Thermally Induced Optical Bistability in GaAs/(AlGa)As Multiple Quantum Wells for Application as a Temperature Sensor

With the aim of realizing a temperature sensor based on thermally induced optical bistability that can be operated by a conventional diode laser, we investigated the absorptive behaviour of GaAs/(AlGa)As multiple quantum well structures. Even at room temperature, these structures exhibit a steep excitonic absorption edge in the near infrared spectral region. With rising temperature, this absorption edge shifts strongly enough to the red to lead to a sharp increase in the absorption of suitable photon energies below the absorption edge of the quantum wells. This opens the possibility of observing thermally induced optical bistability in the sample with moderate pumping intensities. The bistability is observed by focusing an infrared laser beam on the multiple quantum well structure. The transmitted laser intensity shows the switching of the sample between the two possible absorptive states. The incident laser intensities at which this switching occurs are extremely sensitive to the temperature of the material surrounding the sample. Using this effect, an optical temperature sensor can be realized in a very practical design using an optical fiber to guide the incident and reflected laser beam that can possibly be provided by a diode laser.