Reduction of Coupling Loss in a One-to-many Collimating System for a Wavelength Division (de)Multiplexer.
In a 1 x N wavelength division (de)multiplexer, N receiving (Rx-) gradient-index-rod lenses (GRIN's) are connected to a common transmitting (Tx-) GRIN. All GRIN's are a little longer (DZ(0) for the Tx- and DZ(i) with i = 1, 2, ..., N for the Rx-GRIN's) than the quarter-pitch. To reduce the average coupling loss and the deviations, DZ(0) and DZ(i) are optimized independently (unequally) or equally by computer programming for small N, such as N = 4 and 8. For a larger N (e.g., 16), a relay GRIN is required, which is a little (DZ(r)) longer than the half-pitch. The best position of the relay GRIN is located between the seventh and the eighth Rx-GRIN's. Other parameters including DZ(0), DZ(i), and DZ(r) are all optimized. As a result the (de)multiplexer has lower losses.
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