JPS61175517A - Optical fiber ring interferometer - Google Patents

Abstract

PURPOSE:To obtain a clear interference fringe, by arranging an interferable luminous flux, a plurality of focusing rod lenses, a beam splitter and an optical fiber loop to be integrated optically. CONSTITUTION:A luminous flux leaving an interferring light source 8 enters an light isolator 10 via a focusing rod lens 9. Then, the luminous flux enters focusing rod lenses 11A and 11B to be converted to two focusing luminous fluxes passing through two focuses and then, enters a beam splitter 3 to be equally divided into a transmission light and a reflected light with a halfmirror 3R. The two focusing luminous fluxes transmitted through the halfmirror 3R reach end faces A and B of an optical fiber loop 6. The focusing luminous flux leaving the lens 11A and is made incident efficiently into the end face A of the optical fiber loop 6 and emitted at the end face B as dispersing flux passing around the loop 6 and then, after entering the splitter 3, the dispersing luminous flux is bent at the right angle with the halfmirror 3 to reach an interfering surface 7 passing through an optical spacer 13. Thus, a stable and clear interference fringe can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an improvement in a ring interferometer using an optical fiber, which is mainly used as an angular velocity detector.

[Background of the invention]

Previously, for example, Nikkei Mechanical, 1983, 9°26.
An example of an optical fiber ring interferometer as described in 113P, "Optical fiber gyro system with accuracy of 1°/S or less applying COD" will be explained with reference to FIG. First, the coherent light source 1 is composed of a semiconductor device that emits a coherent light beam, for example, a laser, and the light beam emitted from it is corrected by a correction lens into a suitably parallel light beam and enters the beam splitter 3. This beam splitter 3 is a semi-transparent mirror 3R
is the main component, and half of the incident light flux (half in terms of power)
travels straight and the other half is reflected at right angles. The light beams emitted from the beam splitter 3 are changed from parallel light beams to convergent light beams, or from divergent light beams to appropriately parallel light beams, by focusing lenses 4 and 5. The optical fiber loop 6 is, for example, several hundred meters of single-mode polarization-maintaining optical fiber wound into a coil shape, and the light flux incident from the A end face is directed to the B end face, and the light flux incident from the B end face is directed to the A end face. It leads to the end face with little loss. The interference surface 7 is a mere flat surface that causes moderate diffuse reflection when a light beam hits it, or an incident surface of a photodetector or the like.

In such a configuration, first, the light beam exiting the coherent light source 1 is focused on the focusing lens 4 by the action of each component, as described above.
and the focus of the focusing lens 5. The positions of these focal points and the A and B end faces of the optical fiber lube 6 (
When the positions of the input and output end faces of the light beam are perfectly aligned, taking into account the inclination of the optical axis (center line of the light beam), the light beam enters the optical fiber loop 6 most efficiently, increasing the incidence efficiency to several tens of percent. It is also possible to do so. In this case, the convergent light beam incident on the A end face of the optical fiber loop 6 is emitted from the B end face as a diverging light flux as shown by the broken line, is changed into a parallel light flux by the converging lens 5, and is further changed to a parallel light flux by the beam splitter 3. The light is reflected in the right angle direction and reaches the interference surface 7 in the form of a parallel light beam. Similarly, the convergent light beam incident on the B end face of the optical fiber loop 6 also exits from the A end face as a divergent light flux, is changed into a parallel light flux by the converging lens 4, and then passes straight through the beam splitter 3 to become a parallel light flux. reaches the interference surface 7. Therefore, since the optical axes are equal and the spread angles of the light beams (parallel in this case) are equal,
The phase difference between the electric field oscillations of both luminous fluxes is uniform over the entire interference surface 7, and the brightness is uniform and the interference fringes 7A do not have a striped pattern.In this case, the brightness of the entire interference fringes 7A is proportional to the cosine of the phase difference between the two luminous fluxes, and is brightest when the phase difference is zero or an even multiple of π, and darkest when the phase difference is an odd multiple of π. Therefore, as is clear from the fact that the change is cosine-like, when the phase difference is around an integer multiple of π, the brightness does not change even if the phase difference changes.
A problem arises in that minute angular velocities applied to the optical fiber loop 6 cannot be determined due to changes in brightness.

The simplest means to solve this problem is to produce a striped pattern, which is the object of the present invention, and to observe the amount of movement of the striped pattern.

