JPH1073438A - Ring laser gyroscope - Google Patents

Abstract

PURPOSE: To obtain a multipolar field structure for ring laser gyroscope where the axial field is arranged appropriately by providing means including a magnetic means for imparting a nonreciprocal polarized rotation of electromagnetic wave. CONSTITUTION: The ring laser gyroscope comprises an integral hard glass frame 11 and an optical path 20 defines a path connecting corner mirrors 18, 22 and 26. A metallization cathode 12 and a pair of side anodes 14, 16 are arranged along one leg of the optical path 20. When a multioscillator is arranged on a different face, reciprocal splitting of two sets of right and left circularity polarized light is attained through geometrical arrangement of the different face of mirrors 26, 24, 22 and 18 defining the optical path 20. Nonreciprocal splitting between reversely propagating clockwise and counter clockwise modes is attained through the use of a Faraday rotor disposed in a bore 30. In order to attain nonreciprocal rotation of the Faraday rotor, a field for causing nonreciprocal splitting of right and left circularly polarized lights is applied to a glass rotor.

Description

The present invention relates to a ring laser gyroscope, and more particularly to a ring laser gyroscope having a magnetic source outside a bore cavity in a closed optical path defining a gyro. It relates to a glaser gyroscope.

(Prior art) Since its introduction as a laboratory experiment in the early 1960s, ring laser gyroscopes have been commercially developed as theoretical replacements for mechanical gyros used in all types of inertial guidance systems. I have been. Conventionally, a base 2 mode ring laser gyro having two independent electromagnetic wave forms oscillating in one optical cavity has been developed.

Ideally no rotation is allowed when the ring is stationary. When the ring cavity rotates around the central axis, the counter-rotating waves interact and the beat frequency develops. A linear relationship will occur between the beat frequency and the rotational speed of the cavity relative to the inertial reference platform. Ideally, the speed of rotation is proportional to the beat note. In this way, a gyro having a non-moving part is theoretically manufactured.

 In practice, a two-mode laser gyro often requires mechanical dithering to avoid fixing the counter-rotating traveling wave at a low rotational speed. See Laser Applications, pages 133-200, edited by Monte Ross in 1971 for more information on the two-mode lock-in of the pranagyroscope. In an effort to solve this lock-in problem, non-planar ring cavities with more than one set of reverse rotation modes were considered. These multi-oscillator ring laser gyros have been developed to achieve the goal of an accurate complete optical gyro with non-moving parts. However, these multi-oscillator ring laser gyros require the use of a non-reciprocal polarization rotator (eg, a Faraday rotator) that splits the light into two sets of reverse rotation modes within the ring cavity. In general, a multi-oscillator ring laser gyro is divided into a set of right circular polarization and left circular polarization. The right circular polarization is split by the Faraday rotator into clockwise and counterclockwise modes. Similarly, the left circular polarization is also divided into clockwise and counterclockwise modes by the Faraday rotator.

For a thorough discussion of multi-oscillator laser gyros, see LASER HANDBOOK (vol IV), pages 229-332, edited by M.L.Stitch, 1985.

A non-planar structure composed of at least four mirrors and one non-reciprocal Faraday rotator is described in Smith, U.S. Patent No. 4,548,501, filed October 22, 1985. In this type of non-planar configuration, reciprocal rotation is achieved by the non-planar structure of the multimode ring laser gy. The out-of-plane geometry of a folded diamond ring laser gyroscope requires reciprocal splitting of the right and left circularly polarized beams. However, the clockwise and counterclockwise components of each circularly polarized beam are essentially locked at low rotational speeds. A non-reciprocal rotator such as a Faraday rotator is used to further divide the right and left circularly polarized beams into clockwise and counterclockwise frequency components. Multimode ring laser gyroscopes avoid the mode lock-in problem common to two-mode ring laser gyroscopes because the frequencies of the beam modes that make up the right and left circular polarization pairs are widely distributed.

