CA1077602A - Electromagnetic wave ring resonator - Google Patents
Electromagnetic wave ring resonatorInfo
- Publication number
- CA1077602A CA1077602A CA267,744A CA267744A CA1077602A CA 1077602 A CA1077602 A CA 1077602A CA 267744 A CA267744 A CA 267744A CA 1077602 A CA1077602 A CA 1077602A
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- waves
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- laser
- ring resonator
- resonator
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
- G02B26/06—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the phase of light
-
- 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
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- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Electromagnetism (AREA)
- Power Engineering (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Lasers (AREA)
- Gyroscopes (AREA)
Abstract
ELECTROMAGNETIC WAVE RING RESONATOR
Abstract of the Disclosure An electromagnetic wave ring resonator is disclosed including means to spatially rotate the electromagnetic field distribution of waves resonant therein about the direction of propagation of such waves to enable such waves to resonate with opposite senses of circular polarization, and means, including a laser amplifier medium, to provide different indices of refraction to resonant waves of the same sense of circular polarization as they pass through such laser amplifier medium in different directions. With such arrangement the two mentioned means enable the waves to resonate with four different frequencies. In a laser gyroscope using such ring resonator the electromagnetic field distribution rotating means includes a catoptric arrangement which, together with the last-mentioned means, reduces the loss, scatter and linear birefringence associated with the ring resonator included in such gyroscope. The last-mentioned means produces the Zeeman effect in the laser medium and efficiently provides different optical pathlengths for waves passing through such medium because the magnetic field vector of such waves interacts with the precessing atomic magnetic dipoles of the amplifier medium at the emission frequency of such amplifier medium.
Abstract of the Disclosure An electromagnetic wave ring resonator is disclosed including means to spatially rotate the electromagnetic field distribution of waves resonant therein about the direction of propagation of such waves to enable such waves to resonate with opposite senses of circular polarization, and means, including a laser amplifier medium, to provide different indices of refraction to resonant waves of the same sense of circular polarization as they pass through such laser amplifier medium in different directions. With such arrangement the two mentioned means enable the waves to resonate with four different frequencies. In a laser gyroscope using such ring resonator the electromagnetic field distribution rotating means includes a catoptric arrangement which, together with the last-mentioned means, reduces the loss, scatter and linear birefringence associated with the ring resonator included in such gyroscope. The last-mentioned means produces the Zeeman effect in the laser medium and efficiently provides different optical pathlengths for waves passing through such medium because the magnetic field vector of such waves interacts with the precessing atomic magnetic dipoles of the amplifier medium at the emission frequency of such amplifier medium.
Description
Background of the Invention This invention relates generally to electromagnetic wave resonators, and more particularly to electromagnetic wave resonators adapted for use in laser gyroscope apparatus.
As described in U. S. Patent No. 3,741,657 entitled "Laser Gyroscope," Keimpe Andringa inventor, issued June 26, 1973 and assigned to the same assignee as the present invention, a laser ring resonator supports four optical waves, each one of such waves having a different frequency, one pair thereof traveling in a clockwise direction and the other pair thereof traveling in a counterclockwise direction. The optical pathlengths of the waves are such that the pair of frequencies of the waves traveling in one direction, say the counterclockwise direction, is positioned between the frequencies of the waves traveling in the opposite, or clockwise, direction.
Having established this frequency relationship, movement of the laser resonator, for example by rotation of the system about an axis perpendicular to the optical path, produces frequency shifts of the pair of waves propagating in one direction through the laser which are opposite to frequency shifts of the waves moving in the opposite direction through the laser. This, in turn, produces changes in the frequency separation between the lower frequencies of each of said pair oppositely to a change in the frequency separation between the higher frequencies of each of said pairs. The difference between such changes is, substantially, a linsar function of the rate of said rotation and the relative sense of such difference is indicative of the direction of said rotation.
As described in the referenced U. S. Patent No. 3,741,657, `~ 30 such frequency separation results from disposing in the path .
-, - ~, .- ~ . . . . . .
of the waves a polarization dispersive structure which comprises a solid medium Faraday rotator and a crystal rotator. The crystal rotator is an anisotropic medium which restricts the type of polarization of the waves which may be supported in the ring laser to substantially circular polarization and also provides a dif-ferent optical pathlength for right-hand sense circularly polarized ~-waves than for left-hand sense circularly polarized waves. The solid medium Faraday rotator is a nonreciprocal device and pro-vides different time delays to waves of each polarization sense passing in the laser ring in one direction from those of such polarization ~ense passing in the opposite direction. The combina-tion of the crystal rotator and solid medium Faraday rotator ; provides the four-frequency relationship discussed above.
While the described polarization dispersive structure has been found satisfacto~r in many applications, the use of a crystal rotator and solid medium Faraday rotator increases loss and scatter imparted to the propagating waves and introduces linear birefringence to the ring resonator thereby reducing the accuracy of a laser gyroscope using such polarization dispersive structure.
.' , . .
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Summary of the Invention According to the present invention an electromagnetic wave ring resonator includes means for spatially rotating the electromagnetic field distribution of electromagnetic waves resonant in such resonator about the direction of propagation of such waves, and means, including an amplifier medium, for providing different indices of refraction to waves of the same polarization sense passing through such amplifier medium in different direc-tions. With such arrangement such rotating means provides a phase difference between waves of opposite polarization sense and, together with the last mentioned means, enables such waves to resonate with four different fre- -quencies.
In accordance with the invention there is provided in combination:
(a) an electromagnetic wave ring resonator wherein resonant electromagnetic waves propagate through a non-solid medium, such resonator including an amplifier medium; (b) means, included in such ring resonator, for spatially -rotating the electromagnetic field distribution of the resonant electro- ~
magnetic waves as such waves pass through the non-solid medium about the ~ -direction of propagation of such wave~ to enable such electromagnetic waves .
in such resonator to resonate with different frequencies; and (c) means, including the amplifier medium, for providing different indices of refraction to waves of the same polarization sense passing through such medium in differ-ent directions.
~; In accordance with another aspect of this invention there is pro-.~ .
vided a four frequency ring laser resonator comprising: (a) a laser amplifier medium; (b) means for producing different frequencies in such resonator from waves with opposite senses of circular polarization; and (c) means for ,: :
providing substantially different indices of refraction in said laser ampli-;~ fier medium to waves passing through such laser amplifier medium in different directions.
In a preferred embodiment a laser ring resonator includes a plurality~of reflectors positioned in the path of the laser to spatially rotate the electromagnetic field distribution of the laser waves resonant therein and thereby provide a predetermined phase alteration to the waves resonant therein. Such phase alteration correspondingly alters the resonant frequency of each one of such waves in the ring resonator without requiring an anisotropic crystal rotator in such path to alter the optical pathlength of such laser. Since the phase alteration sense is opposite for opposite for opposite senses of circular polarization, such arrangement enables waves of opposite polarization sense to resonate at separate frequencies. The reflectors are preferably oriented to provide a ~ radian phase difference between right and left-hand circularly polarized waves. The use of the Zeeman 10effect in the amplifier medium further reduces the loss and scatter in the resonator by eliminating a solid medium Faraday rotator and more efficiently provides different optical pathlengths for waves of the same polarization sense pa:sing throagh such medium in :
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- opposite directions because the magnetic field vector of such waves interacts with the precessing atomic magnetic dipoles of the ampli~ier medium.at the emission frequency of such amplifier medium.
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Brief Description of the Drawings .
Other and further features and advantages of the invention will become apparent as the description thereof progresses, reference being made to the accompanying drawings wherein:
FIG. 1 illustrates a diagrammatic view of a ring resonator embodying the invention;
FIGS, 2A-2C are sketches useful in understanding the invention;
FIGS. 3A-3C are diagrams useful in understanding the operating characteristics of the system illustrated in FIG. l; and FIG. 4 illustrates a diagrammatic view of an alternative embodiment of a ring resonator according to the invention.
, Description of the Preferred Embodiments Referring now to F~G. 1 there is shown a laser gyrosco~e system 9 having a laser amplifier medium 10 there a helium-neon 3 22 2~
laser medium having a gas mixture: 8 He ~ 0.48 Ne + 0.52 Ne.
A ring laser resonator includes. an even number of reflectors, here six reflectors 12, 14, 16, 18, 20, 22 (suitably mounted, by means not shown, to the surface of a platform 23) which produce a ring path for the laser beams. It is here noted that, as will be described later in connection with FIG. 4, the desired ring path . 10 may be produced by as few as four properly positioned reflectors.
I~owever, the six reflector system will first be discussed in order to establish the principle of operation of the laser gyroscope .
system. Considering the laser beam produced at end 24 of tl-e laser amplifier medium 10, such beam travels along the +~
direction (i.e. along the longitudinal axis of the laser ampli.fier medium 10) through an isotropic medium, preferably subs~antially free space, and is first reflected by reflector 12. The reflector 1 12 has its reflecting surface oriented such ~hat the laser bealn is reflected vertically a distance d along the +Y directiosl to reflector 14. Reflector 14 has its reflective surface ori~nted ~j such that the beam incident thereon becomes reflected hori%ontallya distance d along the -X direction to reflector 16. Reflector 16 has its reflecti~e surface oriented so that the beam incident l~ thereon becomes reflected vertically a distance d along tlle -Y
1~: direction to reflector 18. Reflector 18 has its reflective surfaceoriented so that the beam incident thereon becomes reflected ~: horizontally a distance d along the -X direction to reflector Z0.
It is here noted that the beam passing from end 24 of laser ~ a plifier med~um 10 to reflector 12 and the beam passing from ,~ 30 ~eflector 18 to reflector 20 are orthogonal to each other and : - 6 -. .. . . , - . , . . - . , - - . ~ ~ ~
10'7760Z
define a common horizontal plane 26. The surface of the platform 23 is disposed in a plane parallel to the horizontal plane 26.
~herefore, the beams passing from reflector 12 to reflector 14 to reflector 16 to reflector 18 are disposed in a ~ertical plane.
