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The attitude tracking control problem with preassigned performance requirements has earned tremendous interest in recent years, and the prescribed performance control (PPC) scheme is often adopted to tackle this problem. Nevertheless, traditional PPC schemes may suffer singularity problems when the expected state constraint is violated. This may cause a decrease in the control effect or even instability of the system. Motivated by this issue, this article proposes a singularity-avoidance PPC scheme (SAPPC) to deal with these problems, of which the core is a shear-mapping-based error transformation procedure that globally transforms the original error state without singularity. Based on the presented nonsingular error transformation, this article presents a perspective to guarantee the satisfaction of given transient performance requirements by leading the state trajectory converging along a preassigned smooth trajectory called reference performance function (RPF). Based on the concept of the RPF, this article naturally adopts an error-defined-type state constraint, providing a time-varying constraint boundary and alleviating the potential overcontrol problem at the steady state. Furthermore, in order to validate the proposed SAPPC scheme, a simple backstepping controller is developed by employing the predefined-time stability technique and the dynamic surface control technique. Finally, theoretical analysis and numerical simulation results are presented to validate the proposed control scheme's effectiveness and robustness.

This paper makes a deep investigation of the lock-in behavior in a resonant fiber-optic gyroscope (RFOG). A theoretical model is first set up to reveal the mechanism of how the backscattering creates a lock-in phenomenon at the gyro output. After phase modulation, the RFOG has more than one lock-in zone. These lock-in zones are symmetrically distributed around zero rotation rate originating from the backscattering inside the resonator, but also being affected by the modulation parameters and feedback loops. Experimentally, we tested the lock-in phenomenon in a closed-loop RFOG. The main lock-in range is measured to be 30 °/h which agrees well with the theoretical result. Finally, we successfully demonstrated the elimination of the lock-in behavior by optimizing the modulation parameters in combination with the bandwidth of the feedback loop.

Simultaneous multidirectional orientation tasks on space robots exhibit strong dynamic coupling between the manipulators and the base-spacecraft, and this phenomenon is more obvious in the micronano space robot. Regarding to the highly coupled dynamic system of micronano space robot and its nonholonomic constraints, a multidirectional rapid orientation method of micronano space robot based on optimization theory is proposed in this article. Dynamic model of satellite-manipulators cooperative operation micronano space robot is established by the combination of virtual manipulator and Newton–Euler method. Then, taking the acceleration continuous cubic polynomial trajectory planning method and the dynamics-based feedback linearization controller as an example, the particle swarm optimization method is used to solve the time and path nodes of the orientation process of the micronano space robot. Finally, three typical spatial orientation problems are simulated to verify the feasibility and rapidity of this orientation method: 1) simultaneous orientation; 2) assisted orientation; and 3) cooperative braking. Furthermore, the article presents the structure of the objective function for optimization in different multicomponent and multiobjective coorientation tasks.

This paper reports an approach of in-operation temperature bias drift compensation based on phase-based calibration for a stiffness-tunable MEMS accelerometer with double-sided parallel plate (DSPP) capacitors. The temperature drifts of the components of the accelerometer are characterized, and analytical models are built on the basis of the measured drift results. Results reveal that the temperature drift of the acceleration output bias is dominated by the sensitive mechanical stiffness. An out-of-bandwidth AC stimulus signal is introduced to excite the accelerometer, and the interference with the acceleration measurement is minimized. The demodulated phase of the excited response exhibits a monotonic relationship with the effective stiffness of the accelerometer. Through the proposed online compensation approach, the temperature drift of the effective stiffness can be detected by the demodulated phase and compensated in real time by adjusting the stiffness-tuning voltage of DSPP capacitors. The temperature drift coefficient (TDC) of the accelerometer is reduced from 0.54 to 0.29 mg/°C, and the Allan variance bias instability of about 2.8 μg is not adversely affected. Meanwhile, the pull-in resulting from the temperature drift of the effective stiffness can be prevented. TDC can be further reduced to 0.04 mg/°C through an additional offline calibration based on the demodulated carrier phase representing the temperature drift of the readout circuit.

