CA1320557C - Radio frequency excited ring laser gyroscope - Google Patents
Radio frequency excited ring laser gyroscopeInfo
- Publication number
- CA1320557C CA1320557C CA000602343A CA602343A CA1320557C CA 1320557 C CA1320557 C CA 1320557C CA 000602343 A CA000602343 A CA 000602343A CA 602343 A CA602343 A CA 602343A CA 1320557 C CA1320557 C CA 1320557C
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- Prior art keywords
- ring laser
- laser gyroscope
- radio frequency
- resonator
- radio
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/097—Processes or apparatus for excitation, e.g. pumping by gas discharge of a gas laser
- H01S3/0975—Processes or apparatus for excitation, e.g. pumping by gas discharge of a gas laser using inductive or capacitive excitation
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/58—Turn-sensitive devices without moving masses
- G01C19/64—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams
- G01C19/66—Ring laser gyrometers
- G01C19/661—Ring laser gyrometers details
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/02—Constructional details
- H01S3/03—Constructional details of gas laser discharge tubes
- H01S3/038—Electrodes, e.g. special shape, configuration or composition
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/08—Construction or shape of optical resonators or components thereof
- H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
- H01S3/083—Ring lasers
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Optics & Photonics (AREA)
- Plasma & Fusion (AREA)
- Power Engineering (AREA)
- General Physics & Mathematics (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Gyroscopes (AREA)
- Lasers (AREA)
Abstract
RADIO FREQUENCY EXCITED RING LASER GYROSCOPE
Abstract A radio frequency excitation system is disclosed for use in conjunction with a ring laser gyroscope. The radio frequency excitation system is comprised of a closed resonant cavity which surrounds a helical coil driven at a high radio frequency at a range of 5 to 550 megahertz. This closed resonant coil surrounds one leg of a ring laser gyroscope which is carved out and exposed so that it may be surrounded by the resonant cavity. Using such a radio frequency excitation system eliminates the need for high power DC
discharge components such as cathodes and anodes, as well as problems inherent with properly sealing the cathodes and anodes to the monolithic frame of the ring laser gyroscope.
Abstract A radio frequency excitation system is disclosed for use in conjunction with a ring laser gyroscope. The radio frequency excitation system is comprised of a closed resonant cavity which surrounds a helical coil driven at a high radio frequency at a range of 5 to 550 megahertz. This closed resonant coil surrounds one leg of a ring laser gyroscope which is carved out and exposed so that it may be surrounded by the resonant cavity. Using such a radio frequency excitation system eliminates the need for high power DC
discharge components such as cathodes and anodes, as well as problems inherent with properly sealing the cathodes and anodes to the monolithic frame of the ring laser gyroscope.
Description
Docket ~lo. GCD 86-50 RA~I~ FRFQ~ENCY EXCITE~ RING LAS~R GYROSCOPE :-BAC~GROUN~ OF TIIE INVENTIO~I
~ . .
1. Field of the Invention This invention relates to optical rotation sensors;
and, particularly, this invention relates to ring laser gyros, having an active medium gain that is excited by a radio fre~uency signal emitted from a helical resonator within an enclosed cavity.
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1. Field of the Invention This invention relates to optical rotation sensors;
and, particularly, this invention relates to ring laser gyros, having an active medium gain that is excited by a radio fre~uency signal emitted from a helical resonator within an enclosed cavity.
2. Description of the Related Art -Ring laser gyroscopes are a class of optical rotation sensors that have been developed to provide an alternative form of rotational measurement to the mechanical gyroscope.
A ring laser gyroscope employs the Sagnac effect to detect rotation. A basic two mode ring laser gyroscope has two independent counter rotating light beams which propagate in ~, an optical ring cavity. These two light beams propagate in a closed loop with transit times that differ in direct proportion to the rotation rate of the loop abou~ an axis perpendicular to the plane of the loop. Besides the planar ring laser gyro, other path geometries have been used; for example, a non-planar yyroscope has been disclosed in United States Patent 4,482,249 to Dorschner, which teaches an out-of-plane light path that provides the reciprocal splitting of two pairS of counter rotating beams.
This out-of-plane gyroscope has been known in the literature as the mu~tioscillator ring laser gyroscope.
~.
Yet anotl~er alternative to the multioscillator ring laser gyroscope is a split gain multi-mode ring laser gyroscope. Both the multioscillator ring laser gyroscope and the Split Gain ~lulti-Mode Ring Laser provide out of-plane geometry and at least two pairs of counter propogating mocles of light l)eams to measure rotation with respect to an inertial frame of reference. These non-planar gryos have been developed to avoid the need for mechanical dithering~ Dithering is needed in planar gyroscopes to prevent counter rotating travelling waves from locking at low rotation rates.
lleretofore, ring laser gyros have operated using at least a dome-like configured metallic or glass covered metallic cathode and at least two anodes, which extend outward from the monolithic glass body of the ring laser gyro to excite the gas medium contained within the gyroscope.
DC discharge has been used which excites gas contained in the ring laser gyro pathway between the cathodes and each of the anodes.
Both the prior art and ~he present invention will be described in conjunction with the accompanying drawings in which:
Figure 1 shows a prior art configuration of a DC-excited planar ring laser gyro.
Figure 2 shows a top plan view of a planar ring laser gyro that is radio frequency excited in accordance with the teachings of this invention.
Figure 3 shows a side elevational view of the planar radio frequency excited ring laser gyroscope.
Figure 4 shows a perspective view of a radio frequency excited planar ring laser gyroscope.
Figure 5 shows an alternate embodiment of this invention wherein a multioscillator ring laser gyro is radio frequency excited in accordance with the teachings of this invention.
... ,~. ~.~ .
~ igure 6 is a perspective view of a multi-oscillator ring laser gyroscope showing, in partial section, the configuration of the radio frequency excitation mechanism used ~y a split gain multi-mode ring laser gyroscope in accordance with this invention.
Figure 7 is a schematic diagram showing the control electronics for the radio frequency excitation drive system for driving the resonator means in accordance with this invention.
Figure 8A and 8~ show experimental test results derived from experiments conducted using a radio frequency excited ring laser gyroscope.
Figure 1 shows a prior art planar DC-excited ring laser gyro. The ring laser gyroscope 1~ is formed from a monolithic glass body such as Zerodur, which is a tra~emark of the Schott Glass Works Co. of West Germany. A similar glass that may be used as the ring laser gyro 12 is manufactured under the trademark "CERVIT" sold by Owens-Illinois. Both materials are mixtures o~ glass and ceramic that have opposite temperature expansion coefficients, thus providing an overall minimal dimensional changes over a wide range of temperatures.
A square optical pathway 19 is defined within the gyroscope 10 by 4 legs, 16, 18, 2~, and 22. Leg portion 18A, 22, and 20A ~orm a segment of the optical pathway which glows due to the DC discharge between the cathode 24 and the Page 2a , respective anodes ~6 and 28. During manuEacture, a gaseous mixture of helium and two isotopes of neon provide an active medium that is excited along the DC discharge path defined by segments 1~, 22, and 2~.
Gas is provided to the cavity during manufacture by tl)e fill stem 30 through the anode 26. The cathode is generally grounded, while the anode potentials are each brought up to 15~0 volts, through use of a balast resistor 32. ~t each corner of the pathway 14, a mirror is positioned to reflect light around the ring laser gyro. The mirrors, 34, 36, 38, and 4~ are mounted to the frame 12. ~ more detailed description Or the operation of the planar ring laser gyro together with the particular manncr of DC
excitation is also described in US Patents 9,115,004 to 15 Hutchings and US Patent 4,612,647 to Norvell, each patent being assigned to the common assignee of this application.
