Silicon Photonics Multi-Function Integrated Optical Circuit for Miniaturized Fiber Optic Gyroscope

Draper Laboratory's experience with Interferometer Fiber Optic Gyro (IFOG) technology started via an Internal Research and Development effort in 1978. This work led to developing fiber optic gyros in which significant advances in IFOG component technologies, assembly, integration, and test were achieved. In excess of 30 patents have been issued to Draper as a result of this pioneering effort. More recently, Draper collaborated with JPL to transition their fiber optic breadboard gyro to a space qualifiable instrument for interplanetary long duration missions. During the initial phase, brassboard gyros were designed and fabricated that demonstrated performance that bettered NASA's CRAF-Cassini spacecraft objectives. In the second phase, the Engineering Model gyro was developed to meet mission qualification tests. Concurrent with this later phase, analysis, tests and qualification activities were performed to validate that gyro components would realize the required 16 year life. Two major inventions (patent pending) were conceived; one provides for continuous adaptive scale factor stability and the other integrates the optical source and photodetector into a single component [Source Integrated Detector (SID)], thereby eliminating a coupler and several splices thus reducing loss by 6 db. Using the above technologies and the implementation of common mode rejection of laser noise, Draper has defined a low noise high performance gyro in which rate power spectral density (PSD) is projected to be < 7 X 10-7 (deg/hr)2/Hz. In those applications, where the PSD < 4 X 10-5 (deg/hr)2/Hz is sought, a small size three component (SID, integrated optics circuit and fiber coil) gyro is easily implemented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Background/Objectives: The main objective of this paper is to perform a comparative discussion in gyro parameters for three cases: (i) V2π (vary)&Vπ/2 (constant), (ii) Vπ/2 (vary) and V2π (constant) and (iii) both V2π and Vπ/2 are varying simultaneously. Methods/Statistical Analysis: Fibre optic gyroscope has to be operated in closed-loop approach to achieve the inertial-grade-performance. The Closed-Loop Interferometric Fibre Optic Gyroscope (CLIFOG) system depends upon ramp voltage (V2π of IOC) and square-wave biasing signal frequency (f bias ). The digital-phase-ramp-function is used as feedback to system and makes gyro to null condition. The biasing signal voltage (Vπ/2) is 1/4 th of ramp voltage (V2π). If there are any variations in ramp and biasing signal voltages, then it introduces variations in gyro performance. Results: The ramp voltage (V2π) and square wave biasing signal voltage (Vπ/2) is increased from 1% to 10%, decreased to 1% to 10% and performed the various tests for three cases. From results, it was noted that: (i) When V2π is varying and Vπ/2 is kept constant, the scale-factor change is increasing as the error in the signal voltage is also increases. (ii) When V2π is kept constant and Vπ/2 is varying, the change in scale-factor is very minute and maintains the scale-factor linearity. (iii) While varying both V2π and Vπ/2 voltages simultaneously, the device is not responding accordingly as the error is increasing and also scale-factor is out of range subsequently. The effects on the CLIFOG system are described with the derived values in terms of bias and scale-factor. The gyro performance is very sensitive with respect to V2π variations and the percentage error is high in gyro output, but very less effect due to Vπ/2 variations when the ramp voltage (V2π) is constant. Conclusion/Application: The Closed Loop Interferometric Fiber Optic Gyroscope (CLIFOG) system requires a proper resetting of ramp voltage (V2π) in order to avoid the bias and scale factor instabilities.

