A very low-loss wide-angle Y-branch with a composite diamond-like microprism

A very low-loss wide-angle symmetric Y-branch with a low-index composite diamond-like microprism (CDM) is proposed. The CDM is composed of a diamond-like microprism (DM) and a post-compensating microprism (PM). The former is designed to compensate the phase-front mismatch at the branching point, and it will improve the field mismatch by this diamond-like shape; the latter is used to reduce the coupling between the branches. After complete phase-front compensation of the CDM; the simulated normalized transmission will maintain 96.4% even if the branching angle is up to 200. Besides, the design rules of the indices of CDM are remarkably readily derived and efficient. This structure will also provide various advantages of simple shape, relative insensitivity to fabrication errors, and flexible selection of prism index. Furthermore, detailed examinations of the design parameters have been discussed relative to the transmission characteristics.