In addition to the high voltage and high current regulation require~ents needed for DC excitation, à number of problems have been associaced with the manufacture and reliability of DC discharge ring laser gyroscopes. A prime problem is that of Langmuir flow which can cause a biased and therefore inaccuracies in the rotational sensing capabilities of the ring laser gyro, unless the gyroscope is provided with two balanced current discharge paths. A discharge between a single anode and cathode causes the molecules in a gas laser cavity to flow in a preferred direction. This flow gives rise to a bias or inaccuracy in the rotational sensing capability of a ring laser gyroscope, since each of the clockwise and anti-clockwise modes of light beams propogating in the cavity will be influenced differently by this flow phenomena. In a DC discharge excitation mechanism, as illustrated in Figure 1, the only manner of offsetting the bias problem is to exactly balance the currents and lengths of the two discharge legs 18A and 20A in each half of the discharge region. This is a difficult and costly process.
The power supplies associated with DC excitation are expensive and bulky. A 3-4,0~0 volt potential is necessary to start the discharge processs, and continued operation of the discharge requires a high voltage source of 1500 volts.
The cathodes and anodcs themselves have associated pLoblems including leaks at the seals and shortened lifetimes.
~ lso, a phenomenom known as cathode sputtering arises and limits the lifetime oE the discharge system. Cathode sputtering is characterized by the degradation of a protective oxide coating on the outside o~ the cathode for a good part of its life. The discharge process eventually eats through the oxide coating, exposing the underlying aluminum of the cathode. Once this aluminum is exposed, cathode life deteriorates very quickly and results in an inoperative or non-usable laser structure. This cathode sputtering is a severe limitation on the life of a gas riny laser gyroscope.
Also there are instabilities in the discharge when the DC
discharge is initially activated after filling the ring lasers with gas during manuEacture.
In certain ranges of current operation, instabilities in the current and voltage discharge arise. These instabilities limit the range of current and gas pressure that can be used with a DC discharge ring laser gyroscope.
Also, the DC discharge process is relatively inefficient in providing high energy electrons to pump the gas laser atomic energy level. Some of the problëms associated with DC
discharge in a ring laser gyroscope are also described in Laser_~pplications, edited by Monte ~oss, pages 133-200 (Academic Press r 1971) .
In addition to the operation of the planar ring laser gyro through DC discharge as shown in Figure l, the operation of the multioscillator laser gyroscopes, as described in an article by Chow, et. al., at pages 918-936, IEEE Jo~rnal of Quantum Electronics, vol. QE-16, No. 9, Sept. 198~ is discussed in this article. In both the out-of-plane and Zeeman effect multioscillator ring laser gyroscopes, it is ~ 320557 preferred that the active medium not interfere with certain axially uniform fields needed for the operation of these types of ring laser gyroscopes. As with the planar r-ing laser gyroscope, DC discharge methods have created similar problems for multioscillator ring laser gyroscopes.
Likewise, the Split Gain Multi-Mode Ring Laser Gyro would preferably confine the active medium to the area where a uniform magnetic field is also applied. This is not easily accomplish~d with DC excitation.
For all the fo~egoing reasons, an alternative method of excitation of the gain ;nedium of a ring laser gyroscope is desirable.
In the past, alternative methods of excitation of a laser gas medium have ~een attempted with varying degrees of success. ~F excitation of a helium neon mixture has been reported as early as 1961 in Physical Review Letters, vol. 6, No. 3, pages 1~6-110, in an article by A. Javan. J.P.
Goldsborough has described an RF induction excitation of a continuous wave visible laser in vol. 8, No. 6 of Applied Physics Letters, (15 March 1966), pages 137-139.
US Patent 3,772,611 to Smith, assigned to Bell Telephone Laboratories, issued November 13, 1973, describes an RF excited ring type capallary tube 11 (Figure 1) which may have utility as a rotation rate sensor. The '611 patent, however, does not teach an efEicient design for utilizing the RF excitation. This '611 patent also referred to "A Wave Guide Gas Laser" in an article dated Sept. 1, 1971, in vol.
19, Applied Physics Letters, No. 5t pages 132-134. In this article, Smith described a combined RF and DC voltage excited capillary wave guide containing a mix of helium neon gas.
These inductive coupled RF excitation methods were by necessity high power and created substantial electrical interference and noise which disturbed other instrumentation associated with rotation sensing.
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UK patent application published July 19, 1987 (G~
21858~6~) discloses a ring laser which is excited by transverse electrical discharge operating at a high ~requency alternating voltage. Although this disclosure claims a low voltage excitation range, it operates through capacitive coupling to the gaseous medium in a transverse direction to the passageway between the mirrors. Use of this transverse direction-excited, high frequency, alternating voltage, capacitively coupled to the active medium would result in contamination of the passageways of the ring laser gyroscope cavity due to the constant bombardment of the gaseous media against the walls ancl the high RF powers needed to drive the discharge. This is counter-productive to a long life operation of a ring laser gyroscope.
Thus, although the prior art referenced have disclosed alternative methods of excitation other than DC
discharge for gaseous laser and ring laser gyroscopes, these alternative solutions to the problem of DC dischar~e have been inadequate.
2~ SUMMARY 0~ Tl~E INVEN~10~l Disclosed herein is a radio frequency excited ring laser gyroscope including a resonant closed cavity defining a closed optical path which is filled with a gain medium. The ring laser gyroscope of this invention includes a means for exciting the gas medium which comprises a resonant cavity formed around a helical coil for applying a radio frequency signal to excite the discharge of a gain medium. The high frequency signal that is imparted by the resonant cavity is in the range of 5 Mhz to 550 Mhz. ~ resonant means for applying a radio frequel)cy signal for exciting a discharge of the gain medium should include a helical coil surrounding a portion of the closed optical path where the helical coil is contained within a closed conductive resonator shield. Along at least one leg of the monolithic dielectric body of the ring laser gyroscope a portion of the monolithic body is carved out to allow one of the tubular bores to be surrounded by ti~e helical coil and enclosed in a conductive resonator shield. An RF oscillator is coupled and connected to the resonant means to supply a radio frequency signal to the resonant means for excitation of the active gain medium.
S The advantages of the invention disclosed herein will become more apparent from a review of the accompanying drawings and detailed description of the preEerred embodiment of this invention which follows.
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DETAILED DE~CRIPTION OF THE PREFERRED EI~BODIMENT
With reference to Figures ~, 3 and 4, a radio frequency excited planar ring laser gyroscope 50 is shown.
The ring laser gyroscope is comprised of a low thermal expansion glass body 52 into which an optical pathway defined by legs 54, 56, 58 and 60. Positioned at each corner ar=e mirrors 62, 64, 66 and 68. During manufacture, gas is introduced to the cavity defined by the legs through the passageway 7~.
At least one of the legs 60 has been carved to accomodate the positioning of a helical coil 72 which is surrounded by a resonant cavity shield 74. The coil 72 is driven by an RF frequency oscillator 76 (Figure 2) operating at a voltage of approximately 28 volts. The radio frequency oscillator 76 may be a modified Colpitts Oscillator.
Generally, a signal in the range of 5 to 55~ megahertz is imparted to the coil. By completely enclosing the coil 72 with a resonator cavity shield 74, a closed resonant cavity is formed which serves to amplify the signal produced within 2B the cavity. In the preferred embodiment the resonant shield 74 should be of conductive material with low resistivity.
The helical coil 72 is preferrably formed from copper wire and the resonator shield made from copper tube to form the radio frequency resonant cavity. The shield could be formed from other metals coated on a tubular substrate s~ch as, but not limited to, gold, silver or aluminum~ The resonant cavity 75 encloses the portion of the gain medium 8~ that is excited by the radio frequency discharge. By operating at i the proper radio frequencies, the cavity may be run as a fullwave, halfwave, or quarter wave, length resonator.
