Broadband source-driven resonant micro-optic gyroscope based on a multi-turn waveguide-type ring resonator.

The resonant micro-optic gyroscope (RMOG) is one of the most promising candidates for chip-scale optoelectronic gyroscopes. A broadband source-driven RMOG based on a multi-turn waveguide-type ring resonator (WRR) has been proposed and demonstrated. The theoretical sensitivity is enhanced with the multi-turn structure, while the parasitic backscattering can be resolved by the use of the broadband source, thus greatly improving the long-term bias stability of the RMOG. We also reduce the relative intensity noise (RIN)-induced error of the broadband source at the gyro output by optimizing the number of loop turns of the WRR, and improve the angle random walk (ARW) by 4.8 dB compared with the case of a single-turn WRR. Finally, a bias stability of 1°/h is obtained with a 5-turn WRR of 4.05 cm diameter, achieving the tactical-grade resolution. To the best of our knowledge this is the best result reported to date for an RMOG of similar size.

Navigation-grade three-axis resonant fiber-optic gyroscope employing a multiplexed source.

A three-axis gyroscope is a vital component of an inertial measurement unit that can measure the rotation rates in three directions simultaneously. A novel three-axis resonant fiber-optic gyroscope (RFOG) configuration with a multiplexed broadband light source is proposed and demonstrated. The output light from the two vacant ports of the main gyroscope is reused as drive sources for the other two axial gyroscopes, which effectively improve the power utilization of the source. The interference between different axial gyroscopes is effectively avoided by optimizing the lengths of three fiber-optic ring resonators (FRRs) rather than by inserting other optical elements in the multiplexed link. With the optimal lengths, the influence of the input spectrum on the multiplexed RFOG is suppressed and a theoretical temperature dependence of the bias error as low as 1.08 × 10-4 °/h/°C is obtained. Finally, a navigation-grade three-axis RFOG is demonstrated with a fiber coil length of ∼100 m for each FRR.

Resonant fiber optic gyroscope using a reciprocal modulation and double demodulation technique.

A resonant fiber optic gyroscope (RFOG) using a reciprocal modulation and double demodulation technique based on a single laser source is proposed and demonstrated. The effect of the residual amplitude modulation of the phase modulator is well suppressed thanks to the reciprocal modulation and demodulation. On this basis, the backscattering noise is also eliminated by the double demodulation process. The long-term bias stability of the RFOG is successfully improved to 0.2°/h for a test time of 45 hours.

White-light-driven resonant fiber-optic gyro based on round trip filtering scheme.

As the second generation of the fiber-optic gyro (FOG), a resonant FOG (RFOG) appears as a very viable candidate for a miniaturized optical gyro. However, due to the impediment of laser-induced parasitic noise and system complexity, the actual performance of the RFOG is well below expectations. This paper proposes a novel, to the best of our knowledge, RFOG which is driven by broadband white light rather than a narrow linewidth laser. The fiber-optic ring resonator (FRR) works as a filter, and the rotation under detection is read out from the round trip loss of the FRR. The parasitic noise is effectively avoided due to the low coherence light, and the measuring resolution can be thus improved. In the experiment, a bias instability of 0.012 ∘/h is demonstrated with a 100-m fiber coil and a very simple structure. The proposed method would be a big step forward for making the RFOG practical with high performance and low cost.

Reduction of relative intensity noise in a broadband source-driven RFOG using a high-frequency modulation technique.

A broadband source-driven resonant fiber-optic gyroscope (RFOG) can reduce coherence-related noise, thus achieving a better sensitivity with a much simpler configuration than the traditional system with a coherent source. Its detection sensitivity, however, is still limited by the excess relative intensity noise (RIN) of the broadband source. In this paper, the RIN error mechanism in this broadband source-driven RFOG is revealed and countermeasures are presented. We demonstrate that the use of a high-finesse fiber-optic ring resonator and a high-frequency modulation-demodulation technique can reduce the RIN-induced error. It is indicated that the optimal modulation parameters can provide a RIN-induced error reduction of 6.1 dB, allowing the broadband source-driven RFOG to operate near the shot-noise-limited theoretical sensitivity. With the optimal high-frequency modulation-demodulation technique, an angle random walk of 0.0013°/√h is achieved with a 200-m-long fiber-optic ring resonator of 7.6 cm diameter. This is the best result reported to date, to the best of our knowledge, for fiber-optic gyroscopes of this size.

