How does Tactical Fiber Optic Gyroscope Work？

 

Fiber optic gyroscope industry market

With its unique advantages, fiber optic gyroscope has a broad development prospect in the field of precision physical quantity measurement. Therefore, exploring the influence of optical devices and physical environment on the performance of fiber optic gyros and suppressing the relative intensity noise have become the key technologies to realize the high precision fiber optic gyro. With the deepening of research, the integrated fiber gyroscope with high precision and miniaturization will be greatly developed and applied.

Fiber optic gyroscope is one of the mainstream devices in the field of inertia technology at present. With the improvement of technical level, the application scale of fiber optic gyro will continue to expand. As the core component of fiber optic gyros, the market demand will also grow. At present, China's high-end optical fiber ring still needs to be imported, and under the general trend of domestic substitution, the core competitiveness of China's optical fiber ring enterprises and independent research and development capabilities still need to be further enhanced.

At present, the optical fiber ring is mainly used in the military field, but with the expansion of the application of optical fiber gyroscope to the civilian field, the application proportion of optical fiber ring in the civilian field will be further improved.

According to the "2022-2027 China Fiber Optic Gyroscope industry Market Survey and Investment Advice Analysis Report" :

The fiber optic gyroscope is a sensitive element based on the optical fiber coil, and the light emitted by the laser diode propagates along the optical fiber in two directions. The difference of light propagation path determines the angular displacement of the sensitive element. Modern fiber optic gyro is an instrument that can accurately determine the orientation of moving objects. It is an inertial navigation instrument widely used in modern aviation, navigation, aerospace and national defense industries. Its development is of great strategic significance to a country's industry, national defense and other high-tech development.
Fiber optic gyro is a new all-solid-state fiber optic sensor based on Sagnac effect. Fiber optic gyro can be divided into interferometric fiber optic gyros (I-FOG), resonant fiber optic gyro (R-FOG) and stimulated Brillouin scattering fiber optic gyro (B-FOG) according to its working mode. According to its accuracy, fiber optic gyro can be divided into: low-end tactical level, high-end tactical level, navigation level and precision level. Fiber optic gyroscopes can be divided into military and civilian according to their openness. At present, most fiber optic gyros are used in military aspects: fighter and missile attitude, tank navigation, submarine heading measurement, infantry fighting vehicles and other fields. Civil use is mainly automobile and aircraft navigation, bridge surveying, oil drilling and other fields.
Depending on the accuracy of the fiber optic gyroscope, its applications range from strategic weapons and equipment to commercial grade civilian fields. Medium and high-precision fiber optic gyroscopes are mainly used in high-end weapons and equipment fields such as aerospace, while low-cost, low-precision fiber optic gyroscopes are mainly used in oil exploration, agricultural aircraft attitude control, robots and many other civilian fields with low precision requirements. With the development of advanced microelectronics and optoelectronics technologies, such as photoelectric integration and the development of special fiber optics for fiber optic gyros, the miniaturization and low-cost of fiber optic gyros have been accelerated.

Summary

Ericco's fiber optic gyro is mainly a medium precision tactical fiber optic gyro, compared with other manufacturers, low cost, long service life, the price is very dominant, and the application field is also very wide, including two very hot selling ER-FOG-851, ER-FOG-910, you can click the details page for more technical data,

Tactical Grade Fiber Optic Gyro Comparison

If you have any purchase needs, feel free to send the inquiry, or contact us directly: Phone: +86-13992884879
Email: info@ericcointernational.com.

What is a tactical grade fiber optic gyro?

 

Ericco fiber optic gyro are mainly divided into tactical and navigation levels, and the accuracy of tactical fiber optic gyroscopes is generally 0.x-xº/h. Our tactical fiber-optic gyroscope is ER-FOG-50, https://www.ericcointernational.com/.../single-axis-fog... its accuracy is 0.2~2.0º/h, its size is very small, only Φ50mm×38mm, tactical fiber-optic gyroscope is mainly used in optical pods, missile seeker, UAV, small IMU, inertial navigation system, etc., the measurement range is -500~+500º/s. Both in terms of price and longevity, it will be your choice. If you want to get more technical data, please feel free to contact us at: info@ericcointernational.com. Phone: +86-13992884879

Why is it Called Fiber Optic Gyroscope?