The phase modulation and demodulation technique is widely used in resonant optical gyroscopes to accurately detect resonance frequencies, which directly affect gyro sensitivity. In order to overcome the influences of the system phase fluctuations, an in-phase and quadrature (IQ) demodulation technique is introduced for a resonant micro-optic gyroscope (RMOG). The phase fluctuations in the RMOG are measured, and their influence on the demodulation slope at the resonance point is compared between the traditional sinusoidal demodulation and the IQ demodulation both theoretically and experimentally. It can be concluded that the output of the proposed IQ demodulation is not affected by any phase fluctuations. The demodulation slope is always at its maximum value, thus improving the signal-to-noise ratio of the detection system. By using the IQ demodulation technique, a random walk coefficient of 0.5°/√h is carried out. A long-term bias stability of 9°/h is successfully observed, which is improved by a factor of 1.6 compared with that obtained using the traditional phase-sensitive sinusoidal demodulation technique.

Optical gyros are attractive angular rotation sensors based on the Sagnac effect. The phase modulation technique is adopted to detect the weak resonant frequency shift induced by the Sagnac effect, which determines the detection sensitivity of the gyros. The Pound–Drever–Hall (PDH) modulation is a mature laser frequency stabilization technique that is widely recognized. A resonant optic gyro equipped with a short and high-finesse fiber ring resonator employing the high-frequency PDH modulation technique is proposed and demonstrated. The modulation index and frequency are optimized to maximize the slope of the demodulation curve. Compared with the low-frequency modulation, the high-frequency PDH modulation increases the slope of the demodulation curve by a factor of 1.23 and achieves an extra 15.8 dB of laser frequency noise suppression. The bias stability of the gyro output is improved from 9.6°/h to 8°/h, and the equivalent lock-in frequency accuracy increases 12 dB.

A new record for high-finesse silica waveguide ring resonators (WRRs), to the best of our knowledge, is demonstrated experimentally. The achieved finesse and resonant depths of the silica WRR with a length of 7.9 cm and a diameter of 2.5 cm are 196.7% and 98%, respectively. In addition, the silica WRR chip is coupled with single-polarization fiber to improve the polarization extinction ratio (PER) and, thus, to reduce the polarization error. With the application of this high-finesse and high-PER WRR to the resonant micro-optic gyroscope (RMOG), a bias stability of 0.004°/s is observed over a 1 h timeframe. To the best of our knowledge, this is the first RMOG reported in the open literature that can sense the earth’s rotation rate (15°/h).

A fiber ring resonator is the key element in a resonant fiber optic gyroscope (RFOG). Both reflection and loss characteristics can severely decrease the accuracy of the RFOG. This paper first implements optical frequency domain reflectometry (OFDR) to measure the reflection and loss coefficients of the hybrid air-core photonic-bandgap fiber (PBF) ring resonator. Compared with the traditional measurement method of the resonant curve, OFDR can clearly distinguish the two junctions between the air-core PBF and the solid-core fiber. The measured reflection coefficients at the two splicing points are 1.77% and 2.65%, respectively. The excess losses are 2.28 dB and 3.22 dB, respectively. Thus, the measurement of the junctions in the fiber ring resonator is realized.

New developments are made in the resonant fiber optic gyro (RFOG), which is an optical sensor for the measurement of rotation rate. The digital signal processing system based on the phase modulation technique is capable of detecting the weak frequency difference induced by the Sagnac effect and suppressing the reciprocal noise in the circuit, which determines the detection sensitivity of the RFOG. A new technique based on the sinusoidal wave modulation and square wave demodulation is implemented, and the demodulation curve of the system is simulated and measured. Compared with the past technique using sinusoidal modulation and demodulation, it increases the slope of the demodulation curve by a factor of 1.56, improves the spectrum efficiency of the modulated signal, and reduces the occupancy of the field-programmable gate array resource. On the basis of this new phase modulation technique, the loop is successfully locked and achieves a short-term bias stability of 1.08°/h, which is improved by a factor of 1.47.

