Showing papers on "Ring laser gyroscope published in 2006"

Robust six degree-of-freedom micromachined gyroscope with anti-phase drive scheme and method of operation of the same

Abstract: A method of operating an anti-phase six degree-of-freedom tuning fork gyroscope system comprises the steps of driving a first three degree-of-freedom gyroscope subsystem, and driving a second three degree-of freedom gyroscope subsystem in an anti-phase mode with the first gyroscope subsystem at an anti-phase resonant frequency. Acceleration or an angular rate of motion is sensed by means of the first and second three degree-of-freedom gyroscope subsystems operating in a flat frequency response range where the anti-phase resonant frequency is designed. Response gain and phase are stable and environmental and fabrication perturbations are avoided by such operation. A anti-phase six degree-of-freedom tuning fork gyroscope system which operates as described is also characterized.

Single-photon Sagnac interferometer

Abstract: We present the first experimental demonstration of the optical Sagnac effect at the single-photon level. Using a high quality guided-wave heralded single-photon source at 1550 nm and a fibre optics setup, we obtain an interference pattern with net visibilities up to (99.2 ± 0.4%). On the basis of this high visibility and the compactness of the setup, the interest of such a system for fibre optics gyroscope is discussed.

Resonating star gyroscope

Abstract: Disclosed are resonant vibratory gyroscopes and fabrication methods relating thereto. The angular motion sensor comprises a resonating star gyroscope which comprises a vibratory solid or shell-type structure for rate sensing or measuring angle of rotation. The structure formed as a merged superposition of two square entities, yields in-plane degenerate flexural modes that are used to sense rotation around the axis perpendicular to the substrate. The resonating star gyroscope may be implemented using the primary flexural degenerate modes. Such an implementation has been successfully demonstrated by the authors using trench-refilled polysilicon and epitaxial polysilicon as the structural material. It is also possible to use a solid star-shaped resonator (with or without perforations) for the gyroscope. The authors also suggest the operation of the resonating star gyroscope employing the higher-order flexural modes. In this particular implementation the authors utilized a (100) single crystalline structural material.

Optical Gyroscope Options: Principles and Challenges

Abstract: Several alternatives to the Sagnac-based He-Ne ring laser gyroscope and the fiber interferometer gyroscope have been reviewed. Different CW and pulsed laser RLGs have been examined, as well as, various passive resonator approaches using external lasers. It was clear that much research needs to be done to make such alternatives viable.

The GEOsensor Project: Rotations - a New Observable for Seismology

Abstract: Over the last 40 years ring laser gyroscopes became one of the most important instruments in the field of inertial navigation and precise rotation measurements. They have a high resolution for angular velocities, a very good scale factor stability and a wide dynamic range. These properties made them suitable for aircraft and autonomous submarine navigation. Over the last decade we have developed several very large perimeter ring laser gyroscopes for the application in geodesy and geophysics (Schreiber et al., 2001). Because of a substantial upscaling of these ring lasers, their sensitivity to rotations has been increased by at least 5 orders of magnitudes. At the same time the instrumental drift was reduced by about the same amount. This progress in rotational sensor technology led to the successful detection of rotational signals caused by earthquakes (Pancha et al., 2000) several thousands kilometers away. These observations stimulated the development of a highly sensitive ring laser gyro for specific seismological applications. The GEOsensor provides rotational motions along with the usual translational motions at a high data acquisition rate of at least 20 Hz. Observations of seismic induced rotations show that they are consistent in phase and amplitude with the collocated recordings of transverse accelerations obtained from a standard seismometer over a wide range of distances and frequencies.

Inertial measurement system and method with sensor bias cancellation

Abstract: Inertial measurement system and method in which a base is rotated about an input axis in accordance with a rotation to be measured, rotation about the input axis is sensed with one or more angular rate sensors, fixed bias offset is cancelled by dithering the sensors about an axis perpendicular to their sensing axes to vary the orientation of the sensing axes relative to the base in an oscillatory manner, and signals from the sensors are demodulated at the dithering frequency.

