Showing papers on "Fibre optic gyroscope published in 2002"

Noncontact detection of ultrasonic waves using fiber optic Sagnac interferometer

Abstract: This paper describes a fiber optic sensor suitable for noncontact detection of ultrasonic waves. This sensor is based on the fiber optic Sagnac interferometer, which has a path-matched configuration and does not require active stabilization. Quadrature phase bias between two interfering laser beams in the Sagnac loop is applied by controlling the birefringence using a fiber polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output according to the change of phase bias. Additional signal processing is not needed for the detection of ultrasonic waves using the Sagnac interferometer. Ultrasonic oscillations produced by conventional ultrasonic piezoelectric transducers were successfully detected, and the performance of this interferometer was investigated by a power spectrum analysis of the output signal. Based on the validation of the fiber optic Sagnac interferometer, noncontact detection of laser-generated surface waves was performed. The configured Sagnac interferometer is very effective for the detection of small displacement with high frequency, such as ultrasonic waves used in conventional nondestructive testing (NDT).

Optical fibre-based devices utilising the raman effect

Abstract: An optical fibre device based on the Raman effect comprises a first optical source to provide light at a first wavelength, and a holey optical fibre which receives the light from the first optical source such that optical gain or loss is provided at a second wavelength by the effect of Raman scattering within the fibre. For optical gain, the second wavelength is longer than the first wavelength, and the device can be operated as an amplifier, or as a laser if optical feedback is provided. For optical loss, the second wavelength is shorter than the first, and the device may be used as an optical modulator. The fibre may be fabricated from pure silica, although other undoped or doped materials may alternatively be used to tailor properties of the fibre such as gain spectrum, bandwidth, power handling capability and mode propagation.

Fibre-polarimeter based on grating taps

Abstract: The fabrication of novel tilted fibre Bragg gratings coupling light out of the fibre core into two different directions is demonstrated. These gratings in combination with a fibre based quarter waveplate are used to form a high-speed fibre polarimeter for real-time polarisation monitoring.

Self-Q-switched ytterbium-doped cladding-pumped fibre laser

Abstract: A self-Q-switched ytterbium-doped double-clad fibre laser is described. A samarium-doped fibre is used as a filter for protecting a pump source. A fibre coupler is employed to obtain a nonlinear feedback. The mechanism of pulse formation in the laser is considered, and the dependence of its output pulse on the coupler parameters is studied.

Methods and apparatus for fiber optic gyroscope dead band error suppression modulation

Abstract: According to the preferred exemplary embodiments of the present invention, there is provided a phase jump amplitude and timing controller for suppressing the voltage-dependent errors responsible for the dead band. The phase jump amplitude and timing controller inserts a phase/voltage jump into the feedback signal of the loop closure electronics of the fiber optic gyroscope. The phase/voltage jump is provided at a frequency regular enough to ensure that the fiber optic gyroscope will not have enough time to settle into the dead band before the phase/voltage jump is supplied to the loop closure electronics. By providing a recurring phase/voltage jump with amplitude sufficient to move the signal out of the dead band, the loop closure electronics averages the voltage-dependent errors over the full feedback voltage range. This error averaging process effectively eliminates the voltage-dependent errors that cause the dead band phenomenon and allows the loop closure electronics to sense the actual rate of rotation for the fiber optic gyroscope.

Symmetrical depolarized fiber optic gyroscope

Abstract: A fiber optic gyroscope (FOG) including a depolarizer having substantially equal first and second fiber segments of polarization maintaining (PM) fiber coupled to a single mode (SM) fiber loop. The first PM fiber segment includes sections of fiber connected together via a splice having an angle from about 350 to 550 between major axes of polarization of the sections which it connects. Similarly, the second PM fiber segment includes sections of fiber connected together via a splice having an angle from about 350 to 550 between major axes of polarization of the sections which it connects. The length of each fiber section is chosen to maintain the thermal and mechanical symmetry of the SM fiber loop.

