JPS6138635B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to laser gyroscopes, and specifically to laser gyroscopes that use waves of four different frequencies within a laser gyroscope cavity. More specifically, the present invention extracts a portion of a beam circulating within a cavity and is used to generate an output signal from that portion representing the frequency difference between a pair of beams having the same polarity within the cavity. The present invention relates to an output optical structure. In general, a laser gyroscope is a system in which two or more waves circulate in both directions through a laser medium, and the rotation of the system varies according to the speed and amount of rotation required for the waves to rotate in both directions. This is a device that does this. In systems using two waves, for low rotational speeds corresponding to small theoretical difference frequencies the actual output difference frequency is zero or less than expected due to a phenomenon known as "lock-in". It is known to be quite small. The lock-in problem arises because of coupling between waves that arises from a number of possible factors, including backscattering of wave energy from elements in the path, such as reflectors or Faraday rotators, and centers of scattering within the laser medium itself. It is believed that there is. The earliest attempts to compensate for this problem included the use of Faraday rotators, which caused beams propagating in different directions to undergo different delay times.
This included a proposal to bias two beams to zero rotation far from the zero power level. Unfortunately, simply biasing the two beams far enough apart to avoid lock-in creates a large frequency difference between the two beams;
This frequency difference was in fact so large that the change in frequency caused by a normal amount of rotation became rather meaningless compared to the total frequency. Therefore, any small drift could cancel out the actual desired signal output. Other attempts to achieve biasing have involved switching the Faraday rotator from one direction to the other using a symmetric AC switching waveform. Such a scheme has proven to be somewhat difficult to implement because the symmetry of the AC switching waveform must be maintained to be greater than one part in a million. Furthermore, one of the most successful laser gyroscopes proposed and constructed uses two pairs of four waves each propagating in opposite directions. Such a system is described in U.S. Patent No. 1, granted to Keimpe Andringa.
It is shown in the specifications of No. 3741657 and No. 3854819. This laser system uses circular polarization for each of the four waves. Clockwise propagating wave or beam pairs, as well as counterclockwise propagating wave pairs, include both left-handed and right-handed circular polarizations. Two biasing elements are provided. A device such as a quartz crystal rotator provides a delay for one direction of circular polarization, with a different delay for the other circular polarization, and the delay is reversible. That is, waves of a given polarization traveling in either direction through the crystal are delayed by the same amount of time. Second, devices such as Faraday rotators are also placed in the wave path. This device is irreversible and gives a wave of either polarization direction different time delays for the two directions of propagation through it. In any of these laser gyroscope systems, a portion of each beam circulating within the laser cavity is sampled to calculate the frequency difference between pairs of waves with the same circular polarization direction within the laser cavity, respectively. It is necessary to produce two output signals representing . To achieve this objective, it is desired to combine these two beams at a point within the output structure in such a way as to produce two new beams, each containing waves with the same polarization direction. Known output structures for separating, combining, and detecting output signals are mechanically bulky and wasteful of signal energy, do not adequately separate polarization states, and are This caused interference in the output. Because of the waste of signal energy within the output structure, a relatively large proportion of the output energy must be extracted from the cavity;
Required relatively large gain from the laser gain medium. Mechanical disadvantages of these structures have made these systems difficult to use in many applications. Additionally, because the various components within the output optical structure are not within direct physical contact with each other, misalignment problems between the various components often occur as well as drift problems. Also, in many structures it has not been possible to use two diodes on a single chip for the output detector so that the characteristics of the diodes are approximately equal. It is therefore an object of the invention to provide a mechanically robust and
