A Simple, Full-Dynamic-Range Optical Heterodyne Single-Mode Fiber Gyroscope

Shupe error, a kind of bias error over temperature-varying environments, still exists even with strict quadrupolar winding pattern, and it affects the environment adaptability of fiber optical gyroscope (FOG) and limits its application. A novel configuration to realize optical compensation for Shupe error in FOG is promoted, employing the opposite polarity of Shupe error in two FOGs working with polarization-maintained (PM) fiber’s fast and slow axis, respectively, in a single PM fiber coil. Analysis is also made for polarization non-reciprocity (PNR) in both FOGs, based on which the optimum coupling angles between integrated optic chip and PM fiber coil are obtained to guarantee that Shupe error arising from both FOGs can be counteracted to zero, and PNR error is suppressed to be minimum at the same time.

The degradation of optical symmetry caused by the thermal strain of the fiber coil results in the thermal bias drift of fiber optic gyro (FOG). This paper presents a method for quantitative analysis of the optical symmetry of the fiber coil and accurate prediction of thermal bias drift in FOG. Firstly, a thermal strain model is established to illustrate the strain characteristics of the layer structure in the fiber coil under temperature fields, emphasizing the importance of thermal strain on optical symmetry. Then, an equivalent asymmetric index (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α_Tk</i>) is introduced to quantitatively evaluate the optical symmetry of the fiber coil. By deriving equations for optical symmetry and thermal bias drift caused by thermal strain, a novel method is proposed to predict and optimize the thermal bias drift. This method utilizes high-performance OFDR to measure temperature and strain in a 3 km fiber coil to predict thermal bias drift. It also discusses the relationship between the length of the tail fiber and optical symmetry, predicting the precise length required to optimize thermal bias drift. Subsequently, the same fiber coil is placed in the FOG to verify the accuracy of the thermal bias drift prediction. Adjusting the length of the tail fiber reduces the thermal bias drift from 0.33 °/h to 0.13 °/h.

The fiber optic gyroscope (FOG)based on Sagnac effect has became to one of the most important sensors in developing due to light in quality, high accuracy, compact in dimension and long life and has played a very important role in both military and civil use. It is the most difficult problem that the FOG has an obvious bias drift caused by temperature change and temperature grade, so its application is limited to a great extent. Fiber coil is one of the most critical components in FOG. Here, the characteristic of temperature error of the fiber optical coil was analyzed. At first, by studying the glass transition of coating adhesive in the fiber coil, the element model of the fiber coil with the glass transition of coating adhesive in FOG was built. Then the discrete mathematics model of SHUPE error with the glass transition of coating adhesive in FOG was built. Finally, based on the temperature models mentioned above, the effects caused by the glass transition of coating adhesive on temperature performance of fiber optic gyroscope were analyzed. Theoretical analysis and experimental results show that effect caused by the glass transition of coating adhesive had seriously affected the temperature performance of FOG. By optimizing the glass transition temperature of coating adhesive, the SHUPE error of fiber coils can be reduced. At the same time, the amplitude uniformity of the SHUPE error can be improved greatly to reduce the difficulty in temperature compensation.

Dual-polarization interferometric fiber optic gyroscope (IFOG) is a novel scheme in which the polarization nonreciprocal (PN) phase error of the two orthogonal polarizations can be optically compensated. In this work, we investigate the effective of PN phase error compensation under varying temperature. It is proved that, the thermally induced strain deforms the fiber, and results in perturbations on the birefringence and polarization cross coupling which degrades the IFOG's stability. A wave propagation model and analytical expressions of PN phase error are derived by using coupled-wave equation and Jones matrix. We theoretically and experimentally verify that, although the single-mode (SM) and polarization-maintaining (PM) fiber coils behave different owing to their intrinsic properties of wave propagation, the thermal strain induced PN phase error can still be compensated under slow and adiabatic temperature variations. This could be a promising feature to overcome the temperature fragility of IFOG.