Continuing, reflector 20 has its reflective surface orientcd so - that the beam incident thereon is reflected to reflector 22, the incident beam and the reflected beam being disposed in the horizontal plane 26 and having an included angle here of 60 degrees, Reflector 22, here having a concave surface to aid in concentrating the laser beam through the laser amplifier metliu~ 10 (i.e. to aid in establishing a resonant transverse mode), has its reflective surface oriented so that the beam incident thereon is reflected again along the longitudinal axis of the laser ampl;fier ,medium 10, as shown, such incident and reflected ~eams ~e;ng disposed in the horizontal plane 26 and having an included angle he~e of 30 degrees. The distance between reflectors 22 and 12 along the ~Z axis is d .
It is here noted that, for purposes of explanation, the fol , lowing description neglects the effect of 180 phase changes impartcd to an electric field component upon reflection by a reflector. Such consideration is appropriate here becau~e the ring resonators described herein include an even number of reflectors in the path of the resonant waves and hence the effect of such phase changes cancel upon traversal of the waves through the ring resonator.
Considering the beam produced at end 24 of laser amp],ifier medium 10 and traveling along the +Z axis to have an electric field component B , disposed along the ~X axis, such electric field component remains along the +X axis after re~lection by ~' 30 reflector 12, then be~omes oriented along the ~Y axis to the 11~77602 electric field component E " because of reflector 14, then he-comes oriented along the -X axis because of reflector 16, then becomes oriented along the -Y axis because of r~flector 18 and remains so oriented when it returns to end 24. The effect of the reflectors 12-22 on the orientation of such electric fie]d component E is to rotate into such component -90 degrees al)out the beam axis (i.e. the ~Z axis) to the electric field component .
Considering now the beam produced at the end 24 of la.ser amplifier medium 10 and traveling along the ~Z axis to have an electric field component, E , disposed along the ~Y axis, sncl-l component first becomes oriented along the +Z axis ~to electri.c , field component E ") because of reflec~or 12, remains ori.cnted along the ~Z axis after reflections by reflectors 14, lG a]l~l 18 then becomes disposed in the X-Z plane at a -30 angl.e wi.th respect to the +X axis (to electric field component F, "') an(l then, after reflection by reflector 22, becomes oriented a]ong .. the +X axis at the end 24 to electric field componellt h '. l'he effect of the reflectors 12-22 on the orientation of sucll c].cctric field component E is to rotate such component -90 degrees a~)out the beam axis. The effect of a passage around the ring may thus .
be symbolized: ~
E ~ E ' a ~E
1 1 2, : E ~ E ' ~ E
As described in U. S. Patent No. 3,741,657 entitled "Laser Gyroscope," Keimpe Andringa inventor, issued June 26, 1973 and assigned to the same assignee as the present invention, a laser ring resonator supports four optical waves, each one of such waves having a different frequency, one pair thereof traveling in a clockwise direction and the other pair thereof traveling in a counterclockwise direction. The optical pathlengths of the waves are such that the pair of frequencies of the waves traveling in one direction, say the counterclockwise direction, is positioned between the frequencies of the waves traveling in the opposite, or clockwise, direction.
Having established this frequency relationship, movement of the laser resonator, for example by rotation of the system about an axis perpendicular to the optical path, produces frequency shifts of the pair of waves propagating in one direction through the laser which are opposite to frequency shifts of the waves moving in the opposite direction through the laser. This, in turn, produces changes in the frequency separation between the lower frequencies of each of said pair oppositely to a change in the frequency separation between the higher frequencies of each of said pairs. The difference between such changes is, substantially, a linsar function of the rate of said rotation and the relative sense of such difference is indicative of the direction of said rotation.
As described in the referenced U. S. Patent No. 3,741,657, `~ 30 such frequency separation results from disposing in the path .
-, - ~, .- ~ . . . . . .
of the waves a polarization dispersive structure which comprises a solid medium Faraday rotator and a crystal rotator. The crystal rotator is an anisotropic medium which restricts the type of polarization of the waves which may be supported in the ring laser to substantially circular polarization and also provides a dif-ferent optical pathlength for right-hand sense circularly polarized ~-waves than for left-hand sense circularly polarized waves. The solid medium Faraday rotator is a nonreciprocal device and pro-vides different time delays to waves of each polarization sense passing in the laser ring in one direction from those of such polarization ~ense passing in the opposite direction. The combina-tion of the crystal rotator and solid medium Faraday rotator ; provides the four-frequency relationship discussed above.
While the described polarization dispersive structure has been found satisfacto~r in many applications, the use of a crystal rotator and solid medium Faraday rotator increases loss and scatter imparted to the propagating waves and introduces linear birefringence to the ring resonator thereby reducing the accuracy of a laser gyroscope using such polarization dispersive structure.
.' , . .
, - .
.~ ~ . .. .. .
Summary of the Invention According to the present invention an electromagnetic wave ring resonator includes means for spatially rotating the electromagnetic field distribution of electromagnetic waves resonant in such resonator about the direction of propagation of such waves, and means, including an amplifier medium, for providing different indices of refraction to waves of the same polarization sense passing through such amplifier medium in different direc-tions. With such arrangement such rotating means provides a phase difference between waves of opposite polarization sense and, together with the last mentioned means, enables such waves to resonate with four different fre- -quencies.
In accordance with the invention there is provided in combination:
(a) an electromagnetic wave ring resonator wherein resonant electromagnetic waves propagate through a non-solid medium, such resonator including an amplifier medium; (b) means, included in such ring resonator, for spatially -rotating the electromagnetic field distribution of the resonant electro- ~
magnetic waves as such waves pass through the non-solid medium about the ~ -direction of propagation of such wave~ to enable such electromagnetic waves .
in such resonator to resonate with different frequencies; and (c) means, including the amplifier medium, for providing different indices of refraction to waves of the same polarization sense passing through such medium in differ-ent directions.
~; In accordance with another aspect of this invention there is pro-.~ .
vided a four frequency ring laser resonator comprising: (a) a laser amplifier medium; (b) means for producing different frequencies in such resonator from waves with opposite senses of circular polarization; and (c) means for ,: :
providing substantially different indices of refraction in said laser ampli-;~ fier medium to waves passing through such laser amplifier medium in different directions.
In a preferred embodiment a laser ring resonator includes a plurality~of reflectors positioned in the path of the laser to spatially rotate the electromagnetic field distribution of the laser waves resonant therein and thereby provide a predetermined phase alteration to the waves resonant therein. Such phase alteration correspondingly alters the resonant frequency of each one of such waves in the ring resonator without requiring an anisotropic crystal rotator in such path to alter the optical pathlength of such laser. Since the phase alteration sense is opposite for opposite for opposite senses of circular polarization, such arrangement enables waves of opposite polarization sense to resonate at separate frequencies. The reflectors are preferably oriented to provide a ~ radian phase difference between right and left-hand circularly polarized waves. The use of the Zeeman 10effect in the amplifier medium further reduces the loss and scatter in the resonator by eliminating a solid medium Faraday rotator and more efficiently provides different optical pathlengths for waves of the same polarization sense pa:sing throagh such medium in :
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~ .
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. . . - - - . . . - .
, . ~ , . . . . .
~: ~ - . , : . - .
1~7760Z`
- opposite directions because the magnetic field vector of such waves interacts with the precessing atomic magnetic dipoles of the ampli~ier medium.at the emission frequency of such amplifier medium.
, ,; .
.
,,. :
i ' .
:
~ 4 ~ ' '"
. ~ . . . . . . .. . . .
- . , 10~760Z
Brief Description of the Drawings .
Other and further features and advantages of the invention will become apparent as the description thereof progresses, reference being made to the accompanying drawings wherein:
FIG. 1 illustrates a diagrammatic view of a ring resonator embodying the invention;
FIGS, 2A-2C are sketches useful in understanding the invention;
FIGS. 3A-3C are diagrams useful in understanding the operating characteristics of the system illustrated in FIG. l; and FIG. 4 illustrates a diagrammatic view of an alternative embodiment of a ring resonator according to the invention.
, Description of the Preferred Embodiments Referring now to F~G. 1 there is shown a laser gyrosco~e system 9 having a laser amplifier medium 10 there a helium-neon 3 22 2~
laser medium having a gas mixture: 8 He ~ 0.48 Ne + 0.52 Ne.
A ring laser resonator includes. an even number of reflectors, here six reflectors 12, 14, 16, 18, 20, 22 (suitably mounted, by means not shown, to the surface of a platform 23) which produce a ring path for the laser beams. It is here noted that, as will be described later in connection with FIG. 4, the desired ring path . 10 may be produced by as few as four properly positioned reflectors.
I~owever, the six reflector system will first be discussed in order to establish the principle of operation of the laser gyroscope .
system. Considering the laser beam produced at end 24 of tl-e laser amplifier medium 10, such beam travels along the +~
direction (i.e. along the longitudinal axis of the laser ampli.fier medium 10) through an isotropic medium, preferably subs~antially free space, and is first reflected by reflector 12. The reflector 1 12 has its reflecting surface oriented such ~hat the laser bealn is reflected vertically a distance d along the +Y directiosl to reflector 14. Reflector 14 has its reflective surface ori~nted ~j such that the beam incident thereon becomes reflected hori%ontallya distance d along the -X direction to reflector 16. Reflector 16 has its reflecti~e surface oriented so that the beam incident l~ thereon becomes reflected vertically a distance d along tlle -Y
1~: direction to reflector 18. Reflector 18 has its reflective surfaceoriented so that the beam incident thereon becomes reflected ~: horizontally a distance d along the -X direction to reflector Z0.
It is here noted that the beam passing from end 24 of laser ~ a plifier med~um 10 to reflector 12 and the beam passing from ,~ 30 ~eflector 18 to reflector 20 are orthogonal to each other and : - 6 -. .. . . , - . , . . - . , - - . ~ ~ ~
10'7760Z
define a common horizontal plane 26. The surface of the platform 23 is disposed in a plane parallel to the horizontal plane 26.
~herefore, the beams passing from reflector 12 to reflector 14 to reflector 16 to reflector 18 are disposed in a ~ertical plane.
