, two coils are placed spatially apart by 1/4 of the wavelength of the acoustic wave. the diameter of this coil and its number of turns through each coil. By choosing the time the optical signal passes through to be 174 times the period of the acoustic wave. , utilizes this basic principle. The length of each coil is also By making the space occupied by the acoustic wave extremely small compared to the wavelength of the acoustic wave, so that the coil is substantially uniformly influenced by the acoustic waves at the location where it is located. , has been selected.

In a preferred embodiment, the quantity Q to be detected is Both are applied to the interferometer loops so that they are also spatially asymmetric.

this! Since Q is applied asymmetrically to the loop, changes in Q are opposite to each other. Each wave propagating in the direction will be affected differently, thereby , resulting in a phase difference between them. However, this Q slowly changes like temperature. If there is a quantity that changes rapidly, then at a point on the loop where Q is given, two There may be no suitable change between the arrival times of waves propagating in opposite directions. In this case, each wave will be affected by Q substantially the same way. It becomes. In such a case, the quantity Q can be changed rapidly in time by a conventional modulator. modulates to a rapidly changing base or carrier frequency, and then to the loop at a point away from the geometric path between. In the preferred embodiment Then, this modulated Q is Q(t), which is proportional to the amplitude of q(t). is fed into this loop by a phase modulator that stretches the fiber.

Importantly, this invention overcomes the inherent stability of closed-loop interferometers. By using quiet motion, we can create non-interactive effects from interactive quantities. Therefore, we are trying to detect this bidirectional quantity. As a result, unnecessary amounts of From the effect caused by the desired amount to be detected, The result is a quieter, more sensitive sensor that can discriminate more clearly.

Due to the presence of a delay line function in the closed loop, the sensitivity to jiQ increases, The invention could then be used to detect slowly changing quantities such as temperature. In some cases, the modulation frequency of the quantity Q can be lower.

Therefore, it is an object of this invention to The goal is to provide support.

The objects and features of the invention will be apparent from the following detailed description with reference to the drawings and the appended claims. It will become even clearer from the following.

Brief description of the drawing Figure 1 shows a closed-loop fiber optic device, such as one used as a rotation sensor. FIG.

FIG. 2 illustrates the use of a closed loop fiber optic interferometer according to an embodiment of the invention. FIG. 2 is a schematic diagram of an acoustic sensor.

FIG. 3 is a closed loop fiber optic interferometer according to another embodiment of the invention. 1 is a schematic diagram of an acoustic sensor using

FIG. 4 is a plot of acoustic waves in the sensor of FIG. 3.

FIG. 5 shows a closed loop fiber optic driver according to a preferred embodiment of the invention. 1 is a schematic diagram of a sensor using an interpolator.

Detailed description of the preferred stream Referring now to the drawings, FIG. Disclosed in pending United States Patent Application Serial No. 319.311 A simple example of a closed-loop fiber optics interferometer, such as that used in rotary sensors This is just a schematic diagram. This United States Patent Application Serial No. 319.311 is , United States Patent Application Serial No. 307, filed September 30, 1981. This is a continuation-in-part of ゜095, and this United States Patent Application No. 30 No. 7.095 is a U.S. patent application filed on March 31, 1981. This is a continuation-in-part application of serial number 249°714. All of these patent applications Details are included here by reference. A light source 10 generates a beam of light and The beam passes through optical fiber 12 and polarizer 13 to form a fiber optic bidirectional coupler. 14. This bidirectional coupler also performs the function of separating the beams. It is also used to help. This beam of light is split into two waves, and these two waves The waves move oppositely through the closed loop 116 as shown by the arrows. propagate in the direction. After propagating through the roof 16, these two beams are combined again. and passes through optical fiber 12 to polarizer 13. And that to a second fiber optic bidirectional coupler 18, which fiber optic Bidirectional coupler 18 sends this combined signal to detector 20 . this detector responds to the strength of the combined wave, which is transmitted in two opposite directions. depends on the phase difference between the disseminating waves, so this detector Provides an output signal indicating phase shift. When this fiber coil is rotated, This detector is useful because of the non-reciprocal effect on waves propagating in opposite directions. This means that the rotation of is being detected. Although not shown in Figure 1, this closed loop Loop interferometers also include directional couplers, polarization controllers, phase modulators, and A lock-in amplifier may also be provided. Something like this mentioned before There are some that are described in concurrently ongoing applications, and there are also All single mode fiber with long term stability of vre and shaw Optical Gyroscope'', Q pjiC3L ejjers, Volume 6, No. 10 issue, October 1981, and “All Single Mode Fiber Optical Gyroscope” ゛,　Qpttcs　L　etters, Volume 6, No. 4, April 1981.

It is also described in .

All of the components of the gear interferometer are constructed from a single mode fiber. It can take the form of an all-fiber integrated device. using a phase modulator In this case, this phase modulator acts to bias the response sensitivity and linearity can be increased.

Usually, the differential and dual Examples of directional effects are concentration, force, stress, pressure, displacement, strain, vibration and sound. There are waves.

FIG. 2 illustrates acoustics using a closed loop interferometer according to one embodiment of the invention. FIG. 2 is a schematic diagram of a wave sensor. This acoustic wave sensor is similar to the rotation sensor shown in Figure 1. It has a similar structure. However, in this example, the sound to be detected A widened screw with a longitudinal axis "x" that exists along the direction of propagation of the acoustic wave 26. The coil 24 is wound in a spiral pattern.

