Development of high-sensitivity SWIR APD receivers

Emerging short wavelength infrared (SWIR) LIght Detection And Ranging (LIDAR) and long range laser rangefinder systems, require large optical aperture avalanche photodiodes (APDs) receivers with high sensitivity and high bandwidth. A large optical aperture is critical to increase the optical coupling efficiency and extend the LIDAR sensing range of the above systems. Both APD excess noise and transimpedance amplifier (TIA) noise need to be reduced in order to achieve high receiver sensitivity. The dark current and capacitance of large area APDs increase with APD aperture and thus limit the sensitivity and bandwidth of receivers. Spectrolab has been developing low excess noise InAlAs/InGaAs APDs with impact ionization engineering (I²E) designs for many years and has demonstrated APDs with optical gain over 100 utilizing multiple period I²E structures in the APD multiplier. These high gain I²E APDs have an excess noise factor less than 0.15. With an optical aperture of 200 μm, low excess noise multiple periods I²E APDs have capacitances about 1.7 pF. In addition, optical gains of InAlAs based APDs show very little temperature dependence and will enable APD photoreceivers without thermal electric cooling.