rus
Issue #2/2014
D.Lukyanov, Y.Filatov, Y.Golyaev, V.Kuryatov, V.Vinogradov, K.-U. Schreiber, M.Perlmutter
Laser Gyroscope Is 50 Years Old. Part II
Laser Gyroscope Is 50 Years Old. Part II
Optical gyroscopes still retain leading positions in the navigation systems and tactical targeting systems market. If in the low accuracy sensors market sector dominate MEMS sensors due to their low price and compactability, in the strategic navigation systems laser gyroscopes percent is large in spite of fiber-optic and micromechanical gyroscopes active competition. The article brings of an overview of laser gyroscopes market state.
Теги: kaser gyroscopes navigation tactical targeting systems лазерные гироскопы навигация системы тактического наведения
LG Technologies in 70s
One of shortcomings which showed up at that time in early models of laser gyroscopes (LG) was the long warm-up period. Herewith, most of the potential applications required the sensor to be ready for the operation in several minutes after start. Also, the power consumption was unsatisfactory. Effort to correct these shortcomings became one of the key tasks for American scientists in 70s [9].
Resonator was the main component on which the works were carried out. Its temperature sensitivity caused the long warm-up time and required the availability of heaters. Heaters were the main power consumer in LG. Transition from aluminum to glass ceramics became the solution of the set task. Having practically zero coefficient of temperature expansion such material made it possible to control the perimeter using the piezoelectric converters based on mirrors and abandon the heaters.
Other element affected by the temperature dependence was the totally reflecting prism (TRP). They were replaced by the multilayer dielectrical mirrors. By that time, their production technologies had made a step forward and it became possible to manufacture mirrors with the reflection coefficient of more than 0.999.
The Faraday cell was subject to replacement too. Special magneto-optic mirrors were applied instead. Their operation principle was based on the Kerr effect [13]. Such mirror under the action of magnetic field brought the nonreciprocal phase shifts into the incident rays. Implementation of all above-listed innovations and improvement of discharge tube allowed the creation of LGs of new generation, warm-up period of which was about several minutes. Structure chart and appearance of one such sensor are given in Fig. 10.
De Lange suggestion [14] on the usage of four-wave mode in LG for the reduction of counter-propagating waves coupling should be specifically mentioned. Patent of the USA [15] issued on differential LG (Differential Laser Gyro System) appointed the common abbreviation DILAG for four-wave LGs. Development of one of the earliest DILAG models refers to 1977 [16]. Further, this gyroscope was developed in Litton and Northrop Grumman where it received the name of ZLG (Zero Lock Gyro) and became popular in many systems.
In the middle of 70s, number of inertial measurement modules (IMMs) with three and more axes was developed by the efforts of Sperry company (Lockheed Martin branch). Resonator monolithic construction allowed considerable reduction of the error caused by axes non-orthogonality in comparison with the construction of three one-axial LGs in one body as well as essential decrease of the unit dimensions. Some examples of such sensors are given in Fig. 11.
In the Soviet Union during this period Arsenal Design Bureau in Kiev was actively involved in the development of LG. Having own manufacturing capabilities it could develop the LG theory and form the new concepts of their construction as well as improve the technological aspect of manufacturing. These activities were performed in close cooperation with the leading research and technological organizations of the Soviet Union in the following main areas:
Development of multilayer mirrors;
Development of nonreciprocal elements based on Faraday effect;
Formation of the vacuum treatment technology for LG resonators;
Development of the special glass ceramics with ultralow coefficient of linear expansion;
Development of cold cathodes;
Establishment of research, manufacturing and testing facilities at Arsenal Production Association;
Development of mathematical support and hardware for the processing of LG information etc.
Since 1974 the batch production of LGs of KOG-1 type with the following characteristics had started:
Warm-up time: less than 60 ms;
Shock resistance: more than 4g (since 1976 – more than 60g);
Measurement error: 0.5°/h.
Device is made in the form of solid glass-ceramic unit where three identical LGs are located with the matching sensitivity axes. Differential nonreciprocal element is used in every LG. Appearance of KOG-1 is shown in Fig. 12a.
