Optoplex’s Optical DPSK Demodulator, also known as Delay Line Interferometer (DLI), converts phase modulation to amplitude modulation over the entire C+L band in support of data transmission rates of 2.5, 10 or 40 Gb/s. The DPSK demodulator is designed for phase modulated optical communication systems utilised in commercial, defence and space exploration markets. The device plays a key role in improving signal quality and performance to meet the expanding demand for higher data rates and more complex transmission formats within current and next generation systems without major capital expenditure. Optoplex’s DPSK Demodulator is based on a patented free-space optical design, which is compact, athermal and polarisation independent. The measured frequency drift over temperature is only ~0.02 GHz/°C for our standard passive device. Further, this DPSK Demodulator exhibits a total polarisation-dependent phase shift of less than 2 degrees over the entire operating temperature range with a high extinction ratio.