Low-cost WDM transceivers for the LAN

The HP Labs SpectraLAN/sup TM/ project has pursued two very different approaches to making low-cost WDM LAN transceivers. In the first approach, four VCSELs, at wavelengths of 820, 835, 850, and 865 nm, were used. The four optical signals were combined into a 62.5-/spl mu/m multimode fiber, using a 4-to-1 multimode polymer waveguide combiner. On the receiver side, a multimode polymer waveguide demultiplexer was used to separate the wavelengths, which were then directly coupled to a monolithic GaAs pin photodiode array. Multichannel laser driver and receiver IC´s were used, fabricated in silicon bipolar electronics. A second design, using a zigzag waveguide pattern was also successfully demonstrated. In this design, light is incident on a dielectric filter at an angle, with one wavelength being transmitted, and the remaining wavelengths reflected into the next arm of the zigzag.