In 1976 the serial supply of the reference boresight storage devices based on KOG-1 was started. Since 1978 the modified series of KOG-2 capable to operate under the conditions of radiation and seismic exposure up to 40–120 g with the error of not worse than 0.01°/h and warm-up period of not less than 20 ms has been produced.
In 1979–1981 "Fanza", the new LGs for the surface mobile facilities which provided the gyro-compassing mode were being developed. Differential nonreciprocal element was used in them as well as the first constructions. LG operated with the reverse around the vertical axis. Compassing error was σ≤8´ per 10 minutes of operation. In the mode of measurement of the current orientation the error on angles of course, pitch and roll was σ = 0.3°/hour. Appearance of the device is shown in Fig. 12b. On the basis of this device LG three-axial unit was being developed in 1978–1981 (Fig. 12c).
Development of LG took place in Europe in analogous manner and in the middle of 70s Sagem (France) and Marconi (Great Britain) started the development of strapdown inertial navigation systems based on LGs. However, these activities reached the fullest flourishing only in the following decade which is called "laser gyroscopy decade" by some researchers [10].
80s
Over the years the systems based on LG kept finding newer and newer applications. Herewith, some of them required high vibration and shock resistance from sensors. According to the research, applied glass ceramic resonator unit did not endure the design loads. Metal unit had the necessary strength properties. However, it had a number of obvious shortcomings:
Metal is conductor, thus it is impossible to organize the discharge tube in it;
Metal resonator has high temperature coefficient.
Herewith, transition to the metal resonator in essence was the return to the initial model, sample of the middle of 60s (see Fig. 4). However, specifically it turned out to be the task solution. LG modular construction allowed carrying the discharge tube outside the metal resonator. As it turned out, the temperature effects are not important in this case because the time of the device operation is so short that there is not enough time for the change of resonator temperature. Thus, in early 80s developers of Lockheed Martin managed to produce the vibration- and shock-resistant LG based on the metal resonator (Fig. 13).
Besides the selection of resonator material, there were other tasks set before the developers. Ultrashort time of the sensor operation meant the necessity of practically momentary steady-state operation. Herewith, the operation principle of discharge tube required about several minutes for the first spark occurrence [17]. In order to solve this task small radioisotope which served as the source of the medium constant ionization was added to the discharge tube. As a result, LG warm-up time reduced to several milliseconds.
In the USSR during this period one of the main current tasks was the increase of LG accuracy. It was achieved at the expense of improvement of gyroscope and associated electronics arrangement, transition to the glass ceramic materials. Arsenal Plant with its Central Design Bureau wasn’t exception. In Kiev since the middle of 80s LGs with the "empty" (without nonreciprocal element) resonator for navigation systems were being developed. They used the traditional dithering device and ensured the zero drift up to 0.03°/h.
By the beginning of 90s Arsenal Production Association and Central Design Bureau had the whole range of technologies allowing the production of different modifications of LGs. Low-volume output of the special LGs with triangular configuration can be specified as the example; on the basis of these LGs together with Leningrad Electrotechnical Institute the output of dynamic laser goniometers which were widely applied in CIS as well as abroad was organized [18].
In the beginning of 80s in Great Britain LG demonstration was carried out at the testing area in Farnborough. At this time developments were demonstrated by two companies: British Aerospace and Ferranti. Each of them represented its LG-based system with the perimeter of 30 and 43 cm respectively. As a result, the government concluded the contracts valued at £ 1 mln. with each firm. Companies had to submit 2 new strapdown inertial navigation systems each for aviation purposes by January 1986. It should be noted that British Aerospace used American patents received at the purchase of Sperry Gyroscope branch while Ferranti carried out its own development and research activities [19].
Second Generation of LGs
First of all, the beginning of 90s was marked out by the collapse of the Soviet Union and end of Cold War. It resulted in the sharp reduction of the military developments financing by both sides. Civil market became the key market. American companies were actively reorganized taking over each other. Nevertheless, existing and newly-developed LGs could ensure the stable output of the products which were based on them: inertial modules, strapdown inertial navigation systems and integrated navigation systems. Finished models of control and navigation systems examples of which are given in Fig. 14 started occurring at the product markets.