Continuing, reflector 20 has its reflective surface orientcd so - that the beam incident thereon is reflected to reflector 22, the incident beam and the reflected beam being disposed in the horizontal plane 26 and having an included angle here of 60 degrees, Reflector 22, here having a concave surface to aid in concentrating the laser beam through the laser amplifier metliu~ 10 (i.e. to aid in establishing a resonant transverse mode), has its reflective surface oriented so that the beam incident thereon is reflected again along the longitudinal axis of the laser ampl;fier ,medium 10, as shown, such incident and reflected ~eams ~e;ng disposed in the horizontal plane 26 and having an included angle he~e of 30 degrees. The distance between reflectors 22 and 12 along the ~Z axis is d .
It is here noted that, for purposes of explanation, the fol , lowing description neglects the effect of 180 phase changes impartcd to an electric field component upon reflection by a reflector. Such consideration is appropriate here becau~e the ring resonators described herein include an even number of reflectors in the path of the resonant waves and hence the effect of such phase changes cancel upon traversal of the waves through the ring resonator.
Considering the beam produced at end 24 of laser amp],ifier medium 10 and traveling along the +Z axis to have an electric field component B , disposed along the ~X axis, such electric field component remains along the +X axis after re~lection by ~' 30 reflector 12, then be~omes oriented along the ~Y axis to the 11~77602 electric field component E " because of reflector 14, then he-comes oriented along the -X axis because of reflector 16, then becomes oriented along the -Y axis because of r~flector 18 and remains so oriented when it returns to end 24. The effect of the reflectors 12-22 on the orientation of such electric fie]d component E is to rotate into such component -90 degrees al)out the beam axis (i.e. the ~Z axis) to the electric field component .
Considering now the beam produced at the end 24 of la.ser amplifier medium 10 and traveling along the ~Z axis to have an electric field component, E , disposed along the ~Y axis, sncl-l component first becomes oriented along the +Z axis ~to electri.c , field component E ") because of reflec~or 12, remains ori.cnted along the ~Z axis after reflections by reflectors 14, lG a]l~l 18 then becomes disposed in the X-Z plane at a -30 angl.e wi.th respect to the +X axis (to electric field component F, "') an(l then, after reflection by reflector 22, becomes oriented a]ong .. the +X axis at the end 24 to electric field componellt h '. l'he effect of the reflectors 12-22 on the orientation of sucll c].cctric field component E is to rotate such component -90 degrees a~)out the beam axis. The effect of a passage around the ring may thus .
be symbolized: ~
E ~ E ' a ~E
1 1 2, : E ~ E ' ~ E
2 2 1 - -:The effect of réflectors 12, 14, 16, 18, 20, 22 then is to :~ rotate the electromagnetic field distribution of waves p~ssing around the ring resonator -90 degrees in the plane orthogona,l to .
:~ ,the optical path of such waves. The electromagnetic field .
' distribution ~efers to bo~h the intensity and direction (i.e.
~: . .
. . . ~, - , ~ .
polarization or electric field vector) of an electromagnetic wave at a point in space. For example, if the electromagnetic field distribution of waves produced by the laser amplifier medium 10 has, in the plane P, isophotes (lines 25 of equal intensity) which are elliptically shaped having vertical major axes and vertically oriented electric field components 27 as represented in : FIG. 2A, the effect of the reflectors 12-22 is (1) to rotate the electromagnetic field distribution so that such electric field components and the major axis of the isophotes are oriented horizontally (as shown in FIG. 2B) and (2) to distort such di.s-tribution because of diffraction and because of the concave surface of reflector 22, as shown in FIG. 2C. It is noted that in order for waves to resonate, that is, be a stable mode of tlle ring resonator, such waves, after passing once around SUC}l resonator, must return to a given point with their origi.na].
electromagnetic field distribution. ~lowever, in genera]., n~i.tller the shape of the isophotes nor the polarization (electric field direction) in a given plane will remain unchanged in such l).l.nne after passing once around the resonator. Waves having a re~uency : 20 which is capable of being a resonant frequency will acqui.rc an !:
intensity distribution for which the diffraction of the waves and the focusing of reflector 22 are balanced so that the waves which are resonant have the same intensity distribution upon transversal of the resonator. However, only for circularly polarizcd waves is the polarization also able to re~urn to its initial sta~e after one traversal. Thus, the only self-consistent electromagnetic field distribution ~hich may exist in the resonator is that of waves having circular polarization. The isophotes of such resonant waves will acq~ire a shape which enables support of such circularly polarized waves in the ring resonator. Further, if the' circular polarization of such waves has a right^hand sense polarized component, i.e.
_, ~ ~ i~/2 -i~t r 1 2 ] e the effect of the reflectors 12-22 is to transform such component : into /2 i2~L/A -i~t E ' ~ ~E ' + E 'e ~ e e r 1 2 , i~/2 i2~L/A -i~t ~-E ~ E e ] e e i~/2 i2~L/A E
e e r where L is the length of the path around the ring, measured along the beam axis.
I the circular polarization of such waves has a left-hand sense polarization component, i.e.
/2 -i~t EQ ~ ~El ~ E2e ~ e the effect o a passage around the ring is to transform it to ~ /2 i2~L/A -i~t E ' ~ ~B ' ~ E ' e ~ e e ~, 1 2 -/2 i2~L/A -i~t ~-E ~ E e ~ e . e -i~/2 i2~L/A , e .e E~
~ ~ .
.
.
1~77602 .- The relative phase dif~erence between ~he left and right-hsnd components is, then, .
i~/2 i2~L/A -i~/2 i2~L/A
[e e ~/[e e +lrr
:~ ,the optical path of such waves. The electromagnetic field .
' distribution ~efers to bo~h the intensity and direction (i.e.
~: . .
. . . ~, - , ~ .
polarization or electric field vector) of an electromagnetic wave at a point in space. For example, if the electromagnetic field distribution of waves produced by the laser amplifier medium 10 has, in the plane P, isophotes (lines 25 of equal intensity) which are elliptically shaped having vertical major axes and vertically oriented electric field components 27 as represented in : FIG. 2A, the effect of the reflectors 12-22 is (1) to rotate the electromagnetic field distribution so that such electric field components and the major axis of the isophotes are oriented horizontally (as shown in FIG. 2B) and (2) to distort such di.s-tribution because of diffraction and because of the concave surface of reflector 22, as shown in FIG. 2C. It is noted that in order for waves to resonate, that is, be a stable mode of tlle ring resonator, such waves, after passing once around SUC}l resonator, must return to a given point with their origi.na].
electromagnetic field distribution. ~lowever, in genera]., n~i.tller the shape of the isophotes nor the polarization (electric field direction) in a given plane will remain unchanged in such l).l.nne after passing once around the resonator. Waves having a re~uency : 20 which is capable of being a resonant frequency will acqui.rc an !:
intensity distribution for which the diffraction of the waves and the focusing of reflector 22 are balanced so that the waves which are resonant have the same intensity distribution upon transversal of the resonator. However, only for circularly polarizcd waves is the polarization also able to re~urn to its initial sta~e after one traversal. Thus, the only self-consistent electromagnetic field distribution ~hich may exist in the resonator is that of waves having circular polarization. The isophotes of such resonant waves will acq~ire a shape which enables support of such circularly polarized waves in the ring resonator. Further, if the' circular polarization of such waves has a right^hand sense polarized component, i.e.
_, ~ ~ i~/2 -i~t r 1 2 ] e the effect of the reflectors 12-22 is to transform such component : into /2 i2~L/A -i~t E ' ~ ~E ' + E 'e ~ e e r 1 2 , i~/2 i2~L/A -i~t ~-E ~ E e ] e e i~/2 i2~L/A E
e e r where L is the length of the path around the ring, measured along the beam axis.
I the circular polarization of such waves has a left-hand sense polarization component, i.e.
/2 -i~t EQ ~ ~El ~ E2e ~ e the effect o a passage around the ring is to transform it to ~ /2 i2~L/A -i~t E ' ~ ~B ' ~ E ' e ~ e e ~, 1 2 -/2 i2~L/A -i~t ~-E ~ E e ~ e . e -i~/2 i2~L/A , e .e E~
~ ~ .
.
.
1~77602 .- The relative phase dif~erence between ~he left and right-hsnd components is, then, .
i~/2 i2~L/A -i~/2 i2~L/A
[e e ~/[e e +lrr
3 e or 180 degrees Further, it should be noted that the effect of re~lectors 12-2Z
is to alter the phase of the wave passing through the resonator, here +~/2 for right-hand sense polarized waves and -~/2 for left-hand sense polarized waves. Because the optical pathlengths of the waves in the resonator are the same, as neither wave passes through a medium (here neglecting the effect of the permanent magnet 30 in order to understand the function of reflectors 12-22) to alter such optical pathlength, the ~hase ~ - alteration provided by such reflectors 12-22 correspondingly : alters the resonant frequencies of suc.h waves, the resonant frequencies of the waves of different sense of ~olari.zati.on altering oppositely. The result is that the waves of right-}land zo sense polarization will have a-resonant frequency dif~erellt from . the resonant frequency of the left-hand sense polarized waves.
This effect may be understood by considering a right-hand sense ; polarized wave to be represented as:
B - R ~e ] ~ X cos (~S-~t)-Y sin (~S-~t) .~: R e R
where X, Y and Z are orthogonal unit vectors, S being me~sured along the direction of propagation of the wave, ~ being the angular rotational rate of the electric ield vector and 30 ~ a 2~ f/c ~ 2~/A where f and A are the frequency and wavelength, respecti~ely, of such wave and c is the velocity of light.