Readings of the electro magnetic field outside the resonator reveal that the cavity has localized the electro magnetic field. Any spurious signals have been reduced in order to minimize any undesirable effects of the electro magnetic far field on the operation of the ring laser gyroscope or related measuring electronic components. Thus, unlike radio frequency induced excitation as disclose~ in the prior art, the use of a resonant cavity allows the optimi~ation of a strong excitation with low power and minimal radio frequency interference (RFI)~
An enclosed helical resonator, such as that shown in Figures 2-4, may provide high Q. The helical resonator~
assembly is comprised of a coil 72 within the resonator shield 74, where one end of the coil 72 is solidly connected to the shield 74~ The other end of the coil 72 is an open circuit, except for a possible trimming capacitor (not shown). In this configuration, the resonator assembly resembles an L-C circuit; but, instead of being a lumped-constant device, lts operation can be described in terms of distributed inductance, capacitance, and resistance.
The resonator must be properly aligned for optimum performance. ~ccording to techniques ~;nown in the art (See W. W. MacAlpine, et. al., "Coaxial Resonators with Helical Inner Conductor, Proceedings of the IRE, December, 1959, pp. I
2099 - 2105 at 2100), alignment of the resonator coil can be achieved according to the following equations:
) Qu 50D fo /2' where Qu = unloaded Q;
D = inside diameter of the resonator shield;
and r fO - Resonant frequency lMhz).
(2) N = 1900/(f D) turns where:
N = total number of windings fO = Resonant frequency <MHz>; and, D = inside diameter of the resonator shield.
Additional considerations of parameters needed to achieve optimum RF coil operation have been treated in the conventional arts, as indicated by the MACALPINE Article, SUPR~.
Figure 5 shows an alternative embodiment of the radio frequency excitation system of this invention used in conjunction with a multioscillator ring laser gyroscope 82.
As with the planar ring laser gyroscope, the frame 84 is made from a monolithic dielectric material having a low thermal expansion over a wide temperature range (between -50 deg. C -150 deg. C). As has been disclosed in the art, this form oE
multioscillator ring laser gyroscope is positioned in an out-of-plane configuration in order to provide reciprocal splitting between sets of let and right circular pola~ized beams of light. (A more detailed explanation may be ~ound in the Laser Handbook Vol. g, edited by M.L. Stitch, published by North Holland, 1985, pages 230-332). Heretofor, the multioscillator ring laser gyroscope has had its active medium excited by a DC discharge between a cathode and at least 2 anodes. An alternative form of excitation of the multioscillator ring laser gyroscope is shown in Figure 5.
One of the four legs, positioned between mirrors 86 and 88, of the out-of-plane multioscillator ring laser gyroscope 82 is carved out of the body. The passageway 91 defined by the 25 leg between 86 and 8B is integral with the frame 84 and is preferrably a cylindrical pathway, Wound around this pathway 91 is a Radio Frequency helical coil 94. Surrounding the coil 94 is preferrably a cylindrical radio frequency resonator shield 96. Positioned on the leg opposite 91 30 between mirrors 90 and 92 is the optical rotator 97 ~such as a Faraday rotator~ which provides non-reciprocal splitting between clockwis~ and counter-clockwise beams of light within two sets of left and right circularly polarized beams in the presence of a uniform magnetic field.
It will be noted that the radio frequency resonator shield 96 provides good isolation for all signals generated within the helical coil 94 and the resonator cavity 95. ~y shiel~ing the resonator cavity 95, the radio frequency resonator shield 96 prevents any radio frequency interference from affecting the detection circuitry or any other electronics.
With reference to Figure 6, a Split Gain Multi-Mode Ring Laser Gyroscope 100 is shown. The frame 102 is a mono-lithic dielectric material at a low coefficient of thermalexpansion. The split gain multi-mode ring laser gyroscope is also config~red in an out-of-plane configuration. A strong permanent magnet 116 is used to cause the split gain effect need~d to operate this form of ring laser gyroscope. When the split gain gyroscope is operated by use of conventional DC discharge, a permanent magnet (not shown) must be positioned on a leg opposite the gain medium and the leg where the cathode is positioned. This is not, however, the most desirable positioning of the permanent magnet in the split gain multi-mode ring laser gyroscope.
Preferrably, the split gain multi-mode ring laser gyroscope operates best when the active medium is contained within the permanent magnet 116. This is difficult to achieve when using a conventional DC discharge manner of - Z5 medium excitation. The radio frequency excitation system of this invention provides an optimum alternative to the conventional DC discharge.
~gain with reference to Figure 6, the active medium discharge pathway 104 is positioned between mirrors 106 and 108. Within the pathway 104 gaseous medium (preferrably a helium-neon mixture) is excited by use of a radio frequency helical coil which applies a radio frequency signal from an RF oscillator (not shown) to a resonant cavity 110 formed between the radio frequency helical coil 112 and the radio frequency resonator shield 114. The radio frequency resonator shield 114 may be a copper shield which surrounds copper wire forming the radio frequency helical coil 112. In order to provide compactness and optimum design, the radio frequency sllield 114 may be positioned along the inner diameter of the permanent magnet 116 which also surrounds the medium passageway 110.
By configuring the radio frequency excitatio~ system within the permanent magnet 116 as shown in Figure 6, one is able to achieve optimum results with regard ~o both the excitation of the active medium 118 within the passageway 110 as well as the con~inelnent of that medium 110 within the permanent magnet length 116, a necessary factor in achieving optimum split gain multi- mode ring laser gyroscope operation. Each signal then plays a different role. The high radio frequency signal imparted on the helical coil 112 is used to excite the active medium 118. The low DC si~nal applied simultaneously ~o the coil 112 is used to fine tune the magnetic field arising from the permanent magnet 116.
Since the permanent magnet 116 is preferrably a cylindrical configuration, the radio frequency resonator shield (119) should also be a concentric cylindrical shape within the inner surface of the permanent magnet 116.
~5 In this manner, a radio frequency excited Split Gain Multi-Mode ~ing Laser Gyroscope is disclosed which does not need independent DC magnets positioned on a ley away from the active medium 118, as is required in a DC excited split gain multi-mode ring laser gyroscope.
Figure 7 shows the control electronics for the radio frequency drive system. In order for the radio frequency excitation taught in this invention to operate most efficiently, the radio frequency resonator and coil system 150 must be regulated so that the excited medium is maintained at a relatively constant power level while the radio frequency resonator signal is maintained at a , . , ~
. ,i ' 1 3~557 relatively constant frequency. ~he combination of electronic components shown generally in power control loop 152 controls the power provided to the radio frequency resonator 150, while the frequency control loop 154 controls the frequency of the signal drive in the radio frequency resonator 150.
The power control loop 152 receives an input signal through the photo-diode 15G, in the form of light intensity of the gain medium 155. This signal is then amplified in the pre-amplifier 158 and provided as an output voltage signal to the differential amplifier 160. The diEferential amplier 160 compares the voltage power signal to a reference voltage. If the operating power voltage signal is higher than the reference, or lower than the reference, an output signal resulting from common mode rejection by the differential amplifier 160 provides an error signal input to the integrator 162. The integratcr 162 then provides an output signal which controls the electronic attenuator 169 to adjust the voltage power supply provided to the radio frequency resonator.
The electronic attenuator 164 provides an output signal to the radio frequency amplifier 166 which couples its output signal to the radio frequency coupler 168. The resulting output at 170 will either raise or lower the power provided to the RF frequency coil 172 within the radio frequency resonator 150. Additionally, the frequency of the RF resonator 150 is monitored by the radio frequency coupler 168 and is detected by an amplitude modulator detector 17~.
The output from the detector 174 of the frequency control loop 154 is then amplified by the pre-amplifier 176.
