A system for assessing the quality of the optical connection between a catheter and a console is described that avoids the necessity of a calibration port, although one can still be provided if desired. It operates by monitoring the level of light returning from the catheter head and specifically the degree to which this returning light is attenuated. Reflections will arise at the catheter head's optical window due to the discontinuity between the refractive index of the window and that of air or other medium into which the head is inserted. Since the refractive index of the optical window is known and with the head in a known medium such as air, the level of reflection is known. This enables a controller in the console to calculate the round trip loss and thus monitor the loss in the catheter-console interface. Moreover, since round-trip loss is measured, the accuracy is improved by a factor of two over calibration port systems that only measure loss in a single pass arrangement. One embodiment provides for the assessment of a multi-piece catheter using multiple wavelengths.