An object of the present invention is to provide a laser gyroscope system having a compact and efficient output structure. It is an object of the present invention to provide a laser gyroscope system in which all components of the output structure can be directly mechanically coupled to eliminate the problems of misalignment and associated drift. That's true. Furthermore, it is an object of the invention to provide such an output structure in which the available output signal energy is maximized. Furthermore, it is an object of the present invention to completely separate waves with the same polarization direction from other pairs of waves in the cavity to eliminate interference between the two signal outputs of the detector, making it safer and noise-free. The object of the present invention is to provide a structure that can generate a signal that does not require a signal. Furthermore, it is an object of the present invention to provide an output optical structure that allows the use of two diodes on a single chip. These and other objects of the invention are achieved by providing the following combinations. namely, a laser gyroscope cavity containing a laser gain medium, a polarization dispersive structure producing waves of at least four frequencies, and a plurality of reflecting means forming a loop or closed path for the waves, one of which at least one of the beams is partially transparent to the waves incident thereon); in combination with means for directing the beam splitter to a position such that the beam splitter produces both a transmitted beam and a reflected beam. As used herein, the term "wave" refers to a single electromagnetic wave propagating in one direction, whereas the term "beam" refers to two or more electromagnetic waves propagating along the same path in the same direction. It is used to mean electromagnetic waves. The above combination is
Further, a polarization converting means for converting the circularly polarized wave in the output structure into a linearly polarized wave located in the path of the reflected wave and the transmitted wave from the beam splitter, polarizing means disposed in the path of the linearly polarized wave as it emerges from the means;
and detection means for receiving waves as they emerge from the polarization means. Preferably, the number of waves is 4, and two of these waves in the cavity are circularly polarized with a first polarization direction;
The remaining two of these waves within the cavity are circularly polarized with a second polarization direction. A first of the waves having a first direction of polarization and a first of the waves having a second direction of polarization circulate around the path in the first direction; A second of the waves having a wave direction and a second of the waves having a second polarization direction circulate in opposite directions around the closed path. In a preferred embodiment, the partially transmissive reflecting means, beam splitter, directing means and converting means described above are mechanically coupled and mounted as one rigid unit. Furthermore, the above-described detection means and polarization means may further be included as part of this unit. The partially transmissive reflective means described above can be constituted by a mirror made of a multilayer electrically conductive material including a transparent substrate. Preferably, said converting means is a quarter-wave plate, whereas the directing means is preferably a retro prism. The present invention can also be implemented by the following combinations. a laser gyro cavity containing a laser gain medium; a polarization dispersive structure for generating waves of at least one frequency; and a plurality of polarization dispersive structures arranged to form a loop or closed path for propagating the waves. a first beam from the transparent substrate; a transparent substrate; a plurality of layers of dielectric material on one surface of the transparent substrate forming one of the reflecting means for waves in the cavity; a beam splitter disposed on a portion of the second surface of the transparent substrate at a location where the beam splitter appears, a quarter wave plate disposed on the beam splitter, and adjacent the quarter wave plate; a plurality of at least partially reflective second surfaces having a first surface opposite the first surface and inclined with respect to the first surface;
first and second polarizers disposed adjacent a fourth non-reflective surface of the prism;
and first and second detectors disposed adjacent to the second polarizer. The first beam emerging from the substrate hits the beam splitter at a predetermined position, and the second beam emerging from the substrate hits the beam splitter at a predetermined position.
The beam passes through the quarter-wave plate without touching the beam splitter, and is reflected from both sides of the prism back to the same position on the beam splitter where the first beam hit. This produces transmitted and reflected waves, each containing waves of all four frequencies. A first transmitted wave and a first reflected wave from the same location on the beam splitter pass through the substrate and back through the substrate from behind the layers of dielectric material to the quarter wave plate. and finally from one of the reflective surfaces of the prism to a first polarizer and a first detector. This first polarizer is oriented to pass only the preferred two of the 4% waves contained in the beam at that point. A second transmitted wave and a second reflected wave from that point on the beam splitter are reflected from the same one of the reflective surfaces of the prism to a second polarizer and a second detector. This second polarizer is oriented to couple the other two waves to a second detector. In a preferred embodiment, the layers of dielectric material, substrate, beam splitter, quarter wave plate, and prism are mechanically interconnected to form a rigid structure. Additionally, second and third quarter-wave plates may be provided, the second quarter-wave plate being disposed between the prism and the first polarizer, and the third quarter-wave plate being disposed between the prism and the first polarizer. A single wavelength plate is placed between the prism and the second polarizer. The provision of these second and third quarter wave plates also has the added benefit of reducing interference or crosstalk in the beam caused by depolarization at the surface of the dielectric layer. The present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of a laser gyroscope system in which the present invention may be advantageously used. The laser gyroscope cavity 5 is described in U.S. Pat.
