Optical measurements of rotation velocities have traditionally relied on Sagnac effect interrogation. Due to ultra-small changes in carrier wavelength caused by rotation, such methods have to rely on indirect highly integrated techniques, translating the signal to lower frequency range.

Researchers at Leibniz IPHT have introduced a new concept for the direct detection of the optical Sagnac effect, which is based on the combinations of the benefits of passive instruments based on Mach-Zehnder interferometer with the advancements brought by real-time ultrashort pulses measurement techniques.

In the picture:
Rotation measurement setup based on Mach-Zender interferometer and dispersive Fourier transformation (DFT) techniques (top). Typical DFT measured spectra from the interferometer at rest (bottom left). Relative phase dynamics under rotational exposure by a stepper motor with different step magnitude at 3.33 ms step duration.

Such an approach allows achieving a new level of performance, such as high tolerance to seed laser stability, including timing jitter and the fluctuations of the carrier-envelope phase. The demonstrated methods have enabled increased measurement acquisition rate beyond tens of MHz, making it comparable with ultrafast laser repetition rate, which is at least three orders of magnitude faster than currently available fibre optic gyroscope technologies.

The researchers have illustrated the principle of ultrafast gyroscopic measurements by reconstructing the ultrashort pulse relative phase from the single-shot spectral interferometric pattern. The single-shot resolution of the phase retrieval using the demonstrated methodology from the interferometric pattern reached 7.3 mrad, which allowed to exceed the angular rotation resolution of active ultrafast fibre laser gyroscopes by more than an order of magnitude down to 0.33 mdeg/s with excellent bias stability of 0.06 deg/h.

The work also opens up several new exciting perspectives for other gyroscopic and accelerometer approaches, including translation to semiconductor ultrafast seed lasers to achieve even higher data acquisition rates and miniaturisation of the final design. The suggested methodology can enhance the existing technologies, for example, used in navigation and enables newly emerging applications such as autonomous vehicles, requiring a much higher data acquisition rate than modern gyros can currently provide. Thus, the results demonstrate the readiness of ultrafast optical gyroscopes to be used in highly specialised studies.

Furthermore, the results presented in this article have established that the combination of the DFT technique with interferometric phase measurements is an efficient approach for enabling precision phase measurements at high data rates. Therefore, the concept of DFT interferometry is not limited only to the gyroscopic measurements, and can be extended to other phase-sensitive applications, for example ultrafast refractive index measurements.

Publications:
Kudelin, I., Sugavanam, S., & Chernysheva, M. (2022). Ultrafast Gyroscopic Measurements in a Passive All‐Fiber Mach–Zehnder Interferometer via Time‐Stretch Technique. Advanced Photonics Research, 2200092