Induced Bias Error Research Articles

Residual amplitude modulation induced error in resonant micro-optic gyroscope

A universal expression is proposed for evaluating the residual amplitude modulation (RAM) in a phase modulator. The different effects of the interference and linear terms of the RAM on the resonant micro-optic gyroscope (RMOG) are analyzed. It is found that the effect of RAM depends on the magnitude of RAM itself and the phase component. A theoretical model is then developed to calculate the RAM induced bias error in the RMOG. Finally, a technique for suppression of RAM is proposed and demonstrated, and the bias error of the separate-phase-modulation RMOG is successfully eliminated.

Non-centrosymmetric solid core photonic crystal fiber for suppressing parasitic twist in fiber sensing coil

During the fabrication of fiber sensing coils, the parasitic twist of fibers would lead to the undesired elliptical birefringence in the fiber, which is the main cause of magnetically induced bias error for fiber optic gyroscope(FOG). For the purpose of suppressing the parasitic twist in the fiber coil, a polarization-maintaining solid core photonic crystal fiber (PCF) with non-centrosymmetric distribution of bending stiffness is proposed and investigated. The proposed PCF would bend towards a particular direction under the external forces, resulting in the consistency of birefringent axes arrangement, thus suppressing the nonreciprocal errors induced by both radial and axial components of the magentic field simultaneously. Dependence study of the fiber bending stiffness distribution on several key parameters is provided. The optical properties are also explored and compared with the previously studied PCF. Fiber coils fabricated with the proposed PCF are promising in reducing the magnetical sensitivity of FOG, thus making it possible for FOG to get rid of the thick magnetic shield, which is significant for the miniaturization of FOG.

Thermally induced bias error due to strain inhomogeneity through the fiber optic gyroscope coil.

One of the performance limits of a navigation grade fiber optic gyroscope is the bias error due to the thermal sensitivity of the fiber coil. Thermal stress inside the fiber coil is an important source of the bias error. The reduction of the total stress inside the fiber coil can be limited. In this paper, it is shown that further improvement can be achieved by controlling the strain inhomogeneity through the fiber coil. A validated simulation environment is presented for strain distribution analysis. Thermally induced bias error formation mechanisms are compared. The effect of the strain inhomogeneity is reduced by presenting a different coil cross section and spool material. Experiments utilizing a coil design with better performance are presented for the verification of the approach.

Simultaneous estimation of thermal properties of orthotropic material with non-intrusive measurement

This article presents a simple in-house laboratory experiment method for the simultaneous estimation of principal thermal conductivity and specific heat capacity of an orthotropic composite with non-intrusive temperature measurement. The principle of method involves in symmetrical heating of two identical samples with a planar heater sandwiched in-between them and measuring the temperature of non-heated surface non-intrusively using IR camera. The forward problem that mimics the heat conduction from heater to sample and then to ambient is a 3-D transient conduction equation which is solved using finite volume method whereas inverse problem is solved using Levenberg-Marquardt algorithm. At first numerical estimations are carried out with synthetic temperature data to decide upon the parameters to be identified/fixed as well as to find optimal experimental variables. Then, using measured temperature response of the non-heated surface, the thermal properties of unidirectional fiber reinforced carbon composite are estimated. Induced bias errors in the estimated parameters because of error in the fixed parameters are also approximately quantified. The estimated transverse thermal conductivity is found to be 0.72 W/m K whereas the in-plane conductivities parallel and perpendicular to fiber are 5.43 W/m K, 0.64 W/m K respectively. Also, the estimated specific heat capacity is found to be 1044 J/kg K. A maximum deviation of 10% from the absolute Guarded Hot Plate measurement is found in the estimated thermal conductivity parallel to fiber.

