Min Won Lee

Experimental optimization of the optical and electrical properties of a half-wavelength-thick organic hetero-structure in a Micro-cavity

In the context of progress towards the organic laser diode, we experimentally investigate the optical and electrical optimization of an OLED in a vertical λ/2 microcavity. The microcavity consists of a quarter-wavelength TiO₂/SiO₂ multilayer mirror, a half-wavelength-thick OLED and a semitransparent aluminum cathode. The Alq3/DCM2 guest-host system is used as the emitting layer. This study focuses on the design and the fabrication of a half-wavelength thick organic hetero-structure exhibiting a high current density despite both the thickness increase and the cathode thickness reduction. The emission wavelength, the line-width narrowing and the current-density are studied as a function of two key parameters: the hetero-structure optical thickness and the aluminum cathode thickness. The experimental results show that a 125 nm thick cavity OLED ended by a 20 nm thick aluminum cathode exhibits a resonance at 606 nm with a full width at half maximum of 11 nm, and with current-densities exceeding 0.5 A/cm². We show that even without a top high-quality-mirror the incomplete microcavity λ/2 OLED hetero-structure exhibits a clear modification of the spontaneous emission at normal incidence.

Demonstration of optical rogue waves using a laser diode emitting at 980 nm and a fiber Bragg grating

Rogue waves are observed for the first time, to the best of our knowledge, in a 980 nm laser diode subject to filtered optical feedback via a fiber Bragg grating. By counting the number of rogue waves in a fixed time window, a rogue wave map is established experimentally as a function of both the optical feedback ratio and the laser current. The comparison with low frequency fluctuations (LFFs) reveals that the rogue waves observed in our system are, in fact, LFF jump-ups.

High-resolution low-frequency fluctuation map of a multimode laser diode subject to filtered optical feedback via a fiber Bragg grating

A highly detailed and extended map of low-frequency fluctuations is established for a high-power multi-mode 980 nm laser diode subject to filtered optical feedback from a fiber Bragg grating. The low-frequency fluctuations limits and substructures exhibit substantial differences with previous works.

Study of the Light Coupling Efficiency of OLEDs Using a Nanostructured Glass Substrate

We study theoretically the enhancement of the light extraction from an OLED (Organic Light-Emitting Diode) with nanoair-bubbles embedded inside a glass substrate. Due to such a nanostructure inside the substrate, the critical angle which limits the light extraction outside the substrate from the OLED is increased. The theoretical results show that the nanoair bubbles near by the substrate surface can improve the efficiency of the light extraction by 7%. Such a substrate may also be suitable for photovoltaic cells or display screens.

Investigation of a planar optical waveguide in 2D PPLN using Helium implantation technique

In this work, we report the investigation of a planar waveguide in a 2D periodically-poled lithium niobate (PPLN). The waveguide is fabricated by helium (He(+)) implantation at 2 MeV and a fluence of 1.5 x 10(16) ions/cm(2). Second harmonic generation (SHG) at 532 nm using a Q-switched laser and a CW laser diode at 1064 nm, was measured as a function of angular distribution and temperature. The experimental results show higher gain in SHG conversion efficiency in the waveguide than in the bulk 2D PPLN. In particular, SHGs from 2D reciprocal lattice vectors (RLV) are observed and studied.

Enhanced dual beam generation processes in a two-dimensional χ (2) nonlinear photonic crystal

The signal wavelength of collinear direction is enhanced at two quasi-collinear directions with the generation of two idler wavelengths thanks to simultaneous contribution of reciprocal lattice vectors Km, n in a two-dimensional nonlinear photonic crystal (2D-NLPC).

Simultaneous frequency conversions in nonlinear photonic crystals of lithium tantalate with a square lattice

Nonlinear photonic crystals such as 2D-PPLT (periodically-poled lithium tantalite) are of great interest for multi-wavelengths frequency conversion thanks to the contribution of different reciprocal lattice vectors (RLV) [1]. Such characteristics facilitates optical parametric generation (OPG), second harmonic generation (SHG), sum-frequency generation (SFG) or difference frequency generation (DFG). However, these nonlinear processes do not usually occur at the same time because of the different phase matching conditions. Recently, multi nonlinear process has been demonstrated in a hexagonally-poled LiTaO3 [2]. In this case, SHG and OPG were generated and SFG was then generated by a cascaded process.

Multiwavelength generation from multi-nonlinear optical process in a 2D PPLT

We have demonstrated multi-wavelength generation in a nonlinear photonic crystals of lithium tantalate. The optical parametric generation leads to second harmonic generation, sum-frequency generation and other frequency conversion in a cascade process. These conversions are assisted by all the optical nonlinear process involving χ(2) and achieved by satisfying the quasi-phase matching conditions.

Observation of rogue waves in a 980nm-laser diode subject to filtered optical feedback

Rogue waves are observed in a 980 nm laser diode subject to filtered optical feedback via an FBG. A rogue-wave map is established experimentally as a function of the optical feedback ratio and the laser current.

Revisiting low frequency fluctuations in high power multi-mode laser diodes subject to filtered optical feedback

A highly detailed and extended map of low frequency fluctuations is established for a high power multi-mode 980nm laser diode subject to filtered optical feedback from a fibre Bragg grating. The low frequency fluctuations limits and substructures exhibit substantial differences with previous works.