Ultra-high-stability two-stage superfluorescent fibre sources for fibre optic gyroscopes

Abstract: A two-stage ultra-high-stability Er/sup 3+/-doped superfluorescent fibre source for fibre optic gyroscopes is presented Versatile tunability of the output characteristics against fibre length and pump conditions enables minimisation of all temperature-induced instabilities

Sensor interrogation technique using chirped fibre grating based Sagnac loop

Abstract: A novel and simple sensor interrogation scheme for fibre Bragg grating (FBG)-based sensing systems is demonstrated. In this scheme, a chirped FBG-based Sagnac loop is used as a wavelength-dependent receiver, and a stable and linear readout response is realised. It is a significant advantage of this scheme that the sensitivity and the measurement wavelength range can be easily adjusted by controlling the chirp of the FBG or using an optical delay line in the Sagnac loop.

Microgyro tuning using focused ion beams

Abstract: The present invention discloses methods of manufacturing mechanical resonator microgyroscopes using focused ion beam machining and the mechanical resonator gyroscopes produced therefrom. An exemplary method of tuning a mechanical resonator gyroscope, includes the steps of mounting a mechanical resonator gyroscope in a vacuum chamber with a controllable focused ion beam where the gyroscope includes exciting and sensing elements for measuring a resonant frequency of the gyroscope. The exciting and sensing elements are activated to measure the resonant frequency of the mechanical resonator gyroscope and the resonant frequency of the gyroscope is adjusted to a desired resonant frequency value by controlling the focused ion beam to remove material of the gyroscope.

Extreme current measurements using a fibre optics current sensor

Abstract: We demonstrate that an optical fibre current sensor can measure current over 500 kA with an accuracy of 0.2%. This level of accuracy has never previously been achieved using a traditional non-optical sensor.

Analysis of vibration error in fiber optic gyroscope

Abstract: Fiber Optic Gyro (FOG) is the most typical application example of fiber optic rate sensor. Theoretically, as the potential inertial sensor of next generation, FOG shows considerable advantages over mechanical gyro in many aspects, such as all-solid-state configuration, no-spinning part and etc. Its promising features bring the following performance: vibration-proof and interference-proof and high reliability. As to the practical application, shock and vibration should be considered when the potential drift sources are concerned. The stress change of fiber coil, the vibration of the optical device pigtail and structural resonance would increase dynamic error. Recently, the engineers on development of FOG and its strapdown system focus on how to eliminate or decrease the vibration error of FOG and make good advantage of this kind of gyro.

Application of the NIMI technique to the 3/spl times/3 Sagnac fibre optic current sensor - experimental results

Abstract: The NIMI technique has been proposed as a means to stabilize and improve the performance of the passive 3x3 Sagnac fibre optic current sensor. This paper reviews, and presents results of, the experiments carried out to investigate the performance of the NIMI technique.

Monolithically integrated wavelength converter: Sagnac interferometer integrated with parallel-amplifier structure (SIPAS) and its application

Abstract: A Sagnac interferometer monolithically integrated with parallel-amplifier structure (SIPAS) is described. Filter-free wavelength conversion and full bit-rate conversion from 10-Gb/s random WDM channels to a 40-Gb/s channel were demonstrated.

Data Analysis and Modeling of Fiber Optic Gyroscope Drift

Abstract: A data gathering system is designed for the interferometric fiber optic gyroscope (IFOG) of land strapdown inertial system. IFOG is tested and the testing curve is given. The test data of IFOG are analyzed with Allan variance method and each error coefficient is identified. Furthermore, a random drift error model for IFOG is built by the method of time series analysis. The conclusion provides supports for improving IFOG design and compensating for errors of IFOG in practice.