Next generation navigation systems demand performance enhancements to support new applications with longer range capabilities, provide robust operation in severe thermal and vibration environments while simultaneously reducing weight, size and power dissipation. Compact, inexpensive, advanced guidance components are essential for such applications. In particular, Inertial Reference Units (IRUs) that can provide high-resolution stabilization and accurate inertial pointing knowledge are needed. For space applications, an added requirement is radiation hardening up to 300 krad over 5 to 15 years. Manufacturing specifications for the radiation-induced losses are not readily available and empirical test data is required for all components in order to optimize the system performance. Interferometric Fiber-Optic Gyroscopes (IFOGs) have proven to be a leading technology for tactical and navigational systems. The sensors have no moving parts. This ensures high reliability and a long life compared to the mechanical gyroscopes and dithered ring laser gyroscopes. However, the available architectures limit the potential size and cost of the IFOG. The work reported here describes an innovative approach for the design, fabrication, and testing of the IFOG and enables the production of a small, robust and low cost gyro with excellent noise and bandwidth characteristics with high radiation tolerance. The development is aimed at achieving a sensor volume &lt; 5 cubic inches. The new IFOS gyro uses an open loop configuration, utilizes extremely small diameter radiation-hard fiber with customized all-digital signal processing. The optics is packaged using a combination of highly-integrated optical component assemblies with an allfiber approach that leads to a more flexible yet lower cost optical design. The IFOS gyro prototypes are implemented using a distributed architecture, where the light source, electronics and receiver are integrated in an external package, while the sensor head is integrated in a robust and environmentally rigid package. The sensor package design is compatible with the most severe environmental requirements foreseen for the target applications. This paper presents the current state-of-the-art performance of the prototype gyros and the potential for further reduction of size with improved performance. The gyro sample and data rates are extremely high and can be close to the modulation frequency (up to 80 kHz). IFOS has shown that the noise at high frequencies is not flattening out and extremely high bandwidth operation is possible without any degradation of the operational stability. IFOS has also demonstrated the potential for a future, smaller and extremely robust IFOG. The next phase design will include highly radiation-resistant integrated, compact optical circuits based on InP technology that includes the light source, splitter and receiver in one package, a gyro coil that utilizes small diameter, radiation-hard fiber and a small fiber phase modulator with &gt; 300 krad radiation tolerance. This gyro offers the low noise, low drift, low vibration sensitivity, high accuracy, high bandwidth and high radiation tolerance solution required for next generation systems. We will present both theoretical modeling and experimental results obtained to date

Respecting the requirements of lightweight, small size, low power consumption and especially low cost, commercial off-the-shelf (COTS) analog-to-digital converters (ADCs) are gradually being used to replace specifically designed aerospace -grade ones in space-borne miniature interferometric fiber-optic gyroscopes (IFOGs). However, the total ionizing dose (TID) effect of $\gamma $ -ray radiation in the space environment may cause the damage of COTS ADCs, and lead to performance degradation and even the failure. In order to measure the safety of COTS ADCs in IFOGs under the TID effect, the radiation-induced degradation model and the corresponding reliability model are proposed in this work. First of all, the relationship between the degradation of COTS ADCs and the IFOG's angular random walk (ARW) is deduced. Then, a radiation accelerated test is designed and performed, with a real-time, dynamic data acquisition method based on the first-input-first-output (FIFO) memories to determine the degradation of COTS ADCs. Finally, a degradation path model is established based on the degradation data, and the reliability of COTS ADCs used for space-borne IFOGs is further obtained by using the Monte Carlo method. An engineering application is introduced to show the effectiveness of the proposed model, and the results show that the reliability of the experimental COTS ADCs makes them usable for the space-borne miniature IFOGs in low-earth orbit (LEO) and geostationary earth orbit (GEO) space missions.

In this Letter, two gyro outputs containing identical rotation rates are produced by a twin-peaks light source with peak wavelengths of 1530 nm and 1560 nm. We demonstrate that the two outputs' ratio κ can compensate for the temperature-induced scale factor drift in an interferometric fiber-optic gyroscope (IFOG). When the temperature ranged from -10∘C to 50°C, the scale factor drift after compensation was about 30 times less than that before compensation, and the minimum drift was ±7.7ppm at the rotation rate of 100°/s.