Many of these systems are still applicable up to these days. Particularly, SIGMA 40 inertial navigation system is installed on the ships of 35 European marines. British system FIN3110 (BAE Systems) is to be installed on Agrab Mk.2 mortars for the armed forces of United Arab Emirates in 2013 [20].
In Russia despite the difficult economic situation LG developments continued in the area of accuracy increase, design of integrated navigation systems and strapdown inertial navigation systems. In 1990–1994 the developments of new shock-resistant and two-mode LGs continued. The search for new concepts of LG construction for the surface mobile facilities solving the tasks of gyrocompassing and current orientation was carried out. One of outstanding achievements in the laser-gyroscopic area in 90s is the creation of NSI-2000, integrated strapdown inertial navigation systems based on Zeeman laser gyroscopes. Some examples of the serial LGs produced by Polyus Research Institute are shown in Fig. 15. Characteristics of the most common modern foreign and domestic LGs as well as systems which are based on them are specified in Tables 1–4.
Modern State of the Market of IMMs Based on LG
Nowadays, LG manufacturers rarely supply individual LGs to the market. As a rule, inertial measurement module (IMM) or finished system is the end product. Let us consider the market of IMM in details relying on the study of Yole Développement [21]. Production of inertial measurement modules is the large industrial sector where defense and aerospace applications predominate traditionally. 2011 was the stable year for IMMs with the market volume of $1.75 bln. (Fig. 16).
As is seen from Fig. 16a the largest share of IMM modern market is supported by the small amount of the leading foreign companies: Honeywell, Northrop Grumman and Sagem which are the evident leaders. However, other new manufacturers enter the market offering, first of all, inexpensive IMMs based on microelectromechanical systems (MEMS).
Class of high-precision inertial sensors, which LGs refer to, is the dynamic market segment because increasing number of the final propositions requires the availability of stabilization, guidance and navigation systems. In 2011 the market of high-accuracy gyroscopes was estimated at $1.29 bln., having shown the growth by 4.3% per annum, and as expected it will reach $1.66 bln. by 2017 (Fig. 16b). It should be noted that such increase is mainly ensured by the popularity of fiber-optic gyroscopes and MEMS-gyroscopes which improve their characteristics every year. In order to estimate the role of LG among the whole variety of sensors offered at the market let us refer to the histogram in Fig. 17.
As is seen, currently the optic gyroscopes still predominate at the market by wide margin. Particularly, LGs are widely used in navigation systems and tactical guidance systems. Herewith, LG share considerably grows when increasing the accuracy class. If MEMS-sensors predominate in the area of low-accuracy sensors due to their low cost and compact size, LG share in the area of strategic navigation is more than 60%.
Very Large Laser Gyroscopes
Despite the fact that great efforts of gyroscopic engineers are connected with the decrease of sensor size there is opposite area of activities – development and design of very large LGs discovering the new scopes of their application.
In the middle of 80s the group of scientists from the University of Canterbury (Christchurch, New Zealand) started developing the laser gyroscope capable to detect the various effects which are shown during the Earth rotation. In order to reach the required values of sensitivity it was decided to increase the resonator perimeter in comparison with the common gyroscopes. The first model of such sensor was produced in 1989. It was called C-I and had square resonator with the side of 85 cm. With its help they managed to measure the velocity of the Earth rotation and show the capability of construction of the LG with large perimeter.
Further, few more devices with various perimeters were constructed. The project which was implemented in geophysical observatory of Wetzel, Germany, was the most successful. Structure of the unit located in this laboratory is given in Fig. 18 [22]. Here the gyroscope has square resonator with the side of 4 m made of zerodur. Assembled construction is deployed on the massive concrete foundation at the depth of several meters under the Earth (Fig. 19a).
Laboratory took all measures for the elimination of spurious influence of the external factors on LGs. As a result, the super-precision device capable to measure the Earth rotation with high precision was produced. With its help it was possible to register the daily variations of the Earth axis (period ~24 h, amplitude 5–60 cm), Chandler oscillations (period 433 days, amplitude ~9 m), tidal oscillations. Such devices play the special role in seismology. Due to high sensitivity large-size laser gyroscopes are capable to locate the signal from distant earthquakes (Fig. 19b).
