arXiv subjects

Andrew P. Knights

Publications and source records attributed to Andrew P. Knights.

6 recordsLinked to original sources

arXiv2026

Erbium-implanted tellurite waveguides with low-temperature post-implantation activation and signal enhancement

In this paper, we demonstrate erbium ion implantation and signal enhancement in tellurium oxide hybrid waveguides. Silicon nitride strips with a width of 2 $μ$m and a height of 100 nm were clad with a 110-nm-thick tellurium oxide layer to form hybrid waveguides, followed by erbium ion implantation at an energy of 200 keV and a dose of $1\times10^{15} ions/cm^{2}$, with a projected peak implantation depth of approximately 50 nm into the tellurium oxide layer. After low-temperature annealing at 150 °C for 30 minutes, the propagation loss decreased from 1.7 to 0.9 dB/cm, while the erbium lifetime increased from 40 $μ$m to over 800 $μ$m. We measure a small-signal enhancement of 9 dB in an 11-cm-long waveguide at a wavelength of 1550 nm. These results demonstrate progress towards a low-temperature post-ion implantation process for incorporating erbium and other rare earth ions into tellurium oxide films for integrated photonic applications.

physics.optics↗

arXiv2026

Spontaneous Nanopatterning and Strain Relaxation in SiGe Layers Grown by Oxidative Solid Phase Epitaxy

The wafer-scale monolithic integration of III-V materials on Si would lead to revolutionary optoelectronic hardware for data, computing and other applications. However, heteroepitaxy of III-Vs on Si requires overcoming the large lattice and thermal mismatches between the materials and reducing threading dislocations densities. In this work, we explore the oxidative solid phase epitaxy (SPE) of Ge+ implanted Si(111) to form ultra-thin strain-relieving SiGe metamorphic buffer layers for heteroepitaxy on Si. The SPE process is shown to result in a nanopatterning of the Ge concentration variation across the sample surface, visible by scanning and transmission electron microscopy (SEM and TEM). The concentration patterning is the result of a hexagonal network of Shockley partial dislocations at the SiGe/Si interface. Analyzing the pattern spacing observed by SEM is demonstrated as an easy, non-destructive method for obtaining the local strain state of SiGe layers. This work is important for engineering ultra-thin SiGe metamorphic buffer layers for III-V optoelectronics heteroepitaxy on the silicon platform.

cond-mat.mtrl-sci↗

arXiv2025

Silicon photonic paper-clip spiral delay lines with ultra-low delay loss of 0.5 dB/ns

In this work, we demonstrate compact paper-clip spiral silicon photonic waveguides with ultra-low delay loss. We characterize the optical loss and group delay of single-mode and multi-mode silicon waveguides across the telecom O-, S-, C-, and L-bands. For spiral devices with 2.0-μm-wide waveguides, we measure propagation losses of 0.11 and 0.06 dB/cm at 1310 and 1550 nm, representing 10- and 20-times improvements, respectively, compared to the singlemode waveguides. Additionally, we observe a group delay of 1163 ps for a 9.5 cm-long waveguide with a compact device footprint of (0.30 {\times} 3.00) mm2, yielding a delay loss of 0.5 dB/ns. These results are highly promising for large-scale silicon photonic integration, delay lines, and on-chip programmable systems.

physics.optics↗

arXiv2024

Ultra-thin strain-relieving Si$_{1-x}$Ge$_x$ layers enabling III-V epitaxy on Si

The explosion of artificial intelligence, possible end of Moore's law, dawn of quantum computing and continued exponential growth of data communications traffic have brought new urgency to the need for laser integration on the diversified Si platform. While diode lasers on III-V platforms have long powered internet data communications and other optoelectronic technologies, direct integration with Si remains problematic. A paradigm-shifting solution requires exploring new and unconventional materials and integration approaches. In this work, we show that a sub-10-nm ultra-thin Si$_{1-x}$Ge$_x$ buffer layer fabricated by an oxidative solid-phase epitaxy process can facilitate extraordinarily efficient strain relaxation. The Si$_{1-x}$Ge$_x$ layer is formed by ion implanting Ge into Si(111) and selectively oxidizing Si atoms in the resulting ion-damaged layer, precipitating a fully strain-relaxed Ge-rich layer between the Si substrate and surface oxide. The efficient strain relaxation results from the high oxidation temperature, producing a periodic network of dislocations at the substrate interface, coinciding with modulations of the Ge content in the Si$_{1-x}$Ge$_x$ layer and indicating the presence of defect-mediated diffusion of Si through the layer. The epitaxial growth of high-quality GaAs is demonstrated on this ultra-thin Si$_{1-x}$Ge$_x$ layer, demonstrating a promising new pathway for integrating III-V lasers directly on the Si platform.

cond-mat.mtrl-sci↗

arXiv2022

Subwavelength grating metamaterial waveguides and ring resonators on a silicon nitride platform

We propose and demonstrate subwavelength grating (SWG) metamaterial waveguides and ring resonators on a silicon nitride platform for the first time. The SWG waveguide is engineered such that a large overlap of 53% of the Bloch mode with the top cladding material is achieved, demonstrating excellent potential for applications in evanescent field sensing and light amplification. The devices, which have critical dimensions greater than 100 nm, are fabricated using a commercial rapid turn-around silicon nitride prototyping foundry process using electron beam lithography. Experimental characterization of the fabricated device reveals excellent ring resonator internal quality factor (2.11x10^5) and low propagation loss (~1.5 dB/cm) in the C-band, a significant improvement of both parameters compared to silicon based SWG ring resonators. These results demonstrate the promising prospects of SWG metamaterial structures for silicon nitride based photonic integrated circuits.

physics.optics↗

arXiv2021

A thulium-silicon hybrid microdisk laser

Silicon photonics technology enables compact, low-power and cost-effective optical microsystems on a chip by leveraging the materials and advanced fabrication methods developed over decades for integrated silicon electronics. Silicon foundries now provide many standard building blocks required for high-performance optical circuits, including passive components such as optical waveguides, filters and (de-)multiplexors and active optoelectronic components such as high-speed modulators, switches and photodetectors. However, because silicon is a poor light emitting material, on-chip light sources are still a significant challenge for foundry offerings. Current light-source integration methods are viewed as complex, requiring incompatible and/or expensive materials and processing steps. Here we report on an ultra-compact silicon photonic laser consisting of a thulium-silicon hybrid microdisk resonator. The microdisk design is straightforward and compatible with the fabrication steps and device dimensions available in all silicon photonics foundries, whereas the gain medium is added in a backend (final step), room temperature sputter deposition. This approach allows for low-cost and high-volume wafer-scale manufacturing and co-integration of light sources with silicon passive and active devices with no adjustment to standard process flows. The hybrid laser is pumped at standard telecom wavelengths around 1.6 μm and emits around 1.9 μm, which is within an emerging spectral region of significant interest for communications, nonlinear and quantum optics, and sensing on silicon.

physics.optics↗