Test and Analysis of the Optical Kerr-Effect in Resonant Micro-Optic Gyros

As one kind of the main optical error sources in the resonant micro-optic gyro (RMOG), the optical Kerr-effect brings a nonzero bias to the output of the RMOG. The optical Kerr-effect induced bias error is proportional to the difference between the clockwise (CW) and counterclockwise (CCW) light-intensities input to the resonator. A new method for testing the optical Kerr-effect induced bias error in the RMOG is proposed and demonstrated. A square-wave intensity-modulated optical signal with a symmetrical duty ratio of 50% is achieved by an acousto-optic modulator (AOM), thus making the input-intensity mismatch between the CW and CCW lightwaves change periodically. In this way, we obtain the optical Kerr-effect induced bias errors that vary periodically in accordance with the variation of the square-wave signal. The experimental results show a good agreement with the theoretical value. Moreover, the testing result of the closed-loop RMOG is consistent with the open-loop one. The above method is insusceptible to other noise, such as the backscattering-induced noise and the polarization fluctuation.

Resonance asymmetry induced bias errors in waveguide type optical passive resonator gyro

We present an in-depth analysis of the resonance asymmetry in a silica waveguide ring resonator (WRR) and its influence on the waveguide-type optical passive resonator gyro (OPRG). A big bias error appears at the output of the OPRG. This big error is caused not only by the resonance asymmetry in the WRR, but also by the modulation parameters in the phase modulation spectroscopy technique (PMST). It has been proved that the bias error is proportional to the modulation frequency difference between the clockwise (CW) and counterclockwise (CCW) lightwaves. Three types of resonance asymmetries are thoroughly introduced and discussed. Methods to overcome the big bias error are demonstrated. A high reciprocal resonator is crucial to reduce the bias error. For a certain resonator, a proper temperature needs to be set to minimize the resonance asymmetry. A proper modulation frequency difference between the CW and CCW lightwaves is also helpful to reduce the bias error.

Analysis of Polarization-Fluctuation Induced Bias Error in Resonator Fiber Optic Gyro with Twin 90° Polarization-Axis Rotated Splices

Analysis of Polarization-Fluctuation Induced Bias Error in Resonator Fiber Optic Gyro with Twin 90° Polarization-Axis Rotated Splices

Analysis of Polarization-Fluctuation Induced Bias Error in Resonator Fiber Optic Gyro with Twin 90° Polarization-Axis Rotated Splices

We numerically analyze the polarization-fluctuation induced bias error in a resonator fiber optic gyro (R-FOG) with twin 90° polarization-axis rotated splices in the polarization maintaining fiber (PMF) resonator, especially when polarization dependent loss (PDL) exists inside the resonator. Simulation results indicate that the twin 90° polarization-axis rotated splicing method can effectively suppress the polarization-fluctuation induced bias error in an R-FOG, when the length difference of the fiber segments between the two splicing points is set around a half of the beat-length of the PMF. It is also shown that such an R-FOG is still tolerant to PDL if the polarization crosstalk in the resonator is low, although PDL degrades the performance of the R-FOG.

Mitigation of Adaptive Antenna Induced Bias Errors in GNSS Receivers

Antenna arrays equipped with adaptive filtering allow global navigation satellite system (GNSS) receivers to operate in environments with harsh, sustained interference. However since these antennas utilize spatial and temporal filters, they have the potential to introduce significant bias errors into the code and carrier phase measurements made by GNSS receivers. For precision navigation applications, these biases must be mitigated. A novel bias estimation and correction technique is described in which additional logic is added to the receiver in order to provide runtime compensation for these antenna-induced biases. The technique is general in the sense that it can be applied to a wide variety of adaptive antenna and receiver implementations. It utilizes a computationally efficient bias estimation equation that incorporates stored antenna data, the adaptive filter weights, and the receiver discriminator function. After estimating the bias, the receiver can compensate for the bias errors either in the navigation processor or in the tracking loop of the GNSS receiver. Simulations demonstrate centimeter-level bias correction accuracy for a variety of signals using an adaptive antenna array in an environment with interference.