Non-volatile electrically programmable integrated photonics with a 5-bit operation

Abstract

Scalable programmable photonic integrated circuits (PICs) can potentially transform the current state of classical and quantum optical information processing. However, traditional means of programming, including thermo-optic, free carrier dispersion, and Pockels effect result in either large device footprints or high static energy consumptions, significantly limiting their scalability. While chalcogenide-based non-volatile phase-change materials (PCMs) could mitigate these problems thanks to their strong index modulation and zero static power consumption, they often suffer from large absorptive loss, low cyclability, and lack of multilevel operation. Here, we report a wide-bandgap PCM antimony sulfide (Sb2S3)-clad silicon photonic platform simultaneously achieving low loss (<1.0 dB), high extinction ratio (>10 dB), high cyclability (>1600 switching events), and 5-bit operation. These Sb2S3-based devices are programmed via on-chip silicon PIN diode heaters within sub-ms timescale, with a programming energy density of $$\sim 10\,{fJ}/n{m}^{3}$$ ~ 10 f J / n m 3 . Remarkably, Sb2S3 is programmed into fine intermediate states by applying multiple identical pulses, providing controllable multilevel operations. Through dynamic pulse control, we achieve 5-bit (32 levels) operations, rendering 0.50 ± 0.16 dB per step. Using this multilevel behavior, we further trim random phase error in a balanced Mach-Zehnder interferometer.

Capping Layer Effects on Sb2S3-Based Reconfigurable Photonic Devices

“…In addition, this π phase shift maximizes extinction ratio, thereby improving switching resolution when multilevel switching functionalities are introduced. 35 Changing the cavity length causes the Q-factor to decrease proportionally. To improve the Q-factor of smaller rings, the coupling gap between the ring and bus can be optimized to increase the cavity finesse.…”

“…We first studied the thermal stability of the Sb 2 S 3 and Ag-SbS PCM layers, as shown in Figure a, which gives the PCM thickness reduction for different capping layer thicknesses upon thermal annealing. The thicknesses of the PCM materials were chosen as 33 nm for Sb 2 S 3 and 30 nm for Ag-SbS because they are similar to the typical PCM thicknesses used to control photonic devices. ,,,,− …”

“…Based on these results, we recommend the use of a ZnS-SiO 2 cap with at least a 30 nm thickness to protect Sb 2 S 3 and Ag-SbS films in PIC devices. Note, the optimized capping thickness would be applicable to most Sb 2 S 3 and Ag-SbS-tuned photonic devices as the corresponding PCM thickness is usually around or less than 30 nm. ,,− Moreover, it is also possible for the 30 nm cap to preserve a thicker PCM layer. Previous literature had reported switching cyclability of up to 7000 times in 60 nm Sb 2 S 3 films capped in thinner Al 2 O 3 films (<60 nm).…”

“…However, the common data storage PCMs are lossy at visible and near-infrared frequencies. Recently, therefore, state-of-the-art PCM-tuned photonic devices using low-loss PCMs, like Sb 2 S 3 and Sb 2 Se 3 , have been proposed as better PCM alternatives to the data storage PCM, Ge 2 Sb 2 Te 5 . , The introduction of wide band gap PCMs has led to the rapid development of low-loss PCM based photonic devices. ,,− …”

“…These properties can influence the device design and switching operations. We chose to focus on Sb 2 S 3 as it exhibits the lowest optical loss among the four PCMs, Ge 2 Sb 2 Te 5 , Ge 2 Sb 2 Se 4 Te 1 , Sb 2 Se 3 , and Sb 2 S 3 , and consequently it is of particular interest for tuning a wide range of photonic devices. ,,− ,,, Previously, we showed that lightly doping Sb 2 S 3 with Ag can lower the crystallization temperature and produce smaller crystallites. , The melting point for lightly Ag-doped Sb 2 S 3 (below 12.5%) along the Sb 2 S 3 –Ag 2 S tie line is also lower, suggesting a lower amorphization temperature. For these reasons, we believe that Ag-doped Sb 2 S 3 has potential applications in tunable photonic devices.…”