~(~776~2 In order for such wave to resonate in a resonator, without an electromagnetic field dis~ribution rotation means, having . .
optical pathlength L, ~ and L must satisfy the following:
~ L ~ 2n~ (where n is an integer) and hence the resonant frequencies of such waves are f - nc/L
The effect of rotating the electric field vector of such a wave in the manner described above in connection with FIG. 1 is, as described, to change the phase of such wave and hence sucll .
phase altered wave may, for right-hand sense polarization, be represented by E ' ~ Re~e '] ~ X cos~S-~t + ~/2) R R
-Y sin(~S-~t + ~/2) Por resonance, ~ and L must then satisfy ~ L ~ ~/2 - 2n~, and therefore the resonant frequencies of such wave have been changed to f ' where : f .' - c/2~L (2n~ - ~/2) Considering left-hand sense polarized waves, it follows that ~: 20 such resonant frequency will change, because of the electric field rotation described above, to f ~ a c/2~L (2n~ t ~/2) In summary, then, a phase alteration of ~ ~radians) of : opposite sense for opposite polarization senses correspondi.ng].y , ~; separates the resonant frequencies of opposite sense polarized :.
waves by f ~ c/2~L (2~) It further follows that such reflectors lZ-22 have a reci~rocal effec~; that is, the phase delay will be effected for wa~es exiting ~t end 24 of ~he.laser ampliier medium 10 along the +Z axis, (i.e.
: - ~a - -clockwise) and for waves entering such end 24 along the -Z axis (i.e. counterclockwise).
, .
.
, ~ .
~ ~ .
, ~ ~
, ~: , , ~
~:
. . . . , . . . . . -? . .... .. ': . . . . . .
A permanent magnet ~0 is here mounted, by any convcnient means, not shown, around the laser amplifier medium lO to produce a magnetic field H ~here in the order of 100 gauss (i.e. substan-tially greater than the earth's magnetic field and other stray magnetic fields)) parallel to the -Z axis, as shown, t]lrough tl~e laser amplifier medium. It is noted that, alternatively, such magnetic field H may be produced by encircling such medium 10 with a coil of wire and passing through such wire a suita~le amount of current supplied from a conventional direct current supply source. Such magnetic field causes a precession of the atomic magnetic dipoles of the helium-neon atoms in the laser amplifier medium which react with the waves passing therethrollgh in accordance with the sense of rotation of the magnetic vector component of such circularly polarized electromagnetic waves. In particular, if the sense of rotation of such magnetic vector is the same as the sense of rotation of the precessing atomic m~gnetic dipoles of the helium neon atoms the index of refraction provi~ed to the passing wa~es by such medium 10 under the influence of the magnetic field H will be different from the index of refr.lction provided to passing waves which have a magnetic vector sense of rotation opposite to the sense of rotation of the precessing atomic magnetic dipoles. The described effect has been discu~ed in "Zeem&n Effect In Gaseous Helium-Neon Optical Maser" by H. Statz, R. Paananen and G. F. Koster, Journal of Applied rllysics, Vol. 33, No. 7, pgs. Z319-2321, ~uly 1962, "Zeeman Effects in Gaseous He-Ne Optical Masers" by R. Paananen, C. L. Tang and --H. Statz, Proceedings of the IEEE, Vol. 51, No. 1, January 1963;
and U. S. Patent No. 3,277,396, "Means For Modulating a La~er", inventors H. Statz and R. A. Paananen, issued October 4, 1966 and assigned to the same assignee as the present in~ention~ As .~ ' .
;, . . . .
discussed therein, the effect of the magnetic field ~1 on the laser amplifier medium is to separate the resonant frequencies of right and left-hand circularly polarized waves passing through such medium in the same direction relative to the direction of the magnetic field H, as amount ~F, where ~F Y ~ 'c h where:
g - Lande' g-ratio ~gyromagnetic ratio) ~v 1.3 B - Bohr magneton h 3 Planck's constant c ~ half width of the laser cavity resonance, /Q, where f is the frequency of the o o 14 laser amplifier medium, 10, here ~ 4.74 X 10 IIZ
and Q is the quality factor of the resonator, here ~ 108;
the half width of a neon laser line ~C 1 GIIZ.
Ne Therefore, for a magnetic field, ~I, of 100 gauss, ~P ~ 868 KH~.
In this regard a preferable range for ~F is lO0 Kc to 1.0 MHz.
As described above in connection with FIG. 1, reflectors 12-22 may be considered as enabling waves of opposite circlllar polarization sense to resonate with different frequencies f ,f (FIG. 3A). While the effect of the magnetic ~ield H on the ~: laser amplifier medium 10 is.to provide different indices of refraction to waves having opposite senses of circular polariza-tion an~ passing through such medium 10 in the same direction, the change in the index of refraction for waves having one sense of ~
circular polarization passing in the ring resonato~ in one -direction, say clockwise, i the same as for waves having the : ~ - 15 ^
- .: - . - . : . : , opposit0 sense of circular polari~ation passing through such resonator in the counterclockwise direction. The effect of such magnetic field H then may be considered as "splitting" each one of oppositely polarized waves having frequencies f and f into a b two frequencies, f ', f ", f ', f ", where I '~f "
a a b b a a If '-f "I, the waves of frequencies f ', f ' having opposite circular polarization senses and travelin~ in one direction, say counterclockwise, in the ring resonator and ~he waves of frequency f ", f " also having opposite circular polarization senses but traveling in the ring resonator in the clockwise direction. That is, waves having the same sense of circular polarization traveling in opposite directions in the ring resonator will have different resonant frequencies due to the Zeeman effect. Therefore, thc combination of the reflectors 12-22 and the magnetic field ll in the laser amplifier medium 10 is such that the ring resollator supports waves having frequencies of oscillation as shown in FIG. 3C, the two waves 32, 34 traveling, say clockwise, and two waves 36, 38 traveling, say counterclockwise, ~he two wave~
traveling clockwise havîng opposite sense circular polarizatioil and the two waves traveling counterclockwise also haviIlg opposite sense circular polarizations. These frequencies are shown as positive or negative differences from the center of maximum gain frequency of the laser amplifier medium 10 ~FIG. 3C).
It is here noted that the different indices of refraction provided to the waves by the interaction of the magnetic vector rotation of such waves and the sense of rotation of;~he atomic magnetic dipoles of the helium-neon atoms is greatest near tl~e emission line of the laser amplifier medium. Similarly, the Faraday effect in producing different indices of refraction for waves of opposite polarization sense is greatest near the ... . . . . . . ... . . . . .. . ..
absorption lines (or band) of the medium used therein, SlJCh a~s the abssrption lines of a quartz crystal if such is used in the Faraday rotator. However, the resonant frequencies of the waves to which such effect is impressed on is generally substantially different from the absorption line of the medium used in the Faraday rotator. In the resonator herein described, however, the resonant frequencies of the waves in the resonator are suhstan-tially the same as the frequency of the emission line of the laser medium and hence the use of the laser amplifier medium, as described, provides more efficient separation in the frequencies of waves of opposite polarization sense than the use of a quartz crystal medium for such frequency separation.
~, . .
' - . - . . . . - ~
.. . .. . ,-. . . ,,, .. . - ,. :
. . ~ : ................... . . .
Mirror 20 is here partially transmissive (typically 1ess than0.1 percent) to enable a po~tion of the waves traveling clockwise and the w`aves traveling counterclockwise to pass to the stabiliza-tion system and utilization device 40. Alternatively, specular reflections from the surfaces of the various components in the resonator may be directed, by any conventional optical means (not shown), to such stabilization system and utilization device 40.
Here such device 40 includes a diferential amplifier (not shown) to produce an electrical signal for a piezoelectric element 41 suitably affixed to the reflector 22 to control the positioll of reflector 22 thereby to maintain the four frequencies symmetri-cally about the center maximum gain frequency curve o~ the laser amplifier medium 10 and also includes counters (not shown) for providing an indication of the rotational rate of the laser resonator about the gyroscope axis. Such stabilization system and utilization device 40 is described in the referenced U. S.
Patent No. 3,741,657.
It is here noted that two different isotopes of neon arc u~ed in the laser amplifier medium 10, i.e. 22Ne and ONe. Two different isotopes of lasing medium are pro~ided so that eacll one of the four waves interacts with a different set of the atoms of the lasing medium, i.e. atoms with differènt velocities, w11en the `~ cavity length is stabilized to maintain the four frequencies symmetrically about the center maximum gain curve of the laser amplifier medium. In this regard, the 20Ne isotope constit~ltes , 52~ of the neon atoms in order to compensate for its lesscr atomic weight. That is, in order for the maximum gain associated with a composite laser medium to be half way between the resonant frequencies associated with the two isotopesl, a greater percentage ~ 30 of Ne is used (i.e. 52~) as compared with 22Ne (i.e. 48%).
-~ - 18 -With this arrangement the different sets of atoms interacting with corresponding ones of the four waves will have maximum isolation from each other.
The orientation of the gyroscope axis is along the vector G.
Such vector G is calculated by the following line integral:
G -~ r X dr ..
where dr is the direction of travel along the path at a point on such path and r is the position vector of such point. Consi~lering the ring resonator described in FIG. 1, it is noted that SUCIl waves in the resonator pass in two orthogonal planes, i.e. the horizontal plane 26 and the vertical plane. The area enclosed in the hori-.: .zontal plane is A - 1/2td Id )d . The area enclosed in the . . l 2 3 4 ~ertical plane is A ~ d d . The gyroscope axis then is along the vector G where ~ ~ ~ [+A Y - A Z]
: . : 1 2 Referring now to FIG. 4 a laser ring resonator here inc].udes laser amplifier medium 10 and four reflectors, i.e. reflectors 42, 44, 46, 48 positioned as shown to enable such resonator to ~up~ort waves having circular polarization and so that right-hand sense 20: circularly polarized waves have a different phase alterati.on than the left-hand sense circularly polarized waves, such laser ~mpli- .
fier medium 10 and reflectors 42-48 being suitably mounted l~y conventional means (not shown) to a platform 49. A permanellt magnet 30 is included to enable such laser resonator to sup~ort ; ~ :
cîrcularly polarized waves having four different frequenci.es : thereby enabling such apparatus to be used as a four frequency : : ~
laser as:described in connection with FIG. 1. Also, stabili7.ation : systom and utilization device 40 is included to control the ~osi-tion;of refl~ecto.r 42 (sbch reflector 42 having a piezoelectric 30~ element 41 mounted.thereto). by responding to the portion of the , . . . . .
,~ ~ . . .