It operates in the manner described at the beginning of the column. The laser gyroscope cavity 5 has a closed or reentrant path for propagating four electromagnetic laser waves. This path includes a laser gain medium 10, reflectors 12 and 13, and a crystal rotator 1.
7 and a polarization dispersive structure 16 including a Faraday rotator 18, a reflecting mirror 15, and an output reflecting mirror 2.
Contains 2. There are four electromagnetic waves of frequencies ₁ to ₄ propagating in the closed path due to the biases produced by the crystal rotor 17 and the Faraday rotator 18. Frequency ₁ and ₄
The waves of frequencies 2 _{and 2} circulate clockwise to form one beam in cavity 5, whereas the waves of
Wave ₃ circulates counterclockwise to form a second beam. Preferably, all four waves are circularly polarized, with waves of frequencies ₁ and ₂ being circularly polarized in one direction and waves of frequencies ₃ and ₄ being circularly polarized in the opposite direction. Polarized.
The position on the gain curve for laser gain medium 10 is shown in the lower diagram of FIG. The output signal from this system is a digital number or other signal representing the total amount of rotation experienced by the laser gyroscope cavity 5 starting from a predetermined period of time, or Preferably, it is a digital signal or other signal representative of the current rotational speed. This rotation speed is calculated according to the formula below. Ω=Lλ/8A [( _{4-3 )} -( _2-1 )] Here, Ω represents the rotational speed of the gyroscope around the attenuation axis, L represents _the total path length, and A is represents the effective area enclosed within this path, and λ represents the wavelength of the wave propagating within the laser beam cavity 5. The amount of rotation is obtained by integrating the above equation with respect to time. In order to generate a signal representing the amount of rotation, first obtain a signal representing the frequency difference between the cavity waves of one circularly polarized wave, represented by _4-3 and _{2-1 ,} respectively, and a frequency difference in the other circularly polarized wave _. It is necessary. The operation of combining the beams of frequencies ₁ and ₂ on the first detector diode and the beams of frequencies ₃ and ₄ on the second detector diode allows the presence of two other waves on either diode. It is the function of the output optical structure 30 to perform this without any problems. Output processing circuit 32 converts a signal representing the difference between the right-handed circularly polarized signal and the left-handed circularly polarized signal into a digital number representing the amount of rotation according to the above equation. The output processing circuit 32 further acts on the amplitudes of the signals obtained from the two output diodes so that from those signal amplitudes the gains matching the wave pairs are substantially equal to the laser gyroscope cavity 5. An analog signal is generated that operates the piezoelectric transducer 20 to maintain the appropriate total path length within the oscilloscope. FIG. 2 shows a schematic diagram of an output optical structure embodying the invention. The output reflector 22 forms one of the reflectors defining a closed path within the laser gyroscope cavity 5 . The output reflector 22 is
Preferably, it is more than 99% reflective for the two beams incident on it. However, a portion of each output beam is transmitted through output reflector 22 and emerges from its rear side towards reflectors 40 and 41. Output reflector 2 for the explanation given immediately below.
Consider the case where transmission of a circularly polarized wave through 2 does not substantially change its polarization state. The transmitted counterclockwise beams labeled CCW include, for example, frequencies ₂ and ₃ of left-handed circular polarization and right-handed circular polarization, respectively. As shown in the two small drawings in FIG. 2, the polarization direction of each wave changes from left-hand side to right-hand side or from right-hand side to left-hand side in a known manner upon reflection, so that the direction of polarization of each wave changes from one cavity path to the next. The sides are reversed.
Therefore, the clockwise beams marked CW have frequencies ₁ of right-handed circular polarization and left-handed circular polarization, respectively.
and ₄ waves. The clockwise beam is reflected from reflector 40 to a predetermined position on beam splitter 42 . The counterclockwise beam is similarly reflected by mirror 41 to the same position on beam splitter 42. The beam impinging on beam splitter 42 produces both transmitted and reflected components, which are preferably of approximately equal magnitude. Beam splitter 42 is angularly aligned to equally linearly combine the beam transmitted through the beam splitting surface and the beam reflected therefrom.
