Implementation of a semi-transparent mid-infrared quantum well infrared photodetector simultaneously as a beamsplitter and a reference detector

We demonstrate a dual purpose quantum well infrared photodetector (QWIP) useful in laser-based gas sensing systems. This photodetector functions simultaneously as a beamsplitter and a photodetector. By varying the incidence angle and light polarization, the QWIP has the ability to reflect, absorb, and transmit varying percentages of the incident mid-infrared light. At 45° incidence angle, ∼25% of a transverse magnetic polarized light is reflected, ∼16% is transmitted, and ∼59% is absorbed by the QWIP (at 80 K). The absorbed and transmitted signals are useful as reference signals for laser source monitoring and stabilizing. The reflected signal remains available as the primary beam.