We propose and demonstrate a nondestructive method for loss measurement in optical guided structures. In the proposed approach, the device under test does not require connectors at its ends, thus making this technique available for both optical fibers and integrated optical waveguides. The loss measurement is feasible over a broad range, from low ($0.2\mathrm{dB}/\mathrm{km}$) to high (of the order of $1\mathrm{dB}/\mathrm{mm}$) loss values. This method is validated through measurements performed on a microstructured holey fiber and on a photonic-crystal waveguide. The obtained results are in good agreement with theoretical calculations and measurements obtained by other approaches.