송석호 교수

Parity-time (PT) symmetry and associated non-Hermitian properties in open physical systems have been intensively studied in search of new interaction schemes and their applications. Here, we experimentally demonstrate an electrical circuit producing key non-Hermitian properties and unusual wave dynamics grounded on anti-PT (APT) symmetry. Using a resistively coupled amplifying-LRC-resonator circuit, we realize a generic APT-symmetric system that enables comprehensive spectral and time-domain ana

Time-asymmetric state-evolution properties while encircling an exceptional point are presently of great interest in search of new principles for controlling atomic and optical systems. Here, we show that encircling-an-exceptional-point interactions that are essentially reciprocal in the linear interaction regime make a plausible nonlinear integrated optical device architecture highly nonreciprocal over an extremely broad spectrum. In the proposed strategy, we describe an experimentally realizabl

Recently, synthetic optical materials represented via non-Hermitian Hamiltonians have attracted significant attention because of their nonorthogonal eigensystems, enabling unidirectionality, nonreciprocity and unconventional beam dynamics. Such systems demand carefully configured complex optical potentials to create skewed vector spaces with a desired metric distortion. In this paper, we report optically generated non-Hermitian photonic lattices with versatile control of real and imaginary sub-l

Abstract The topological properties of photonic microstructures are of great interest because of their experimental feasibility for fundamental study and potential applications. Here, we show that robust guided‐mode‐resonance states exist in photonic domain‐wall structures whenever the complex photonic band structures involve certain topological correlations in general. Using the non‐Hermitian photonic analogy of the one‐dimensional Dirac equation, we derive essential conditions for photonic Jac

We demonstrate a new type of multifocal and extended depth of focus (EDOF) intraocular lenses (IOLs) embedding μm-thin geometric phase (GP) lens layers. As an emerging approach for lens phase design, the GP modulated IOLs outperform conventional diffractive IOLs in multifocality while completely avoiding the clinically undesirable demand for additional surface patterns to standard monofocal IOL designs. The number of foci and light splitting ratio of the GP IOLs are adjusted by changing the numb

A new holographic associative memory (HAM) using optical polarization is proposed. Picture elements (pixels) of binary objects are encoded with two mutually perpendicular states of linear polarization, and they are stored in the HAM using a lensless diffuser system. Experimental results of recognizing various inputs are presented. Analytical expressions about the present HAM are derived, and results of computer simulation are also presented.

We propose a free-space electro-optic transmission modulator based on multiple p-n-junction semiconductor subwavelength gratings. The proposed device operates with a high-Q guided-mode resonance undergoing electro-optic resonance shift due to direct electrical control. Using rigorous electrical and optical modeling methods, we theoretically demonstrate a modulation depth of 84%, on-state efficiency 85%, and on-off extinction ratio of 19 dB at 1,550 nm wavelength under electrical control signals

Abstract Recent study on topological operations around an exceptional point singularity has shown remarkably robust chiral processes that potentially create time-asymmetric or nonreciprocal systems and devices. Nevertheless, direct observation of the entire dynamics in the courses of the topological operations has not been revealed in experiments thus far. Here, we report a comprehensive experimental study on fully time-resolved dynamic-state evolution passages during encircling-an-exceptional-p

Balanced radiation and absorption rates of an optical resonator are necessary for coherent perfect light absorption in many active device applications. This balance is referred to as critical coupling condition. We propose a gain-assisted method for exact access to critical coupling conditions without altering any structure parameters. In a coherent absorber with additional internal gain media, critical coupling with arbitrarily high coherent signal extinction can be obtained by continuously tun

Persistent photoconductors of npnp doping-modulated amorphous silicon multilayers are investigated for the implementation of variable analog and nonvolatile synaptic weights of an optoelectronic neural processor. The time dependence of the persistent photoconductance of the amorphous silicon multilayers is characterized in experiments. The learning performance of an optical pattern classifier with the persistent photoconductive array is analyzed by computer simulations.

PURPOSE: To evaluate the image quality of intraocular lenses (IOLs) using field-tracing optical simulation and then compare it with the image quality using conventional ray-tracing simulation. METHODS: We simulated aspheric IOLs with a decenter, tilt, and no misalignment using an aspheric corneal eye model with a positive spherical aberration. The retinal image, Strehl ratio, and modulation transfer function (MTF) were compared between the ray-tracing and field-tracing optical simulation and con