The output of the pre-amplifier 176 is then provided to the phase lock loop 180. The phase lock loop 180 is comprised of synchronous detector 178, an integrator 179, and a local oscillator 177. (This is a known configuration for an analog phase lock loop). The phase lock loop 180 locks in on a frequency determined by the local oscillator 177 and the output of the phase lock loop 180 i 5 then provided to the summing amplifier 1~2. The summing amplifier 182 then adjusts the voltage to the voltage controlled oscillator 184.
The voltage controlled oscillator 184 provides an output adjustment to the electronic attenuator 169 which in S turn, as previously described, provides frequency control through the radio frequency coupler 168 to the frequency of the signal applied to the coil 172 of the ~F resonator 15C.
In this manner, both power and frequency control and consistency are maintained.
If it is desired to operate the ring laser gyroscope at full wave resonance the gain medium 155 may be captured within the coil 172 of the RF resonator 150. The positioning of this gain medium 155 may be controlled by the electronics shown in Figure 7; but, this is only one embodiment for accomplishing this goal. It would be known generally that a digital or other hybrid analog digital servo system may also be used to control power and frequency of the RF resonator 15~. ~
Figures 8~ and 8~ show the results of radio frequency excitation experiments for a planar ring laser gyroscope.
When radio frequency excitation is applied to the ring laser gyroscope, curves 190 and 192 of Figure 8A show that the optimum power is provided at the center of the radio frequency resonator tuning frequency at 189 and 191 respectively. Curve 190 is shown at 29 decibels referred to one milliwatt (dBm) or .75 watts, while curve 192 shows a 30 dBm input or 1 watt. In either case it can be shown that as one detunes the resonator from the central frequency only 3 Mhz lower or 6 Mhz higher, there is a significant drop off in excitation. ~rhus the fine tunability of the radio freguency excited gyroscope is shown in figure 8A. Figure 8B shows that the power increases relatively linearly. As input power and voltage is increased from a 27 volt input to a 32 volt input, curves 194 and 196 show that the wattage output oE the linear laser increases in a substantially linear fashion.
Curve 194 exhibits the 200 Mhz signal with 31 turns while curve 196 shows a 112 Mhæ signal with 55 turns. It thus can be seen from Figure 8B that there is a linear relationship between output and input power that is smooth and provides a high optimum efficiency for excitation of the gain medium in the ring laser gyroscope.
While a preferred embodiment of the radio frequency excitation system for a variety of embodiments of ring laser gyroscopes have been shown, it is clear that alternative resonator configurations may be used. These configurat;ons could also provide a low power, high efficiency output that is simple and avoids all the disadvantages of the traditional DC discharge medium excitation devices of the prior art.
While preferred embodiments have been shown, alternative e~uivalent embodiments are intended to be covered in the appended claims which follow this disclosure.
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A ring laser gyroscope employs the Sagnac effect to detect rotation. A basic two mode ring laser gyroscope has two independent counter rotating light beams which propagate in ~, an optical ring cavity. These two light beams propagate in a closed loop with transit times that differ in direct proportion to the rotation rate of the loop abou~ an axis perpendicular to the plane of the loop. Besides the planar ring laser gyro, other path geometries have been used; for example, a non-planar yyroscope has been disclosed in United States Patent 4,482,249 to Dorschner, which teaches an out-of-plane light path that provides the reciprocal splitting of two pairS of counter rotating beams.
This out-of-plane gyroscope has been known in the literature as the mu~tioscillator ring laser gyroscope.
~.
Yet anotl~er alternative to the multioscillator ring laser gyroscope is a split gain multi-mode ring laser gyroscope. Both the multioscillator ring laser gyroscope and the Split Gain ~lulti-Mode Ring Laser provide out of-plane geometry and at least two pairs of counter propogating mocles of light l)eams to measure rotation with respect to an inertial frame of reference. These non-planar gryos have been developed to avoid the need for mechanical dithering~ Dithering is needed in planar gyroscopes to prevent counter rotating travelling waves from locking at low rotation rates.
lleretofore, ring laser gyros have operated using at least a dome-like configured metallic or glass covered metallic cathode and at least two anodes, which extend outward from the monolithic glass body of the ring laser gyro to excite the gas medium contained within the gyroscope.
DC discharge has been used which excites gas contained in the ring laser gyro pathway between the cathodes and each of the anodes.
Both the prior art and ~he present invention will be described in conjunction with the accompanying drawings in which:
Figure 1 shows a prior art configuration of a DC-excited planar ring laser gyro.
Figure 2 shows a top plan view of a planar ring laser gyro that is radio frequency excited in accordance with the teachings of this invention.
Figure 3 shows a side elevational view of the planar radio frequency excited ring laser gyroscope.
Figure 4 shows a perspective view of a radio frequency excited planar ring laser gyroscope.
Figure 5 shows an alternate embodiment of this invention wherein a multioscillator ring laser gyro is radio frequency excited in accordance with the teachings of this invention.
... ,~. ~.~ .
~ igure 6 is a perspective view of a multi-oscillator ring laser gyroscope showing, in partial section, the configuration of the radio frequency excitation mechanism used ~y a split gain multi-mode ring laser gyroscope in accordance with this invention.
Figure 7 is a schematic diagram showing the control electronics for the radio frequency excitation drive system for driving the resonator means in accordance with this invention.
Figure 8A and 8~ show experimental test results derived from experiments conducted using a radio frequency excited ring laser gyroscope.
Figure 1 shows a prior art planar DC-excited ring laser gyro. The ring laser gyroscope 1~ is formed from a monolithic glass body such as Zerodur, which is a tra~emark of the Schott Glass Works Co. of West Germany. A similar glass that may be used as the ring laser gyro 12 is manufactured under the trademark "CERVIT" sold by Owens-Illinois. Both materials are mixtures o~ glass and ceramic that have opposite temperature expansion coefficients, thus providing an overall minimal dimensional changes over a wide range of temperatures.
A square optical pathway 19 is defined within the gyroscope 10 by 4 legs, 16, 18, 2~, and 22. Leg portion 18A, 22, and 20A ~orm a segment of the optical pathway which glows due to the DC discharge between the cathode 24 and the Page 2a , respective anodes ~6 and 28. During manuEacture, a gaseous mixture of helium and two isotopes of neon provide an active medium that is excited along the DC discharge path defined by segments 1~, 22, and 2~.
Gas is provided to the cavity during manufacture by tl)e fill stem 30 through the anode 26. The cathode is generally grounded, while the anode potentials are each brought up to 15~0 volts, through use of a balast resistor 32. ~t each corner of the pathway 14, a mirror is positioned to reflect light around the ring laser gyro. The mirrors, 34, 36, 38, and 4~ are mounted to the frame 12. ~ more detailed description Or the operation of the planar ring laser gyro together with the particular manncr of DC
excitation is also described in US Patents 9,115,004 to 15 Hutchings and US Patent 4,612,647 to Norvell, each patent being assigned to the common assignee of this application.
In addition to the high voltage and high current regulation require~ents needed for DC excitation, à number of problems have been associaced with the manufacture and reliability of DC discharge ring laser gyroscopes. A prime problem is that of Langmuir flow which can cause a biased and therefore inaccuracies in the rotational sensing capabilities of the ring laser gyro, unless the gyroscope is provided with two balanced current discharge paths. A discharge between a single anode and cathode causes the molecules in a gas laser cavity to flow in a preferred direction. This flow gives rise to a bias or inaccuracy in the rotational sensing capability of a ring laser gyroscope, since each of the clockwise and anti-clockwise modes of light beams propogating in the cavity will be influenced differently by this flow phenomena. In a DC discharge excitation mechanism, as illustrated in Figure 1, the only manner of offsetting the bias problem is to exactly balance the currents and lengths of the two discharge legs 18A and 20A in each half of the discharge region. This is a difficult and costly process.
