Effect of an electric field on the electronic subbands in strained In0.65Ga0.35As/In0.52Al0.48As coupled double quantum wells has been investigated theoretically with the goal of producing the large Stark shifts and of their application possibilities to a tunable photodetector. The energy states, the corresponding energy wavefunctions, the absorption peaks, and the Stark shifts in strained In0.65Ga0.35As/In0.52Al0.48As coupled double quantum wells under applied electric fields are calculated by the transfer matrix method taking into account strain effects. The operation of this device is based on the infrared absorption by the electrons in the ground state transited from the ground state subband to the excited state subbands of the coupled double quantum wells. When an electric field is applied to a coupled double quantum well, the shifts of the intersubband energy transitions and the absorption peaks in the coupled double quantum well are shifted much larger than those in the single quantum well. The excited energy states with and without applied electric fields in the In0.65Ga0.35As/In0.52Al0.48As coupled double quantum wells are strongly dependent on the In0.65Ga0.35As well width in comparison with their ground states. The coupling of the electronic subband energies in the two In0.65Ga0.35As/In0.52Al0.48As quantum wells leads to an enhancement of the quantum-confined Stark effect. These results indicate that strained In0.65Ga0.35As/In0.52Al0.48As coupled double quantum wells hold promise for potential applications to new kinds of optical modulation devices and tunable photodetectors.