We first introduce optical compensation into the field of interferometric fiber-optic gyroscopes (IFOGs), using the opposite polarity of the disturbance between two orthogonal polarization states to suppress polarization-fluctuation-induced noise. A dual-polarized IFOG, in which the fast and slow axes of polarization-maintaining fiber work simultaneously, is implemented and tested. Interference signals of the two axes are added to achieve optical compensation. Experiments show that the IFOG's sensitivity is effectively enhanced in compensated output: all Allan variance indices are improved, among which bias instability is reduced from 0.335 and 0.227 deg/h(fast and slow axes output, respectively) to 0.061 deg/h.

Optically compensated dual-polarization interferometric fiber-optic gyroscope

We demonstrate a novel dual-polarization interferometric fiber-optic gyroscope (IFOG), which needs only one coupler and no polarizer. Polarization nonreciprocity (PN) errors in common IFOGs will increase significantly if the polarizer is absent, or if only one coupler is used. In our setup, however, PN errors are effectively compensated by using two balanced polarizations. The 2 km coil, open-loop configuration obtains a bias instability of 0.02°/h in detecting the Earth’s rotation rate. Its performance difference from the conventional two-coupler IFOG is only a stable bias, caused by coupler nonreciprocity.

Dual-polarization interferometric fiber-optic gyroscope with an ultra-simple configuration

We propose and demonstrate a novel configuration for depolarized interferometric fiber-optic gyroscopes (IFOGs). This configuration utilizes optical compensation between two orthogonal polarizations for suppressing errors induced by polarization nonreciprocity. Theoretical analysis shows that it is a new approach different from conventional IFOGs where a polarizer is mandatory. An experimental demonstration of the proposed IFOG (2097-m coil, open-loop configuration) achieves a low bias drift of 0.016 °/h in detecting the Earth's rotation rate. Furthermore, this configuration requires no polarizer or any other polarization-maintaining device.

All-Depolarized Interferometric Fiber-Optic Gyroscope Based on Optical Compensation

Polarization reciprocity is studied both theoretically and experimentally in an optically compensated configuration of interferometric fiber optic gyroscope (IFOG). In conventional IFOGs based on the minimal scheme, the output port of the coil coupler cannot be used mainly because of its polarization nonreciprocity (PN), and thus it is usually called the “nonreciprocal port”. We show that the PN errors at the nonreciprocal port are effectively eliminated by optical compensation. With this unique property, the optically compensated IFOG can possess two low-PN ports for rotation sensing at the same time. From another perspective, one port IFOGs are possible to be constructed with less structural complexity.

Optically compensated polarization reciprocity in interferometric fiber-optic gyroscopes.

The miniaturization of the gyroscope is critical for spacecrafts, drones, wellbore surveys, etc. The resonant fiber-optic gyroscope (RFOG) is a competitive candidate due to its potential in both miniaturization and high resolution, while its actual performance is well below expectation because of laser-induced noise and complexity. Here we report the first navigation grade RFOG with a bias instability of 0.009°/h and an angle random walk of 0.0093°/ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:msqrt> <mml:mrow> <mml:mi mathvariant="normal">h</mml:mi> </mml:mrow> </mml:msqrt> </mml:mrow> </mml:math> . The results are realized using a fiber resonator with finesse of 63 containing 100-m long fiber. Compared with the traditional RFOGs using narrow-linewidth lasers, the key feature of the proposed RFOG is that it is driven with a broadband light source. A white-light multibeam interference method is proposed to detect the Sagnac effect, representing the simplest scheme of RFOG to date. The complexity caused by multiple feedback loops and coherent noise suppression in traditional RFOG scheme is avoided. The minimal scheme and simple modulation algorithm will also promote the on-chip waveguide gyroscope. 

Navigation-grade resonant fiber-optic gyroscope using ultra-simple white-light multibeam interferometry

We propose a novel method of quadrature demodulation with synchronous difference for suppressing noise in interferometric fiber-optic gyroscopes (IFOGs). For an IFOG with sine wave phase modulation, an in-phase result and a quadrature result are obtained simultaneously by coherent detection. Eigenfrequency modulation is used and a phase shift of 45° is set between the modulation signal and the reference signal, so that two results have the same expectation of amplitude but with opposite signs. A synchronous difference procedure is carried out for output, in which signals are added up and common noise between two results is eliminated. Theoretical analysis and experimental results show that both short term noise and long term instability of the IFOG are reduced by this method. In experimental comparison with the traditional demodulation method on the same IFOG with a 1982 m fiber coil, this method reduces the bias drift from 0.040°/h to 0.004°/h.

