Multi-oscillator ring laser gyro has no moving part in comparing with dither biased ring laser gyro, thus it is very suitable for wide band vibration measurement. Random noise in the output of ring laser gyro will constrain its performance dramatically. The random noise can be typically divided into quantization noise, white rate noise, bias instability (1/f or flicker rate), rate random walk and flicker rate ramp etc.. Allan variance method is a powerful tool in the time domain for the analysis of random noise, but because different noise has different correlation time, the Allan Variance need long test time such as more than a few hours. A noise analysis method of multi-oscillator ring laser gyro based on power spectral density (PSD) is put forward which need very short test time than Allan Variance method. the analyze is carried out in frequency domain other than time domain, curve fitting method is then used to get noise coefficients. Contrast experiments with the Allan variance analysis method are carried out. The results show that the noise coefficients calculated by the PSD method in which the test time is a few seconds are in good agreement with the coefficients calculated by Allan variance method in which the test time is 16384 seconds. Thus, it is feasible to calculated angle random walk coefficient by the PSD method. Moreover, due to less test time, the trend of the noise coefficients can also be observed by this new method.
A laser Diode (LD) driver with constant current and temperature control system is designed according to the LD working characteristics. We deeply researched the protection circuit and temperature control circuit based on thermos-electric cooler(TEC) cooling circuit and PID algorithm. The driver could realize constant current output and achieve stable temperature control of LD. Real-time feedback control method was adopted in the temperature control system to make LD work on its best temperature point. The output power variety and output wavelength shift of LD caused by current and temperature instability were decreased. Furthermore, the driving current and working temperature is adjustable according to specific requirements. The experiment result showed that the developed LD driver meets the characteristics of LD.
The performance of radio frequency (RF) exciting He-Ne laser is exposed. This text sets out from power circuit, aiming at providing the pumping of gain medium. In order to study the frequency characteristic of RF excitation in He- Ne laser, the frequency ranging from 300MHz to 700MHz is chose to test the discharge property of active medium. It also obtains the optimal RF frequency (432MHz) through experiment, which is important to the improved design of RF exciting He-Ne laser.
The performance of radio frequency (RF) exciting He-Ne laser is exposed. This text sets out from kinetics property of the electronics inside the high-frequency, aiming at getting the relationship between radio frequency and plasma energy. In order to study the frequency characteristic of RF excitation in He-Ne laser, the frequency ranging from 300MHz to 700MHz is chose to test the discharge property of active medium. It also obtains the optimal RF frequency (432MHz) through experiment, which is important to the improved design of RF exciting He-Ne laser.
The existence of mode deflection angle in the cylindrical resonator gyroscope (CRG) leads to the signal drift on the detecting nodes of the gyro vibration and significantly decreases the performance of the CRG. Measuring the mode deflection angle efficiently is the foundation of tuning for the imperfect cylindrical shell resonator. In this paper, an optical method based on the measuring gyroscopic resonator’s vibration amplitude with the laser Doppler vibrometer and an electrical method based on measuring the output voltage of the electrodes on the resonator are both presented to measure the mode deflection angle. Comparative experiments were implemented to verify the methodology and the results show that both of the two methods could recognize the mode deflection angle efficiently. The precision of the optical method relies on the number and position of testing points distributed on the resonator. The electrical method with simple circuit shows high accuracy of measuring in a less time compared to the optical method and its error source arises from the influence of circuit noise as well as the inconsistent distribution of the piezoelectric electrodes.
A laser Doppler angular vibrometer using a He–Ne dual-frequency ring laser (DF-RL) is demonstrated. By detecting the interference signal of two beams which are diffracted by the surface of two gratings, the displacement of angular vibration can be measured. To our knowledge, this is the first time that a DF-RL has been utilized as the source of a Doppler angular vibrometer. It shows in theory and experiment that this dual-differential laser Doppler angular vibrometer possesses a high precision and can suppress the error in horizontal vibration at the same time, which can be applied to high-frequency microangular vibration measurement.
In order to lower production cost of Laser Doppler velocimeter (LDV) and simplify the system structure, a grating Doppler detection system has been designed. This LDV was carried out by differential measurement mode. Two beams of diffracted light from the grating are mixed, and the beat frequency will be detected by a detector when the grating is moving. Fundamentals also have been introduced and partial experiment results of this system are given out. The result indicates the experimental value is agreement with the theoretical value. Errors have been analyzed and the main factors affecting the accuracy were discussed. Upon inspection, the inexpensive and ease LDV is efficient to administer and feasible.