The power supplies associated with DC excitation are expensive and bulky. A 3-4,0~0 volt potential is necessary to start the discharge processs, and continued operation of the discharge requires a high voltage source of 1500 volts.
The cathodes and anodcs themselves have associated pLoblems including leaks at the seals and shortened lifetimes.
~ lso, a phenomenom known as cathode sputtering arises and limits the lifetime oE the discharge system. Cathode sputtering is characterized by the degradation of a protective oxide coating on the outside o~ the cathode for a good part of its life. The discharge process eventually eats through the oxide coating, exposing the underlying aluminum of the cathode. Once this aluminum is exposed, cathode life deteriorates very quickly and results in an inoperative or non-usable laser structure. This cathode sputtering is a severe limitation on the life of a gas riny laser gyroscope.
Also there are instabilities in the discharge when the DC
discharge is initially activated after filling the ring lasers with gas during manuEacture.
In certain ranges of current operation, instabilities in the current and voltage discharge arise. These instabilities limit the range of current and gas pressure that can be used with a DC discharge ring laser gyroscope.
Also, the DC discharge process is relatively inefficient in providing high energy electrons to pump the gas laser atomic energy level. Some of the problëms associated with DC
discharge in a ring laser gyroscope are also described in Laser_~pplications, edited by Monte ~oss, pages 133-200 (Academic Press r 1971) .
In addition to the operation of the planar ring laser gyro through DC discharge as shown in Figure l, the operation of the multioscillator laser gyroscopes, as described in an article by Chow, et. al., at pages 918-936, IEEE Jo~rnal of Quantum Electronics, vol. QE-16, No. 9, Sept. 198~ is discussed in this article. In both the out-of-plane and Zeeman effect multioscillator ring laser gyroscopes, it is ~ 320557 preferred that the active medium not interfere with certain axially uniform fields needed for the operation of these types of ring laser gyroscopes. As with the planar r-ing laser gyroscope, DC discharge methods have created similar problems for multioscillator ring laser gyroscopes.
Likewise, the Split Gain Multi-Mode Ring Laser Gyro would preferably confine the active medium to the area where a uniform magnetic field is also applied. This is not easily accomplish~d with DC excitation.
For all the fo~egoing reasons, an alternative method of excitation of the gain ;nedium of a ring laser gyroscope is desirable.
In the past, alternative methods of excitation of a laser gas medium have ~een attempted with varying degrees of success. ~F excitation of a helium neon mixture has been reported as early as 1961 in Physical Review Letters, vol. 6, No. 3, pages 1~6-110, in an article by A. Javan. J.P.
Goldsborough has described an RF induction excitation of a continuous wave visible laser in vol. 8, No. 6 of Applied Physics Letters, (15 March 1966), pages 137-139.
US Patent 3,772,611 to Smith, assigned to Bell Telephone Laboratories, issued November 13, 1973, describes an RF excited ring type capallary tube 11 (Figure 1) which may have utility as a rotation rate sensor. The '611 patent, however, does not teach an efEicient design for utilizing the RF excitation. This '611 patent also referred to "A Wave Guide Gas Laser" in an article dated Sept. 1, 1971, in vol.
19, Applied Physics Letters, No. 5t pages 132-134. In this article, Smith described a combined RF and DC voltage excited capillary wave guide containing a mix of helium neon gas.
These inductive coupled RF excitation methods were by necessity high power and created substantial electrical interference and noise which disturbed other instrumentation associated with rotation sensing.
",~ .
UK patent application published July 19, 1987 (G~
21858~6~) discloses a ring laser which is excited by transverse electrical discharge operating at a high ~requency alternating voltage. Although this disclosure claims a low voltage excitation range, it operates through capacitive coupling to the gaseous medium in a transverse direction to the passageway between the mirrors. Use of this transverse direction-excited, high frequency, alternating voltage, capacitively coupled to the active medium would result in contamination of the passageways of the ring laser gyroscope cavity due to the constant bombardment of the gaseous media against the walls ancl the high RF powers needed to drive the discharge. This is counter-productive to a long life operation of a ring laser gyroscope.
Thus, although the prior art referenced have disclosed alternative methods of excitation other than DC
discharge for gaseous laser and ring laser gyroscopes, these alternative solutions to the problem of DC dischar~e have been inadequate.
2~ SUMMARY 0~ Tl~E INVEN~10~l Disclosed herein is a radio frequency excited ring laser gyroscope including a resonant closed cavity defining a closed optical path which is filled with a gain medium. The ring laser gyroscope of this invention includes a means for exciting the gas medium which comprises a resonant cavity formed around a helical coil for applying a radio frequency signal to excite the discharge of a gain medium. The high frequency signal that is imparted by the resonant cavity is in the range of 5 Mhz to 550 Mhz. ~ resonant means for applying a radio frequel)cy signal for exciting a discharge of the gain medium should include a helical coil surrounding a portion of the closed optical path where the helical coil is contained within a closed conductive resonator shield. Along at least one leg of the monolithic dielectric body of the ring laser gyroscope a portion of the monolithic body is carved out to allow one of the tubular bores to be surrounded by ti~e helical coil and enclosed in a conductive resonator shield. An RF oscillator is coupled and connected to the resonant means to supply a radio frequency signal to the resonant means for excitation of the active gain medium.
S The advantages of the invention disclosed herein will become more apparent from a review of the accompanying drawings and detailed description of the preEerred embodiment of this invention which follows.
, ~ .
DETAILED DE~CRIPTION OF THE PREFERRED EI~BODIMENT
With reference to Figures ~, 3 and 4, a radio frequency excited planar ring laser gyroscope 50 is shown.
The ring laser gyroscope is comprised of a low thermal expansion glass body 52 into which an optical pathway defined by legs 54, 56, 58 and 60. Positioned at each corner ar=e mirrors 62, 64, 66 and 68. During manufacture, gas is introduced to the cavity defined by the legs through the passageway 7~.
At least one of the legs 60 has been carved to accomodate the positioning of a helical coil 72 which is surrounded by a resonant cavity shield 74. The coil 72 is driven by an RF frequency oscillator 76 (Figure 2) operating at a voltage of approximately 28 volts. The radio frequency oscillator 76 may be a modified Colpitts Oscillator.
Generally, a signal in the range of 5 to 55~ megahertz is imparted to the coil. By completely enclosing the coil 72 with a resonator cavity shield 74, a closed resonant cavity is formed which serves to amplify the signal produced within 2B the cavity. In the preferred embodiment the resonant shield 74 should be of conductive material with low resistivity.
The helical coil 72 is preferrably formed from copper wire and the resonator shield made from copper tube to form the radio frequency resonant cavity. The shield could be formed from other metals coated on a tubular substrate s~ch as, but not limited to, gold, silver or aluminum~ The resonant cavity 75 encloses the portion of the gain medium 8~ that is excited by the radio frequency discharge. By operating at i the proper radio frequencies, the cavity may be run as a fullwave, halfwave, or quarter wave, length resonator.
Readings of the electro magnetic field outside the resonator reveal that the cavity has localized the electro magnetic field. Any spurious signals have been reduced in order to minimize any undesirable effects of the electro magnetic far field on the operation of the ring laser gyroscope or related measuring electronic components. Thus, unlike radio frequency induced excitation as disclose~ in the prior art, the use of a resonant cavity allows the optimi~ation of a strong excitation with low power and minimal radio frequency interference (RFI)~
An enclosed helical resonator, such as that shown in Figures 2-4, may provide high Q. The helical resonator~
assembly is comprised of a coil 72 within the resonator shield 74, where one end of the coil 72 is solidly connected to the shield 74~ The other end of the coil 72 is an open circuit, except for a possible trimming capacitor (not shown). In this configuration, the resonator assembly resembles an L-C circuit; but, instead of being a lumped-constant device, lts operation can be described in terms of distributed inductance, capacitance, and resistance.
