Every LiDAR design faces the classic balancing act of signal versus noise. In order to maximize the range of a LiDAR, a receiver must amplify fractions of a micro-amp of photo current into a usable range for signal processing to occur, but without adding significant amounts of noise. Additionally, LiDAR receiver designs must exhibit very wide dynamic ranges because of the uncertainty in return signal amplitude. Meeting all these requirements in a small size, weight, and power form factor while keeping costs low is a major challenge.
A radiation-hardened, highly sensitive, high-bandwidth, wide-field-of-view, short-wave infrared (SWI) receiver has been developed as a front end component for the GRSSLi LiDAR. Optimized for 1550-nm laser detection over a ±20-degree field of view, this receiver can detect pulses with a 250-MHz bandwidth and near shot-noise-limited performance. This receiver is extremely compact and low cost while maintaining the highest level of performance.
To maximize signal-to-noise ratio (SNR), most scanning LiDARs mechanically scan a large optic to collect and condense reflected light. This innovation separates the receiver completely from the transmitter, enabling a single, small, simple optic called a fused fiber taper to be used, and the receiver to be built as a drop-in module. In effect, a LiDAR that uses this receiver becomes a bi-static system in which the receiver stares at a scene while a separate transmitter provides illumination. Separating the receiver and the transmitter also allows for very high laser scanning rates.
At the output of the fused fiber taper, four large-area InGaAs photodiode dies are bonded directly to the printed circuit board, and are used to collect the concentrated light to produce photocurrent for amplification. The amplifier design utilizes new radiation-hard GaAs Field Effect Transistors (FETs) to multiply the photocurrent at very high bandwidths and extremely low noise factor.