 What is important for non-reciprocal splitting in a multi-oscillator ring laser gyroscope is the need to create a uniform low gradient magnetic field inside the Faraday rotator plate. A fully optical non-planar geometric laser gyroscope without internal cavity elements applicable to either reciprocal or non-reciprocal splitting is a patent application commonly assigned by Graham Martin and designated by the name of "SPLIT GAIN". MULTI-MO DE RING LAZER GYROSCOPE AND METHOD ”, October 28, 1987, serial number 115,018 (specified as secret on May 17, 1988). As detailed in the cited joint application, this new ring laser gyroscope is a powerful tool that divides the gain curve into Q and (Q + 1) modes to achieve the desired effect equivalent to Faraday rotation. Use a uniform magnetic field. This division of gain is achieved through the use of strong, highly concentrated magnetic fields that are appropriately positioned along the bore cavity of the ring laser gyroscope.

 Conventionally, a multi-oscillator ring laser gyroscope and a split gain ring laser gyroscope are formed by a bore cavity using a group of cylindrical, hollow magnets arranged around the bore portion or parallel to the inside of the bore portion. An axial magnetic field along the line segment of the closed optical path was used. Multi-oscillator ring laser gyroscope, Faraday rotator glass is typically placed concentrically in a tubular axially oriented magnetic field, and all components are bore cavities in which the Faraday rotator is aligned with the optical path. Within the "mask load". This was a difficult and time-consuming procedure. The “mask load” of the Faraday rotator and the magnet assembly must not scratch the sidewalls of the bore cavity. The "mask-loading" assembly of such a Faraday rotator in a multi-oscillator ring laser gyroscope has been a difficult assembly operation. It was also difficult to place a magnet in the cavity bore away from the cavity area.

 In the case of a split-gain multi-oscillator ring laser gyroscope, a hollow cylinder in which the entire legs of the integrated glass block, which is the material for manufacturing the ring laser gyroscope, is arranged parallel to the closed optical path and around the above optical path. Must be cut out to fit the shape magnet. This concept requires rigorous and expensive machining of the closed laser path section of the ring laser gyroscope and bore cavities to accommodate the placement of the surrounding cylindrical magnet. The split gain ring laser gyroscope requires precision machining to match the cylindrical permanent magnet arrangement around the ring laser gyroscope body along the closed optical path.

(Problems to be solved by the invention) A ring laser that achieves proper placement of a strong axial magnetic field along the closed optical path of a ring laser gyroscope without improperly manufacturing and machining an integrated glass frame. A multi-pole magnetic field structure for the gyroscope is required.

 In order to solve the problems described with respect to the prior art, it is clear that ring laser gyroscopes have a closed optical path defined by a bore cavity that causes a reciprocal image rotation of multiple electromagnetic modes propagating in the optical path. To Non-reciprocal polarization rotation is caused by a mechanism of magnetic geometry comprising essentially opposing magnetic elements outside the bore cavity defined by a plurality of closed optical paths. Therefore, in a multi-oscillator ring laser gyroscope, a plurality of magnetic elements in the shape of a cylindrical column are arranged along both sides of the closed optical path.

Each magnetic element is a cylindrical column made of strong permanent magnet material with poles along its diameter. Coarse adjustment of the magnetic elements is achieved by rotation of each element about the axis within the chamber. Preferably, an equal number of magnetic elements of equal magnetic force are arranged along opposite sides of the closed optical path portion within the integral body of the ring laser gyroscope. In this way, the strength of the magnetic field created by the magnetic element balances along the optical path. The magnetic element may be of a structure that forms an octupole or a dipole over an octopole.

 For a split gain multi-oscillator ring laser gyroscope, the resonant cavity has a closed optical path and an amplification medium in the cavity. The amplification means is excited to create at least four laser emission modes in the cavity, for example, the amplification means creates a gain curve corresponding to each laser emission mode.

Magnetic means are provided for adjusting the amplifying means which causes a frequency shift between the selected gain curves to suppress the laser emission activity of the preselected mode in the cavity. These magnetic elements include a plurality of transverse magnetic posts outside the cavity that define a closed optical path. These magnetic elements, as well as the magnetic elements revealed for use in a multi-oscillator ring laser gyroscope, have a unique lateral chamber created in the mold and frame that forms the ring laser gyroscope. It is roughly adjusted by rotating each column inside.

 The geometric magnetic structure of the ring laser gyroscope of the present invention and its various effects will become apparent from the following detailed description of preferred embodiments and the accompanying drawings.