The sensor includes a closed loop fiber optic waveguide 24, which The wave guide 24 is wound with a large number of turns to form a coil. Diameter D1 Number of turns N1 The spacing of turns along the longitudinal axis X is determined according to certain standards. select. This standard means that the acoustic wave 26 to be detected is The optical signal traveling along this coil 24 to section B has must move along the longitudinal axis of this coil at the same speed as the That is what it is. That is, as the light wave travels around the turns in the coil, It is as if this light wave were traveling along the threads of a screw with extremely fine threads. It means to move toward end B at a predetermined axial speed as if climbing. light wave saw The axial velocity of is much smaller than the actual propagation velocity in the fiber. However, there are many windings, and each of them has a surface of the acoustic wave. This is because it is almost parallel to 28.

An acoustic wave is generated in an acoustically compressed plane perpendicular to the direction of propagation of this acoustic wave and It has a diluted aspect. The surface 28 in the acoustic wave is the area where the pressure is high in the acoustic wave. The space 30 shows a peak in the medium where the pressure is low. It shows the area where the

In the embodiment shown in FIG. The coils are arranged so that the overall effect is maximized. This coil The effect of acoustic waves on the coil is temporally variable and spatially non-uniform. This causes a relative phase shift between waves propagating in opposite directions. It is placed against the acoustic wave. The optical wave travels the entire length of the coil 24. The time T1 required for the acoustic wave to travel the length of the helical coil 24 in the axial direction The diameter of this coil and the number of turns are chosen so that the time Ta is equal to . Therefore, the wave propagating through the coil from left to right is the result of this acoustic wave. Under constant pressure, on the other hand, an optical wave traveling from right to left changes continuously You will receive the effect.

That is, when a light wave enters end A of the fiber, it is directed toward end B in the x-axis direction. The speed at which the acoustic wave 26 travels along the X axis is the same as the speed at which the acoustic wave 26 propagates toward the end B along the The number of turns, their diameter and their spacing in the coil 24 are chosen to suit. . For this reason, the end A is surrounded by the high pressure region of the acoustic wave peak 28. Sometimes, if a pulse or burst of light enters end A, this light pattern A pulse or burst is a wave that is exposed to the same pressure from the same part of the acoustic wave 28. It will be a continuous process of progress through the darkness. With this pressure, from A to day The geometric path length of the propagating wave changes. It is the part of the fiber through which light waves travel. Each segment is equally stretched due to the pressure effect from the traveling acoustic wave. This is because they are expanded or compressed. However, in the opposite direction On one side of the propagating wave, the situation is different. From end B to end A One light wave propagating in the opposite direction, traveling with The segment of fiber thus compressed is encountered and then extended by the valley 30. encounter a segment of fiber that has been blown out. Therefore, while propagating in the opposite direction The geometric path length of the light wave is alternately lengthened and shortened by the acoustic wave. do. When the length of the coil 24 is equal to an integral multiple of the wavelength of the acoustic wave, the opposite direction is applied. The pure path length of one wave propagating in the direction does not change at all. As a result, 2 The pure phase shift between the two oppositely propagating light waves is the amplitude of the acoustic wave 26. It will be linearly proportional to the width and length of the coil 24.

In other words, as the length of the coil increases, these co-propagating light waves The interaction distance between the fiber and this acoustic wave becomes large. interaction distance As the path length increases, the overall path length increases and The increase in phase shift becomes large.

When the length L of the coil is selected to be several times the wavelength of the acoustic wave, the indicating performance of the coil 24 is In other words, the discrimination performance is maximized. In this case, waves propagating in the opposite direction That is, the pure wave propagating through the fiber in the direction opposite to the direction in which the acoustic wave propagates This is because the phase shift becomes zero. At this time, this sensor has the best performance. That's one thing. However, L does not have to be an integer multiple of the wavelength of the acoustic wave; the relative phase shift between waves propagating in opposite directions, which dictates the amplitude of the waves It suffices if it is sufficient for recognition. A circular wave propagating at a known velocity. In an acoustic wave whose wave number is unknown, its frequency is determined by a delay whose length can be changed. This is done using a wire extension so that the phase shift of one wave propagating in the opposite direction is zero. This can be determined by tuning the delay line.

Light waves propagating in opposite directions within loop 24 couple the light waves into fiber 34. generated by a light source 32. This fiber 34 is passed through a polarizer 36. and guides this wave to a fiber optic bidirectional coupler 38. This fiber optic A bidirectional coupler 38 is coupled to the two ends of the coil 24. this light 8!32 may have a very short coherence length. In other words, this The coherence length of the light source is the differential path length through the coil caused by the acoustic wave. These two waves propagating in opposite directions are connected to the coil as long as is still coherent even after proceeding over the length of They can mix sufficiently and interfere with each other.

This interference is what is needed to determine the amount of this relative phase shift. be.

In the preferred embodiment, fiber 34 is a single mode fiber. polarizer 36 is bidirectional and allows only light with a predetermined polarization state to pass through. Can be adjusted. As is known in the art, this polarizer 3 6 is important in maintaining the bidirectional operating characteristics of the closed-loop interferometer. be. This polarizer ensures that the light entering the loop has only one polarization state. Guaranteed to have it. Some birefringence in the fibers that make up the loop exists, it couples some of the energy into modes with orthogonal polarization states, Here, the propagation velocity will be different from the velocity in the selected polarization state. . If the birefringence is not symmetric with respect to the center of the geometric path, then the opposite directions A wave propagating in That will happen. Due to the presence of the polarizer, only light of one polarization state enters the fiber. and a mode of polarization different from this input polarization state mode. Block all returning light energy in the mode of the state. For this reason , the detectors travel in opposite directions through the loop in the mode of the selected polarization state. We are looking at only the optical energy from the wave component propagating to the , and the phase shift is not exist.