The resonator must be properly aligned for optimum performance. ~ccording to techniques ~;nown in the art (See W. W. MacAlpine, et. al., "Coaxial Resonators with Helical Inner Conductor, Proceedings of the IRE, December, 1959, pp. I
2099 - 2105 at 2100), alignment of the resonator coil can be achieved according to the following equations:
) Qu 50D fo /2' where Qu = unloaded Q;
D = inside diameter of the resonator shield;
and r fO - Resonant frequency lMhz).
(2) N = 1900/(f D) turns where:
N = total number of windings fO = Resonant frequency <MHz>; and, D = inside diameter of the resonator shield.
Additional considerations of parameters needed to achieve optimum RF coil operation have been treated in the conventional arts, as indicated by the MACALPINE Article, SUPR~.
Figure 5 shows an alternative embodiment of the radio frequency excitation system of this invention used in conjunction with a multioscillator ring laser gyroscope 82.
As with the planar ring laser gyroscope, the frame 84 is made from a monolithic dielectric material having a low thermal expansion over a wide temperature range (between -50 deg. C -150 deg. C). As has been disclosed in the art, this form oE
multioscillator ring laser gyroscope is positioned in an out-of-plane configuration in order to provide reciprocal splitting between sets of let and right circular pola~ized beams of light. (A more detailed explanation may be ~ound in the Laser Handbook Vol. g, edited by M.L. Stitch, published by North Holland, 1985, pages 230-332). Heretofor, the multioscillator ring laser gyroscope has had its active medium excited by a DC discharge between a cathode and at least 2 anodes. An alternative form of excitation of the multioscillator ring laser gyroscope is shown in Figure 5.
One of the four legs, positioned between mirrors 86 and 88, of the out-of-plane multioscillator ring laser gyroscope 82 is carved out of the body. The passageway 91 defined by the 25 leg between 86 and 8B is integral with the frame 84 and is preferrably a cylindrical pathway, Wound around this pathway 91 is a Radio Frequency helical coil 94. Surrounding the coil 94 is preferrably a cylindrical radio frequency resonator shield 96. Positioned on the leg opposite 91 30 between mirrors 90 and 92 is the optical rotator 97 ~such as a Faraday rotator~ which provides non-reciprocal splitting between clockwis~ and counter-clockwise beams of light within two sets of left and right circularly polarized beams in the presence of a uniform magnetic field.
It will be noted that the radio frequency resonator shield 96 provides good isolation for all signals generated within the helical coil 94 and the resonator cavity 95. ~y shiel~ing the resonator cavity 95, the radio frequency resonator shield 96 prevents any radio frequency interference from affecting the detection circuitry or any other electronics.
With reference to Figure 6, a Split Gain Multi-Mode Ring Laser Gyroscope 100 is shown. The frame 102 is a mono-lithic dielectric material at a low coefficient of thermalexpansion. The split gain multi-mode ring laser gyroscope is also config~red in an out-of-plane configuration. A strong permanent magnet 116 is used to cause the split gain effect need~d to operate this form of ring laser gyroscope. When the split gain gyroscope is operated by use of conventional DC discharge, a permanent magnet (not shown) must be positioned on a leg opposite the gain medium and the leg where the cathode is positioned. This is not, however, the most desirable positioning of the permanent magnet in the split gain multi-mode ring laser gyroscope.
Preferrably, the split gain multi-mode ring laser gyroscope operates best when the active medium is contained within the permanent magnet 116. This is difficult to achieve when using a conventional DC discharge manner of - Z5 medium excitation. The radio frequency excitation system of this invention provides an optimum alternative to the conventional DC discharge.
~gain with reference to Figure 6, the active medium discharge pathway 104 is positioned between mirrors 106 and 108. Within the pathway 104 gaseous medium (preferrably a helium-neon mixture) is excited by use of a radio frequency helical coil which applies a radio frequency signal from an RF oscillator (not shown) to a resonant cavity 110 formed between the radio frequency helical coil 112 and the radio frequency resonator shield 114. The radio frequency resonator shield 114 may be a copper shield which surrounds copper wire forming the radio frequency helical coil 112. In order to provide compactness and optimum design, the radio frequency sllield 114 may be positioned along the inner diameter of the permanent magnet 116 which also surrounds the medium passageway 110.
By configuring the radio frequency excitatio~ system within the permanent magnet 116 as shown in Figure 6, one is able to achieve optimum results with regard ~o both the excitation of the active medium 118 within the passageway 110 as well as the con~inelnent of that medium 110 within the permanent magnet length 116, a necessary factor in achieving optimum split gain multi- mode ring laser gyroscope operation. Each signal then plays a different role. The high radio frequency signal imparted on the helical coil 112 is used to excite the active medium 118. The low DC si~nal applied simultaneously ~o the coil 112 is used to fine tune the magnetic field arising from the permanent magnet 116.
Since the permanent magnet 116 is preferrably a cylindrical configuration, the radio frequency resonator shield (119) should also be a concentric cylindrical shape within the inner surface of the permanent magnet 116.
~5 In this manner, a radio frequency excited Split Gain Multi-Mode ~ing Laser Gyroscope is disclosed which does not need independent DC magnets positioned on a ley away from the active medium 118, as is required in a DC excited split gain multi-mode ring laser gyroscope.
Figure 7 shows the control electronics for the radio frequency drive system. In order for the radio frequency excitation taught in this invention to operate most efficiently, the radio frequency resonator and coil system 150 must be regulated so that the excited medium is maintained at a relatively constant power level while the radio frequency resonator signal is maintained at a , . , ~
. ,i ' 1 3~557 relatively constant frequency. ~he combination of electronic components shown generally in power control loop 152 controls the power provided to the radio frequency resonator 150, while the frequency control loop 154 controls the frequency of the signal drive in the radio frequency resonator 150.
The power control loop 152 receives an input signal through the photo-diode 15G, in the form of light intensity of the gain medium 155. This signal is then amplified in the pre-amplifier 158 and provided as an output voltage signal to the differential amplifier 160. The diEferential amplier 160 compares the voltage power signal to a reference voltage. If the operating power voltage signal is higher than the reference, or lower than the reference, an output signal resulting from common mode rejection by the differential amplifier 160 provides an error signal input to the integrator 162. The integratcr 162 then provides an output signal which controls the electronic attenuator 169 to adjust the voltage power supply provided to the radio frequency resonator.
The electronic attenuator 164 provides an output signal to the radio frequency amplifier 166 which couples its output signal to the radio frequency coupler 168. The resulting output at 170 will either raise or lower the power provided to the RF frequency coil 172 within the radio frequency resonator 150. Additionally, the frequency of the RF resonator 150 is monitored by the radio frequency coupler 168 and is detected by an amplitude modulator detector 17~.
The output from the detector 174 of the frequency control loop 154 is then amplified by the pre-amplifier 176.
The output of the pre-amplifier 176 is then provided to the phase lock loop 180. The phase lock loop 180 is comprised of synchronous detector 178, an integrator 179, and a local oscillator 177. (This is a known configuration for an analog phase lock loop). The phase lock loop 180 locks in on a frequency determined by the local oscillator 177 and the output of the phase lock loop 180 i 5 then provided to the summing amplifier 1~2. The summing amplifier 182 then adjusts the voltage to the voltage controlled oscillator 184.
The voltage controlled oscillator 184 provides an output adjustment to the electronic attenuator 169 which in S turn, as previously described, provides frequency control through the radio frequency coupler 168 to the frequency of the signal applied to the coil 172 of the ~F resonator 15C.
In this manner, both power and frequency control and consistency are maintained.