EXAMPLE A multi-pole magnetic geometry of the present invention is a split-gain multi-oscillator ring laser gyroscope without internal cavity elements and a multi-oscillator that requires a Faraday rotator for non-reciprocal splitting of counter-rotating beams. -Applicable to both ring laser gyroscope. In FIGS. 1 and 3, an irregular multi-oscillator ring gray comprising a number of magnet columns 32, 36, 38 and 40 laterally integrated around a bore 30 (with a Faraday rotator assembly). The gyroscope is indicated at 10. The multi-oscillator ring laser gyroscope 10 has an integral hard glass frame 11, usually made of Schott's ceramic material from the Optics Division of Mainz, West Germany under the name Zerodur. The optical path 20 of the multi-oscillator ring laser gyroscope 10 of FIG. 1 defines a path connecting the corner mirrors 18, 22, and 26. Positioned along one leg of the optical path 20 is a metallized cathode 12 and a pair of laterally disposed anodes 14 and 16.

The integrated ring laser gyroscope 10 is installed on a central cylinder 28 made of a metal material of the registered trademark Invar. Invar 28 helps to isolate the magnetic field created by columns 32, 36, 38 and 40 and minimizes the effects of far magnetic fields created in the amplification bore bounded by anodes 14 and 16 and passing by anode 12. To As is conventionally known for ring laser gyroscopes, when multi-oscillators (multi-oscillators as shown in Fig. 1) are arranged in different planes, reciprocal division of two sets of right and left circularly polarized lights is performed. Is obtained by the irregular geometry of the mirrors 26, 24, 22 and 18 defining the optical path 20. The nonreciprocal division between counter-propagating clockwise and counterclockwise modes is obtained by the use of a Faraday rotator installed in bore 30 of FIG. In order for the Faraday rotator to perform non-reciprocal rotation, a magnetic field must be applied to the glass rotator 43 (FIG. 3) so as to cause non-reciprocal division of left and right circularly polarized lights. Unlike the “masket loading” method used in the prior art, the Faraday rotator 43 is inserted at the bottom of the glass frame and inserted at the center of the magnetic field created by the multipole method. The Faraday rotator assembly is installed in the glass frame 11 using a supporting column 53 that supports the glass Faraday rotator 43. The rotor 43 and the support column 53 are inserted using an optically sealed plug 45.

Each magnet, such as 32 and 38, is located in a respective bore outside the optical path 20 and produces a low gradient axial magnetic field. This magnetic field is perpendicular to the plane of the Faraday rotator glass 43. A multi-oscillator ring laser Invar support rod 28 at the center of the gyroscope 10 is used to protect the magnetic field from interference of the discharge of the amplification medium located between the cathode 12 and each of the anodes 14 and 16.

 Fig. 2 shows an example of the magnetic field distribution when using a Faraday glass in combination with a magnet column. The Faraday rotator 52 is disposed in the optical path 54 at a small angle θ. An octupole structure composed of magnets 44, 46, 48 and 56 is positioned to produce an axial magnetic field across Faraday rotator 52.

 The magnitude of the Faraday rotation in the nonreciprocal splitting of the counterpropagating beam is determined by the axial length of the glass 52 of the Faraday glass rotator and each of the magnets 44, 46, 48 and 56 acting together in an octupole structure. It is well known in the art that it depends on the strength of the resulting magnetic field and the verdet constant, which is related to the intrinsic properties of the glass material used for the Faraday rotator 52. Glass such as SF57 or FR5 is used for the thin Faraday rotator 52 of FIG. The configuration of FIG. 2 is preferred to produce the desired effect on a suitably strong axial magnetic field.

 Notably, each of the magnets 44-56 in FIG. 2 is not a conventional dipole (both the north and south poles are at the longitudinal ends of the magnet), but the magnetic north and south poles are the full axial length of the column. Along the diametrically opposite sides. One example of a radial directed magnet used as a bearing is described in U.S. Pat. No. 4,451,811 issued May 29, 1984 to Hoffman, who is also a designated co-author of the present invention. However, while Hoffman's patent revealed a radially oriented magnetic field, the applicant of the present invention chose that the poles of each magnet be diametrically opposed, and the longitudinal axis of each of the magnets 44-56, In addition, a magnetic field crossing both the entire surface and the back surface of the Faraday rotator 52 is generated. Thus, an extremely high magnetic flux density has been established which is effective for assembling the Faraday rotator of the multi-oscillator ring laser gyroscope.

