Quantum cascade laser as a mid-infrared photovoltaic and photoconductive detector

We report the operation of quantum cascade lasers (QCLs) as a mid-infrared (mid-IR) photo-detector under both photovoltaic and photoconductive modes. When operated at photoconductive mode, negative photo-conductance is observed at low bias current. The photo-conductance of the device changes from negative to positive when the bias is increased over a transparency point. These interesting mid-IR detection characteristics of QCL gain material can help and simplify the design and testing of mid-IR photonic integrated devices and circuits by using them to measure the coupling and waveguide loss and provide gain at any location in a mid-IR photonic circuit.