CA1116279A - Laser gyroscope system - Google Patents
Laser gyroscope systemInfo
- Publication number
- CA1116279A CA1116279A CA317,534A CA317534A CA1116279A CA 1116279 A CA1116279 A CA 1116279A CA 317534 A CA317534 A CA 317534A CA 1116279 A CA1116279 A CA 1116279A
- Authority
- CA
- Canada
- Prior art keywords
- path
- combination
- waves
- passages
- solid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/58—Turn-sensitive devices without moving masses
- G01C19/64—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams
- G01C19/66—Ring laser gyrometers
- G01C19/667—Ring laser gyrometers using a multioscillator ring laser
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/08—Construction or shape of optical resonators or components thereof
- H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
- H01S3/083—Ring lasers
Abstract
ABSTRACT OF THE DISCLOSURE
A four-frequency laser gyroscope system having improved accuracy is constructed using a single solid block of low thermal coefficient of ex-pansion material. A four-segment nonplanar propagation path provides a first frequency splitting. A second splitting is provided by a Faraday ro-tator having a thin slab of rare earth-doped glass positioned within an aperture in a permanent magnet. A narrow angle of incidence is provided for the beams of incident upon the output mirror to prevent cross coupling between beams within the output optics structure. Blocking the gaseous flow path reduces output frequency drift caused by contaminating particles.
A four-frequency laser gyroscope system having improved accuracy is constructed using a single solid block of low thermal coefficient of ex-pansion material. A four-segment nonplanar propagation path provides a first frequency splitting. A second splitting is provided by a Faraday ro-tator having a thin slab of rare earth-doped glass positioned within an aperture in a permanent magnet. A narrow angle of incidence is provided for the beams of incident upon the output mirror to prevent cross coupling between beams within the output optics structure. Blocking the gaseous flow path reduces output frequency drift caused by contaminating particles.
Description
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- Background of the Invention 1. Field of the Invention-The invention per~ains broadly to the field of laser gyro-scopes. More particularly, the invention pertains to four-frequency laser gyroscope systems having effectively two laser gyroscopes operating simultaneously with a common propagation path.
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- Background of the Invention 1. Field of the Invention-The invention per~ains broadly to the field of laser gyro-scopes. More particularly, the invention pertains to four-frequency laser gyroscope systems having effectively two laser gyroscopes operating simultaneously with a common propagation path.
2. Description o~ the Prior Art:
The operation of a basic four-frequency laser gyroscope is described in United States Patent No. 3,7417657 issued June 26, 1973 to K. Andringa and assigned to the present assignee. In such - systems as dèscribed in the referenced patent, waves of four distinct frequencies propagate around a closed propagation path defined by three or more mirrors. Two of these beams circulate around the closed propagation path in the clockwise direction while the other two circulate in the counterclockwise direction. One of the clockwise beams and one of the counterclockwise beams are of a first polarization sense while the other one of the clockwise ` and the other one of the counterclockwise beams are of another ~`;; polarization sense. For example, the first clockwise beam andfirst counterclockwise beam may be of right-hand ~ircular polari-zation while the second clockwise and second counterclockwise beams ~` may be of a left-hand circular polarization. The two right-hand circularly polarized beams may be, for example, of the highest two frequencies while the two left-hand circularly polarized beams may be of the lowest two frequencies.
Rotation of the laser gyroscope about its sensitive axis causes the two right-hand circularly polarized beams to become ` further apart in frequency than at the rest state while the two left-hand circularly polarized beams become closer together in frequency. The opposite frequency shifts occur for the opposite direction of rotationO As shown in the referenced path, the ~' ~ ..
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difference between the frequency shifts in the right-hand circularly polarized beams and the left-hand circularly polarized beams is directly proportional to the rate of rotation of the system. The time integral of this difference is directly proportional to the total amount of rotation about the sensitive axis.
Two separate means are provided within the propagation path for producing frequency splitting in order to maintain the beams of four separate frequencies. In the system described in the referenced patent, a cr,vstal rotator provides a split between ~he average of the freqeuncies of the right and left-hand circularly polarized beams. This split is accomplished by the crystal pro-viding a phase delay for circularly polarized waves that is dif-ferent for one sense of circular polarization than for the opposite sense and is reciprocal. A Faraday rotator further provides the frequency split between the frequencies of the clockwise and ~ counterclockwise beams of like polarization. The Faraday rotator ; is non-reciprocal providing different phase delays for waves of,~ the same polarization states propagating in opposite directions.
Although the system of the referenced patent has been found to function quite well, it has been found desirable to provide : still further improvements. For example, it is desirable to eliminate as much solid material from the propagation path as possible as presence of any solid material within the path provides scattering centers from which light may be undesirably coupled from one beam to another thereby inducing output frequency drift into the system. Furthermore, it is desirable to provide a laser gyroscope system in which the coupling between beams of the opposite sense of polarization at the output detector is substan-- 30 tially eliminated.
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Summary of the Invention Accordingly, it is an object of the present invention to provide a laser gyroscope system having a minimum amount of material and hence scattering sites disposed within the propagation path of the circulating beams.
Furthermore, it is an object of the invention to provide a laser gyroscope in which unwan~ed coupling between beams incident upon an output detector are minimized.
Also, it is an objec~ of the present invention to provide a laser gyroscope system in which drift due to flow of the gaseous gain medium is minimized. These, as well as other objects of the invention, may be met by providing the combination of means for providing a closed nonplanar propagation path sustaining electro-magnetic waves and means for producing an indication of the rate of rotation of said path providing means. As herein used the term closed propagation path relates to a re-entrant path having a non-zero area projected upon some plane. The indication is preferably in the form of one or more electrical signals which have a parameter such as frequency or amplitude which varies in accordance with the rate of rotation. Digital signals may be so employed. Waves of at least two distinct frequencies propagate around the closed path.
The indication means may produce a signal having a frequency sub-stantially proportional to the difference in frequency between at least two of said waves. If waves of four frequencies are used, the indication may be in proportion to the difference between two differences between a separate two of the waves. In preferred embodiments, the waves are substantially circularly polarized.
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Four ~r more reflec~ing means may be used to provide the closed " path. Objects of the invention may further be met by providing the ~ 30 combination of a closed nonplanar propagation or electromagne~ic ,:, !.~
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waves and means for providing different delays for waves propagating in opposed directions around said closed path.
Means may also be provided for extracting a portion of the waves propagating around said closed path and for producing at least one output signal in response to the extrac~ed portion of the waves. In one preferred embodiment, the means for providing different delays may comprise a Faraday rotator.
In a preferred embodiment the invention may be practiced with the combination of means or providing a closed nonplanar propagation path for electromagnetic waves and means disposed in the path for delaying waves propagating in different directions along the path by different amounts of time, the delaying means comprising a slaD of material having a thickness of less than 0.5 mm. Means should be provided for producing a magnetic field within the slab The slab material has a preferred Verdet constant in excess of 0.25 min~/cm. Oe. the operating wavelength. A glass `` with an appropriate rare-earth dopant will fulfill this purpose.
Also, objects of the invention may be met by providing the combin-ation of means for forming a closed path for propagation of electro-magnetic waves and means for coupling a portion of the waves out .
of the path with the waves incident upon the coupling means having an angle between them of thirty degrees or less. The means for `~ forming the closed path preferably comprises a block of solid .i~ material having a plurality of passages provided therein along which the electromagnetic waves may propagate. Refelecting means are positioned at the intersections of the passages. One of the .;
reflecting means may be partially transmitting for performing the function of coupling a portion of the waves out of the path. Pre-ferably, the closed path is nonplanar; that is, the various segments ~` 30 of the closed path do not line within a single plane.
Moreover, objects of the invention may be met by providing , -4-:
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the combination of a plurality of reflecting means which provide a closed path for propagation of electromagnetic waves with the path having straight line segments between the reflecting means with one of the reflecting means being partially trans-mitting and means for producing one or more electrical signals in response to the electromagnetic waves propagating along the closed path wherein the signal producing means operates on portions of the electromagnetic waves transmitted by the partially transmitting one of the reflecting means with the angle between ones of the electromagnetic waves incident upon the partially transmitting reflecting means being thirty degrees or less. The combination may further include means for delaying waves propagating in one direction along the path by a different amount of time than waves traveling in the other direction along the path. The delaying means may be a Faraday rotator. Preferably, the path is nonplanar and is provided within a block of solid material.
The invention may also be practiced by providing the combin-` ation of a block of solid material having a low thermal coefficient- of expansion a plurality of straight passages being provided within `` 20 the block intersecting one another to form a closed path for propagation for electromagnetic waves, a plurality of reflecting means one of which is positioned at each intersection between the ; passages to reflect the electromagnetic waves along the closed ' path with at least one reflecting means being partially trans-mitting with the angle between the passages intersecting at the ` partially transmitting one of the reflecting means being thirty degrees or less, and means for producing output signals in response :
to portions of the electromagnetic waves transmitted through the ,~ partially transmitting one of the reflecting means. The closed '` 30 path is again preferably nonplanar providing an image rotation ~ -5-. .
