Numerous modern technologies are reliant on the low-phase noise and exquisite timing stability of microwave signals. Substantial progress has been made in the field of microwave photonics, whereby low-noise microwave signals are generated by the down-conversion of ultrastable optical references using a frequency comb^1–3. Such systems, however, are constructed with bulk or fibre optics and are difficult to further reduce in size and power consumption. In this work we address this challenge by leveraging advances in integrated photonics to demonstrate low-noise microwave generation via two-point optical frequency division^4,5. Narrow-linewidth self-injection-locked integrated lasers^6,7 are stabilized to a miniature Fabry–Pérot cavity⁸, and the frequency gap between the lasers is divided with an efficient dark soliton frequency comb⁹. The stabilized output of the microcomb is photodetected to produce a microwave signal at 20 GHz with phase noise of −96 dBc Hz⁻¹ at 100 Hz offset frequency that decreases to −135 dBc Hz⁻¹ at 10 kHz offset—values that are unprecedented for an integrated photonic system. All photonic components can be heterogeneously integrated on a single chip, providing a significant advance for the application of photonics to high-precision navigation, communication and timing systems.

Next-generation communications, radar, and navigation systems will extend and exploit the higher bandwidth of the millimeter-wave domain for increased communication data rates as well as radar with higher sensitivity and increased spatial resolution. However, realizing these advantages will require the generation of millimeter-wave signals with low phase noise in simple and compact form-factors. Photonic integration addresses this challenge and provides a path toward simplified and portable, low-noise mm-wave generation. We leverage these advances by heterodyning two silicon photonic chip lasers, phase-locked to different axial modes of a miniature Fabry–Perot (F-P) cavity to demonstrate a simple framework for generating low-noise millimeter-waves. By reducing technical noise, we achieve common-mode rejection of the thermally driven Brownian noise such that the millimeter-wave phase noise surpasses that of the thermal limit of a single laser locked to the F-P cavity. This leads to a 118.1 GHz millimeter-wave signal with phase noise of −118dBc/Hz at 10 kHz offset, decreasing to −120dBc/Hz at 30 kHz offset. We achieve this with technologies that can be integrated into a platform less than ≈10mL. Our work overcomes fundamental thermal-mechanical noise limits intrinsic to integrated photonics, while illustrating advantages of the same for providing low-size, -weight, and -power (SWaP) mm-waves that will be enabling for multiple applications in communications and sensing.

Real-time observation of the emergence of coherent structures from noise via instabilities is of particular interest across disciplines ranging from biology to astrophysics. In the context of photonics, ultrafast fibre lasers provide an ideal test-bed for experimental observation of dynamical instabilities and generation of coherent structures of ultrashort pulses. Here we present experimentally obtained switch-on dynamics of counter-propagating ultrashort pulses in a bidirectional mode-locked fibre laser with delayed pulse formation via Q-switched and modulation instabilities, pronounced central wavelength drift, with the multiple-pulse formation. We define a localisation parameter using the round-trip resolved autocorrelation function to quantify the extent of the pulse formation, indicating an energy interchange between coherent features and background radiation. Furthermore, we report the formation of synchronised and unsynchronised dispersion waves. Our results reveal the complexity of the establishment of coherent features and their interaction with background radiation, contributing further towards the understanding of nonlinear systems in general.

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.

We have studied the ultrafast saturation behavior of a high-density well-aligned single-walled carbon nanotubes saturable absorber (HDWA-SWCNT SA), obtained by a high-pressure and high-temperature treatment of commercially available single-wall carbon nanotubes (SWCNTs) and related it to femtosecond erbium-doped fiber laser performance. We have observed the polarization dependence of a nonlinear optical saturation, along with a low saturation energy level of <1 fJ, limited to the detector threshold used, and the ultrafast response time of <250 fs, while the modulation depth was approximately 12%. We have obtained the generation of ultrashort stretched pulses with a low mode-locking launching threshold of ~100 mW and an average output power of 12.5 mW in an erbium-doped ring laser with the hybrid mode-locking of a VDVA-SWNT SA in combination with the effects of nonlinear polarization evolution. Dechirped pulses with a duration of 180 fs were generated, with a repetition rate of about 42.22 MHz. The average output power standard deviation was about 0.06% RMS during 3 h of measurement.