A better understanding of the optical properties of random photonic structures is beneficial for many applications, such as random lasing, optical imaging and photovoltaics. Here we investigated the light transmission properties of disordered photonic structures in which the high refractive index layers are aggregated in clusters. We sorted the size of the clusters from a power law distribution tuning the exponent a of the distribution function. The sorted high refractive layer clusters are randomly distributed within the low refractive index layers. We studied the total light transmission, within the photonic band gap of the corresponding periodic crystal, as a function of the exponent in the distribution. We observed that, for 0≤a≤3.5, the trend can be fitted with a sigmoidal function.
IntroductionLight propagation in dielectric random media offers a variety of fascinating features in the field of diffuse optical imaging [1], random lasing [2--6] and light harvesting for solar devices [7,8]. It is well known that the light transport depends on the dimensionality of the material structure [9]. One--dimensional systems are realized by modulating the dielectric constant in a linear arrangement, as, for example, a random multilayer [3,10,11]. For sake of clarity, a periodic alternation of the dielectric constant results in a one--dimensional photonic crystal [12--15], while a modulation of the dielectric constant that follow a deterministic generation rule gives rise to a quasicrystal [16--20]. In one--dimensional disordered photonic systems clear features related to Anderson localization have been observed [21,22], but also transport phenomena as optical Bloch oscillations and necklaces states [23--26]. Studying the light transmission for different lengths of these systems, oscillations of the average transmission, in a specific spectral range, have been observed as a function of the sample length [27]. Moreover, by grouping high refractive index layers in one--dimensional clusters, randomly distributed within layers of low refractive index, the total transmission, in a specific spectral range, oscillates as a function of the cluster size [28,29]. In this work, we investigated the light transmission properties of disordered photonic structures in which the high refractive index layers are aggregated in clusters. The size of the high refractive index layer clusters is sorted from a family of power law distribution functions. We studied the total light transmission, within the photonic band gap of the periodic crystal, as a function of the power law function exponent shaping the distribution. We discovered that the total light transmission trend as a function of the exponent a of the distribution can be fitted, 0≤a≤3.5, with a sigmoidal function.
MethodsWe realized one dimensional photonic structures made by 360 layers with refractive index n1=1.6 and a thickness d1=70nm, and by 2520 layer with refractive index n2=1.4 and a thickness d2=80nm. Thus, the ratio of high/low refractive index layers in the structure is 1/8.