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for the electromagnetic waves. The intersections of the passages are at the surfaces of the block~
The invention may otherwise be practiced by providing the combination of a block of solid material having a low thermal coefficent of expansion and a plurality of straight line passages within the block intersecting one another to form a nonplanar closed path for propagation of electromagnetic waves within the block with a plurality of reflecting means one of which is positioned at each interesection between the passages to reflect the electromagnetic waves between the passages with the reflecting means providing rotation for electromagnetic waves within the path.
A Faraday rotator is disposed within the path. The Faraday rotator preferably comprises a thin slab of rare earth-doped glass the thickness of the crystal being less than .5 mm and means for providing a longitudinal magnetic field within the slab. The intersections between the passages are located upon the surfaces of the block, Each of the surfaces of the block in a plane pelpendicular to a line bisecting the angle formed between the ones of the passages intersecting at each of the surfaces. A
laser gain medium such as a gas mixture consisting of, for example, 8 parts He to .53 parts 20Ne to .47 parts 22Ne at a total pressure of 3 torr, should also be provided within the closed path.
A plurality of electrode means for exciting the laser gain medium are also provided.
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~' The objects of the invention can further be met by providing ` ` the combination of a block of solid material having at least one .. ~
first bore therein for propagation of electromagnetic waves with the first bore having first and second colinear portions with the first portion lying between a surface of the block and the : 30 second portion and with the first having a larger cross section ; than the second portion, reflecting means positioned at ~he :
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intersection of the first portion of the first bore with the surface of the block, and at least one electrode positioned in a second bore inter-secting the second portion of the first bore. The distance between the intersection of the second bore with the second portion of the first bore to the intersection of the first and second portion of the first bore is preferably less than twice the diameter of the second portion of the first bore.
In accordance with the present invention, there is provided in combination: means for providing a closed nonplanar path for sustaining the propagation of electromagnetic waves in opposite direc-tions along said path; means comprising a solid segment of said path which is less than one-half millimeter long for providing different propagation times for waves traveling in said opposite directions along said path, the aperture of said path in region of said segment being substantially greater than one-half millimeter; and means for producing an indication of the rate of rotation of said path providing means.
; In accordance with the present invention, there is also provided ln combination: means for providing a closed nonplanar propagation path for electromagnetic waYes; means disposed in said path for delaying waves propagating in opposed directions by different amounts of time; said delaying means comprising a region containing solid optically transparent material having a Verdet constant of at least 0.25 min./cm. Oe; and the segment of said path through said ;!` ~ '~
solid optically transparent material having a length which is sub- ~ -stantially less than the diameter of said path through said material.
In accordance with the present invention, there is also .~ ~
provided a laser gyro comprising: means for forming a closed path for propagation of electromagnetic waves having at least four simul-taneous frequencies; means for coupling a portion of said waves out of said path, said wave being incident upon said coupling means, the angle between said waves heing thirty degrees or less; means disposed B
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in said path for delaying waves propagating in opposed directions by different amounts of time; said delaying means comprising a region containing solid optically transparent material having a Verdet con-stant of at least 0.25 min./cm. Oei and the segment of said path through said solid optically transparent material having a length which is substantially less than the diameter of said path through said material.
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Brief Description of the Drawings .
; FIG. 1 shows a top isometric view taken from a first corner of a laser gyroscope system of the invention;
FIG. 2 is a lower isometric view ta,ken from a second corner of the device shown in FIG. l;
FIGS. 3 and 4 are isometric views of the gyro block of the system shown in FIG. 1 showing the internal construction and passages of the device therein;
FIG. 5 is a cross-sectional view showing the internal construction of the system shown in FIG. 1 in the region of one of the terminal chambers and mirror substrate;
FIG. 6 is a cross-sectional view showing the details of ~ construction of the Faraday rotator device of the laser gyro -, system shown in FIG. l;
FIG. 6A is a cross-sectional view showing portions of the ; Faraday rotator of FIG. 6;
PIG. 7 is a graph showing the gain versus frequency of the gaseous laser medium employed with the laser gyro system of FIG. 1 indicating the relative positions of the frequencies of the four beams within ~he system; and FIG. 8 l5 a graph showing the power reduction factor as a function of the angle of incidence of beams upon an output mirror structure.
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Description of the Preferred Embodiments Referring simul~aneously to the views of Figures 1-4, the construction and operation of a laser gyroscope system in ' accordance with the teachings of the present invention will be described. Gyro block 102 forms the frame upon which the system is constructed. Gyro block 102 is preferably constructed with a material having a low thermal coefficient of expansion such as a glass-ceramic material to minimize the effects of temperature change upon the laser gyroscope system. A preferred commercially available material is sold under the name of Cer-VitTM material C-101 by Owens-Illinois Company.
Gyro block 102 has nine substantially planar faces as shown in the various views of Figures 1-4. As shown most clearly in the views of Figures 3 and 4 which show gyro block 102 without the other components of the system, passages 108, 110~ 112 and 114 are provided between four of the faces of gyro block 102. The passages define a nonplanar closed propagation path within laser gyro block 102.
`~ Mirrors are provided upon faces 122, 124, 126 and 128, at ~,~ 20 the intersection of the passages with the faces. Substrates 140 and ~ 142 having suitable reflecting surfaces provide the mirrors posi-; tioned upon faces 124 and 126 respectively. A mirrored surface is i~ also provided directly adjacent face 128 in the front of path length ; control transducer 160. One of these mirrors should be concave to ` insure that the beams are stable and confined essentially to the 7~` center of the passages. Also, a partially transmitting mirror is provided upon face 122 to allow a portion of each beam traveling along the closed path within the gyro block 102 to be coupled into output optics 144. The structure of output optics 144 is disclosed in Canadian Patent No. 1,079,368 on June 10, 1980, naming the present , ::
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inventors and assigned to the present assignee.
Because passages 108, 110, 112 and 114 define a nonplanar propagation path for the various beams within the system, each beam undergoes a polarization rotation as it passes around the closed path. Only beams of substantially circular polariza-tion can exist in the nonplanar cavity of the invention. With circularly polarized beams, drift due to beam scattering or coupling from one beam to the other is minimized. This reduction occurs because light of one circular polarization state when scattered is not of the proper polarization to be coupled into and affect the other beams. For other types of light polarization this is not the case because there will always be some component of the scattered beam which will couple to other beams.
In the preerred embodiment, the passages and reflecting mirrors are so arranged as to provide a substantially ninety-degree polarization rotation for the various beams. Because beams of right and left-hand circular polarization are rotated in opposite senses by this same amount independent of their direction of propagaton, a frequency splitting between beams of right and - 20 lef~-hand circular polarization must occur in order or the beams .` to resonate within the optical cavity. This is ~hown in FIG. 7 as the frequency split between the beams of left-hand and right-hand circular pola~ization. In the preferred embodi~ent, a `~` ninety-degree rotat~on corresponding to a 180-degr0e relative phase shift is employed although other phase shifts as well may ~` be used depending upon the frequency separation desired. Rotation will occur as long as the closed propagation path i5 nonplanar.
The precise arrangement of the paths will determine the amount of ` rotation.
In the known systems of the prior art such as that described in the above-referenced pntent to K. Andringa, the frequency .~
: . . , , . .;, . ~, , . ~ , , splitting between beams of right and left-hand clrcular polariza-tion was accomplished with the use of a block of solid material of significant optical thickness disposed in the propagation path.
As discussed above, the presence of any solid material directly in the path of beam propagation provides sca*tering centers from ;~ which li~ht may undesirably be coupled from one beam to another causing an error in the gyro output. The amount of coupling and thus error is thermally very sensitive. Hence, the output frequency of such devices was subject to a temperature dependent drift which could not be compensated for with a fixed output bias.
With the present invention, the solid material which had been used for the crystal rotator has been completely eliminated from the beam propagation path thereby eliminating the sources of error and drift associated with the material.
To aid in understanding how the phase shift occurs, it is useful to imagine a linearly polarized beam propagating around the path. Suppose, for example, that the beam traveling between face 122 and face 124 is linearly polaTiæed with the electric .
vector pointing in the upper direction. ~s the beam is reflected `~ 20 from the mirror provided upon face 124 the electric vector is still nearly pointed upward but with a slight forward tilt because passage 112 drops between face 124 and face 128. As the beam is ;
reflected from the mirror upon face 128 it will be pointing nearly to the left with a slight downward tilt as would be seen in FIGS. 3 and 4. As the beam is reflected from face 151, the electric vector of the beam within passage 108 would point to the left with a slight upward slope again in the views of FIGS. 3 and 4. Thus, it may be seen that the beam as it arrives back at face 122 has experienced a polarization rotation of approximately ninety degrees. Of course, such a rotated linearly polarized .
