An Optical Packet Switch based on Parametric Wavelength Converters

In an OPS, an optical fiber carries several wavelengths to transmit packets. An input fiber may carry as many packets as wavelengths that could be destined to one or several output fibers. The output contention occurs when multiple packets from different input fibers are destined to a single output fiber using the same wavelength at the same time. Only one packet is forwarded to the output fiber and the others are dropped. Some proposed methods for resolving output contention are: i) optical buffering through fiber delay lines (FDLs) to store packets. However, the feasible delays of FDLs are smaller than the delays packets would have to wait for transmission. ii) Bufferless deflection routing [1], but network control might be complex. iii) Wavelength conversion (WC) [2] where the wavelength carrying a packet that cannot be connected to its destined output because of output contention is converted to a wavelength available at the output fiber. A full wavelength converter (FWC) can convert a wavelength to any other wavelength. However, this approach is expensive for practical applications as dedicated FWCs must be provisioned. To decrease the cost of FWCs, inputs can share a wavelength converter. A parametric wavelength converter (PWC) [3] allows multiple wavelengths to be simultaneously converted from one to another. Multiple wavelength conversion based on parametric process is considered becoming feasible [4]. The shared-per-node with parametric wavelength converters (SPN-PWC) switch [5] uses a number of PWCs smaller than that of a switch with single-channel wavelength converters. In this switch, however, wavelength blocking occurs as outputs of PWCs are connected into a single input port of the switch fabric. To define both which wavelength can be converted and onto which other by a PWC, a continuous pump wavelength, λp, is set. Therefore, the selection of λp defines the conversion pairs. The symmetry in wavelength conversion by a PWC provides the largest number of wavelengths converted by setting the pump wavelength in the middle of wavelength transmission interval [5]. This policy is called number rich (NR). This switch uses multiple PWCs using the same pump wavelengths to maximize the number of pairs. However, the lack of variety in these conversion pairs, as one wavelength can be converted to only another wavelength in the blocking OPS, can severely limit the achievable performance improvement by PWCs. Therefore, this paper proposes a policy with large variety size of connection pairs, called a variety rich (VR) policy. VR in an OPS with multiple PWCs uses a different pump wavelength in each PWC.