It means that both signals propagating in opposite directions have the same polarization state, i.e. This is because they travel at the same speed and along the same geometric path length.

The directional coupler 38 converts the polarized light traveling from the polarizer 36 toward the loop. Separates into two coherent light waves and sends each wave to one of the coils 24. two ends and propagate them in opposite directions. This directional knot A beam splitter may be used instead of the combiner 38, but a directional coupler is better. This is a preferred embodiment. That is, the fiber passes from the light source 32 through the coupler. This is because it is continuous until it returns to the detector.

Beamsplitters, on the other hand, couple separate fibers, so they A reflected wave is generated at the end of the fiber. Such reflected waves , bounces back to the input fiber, interferes with the input light wave, and creates unnecessary standing waves. may cause. Beam splitter when using pulsed operation Even if you use it, there is no problem in terms of reflection. In pulsed operation, light Pulses separated by periods of absence are provided by light source 32.

Adjust fiber length and pulse spacing and duration in this system The reflected signal propagates in the opposite direction from the initial pulse by During the period when there is no light between the combined pulse and the pulse that returns , to the detector.

The fiber optic bidirectional coupler 38 also connects the fibers in the opposite direction that have passed through the loop. Recombines propagating optical signals.

The combined signal is then coupled into input fiber 34 and passed through polarizer 36. between the polarizer 36 and the light source 32. A fiber optic bidirectional coupler 42 is coupled to input fiber 34.

This second combiner 42 absorbs the energy of the combined signal returned from the loop 24. A portion of the photodetector 4o is directed toward the input of the photodetector 4o. And this photodetector is It generates a signal proportional to the strength of the combined signal, but this signal has a phase Already known in the art.

In a preferred embodiment, a polarization controller 44 is placed within the loop 24. By this, the polarization state of the optical signal traveling through this loop is controlled. this occurs because polarizer '36 interacts with the birefringent zone in loop 24. This is desirable in order to avoid ``signal attenuation'', e.g. by a polarizer. Therefore, only vertically polarized light can enter and exit the loop, and Birefringence in the loop absorbs all the energy from the optical signals propagating in opposite directions. This polarizer 36 is used to couple the light into a horizontally polarized mode. It will block all of the power light and the detector will show zero output. polarization con Trawler constructions are known in the prior art.

These devices take input light in one polarization state and shift it. and outputs light with an arbitrarily selected polarization state.

By suitably adjusting polarization controller 44, at least one of the light portion, preferably most of the light, is passed by the polarizer 36. We can ensure that we exit this loop in a polarized state.

That is, this polarization controller is designed to maximize the output signal from the detector. can be used. This eliminates birefringence caused by the environment and Birefringence in the fiber structure due to stresses left behind by the manufacturing process can cause signal attenuation. prevent the occurrence of Because acoustic waves change temporally and are spatially non-uniform, due to the effect that occurs on the light waves propagating in opposite directions through the coil 24. , the intensity of the recombined optical wave changes, and this is detected to determine the amplitude of the acoustic wave. The width is measured.

One possible use of the embodiment shown in FIGS. 2 and 3 is to It is a wave direction finder. This direction finding continues until the output signal is at its maximum. This is done by rotating the longitudinal axis of the

Because the length of the coil is directly proportional to the total amount of phase shift of the light propagating together. , the sensitivity of this sensor is increased by increasing L. This is especially true for This is noticeable when the wavelength of the acoustic wave 26 is large.

FIG. 3 shows an acoustic sensor using a closed loop interferometer according to another embodiment of the invention. FIG. In this embodiment, coil 46 is connected to C1 and C2. Therefore, a group consisting of two coils separated and spaced apart from each other as shown It is said that One of these is the first, adjacent N/2 in the optical fiber. It is made up of N/2 turns, one after the other in the optical fiber. It is composed of volumes. These two groups of coils are at a distance d from each other. The planes of the two groups of coils, separated along the x-axis, are mutually is said to be parallel to

The distance ld between the two groups of coils is , generally chosen to be an odd multiple of a quarter of the wavelength of the acoustic wave shown in 47. It's been revealed. The fiber used to form these two groups of coils The total length of the bar is determined by the time it takes the light to pass through both coils at the frequency of the acoustic wave. It is chosen to be one half of the period. In other embodiments, the acoustic wave The ratio of the transit time of light to the period is equal to the ratio of distance @ d to the wavelength of the acoustic wave. In other embodiments, if the sizes of coils C1 and C2 are adjusted so that , the distance d is a fraction of the wavelength of the acoustic wave (not an integer multiple of a quarter) and It is also possible to do so. However, in these embodiments, this sensor cannot be used to select direction. That is, these alternative In an embodiment, the sensor propagates in a direction parallel to the longitudinal axis X of the coil. an acoustic wave that propagates in a direction that is not parallel to the longitudinal axis of the coil. , cannot be clearly distinguished.

By adopting the structure described above, N acoustic waves propagating along the X-axis at a given wavelength can be When there is a relative phase shift between light waves propagating in opposite directions, Occur.

This phase shift causes light waves propagating in opposite directions to overlap each other in a non-bidirectional manner. It is generated by the applied acoustic wave pressure. Such waves are usually In an interferometer structure such as the device shown in Figure 1, bidirectional effects can occur. That's what I used to do.