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beam cannot reinforce itself and resonate along the closed path.
Only circularly polarized beams having a frequency shifted from the frequency at which such beams would resonate for a planar closed path of the same length will be resonant.
A two-frequency laser gyroscope may be constructed using a nonplanar propagation path to provide the only frequency splitting.
No Faraday rotator or other such element is required in such an embodiment. To detec~ the rate of rotation, an output signal is produced by beating the extracted portions of the two beams together to form an output signal having a frequency equal to the diffe~ence in frequency between the two beams. At rest, the output signal will remain at some value fO. For rotation in one direction the output signal will increase to a value fO+~f, where Qf is ; proportional to the rate of rotation9 and will decrease to a value :~ of fO-~f for rotation in the other direction. Use of circularly . polarized waves in accordance with the invention significantly reduces cross-coupling due to backscattering so that the lock-in range diminishes permitting such a laser gyroscope to be used in many ~pplications without complete elimination of lock in.
The second frequency splitting between the clockwise and counterclockwise beams is caused by Faraday rotator 156. Faraday rotator 156 is positioned within an aperture in face 151 as may be seen in the views of FIGS. 2 and 4. The details of the construction of Faraday rotator 156 are seen in the views of FIGS. 6 and 6A. The Faraday rotator mount 154, preferably formed ` of the same material as laser gyro block 102, ~orms the base upon which the structure is constructed. Faraday rotator mount 154 has a central cylindrical portion with one end flanged to restrain lateral movement of the device within aperture 120 provided in laser gyro block 102. The other end of Faraday rotator mount 154 .
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is cut away to leave a pla~form for mounting the active components.
Aperture 155 is provided aligned with passage 112 and having substantially the same diameter as passage 112. Pernlanent magnet 166, of hollow cylindrical shape, is positioned around aperture 155. Within the aperture in permanent magnet 166 is aperture 155. Within the aperture in permanent magnet 166 is positioned slightly wedge-shaped Faraday rotator slab 165.
Faraday rotator slab 165 may be preferably formed of a rare earth-doped glass or a similar high Verdet constant material.
A Verdet constant of magnitude in excess of 0.25 min./cm./Oe.
at the operating wavelength is prefer~ed to reduce the thickness of the slab required to produce the desired amount of frequency splitting. It is desirable to use as thin a slab as possible because the amoutn of thermally induced drift in the output of the device has been found to be a strong positive function of the thickness of solid material in the path of the waves. A
commercially available material is Hoya Optics, Inc. material no.
FR-5. A thickness of 0.5 mm or less is preferred to reduce ., drift to an acceptable level.
Faraday rotator slab 165 is held against Faraday rotator ` mount 154 by coil spring 168. Pole piece 170, which is formed of unmagnetized ferromagnetic material, is held against permanent magnet 166 by the magnetic field of permanent magnet 166. Pole piece 170 has an aperture in the center thereof of substantially the same diameter as that of aperture 155 and passage 112 which is of slightly smaller diamater than the aperture within permanent magnet 166. Coil spring 168 is thus restrained by the portion of pole piece 170 extending within the aperture in peTmanent magnet 166.
In an alternate embodiment, two cylindrical permanent magnets are positioned end-to-end with like poles adjacent one another at the juncture between the two magnets. The Faraday rotator slab is placed adjacent one end of the two magnet pair. A longitudinal magnetic field is produced in the slab but this fiel~ attenuates rapidly upon moving a short distance away from ~he slab or magnets.
This embodiment has the advantage that essentially no stray magnetic field is produced which could extend into the gaseous discharge region and, by the Zeeman effect) produce unwanted modes or frequency offset.
-. 10 Besides providing the frequency splitting between the clock-wise and counterclockwise circulating ~eams, Faraday rotator 156 performs a second function. Because of the close fit provided within aperture 120 in gyro block 102, Faraday rotator 156 blocks the longitudinal flow of gas through passage 112. Because there can be no net circulation of gas through the closed path, the - possibility of circulation of scatter particles carried by the gas is substantially reduced. Both surfaces of Faraday rotator slab 165 are preferably provided with an anti-reflection coating to prevent backscattering of the incident radiation. Also, some reflection may be permitted with the reflected radiation utilized for the output signal. A partially transmitting mirror is not then required.
Referring again to the views of FIGS. 1, 3 and 4, it may be seen that a low angle of incidence is provided for the beams striking the partially transmitting mirror disposed upon face 122.
The beams traveling within each passage 108, 110, 112 and 114 are ` generally circularly polarized. The nearer to normal that one of these beams strikes a reflecting mirror or a surface the nearer to circular will be the polarization of the beam trans-mitted ~hrough ~he mirror sur~ace. As the angle of incidence `":
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moves away from the normal the partially transmitted beams begins to assume an elliptical polarization.
~s explained iJI the above-referenced Canadian patent No. 1,079,386, if the beams within the output optics and detector structure are entirely circularly polarized there will . be essentially no unwanted cross coupling and interference -~ between the beams of the upper two frequencies and the beams of ~j the lower two frequencies within the detector structure. As the amount of ellipticity increases, cross coupling begins to become evident and appears as an amplitude modulation upon the output signals from detector diodes 143. It has been discovered that the amount of the unwanted cross coupling is a nonlinear monotonically increasing function of the degree of ellipticity. It has been found that the cross coupling is relatively low ~or angles of incidence below approximately fifteen degrees. However, the amount of cross coupling increases quite rapidly above this angle of incidence. ~lis cross coupling may ~e eliminated by means of a suitable polarization filter, but the available filtered ;~
power decreases as the unfiltered cross coupling increases.
Furthermore, as an angle of incidence of each beam upon the output mirror increases, the power available at the detector diodes for each beam decreases. A calculated graph of power reduction factor, the ratio of power available at the detectors at a given angle of incidence to that available for the same beam normal to the mirror surface, is shown in Figure 8 for the output structure described in the above-re~erenced Canadian patent No. 1,079,386. As may readily be seen, the power reduction factor falls rapidly for angles of incidences greater than approximately fifteen degrees. Hence, in accordance with one aspect of the invention, the angle of incidence of the beams in passages 108 ~r . ~ , .
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and 110 to the partially transmitting mirror disposed upon face 122 is made to be fifteen degrees or less. Alternately stated, the angle between passages 108 and 110 is thirty degrees or less.
Still referring to the views of FIGS. 1, 3 and 4, electrodes for exciting the gaseous gain medium disposed within passages 108 and llO are positioned within electrode apertures 104. Preferably, center cathode electrodes 132 and 136 are connected to the negative terminal of an external power supply while electrodes 127, 130, `~ 134 and 138 are connected to the positive terminal. The cathode electrodes are in the form of hollow metal cylinders capped at the end most distant from the seal to the laser gyro block 102 while the positive electrodes are in the form of metal rods extending into the various electrode apertures 104. With this connection, the current flows outward toward electrodes 132 and 136 in two opposed directions within a single passage. Negative electrode 136 is preferably located mid~ay between positive electrodes 134 and 138 as negative electrode 132 is located midway betwaen positive electrodes 130 and 127. In this manner, because a beam traversing ane of the passages in which the electrodes are located. passes through equal lengths of current flow of opposite direction, the effects o drag on the beam caused by unequal current flow through the gaseous gain medium are substantially eliminated. However, because o~ manufacturing tolerances in the positions of the various electrodes the distances between the positive and two negative electrodes in each passage may not be precisely equal. To compensate for the inequality, the current flow between the positive electrodes and thereta adjacent negative electrodes may be made unequal.
The gaseous gain medium which fills passages 108, 110, 112 and 114 is supplied through gas fill aperture 106 through gas fill .:
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tube 146 from an e~ternal gas source. A mixture 3He,20Ne and 22Ne in the ratio of 8:0.53:0.47 is preferred.
The details of construction of ~he laser gyroscope system in the region of one of the positive electrodes are shown in ; detail in the cross-sectional view of FIG. 5. Metal electrode 130, held in place by glass electrode seal 131, is positioned within electrode aperture 104. Electrod0 130 extends somewhat more than half way between the surface of gyro block 102 and passage 110. Electrode aperture 104 intersects passage 110 preferably at a right angle. Terminal chamber 125 is formed between the surface of gyro block 102 upon which is positioned mirror substrate 140. Terminal chamber 125 is cylindrical in shape having a diameter at least twice that of passage 110.
Terminal chamber 125 and passage 110 are coa~ial with one another.
Because passage 110 extends slightly beyond electrode aperture 104 before intersecting with terminal chamber 125, a baffle 145 is formed b~tween electrode 104 and terminal chamber 125.
