Next Generation Vertical-Cavity Surface-Emitting Laser (VCSEL) Design and Integration with Gratings

Vertical-cavity surface-emitting lasers (VCSELs) are key optical components used in optical communication, datacom, and many other applications. Recently, as 3D sensing technology has become more popular, VCSEL arrays have attracted more attention. As a result, VCSELs with more advanced and improved performance are needed to satisfy the increasing trend. This is very hard to achieve by traditional VCSELs alone. Therefore, it creates an opportunity for VCSELs to integrate with other optical elements.Grating is such a traditional optical element but with many unique properties. It has been studied by researchers for a long time. There are many reasons why grating is an ideal candidate for such integration. Besides its various optical properties, its fabrication is usually very simple as well. Therefore, this thesis will focus on different ways that gratings can be integrated with VCSELs to bring novel and unique properties.First, we will introduce a design toolbox we developed to model such grating structures. With this toolbox, we will demonstrate a novel wavelength tunable VCSEL design. By replacing the traditional VCSEL top mirror by high-contrast grating (HCG) and changing the cavity design, the laser tuning range can be greatly extended. Second, we will discuss a more compact HCG VCSEL architecture by incorporating a low-index oxide spacer. By carefully optimizing HCG design, the highest efficiency HCG VCSEL has been demonstrated. Finally, we will introduce a two-step growth method to fabricate a new grating aperture VCSEL. By replacing the traditional oxide aperture by a grating, large-aperture, single-mode laser can be achieved. In addition, polarization selective emission is also possible. With these three examples, we hope to show the capability of integrating grating structures to VCSELs and pave the road for future VCSEL design

When and why skill variety influences employee job crafting: Regulatory focus and social exchange perspectives

Purpose: The literature on job crafting has paid scant attention to the role of skill variety, one dimension of job characteristics, as a predictor of employee job crafting. By integrating regulatory focus and social exchange perspectives with job crafting literature, the authors investigate how skill variety promotes employee job crafting and the moderating roles of employee's promotion focus and procedural justice climate. Design/methodology/approach: The authors conducted two questionnaire surveys, one with a sample of 205 employees from a variety of organizations in China, and the other one with a sample of 265 employees within 44 work groups at a state-owned enterprise in China, to examine the hypotheses. Findings: Results suggest that a high level of skill variety within a job promotes employee job crafting, that such an effect is stronger when the employee's promotion focus is high rather than low, and that procedural justice climate mitigates the negative influence of a low level of promotion focus. Originality/value: The authors' findings suggest that both self-regulatory and social exchange mechanisms play a critical role in promoting employee job crafting when individuals are engaged in jobs that entail a high level of skill variety

Corporate Social Responsibility Disclosure and Stock Price Crash Risk: Evidence from China

We take Chinese A-share listed companies in years 2010–2015 as a sample to examine the relationship between Corporate Social Responsibility (CSR) information disclosure and stock price crash risk using the fixed effect model. The results show that: (1) There is an inverted U-shaped nonlinear relationship between CSR information disclosure and stock price crash risk. That is, as the CSR information disclosure level increases, the CSR information disclosure first aggravates and then reduces the stock price crash risk; (2) under different disclosure motives, there is a significant difference in the impact of CSR information disclosure on stock price crash risk. There is still an inverted U-shaped relationship between mandatory CSR information disclosure and stock price crash risk, but not for the semi-mandatory and voluntary disclosure; (3) the academic independent director has a positive adjustment effect on the relationship between CSR information disclosure and stock price crash risk, while the institutional investor has a negative adjustment effect on the relationship between CSR information disclosure and stock price crash risk. The research is of great significance for promoting the fulfillment of CSR, improving corporate governance and stabilizing the capital market

The Influence of terrorism on Foreign Direct Investment

In the process of globalization, the spread of terrorism has brought risks and uncertainties to multinational enterprises. In order to find out the influence of terrorism, this research use the Chinese multinational enterprises’(MNEs) 2089 investments in 125 countries to studies the impact of terrorist events on their investment decisions. The research find that the the more people affected by the terrorism in one country, the less subsidiaries set up in the countries. Terrorist events have brought severe challenges to investment. Governments of countries should improve their own security protection systems, while enterprises should also strengthen the risk management system

The Carbon-Coated ZnCo2O4 Nanowire Arrays Pyrolyzed from PVA for Enhancing Lithium Storage Capacity

In this paper, ZnCo2O4 nanowire arrays with a uniform carbon coating were introduced when polyvinyl alcohol (PVA) served as the carbon source. The coating process was completed by a facile bath method in PVA aqueous solution and subsequent pyrolyzation. The PVA-derived carbon-coated ZnCo2O4 nanowire array composites can be used directly as the binder-free and self-supported anode materials for lithium-ion batteries. In the carbon-coated ZnCo2O4 composites, the carbon layer carbonized from PVA can accelerate the electron transfer and accommodate the volume swing during the cycling process. The lithium storage properties of the carbon-coated ZnCo2O4 composites are investigated. It is believed that the novel carbon-coating method is universal and can be applied to other nanoarray materials

Air-cavity dominated HCG-VCSEL with a wide continuous tuning

We present continuously tuned emission of 940-1000 mm wavelength from an electrically-pumped VCSEL without top DBR layers via an electrostatically controlled HCG mirror. Large tuning range results from a high optical intensity in the air cavity

Promoting the electrochemical properties of yolk-shell-structured CeO2 composites for lithium-ion batteries

Lithium-ion batteries offer significant convenience to modern portable technology and our daily lives due to their high energy density and cycling capabilities. Cerium oxides are attracting significant attention as Li-ion battery anode materials due to their nontoxicity and fast redox kinetics. However, these anodes face critical issues, such as poor electronic conductivity and serve volume expansion upon Li-ion intercalation. Herein, yolk-shell-structured CeO2 encapsulated in mesoporous carbon nanospheres (CeO2@void@C) is proposed with an adjustable void between the CeO2 core and the outer carbon layer. A significantly enhanced capacity and rate performance are obtained for the target CeO2@void@C when compared with the untreated CeO2 anode. The reversible capacity of CeO2@void@C is double that of the untreated CeO2 anode. Additionally, the yolk-shell-structured CeO2 shows a slow capacity decay and maintains a capacity of 210 mAh·g-1 at a current density of 1000 mA·g-1 with a ~100% Coulombic efficiency even after 1000 cycles. This improvement originates from the conductivity of the coating carbon layer and the void that constrains the volume change upon electrochemical lithiation/delithiation