Performance of directional coupler for photonic applications


    Pablo Sanchis Kilders


The directional coupler is a device based on two optical waveguides placed closed together. A coupling section appears where a periodic optical power exchange occurs between these two optical waveguides. In this case, the two waveguides are considered identical and singlemode.


- Analyze the influence of the effective indices of the even and odd modes.
- Analyze the influence of the coupler length.
- Optimize the coupler performance depending on the target application.


The performance of the directional coupler is simulated by considering that light is injected through one of the inputs ports. The normalized optical power is shown at both output ports (parallel and cross). The response will depend on the effective indices of the even and odd modes (ne and no) as well as the coupler length (L in µm). The corresponding beat length (LB in µm) and its variation with wavelength is also shown. It is assumed that the effective indices of the even and odd modes are constant in the simulated wavelength range.


Initial wavelength (nm)

Final wavelength (nm)

Effective index of even mode

Effective index of odd mode

Directional coupler length (µm)


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