, ............ . . . . ... . .. . . .
waves passing throu~h reflector 44, as discussed in connection with FIG. 1.
It is noted that the laser waves incident on and reflected by reflector 42 (here having a concave surface~ are disposed in a plane 45 parallel to the plane o the platform 49. Consideri.ng the waves produced at the output of end 43 of laser medium ].0, reflector 44 directs the beam incident thereon out of the ~ ne 45 to reflector 46. Reflector 46 directs the beam incident thereon to reflector 48, the latter reflector redirecting such beam along the longitudinal axis of the laser amplifier medium lO in the plane parallel to the plane of the platform 49 (as shown). 'rha~
is, segments A and B are disposed in the plane parallel to 1:he plane of the platform 49 and segments C and D are disposed in a plane which intersects the plane of platform 49.
The reflectors 42-48 are oriented to rotate the electro-magnetic field distribution of the waves resonant in the rinlr laser -~/2 radians about the direction of propagation of such waves as such waves traverse the ring resonator. In or(1Or t-~
;~ ~
determine the proper orientation of such reflectors it may be helpful to analyze the ref~ections produced by pairs o rcf1~Gtors 42-48. First, considering reflectors 46 and 48, it sl1oll]rl 1-e ~; noted that the surfaces of such reflectors are disposed in two ` ~ intersecting planes, 60, 62, (shown in phantom) respectively.
Such planes intersect along a dihedral axis 64 and form a ,~ ~
dihedral angle Y. The dihedral axis is disposed along the Ul1it : vector r. As is known, two successive reflections of an i.mage are equivalent to a rotation of such image through an angle 2 ~
about the dihedral axis formed by the intersecting planes in which the surfaces of.such reflectors are disposed. That is, if the normals to the surfaces of the reflectors a~e n and n , l 2 .. :. . . --- ,-107760~
: respectively, r sin~ - n X n Referring again to FIG. 4, reflectors 46, 48 are orientcd so that the waves passing in segment C of the ring resona~or arc, after reflection by such reflectors 46, 48, directed along tll~
longitudinal axis of the laser medium 10 when such waves pass in segment A (between reflectors 42 and 48) of such resonator (~s shown). With such orientation of reflectors 46, 48 the electro-magnetic field distribution of waves in segment C will, in seglllent A, be rotated by such reflectors 2~ degrees about the unit vector r. Similarly, a dihedral angle and axis direction is associated with reflectors 42 and 46, and the electromagnetic field distribu-: tion of waves in segment A will, in segment C, be add.itionally ;~ rotated in accordance with such angle and axis direction. In order to effectuate a -~/2 radian rotation of the electromagne~ic ri~ld .. distribution about the direction of propagation thereby to ~rovide a ~ radian phase difference between right and left-hand circularly . polarized waVes, such re1ectors 42-48 may have the followi.ng orientations:
~ 20 Reflector Direction Cosine of .: Normal to Surface of rl~ce~r_ `: X Axis Y Axis Z Axis 42 0.866413 -.499328 0.0 44 .003688 .999298 .037273 46 -.209766 -.722611 -.658659 :~ . 48 -.769676~.164503 l.616877 . ~, . .
.~ It is noted that with such orientation reflectors 42 alld 44 . . .
is to alter the phase of the wave passing through the resonator, here +~/2 for right-hand sense polarized waves and -~/2 for left-hand sense polarized waves. Because the optical pathlengths of the waves in the resonator are the same, as neither wave passes through a medium (here neglecting the effect of the permanent magnet 30 in order to understand the function of reflectors 12-22) to alter such optical pathlength, the ~hase ~ - alteration provided by such reflectors 12-22 correspondingly : alters the resonant frequencies of suc.h waves, the resonant frequencies of the waves of different sense of ~olari.zati.on altering oppositely. The result is that the waves of right-}land zo sense polarization will have a-resonant frequency dif~erellt from . the resonant frequency of the left-hand sense polarized waves.
This effect may be understood by considering a right-hand sense ; polarized wave to be represented as:
B - R ~e ] ~ X cos (~S-~t)-Y sin (~S-~t) .~: R e R
where X, Y and Z are orthogonal unit vectors, S being me~sured along the direction of propagation of the wave, ~ being the angular rotational rate of the electric ield vector and 30 ~ a 2~ f/c ~ 2~/A where f and A are the frequency and wavelength, respecti~ely, of such wave and c is the velocity of light.
~(~776~2 In order for such wave to resonate in a resonator, without an electromagnetic field dis~ribution rotation means, having . .
optical pathlength L, ~ and L must satisfy the following:
~ L ~ 2n~ (where n is an integer) and hence the resonant frequencies of such waves are f - nc/L
The effect of rotating the electric field vector of such a wave in the manner described above in connection with FIG. 1 is, as described, to change the phase of such wave and hence sucll .
phase altered wave may, for right-hand sense polarization, be represented by E ' ~ Re~e '] ~ X cos~S-~t + ~/2) R R
-Y sin(~S-~t + ~/2) Por resonance, ~ and L must then satisfy ~ L ~ ~/2 - 2n~, and therefore the resonant frequencies of such wave have been changed to f ' where : f .' - c/2~L (2n~ - ~/2) Considering left-hand sense polarized waves, it follows that ~: 20 such resonant frequency will change, because of the electric field rotation described above, to f ~ a c/2~L (2n~ t ~/2) In summary, then, a phase alteration of ~ ~radians) of : opposite sense for opposite polarization senses correspondi.ng].y , ~; separates the resonant frequencies of opposite sense polarized :.
waves by f ~ c/2~L (2~) It further follows that such reflectors lZ-22 have a reci~rocal effec~; that is, the phase delay will be effected for wa~es exiting ~t end 24 of ~he.laser ampliier medium 10 along the +Z axis, (i.e.
: - ~a - -clockwise) and for waves entering such end 24 along the -Z axis (i.e. counterclockwise).
, .
.
, ~ .
~ ~ .
, ~ ~
, ~: , , ~
~:
. . . . , . . . . . -? . .... .. ': . . . . . .
A permanent magnet ~0 is here mounted, by any convcnient means, not shown, around the laser amplifier medium lO to produce a magnetic field H ~here in the order of 100 gauss (i.e. substan-tially greater than the earth's magnetic field and other stray magnetic fields)) parallel to the -Z axis, as shown, t]lrough tl~e laser amplifier medium. It is noted that, alternatively, such magnetic field H may be produced by encircling such medium 10 with a coil of wire and passing through such wire a suita~le amount of current supplied from a conventional direct current supply source. Such magnetic field causes a precession of the atomic magnetic dipoles of the helium-neon atoms in the laser amplifier medium which react with the waves passing therethrollgh in accordance with the sense of rotation of the magnetic vector component of such circularly polarized electromagnetic waves. In particular, if the sense of rotation of such magnetic vector is the same as the sense of rotation of the precessing atomic m~gnetic dipoles of the helium neon atoms the index of refraction provi~ed to the passing wa~es by such medium 10 under the influence of the magnetic field H will be different from the index of refr.lction provided to passing waves which have a magnetic vector sense of rotation opposite to the sense of rotation of the precessing atomic magnetic dipoles. The described effect has been discu~ed in "Zeem&n Effect In Gaseous Helium-Neon Optical Maser" by H. Statz, R. Paananen and G. F. Koster, Journal of Applied rllysics, Vol. 33, No. 7, pgs. Z319-2321, ~uly 1962, "Zeeman Effects in Gaseous He-Ne Optical Masers" by R. Paananen, C. L. Tang and --H. Statz, Proceedings of the IEEE, Vol. 51, No. 1, January 1963;
and U. S. Patent No. 3,277,396, "Means For Modulating a La~er", inventors H. Statz and R. A. Paananen, issued October 4, 1966 and assigned to the same assignee as the present in~ention~ As .~ ' .
;, . . . .
discussed therein, the effect of the magnetic field ~1 on the laser amplifier medium is to separate the resonant frequencies of right and left-hand circularly polarized waves passing through such medium in the same direction relative to the direction of the magnetic field H, as amount ~F, where ~F Y ~ 'c h where:
g - Lande' g-ratio ~gyromagnetic ratio) ~v 1.3 B - Bohr magneton h 3 Planck's constant c ~ half width of the laser cavity resonance, /Q, where f is the frequency of the o o 14 laser amplifier medium, 10, here ~ 4.74 X 10 IIZ
and Q is the quality factor of the resonator, here ~ 108;
the half width of a neon laser line ~C 1 GIIZ.
Ne Therefore, for a magnetic field, ~I, of 100 gauss, ~P ~ 868 KH~.
In this regard a preferable range for ~F is lO0 Kc to 1.0 MHz.
As described above in connection with FIG. 1, reflectors 12-22 may be considered as enabling waves of opposite circlllar polarization sense to resonate with different frequencies f ,f (FIG. 3A). While the effect of the magnetic ~ield H on the ~: laser amplifier medium 10 is.to provide different indices of refraction to waves having opposite senses of circular polariza-tion an~ passing through such medium 10 in the same direction, the change in the index of refraction for waves having one sense of ~
circular polarization passing in the ring resonato~ in one -direction, say clockwise, i the same as for waves having the : ~ - 15 ^
- .: - . - . : . : , opposit0 sense of circular polari~ation passing through such resonator in the counterclockwise direction. The effect of such magnetic field H then may be considered as "splitting" each one of oppositely polarized waves having frequencies f and f into a b two frequencies, f ', f ", f ', f ", where I '~f "
a a b b a a If '-f "I, the waves of frequencies f ', f ' having opposite circular polarization senses and travelin~ in one direction, say counterclockwise, in the ring resonator and ~he waves of frequency f ", f " also having opposite circular polarization senses but traveling in the ring resonator in the clockwise direction. That is, waves having the same sense of circular polarization traveling in opposite directions in the ring resonator will have different resonant frequencies due to the Zeeman effect. Therefore, thc combination of the reflectors 12-22 and the magnetic field ll in the laser amplifier medium 10 is such that the ring resollator supports waves having frequencies of oscillation as shown in FIG. 3C, the two waves 32, 34 traveling, say clockwise, and two waves 36, 38 traveling, say counterclockwise, ~he two wave~
traveling clockwise havîng opposite sense circular polarizatioil and the two waves traveling counterclockwise also haviIlg opposite sense circular polarizations. These frequencies are shown as positive or negative differences from the center of maximum gain frequency of the laser amplifier medium 10 ~FIG. 3C).
