Optical interconnects made of silicon are viewed as emerging efficient solutions for addressing the communication bottlenecks that plague high-performance computing systems and big-data centers. Due to large index contrast and optical nonlinearity of silicon, waveguides and active devices based on silicon can be scaled down to sub-wavelength size, making silicon photonics an ideal platform towards integrated on-chip photonic circuits. In order for this potential to be fulfilled, one needs to understand the factors that affect the quality of optical signals propagating in silicon optical interconnects, namely the bit-error ratio (BER), as well as the relationship between the parameters characterizing the optical signal and the BER.
In this work, an accurate approach to calculate the BER in single-channel silicon optical interconnects utilizing arbitrarily-shaped pulsed signals is presented. The optical interconnects consist of either strip single-mode silicon photonic waveguides (Si-PhWs) or silicon photonic crystal (PhC) waveguides (Si-PhCWs), and are linked to a direct-detection receiver. The optical signal consists of a superposition of Gaussian pulses and white noise. The signal dynamics in the silicon waveguides is modelled using a modified nonlinear Schrodinger equation, whereas the Karhunen-Loeve series expansion method is employed to calculate the system BER. Our analysis reveals that in the case of the Si-PhWs the pulse width is the main parameter that determines the BER, whereas in the case of Si-PhCWs the BER is mostly affected by the waveguide properties via the pulse group-velocity. A good system performance is achieved in centimeter-long Si-PhWs whereas similar system performance is obtained using 100× and 200× shorter Si-PhCWs operating in the fast- and slow-light regimes, respectively.
We present an effective approach to evaluate the performance of multi-channel silicon (Si) photonic systems. The system is composed of strip Si photonic waveguides (Si-PhWs) with uniform cross-section or photonic-crystal (PhC) Si waveguides (Si-PhCWs), combined with a set of direct-detection receivers. Moreover, the optical field in each channel is the superposition of a continuous-wave nonreturn-to-zero ON-OFF keying modulated signal and a white Gaussian noise. In order to characterize the optical signal propagation in the waveguides, an accurate mathematical model describing all relevant linear and nonlinear optical effects and its linearized version is employed. In addition, two semi-analytical methods, time- and frequency-domain Karhunen-Loève series expansion, are used to assess the system bit-error-rate (BER). Our analysis reveals that Si-PhCWs provide similar performance as Si-PhWs, but for 100× shorter length. Importantly, much worse BER is achieved in Si-PhCWs when one operates in slow-light regime, due to the enhanced linear and nonlinear effects.
We present recent results pertaining to pulse reshaping and optical signal processing using optical nonlinearities of silicon-based tapered photonic wires and photonic crystal waveguides. In particular, we show how nonlinearity and dispersion engineering of tapered photonic wires can be employed to generate optical similaritons and achieve more than 10× pulse compression. We also discuss the properties of four-wave mixing pulse amplification and frequency conversion efficiency in long-period Bragg waveguides and photonic crystal waveguides. Finally, the influence of linear and nonlinear optical effects on the transmission bit-error rate in uniform photonic wires and photonic crystal waveguides made of silicon is discussed.
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