Abstract
Standard multilayer dielectric beam splitter is limited by spectrum interference ripples, high production complexity and strict tolerance of the thickness. Here we report a compositionally tuned TiO2-SiO2 mixed dielectric thin film as an effective single-layer broadband beam splitter. The composite films were produced on glass substrates with pulsed laser deposition (PLD) which allowed fine control over layer thickness and equilibrium stoichiometry by varying the number of laser pulses. The TiO₂:SiO₂ ratio was optimized using the effective medium model of Lorentz-Lorenz to attain a refractive index in between (~1.95-2.05) for controlled amplitude division with no multilayer interference stacking. X-ray diffraction (XRD) study revealed a nanostructured mixed-phase morphology using crystallite sizes in the range of 16-46 nm, ideal for low-scattering optical applications. The transmission-reflection ratios were steady and adjustable from 65/35 to 80/20 with small spectral ripples (ΔT_ripple < 4%) as demonstrated by UV–Vis–NIR spectroscopy in the range 400–1100 nm. The experimental results agree well with transfer matrix method (TMM) simulations, which validates the effective refractive index technique. The suggested single-layer design outperforms existing multilayer designs in terms of structural complexity, thickness sensitivity and number of manufacturing processes, while maintaining broadband and spectrally flat optical performance. Here, we show a simple and scalable way to achieve broadband beam splitting by changing the refractive index in a single dielectric layer.