A four-channel lightwave subsystem using wavelength division multiplexing

A four-channel multimode transmission subsystem employing wavelength division multiplexing (WDM) was assembled and optically evaluated. Diffraction grating devices with identical fibers for inputs and outputs were used for both multiplexing and demultiplexing. The 1-dB full width of the passbands was ∼4 nm thus there was a requirement for wavelength selection and temperature tuning of the corresponding laser sources. A temperature excursion of 7°C from the optimum resulted in 1 dB of additional attenuation. Insertion losses for the multiplexer/demultiplexer (Mux/Demux) pair were 3.7, 3.6, 4.7, and 7.3 dB at 812, 830, 867, and 885 nm, respectively. The higher losses at 867 and 885 nm were due to chromatic abberation. The channel spacing of 18 nm is smaller than could be achieved with state-of-the-art filter devices. For unidirectional transmission the out of band rejection exceeded 40 dB in all channels.