As shown in the figure, the interference fringes 7A with a striped pattern occur when the apparent starting points of the respective diverging light beams emitted from both end faces of the optical fiber loop 6 are intentionally different, and the apparent starting points are aligned with the optical axis. When the interference fringes 7A are on parallel straight lines, the interference fringes 7A have a concentric striped pattern as shown in the figure. On the other hand, when the apparent starting point is on a straight line perpendicular to the optical axis, the interference fringes 7A have a plurality of equally spaced stripes. These interference fringes 7A move around the optical fiber loop 6 in opposite directions and move in proportion to the phase difference between the electric field oscillations of the two light beams that reach the interference surface 7, so the amount of movement is detected by a photodetector or the like. By doing this, you can find the phase difference from that value, and further.

For example, angular velocity can be determined from the value of the phase difference. However, in such a state where interference fringes 7A are generated, the focus of the focusing lenses 4 and 5 and the points A and B of the optical fiber loop 6 are
Since the positions of the end faces do not match, only about 0.1% of the convergent light flux exiting the converging lenses 4 and 5 enters the optical fiber loop 6.

On the other hand, the reflection at the A and B end faces of the optical fiber loop 6 reaches several percent of the light flux that hits the A and B end faces, and the light flux reflected at the A and B end faces also passes through the focusing lens 4°5 and the beam splitter 3. Interference occurs between the light beams that reach the interference surface 7 and are reflected once, resulting in various patterns on the interference surface 7, and these patterns change significantly due to changes in reflection conditions, resulting in optical noise. The intensity of the noise reaches about several tens of times that of the normal signal (interference fringes formed by the interference of the light beams emitted from both ends A and B of the optical fiber loop 6). That is, conventionally, it has been difficult to simultaneously generate the interference fringes 7A and efficiently input the light beam into the optical fiber loop 6, and there has been a problem that clear interference fringes 7A cannot be obtained.

[Purpose of the invention]

An object of the present invention is to provide a high-performance optical fiber ring interferometer.

[Summary of the invention]

According to the present invention, a single beam of light is divided into two convergent beams with different focus positions by a special focusing means.

By matching the position of each focal point with the position of the end face of the optical fiber loop, the converging light flux is made to enter the optical fiber loop under favorable conditions, and at the same time, by changing the starting point position of the diverging light flux exiting from the optical fiber loop. This provides clear interference fringes.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below with reference to FIG. The coherent light source 8 is one whose original characteristics do not change even if it is directly combined with other optical components (combined by optical adhesive, etc.), such as a distributed feedback laser diode that does not require an arm opening. The focusing rod lens 9 is a cylindrical optical glass body whose refractive index is distributed, for example, in a parabolic manner from the central axis toward the outer circumferential surface, and the coherent light source 8
This corrects the luminous flux emitted from the lens to make it parallel. The optical isolator 10 is composed of, for example, a Faraday rotator or a polarizer, and prevents light from returning to the coherent light source 8, thereby preventing the operation of the coherent light source 8 from becoming unstable due to the returning light. What prevents this, focusing rod lens IIA,
IIB is a lens that is almost the same as the focusing rod lens 9, cut along the central axis, divided into two parts, shifted in a direction perpendicular to the optical axis, and fixed via a spacer 12.
It has two focal points on the same line perpendicular to the optical axis. Here, the distance between the focal points coincides with the distance between the focusing rod lenses 11A and 11B (the thickness of the spacer 12, assuming that the cutting margin is zero). The spacer 12 serves to maintain the distance between the converging rod lenses 11A and 11B, and allows the light beam to pass through this space to form the optical fiber loops A and B of the optical fiber loop 6.
This prevents it from reaching the end face. The positions of the A and B end faces of the optical fiber loop 6 are the focusing rod lens 11A,
The focal point of the converging rod lens IIA is aligned with the focal point of the optical fiber loop 6, and the focal point of the converging rod lens IIA is the position of the A end surface of the optical fiber loop 6, and the focal point of the converging rod lens 11B is the position of the B end surface of the optical fiber loop 6. However, the angle with respect to the optical axis is also taken into account to match the angle. The optical spacer 13 connects the beam splitter 3 and the interference surface 7, and the outer dimensions of the interference fringes 7B change depending on the length in the optical axis direction.

Note that these parts are optically joined (adhesive methods that do not use adhesives are optimal) and integrated.

