In this work we investigate the reflectance spectra of the GaAs/AlGaAs/AlAs-based coupled microcavities consisting of two cavity layers separated and surrounded by distributed Bragg reflectors (DBRs). The observed optical modes are described by the coupled harmonic oscillators model with parameters derived from the modelling of the layered structure by the transfer matrix method. The theory explains the observed anticrossing behaviour of optical modes with position on the sample, being able to reveal the cavities thickness gradients.