Ultra-compact nonvolatile phase shifter based on electrically reprogrammable transparent phase change materials

Abstract

Optical phase shifters constitute the fundamental building blocks that enable programmable photonic integrated circuits (PICs)—the cornerstone of on-chip classical and quantum optical technologies [1, 2]. Thus far, carrier modulation and thermo-optical effect are the chosen phenomena for ultrafast and low-loss phase shifters, respectively; however, the state and information they carry are lost once the power is turned off—they are volatile. The volatility not only compromises energy efficiency due to their demand for constant power supply, but also precludes them from emerging applications such as in-memory computing. To circumvent this limitation, we introduce a phase shifting mechanism that exploits the nonvolatile refractive index modulation upon structural phase transition of Sb2Se3, a bi-state transparent phase change material (PCM). A zero-static power and electrically-driven phase shifter is realized on a CMOS-backend silicon-on-insulator platform, featuring record phase modulation up to 0.09 π/µm and a low insertion loss of 0.3 dB/π, which can be further improved upon streamlined design. Furthermore, we demonstrate phase and extinction ratio trimming of ring resonators and pioneer a one-step partial amorphization scheme to enhance speed and energy efficiency of PCM devices. A diverse cohort of programmable photonic devices is demonstrated based on the ultra-compact PCM phase shifter.

Electrically programmable phase-change photonic memory for optical neural networks with nanoseconds in situ training capability

“…Finally, the PIN diode microheater can reduce the driving voltage needed for phase switching of PCM compared to the PIP or NIN doping profile. 31,40…”

Nonvolatile Multilevel Switching of Silicon Photonic Devices with In2O3/GST Segmented Structures

“…[36] For the sizes of PCMs which are usually on the wavelength scale in photonic applications, electrical switching using external resistive heaters is suitable for achieving uniform phase change in large-scale arrays with increased integration density and does not require the sophisticated excitation or alignment processes in the optical switching scheme. The heaters are based on doped silicon, [13,16,37,38] silicon PIN diode, [15,39] graphene, [40,41] and indium tin oxide (ITO). [11,[42][43][44] As for the doping scheme that has been widely investigated recently, ridge waveguides are required, resulting in increased heat capacity and conductivity, hence higher power consumption.…”

“…[16] In addition, using doped-silicon microheaters with "bridges", a single-step partial amorphization scheme with around ten intermediate states is demonstrated. [38] In this work, we demonstrate repeatable and reversible multi-stage phase transitions of GST between the crystalline and amorphous states induced electro-thermally by using the resistive heater based on transparent conductive oxides (TCOs) In 2 O 3 , which are compatible with diverse material platforms. The In 2 O 3 /GST segmented structure is proposed and demonstrated to enable the capability of multistage phase transitions of a long GST strip (≈10 µm).…”

“…[ 16 ] In addition, using doped‐silicon microheaters with “bridges”, a single‐step partial amorphization scheme with around ten intermediate states is demonstrated. [ 38 ]…”

Investigation of coupling loss caused by misalignment in optical fiber

“…Edge couplers have been designed, manufactured, and tested to target industry-standard SMF-28 silicon photonic fibers. These couplers are fabricated on a SOI platform using a SiN reverse taper and include a process for removing the etch-based substrate that prevents silicone substrate leakage [23]. Numerous studies on the polarization of the fiber (PMF) coupler with novel transmission properties have been conducted [24].…”