Compact and robust open-loop fiber-optic gyroscope for applications in harsh environments

Abstract

Next generation navigation systems demand performance enhancements to support new applications with longer range capabilities, provide robust operation in severe thermal and vibration environments while simultaneously reducing weight, size and power dissipation. Compact, inexpensive, advanced guidance components are essential for such applications. In particular, Inertial Reference Units (IRUs) that can provide high-resolution stabilization and accurate inertial pointing knowledge are needed. For space applications, an added requirement is radiation hardening up to 300 krad over 5 to 15 years. Manufacturing specifications for the radiation-induced losses are not readily available and empirical test data is required for all components in order to optimize the system performance. Interferometric Fiber-Optic Gyroscopes (IFOGs) have proven to be a leading technology for tactical and navigational systems. The sensors have no moving parts. This ensures high reliability and a long life compared to the mechanical gyroscopes and dithered ring laser gyroscopes. However, the available architectures limit the potential size and cost of the IFOG. The work reported here describes an innovative approach for the design, fabrication, and testing of the IFOG and enables the production of a small, robust and low cost gyro with excellent noise and bandwidth characteristics with high radiation tolerance. The development is aimed at achieving a sensor volume < 5 cubic inches. The new IFOS gyro uses an open loop configuration, utilizes extremely small diameter radiation-hard fiber with customized all-digital signal processing. The optics is packaged using a combination of highly-integrated optical component assemblies with an allfiber approach that leads to a more flexible yet lower cost optical design. The IFOS gyro prototypes are implemented using a distributed architecture, where the light source, electronics and receiver are integrated in an external package, while the sensor head is integrated in a robust and environmentally rigid package. The sensor package design is compatible with the most severe environmental requirements foreseen for the target applications. This paper presents the current state-of-the-art performance of the prototype gyros and the potential for further reduction of size with improved performance. The gyro sample and data rates are extremely high and can be close to the modulation frequency (up to 80 kHz). IFOS has shown that the noise at high frequencies is not flattening out and extremely high bandwidth operation is possible without any degradation of the operational stability. IFOS has also demonstrated the potential for a future, smaller and extremely robust IFOG. The next phase design will include highly radiation-resistant integrated, compact optical circuits based on InP technology that includes the light source, splitter and receiver in one package, a gyro coil that utilizes small diameter, radiation-hard fiber and a small fiber phase modulator with > 300 krad radiation tolerance. This gyro offers the low noise, low drift, low vibration sensitivity, high accuracy, high bandwidth and high radiation tolerance solution required for next generation systems. We will present both theoretical modeling and experimental results obtained to date