Minicomposite unit bridging, which was experimentally determined to be the dominant toughening mechanism resulting in the R-curve behavior of the Al2O3-ZrO2 minicomposite-reinforced glass matrix optomechanical composite, was studied quantitatively using luminescence spectroscopy. Applied stress induced shift of the luminescence bands of the minicomposite reinforcement was calibrated. Using the experimentally obtained calibration curve, axial stresses could be mapped along the minicomposite embedded in the glass matrix. In situ fracture mechanical test of the fabricated glass matrix optomechanical composite was conducted using a specially designed loading system that can be placed under a high-resolution micro-Raman spectrophotometer. Axial minicomposite stress distributions were mapped in the matrix-cracked optomechanical composite, and its interfacial properties were determined using the obtained stress profiles. The apparent interface shear frictional stress in the present composite was determined to be similar to 75 MPa. Using the obtained interfacial properties and crack opening displacement versus crack length relations, R-curve behavior of the optomechanical composite was studied quantitatively assuming that minicomposite unit bridging is the only toughening mechanism operative in the structure. Theoretical prediction agreed well with the experimentally obtained R-curve of the glass matrix optomechanical composite, which proves the dominance of minicomposite unit bridging in the improvement of its fracture resistance. (c) 2005 Elsevier B.V. All rights reserved.