Compact Wavelength Selective Crossbar Switch with Cascaded First Order Micro-Ring Resonators

We demonstrate a compact 4x4 wavelength selective switch with 50 % fewer electrical pads as compared with our previous generation. We report loss and crosstalk for different paths of the switch. We measure median loss of 5.32 dB and worst case crosstalk of -35 dB. The microring resonators tune by more than one free spectral range, which is an improvement over our previous generation of switches. This switch can support 8 channels at 400 GHz spacing. We conclude that it is not possible to drive both microring resonators with the same voltage and separate control is required because of fabrication variation of the current technology.

Variation of Signal Reflection on Electrodes of Silicon Mach-Zehnder Modulators: Influence of Nanoscale Variation and Mitigation Strategies

Driving signal reflection on traveling wave electrodes (TWEs) is a critical issue in Mach–Zehnder modulators. Fabrication variation often causes a random variation in the electrode impedance and the signal reflection, which induces modulation characteristics variation. The variation of reflection could be intertwined with the variation of other electrode characteristics, such as microwave signal attenuation, resulting in complexity. Here, we characterize the (partial) correlation coefficients between the reflection and modulation characteristics at different bit rates. Decreasing correlation at higher bit rates is observed. Device physics analysis shows how the observed variation can be related to nanoscale variation of material properties, particularly in the embedded diode responsible for electro-optic modulation. We develop a detailed theory to analyze two variation modes of the diode (P-i-N diode or overlapping P/N regions), which reveal insight beyond simplistic diode models. Microwave signal attenuation tends to reduce the correlation with on-electrode reflection, particularly at high bit rates. The theory shows the relative importance of conductor-induced attenuation and “dielectric”-induced attenuation, with different dependence on the frequency and fabrication variation. Strategies on how to mitigate the effect of variation for better fabrication tolerance are discussed by considering three key factors: pre-shift in structural design, bias condition, and fabrication control accuracy.

Stiffness Measurement of Micro-Cantilever Based on Negative Electrostatic Stiffness

Micro-cantilever is basic structure of Micro-Electro-Mechanical-Systems (MEMS) sensor, and mechanical stiffness is the most important parameter of micro-cantilever. The mechanical stiffness can be affected by shape, size and material, and it should be experimentally measured for fabrication variation. Yet, the micro scale of MEMS cantilever makes the measurement difficult, and the traditional method isn't suitable for the micro-cantilever. This study proposes a new method for measuring the mechanical stiffness of micro-cantilever, and measurement of MEMS accelerometer was also experimentally carried out. The proposed method exploits the feature that the voltage applied on cantilever can lead to negative electrostatic stiffness, and this stiffness can change the deformation of cantilever. The mechanical stiffness can be obtained through analyzing the change of output. Results from this study coincided with our theoretical model, and the difference between results obtained by this method and SEM was 2.2%. This work provides a new way to precisely obtain mechanical stiffness of micro-cantilever using non-destructive method, making it helpful for researchers to design micro-cantilever and MEMS devices.