 Like ring laser gyro, fiber optic gyro has the advantages of no mechanical moving parts, no preheating time, insensitive acceleration, wide dynamic range, digital output and small size. In addition, fiber optic gyro also overcomes the fatal shortcomings of ring laser gyro such as high cost and blocking phenomenon.

Fiber optic gyro is a kind of optical fiber sensor used in inertial navigation.
Because it has no moving parts - high-speed rotor, called solid state gyroscope. This new all-solid gyroscope will become the leading product in the future and has a wide range of development prospects and application prospects.

1. Fiber optic gyro classification

According to the working principle, fiber optic gyroscope can be divided into interferometric fiber optic gyro (I-FOG), resonant fiber optic gyro (R-FOG) and stimulated Brillouin scattering fiber optic gyroscope (B-FOG). At present, the most mature fiber optic gyro is the interferometric fiber optic gyroscope (that is, the first generation of fiber optic gyroscope), which is the most widely used. It uses multi-turn optical fiber coil to enhance SAGNAC effect. A double-beam ring interferometer composed of multi-turn single-mode optical fiber coil can provide high accuracy, but also will inevitably make the overall structure more complicated.
Fiber optic gyros are divided into open ring fiber optic gyroscopes and closed loop fiber optic gyros according to the type of loop. Open-loop fiber optic gyro without feedback, directly detect the optical output, save many complex optical and circuit structure, has the advantages of simple structure, cheap price, high reliability, low power consumption, the disadvantage is the input-output linearity is poor, small dynamic range, mainly used as an Angle sensor. The basic structure of an open-loop interferometric fiber optic gyro is a ring dual-beam interferometer. It is mainly used for occasions where the accuracy is not high and the volume is small.

2. Status and future of fiber optic gyroscope

With the rapid development of fiber optic gyro, many large companies, especially military equipment companies, have invested huge financial resources to study it. The main research companies for the United States, Japan, Germany, France, Italy, Russia, low and medium precision gyroscope has completed the industrialization, and the United States has maintained a leading position in this area of research.
The development of fiber optic gyroscope is still at a relatively backward level in our country. According to the level of development, the gyro development is divided into three echelons: the first echelon is the United States, the United Kingdom, France, they have all the gyro and inertial navigation research and development capabilities; The second tier is mainly Japan, Germany, Russia; China is currently in the third tier. The research of fiber optic gyro in China started relatively late, but with the efforts of the majority of scientific researchers, it has gradually narrowed the gap between us and the developed countries.
At present, China's fiber optic gyro industry chain is complete, and manufacturers can be found upstream and downstream of the industry chain, and the development accuracy of fiber optic gyro has reached the requirements of middle and low accuracy of inertial navigation system. Although the performance is relatively poor, it will not bottleneck like the chip.
The future development of fiber optic gyro will focus on the following aspects:
(1) High precision. Higher precision is an inevitable requirement for fiber optic gyro to replace laser gyro in advanced navigation. At present, the high precision fiber optic gyro technology is not fully mature.
(2) High stability and anti-interference. Long-term high stability is also one of the development directions of fiber optic gyroscope, which can maintain navigation accuracy for a long time under harsh environment is the requirement of inertial navigation system for gyroscope. For example, in the case of high temperature, strong earthquake, strong magnetic field, etc., the fiber optic gyro must also have sufficient accuracy to meet the requirements of users.
(3) Product diversification. It is necessary to develop products with different precision and different needs. Different users have different requirements for navigation accuracy, and the structure of the fiber optic gyro is simple, and only the length and diameter of the coil need to be adjusted when changing the accuracy. In this respect, it has the advantage of surpassing mechanical gyro and laser gyro, and its different precision products are easier to achieve, which is the inevitable requirement of the practical application of fiber optic gyro.
(4) Production scale. The reduction of cost is also one of the preconditions for fiber optic gyro to be accepted by users. The production scale of various components can effectively promote the reduction of production costs, especially for middle and low precision fiber optic gyro.