It is here noted that the different indices of refraction provided to the waves by the interaction of the magnetic vector rotation of such waves and the sense of rotation of;~he atomic magnetic dipoles of the helium-neon atoms is greatest near tl~e emission line of the laser amplifier medium. Similarly, the Faraday effect in producing different indices of refraction for waves of opposite polarization sense is greatest near the ... . . . . . . ... . . . . .. . ..
absorption lines (or band) of the medium used therein, SlJCh a~s the abssrption lines of a quartz crystal if such is used in the Faraday rotator. However, the resonant frequencies of the waves to which such effect is impressed on is generally substantially different from the absorption line of the medium used in the Faraday rotator. In the resonator herein described, however, the resonant frequencies of the waves in the resonator are suhstan-tially the same as the frequency of the emission line of the laser medium and hence the use of the laser amplifier medium, as described, provides more efficient separation in the frequencies of waves of opposite polarization sense than the use of a quartz crystal medium for such frequency separation.
~, . .
' - . - . . . . - ~
.. . .. . ,-. . . ,,, .. . - ,. :
. . ~ : ................... . . .
Mirror 20 is here partially transmissive (typically 1ess than0.1 percent) to enable a po~tion of the waves traveling clockwise and the w`aves traveling counterclockwise to pass to the stabiliza-tion system and utilization device 40. Alternatively, specular reflections from the surfaces of the various components in the resonator may be directed, by any conventional optical means (not shown), to such stabilization system and utilization device 40.
Here such device 40 includes a diferential amplifier (not shown) to produce an electrical signal for a piezoelectric element 41 suitably affixed to the reflector 22 to control the positioll of reflector 22 thereby to maintain the four frequencies symmetri-cally about the center maximum gain frequency curve o~ the laser amplifier medium 10 and also includes counters (not shown) for providing an indication of the rotational rate of the laser resonator about the gyroscope axis. Such stabilization system and utilization device 40 is described in the referenced U. S.
Patent No. 3,741,657.
It is here noted that two different isotopes of neon arc u~ed in the laser amplifier medium 10, i.e. 22Ne and ONe. Two different isotopes of lasing medium are pro~ided so that eacll one of the four waves interacts with a different set of the atoms of the lasing medium, i.e. atoms with differènt velocities, w11en the `~ cavity length is stabilized to maintain the four frequencies symmetrically about the center maximum gain curve of the laser amplifier medium. In this regard, the 20Ne isotope constit~ltes , 52~ of the neon atoms in order to compensate for its lesscr atomic weight. That is, in order for the maximum gain associated with a composite laser medium to be half way between the resonant frequencies associated with the two isotopesl, a greater percentage ~ 30 of Ne is used (i.e. 52~) as compared with 22Ne (i.e. 48%).
-~ - 18 -With this arrangement the different sets of atoms interacting with corresponding ones of the four waves will have maximum isolation from each other.
The orientation of the gyroscope axis is along the vector G.
Such vector G is calculated by the following line integral:
G -~ r X dr ..
where dr is the direction of travel along the path at a point on such path and r is the position vector of such point. Consi~lering the ring resonator described in FIG. 1, it is noted that SUCIl waves in the resonator pass in two orthogonal planes, i.e. the horizontal plane 26 and the vertical plane. The area enclosed in the hori-.: .zontal plane is A - 1/2td Id )d . The area enclosed in the . . l 2 3 4 ~ertical plane is A ~ d d . The gyroscope axis then is along the vector G where ~ ~ ~ [+A Y - A Z]
: . : 1 2 Referring now to FIG. 4 a laser ring resonator here inc].udes laser amplifier medium 10 and four reflectors, i.e. reflectors 42, 44, 46, 48 positioned as shown to enable such resonator to ~up~ort waves having circular polarization and so that right-hand sense 20: circularly polarized waves have a different phase alterati.on than the left-hand sense circularly polarized waves, such laser ~mpli- .
fier medium 10 and reflectors 42-48 being suitably mounted l~y conventional means (not shown) to a platform 49. A permanellt magnet 30 is included to enable such laser resonator to sup~ort ; ~ :
cîrcularly polarized waves having four different frequenci.es : thereby enabling such apparatus to be used as a four frequency : : ~
laser as:described in connection with FIG. 1. Also, stabili7.ation : systom and utilization device 40 is included to control the ~osi-tion;of refl~ecto.r 42 (sbch reflector 42 having a piezoelectric 30~ element 41 mounted.thereto). by responding to the portion of the , . . . . .
,~ ~ . . .
, ............ . . . . ... . .. . . .
waves passing throu~h reflector 44, as discussed in connection with FIG. 1.
It is noted that the laser waves incident on and reflected by reflector 42 (here having a concave surface~ are disposed in a plane 45 parallel to the plane o the platform 49. Consideri.ng the waves produced at the output of end 43 of laser medium ].0, reflector 44 directs the beam incident thereon out of the ~ ne 45 to reflector 46. Reflector 46 directs the beam incident thereon to reflector 48, the latter reflector redirecting such beam along the longitudinal axis of the laser amplifier medium lO in the plane parallel to the plane of the platform 49 (as shown). 'rha~
is, segments A and B are disposed in the plane parallel to 1:he plane of the platform 49 and segments C and D are disposed in a plane which intersects the plane of platform 49.
The reflectors 42-48 are oriented to rotate the electro-magnetic field distribution of the waves resonant in the rinlr laser -~/2 radians about the direction of propagation of such waves as such waves traverse the ring resonator. In or(1Or t-~
;~ ~
determine the proper orientation of such reflectors it may be helpful to analyze the ref~ections produced by pairs o rcf1~Gtors 42-48. First, considering reflectors 46 and 48, it sl1oll]rl 1-e ~; noted that the surfaces of such reflectors are disposed in two ` ~ intersecting planes, 60, 62, (shown in phantom) respectively.
Such planes intersect along a dihedral axis 64 and form a ,~ ~
dihedral angle Y. The dihedral axis is disposed along the Ul1it : vector r. As is known, two successive reflections of an i.mage are equivalent to a rotation of such image through an angle 2 ~
about the dihedral axis formed by the intersecting planes in which the surfaces of.such reflectors are disposed. That is, if the normals to the surfaces of the reflectors a~e n and n , l 2 .. :. . . --- ,-107760~
: respectively, r sin~ - n X n Referring again to FIG. 4, reflectors 46, 48 are orientcd so that the waves passing in segment C of the ring resona~or arc, after reflection by such reflectors 46, 48, directed along tll~
longitudinal axis of the laser medium 10 when such waves pass in segment A (between reflectors 42 and 48) of such resonator (~s shown). With such orientation of reflectors 46, 48 the electro-magnetic field distribution of waves in segment C will, in seglllent A, be rotated by such reflectors 2~ degrees about the unit vector r. Similarly, a dihedral angle and axis direction is associated with reflectors 42 and 46, and the electromagnetic field distribu-: tion of waves in segment A will, in segment C, be add.itionally ;~ rotated in accordance with such angle and axis direction. In order to effectuate a -~/2 radian rotation of the electromagne~ic ri~ld .. distribution about the direction of propagation thereby to ~rovide a ~ radian phase difference between right and left-hand circularly . polarized waVes, such re1ectors 42-48 may have the followi.ng orientations:
~ 20 Reflector Direction Cosine of .: Normal to Surface of rl~ce~r_ `: X Axis Y Axis Z Axis 42 0.866413 -.499328 0.0 44 .003688 .999298 .037273 46 -.209766 -.722611 -.658659 :~ . 48 -.769676~.164503 l.616877 . ~, . .
.~ It is noted that with such orientation reflectors 42 alld 44 . . .
4``':",."i ~ rotate the electromagnetic field distribution of propagati.n~ waves of one circular.polarization sense -4.300 deg~ees and reflectors 46, 48 rotate the electromagnetic field distrîbution o~ such waves , . ~
~ ~ - 21 -, i: .
., .
i, ~ .
~7760Z
-85.700 degrees, the total rotation being -90 degrees.
In such configuration, segment A is here 15.7 centimeters (cm.).
The optical pathlength around the ring resonator is here 50 cm.. Therefore, because the intermode spacing for resonant modes (for waves of a particular polarization), ~, is given hy ~v = c/l, where c is the velocity of light and 1 is the ol?tical pathlength.~ here equals 600 MIIz. Because the reflectors ~2-48 are arranged to provide a 180 phase difference between opl~ositely polarized waves, the frequency separation between such wav~s of opposite polarization is 300 MHz, that is, half the intermocl~
spacing, i.e. Qv/2. It is noted that the 180 phase differellce i,~ provides maximum separation between such oppositely pol~rJ%ecl~aves. Further, such separation varies from zerO to such m~ximllm as the phase difference varies from 0 to 180. As the phase difference increases from 180 to 360 the separation corres~ond-ingly varies from such maximum back to zero.
It is now readily apparent from the foregoing th~t tlle catoptric arrangement used to rotate the electromagnetic ficl-l distribution of the waves propagating through the ring resonat:or to establish circularly polarized waves of opposite pol~ri7,.ltion "
~; sense, each having a different resonant frequency, reduces the; loss and scatter associated with the resonator when compare(l to an~arrangement which includes an anisotropic crystal rotator to establish such different resonant frequency circularly polarized waves. Further, such catoptric arrangement reduces the amount of . ~ .
linear birefringence in the resonator by removing the anisotropic ~-~ crystal rotator and hence reduces the degree of ellipticity , ~
resulting there~rom on the propagating waves as compared with such aniso~ropic crystal rotator. Misalignment in the optic axis of ,,:
~ 22 -, ~ ~
. .