Resonating star gyroscope and fabrication methods

Abstract: Disclosed are resonant vibratory gyroscopes and fabrication methods relating thereto. The angular motion sensor comprises a resonating star gyroscope which comprises a vibratory solid or shell-type structure for rate sensing or measuring angle of rotation. The structure formed as a merged superposition of two square entities, yields in-plane degenerate flexural modes that are used to sense rotation around the axis perpendicular to the substrate. The resonating star gyroscope may be implemented using the primary flexural degenerate modes. Such an implementation has been successfully demonstrated by the authors using trench-refilled polysilicon and epitaxial polysilicon as the structural material. It is also possible to use a solid star-shaped resonator (with or without perforations) for the gyroscope. The authors also suggest the operation of the resonating star gyroscope employing the higher-order flexural modes. In this particular implementation the authors utilized a (100) single crystalline structural material.

Initial Test Results from a 3-axis Vibrating Ring Gyroscope

Abstract: There are several application areas where the simultaneous measurement of rates of rotation about three mutually orthogonal axes is required. In this paper the principle features of a 3-axis vibrating ring gyroscope are described. The fabrication process for the gyroscope is presented and employs standard MEMS techniques. The modal properties for the ring are measured experimentally using laser vibrometry and electrostatic sensing and compared with the design predictions. In operation as a rate gyroscope it is necessary to excite the primary motion of the gyroscope and control is amplitude. As Q-factors of vibratory gyroscope are typically of the order 103-104 slight variations in environmental conditions will perturb the natural frequency of the primary mode significantly. To ensure the primary motion of the gyroscope is maintained with constant amplitude a control scheme employing both frequency tracking and amplitude control is required. An electronic control system using digital signal processing (DSP) has been developed to ensure excitation of the primary motion occurs at resonance with controlled amplitude. The control scheme employs an embedded processor to generate the drive frequency (via a D/A converter) and to monitor the primary vibration (via an A/D converter). Experimental results from the control scheme highlighting its effectiveness over conventional PLL approaches are presented.

Sagnac Beat Signals Observed in Semiconductor Fiber-Optic Ring Laser Gyroscope

Abstract: A semiconductor fiber-optic ring laser gyroscope, which consist of a semiconductor optical amplifier as a gain medium and polarization-maintaining fiber to form a ring resonator, generate Sagnac beat signals demonstrating good agreement with theoretical calculations.

Solid-state laser gyro having orthogonal counter-propagating modes

Abstract: The invention concerns solid-state laser gyros used in inertial navigation unit. However, the design of this type of laser gyros involves some technical difficulties related partly to the fact that the counter-propagating waves interfere in the amplifying medium. The inventive laser gyro comprises at least one solid-state amplifying medium (2) and one ring optical cavity (1) including first optical means (4) enabling a first common linear polarization state to be imparted to the two counter-propagating optical waves in input and output of the zone containing the amplifying medium and second optical means (30, 31) enabling, inside the amplifying medium, a second linear polarization state to be imparted to the first optical wave and a third linear polarization state to the second optical wave, said polarization states being perpendicular, thereby eliminating all the inconveniences related to interferences.

Method for operating a vibrating gyroscope and sensor arrangement

Abstract: The invention relates to a method for operating a vibrating gyroscope and to a sensor arrangement comprising such a vibrating gyroscope. Said vibrating gyroscope is used as a resonator and is part of at least one control circuit that excites the vibration gyroscope by feeding an excitation signal with its natural frequency. An output signal can be tapped from the vibrating gyroscope from which the excitation signal can be derived by filtering and amplification. The invention is characterized in that, once the sensor arrangement is switched on, the frequency of the excitation signal is adjusted by exciting the vibrating gyroscope, before the excitation signal is fed, to oscillate freely, measuring the frequency of the free oscillation and feeding the excitation signal to the vibrating gyroscope with the measured frequency.

