A novel low-loss passive planar 4×4 star coupler consisting of four interconnected 3 dB couplers was fabricated on x-cut Ti: LiNbO3 using z-propagation. Almost even distribution was achieved for both TE and TM polarised light incident on any of the four inputs. Excess loss including fibre coupling was <4.2 dB.
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Heidrich et al. (1984) studied this question.
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