Rotation Active Sensors Based on Ultrafast Fibre Lasers

Abstract

Gyroscopes merit an undeniable role in inertial navigation systems, geodesy and seismology. By employing the optical Sagnac effect, ring laser gyroscopes provide exceptionally accurate measurements of even ultraslow angular velocity with a resolution up to 10-11 rad/s. With the recent advancement of ultrafast fibre lasers and, particularly, enabling effective bidirectional generation, their applications have been expanded to the areas of dual-comb spectroscopy and gyroscopy. Exceptional compactness, maintenance-free operation and rather low cost make ultrafast fibre lasers attractive for sensing applications. Remarkably, laser gyroscope operation in the ultrashort pulse generation regime presents a promising approach for eliminating sensing limitations caused by the synchronisation of counter-propagating channels, the most critical of which is frequency lock-in. In this work, we overview the fundamentals of gyroscopic sensing and ultrafast fibre lasers to bridge the gap between tools development and their real-world applications. This article provides a historical outline, highlights the most recent advancements and discusses perspectives for the expanding field of ultrafast fibre laser gyroscopes. We acknowledge the bottlenecks and deficiencies of the presented ultrafast laser gyroscope concepts due to intrinsic physical effects or currently available measurement methodology. Finally, the current work outlines solutions for further ultrafast laser technology development to translate to future commercial gyroscopes.

Keywords: Dispersive Fourier Transform; fibre gyroscope; fibre sensors; mode-locked laser.

Figure 1

Schematic representation of: (a) passive Sagnac interferometer; and (b) ring laser gyroscope.

Figure 2

The interference of counter-propagation pulse on photodetector measured from gyroscope at rest and in rotation.

Figure 3

Map of the performance capabilities of state-of-the-art gyroscopes.

Figure 4

(a) Schematic demonstration of the phase locking of multiple longitudinal wave modes. Ultrashort pulse representation in: (b) time domain; and (c) frequency domain.

Figure 5

Characteristic of ultrafast lasers: (a) radio frequency spectrum at the fundamental repetition rate; (b) Allan deviation of fundamental rate; and (c) relative intensity noise for soliton operation regimes in a free-running fibre laser with total intracavity dispersion of −0.005 (red line) and −0.021 (blue line). Adapted with permission from [138] © The Optical Society.

Figure 6

Principles of real-time measurements of spatiotemporal dynamics: (a) periodic pulses recorded by the oscilloscope are converted to 2D evolution of selected pulse pairs separated by the round trip time; and (b) example of spatiotemporal dynamics of two pulses. Adapted from [29] (© CC BY licence).

Figure 7

Principles of real-time measurements using the dispersive Fourier transform technique: (a) a train of closely-separated pair of optical solitons while propagating through highly dispersive media, mapping their temporal profile to spectral; (b) example of recorded single-shot spectral evolution; and (c) real-time evolution of field autocorrelation, obtained by fast Fourier transform of single-shot spectra. Adapted from [29] (© CC BY licence).

Figure 8

Ultrafast fibre laser cavity designs for gyroscopic applications: (a) laser cavity based on nonlinear fibre loop, controlled by phase modulator; (b) bidirectional ring all-fibre cavity with possible approaches for saturable absorbers implementations, operating in transmission or reflection; and (c) ring cavity setup with separated optical paths for counter-propagating pulses at saturable absorber.

Figure 9

Optical Sagnac effect detection using beat-note measurement: (a) RF spectrum and (b) oscilloscope trace of combined counter-propagating pulses; and (c) rotation measurements at slow and fast angular velocities, demonstrating the scale factor of 6.95 kHz/(deg/s). Adapted with permission from [123] © The Optical Society.

Figure 10

Measurement of optical Sagnac effect using beat-note measurement in bidirectional dark soliton fibre laser: (a) typical pulse trace of dark solitons; (b) RF spectrum of combined counter-propagating pulses; and (c) rotation measurement demonstrating sensitivity of 3.31 kHz/(deg/s). Adapted with permission from [199] © The Optical Society.

Figure 11

Optical Sagnac effect detection through spatiotemporal pulse evolution: (a) the spatiotemporal dynamics of counter-propagating pulses with different repetition frequencies; (b) temporal shift of combined pulses after 10${}^4$ round trips at different angular velocities; and (c) pulse temporal shift due to the optical Sagnac effect (in reference to the platform at rest) at 10 000 round trips beyond the point of pulse overlapping. Adapted from [29] © CC BY.

Figure 12

Optical Sagnac effect measurements by single-shot spectral evolution using DFT: (a) the spatiotemporal dynamics of counter-propagating pulses with synchronised repetition frequencies; (b) single-shot spectra dynamics within 500 round trips. Inset: zoomed-in central part of spectral evolution; (c) frequency shift for two different angular velocities; and (d) DFT response to different angular velocities. Adapted from [29] © CC BY.

Figure 13

Bidirectional fibre optical parametric oscillator for rotation measurement: (a)schematic setup (inset: output spectrum); (b) RF spectrum of observed frequency beating; and (c) beating of the two frequency combs in time domain (inset: Fourier transform of the time domain signal, showing beat-note frequency). Adapted with permission from [152] © The Optical Society.