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Exceptional points are singularities of open systems, and among their many remarkable properties, they provide a way to enhance the responsivity of sensors. Here we show that the improved responsivity of a laser gyroscope caused by operation near an exceptional point is precisely compensated by increasing laser noise. The noise, of fundamental origin, is enhanced because the laser mode spectrum loses the oft-assumed property of orthogonality. This occurs as system eigenvectors coalesce near the exceptional point and a bi-orthogonal analysis confirms experimental observations. While the results do not preclude other possible advantages of the exceptional-point-enhanced responsivity, they do show that the fundamental sensitivity limit of the gyroscope is not improved through this form of operation. Besides being important to the physics of microcavities and non-Hermitian photonics, these results help clarify fundamental sensitivity limits in a specific class of exceptional-point sensor. Operating a laser gyroscope near an exceptional point has been shown to enhance its responsivity. However, here the authors demonstrate in theory and experiment that the enhanced responsivity is exactly compensated by increased noise that is inherent to this system near the exceptional point.

Gyroscopes are essential to many diverse applications associated with navigation, positioning and inertial sensing 1 . In general, most optical gyroscopes rely on the Sagnac effect—a relativistically induced phase shift that scales linearly with the rotational velocity 2 , 3 . In ring laser gyroscopes (RLGs), this shift manifests as a resonance splitting in the emission spectrum, which can be detected as a beat frequency 4 . The need for ever more precise RLGs has fuelled research activities aimed at boosting the sensitivity of RLGs beyond the limits dictated by geometrical constraints, including attempts to use either dispersive or nonlinear effects 5 – 8 . Here we establish and experimentally demonstrate a method using non-Hermitian singularities, or exceptional points, to enhance the Sagnac scale factor 9 – 13 . By exploiting the increased rotational sensitivity of RLGs in the vicinity of an exceptional point, we enhance the resonance splitting by up to a factor of 20. Our results pave the way towards the next generation of ultrasensitive and compact RLGs and provide a practical approach for the development of other classes of integrated sensor. A method based on non-Hermitian singularities, or exceptional points, is established and used to increase the Sagnac scale factor and enhance the sensitivity of ring-laser gyroscopes.

Optical gyroscopes are among the most accurate rotation measuring devices and are widely used for navigation and accurate pointing. Since the advent of photonic integrated components for communications, and with their increasing complexity, there has been interest in the possibility of chip-scale optical gyroscopes1. Besides the potential benefits of integration, such solid-state systems would be robust and resistant to shock. Here, we report a gyroscope using Brillouin ring lasers on a silicon chip. Its stability and sensitivity enable measurement of Earth’s rotation, representing a major milestone for this new class of gyroscope.A Sagnac gyroscope based on Brillouin ring lasers on a silicon chip is presented. The stability and sensitivity of this on-chip planar gyroscope allow measurement of the Earth’s rotation, with an amplitude sensitivity as small as 5 deg h−1 for a sinusoidal rotation, an angle random walk of 0.068 deg h−1/2 and bias instability of 3.6 deg h−1.

The Gaussian laser mode can be converted into a hollow-ring laser mode through beam conversion system, realizing the conversion of circular and solid spot into a hollow-ring spot, which changes the energy distribution form of the laser spot. In order to study the effects of the Gaussian and hollow-ring laser modes on temperature and stress fields in cladding layers, the numerical simulation and experimental investigation were performed. The results showed that molten pool experienced once temperature peak and generated sharp temperature change under the Gaussian laser, while the molten pool experienced twice temperature peaks and temperature changed relatively gentle when using hollow-ring laser. Comparing with the Gaussian laser, the maximum temperature gradient along the depth of cladding layer decreased by 72.3% from 1.79 × 106 to 4.95 × 105 ℃/m, and the maximum residual stress decreased from 272 to 251 MPa under hollow-ring laser. Meanwhile, the simulation results were validated by experiments with the same process. Furthermore, the sample microstructure was studied from the experiment. The microstructure was finer and more uniform using hollow-ring laser. This paper can provide guidance and advantage for laser cladding and direct metal deposition based on the hollow-ring mode and expand the application of laser field.

In this paper, we investigate the possibility of using optical injection to efficiently suppress the time-delay (TD) signatures of chaotic signals in a large experimentally accessible parameter range of semiconductor ring lasers (SRLs). We also study how this optical injection can improve the signal bandwidths. The injection signal is obtained from a master SRL with either optical self- or cross-feedback. For optical self-feedback configurations, it is found that the suppression of TD signatures is similar to what has been found in injected Fabry–Perot semiconductor lasers, i.e., narrow range of parameters with respect to the detuning and injection strengths. For cross-feedback configurations, however, the TD signatures can be suppressed in a wide range of parameters; meanwhile, the bandwidths are significantly improved for the same range of parameters. This is particularly useful for the security in chaos-based communications and also for generating random bits with improved properties.

