Junying Li

Chalcogenide glass-on-graphene photonics

Two-dimensional (2D) materials are of tremendous interest to integrated photonics, given their singular optical characteristics spanning light emission, modulation, saturable absorption and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. Here, we present a new route for 2D material integration with planar photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material that can be directly deposited and patterned on a wide variety of 2D materials and can simultaneously function as the light-guiding medium, a gate dielectric and a passivation layer for 2D materials. Besides achieving improved fabrication yield and throughput compared with the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light–matter interactions in the 2D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as graphene-based mid-infrared waveguide-integrated photodetectors and modulators.Exploiting the peculiar properties of graphene, a series of high-performance glass-on-graphene devices, such as polarizers, thermo-optic switches and mid-infrared waveguide-integrated photodetectors and modulators are realized.

Monolithically integrated stretchable photonics

Mechanically stretchable photonics provides a new geometric degree of freedom for photonic system design and foresees applications ranging from artificial skins to soft wearable electronics. Here we describe the design and experimental realization of the first single-mode stretchable photonic devices. These devices, made of chalcogenide glass and epoxy polymer materials, are monolithically integrated on elastomer substrates. To impart mechanical stretching capability to devices built using these intrinsically brittle materials, our design strategy involves local substrate stiffening to minimize shape deformation of critical photonic components, and interconnecting optical waveguides assuming a meandering Euler spiral geometry to mitigate radiative optical loss. Devices fabricated following such design can sustain 41% nominal tensile strain and 3000 stretching cycles without measurable degradation in optical performance. In addition, we present a rigorous analytical model to quantitatively predict stress-optical coupling behavior in waveguide devices of arbitrary geometry without using a single fitting parameter.

Gamma radiation effects in amorphous silicon and silicon nitride photonic devices

Understanding radiation damage is of significant importance for devices operating in radiation-harsh environments. In this Letter, we present a systematic study on gamma radiation effects in amorphous silicon and silicon nitride guided wave devices. It is found that gamma radiation increases the waveguide modal effective indices by as much as 4×10-3 in amorphous silicon and 5×10-4 in silicon nitride at 10 Mrad dose. This Letter further reveals that surface oxidation and radiation-induced densification account for the observed index change.

On-chip infrared spectroscopic sensing: Redefining the benefits of scaling

Infrared (IR) spectroscopy is widely recognized as a gold standard technique for chemical analysis. Recent strides in photonic integration technologies offer a promising route towards enabling miniaturized, rugged platforms for IR spectroscopic analysis. Here we show that simple size scaling by replacing bulky discrete optical elements used in conventional IR spectroscopy with their on-chip counterparts is not a viable route for on-chip infrared spectroscopic sensing, as it cripples the system performance due to the limited optical path length accessible on a chip. In this context, we discuss two novel photonic sensor designs uniquely suited for microphotonic integration. We leverage strong optical and thermal confinement in judiciously designed microcavities to circumvent the thermal diffusion and optical diffraction limits in conventional photothermal sensors and achieve parts-per-billion level gas molecule limit of detection. In the second example, an on-chip spectrometer design with Fellgetts advantage is proposed for the first time. The design enables sub-nm spectral resolution on a millimeter-sized, fully packaged chip without mechanical moving parts.

Reconfigurable photonics enabled by optical phase change materials (Conference Presentation)

The dramatic optical property change of optical phase change materials (O-PCMs) between their amorphous and crystalline states potentially allows the realization of reconfigurable photonics devices with low power consumption, such as optical switches and routers, reconfigurable meta-optics, displays, and photonic memories. However, conventional O-PCMs, such as VO2 and Ge2Sb2Te5, are inherently plagued by their excessive optical losses even in dielectric states, limiting their optical performance and hence application space. In this talk, we present the development of a new group of O-PCMs and their implementations in novel photonic devices. Ge-Sb-Se-Te (GSST), obtained by partially substituting Te with Se in traditional GST alloys, feature unprecedented broadband optical transparency covering the telecommunication bands to LWIR. Capitalizing on the dramatically-enhanced optical performance, novel non-volatile, reconfigurable on-chip photonics devices and architectures are demonstrated. GSST-integrated Si photonics based on the material innovation and novel “non-perturbative” designs exhibit significantly improved switching performance over state-of-the-art GST-based approaches. The technology is further scalable to realize non-blocking matrix switches with arbitrary network complexity, paving the path towards high performance reconfigurable photonics chips.

Chalcogenide glass-on-2D-materials photonics (Conference Presentation)

Two-dimensional (2-D) materials are of tremendous interest to silicon photonics given their singular optical characteristics spanning light emission, modulation, saturable absorption, and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. Here we present a new route for 2-D material integration with silicon photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material which can be directly deposited and patterned on a wide variety of 2-D materials and can simultaneously function as the light guiding medium, a gate dielectric, and a passivation layer for 2-D materials. Besides achieving improved fabrication yield and throughput compared to the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light-matter interactions in the 2-D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators based on graphene and black phosphorus.

Broadband low-loss optical phase change materials and devices (Conference Presentation)

Optical phase change materials (O-PCMs) are a unique class of materials which exhibit extraordinarily large optical property change (e.g. refractive index change > 1) when undergoing a solid-state phase transition. These materials, exemplified by Mott insulators such as VO2 and chalcogenide compounds, have been exploited for a plethora of emerging applications including optical switching, photonic memories, reconfigurable metasurfaces, and non-volatile display. These traditional phase change materials, however, generally suffer from large optical losses even in their dielectric states, which fundamentally limits the performance of optical devices based on traditional O-PCMs. In this talk, we will discuss our progress in developing O-PCMs with unprecedented broadband low optical loss and their applications in novel photonic systems, such as high-contrast switches and routers towards a reconfigurable optical chip.

Suspended chalcogenide microcavities for ultra-sensitive chemical detection

Here we report on the fabrication and characterization of air-clad on-chip chalcogenide microdisk cavities (Q=32,000) at wavelengths of 2.0–2.5 microns for infrared spectroscopy. In addition, we analyze a method of photothermal sensing that leverages high-thermal confinement in optical microcavities that is theoretically capable of achieving part-perbillion (ppb) level detection of trace gas molecules.