If it is desired to operate the ring laser gyroscope at full wave resonance the gain medium 155 may be captured within the coil 172 of the RF resonator 150. The positioning of this gain medium 155 may be controlled by the electronics shown in Figure 7; but, this is only one embodiment for accomplishing this goal. It would be known generally that a digital or other hybrid analog digital servo system may also be used to control power and frequency of the RF resonator 15~. ~
Figures 8~ and 8~ show the results of radio frequency excitation experiments for a planar ring laser gyroscope.
When radio frequency excitation is applied to the ring laser gyroscope, curves 190 and 192 of Figure 8A show that the optimum power is provided at the center of the radio frequency resonator tuning frequency at 189 and 191 respectively. Curve 190 is shown at 29 decibels referred to one milliwatt (dBm) or .75 watts, while curve 192 shows a 30 dBm input or 1 watt. In either case it can be shown that as one detunes the resonator from the central frequency only 3 Mhz lower or 6 Mhz higher, there is a significant drop off in excitation. ~rhus the fine tunability of the radio freguency excited gyroscope is shown in figure 8A. Figure 8B shows that the power increases relatively linearly. As input power and voltage is increased from a 27 volt input to a 32 volt input, curves 194 and 196 show that the wattage output oE the linear laser increases in a substantially linear fashion.
Curve 194 exhibits the 200 Mhz signal with 31 turns while curve 196 shows a 112 Mhæ signal with 55 turns. It thus can be seen from Figure 8B that there is a linear relationship between output and input power that is smooth and provides a high optimum efficiency for excitation of the gain medium in the ring laser gyroscope.
While a preferred embodiment of the radio frequency excitation system for a variety of embodiments of ring laser gyroscopes have been shown, it is clear that alternative resonator configurations may be used. These configurat;ons could also provide a low power, high efficiency output that is simple and avoids all the disadvantages of the traditional DC discharge medium excitation devices of the prior art.
While preferred embodiments have been shown, alternative e~uivalent embodiments are intended to be covered in the appended claims which follow this disclosure.
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Claims (19)
1. A ring laser gyroscope, including a resonant cavity defining a closed optical path having a gain medium therein, comprising:
closed cavity resonant means for applying a radio frequency signal for exciting discharge of the gain medium.
closed cavity resonant means for applying a radio frequency signal for exciting discharge of the gain medium.
2. The ring laser gyroscope of claim 1, wherein said closed cavity resonant means for applying a radio frequency signal further comprises:
a helical coil surrounding a portion of said closed optical path;
said helical coil contained within an enclosed conductive resonator shield;
whereby, discharge of the gain medium of the ring laser gyroscope is achieved.
a helical coil surrounding a portion of said closed optical path;
said helical coil contained within an enclosed conductive resonator shield;
whereby, discharge of the gain medium of the ring laser gyroscope is achieved.
3. The ring laser gyroscope of Claim 2, wherein:
said ring laser gyroscope includes a monolithic dielectric material body;
said body having a plurality of tubular bores connected end to end in a polygonal configuration defining said closed optical path;
at least one side of said body being carved out to allow at least one of said tubular bores to be surrounded by said helical coil and enclosed conductive resonator shield;
whereby discharge of the gain medium of the ring laser gyroscope is achieved.
said ring laser gyroscope includes a monolithic dielectric material body;
said body having a plurality of tubular bores connected end to end in a polygonal configuration defining said closed optical path;
at least one side of said body being carved out to allow at least one of said tubular bores to be surrounded by said helical coil and enclosed conductive resonator shield;
whereby discharge of the gain medium of the ring laser gyroscope is achieved.
4. The ring laser gyroscope of claim 2, wherein an RF
oscillator is connected to said resonant means to supply radio frequency signal to said resonator.
oscillator is connected to said resonant means to supply radio frequency signal to said resonator.
5. The ring laser gyroscope of claim 4, wherein the RF
oscillator provides 3 radio frequency signal within a range from 5 to 550 megahertz.
oscillator provides 3 radio frequency signal within a range from 5 to 550 megahertz.
6. A ring laser gyroscope including a resonant cavity defining a closed optical path having a gain medium therein, comprising:
full wave resonant means for applying a full wave radio frequency signal for exciting discharge of the gain medium
full wave resonant means for applying a full wave radio frequency signal for exciting discharge of the gain medium
7. A ring laser gyroscope, including a resonant cavity defining a closed optical path having a gain medium therein, comprising:
resonant means for applying a half wave radio frequency signal for exciting discharge of the gain medium.
resonant means for applying a half wave radio frequency signal for exciting discharge of the gain medium.
8. A ring laser gyroscope, including a resonant cavity defining a closed optical path having a gain medium therein, comprising:
resonant means for applying a quarterwave radio frequency signal for exciting discharge of the gain medium.
resonant means for applying a quarterwave radio frequency signal for exciting discharge of the gain medium.
9. In a split gain multi mode ring laser gyroscope, including a resonant cavity defining a closed out-of-plane optical path having a gain medium therein, comprising:
an optical pathway having at least four legs;
at least one of said legs of said optical pathway being carved out and exposed from an integral width a ring laser gyroscope frame;
said exposed leg having a radio frequency helical coil wound around its length;
said radio frequency helical coil surrounded by a closed resonant shield forming a resonant cavity around said radio frequency helical coil;
a permanent magnet surrounding said resonator shield, said coil and said resonator shield being concentric and within said permanent magnet;
whereby, a radio frequency-excited split gain multi-mode ring laser gyroscope is provided where a permanent magnet necessary to achieve split gain within the ring laser gyroscope is positioned along the same axis as the resonator excitation means so that the active medium which arises is confined to the length of said permanent magnet.
an optical pathway having at least four legs;
at least one of said legs of said optical pathway being carved out and exposed from an integral width a ring laser gyroscope frame;
said exposed leg having a radio frequency helical coil wound around its length;
said radio frequency helical coil surrounded by a closed resonant shield forming a resonant cavity around said radio frequency helical coil;
a permanent magnet surrounding said resonator shield, said coil and said resonator shield being concentric and within said permanent magnet;
whereby, a radio frequency-excited split gain multi-mode ring laser gyroscope is provided where a permanent magnet necessary to achieve split gain within the ring laser gyroscope is positioned along the same axis as the resonator excitation means so that the active medium which arises is confined to the length of said permanent magnet.
10. The ring laser gyroscope of claim 4, including:
means for regulating said RF oscillator to provide a radio frequency signal to said helical coil within a predetermined range, said regulating means including frequency control means further comprising frequency detection coupling and amplification means coupled to phase lock loop means, said phase lock loop means controlling regulation of frequency provided by said RF oscillator to said helical coil; and, means for controlling power provided to said resonator means including photodetection means coupled to a signal comparator means, said signal comparator means adjusting an attenuator means with reference to a pre-determined optimum power supply level.
means for regulating said RF oscillator to provide a radio frequency signal to said helical coil within a predetermined range, said regulating means including frequency control means further comprising frequency detection coupling and amplification means coupled to phase lock loop means, said phase lock loop means controlling regulation of frequency provided by said RF oscillator to said helical coil; and, means for controlling power provided to said resonator means including photodetection means coupled to a signal comparator means, said signal comparator means adjusting an attenuator means with reference to a pre-determined optimum power supply level.