A novel hybrid integrated scheme is proposed for a high-performance resonant micro-optic gyro (RMOG), which requires a low-loss micro-ring resonator for mass production. A new record for the RMOG is established experimentally with a short fiber ring resonator and an integrated signal detecting and processing circuit. The finesse of the short fiber ring resonator with a length of 60 cm and a diameter of 4.77 cm is as high as 202, and the theoretical sensitivity of the RMOG is better than 0.3°/h assuming the average optical intensity at the photodetector is 1 mW. The 60 cm long spliceless micro-ring resonator is experimentally proved to be sufficient for a tactical-grade RMOG. An angle random walk coefficient of 0.64°/√h and a typical bias stability below 9.6°/h for the integration time of 50 s are successfully demonstrated using an innovative open-loop approach for an operation time of 1600 s.

Single event upset (SEU) effect, caused by highly energized particles in aerospace, threatens the reliability and security of small satellites composed of commercial-off-the-shelves (COTS). SEU-induced control flow errors (CFEs) may cause unpredictable behavior or crashes of COTS-based small satellites. This paper proposes a generic software-based control flow checking technique (CFC) and bipartite graph-based control flow checking (BGCFC). To simplify the types of illegal branches, it transforms the conventional control flow graph into the equivalent bipartite graph. It checks the legality of control flow at runtime by comparing a global signature with the expected value and introduces consecutive IDs and bitmaps to reduce the time and memory overhead. Theoretical analysis shows that BGCFC can detect all types of inter-node CFEs with constant time and memory overhead. Practical tests verify the result of theoretical analysis. Compared with previous techniques, BGCFC achieves the highest error detection rate, lower time and memory overhead; the composite result in evaluation factor shows that BGCFC is the most effective one among all these techniques. The results in both theory and practice verify the applicability of BGCFC for COTS-based small satellites.

As a type of main optical error source in the resonant micro-optic gyro (RMOG), the optical Kerr-effect brings a nonzero bias to the output of the RMOG. The light-intensity fluctuations are interpreted as the cause. To eliminate the drifts due to the optical Kerr-effect, the intensities of the clockwise (CW) and counterclockwise (CCW) lightwaves circulating in the resonator should be equal at all times. Through theoretical analysis and experimental investigation, a linear relationship between the second-harmonic demodulated signal and the light-intensity input to the resonator is demonstrated for the sinusoidally phase modulated RMOG. Both our numerical simulation and experimental verification are carried out, which, for the first time to the best of our knowledge, demonstrate that the second-harmonic demodulated signal can be used as a feedback error signal to reduce both the input-intensity mismatch between the CW and CCW lightwaves and their intensity fluctuations. By applying the light-intensity feedback loop to the closed-loop RMOG, the light-intensity fluctuations are reduced to 2.7×10^−5, down from 5.86%. As a result, the optical-Kerr effect induced error is effectively reduced.

The accuracy of the resonant frequency servo loop is a major concern for high-performance operation of a resonant fiber optic gyro. This is usually resolved by adopting the central frequency of the laser source to track the resonance of the optical fiber ring resonator in one direction. However, the drift of the resonant frequency arising from resonator temperature fluctuation must be eliminated to maintain this accuracy. The traditional proportional integral (PI) frequency servo loop cannot address this issue very well. For instance, a bias error as large as tens or even hundreds of degrees/hour has been observed at the demodulated output of a resonant frequency servo loop. In this paper, we propose a method to eliminate this bias error by adding a double integral term in the traditional PI-based resonant frequency servo loop. We demonstrate that the double integral term can precisely track the linear resonant frequency drift, evidenced by our experimentally achieved close-to-zero bias error of −0.0009  deg/h at the demodulated output of the resonant frequency servo loop.

A sensitive birefringent thermometer based on a SiO_2 waveguide ring resonator is demonstrated in this paper. It can be used to fabricate a terahertz thermal detector. The temperature sensitivity is enhanced by the resonances of two polarization modes in the waveguide ring resonator. A high degree of common rejection exists for external influence. A linear temperature range from 6°C to 40°C has been detected with resolution of 0.025°C.