This non-interactive effect is shown plotted in Figure 4, where time At t1 and t2, in the first set of coils C1 and the second set of coils C2 acoustic waves are shown. In the preferred embodiment, the two coil groups The distance d between the loops is chosen to be 174 wavelengths of the acoustic waves. Also , the coils C1 and C2 are such that the time the light passes through them is 174 times the period of the acoustic wave. Its size is determined so that it is equal to . These coils also Their sizes are adjusted so that their lengths Ll and L2 are small compared to the wavelength of the acoustic wave. The standards are set. Similar to the embodiment shown in FIG. The sensitivity is increased by making the axis of direction X parallel to the axis of acoustic wave propagation. It is set as the maximum.

Curves 48 and 50 show only 1/4 wavelength at two times t1 and t2. The two times are separated by 174 times the period of the acoustic waves. ing. That is, the curve 48 shows the state at time t1, which is the state at time t1. What happens to the coils C1 and C2 depending on the peak and valley of the acoustic pressure at time t1? It shows how it is wrapped in. Here, the peak and valley of pressure are respectively indicated by areas 52 and 54. Similarly, curve 50 has only 174 periods. Later at t2, how are coils C1 and C2 wrapped by the acoustic waves? It shows whether there are any. At time t1, coil C1 is indicated by 56. pressure level that exposes the entire coil to a virtually uniform acoustic pressure. It is. This means that the plane of each loop of the coil C1 is on the plane 60 of the acoustic wave 47. The length Ll of the coil C1 is substantially parallel to the acoustic wave. This is caused by the fact that it is short compared to its length. Similar situation is point 5 This also holds true for the coil C2 surrounded by the acoustic waves at 8.

Here the pressure at 58 is equal to the pressure at 56. this is, Coils C1 and C2 are separated by 174 wavelengths of acoustic waves, and time t1 is This is because the wave peak is exactly at the center between the coils. be. At later or earlier times, the situation will be different. . However, for any time t, the operation of the embodiment shown in FIG. The principle is the same.

By applying a uniform positive compression effect to coils 1 and C2, the coil The geometric path lengths in both channels C1 and C2 vary uniformly. therefore , an optical signal propagating in the same direction in coil C1, and an optical signal propagating in the opposite direction in coil C2. The optical signals propagating in of each optical signal propagating through this loop. Transit times will vary. Coils C1 and C2 transmit electricity in opposite directions. The light signal propagates through each coil with a period of 1/4 of the acoustic wave. out of the fiber segment 62 due to its size. Until the exit time t2, the optical signal in C1 propagating in the same direction remains in the coil C1. There will be. After a very short time, this optical signal propagating in the same direction becomes into the coil C2, but here, in Figure 4(B) above the curve 50. The user will be exposed to acoustic waves such as those shown at 64. Similarly, at time t1 , the oppositely propagating wave existing in coil C2 remains in the coil until time t2. coil C2 and enters coil C1 through segment 62. child Therefore, at time t2, coils C1 and C2 are at points 64 and 64, respectively. and 66, with corresponding amplitudes.

exists in group C1 of coils at time t1, and in FIG. The optical signal propagating in the same direction that was under the pressure shown at 56 at t2 is present in group C2 of coils at this point, and in FIG. 4(B). It experiences the same positive compression effect as before from the acoustic wave 47, indicated at 64. these Due to the effect of compression, the geometric path length through coil C2 becomes at time t1 It changes by the same amount and with the same sign as was occurring in coil C1. Therefore, The transit time for passing through the coil C2 changes and the reception time at the coil C1 at time t1 changes. The change in transit time has the same sign as the change in transit time. Therefore, they propagate in the same direction. The total change in transit time for a signal is additive and nonzero. It has become a thing.

However, at time t1, the fourth <A ) In the opposite direction, it received the pressure of 58 in the figure and then proceeded to the left. The propagating optical signal is present in the coil C1 at time t2, where the fourth ( B) Pressures of the same magnitude but opposite sign, indicated by 66 in the diagram. receive. Therefore, the change in transit time caused by coil C2 is This opposite effect cancels out the change in transit time caused by C1. The pure change in time of the optical signal propagating in the direction passing through the coil 46 is zero. .

In summary, the effect on the wave propagating from coil C1 to 02 is reinforcing. On the other hand, the effect on the signal propagating from coil C2 to C1 is countervailing. Become something.

Therefore, when recombined after propagating through two groups of coils, There is a relative phase shift between these waves propagating in opposite directions. It becomes. This phase shift is then detected and proportionally converted into an acoustic wave. The amplitude of is determined.

The time the light passes through each coil and the spacing between the coils are each 1 /4 period and 174 wavelengths, the sensor detects the wave Transit time of waves propagating in the opposite direction, but still functioning to detect presence A pure change in will be non-zero. The sensor response in this case is non-linear Become something.

Both of the sensors shown in Figures 2 and 3 can be used in practice. It has a specified bandwidth. The center frequency of each bandwidth is The frequency corresponding to the wavelength such that the pure phase shift of the propagating optical signal is zero It is. At other wavelengths, the response is degraded to some extent due to the edge effect. It's coming.

In the embodiment shown in FIGS. 2 and 3, this optical coil interferometer also It also functions as a sensor for measured acoustic waves. Furthermore, in the prior art Something like a known delay line that can be varied over an infinite range. Both of these embodiments, except that the length of the coil can be varied using In this case, a coil is designed to work optimally at a specific frequency of acoustic waves. It is necessary to This can be used to vary the delay time over an infinite range. Details of the possible delay line structure can be found in E 1e, published on November 11, 1982. ctronics L etters.

Vol. This type of variable delay line is described in the article titled ``Extension line''. can be used for the coil 24 of FIG. 3 or the coils C1 and C2 of FIG. Thereby, the frequency at the center of the sensor's bandwidth can be changed.

