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Optical Orthogonal Frequency Division Multiplexing (OOFDM) has been proposed as a highly spectrum-efficient modulation technique, which can provide flexible spectrum assignment with fine granularity. In OOFDM-based flexible optical networks, Routing and Spectrum Assignment (RSA) has become a key problem. However, widely used dynamic RSA schemes, such as Fixed Routing (FR) and K-shortest Paths (KSP) routing schemes, are not able to realize route computation based on the link state information, thus leading to poor blocking performance and inefficient resource utilization. To solve this problem, Adaptive Routing (AR) schemes, e.g., the Entire Path Searching (EPS) scheme, have been proposed recently. These schemes have low blocking probability; however, since their computational complexities are factorial, they are not suitable for use in real networks. In this paper, we propose a novel Spectrum-Scan Routing (SSR) scheme in dynamic flexible optical networks. To the best of our knowledge, SSR is the first polynomial-time AR scheme that can realize adaptive shortest-route computation. Simulation results show that our proposed SSR scheme has lower blocking probability and higher resource utilization compared with FR and EPS. Moreover, the worst-case computational complexity of SSR increases linearly with the network scale of the torus topologies, making it applicable to real networks.

Long-term single-frequency stabilisation of an external-cavity semiconductor laser has been demonstrated using a multisegment composite-cavity configuration and an automatic frequency control loop with feedback to the external cavity. Mode-hopping free single-longitudinal-mode oscillation with a linewidth of about 200 kHz and a frequency shift within 28 MHz has been observed over 24 h.

A new way to improve the single-longitudinal-mode spectrum of short-coupled-cavity (SCC) semiconductor lasers is reported. It is found that an antireflective coating on the end facet of the laser diode in the SCC cavity is necessary for high-quality single-mode operation. Based on the theoretical analyses, a new type of miniature SCC laser has been constructed and demonstrated. Single-mode output with 35–40 dB side-mode suppression ratio has been obtained under CW and 150 MHz modulation conditions.