In prior art system, no terminal chamber or baffle was provided. The passage way extended directly through the electrode apertures out to the surface of the laser gyro block. When the - electrodes were excited, dust or other unwanted particles which may be produced such as by ion bombardment and sputtering of the laser gyro block would collect around the intersection of the . electrode aperture and beam passageways. The suspended particles acted as scattering centers increasing the op*ical loss of the structure. In contrast, with the present invention it has been found that dust or other unwanted particles will not be suspended in the region of the intersection of electrode apertures 10~ and ,` passage 110. Thus, a potential source of drift is eliminated.
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This concludes the description of the preferred embodiments of the invention. Although preferred embodiments have been disclosed, it is believed that numerous modiications and alterations thereto would be apparent to one having ordinary skill in the art without departing from the spirit and scope ' of the invention.
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The operation of a basic four-frequency laser gyroscope is described in United States Patent No. 3,7417657 issued June 26, 1973 to K. Andringa and assigned to the present assignee. In such - systems as dèscribed in the referenced patent, waves of four distinct frequencies propagate around a closed propagation path defined by three or more mirrors. Two of these beams circulate around the closed propagation path in the clockwise direction while the other two circulate in the counterclockwise direction. One of the clockwise beams and one of the counterclockwise beams are of a first polarization sense while the other one of the clockwise ` and the other one of the counterclockwise beams are of another ~`;; polarization sense. For example, the first clockwise beam andfirst counterclockwise beam may be of right-hand ~ircular polari-zation while the second clockwise and second counterclockwise beams ~` may be of a left-hand circular polarization. The two right-hand circularly polarized beams may be, for example, of the highest two frequencies while the two left-hand circularly polarized beams may be of the lowest two frequencies.
Rotation of the laser gyroscope about its sensitive axis causes the two right-hand circularly polarized beams to become ` further apart in frequency than at the rest state while the two left-hand circularly polarized beams become closer together in frequency. The opposite frequency shifts occur for the opposite direction of rotationO As shown in the referenced path, the ~' ~ ..
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difference between the frequency shifts in the right-hand circularly polarized beams and the left-hand circularly polarized beams is directly proportional to the rate of rotation of the system. The time integral of this difference is directly proportional to the total amount of rotation about the sensitive axis.
Two separate means are provided within the propagation path for producing frequency splitting in order to maintain the beams of four separate frequencies. In the system described in the referenced patent, a cr,vstal rotator provides a split between ~he average of the freqeuncies of the right and left-hand circularly polarized beams. This split is accomplished by the crystal pro-viding a phase delay for circularly polarized waves that is dif-ferent for one sense of circular polarization than for the opposite sense and is reciprocal. A Faraday rotator further provides the frequency split between the frequencies of the clockwise and ~ counterclockwise beams of like polarization. The Faraday rotator ; is non-reciprocal providing different phase delays for waves of,~ the same polarization states propagating in opposite directions.
Although the system of the referenced patent has been found to function quite well, it has been found desirable to provide : still further improvements. For example, it is desirable to eliminate as much solid material from the propagation path as possible as presence of any solid material within the path provides scattering centers from which light may be undesirably coupled from one beam to another thereby inducing output frequency drift into the system. Furthermore, it is desirable to provide a laser gyroscope system in which the coupling between beams of the opposite sense of polarization at the output detector is substan-- 30 tially eliminated.
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Summary of the Invention Accordingly, it is an object of the present invention to provide a laser gyroscope system having a minimum amount of material and hence scattering sites disposed within the propagation path of the circulating beams.
Furthermore, it is an object of the invention to provide a laser gyroscope in which unwan~ed coupling between beams incident upon an output detector are minimized.
Also, it is an objec~ of the present invention to provide a laser gyroscope system in which drift due to flow of the gaseous gain medium is minimized. These, as well as other objects of the invention, may be met by providing the combination of means for providing a closed nonplanar propagation path sustaining electro-magnetic waves and means for producing an indication of the rate of rotation of said path providing means. As herein used the term closed propagation path relates to a re-entrant path having a non-zero area projected upon some plane. The indication is preferably in the form of one or more electrical signals which have a parameter such as frequency or amplitude which varies in accordance with the rate of rotation. Digital signals may be so employed. Waves of at least two distinct frequencies propagate around the closed path.
The indication means may produce a signal having a frequency sub-stantially proportional to the difference in frequency between at least two of said waves. If waves of four frequencies are used, the indication may be in proportion to the difference between two differences between a separate two of the waves. In preferred embodiments, the waves are substantially circularly polarized.
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Four ~r more reflec~ing means may be used to provide the closed " path. Objects of the invention may further be met by providing the ~ 30 combination of a closed nonplanar propagation or electromagne~ic ,:, !.~
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waves and means for providing different delays for waves propagating in opposed directions around said closed path.
Means may also be provided for extracting a portion of the waves propagating around said closed path and for producing at least one output signal in response to the extrac~ed portion of the waves. In one preferred embodiment, the means for providing different delays may comprise a Faraday rotator.
In a preferred embodiment the invention may be practiced with the combination of means or providing a closed nonplanar propagation path for electromagnetic waves and means disposed in the path for delaying waves propagating in different directions along the path by different amounts of time, the delaying means comprising a slaD of material having a thickness of less than 0.5 mm. Means should be provided for producing a magnetic field within the slab The slab material has a preferred Verdet constant in excess of 0.25 min~/cm. Oe. the operating wavelength. A glass `` with an appropriate rare-earth dopant will fulfill this purpose.
Also, objects of the invention may be met by providing the combin-ation of means for forming a closed path for propagation of electro-magnetic waves and means for coupling a portion of the waves out .
of the path with the waves incident upon the coupling means having an angle between them of thirty degrees or less. The means for `~ forming the closed path preferably comprises a block of solid .i~ material having a plurality of passages provided therein along which the electromagnetic waves may propagate. Refelecting means are positioned at the intersections of the passages. One of the .;
reflecting means may be partially transmitting for performing the function of coupling a portion of the waves out of the path. Pre-ferably, the closed path is nonplanar; that is, the various segments ~` 30 of the closed path do not line within a single plane.
Moreover, objects of the invention may be met by providing , -4-:
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the combination of a plurality of reflecting means which provide a closed path for propagation of electromagnetic waves with the path having straight line segments between the reflecting means with one of the reflecting means being partially trans-mitting and means for producing one or more electrical signals in response to the electromagnetic waves propagating along the closed path wherein the signal producing means operates on portions of the electromagnetic waves transmitted by the partially transmitting one of the reflecting means with the angle between ones of the electromagnetic waves incident upon the partially transmitting reflecting means being thirty degrees or less. The combination may further include means for delaying waves propagating in one direction along the path by a different amount of time than waves traveling in the other direction along the path. The delaying means may be a Faraday rotator. Preferably, the path is nonplanar and is provided within a block of solid material.
The invention may also be practiced by providing the combin-` ation of a block of solid material having a low thermal coefficient- of expansion a plurality of straight passages being provided within `` 20 the block intersecting one another to form a closed path for propagation for electromagnetic waves, a plurality of reflecting means one of which is positioned at each intersection between the ; passages to reflect the electromagnetic waves along the closed ' path with at least one reflecting means being partially trans-mitting with the angle between the passages intersecting at the ` partially transmitting one of the reflecting means being thirty degrees or less, and means for producing output signals in response :
to portions of the electromagnetic waves transmitted through the ,~ partially transmitting one of the reflecting means. The closed '` 30 path is again preferably nonplanar providing an image rotation ~ -5-. .
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for the electromagnetic waves. The intersections of the passages are at the surfaces of the block~
The invention may otherwise be practiced by providing the combination of a block of solid material having a low thermal coefficent of expansion and a plurality of straight line passages within the block intersecting one another to form a nonplanar closed path for propagation of electromagnetic waves within the block with a plurality of reflecting means one of which is positioned at each interesection between the passages to reflect the electromagnetic waves between the passages with the reflecting means providing rotation for electromagnetic waves within the path.
A Faraday rotator is disposed within the path. The Faraday rotator preferably comprises a thin slab of rare earth-doped glass the thickness of the crystal being less than .5 mm and means for providing a longitudinal magnetic field within the slab. The intersections between the passages are located upon the surfaces of the block, Each of the surfaces of the block in a plane pelpendicular to a line bisecting the angle formed between the ones of the passages intersecting at each of the surfaces. A
laser gain medium such as a gas mixture consisting of, for example, 8 parts He to .53 parts 20Ne to .47 parts 22Ne at a total pressure of 3 torr, should also be provided within the closed path.
A plurality of electrode means for exciting the laser gain medium are also provided.
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~' The objects of the invention can further be met by providing ` ` the combination of a block of solid material having at least one .. ~
first bore therein for propagation of electromagnetic waves with the first bore having first and second colinear portions with the first portion lying between a surface of the block and the : 30 second portion and with the first having a larger cross section ; than the second portion, reflecting means positioned at ~he :
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intersection of the first portion of the first bore with the surface of the block, and at least one electrode positioned in a second bore inter-secting the second portion of the first bore. The distance between the intersection of the second bore with the second portion of the first bore to the intersection of the first and second portion of the first bore is preferably less than twice the diameter of the second portion of the first bore.