Figure 5 shows a sensor that uses only optical coils as an interferometer and a delay line. FIG. In this example, the signal to be detected is denoted by Q. The detected quantity Q is applied to a modulator 68, which modulates the sensed change in quantity Q. Therefore, we have a directly varying signal Q(t) and a high frequency modulated by the quantity Q. emit a time-varying signal q(t) formed by any of the carrier signals live. Any structure suitable for the modulator 50 may be used in the present invention. is sufficient for the purpose, and the signal Q(t) is also mQ itself. It may also be an electrical signal proportional to this quantity.

The signal q(t) is applied to a converter 70, which converts the polarization control The optical transmission characteristics of the fiber at the location of the transducer 70 may also be Any other device that affects the In a preferred embodiment , this signal q(t) is a carrier or bias frequency modulated in amplitude by a quantity Q. It is the wave number. In a preferred embodiment, this transducer 70 is a phase modulator. .

This transducer is placed away from the geometric center of the loop's geometric path length. need to be The signal Q(t) is generated by the closed-loop fiber optic interference needle structure and The rate of change is faster than the natural filtering effect caused by reading and movement. There is a need to change. This signal q(t) is defined as This gives the coil 72 a spatially non-uniform effect.

The details of the structure of transducer 70 and modulator 68 are critical to this invention. isn't it. The transducer 70 has multiple fibers at the location of the transducer 70. Any device that can change the refraction may or may not q(t), a device that applies bending or other stress to the fiber in response to q(t) It may be a vise.

Additionally, the transducer 70 can change the speed of light propagating through the location of the transducer 70. It can be any device that can do this. Such a speed modulation device is , q(t) to give the lateral size of the fiber at that transducer location: It can be any structure that can be physically changed. On this Ii machine propagates through a region of changed lateral magnitude due to wave-guiding effects. The speed of the light signal changes. In other embodiments, the transducer 70 is a transducer 70 of the optical signals propagating in opposite directions in response to q(t). It may also be a light controller that changes the polarization state.

83 in the preferred embodiment, this converter 7o sends the signal @q(1) into the loop. due to changes in the path length of the fiber optic waveguide at the location of this transducer 70. It is a phase converter that converts the That is, this fiber Accordingly, it is stretched within the transducer 70. .

A suitable structure for such a phase modulator includes a fiber coil 7 surrounding it. There is a drum of piezoelectric material wrapped around 2. Then, J of signal q(t): Una When a driving electrical signal is applied to this piezoelectric material, the magnitude of this driving signal is The material expands or contracts in the radial direction accordingly. Released in this way When expanded in the direction of radiation, the fibers surrounding this drum are stretched. Become.

In other embodiments, the signal @q('t) is a polarization controller as converter 7o. can be used to adjust this by controlling the three In any of the embodiments of the For details on the structure of the polarization controller that can be used, please refer to Electronics Lett ers, Vol. 16, No. 20, H.C.

The 1° single mod fiber partial wave device and and Polarization Conte [] - Article named Rava and filed on September 4, 1980. Found in United States Patent Application Serial No. 183,975 Can be done.

Light source 32, coupler 42, detector 40. Polarizer 36, fiber optic directional coupler 3 8 dj If 42, and the details of polarization controller 0-44's 0 function 411 are as follows. , in the example shown in Figure 5 and the implementation date shown in Figure 21 and Figure 3. are the same. In these three real Pi examples, it is also possible to use a beam splitter. However, as explained above with reference to the embodiment of FIG. 5. Since til occurs, it is more difficult to perform pulse-like operation. Desirable things are booming. In all three embodiments of this invention, the file Optical directional couplers have become desirable. Details of the structure and operation of the polarizer 36 Details are in □pttcs 1-etters, No. 5, published in October 1980. Volume, No. 11.

On pages 479 to 481, the term "single mode fiber optical polarizer" It is mentioned in the article named. Details of the structure and operation of the directional couplers 42 and 38 For details, see the IE E E J internal of Quan dated April 1982. tulIE 1ectr.

D in Tsugumi, Volume QE-18, No. 4 @, pages 746 to 75/I igcnnet and Shaw's ``tunable single mode optical fiber coupler'' The details are also described in the 1980 United States Patent Application Serial No. 139.511’j filed on April 11th Some rUs continue to appear [1 title, United States patent application filed on September 10, 1981] It is also disclosed in U.S. Patent Application Serial No. 300.955.

The operation of the actual 1J1 example shown in the fifth factor is as shown below. The light source 32 is a light provides a signal, the optical signal is coupled into a single mode optical fiber 34, and , directional coupler 42 and polarizer 36 , directional coupler 38 Head to. Polarizer 36 determines whether the light is traveling toward loop 72 or 72 with the selected polarization state. Only the light that passes through this polarizer. The directional coupler 38 receives this optical signal. into two coherent optical signals propagating in opposite directions around the loop. , and then combine these optical signals propagating in opposite directions that have returned to 'C1. Assume that one optical signal travels through the fiber 34 toward the light [32]. ,Polarization The controller 44 polarizes the light traveling in either direction within the loop. It gives you a choice of states. The combiner 42 is a portion of the light traveling toward the light source. The light is guided to the input of the photodetector 4o, where the light is It is converted into an electrical signal based on the squared amplitude, that is, its intensity. of course , the combined signal of the signals propagating in opposite directions in the loop 72 has an amplitude of is the relative relationship between these signals caused by the optical conditions inside the loop. It depends on the phase shift. Optical signals propagated in opposite directions in the loop 72 The signals are shifted in relative phase by the action of transducer 70. The quantity Q is It may be a quantity that changes rapidly or it may be a quantity that changes slowly. ,amount. In such cases, this quantity may be applied directly to the converter The transducer 70 converts this into the fiber path at the location of the transducer 70. Time-varying deviations in path length or birefringence of the fiber at the location of transducer 70 Changes from time to time.

