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Optical phase locked loop (OPLL) photonic integrated circuits (PIC) are critical for the high dynamic range phase modulated RF/photonic links. They provide for linear phase demodulation. A challenge for implementing the OPLL PICs is how to reduce the loop propagation delay. In this paper we analyze the delay of a waveguide photodetector, which is a critical component of an OPLL. We also introduce and experimentally validate a counter propagating photodetector device concept. This enables the elimination of the propagation delay due to the finite length of a waveguide photodetector.