Deflection routing may become an appealing routing principle in the metropolitan area because of the increasing gap between the WDM transmission capacities and the processing power available in the nodes. Deflection routing is fast, simple, naturally copes with local transient or permanent congestion states and may easily be tailored for service differentiation. Deflection routing however suffers from a limited throughput and relatively large delay jitters as compared to the classical store-and-forward approach, especially if the traffic is uniform and uniformly distributed. In this contribution, we have shown how the use of wavelength converters dramatically improves the deflection routing performance for both synchronous and asynchronous deflection routing. Therefore, the larger the number of wavelengths, the better the network performance, a property which indeed makes deflection routing a future-proof paradigm in the metropolitan area.We have also shown that this improvement is stronger in the case of asynchronous deflection routing networks; this is a very important result since it allows to make use the full flexibility of deflection routing with variable packet lengths (encapsulated IP datagrams for instance) without sacrificing much performance in terms of throughput or jitter.