Si photonic waveguides with broken symmetries: applications from modulators to quantum simulations

Abstract

Symmetries of waveguides determine fundamental properties of photons such as mode profiles, polarisation, and effective refractive indexes as well as practical properties affecting the propagation loss. Here, we review our recent progress on manipulating symmetries of silicon (Si) photonic waveguides. Starting from the strategic choice of Si-On-Insulator (SOI) wafer specifications, we established the process technologies to fabricate Si wire and slot waveguides with atomically-flat interfaces, defined by Si (111) planes. These waveguides have relatively low propagation loss (∼ 1 dB/cm), even though they were fabricated in a university line. By combining patterning and re-growth of deposited amorphous Si, we also fabricated an Si slot waveguide with a nano-meter-scale vertical oxide layer, which is useful for optical modulators and various sensing applications. We also fabricated a horizontal slot waveguide using our manually bonded double-SOI substrate. The self-limited alkali-wet-etching allowed us to pattern the bottom SOI layer on top of the top SOI layer, by properly designing the mask to align along the mirror asymmetric Si (110) surface, allowing to access to top and bottom SOI layers individually through connected multiple-fin arrays. The patterning technique can be readily applicable to the other platform such as Si/LiNbO 3 -hybrid wafers, and we discuss our design of electro-optic (EO) modulator towards zero-power consumptions. We also investigate photonic crystal waveguides with broken mirror symmetries. By manipulating the mismatch between adjacent photonic crystals across the waveguide made of line defects, we could continuously control the band gap of the photonic crystals. Moreover, the phase profiles of modes exhibited photonic graphene and poly-acetylene shapes, made of optical vortices with optical orbital angular momentum (OAM). This shows that the most energetically favourable configuration of a photonic material under the triangular lattice is topologically equivalent to an organic material. We discuss the potential for the photonic organic chemistry and possible applications in quantum technologies.

Poincaré Rotator for Vortexed Photons

“…One might think that one bus arrangement is enough to generate both left-and right-vortexed states, as demonstrated in previous works [29,68]. In our case, however, we are considering to connect the waveguides to integrated Si photonic optical modulators [70,71,77] to allow the phase-shift for left-and right-vortices. Unfortunately, the coupling efficiency to a ring resonator from a waveguide is not high [70,78,79], and it is extremely sensitive to temperatures.…”

“…In order to achieve it, the amplitude of the input 1 must be cos( /2) and the amplitude of the input 2 must be sin( /2), while the phase factor of the input 1 must be e −i /2 and the phase factor of the input 2 must be e i /2 . This is easily achievable in a Si photonic platform [70,71]. Therefore, the vortexed state can be controlled in our hyper-Poincaré sphere (Figure 15).…”

“…The device structure is schematically shown in Figure 1. We assume the use of Si-On-Insulator (SOI) substrate with the top Si layer thickness t of 220 nm, on the buried-oxide (BOX) thickness of 2µm or beyond on top of the supporting Si substrate [70,71]. Two standard straight wire waveguides are designed to be single mode with the width W of 440 nm.…”

“…In particular, the micro-gears [29,68,69] in a silicon (Si) photonic platform [70,71] are promising to encode various vortexed states, such as amplitudes, phases, and vorticities (topological charges) for high-speed optical communications [72] as well as for potential quantum communications [46].…”

Diode-Like Current Leakage and Ferroelectric Switching in Silicon SIS Structures with Hafnia-Alumina Nanolaminates

“…Recently, the high energy efficiency of optical switches based on semiconductor-insulator-semiconductor (SIS) structures has been reported, reaching femto- and even attojoules per operation when using a design of hybrid structures based on III-V/Si semiconductor pairs [ 1 , 2 , 3 , 4 , 5 ]. The development of more energy-efficient switches, compared to thermo-optical or MEMS devices, means real progress in the implementation of not only fast intrachip communication with switch frequencies of up to 200 GHz [ 4 , 5 , 6 , 7 , 8 ], but also perspectives in building deep learning artificial neural networks based on ferroelectric transistors (FeFET), optical or quantum gates [ 9 , 10 ] compatible with the industrial CMOS technology. Hybrid III-V/Si structures noticeably increase the complexity of mass production of integral circuits (ICs) by the industrial CMOS silicon technology.…”