Research on the performance of polarization-maintaining fiber (PMF) for fiber coils is significant for the precision improvement of an interferometric fiber optic gyroscope (IFOG) working in harsh environments. In this paper, we firstly report analytical models of the fiber polarization theory and present two types of hybrid PMF structures by a collaboration of geometry and stress effects: a Panda-type horizontal-elliptical core PMF (Panda-type HE-PMF) based on a superposition of geometry and stress, and a Panda-type longitudinal-elliptical core PMF (Panda-type LE-PMF) with geometry offset stress effect, achieving enhanced and suppressed modal performance by adjusting geometric anisotropy of elliptical-core in different directions. Then, the influence mechanisms of the geometric birefringence on the modal performance of both PMFs as the variation of fiber structural parameters are investigated via numerical simulations to determine the target fiber designs. The other significant attribute, including effective mode area (Aeff), nonlinear coefficient (γ), and chromatic dispersion (D), and their tolerance to PMF parameter fluctuations are also evaluated. Finally, both target PMFs with structural optimization are practically fabricated and wound into four fiber coils with quadrupolar (QAD) and 16-polar symmetrical winding patterns, respectively. The polarization ability and thermal performance are further demonstrated by experiments conducted on both PMFs, wound fiber coils, and built IFOGs under static and dynamic environments (over a wide temperature range of -40 °C to 70 °C), and compared with a conventional PMF. The testing results suggest that designed HE-PMF coils both achieve high birefringence, static extinction ratio (ER) values of up to 30.80 dB and 31.93 dB, respectively, corresponding to an almost one-fold increase over conventional coils. Remarkably, the ER property of the HE-PMF coil by combining this HE-PMF design and a 16-polar winding pattern consistently remains above 29.5 dB with a minimal fluctuation in ER of only 3.0 dB across the entire variable temperature conditions. The bias stability of the IFOG assembled with this coil is strongly enhanced to 0.0019 °/h and 0.082 °/h under static and dynamic conditions, respectively, which is a significant improvement over conventional coils of 0.136 °/h. Also, the static angle random walk performance of the improved IFOG is reduced to 0.000624 °/√h. In contrast, the LE-PMF as a comparison is shown to limited polarization characteristics with a low birefringence and ER due to the suppression effect of the geometric birefringence, and the applied IFOG output also exhibits larger drift, indicating a poor thermal ability. Experimental results show great agreement with theoretical analysis and numerical simulations, confirming the validity of design principles. The advances in both designs are instructive for the engineering applications of PMFs for IFOGs and for improving the accuracy of fiber sensors.

The introduction of closed-loop mechanisms has significantly enhanced the performance of interferometric fiber optic gyroscopes (IFOGs). However, the poor scale factor (SF) stability limits its further application due to the use of broadband light sources. This study first reviewed the impact of the average wavelength of a light source on SF stability in a closed-loop IFOG setup. A simulation model is developed according to modulation and demodulation principles, and the SF error is found to be proportional to the wavelength drift in a closed-loop IFOG. Additionally, employing a laser with a more stable average wavelength instead of a super fluorescent fiber source (SFS) for driving the IFOG enhanced the SF stability by an order of magnitude to 0.38 ppm in ambient-air experiments, which is one of the best SF performances achieved thus far. With the significant improvement in stability during the variable temperature tests, the IFOG measures rotation rates more accurately.

Pointing, acquisition, and tracking (PAT) systems in spaceborne optical communications terminals can exploit inertial sensors and actuators to counter platform vibrations and maintain steady beam pointing. Interferometric fiber optic gyroscopes (IFOGs) can provide sensitive angle rate measurements down to very low (sub-milliHertz) mechanical frequencies, potentially reducing the required beacon power and facilitating acquisition for a spaceborne optical communications terminals. Incoherent broadband light sources are used in IFOGs to alleviate detrimental effects of optical nonlinearities, backscattering, and polarization non-reciprocity. But incoherent broadband sources have excess noise or relative intensity noise (RIN), caused by the beating of different spectral components on the photodetector. Unless RIN noise is suppressed, IFOG performance cannot be improved once the light on the photodetector exceeds one photon per coherence time (~microWatts). We propose a simple method to dramatically suppress the RIN of an incoherent light source and thereby reduce the angle random walk (ARW) of an IFOG using such a source. We demonstrate 20 dB RIN suppression of a broadband EDFA source, which we predict could improve the angle random walk (ARW) of an IFOG using this source by 12 dB.

Dual-polarization interferometric fiber optic gyroscope (IFOG) is a novel scheme in which the polarization nonreciprocal (PN) phase error of the two orthogonal polarizations can be optically compensated. In this work, we investigate the effective of PN phase error compensation under varying temperature. It is proved that, the thermally induced strain deforms the fiber, and results in perturbations on the birefringence and polarization cross coupling which degrades the IFOG's stability. A wave propagation model and analytical expressions of PN phase error are derived by using coupled-wave equation and Jones matrix. We theoretically and experimentally verify that, although the single-mode (SM) and polarization-maintaining (PM) fiber coils behave different owing to their intrinsic properties of wave propagation, the thermal strain induced PN phase error can still be compensated under slow and adiabatic temperature variations. This could be a promising feature to overcome the temperature fragility of IFOG.