Rotational Motions in Seismology

Abstract: The seismic waves that spread out from the earthquake source to the entire Earth are usually measured at the ground surface by a seismometer which consists of three orthogonal components (Z (vertical), N (north-south), and E (east-west) or R (radial), T (transversal), and Z (vertical)). However, a complete representation of the ground motion induced by earthquakes consists not only of those three components of translational motion, but also three components of rotational motion plus six components of strain. Altough theoretical seismologists have pointed out the potential benefits of measurements of rotational ground motion, they were not made until quite recently. This was mainly because precise instruments to measure ground rotational motion were not available. The measurement of rotational motion induced by earthquakes is relatively new in the field of seismology. To the best of our knowledge, the first experiment to measure ground rotational motion using rotational sensor was done by Nigbor (1994}. He successfully measured translational and rotational ground motion during an underground chemical explosion experiment at the Nevada Test Site using a triaxial translational accelerometer and a solid-state rotational velocity sensor. The same type of sensor was also used by Takeo (1998} for recording an earthquake swarm on Izu peninsula, Japan. However, because of the limitation of the instrument sensitivity, this kind of sensor was only able to sensing the rotational ground motion near the earthquake sources of other artificial sources. Another type of rotational sensor was assembled using two oppositely oriented seismometers. This is possible since in principle the rotational component of the ground motions is equal to half the curl of the ground velocity. This kind of sensor was intensively researched and developed by the seismology group in Institute of geophysics, Polish Academy of Sciences. However, they report several problems especially due to the small differences in the seismometer's response function. Like the solid state rotational sensors, this sensor was only able to measure rotational motion near the seismic sources. The application of the Sagnac effect for sensing the inertial rotation using optical devices were intensively investigated, since the advent of lasers in the sixties. However, the first application of a ring laser gyroscope as a rotational sensor applied in the field of seismology was reported by Stedman et al. (1995}. Fully consistent rotational motions were recorded by a ring laser gyro installed at the fundamental station Wettzell, Germany (Igel et al., 2005). They showed that the rotational motions were compatible with collocated recordings of transverse acceleration by a standard seismometer, both in amplitude and phase. They mentioned that "standard" rotational sensors with sufficient resolution may be possible in the near future. Among the other type of rotational sensor, ring lasers seem more reliable in seismic applications since it has been provenable to sensing the ground rotational motion from near source as well as teleseismic earthquake events with a broad magnitude range (Igel et al., 2007}. In earthquake engineering, observations of rotational components of seismic strong motions may be of interest as this type of motion may contribute to the response of structures to earthquake-induced ground shaking. Most of rotational/torsional studies of ground motion in earthquake engineering are so far still carried out by indirect measurements. It can be done since the rotational component of motion is a linear combination of the space derivatives of the horizontal component of the motion. However, to the best of our knowledge, there are no comparison of array-derived rotation rate and direct measurement from rotational sensors mentioned in the literature. The first objective of my thesis is to study the effect of noise and various uncertainties to the derivation of rotation rate and to compare directly the result with the ring laser data. Here we present for the first time a comparison of rotational ground motions derived from seismic array with those observed directly with ring laser. Our study suggest that - given accurate measurements of translational motions in an array of appropriate size and number of stations - the array-derived rotation rate may be very close to the "true" rotational signal that would be measured at the center of the array (or the specific reference station). However, it is important to note that it may be dangerous to use only the minimally required three stations as even relatively small noise levels may deteriorate the rotation estimates. Furthermore, it is clear that the logistic effort to determine rotations from array is considerably larger than direct measurements. In the light of this, the necessity to develop field-deployable rotational sensors with the appropriate resolution for use in local and regional seismology remains an outstanding issue. More recently, Igel et al. (2005) introduced a method to estimate the horizontal phase velocity by using collocated measurements from a ring laser and seismometer. A simple relationship between transverse acceleration and rotation rate (around a vertical axis) shows that both signals should be in phase and their ratio proportional to horizontal phase velocity. Comparison with synthetic traces (rotations and translations) and phase velocities determined in the same way showed good agreement with the observations. The second objective of my thesis is to study the accuracy of phase velocity determination using collocated measurement of rotational and translational motion and derive the Love wave dispersion curve using spectral ratio for both synthetic and real observed data. Whether the accuracy of the dispersion curves derived with the approach presented in this thesis is enough for tomographic purposes remains to be evaluated. Nevertheless, the results shown here indicate that through additional measurements of accurate rotational signals, wavefield information is accessible that otherwise requires seismic array data. However, to make this methodology practically useful for seismology will require the development of an appropriate high-resolution six-component broadband sensor. Efforts are underway to coordinate such developments on an international scale (Evans et al., 2006). The ground tilt is generally small but not negligible in seismology, especially in the strong-motion earthquake. It is well known that the tilt signal is most noticeable in the horizontal components of the seismometer. Ignoring the tilt effects leads to unreliable results, especially in calculation of permanent displacements and long-period calculations. The third objective of my thesis is to study the array-derived tilt, a further application of measuring tilt. An interesting result concerning tilt study based on a synthetic study is the possibility to derive the Rayleigh wave phase velocity as well as Rayleigh wave dispersion curve from collocated measurement of tilt rate and translational motions. The synthetic study shows that there is a frequency dependent phase velocity from collocated radial acceleration and transverse tilt.