Inter-mode soliton linear-wave scattering in a Kerr microresonator.

Soliton microresonator frequency combs (microcombs) have recently emerged as an attractive new type of optical comb source with a wide range applications proposed and demonstrated. To extend the optical bandwidth of these microresonator sources, several previous studies have proposed and studied the injection of an additional optical probe wave into the resonator. In this case, nonlinear scattering between the injected probe and the original soliton enables the formation of new comb frequencies through a phase-matched cascade of four-wave mixing processes. In this work, we expand the relevant analyses to consider soliton-linear wave interactions when the soliton and the probe fields propagate in different mode families. We obtain an expression for the phase-matched idler locations as a function of the dispersion of the resonator and the phase detuning of the injected probe. We confirm our theoretical predictions in experiments performed in a silica waveguide ring microresonator.

Important Role of Concave Surfaces in Deposition of Colloids under Favorable Conditions as Revealed by Microscale Visualization.

This study conducted saturated column experiments to systematically investigate deposition of 1 µm positively charged polystyrene latex micro-colloids (representing microplastic particles) on negatively charged rough sand, glass beads, and soil with pore water velocities (PWV) from 4.9 × 10-5 to 8.8 × 10-4 m/s. A critical value of PWV was found below which colloidal attachment efficiency (AE) increased with increasing PWV. The increase in AE with PWV was attributed to enhanced delivery of the colloids and subsequent attachment at concave locations of rough collector surfaces. The AE decreased with further increasing PWV beyond the threshold because the convex sites became unavailable for colloid attachment. By simulating the rough surfaces using the Weierstrass-Mandelbrot equation, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) interaction energy calculations and torque analysis revealed that the adhesive torques could be reduced to be comparable or smaller than hydrodynamic torques even under the favorable conditions. Interestingly, scanning electron microscopic experiments showed that blocking occurred at convex sites at all ionic strengths (ISs) (e.g., even when the colloid-colloid interaction was attractive), whereas at concave sites, blocking and ripening (i.e., attached colloids favor subsequent attachment) occurred at low and high ISs, respectively. To our knowledge, our work was the first to show coexistence of blocking and ripening at high ISs due to variation of the collector surface morphology.

Polarization error in resonant micro-optic gyroscope with different waveguide-type ring resonator structures.

The waveguide-type ring resonator (WRR) is the key rotation-sensing element in a resonant micro-optic gyroscope (RMOG). A universal model used to analyze both the polarization characteristics of the WRR and corresponding temperature-related polarization error in the RMOG is presented. It indicates that the polarization problem stems from the excitation of two polarization states within the WRR. Unequal variations of incident lights on the cavity in the two directions can cause bias errors at the RMOG output. With the application of different silica WRRs to the RMOG, the polarization errors are tested and verify the theoretical results. Finally, a segment of tilted waveguide gratings with Brewster's angle is fabricated on the silica waveguide within the cavity. The measured polarization extinction ratio of the output light from the WRR is as high as 35.2 dB. The corresponding temperature dependence of the polarization error is theoretically reduced to 0.0019 (°/s)/°C, which indicates that temperature control is sufficient for a tactical grade RMOG.

Suppressing backscattering noise of a resonant fiber optic gyroscope using coherent detection.

This paper provides a novel, to the best of our knowledge, method for suppressing backscattering noise of a resonant fiber optic gyroscope (RFOG) with a coherent detection technique. The light from the fiber ring resonator is mixed with a reference beam rather than being demodulated directly in traditional configurations, generating a coherent signal with a radio frequency. The central frequencies of the two reference lights used for the clockwise and counterclockwise waves are different to avoid the effect of backscattered waves. Besides, a common phase modulation is applied on the two counter-propagating waves to eliminate the parasitic effect due to the residual amplitude modulation in the phase modulator. Two demodulation schemes for the rotation rate detection from the coherent signals are then proposed and demonstrated, with performance on noise suppression tested. One is the beat-frequency demodulation, and the other is the self-mixing demodulation technique. The influence of backscattering intensity is reduced from 270°/h to 3°/h and 0.05°/h with the two demodulation techniques, respectively, showing a full suppression of backscattering noise.

Performance of a resonant fiber-optic gyroscope based on a broadband source.

