Design of a Compact Low-Loss Phase Shifter Based on Optical Phase Change Material

Abstract

We propose the design of a nonvolatile, low-loss optical phase shifter based on optical phase change material (O-PCM). The optical phase change material Ge 2 Sb 2 Se 4 Te 1 (GSST), which exhibits low loss at telecommunication wavelength 1.55 µm as compared to other commonly used O-PCMs, is used in this work as the active material. Instead of direct interaction of the waveguide mode with the O-PCM, the design utilizes coupling between the primary SiN strip waveguide and a waveguide formed by O-PCM, in its amorphous state. The phase matching in the amorphous state inhibits the interaction of the waveguide mode with GSST in its highly lossy crystalline state resulting in low loss operation. Due to a high differential refractive index between the two states of GSST, the design requires a very small length of the phase shifter to accumulate the desired phase difference. The overall response of the Mach-Zehnder Interferometer (MZI) configuration using the designed phase shifter shows that the design can be used to obtain optical switching with a very small insertion loss and crosstalk over the entire C-band. Index Terms-Coupled mode analysis, Optical Switches, Phase change materials. I. INTRODUCTION hase shift for optical switching in silicon photonic devices is mainly achieved by free carrier injection [1-3] and thermo-optic effects [4]. These effects give rise to a small change in the refractive index, which results in large device length to obtain the required phase change. The alternative is to use the resonant structures to obtain devices with a small footprint, however, at the expense of low bandwidth and high sensitivity [5,6]. The compact hybrid plasmonic-photonic switches based on 3-waveguide directional couplers have also been reported, but the associated insertion loss is high [7,8]. In recent years, optical phase change materials (O-PCMs) have

Transient Tap Couplers for Wafer-Level Photonic Testing Based on Optical Phase Change Materials

“…For this application, we chose GSST as the O-PCM, since it claims a large refractive index contrast (Δ n = 1.8 at 1550 nm) while showing significantly reduced optical attenuation compared to the archetypal Ge 2 Sb 2 Te 5 (GST) alloy . These desirable attributes of GSST have previously been exploited in low-loss on-chip optical switch designs. ,− In addition to their excellent optical properties, chalcogenide O-PCMs are also uniquely poised for platform-agnostic integration given their amorphous structure and low processing temperatures. , …”

Scaling Up Silicon Photonic-based Accelerators: Challenges and Opportunities

“…Phase change materials (PCMs) such as Ge 2 Sb 2 Se 4 Te(GSST ) have been demonstrated as compact phase shifters in which the optical phase shift is obtained by tuning the state of the material from amorphous and crystalline 104,105 . Being able to sustain their crystallization state with the absence of power renders them as good candidates for tuning low-speed weights in SiP implementations with no static power consumption.…”

Rapid characterisation of linear-optical networks via PhaseLift

“…Notably, a programmable optical circuit able to generate light amplitudes proportional to RECR vectors requires to set as little as four alternative phases and two intensity levels at each input mode. We envisage that photonic devices can be optimised to implement such discrete input configurations; even phaseshifting strategies that are not tunable across a continuous range of phase shifts can be advantageously used to this scope [47,48]. Performance guarantees.…”