Nowadays, there is a number of such devices which are located in different countries and pursue the various aims: detection of seismic activity, study of the Earth motion, estimation of oscillations of the building supports, finding of shifts in the construction of gravitational wave detector etc. Nowadays, UG-2 gyroscope has the largest perimeter (39.7×21 m); it is located in Cashmere Cave Laboratory (New Zealand). This project is aimed on the assessment of the capability of further increase of laser gyroscopes perimeter. As the researchers note, such models showed that upon the increase of dimensions the non-stability of scale coefficient grows considerably faster than the sensitivity.
Conclusion
By their occurrence in 1962 LGs opened the new era of wave gyroscopes as well as formed the conditions for the rapid development of strapdown inertial and subsequently integrated navigation systems. Over 50 years scientists from all over the world have accomplished great work in order to give us opportunity today to state the following boldly: "Laser gyroscope is the key part of modern navigation, position control and stabilization systems". Unfortunately, it is impossible to mention all scientists and companies participating in LG development in one report, therefore the companies, information on which is given in some open sources, are specified as examples in the paper.
For many years already the laser gyroscopy has been keeping the status of "critical technologies". Given review of the market shows that despite the active competition between fiber-optic gyroscopes and micromechanical gyroscopes LGs keep the leading positions today in the area of high-accuracy strapdown inertial navigation systems. The following forecast made by V.G.Peshekhonov, Academician, in the paper [1] is completely proved to be correct: "High-accuracy and medium-accuracy strapdown inertial navigation systems will be constructed on the basis of optic wave gyroscopes and produced in bulk quantities".
Truly, laser gyroscopes refer to the number of the most science-intensive and unique laser devices, production of which accumulates and stimulates the development of advanced technologies including nanotechnologies. Nowadays, Polyus Research Institute named by M.F.Stelmakh, OJSC, is the leading national enterprise in the area of laser gyroscopy. Y.D.Golyaev, Head of Scientific and Production Complex 470, responsible for the development of Zeeman LGs, marks the growth of LG demand as well as LG production volumes. Current lag of Russia in the area of production capabilities is gradually eliminated. This process can be quickened at the expense of involvement of foreign technologies as it is accomplished in the area of MEMS or automobile industry. Even today, the enterprises combining the efforts of optic, electronic and other productions supply the best models of modern technological and testing equipment to LG industry for the drastic re-equipment of manufacturing base. These steps and existing scientific capacity for the design and improvement of new LG models must ensure the quality enhancement of produced devices and systems based on LGs.
One of shortcomings which showed up at that time in early models of laser gyroscopes (LG) was the long warm-up period. Herewith, most of the potential applications required the sensor to be ready for the operation in several minutes after start. Also, the power consumption was unsatisfactory. Effort to correct these shortcomings became one of the key tasks for American scientists in 70s [9].
Resonator was the main component on which the works were carried out. Its temperature sensitivity caused the long warm-up time and required the availability of heaters. Heaters were the main power consumer in LG. Transition from aluminum to glass ceramics became the solution of the set task. Having practically zero coefficient of temperature expansion such material made it possible to control the perimeter using the piezoelectric converters based on mirrors and abandon the heaters.
Other element affected by the temperature dependence was the totally reflecting prism (TRP). They were replaced by the multilayer dielectrical mirrors. By that time, their production technologies had made a step forward and it became possible to manufacture mirrors with the reflection coefficient of more than 0.999.
The Faraday cell was subject to replacement too. Special magneto-optic mirrors were applied instead. Their operation principle was based on the Kerr effect [13]. Such mirror under the action of magnetic field brought the nonreciprocal phase shifts into the incident rays. Implementation of all above-listed innovations and improvement of discharge tube allowed the creation of LGs of new generation, warm-up period of which was about several minutes. Structure chart and appearance of one such sensor are given in Fig. 10.
De Lange suggestion [14] on the usage of four-wave mode in LG for the reduction of counter-propagating waves coupling should be specifically mentioned. Patent of the USA [15] issued on differential LG (Differential Laser Gyro System) appointed the common abbreviation DILAG for four-wave LGs. Development of one of the earliest DILAG models refers to 1977 [16]. Further, this gyroscope was developed in Litton and Northrop Grumman where it received the name of ZLG (Zero Lock Gyro) and became popular in many systems.