A resonant fiber-optic gyroscope (RFOG) based on a broadband source can avoid the fundamental drawback of coherence detection processing while possessing the greater sensitivity afforded by the finesse of the fiber-optic ring resonator. In this paper, the basic operation principle is presented and demonstrated in detail, and various noise sources, as well as the temperature effect encountered in this broadband source-driven RFOG, are studied and analyzed. Then a combined modulation technique is proposed to suppress the residual backscattering noise. To further reduce the effect of temperature transience, an asymmetric fiber ring resonator is designed. In the experiment, a bias stability of 0.01°/h is successfully demonstrated with a 100 m-long fiber ring resonator of 8 cm diameter in a laboratory environment without temperature control.

Dual-microcomb generation in a synchronously driven waveguide ring resonator.

Microcombs-optical frequency combs generated in coherently driven nonlinear microresonators-have attracted significant attention over the last decade. The ability to generate two such combs in a single resonator device has, in particular, enabled a host of applications from spectroscopy to imaging. Concurrently, novel comb generation techniques such as synchronous pulsed driving have been developed to enhance the efficiency and flexibility of microcomb generation. Here, we report on the first, to the best of our knowledge, experimental demonstration of dual-microcomb generation via synchronous pulsed pumping of a single microresonator. Specifically, we use two electro-optically generated pulse trains derived from a common continuous wave laser to simultaneously drive two orthogonal polarization modes of an integrated silica ring resonator, observing the generation of coherent dissipative Kerr cavity soliton combs on both polarization axes. Thanks to the resonator birefringence, the two soliton combs are associated with different repetition rates, thus realizing a dual-microcomb source. To illustrate the source's application potential, we demonstrate proof-of-concept spectroscopic measurements.

Resonant fiber optical gyroscope using the single-mode fiber ring resonator.

This paper provides a scheme for realizing high-accuracy, low-cost resonant fiber optical gyroscopes (RFOGs) with single-mode (SM) fibers. The temperature-related polarization noise, which deteriorates the bias stability of the RFOG, has been suppressed thanks to a much longer birefringence beat length of SM fibers. It is also helpful to improve the theoretical sensitivity of the RFOG because of the very low loss of the SM fiber components. A transmissive 39-m-long SM fiber ring resonator (FRR) is fabricated. The measured finesse is 58.7, and its total loss is calculated to be less than 0.3 dB. Using this SM-FRR as the sensing element, an RFOG is then set up that achieves an angular random walk of 0.0039∘/√h and a bias stability of 0.05°/h. The experimental results show that the SM-FRR scheme would be a good candidate for producing high-accuracy and low-cost RFOGs.

Signal processing improvement of passive resonant fiber optic gyroscope using a reciprocal modulation-demodulation technique.

A resonant fiber optic gyroscope (RFOG) based on the reciprocal phase modulation-demodulation technique is proposed and demonstrated. The residual amplitude modulation induced error of the phase modulator, and the effect of laser frequency noise are all suppressed thanks to the reciprocity of the proposed signal processing scheme. Compared with the past separate modulation-demodulation RFOG, the angular random walk is improved by a factor of 15 times from 0.08°/√h to 0.0052°/√h, and the bias stability is improved from 0.3°/h to 0.06°/h.

Improving thermal stability of a resonant fiber optical gyroscope using triple closed loops.

A closed-loop resonant fiber optic gyroscope (RFOG) configuration with three resonance frequency servo loops is proposed. By using one laser-servo loop and two symmetrical phase modulator (PM) servo loops, the effect of the reset due to the limited tracking range of the laser-servo loop is solved. Further long-term stability for 48 h and thermal stability at moderate rate measurements show that the output of the triple closed-loop RFOG is insensitive to environmental temperature variations. When the temperature increased from 17.5°C to 40.7°C in 1800 s and the maximum temperature rate was about 0.025°C/s during heating, the laser-servo loop was reset a total of 413 times. However, the output of the triple closed-loop RFOG is not affected by those frequent resets in the laser-servo loop because the two PM-servo loops are free of glitch pulses under this new scheme. Compared to the traditional double closed-loop RFOG, the thermal bias stability of the triple closed-loop RFOG is improved by a factor of 15 times from 29.8°/h to 1.88°/h.

Rotation and Retention Dynamics of Rod-Shaped Colloids with Surface Charge Heterogeneity in Sphere-in-Cell Porous Media Model.