The strap-down inertial navigation system (SINS), especially the SINS composed by dithered ring laser gyroscope (DRLG) is a kind of equipment, which providing high reliability and performance for moving vehicles. However, the mechanical dither which is used to eliminate the “Lock-In” effect can cause vibration disturbance to the INS and lead to dithering coupling problem in the inertial measurement unit (IMU) gyroscope triad, so its further application is limited. Among DRLG errors between the true gyro rotation rate and the measured rotation rate, the frequently considered one is the input axis misalignment between input reference axis which is perpendicular to the mounting surface and gyro angular rate input axis. But the misalignment angle between DRLG dither axis and gyro angular rate input axis is often ignored by researchers, which is amplified by dither coupling problem and that would lead to negative effects especially in high accuracy SINS. In order to study the problem more clearly, the concept of misalignment between DRLG dither axis and gyro angle rate input axis is researched. Considering the error of misalignment is of the order of 10-3 rad. or even smaller, the best way to measure it is using DRLG itself by means of an angle exciter as an auxiliary. In this paper, the concept of dither axis misalignment is explained explicitly firstly, based on this, the frequency of angle exciter is induced as reference parameter, when DRLG is mounted on the angle exciter in a certain angle, the projections of angle exciter rotation rate and mechanical oscillation rate on the gyro input axis are both sensed by DRLG. If the dither axis has misalignment error with the gyro input axis, there will be four major frequencies detected: the frequency of angle exciter, the dither mechanical frequency, sum and difference frequencies of the former two frequencies. Then the amplitude spectrum of DRLG output signal obtained by the using LabVIEW program. if there are only angle exciter and the dither mechanical frequencies, the misalignment may be too small to be detected, otherwise, the amplitude of the sum and difference frequencies will show the misalignment angle between the gyro angle rate input axis and the dither axis. Finally, some related parameters such as frequency and amplitude of the angle exciter and sample rate are calculated and the results are analyzed. The simulation and experiment result prove the effectiveness of the proposed method..
Proc. SPIE. 8418, 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Smart Structures, Micro- and Nano-Optical Devices, and Systems
KEYWORDS: Energy efficiency, Digital signal processing, Modulation, Sensors, Laser applications, Control systems, Signal processing, Gyroscopes, Feedback signals, Phase shifts
To avoid lock-in phenomenon, a rotational oscillation is implemented in mechanically dithered ring laser gyros. This
oscillation or dither is typically provided by a dither motor. The dither motor needs to be driven at the resonant
frequency, so dither controlling systems must track the resonant frequency of dither motors. In this paper, a frequency track method based on phase sensitive detector technology is put forward and compared with the traditional selfoscillation method in details. In high-low temperature experiments (-40℃ to 60℃), this method and the traditional one are compared. The results show that the new method has the equivalent accuracy as the traditional one. But this method has more compact dimension, and the amplitude evaluation and noise injection are easier.
The mechanical dithered ring laser gyro (MDRLG) has to go across lock-in region twice every dither cycle, thus the information loss is inevitable. According to the lock-in equation, the lock-in error can be expressed by observable signals. The lock-in error compensation of MDRLG based on synchronous filtering is demonstrated in this paper. The outputs of MDRLG and error accumulations are filtered synchronized to insure their alignment in the time domain. Experimental results show that the effect of lock-in compensation is improved.
The lock-in effect can reduce the performance of ring laser gyros. The lock-in effect is a result of backscattering.
Self-consistent equations for ring laser gyro show that the intensity of the opposite beams has AC modulation at the
frequency of beat frequency signal because of the backscattering. The amplitude and phase of the AC modulations have
important information about the backscattering. Comparing to the DC component in intensity signal, The AC
components are much smaller, it is not suitable to measure the AC components directly using analog to digital
conversion. A novel synchronous demodulation method is proposed which taking advantage of the heterodyne read-out
signals in quadrature. The coupling modulation under different rotation rate is measured, experiments of this system
show that this system works well and we can draw beneficial conclusion from the experiments.
Although a sinusoidal bias method is introduced to avoid working in the death band for a majority of time, the mechanical dithered ring laser gyro (RLG) still encounters information loss when crossing the zero rate point. A novel lock-in error correction method is proposed which can pick up the lost information and remove the random walk error radically. The lost information at the zero rate crossing can be expressed by such parameters as the phase and phase acceleration of a beat frequency signal. These parameters are sampled every time the phase crosses the zero rate point, and two correction trains are formed. Using the minimum variance method, the correction trains are properly scaled to compensate the output of RLG. Experiment shows that even in a bad working condition, this method can achieve satisfactory results.