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To reduce the random error of the output data of a laser Doppler velocimeter (LDV) and improve its measurement accuracy, a new method to filter the drift data of the LDV is proposed: a metabolic time-series–grey model that combines a metabolic time-series model with a metabolic grey model. The basic principle is first introduced. Then, the metabolic time-series–grey model is applied to filter the drift data of an LDV and compared with the metabolic time-series model and the metabolic grey model. The variance analysis and the Allan variance are used to analyze the drift data before and after being modeled and filtered. The results show that the metabolic time-series–grey model can effectively reduce the random error of the LDV in real time and greatly improve its measurement accuracy, and its filtering effect outperforms that of the metabolic time-series model and the metabolic grey model.

To effectively reduce the random drift of a laser Doppler velocimeter (LDV), a real-time filtering model is presented for filtering the drift data of an LDV, which is a combination of the metabolic grey model (1, 1) and the metabolic time series model AR (2). The basic principle of the metabolic grey-time series model is introduced in detail first. Then, the model is established for the static and dynamic drift data, and a Kalman filter is used to filter the drift data based on the model. The variance analysis method and the Allan variance method are employed to analyse the static drift data. The dynamic drift data are also compared before and after being modelled and filtered. The results demonstrate that the metabolic grey-time series method cannot only effectively reduce the static random drift of an LDV, but can also reduce the dynamic random drift in real time.

This paper presents an innovative interferometer based on the phase-generated-carrier method to meet the requirement of micro-vibration detection on an absolute gravimeter. Our results, including those of both simulation and experiments, verified the feasibility of the interferometer. Based on this interferometer, continuous micro-vibrations are obtained and synchronously compared with the results detected by a 991B seismometer. The interferometer’s accuracy reaches 10 − 8 m , and the detected vibration frequency is less than 100 Hz. These findings can help broaden the application of interferometers and provide new guidelines for vibration measurement.

A technique to selectively excite spin-polarized alkali atoms in one of the two ground-state hyperfine levels is demonstrated, which can separately create the transverse spin component of spin-polarized alkali atoms in either ground-state hyperfine level. The principle of this technique is analyzed, and the experimental results are found to be in good agreement with the theoretical predictions, thereby demonstrating the feasibility of this technique. This technique can be used to accurately measure spin relaxation and polarization of alkali atoms in either ground-state hyperfine level. An example of its applications to measure the transverse relaxation time is presented.

In the Ring Laser Gyro Inertial Navigation System (RLG INS), the temperature characteristics of the accelerometer can directly influence the measurement results. In order to improve navigation accuracy in long-endurance marine navigation, the operating temperature of the accelerometer should be precisely controlled. Based on thermal studies on the accelerometer, temperature control precision should be better than 0.01 °C to achieve 1 × 10−5 m/s2 output accuracy of the accelerometer. However, this conclusion is obtained by approximate calculations and cannot be directly applied to different inertial navigation systems. In order to verify this thermal conclusion and broaden its application, the Back Propagation Neural Network (BP-NN) algorithm is adopted to validate the feasibility of temperature control in this paper. In addition, a multi-level temperature control system is also set up and carefully designed to support the validation and experiments under different conditions. Test results of the temperature control system prove that operating temperature variation can be reduced to 0.01 °C. Meanwhile, the standard deviation per hundred seconds of the accelerometer outputs, after temperature control, reaches 1 × 10−5 m/s2. Static altitude and navigation results were improved by 41.97% and 62.91%, respectively, with the precision temperature control system, which meets the long-endurance marine navigation requirements.

In order to obtain the accurate velocity of a vehicle, calibration of a laser Doppler velocimeter (LDV) is particularly important after installation of the inertial navigation system (INS) and LDV. The calibration accuracy determines the navigational accuracy of the INS/LDV integrated navigation system. In this paper, a highly accurate calibration method based on the error equations of the INS/LDV integrated system is presented. The basic principles of analytic calibration and filtering calibration methods are discussed in detail. The test results show that the scale factor and the installation error of the LDV can be automatically calibrated by our novel calibration method with sufficient accuracy. For a high-precision INS and a 2-D LDV integrated navigation system, after calibration, the position error of dead reckoning (DR) decreased from 1180 m in 2 h to 8 m in 2 h. For a medium precision INS and a 1-D LDV integrated navigation system, after calibration, the position error of DR decreased from 1300 m in 1 h to 25 m in 1 h. The excellent parameter stability of the LDV is also illustrated.