3.Summary

The accuracy of the fiber optic gyroscope ER-FOG-50 is 0.2~2.0º/h, and the accuracy of the ER-FOG-60 is 0.06~0.5º/h. Their application fields are basically the same, and can be used in small IMU, INS, missile seeker servo tracking, photoelectric pod, UAV and other application fields. If you want more technical data, please feel free to contact us.

Do You Know Minimum FOG IMU?

 

ER-FIMU-50 FOG IMU is a minimum cost-effective inertial measurement device for navigation, control and dynamic measurement. The system adopts high reliability closed-loop

hashtagfiber optic gyroscope and hashtagaccelerometer, and ensures the measurement accuracy through multiple compensation techniques.

Applications

hashtagAHRS
Guidance control system
Vehicle and ship attitude measurement
Inertial/satellite hashtagintegrated hashtagnavigation hashtagsystem
Drilling system
Mobile mapping system
Satellite communication in motion

Measurement Error and Calibration of FOG IMU

 

1. What causes FOG IMU measurement errors?

Inertial measurement unit is the core component of navigation information and heading attitude reference system, which determines the accuracy and environmental adaptability of the system. Fiber optic gyro is a kind of photoelectric inertial sensor based on Sagnac effect. It has the advantages of high precision, strong resistance to vibration and shock, fast start, etc. It is an ideal angular velocity sensor for rotorcraft, high performance navigation information and heading attitude measurement system. FOG's adaptability to temperature environment is poor, and the dynamic temperature environment in the working process of rotorcraft is harsh, which leads to the measurement error of FOG inertial measurement unit. It is necessary to study the precise calibration compensation method of FOG inertial measurement unit error to improve its environmental adaptability and measurement accuracy.

2. Calibration method 

Traditional IMU calibration methods include static multi-position calibration under normal temperature environment, angular rate calibration and hybrid calibration, etc. Among them, static multi-position calibration method can calibrate the error coefficient of IMU acceleration channel with high precision, but due to the small Earth rotation rate, The precision of the small FOG used in the high performance navigation information and heading attitude measurement system of the rotorcraft is similar to the earth rotation rate, resulting in low calibration accuracy of the error coefficient of the angular velocity channel. The error coefficient of FOG IMU angular velocity channel can be accurately calibrated by the traditional simple angular velocity calibration method, but the error coefficient of acceleration channel cannot be accurately calibrated. How to further reduce the calibration workload and improve the calibration accuracy is the key technology to be solved by FOG inertial measurement unit. In addition, parameters calibrated at room temperature will reduce FOG inertial measurement unit measurement accuracy if applied at high or low temperatures. Methods such as least squares fitting are often used to compensate the zero-bias or scale-factor temperature errors of inertial devices. Among them, the high-order least squares fitting compensation method can improve the system accuracy, but significantly increase the calculation amount of real-time compensation. The one-time fitting method has a small calculation amount, but it cannot meet the actual compensation accuracy requirements. Therefore, it is another key problem for FOG inertial measurement unit, a high performance and reliable navigation information and heading attitude measurement system of rotorcraft, to study the compensation method with small amount of computation and high precision.
Based on the FOG inertial measurement unit integrated error modeling in the high performance navigation information and heading attitude measurement system of rotorcraft, we calibrate and compensate the temperature and dynamic errors of the small low-precision FOG inertial measurement unit system, and propose a FOG inertial measurement unit full temperature tripartite positive and negative rate/position calibration method and piecewise linear interpolation compensation method for temperature errors. A tripartite positive and negative speed/one position calibration scheme is designed at each constant temperature point, and piecewise linear interpolation method is used to compensate the zero deviation of angular velocity channel, zero deviation of acceleration channel and scale factor temperature errors. The vehicle-mounted experiments show that the method can improve the system's environmental adaptability and measurement precision significantly, which lays a foundation for the further development of a small and high-performance fiber optic gyro IMU aircraft navigation information and heading attitude reference system.