Quadrature demodulation with synchronous difference for interferometric fiber-optic gyroscopes

The invention provides a line cavity laser with super-narrow line width based on parallel feedback, which comprises a DFB (Distributed Feedback) laser, a 90:10 coupler, a reflection unit, multiple sections of single mode optical fibers and multiple mold optical fibers, wherein the DFB laser and the 90:10 coupler as well as the 90:10 coupler and the reflection unit are respectively coupled throughan optical fiber structure composed of the single mode optical fibers and the multiple mold optical fibers.

Line cavity laser with super-narrow line width based on parallel feedback

The invention provides a multi-core fiber based multipath parallel optical transmission structure, comprising multiple single mode/multimode fibers and multiple multi-core fibers, wherein multiple single mode/multimode fibers and multiple multi-core fibers are alternately connected By applying the optical transmission structure, the power loss during the optical coupling process can be reduced, and the influence of a high order mode to an optical path can be weakened

Multi-core fiber based optical transmission structure and device applying same

In traditional fiber-optic gyroscopes (FOG), the polarization state of counter
propagating waves is critically controlled, and only the mode polarized along one particular
direction survives. This is important for a traditional single mode fiber gyroscope as the
requirement of reciprocity. However, there are some fatal defects such as low accuracy and poor
bias stability in traditional structures. In this paper, based on the idea of polarization multiplexing,
a double-polarization structure is put forward and experimentally studied. In highly birefringent
fibers or standard single mode fibers with induced anisotropy, two orthogonal polarization modes
can be used at the same time. Therefore, in polarization maintaining fibers (PMF), each pair of
counter propagating beams preserve reciprocity within their own polarization state. Two series of
sensing results are gotten in the fast and slow axes in PMF. The two sensing results have their own
systematic drifts and the correlation of random noise in them is approximately zero. So, beams in
fast and slow axes work as two independent and orthogonal gyroscopes. In this way, amount of
information is doubled, providing opportunity to eliminate noise and improve sensitivity.
Theoretically, this double-polarization structure can achieve a sensitivity of 10 -18 deg/h. Computer
simulation demonstrates that random noise and systematic drifts are largely reduced in this novel
structure. In experiment, a forty-hour stability test targeting the earth's rotation velocity is carried
out. Experiment result shows that the orthogonal fiber-optic structure has two big advantages
compared with traditional ones. Firstly, the structure gets true value without any bias correction in
any axis and even time-varying bias does not affect the acquisition of true value. The unbiasedness
makes the structure very attractive when sudden disturbances or temperature drifts existing in
working environment. Secondly, the structure lowers bias for more than two orders and enhances
bias stability for an order higher (compared with single axis result), achieving a bias stability of
0.01 deg/h. The evidences from all aspects convincingly show that the orthogonal fiber-optic
structure is robust against environmental disturbance and material defects, achieving high stability
and sensitivity.

Highly sensitive rotation sensing based on orthogonal fiber-optic structures

The invention provides a laser gyroscope based on parallel feedback, comprising an Er-doped fiber amplifier, an F-P cavity filter, a multimode light transmission medium, a 90/10 coupler, a 50/50 coupler and a photoelectric detector, wherein the Er-doped fiber amplifier is connected with the F-P cavity filter, the multimode light transmission medium and the 90/10 coupler in series via single mode light transmission media so as to form an annular cavity, the through end of the 90/10 coupler is connected to the annual cavity, two coupling ends of the 90/10 coupler serve as output ports of a bidirectional light path, two coupling output ends of the 90/10 coupler are connected with the two input ends of the 50/50 coupler, and the output ends of the 50/50 coupler are connected with the photosensitive detector. The multimode light transmission medium can be utilized to compress line width based on the ultra-narrow line width laser gyroscope without increasing the length of Er-doped fiber greatly, thus greatly enhancing the measurement precision of the laser gyroscope and reducing the cost. In addition, the Sagnac effect can be amplified by the laser gyroscope in the invention.

Xiaoqi Yu

Papers

Quadrature demodulation with synchronous difference for interferometric fiber-optic gyroscopes

Line cavity laser with super-narrow line width based on parallel feedback

Multi-core fiber based optical transmission structure and device applying same

Highly sensitive rotation sensing based on orthogonal fiber-optic structures

Laser gyroscope based on parallel feedback