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The continuous growth of telecommunications traffic has placed huge demands on the traditional networks. Bottlenecks are particularly evident at the routers, where optical to electrical conversion must take place to read the routing information. Using optical-only routing, the traffic flow would be much faster, and more streamlined. A key component in this optical router is the tunable laser. When the laser is switched at high speeds, red-shifted thermal effects, due to the heating effects of the applied currents, cause a drift in the frequency, in the opposite direction to the blue-shifted carrier effects. The thermal effects have been quantified theoretically and experimentally here. The impact of the thermal effects, both on the frequency switching and on the frequency-shift keying (FSK), has been investigated. Methods of compensating for the thermal effects have been developed and verified by simulation and by experiment.