3.FOG IMU deterministic error modeling

3.1 Angular velocity channel error model

FOG inertial measurement unit in rotorcraft, high performance navigation information and heading attitude measurement system consists of three fiber optic gyroscopes and accelerometers, IMU structure and data acquisition and preprocessing module. Three domestic small low-precision 11-FA fiber optic gyroscope sensitive carrier external input angular velocity, three GJ-27 quartz flexible accelerometers sensitive carrier external linear acceleration. FOG is insensitive to g and g2 terms. Considering the installation error, scale factor error and zero bias error of FOG IMU, the angular velocity channel error model of FOG inertial measurement unit in northeast sky coordinate system is established as

Where, i is the output angular velocity of FOG inertial measurement unit i axial gyro, and i is the input angular velocity of i axial gyro. i is zero deviation of i axis gyroscope; Ki is the scale factor of i axial gyroscope; Eij is the installation error coefficient of the angular velocity channel, and i and j are collectively referred to as the coordinate axes X, Y and Z.

3.2 Acceleration channel error model

FOG IMU acceleration channel error model is:

Where, ai is the output of FOG inertial measurement unit i axial addition, ai is the input of i axial addition,  i is zero deviation of i axial addition, Kai is the scale factor of i axial addition, Mij is the installation error coefficient of acceleration channel.

3.3 Full temperature tripartite positive/negative speed/one position calibration

The precision of inertial devices in FOG IMU is mainly related to external environment mechanics and temperature excitation. The operating environment temperature of rotorcraft varies greatly with the different seasons and flight altitudes. Due to the large random dynamic disturbance caused by wind gust and turbulence during successive flights, the influence of different temperatures and dynamic environment on FOG inertial measurement unit accuracy is mainly studied. The calibration temperature range, temperature point distribution density and calibration dynamic range are set according to the actual working environment and accuracy requirements of the system.
According to the mathematical model of system error, a FOG inertial measurement unit tripartite positive and negative rate/one position error calibration method is designed based on a temperature-controlled single-axis speed turntable without pointing north and a high-precision hexahedron tool. As shown in Figure 1, the hexahedron tooling is turned three times at each calibrated temperature point to ensure that the X, Y, and Z axes of FOG inertial measurement unit and the ZT axis of the turntable are reconnected respectively. According to the dynamic environment of the system, set the turntable in each direction to calibrate the positive and negative speed, and ensure that the rotation is above 360° at the speed point.

4. Full temperature piecewise linear interpolation compensation

In order to solve the problem of using FOG IMU in the navigation information and heading attitude measurement system of rotorcraft with high performance and small amount of computation and high precision error compensation, we use the segmented low-order linear interpolation method, dividing the interpolation interval into several cells, and using linear interpolation polynomial on each cell. It can be seen that the FOG inertial measurement unit angular velocity channel and acceleration channel zero bias, scale factor temperature error piecework linear interpolation compensation algorithm of rotor aircraft operating environment are between -10℃ and 40℃, so the calibration temperature points are set as -10℃, 5℃, 20℃, 30℃ and 40℃ respectively. The FOG inertial measurement unit is installed in the center of the hexahedron tool, and the X, Y and Z axes of the inertial navigation system are respectively parallel to the datum normal of the hexahedron tool through the high-precision positioning table. Then the hexahedral tooling is fixed horizontally on the plane of the temperature controlled single-axis rate turntable. The three-bit positive and negative speed/one-position calibration as shown in Figure 1 was realized by flipping the hexahedron tooling. Then change the temperature setting value, according to the above method, carry out the calibration experiment at -10℃, 5℃, 20℃, 30 ℃, 40 ℃ in turn.

