The Sagnac effect, also called Sagnac interference, named after French physicist Georges Sagnac, is a phenomenon encountered in interferometry that is elicited by rotation. The Sagnac effect manifests itself in a setup called a ring interferometer or Sagnac interferometer. A beam of light is split and the two beams are made to follow the same path but in opposite directions. On return to the point of entry the two light beams are allowed to exit the ring and undergo interference. The relative phases of the two exiting beams, and thus the position of the interference fringes, are shifted according to the angular velocity of the apparatus. In other words, when the interferometer is at rest with respect to a nonrotating frame, the light takes the same amount of time to traverse the ring in either direction. However, when the interferometer system is spun, one beam of light has a longer path to travel than the other in order to complete one circuit of the mechanical frame, and so takes longer, resulting in a phase difference between the two beams. Georges Sagnac set up this experiment in an attempt to prove the existence of the aether that Einstein's theory of special relativity had discarded.
A gimbal mounted mechanical gyroscope remains pointing in the same direction after spinning up, and thus can be used as a rotational reference for an inertial navigation system. With the development of so-called laser gyroscopes and fiber optic gyroscopes based on the Sagnac effect, bulky mechanical gyroscopes can be replaced by those with no moving parts in many modern inertial navigation systems. A conventional gyroscope relies on the principle of conservation of angular momentum whereas the sensitivity of the ring interferometer to rotation arises from the invariance of the speed of light for all inertial frames of reference.
Typically three or more mirrors are used, so that counter-propagating light beams follow a closed path such as a triangle or square (Fig. 1). Alternatively fiber optics can be employed to guide the light through a closed path (Fig.
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The Fizeau experiment was carried out by Hippolyte Fizeau in 1851 to measure the relative speeds of light in moving water. Fizeau used a special interferometer arrangement to measure the effect of movement of a medium upon the speed of light. According to the theories prevailing at the time, light traveling through a moving medium would be dragged along by the medium, so that the measured speed of the light would be a simple sum of its speed through the medium plus the speed of the medium.
The Sagnac effect, also called Sagnac interference, named after French physicist Georges Sagnac, is a phenomenon encountered in interferometry that is elicited by rotation. The Sagnac effect manifests itself in a setup called a ring interferometer or Sagnac interferometer. A beam of light is split and the two beams are made to follow the same path but in opposite directions. On return to the point of entry the two light beams are allowed to exit the ring and undergo interference.
A ring laser gyroscope (RLG) consists of a ring laser having two independent counter-propagating resonant modes over the same path; the difference in phase is used to detect rotation. It operates on the principle of the Sagnac effect which shifts the nulls of the internal standing wave pattern in response to angular rotation. Interference between the counter-propagating beams, observed externally, results in motion of the standing wave pattern, and thus indicates rotation.
Comprendre les principes physiques utilisés dans les capteurs. Vue générale des différents principes de transduction et de l'électronique associée. Montrer des exemples d'application.
Information is processed in physical devices. In the quantum regime the concept of classical bit is replaced by the quantum bit. We introduce quantum principles, and then quantum communications, key d
This thesis aims at investigating the performance of figure-9 (figure-of-nine) optical fiber resonators as a practical solution for light storage, light generation and manipulation.
The first part of the thesis focuses on a theoretical and experimental study describing the performance of the figure-9 laser as a function of different coupling strengths and output coupling conditions. The study provides new insights on Sagnac interferometer-based fiber lasers, which can be useful also for other types of cavities that include this structure, such as the figure-8 (figure-of-eight) or the theta cavity laser.
The work on the figure-9 laser is then followed by a generalized theoretical model, validated by numerical results, to demonstrate that resonant systems with a decoupled input and output energy rates can exhibit an arbitrarily high time-bandwidth performance, thus providing a longer delay/storage time. The developed model shows that the time-bandwidth product (TBP) of such a resonant system is only limited by the cavity finesse. This description fits with the time-bandwidth limit (TBL), which states that the cavity bandwidth Δωcav is the inverse of the photon lifetime τ (i.e. Δωcav⋅τ=1), only when the resonator is reciprocal. The results also show that a longer storage time is accompanied by a significant improvement of the intra-cavity power enhancement, with respect to that provided by a reciprocal resonator, which is strongly desirable in all the applications that demand high efficiency in nonlinear processes. By comparing the total power enhancement in the reciprocal and nonreciprocal case, we prove that the TBP can be used as a figure of merit that characterizes the gain of total power enhancement, attained over one free spectral range (FSR) through nonreciprocal coupling, with respect to the reciprocal case considering the same amount of in-coupled power.
The model is then used as a reference for an experimental implementation of such a system, at telecommunication wavelengths (around 1.55μm), using a time-variant figure-9 cavity. The results report a TBP that exceeds by a factor of 30 the TBL and is limited only by experimental constraints of the setup used.
Lastly, the Sagnac interferometer in the context of generation of light is explored as to achieve electro-optic comb generation with a flat-topped spectral shape.
EPFL2021
Explores the Mach-Zehnder interferometer, density matrices, and detection probabilities in quantum systems.
Explores optical sensors' principles and applications, including Doppler velocimetry and optical pyrometry.
Explores the principles of coupling excitation modes and discusses gyroscope sensitivity.