In this work, the fiber optic gyroscope (FOG) with an elliptic fiber coil (EFC) is applied to the inertial measurement of petroleum well trajectory for the special condition of the borehole diameter limitation in the inclinometer while drilling (IWD). The three-dimensional (3D) Shupe error mathematical model and finite element model of the EFC are established by the quadrupole symmetrical technique, which is based on the Shupe effect of fiber coil. Then, the simulation experiments and the temperature experiments of the EFC are carried out to verify the correctness of the mathematical model. Under this prerequisite, the influence of the structure parameters of the EFC on the Shupe error is analyzed. In order to compare the rotation rate error between the EFC and the circular fiber coil (CFC), the temperature experiments of the EFC and the CFC are carried out with the same temperature excitation when the fiber length, the layers of fiber coil, and the radius of fiber coil of the EFC are the same as those of the CFC. The results show that the bias stability of the EFC is 35% to 39% smaller than that of the CFC before the temperature compensation, and after the temperature compensation, the bias stability of the EFC is 49% to 70% smaller than that of the CFC.

Firstly, this paper determines that the main cause of the Shupe error is the temperature distribution gradient in the fiber coil that changes with time and space by studying the Shupe error mathematical model of fiber optic gyroscope (FOG). To solve this problem, according to the structural form and composition of the fiber coil, the equivalent physical property parameters of the fiber coil are analyzed and obtained, and the equivalent model of the fiber coil is established. Then, a variety of structural forms with different protective layers are designed for the optical fiber coil under the condition that space allows, such as thermal conduction layer and thermal insulation layer, and the finite element transient temperature field simulation analysis is performed for each structural form. The simulation results show that the optimal protective layer structure is that the inner layer is thermal conduction layer, and the outer layer is thermal insulation layer. Compared with the structure without protective layer outside the fiber coil, the temperature difference within the fiber coil is reduced from 9.32℃ to 0.5℃, and the average temperature rise of the fiber coil is reduced from33.34℃ to 4.26℃. Finally, a local heating experiment is performed on the FOG with such protective layer structure, and the results show that the zero bias stability of the FOG is improved from the original 0.0118°/h to 0.0055°/h, which is of great significance for improving the temperature performance of FOG.

Draper Laboratory's experience with Interferometer Fiber Optic Gyro (IFOG) technology started via an Internal Research and Development effort in 1978. This work led to developing fiber optic gyros in which significant advances in IFOG component technologies, assembly, integration, and test were achieved. In excess of 30 patents have been issued to Draper as a result of this pioneering effort. More recently, Draper collaborated with JPL to transition their fiber optic breadboard gyro to a space qualifiable instrument for interplanetary long duration missions. During the initial phase, brassboard gyros were designed and fabricated that demonstrated performance that bettered NASA's CRAF-Cassini spacecraft objectives. In the second phase, the Engineering Model gyro was developed to meet mission qualification tests. Concurrent with this later phase, analysis, tests and qualification activities were performed to validate that gyro components would realize the required 16 year life. Two major inventions (patent pending) were conceived; one provides for continuous adaptive scale factor stability and the other integrates the optical source and photodetector into a single component [Source Integrated Detector (SID)], thereby eliminating a coupler and several splices thus reducing loss by 6 db. Using the above technologies and the implementation of common mode rejection of laser noise, Draper has defined a low noise high performance gyro in which rate power spectral density (PSD) is projected to be < 7 X 10-7 (deg/hr)2/Hz. In those applications, where the PSD < 4 X 10-5 (deg/hr)2/Hz is sought, a small size three component (SID, integrated optics circuit and fiber coil) gyro is easily implemented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The DoD goals for inertial sensors have included achieving high accuracy performance and small size at a low cost. This goal has always been a challenging endeavor, since small size and high accuracy have often been costly and technically difficult to achieve. In 1998, the Army patented a fiber sensor coil winding concept that would facilitate the opportunity to make the Fiber Optic Gyroscope (FOG) more competitive in cost with relation to the commonly-used Ring Laser Gyro (RLG). Recent advances in FOG sensor coil winding techniques appear to show great promise in the improved performance. The novel Crossover-Free (CF) winding technique eliminates fiber crossovers and allows the use of inexpensive single-mode fiber (SMF). Experiments were conducted with the use of an analog, open-loop testbed, which was characterized with a 1 km quadrupolar SM sensor coil. Various sensor coil configurations were spliced into the FOG testbed and bias drift tests were conducted. Different fiber lengths, coil diameters, and fiber wind configurations were evaluated. The Crossover-Free sensor coils were precision wound by a semi-automated Fiber Placement Machine (FPM) developed by Stanley Associates. The Crossover-Free sensor coils test results are compared to standard precision wound coils. The bias errors caused by the fiber crossovers in standard SM sensor coils are also discussed and compared to the near elimination of the crossovers in the CF design.