Demonstration of a 16-sensor time-division-multiplexed Sagnac-interferometer-based acoustic sensor array with an amplified telemetry and a polarization-based biasing scheme

Abstract: We have previously proposed the use of a Sagnac-interferometer in underwater acoustic sensor array applications. In these proposals, we described a configuration that passively desensitises the delay coil required by the Sagnac interferometer and passively eliminates polarization-induced signal fading (PISF). Additionally, an all-passive polarization-based biasing scheme that yields arbitrarily biased outputs was given. Here, we describe an experimental demonstration of a time-division-multiplexed (TDM) Sagnac-based array including all features described previously and supporting 16 individual sensors with an erbium-doped fiber amplifier (EDFA) telemetry.

Experimental research on the diode-pumped solid-state ring laser

Abstract: The experimental research on diode-pumped solid-state ring laser (DPSSL) is reported in this paper. The research target is to develop a new style optical gyroscope. The ring cavity is a plane, 8-shape 4-mirror laser resonator. Nd:YVO4 crystal is exploited as a laser media which is longitudinally pumped by a 2w laser diode. An optical delay path attached to the cavity is composed of a beam splitter and a prism. The bidirectional traveling waves partly output from one of the flat mirror and one directional beam interferes with the other on a photo detector with optical delay. The resonator design is discussed; the pump power threshold is about 600mW. We obtain the bidirectional continuous TEM00 mode outputs and their interfering pattern. In the experiment, Sagnac effect is watched, which indicates that the DPSSRL can be used as optical gyroscope.

Driving Technology of the Light Source of FOG

Abstract: For the purpose of improving precision and practicability of fiber optic gyroscope(FOG) , a current source and a temperature control circuit were designed for driving the light source of FOG Considering the characteristics of the FOG, a scheme of controlling the driving current by the feed back light from the coupler and detector of FOG was discussed The testing results indicated that, in a temperature range of -20℃ to 55℃, the present technology can yield a current precision as high as 006%, a temperature control precision of 01℃, and a variation of light power less than 01%

Measuring system, for horizontal or vertical drilling, comprises measuring unit with fibre optic or ring laser gyroscopes, microelectromechanical system or tempo sensor

Abstract: A measuring system for a drilling arrangement comprises a measuring unit (10) with sensors and a means for moving the unit along a borehole. The sensors include at least one of the following - a fibre optic gyroscope, a ring laser gyroscope, a microelectromechanical system and a tempo sensor. An Independent claim is also included for a method of measuring a distance between two points in a borehole. DGPS (RTK) readings are taken at both points in the borehole, a measuring unit with an optical gyroscope is moved from the first point to the second point, and the positions of locations between these two points are determined by dead reckoning based on signals generated by the gyroscope. Dead reckoning is then used to determine a position for the second point, the difference between the DGPS (RTK) reading and the dead reckoning calculated position for the second point is calculated, and this difference is used to correct the positions of the locations between the first and second points.

Method of phase modulation in circular interferometer of fiber-optic gyroscope

Abstract: FIELD: fiber optics; designing fiber-optic gyroscopes and other fiber sensors on base of circular optic-fiber interferometer. SUBSTANCE: circular interferometer uses auxiliary phase modulation in form of pulse succession of phase difference of beams of circular interferometer at amplitudes ±(pi-DELTA) and ±(pi+DELTA) rad formed by supply of stepped saw-tooth voltage pulses to phase modulator whose parameters are defined by figures m and n, where m and n may have any integer positive nonzero magnitudes and DELTA is selected within range 0,05pi rad to =2. in this case. EFFECT: enhanced sensitivity of fiber-optic gyroscope. 8 dwg

Effect of Fluctuation of Optical Power on Closedloop IFOG Output

Abstract: This paper deduced the formula which formulatd the input and output of the closed-loop interferrometric fiber optic gyroscope (IFOG) by analyzing IFOG theory. We were of the opinion that the fluctuation of optical power made output errors of the IFOG under the condition of angular acceleration,and simulated the errors. In developing the high-precise IFOG, we must make compensation for the output errors resulting from the fluctuation of optical power.

