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 (Ge 2 Sb 1 Te 4 ), which offers extraordinary characteristics including a high change in both the real (Δ n ≈ 3.44) and imaginary (Δ k ≈ 1.3) components of the refractive index, along with a low absorption coefficient ( k ≈ 0.03) in the amorphous phase. By integration of Ge 2 Sb 1 Te 4 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 (Δ R ) 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.