When the transducer 70 changes the path length within the transducer 70 rapidly over time. In a loop, optical signals propagating in opposite directions travel different path lengths through a loop. Then, the two phases are shifted relative to each other. This is the converter 70 However, because these signals are located far from the center, these signals may appear at different times. This is because it reaches the converter 70. Optical signals propagating in opposite directions experience this change. At two different times of arrival at the converter, the path length through the converter 70 is Because they are different, these two signals propagating in opposite directions are As it passes through loop 70, it will have two different transit times.

Therefore, these signals arrive at directional coupler 38 at different times and are Therefore, they are relatively out of phase with each other.

The combined signal will have an amplitude that depends on this relative phase shift.

The amplitude of the combined optical signal is such that the quantity Q can be determined. It has become.

This is because the relative phase shift is proportional to Q. be.

Q is a differential and bidirectional quantity that changes slowly over time, such as temperature and pressure. force, Q is an asymmetrically applied, rapidly varying transport force in time. It is necessary to modulate it into a signal. As it is well known in the prior art , closed-loop fiber-optic interferometers typically vary slowly in time. This is because it is not sensitive to interactive effects. In fact, this is a closed loop. This is a major advantage of the interferometer. It is due to this property that this interferometer This is because it is extremely quiet and stable.

Q is modulated to the bias or carrier frequency by amplitude modulation or frequency modulation, Also, if the transducer 70 is a phase modulator, the above description still applies. can. When using amplitude modulation, the path length in the transducer is determined by the bias or carrier. A sinusoidal change occurs in the transmission frequency, but the amplitude of the vibration of the path length is It will change accordingly. Therefore, the relative position produced by transducer 70 The phase shift causes a sinusoidal change. Furthermore, the relative phase shift of the sinusoids That is, the amplitude envelope for a sinusoidal oscillation of relative phase shift is , will correspond to the quantity Q. This envelope shows that Q changes with respect to time. As it changes, it also changes with respect to time.

If the transducer changes the birefringence of the fiber at the location of the transducer 70 is due to the coupling of light from one polarization state mode with the other, resulting in the relative phase A deviation occurs. Birefringence is the propagation of light in modes with different polarization states. It is a property of optical fibers that they propagate at different speeds. Weird M k converter 70 at the location of its converter 70, proportional to the signal q(t) or Q. , when changing the birefringence of this fiber, this transducer This will change the relative phase shift between the signals propagating to each other. This is weird The exchanger has a different amount of energy going in a slow mode and one going in a fast mode. This is because the ratio to the amount of energy is controlled. That is, for one polarization state When light traveling through a waveguide in a mode encounters birefringence, the energy of this light A portion of the beam is coupled into a mode with a polarization state orthogonal to it, and then propagate at different speeds corresponding to the new polarization state modes. The amount of birefringence If IQ is a function of Q(t), then IQ is a function of the polarization shape established by polarizer 36. The two modes propagate in opposite directions from each other into modes with orthogonal polarization states. determined by the amount of energy in the optical signal. This is a model with orthogonal polarization states. The amplitude of the combined signal obtained from signals propagating in opposite directions at the You can decide. In the embodiment shown in FIG. In order to determine the amplitude of the coupled signal, Add a coupler to tune a portion of the returned energy to this orthogonal mode. It is necessary to receive the light into a polarizer. Also, the output of the second polarizer is connected to another light detector. It is necessary to combine the vessels.

Methods of detecting acoustic waves or other waves detect optical signals that propagate in opposite directions. A closed loop fiber optic interferometer core that is wound and positioned in a predetermined manner. This includes guiding you through the process. This predetermined method refers to the sound to be detected. When an acoustic wave or other wave propagates in the same direction as this wave, a light wave propagates along the axis of the coil. propagates along the longitudinal axis of the coil at the same speed as the The first step is to assemble this coil. Then, the target wave moves inside the coil. The phase difference between optical signals propagating in opposite directions through this coil as they propagate. is detected.

In particular, the method generates an optical signal and alters the optical signal to a selected polarization state. including doing. The polarized light is then separated into two optical signals. child The separated two optical signals are then passed through a closed loop fiber optic interferometer. propagate in opposite directions through the spirally wound loops of This interferometer is so that the longitudinal axis of the loop is parallel to the direction of propagation of the wave of interest. , the loop is placed. This loop travels through the fiber in the same direction. Light propagating in the direction (g is affected by a substantially uniform phase shift due to the wave of interest) waves propagating in the opposite direction traveling through the fiber are is coiled so that it is affected by a non-uniform phase shift due to the wave , its size is determined. This phase difference is then detected.

The method for detecting the phenomenon or quantity Q is to detect optical signals propagating in opposite directions in a closed The loop consists of guiding a fiber optic interferometer through the coil.

The quantity Q is sensed by a modulator that changes this quantity depending on Q. Convert to the signal q ([). This signal q(t) may be Q itself, or Alternatively, in some applications, it may be an electrical signal that changes in proportion to Q. . The signal q(t) is from the center of the geometric path of the coil in the fiber optic interferometer. It is fed to the coil at a remote location. In such places, it is important to This is because the optical transmission characteristics of the bar change. Then they propagate in opposite directions The relative phase shift between the optical signals is detected.