In the middle of 70s, number of inertial measurement modules (IMMs) with three and more axes was developed by the efforts of Sperry company (Lockheed Martin branch). Resonator monolithic construction allowed considerable reduction of the error caused by axes non-orthogonality in comparison with the construction of three one-axial LGs in one body as well as essential decrease of the unit dimensions. Some examples of such sensors are given in Fig. 11.
In the Soviet Union during this period Arsenal Design Bureau in Kiev was actively involved in the development of LG. Having own manufacturing capabilities it could develop the LG theory and form the new concepts of their construction as well as improve the technological aspect of manufacturing. These activities were performed in close cooperation with the leading research and technological organizations of the Soviet Union in the following main areas:
Development of multilayer mirrors;
Development of nonreciprocal elements based on Faraday effect;
Formation of the vacuum treatment technology for LG resonators;
Development of the special glass ceramics with ultralow coefficient of linear expansion;
Development of cold cathodes;
Establishment of research, manufacturing and testing facilities at Arsenal Production Association;
Development of mathematical support and hardware for the processing of LG information etc.
Since 1974 the batch production of LGs of KOG-1 type with the following characteristics had started:
Warm-up time: less than 60 ms;
Shock resistance: more than 4g (since 1976 – more than 60g);
Measurement error: 0.5°/h.
Device is made in the form of solid glass-ceramic unit where three identical LGs are located with the matching sensitivity axes. Differential nonreciprocal element is used in every LG. Appearance of KOG-1 is shown in Fig. 12a.
In 1976 the serial supply of the reference boresight storage devices based on KOG-1 was started. Since 1978 the modified series of KOG-2 capable to operate under the conditions of radiation and seismic exposure up to 40–120 g with the error of not worse than 0.01°/h and warm-up period of not less than 20 ms has been produced.
In 1979–1981 "Fanza", the new LGs for the surface mobile facilities which provided the gyro-compassing mode were being developed. Differential nonreciprocal element was used in them as well as the first constructions. LG operated with the reverse around the vertical axis. Compassing error was σ≤8´ per 10 minutes of operation. In the mode of measurement of the current orientation the error on angles of course, pitch and roll was σ = 0.3°/hour. Appearance of the device is shown in Fig. 12b. On the basis of this device LG three-axial unit was being developed in 1978–1981 (Fig. 12c).
Development of LG took place in Europe in analogous manner and in the middle of 70s Sagem (France) and Marconi (Great Britain) started the development of strapdown inertial navigation systems based on LGs. However, these activities reached the fullest flourishing only in the following decade which is called "laser gyroscopy decade" by some researchers [10].
80s
Over the years the systems based on LG kept finding newer and newer applications. Herewith, some of them required high vibration and shock resistance from sensors. According to the research, applied glass ceramic resonator unit did not endure the design loads. Metal unit had the necessary strength properties. However, it had a number of obvious shortcomings:
Metal is conductor, thus it is impossible to organize the discharge tube in it;
Metal resonator has high temperature coefficient.
Herewith, transition to the metal resonator in essence was the return to the initial model, sample of the middle of 60s (see Fig. 4). However, specifically it turned out to be the task solution. LG modular construction allowed carrying the discharge tube outside the metal resonator. As it turned out, the temperature effects are not important in this case because the time of the device operation is so short that there is not enough time for the change of resonator temperature. Thus, in early 80s developers of Lockheed Martin managed to produce the vibration- and shock-resistant LG based on the metal resonator (Fig. 13).
Besides the selection of resonator material, there were other tasks set before the developers. Ultrashort time of the sensor operation meant the necessity of practically momentary steady-state operation. Herewith, the operation principle of discharge tube required about several minutes for the first spark occurrence [17]. In order to solve this task small radioisotope which served as the source of the medium constant ionization was added to the discharge tube. As a result, LG warm-up time reduced to several milliseconds.
