There is an ever increasing need for bandwidth in the Internet and various other bandwidth hungry applications. This demand can be satisfied using optical WDM that allows the same fiber to carry many signals as long as each of these uses a different wavelength. WDM is a step towards furnishing the capabilities of the optical fiber which uses wavelength routing that is the networks ability to route a signal at intermediate nodes based on their wavelength.It has the ability to create a virtual topology upon the underlying physical topology of the network. The design of a virtual topology requires setting up of lightpaths which can traverse multiple links in the physical network and yet transmission is entirely optical without any opto-electronic conversion at the intermediate nodes.The potential of the virtual topology is dependent on the virtual topology design. The designing process is a complex problem.A designed virtual topology can be considered for various objective functions such as congestion control, delay minimization, hop length minimization, reducing the number of optical transceivers employed, minimizing the number of wavelengths utilised etc.