Parameters optimization of interferometric fiber optic gyroscope for improvement of random walk coefficient degradation in space radiation environment

This article describes a novel design of the interferometric fiber-optic gyroscope (IFOG) program, that is, a structure of hybrid optical IFOG. It is characterized by using low-polarized light source and single-mode optical fiber coupler in optical head. This optical structure not only can reduce the effect of polarization crosstalk, but also simplifies the assembly process and improves production efficiency. In addition, through the application of all-digital closed-loop control and random modulation signal processing technology, the dead-zone problem in IFOG caused by electronic cross-coupling have been eliminated, and the SNR of gyro output is improved. A large number of experimental testing results have proved that the gyro's zero-bias instability achieves 0.01°/h, random walk coefficient reaches 0.001°¿(h), and scale factor nonlinearity is less than Sppm (room temperature). The gyro's performance can meet the requirements of navigation, guidance and control in various fields.

We have proposed an interferometric fiber optic gyro (I-FOG) with a novel sensing fiber coil consisting of multi-core fiber (MCF) spliced with fan-in/fan-out (FIFO) devices. This sensing coil can improve the sensitivity of I-FOG without escalating the hardship of winding process of fiber to form coils. We have fabricated a seven-core MCF coil with FIFO devices and demonstrated the proper operation of the proposed I-FOG for the first time. The angular random walk performance of 0.002 deg/√h was achieved, thereby confirming that the seven-core waveguide loop works successfully as a Sagnac interferometer as expected. In addition, we evaluated the effect of temperature changes ofMCF and FIFO devices that cause fluctuations in the measured rotation rate. We confirmed that this effect shows essentially the same features as Shupe effect (non-reciprocal phase shift error due to changing environmental temperature) which is a well-known feature of conventional I-FOGs.

To control the product quality of interferometric fiber-optic gyroscope (IFOG), an integrated evaluation method of manufacture process is proposed. First, some key manufacture processes are selected: the winding and length control of fiber-optic coil, the fiber splicing operation, and the light leakage detection of IFOG light path. Second, the important test data of each key manufacture process are collected as the evaluation indexes. The test data include the winding precision, the length control precision, the splicing effect, and the light leakage intensity. Third, the classic analytic hierarchy process (AHP) technique is utilized to evaluate the manufacture process effect of IFOG. By using the proposed technique, the process quality of IFOG can be controlled effectively. Many experiment results have proved the correctness and effectiveness of our proposed method.

We present a groundbreaking navigation-grade interferometric air-core fibre optic gyroscope (IFOG) using a quadrupolar-wound coil of four-tube truncated double nested antiresonant nodeless fibre (tDNANF). This state-of-the-art tDNANF simultaneously achieves low loss, low bend loss, single-spatial-mode operation, and exceptional linear polarization purity over a broad wavelength range. Our 469 m tDNANF coil demonstrated a polarization extinction ratio (PER) of ~20 dB when illuminated by an amplified spontaneous emission (ASE) source spanning 1525-1565 nm. Under these conditions, the gyro archives an angular random walk (ARW) of 0.00383 deg h−1/2 and a bias instability (BI) drift of 0.0017 deg h−1, marking the first instance of navigation-grade performance in air-core FOGs. Additionally, we validated the low thermal sensitivity of air-core FOGs, with reductions of 9.24/10.68/6.82 compared to that of conventional polarization-maintaining solid-core FOGs of the same size across various temperature ranges. These results represent a significant step towards long-standing promise of high-precision inertial navigation applications with superior environmental adaptability.

The impact of residual coherent phase error in a dual-polarization interferometric fiber optic gyroscope (IFOG) is investigated. Although it has been intuitively assumed that the coherence of a light source can be eliminated by a sufficient long fiber delay, the experiment and theory indicate that it still contributes a remarkable portion to long-term instability. After the residual coherent phase error is well handled, we demonstrate a dual-polarization IFOG with bias instability of 3.56×10-4°/h. Comparisons show that such performance is even better than the conventional "minimal scheme" that operates on one polarization.