Instead of monitoring the optical power coming out of a waveguide, a direct method of monitoring the optical power inside the waveguide without affecting device or system performance is provided. A waveguide comprises a p-i-n structure which induces a TPA-generated current and may be enhanced with reverse biasing the diode. The TPA current may be measured directly by probing metal contacts provided on the top surface of the waveguide, and may enable wafer-level testing. The p-i-n structures may be implemented at desired points throughout an integrated network, and thus allows probing of different devices for in-situ power monitor and failure analysis.