:.,. ' :. ~ ' ~ , ' -- . ." .
of such rotator may giYe rise to an undesirable residual elli~-ticity. Such residual ellipticity causes undesirable instabilities in a ring resonator having such crystal rotator~ The catoptric system herein described has thereby effectively eliminated this source of residual ellipticity and therefore reduces this in-stability. Further removal of the anisotropic medium of t11e crystal rotator eliminates the Fizeau-Fresnel drag effect on waves passing through such medium. Still further, the gain of thc resonator is improved by elimination of the loss attributable to ~0 the two relatively lossy anti-reflection coatings generally used on the surfaces of a crystal rotator and a solid medium l'ar.~d~y rotator.
Having described preferred embodiments of the illVCllt.i 0~1, it is now evident that other embodiments incorporating these concepts ~may be used. For example J other lasing media including other '~mixtures of neon isotopes may be used for the laser amplifi~r medium 10. It should, therefore, be clearly understood th~t the details of such embodiments are set forth by way o oxnm~ lly and it should be understood that it will now be readily ~pl-~rent ;-~20 to those of skill in the art that various changes in form ~nd detail thereof may be made therein without departing from the spirit an~ scope of the invention as defined by the appended claims~
'.. . .
, ~;
~ .
''.~ ''
~ ~ - 21 -, i: .
., .
i, ~ .
~7760Z
-85.700 degrees, the total rotation being -90 degrees.
In such configuration, segment A is here 15.7 centimeters (cm.).
The optical pathlength around the ring resonator is here 50 cm.. Therefore, because the intermode spacing for resonant modes (for waves of a particular polarization), ~, is given hy ~v = c/l, where c is the velocity of light and 1 is the ol?tical pathlength.~ here equals 600 MIIz. Because the reflectors ~2-48 are arranged to provide a 180 phase difference between opl~ositely polarized waves, the frequency separation between such wav~s of opposite polarization is 300 MHz, that is, half the intermocl~
spacing, i.e. Qv/2. It is noted that the 180 phase differellce i,~ provides maximum separation between such oppositely pol~rJ%ecl~aves. Further, such separation varies from zerO to such m~ximllm as the phase difference varies from 0 to 180. As the phase difference increases from 180 to 360 the separation corres~ond-ingly varies from such maximum back to zero.
It is now readily apparent from the foregoing th~t tlle catoptric arrangement used to rotate the electromagnetic ficl-l distribution of the waves propagating through the ring resonat:or to establish circularly polarized waves of opposite pol~ri7,.ltion "
~; sense, each having a different resonant frequency, reduces the; loss and scatter associated with the resonator when compare(l to an~arrangement which includes an anisotropic crystal rotator to establish such different resonant frequency circularly polarized waves. Further, such catoptric arrangement reduces the amount of . ~ .
linear birefringence in the resonator by removing the anisotropic ~-~ crystal rotator and hence reduces the degree of ellipticity , ~
resulting there~rom on the propagating waves as compared with such aniso~ropic crystal rotator. Misalignment in the optic axis of ,,:
~ 22 -, ~ ~
. .
:.,. ' :. ~ ' ~ , ' -- . ." .
of such rotator may giYe rise to an undesirable residual elli~-ticity. Such residual ellipticity causes undesirable instabilities in a ring resonator having such crystal rotator~ The catoptric system herein described has thereby effectively eliminated this source of residual ellipticity and therefore reduces this in-stability. Further removal of the anisotropic medium of t11e crystal rotator eliminates the Fizeau-Fresnel drag effect on waves passing through such medium. Still further, the gain of thc resonator is improved by elimination of the loss attributable to ~0 the two relatively lossy anti-reflection coatings generally used on the surfaces of a crystal rotator and a solid medium l'ar.~d~y rotator.
Having described preferred embodiments of the illVCllt.i 0~1, it is now evident that other embodiments incorporating these concepts ~may be used. For example J other lasing media including other '~mixtures of neon isotopes may be used for the laser amplifi~r medium 10. It should, therefore, be clearly understood th~t the details of such embodiments are set forth by way o oxnm~ lly and it should be understood that it will now be readily ~pl-~rent ;-~20 to those of skill in the art that various changes in form ~nd detail thereof may be made therein without departing from the spirit an~ scope of the invention as defined by the appended claims~
'.. . .
, ~;
~ .
''.~ ''
Claims (28)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In combination:
(a) an electromagnetic wave ring resonator wherein resonant electromagnetic waves propagate through a non-solid medium, such resonator including an amplifier medium;
(b) means, included in such ring resonator, for spatially rotating the electromagnetic field distribution of the resonant electromagnetic waves as such waves pass through the non-solid medium about the direction of pro-pagation of such waves to enable such electromagnetic waves in such resonator to resonate with different frequencies; and (c) means, including the amplifier medium, for providing different indices of refraction to waves of the same polarization sense passing through such medium in different directions.
(a) an electromagnetic wave ring resonator wherein resonant electromagnetic waves propagate through a non-solid medium, such resonator including an amplifier medium;
(b) means, included in such ring resonator, for spatially rotating the electromagnetic field distribution of the resonant electromagnetic waves as such waves pass through the non-solid medium about the direction of pro-pagation of such waves to enable such electromagnetic waves in such resonator to resonate with different frequencies; and (c) means, including the amplifier medium, for providing different indices of refraction to waves of the same polarization sense passing through such medium in different directions.
2. The combination recited in claim 1 wherein the rotating means includes a plurality of reflectors arranged to provide a phase difference between circularly polarized electromagnetic waves of opposite polarization senses to enable such waves of opposite polarization senses to resonate in such ring resonator with different frequencies.
3. The combination recited in claim 2 wherein such ring resonator includes a non-solid medium and wherein such rotating means rotates the electromagnetic field distribution of such resonant electromagnetic waves as such waves pass through such non-solid medium.
4. The combination recited in claim 3 wherein such rotating means includes a catoptric system for directing the electromagnetic waves through the non-solid medium.
5. The combination recited in claim 4 wherein a section of such resonant electromagnetic waves is disposed in a first plane and a second section of such resonant electromagnetic waves is disposed in a second, intersecting plane.
6. The combination recited in claim 5 including a laser amplifier medium disposed in the ring resonator.
7. In combination:
(a) an electromagnetic wave ring resonator including an amplifier medium;
(b) a plurality of reflectors, included in such resonator, for directing electromagnetic waves resonant in such resonator through a predeter-mined path as such waves pass through a non-solid medium, one section of such path being disposed in a first plane and a second section of such path being disposed in a second intersecting plane such plurality of reflectors being arranged to enable circularly polarized waves of opposite polarization senses to resonate in such resonator with different frequencies; and (c) means, including the laser amplifier medium, for providing different indices of refraction to waves of the same polarization sense pass-ing through such medium in different directions.
(a) an electromagnetic wave ring resonator including an amplifier medium;
(b) a plurality of reflectors, included in such resonator, for directing electromagnetic waves resonant in such resonator through a predeter-mined path as such waves pass through a non-solid medium, one section of such path being disposed in a first plane and a second section of such path being disposed in a second intersecting plane such plurality of reflectors being arranged to enable circularly polarized waves of opposite polarization senses to resonate in such resonator with different frequencies; and (c) means, including the laser amplifier medium, for providing different indices of refraction to waves of the same polarization sense pass-ing through such medium in different directions.
8. The combination recited in claim 7 wherein such directing means enables such resonant electromagnetic waves to resonate in such ring laser with circular polarization.
9. The combination recited in claim 8 wherein such ring resonator includes a non-solid medium and wherein the plurality of reflectors directs the resonant electromagnetic waves through such non-solid medium.
10. In combination:
(a) an electromagnetic wave ring resonator including an amplifier medium;
(b) a plurality of reflectors included in such resonator, arranged to enable circularly polarized waves of opposite polarization senses to resonate in such resonator with different frequencies; and (c) means for producing a magnetic field in such amplifier medium to enable such waves to resonate with four different frequencies.
(a) an electromagnetic wave ring resonator including an amplifier medium;
(b) a plurality of reflectors included in such resonator, arranged to enable circularly polarized waves of opposite polarization senses to resonate in such resonator with different frequencies; and (c) means for producing a magnetic field in such amplifier medium to enable such waves to resonate with four different frequencies.
11. The combination recited in claim 10 wherein such plurality of reflectors directs electromagnetic waves resonant in such ring resonator through a predetermined path, one section of such path being disposed in a first plane and a second section of such path being disposed in a second, intersecting plane.
12. In combination:
(a) an electromagnetic wave ring resonator including an amplifier medium;
(b) a non-solid medium disposed in the path of circularly polarized electromagnetic waves resonant in such ring resonator;
(c) means for altering the electromagnetic field distribution of the waves passing through such non-solid medium to enable such circularly polarized electromagnetic waves to resonate with different frequencies and having opposite senses of circular polarization; and (d) means for producing a magnetic field in the amplifier medium to provide different indices of refraction to such waves of the same circular polarization sense as such waves pass through the amplifier medium in the different directions.
(a) an electromagnetic wave ring resonator including an amplifier medium;
(b) a non-solid medium disposed in the path of circularly polarized electromagnetic waves resonant in such ring resonator;
(c) means for altering the electromagnetic field distribution of the waves passing through such non-solid medium to enable such circularly polarized electromagnetic waves to resonate with different frequencies and having opposite senses of circular polarization; and (d) means for producing a magnetic field in the amplifier medium to provide different indices of refraction to such waves of the same circular polarization sense as such waves pass through the amplifier medium in the different directions.
13. In a laser gyroscope wherein a ring resonator is included to support two pairs of circularly polarized waves, the waves of each of such pairs having opposite polarization senses, one of such pairs of waves propagating around the ring resonator in a first direction and the other one of such pairs of waves propagating around such ring resonator in the opposite direc-tion, each one of the waves in the two pairs thereof having a different fre-quency, the improvement characterized by a plurality of reflectors, included in such ring resonator, arranged to provide a phase difference between waves of opposite polarization senses to enable such waves of opposite polarization senses to resonate at different frequencies, and means, including a laser amplifier medium, for providing different indices of refraction to waves of the same polarization sense passing through such medium in different direc-tions.