Thus, the combined transmitted and reflected beams from beam splitter 42 each contain waves of all four frequencies. The transmitted portion of the clockwise beam and the reflected portion of the counterclockwise beam propagate along the same path to quarter wavelength 53. Similarly, both the transmitted portion of the counterclockwise beam and the reflected portion of the clockwise beam propagate along the same path to quarter wave plate 43. Therefore, between the beam splitter 42 and the quarter-wave plates 43 and 53, the pair of right-handed circularly polarized frequencies and the pair of left-handed circularly polarized frequencies are coupled, and both follow the same path. It's progressing in the same direction. For example, in front of the quarter-wave plate 53, there is a frequency that is left-handed circularly polarized.
There are waves ₁ and ₂ and waves of frequencies ₃ and ₄ that are right-handed circularly polarized. These waves of the same frequency are transmitted through a beam splitter 42 and a quarter wave plate 4.
3 and exist with opposite circular polarization directions. Quarter-wave plates 43 and 53 are oriented, for example, so that left-handed circularly polarized waves are converted to vertically polarized waves and right-handed circularly polarized waves are converted to horizontally polarized waves. Polarizers 44 and 54 are provided that pass only linearly polarized waves. These are oriented in orthogonal relation to each other, so that, for example, polarizer 44 passes only horizontally polarized waves and polarizer 54 only passes vertically polarized waves.
In this configuration, the polarizer 54 and the detector diode 5
The beam has a linear vertical polarization between 5 and 5 frequencies
The beam between the _polarizer 44 and the detector diode ₄₅ consists only of frequencies ₃ and ₄ with horizontal polarization. simply 2
It will be readily appreciated that waves of only one frequency impinge on each detector diode, while waves of the other two frequencies are completely dropped. It is a significant advantage of the present invention that both the transmitted beam and the reflected wave from the combining beam splitter are utilized to form the final output beam. In prior art output optics, only one of the two output beams from the beam splitter was utilized. Therefore, using the present invention, half the waste of output energy is eliminated. As before, only half of that energy needs to be extracted from the laser gyroscope cavity, thus reducing the gain required from the laser amplifier and laser gain medium. FIG. 3 shows an embodiment of the invention in which all output optical components are mechanically interconnected within a mechanically rigid honeycomb structure.
In this embodiment, a reflector substrate 104, which may be constructed of fully transparent glass, is coated with multiple layers of dielectric material 102 to form a most reflective reflector on one smooth surface thereof. . This reflector forms one of the reflective elements defining the closed path of the laser gyroscope cavity 5. The number and configuration of dielectric material layers 102 are chosen such that a small portion of the beam incident thereon is transmitted into the mirror substrate 104. Typically, 1/2% of the energy in the incident beam is transmitted into the mirror substrate 104. Beam splitter 1 also made of dielectric material
06 is a reflection mirror substrate 10 from a plurality of dielectric layers 102.
placed next to opposite parallel surfaces of 4. A beam splitter 106 is formed to allow the beam to pass therethrough as shown in the drawings. In practice, the beam splitter 106 consists of four
It can be formed by depositing a dielectric material on the surface of the half-wave plate 108 and then etching the annulus using, for example, ion beam etching techniques to form the necessary openings. By providing an annular aperture in the beam splitter 106, the structure consisting of the quarter-wave plate 108 and the splitter 106 can be rotated to separate the quarter-wave plate 108 and the beam incident thereon. For example, a left-handed circularly polarized beam is completely converted to a vertical linearly polarized beam, and a left-handed circularly polarized beam is completely converted to a horizontally linearly polarized beam. can do. The lower surface of retro prism 110 is disposed adjacent to the upper surface of No. 4 one-wavelength plate 106.
Retrobrism 110 is preferably constructed of highly transparent glass. Quarter wavelength plate 108
Two additional surfaces of retro prism 110 are opposed so as to provide the surfaces of retro prism 110 in contact with the beam reflection angles shown in the figures. These surfaces are provided with reflective coatings 112 and 114, which may consist of either multiple dielectric layers or a metallized coating. Polarizers 116 and 118 are positioned adjacent the fourth surface of retro prism 110, shown on the left hand side in FIG. Detector diodes 120 and 122 are polarizers 116 and 118
are placed opposite to each other to receive linearly polarized waves transmitted by these polarizers. Polarizers 116 and 118 are oriented in orthogonal relation to each other as before. Diode mounting member 124 includes detector diodes 120 and 122 as well as polarizer 116.
and 118 are fixed to the left surface of retro prism 110. The device shown in FIG. 3 operates in a similar manner to the device shown in FIG. 2 to combine cavity waves of the same circular polarization direction while rejecting waves of opposite circular polarization directions, and This combined wave is sent to the detector diode without significant waste of signal energy. The operation of the apparatus shown in FIG. 3 is illustrated in Table 1 below, which shows the polarization states for various waves at selected points within the apparatus.

