The back reflection in photodiodes is caused by an abrupt index contrast between the input waveguide and the composite waveguide/light absorbing material. In order to improve the back reflection, it is proposed to introduce an angle between the waveguide and the leading edge of the light absorbing material. The angle will result in gradually changing the effective index between the index of the waveguide and the index of the composite section, and consequently lower the amount of light reflecting back.