 FIG. 5 shows the assembly of FIGS. 1 and 3 for mounting the glass Faraday rotator 43 along the central axis of the optical path in a magnetic structure with four columnar magnets.

Each of the magnets 32, 36, 38 and 40 is spaced apart along the central axis of the optical path outside the bore cavity. As shown in FIG. 1, this assembly comprises a support column 53 supported by a base 45 serving as a bottom surface when the multi-laser ring laser gyro is mounted on an integrated formwork. A support post 53 defines a bore 27 which is axially oriented (see FIG. 5) to expose both sides of the Faraday rotator to the optical path of the ring laser gyroscope.

 4 and 5 show another embodiment of a Faraday rotator assembly suitable for use in high radiation environments. The integral frame 13 defines a chamber 57 into which a mounting support 56 is inserted from the bottom of the frame 13.

A support column 56 mounted on an optically connected plug 55 supports a substantially cubic fused quartz Faraday rotator 58. Such a Faraday rotator satisfies the current performance requirements for ring laser gyroscope operation in a nuclear-enhanced environment.

We propose to make the Faraday rotator into a cubic shape to facilitate manufacturing. If a fused quartz material is used to meet the requirement and the rotor 58 should meet this requirement, the design of the multipolar magnetic structure should be such that the Verdet constant of the fused quartz is as shown in FIGS. It is necessary to consider that it is about 1/5 of the Verdet constant of SF57 glass used for the thin glass Faraday rotator shown in Fig. 5 and Fig. 5. The fused silica Faraday rotator 58 has a substantially lower Verdet constant than the previously used SF57 glass. Therefore, in order to produce a comparable non-inverted split of a counter-propagating beam in the optical path of a multi-oscillator ring laser gyroscope, the Faraday rotator 58 is about 3-5 times the size of a conventional glass rotator. It is twice as thick.

 The magnetic field used in the fused silica Faraday rotator assembly is better tuned using a hexapole structure as shown in FIG. FIG. 6 shows the optical path and the fused quartz rotator 58 located inside the bore 15. The Faraday rotator 58 is rotatably mounted in a chamber 57 defined by the glass frame 13 (see FIG. 4). Rotor 58 is also positioned off-axis (at an angle β) to eliminate retro-reflection in the ring laser cavity. The shape shown in FIG. 6 represents an octupole composed of magnets 60, 62, 64 and 66. These magnets create an axial magnetic field through the Faraday rotator 58, as indicated in particular by the magnetic field lines 72 and 74. The Faraday rotator 58 is much thicker than the conventional rotator, 51 in FIG. 5, so that if only octupoles 60, 62, 64 and 66 are used, the magnetic field lines 72 and 74 will tend to bend considerably. There is. Therefore, in order to arrange the magnetic fluxes passing through the Faraday rotator 58 more evenly and uniformly when the magnetic fluxes 72 and 74 pass through the fused silica Faraday rotator 58, two small dipole magnets 70 and 68 are provided. The resulting dipole shapes 35 are arranged as shown in FIG. It should be noted that in all of the concepts discussed so far, each magnet column is cylindrical. This facilitates the coarse adjustment of the magnets that appropriately arrange the diametrically opposite North-South Pole to obtain optimal magnetic field conditions.

 7 and 8 show a DC discharge division gain multi-oscillator ring laser gyroscope. This split gain structure, discussed in U.S. Patent Application No. 115,081, filed October 28, 1987, and commonly designated as the present invention, describes a split gain variant multi-oscillator structure that does not require internal cavity elements. By splitting the gain curve to obtain both Q and Q + 1 modes, four active modes, two of which are counterpropagated, can be obtained without the need for a Faraday rotator. However, in order to obtain the desired split gain required for the ring laser gyroscope to operate properly, a strong and surrounding amplification medium to create the split gain curve and cause the split gain effect to be anastomosed to the lasing mode frequency. A local magnetic field is required. In the DC discharge concept shown in both FIGS. 7 and 8, two sets of mirrors 84, 86, 88 and 91 are used to obtain a high magnetic field only along the portion of the discharge optical path that overlaps the optical path 82. Bores 96 'and 97' surround each of the anodes 78 and 79.