The Performance Modeling of Ring Laser Gyro In Inertial Navigation

Abstract: In this paper, the performance of a Ring Laser Gyro based inertial navigation is studied. It is modeled by using two methods; in the dynamic modeling, some parameters such as scale factor and environmental sensitivity have been determined, whereas in the statistical model, the other parameters such as random drift have been computed. Also the performance of the system is evaluated for several inputs and the dither influences on Gyro's output, locking effect, scale factor and drift errors are investigated.

Dynamic analysis of a microelectromechanical systems resonant gyroscope excited using combination parametric resonance

Abstract: This paper investigates the application of parametric excitation to a resonant microelectromechanical systems (MEMS) gyroscope. The modal equations of motion of an electrostatically actuated ring are derived and shown to be coupled via the electrostatic stiffness. Such electrostatic coupling between in-plane modes of vibration permits parametric instabilities that may be exploited in a novel excitation scheme. A multiple time scale perturbation method is used to analyse the response of the ring gyroscope to the combination parametric excitations with the principal objective of separating the drive and response frequencies of the ring gyroscope. As pairs of flexural modes of the perfect ring are degenerate, the combination excitation between distinct modes demand the ring to be analysed as a four degree of freedom system. Slight mis-tuning between the otherwise degenerate modes is incorporated in the perturbation analysis. The results of the perturbation analysis are subsequently used to determine ...

Investigation on the temperature compensating model for ring laser gyroscope

Abstract: Thermal effects impose the greatest limit on the precision of a ring laser gyro (RLG). Selections of temperature sensing points were comparatively discussed based on large numbers of experimental data to improve its precision, and the optimum combination was selected to establish a practical compensating model. The model is applied to new experimental data under the given and varied temperatures. Results show that the bias trend changing with the temperature is basically eliminated and the bias stability is enhanced significantly.

Parametric design consideration of a vibro-elastic bimorph piezoelectric converter for a ring laser gyroscope

Abstract: Gyroscopes have been used as suitable inertial instruments for navigation, guidance, and attitude controls. Their accuracy as very sensitive sensors is limited by the lock-in region (dead band) due to frequency coupling between two counter-propagating waves at low rotation rates. This frequency coupling gives no phase difference, and no angular increment is detected. The problem can be overcome by mechanically dithering the gyroscope. Mechanically, the vibro-elastic bimorph piezoelectric converter (hereinafter, dither) is used for feasible control. This paper presents the design considerations of the mechanical dither, taking mechanical and piezoelectric parameters into account. Verification of the theoretical equations is performed through FEM (finite-element method) applications.

