Optical subcarrier label switching using nonlinear harmonic modilation in external mach-zehnder modulator

Abstract

All-optical label switching networks require a simple and effective method to swap optical headers in real time without affecting payload data in order to realize low-latency packet forwarding and routing. An optical subcarrier multiplexed (OSCM) optical header attatched to each optical packet can be processed and replaced using relatively low-speed optoelectronics, while the high-speed payload data easily separated from the optical header data remains transparently in the optical domain. This dissertation proposes a novel method to generate the $2^{nd}$ harmonic subcarrier (2$\omega_{sc}$) multiplexed optical header signals and detect the optical headers without RF fading effects from interaction between the double-sideband (DSB)-OSCM header signal and the optical payload signal. By separating the $2^{nd}$ harmonic DSB-OSCM optical header signal from the combined signal with a conventional fiber Bragg grating filter at the receiver node, we can detect the optical header by a simple square law detector. The proposed scheme is validated by numerical analysis, simulation and finally by experiments. We first derive an analytic expression for the $2^{nd}$ harmonic optical subcarrier label signal. We can generate the conventional $1^{st}$ harmonic DSB-OSCM signal and the $2^{nd}$ harmonic DSB-OSCM signal by adjusting the bias voltage of external MZ intensity modulator. Next, we simulate the proposed $2^{nd}$ harmonic DSB-OSCM using VPITransmissionMaker. From the simulation study, we obtain the optimum modulation depth of header signals and improve receiver sensitivity. To confirm the proposed scheme experimentally, optical spectra before and after an FBG filter are compared. BER measurements also show that the header power penalties are maintained within 0.5 dB against $\plusmn$0.04nm wavelength shifts of the fiber Bragg grating filter``s center frequency. Our scheme is proved to be robust under environmental change. From several experiments, it is confirm...