Co-packaged optics (CPO): status, challenges, and solutions.

Due to the rise of 5G, IoT, AI, and high-performance computing applications, datacenter traffic has grown at a compound annual growth rate of nearly 30%. Furthermore, nearly three-fourths of the datacenter traffic resides within datacenters. The conventional pluggable optics increases at a much slower rate than that of datacenter traffic. The gap between application requirements and the capability of conventional pluggable optics keeps increasing, a trend that is unsustainable. Co-packaged optics (CPO) is a disruptive approach to increasing the interconnecting bandwidth density and energy efficiency by dramatically shortening the electrical link length through advanced packaging and co-optimization of electronics and photonics. CPO is widely regarded as a promising solution for future datacenter interconnections, and silicon platform is the most promising platform for large-scale integration. Leading international companies (e.g., Intel, Broadcom and IBM) have heavily investigated in CPO technology, an inter-disciplinary research field that involves photonic devices, integrated circuits design, packaging, photonic device modeling, electronic-photonic co-simulation, applications, and standardization. This review aims to provide the readers a comprehensive overview of the state-of-the-art progress of CPO in silicon platform, identify the key challenges, and point out the potential solutions, hoping to encourage collaboration between different research fields to accelerate the development of CPO technology.

High-efficiency grating coupler based on fast directional optimization and robust layout strategy in 130†nm CMOS process.

We experimentally demonstrated a high-efficiency grating coupler by combining an interleaved etch and apodized structure for fiber-to-chip coupling. The grating coupler was optimized using the fast directional optimization method to achieve apodization. The grating coupler utilized a layout strategy involving an extended mask to avoid alignment errors for a multi-etch structure. The coupling efficiency was measured to be -2.2 dB at a wavelength of 1549 nm with a 3 dB bandwidth of 47 nm. The grating coupler, having no gold reflector, subwavelength index matching structure, or additional material layers, was fabricated using a commercial silicon photonics process with a minimum feature size of 140 nm. This grating coupler design provides a robust and effective coupling scheme and the proposed method can be employed to adopt the design in accordance with standard foundry design rules.

Silicon photonic dual-gas sensor for H2 and CO2 detection.

We report a silicon photonic dual-gas sensor based on a wavelength-multiplexed microring resonator array for simultaneous detection of H2 and CO2 gases. The sensor uses Pd as the sensing layer for H2 gas and a novel functional material based on the Polyhexamethylene Biguanide (PHMB) polymer for CO2 gas sensing. Gas sensing experiments showed that the PHMB-functionalized microring exhibited high sensitivity to CO2 gas and excellent selectivity against H2. However, the Pd-functionalized microring was found to exhibit sensitivity to both H2 and CO2 gases, rendering it ineffective for detecting H2 in a gas mixture containing CO2. We show that the dual-gas sensing scheme can allow for accurate measurement of H2 concentration in the presence of CO2 by accounting for the cross-sensitivity of Pd to the latter.

Silicon microring refractometric sensor for atmospheric CO(2) gas monitoring.

We report a silicon photonic refractometric CO(2) gas sensor operating at room temperature and capable of detecting CO(2) gas at atmospheric concentrations. The sensor uses a novel functional material layer based on a guanidine polymer derivative, which is shown to exhibit reversible refractive index change upon absorption and release of CO(2) gas molecules, and does not require the presence of humidity to operate. By functionalizing a silicon microring resonator with a thin layer of the polymer, we could detect CO(2) gas concentrations in the 0-500ppm range with a sensitivity of 6 × 10(-9) RIU/ppm and a detection limit of 20ppm. The microring transducer provides a potential integrated solution in the development of low-cost and compact CO(2) sensors that can be deployed as part of a sensor network for accurate environmental monitoring of greenhouse gases.

Characteristics of surface plasmon polaritons at a chiral-metal interface.

The characteristics of surface plasmon polaritons at a chiral-metal interface are analyzed in detail. Compared to conventional surface plasmon waves at a dielectric-metal interface, it is shown that chiral surface plasmon waves have distinguishing features such as the presence of an s-wave at the metal surface, the existence of a cutoff frequency and chirality value, and the dependence of the propagation length on the chiral parameter. These properties of chiral surface plasmon waves can be exploited for on-chip chiral sensing and enantiometric detection applications.

Improvement of range accuracy of range-gating laser radar using the centroid method.

An improved processing approach based on the relation between range accuracy and slicing number is proposed to improve the range accuracy of range-gating laser radar. The sequence of time-slice images is segmented according to their optimal slicing number and processed in segments to achieve the range information of objects. Experimental results indicate that the slicing number has a significant impact on range accuracy, and the highest range accuracy can be achieved when the systems work with an optimal slicing number.