Sensitivity and Stability of an Air-Core Fiber Gyroscope

Abstract: We report an air-core fiber-optic gyroscope with similar short-term noise as a conventional gyroscope (random walk of ~0.015 deg/√hr) and a dramatically reduced sensitivity to Kerr effect (>50), temperature transients (~6.5), and Faraday effect (>10).

On the calculation of the gyro-factor in a semiconductor ring laser

Abstract: The frequency splitting due to the Sagnac effect is considered in the active laser gyro with a ring cavity filled with a medium having the high refraction index and nonzero dispersion. It is shown that the medium reduces the gyro-factor by n* times, where n* is the group refractive index. However, in the case of dynamic anomalous dispersion, it is possible in principle to increase the gyro-factor without increasing the ring cavity size.

Design of A Novel Micro Thermo-Fluidic Gyroscope

Abstract: This paper reports the design and analysis of a novel micro thermo-fluidic gyroscope utilizing dual directional liquids. Compared with the traditional jet deflection method, the proposed gyroscope comprises two pairs of symmetric microchannels splitting from the main channel. When the Coriolis force induced by external rotation acts on the fluid, the mass flow rate of the symmetric microchannels will be unequal, which results in different thermal convections between the fluid and thermistors inside the split microchannels. Through measuring the temperature difference between the symmetric thermistors, the angular rate is obtained. The gyroscope is applicable for both even and uneven angular rate condition. Numerical simulation is applied to investigate the gyroscope performance, which concludes that the mass flow rate difference between the symmetric microchannels and the temperature difference between the symmetric thermistors show good linearity to the angular rate, the nonlinearity are 0.099% and 0.15% respectively.

Demonstration of Tunable Displacement-Measurement-Sensitivity using Variable Group Index in a Ring Resonator

Abstract: We show that an intra-cavity medium with normal dispersion reduces the sensitivity of the cavity resonance frequency to a change in its length by a factor inversely proportional to the group index. Since the group index in an atomic medium can be very large, this effect can help in constructing highly frequency-stable cavities for various potential applications without taking additional measures for mechanical stability. The results also establish indirectly the opposite effect of enhanced sensitivity that can be realized for a negative dispersion corresponding to a group index close to a null value. This enhancement in turn can be employed to increase significantly the sensitivity of a ring laser gyroscope.

Matter-wave Optics of Dark-state Polaritons: Applications to Interferometry and Quantum Information

