A Low-cost Interferometric Fiber Optic Gyro for Autonomous Driving

Abstract

Recent progress in advanced autonomous driving techniques, such as level 5 or level 4, requires precise dead reckoning in order to compensate main positioning systems such as GNSS, visual SLAMs or LIDARs. This kind of precise dead reckoning is established by using a gyroscope of 0.1 deg/ hr. class. Currently, gyroscopes that satisfy this accuracy include Fiber Optic Gyros (FOGs) and Ring Laser Gyros (RLGs) and their price range is more than $10,000 per axis. So it is strongly required to reduce the price of gyroscopes with equivalent accuracy for practical application and commercialization of autonomous driving. In order to respond these requirements, we have established price down scheme for fabrication of interferometric Fiber Optical Gyroscope (iFOG). The i-FOG is a sensor that detects the rotation speed of the object from the optical interference phase difference caused by the light relativistic effect (so-called Sagnac effect of light). Light incident from both ends of the optical path inside the optical fiber coil interferes with a phase difference proportional to the rotation speed of the optical path, so the rotation speed is detected by measuring this interference phase difference. To have precise optical phase difference, which comes only from actual input rotation speed i.e. without unwanted phase difference error comes from other than actual input rotation, we should use precisely aligned quadrupole optical fiber coil and modulation element parts, called IOC (Integrated Optical Circuit). The former contributes to reduce thermally induced optical phase difference, so-called Shupe effect, and the later contributes to reject unwanted polarization crosstalk which result in optical phase change by its excellent polarization rejection ratio. When considering fabrication cost of the i-FOG, production costs of these two important components have substantial ratio in total production cost. Especially the former one generally thought to be very difficult to reduce because it depends upon human hand-work to achieve quadrupole winding arrangement and precise alignment of optical fiber on the coil bobbin simultaneously. To solve this difficulty, we have developed automatic optical fiber winding machine which can execute automatic quadrupole winding with fine alignment of optical fiber by adopting double-flyer winding mechanism. This mechanism allow us to avoid extra and time consuming hand work for changing the optical fiber source from left to right and right to left for each layer of the fiber coil. This has reduced the man-time to 1/5. By combination of this technique and our fabrication process of IOCs, we have acquired the potential to reduce fabrication cost of i-FOGs.