 In FIG. 7, bar magnets 94A, 94B and 94C are respectively inserted into the lower column positions below the anode pedestal 99. The bar magnets 96A, 96B and 96C are located above the optical path 82 of the anode stage 99. The integrated frame 81 of the multi-oscillator gain split ring laser gyroscope 80 has DC wire loops 92 on both sides of the anode mount 99 between the columns of the magnetic structure formed by the magnets 94A, 94B, 94C, 96A, 96B and 96C. And 90 are formed and curved to form a set of channels such as 93 to accommodate placement.

These loops 92 and 90 resemble the Helmholtz pair structure and apply the magnetic field generated by the magnet columns 94A, 94B, 94C, 96A, 96B and 96C so that the split gain curve is accurately anastomosed to the lasing mode frequency. Used to fine tune electrically. Move to FIG. This sketch is drawn along the portion of the optical path 82A between the mirrors 86 and 84. Fine adjustment loops 92 and 90 are shown to include a portion of DC amplification 100A within the axial spacing of magnets 96A and 96C and 94A and 94C.

The field lines 102 and 104 are substantially uniform throughout the amplification medium 100A to obtain a strong and symmetric gain curve for each lasing mode.

 The experimental results of the magnetic field generated by the multipolar magnetic structure (six magnet columns) described in this application are shown in FIG. It should be noted that the curve 106 intersects the axis 108 on both sides of the curve, about 10 and 30 mm.

 Thus, the multi-oscillator ring laser gyroscope using the Faraday element shown in FIG. 1 can form a uniform magnetic field at the location of the Faraday rotator while minimizing the influence of the far magnetic field. Thus, the undesirable Zeeman effect on the glow discharge medium located between the cathode 12 and each of the cathodes 14 and 16 is prevented. The test results in FIG. 10 show that the multipolar magnetic structure of the present invention forms a strong isolating magnetic field. The uniformity of the magnetic field strength is such that the gain split ring laser gyroscope obtains the maximum magnetic field strength where the excitation medium 100A (FIG. 9) is located along the optical path 82A, while the gain medium It makes it possible to prevent interference of distant magnetic fields due to external optical paths.

 As described above, the effect of the optimum and simple multi-pole ring laser is clear. The structure is preferably made of a cylinder suitable for coarse adjustment and control of the magnetic field during assembly. Having described the four and six pillar concept, other magnets that form the balanced, uniform and low-field magnetic field required for the multi-oscillator ring laser gyroscope described here. A combination of pillars is also conceivable. Accordingly, the scope of the present invention is not construed as being limited to the embodiments described herein, but also covers equivalent multipole magnetic field structures used in multi-oscillators and gain split ring laser gyroscopes. It is desirable.

[Brief description of the drawings]

 FIG. 1 is a sketch of a preferred embodiment of a multipole magnetic structure for a ring laser gyroscope using a Faraday rotator. FIG. 2 is a top view of a ring laser gyroscope having a multi-pole magnetic structure of the present invention applied to a magnetic field for a Faraday rotator element. FIG. 3 is a sectional view taken along line III-III in FIG. FIG. 4 is a front view of another Faraday rotator assembly used in connection with a multipole magnetic structure suitable for radioactivity enhanced conditions. FIG. 5 is a schematic drawing of another embodiment of a carrier assembly holding a glass Faraday rotator with respect to the concept of a multi-pole magnetic structure of a ring laser gyroscope. FIG. 6 is a schematic diagram showing magnetic field lines illustrating the interaction between six different magnets used for an antiradiation Faraday rotator for a ring laser gyroscope. FIG. 7 is a sketch of a DC discharge split gain gyro having magnet poles symmetrically arranged on both anodes. FIG. 8 is a schematic diagram of a split gain gyroscope using the multipole magnetic geometry of the present invention showing where high field strength magnets are placed in relation to the discharge. FIG. 9 is a schematic diagram showing the interaction of the magnetic field lines of six bar magnets placed along a single leg with the optical path of the split gain gyroscope of FIG. FIG. 10 shows experimental data indicating that the proper rotation and alignment of the magnet cylinder can produce a relatively uniform magnetic field of specified strength in the center of the multipole magnetic geometry. (Explanation of symbols) 12: Metallized cathode 14, 16: Anode 18, 22, 24, 26 ... Corner mirror 32, 36, 38, 40 ... Magnet column 43 ... Glass Faraday rotator 44, 46, 48 ... Magnet column 52 … Faraday rotator 56… Magnet column 57… Chamber 58… Fused quartz Faraday rotator 60,62,64,66… Magnet column 68,70… Dipole magnet 78,79… Anode 86,84,88,91… Mirror 94A 94B 94C 96A 96B 96C Magnet column