Resonant fiber-optic gyro (RFOG) based on the Sagnac effect has the potential to achieve the inertial navigation system requirement with a short sensing coil. A high-accuracy resonant frequency servo loop is indispensable for a high-performance RFOG. A digital proportional-integral (PI) controller is always adopted in the resonant frequency servo loop. The resonant frequency of the optical fiber ring resonator drifts with environmental temperature changes. When the resonant frequency drift is beyond the tracking range of the resonant frequency servo loop, the digital PI controller overflows and outputs a reset signal. A large reset pulse, which is equivalent to a rotation rate error of 26°/h, has been observed at the output of the RFOG, while a long time is required for returning to the lock-in state simultaneously. To reduce the effect of the overflow resetting in the digital PI controller, an auto-controlled reset technique is proposed and experimentally demonstrated. As a result, the time for returning to the lock-in state is reduced to 5 ms from 8 s. With the integration time of 1 s, the equivalent accuracy of the resonant frequency servo loop is improved to 0.18°/h.

A low power consumption digital processing circuit with large dynamic range and low noise density for micromachined capacitive accelerometer is proposed. To reduce the power consumption, the sampling rate and the number of logic units used are analyzed. We lower the sampling rate to 2.5 MHz that is only 1/16 of previous scheme. At this frequency, the dynamic range is still as high as 120 dB that has been tested, while the dynamic power is as low as 5.4 mW that is only about 1/16 of previous scheme. To reduce the amount of logic units, we adopt square-wave demodulator instead of sinusoidal demodulator (realized by coordinate rotation digital computer algorithm). The entire digital processing circuit with square-wave demodulator uses 577 slice registers, about 1/10 of the circuit with sinusoidal demodulator. The dynamic power is even reduced to 0.54 mW. Most of all, almost no additional noise is added into this circuit, and the output noise density is as low as 0.01 mg/√Hz.

An optical fiber ring resonator (OFRR) is the key rotation-sensing element in the resonator fiber optic gyro (R-FOG). In comparing between different OFRR types, a simulation model that can apply to all cases is set up. Both the polarization crosstalk and polarization-dependent loss in the coupler are fully investigated for the first time to our knowledge. Three different splicing schemes, including a single 0°, a single 90°, and twin 90° polarization axis rotated spices, are compared. Two general configurations of the OFRR are considered. One is a reflector OFRR, the other is a transmitter OFRR. This leads to six different OFRR types. The output stability of the R-FOG with six OFRR types is fully investigated theoretically and experimentally. Additional Kerr noise due to the polarization fluctuation is discovered. The OFRR with twin 90° polarization axis rotated splices is of lower additional Kerr noise and hence has better temperature stability. As the coupler is polarization dependent, we notice that in a reflector OFRR, the straight-through component of the output lightwave, which can be isolated by a transmitter configuration, would produce large polarization fluctuation–induced noise. The experimental results show that the bias stability of the transmitter OFRR is 8 times improved over that of the reflector OFRR, which is in accord with the theoretical analysis. By the analysis and experiments above, it is reasonable to make a conclusion that an R-FOG based on a transmitter OFRR with twin 90° polarization axis rotated splices is of better temperature stability and smaller additional Kerr effect noise.

Resonator fiber-optic gyro (RFOG) is a high-accuracy inertial rotation sensor based on the Sagnac effect. A high-accuracy resonant frequency servo loop is indispensable for a high-performance RFOG. It is composed of a frequency discriminator, a loop filter, and a laser actuator. Influences of the loop parameters are fully developed. Optimized loop parameters are obtained by considering the noise reduction and wide dynamic performance of the RFOG. As a result, with the integration time of 10 s, the accuracy of the resonant frequency loop is increased to 0.02 Hz (1σ). It is equivalent to a rotation rate of 0.067°/h, which is close to the shot noise limit for the RFOG, while a minimum rotation of ±0.05°/s has been carried out simultaneously. These are the best results reported to date, to the best of our knowledge, for an RFOG using the miniature semiconductor laser that benefits from the optimization of the resonant frequency servo-loop parameters.

Resonator fiber optic gyro (RFOG) based on the Sagnac effect has the potential to achieve the inertial navigation system requirement with a short sensing coil. Semiconductor laser is one of the key elements for integration and miniaturization of the RFOG. In this paper, an RFOG employing a semiconductor laser is demonstrated. The model of the laser frequency noise induced error in the RFOG is described. To attenuate the laser frequency noise induced error, active frequency stabilization is applied. An online laser frequency noise observation is built, as a powerful optimum criterion for the loop parameters. Moreover, the laser frequency noise observation method is developed as a new measurement tool. With a fast digital proportional integrator based on a single field programmable gate array applied in the active stabilization loop, the laser frequency noise is reduced to 0.021 Hz (1σ). It is equivalent to a rotation rate of 0.07°/h, and close to the shot noise limit for the RFOG. As a result, a bias stability of open-loop gyro output is 9.5°/h (1σ) for the integration time 10 s in an hour observed in the RFOG. To the best of our knowledge, this result is the best long-term stability using the miniature semiconductor laser.