14. The improvement recited in claim 13 wherein such ring resonator includes a non-solid medium and wherein such plurality of reflectors rotates the electromagnetic field distribution of such resonant waves as such waves pass through such non-solid medium.
15. The combination recited in claim 14 wherein such plurality of reflectors direct the waves through the non-solid medium.
16. The combination recited in claim 15 wherein a section of such resonant waves is disposed in a first plane and a second section of such waves is disposed in a second, intersecting, plane.
17. In a laser gyroscope wherein four circularly polarized laser waves resonate in a ring resonator, the improvement characterized by means included in such ring resonator for directing such waves through a predeter-mined path, one section of such path being disposed in a first plane and a second section of such path being disposed in a second, intersecting plane to enable such waves to resonate with different frequencies and opposite polarization senses and means, including a laser amplifier medium, for pro-viding different indices of refraction to waves of same polarization sense, passing through such medium in different directions.
18. The improvement recited in claim 17 wherein such waves pass through a non-solid medium and wherein such plurality of reflectors directs the waves through such medium.
19. In a laser gyroscope wherein laser waves resonate in a ring resonator, the improvement comprising:
(a) a non-solid medium disposed in the path of the waves;
(b) means for spatially rotating the electromagnetic field distri-bution of such waves about the direction of propagation of such waves as such waves pass through the non-solid medium to enable electromagnetic waves in such resonator to resonate at different frequencies, and (c) means including a laser amplifier medium for providing differ-ent indices of refraction to waves of same polarization sense passing through such laser amplifier medium in different directions.
(a) a non-solid medium disposed in the path of the waves;
(b) means for spatially rotating the electromagnetic field distri-bution of such waves about the direction of propagation of such waves as such waves pass through the non-solid medium to enable electromagnetic waves in such resonator to resonate at different frequencies, and (c) means including a laser amplifier medium for providing differ-ent indices of refraction to waves of same polarization sense passing through such laser amplifier medium in different directions.
20. The improvement recited in claim 19 wherein such rotating means directs the waves through a predetermined path, one section of such path being disposed in a first plane, and a second section of such path being disposed in a second, intersecting plane.
21. The improvement recited in claim 20 wherein the rotating means includes a catoptric system.
22. In a laser gyroscope wherein laser waves resonate in a ring resonator, the improvement comprising:
(a) a non-solid medium disposed in the path of circularly polarized waves;
(b) means for altering the electromagnetic field distribution of the waves passing through such non-solid medium to enable such circularly polarized waves to resonate with different frequencies; and (c) means, including a laser amplifier medium, for providing different indices of refraction to waves of the same polarization sense pass-ing through such laser amplifier medium in different directions.
(a) a non-solid medium disposed in the path of circularly polarized waves;
(b) means for altering the electromagnetic field distribution of the waves passing through such non-solid medium to enable such circularly polarized waves to resonate with different frequencies; and (c) means, including a laser amplifier medium, for providing different indices of refraction to waves of the same polarization sense pass-ing through such laser amplifier medium in different directions.
23. A ring laser resonator producing at least four frequencies and com-prising:
(a) a laser amplifier medium;
(b) means for producing a pair of circularly polarized waves having different frequencies comprising means for rotating the electromagnetic field distribution of said waves passing through said laser amplifier medium in the same direction; and (c) means for providing substantially different indices of refrac-tion in said laser amplifier medium to waves passing through said laser ampli-fier medium in opposite directions by producing a magnetic field in the laser amplifier medium.
(a) a laser amplifier medium;
(b) means for producing a pair of circularly polarized waves having different frequencies comprising means for rotating the electromagnetic field distribution of said waves passing through said laser amplifier medium in the same direction; and (c) means for providing substantially different indices of refrac-tion in said laser amplifier medium to waves passing through said laser ampli-fier medium in opposite directions by producing a magnetic field in the laser amplifier medium.
24. A four frequency ring laser resonator comprising:
(a) a laser amplifier medium, (b) means for producing different frequencies in such resonator from waves with opposite senses of circular polarization, and (c) means for providing substantially different indices of refrac-tion in said laser amplifier medium to waves passing through such laser amplifier medium in different directions.
(a) a laser amplifier medium, (b) means for producing different frequencies in such resonator from waves with opposite senses of circular polarization, and (c) means for providing substantially different indices of refrac-tion in said laser amplifier medium to waves passing through such laser amplifier medium in different directions.
25. The combination recited in claim 24 wherein said providing means includes means for producing a magnetic field in the laser amplifier medium.
26. A laser gyroscope wherein a ring resonator is included to support two pairs of circularly polarized waves, the waves of each of the pairs hav-ing opposite polarization senses, one wave of each pair of waves propagating around the ring resonator in a first direction and the other wave of each pair of waves propagating around the ring resonator in the opposite direction, each one of the waves in the two pairs having a different frequency, the improvement characterized by a plurality of reflectors, included in the ring resonator arranged for spatially rotating the electromagnetic field distribu-tion of the resonant waves about the direction of propagation of the waves to provide a phase difference between waves of opposite polarization senses to enable the waves of opposite polarization senses to resonate at different frequencies, a laser amplifier medium, and means for applying a magnetic field to the laser amplifier medium for providing predetermined indices of refrac-tion to waves passing through the laser amplifier medium.
27. A laser gyroscope wherein a ring resonator is included to support two pairs of circularly polarized waves, the waves of each of the pairs having opposite polarization senses, one wave of each pair of waves propagating around the ring resonator in a first direction and the other wave of each pair of waves propagating around the ring resonator in the opposite direction, each one of the waves in the two pairs having a different frequency, the improve-ment characterized by means for providing a nonplanar propagation path for spatially rotating the electromagnetic field distribution of the resonant waves about the direction of propagation of the waves to provide a phase difference between waves of opposite polarization senses to enable the waves of opposite polarization senses to resonate at different frequencies, a laser amplifier medium, and means for applying a magnetic field to the laser amplifier medium for providing predetermined indices of refraction to waves passing through the laser amplifier medium.
28. A laser gyroscope wherein a ring resonator is included to support two pairs of circularly polarized waves, the waves of each of the pairs hav-ing opposite polarization senses, one wave of each pair of waves propagating around the ring resonator in a first direction and the other wave of each pair of waves propagating around such ring resonator in the opposite direction, each one of the waves in the two pairs having a different frequency, the im-provement characterized by means for providing a nonplanar propagation path for spatially rotating the electromagnetic field distribution of the resonant waves about the direction of propagation of the waves to provide a phase difference between waves of opposite polarization senses to enable the waves of opposite polarization senses to resonate at different frequencies, and means, including a laser amplifier medium, for providing different indices of refraction to waves of the same polarization sense passing through the laser amplifier medium in different directions.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US64630776A | 1976-01-02 | 1976-01-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1077602A true CA1077602A (en) | 1980-05-13 |
Family
ID=24592548
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA267,744A Expired CA1077602A (en) | 1976-01-02 | 1976-12-13 | Electromagnetic wave ring resonator |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS596518B2 (en) |
| CA (1) | CA1077602A (en) |
| DE (1) | DE2700045C2 (en) |
| FR (1) | FR2337447A1 (en) |
| GB (1) | GB1535444A (en) |
| IT (1) | IT1077505B (en) |
| NL (1) | NL7614434A (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1116279A (en) * | 1978-01-03 | 1982-01-12 | Terry A. Dorschner | Laser gyroscope system |
| CA1132692A (en) * | 1978-04-07 | 1982-09-28 | James B. Matthews | Phase-locked laser gyroscope system |
| DE2816937C2 (en) * | 1978-04-19 | 1982-07-15 | Basf Ag, 6700 Ludwigshafen | Use of reactive dyes for dyeing cellulosic textile material or leather |
| FR2430598A1 (en) * | 1978-07-03 | 1980-02-01 | Litton Systems Inc | Four-mode ring laser gyroscope - has reflecting mirror surfaces mounted on quartz block producing small incident angles |
| US4213705A (en) * | 1978-11-09 | 1980-07-22 | Litton Systems, Inc. | Four mode Zeeman laser gyroscope with minimum hole burning competition |
| CA1189600A (en) * | 1980-10-17 | 1985-06-25 | Raytheon Company | Dispersion equalized ring laser gyroscope |
| US4519708A (en) * | 1981-05-20 | 1985-05-28 | Raytheon Company | Mode discrimination apparatus |
| 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 |
| GB2227879B (en) * | 1989-02-03 | 1994-02-09 | Ferranti Int Signal | Multi-oscillator ring laser gyroscope |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1287836B (en) * | 1963-12-18 | |||
| US3473031A (en) * | 1965-06-23 | 1969-10-14 | Philco Ford Corp | Laser transmitter for generation of simultaneous frequency modulated and unmodulated beams |
| US3480878A (en) * | 1966-09-20 | 1969-11-25 | Sperry Rand Corp | Ring laser with means for reducing coupling to backscattered waves |
| US3741657A (en) * | 1971-03-03 | 1973-06-26 | Raytheon Co | Laser gyroscope |
-
1976
- 1976-12-13 CA CA267,744A patent/CA1077602A/en not_active Expired
- 1976-12-20 GB GB53024/76A patent/GB1535444A/en not_active Expired
- 1976-12-27 NL NL7614434A patent/NL7614434A/en not_active Application Discontinuation
- 1976-12-28 JP JP51160830A patent/JPS596518B2/en not_active Expired
- 1976-12-31 FR FR7639770A patent/FR2337447A1/en active Granted
-
1977
- 1977-01-03 IT IT19010/77A patent/IT1077505B/en active
- 1977-01-03 DE DE2700045A patent/DE2700045C2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1535444A (en) | 1978-12-13 |
| JPS596518B2 (en) | 1984-02-13 |
| IT1077505B (en) | 1985-05-04 |
| FR2337447B1 (en) | 1982-11-19 |
| FR2337447A1 (en) | 1977-07-29 |
| DE2700045A1 (en) | 1977-07-14 |
| DE2700045C2 (en) | 1984-10-18 |
| JPS5285497A (en) | 1977-07-15 |
| NL7614434A (en) | 1977-07-05 |
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| MKEX | Expiry |