Figure 14. 3dB coupler with 90 degree phase shift

From

Principle of Coherence Optical Systems-Current Applications and Future Challenges

Arun Agarwal, Kabita Agarwal, Gourav Misra, Subrat Kumar Panda

American Journal of Electrical and Electronic Engineering. 2019, 7(4), 94-98 doi:10.12691/ajeee-7-4-2