5. Summary

FOG IMU is the core component of the navigation information and heading attitude reference system of small rotorcraft. ericco's ER-FIMU-50 and ER-FIMU-70, we can use full-temperature three-way positive and negative rate/one position calibration and PLI compensation method. According to the error characteristics of fiber optic gyro and quartz flexible accelerometer, the FOG inertial measurement unit error model is established, and the three-bit positive and negative rate/one-position calibration scheme is designed at each constant temperature point. The PLI algorithm is used to compensate the zero bias and scale factor temperature errors of the system in real time, reducing the calibration workload and the calculation amount of the compensation algorithm, and improving the system dynamics, temperature environment adaptability and measurement accuracy.

Fiber Optic Gyroscopes for Inertial Navigation

 

1. What is inertial navigation

To understand what inertial navigation is, we first need to break the phrase into two parts, that is, navigation + inertia.
Navigation, in simple terms, solves the problem of getting from one place to another, indicating the direction, typically the compass.
Inertia, originally derived from Newtonian mechanics, refers to the property of an object that maintains its state of motion. It has the function of recording the motion state information of the object.
A simple example is used to illustrate inertial navigation. A child and a friend play a game at the entrance of a room covered with tiles, and walk on the tiles to the other side according to certain rules. One forward, three left, five front, two right... Each of his steps is the length of a floor tile, and people outside the room can get his complete motion trajectory by drawing the corresponding length and route on the paper. He doesn't need to see the room to know the child's position, speed, etc.
The basic principle of inertial navigation and some other types of navigation is pretty much like this: know your initial position, initial orientation (attitude), the direction and direction of movement at each moment, and push forward a little bit. Add these together (corresponding to the mathematical integration operation), and you can just get your orientation, position and other information.
So how to get the current orientation (attitude) and position information of the moving object? You need to use a lot of sensors, in inertial navigation is the use of inertial instruments: accelerometer + gyroscope.
Inertial navigation uses gyroscope and accelerometer to measure the angular velocity and acceleration of the carrier in the inertial reference frame, and integrates and calculates the time to obtain the velocity and relative position, and transforms it into the navigation coordinate system, so that the carrier's current position can be obtained by combining the initial position information.
Inertial navigation is an internal closed loop navigation system, and there is no external data input to correct the error during the carrier movement. Therefore, a single inertial navigation system can only be used for short periods of navigation. For the system running for a long time, it is necessary to periodically correct the internal accumulated error by means of satellite navigation.

2. Gyroscopes in inertial navigation

Inertial navigation technology is widely used in aerospace, navigation satellite, UAV and other fields because of its high concealment and complete autonomous ability to obtain motion information. Especially in the fields of micro-drones and autonomous driving, inertial navigation technology can provide accurate direction and speed information, and can play an irreplaceable role in complex conditions or when other external auxiliary navigation signals fail to play the advantages of autonomous navigation in the environment to achieve reliable attitude and position measurement. As an important component in inertial navigation system, fiber optic gyro plays a decisive role in its navigation ability. At present, there are mainly fiber optic gyroscopes and MEMS gyroscopes on the market. Although the precision of the fiber optic gyroscope is high, its entire system is composed of couplers,
Modulator, optical fiber ring and other discrete components, resulting in large volume, high cost, in the micro UAV, unmanned and other fields can not meet the requirements for its miniaturization and low cost, the application is greatly limited. Although MEMS gyro can achieve miniaturization, its accuracy is low. In addition, it has moving parts, poor resistance to shock and vibration, and is difficult to apply in harsh environments.

