Light field analysis for modeling and transmission characteristics of partially coherent light-emitting diodes

Abstract

When analyzing the transmission characteristics of LEDs for long-distance lighting and communication applications, the light field is commonly assumed to be fully incoherent. However, in reality, the LED light source emits partially coherent light with a spatial coherence length on the order of microns. This paper is based on the generalized higher-order Lambert model of LEDs and aims to construct a Gaussian-Schell model for the LED beam (LED-GSM) on the near-field source plane, with a half-power angle of no more than 10o. Utilizing the cross-spectral density function transmission theory for partially coherent light, this paper provides the LED-GSM model’s spatial coherence length and beam radius at different distances and designs an experiment for measuring the spatial coherence length of LED beams. Experimental measurements of the spatial coherence length and beam spot size of LED beams at different distances are carried out using a Thorlabs LED528EHP light source. The experimental results match well with the theoretical simulations of the LED-GSM model, thus validating its effectiveness. Then, the proposed LED-GSM model is utilized to investigate the long-distance transmission characteristics of partially coherent narrow-beam LED light. Simulation results indicate that the spatial coherence length of the LED light field can reach tens to hundreds of millimeters over transmission distances of several kilometers. The beam radius is much smaller than that of the beam radius based on the fully incoherent model, and the beam intensity distribution also displays distinct differences.

Transmission Characteristics and Spatial Coherence of Partially Coherent Light-Emitting Diode Array in the Ocean

“…The narrow beam light field E(r, z 1 , t) satisfies the Gaussian distribution property under the conditional constraints of Φ 1/2 ≤ 10 o , r 2 z 2 1 , where Φ 1/2 is the half-power angle and z 1 refers to the distance from the LED light emission area. The expression for the complex amplitude on the observation plane at z = z 1 is given by [17].…”

“…In this paper, we extend our research beyond the analysis of the combined effects of channel attenuation and oceanic turbulence. Building upon previous work [17], we also consider the partial coherence of the LED array. It is essential to incorporate the variations in optical intensity attenuation, beam spreading, and coherence during the optical transmission.…”