Papers by Author: Hong Cai

Abstract: In the broadband communication network, the wavelength-division-multiplexed (WDM) system is widely used to maximize the information that the signals can carry. As a result, the number of channels which are carried by different optical wavelengths in the WDM optical fiber network also keeps increasing. To separate the huge number of different wavelength signals, optical filter is required. The optical filter based on semiconductor has been widely studied due to the maturation of semiconductor fabrication technology and that it is possible to integrate the filter with the stable semiconductor devices such as laser diodes and MOSFETS. The tunable optical filter is basically a selective optical resonator that only allows the resonant modes passing through. Various mechanical methods are studied to achieve the tunable effect by tuning the physical structure of the filter; however, there is not much research on how the semiconductor material will affect the tuning function. In this paper, the author studied the influence of refractive index of the multi-silicon-slabs on the filter, whereby the tuning of refractive index is reached by thermal effect. It is found by simulation that when heating the silicon slabs, the increasing refractive index of silicon will lead to a shift of the resonant mode wavelength. This shift is almost linear with the change of the temperature, which is about 1nm with every 20K temperature increase. For certain devices, the result of the simulation showed it is possible to tune the resonant mode from C band to L band in the Fiber Optical Communication.

Abstract: This paper presents a photonic polarization switch based on microelectromechanical systems (MEMS) technology. The polarization switch can change the pathway of the different polarized light via optical tunneling effects. By controlling the incident angle of the input light, the output polarization state can be switched between two different polarization states. The polarization switch has promising applications on both photonic circuit and bio-detecting.

Abstract: This paper reports a new kind Terahertz generator using tunable dual-wavelength generator based on MEMS technology, which are developed based on free-carrier effect (FCE) and thermo-optic effect (TOE) [1-3]. The approach provides a wide tuning range from 0 to 15 nm by adjusting the current of laser diodes and heating up common silicon Fabry-Perot (FP) external cavity. Compared to the conventional optical generation methods, this method has fast tuning speed (<1 ms), small size (2.2 mm 0.8 mm), high integration and quite stability performance.

Abstract: This papers deals with the study of novel building blocks suitable for architectures of MEMS tunable lasers integrated in SOI platforms. These building blocks are based on the use of 1D photonic crystals (1D PCs) made of silicon-air thin layers stacks. These provide high reflectivity in certain wavelength range as well as access to simple Fabry-Perot cavities. The latter was studied more in detail and simulations are presented along with preliminary experimental results. A tilted Fabry-Perot cavity was analyzed for its potential of mode selector to prevent for mode hopping and thus enable continuous mode tuning by control of separation gap. As 1D PCs exhibit dispersion characteristics, this behavior is analyzed as well for its potential use for compensation purposes of wavelength dependence of the refractive index in the III-V gain medium.