Shiyu Sun

High-efficiency wavelength conversion into the 2 μm region has been achieved through Raman enhanced four-wave mixing in a planar silicon waveguide. By aligning the FWM phase-matching conditions with the Raman gain bandwidth, a wavelength conversion efficiency of −25 dB was achieved with a continuous-wave pump power of only ∼45 mW. The maximum Raman enhancement in this hybrid wavelength conversion process is ∼7 dB. Simulations show that by further optimizing the planar waveguide dispersion profile, the wavelength conversion efficiency could be increased to ∼−11 dB using a standard continuous-wave pump source.

Background: The timely management of large-scale wounds and the regeneration of skin appendages constitute major clinical issues. The production of high-precision and customizable artificial skin via 3D bioprinting offers a feasible means to surmount the predicament, within which the selection of bioactive materials and seed cells is critical. This study is aimed at employing skin stem cells and multicomponent hydrogels to prefabricate artificial skin through 3D bioprinting, which enables the regeneration of skin and its appendages.

Silicon photonics is one of the most dynamic fields within photonics, and it has seen huge progress in the last 20 years, addressing applications in data centers, autonomous cars, and sensing. It is mostly focused on the telecommunications wavelength range (1.3 and 1.55 µm), where silicon becomes transparent. In this range, there are excellent light sources and photodetectors, as well as optical fibers operating with extremely low losses and dispersion. It is a technology that hugely benefits from the availability of complementary metal–oxide–semiconductor (CMOS) fabrication infrastructure and techniques used for microelectronics. Silicon and germanium, as another CMOS compatible group IV material, are transparent beyond the wavelength of 2 µm. The mid-IR wavelength range (2–20 µm) is of particular importance as it contains strong absorption signatures of many molecules. Therefore, Si- and Ge-based platforms open up the possibility of small and cost-effective sensing in the fingerprint region for medical and environmental monitoring. In this paper, we discuss the current mid-IR silicon photonics landscape, future directions, and potential applications of the field.

Silicon planar waveguides are designed to maximize the wavelength conversion efficiency via the use of Raman-enhanced four-wave mixing in the telecom band. By investigating the dispersion properties of various rib waveguide structures, the optimum etch depth and width are selected to obtain efficient phase-matching for a continuous-wave pump at 1545 nm. The design benefits from good fabrication tolerance in the structural parameters, which are well within the precision of standard lithography and etching processes. Using the optimized waveguides, simulations show that it is possible to reach conversion efficiencies as high as ∼45 dB for waveguide lengths as short as 4.6 cm, with a pump power of only 130 mW. This enhancement in the conversion efficiency is about 50 dB higher than conventional values for FWM in integrated silicon photonic systems, highlighting the benefits of exploiting the coupling between the two nonlinear processes.

Wavelength conversion via four-wave mixing holds great promise for the construction of broadband and tunable light sources at wavelengths beyond 2 μm. In this work, we design and fabricate a tapered silicon core optical fiber with a dispersion profile that supports efficient conversion spanning the telecom band up to the edge of the mid-infrared spectral region over an extended propagation length. By pumping with a fiber laser centered around 1.99 μm, a tuning range of 690 nm has been measured, although simulations predict that a bandwidth of up to 1255 nm could be observed if a suitable seed source was available. Conversion efficiencies of ∼−30 dB have been obtained over a bandwidth of 380 nm when using an input pump power of only 6 dBm, with a maximum efficiency of −18 dB achieved when the conversion overlaps the strong Raman gain of the silicon core.

Raman scattering provides a convenient mechanism to generate or amplify light at wavelengths where gain is not otherwise available. When combined with recent advancements in high-power fiber lasers that operate at wavelengths ~2 μm, great opportunities exist for Raman systems that extend operation further into the mid-infrared regime for applications such as gas sensing, spectroscopy, and biomedical analyses. Here, a thulium-doped fiber laser is used to demonstrate Raman emission and amplification from a highly nonlinear silicon core fiber (SCF) platform at wavelengths beyond 2 μm. The SCF has been tapered to obtain a micrometer-sized core diameter (~1.6 μm) over a length of 6 cm, with losses as low as 0.2 dB cm⁻¹. A maximum on-off peak gain of 30.4 dB was obtained using 10 W of peak pump power at 1.99 μm, with simulations indicating that the gain could be increased to up to ~50 dB by extending the SCF length. Simulations also show that by exploiting the large Raman gain and extended mid-infrared transparency of the SCF, cascaded Raman processes could yield tunable systems with practical output powers across the 2–5 μm range.

A strong Raman enhancement to the four-wave mixing (FWM) conversion efficiency is obtained in a silicon core fiber (SCF) when pumped with a continuous-wave (CW) source in the telecom band. By tapering the SCFs to alter the core diameter and length, the role of phase-matching on the conversion enhancement is investigated, with a maximum Raman enhancement of ∼15 dB obtained for an SCF with a zero dispersion wavelength close to the pump. Simulations show that by optimizing the tapered waist diameter to overlap the FWM phase-matching with the peak Raman gain, it is possible to obtain large Raman enhanced FWM conversion efficiencies of up to ∼2 dB using modest CW pump powers over wavelengths covering the extended telecom bands.

Raman-enhanced four-wave mixing is investigated in silicon core fibers that have been tapered to control the phase-matching conditions. The large estimated conversion efficiencies (~1 dB) will be useful for high-power amplification of telecom signals.

Silicon core fibers represent a versatile platform for all-fiber integrated nonlinear optical applications. This paper describes the state of the art in four-wave mixing-based parametric amplification and wavelength conversion in silicon fibers that have been tapered to improve the material quality and engineer the dispersion profile. Fibers with submicron core dimensions have been fabricated and used to demonstrate high gain parametric amplification in the C-Band and broadband wavelength conversion extending out to the S- and L-bands. The potential to use these fibers for all-optical signal processing of 20 Gbit/s data signals has also been demonstrated, with a robust all-fiber coupling scheme presented to improve the efficiency and practicality of these devices. These results highlight the potential of silicon core fibers for use in nonlinear signal processing within future telecommunication systems.

We report efficient dual‐mode up‐conversion (UC) and down‐shifting (DS) emission in a single Yb ³⁺ /Er ³⁺ ‐co‐doped β‐NaYF ₄ microcrystals with controlled morphology and size via a simple Na ⁺ ion‐exchange modification (IEM) method. IEM well preserves the crystal structure and monodispersed morphology of hydrothermal‐synthesized β‐Na YF ₄ . Meanwhile, IEM gives rise to the significant enhancement of UC emission intensity up to 3800 times and strongly enhanced DS emission intensity of Er ³⁺ and Yb ³⁺ by several times in β‐Na YF ₄ :Yb ³⁺ ,Er ³⁺ microcrystals. IEM also strongly prolongs the DS emission lifetimes of Er ³⁺ and Yb ³⁺ in visible and near‐infrared region. The enhanced UC and DS emission intensities and prolonged lifetimes in β‐Na YF ₄ :Yb ³⁺ ,Er ³⁺ are mainly ascribed to the dispersing of localized Yb ³⁺ and Er ³⁺ clusters during IEM .