In accordance with the present invention, there is provided in combination: means for providing a closed nonplanar path for sustaining the propagation of electromagnetic waves in opposite direc-tions along said path; means comprising a solid segment of said path which is less than one-half millimeter long for providing different propagation times for waves traveling in said opposite directions along said path, the aperture of said path in region of said segment being substantially greater than one-half millimeter; and means for producing an indication of the rate of rotation of said path providing means.
; In accordance with the present invention, there is also provided ln combination: means for providing a closed nonplanar propagation path for electromagnetic waYes; means disposed in said path for delaying waves propagating in opposed directions by different amounts of time; said delaying means comprising a region containing solid optically transparent material having a Verdet constant of at least 0.25 min./cm. Oe; and the segment of said path through said ;!` ~ '~
solid optically transparent material having a length which is sub- ~ -stantially less than the diameter of said path through said material.
In accordance with the present invention, there is also .~ ~
provided a laser gyro comprising: means for forming a closed path for propagation of electromagnetic waves having at least four simul-taneous frequencies; means for coupling a portion of said waves out of said path, said wave being incident upon said coupling means, the angle between said waves heing thirty degrees or less; means disposed B
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in said path for delaying waves propagating in opposed directions by different amounts of time; said delaying means comprising a region containing solid optically transparent material having a Verdet con-stant of at least 0.25 min./cm. Oei and the segment of said path through said solid optically transparent material having a length which is substantially less than the diameter of said path through said material.
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Brief Description of the Drawings .
; FIG. 1 shows a top isometric view taken from a first corner of a laser gyroscope system of the invention;
FIG. 2 is a lower isometric view ta,ken from a second corner of the device shown in FIG. l;
FIGS. 3 and 4 are isometric views of the gyro block of the system shown in FIG. 1 showing the internal construction and passages of the device therein;
FIG. 5 is a cross-sectional view showing the internal construction of the system shown in FIG. 1 in the region of one of the terminal chambers and mirror substrate;
FIG. 6 is a cross-sectional view showing the details of ~ construction of the Faraday rotator device of the laser gyro -, system shown in FIG. l;
FIG. 6A is a cross-sectional view showing portions of the ; Faraday rotator of FIG. 6;
PIG. 7 is a graph showing the gain versus frequency of the gaseous laser medium employed with the laser gyro system of FIG. 1 indicating the relative positions of the frequencies of the four beams within ~he system; and FIG. 8 l5 a graph showing the power reduction factor as a function of the angle of incidence of beams upon an output mirror structure.
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Description of the Preferred Embodiments Referring simul~aneously to the views of Figures 1-4, the construction and operation of a laser gyroscope system in ' accordance with the teachings of the present invention will be described. Gyro block 102 forms the frame upon which the system is constructed. Gyro block 102 is preferably constructed with a material having a low thermal coefficient of expansion such as a glass-ceramic material to minimize the effects of temperature change upon the laser gyroscope system. A preferred commercially available material is sold under the name of Cer-VitTM material C-101 by Owens-Illinois Company.
Gyro block 102 has nine substantially planar faces as shown in the various views of Figures 1-4. As shown most clearly in the views of Figures 3 and 4 which show gyro block 102 without the other components of the system, passages 108, 110~ 112 and 114 are provided between four of the faces of gyro block 102. The passages define a nonplanar closed propagation path within laser gyro block 102.
`~ Mirrors are provided upon faces 122, 124, 126 and 128, at ~,~ 20 the intersection of the passages with the faces. Substrates 140 and ~ 142 having suitable reflecting surfaces provide the mirrors posi-; tioned upon faces 124 and 126 respectively. A mirrored surface is i~ also provided directly adjacent face 128 in the front of path length ; control transducer 160. One of these mirrors should be concave to ` insure that the beams are stable and confined essentially to the 7~` center of the passages. Also, a partially transmitting mirror is provided upon face 122 to allow a portion of each beam traveling along the closed path within the gyro block 102 to be coupled into output optics 144. The structure of output optics 144 is disclosed in Canadian Patent No. 1,079,368 on June 10, 1980, naming the present , ::
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inventors and assigned to the present assignee.
Because passages 108, 110, 112 and 114 define a nonplanar propagation path for the various beams within the system, each beam undergoes a polarization rotation as it passes around the closed path. Only beams of substantially circular polariza-tion can exist in the nonplanar cavity of the invention. With circularly polarized beams, drift due to beam scattering or coupling from one beam to the other is minimized. This reduction occurs because light of one circular polarization state when scattered is not of the proper polarization to be coupled into and affect the other beams. For other types of light polarization this is not the case because there will always be some component of the scattered beam which will couple to other beams.
In the preerred embodiment, the passages and reflecting mirrors are so arranged as to provide a substantially ninety-degree polarization rotation for the various beams. Because beams of right and left-hand circular polarization are rotated in opposite senses by this same amount independent of their direction of propagaton, a frequency splitting between beams of right and - 20 lef~-hand circular polarization must occur in order or the beams .` to resonate within the optical cavity. This is ~hown in FIG. 7 as the frequency split between the beams of left-hand and right-hand circular pola~ization. In the preferred embodi~ent, a `~` ninety-degree rotat~on corresponding to a 180-degr0e relative phase shift is employed although other phase shifts as well may ~` be used depending upon the frequency separation desired. Rotation will occur as long as the closed propagation path i5 nonplanar.
The precise arrangement of the paths will determine the amount of ` rotation.
In the known systems of the prior art such as that described in the above-referenced pntent to K. Andringa, the frequency .~
: . . , , . .;, . ~, , . ~ , , splitting between beams of right and left-hand clrcular polariza-tion was accomplished with the use of a block of solid material of significant optical thickness disposed in the propagation path.
As discussed above, the presence of any solid material directly in the path of beam propagation provides sca*tering centers from ;~ which li~ht may undesirably be coupled from one beam to another causing an error in the gyro output. The amount of coupling and thus error is thermally very sensitive. Hence, the output frequency of such devices was subject to a temperature dependent drift which could not be compensated for with a fixed output bias.
With the present invention, the solid material which had been used for the crystal rotator has been completely eliminated from the beam propagation path thereby eliminating the sources of error and drift associated with the material.
To aid in understanding how the phase shift occurs, it is useful to imagine a linearly polarized beam propagating around the path. Suppose, for example, that the beam traveling between face 122 and face 124 is linearly polaTiæed with the electric .
vector pointing in the upper direction. ~s the beam is reflected `~ 20 from the mirror provided upon face 124 the electric vector is still nearly pointed upward but with a slight forward tilt because passage 112 drops between face 124 and face 128. As the beam is ;
reflected from the mirror upon face 128 it will be pointing nearly to the left with a slight downward tilt as would be seen in FIGS. 3 and 4. As the beam is reflected from face 151, the electric vector of the beam within passage 108 would point to the left with a slight upward slope again in the views of FIGS. 3 and 4. Thus, it may be seen that the beam as it arrives back at face 122 has experienced a polarization rotation of approximately ninety degrees. Of course, such a rotated linearly polarized .
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beam cannot reinforce itself and resonate along the closed path.
Only circularly polarized beams having a frequency shifted from the frequency at which such beams would resonate for a planar closed path of the same length will be resonant.
A two-frequency laser gyroscope may be constructed using a nonplanar propagation path to provide the only frequency splitting.
No Faraday rotator or other such element is required in such an embodiment. To detec~ the rate of rotation, an output signal is produced by beating the extracted portions of the two beams together to form an output signal having a frequency equal to the diffe~ence in frequency between the two beams. At rest, the output signal will remain at some value fO. For rotation in one direction the output signal will increase to a value fO+~f, where Qf is ; proportional to the rate of rotation9 and will decrease to a value :~ of fO-~f for rotation in the other direction. Use of circularly . polarized waves in accordance with the invention significantly reduces cross-coupling due to backscattering so that the lock-in range diminishes permitting such a laser gyroscope to be used in many ~pplications without complete elimination of lock in.
The second frequency splitting between the clockwise and counterclockwise beams is caused by Faraday rotator 156. Faraday rotator 156 is positioned within an aperture in face 151 as may be seen in the views of FIGS. 2 and 4. The details of the construction of Faraday rotator 156 are seen in the views of FIGS. 6 and 6A. The Faraday rotator mount 154, preferably formed ` of the same material as laser gyro block 102, ~orms the base upon which the structure is constructed. Faraday rotator mount 154 has a central cylindrical portion with one end flanged to restrain lateral movement of the device within aperture 120 provided in laser gyro block 102. The other end of Faraday rotator mount 154 .
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is cut away to leave a pla~form for mounting the active components.
