Design of an All‐Dielectric Electro‐Optical Modulator Using Phase Change Material With High Modulation Efficiency

Dynamic amplitude modulation is essential for imaging, beam shaping, optical information processing and free‐space optical communication. However, achieving high‐contrast, broadband, and energy‐efficient amplitude modulators without relying on lossy metal reflectors or mechanically driven architectures remains challenging. Here, we introduce an all‐dielectric, metal‐free reflective optical modulator that combines a Ge 2 Sb 1 Te 4 phase change material (PCM) with a Si/SiO 2 distributed Bragg reflector (DBR). The DBR ensures near‐unity reflectivity at 1550 nm, while a SiN x capping layer suppresses residual reflections. The large refractive‐index contrast of the GST214 (Δ n ≈ 3, Δ k ≈ 1.2) enables a strong transition between highly reflective and highly absorptive states. Transfer‐matrix simulations show a reflectance of ∼96% in the amorphous phase and ∼7% in the crystalline phase at 1550 nm, corresponding to a modulation depth of ∼90%. The design maintains a contrast ratio greater than 80% across 0°–60° incidence angles and a broad wavelength range of 1400–1650 nm. Electro‐thermal modelling confirms reliable electrical switching using a doped‐silicon heater isolated by a thin SiO 2 buffer. Together, these results demonstrate a simple, robust, and broadband PCM‐based platform for next‐generation free‐space and integrated photonic modulators.