Active ring laser gyroscopes (RLG) operating on the principle of the optical Sagnac effect are used in a range of applications, such as inertial guidance systems, seismology and geodesy, which require both high bias stability and high angular velocity resolutions. Operating at such accuracy levels demands special precautions like dithering or multi-mode operation to eliminate frequency lock-in or similar effects introduced due to synchronisation of counter-propagating channels. In our work, we showed how bidirectional ultrafast fibre lasers can be used to circumvent the limitations of continuous wave RLGs. Instead of using traditional averaged approaches of measurement, we used real-time intensity and spectral measurement techniques like spatio-temporal dynamics and the dispersive Fourier transform, transforming the bidirectional ultrafast laser to an ultrafast gyroscope with acquisition rates of the order of the laser repetition rate. This is at least two orders of magnitude faster than commercially deployed versions. Our results reveal the high potential of application of novel methods of optical Sagnac effect measurements, allowing enhancement of rotation sensitivity and resolution by several orders of magnitude.
The figure on the left above shows the spatio-temporal dynamics of the co- and counter-propagating pulses. The skew between them arises due to a difference in their repetition periods. This is further accentuated the Sagnac effect (right, top) with changing angular velocity of the rotating stage, and is seen to follow the expected linear dependence (right, bottom). You can know more about this work here –
In more recent work (CLEO 2021), we show how we can use a conventional ultrashort pulse fibre laser to realize a gyroscope in a passive configuration, in a real-time configuration. More on this will follow!
Some works aligned to our work on the use of ultrashort pulsed fibre lasers for gyroscopic applications are as follows.
OSA | Build-up dynamics in bidirectional soliton fiber lasers (osapublishing.org) – and Pulse-onset dynamics in a bidirectional mode-locked fibre laser via instabilities | Communications Physics (nature.com) – where we investigate in depth the origination dynamics of the bidirectional ultrashort pulses.
We have also published a review on the topic of active rotation sensors. This gives an overview of the common measurands, fibre laser technology, and state of the art in the field (till early 2021).
PS – if you want to know more about how we did the work behind the scenes, you can read it here!