Selective Amplification of Scars in a Chaotic Optical Fiber

Abstract

In this letter we propose an original mechanism to select scar modes through coherent gain amplification in a multimode D-shaped fiber. More precisely, we numerically demonstrate the selective amplification of scar modes by positioning a gain region in the vicinity of the self-focal point of the shortest periodic orbit in the transverse motion. [5,6,7]. The violation of the ergodic hypothesis implied by the existence of scars is justified by various theoretical approaches [10] but remains mathematically uncertain [11].In previous works we showed that a passive optical fiber with a chaotic-billiard-shape transverse section constitutes a powerful experimental system for studying (and imaging) wave chaos [12], and particularly when scars are involved [4]. Indeed, at the output of a multimode D-shaped chaotic fiber we were able to put to evidence a scar mode associated to the shortest PO. Unfortunately, diffraction due to the finite aperture of the fiber precludes any truly selective excitation of a single mode. For an input illumination privileging the lowest order modes, a few tens of modes contribute to the optical field, and the best that one can do is to slightly enhance one of the lowest order scars. For larger orders, the increasing number of excited modes hampers the scar enhancement effect. Scar modes have also been observed in microlasers [6]. These devices are more and more present in photonics, for which high directionality and low lasing threshold are required. Scar modes constitute the cavity modes with the highest quality factors [7] and privileged directions of emission. In such lasing microcavities, boundary losses play a dominant role in the mode selection mechanism and, for a given shape, only a few efficient scar modes are supported [7]. A different selection mechanism may be found in the domain of wave propagation in random media. In this context, the amplification of localized modes is observed with random lasers (see Ref.[13] for a recent review), where they play similar to scar modes. Both types of modes rely on strong coherent effects and display common statistical features [14]. Numerical investigations recently showed that, in the localized regime, the lasing modes in a random laser just above threshold are the modes of the passive disordered system [15]. The identification between lasing and passive modes even holds when the gain region is smaller than the mode size [16]. Inspired by these results, we present an original way to achieve a selective amplification of scar modes in a highly multimode D-shaped optical fiber. More precisely, we demonstrate how scar modes can be selectively amplified by positioning a gain region in the vicinity of specific points along a short PO known to give rise to scar modes. We also illustrate the robustness of this amplification with a spatially incoherent speckle-like input.We recently showed that multimode D-shaped fibers are perfectly suited to achieve high power optical amplification [17]. In the single-mode doped core of an optical amplifier, the gui...

Whispering gallery modes formed by partial barriers in ultrasmall deformed microdisks

“…The deformed microcavities have been experimentally realized with several different cross-sectional shapes and various materials [6-10]. Also, they become important models in the field of quantum chaos [11,12] for the study of ray-wave correspondence in open systems [13][14][15][16][17].Nonetheless, it is not easy to understand and predict the spectrum and emission directionality because the internal ray dynamics is chaotic due to the broken rotational symmetry. Therefore, many studies have concentrated on the properties of the spectrum and the role of the chaotic dynamics to generate directional light emission from high-Q WGMs.…”

Regular modes in a mixed-dynamics-based optical fiber

“…It is worth mentioning that the latter geometry has also been fully studied in optical fibers over the past few years [11,12]. In particular, we experimentally demonstrated that some specific scarred modes of a chaotic optical fiber -spatially localized along the least unstable periodic orbits -can be selectively enhanced through an optical amplification process [14,20]. Moreover, as the pump absorption is clearly improved by the use of a chaotic double-clad fiber amplifier, the device has been proposed as an optimization of existing amplifiers [7,21].…”

Gain-controlled wave chaos in a chaotic optical fibre

“…To analyse the guided modes present in the propagating signal we calculate what we call the pseudo-time-frequency spectrum C(κ; z) in which z is the pseudo-time [31]. More precisely, C(κ; z) is obtained by the Fourier transform of the correlation function of the propagating field ψ s (r, z) with its initial condition, along a propagation length L z…”