[Table] In Table 1, the symbol "L" diagonally above indicates left-handed circular polarization, the symbol "R" indicates right-handed circular polarization, and the symbol "V" indicates vertical linear polarization. The symbol "H" indicates horizontal linear polarization. As before, the symbol at the bottom indicates the frequency of the particular wave. 1/1
The wave plate 108 is configured such that the right-handed circularly polarized wave and the left-handed circularly polarized wave are converted into horizontally linearly polarized waves and vertically linearly polarized waves, respectively, that is, the fast axis direction is +45.
It is oriented so that ゜. It should also be noted that when horizontally polarized waves and vertically polarized waves pass through the quarter-wave plate 108 in either direction, they are converted into right-handed circularly polarized waves and left-handed circularly polarized waves, respectively. That's true. All beams below quarter wave plate 108 are circularly polarized and quarter wave plate 1
It is understood that the beam above 08 is linearly polarized. Because horizontally and vertically polarized waves are stationary modes for reflection from surfaces with normals in the plane of incidence, interference occurs when reflected from any of the surfaces above quarter-wave plate 108. There is no loss of polarization induced by . The passage of a representative beam can be traced through the device. The beams circulating counterclockwise at point A within the laser gyroscope cavity 5 have frequencies ₂ and ₃ which are left-handed and right-handed circularly polarized, respectively. A small portion of these beams is transmitted through dielectric layer 102 and into mirror substrate 104 . The polarization of the incident beam is substantially maintained due to the small angle of incidence with respect to the normal to dielectric layer 102. Preferably, the laser gyroscope cavity 5 is constructed in such a way that the angle between the incoming beams is less than 30°. By maintaining such a small angle of incidence on the dielectric layer 102, a high degree of maintenance of circular polarization is achieved. For large angles of incidence, the flatness of the beam emerging from the rear surface of dielectric layer 102 increases rapidly. As the flatness increases, the signal energy available at each detector diode is reduced because the polarizer must be oriented either to completely eliminate the undesired component or to pass the maximum amplitude of the desired signal. I get tired. Since the beam is no longer at orthogonal energy to the elliptical polarization, the polarizer cannot be directed to pass both the maximum amplitude of the desired signal while rejecting all of the undesired components. In the former case, interference occurs between the desired output signals;
In the latter case a reduction in signal amplitude occurs. At point B, which is within the reflector substrate 104, there is a counterclockwise component from the four waves circulating within the laser gyroscope cavity. These are frequencies ₂ for left-handed circularly polarized waves and right-handed circularly polarized waves, respectively.
and ₃ . When passing through the aperture of beam splitter 106 and quarter wave plate 108, these waves are converted to vertical and horizontal polarization, respectively. The same polarization is maintained after reflection from reflective coatings 114 and 112 on the top surface of retro prism 110, however, this beam has frequencies ₁ and ₄ of right-handed and left-handed circular polarization, respectively. is displaced a lateral distance in such a way as to coincide on the top surface of beam splitter 106 at the same location as the beam labeled "I" containing a component from the clockwise beam of . Transmitted and reflected components are produced from the beams in such a way that both the reflected and transmitted beams from a common point of incidence on beam splitter 106 contain waves of all four frequencies. Beam J includes horizontally polarized waves at frequencies ₁ and ₂ and vertically polarized waves at frequencies ₃ and ₄ , the latter two being converted from circularly to linearly polarized by quarter-wave plate 108. It has been converted. Similarly, beam D includes waves of frequencies ₁ and ₂ of left-handed circular polarization and waves of frequencies ₃ and ₄ of right-handed circular polarization. The polarization direction is the dielectric layer 102
The opposite occurs when it is reflected from the rear side. Beam E passes through the aperture of beam splitter 106 and is converted back to linear polarization at frequency ₁ of horizontal polarization.