We present an in-depth analysis of the resonance asymmetry in a silica waveguide ring resonator (WRR) and its influence on the waveguide-type optical passive resonator gyro (OPRG). A big bias error appears at the output of the OPRG. This big error is caused not only by the resonance asymmetry in the WRR, but also by the modulation parameters in the phase modulation spectroscopy technique (PMST). It has been proved that the bias error is proportional to the modulation frequency difference between the clockwise (CW) and counterclockwise (CCW) lightwaves. Three types of resonance asymmetries are thoroughly introduced and discussed. Methods to overcome the big bias error are demonstrated. A high reciprocal resonator is crucial to reduce the bias error. For a certain resonator, a proper temperature needs to be set to minimize the resonance asymmetry. A proper modulation frequency difference between the CW and CCW lightwaves is also helpful to reduce the bias error.

The resonance asymmetry in the waveguide ring resonator and its influence on the offset errors of the waveguide-type optical passive resonator gyro (OPRG) are demonstrated experimentally and theoretically. The offset errors are produced by the resonance asymmetry especially when the phase modulation spectroscopy technique is involved in the OPRG. Modulation frequencies of both the clockwise and counterclockwise lightwaves are determined to decrease the offset errors. The fundamental solution to eliminate the asymmetry influence on the OPRG is also proposed.

A resonator micro optic gyro (RMOG) with the proposed FPGA-based digital processor is set up. The double phase modulation technique is applied to achieve high total carrier suppression. Rotation tests from ±0.1 °/s to ±5 °/s are tested, where the processing circuit of RMOG is implemented by the instruments. The rotation test over a range of ±550 °/s has been successfully obtained with all the processing circuit implemented in FPGA. To the best of our knowledge, these results are the best results of RMOG ever demonstrated in silica resonator with the ring length as short as 7.9 cm.

We present an in-depth analysis of the transient response of a resonator fiber optic gyro based on triangular wave phase modulation. Unusual effects have been observed in the process of tracking the resonant frequency of an optical fiber ring resonator (OFRR). There is a distortion phenomenon, unlike the ideally square wave or a pure DC output of the OFRR, but signal overshoot or undershoot occurs. A deep analysis of the influence of the nonideal square wave or pure DC output on gyro performance is fully developed for the first time, to the best of our knowledge. Further analysis shows that this is the transient response process after modulation by the triangular wave, and the process is related both to the parameters of the OFRR and the modulation frequency of the triangular wave. By sampling the steady-state signal of the distortion square wave, or by oversampling the distortion signal to get a number of data, and then accumulating and averaging these data to be demodulated, the distortion’s effect can be considerably decreased.

A method to realize room-temperature operation of a multifrequency Er-doped fiber laser with low-frequency shift feedback placed within a linear laser cavity is theoretically proposed and experimentally demonstrated. Simultaneous multiwavelength lasing with 0.5 nm wavelength spacing is experimentally demonstrated by applying a sinusoidal signal of 10 kHz to a fiber phase modulator inserted within the linear cavity to prevent single wavelength steady-state oscillation. In the linear cavity, an all-polarization-maintaining fiber Sagnac loop is used as a periodic filter, and a single-mode fiber loop with a polarization controller is used as a partial reflector and also as an output port.

A resonator fiber-optic gyro (R-FOG) is a high-accuracy inertial rotation sensor based on the Sagnac effect. A fiber ring resonator is the core sensing element in the R-FOG. When the frequency of the fiber ring resonator input laser is swept linearly with time, ringing of the output resonance curve is observed. The output field of the fiber ring resonator is derived from the superposition of the light transmitted through the directional coupler directly and the multiple light components circulated in the fiber ring resonator when the frequency of the laser is swept. The amplitude and phase of the output field are analyzed, and it is found that the difference in time for different light components in the fiber ring resonator to reach a point of destructive interference causes the ringing phenomenon. Finally the ringing phenomenon is observed in experiments, and the experimental results agree with the theoretical analysis well.