Colloid surface charge heterogeneity was incorporated into a three-dimensional trajectory model, which simulated particle translation and rotation via a force/torque analysis, to study the transport and retention dynamics of rod-shaped colloids over a wide size range in porous media under unfavorable conditions (energy barriers to deposition exist). Our previous study Li , K. ; Ma , H. Deposition Dynamics of Rod-Shaped Colloids during Transport in Porous Media under Favorable Conditions , Langmuir , 2018 , 34 , 9 , 2967 - 2980 , 10.1021/acs.langmuir.7b03983 for rod transport under favorable conditions (lacking energy barriers) demonstrated that particle rotation due to the coupled effect of flow hydrodynamics and Brownian rotation governed rod transport and retention. In this work, we showed that the shape of a colloid affected both transport process and colloid-collector interactions, but shape alone could not make rods to overcome energy barriers of over tens of kT for attachment under unfavorable conditions. The location of colloid surface heterogeneity did not affect transport but predominantly affected colloid-surface interactions by influencing the likelihood of heterogeneity patches facing the collector due to particle rotation. For surface heterogeneity located on the end(s) of a colloid, rods displayed enhanced retention compared with spheres; for surface heterogeneity located on the middle band, rods showed less retention compared with spheres. It was more effective to arrest a traveling rod when surface heterogeneity was located on the end relative to the side, because the tumbling motion greatly increased the likelihood of the end to intercept collector surfaces, and also because a rod would experience less repulsion with an end-on orientation relative to the collector surface compared to a side-on orientation due to the curvature effect. The influences of the particle aspect ratio on retention strongly depended upon the location of colloid surface heterogeneity. Our findings demonstrated that rods had distinct rotation and retention behaviors from spheres under conditions typically encountered in the environment; thus, particle rotation should be considered when studying the transport process of nonspherical colloids or spherical particles with inhomogeneous surface properties.

Synchronous in-phase and quadrature demodulation technique for resonant micro-optic gyroscope.

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.

Performance improvement of a resonant fiber optic gyroscope with a hybrid photonic crystal fiber ring resonator.

The photonic crystal fiber (PCF) with better thermal stability and polarization-maintaining performance is applied to the resonant fiber optic gyroscope (RFOG). A hybrid fiber ring resonator is fabricated using the conventional polarization-maintaining fiber (PMF) and PCF with close mode field diameters (MFDs) to reduce MFD-mismatch-induced splicing loss. Furthermore, the temperature-dependent birefringence coefficients of the PMF and the PCF are measured to differ almost four times in absolute value and be opposite in sign. The polarization stability of the hybrid PCF-PMF ring resonator is improved by a factor of 7 compared with the PMF ring resonator with the same length of PMF. The RFOG equipped with this hybrid PCF-PMF ring resonator achieves a bias stability of 1.67°/h.

Deposition Dynamics of Rod-Shaped Colloids during Transport in Porous Media under Favorable Conditions.

A three-dimensional computational modeling study of the deposition dynamics of rod-shaped colloids during transport in porous media under favorable conditions (no energy barrier to deposition) is presented. The objective was to explore the influences of the particle shape on colloid transport and retention. During simulation, both translation and rotation of ellipsoidal particles were tracked and evaluated based on an analysis of all forces and torques acting on the particle. We observed that the shape was a key factor affecting colloid transport and attachment. Rod particles exhibited enhanced retention compared with spheres of equivalent volume in the size range greater than ∼200 nm. The shape effect was the most pronounced for particles around 200 nm to 1 µm under simulated conditions. The shape effect was also strongly dependent upon the fluid velocity; it was most significant at high velocity, but not so at very low velocity. The above-described shape effect on retention was directly related to particle rotation dynamics due to the coupled effects from rotational diffusion and flow hydrodynamics. Rotational diffusion changed the particle orientation randomly, which caused the rod particles to drift considerably across flow streamlines for attachment in the size range from 200 nm to 1 µm. The hydrodynamic effect induced periodic particle rotation and oscillation, which rendered large-sized rod particles to behave like "spinning bodies," prescribed by their long axes so as to easily intercept with the collector surface for retention. Our findings demonstrated that the practice of using equivalent spheres to approximate rods is inadequate in predicting the transport fate and adhesion dynamics of rod-shaped colloids in porous media.

Short fiber resonant optic gyroscope using the high-frequency Pound-Drever-Hall 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.

Single-polarization fiber-pigtailed high-finesse silica waveguide ring resonator for a resonant micro-optic gyroscope.

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).