Abstract: The present work "Materwave Optics with Dark-state Polaritons: Applications to Interferometry and Quantum Information" deals in a broad sense with the subject of dark-states and in particular with the so-called dark-state polaritons introduced by M. Fleischhauer and M. D. Lukin. The dark-state polaritons can be regarded as a combined excitation of electromagnetic fields and spin/matter-waves. Within the framework of this thesis the special optical properties of the combined excitation are studied. On one hand a new procedure to spatially manipulate and to increase the excitation density of stored photons is described and on the other hand the properties are used to construct a new type of Sagnac Hybrid interferometer. The thesis is devided into four parts. In the introduction all notions necessary to understand the work are described, e.g.: electromagnetically induced transparency (EIT), dark-state polaritons and the Sagnac effect. The second chapter considers the method developed by A. Andre and M. D. Lukin to create stationary light pulses in specially dressed EIT-media. In a first step a set of field equations is derived and simplified by introducing a new set of normal modes. The absorption of one of the normal modes leads to the phenomenon of pulse-matching for the other mode and thereby to a diffusive spreading of its field envelope. All these considerations are based on a homogeneous field setup of the EIT preparation laser. If this restriction is dismissed one finds that a drift motion is superimposed to the diffusive spreading. By choosing a special laser configuration the drift motion can be tailored such that an effective force is created that counteracts the spreading. Moreover, the force can not only be strong enough to compensate the diffusive spreading but also to exceed this dynamics and hence to compress the field envelope of the excitation. The compression can be discribed using a Fokker-Planck equation of the Ornstein-Uhlenbeck type. The investigations show that the compression leads to an excitation of higher-order modes which decay very fast. In the last section of the chapter this exciation will be discussed in more detail and conditions will be given how the excitation of higher-order modes can be avoided or even suppressed. All results given in the chapter are supported by numerical simulatons. In the third chapter the matterwave optical properties of the dark-state polaritons will be studied. They will be used to construct a light-matterwave hybrid Sagnac interferometer. First the principle setup of such an interferometer will be sketched and the relevant equations of motion of light-matter interaction in a rotating frame will be derived. These form the basis of the following considerations of the dark-state polariton dynamics with and without the influence of external trapping potentials on the matterwave part of the polariton. It will be shown that a sensitivity enhancement compared to a passive laser gyroscope can be anticipated if the gaseous medium is initially in a superfluid quantum state in a ring-trap configuration. To achieve this enhancement a simultaneous coherence and momentum transfer is furthermore necessary. In the last part of the chapter the quantum sensitivity limit of the hybrid interferometer is derived using the one-particle density matrix equations incorporating the motion of the particles. To this end the Maxwell-Bloch equations are considered perturbatively in the rotation rate of the noninertial frame of reference and the susceptibility of the considered 3-level \(\Lambda\)-type system is derived in arbitrary order of the probe-field. This is done to determine the optimum operation point. With its help the anticipated quantum sensitivity of the light-matterwave hybrid Sagnac interferometer is calculated at the shot-noise limit and the results are compared to state-of-the-art laser and matterwave Sagnac interferometers. The last chapter of the thesis originates from a joint theoretical and experimental project with the AG Bergmann. This chapter does no longer consider the dark-state polaritons of the last two chapters but deals with the more general concept of dark states and in particular with the transient velocity selective dark states as introduced by E. Arimondo et al. In the experiment we could for the first time measure these states. The chapter starts with an introduction into the concept of velocity selective dark states as they occur in a \(\Lambda\)-configuration. Then we introduce the transient velocity selective dark-states as they occur in an particular extension of the \(\Lambda\)-system. For later use in the simulations the relevant equations of motion are derived in detail. The simulations are based on the solution of the generalized optical Bloch equations. Finally the experimental setup and procedure are explained and the theoretical and experimental results are compared.

Development of crossover-free fiber optic gyroscope sensor coils

Abstract: The DoD goals for inertial sensors have included achieving high accuracy performance and small size at a low cost. This goal has always been a challenging endeavor, since small size and high accuracy have often been costly and technically difficult to achieve. In 1998, the Army patented a fiber sensor coil winding concept that would facilitate the opportunity to make the Fiber Optic Gyroscope (FOG) more competitive in cost with relation to the commonly-used Ring Laser Gyro (RLG). Recent advances in FOG sensor coil winding techniques appear to show great promise in the improved performance. The novel Crossover-Free (CF) winding technique eliminates fiber crossovers and allows the use of inexpensive single-mode fiber (SMF). Experiments were conducted with the use of an analog, open-loop testbed, which was characterized with a 1 km quadrupolar SM sensor coil. Various sensor coil configurations were spliced into the FOG testbed and bias drift tests were conducted. Different fiber lengths, coil diameters, and fiber wind configurations were evaluated. The Crossover-Free sensor coils were precision wound by a semi-automated Fiber Placement Machine (FPM) developed by Stanley Associates. The Crossover-Free sensor coils test results are compared to standard precision wound coils. The bias errors caused by the fiber crossovers in standard SM sensor coils are also discussed and compared to the near elimination of the crossovers in the CF design.

