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Register a new userTransverse-mode coupling and diffraction loss in tunable Fabry-Perot microcavities
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We report on measurements and modeling of the mode structure of tunable Fabry-Perot optical microcavities with imperfect mirrors. We find that non-spherical mirror shape and finite mirror size lead to loss, mode deformation, and shifted resonance frequencies at particular mirror separations. For small mirror diameters, the useful cavity length is limited to values significantly below the expected stability range. We explain the observations by resonant coupling between different transverse modes of the cavity and mode-dependent diffraction loss. A model based on resonant state expansion that takes into account the measured mirror profile can reproduce the measurements and identify the parameter regime where detrimental effects of mode mixing are avoided.
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A narrow linewidth laser operating at the telecommunications band combined with both fast and wide-band tuning features will have promising applications. Here, we demonstrate a single-mode (both transverse and longitude mode) continuous microlaser around 1535 nm based on a fiber Fabry-Perot microcavity, which achieves wide-band tuning without mode hopping to 1.3 THz range and fast tuning rate to 60 kHz, yields a frequency scan rate of $1.6times10^{17}$ Hz/s. Moreover, the linewidth of the laser is measured as narrow as 3.1 MHz. As the microlaser combines all these features into one fiber component, it can serve as the seed laser for versatile applications in optical communication, sensing, frequency-modulated continuous-wave radar and high resolution imaging.
Optical half-wave microresonators enable to control the optical mode density around a quantum system and thus to modify the temporal emission properties. If the coupling rate exceeds the damping rate, strong coupling between a microresonator and a quantum system can be achieved, leading to a coherent energy exchange and the creation of new hybrid modes. Here, we investigate strong coupling between two adjacent lambda/2 Fabry-Perot microresonators, where the resonance of one microresonator can be actively tuned across the resonance of the other microresonator. The transmission spectra of the coupled microresonators show a clear anticrossing behavior, which proves that the two cavity modes are strongly coupled. Additionally, we can vary the coupling rate by changing the resonator geometry and thereby investigate the basic principles of strong coupling with a well-defined model system. Finally, we will show that such a coupled system can theoretically be modelled by coupled damped harmonic oscillators.
We propose a novel photonic structure composed of metal nanolayer, Bragg mirror and metal nanolayer. The structure supports resonances that are transitional between Fabry-Perot and Tamm modes. When the dielectric contrast of the DBR is removed these modes are a pair of conventional Fabry-Perot resonances. They spectrally merge into a Tamm mode at high contrast. Such behavior differs from the results for structures supporting Tamm modes reported earlier. The optical properties of the structure in the frequency range of the DBR stop band, including highly beneficial 50% transmittivity through thick structures, are determined by the introduced in the paper hybrid resonances. The results can find a wide range of photonic applications.
Optical cavities with both optimized resonant conditions and high quality factors are important metrological tools. In particular, they are used for laser gravitational wave (GW) detectors. It is necessary to suppress the parametric instability by damping the resonant conditions of harmful higher order optical modes (HOOM) in order to have high cavity powers in GW detectors. This can be achieved effectively by using non spherical mirrors in symmetric Fabry-Perot (FP) cavities by increasing roundtrip losses of HOOMs. Fabry-Perot cavities in most of the GW detectors have non-identical mirrors to optimize clipping losses and reduce thermal noise by reducing the beam size on one side of the cavity facing to the beam splitter and recycling cavities. We here present a general method to design non spherical non-identical mirrors in non-symmetric FP cavities to damp HOOMs. The proposed design allows to the suppress the loss of the arm power caused by point absorbers on test masses.
A class of multiwavelength Fabry-Perot lasers is introduced where the spectrum is tailored through a non-periodic patterning of the cavity effective index. The cavity geometry is obtained using an inverse scattering approach and can be designed such that the spacing of discrete Fabry-Perot lasing modes is limited only by the bandwidth of the inverted gain medium. A specific two-color semiconductor laser with a mode spacing in the THz regime is designed, and measurements are presented demonstrating the simultaneous oscillation of the two wavelengths. The extension of the Fabry-Perot laser concept described presents significant new possibilities in laser cavity design.
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