and ₂ waves and vertically polarized waves of frequencies ₃ and ₄ . Beams 6 and J are reflected by reflective coating 112 onto polarizers 116 and 118. Polarizer 116 is oriented to pass only horizontally polarized waves, whereas polarizer 118 is oriented to pass only vertically polarized waves. In this way, waves with frequencies ₁ and ₂ are coupled to detector 120, and waves with frequencies ₃ and ₄ are coupled to detector 120.
waves are coupled to a detector 122. Heterodyne action between the two waves incident on each detector occurs within that detector resulting in an output signal in the form of a sine wave that is biased by a low frequency or DC component. The frequency of each sine wave is equal to the frequency difference between the two waves incident on a particular detector, whereas the magnitude of each DC component, which is proportional to the average amplitude of the output signal, is the magnitude of the intensity of these two incident waves. Proportional to the sum. Further processing from the output processing circuit 32 generates a digital signal representing the amount of rotation and an analog signal used for the operation of the piezoelectric transducer 20 to maintain the appropriate path length within the laser gyroscope cavity 5. be done. It will be appreciated that the invention described in connection with FIG. 3 provides a durable, compact and mechanically sound structure. In the prior art, each individual optical component was mounted separately on an individual frame, which was fixed to the underlying substrate. Utilizing the present invention, the output optical structure is provided in a single, rigid unit, greatly saving space. This advantage is extremely important in many applications where both the space occupied by any component and the total weight are to be minimized. FIG. 4 shows a cross-sectional view of another embodiment of the invention in which a compact and robust mechanical output optical structure is provided. The apparatus of the embodiment shown in FIG. 4 operates in much the same manner as that shown in FIG. 3, except that the positions of the beam splitter and quarter-wave plate are reversed. The difference is that a point and a different shaped prism 130 are used to produce different beam paths. Polarizers 116 and 118 and detector diodes 120 and 122 are also mounted on the same surface of retro-brism 130, which is partially covered with reflective coating 134. The operation of the device shown in FIG. 4 is detailed in Table 2 which shows the frequency and polarization state of the waves present in the device.

[Table] In Table 2, the polarization state symbols "+" and "-" indicate linearly polarized waves oriented positively and negatively relative to the horizontal at an angle, typically 30° to 45°. means. Transmission through the multilayer dielectric coating changes the polarization state of the circularly polarized waves, making them elliptical. This effect results from the difference in transmission of electromagnetic waves in which the principal plane of electric field oscillation lies within the plane of incidence ("P" polarization) compared to waves oscillating perpendicular to the plane of incidence ("S" polarization). The ratio of the transmittance for these two polarizations depends on the angle of incidence and typically has a value of 1, 2 to 5.
This causes a corresponding flattening of the transmitted wave, resulting in a wave with elliptical rather than linear polarization. Therefore, the polarizer cannot block the two undesirables in each diode. However, in the quarter wave plates 136 and 138 of FIG. 4, the polarization of the undesired wave is straightened in each case with the polarizer oriented to block the undesired polarization. Interference is therefore completely eliminated. Furthermore, if there was a change in polarization during reflection on the back side of the reflecting mirror 102, this would be 1/4 of the same amount.
It can be compensated at the same time with wave plate 138. As previously mentioned, the desirability of eliminating interference can be understood from a consideration of gyroscope output noise. The present invention allows interference rejection even in the presence of different "S" and "P" transmissions of the output reflector 102 while reducing the signal energy by only a small amount. In the embodiment shown in FIGS. 4 and 5, the quarter wave plate can be oriented at 0° rather than 45°. In this case, reflector 1
The elliptically polarized wave emerging from 02 is immediately converted by a quarter-wave plate into two generally linearly polarized waves in non-orthogonal planes. Therefore, when these waves do not encounter further polarization-depleting elements, interference can be eliminated by the use of polarizers 116 and 118 without the need for additional quarter-wave plates. It is possible. FIG. 5 shows another embodiment of the invention in the form of a mechanically strong, rigid and compact structure. The polarization states of the various beams are shown in Table 3.