In the USSR during this period one of the main current tasks was the increase of LG accuracy. It was achieved at the expense of improvement of gyroscope and associated electronics arrangement, transition to the glass ceramic materials. Arsenal Plant with its Central Design Bureau wasn’t exception. In Kiev since the middle of 80s LGs with the "empty" (without nonreciprocal element) resonator for navigation systems were being developed. They used the traditional dithering device and ensured the zero drift up to 0.03°/h.
By the beginning of 90s Arsenal Production Association and Central Design Bureau had the whole range of technologies allowing the production of different modifications of LGs. Low-volume output of the special LGs with triangular configuration can be specified as the example; on the basis of these LGs together with Leningrad Electrotechnical Institute the output of dynamic laser goniometers which were widely applied in CIS as well as abroad was organized [18].
In the beginning of 80s in Great Britain LG demonstration was carried out at the testing area in Farnborough. At this time developments were demonstrated by two companies: British Aerospace and Ferranti. Each of them represented its LG-based system with the perimeter of 30 and 43 cm respectively. As a result, the government concluded the contracts valued at £ 1 mln. with each firm. Companies had to submit 2 new strapdown inertial navigation systems each for aviation purposes by January 1986. It should be noted that British Aerospace used American patents received at the purchase of Sperry Gyroscope branch while Ferranti carried out its own development and research activities [19].
Second Generation of LGs
First of all, the beginning of 90s was marked out by the collapse of the Soviet Union and end of Cold War. It resulted in the sharp reduction of the military developments financing by both sides. Civil market became the key market. American companies were actively reorganized taking over each other. Nevertheless, existing and newly-developed LGs could ensure the stable output of the products which were based on them: inertial modules, strapdown inertial navigation systems and integrated navigation systems. Finished models of control and navigation systems examples of which are given in Fig. 14 started occurring at the product markets.
Many of these systems are still applicable up to these days. Particularly, SIGMA 40 inertial navigation system is installed on the ships of 35 European marines. British system FIN3110 (BAE Systems) is to be installed on Agrab Mk.2 mortars for the armed forces of United Arab Emirates in 2013 [20].
In Russia despite the difficult economic situation LG developments continued in the area of accuracy increase, design of integrated navigation systems and strapdown inertial navigation systems. In 1990–1994 the developments of new shock-resistant and two-mode LGs continued. The search for new concepts of LG construction for the surface mobile facilities solving the tasks of gyrocompassing and current orientation was carried out. One of outstanding achievements in the laser-gyroscopic area in 90s is the creation of NSI-2000, integrated strapdown inertial navigation systems based on Zeeman laser gyroscopes. Some examples of the serial LGs produced by Polyus Research Institute are shown in Fig. 15. Characteristics of the most common modern foreign and domestic LGs as well as systems which are based on them are specified in Tables 1–4.
Modern State of the Market of IMMs Based on LG
Nowadays, LG manufacturers rarely supply individual LGs to the market. As a rule, inertial measurement module (IMM) or finished system is the end product. Let us consider the market of IMM in details relying on the study of Yole Développement [21]. Production of inertial measurement modules is the large industrial sector where defense and aerospace applications predominate traditionally. 2011 was the stable year for IMMs with the market volume of $1.75 bln. (Fig. 16).
As is seen from Fig. 16a the largest share of IMM modern market is supported by the small amount of the leading foreign companies: Honeywell, Northrop Grumman and Sagem which are the evident leaders. However, other new manufacturers enter the market offering, first of all, inexpensive IMMs based on microelectromechanical systems (MEMS).
Class of high-precision inertial sensors, which LGs refer to, is the dynamic market segment because increasing number of the final propositions requires the availability of stabilization, guidance and navigation systems. In 2011 the market of high-accuracy gyroscopes was estimated at $1.29 bln., having shown the growth by 4.3% per annum, and as expected it will reach $1.66 bln. by 2017 (Fig. 16b). It should be noted that such increase is mainly ensured by the popularity of fiber-optic gyroscopes and MEMS-gyroscopes which improve their characteristics every year. In order to estimate the role of LG among the whole variety of sensors offered at the market let us refer to the histogram in Fig. 17.
As is seen, currently the optic gyroscopes still predominate at the market by wide margin. Particularly, LGs are widely used in navigation systems and tactical guidance systems. Herewith, LG share considerably grows when increasing the accuracy class. If MEMS-sensors predominate in the area of low-accuracy sensors due to their low cost and compact size, LG share in the area of strategic navigation is more than 60%.