Aperture 155 is provided aligned with passage 112 and having substantially the same diameter as passage 112. Pernlanent magnet 166, of hollow cylindrical shape, is positioned around aperture 155. Within the aperture in permanent magnet 166 is aperture 155. Within the aperture in permanent magnet 166 is positioned slightly wedge-shaped Faraday rotator slab 165.
Faraday rotator slab 165 may be preferably formed of a rare earth-doped glass or a similar high Verdet constant material.
A Verdet constant of magnitude in excess of 0.25 min./cm./Oe.
at the operating wavelength is prefer~ed to reduce the thickness of the slab required to produce the desired amount of frequency splitting. It is desirable to use as thin a slab as possible because the amoutn of thermally induced drift in the output of the device has been found to be a strong positive function of the thickness of solid material in the path of the waves. A
commercially available material is Hoya Optics, Inc. material no.
FR-5. A thickness of 0.5 mm or less is preferred to reduce ., drift to an acceptable level.
Faraday rotator slab 165 is held against Faraday rotator ` mount 154 by coil spring 168. Pole piece 170, which is formed of unmagnetized ferromagnetic material, is held against permanent magnet 166 by the magnetic field of permanent magnet 166. Pole piece 170 has an aperture in the center thereof of substantially the same diameter as that of aperture 155 and passage 112 which is of slightly smaller diamater than the aperture within permanent magnet 166. Coil spring 168 is thus restrained by the portion of pole piece 170 extending within the aperture in peTmanent magnet 166.
In an alternate embodiment, two cylindrical permanent magnets are positioned end-to-end with like poles adjacent one another at the juncture between the two magnets. The Faraday rotator slab is placed adjacent one end of the two magnet pair. A longitudinal magnetic field is produced in the slab but this fiel~ attenuates rapidly upon moving a short distance away from ~he slab or magnets.
This embodiment has the advantage that essentially no stray magnetic field is produced which could extend into the gaseous discharge region and, by the Zeeman effect) produce unwanted modes or frequency offset.
-. 10 Besides providing the frequency splitting between the clock-wise and counterclockwise circulating ~eams, Faraday rotator 156 performs a second function. Because of the close fit provided within aperture 120 in gyro block 102, Faraday rotator 156 blocks the longitudinal flow of gas through passage 112. Because there can be no net circulation of gas through the closed path, the - possibility of circulation of scatter particles carried by the gas is substantially reduced. Both surfaces of Faraday rotator slab 165 are preferably provided with an anti-reflection coating to prevent backscattering of the incident radiation. Also, some reflection may be permitted with the reflected radiation utilized for the output signal. A partially transmitting mirror is not then required.
Referring again to the views of FIGS. 1, 3 and 4, it may be seen that a low angle of incidence is provided for the beams striking the partially transmitting mirror disposed upon face 122.
The beams traveling within each passage 108, 110, 112 and 114 are ` generally circularly polarized. The nearer to normal that one of these beams strikes a reflecting mirror or a surface the nearer to circular will be the polarization of the beam trans-mitted ~hrough ~he mirror sur~ace. As the angle of incidence `":
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moves away from the normal the partially transmitted beams begins to assume an elliptical polarization.
~s explained iJI the above-referenced Canadian patent No. 1,079,386, if the beams within the output optics and detector structure are entirely circularly polarized there will . be essentially no unwanted cross coupling and interference -~ between the beams of the upper two frequencies and the beams of ~j the lower two frequencies within the detector structure. As the amount of ellipticity increases, cross coupling begins to become evident and appears as an amplitude modulation upon the output signals from detector diodes 143. It has been discovered that the amount of the unwanted cross coupling is a nonlinear monotonically increasing function of the degree of ellipticity. It has been found that the cross coupling is relatively low ~or angles of incidence below approximately fifteen degrees. However, the amount of cross coupling increases quite rapidly above this angle of incidence. ~lis cross coupling may ~e eliminated by means of a suitable polarization filter, but the available filtered ;~
power decreases as the unfiltered cross coupling increases.
Furthermore, as an angle of incidence of each beam upon the output mirror increases, the power available at the detector diodes for each beam decreases. A calculated graph of power reduction factor, the ratio of power available at the detectors at a given angle of incidence to that available for the same beam normal to the mirror surface, is shown in Figure 8 for the output structure described in the above-re~erenced Canadian patent No. 1,079,386. As may readily be seen, the power reduction factor falls rapidly for angles of incidences greater than approximately fifteen degrees. Hence, in accordance with one aspect of the invention, the angle of incidence of the beams in passages 108 ~r . ~ , .
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and 110 to the partially transmitting mirror disposed upon face 122 is made to be fifteen degrees or less. Alternately stated, the angle between passages 108 and 110 is thirty degrees or less.
Still referring to the views of FIGS. 1, 3 and 4, electrodes for exciting the gaseous gain medium disposed within passages 108 and llO are positioned within electrode apertures 104. Preferably, center cathode electrodes 132 and 136 are connected to the negative terminal of an external power supply while electrodes 127, 130, `~ 134 and 138 are connected to the positive terminal. The cathode electrodes are in the form of hollow metal cylinders capped at the end most distant from the seal to the laser gyro block 102 while the positive electrodes are in the form of metal rods extending into the various electrode apertures 104. With this connection, the current flows outward toward electrodes 132 and 136 in two opposed directions within a single passage. Negative electrode 136 is preferably located mid~ay between positive electrodes 134 and 138 as negative electrode 132 is located midway betwaen positive electrodes 130 and 127. In this manner, because a beam traversing ane of the passages in which the electrodes are located. passes through equal lengths of current flow of opposite direction, the effects o drag on the beam caused by unequal current flow through the gaseous gain medium are substantially eliminated. However, because o~ manufacturing tolerances in the positions of the various electrodes the distances between the positive and two negative electrodes in each passage may not be precisely equal. To compensate for the inequality, the current flow between the positive electrodes and thereta adjacent negative electrodes may be made unequal.
The gaseous gain medium which fills passages 108, 110, 112 and 114 is supplied through gas fill aperture 106 through gas fill .:
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tube 146 from an e~ternal gas source. A mixture 3He,20Ne and 22Ne in the ratio of 8:0.53:0.47 is preferred.
The details of construction of ~he laser gyroscope system in the region of one of the positive electrodes are shown in ; detail in the cross-sectional view of FIG. 5. Metal electrode 130, held in place by glass electrode seal 131, is positioned within electrode aperture 104. Electrod0 130 extends somewhat more than half way between the surface of gyro block 102 and passage 110. Electrode aperture 104 intersects passage 110 preferably at a right angle. Terminal chamber 125 is formed between the surface of gyro block 102 upon which is positioned mirror substrate 140. Terminal chamber 125 is cylindrical in shape having a diameter at least twice that of passage 110.
Terminal chamber 125 and passage 110 are coa~ial with one another.
Because passage 110 extends slightly beyond electrode aperture 104 before intersecting with terminal chamber 125, a baffle 145 is formed b~tween electrode 104 and terminal chamber 125.
In prior art system, no terminal chamber or baffle was provided. The passage way extended directly through the electrode apertures out to the surface of the laser gyro block. When the - electrodes were excited, dust or other unwanted particles which may be produced such as by ion bombardment and sputtering of the laser gyro block would collect around the intersection of the . electrode aperture and beam passageways. The suspended particles acted as scattering centers increasing the op*ical loss of the structure. In contrast, with the present invention it has been found that dust or other unwanted particles will not be suspended in the region of the intersection of electrode apertures 10~ and ,` passage 110. Thus, a potential source of drift is eliminated.
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This concludes the description of the preferred embodiments of the invention. Although preferred embodiments have been disclosed, it is believed that numerous modiications and alterations thereto would be apparent to one having ordinary skill in the art without departing from the spirit and scope ' of the invention.
` 20 ~0 JRI:d:jd
Claims (43)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In combination:
means for providing a closed nonplanar path for sustaining the propagation of electromagnetic waves in opposite directions along said path;
means comprising a solid segment of said path which is less than one-half millimeter long for providing different propagation times for waves traveling in said opposite directions along said path, the aperture of said path in region of said segment being substantially greater than one-half millimeter; and means for producing an indication of the rate of rotation of said path providing means.
means for providing a closed nonplanar path for sustaining the propagation of electromagnetic waves in opposite directions along said path;
means comprising a solid segment of said path which is less than one-half millimeter long for providing different propagation times for waves traveling in said opposite directions along said path, the aperture of said path in region of said segment being substantially greater than one-half millimeter; and means for producing an indication of the rate of rotation of said path providing means.
2. The combination of Claim 1 wherein waves of at least two fre-quencies propagate in each of said directions within said path providing means.
3. The combination of Claim 1 wherein said indication producing means comprises:
means for producing a signal having a frequency substantially pro-portional to the difference in frequency between at least two of said waves.
means for producing a signal having a frequency substantially pro-portional to the difference in frequency between at least two of said waves.