A sacrificial layer etching process in joint channels is studied in this paper. If the etching process proceeds from a wide channel to a narrow one, the etching front presents a straight line during the whole process according to the experiments. If the etching process proceeds from a narrow channel connected with a wide channel, it is an arc rather than a straight line when the etching front reaches the wide channel. Some other interesting phenomena are also observed during etching the joint structure. For a narrow-wide channel, the etching rate decreases suddenly near the joint area, while for a wide-narrow channel, the etching rate increases quickly near the joint area and decreases gradually after that. A new model is proposed to explain these phenomena, which is proved to match the experimental data well.

A method to decrease the polarization-fluctuation induced drift in a resonator fiber optic gyro (R-FOG) is demonstrated by inserting two in-line polarizers in a polarization-maintaining fiber resonator with twin 90° polarization-axis rotated splices. The in-line polarizers attenuate the unwanted resonance by introducing high loss for the unwanted eigenstates of polarization in the resonator. Compared to the resonator without in-line polarizers, the polarization-fluctuation induced drift is reduced by 6×10^3 times. The desired resonance in the resonator can keep excellent stability in a wide temperature range; thus the temperature-dependent polarization-fluctuation drift in the R-FOG is sufficiently suppressed. A typical bias stability of 4.7°/h over 6500 s with an integration time of 10 s has been carried out. To the best of our knowledge, the long-term bias stability and high temperature stability are the best ever demonstrated in an R-FOG.

Modern spacecraft missions place stringent performance requirements on the reliability and stability of spacecraft attitude control system. However, during long-term in-orbit mission, actuators may suffer faults. In this paper, we proposed an adaptive fault tolerant control law for attitude control under actuator failures and external disturbances. Firstly, the attitude dynamic model under actuator faults and attitude kinematics are described. Then, in order to solve the attitude control problem under actuator faults and external disturbances, an adaptive backstepping sliding mode fault tolerant control scheme is designed. According to Lyapunov theory, the closed-loop system is proved to be globally asymptotically stable. Finally, the numerical simulation results demonstrate that the proposed adaptive controller can achieve anticipative attitude control performance, fault information estimation and well fault-tolerant capability.

A resonator fiber optic gyro (RFOG) based on a fiber-coupled semiconductor DFB-LD with an FPGA-based digital processor is set up. A bias stability of 23deg/h over one hour is successfully demonstrated. This is the best result in long time stability reported to date, to the best of our knowledge, for the RFOG based on a miniaturized laser source.

We report the first demonstration of silica waveguide optical passive ring resonator gyro (OPRG) based on the phase modulation spectroscopy technique. The ring resonator is composed of a 6-cm-long silica waveguide. Observed from the resonance curve, the free spectral range (FSR) of the resonator, the full width at half maximum (FWHM) of the resonance curve, the finesse (F) of the resonator, and the resonance depth are 3.4 GHz, 62 MHz, 54.8, and 70&percent;, respectively. The detection sensitivity of this OPRG will be 7.3×10−5 rad/s. In the experiments, there is an acoustic-optical modulator (AOM) in each light loop. We lock the lasing frequency at the resonance frequency of the silica waveguide ring resonator for counterclockwise (CCW) lightwave; the frequency difference between the driving frequencies of the two AOMs is equivalent to the Sagnac frequency difference caused by gyro rotation. Thus, the gyro output is observed.

A study on the reaction of Ni and amorphous Si0.68Ge0.32film on SiO2is reported. The reaction was performed at 520° C in a conventional furnace. The resulting film was characterized using X-ray photoelectron spectroscopy (XPS) and Raman scattering spectroscopy. Ni induced crystallization of SiGe was confirmed by the Raman spectra. XPS results indicate Ni piled up at or near the interface of the crystallized SiGe and the SiO2substrate. The small amount of Ni inside the SiGe layer exists in more of a silicide- or germanide-like form. Ni enhanced oxidation of SiGe was found during the reaction and the oxidized layer was found to be a mixture of oxides of Si and Ge, with Ge piling up at the surface.