Inertial sensors are important at application level and also in fundamental physics. Ring laser gyroscopes, which measure angular rotation rates, are among the most sensitive ones. Large area ring laser reach sensitivities at the level of fractions of prad/s, allowing measurements of relevant geophysical signals. Improvements of a factor 10–100 would make these instruments able to measure general relativity effects; this is the goal e.g. of the GINGER project, an Earth based experiment aiming to test the Lense–Thirring effect with an accuracy of \\[1\\%\\]. However, the laser induces non-linearities, effects larger in small scale instruments. We discuss a novel technique to analyse data, able to reduce non-linear laser effects. We apply this technique to data from two ring laser prototypes, and compare the precision of the measurement of the angular rotation rate obtained with the new and the standard methods. We show that the back-scatter problem of the ring laser gyroscopes is negligible with a proper analysis of the data. These results not only allow to improve the performance of large scale ring laser gyroscopes but also pave the way to the development of small scale instruments with nrad/s sensitivity, which are precious for environmental studies and as inertial platforms.

Additive manufacturing (AM) has the potential for improving the sustainability of metal processing through decreased energy and materials usage compared to casting and forging. Laser powder bed fusion (LPBF) of high-temperature alloys such as nickel alloy 718 is one of the key modalities supporting this effort. One of the major drawbacks to LPBF is its slow build speed on the order of 5–10 cubic centimeters per hour print speed. This experimental study investigates how to increase the productivity of the LPBF process by switching from a traditional Gaussian laser shape to a ring laser shape using a nLight multi-modal laser. The objective is to increase productivity, reducing energy consumption and time, without sacrificing mechanical properties by switching to the ring laser thereby improving the sustainability of LPBF. Results include measuring the energy consumption of an Open Additive LPBF system during 718 printing and comparing the microstructure and mechanical properties of the two different lasers.

The ring laser gyroscope (RLG) technique has been investigated for over 20 years as a potential complement to space geodetic techniques in measuring Earth rotation. However, RLGs are also sensitive to changes in their terrestrial orientation. Therefore in this paper, we review how the high-frequency band (i.e. signals shorter than 0.5 cycle per day) of the known phenomena causing site deformation contribute to the RLG observable, the Sagnac frequency. We study the impact of solid Earth tides, ocean tidal loading and non-tidal loading phenomena (atmospheric pressure loading and continental hydrosphere loading). Also, we evaluate the differences between available models of the phenomena and the importance of the Love numbers used in modeling the impact of solid Earth tides. Finally, we compare modeled variations in the instrument orientation with the ones observed with a tiltmeter. Our results prove that at the present accuracy of the RLG technique, solid Earth tides and ocean tidal loading effects have significant effect on RLG measurements, and continental hydrosphere loading can be actually neglected. Regarding the atmospheric loading model, its application might introduce some undesired signals. We also show that discrepancies arising from the use of different models can be neglected, and there is almost no impact arising from the use of different Love numbers. Finally, we discuss differences between data reduced with tiltmeter observations and these reduced with modeled signal, and potential causes of this discrepancies.

The first tunable fibre ring laser in the 1700 nm wavelength region has been developed. To achieve this fibre laser, a Tm3+–Tb3+-doped fibre is used as the active fibre, along with a tunable bandpass filter. A fibre ring laser that consisted of a 1.2/1.7 μm band wavelength division multiplexing coupler, a tunable bandpass filter, an active fibre and one 1.21 μm pump laser diode has been realised. A wide tuning wavelength band of 130.4 nm (from 1635.6 to 1766.0 nm) was achieved with a launched pump power of over ∼ 30 mW. The lasing threshold pump power at 1716 nm was ∼ 9 mW.

In this paper, a method of generating controllable spikes utilizing symmetric semiconductor ring lasers (SRLs) is investigated, and various optical behaviors of biological neurons are successfully emulated on a faster timescale. We demonstrate the synchronized spike phenomena in two directions, generated in both the clockwise (CW) and counterclockwise (CCW) modes of the tunable laser (TL)-injected SRL. The size of the peaks and the interval between them can be manipulated by adjusting the output complex amplitude of the TL and bias current. At the same time, we also analyzed the CW mode of the TL-injected SRL and successfully replicated the four distinct discharge patterns of biological neurons. These findings offer promising prospects for future neuromorphic research.