A scalable and switchless optical network structure, employing a single 32 x 32 free-space grating multiplexer

Use of a single N/spl times/N wavelength multiplexer, to interconnect optically off order N/sup 2/ terminals without the use of space switches (hence switchless), is limited by call blocking and crosstalk in the multiplexer. Since all ports re-use the same wavelengths, poor crosstalk can cause severe homodyne beat-noise, particularly in planar N/spl times/N multiplexers. A scalable, distributed, optical broadcast-switching network structure has been demonstrated, which overcomes blocking by using wavelength conversion in "dummy" ports around a 32/spl times/32-port free-spare grating multiplexer. Measured background crosstalk rejection below -60 dB would allow 170/spl times/170 ports with tolerable beat-noise, supporting 7300 terminals (without concentration or time-sharing). With further expected crosstalk improvements, free-space N/spl times/N multiplexers are essential for scaling the architecture to large networks, which could interconnect up to millions of terminals (with concentration or time-sharing).