The signal q(t) is given the birefringence of q(t) at the location where this q(t) is given. in the fiber in such a way that it varies proportionally or at a location that gives this The propagation speed can be given to vary in accordance with q(t). difference Furthermore, the polarization state of the light passing through the location in the coil given a(t) a(t) may be given such that a(t) changes in proportion to Q(t). preferred method is the geometric representation of one of the signals propagating in opposite directions, depending on q(t) one path length with respect to the other.

All of these methods involve introducing light from optical signals propagating in opposite directions into a coil. before polarized to the same polarization state, and then opposite to each other combined into a loop The polarization state of the optical signal propagating in the opposite direction is different from that of the 1ζ It involves filtering the light propagating in the direction. This bond is back to each other This must be done before detecting the relative phase shift between optical signals propagating in opposite directions. Must be.

All of these methods also involve optical signals propagating in opposite directions in the loop. controlling and adjusting the polarization state of the selected polarization state to another selected polarization state. can be included.

All methods of detecting MQ also require the quantity Q before feeding q(t) into the loop. to a bias or carrier frequency to generate a C1 signal q(t). can include.

This quantity may be applied directly to the transducer and its rate of change detected. . For example, ff1Q may be the ambient concentration, then the signal (+( t) will be a measure of the time-varying concentration. Then, this signal q(1 ) into one or more small segments within the optical coil. is applied to this interferometer. Therefore, the recombined optical signal There will be a detectable change in the number. In addition to the devices mentioned above, Transducer 70 can also be an electro-optical device, an optical device, or an electro-optical device. may be a magnetostrictive device.

includes a closed-loop optical interferometer to detect the sensed quantity Q; have described various embodiments of sensors using the same. In this example In both cases, the detected quantity is spatially non-uniform with respect to the closed loop. It has become a thing. It is also possible to use the entire coil as a sensor element, This amount can also be calculated by substituting one or more asymmetric locations above the coil. It can also be given to points.

Having described this invention by means of preferred embodiments, the appended claims that many variations can be made without departing from the spirit of the surroundings; will be obvious to those skilled in the art. Such variations are included within the scope of the claims. It should be done.

FIG.-5 International research report

Claims (1)

