120-GBaud 16-QAM silicon photonics IQ modulator for data center interconnection.

We demonstrated all-silicon IQ modulators (IQMs) operating at 120-GBaud 16-QAM with suitable bandwidth, and output power. We required optical signal-to-noise-ratio (rOSNR) that have promising potential to be used in 800-Gbps small-form-factor pluggable transceivers for data center interconnection. First, we tested an IQM chip using discrete drivers and achieved a per-polarization TX output power of -18.74 dBm and an rOSNR of 23.51 dB over a 100-km standard SMF. Notably, a low BER of 1.4e-3 was obtained using our SiP IQM chip without employing nonlinear compensation, optical equalization, or an ultra-wide-bandwidth, high-ENOB OMA. Furthermore, we investigated the performance of a 3D packaged transmitter by emulating its frequency response using an IQM chip, discrete drivers, and a programmable optical filter. With a laser power of 17 dBm, we achieved a per-polarization output power of -15.64 dBm and an rOSNR of 23.35 dB.

Coupling angle tolerance of the 850-nm single-mode VCSEL output collimated by lensed OM4-MMF or GI-SMF for a NRZ-OOK link.

By collimating the single-mode (SM) vertical-cavity surface-emitting laser (VCSEL) at 850 nm with either the OM4 multi-mode fiber (OM4-MMF) or the graded-index single-mode fiber (GI-SMF) with lensed end-face, the directly encoded non-return-to-zero on-off keying (NRZ-OOK) data transmission performance is characterized when tilting the coupling angle with respect to the surface normal of the SM-VCSEL. In comparison with the lensed OM4-MMF and lensed SMF coupling, the lensed OM4-MMF collimator shows a large coupling angle tolerance with the coupling efficiency only degraded by 5% when enlarging the tilted angle from 0° to 10°. In contrast, the lensed GI-SMF collimator attenuates the coupled SM-VCSEL output by more than 50% when tilting the coupling angle up to 10°. For the lensed OM4-MMF coupling, the receivable NRZ-OOK data rate in BtB and after 100-m OM4-MMF cases can achieve 50 Gbit/s with its corresponding BER degraded from 6.5 × 10-10 to 8.8 × 10-10 when enlarging its tilting angle ranged from 0° to 10°. By changing the collimator to the lensed SMF, the decoded BER significantly degrades from 5.8 × 10-5 to 1.2 × 10-1 when coupling and transmitting the NRZ-OOK data at 50 Gbit/s. Owing to the low coupling efficiency via the lensed SMF collimator, the error-free NRZ-OOK data rate under the lensed SMF coupling somewhat decreases to 35 Gbit/s in the BtB link and to 32 Gbit/s after the 100-m GI-SMF link with allowable coupling angle tilted from 0° to 4°. This work confirms the applicability of the lensed MMF or SMF collimator for coupling the SM-VCSEL output with a relatively large tolerance on the tilting angle with respect to the surface normal of the SM-VCSEL.

Ultra-low-power four-wave mixing wavelength conversion in high-Q chalcogenide microring resonators.

A compact Ge11.5As24Se64.5 chalcogenide microring resonator is fabricated with an intrinsic quality factor of 3.0×105 in the telecom band. By taking advantage of the strong nonlinearity and cavity enhancement, highly efficient wavelength conversion via four-wave mixing is demonstrated using a microring resonator. Conversion efficiency of -33.7dB is obtained by using an ultra-low pump power of 63.8 µW. This work shows that Ge11.5As24Se64.5 chalcogenide microring devices are promising for quantum photonics.

High data rate few-mode transmission over graded-index single-mode fiber using 850 nm single-mode VCSEL.

A few-mode transmission system is proposed using 850 nm single-mode VCSEL based transceivers over graded-index single-mode fibers for high data rate data center applications. A graded-index single-mode fiber that supports two mode groups at 850 nm window with a high modal bandwidth of 48.3 GHz·km is realized for the first time. 25 Gb/s transmission experiments using a 850 nm single-mode VCSEL over such fiber demonstrate that the system can support a link distance up to 1.5 km. Additionally, link model analysis provides more insights on how fiber and single-mode VCSEL parameters impact the system performance.

Four-wave mixing Bragg scattering in hydrogenated amorphous silicon waveguides.

