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Register a new userExceptional Point and Toward Mode Selective Optical Isolation
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Dynamical encirclement of an Exceptional Point (EP) and corresponding time-asymmetric mode evolution properties due to breakdown in adiabatic theorem have been a key to range of exotic physical effects in various open atomic, molecular and optical systems. Here, exploiting a gain-loss assisted dual-mode optical waveguide that hosts a dynamical EP-encirclement scheme, we have explored enhanced nonreciprocal effect in the dynamics of light with onset of saturable nonlinearity in the optical medium. We propose a prototype waveguide-based isolation scheme with judicious tuning of nonlinearity level where one can pass only a chosen mode in any of the desired directions as per device requirement. The deliberate presence of EP enormously enhances the nonreciprocal transmission contrast even up to 40 dB over the proposed device length with a scope of further scalability. This exclusive topologically robust mode selective all-optical isolation scheme will certainly offer opportunities in integrated photonic circuits for efficient coupling operation from external sources and improve device performances.
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One of the most intriguing topological features of open systems is exhibiting exceptional point (EP) singularities. Apart from the widely explored second-order EPs (EP2s), the explorations of higher-order EPs in any system requires more complex topology, which is still a challenge. Here, we encounter a third-order EP (EP3) for the first time in a simple fabrication feasible gain-loss assisted optical microcavity. Using scattering-matrix formalism, we study the simultaneous interactions between three successive coupled states around two EP2s, which yield an EP3. Following an adiabatic parametric variation around the identified EP3, we present a robust successive-state-conversion mechanism among three coupled states. The proposed scheme indeed opens a unique platform to manipulate light in integrated devices.
The finite gain-bandwidth product is a fundamental figure of merit that restricts the operation of standard optical amplifiers. In microcavity setups, this becomes a serious problem due to the narrow bandwidth of the device. Here we introduce a new design paradigm based on exceptional points, that relaxes this limitation and allows for building a new generation of optical amplifiers that exhibits better gain-bandwidth scaling relations. Importantly, our results can be extended to other physical systems such as acoustics and microwaves.
We demonstrate experimentally that optical wavefront shaping selectively couples light into the fundamental diffusion mode of a scattering medium. The total energy density inside a scattering medium of zinc oxide (ZnO) nanoparticles was probed by measuring the emitted fluorescent power of spheres that were randomly positioned inside the medium. The fluorescent power of an optimized incident wave front is observed to be enhanced compared to a non-optimized incident front. The observed enhancement increases with sample thickness. Based on diffusion theory, we derive a model wherein the distribution of energy density of wavefront-shaped light is described by the fundamental diffusion mode. The agreement between our model and the data is striking not in the least since there are no adjustable parameters. Enhanced total energy density is crucial to increase the efficiency of white LEDs, solar cells, and of random lasers, as well as to realize controlled illumination in biomedical optics.
We designed and built a new type of spatial mode multiplexer, based on Multi-Plane Light Conversion (MPLC), with very low intrinsic loss and high mode selectivity. In this first demonstration we show that a typical 3-mode multiplexer achieves a mode selectivity better than -23 dB and a total insertion efficiency of -4.1 dB (optical coating improvements could increase efficiency to -2.4 dB), across the full C-band. Moreover this multiplexer is able to perform any mode conversion, and we demonstrate its performance for the first 6 eigenmodes of a few-mode fiber: LP$_{01}$, LP$_{11mathrm{a}}$, LP$_{11mathrm{b}}$, LP$_{02}$, LP$_{21mathrm{a}}$ and LP$_{21mathrm{b}}$.
Hyperbolic Meta-Materials~(HMMs) are anisotropic materials with permittivity tensor that has both positive and negative eigenvalues. Here we report that by using a type II HMM as cladding material, a waveguide which only supports higher order modes can be achieved, while the lower order modes become leaky and are absorbed in the HMM cladding. This counter intuitive property can lead to novel application in optical communication and photonic integrated circuit. The loss in our HMM-Insulator-HMM~(HIH) waveguide is smaller than that of similar guided mode in a Metal-Insulator-Metal~(MIM) waveguide.
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