Very Large Laser Gyroscopes
Despite the fact that great efforts of gyroscopic engineers are connected with the decrease of sensor size there is opposite area of activities – development and design of very large LGs discovering the new scopes of their application.
In the middle of 80s the group of scientists from the University of Canterbury (Christchurch, New Zealand) started developing the laser gyroscope capable to detect the various effects which are shown during the Earth rotation. In order to reach the required values of sensitivity it was decided to increase the resonator perimeter in comparison with the common gyroscopes. The first model of such sensor was produced in 1989. It was called C-I and had square resonator with the side of 85 cm. With its help they managed to measure the velocity of the Earth rotation and show the capability of construction of the LG with large perimeter.
Further, few more devices with various perimeters were constructed. The project which was implemented in geophysical observatory of Wetzel, Germany, was the most successful. Structure of the unit located in this laboratory is given in Fig. 18 [22]. Here the gyroscope has square resonator with the side of 4 m made of zerodur. Assembled construction is deployed on the massive concrete foundation at the depth of several meters under the Earth (Fig. 19a).
Laboratory took all measures for the elimination of spurious influence of the external factors on LGs. As a result, the super-precision device capable to measure the Earth rotation with high precision was produced. With its help it was possible to register the daily variations of the Earth axis (period ~24 h, amplitude 5–60 cm), Chandler oscillations (period 433 days, amplitude ~9 m), tidal oscillations. Such devices play the special role in seismology. Due to high sensitivity large-size laser gyroscopes are capable to locate the signal from distant earthquakes (Fig. 19b).
Nowadays, there is a number of such devices which are located in different countries and pursue the various aims: detection of seismic activity, study of the Earth motion, estimation of oscillations of the building supports, finding of shifts in the construction of gravitational wave detector etc. Nowadays, UG-2 gyroscope has the largest perimeter (39.7×21 m); it is located in Cashmere Cave Laboratory (New Zealand). This project is aimed on the assessment of the capability of further increase of laser gyroscopes perimeter. As the researchers note, such models showed that upon the increase of dimensions the non-stability of scale coefficient grows considerably faster than the sensitivity.
Conclusion
By their occurrence in 1962 LGs opened the new era of wave gyroscopes as well as formed the conditions for the rapid development of strapdown inertial and subsequently integrated navigation systems. Over 50 years scientists from all over the world have accomplished great work in order to give us opportunity today to state the following boldly: "Laser gyroscope is the key part of modern navigation, position control and stabilization systems". Unfortunately, it is impossible to mention all scientists and companies participating in LG development in one report, therefore the companies, information on which is given in some open sources, are specified as examples in the paper.
For many years already the laser gyroscopy has been keeping the status of "critical technologies". Given review of the market shows that despite the active competition between fiber-optic gyroscopes and micromechanical gyroscopes LGs keep the leading positions today in the area of high-accuracy strapdown inertial navigation systems. The following forecast made by V.G.Peshekhonov, Academician, in the paper [1] is completely proved to be correct: "High-accuracy and medium-accuracy strapdown inertial navigation systems will be constructed on the basis of optic wave gyroscopes and produced in bulk quantities".
Truly, laser gyroscopes refer to the number of the most science-intensive and unique laser devices, production of which accumulates and stimulates the development of advanced technologies including nanotechnologies. Nowadays, Polyus Research Institute named by M.F.Stelmakh, OJSC, is the leading national enterprise in the area of laser gyroscopy. Y.D.Golyaev, Head of Scientific and Production Complex 470, responsible for the development of Zeeman LGs, marks the growth of LG demand as well as LG production volumes. Current lag of Russia in the area of production capabilities is gradually eliminated. This process can be quickened at the expense of involvement of foreign technologies as it is accomplished in the area of MEMS or automobile industry. Even today, the enterprises combining the efforts of optic, electronic and other productions supply the best models of modern technological and testing equipment to LG industry for the drastic re-equipment of manufacturing base. These steps and existing scientific capacity for the design and improvement of new LG models must ensure the quality enhancement of produced devices and systems based on LGs.
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