Minoru Higashiguchi

Effect of Rayleigh backscattering in an optical passive ring-resonator gyro

Resonance characteristics of Rayleigh backscattering in an optical passive ring-resonator gyro (OPRG) are theoretically formulated taking the temporal coherence of the optical source into account. This resonance has two peaks with separation equal to the Sagnac phase shift when rotation is induced. This phenomenon degrades the gyro’s linearity in a configuration to obtain the frequency output. Rayleigh backscattering also can induce an enhanced noise at specific input rotation rates. The methods of solving these problems are discussed. The theoretical limit of rotation sensing, given by the detector shot noise, is also computed taking into account the optical source coherence. A spectrum width narrower than several tens of kHz is required to realize the OPRG for navigation use.

Eigenstate of polarization in a fiber ring resonator and its effect in an optical passive ring-resonator gyro.

Resonance characteristics of an optical fiber ring resonator are derived taking the effect of birefringence into account. We introduce the concept of the eigenstate of polarization to discuss the resonance characteristics resulting from the polarization fluctuation. Using this concept, the polarization problem in an optical passive ring-resonator gyro (OPRG) is discussed to reveal that this causes gyro drift. A way to reduce the drift is to use not polarizers but two polarization controllers. The precision required for polarization control is estimated; it is found difficult to do in practice. We discuss another configuration to solve the polarization problem in an OPRG without polarization controllers.

Kerr effect in an optical passive ring-resonator gyro

The Kerr effect in an optical passive ring-resonator gyro (OPRG) is analyzed considering the optical source coherence. This effect causes the drift to be much greater than the theoretical limit of rotation sensing given by the detector shot noise for an OPRG with high sensitivity. The drift depends not only on the fluctuation of the power splitting ratio between two counter-propagating beams in the resonator, but also on the frequency modulation indices used to set the operating point. Square-wave intensity modulation of the incident beam is also discussed as a way to eliminate the drift. It is found that the ratio of the signal-beam round-trip time in the resonator to the modulation period must be an integer to optimize the drift elimination. From the practical viewpoint, the requirement for the modulation parameters is analyzed numerically.

Backscattering in an optical passive ring-resonator gyro: experiment

We report the experimental results of the resonance characteristics of the backscattering in an optical passive ring-resonator gyro (OPRG). This resonance has two peaks with a separation equal to the Sagnac phase shift when rotation is given. The experimental results are in good agreement with the theory that we have already presented. This phenomenon degrades the gyro linearity almost 10% in a high sensitivity OPRG with the frequency output. A method to eliminate this noise is proposed.

Rotation detection by optical heterodyne fiber gyro with frequency output

A fiber gyro with optical heterodyne detection is proposed. The experimental setup has been constructed and tested. Both the frequency difference in the fiber and the path-length difference between counterpropagating waves are eliminated to reduce output drift. An electronic circuit for phase-nulling detection has been constructed, which gives an electronic frequency output in proportion to the rotation rate. Direct frequency modulation of a single-mode laser diode has been adopted to reduce the noise that is due to the backward Rayleigh scattering. A short time resolution of the rotation rate of about 5 deg/h for an integration time of 1 sec. (0.0014 deg/sec) has been achieved with good linearity, for an integration time of 1 sec.

Fiber-optic laser gyro with easily introduced phase-difference bias.

An optical system for easy introduction of phase-difference bias to optimize the sensitivity of the fiber-optic laser gyro is proposed. The theory of using a laser diode has been considered, and the rotation detection experiment has been performed. The experimental setup consists of a 300-m long single-mode optical fiber, individual optical components, and a laser diode stabilized by a thermal controller and an optical isolator. Short-time resolution of the rotation rate better than 0.87 mrad/sec has been achieved with good linearity.

Rayleigh Backscattering In Optical Passive Ring-Resonator Gyro

The Rayleigh backscattering in Optical Passive Ring-Resonator Gyro (OPRG) is newly formulated in consideration of the temporal coherence of the optical source. This scattering degrades the gyro linearity due to its resonance peak splitting under the rotation. The theoretical limit of rotation sensing is also computed considering the optical source coherence.

Estimation of vehicle position based on projective function using the sequence of a 2D image

The paper proposes a method to estimate the position of an autonomous land vehicle based on the projective function. Usually, there is the fact that obtaining the yaw angle as the motion parameters of the vehicle leads to estimating the lateral variation obtained from the information of a 2D image. From this, an effective method to estimate the lateral variation is shown. In the estimation processing, a projective function from a 2D image into 1D data is considered, and a cross-correlation function for the 1D data, play important roles to reduce the computational effort and the noise effect on a 2D image. Setting up the method in the test vehicle, the experimental result in the case that the vehicle moves in a real passageway is shown.

Optical Fiber Laser Gyro: Homodyne and Heterodyne Detections

The ring interferometer with a multiturn single-mode optical fiber loop has been investigated for use as a rotation rate sensor utilizing the Sagnac effect. We have proposed an optical system with homodyne detection, in which the phase-difference bias can easily be introduced, and the rotation detection experiment was performed using the preliminary test setup with a He-Ne laser [1].

A Camera System for Picking Moving Objects

Abstract In the environment that rejects human investigation because of burning and/or disasterous situation, searching by an autonomous vehicle shall be the reasonable solution. In this paper, we show a camera system to detect moving objects quickly in these conditions. This paper shows the system that makes the camera positioned at stationary irrespective to the vehicle motion. Using this system, it is possible to regard the position of the camera as being at a standstill on the moving vehicle, the variation of image is caused by target’s motion only. This paper detects these variations by vertical projection functions of image data. Using projection functions give robustness and quickness on detection moving objects.