 

3 Summary

Ericco's fiber optic gyroscope ER-FOG-851 is specially designed according to the concept of traditional fiber optic gyroscopes, with a small size of 78.5*78.5*35mm; Light weight, less than or equal to 300g; Low power consumption, less than or equal to 4W; Start fast, start time is only 5s; This fiber optic gyroscope easy to operate and easy to use, and is widely used in INS, IMU, positioning system, north finding system, platform stability and other fields.
The accuracy of our ER-FOG-851 is between 0.05 and 0.1, and the 851 is divided into ER-FOG-851D and ER-FOG-851H. The biggest difference between these two fiber optic gyroscope is that the measurement range is different, of course, the accuracy is different, and the measurement range of ER-FOG-851D is wider. The application range is naturally wider than the ER-FOG-851H. Our fiber optic gyroscope can be used in inertial navigation, you can make a detailed choice according to the accuracy value and measurement range, you are welcome to consult us at any time and get more technical data.

 

Features of Fiber Optic Gyroscope

 

1.Characteristics of fiber optic gyro

Compared with electromechanical gyro or laser gyro, fiber optic gyro has the following characteristics:

(1) fewer parts, the instrument is firm and stable, and has a strong ability to resist impact and accelerate movement;
(2) The wound fiber is longer, so that the detection sensitivity and resolution are several orders of magnitude higher than that of the laser gyroscope;
(3) No mechanical transmission parts, no wear problems, so it has a long service life;
(4) Easy to use integrated optical path technology, signal stability, and can be directly digital output, and connected with the computer interface;
(5) By changing the length of the fiber or the number of times the light circulates in the coil, different accuracy can be achieved and a wide dynamic range can be achieved;
(6) The propagation time of the coherent beam is short, so in principle it can be started instantaneously without preheating;
(7) can be used with ring laser gyro to form sensors of various inertial navigation systems, especially sensors of strapdown inertial navigation systems;
(8) Simple structure, low price, small size, light weight.

2.Principle of fiber optic gyroscope

Fiber optic gyro is a fiber optic angular velocity sensor, which is the most promising one among all kinds of fiber optic sensors. Like ring laser gyro, fiber optic gyro has the advantages of no mechanical moving parts, no preheating time, insensitive acceleration, wide dynamic range, digital output and small size. In addition, fiber optic gyro also overcomes the fatal shortcomings of ring laser gyro such as high cost and blocking phenomenon. Therefore, fiber optic gyro has been paid attention to by many countries. Low precision civilian fiber optic gyro has been produced in small batch in Western Europe, it is estimated that in 1994, the sales of fiber optic gyro in the United States gyro market reached 49%, and the cable gyro fell to the second place (accounting for 35% of sales).

The working principle of fiber optic gyroscopes is based on the Sagnac effect. Sagnac effect is a general correlation effect of light propagated in a closed loop optical path rotating relative to inertial space, that is, two beams of light with equal characteristics emitted from the same light source in the same closed optical path propagate in opposite directions, and finally converge to the same detection point.

3.Application of fiber optic gyro

What if a car with a satellite navigation system is driving and suddenly can't receive GPS navigation signals? With the addition of a fiber optic gyroscope, it can form integrated navigation with GDS to achieve automatic driving.

Fiber optic gyro technology is based on mechanical gyro, MEMS gyro, laser gyro upgrade and development, with self-correcting, high sensitivity, long life, low temperature and high temperature resistance, no electromagnetic interference and many other advantages, is the best comprehensive performance of inertial sensors. Due to high cost, it is mainly used in military industry, aerospace and other fields.

Fiber optic gyro technology can be widely used in automotive navigation, high-speed rail track detection, Internet of Things components module, smart grid transmission, consumer electronics and many other fields, experts predict that the potential market size of domestic fiber optic gyro reached 100 billion, the next 5-10 years, most of China's traditional gyro market will be replaced by fiber optic gyro.

4.Summary

Ericco's fiber optic gyro is also a leading level in the world, ER-FOG-851 (≤0.05 ~ 0.1º/h), ER-FOG-910(0.02º/h) are a good choice, because they are medium precision, widely used, if you want to get more technical parameters, please feel free to contact us.

