Electro-optical phase-change 2 × 2 switching using three- and four-waveguide directional couplers

Abstract

Theoretical modeling and numerical simulation have been performed at λ=2100 nm on silicon-on-insulator channel-waveguide directional couplers in which the outer two Si waveguides are passive and the central waveguide(s) are electro-optical (EO) "islands." The EO channel(s) utilize a 10 nm layer of Ge2Sb2Te5 phase-change-material sited at midlevel of a doped Si channel. A voltage-driven phase change produces a large change in the effective index of the TE(o) and TM(o) modes, thereby inducing crossbar 2×2 switching. A mode-matching method is employed to estimate EO switching performance in the limit of strong interguide coupling. Low-loss switching is predicted for cross-to-bar and bar-to-cross coupling lengths. These "self-holding" switches had active lengths of 500-1000 μm, which are shorter than those in couplers relying upon free-carrier injection. The four-waveguide devices had lower cross talk but higher loss than the three-waveguide devices. For the crystalline phase we sometimes used an active length that was smaller than that for the amorphous phase.

On-Chip Integrated Photonic Devices Based on Phase Change Materials

“…The author simulated electrically switched switches and modulators for an operating wavelength of 2.1 µm and was able to numerically validate an MZI with a device length of 38 µm and insertion loss of −16 dB, while achieving a state transition time of less than 100 ns. In subsequent work, the group also numerically demonstrated modulation of 2.1 µm wavelength using 2 × 2 devices along with one-and two-island waveguides between them [167].…”

Tutorial: Integrated-photonic switching structures

“…At the 2.1 µm wavelength, Liang et al 52,53 performed modeling and simulation of the PCM layer embedded in doped-silicon channels and found fairly good IL and CT metrics in both MZI and directional-coupler configurations for interaction lengths on the 40 µm scale. No confirmation of that yet.…”

Plasmonic nanogap enhanced phase-change devices with dual electrical-optical functionality

“…Phase change materials are considered outstanding candidates for dual mode operation as they in principle provide both electrical and optical modulation functionality. To this effect, several devices implementing non-volatile, optical phase-change materials (PCMs) have been proposed (6)(7)(8), but none have been successfully demonstrated on an integrated platform. This is because the high electrical contrast between the conductive and insulating state in PCMs requires very close spacing between the metal contacts (usually tens of nm) to initiate a phase transition (9).…”