Thin film of GaAs/AlGaAs multiple quantum well (MQW) structure have been bonded to the lithium tantalate (LiTaO3) or calcium carbonate (CaCO3) substrates cut such that one of the linear thermal expansion coefficients almost matches that of the MQW while its orthogonal counterpart does not. By choosing the proper bonding and operating temperatures, in-plane anisotropic strain up to 0.3% has been achieved. The transmission spectrum shows an anisotropy in excitonic absorption which results in a polarization rotation of a light beam at normal incidence to the structure. The theoretical calculation is in agreement with the experimental results. Using the polarization rotation, we have demonstrated a novel MQW light modulator with an exceedingly high contrast ratio of 330:1.