Optical limiters are designed to transmit low-intensity light, while blocking the light with excessively high intensity. A typical passive limiter absorbs excessive electromagnetic energy, which can cause its overheating and destruction. We propose the concept of a photonic reflective limiter based on resonance transmission via a localized mode. Such a limiter does not absorb the high-level radiation, but rather reflects it back to space. Importantly, the nearly total reflection occurs within a broad frequency range and direction of incidence. The same concept can be applied to infrared and microwave frequencies.
Optical limiters transmit low-level radiation while blocking electromagnetic pulses with excessively high energy (energy limiters) or with excessively high peak intensity (power limiters). A typical optical limiter absorbs most of the high-level radiation which can cause its destruction via overheating. Here we introduce the novel concept of a reflective energy limiter which blocks electromagnetic pulses with excessively high total energy by reflecting them back to space, rather than absorbing them. The idea is to use a defect layer with temperature dependent loss tangent embedded in a low-loss photonic structure. The low energy pulses with central frequency close to that of the localized defect mode will pass through. But if the cumulative energy carried by the pulse exceeds certain level, the entire photonic structure reflects the incident light (and does not absorb it!) for a broad frequency window. The underlying physical mechanism is based on self-regulated impedance mismatch which increases dramatically with the cumulative energy carried by the pulse.
Optical limiters transmit low-intensity light, while blocking laser radiation with excessively high intensity or fluence. A typical passive optical limiter absorbs most of the high level radiation, which can cause irreversible damage. In this communication we report the first experimental realization of a reflective optical limiter, which does not absorb the high-level laser radiation, but rather reflects it back to space. The design is based on a periodic layered structure composed of alternating SiO2 and Si3N4 layers with a single GaAs defect layer in the middle. At low intensities, the layered structure displays a strong resonant transmission via the localized defect mode. At high intensities, the two-photon absorption in the GaAs layer suppresses the localized mode along with the resonant transmission, the entire layered structure turns highly reflective within a broad frequency range covering the entire photonic band gap of the periodic layered structure. By contrast, a stand-alone GaAs layer would absorb most of the high-level radiation, thus acting as a basic absorptive optical limiter. The proposed design can only perform at shortwave IR, where GaAs displays negligible linear absorption and very strong nonlinear two-photon absorption. With judicious choice of optical materials, the same principle can be replicated for any other frequency range.Comment: We present the first experimental realization of reflective limiters in the optical domain (see theoretical proposals in arXiv:1412.6207, arXiv:1309.2595
We propose a concept of chiral photonic limiters utilising topologically protected localised midgap defect states in a photonic waveguide. The chiral symmetry alleviates the effects of structural imperfections and guaranties a high level of resonant transmission for low intensity radiation. At high intensity, the light-induced absorption can suppress the localised modes, along with the resonant transmission. In this case the entire photonic structure becomes highly reflective within a broad frequency range, thus increasing dramatically the damage threshold of the limiter. Here we demonstrate experimentally the principle of operation of such photonic structures using a waveguide consisting of coupled dielectric microwave resonators.Photonic limiters are protecting filters transmitting input signal with low power (or energy) while blocking the signals of excessively high power (or energy) [1][2][3][4][5][6][7]. Usually, a passive limiter absorbs the high-level signal, which can cause its overheating or other irreversible damage. The input level above which the transmitted signal intensity doesn't grow with the input is the limiting threshold (LT). Another critically important characteristic is the limiter damage threshold (LDT), above which the limiter sustains irreversible damage. The domain between LT and LDT is the dynamical range of the limiter -the larger it is, the better. Unfortunately, material limitations impose severe restrictions on both thresholds. It is, therefore, imperative to utilise appropriate photonic platforms which are both flexible enough to provide simultaneously tunable and low LT and high enough LDT. Importantly, these structures should provide broadband protection and they should be tolerant to deviation of the material and geometrical parameters from their ideal values. Along these lines, the defect modes hosted by photonic band-gap structures have been exploited as an alternative to achieve flexible, high efficiency photonic limiters. In most occasions, however, limiting action is achieved by a non-linear frequency shift of the transparency window of the photonic structure [8][9][10][11][12][13][14]. Such a shift is inherently small and, therefore, cannot provide broadband protection from high-power input. To address this issue we have recently proposed a concept of a reflective photonic limiter [15,16]. Such a limiter does not absorb but reflects the high radiation, thereby, protecting itself -not just the receiving device. The principle of operation is based on resonant transmission via a localised defect mode with purely nonlinear absorption. The resonant frequency is engineered to fall in the middle of a photonic band-gap, allowing for the structure to provide a broadband protection in case of self-destruction of the defect mode. This self-destruction occurs at high input intensity, which triggers nonlinear losses suppressing the localised mode. As a result, the incident harmful signal experiences nearly total reflection. In contrast, at low intensity the losses at the nonlinear def...
The ability to control and direct acoustic energy is essential for many engineering applications such as vibration and noise control, invisibility cloaking, acoustic sensing, energy harvesting, and phononic switching and rectification. The realization of acoustic regulators requires overcoming fundamental challenges inherent to the time-reversal nature of wave equations. Typically, this is achieved by utilizing either a parameter that is oddsymmetric under time-reversal or by introducing passive nonlinearities. The former approach is power consuming while the latter has two major deficiencies: it has high insertion losses and the outgoing signal is harvested in a different frequency than that of the incident wave due to harmonic generation. Here, we adopt a unique approach that exploits spatially distributed linear and nonlinear losses in a fork-shaped resonant metamaterial. Our compact design demonstrates asymmetric acoustic reflectance and transmittance, and acoustic switching. In contrast to previous studies, our non-Hermitian metamaterial exhibits asymmetric transport with high frequency purity of the outgoing signal.
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