Disclosed is a customer sided termination unit for an optical access network, which comprises an optical interface adapted to receive a downstream signal having a wavelength λ 1, an optical receiver, a first and a second distributed Bragg reflector, essentially reflecting a signal at said wavelength, and a symmetric optical coupler with at least two first ports at a first side and at least two second ports at a second side. The effective optical distance between an effective reflection plane of the first distributed Bragg reflector and the symmetric optical coupler and an effective optical distance between an effective reflection plane of the second distributed Bragg reflector and the symmetric optical coupler are chosen such, that a difference between said effective optical distance is chosen as an integer multiple of the wavelength.