When the influence of hyperfine structure is ignored for atomic magnetometers, it will lead to considerable measuring errors in some cases. Considering the Cs hyperfine structure, an analytical form of magnetic resonance spectrum of the exciting-field frequency response is obtained through theoretical derivation, which is verified by the experiment. Based on the results of the experimental scheme, the optimal frequency and intensity of pump light for a Cs atomic magnetometer with well-resolved magnetic resonance spectrum are found. Additional applications in minimizing the measuring error of atomic magnetometers and the study of optical pumping are explored.

To study the spectral effect further, which exists in fold-type cavity ring-down or enhanced absorption spectrometer, a set of laser scattering measurement apparatus was presented and applied to evaluate the surface status of high-reflectivity coatings. Based on this apparatus and another set of optical-feedback cavity ring-down spectrometer with the equivalent noise absorption coefficient of 9.0×10−9 cm−1, some experiments are carried out to inspect some analyses about the effect's mechanism. It is determined that the spectral ripple originates from the interference fringe's movement of resonance light beams along the surface of folding mirror, which causes the folding mirror's loss to change with the laser wavelength's scanning. Based on this conclusion, the potential application and the processing methods of spectral ripple are proposed and discussed.

The qualitative and quantitative analysis to trace gas in exhaled human breath has become a promising technique in biomedical applications such as disease diagnosis and health status monitoring. This paper describes an application of a high spectral resolution optical feedback cavity enhanced absorption spectroscopy (OF-CEAS) for ammonia detection in exhaled human breath, and the main interference of gases such as CO2 and H2O are approximately eliminated at the same time. With appropriate optical feedback, a fibered distributed feedback (DFB) diode laser emitting at 1531.6 nm is locked to the resonance of a V-shaped cavity with a free spectral range (FSR) of 300 MHz and a finesse of 14,610. A minimum detectable absorption coefficient of &alpha, min = 2.3 &times, 10&minus, 9 cm&minus, 1 is achieved in a single scan within 5 s, yielding a detection limit of 17 ppb for NH3 in breath gas at low pressure, and this stable system allows the detection limit down to 4.5 ppb when the spectra to be averaged over 16 laser scans. Different from typical CEAS with a static cavity, which is limited by the FSR in frequency space, the attainable spectral resolution of our experimental setup can be up to 0.002 cm&minus, 1 owing to the simultaneous laser frequency tuning and cavity dither. Hence, the absorption line profile is more accurate, which is most suitable for low-pressure trace gas detection. This work has great potential for accurate selectivity and high sensitivity applications in human breath analysis and atmosphere sciences.

In order to improve the accuracy and manoeuvrability of terrestrial self-contained navigation system, an idea of building an integrated navigation system using a novel laser Doppler velocimeter together with an inertial navigation system is proposed. The structure and performance of the split reuse-type structure of the laser Doppler velocimeter are expounded, and the integrated technology of marching initial alignment and real-time errors compensation are also discussed in detail. The static inertial alignment of the inertial navigation system can be skipped over and the position error of navigation has been decreased from 1180 m in 2 h to 6 m in 2 h. The experiment results show that the strapdown inertial navigation system/laser Doppler velocimeter integrated navigation system can work effectively without parking and the high-accuracy self-contained navigation can be achieved.