Now, the light beam that has exited the coherent light W8 is corrected into a parallel light beam by the converging rod lens 9 and enters the optical isolator 10. The light beam exiting the optical isolator 10 enters the convergent rod lenses IIA and IIB, is changed into two convergent light beams passing through two focal points, and enters the beam splitter 3. The two convergent beams entering the beam splitter 3 are equally divided into transmitted light and reflected light by the semi-transparent mirror 3R, and the reflected light is not utilized and exits from the C end face and disappears. On the other hand, the two convergent beams transmitted through the semi-transparent mirror 3R are A and B of the optical fiber loop 6.
Reach the end face. The convergent light beam emitted from the convergent rod lens IIA efficiently enters the A end face of the optical fiber loop 6, goes around the optical fiber loop 6, and exits from the B end face in the form of a diverging light flux as shown by the broken line. , enters the beam splitter 3 again. The diverging light beam entering the beam splitter 3 is bent in the right angle direction by the semi-transparent mirror 3R, passes through the optical spacer 13, and reaches the interference surface 7. In addition, the convergent light flux emitted from the convergent rod lens IIB efficiently enters the B end face of the optical fiber loop 6, and as described above, this convergent light flux goes around the optical fiber loop 6 and passes through the beam splitter 3. street.

Furthermore, it passes through the optical spacer 13 and reaches the interference surface 7 . Note that the diverging light beam that has passed through the semi-transparent mirror 3R is changed into a parallel light beam by the converging rod lenses IIA and IIB and enters the optical isolator 10, but disappears due to the action of the optical isolator 10. Furthermore, since the interface between the beam splitter 3 and the optical fiber loop 5 is optically joined, there is almost no step in the refractive index value at this portion.

Reflection does not occur due to the difference in the refractive index value, so the interference fringes 7B generated at this time have a large signal light;
In addition, since there is no reflected light, an extremely clear linear pattern with equally spaced stripes is formed. In addition, since each component is optically bonded, there is almost no reflection due to differences in refractive index values.
A stable striped pattern is created that is not affected by changes in reflection conditions. Furthermore, when detecting the amount of movement of the interference fringes 7B with a photodetector, there is no need to use a special photodetector, and for example, a general photodiode array or the like can be used to detect the interference fringes 7B.
The average movement of the entire B can be easily detected.

In addition, since all the parts are made of glass or glass-like material with a small coefficient of linear expansion, they do not deform due to temperature changes and, as a result, do not change the state of the interference fringes 7B, unlike conventional devices. Since there are no metal fittings or the like for fixing each component, the optical fiber loop 6 can be removed and the device can be made smaller.

As described above, according to this embodiment, not only the stable and clear interference fringes 7B can be obtained with an extremely simple configuration, but also the amount of movement of the interference fringes 7B can be easily detected.

In the embodiment, if the light beam emitted from the coherent light source 8 is a parallel light beam, the converging rod lens 9 may be omitted, and the effect of the embodiment is not lost thereby.

Furthermore, although the spacer 12 is provided in the embodiment,
This is provided for ease of explanation and may be omitted. However, in that case, although the parallel light flux passes through the gap between the convergent rod lenses IIA and 11B and reaches the end faces A and B of the optical fiber loop 6, the amount of light incident from this end face is small, and the interference fringes 7B There is no impact on

In addition, in the embodiment, the A and B end faces of the optical fiber loop 6 are joined to the transmission side surface of the beam splitter 3, but even if they are joined to the reflection side (C end face side) of the beam splitter 3, the embodiment The effect remains the same.

Further, in the embodiment, the optical spacer 13 may be a focusing Rondo lens, and in that case, the external dimensions of the interference fringes 7B can be easily enlarged or reduced. In addition, interference fringe 7
If there is no need to increase the external dimensions of B, the optical spacer 13 may be omitted, and if the interference fringes 7B may be somewhat unstable, the optical isolator 10 may be omitted.

In the embodiment, when the optical fiber of the optical fiber loop 6 is a single mode polarization maintaining optical fiber, the direction of polarization of the convergent light beams exiting the focusing rod lenses IIA and IIB and the single mode polarization maintaining light By matching the polarization axes of the fibers, the clearest interference fringes 7B can be obtained.

〔Effect of the invention〕

According to the present invention, a high-performance optical fiber ring interferometer can be provided.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a conventional optical fiber ring interferometer, Figure 2 is a schematic diagram of a conventional optical fiber ring interferometer.
The figure is a schematic diagram of an embodiment of the optical fiber ring interferometer of the present invention. 8...Coherent light source, 3...Beam splitter, I
I.A.

Claims (1)

[Claims] 1. A coherent light beam, a plurality of convergent rod lenses that convert the light beam emitted from the coherent light source into convergent light beams at a plurality of focal points, a beam splitter that distributes this convergent light beam, and the above-mentioned focusing 1. An optical fiber ring interferometer comprising: an optical fiber loop having both end surfaces located at a predetermined focal point of an optical beam; and an optical fiber ring which is optically joined and integrated.