A Segmented Heater-Driven, Low-Loss, Reconfigurable Photonic Phase-Change Material-Based Phase Shifter

TL;DR

This work addresses the challenge of achieving finely spaced, non-volatile, multilevel phase shifts in PCM-based photonic phase shifters. It first analyzes a GeSe PCM on a silicon waveguide with a conventional rectangular heater under PWM and PAM, revealing non-uniform heating leads to highly non-linear phase steps. To overcome this, it introduces a segmented heater with gradually increasing width along the light propagation direction, producing smoother amorphization across multiple GeSe segments and enabling hundreds of well-spaced phase levels between 0 and $\pi$ with low insertion loss ($\leq 0.6$ dB). The results, validated under both PWM and PAM driving, show a markedly smoother phase response and a large, high-resolution phase-tuning range, making the approach favorable for energy-efficient, high-precision photonic neural networks and programmable PICs. The method holds promise for extending to other waveguides and PCM materials while reducing energy requirements for large-scale photonic systems.

Abstract

Phase-change material (PCM)-based non-volatile multilevel phase shifters are key components in photonic integrated circuits. Electrically, multiple phase levels can be encoded by controlling the heater power and employing different microheater architectures to induce varying degrees of PCM amorphization. However, encoding a large number of levels is not straightforward. In this work, we first investigate a phase shifter structure based on a GeSe PCM integrated on top of a silicon-on-insulator waveguide, employing a simple rectangular-shaped heater under pulse-width modulation (PWM). We numerically demonstrate that multilevel phase shifts can be achieved because of non-uniform heating in the GeSe PCM layer. However, the resulting phase levels for this basic configuration are highly non-linear because of the uniform power dissipation along the light propagation direction characterized by the same cross-section. To overcome this limitation, we designed a novel PCM-based phase shifter with a segmented heater whose width gradually increases along the light propagation direction. This configuration enables the encoding of hundreds of well-spaced phase levels between 0 and $π$, facilitated by smoother amorphization arising from the combined effects of non-uniform heating across segments and within each segment, while achieving an insertion loss of only 0.6 dB in the worst case. Furthermore, when evaluating both heater architectures under pulse amplitude modulation (PAM) at a fixed pulse duration, we observe behavior consistent with the trends observed for PWM, confirming the superior performance of the segmented heater design.

Figures (9)

• Figure 1: Schematic of the cross-section of the considered phase shifter structure for the thermal calculations.
• Figure 2: Temporal variation of temperature at four specific locations within the GeSe.
• Figure 3: (a) Schematic of the simulation domain for the calculation of optical propagation characteristics; spatial distribution of electric field intensity in (b) crystalline and (c) amorphous states of GeSe.
• Figure 4: Variation of (a) phase shift, (b) amorphous fraction, (c) difference between adjacent phase shift levels (d$\phi$), and (d) the change in confinement factor in GeSe ($\Delta$CF), with the pulse duration for a heater with constant-width along the light propagation direction.
• Figure 5: Variation of (a) phase shift, and (b) difference between adjacent phase shift levels (d$\phi$), with the pulse power