The idea of applying differential weighting function of a spatial filter to spatial filtering velocimeter is put forward. The principle of this velocimeter is described on the basis of differential spatial filter constructed by a linear image sensor. The filtering characteristics of differential rectangular-type spatial filter with rectangular transmittance are theoretically analyzed by using a power spectral density function. This differential method is used to measure very low velocities of a conveyor belt driven by a high-precision rotary table. And it is also used in experiments of elimination of directional ambiguity by using frequency shifting. The theoretical and experimental results show that this differential-type velocimeter is suitable and practical for measuring very low speeds of solid surfaces. It is proved experimentally that the shifting frequency components result from the pedestal component, and both of them can be removed effectively by the method used.

In the field of land navigation, a laser Doppler velocimeter (LDV) can be used to provide the velocity of a vehicle for an integrated navigation system with a strapdown inertial navigation system. In order to suppress the influence of vehicle jolts on a one-dimensional (1D) LDV, this paper designs a split-reuse two-dimensional (2D) LDV. The velocimeter is made up of two 1D velocimeter probes that are mirror-mounted. By the different effects of the vertical vibration on the two probes, the velocimeter can calculate the forward velocity and the vertical velocity of a vehicle. The results of the vehicle-integrated navigation experiments show that the 2D LDV not only can actually suppress the influence of vehicle jolts and greatly improve the navigation positioning accuracy, but also can give high-precision altitude information. The maximum horizontal position errors of the two experiments are 2.6 m and 3.2 m in 1.9 h, and the maximum altitude errors are 0.24 m and 0.22 m, respectively.

A new approach of frequency shifting by rotating kernel is proposed to improve the performance of a spatial filtering velocimeter, used to provide accurate velocity information for a vehicle self-contained navigation system. A linear CMOS image sensor was employed both as a spatiotemporal differential spatial filter and as a photodetector. The filtering operation was fully performed in FPGA and is realized by applying a rotating kernel to the pixel values of the image. Theoretical analysis showed this method could double the maximum measurable velocity. The power spectrum of the output signal was obtained by fast Fourier transform (FFT), and was corrected by a frequency spectrum correction algorithm, named energy centrobaric correction. This velocimeter was used to measure the moving velocities of a conveyor belt. Experimental results verified the method’s ability of reducing the output signal frequency and standard uncertainty of velocity measurement. What is more, the undesired output introduced by frequency shifting to the power spectrum of the output signal was deeply investigated and a new method was proposed to eliminate the undesired component in output signals. This velocimeter aims at providing accurate velocity information for vehicle autonomous navigation system.

This paper presents a mathematical model and a finite element model to investigate the model parameters of me- chanical dither in a ring laser gyroscope in which the bimorph piezoelectric actuator are employed as driving mechanisms to avoid the problem of so-called lock-in effects. The validity and efficiency of the mathematical model and finite element model are conformed by comparing with the sinusoidal experimental results, and the errors are 3.14% and 1.79% respectively. Moreover, the parametric design for the geometric dimensions of mechanical dither and the bimorph piezoelectric actuators is easily achieved through finite element model. It is shown that careful selection of the structural parameters allows the resonant frequency to be suitable. These results are important for the mechanical dither design and improvement of high accuracy ring laser gyroscopes and inertial navigation system.

In order to select a suitable spatial filter for the spatial filtering velocimeter, the filtering characteristics of the spatial filters with a rectangular window and rectangular transmittance are investigated by the power spectrum of transmittance function method. The filtering characteristics of differential filters are investigated and compared with that of common ones. The influences of the number of spatial periods on the spectral bandwidth, deviation to central frequency, and peak transmittance are deeply analyzed. The results show that the influence is due to the form of superposition of the signal components and other components, the pedestal and higher-order components, and the superposition results from the finite size of the spatial filter. According to the results, a method is proposed to compensate for the deviation to central frequency.

The idea of using spatial filtering method to measure velocity of vehicles for an inertial navigation system is put forward. Corresponding optical system, including a 532 nm solid-state laser as active illumination, is established. A 17.92 mm × 14.34 mm area charge coupled device (CCD) is employed both as detector and as spatial filter. The spatial filtering characteristics are theoretically analyzed using a power spectral density function. The spatial filtering operation of CCD is performed fully by software. Therefore, the parameters of the spatial filter, such as the size and the number of spatial period, are changeable. In addition, the CCD is arranged as two differential spatial filters without any other additional elements. Experiments are carried out to examine the feasibility of CCD as two differential spatial filters and the influence of the number of spatial period on the signal frequency. The results indicate that the more number of spatial period the more accurate measurements can be obtained, and show that the relation between signal frequency and velocity has good linearity. So this velocimeter is suitable to provide velocity information for a vehicle self-contained inertial navigation system.

