Wide Angle Polarization-Independent 6-Bit Optical Modulator Using Phase Change Material

Reflective optical modulators that dynamically control the intensity or phase of the reflected light are indispensable for free-space optical communication. However, achieving angle, wavelength, and polarization independence with high modulation depth remains a key challenge. Here, we present a reflective-optical modulator based on a phase change material (Ge₂Sb₁Te₄), which offers extraordinary characteristics including a high change in both the real (Δn ≈ 3.44) and imaginary (Δk ≈ 1.3) components of the refractive index, along with a low absorption coefficient (k ≈ 0.03) in the amorphous phase. By integration of Ge₂Sb₁Te₄ into a planar cavity capped with SiN_x without a meta-surface or a plasmonic architecture, an efficient modulation of 1550 nm light with an extremely high modulation depth (ΔR) of 87% is achieved at near-normal incidence. Furthermore, 64 discrete reflectance states between the crystalline and amorphous phases are realized through controlled optical excitation, enabling 6-bit multilevel encoding for high-density optical data transmission.