Polarization Mode Dispersion Measurement Using Sagnac Interferometer and Fixed Analyzer

Abstract: The principle and measurement system of Sagnac interferometer and fixed analyzer are introduced. The polarization mode dispersion of optical fiber by a Sagnac interferometer is measured. Comparing with fixed analyzer, Sagnac interferometer is simpler and spectrum is more readable.

Application of pseudo-random modulation in full-digital closed-loop optic fiber gyroscope

Abstract: The pseudo-random modulated signal has a powerful anti-interference capacity. When we try to obtain a same signal, the influence of interference level produced by the pseudo-random modulated signal on the normally operating system is lower than the other testing signals. The output signal of optic fiber gyroscope is weak with respect to the strong background noise and randomly distributed in frequency domain, thus increases the difficulty in signal processing. Combing the advantages of pseudorandom modulation, a new signal-processing scheme is proposed on the basis of the original digital closed-loop signal processing. Combining pseudo-random modulation-demodulation scheme and mutually matching with digital closed-loop scheme, the gyroscope stability can be effectively improved through effectively extracting environment factor variable and feeding back to the system, then a compensation can be carried out at real time.

Fiber optic gyro and bobbin for sensing coil thereof

Abstract: PROBLEM TO BE SOLVED: To provide a fiber optic gyro and a bobbin for a sensing coil thereof which enable restricting of a side pressure working on an optical fiber. SOLUTION: In the bobbin for a sensing coil of a fiber optic gyro, an optical fiber winding surface (30A) of a bobbin (30) for the sensing coil of the fiber optic gyro, on which the optical fiber (31) of the fiber optic gyro (30) is wound for measuring angular velocity to be measured utilizing sagnac effect of light, is coated with a high polymer gel (32).

Fiber Optic Gyroscope Sensing Coils and Their Winding Method

Abstract: The effect of temperature gradients on fiber optic gyroscope sensing coils is analyzed Some winding methods of fiber optic sensing coils are introduced The effect of suppression of the different winding methods on temperature gradients is briefly explained

A Digital Frequency-Stabilization Method for Laser Gyroscope

Abstract: A digital method for the frequency stabilization of laser gyroscope is described. A digital circuit for the frequency stabilization control of the laser, including the interrelated software, is designed and developed. The experimental results show that the digital method is feasible and better than the analog one.

Sensor system employing fiber optic gyro to detect low-frequency vibration

Abstract: A new approach of sensing low frequency vibration is discussed. Fiber optic gyro (FOG) is used as pendulum bob of a simple pendulum in this sensor system to sense angular vibration. The pendulum can be vibrated when the external force in one direction excites the whole system. The angular velocity must be measured firstly. The relationship between angular velocity and accelerated velocity can be given if known natural frequency of the simple pendulum, which can be obtained before measurement. Consequently vibration frequency can be derived. The result shows that this sensor system is sensitive to vibration frequency lower than 2Hz, but insensitive to higher frequency. The breakthrough lies on the different way to measure the vibration frequency. This approach is fit to the measurement of earthquake wave or other construction vibration.

Effects of Components in IFOG with Simplest Structure upon System Performance

Abstract: The effects of the elements in the fiber-optic gyro with the simplest structure upon the system performance were analyzed through theoretical analysis, computer simulations and comparison with a mathematical model established. The results show that the optical source, polarizer and couplers have the remarkable influences on the system performance.

The Modulated Signal of Frequency Division Multiplexing of Multiaxis Interferometric Fiber Optic Gyro System

Abstract: The Principle of operation of three axes frequency division multiplexed of interferometric fiber optic gyro(IFOG) system sharing the same light source,detector and signal processing system is presented theoreticallyAnd the focus is on the relationship among the output signal with modulation frequency and depthThe simulation results show that the output signal intensity of IFOG shows the "hump" effect on the condition that the modulation depth varies under a certain rangeThen the modulation frequency and the depth of each fiber optic gyro can be optimized