A study of the depolarisation effect which occurs in a light beam passing through a thin homogenously oriented layer of nematic liquid crystal (N-(methoxybenzylidene)-4-butylaniline) driven to the turbulence by an external ac voltage is reported. The time behaviour of the transmitted light polarization degree (P) has been recorded for different values of both applied voltage and polarization of the incident light beam. The features of the DSM's regimes strongly depend on the state of polarization of the probe light beam. In particular, the transition can be evidenced by looking at P when the incident states of polarization are oriented at different angles with respect to the liquid crystal anchoring direction. Although the DSM's transition was unambiguously characterized as a transition from a 2-D structured turbulence to a 3-dimensional turbulence (DSM2), our measurements emphasize that oriented turbulent structures coexist in the latter regime.