4. The combination of Claim 1 wherein:
said waves comprise a component of substantially circular polar-ization.
said waves comprise a component of substantially circular polar-ization.
5. The combination of Claim 4 wherein said path providing means com-prises:
a plurality of reflecting means.
a plurality of reflecting means.
6. In combination:
means for providing a closed nonplanar propagation path for electromagnetic waves;
means disposed in said path for delaying waves propagating in op-posed directions along said path by different amounts of time;
said delaying means comprising a region containing solid optically transparent material having a thickness less than 0.5 mm, and said delaying means further comprising means for producing a magnetic field in said region having a component parallel to the axis of a segment of said path through said region comprising a magnetic pole piece having an aperture for said path whose diameter is substantially greater than said thickness.
means for providing a closed nonplanar propagation path for electromagnetic waves;
means disposed in said path for delaying waves propagating in op-posed directions along said path by different amounts of time;
said delaying means comprising a region containing solid optically transparent material having a thickness less than 0.5 mm, and said delaying means further comprising means for producing a magnetic field in said region having a component parallel to the axis of a segment of said path through said region comprising a magnetic pole piece having an aperture for said path whose diameter is substantially greater than said thickness.
7. The combination of Claim 6 wherein:
said means for providing a magnetic field comprises a permanent magnet.
said means for providing a magnetic field comprises a permanent magnet.
8. The combination of Claim 7 wherein said material has a Verdet con-stant of at least 0.25 min./cm. Oe.
9. The combination of Claim 6 wherein said material comprises:
a rare earth-doped glass.
a rare earth-doped glass.
10. In combination:
means for providing a closed nonplanar propagation path for electromagnetic waves;
means disposed in said path for delaying waves propagating in op-posed directions by different amounts of time;
said delaying means comprising a region containing solid optically transparent material having a Verdet constant of attleast 0.25 min./cm. Oe;
and the segment of said path through said solid optically transparent material having a length which is substantially less than the diameter of said path through said material.
means for providing a closed nonplanar propagation path for electromagnetic waves;
means disposed in said path for delaying waves propagating in op-posed directions by different amounts of time;
said delaying means comprising a region containing solid optically transparent material having a Verdet constant of attleast 0.25 min./cm. Oe;
and the segment of said path through said solid optically transparent material having a length which is substantially less than the diameter of said path through said material.
11. The combination of Claim 10 further comprising:
means for providing a magnetic field within said region.
means for providing a magnetic field within said region.
12. The combination of Claim 10 wherein said material comprises:
a rare earth-doped glass.
a rare earth-doped glass.
13. A laser gyro comprising:
means for forming a closed path for propagation of electromagnetic waves having at least four simultaneous frequencies;
means for coupling a portion of said waves out of said path, said wave being incident upon said coupling means, the angle between said waves being thirty degrees or less;
means disposed in said path for delaying waves propagating in op-posed directions by different amounts of time;
said delaying means comprising a region containing solid optically transparent material having a Verdet constant of at least 0.25 min./cm. Oe;
and the segment of said path through said solid optically transparent material having a length which is substantially less than the diameter of said path through said material.
means for forming a closed path for propagation of electromagnetic waves having at least four simultaneous frequencies;
means for coupling a portion of said waves out of said path, said wave being incident upon said coupling means, the angle between said waves being thirty degrees or less;
means disposed in said path for delaying waves propagating in op-posed directions by different amounts of time;
said delaying means comprising a region containing solid optically transparent material having a Verdet constant of at least 0.25 min./cm. Oe;
and the segment of said path through said solid optically transparent material having a length which is substantially less than the diameter of said path through said material.
14. The combination of Claim 13 wherein said means for forming said closed path comprises:
a block of solid material having a plurality of passages therein along which said electromagnetic waves propagate.
a block of solid material having a plurality of passages therein along which said electromagnetic waves propagate.
15. The combination of Claim 14 further comprising:
a plurality of reflecting means, said reflecting means being positioned at intersections of said passages.
a plurality of reflecting means, said reflecting means being positioned at intersections of said passages.
16. The combination of Claim 15 wherein:
one of said reflecting means comprises said coupling means, said reflecting means being partially transmitting.
one of said reflecting means comprises said coupling means, said reflecting means being partially transmitting.
17. The combination of Claim 13 wherein:
said closed path is nonplanar.
said closed path is nonplanar.
18. In combination:
a plurality of reflecting means,said reflecting means providing a closed path for propagation of electromagnetic waves, said path comprising straight lines between said reflecting means, one of said reflecting means being partially transmitting;
means for producing electromagnetic waves having a plurality of frequencies propagating along said closed path, said closed path including a region of solid optically transparent material with the segment of said path through said region being less than one-half millimeter;
the segment of said path through said solid optically transparent material having a length which is substantially less than the diameter of said path through said material; and electrical signal producing means operating upon portions of said electromagnetic waves transmitted by said partially transmitting one of said reflecting means.
a plurality of reflecting means,said reflecting means providing a closed path for propagation of electromagnetic waves, said path comprising straight lines between said reflecting means, one of said reflecting means being partially transmitting;
means for producing electromagnetic waves having a plurality of frequencies propagating along said closed path, said closed path including a region of solid optically transparent material with the segment of said path through said region being less than one-half millimeter;
the segment of said path through said solid optically transparent material having a length which is substantially less than the diameter of said path through said material; and electrical signal producing means operating upon portions of said electromagnetic waves transmitted by said partially transmitting one of said reflecting means.
19. The combination of Claim 18 further including a magnetic field having a component parallel to said segment.
20. The combination of Claim 18 wherein a Faraday rotator comprising said solid optically transparent material is disposed in said closed path.
21. The combination of Claim 18 wherein: said path is nonplanar.
22. The combination of Claim 18 wherein: said path is provided with-in a block of solid material.
23. In combination:
a block of solid material having a low thermal coefficient of expansion;
a plurality of straight passages within said block, said passages intersecting to form a closed path for propagation of electromagnetic waves with at least one of said passages containing a lasing medium;
a plurality of reflecting means positioned at intersections be-tween said passages;
at least one of said reflecting means being partially transmit-ting, the angle between the passages intersecting at said partially transmit-ting one of said reflecting means being 30° or less;
means comprising a region of solid material for producing a plurality of frequencies propagating along said path;
the length of the segment of said path through said region being less than one-half millimeter;
the segment of said path through said solid optically transparent material having a length which is substantially less than the diameter of said path through said material; and means for producing output signals in response to portions of said electromagnetic waves transmitted through said partially transmitting one of said reflecting means.
a block of solid material having a low thermal coefficient of expansion;
a plurality of straight passages within said block, said passages intersecting to form a closed path for propagation of electromagnetic waves with at least one of said passages containing a lasing medium;
a plurality of reflecting means positioned at intersections be-tween said passages;
at least one of said reflecting means being partially transmit-ting, the angle between the passages intersecting at said partially transmit-ting one of said reflecting means being 30° or less;
means comprising a region of solid material for producing a plurality of frequencies propagating along said path;
the length of the segment of said path through said region being less than one-half millimeter;
the segment of said path through said solid optically transparent material having a length which is substantially less than the diameter of said path through said material; and means for producing output signals in response to portions of said electromagnetic waves transmitted through said partially transmitting one of said reflecting means.
24. The combination of Claim 23 wherein:
said path is nonplanar.
said path is nonplanar.
25. The combination of Claim 23 wherein:
said path provides an image rotation for said electromagnetic waves.
said path provides an image rotation for said electromagnetic waves.
26. The combination of Claim 23 wherein:
the intersections of said passages are substantially at surfaces of said block.
the intersections of said passages are substantially at surfaces of said block.
27. The combination of Claim 23 wherein:
at least one of said passages contains a gaseous laser gain medium.
at least one of said passages contains a gaseous laser gain medium.
28. The combination of Claim 23 wherein:
said path comprises a region having a gaseous laser gain medium which is prevented from circulating around said closed path.
said path comprises a region having a gaseous laser gain medium which is prevented from circulating around said closed path.
29. In combination:
a block of solid material having a low thermal coefficient of expansion;
a plurality of straight passages within said block, said passages intersecting to form a nonplanar closed path for propagation of electro-magnetic waves;
means comprising a region of solid optically transparent material for producing a plurality of frequencies propagating along said path;
the length of the segment of said path through said region of solid optically transparent material being substantially less than the diameter of said path through said material; and a plurality of reflecting means, one of said reflecting means being positioned at each intersection between said passages, to reflect electro-magnetic waves between said passages, said reflecting means providing an image rotation for said electromagnetic waves.
a block of solid material having a low thermal coefficient of expansion;
a plurality of straight passages within said block, said passages intersecting to form a nonplanar closed path for propagation of electro-magnetic waves;
means comprising a region of solid optically transparent material for producing a plurality of frequencies propagating along said path;
the length of the segment of said path through said region of solid optically transparent material being substantially less than the diameter of said path through said material; and a plurality of reflecting means, one of said reflecting means being positioned at each intersection between said passages, to reflect electro-magnetic waves between said passages, said reflecting means providing an image rotation for said electromagnetic waves.
