Estimation of the Maximum Transmission Rate for the Silicon-Based Racetrack MicroResonator

Abstract

The maximal transmission rate for an optical signals getting through the devices can be determined directly from the impulse response outing from the device. This could be done by a simple tracing the behavior of an optical pulse transmitting through the device using the method of finite-difference time-domain (FDTD) The device consists of a straight coupling structure with a gap of 0.2 μm and a curved section with radius of 1 mm, with the cross section dimension of 0.4 μm × 0.4 μm for the optimal coupling. The device was set the straight sections, for the energy coupling, of 3 μm and the curved section with the curvature of 1 μm. An optical pulse train was launched into and observed the output from the device. To investigate the transient response, we observed the outputs for a number of round trips. We found that the coupling will get settled at the steady coupling power by letting the optical pulse traveling for a number of roundtrips. This behavior is similar to the energy accumulating in the capacitor and inductor for the electrical signal, which leads to the delay characteristics of the pulse response. Furthermore, the optical signal response along the time was also observed as the signals in Figure 2. When an optical pulse was launched into the device, the output pulse would gradually develop its power to a maximum level. And at the end of the input pulse, the output pulse would exponential decay. It needs approximately 2.5 ps for rising time to the maximum level, and 1.5 ps for the falling time down to the zero level. Namely, the pulse requires the totally minimal time of 4 ps. This implies that the device can transmit the maximal bit rate of 125 Gb/s.