A Six Channel Single Mode Wavelength Multiplexer With A Waveguide Concentrator

Devices based on diffraction gratings offer the only clear vehicle for progressing to many channels of wavelength multiplexing.1 This is because the loss in any channel is independent of the total number of channels. In single mode implementations the critical device is the multiplexer because, unlike the demultiplexer, the input and output fibers must have nearly identical cores. This results in pass-bands with a Gaussian shape. As the dispersion of the lens-grating combination is linear the ratio of channel width to channel separation is maximized when the cores are nearly close packed. For single mode it is impractical to accomplish this with actual fiber because the outer diameters become unacceptably small. The alternative is to obtain the required separation using strip waveguides. The waveguides may have an initial spacing appropriate for fiber pigtailing which can then be gradually reduced to the desired value. In this summary we report on the first such implementation.