Research on Hybrid Integrated Optical Chip of Fiber Optic Gyro

 With the advantages of all-solid state, high performance and flexible design, fiber optic gyroscope has become the mainstream inertial gyroscope, which is widely used in many fields such as positioning and navigation, attitude control and oil well inclination measurement. Under the new situation, the new generation of inertial navigation system is developing towards miniaturization and low cost, which puts forward higher and higher requirements for the comprehensive performance of gyroscope such as volume, accuracy and cost. In recent years, hemispherical resonator gyro and MEMS gyro have developed rapidly with the advantage of small size, which has a certain impact on the fiber optic gyro market. The main challenge of traditional optical gyro volume reduction is the reduction of optical path volume. In the traditional scheme, the optical route of fiber optic gyro is composed of several discrete optical devices, each of which is realized based on different principles and processes and has independent packaging and pigtail. As a result, the device volume under the prior art is close to the reduction limit, and it is difficult to support the further reduction of the volume of fiber optic gyro. Therefore, it is urgent to explore new technical solutions to realize the effective integration of different functions of the optical path, greatly reduce the volume of the gyro optical path, improve the process compatibility, and reduce the production cost of the device.

With the development of semiconductor integrated circuit technology, integrated optical technology has gradually achieved breakthroughs, and the feature size has been continuously reduced, and it has entered the micro and nano level, which has greatly promoted the technical development of integrated optical chips, and has been applied in optical communication, optical computing, optical sensing and other fields. The integrated optical technology provides a new and promising technical solution for the miniaturization and low cost of fiber optic gyro optical path.

1 Integrated optical chip scheme design

1.1 Overall Design

The traditional optical routing light source (SLD or ASE), fiber taper coupler (referred to as "coupler"), Y branch waveguide phase modulator (referred to as "Y waveguide modulator"), detector, sensitive ring (fiber ring). Among them, the sensitive ring is the core unit of the sensitive Angle rate, and its volume size directly affects the precision of the gyro.
We propose a hybrid integrated chip, which consists of a light source component, a multifunctional component and a detection component through hybrid integration. Among them, the light source part is an independent component, which is composed of SLD chip, isolation collimation component and peripheral components such as heat sink and semiconductor cooler. The detection module consists of a detection chip and a transresistance amplifier chip. The multifunctional module is the main body of hybrid integrated chip, which is realized based on lithium niobate thin film (LNOI) chip, and mainly includes optical waveguide, mode-spot conversion, polarizer, beam splitter, mode attenuator, modulator and other on-chip structures. The beam emitted by the SLD chip is transmitted into the LNOI waveguide after isolation and collimation.
The polarizer deflects the input light, and the mode attenuator attenuates the non-working mode. After the beam splitter splits the beam and modulator modulates the phase, the output chip enters the sensitive ring and the sensitive angular rate. The light intensity is captured by the detector chip, and the generated photoelectric output flows through the transresistance amplifier chip to the demodulation circuit.
The hybrid integrated optical chip has the functions of luminescence, beam splitting, beam combining, deflection, modulation, detection, etc. It realizes the "multi-in-one" integration of non-sensitive functions of gyro optical path. Fiber optic gyroscopes depend on the sensitive Angle rate of coherent beam with high degree of polarization, and the polarization performance directly affects the precision of gyroscopes. The traditional Y-waveguide modulator itself is an integrated device, which has the functions of deflection, beam splitting, beam combining and modulation. Thanks to material modification methods such as proton exchange or titanium diffusion, Y-waveguide modulators have extremely high deflection ability. However, thin film materials need to take into account the requirements of size, integration and deflection ability, which can not be met by material modification methods. On the other hand, the mode field of thin film optical waveguide is much smaller than that of bulk material optical waveguide, resulting in changes in electrostatic field distribution and electrorefractive index parameters, and the electrode structure needs to be redesigned. Therefore, the polarizer and modulator are the core design points of the "all-in-one" chip.