[Table] The prism shape used in the apparatus of FIG. 4 is used in this example. However, no quarter wave plate is provided adjacent to beam splitter 106. However, individual quarter-wave plates 136 and 138
It is located adjacent to 8. This embodiment achieves the advantage that the quarter wave plate for each detector diode can be adjusted individually. This may result in some degree of polarization loss resulting in phase error differences or reflectance differences from or through the various reflective coatings and dielectric layers, or non-ideally from quarter-wave plates. Useful in situations where elliptical polarization occurs due to differences in transmittance. Additionally, in the embodiment of FIG.
A half-wave plate may be provided or, equivalently, the polarizer 116 of the embodiment of FIG.
and 118 may be preceded by individual quarter-wave plates. Dual quarter-wave plates have the advantage of eliminating almost all aberrations caused by the loss of polarization of the individual beams. It will be understood that the invention is not limited to the embodiments shown in the drawings, but that various modifications are possible within the scope of the invention.

[Brief explanation of the drawing]

1 is a block diagram of a laser gyroscope system in which the invention may be advantageously used; FIG. 2 shows an output structure according to the invention with separately mounted optical components; FIG. 4 is a sectional view of an output structure according to the invention in which all output components are combined in one mechanically rigid structure; FIG. 4 is a sectional view of another embodiment of the invention; FIG. is a cross-sectional view of yet another embodiment of the present invention. 5... Laser gyroscope cavity, 10...
... Laser gain medium, 12, 13, 15 ... Reflector, 16 ... Polarization dispersive structure, 17 ... Crystal rotator, 18 ... Faraday rotator, 20 ... Piezoelectric transducer, 22 ... Output Reflector, 30... Output optical structure, 32... Output processing circuit.

Claims (1)

[Claims] 1. (a) A laser gyroscope cavity comprising a laser gain medium and a polarization dispersion structure that generates two pairs of circularly polarized waves, each having a different frequency, the cavity comprising: In order to maintain the two pairs of circularly polarized waves, a plurality of reflecting means are arranged to form a closed path passing through the gain medium, and each of the two pairs of circularly polarized waves propagates in opposite directions, and the two pairs of circularly polarized waves propagate in opposite directions. A first pair of circularly polarized waves has a first direction of polarization at frequencies ₁ and ₂ , and a second pair of waves has a second direction of polarization opposite to the first at frequencies ₃ and _f4 . a cavity output window having a first surface area that is partially transparent to the two pairs of waves impinging thereon, and producing a pair of cavity output beams;
One of the pair of cavity output beams (the first cavity output beam) has a portion of the wave propagating in the first direction of the first pair and a portion of the wave propagating in the first direction of the second pair. the other of the pair of cavity output beams (the second cavity output beam) comprises a portion of the wave of the first pair propagating in the second direction; a portion of the wave propagating in a second direction, the pair of cavity output beams each having an opposite polarization direction; (b) a beam splitter; , (c) directing the first cavity output beam along a first path;
directing means for directing a second cavity output beam along a second path to a common area of the beam splitter, the directing means being disposed within the second path and directing the second cavity output beam; a retroreflector for redirecting, the beam splitter transmitting a portion of the first cavity output beam and reflecting a portion of the redirected second cavity output beam along a first common path; generating a first mixed beam, transmitting a portion of the redirected second cavity output beam and reflecting a portion of the first cavity output beam;
generating a mixed beam, a second mixed beam being reflected by a second surface area of the cavity output window and directed along a second common path, the first and second mixed beams each having a frequency of ₁ ; , ₂ , ₃
and ( _d ) a directing means disposed in the first and second common paths of the mixed beam and offset from the first and second paths of the cavity output beam; means for converting the waves of the first and second mixed beams into substantially linearly polarized waves, the means for converting the waves in opposite polarization directions into substantially orthogonal linearly polarized waves; (e) said conversion; detection means for generating a pair of electrical signals in response to the energies of the first and second mixed beams, one of the pair of electrical signals being at a frequency of the first pair of waves within the cavity; ₁ and ₂ , and the other of the pair of electrical signals represents the difference between frequencies ₃ and ₄ of a second pair of waves in the cavity. .