Claims (13)

[Claims] 1. A ring laser gyroscope, wherein said optical path is defined by one bore cavity that gives a different surface reciprocal image rotation to a plurality of electromagnetic waves propagating in one closed optical path. A ring laser gyro comprising: means including magnetic means for providing reciprocal polarization rotation; and the magnetic element including a plurality of external magnetic elements oriented transverse to the bore cavity defining the closed optical path. scope. 2. A ring laser gyroscope according to claim 1, wherein said magnetic element has a north and south pole of each magnetic element located on the opposite side of the diameter of a cylindrical column, respectively. A ring laser gyroscope, wherein the column is a column having a cylindrical shape, and a magnetic field passes through a plane perpendicular to the column. 3. The ring laser gyroscope according to claim 2, wherein said magnetic elements are disposed within a unitary body, and wherein each of said magnetic elements is oriented transverse to said bore cavity. Wherein the coarse adjustment of the magnetic elements is achieved by rotation of each element about an axis for each element. 4. The ring laser gyroscope according to claim 3, wherein the same number of magnetic elements, each producing a magnetic field of equal strength, are disposed on the integral body along opposite sides of a portion of the optical path; A ring laser gyroscope, wherein the strength of the magnetic field is balanced along the entire portion of the optical path. 5. The ring laser gyroscope of claim 3, wherein the four magnetic elements form an octupole to provide a uniform magnetic field over a portion of the closed optical path. A ring laser gyroscope, wherein the ring laser gyroscope is arranged mutually. 6. The ring laser gyroscope according to claim 5, wherein a dipole arrangement of a magnetic element is superimposed on the octupole in order to strengthen the magnetic field and expand the uniformity of the magnetic field. A ring laser gyroscope to be placed. 7. The ring laser gyroscope according to claim 5, wherein the fused silica Faraday rotator in which the gyroscope is substantially strengthened with respect to nuclei gives non-reciprocal polarization of the electromagnetic wave. Ring laser gyroscope. 8. A ring laser gyroscope, comprising: a resonant cavity defining a closed optical path within the cavity and an amplifying medium; at least a cavity within the cavity such that the amplifying medium provides a corresponding gain curve for each lasing mode. Medium excitation means for producing four lasing modes, for adjusting the amplification medium to produce a frequency shift between gain curves selected to suppress a preselected mode lasing reaction inside the cavity. A ring laser gyroscope comprising: a magnetic means; and the magnetic means, including a plurality of magnetic elements that are outside the cavity that defines the closed optical path and are oriented in a basically transverse direction. 9. The ring laser gyroscope according to claim 8, wherein said magnetic element has a north and south pole of each magnetic element located on the opposite side of the diameter of a cylindrical column, respectively. A ring laser gyroscope, wherein the column is a column having a cylindrical shape, and a magnetic field passes through a plane perpendicular to the column. 10. The ring laser gyroscope according to claim 9, wherein said magnetic elements are disposed within a one-piece body, each of said magnetic elements being transverse to said bore cavity. A ring laser gyroscope, wherein the coarse adjustment of the magnetic elements is achieved by rotation of each element about an axis for each element. 11. The ring laser gyroscope of claim 10, wherein an equal number of magnetic elements, each producing a magnetic field of equal strength, are disposed on the unitary body along opposite sides of a portion of the optical path; A ring laser gyroscope, wherein the strength of the magnetic field is balanced along the entire portion of the optical path. 12. The ring laser gyroscope according to claim 11, wherein the four magnetic elements form an octupole to provide a uniform magnetic field over a portion of the closed optical path. A ring laser gyroscope, wherein the ring laser gyroscope is arranged mutually. 13. The ring laser gyroscope according to claim 12, wherein a dipole arrangement of a magnetic element is superimposed on the octupole to strengthen the magnetic field and expand the uniformity of the magnetic field. A ring laser gyroscope to be placed.