Bandwidth of fiber optic gyroscope (FOG) was a parameter that can not be fully measured at present. Measurement range of the traditional method (based on the dynamic test turn table) was several hundred Hertz, could only measure low frequency section of the FOG. To solve this problem, proposed the measurement principle based on the magneto-optic Faraday effect of the FOG. The finite element transmission model of the fiber coil was established. Derived the Faraday effect output model of the FOG under the high birefringence optic fiber and packaged fiber coil were used. The Faraday effect output of FOG is proportional to the magnetic field intensity. Based on the detection principle of the FOG, the equivalence of this method and the traditional method was analyzed. High frequency magnetic field could be easily obtained by using high frequency current, the measurement range can cover the bandwidth of the FOG. Established bandwidth measurement system, frequency is more than 50 kHz and distortion is less than 0.1%. The measurement results were presented. Magnitude-frequency and phase-frequency figure shows that the bandwidth of FOG with 1500 m length fiber coil is about 2.1 kHz. This method can solve the low frequency output disadvantage of the dynamic test turn table and test the whole bandwidth frequency response of the FOG.

A concept of a fiber optic sensor consisting of a light source, a fiber coil, and a two-beam interferometer measuring angular acceleration is described. The principle differs essentially from common fiber optic gyroscopes (FOGs) still exploiting the Sagnac effect but sending light of the monochromatic source only unidirectionally into the fiber coil. A change in the optical path length in the fiber coil due to the Sagnac effect maintains proportionality to angular acceleration and could be detected by means of a subsequent two-beam interferometer. The sensitivity of this approach is in contrast to common FOGs determined not only by the total surface area enclosed by the fiber turns but also by the characteristics of the particular interferometer used.

For a high precision interferometric fiber optic gyroscope (IFOG) under temperature control, a short start-up time and small temperature drift are important for its applications. The start-up time and the temperature drift of IFOG with the same fiber length but with a different fiber coil layer number are investigated and compared. Simulation by finite difference time domain method is done to illustrate the existence of optimal layer number for the fiber coil wound by the quadrupolar method. Theoretical analysis is then provided and a closed-form formulation is given to calculate the optimal layer number of the fiber coil, which can effectively reduce both the start-up time and temperature drift of IFOG. Our study is meaningful in improving the thermal performance of the fiber coil.

Chiral molecules are characterized by a specific rotation angle, the angle through which plane-polarized light is rotated on passing through an enantiomerically enriched solution. Recent developments in methodology allow computation of both the sign and the magnitude of these rotation angles. However, a general strategy for assigning the individual contributions that atoms and functional groups make to the optical rotation angle and, more generally, to the molecular chirality has remained elusive. Here, a method to determine the atomic contributions to the optical rotation angle is reported. This approach links chemical structure with optical rotation angle and provides a quantitative measure of molecular asymmetry propagation from a center, axis, or plane of chirality.

Reduced phase error of a fiber optic gyroscope using a polarization maintaining photonic crystal fiber

The controversial question of whether optical rotation data can be used to distinguish floral from honeydew honey was investigated. Specific optical rotation angles were determined for 41 honey samples, including floral, honeydew, and adulterated honey, indicating that moderate to high positive optical rotation angles were found for all adulterated samples measured. A strong correlation between the sugar profile and the specific optical rotation angle of honey was confirmed, and a method based on 13C NMR metabolomics was proposed to calculate specific optical rotation angles with good correlation with the experimental values. The results indicate that optical rotation is not a reliable method for distinguishing the origin of honey but could indicate adulteration.

An ultra-short coil fiber optic gyroscope