Metastable Refractive Index Manipulation in Hydrogenated Amorphous Silicon for Reconfigurable Photonics

Abstract

Hydrogenated amorphous silicon (a‐Si:H) is known for exhibiting light‐induced metastable properties that are reversible upon annealing. While these are commonly associated with the well‐known deleterious Staebler–Wronski effect in the field of thin‐film silicon solar cells, the associated changes in optical properties have not been well studied. Emerging reconfigurable photonic devices and applications can benefit from metastable optical properties where two states of the material are reversibly accessible without the need for continuous stimulation. The study demonstrates a light‐induced 0.3% increase of the metastable refractive index of a‐Si:H that is reversed upon annealing over several cycles using a highly sensitive Fabry–Pérot interferometric technique. Utilizing this technique, a metastable optical switch based on a micro‐ring resonator is demonstrated with reversible distinct switching states separated by 0.3 nm between the light‐soaked and annealed states, a switching extinction exceeding 20 dB and an unchanged Q‐factor, suggesting no excess discernible optical loss. Furthermore, metastable strain changes in a‐Si:H‐based freestanding membrane structures are linked to the observed metastable optical properties and present a possible route to stable photonic devices. Our proof‐of‐concept demonstration showcases a‐Si:H‐based reconfigurable photonics that support multiple purpose photonic integrated circuits, reconfigurable metamaterials, and advanced optomechanical devices.

Reversibly Programmable Photonics via Responsive Polyelectrolyte Multilayer Cladding

“…In this respect, a reconfigurable photonic device has been demonstrated recently by exploiting the metastable refractive index of hydrogenated amorphous silicon. [ 12,13 ] However, this technique is limited by long programming time and small changes in refractive index. On the other hand, optical‐phase changing materials (O‐PCM, e.g., GST), that allow fast programming of high contrast refractive index between two or more stable states have received significant attention.…”

Hybrid Silicon‐Polymer Photodetector Engineered Using Oxidative Chemical Vapor Deposition for High‐Performance and Bias‐Switchable Multi‐Functionality

“…Moreover, the high refractive index of the inorganic layers (e.g., 3.5-4.5 for a-Si:H), suppressing the anti-reflective effect, provokes an additional issue due to an undesirable increment of the reflectance. [15,16] Conductive polymers, such as poly(3,4-ethylene dioxythiophene) (PEDOT) and its derivatives, are promising alternatives for the transport layers due to their low refractive index (1.2-1.6) close to air. [17][18][19][20][21] Furthermore, their relatively affordable and straightforward process is another key benefit for making the materials attractive compared to other inorganic counterparts.…”

Deep Silicon Amorphization Induced by Femtosecond Laser Pulses up to the Mid‐Infrared

“…Only recently, reconfigurable switching operations of amorphous Si ridge waveguides on top of crystalline silicon, fabricated by electron beam lithography, have been demonstrated. [ 4 ] Making available a laser‐based tool for direct writing of embedded waveguides holds great potential for a new booster for the already rapidly growing field of silicon photonics.…”

“…Only recently, reconfigurable switching operations of amorphous Si ridge waveguides on top of crystalline silicon, fabricated by electron beam lithography, have been demonstrated. [4] Making available a laser-based tool for direct writing of embedded waveguides holds great potential for a new booster for the already rapidly growing field of silicon photonics.The ability of ultrashort pulsed laser irradiation to melt silicon and induce resolidification into either the crystalline or amorphous phase has already been observed in 1979 by the Bloembergen group. [5,6] The experimental parameters that influence the melting and quenching kinetics of the materialand thus the final phase obtained-are the laser wavelength, pulse duration, number of pulses, as well as the crystal orientation.…”