In order to eliminate the magnetic bias sensitivity of square ring laser gyros, a novel practical method by adjusting the nonplanar angle of a ring resonator in the assembly process has been proposed. The ratio coefficient of the magnetic bias sensitivity to non-planarity has been obtained experimentally for the first time and it is found to be almost constant for this kind of square ring laser gyros. This result is useful for the practical elimination of the magnetic bias sensitivity. The magnetic bias sensitivity of every square ring laser gyroscope can be reduced to near zero with the novel method theoretically and it is proved experimentally. These findings are extremely useful for the research on super high precision ring laser gyroscopes.

A novel multipoint layer-type laser Doppler velocimeter (MLLDV) is designed to measure the velocity of a vehicle for the self-contained navigation system. In order to investigate the speckle's influence on the Doppler spectrum, formulas of time-lagged covariance and speckle broadening were derived for our MLLDV. Simulations and experiments are made for detailed analysis. The results show that the time-lagged covariance of photocurrent is directly proportional to the incident angle, and is inversely proportional to the elevation fluctuation of the ground together with the velocity of the vehicle. Speckle broadening is a function of the vehicle's velocity, the 1/e2 Gaussian spot radius and the phase correlation length of the ground. For our MLLDV, Doppler frequency and Doppler broadening are both directly proportional to the velocity of the vehicle. Besides, the ratio between Doppler broadening and the corresponding Doppler frequency is about 0.72% when the speed of the vehicle varies from 0 to 9.6 m/s.

A problem in fundamental 2 × 2 ray matrix for refraction at curved interface proposed by A. E. Siegman was found out and a novel one was derived in this paper. An experiment is introduced in detail to verify the reasonability of the novel ray matrix. Using the novel 2 × 2 ray matrix, augmented 5 × 5 ray matrix of refraction at misaligned curved interface between media of different refractive indices was deduced. With the refraction matrix, it is easy to characterize the effect of an astigmatic thick lens. The augmented ray matrix approach was applied to model and estimate the performance of an optical alignment system. Utilizing these matrices, one can readily design and evaluate optical systems, where contain astigmatic elements such as tilted spherical or cylindrical lenses, mirrors and so on. These results are also useful for cavity design, alignment, ray tracing and beam position control in 3D optical systems.

Inertial navigation system has been the core component of both military and civil navigation systems. Dual-axis rotation modulation can completely eliminate the inertial elements constant errors of the three axes to improve the system accuracy. But the error caused by the misalignment angles and the scale factor error cannot be eliminated through dual-axis rotation modulation. And discrete calibration method cannot fulfill requirements of high-accurate calibration of the mechanically dithered ring laser gyroscope navigation system with shock absorbers. This paper has analyzed the effect of calibration error during one modulated period and presented a new systematic self-calibration method for dual-axis rotation-modulating RLG-INS. Procedure for self-calibration of dual-axis rotation-modulating RLG-INS has been designed. The results of self-calibration simulation experiment proved that: this scheme can estimate all the errors in the calibration error model, the calibration precision of the inertial sensors scale factor error is less than 1ppm and the misalignment is less than 5″. These results have validated the systematic self-calibration method and proved its importance for accuracy improvement of dual -axis rotation inertial navigation system with mechanically dithered ring laser gyroscope.