[Claims] 1. A medium that can tell the amount to be detected and a coil of fiber optic waveguide (2 4>, wherein the coil receives an optical signal traveling in one direction within the waveguide. is arranged so as to be influenced non-reciprocally by the amount, further detecting a difference in the first optical signal when influenced by the amount; A sensor comprising a detector (40). 2. The coil (24) of the fiber optic waveguide has many unwound coils. a fiber optic waveguide (24) with a diameter of the turns of said coil; The spacing is such that W propagates through the wave guide (24) around the longitudinal @(x). The same speed as the axial speed of the optical signal moving in the direction of the axis (X) Now the wave (26) to be detected travels along the longitudinal axis (X) of said coil. The sensor device according to claim 1, wherein the sensor device is defined as follows. 3. Light a(32, 34, 36) of the selected polarization state, The polarized light is separated and the coil (24) of the fiber optic waveguide is separated. a separator (38) that allows the first and second lights to propagate in opposite directions to each other; The apparatus of claim 1, further comprising: 4. The first and second optical signals are affected differently by the wave (26). The coil (24y) of the fiber optic waveguide is disposed in the medium as shown in FIG. 4. The apparatus of claim 3, wherein: 5. Roughly speaking, the phase shift between the first and second light waves propagating in opposite directions 4. The device according to claim 3, comprising a detector (4o) for detecting this. 6. The axial length of the coil (24) is the wavelength of the wave (26) to be detected. 3. The device according to claim 2, wherein the device is a predetermined proportion of . 7. The detector (40) passes through the polarizer (36) to the coil (24). and the polarizer (36) is coupled to the polarizer (36) for transmitting the light from the coil (24). [To allow only light in the selected polarization state of 1 (32, 34° 36) to pass through] The coil (24) is set to transmit the first and second optical signals. Claim 5, further comprising a polarization controller for controlling the mode of polarization state of the polarization. equipment. 8. Light m (32) and from the light source (32) to the coil (24) and from the coil (24). A fiber optic waveguide guides light to the detector (4o) for detection. Ido (34) and the fiber coupling optical signals from the coil (24) to the detector (4o); a first directional coupler (42) in the optical waveguide (34); Optical signals that are not in the selected polarization state are blocked and inserted into the waveguide (34). a polarizer (36) in the waveguide (34) for preventing the movement of the waveguide; a second directional connection coupling said wave guide (34) to said coil (24); 2. The device of claim 1, further comprising a combiner (38). 9. Light w4 (32, 34, 36) of light in the selected polarization state, The light from the light m (32, 34, 36) is a first optical signal propagating in the same direction. , and a second optical signal propagating in the opposite direction. The sensor according to claim 1, further comprising: 10. The light m (32, 34, 36) has substantially no polarization state other than the selected Sareta polarization state. The light a is coupled to a polarizer (38) that does not pass any light in either direction. 10. The apparatus of claim 9, comprising (32). 11. The coil (24) of the fiber optic waveguide includes a plurality of delay coils ( CI and C2), and the plurality of delay coils (CI and 02) are The optical signal traveling through the coils (C1 and 02) is delayed by a predetermined time. ) are separated by a predetermined length by the connection of the transfer wave guide (62), The sensor according to claim 9. 12. Each of the delay coils (C1 and C2) has a longitudinal axis (X) formed of a number of turns of predetermined diameter around the The optical signal propagating through the delay coils (C1 and C2) is the wave of interest (47) travels in a plane substantially parallel to the plane (60) of the object, and the optical transit time is are spaced apart along said axis so as to be approximately 1/4 times the period of the wave (26). 12. The apparatus according to claim 11. 13. between the first and second delay coils (C1 and C2); The optical transit time of an optical signal propagating in the opposite direction to the delay coil (CI and and C2) is substantially faster than the transit time of said wave of interest (47) between so that the transfer waveguide (62) is between the delay coils (CI and 02> the first optical signals propagating in the same direction are arranged with a delay after each; The time when the target wave (47) arrives at the coil (C2) is determined by the time when the target wave (47) arrives at the coil (C2). This is the time when the wave (47) becomes the target wave (47). When the light propagating in the same direction propagates in the next advanced delay coil (C1) The effect of the above method on the optical properties of the advanced delay coil (C1) and approximately The size and spacing of the delay coils (CI and C2) are determined so that they are the same. 12. The apparatus of claim 11, wherein: 14. The detector (40) detects the first optical signal propagating in the same direction and the first optical signal propagating in the same direction. The phase difference between the two optical signals propagating in opposite directions is determined by the interference between the two optical signals. The detection is performed by detecting the amplitude of the combined signal resulting from the The equipment described in item 1, item 9, item 10, item 11, item 12 or item 13 Place. 15, each said delay coil (CI and C2>) The transit time of the first and second optical signals passing through the coils (CI and C2) is , about 1/4 times the period of the target wave (47), and the delay coil (C1 and C2) such that the interval between them is 1/4 of the wavelength of the wave of interest (47), 12. The device of claim 11, wherein the size is defined. 16, Each of the delay coils (01 and C2) is connected to the delay coil (C2). 1 and 02) for the first and second optical signals to pass through the target wave (4 7) Its size is determined to be equal to a predetermined percentage of the period of The delay coils (C1 and C2) are separated by a predetermined distance, and the delay coils (C1 and C2) are separated by a predetermined distance. The ratio of distance to wavelength is when passing through each delay coil (C1 and C2). The ratio between the period and the period of the target wave (47) is approximately equal. The device according to item 11. 17. A polarization controller that controls the polarization states of the first and second optical signals. Further comprising claims 9, 10, 11, 12, 13, and The device according to item 15 or 16. 18. a modulator (68) for sensing a quantity Q and generating a signal q(t); signal q(t) corresponding to changes in the optical transmission characteristics of said coil (24); a converter (70) for converting the change into a equipment. 19, generating first and second optical signals propagating in opposite directions; further comprising a light source (32, 34, 38) for propagating the light source (32, 34, 38) to the A container (70) is positioned at a location above said coil (24), said location being above said coil. away from the geometric center of the optical path formed by the ile (24) , the apparatus according to claim 18. 20. The light source couples light of a selected polarization state to the coil (24). 20. The polarizer according to claim 19, further comprising a polarizer (36) for causing Device. 21, the signal Q(t) is the same as the coil of the optical signal propagating in the opposite direction. a bias signal having a predetermined relationship with the optical transit time around the loop (24); 21. The device of claim 20, wherein the quantity Q is modulated to . 22, the predetermined relationship is such that the first and second optical signals are such that the signal q(t) has different amplitudes at different times when it arrives at the location. 22. The apparatus of claim 21, wherein: 23, the converter (70) is configured such that each of the first and second optical signals is The coils (24) each travel in the absence of the signal Q(t). The transducer (70 ) stretching the fiber optic waveguide of the coil (24) at a location of 22. The device of claim 21, wherein the device is a phase modulator. 24. at different times when the first and second signals arrive at the converter; The phase modulator stretches the fiber by different amounts, thereby causing the first optical signal to have a phase shift with respect to the second optical signal; Apparatus according to claim 23. 25. Claim wherein the detector (40) is characterized by the relative phase shift. Apparatus according to clause 24. 26, the Q changes rapidly over time, and the Q (M is the first and second such that the optical signal has different amplitudes at different times when it arrives at the converter; 22. The apparatus of claim 21, wherein said Q is directly proportional to said Q. 27. The transducer (70) changes the birefringence of the fiber in response to q<t. 27. The apparatus according to claim 21 or 26, wherein the device 28, the converter (70) converts the first and second lights in response to q(t). 27. Apparatus according to claim 21 or 26, for changing the propagation speed of the signal. 29, the converter is configured to change the phase of the first and second optical signals in response to q(t); 27. Apparatus according to claim 21 or claim 26, for shifting the relative phase. 30. Method for detecting fAQ by closed loop optical fiber interferometer is a method that applies bidirectional flQ to the measured loop non-bidirectionally, and A method comprising detecting a change in an optical signal in a measured loop. 31. The quantity Q is modulated into a signal q(t), where q(1) is a non-bidirectional 31. The method of claim 30, wherein: 32. The above 1q(t) is the minimum of the optical fiber interferometer of the measured loop. both are given to one point, said point being the optical path formed by said loop. 32. The method of claim 31, wherein the method is away from the geometric center of. 33. The step of providing the lIQ is: the first optical signal is in the loop. When the first signal travels through the loop, the first signal passes through the ! By Q, one a second, oppositely propagating optical signal moves through the loop. when the quantity Q is such that the second signal is non-uniformly influenced by the quantity Q. 31. The method of claim 30, including the step of providing Q to the loop. 34, said second optical signal is first affected by a change having a first mathematical sign; , and is then affected by a change with the other mathematical sign. The method according to item 33. 35, the magnitudes of changes with mutually opposite signs to the second optical signal are mutually , whereby no pure change occurs. .