11. A ring laser gyroscope, comprising:
a resonant optical cavity formed within a monolithic block, said block defining a closed optical path, defined by at least three legs, having again medium therein; and a closed Radio-Frequency cavity resonator positioned along a portion of said closed optical path, including at least one of said legs, which applies a localized longitudinal radio frequency signal for exciting discharge of the gain medium;
said closed Radio-Frequency cavity resonator having a helical coil powered up by a power source exhibiting reduced power dissipation surrounding a portion of said closed optical path; and said helical coil contained within an enclosed conductive resonator shield, said helical coil and enclosed conductive resonator shield forming a high-Q, distributed parameter coaxial Radio-Frequency resonator assembly, and substantially aligned according to the following equations:
Qu = 50 D fo 1/2; and, N = (l900/fo D) turns;
where Qu is unloaded Q (quality factor);
D is the inside diameter of the resonator shield;
Fo is a resonant frequency (MHz) of said resonator assembly, and, N is the total number of windings of said helical coil.
a resonant optical cavity formed within a monolithic block, said block defining a closed optical path, defined by at least three legs, having again medium therein; and a closed Radio-Frequency cavity resonator positioned along a portion of said closed optical path, including at least one of said legs, which applies a localized longitudinal radio frequency signal for exciting discharge of the gain medium;
said closed Radio-Frequency cavity resonator having a helical coil powered up by a power source exhibiting reduced power dissipation surrounding a portion of said closed optical path; and said helical coil contained within an enclosed conductive resonator shield, said helical coil and enclosed conductive resonator shield forming a high-Q, distributed parameter coaxial Radio-Frequency resonator assembly, and substantially aligned according to the following equations:
Qu = 50 D fo 1/2; and, N = (l900/fo D) turns;
where Qu is unloaded Q (quality factor);
D is the inside diameter of the resonator shield;
Fo is a resonant frequency (MHz) of said resonator assembly, and, N is the total number of windings of said helical coil.
12. The ring laser gyroscope of claim 11, wherein:
said block is made from a dielectric material having a plurality of tubular bores connected end to end in a polygonal configuration defining said closed optical path;
at least one side of said body being carved out to allow at least one of said tubular bores to be surrounded by said helical coil and enclosed conductive resonator shield;
whereby discharge of the gain medium of the ring laser gyroscope is achieved.
said block is made from a dielectric material having a plurality of tubular bores connected end to end in a polygonal configuration defining said closed optical path;
at least one side of said body being carved out to allow at least one of said tubular bores to be surrounded by said helical coil and enclosed conductive resonator shield;
whereby discharge of the gain medium of the ring laser gyroscope is achieved.
13. The ring laser gyroscope of claim 11, wherein an RF oscillator is connected to said closed Radio-Frequency cavity resonator to supply said localized longitudinal radio frequency signal to said resonant optical cavity to achieve gain medium discharge within said ring laser gyroscope.
14. The ring laser gyroscope of claim 13, wherein the RF oscillator provides a radio frequency signal within a range of 5 to 550 megahertz.
15. The ring laser gyroscope of claim 11, wherein:
said closed Radio-Frequency cavity resonator applies a localized longitudinal half wave radio frequency signal along a portion of said closed optical path for exciting discharge of the gain medium.
said closed Radio-Frequency cavity resonator applies a localized longitudinal half wave radio frequency signal along a portion of said closed optical path for exciting discharge of the gain medium.
16. The ring laser gyroscope of claim 11, wherein:
said closed Radio-Frequency cavity resonator applies a localized longitudinal quarterwave wave radio frequency signal along a portion of said closed optical path for exciting discharge of the gain medium.
said closed Radio-Frequency cavity resonator applies a localized longitudinal quarterwave wave radio frequency signal along a portion of said closed optical path for exciting discharge of the gain medium.
17. The ring laser gyroscope of claim 11, wherein the helical coil of said closed Radio-Frequency cavity resonator is powered up by an RF oscillator system connected to said closed Radio-Frequency cavity resonator to supply radio frequency signals to said cavity resonator, said oscillator system including:
an RF oscillator;
means for regulating said RF oscillator to provide a radio frequency signal to said helical coil within a predetermined range;
said regulating means including frequency control means coupled to phase lock loop means, said phase lock loop means controlling regulation of frequency provided by said RF
oscillator to said helical coil; and means for controlling power provided to said Radio-Frequency cavity resonator including photodetection means coupled to a signal comparator means, said signal comparator means adjusting an attenuator means with reference to a predetermined optimum power supply level.
an RF oscillator;
means for regulating said RF oscillator to provide a radio frequency signal to said helical coil within a predetermined range;
said regulating means including frequency control means coupled to phase lock loop means, said phase lock loop means controlling regulation of frequency provided by said RF
oscillator to said helical coil; and means for controlling power provided to said Radio-Frequency cavity resonator including photodetection means coupled to a signal comparator means, said signal comparator means adjusting an attenuator means with reference to a predetermined optimum power supply level.
18. The ring laser gyroscope of claim 11, including:
feedback means for regulating said Radio-Frequency cavity resonator to provide a stable radio frequency signal to said helical coil within a predetermined frequency and power range;
whereby, excitation is lowered with minimal power dissipation and radio frequency interference.
feedback means for regulating said Radio-Frequency cavity resonator to provide a stable radio frequency signal to said helical coil within a predetermined frequency and power range;
whereby, excitation is lowered with minimal power dissipation and radio frequency interference.
19. The ring laser gyroscope of claim 18, wherein:
said feedback means for regulating said Radio-Frequency cavity resonator includes:
photodetection means for controlling and stabilizing the power provided to said Radio-Frequency cavity resonator;
and frequency control means for locking in the Radio-Frequency cavity resonator at a stable frequency.
said feedback means for regulating said Radio-Frequency cavity resonator includes:
photodetection means for controlling and stabilizing the power provided to said Radio-Frequency cavity resonator;
and frequency control means for locking in the Radio-Frequency cavity resonator at a stable frequency.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US21840588A | 1988-06-22 | 1988-06-22 | |
| US218,405 | 1988-06-22 |
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| CA1320557C true CA1320557C (en) | 1993-07-20 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000602343A Expired - Fee Related CA1320557C (en) | 1988-06-22 | 1989-06-09 | Radio frequency excited ring laser gyroscope |
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| CA (1) | CA1320557C (en) |
| FR (1) | FR2633389B1 (en) |
| GB (1) | GB2220098B (en) |
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|---|---|---|---|---|
| CN103674002B (en) * | 2012-09-07 | 2016-06-22 | 中国航空工业第六一八研究所 | A kind of faraday's alternation offset frequency two frequency laser gyro |
| CN103674003B (en) * | 2012-09-07 | 2016-06-01 | 中国航空工业第六一八研究所 | A kind of electromagnetic drive type shaking laser gyroscope mechanism |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3614657A (en) * | 1963-12-27 | 1971-10-19 | Jeol Ltd | Cylindrical plasma laser |
| US3521119A (en) * | 1968-01-10 | 1970-07-21 | Rca Corp | Rf excitation pumping of gas lasers by means of a wave guide and coupling coils |
| US3602837A (en) * | 1970-03-31 | 1971-08-31 | Us Army | Method and apparatus for exciting an ion laser at microwave frequencies |
| US3772611A (en) * | 1971-12-27 | 1973-11-13 | Bell Telephone Labor Inc | Waveguide gas laser devices |
| GB8521065D0 (en) * | 1985-08-22 | 1985-09-25 | English Electric Valve Co Ltd | Discharge tube arrangements |
| GB2185846B (en) * | 1986-01-24 | 1989-12-20 | Ferranti Plc | Ring laser |
| GB2194380A (en) * | 1986-08-04 | 1988-03-02 | Dr Jeremy Kenneth Arth Everard | Laser plasma and optical resonator structures |
| JPS6381878A (en) * | 1986-09-25 | 1988-04-12 | Toshiba Corp | Gas laser oscillator |
-
1989
- 1989-06-09 CA CA000602343A patent/CA1320557C/en not_active Expired - Fee Related
- 1989-06-21 FR FR8908290A patent/FR2633389B1/en not_active Expired - Fee Related
- 1989-06-22 GB GB8914321A patent/GB2220098B/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| FR2633389A1 (en) | 1989-12-29 |
| GB2220098B (en) | 1992-09-09 |
| FR2633389B1 (en) | 1992-10-16 |
| GB2220098A (en) | 1989-12-28 |
| GB8914321D0 (en) | 1989-08-09 |
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