As a highly reliable positioning and orientation equipment, the redundant inertial navigation system (INS) is widely used in aerospace and other fields. For INS, high-precision calibration is the basis of high-precision navigation. Different from the calibration error modeling method of traditional orthogonal system, the nonorthogonal redundant ring laser gyro INS is installed with multi-device obliquely, and with the complexity of the configuration, the difficulty of separating the calibration parameters is also increased. Therefore, it is very significant to find a high precision calibration scheme for the non-orthogonal redundant INS. In this paper, the high precision calibration of non-orthogonal redundant INS in laboratory is studied, and a new calibration model of redundant system is summarized. A regular tetrahedral configuration prototype consisting of four Ring Laser Gyro and four Quartz Accelerometer is designed, and the calibration error modeling method and calibration accuracy are verified.

There are the scale factor error of LDV (laser Doppler velocimeter) and the misalignment between the SINS (Strapdown inertial navigation system) and the vehicle in a SINS/LDV integrated navigation system. In this paper, the effects of these errors on the attitude, velocity and position of dead reckoning are derived, and a new online calibration method aiming to calibrate the scale factor of LDV and the misalignment between the SINS and the vehicle for the integrated system is put forward. This method, which is utilize the velocity and position of the Global Position System (GPS) as references, use the velocity error and position error of dead reckoning to estimate these errors. Through simulation and experiment, the validity and feasibility of the method are verified. The results show that the scale factor and the misalignment can be calibrated with satisfying accuracy, and the related research can provide technical support for high precision navigation of SINS/LDV integrated navigation systems.

An improved interferometric system aiming at measuring micro displacement is put forward on the basis of phase generated carrier(PGC) demodulation of space optics. This system can improve the accuracy of Absolute Gravimeter(AG) by measuring the amplitude and direction of ground vibration. While the carrier frequency is between 1K and 2K, ground vibration with low frequency (10Hz to 100Hz) and micro vibration amplitude (30nm to 300nm) can be obtained, which satisfies the requirements of AG.

Cavity-enhanced absorption spectroscopy (CEAS) is a technology in which the intracavity absorption is deduced from the intensity of light transmitted by the high finesse optical cavity. Then the samples’ parameters, such as their species, concentration and absorption cross section, would be detection. It was first proposed and demonstrated by Engeln R. [1] and O’Keefe[2] in 1998. This technology has extraordinary detection sensitivity, high resolution and good practicability, so it is used in many fields , such as clinical medicine, gas detection and basic physics research. In this paper, we focus on the use of gas trace detection, including the advance of CEAS over the past twenty years, the newest research progresses, and the prediction of this technology’s development direction in the future.

As an indispensable equipment in inertial technology tests, the three-axis turntable is widely used in the calibration of various types inertial navigation systems (INS). In order to ensure the calibration accuracy of INS, we need to accurately measure the initial state of the turntable. However, the traditional measuring method needs a lot of exterior equipment (such as level instrument, north seeker, autocollimator, etc.), and the test processing is complex, low efficiency. Therefore, it is relatively difficult for the inertial measurement equipment manufacturers to realize the self-inspection of the turntable. Owing to the high precision attitude information provided by the laser gyro strapdown inertial navigation system (SINS) after fine alignment, we can use it as the attitude reference of initial state measurement of three-axis turntable. For the principle that the fixed rotation vector increment is not affected by measuring point, we use the laser gyro INS and the encoder of the turntable to provide the attitudes of turntable mounting plat. Through this way, the high accuracy measurement of perpendicularity error and initial attitude of the three-axis turntable has been achieved.

Inertial navigation system has been the core component of both military and civil navigation systems. Before the INS is put into application, it is supposed to be calibrated in the laboratory in order to compensate repeatability error caused by manufacturing. Discrete calibration method cannot fulfill requirements of high-accurate calibration of the mechanically dithered ring laser gyroscope navigation system with shock absorbers. This paper has analyzed theories of error inspiration and separation in detail and presented a new systematic calibration method for ring laser gyroscope inertial navigation system. Error models and equations of calibrated Inertial Measurement Unit are given. Then proper rotation arrangement orders are depicted in order to establish the linear relationships between the change of velocity errors and calibrated parameter errors. Experiments have been set up to compare the systematic errors calculated by filtering calibration result with those obtained by discrete calibration result. The largest position error and velocity error of filtering calibration result are only 0.18 miles and 0.26m/s compared with 2 miles and 1.46m/s of discrete calibration result. These results have validated the new systematic calibration method and proved its importance for optimal design and accuracy improvement of calibration of mechanically dithered ring laser gyroscope inertial navigation system.