30. The combination of Claim 29 wherein:
a Faraday rotator comprising said solid optical material is disposed in said path.
a Faraday rotator comprising said solid optical material is disposed in said path.
31. The combination of Claim 29 wherein said material comprises a slab of rare earth-doped glass having a thickness of 0.5 mm or less; and a magnetic field is produced within said material.
32. The combination of Claim 29 wherein:
the intersections between said passages are located substantially at surfaces of said block.
the intersections between said passages are located substantially at surfaces of said block.
33. The combination of Claim 29 wherein:
a plurality of the surfaces of said block are in a plane perpendic?
ular to a line bisecting the angle formed between pairs of said passages which intersect at said each of said surfaces.
a plurality of the surfaces of said block are in a plane perpendic?
ular to a line bisecting the angle formed between pairs of said passages which intersect at said each of said surfaces.
34. The combination of Claim 29 wherein:
a laser gain medium is disposed in said path.
a laser gain medium is disposed in said path.
35. The combination of Claim 29 wherein:
a laser gain medium comprising a gas mixture comprising 3He, 2ONe and 22Ne is disposed in said path.
a laser gain medium comprising a gas mixture comprising 3He, 2ONe and 22Ne is disposed in said path.
36. The combination of Claim 29 wherein:
a Faraday rotator substantially prevents the circulation of a gaseous lasing medium around said closed path.
a Faraday rotator substantially prevents the circulation of a gaseous lasing medium around said closed path.
37. The combination of Claim 29 wherein:
means are provided for exciting a laser gain medium in said path.
means are provided for exciting a laser gain medium in said path.
38. In combination:
a block of solid material having a plurality of bores therein for propagation of electromagnetic waves along a closed path;
a first of said bores having first and second co-linear portions, said first portion lying between a surface of said block and said second portion, said first portion having a larger cross-section than said second portion;
reflecting means, said reflecting means being positioned at the intersection of said first portion of said first bore with said surface of said block of solid material;
at least one electrode, said electrode being positioned in a second of said bores intersecting said second portion of said first bore;
means comprising a region of solid optically transparent material for producing a plurality of frequencies propagating along said path; and the length of the segment of said path through said region of solid optically transparent material being substantially less than the diameter of said path through said material.
a block of solid material having a plurality of bores therein for propagation of electromagnetic waves along a closed path;
a first of said bores having first and second co-linear portions, said first portion lying between a surface of said block and said second portion, said first portion having a larger cross-section than said second portion;
reflecting means, said reflecting means being positioned at the intersection of said first portion of said first bore with said surface of said block of solid material;
at least one electrode, said electrode being positioned in a second of said bores intersecting said second portion of said first bore;
means comprising a region of solid optically transparent material for producing a plurality of frequencies propagating along said path; and the length of the segment of said path through said region of solid optically transparent material being substantially less than the diameter of said path through said material.
39. The combination of Claim 38 wherein:
said block of solid material has a low temperature coefficient of expansion.
said block of solid material has a low temperature coefficient of expansion.
40. The combination of Claim 38 wherein:
the distance from the intersection between said second bore and said second portion of said first bore and the intersection between said first and second portions of said first bore is less than twice the diameter of said second portion of said first bore.
the distance from the intersection between said second bore and said second portion of said first bore and the intersection between said first and second portions of said first bore is less than twice the diameter of said second portion of said first bore.
41. The combination of Claim 38 wherein:
said block of solid material has a plurality of bores for forming a closed path for propagation of electromagnetic waves.
said block of solid material has a plurality of bores for forming a closed path for propagation of electromagnetic waves.
42, The combination of Claim 38 wherein said path is nonplanar
43. The combination of Claim 38 wherein:
one of said bores contains a gaseous medium for providing amplifi-cation of said waves.
one of said bores contains a gaseous medium for providing amplifi-cation of said waves.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US86809678A | 1978-01-03 | 1978-01-03 | |
| US868.096 | 1978-01-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1116279A true CA1116279A (en) | 1982-01-12 |
Family
ID=25351066
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA317,534A Expired CA1116279A (en) | 1978-01-03 | 1978-12-07 | Laser gyroscope system |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5498195A (en) |
| CA (1) | CA1116279A (en) |
| DE (1) | DE2900125A1 (en) |
| FR (1) | FR2413635A1 (en) |
| GB (1) | GB2012101B (en) |
| IT (1) | IT1113711B (en) |
| NL (1) | NL189980C (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2471583A1 (en) * | 1979-12-14 | 1981-06-19 | Thomson Csf | METHOD AND DEVICE FOR MODULATING THE WAVE PHASE CIRCULATING IN A RING INTERFEROMETER |
| CA1189600A (en) * | 1980-10-17 | 1985-06-25 | Raytheon Company | Dispersion equalized ring laser gyroscope |
| US4397027A (en) * | 1981-01-05 | 1983-08-02 | Raytheon Company | Self-compensating gas discharge path for laser gyro |
| GB2120839A (en) * | 1982-05-19 | 1983-12-07 | Raytheon Co | Ring laser gyroscope |
| US4616930A (en) * | 1983-04-20 | 1986-10-14 | Litton Systems, Inc. | Optically biased twin ring laser gyroscope |
| JPS6068684A (en) * | 1983-09-26 | 1985-04-19 | Fujitsu Ltd | Laser light source |
| GB2184285B (en) * | 1983-11-07 | 1990-08-01 | Raytheon Co | Ring laser gyroscope |
| US4578793A (en) * | 1984-07-13 | 1986-03-25 | The Board Of Trustees Of The Leland Stanford Junior University | Solid-state non-planar internally reflecting ring laser |
| US4962506A (en) * | 1988-04-14 | 1990-10-09 | Litton Systems, Inc. | Scatter symmetrization in multi-mode ring laser gyros |
| US5469256A (en) * | 1988-07-29 | 1995-11-21 | Litton Systems, Inc. | Multipole magnetic geometry for a ring laser gyroscope |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3245314A (en) * | 1962-06-28 | 1966-04-12 | Bell Telephone Labor Inc | Optical rotation devices employing a ferromagnetic chromium trihalide |
| US3373650A (en) * | 1965-04-02 | 1968-03-19 | Honeywell Inc | Laser angular rate sensor |
| US3741657A (en) * | 1971-03-03 | 1973-06-26 | Raytheon Co | Laser gyroscope |
| JPS5045904Y2 (en) * | 1972-06-07 | 1975-12-25 | ||
| DE2335597A1 (en) * | 1972-07-17 | 1974-01-31 | North American Rockwell | RING LASER GYROSCOPE |
| JPS4940557A (en) * | 1972-08-16 | 1974-04-16 | ||
| US3841758A (en) * | 1972-09-28 | 1974-10-15 | J Gievers | Rotation sensitive retarder |
| JPS5146340B2 (en) * | 1972-12-12 | 1976-12-08 | ||
| DE2432479C2 (en) * | 1974-07-04 | 1985-05-30 | Sperry Corp., New York, N.Y. | Ring laser |
| JPS5349629Y2 (en) * | 1974-10-02 | 1978-11-29 | ||
| CA1077602A (en) * | 1976-01-02 | 1980-05-13 | Raytheon Company | Electromagnetic wave ring resonator |
-
1978
- 1978-12-07 CA CA317,534A patent/CA1116279A/en not_active Expired
- 1978-12-20 GB GB7849292A patent/GB2012101B/en not_active Expired
- 1978-12-27 JP JP16463378A patent/JPS5498195A/en active Granted
- 1978-12-29 NL NLAANVRAGE7812668,A patent/NL189980C/en not_active IP Right Cessation
- 1978-12-29 FR FR7836927A patent/FR2413635A1/en active Granted
-
1979
- 1979-01-02 IT IT47511/79A patent/IT1113711B/en active
- 1979-01-03 DE DE19792900125 patent/DE2900125A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| NL189980B (en) | 1993-04-16 |
| GB2012101A (en) | 1979-07-18 |
| DE2900125A1 (en) | 1979-07-12 |
| IT1113711B (en) | 1986-01-20 |
| FR2413635A1 (en) | 1979-07-27 |
| DE2900125C2 (en) | 1993-04-01 |
| GB2012101B (en) | 1982-04-21 |
| IT7947511A0 (en) | 1979-01-02 |
| NL7812668A (en) | 1979-07-05 |
| FR2413635B1 (en) | 1984-09-14 |
| JPS5498195A (en) | 1979-08-02 |
| JPH0321889B2 (en) | 1991-03-25 |
| NL189980C (en) | 1993-09-16 |
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| MKEX | Expiry |