The receiver is in three parts. The first is a PIN diode as the transducer. There can be a lens in front of it for more gain Then you have amplification electronics (first stage is a transimpedance amplifier) to get the signal level up. Then there is signal proceessing to detect the pulse rate of the light packets.
If this is not just a hobby project for the fun of it, it would be cheaper to buy a ready made system.