Taking the one-dimensional Laser Doppler Velocimeter (LDV) and a certain type of Laser Gyro Strapdown Inertial Navigation System (SINS) developed our staff room for object, the paper verifies that dynamic calibration technique can be achieved by SINS/LDV integrated system on the basis of the analysis of the software and hardware conditions. Extended Kalman filter states of SINS/LDV integrated system were chosen based on the error models of SINS and LDV. Using the difference of the output speed of the SINS and LDV as measurement, the error of bias and scale factor of the integrated navigation system are estimated effectively by setting up a reasonable calibration path. The effectiveness of the algorithm is further verified through the vehicular experiments. The results of experiments show that the dynamic calibration technique can be achieved through SINS/LDV integrated system and ensure the maneuverability of terrestrial inertial navigation system. The estimate of LDV scale factor is about 0.003%. The estimate error of accelerometer bias no more than 13μg. The estimate error of gyroscope drift no more than 1.7×10-3°/h. The yaw angle error is less than 0.19 ' within 20min.

A practical method to determine the emission frequency of a distributed feedback diode laser at the D1 line of 133Cs is reported. By fitting the extracted dips of the saturated absorption spectrum using linear or quadratic function, this method can realize the measurement of the emission frequency with low cost and simple structure. The test results show that this method can achieve an appreciable measurement range and a high measuring precision of approximately 10 MHz.A practical method to determine the emission frequency of a distributed feedback diode laser at the D1 line of 133Cs is reported. By fitting the extracted dips of the saturated absorption spectrum using linear or quadratic function, this method can realize the measurement of the emission frequency with low cost and simple structure. The test results show that this method can achieve an appreciable measurement range and a high measuring precision of approximately 10 MHz.

Ray matrix approach with appropriate coordinate systems has been proposed in this paper. It is employed to analyze the optical-axis perturbation in nonplanar ring resonators. The sensitivities of optical-axis decentration (SD) and optical-axis tilt (ST) in nonplanar resonators with 90° and 270° image rotation are discussed in detail in the region of 0

A general beam position controlling method for 3D optical systems based on the method of solving ray matrix equations has been proposed in this paper. As a typical 3D optical system, nonplanar ring resonator of Zero-Lock Laser Gyroscopes has been chosen as an example to show its application. The total mismatching error induced by Faraday-wedge in nonplanar ring resonator has been defined and eliminated quite accurately with the error less than 1 μm. Compared with the method proposed in Ref. [14] , the precision of the beam position controlling has been improved by two orders of magnitude. The novel method can be used to implement automatic beam position controlling in 3D optical systems with servo circuit. All those results have been confirmed by related alignment experiments. The results in this paper are important for beam controlling, ray tracing, cavity design and alignment in 3D optical systems.

A novel compact super sensitive nonplanar ring laser magnetometer with the wavelength at 632.8 nm is proposed. A well-designed structure enables the super sensitivity of the magnetometer to the magnetic field. The device obtains a scale factor of 150 Hz/nT and achieves a magnetic field noise limited sensitivity of 13 fT/Hz1/2. The device inherits with all the advantages of the ring laser gyros such as large bandwidth (fast response), large measurement range, short starting time and higher impact resistance, good temperature performance.

A new method based on the maximum likelihood estimation (MLE) is proposed aiming at the Fourier spectrum broadening of the laser Doppler signal when acceleration occurs. First, the fast Fourier transform (FFT) method is performed on the Doppler signal to get an approximate velocity. Then a fine search of the likelihood function's maximum value is carried on in the area nearby the approximate velocity. For a high precision and quick calculation, the search area is zoomed down step by step. The simulations show that the new method based on the FFT and MLE ensures the velocity precision, and highly decrease the calculation time, which is good for the real-time system.