We demonstrate 15% on-chip conversion efficiency of four-wave mixing Bragg scattering in a hydrogenated amorphous silicon waveguide with only 55 and 194 mW peak pump powers in the waveguide. The lightwaves can be maintained in the telecommunication band, and the operational bandwidth is measured to be larger than 4 nm.

High-speed all-optical NAND/AND logic gates using four-wave mixing Bragg scattering.

A high-speed all-optical NAND logic gate is proposed and experimentally demonstrated using four-wave mixing Bragg scattering in highly nonlinear fiber. NAND/AND logic functions are implemented at two wavelengths by encoding logic inputs on two pumps via on-off keying. A 15.2-dB depletion of the signal is obtained for NAND operation, and time domain measurements show 10-Gb/s NAND/AND logic operations with open eye diagrams. The approach can be readily extended to higher data rates and transferred to on-chip waveguide platforms.

Adjoint-optimized metasurfaces for compact mode-division multiplexing.

Optical fiber communications rely on multiplexing techniques that encode information onto various degrees of freedom of light to increase the transmission capacity of a fiber. However, the rising demand for larger data capacity is driving the need for a multiplexer for the spatial dimension of light. We introduce a mode-division multiplexer and demultiplexer design based on a metasurface cavity. This device performs, on a single surface, mode conversion and coupling to fibers without any additional optics. Converted modes have high fidelity due to the repeated interaction of light with the metasurface's phase profile that was optimized using an inverse design technique known as adjoint analysis. We experimentally demonstrate a compact and highly integrated metasurface-based mode multiplexer that takes three single-mode fiber inputs and converts them into the first three linearly polarized spatial modes of a few-mode fiber with fidelities of up to 72% in the C-band (1530-1565 nm).

Study on the effect of surface characteristics of short-pulse laser patterned titanium alloy on cell proliferation and osteogenic differentiation.

Concise, low-cost preparation of titanium alloy implants with high cell proliferation and osteogenic differentiation is urgently needed. Nanosecond laser ablation of titanium alloy has the advantages of short processing time, less pollution, and non-contact. In this research, we adopt a nanosecond UV laser to process the closed groove and cross groove titanium alloys with length to width ratio of 1:1, 2.5:1, 4:1, and 6:1. The surface morphology, surface roughness, phase, element distribution, surface chemistry, and wettability were characterized. The effect of the patterned surface's properties on the adhesion, proliferation, and osteogenic differentiation of stem cells was studied. The results show the laser-ablated lattice structure's surface energy can increase rapidly in the natural environment. The cell adhesion of stem cells on a lattice structure with low roughness and high surface energy is optimal. The element concentration at the ablated edges is higher than at the bottom under Marangoni and surface tension. Stem cells preferentially adhere to the ablated edges with high roughness, element concentration, and hardness. Cell differentiation is chiefly affected by patterning structure. On the surface of the boss structure with a length to width ratio of 2.5:1, the proportion of cell length to diameter is about 2.5, and the cell area is greater. The osteogenic differentiation of cells is the highest on the surface.

Numerical investigation of the tribological performance of micro-dimple textured surfaces under hydrodynamic lubrication.

Surface texturing is an important approach for controlling the tribological behavior of friction pairs used in mechanical and biological engineering. In this study, by utilizing the method of three-dimensional computational fluid dynamics (CFD) simulation, the lubrication model of a friction pair with micro-dimple array was established based on the Navier-Stokes equations. The typical pressure distribution of the lubricant film was analyzed. It was found that a positive hydrodynamic pressure is generated in the convergent part of the micro-dimple, while a negative hydrodynamic pressure is generated in the divergent part. With suitable parameters, the total integration of the pressure is positive, which can increase the load-carrying capacity of a friction pair. The effects of the micro-dimple parameters as well as fluid properties on tribological performance were investigated. It was concluded that under the condition of hydrodynamic lubrication, the main mechanism for the improvement in the tribological performance is the combined effects of wedging and recirculation. Within the range of parameters investigated in this study, the optimum texture density is 13%, while the optimum aspect ratio varies with the Reynolds number. For a given Reynolds number, there exists a combination of texture density and aspect ratio at which the optimum tribological performance could be obtained. Conclusions from this study could be helpful for the design of texture parameters in mechanical friction components and even in artificial joints.