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The tremendous growth of data traffic has spurred a rapid evolution of optical communications for a higher data transmission capacity. Next-generation fiber-optic communication systems will require dramatically increased complexity that cannot be obtained using discrete components. In this context, silicon photonics is quickly maturing. Capable of manipulating electrons and photons on the same platform, this disruptive technology promises to cram more complexity on a single chip, leading to orders-of-magnitude reduction of integrated photonic systems in size, energy, and cost. This paper provides a system perspective and reviews recent progress in silicon photonics probing all dimensions of light to scale the capacity of fiber-optic networks toward terabits-per-second per optical interface and petabits-per-second per transmission link. Firstly, we overview fundamentals and the evolving trends of silicon photonic fabrication process. Then, we focus on recent progress in silicon coherent optical transceivers. Further scaling the system capacity requires multiplexing techniques in all the dimensions of light: wavelength, polarization, and space, for which we have seen impressive demonstrations of on-chip functionalities such as polarization diversity circuits and wavelength- and space-division multiplexers. Despite these advances, large-scale silicon photonic integrated circuits incorporating a variety of active and passive functionalities still face considerable challenges, many of which will eventually be addressed as the technology continues evolving with the entire ecosystem at a fast pace.

I use data on U.S. manufacturing establishments to study the spatial reallocation of resources that takes place within surviving firms as they open and close establishments in different regions. To motivate the empirical analysis, I extend existing models of industry dynamics to include production-location decisions within firms. Consistent with the theory, the empirical results show that only a fraction of firms make the same product in multiple regions, that multiregional firms are larger and more productive on average compared to single-region firms, and that 'region switching' is pervasive among multiregional firms and correlated with changes infirm and firm-region characteristics. (JEL L2, F12, F23), I. INTRODUCTION Empirical research using producer-level microdata demonstrates the importance of within-industry reassignment of resources across producers in explaining industry performance (e.g., Baily et al. 1992; Bartelsman and Doms 2000; [...]

Abstract: Standard techniques used to estimate gravity equations, rely on bilateral variation to identify the effect of trade barriers on bilateral trade flows. In this paper, I develop a method that estimates the effects of country‐level variables on trade between countries in the presence of firm heterogeneity and country selection into trade, a natural extension of existing empirical models of international trade. I implement the method in services data, where available measures of trade policy provide information on the average level of regulations restricting entry into a country. The results suggest that policy barriers are important determinants of services trade flows. [ABSTRACT FROM AUTHOR]

This paper develops a framework for studying the general equilibrium effects of endogenous quality upgrading, a new margin of trade, on the welfare impact of trade liberalization. The theoretical model introduces product quality differentiation amongst heterogeneous firms and focuses on supply-side determinants of international trade. Among other results, in general equilibrium, trade liberalization decreases the share of high-quality varieties in exports and the average productivity of exporters. These changes affect average export price in opposite ways. Nevertheless, trade liberalization in the quality-extended model increases consumers’ welfare by more than in the benchmark model. [ABSTRACT FROM AUTHOR]