Performance Modeling of Ring Laser Gyro in Inertial Navigation System

Abstract: In this paper, the performance of a Ring Laser Gyro based inertial navigation is investigated. Dynamic and stochastic modeling are applied to gyro simulation and performance evaluation. In the dynamic model, some parameters such as scale factor and environmental sensitivity have been determined, whereas in the stochastic model, the other parameters such as random drift and measurement noise have been computed. The performance of the system is evaluated for several inputs. Also, the parameter variation of output noise as a result of changing the dither characteristics is analyzed.

Systematic Calibration Method for the Laser Gyro Strapdown Inertial Navigation System

Abstract: In this paper, based on the inertial navigation equation, a novel systematic calibration model for the laser gyro strapdown inertial navigation system is proposed. The observability of the error parameters is analyzed. Then a calibration algorithm, which can identify twenty four error parameters of the inertial navigation unit is studied.

Research on Inertial Measurement Unit of High Rotation Vehicle

Abstract: At present,the measurement range of micro gyroscope is limited and can not be applied to axial angular rate measurement of high rotation vehicle.Three inertial measurement schemes using dimension effect of accelerometers for the axial angular rate test and two-axis gyroscope for the yaw and pitch angular rate measurement were presented.Based on the random error formulas of function,the error transfer formulas of acceleration at the vehicle mass center and axial angular rate were provided which were helpful to select sensors and form the measurement system.The simulation result indicates that three schemes can be applied to attitude measurement of high rotation vehicle when the measurement range of micro gyroscope is limited.The second scheme that the inertial measurement unit is constituted by 4 accelero-meters and 1 two-axis gyroscope should be chose preferentially.

Measurement of low loss and mirrors' reflectivity using cavity ring down spectroscopy with high accuracy

Abstract: Differential laser gyro is an ideal equipment to solve the "lock-in" behavior. The ring cavity must be low loss and the reflectivity of mirrors in gyro must be more than 99.99%. But the insertion of a piece of quartz glass and a Faraday cell in the cavity will broaden the "lock-in" area due to additional loss, so it is very important to measure ultra-high reflectivity of mirrors and the loss of transparent glass plate used in gyro. 632.8nm He-Ne laser is the most suitable light to travel around the ring cavity in gyro, so the traditional cavity ring down spectroscopy (CRDS) must be improved by using continuous-wave (CW) He-Ne laser instead of pulsed one. The results show that the single-pass loss through the glass plate can be kept below 3.0×10 -11 cm -1 . Using combination of linear and folded cavity ring down spectroscopy, the loss such as absorption of gas in the cavity are counteracted due to the equalized length of cavity, so the reflectivity of the mirrors is measured with high accuracy. The ring down time of the cavity with and without a sample is obtained respectively, and then the total loss of the measured sample is calculated. The results show that the improved CRDS is suitable for accurately measuring low loss of medium and reflectivity of mirrors.

Mechanical-electrostatic coupling research for MEMS line vibration gyroscope

Abstract: MEMS line vibration gyroscope is one of the most extensive applications of the MEMS gyroscope now. Its driving mode is always the electrostatic. When the MEMS line vibration gyroscope works in normal mode, its mass is vibrated in line at one direction (it is x direction here) and detected the rotation speed at other direction ( it is y direction here) in horizontal. At this time, the mass is in balance at y direction. But when the configuration of the MEMS line vibration gyroscope is not asymmetry, the electrostatic that putted on the mass at y direction is destroyed. So the mass is vibrated in line at y direction. The MEMS line vibration gyroscope will couple the rotation speed of x direction and produce zero signals because of this movement. Aim at this phenomenon, the mechanical-electrical error model because of the asymmetry of the configuration of the MEMS line vibration gyroscope is built. There is simulation analysis by using Matlab. And according to the method of Limited Element, the distributing fig of the electric field and the electrostatic force because of the asymmetry of the configuration is got by using ANSYS. These researches act important effect on improving the precision of the MEMS line vibration gyroscope.