1.2 Specific Design

The polarization characteristics are obtained by structural bias, and an on-chip polarizer is designed, which consists of curved waveguide and straight waveguide
Agreed. The curved waveguide can limit the difference between the transmission mode and the non-transmission mode, and achieve the effect of mode bias. The transmission loss of the transmission mode is reduced by setting the offset.
The transmission characteristics of optical waveguide are mainly affected by scattering loss, mode leakage, radiation loss and mode mismatch loss. Theoretically, the scattering loss and mode leakage of small curved waveguides are small, which are mainly limited by the late process. However, the radiation loss of curved waveguides is inherent and has different effects on different modes. The transmission characteristics of the curved waveguide are mainly affected by the mode mismatch loss, and there is mode overlap at the junction of the straight waveguide and the curved waveguide, resulting in a sharp increase in mode scattering. When the light wave is transmitted into the polarized waveguide, due to the existence of curvature, the effective refractive index of the light wave mode is different in the vertical direction and the parallel direction, and the mode restriction is different, which results in different attenuation effects for TE and TM modes.
Therefore, it is necessary to design the bending waveguide parameters to achieve the deflection performance. Among them, bending radius is the key parameter of bending waveguide. The transmission loss under different bending radius and the loss comparison between different modes are calculated by FDTD eigenmode solver. The calculated results show that the loss of the waveguide decreases with the increase of the radius at small bending radius. On this basis, the relationship between polarization property (ratio of TE mode to TM mode) and bending radius is calculated, and the polarization property is inversely proportional to bending radius. The determination of the bending radius of the on-chip polarizer should consider the theoretical calculation, the simulation results, the technological capability and the actual demand.
The finite difference Time domain (FDTD) is used to simulate the transmitted light field of the on-chip polarizer. The TE mode can pass through the waveguide structure with low loss, while the TM mode can produce obvious mode attenuation, so as to obtain polarized light with high extinction ratio. By increasing the number of cascaded waveguides, the extinction ratio of the polarization-extinction ratio can be further improved, and better than -35dB polarization extinction ratio performance can be obtained on the micron scale. At the same time, the structure of the waveguide on chip is simple, and it is easy to realize the low-cost fabrication of the device.

2 Integrated optical chip performance verification

The LNOI main chip of the integrated optical chip is an unsliced sample engraved with multiple chip structures, and the size of a single LNOI main chip is 11mm×3mm. The performance test of integrated optical chip mainly includes the measurement of spectral ratio, polarization extinction ratio and half-wave voltage.
Based on the integrated optical chip, a gyroscope prototype is built, and the performance test of the integrated optical chip is carried out. Static zero bias performance of a gyro prototype based on integrated optical chip in a non-vibration isolated foundation at room temperature. set-based
The gyroscope formed into optical chip has a long time drift in the start-up segment, which is mainly caused by the start-up characteristic of light source and the large loss of optical link. In the 90min test, the zero bias stability of the gyroscope is 0.17°/h (10s). Compared with the gyroscope based on traditional discrete devices, the zero bias stability index deteriorates by an order of magnitude, indicating that the integrated optical chip needs to be further optimized. Main optimization directions: improve the polarization extinction ratio of the chip, improve the luminous power of the light-emitting chip, improve the end-coupling efficiency of the chip, and reduce the overall loss of the integrated chip.

3 Summary

We propose an integrated optical chip based on LNOI, which can realize the integration of non-sensitive functions such as luminescence, beam splitting, beam combining, deflection, modulation and detection. The zero bias stability of the gyro prototype based on the integrated optical chip is 0.17°/h. Compared with the traditional discrete devices, the performance of the chip still has a certain gap, which needs to be further optimized and improved. We preliminarily explore the feasibility of fully integrated optical path functions except ring, which can maximize the application value of integrated optical chip in gyro, and meet the development needs of miniaturization and low cost of fiber optic gyro.

Ericco's ER-FOG-851, ER-FOG-910 small size, low power consumption, of course, the cost is also low, the application field is particularly wide, such as IMU, INS, north finding system, etc., I believe you must want to know their specific technical parameters, please feel free to contact us.