## 1 Introduction  
Optical modeling of organic light-emitting diodes (OLEDs) based on the transfer matrix formulation has been intensively studied to optimize various output emission characteristics such as the out-coupling efficiency and angular emission dependence [1, 2, 3, 4, 5, 6, 7, 8]. Modal analysis is important to identify how the radiation of a dipole exciton inside the emission layer (EML) is coupled into various optical modes of the OLED. In the case of a top-emitting OLED, it is widely known that exciton dissipation is coupled into the air mode, absorption loss, trapped waveguide (WG) mode, and evanescent surface plasmon (SP) mode [9]. According to the classical electromagnetic models, these exciton dissipation mechanisms have been successfully quantified based on the power dissipation spectrum, where the spectral power density is calculated with respect to the normalized in-plane wave vector \(u\)[10, 11, 12, 13, 14]. In the evanescent spectral region of the power dissipation spectrum (\(u>1\)), the radiated wave from the dipole emitter is evanescent in nature because it exponentially decays in the direction normal to a dielectric/metal interface. When the in-plane wave vector satisfies the SP resonance condition, the evanescent wave becomes an SP mode, which propagates in the direction parallel to the dielectric/metal interface without changing its profile of the electric field. There have been several research reports to theoretically analyze and calculate the formation and behavior of SP modes in various OLED structures [15; 16; 17]. Besides the SP modes in the evanescent spectral region, there is another dissipation mechanism of the near-field (NF) absorption, which occurs due to the interaction between an evanescent wave with a large in-plane wave vector and a planar metal layer in the vicinity of the dipole radiation [18]. The exciton dissipation coupled to the NF absorption is different from the exciton dissipation coupled to the SP mode in the following aspects. As the NF absorption is not a resonant behavior like the SP mode, the NF absorption occurs at all the in-plane wave vectors in the evanescent region rather than at the specific in-plane wave vectors that satisfy their own SP resonance conditions. The fast-decaying evanescent wave that contributes to the NF absorption does not maintain its profile of the electric field unlike the SP mode. According to the conventional electromagnetic models, the contribution of the NF absorption and its dependence on the distance to the metal electrode has been typically included in the exciton dissipation coupled to the evanescent mode [19; 20], where the contributions between the SP mode and NF absorption are not clearly distinguished. There have been few papers to distinguish the specific contribution of the NF absorption in the evanescent spectral region of the exciton power dissipation. In the case of the dielectric/metal interface system, analytical expressions for the exciton power dissipation coupled to the SP mode and NF absorption were derived [18]. It was theoretically demonstrated that the NF absorption significantly contributed to the power dissipation spectrum at a large in-plane wave vector. Recently, we quantified the excitation efficiency of the respective WG and SP modes in a bottom-emitting OLED, where the power dissipation spectrum was approximated by the summation of Lorentzian line shape functions [21]. It was found that the contribution of the SP modes fitted by the Lorentzian line shape functions was not enough at larger in-plane wave vectors. The exciton power dissipation coupled to the NF absorption became noticeable when the distance between the dipole emitter and the dielectric/metal interface was less than 50 nm. However, we could not quantify the contribution of the NF absorption in the evanescent region of the power dissipation spectrum based on any specified theoretical model for the NF absorption.