Toshiya Yuhara

Commercial applications of mass-produced fiber optic gyros

The open-loop I-FOG has been applied to a number of industrial and consumer applications such as vehicle navigation systems, attitude control systems of unmanned agricultural helicopter, pipe-mapping systems, north-finding systems, etc. Its mass production technology is also described.

Fiber optic gyroscopes for vehicle navigation systems

Fiber optic gyroscopes (FOGs) have been developed for vehicle navigation systems and are used in Toyota Motor Corporation models Mark II, Chaser and Cresta in Japan. Use of FOGs in these systems requires high reliability under a wide range of conditions, especially in a temperature range between -40 and 85 degree(s)C. In addition, a high cost-performance ratio is needed. We have developed optical and electrical systems that are inexpensive and can perform well. They are ready to be mass-produced. FOGs have already been installed in luxury automobiles, and will soon be included in more basic vehicles. We have developed more inexpensive FOGs for this purpose.

Secondary-phase-modulation method for open-loop fiber-optic gyroscopes

A proposed method of secondary phase modulation for open-loop fiber-optic gyroscopes is examined in general terms. To detect the rotation rate of a system through a beat-frequency channel, we employ linearly combined signals with different frequencies for the optical phase modulation. We find that the proper combinations of the modulation frequencies can optimize the sensitivity of gyroscopes. With this method we can employ a high-frequency band for optical phase modulations while keeping relative a lower-frequency band of the detection channel. The theoretically derived result is experimentally confirmed by using a lithium-niobate (LiNbO(3)) optical phase modulator. We also discuss the combination setup with an optical integrated-circuit device and digital signal processing.

New interferometric fiber-optic gyroscope with amplified optical feedback.

A novel interferometric fiber-optic gyroscope with amplified optical feedback by an Er-doped fiber amplifier (EDFA) is proposed and theoretically investigated (the proposed gyroscope is named the feedback EDFA-FOG, FE-FOG in what follows). The FE-FOG functions like a resonant fiber-optic gyro (R-FOG) because of its multiple utilization of the Sagnac loop; however, it is completely different because a low-coherence light source is used. In addition, the gyro output signal is pulsed because the modulation frequency of the phase modulator placed in the Sagnac loop is selected to match the total round-trip time delay of the light, which includes the Sagnac-loop delay plus that of the feedback loop of the fiber amplifier. The sharpness of the output pulse can be adjusted by both the gain of an EDFA and the modulation depth of the phase modulator. When rotation occurs the peak position of the output pulse is shifted as a result of the Sagnac effect. The resolution of the rotation measurement depends on the sharpness of the output pulse. The techniques of both the open-loop and closed-loop methods are described in detail, which shows the great advantage of the proposed gyroscope over the to the conventional interferometric fiber-optical gyroscope (I-FOG).

FIBER-OPTIC GYROSCOPES FOR AUTOMOTIVE APPLICATIONS

We review recent developments in interferometric fiber-optic gyroscopes for automotive applications. These gyroscopes use only elliptical-jacket or elliptical-core polarization-maintaining fibers to make their optical systems immune to environmental effects, and all of them use open-loop phase-modulation signal processing circuitry. We have begun mass-production of a gyroscope for automotive navigation and location systems. Another gyroscope employing an application specific integrated circuit developed for reducing size, cost and power consumption outputs the rotation rate as an analog voltage, and can be used for automotive chassis control and navigation systems. A more accurate gyroscope and a three-axis FOG system combined with clinometers can be applied to motion measurement systems for chassis development and testing. For further enhancement in terms of size, cost, and accuracy, we have developed an integrated optical circuit and a gyroscope that uses it.

Development of fiber optic gyroscopes for industrial and consumer applications

This paper will present the current status of the fiber optic gyroscope (FOG), a ring interferometric rotation sensor for commercial applications by industries and consumers. An open-loop FOG with all polarization-maintaining fiber components is being used in these applications. One primary application is in vehicle navigation systems for automobiles, and a mass-produced has already been installed in luxury automobiles in Japan. Another application is in sweeper robots, Other applications such as a route-measuring system for boreholes, an attitude-controlling system for industrial helicopters, and an optocompass or north-seeking instrument will also be described. These FOGs are compact and reliable and need only a +12 V or a +24 V DC power source. This bias error is determined by the electrical system rather than the optical system and varies between 0.01 and 36 deg/h depending on the design of the signal-processing unit. The scale factor error varies between 0.1% and 1% also depending on the design, however, it is stable over the temperature range from -30 to 85 degree(s)C.

Fabrication of integrated optical gyrochip pigtailed with elliptical-core polarization-maintaining optical fiber for industrial applications

An integrated optical gyrochip has been developed for industrial and consumer fiber-optic gyroscope applications. The gyrochip is pigtailed with low-cost elliptical-core polarization- maintaining optical fiber. An alignment technique was developed that uses image processing technology to align the polarization axis of the fiber without launching light into its core. The fiber-to-fiber insertion loss deviation of the pigtailed waveguide was less than +/- 0.8 dB at a wavelength of 0.78 micrometers over 100 temperature-change cycles, ranging from -30 to +80 degree(s)C, with a fiber mode-field size as small as 3.5 X 2.6 micrometers .

Fiber optic gyroscope for automobiles utilizing integrated optical gyrochip and elliptical core polarization-maintaining optical fiber

We have investigated fiber optic gyroscopes that use phase-modulation signal processing for use in automobiles. These gyroscopes use an integrated optical gyrochip and low-cost elliptical-core polarization-maintaining optical fiber. Fiber-to-fiber insertion loss deviation is less than +/- 0.4 dB at a wavelength of 0.83 micrometers over a temperature range of -30 to +80 degree(s)C, while the core dimensions of pigtailed fiber are as small as 4 X 1 micrometers 2. A gyroscope was developed for navigation systems and on board testing is now being performed. A gyroscope for chassis control systems is also being developed.