Methods for performing in-service upgrades of optical wavelength cross connects

A method for performing an in-service upgrade of a Ki1×Kj1 optical wavelength cross connect to a Ki2×Kj2 optical wavelength cross connect, each Ki×Kj optical wavelength cross connect comprising (1) a working fabric having Kj wavelength routing elements, each adapted for selectively routing wavelength components from Ki equivalent input optical signals to a corresponding output optical signal according to a configurable state of such wavelength routing element, and configured on the working fabric to receive the Ki equivalent input optical signals from Ki input optical signals transmitted through a plurality Ki of optical splitters, and (2) a protection fabric configured to bypass at least one of the wavelength routing elements in the event of a fault, the method comprising:

• adding Kj2−Kj1 wavelength routing elements, each additional wavelength routing element being adapted for routing spectral bands from Kj2 equivalent input optical signals to a corresponding output signal;
• upgrading the protection fabric to accommodate at least Ki2 input optical signals;
• and
• sequentially, for each of the Kj1 wavelength routing elements initially included on the working fabric,
• bypassing optical traffic received by that wavelength routing element to the protection fabric;
• thereafter, upgrading that wavelength routing element to receive Ki2 equivalent input optical signals and adding a further optical splitter to each optical-splitter output connected with that wavelength routing element;
• and
• thereafter, returning the bypassed optical traffic to that wavelength routing element.